Next Article in Journal
Catalysts of PtSn/C Modified with Ru and Ta for Electrooxidation of Ethanol
Next Article in Special Issue
Synthesis of Spherical TiO2 Particles with Disordered Rutile Surface for Photocatalytic Hydrogen Production
Previous Article in Journal
Hydrogenation of Carbon Dioxide to Value-Added Chemicals by Heterogeneous Catalysis and Plasma Catalysis
Previous Article in Special Issue
In-Situ Synthesis of Nb2O5/g-C3N4 Heterostructures as Highly Efficient Photocatalysts for Molecular H2 Evolution under Solar Illumination
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Photocatalytic Hydrogen Production: Role of Sacrificial Reagents on the Activity of Oxide, Carbon, and Sulfide Catalysts

1
Department of Environmental Science, School of Science, Institute of Technology Sligo, Ash Lane, F91 YW50 Sligo, Ireland
2
Centre for Precision Engineering, Materials and Manufacturing Research (PEM), Institute of Technology Sligo, Ash Lane, F91 YW50 Sligo, Ireland
3
Chemical Engineering Program, Texas A&M University at Qatar, Doha 23874, Qatar
4
Department of Chemistry, College of Natural Sciences, Yeungnam University, Gyeongsan, Gyeongbuk 38541, Korea
*
Authors to whom correspondence should be addressed.
Catalysts 2019, 9(3), 276; https://doi.org/10.3390/catal9030276
Submission received: 15 February 2019 / Accepted: 11 March 2019 / Published: 18 March 2019
(This article belongs to the Special Issue Photocatalytic Hydrogen Evolution)

Abstract

:
Photocatalytic water splitting is a sustainable technology for the production of clean fuel in terms of hydrogen (H2). In the present study, hydrogen (H2) production efficiency of three promising photocatalysts (titania (TiO2-P25), graphitic carbon nitride (g-C3N4), and cadmium sulfide (CdS)) was evaluated in detail using various sacrificial agents. The effect of most commonly used sacrificial agents in the recent years, such as methanol, ethanol, isopropanol, ethylene glycol, glycerol, lactic acid, glucose, sodium sulfide, sodium sulfite, sodium sulfide/sodium sulfite mixture, and triethanolamine, were evaluated on TiO2-P25, g-C3N4, and CdS. H2 production experiments were carried out under simulated solar light irradiation in an immersion type photo-reactor. All the experiments were performed without any noble metal co-catalyst. Moreover, photolysis experiments were executed to study the H2 generation in the absence of a catalyst. The results were discussed specifically in terms of chemical reactions, pH of the reaction medium, hydroxyl groups, alpha hydrogen, and carbon chain length of sacrificial agents. The results revealed that glucose and glycerol are the most suitable sacrificial agents for an oxide photocatalyst. Triethanolamine is the ideal sacrificial agent for carbon and sulfide photocatalyst. A remarkable amount of H2 was produced from the photolysis of sodium sulfide and sodium sulfide/sodium sulfite mixture without any photocatalyst. The findings of this study would be highly beneficial for the selection of sacrificial agents for a particular photocatalyst.

1. Introduction

Photocatalytic hydrogen (H2) production via water splitting is a sustainable and renewable energy production technology with negligible impact on the environment [1] (Figure 1). H2 is one of the most promising and clean energy sources for the future, with water as the only combustion product. After the invention of photo-electrochemical water splitting in 1972 [2] by Fujishima and Honda, nearly 9000 research articles have been published, outlining the use of various photocatalysts. In particular, most of the research works have been carried out using powder photocatalysts (except photo-electrochemical studies). The reported materials in the recent years are categorized as oxide [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149], carbon [3,81,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167,168,169,170,171,172,173,174,175,176,177,178,179,180,181,182,183,184,185,186,187,188,189,190,191,192,193,194,195,196,197,198,199,200,201,202,203,204,205,206,207,208,209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,224,225,226,227,228,229,230,231,232,233,234,235,236,237], and sulfide [3,14,17,35,58,59,113,114,119,128,133,154,164,169,177,181,195,203,208,210,215,220,227,230,235,238,239,240,241,242,243,244,245,246,247,248,249,250,251,252,253,254,255,256,257,258,259,260,261,262,263,264,265,266,267,268,269,270,271,272,273,274,275,276,277,278,279,280,281,282,283,284,285,286,287,288,289,290,291,292,293,294,295,296,297,298,299,300,301,302,303,304,305,306,307,308,309,310,311,312,313,314,315,316,317,318,319,320,321,322,323,324,325,326,327,328,329,330,331,332,333,334,335,336,337,338,339,340,341,342,343,344,345] photocatalysts. Titanium oxide–P25 (TiO2-P25), graphitic carbon nitride (g-C3N4), and cadmium sulfide (CdS) are the most extensively studied photocatalysts for water splitting. Many review articles have also been published [1,116,163,167,225,237,238,245,346,347,348,349,350,351,352,353,354,355,356,357,358,359,360,361,362,363,364,365,366,367,368,369,370,371,372,373,374,375,376,377,378,379,380,381,382,383,384,385,386,387,388,389,390,391,392,393,394,395,396,397,398,399,400,401,402,403,404,405,406,407,408,409,410,411,412,413,414,415,416,417,418,419] discussing the various features of the photocatalytic water splitting, such as fundamental concepts, theoretical principles, nature (morphology, surface characteristics, and optical properties) of the photocatalyst, role of co-catalyst/sacrificial reagents, mechanism, kinetics, etc. Nevertheless, there is still not many comprehensive studies to identify an appropriate sacrificial reagent with respect to the nature of a photocatalyst.
Sacrificial agents or electron donors/hole scavengers play a prominent role in photocatalytic H2 production because the water splitting is energetically an uphill reaction (ΔH0 = 286 kJ mol−1). It is realized that methanol, triethanolamine, and sodium sulfide/sodium sulfite are the most commonly used sacrificial reagents for oxide, carbon, and sulfide photocatalysts, respectively. In most of the cases, fresh water (e.g., deionized water or double distilled water) has been used to evaluate the H2 production efficiency in a micro photo-reactor (volume in the range of 30 to 70 mL) with a strong light irradiation source (nearly ≤ 300 W). However, the vitality and utilization of this technology have not been comprehensively studied in a real environment. Moreover, the commercialization of this technology is still restrained by its poor efficiency and the use of expensive noble metals (like Pt, Au, Pd, Rh) as co-catalysts. Most of the published results do not have much consistency in terms of efficiency. For example, different efficiency values have been reported for pure TiO2 using methanol as a scavenger (Table 1). This discrepancy is ascribed to the following reasons: photo-reactor design, inert gas (Ar or N2) purging flow rate, light irradiation source, gas sampling method, gas chromatography (GC) analysis conditions, calculations, etc.
The photochemical reactions of sacrificial agents (methanol, ethanol, isopropanol, ethylene glycol, glycerol, glucose, lactic acid, triethanolamine, sodium sulfide, sodium sulfite, and sodium sulfide/sodium sulfite mixture) and their degradation products during H2 production are summarized as follows:
Methanol [422] (MeOH):
H 2 O ( l )   +   h +   OH   +   H +
CH 3 OH   ( l )   +   OH   CH 2 OH   +   H 2 O   ( l )
  CH 2 OH     HCHO   ( l ) +   H + +   e  
2 H +   +   2 e   H 2   ( g )
HCHO   ( l )   +   H 2 O   ( l )     HCOOH   ( l )   +   H 2   ( g )
HCOOH   ( l )     CO 2   ( g )   +   H 2   ( g )
Overall reaction:
CH 3 OH   ( l )   +   H 2 O   ( l )     CO 2   ( g )   +   3 H 2   ( g )
Ethanol [423] (EtOH):
CH 3 CH 2 OH   +   TiO 2   ( S )   CH 3 CH 2 O Ti 4 +   +   ( S )   OH
TiO 2   +   UV   light     2 e   ( a )   +   2 h +
  ( s )   CH 3 CH 2 O Ti 4 + +   2 h + ( S )   CH 3 CHO   +   Ti 4 +
  ( s )   2 OH   +   e   ( a )     H 2   +   ( S )   2 O 2 +
Here, (s) represents the photocatalyst surface and (a) denotes the photo-excited electrons by UV light.
Isopropanol [424] (IPA):
[ Cd 2 + S 2 > ( CdS ) ] 2 + H 2 O   Cd 2 + S 2 > Cd ( II ) SH   +   Cd 2 + S 2 > S ( II ) Cd ( II ) OH
Cd 2 + S 2 > CdSH 2 + Cd 2 + S 2 > CdSH   +   H +
Cd 2 + S 2 >   CdSH   Cd 2 + S 2 > CdS   +   H +
Cd 2 + S 2 > CdOH 2 + Cd 2 + S 2 > CdOH   +   H +
Cd 2 + S 2 >   CdOH   Cd 2 + S 2 > CdO   + H +
Cd 2 + S 2 >   Cd ( + II ) S ( 0 ) +   +   C 3 H 7 OH   Cd 2 + S 2 > Cd ( + II ) S ( I ) H + +   C 3 H 6 OH
Cd 2 + S 2 >   Cd ( + II ) S ( I ) H + + C 3 H 7 OH   Cd 2 + S 2 > Cd ( + II ) S ( II ) H 2 +   +   C 3 H 6 OH
2 H H 2
2   C 3 H 6 OH   2   C 3 H 5 O   +   H 2
Cd 2 + S 2 > Cd ( + II ) S ( II ) H 2 + Cd 2 + S 2 > Cd ( + II ) S ( II ) H   +   H +
Cd 2 + S 2 >   CdOH   +   e CB Cd 2 + S 2 > CdO + H +
Ethylene Glycol [76,425] (EG):
OHCH 2 CH 2 OH + H 2 O   TiO 2 ,   hv   OHCH 2 CHO
OHCH 2 CHO   OH   OHCH 2 COOH
OHCH 2 COOH     CH 3 COOH
OHCH 2 COOH     HOOC COOH
HOOC COOH     HCOOH
HCOOH   ( or )   CH 3 COOH   ( or )   HOOC COOH     CO 2 + H 2 + CH 4 + C 2 H 4 + C 2 H 6 + H 2 O
Glycerol [130] (GLY):
C 3 H 8 O 3 + 3 H 2 O + 14   h ( VB ) +   intermediates   ( C 2 H 4 O 2 ,   C 2 H 2 O 3 ,   C 2 H 4 O 3 ,   C 3 H 6 O 3 ,   etc )   3 CO 2 + 14   H +
14 H +   +   14 e CB 7 H 2   ( g )  
Glucose [9] (GLU):
C 6 H 12 O 6   +   H 2 O   ( anaerobic )     C 5 H 10 O 5   +   HCOOH   +   H 2 ( g )
C 5 H 10 O 5   +   H 2 O     C 4 H 8 O 4   +   HCOOH   +   H 2   ( g )
C 4 H 8 O 4   +   H 2 O   +   HCOOH   +   H 2   ( g ) ( aerobic )   HCOOH   +   H 2 ( g )   +   CO 2   ( g )
C 6 H 12 O 6 TiO 2 ,   hv , H 2 O ,   O 2   C 6 H 12 O 7
C 6 H 12 O 7 TiO 2 ,   hv , H 2 O ,   O 2 C 6 H 10 O 8
C 6 H 10 O 8   TiO 2 ,   hv , H 2 O ,   O 2 HCOOH   +   H 2 ( g )   +   CO 2 ( g )
Lactic Acid [426] (LA):
CH 3 CH ( OH ) COOH + H 2 O   TiO 2 ,   hv   CO 2 + H 2 + CH 3 CO COOH  
Triethanolamine [427] (TEOA):
C 6 H 15 NO 3   C 6 H 15 NO 3 +   +   e
C 6 H 15 NO 3 +   C 6 H 14 NO 3   +   H +
C 6 H 14 NO 3   C 6 H 14 NO 3 + +   e
C 6 H 14 NO 3 +   +   H 2 O     C 4 H 11 NO 3   +   CH 3 CHO   +   H +
Sodium sulfide (Na2S) [428]:
Na 2 S   +   H 2 O     2 Na + +   S 2  
S 2 +   H 2 O     HS   +   OH  
HS   +   hv     HS   *
HS * +   HS   [ ( HS ) 2 ] *   H 2   +   S 2 2  
Sodium sulfite (Na2SO3) [429]:
Irradiation :   SO 3 2       hv   SO 3 2 *  
Oxidation :   SO 3 2 *   +   2 OH   SO 4 2   +   H 2 O   +   2 e  
Reduction :   2 H 2 O   +   2 e   H 2   +   2 OH
Oxidation :   2 SO 3 2   S 2 O 6 2   +   2 e
Reduction :   2 H 2 O   +   2 e   H 2   +   2 OH
Sodium sulfide and sodium sulfite mixture (Na2S and Na2SO3) [430]:
Two different reaction pathways are involved when sodium sulfide and sodium sulfite mixture is used as a sacrificial agent.
HS ( aq )   HS ( ads )
HS ( ads )       hv   [ HS ( ads ) ] *
Path A:
[ HS ( ads ) ] *   H *   +   S ( ads )
S ( ads )   +   [ HS ( ads ) ] *   [ HS 2 2 ] ȹ
[ H S 2 2 ] ȹ     H *   +   S 2 2   ( ads )
2 H *   H 2
Path B:
[ HS ( ads ) ] *   +   S 0 ( ads )   [ HS 2 ] ȹ  
[ HS 2 ] ȹ   +   OH   +   SO 3 2   +   S 0 ( ads )     [ HS 2 2 ] ȹ   +   OH   +   S 2 O 3 2  
OH   +   SO 3 2       hv   SO 4 2   +   H *  
2 H *   H 2
[ HS ( ads ) ] *   +   H 2 O     S 0 ( ads )   +   H 2   +   OH  
[ HS 2 ] ȹ   +   OH   H 2 O   +   S 2 2
where (ads) denotes adsorption and ȹ represents species, which can undergo intramolecular charge transfer.
The previous articles reported H2 production efficiencies with various combinations of photocatalysts and sacrificial reagents. This study provides detailed information on the selection of sacrificial reagents and photocatalysts for H2 production. The efficiencies of TiO2-P25, g-C3N4, and CdS were evaluated using methanol (MeOH), ethanol (EtOH), isopropanol (IPA), ethylene glycol (EG), glycerol (GLY), lactic acid (LA), glucose (GLU), sodium sulfide (Na2S), sodium sulfite (Na2SO3), sodium sulfide/sodium sulfite mixture (Na2S/Na2SO3), and triethanolamine (TEOA) as sacrificial reagents (organic and inorganic). The efficiency of a photocatalyst was described in terms of pH of medium and nature of the sacrificial agent (carbon chain length, alpha hydrogen, hydroxyl groups, binding interactions, etc). Besides, control experiments were executed to investigate the H2 production with only sacrificial reagents under solar light irradiation in the absence of photocatalyst.

2. Results and Discussion

2.1. TiO2 P25

Figure 2 shows the H2 production efficiency of TiO2 P25 using various sacrificial agents. H2 production efficiencies of TiO2/EG, TiO2/GLY, TiO2/Na2S/Na2SO3, TiO2/GLU, TiO2/Na2S were found to be 190.2 µmol, 130.8 µmol, 126 µmol, 120 µmol, and 120 µmol, respectively. H2 production efficiency of TiO2/MeOH system reduced to 81.6 µmol for the same period. The use of TEOA, EtOH, IPA, and Na2SO3 as sacrificial reagents resulted in poor H2 production, yielding 61.8 µmol, 49.8 µmol, 46.2 µmol, and 40.8 µmol, respectively. TiO2/LA mixture displayed the lowest yield of H2 production (only 27.6 µmol). TiO2/EG mixture showed the maximum H2 production (190.2 µmol) efficiency as compared to all other combinations. This is ascribed to the faster charge transfer reaction in the TiO2/EG system compared to the photo-generated electron-hole recombination process [431,432]. The length of the carbon chain, the number of hydroxyl groups, and dehydrogenation/decarbonylation characteristics of sacrificial agents are the primary features in controlling the H2 production efficiency. Moreover, the following properties of sacrificial agents could also strongly influence the efficiency: polarity and electron donating ability, adsorption capability on the photocatalyst surface, the formation of by-products, and the selectivity for reaction with photo-generated holes (e.g., decarboxylation process) [10,94,431,432,433,434,435,436]. Carbon monoxide (CO) is one of the main intermediates for the alcohols with a short carbon chain. Hence, the adsorption of CO on the active sites of TiO2 via chemisorption restricts further adsorption of alcohol on the photocatalyst surface [437]. The removal of CO as CO2 is the rate-determining step in H2 production. It depends on the adsorption efficiency and the number of alpha hydrogens of the sacrificial agent [437]. During the water-splitting process, the hydroxyl radical (OH) abstracts alpha hydrogen from the alcohol to create RCH2-OH radical, which gets further oxidized into an aldehyde, carboxylic acid, and CO2 [437]. Bahruji et al. [437] suggested that alkyl groups connected to the alcohol (e.g., CxHyOH) could yield the respective alkanes (e.g., Cx−1) during the water-splitting process. The alkane production rate was decreased with the increase of OH groups in alcohol [438]. In the case of polyols, the hydrogen atoms from the alpha carbon could be easily extracted and evolved in the form of H2 [438]. The alpha carbon atoms could be oxidized into CO2. The C atoms without OH groups (other than alpha C atoms) would be evolved in the form of alkanes [438]. Time-resolved transient absorption spectroscopy results revealed that carbohydrates and polyols (C2–C6) could rapidly react with ~50–60% holes (h+) within 6 ns as compared to other alcohols [439,440]. The OH groups could act as an anchor for the chemisorption of alcohols on the photocatalyst surface [438]. The coordination efficiency of alcohols with the Ti sites relies on the number of OH groups and the carbon chain length. This type of linkage could be beneficial for the utilization of holes to improve the H2 production and suppress the charge carrier recombination [438]. The first principle calculations showed that the formation of gap levels in TiO2 via the adsorption polyols could accelerate the hole trap** process [441]. Though EG showed maximum efficiency for TiO2-P25, glycerol and glucose are the most appropriate sacrificial agents for any kind of oxide photocatalyst. This owes to their (glucose and glycol) most abundance, less toxicity, low cost, and they can readily undergo dehydrogenation as compared to other alcohols [40,63,435].

2.2. g-C3N4

H2 production efficiency of g-C3N4 with various sacrificial agents is shown in Figure 3. In this case, only the use of TEOA, Na2S, Na2SO3, and Na2S/Na2SO3 resulted in H2 production. H2 production efficiency of g-C3N4/Na2S (139.8 µmol) system was higher than that of g-C3N4/Na2S/Na2SO3 (127.2 µmol) and g-C3N4/Na2SO3 (5.4 µmol). g-C3N4/TEOA mixture showed the best efficiency (247.2 µmol) when compared to all other sacrificial agents. This can be ascribed to the fact that photo-corrosion and degradation of π conjugated structure [304] of amine rich g-C3N4 is secured by the effective binding of TEOA on the catalyst surface [112]. TEOA excellently consumes the photo-generated holes, improves the dispersion of photocatalyst, and acts as a binding ligand to improve the interaction of g-C3N4 with water molecules [204,442]. The results shown in Figure 3 also suggest that alcohols and glucose are not strongly adsorbed on the g-C3N4 surface for water-splitting reaction. This is attributed to the absence of hydrophilicity and surface characteristics (e.g., active sites, poor electrical conductivity, water oxidation ability) of g-C3N4 to facilitate a strong interfacial electron/hole transfer process on the catalyst surface. The poor crystallinity and basal planar structure of g-C3N4 endorse the electron-hole recombination [443]. Moreover, high activation energy and overpotential are required for H2 production on the g-C3N4 surface [182,211]. This could be rectified by the loading of noble metals or co-catalysts over g-C3N4 or fabricating Z-scheme photocatalysts. In most of the studies, it was reported that g-C3N4 acts as an outstanding template and there was no H2 production on g-C3N4 without any noble metal co-catalyst [444,445]. The results also demonstrated that the light absorption capability, chemical stability, and suitable band edge positions of narrow band-gap g-C3N4 are not the only decisive factors to enhance the H2 production efficiency.

2.3. CdS

Photocatalytic H2 production efficiency of CdS using various sacrificial agents is shown in Figure 4. The use of TEOA, Na2S, Na2SO3, Na2S/Na2SO3, and LA as sacrificial reagents resulted in H2 formation. CdS/TEOA system showed the maximum efficiency of 283.2 µmol of H2 as compared to all other sacrificial agents. The efficiency of CdS/Na2S, CdS/Na2SO3, CdS/LA systems was found to be 181.2 µmol, 154.8 µmol, and 84 µmol, respectively. The mixture of CdS/Na2S/Na2SO3 showed the lowest H2 production of 54 µmol after 6 h. Bare CdS is not stable under prolonged light irradiation because the sulfide ions on its surface are rapidly oxidized into sulfur through the reaction with photo-generated holes (photo-corrosion – CdS + 2h+ → Cd2+ + S) [308,446,447]. The sulfide oxidation of CdS can occur before the oxidation of water by holes [308,447]. Hence, the H2 production efficiency of CdS highly relies on the effective binding of sacrificial agents on its surface. The results showed that amine and sulfide/sulfite might be strongly bound to the CdS surface and it could effectively consume the holes as compared to alcohol and sugars. It is obviously noted that H2 is produced in high alkaline (amine, sulfide, and sulfite) and acidic (LA) pH mixtures when compared to neutral pH (alcohols and sugar). LA is converted into pyruvic acid and CO2 during the water-splitting reaction; this may slightly influence the pH and polarity of the reaction mixture. The sulfide ions from Na2S stabilizes CdS surface to terminate the surface defects originated from photo-corrosion. The electron-hole recombination process is strongly restrained by the sulfide ions at alkaline pH. When CdS is suspended in a water medium, thiol (Cd-SH) and hydroxyl (Cd-OH) groups are developed on its surface, which are highly pH dependent [310]. In the case of Na2S, the pH of the medium is alkaline, sulfide (S2) and hydrogen sulfide (HS) are formed when Na2S is dissolved in water [310]. During light irradiation, S2 and HS- are quickly oxidized into sulfate (SO42−) and polysulfide (S42−, S52−) ions, respectively [310]. The oxidation of sulfide by the photo-generated holes is much preferential as compared to the photo-corrosion of CdS [112]. The precipitation of yellow colored polysulfide ions diminishes the photocatalytic efficiency via acting as an optical filter and competing with the H2 generation reaction. This could be restricted by the addition of Na2SO3 to generate more HS- and S2O32− ions to enhance the photocatalytic activity [292]. However, the results shown in Figure 4 suggest that H2 production efficiency of Na2S/CdS or CdS/Na2SO3 are higher than that of CdS/Na2S/Na2SO3. The reasons could be predicted by the photolysis experiments of sacrificial agents. The pH of TEOA/water mixture would be around 12, which could enhance the H2 production efficiency via strong interfacial bonding on the CdS surface and its reaction with photo-generated holes [204].

2.4. Photolysis

Photolysis experiments were carried out for all sacrificial agents in water for 6 h of light irradiation without the additions of photocatalysts. Control experiments were also carried out in the absence of sacrificial agents to evaluate the efficiency of the photocatalyst. There was no H2 production in the absence of any sacrificial agents for TiO2-p25, g-C3N4, and CdS. The results of photolysis experiments with sacrificial reagents under solar light in the absence of photocatalysts are shown in Figure 5. Interestingly, a remarkable amount of H2 was evolved from Na2S/water (159 µmol), Na2SO3/water (51 µmol), and Na2S/Na2SO3/water (134.4 µmol) systems without photocatalyst. It was observed that the H2 production efficiency was increased with respect to the concentration of sulfide or sulfite. When compared to results obtained in the presence of photocatalysts, it could be observed that the photocatalysts, such as TiO2-p25 and g-C3N4, surprisingly reduced the actual H2 production efficiency of sulfide system. There was not a significant increment in the efficiency of CdS/Na2S as compared to the photolysis of Na2S. However, the efficiency of CdS/Na2SO3 was higher than that of Na2SO3 photolysis. It is also noted that a high concentration of sulfide/sulfite mixture (in the range of 0.2 M to 1 M) was used in most of the studies for H2 production [246,264,273,300,448,449,450,451]. In such cases, the photolysis of sulfide or sulfite solutions were not evaluated. Hence, the H2 production should have been mainly originated via photolysis of sulfide/sulfite mixture rather than the photocatalytic effect. The photochemical reactions involved in H2 generation from sulfide and sulfite solutions are described in detail from Equations (42)–(62) [428,429,430].
Li et al. [430] investigated the photochemical generation of H2 from sulfide and sulfite mixture solutions. They found that the pH of sulfide/sulfite mixture (~13.14) was slightly decreased (~12.94) after the completion of photolysis experiments. The addition of a small amount of sulfite into the sulfide solution could not amplify the H2 production. Nevertheless, the elemental sulfur or polysulfide originated from HS is efficiently consumed by SO32− to improve the photonic efficiency. It is strongly recommended to study the effect of photolysis when the sulfide/sulfite mixture is used as the sacrificial agent to evaluate the H2 production efficiency of the photocatalyst. The elemental sulfur could be filtered out by passing hydrogen sulfide (H2S) gas in the aqueous solution under nitrogen atmosphere [428]. The resulting filtrate could be reused for photolytic H2 production [428].
Wang et al. [112] suggested that Na2S/Na2SO3, MeOH, and TEOA were the most appropriate sacrificial agents for sulfide, oxide, and carbon-based photocatalysts. However, the experiments were not performed to study the effect of photolysis, especially the sulfide or sulfite solutions. A high concentration of sacrificial agents was used to evaluate the photocatalytic activity. The photocatalytic experiments were not described in detail. Moreover, the effect of most earth abundant glucose and glycerol were not investigated on the H2 production efficiency. Sulfur dioxide (SO2) emission from the flue gas can be absorbed as Na2SO3 solution using dilute sodium hydroxide. The photolysis of such sodium sulfite solution is an eco-friendly way to produce H2 gas [429]. Only a few studies were focused on using wastewater for H2 generation. Souza and Silva [310] studied the feasibility of using tannery sludge wastewater for photocatalytic H2 generation using CdS. The photolysis of sulfide-rich wastewater or industrial effluent is the foremost choice to produce green energy in a sustainable way via photocatalysis.

2.5. TOC Analysis

TOC analysis was carried out for solutions after the photocatalytic experiments, to assess the degradation of organic sacrificial agents in the solutions at the end of 6 h experiment. Table 2 summarizes the TOC results for the solutions of TiO2-p25. The results suggest the effective utilization of the organic sacrificial agents by TiO2-P25 for H2 production. TOC was reduced almost half for most of the sacrificial agents after 6 h except for glucose. This is ascribed to the formation of more organic intermediates when glucose is utilized as the sacrificial agent.

3. Experimental

All the chemicals used were of analytical grade and used as received without further purification. TiO2 P25 was purchased from Sigma Aldrich (Darmstadt, Germany), g-C3N4 was synthesized by the calcination of urea at 550 °C for 2 h [452]. CdS was synthesized via the hydrothermal method [453]. Photocatalytic experiments were carried out using an immersion type reactor (Lelesil innovative systems, Thane, Maharashtra, India) as shown in Figure 6. All the reactions were carried out without any noble metal co-catalyst. The reactor is a tightly closed setup with a total volume of 1000 mL. Reactions were carried out using 500 mL of double distilled water with 0.5 g/L of photocatalyst and desired amount of sacrificial reagent (based on the literature). The empty headspace was kept constant at 500 mL for all reactions. The sacrificial agent concentration was fixed at 10% (alcohol, amine, acid) and 0.1 M (glucose, sodium sulfide, sodium sulfite, sodium sulfide/sodium sulfite mixture). The mixture was stirred under nitrogen purging for 1 h after which, the purging was stopped, and the reactor was closed immediately. The mixture was irradiated using a 300 W Xenon arc lamp without any UV cutoff filter (simulated solar light source). H2 sampling was carried out for every 1 h using a 250 µL sample lock gas tight syringe. At the end of the photoreaction time, when organic sacrificial reagents were used, the mixture was filtered using a 0.45 μm micro-filter, and the filtrate was analyzed using a total organic carbon (TOC; Shimadzu, Japan) analyzer to measure the loss of reagents by mineralization. H2 was analyzed using Agilent gas chromatography (USA) with thermal conductivity detector (TCD), manual injection, carrier gas N2, molecular sieve 5 A° column with 2-m length, front inlet temperature 140 °C, and detector temperature 150 °C.

4. Summary and Outlook

Different types of photocatalysts have been successfully investigated for H2 production using various organic and inorganic sacrificial agents. The surface of an oxide photocatalyst would be more suitable for polyols and sugars for adsorption as compared to amines and sulfides. Amines are the most appropriate of sacrificial agents for carbon and sulfide photocatalysts. CdS/TEOA (283.2 µmol), g-C3N4/TEOA (247.2 µmol), and TiO2/EG (190.2 µmol) are the three best systems with maximum H2 production in this study. H2 could also be generated via the direct photolysis of sodium sulfide solution in the absence of any catalyst. TiO2-p25 and g-C3N4 suppress the self-H2 generation efficiency of Na2S photolysis. More technological developments are required for the practical application of water-splitting in a scalable and economically feasible way. Stable, affordable, and active co-catalysts should be developed in the future to replace the expensive noble metals to achieve a significant amount of H2 production. In most of the studies, precious fresh water with a high concentration of sacrificial agents was used in a small reactor to generate H2. Hence, future studies should be focused on a pilot scale using industrial wastewater and seawater rather than using fresh water.

Author Contributions

Conceptualization V.K. and A.A-W.; Supervision, V.K., A.A-W. and M.K.; Methodology, design, investigation, data creation and analysis, V.K.; Methodology, data analysis, and original draft preparation, M.D.I and A.B.; Methodology and data analysis, J.Y.D. and R.K.C.

Funding

The authors are grateful to Texas A&M University at Qatar and Qatar Foundation for financial support.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Kumaravel, V.; Mathew, S.; Bartlett, J.; Pillai, S.C. Photocatalytic hydrogen production using metal doped TiO2: A review of recent advances. Appl. Catal. B Environ. 2019, 244, 1021–1064. [Google Scholar] [CrossRef]
  2. Fujishima, A.; Honda, K.J. Electrochemical photolysis of water at a semiconductor electrode. Nature 1972, 238, 37–38. [Google Scholar] [CrossRef] [PubMed]
  3. Abdullah, H.; Kuo, D.-H.; Chen, X. High efficient noble metal free Zn (O, S) nanoparticles for hydrogen evolution. Int. J. Hydrogen Energy 2017, 42, 5638–5648. [Google Scholar] [CrossRef]
  4. Agegnehu, A.K.; Pan, C.-J.; Tsai, M.-C.; Rick, J.; Su, W.-N.; Lee, J.-F.; Hwang, B.-J. Visible light responsive noble metal-free nanocomposite of V-doped TiO2 nanorod with highly reduced graphene oxide for enhanced solar H2 production. Int. J. Hydrogen Energy 2016, 41, 6752–6762. [Google Scholar] [CrossRef]
  5. Alharbi, A.; Alarifi, I.M.; Khan, W.S.; Asmatulu, R. Synthesis and analysis of electrospun SrTiO3 nanofibers with NiO nanoparticles shells as photocatalysts for water splitting. In Proceedings of the 14th Brazilian Polymer Conference, São Paulo, Brazil, 22–26 October 2017; 22-26. [Google Scholar]
  6. Al-Mayman, S.I.; Al-Johani, M.S.; Mohamed, M.M.; Al-Zeghayer, Y.S.; Ramay, S.M.; Al-Awadi, A.S.; Soliman, M.A. TiO2 ZnO photocatalysts synthesized by sol–gel auto-ignition technique for hydrogen production. Int. J. Hydrogen Energy 2017, 42, 5016–5025. [Google Scholar] [CrossRef]
  7. Bai, Y.; Chen, T.; Wang, P.; Wang, L.; Ye, L. Bismuth-rich Bi4O5X2 (X = Br, and I) nanosheets with dominant {101} facets exposure for photocatalytic H2 evolution. Chem. Eng. J. 2016, 304, 454–460. [Google Scholar] [CrossRef]
  8. Barreca, D.; Carraro, G.; Gasparotto, A.; Maccato, C.; Warwick, M.E.; Toniato, E.; Gombac, V.; Sada, C.; Turner, S.; Van Tendeloo, G. Iron–Titanium Oxide Nanocomposites Functionalized with Gold Particles: From Design to Solar Hydrogen Production. Adv. Mater. Interfaces 2016, 3, 1600348. [Google Scholar] [CrossRef]
  9. Bellardita, M.; García-López, E.I.; Marcì, G.; Palmisano, L. Photocatalytic formation of H2 and value-added chemicals in aqueous glucose (Pt)-TiO2 suspension. Int. J. Hydrogen Energy 2016, 41, 5934–5947. [Google Scholar] [CrossRef]
  10. Beltram, A.; Romero-Ocana, I.; Jaen, J.J.D.; Montini, T.; Fornasiero, P. Photocatalytic valorization of ethanol and glycerol over TiO2 polymorphs for sustainable hydrogen production. Appl. Catal. A Gen. 2016, 518, 167–175. [Google Scholar] [CrossRef]
  11. Betzler, S.B.; Podjaski, F.; Beetz, M.; Handloser, K.; Wisnet, A.; Handloser, M.; Hartschuh, A.; Lotsch, B.V.; Scheu, C. Titanium Do** and Its Effect on the Morphology of Three-Dimensional Hierarchical Nb3O7 (OH) Nanostructures for Enhanced Light-Induced Water Splitting. Chem. Mater 2016, 28, 7666–7672. [Google Scholar] [CrossRef]
  12. Cargnello, M.; Montini, T.; Smolin, S.Y.; Priebe, J.B.; Jaén, J.J.D.; Doan-Nguyen, V.V.; McKay, I.S.; Schwalbe, J.A.; Pohl, M.-M.; Gordon, T.R. Engineering titania nanostructure to tune and improve its photocatalytic activity. Proc. Natl. Acad. Sci. 2016, 113, 3966–3971. [Google Scholar] [CrossRef]
  13. Cha, G.; Altomare, M.; Truong Nguyen, N.; Taccardi, N.; Lee, K.; Schmuki, P. Double-Side Co-Catalytic Activation of Anodic TiO2 Nanotube Membranes with Sputter-Coated Pt for Photocatalytic H2 Generation from Water/Methanol Mixtures. Chem. Asian J. 2017, 12, 314–323. [Google Scholar] [CrossRef]
  14. Yuan, Q.; Liu, D.; Zhang, N.; Ye, W.; Ju, H.; Shi, L.; Long, R.; Zhu, J.; ** as a facile strategy to improve photocatalytic activity of standalone reduced graphene oxide in hydrogen evolution. ACS Appl. Mater. Interfaces 2017, 9, 4558–4569. [Google Scholar] [CrossRef]
  15. Qiao, S.; Mitchell, R.W.; Coulson, B.; Jowett, D.V.; Johnson, B.R.; Brydson, R.; Isaacs, M.; Lee, A.F.; Douthwaite, R.E. Pore confinement effects and stabilization of carbon nitride oligomers in macroporous silica for photocatalytic hydrogen production. Carbon 2016, 106, 320–329. [Google Scholar] [CrossRef] [Green Version]
  16. Qu, A.; Xu, X.; ** for Enhanced Photocatalytic H2 Evolution in CdS Nanorods. Nano Lett. 2017, 17, 3803–3808. [Google Scholar] [CrossRef]
  17. Huang, T.; Chen, W.; Liu, T.-Y.; Hao, Q.-L.; Liu, X.-H. Hybrid of AgInZnS and MoS2 as efficient visible-light driven photocatalyst for hydrogen production. Int. J. Hydrogen Energy 2017, 42, 12254–12261. [Google Scholar] [CrossRef]
  18. Huang, T.; Chen, W.; Liu, T.-Y.; Hao, Q.-L.; Liu, X.-H. ZnIn2S4 hybrid with MoS2: A non-noble metal photocatalyst with efficient photocatalytic activity for hydrogen evolution. Powder Technol. 2017, 315, 157–162. [Google Scholar] [CrossRef]
  19. Irfan, R.M.; Jiang, D.; Sun, Z.; Lu, D.; Du, P. Enhanced photocatalytic H2 production on CdS nanorods with simple molecular bidentate cobalt complexes as cocatalysts under visible light. Dalton Trans. 2016, 45, 12897–12905. [Google Scholar] [CrossRef]
  20. Jiang, F.; Pan, B.; You, D.; Zhou, Y.; Wang, X.; Su, W. Visible light photocatalytic H2-production activity of epitaxial Cu2ZnSnS4/ZnS heterojunction. Catal. Commun. 2016, 85, 39–43. [Google Scholar] [CrossRef]
  21. Jiang, Z.; Liu, J.; Gao, M.; Fan, X.; Zhang, L.; Zhang, J. Assembling Polyoxo-Titanium Clusters and CdS Nanoparticles to a Porous Matrix for Efficient and Tunable H2-Evolution Activities with Visible Light. Adv. Mater. 2017, 29, 1603369. [Google Scholar] [CrossRef]
  22. Jo, W.-K.; Selvam, N.C.S. Fabrication of photostable ternary CdS/MoS2/MWCNTs hybrid photocatalysts with enhanced H2 generation activity. Appl. Catal. A Gen. 2016, 525, 9–22. [Google Scholar] [CrossRef]
  23. Kandiel, T.A.; Takanabe, K. Solvent-induced deposition of Cu–Ga–In–S nanocrystals onto a titanium dioxide surface for visible-light-driven photocatalytic hydrogen production. Appl. Catal. B Environ. 2016, 184, 264–269. [Google Scholar] [CrossRef] [Green Version]
  24. Kaur, M.; Nagaraja, C. Template-Free Synthesis of Zn1–xCdxS Nanocrystals with Tunable Band Structure for Efficient Water Splitting and Reduction of Nitroaromatics in Water. ACS Sustain. Chem. Eng. 2017, 5, 4293–4303. [Google Scholar] [CrossRef]
  25. Kim, Y.G.; Jo, W.-K. Photodeposited-metal/CdS/ZnO heterostructures for solar photocatalytic hydrogen production under different conditions. Int. J. Hydrogen Energy 2017, 42, 11356–11363. [Google Scholar] [CrossRef]
  26. Kim, Y.K.; Lim, S.K.; Park, H.; Hoffmann, M.R.; Kim, S. Trilayer CdS/carbon nanofiber (CNF) mat/Pt-TiO2 composite structures for solar hydrogen production: Effects of CNF mat thickness. Appl. Catal. B Environ. 2016, 196, 216–222. [Google Scholar] [CrossRef]
  27. Kimi, M.; Yuliati, L.; Shamsuddin, M. Preparation and characterization of In and Cu co-doped ZnS photocatalysts for hydrogen production under visible light irradiation. J. Energy Chem. 2016, 25, 512–516. [Google Scholar] [CrossRef] [Green Version]
  28. Kong, Z.; Yuan, Y.-J.; Chen, D.; Fang, G.; Yang, Y.; Yang, S.; Cao, D. Noble-metal-free MoS2 nanosheet modified-InVO4 heterostructures for enhanced visible-light-driven photocatalytic H2 production. Dalton Trans. 2017, 46, 2072–2076. [Google Scholar] [CrossRef] [PubMed]
  29. Kumar, D.P.; Hong, S.; Reddy, D.A.; Kim, T.K. Ultrathin MoS2 layers anchored exfoliated reduced graphene oxide nanosheet hybrid as a highly efficient cocatalyst for CdS nanorods towards enhanced photocatalytic hydrogen production. Appl. Catal. B Environ. 2017, 212, 7–14. [Google Scholar] [CrossRef]
  30. Leo, I.M.; Soto, E.; Vaquero, F.; Mota, N.; Navarro, R.; Fierro, J. Influence of the reduction of graphene oxide (rGO) on the structure and photoactivity of CdS-rGO hybrid systems. Int. J. Hydrogen Energy 2017, 42, 13691–13703. [Google Scholar]
  31. Li, M.; Zhang, L.; Fan, X.; Wu, M.; Du, Y.; Wang, M.; Kong, Q.; Zhang, L.; Shi, J. Dual synergetic effects in MoS2/pyridine-modified gC3N4 composite for highly active and stable photocatalytic hydrogen evolution under visible light. Appl. Catal. B Environ. 2016, 190, 36–43. [Google Scholar] [CrossRef]
  32. Li, X.; Liu, H.; Liu, S.; Zhang, J.; Chen, W.; Huang, C.; Mao, L. Effect of Pt–Pd hybrid nano-particle on CdS’s activity for water splitting under visible light. Int. J. Hydrogen Energy 2016, 41, 23015–23021. [Google Scholar] [CrossRef]
  33. Li, Y.; Hou, Y.; Fu, Q.; Peng, S.; Hu, Y.H. Oriented growth of ZnIn2S4/In(OH)3 heterojunction by a facile hydrothermal transformation for efficient photocatalytic H2 production. Appl. Catal. B Environ. 2017, 206, 726–733. [Google Scholar] [CrossRef]
  34. Li, Y.; **, R.; **ng, Y.; Li, J.; Song, S.; Liu, X.; Li, M.; **, R. Macroscopic Foam-Like Holey Ultrathin g-C3N4 Nanosheets for Drastic Improvement of Visible-Light Photocatalytic Activity. Adv. Energy Mater. 2016, 6, 1601273. [Google Scholar] [CrossRef]
  35. Li, Z.; Chen, X.; Shangguan, W.; Su, Y.; Liu, Y.; Dong, X.; Sharma, P.; Zhang, Y. Prickly Ni3S2 nanowires modified CdS nanoparticles for highly enhanced visible-light photocatalytic H2 production. Int. J. Hydrogen Energy 2017, 42, 6618–6626. [Google Scholar] [CrossRef]
  36. Lin, H.; Li, Y.; Li, H.; Wang, X. Multi-node CdS hetero-nanowires grown with defect-rich oxygen-doped MoS2 ultrathin nanosheets for efficient visible-light photocatalytic H2 evolution. Nano Res. 2017, 10, 1377–1392. [Google Scholar] [CrossRef]
  37. Liu, H.; Xu, Z.; Zhang, Z.; Ao, D. Novel visible-light driven Mn0.8Cd0.2S/gC3N4 composites: Preparation and efficient photocatalytic hydrogen production from water without noble metals. Appl. Catal. A Gen. 2016, 518, 150–157. [Google Scholar] [CrossRef]
  38. Liu, M.; Chen, Y.; Su, J.; Shi, J.; Wang, X.; Guo, L. Photocatalytic hydrogen production using twinned nanocrystals and an unanchored NiSx co-catalyst. Nat. Energy 2016, 1, 16151. [Google Scholar] [CrossRef]
  39. Liu, X.; **ng, Z.; Zhang, Y.; Li, Z.; Wu, X.; Tan, S.; Yu, X.; Zhu, Q.; Zhou, W. Fabrication of 3D flower-like black N-TiO2-x@ MoS2 for unprecedented-high visible-light-driven photocatalytic performance. Appl. Catal. B Environ. 2017, 201, 119–127. [Google Scholar] [CrossRef]
  40. Liu, Y.; Tang, C. Enhancement of photocatalytic H2 evolution over TiO2 nano-sheet films by surface loading NiS nanoparticles. Russ. J. Phys. Chem. A 2016, 90, 1042–1048. [Google Scholar] [CrossRef]
  41. Lu, D.; Wang, H.; Zhao, X.; Kondamareddy, K.K.; Ding, J.; Li, C.; Fang, P. Highly efficient visible-light-induced photoactivity of Z-scheme g-C3N4/Ag/MoS2 ternary photocatalysts for organic pollutant degradation and production of hydrogen. ACS Sustain. Chem. Eng. 2017, 5, 1436–1445. [Google Scholar] [CrossRef]
  42. Ma, L.; Chen, K.; Nan, F.; Wang, J.H.; Yang, D.J.; Zhou, L.; Wang, Q.Q. Improved Hydrogen Production of Au–Pt–CdS Hetero-Nanostructures by Efficient Plasmon-Induced Multipathway Electron Transfer. Adv. Funct. Mater. 2016, 26, 6076–6083. [Google Scholar] [CrossRef]
  43. Ma, X.; Li, J.; An, C.; Feng, J.; Chi, Y.; Liu, J.; Zhang, J.; Sun, Y. Ultrathin Co (Ni)-doped MoS- nanosheets as catalytic promoters enabling efficient solar hydrogen production. Nano Res. 2016, 9, 2284–2293. [Google Scholar] [CrossRef]
  44. Majeed, I.; Nadeem, M.A.; Hussain, E.; Badshah, A.; Gilani, R.; Nadeem, M.A. Effect of deposition method on metal loading and photocatalytic activity of Au/CdS for hydrogen production in water electrolyte mixture. Int. J. Hydrogen Energy 2017, 42, 3006–3018. [Google Scholar] [CrossRef]
  45. Malekshoar, G.; Ray, A.K. In-situ grown molybdenum sulfide on TiO2 for dye-sensitized solar photocatalytic hydrogen generation. Chem. Eng. Sci. 2016, 152, 35–44. [Google Scholar] [CrossRef]
  46. Mancipe, S.; Tzompantzi, F.; Gómez, R. Synthesis of CdS/MgAl layered double hydroxides for hydrogen production from methanol-water decomposition. Appl. Clay Sci. 2017, 136, 67–74. [Google Scholar] [CrossRef]
  47. Manjunath, K.; Souza, V.; Nagaraju, G.; Santos, J.M.L.; Dupont, J.; Ramakrishnappa, T. Superior activity of the CuS–TiO2/Pt hybrid nanostructure towards visible light induced hydrogen production. New J. Chem. 2016, 40, 10172–10180. [Google Scholar] [CrossRef]
  48. Mei, Z.; Zhang, M.; Schneider, J.; Wang, W.; Zhang, N.; Su, Y.; Chen, B.; Wang, S.; Rogach, A.L.; Pan, F. Hexagonal Zn1−xCdxS (0.2 ≤ x ≤ 1) solid solution photocatalysts for H2 generation from water. Catal. Sci. Technol. 2017, 7, 982–987. [Google Scholar] [CrossRef]
  49. Nandy, S.; Goto, Y.; Hisatomi, T.; Moriya, Y.; Minegishi, T.; Katayama, M.; Domen, K. Synthesis and Photocatalytic Activity of La5Ti2Cu (S1−xSex)5O7 Solid Solutions for H2 Production under Visible Light Irradiation. ChemPhotoChem 2017, 1, 265–272. [Google Scholar] [CrossRef]
  50. Núñez, J.; Fresno, F.; Collado, L.; Jana, P.; Coronado, J.M.; Serrano, D.P.; Víctor, A. Photocatalytic H2 production from aqueous methanol solutions using metal-co-catalysed Zn2SnO4 nanostructures. Appl. Catal. B Environ. 2016, 191, 106–115. [Google Scholar] [CrossRef]
  51. Oros-Ruiz, S.; Hernández-Gordillo, A.; García-Mendoza, C.; Rodríguez-Rodríguez, A.A.; Gomez, R. Comparative activity of CdS nanofibers superficially modified by Au, Cu, and Ni nanoparticles as co-catalysts for photocatalytic hydrogen production under visible light. J. Chem. Technol. Biotechnol. 2016, 91, 2205–2210. [Google Scholar] [CrossRef]
  52. Park, H.; Ou, H.-H.; Kim, M.; Kang, U.; Han, D.S.; Hoffmann, M.R. Photocatalytic H2 production on trititanate nanotubes coupled with CdS and platinum nanoparticles under visible light: Revisiting H2 production and material durability. Faraday Discuss. 2017, 198, 419–431. [Google Scholar] [CrossRef]
  53. Qiu, F.; Han, Z.; Peterson, J.J.; Odoi, M.Y.; Sowers, K.L.; Krauss, T.D. Photocatalytic hydrogen generation by CdSe/CdS nanoparticles. Nano Lett. 2016, 16, 5347–5352. [Google Scholar] [CrossRef] [PubMed]
  54. Rahman, M.; Davey, K.; Qiao, S.Z. Counteracting Blueshift Optical Absorption and Maximizing Photon Harvest in Carbon Nitride Nanosheets Photocatalyst. Small 2017, 13, 1700376. [Google Scholar] [CrossRef]
  55. Rahmawati, F.; Yuliati, L.; Alaih, I.S.; Putri, F.R. Carbon rod of zinc-carbon primary battery waste as a substrate for CdS and TiO2 photocatalyst layer for visible light driven photocatalytic hydrogen production. J. Environ. Chem. Eng. 2017, 5, 2251–2258. [Google Scholar] [CrossRef]
  56. Ran, J.; Gao, G.; Li, F.-T.; Ma, T.-Y.; Du, A.; Qiao, S.-Z. Ti3C2 MXene co-catalyst on metal sulfide photo-absorbers for enhanced visible-light photocatalytic hydrogen production. Nat. Commun. 2017, 8, 13907. [Google Scholar] [CrossRef]
  57. Rao, H.; Yu, W.-Q.; Zheng, H.-Q.; Bonin, J.; Fan, Y.-T.; Hou, H.-W. Highly efficient photocatalytic hydrogen evolution from nickel quinolinethiolate complexes under visible light irradiation. J. Power Sources 2016, 324, 253–260. [Google Scholar] [CrossRef]
  58. Reddy, D.A.; Park, H.; Hong, S.; Kumar, D.P.; Kim, T.K. Hydrazine-assisted formation of ultrathin MoS2 nanosheets for enhancing their co-catalytic activity in photocatalytic hydrogen evolution. J. Mater. Chem. A 2017, 5, 6981–6991. [Google Scholar] [CrossRef]
  59. Reddy, D.A.; Park, H.; Ma, R.; Kumar, D.P.; Lim, M.; Kim, T.K. Heterostructured WS2-MoS2 Ultrathin Nanosheets Integrated on CdS Nanorods to Promote Charge Separation and Migration and Improve Solar-Driven Photocatalytic Hydrogen Evolution. ChemSusChem 2017, 10, 1563–1570. [Google Scholar] [CrossRef] [PubMed]
  60. Shi, Z.; Dong, X.; Dang, H. Facile fabrication of novel red phosphorus-CdS composite photocatalysts for H2 evolution under visible light irradiation. Int. J. Hydrogen Energy 2016, 41, 5908–5915. [Google Scholar] [CrossRef]
  61. Sola, A.; Homs, N.; de la Piscina, P.R. Photocatalytic H2 production from ethanol (aq) solutions: The effect of intermediate products. Int. J. Hydrogen Energy 2016, 41, 19629–19636. [Google Scholar] [CrossRef]
  62. Souza, E.A.; Silva, L.A. Energy recovery from tannery sludge wastewaters through photocatalytic hydrogen production. J. Environ. Chem. Eng. 2016, 4, 2114–2120. [Google Scholar] [CrossRef]
  63. Su, J.; Zhang, T.; Li, Y.; Chen, Y.; Liu, M. Photocatalytic activities of copper doped cadmium sulfide microspheres prepared by a facile ultrasonic spray-pyrolysis method. Molecules 2016, 21, 735. [Google Scholar] [CrossRef]
  64. Vaquero, F.; Navarro, R.; Fierro, J. Evolution of the nanostructure of CdS using solvothermal synthesis at different temperature and its influence on the photoactivity for hydrogen production. Int. J. Hydrogen Energy 2016, 41, 11558–11567. [Google Scholar] [CrossRef]
  65. Sun, S.; Gao, P.; Yang, Y.; Yang, P.; Chen, Y.; Wang, Y. N-doped TiO2 nanobelts with coexposed (001) and (101) facets and their highly efficient visible-light-driven photocatalytic hydrogen production. ACS Appl. Mater. Interfaces 2016, 8, 18126–18131. [Google Scholar] [CrossRef]
  66. Wang, F.; **, Z.; Jiang, Y.; Backus, E.H.; Bonn, M.; Lou, S.N.; Turchinovich, D.; Amal, R. Probing the charge separation process on In2S3/Pt-TiO2 nanocomposites for boosted visible-light photocatalytic hydrogen production. Appl. Catal. B Environ. 2016, 198, 25–31. [Google Scholar] [CrossRef]
  67. Wang, H.; Li, Y.; Shu, D.; Chen, X.; Liu, X.; Wang, X.; Zhang, J.; Wang, H. CoPtx-loaded Zn0.5Cd0.5S nanocomposites for enhanced visible light photocatalytic H2 production. Int. J. Energy Res. 2016, 40, 1280–1286. [Google Scholar] [CrossRef]
  68. Wang, J.; Chen, Y.; Zhou, W.; Tian, G.; **ao, Y.; Fu, H.; Fu, H. Cubic quantum dot/hexagonal microsphere ZnIn2S4 heterophase junctions for exceptional visible-light-driven photocatalytic H2 evolution. J. Mater. Chem. A 2017, 5, 8451–8460. [Google Scholar] [CrossRef]
  69. Wang, J.; Wang, Z.; Zhu, Z. Synergetic effect of Ni(OH)2 cocatalyst and CNT for high hydrogen generation on CdS quantum dot sensitized TiO2 photocatalyst. Appl. Catal. B Environ. 2017, 204, 577–583. [Google Scholar] [CrossRef]
  70. Wang, L.; Di, Q.; Sun, M.; Liu, J.; Cao, C.; Liu, J.; Xu, M.; Zhang, J. Assembly-promoted photocatalysis: Three-dimensional assembly of CdSxSe1−x (x = 0–1) quantum dots into nanospheres with enhanced photocatalytic performance. J. Mater. 2017, 3, 63–70. [Google Scholar] [CrossRef]
  71. Wang, Y.; Zhang, Y.; Jiang, Z.; Jiang, G.; Zhao, Z.; Wu, Q.; Liu, Y.; Xu, Q.; Duan, A.; Xu, C. Controlled fabrication and enhanced visible-light photocatalytic hydrogen production of Au@ CdS/MIL-101 heterostructure. Appl. Catal. B Environ. 2016, 185, 307–314. [Google Scholar] [CrossRef]
  72. Wang, Z.; Wang, S.; Liu, J.; Jiang, W.; Zhou, Y.; An, C.; Zhang, J. Synthesis of AgInS2-xAg2S-yZnS-zIn6S7 (x, y, z = 0, or 1) Nanocomposites with Composition-Dependent Activity towards Solar Hydrogen Evolution. Materials 2016, 9, 329. [Google Scholar] [CrossRef]
  73. Wu, A.; Tian, C.; Jiao, Y.; Yan, Q.; Yang, G.; Fu, H. Sequential two-step hydrothermal growth of MoS2/CdS core-shell heterojunctions for efficient visible light-driven photocatalytic H2 evolution. Appl. Catal. B Environ. 2017, 203, 955–963. [Google Scholar] [CrossRef]
  74. Wu, L.; Gong, J.; Ge, L.; Han, C.; Fang, S.; **n, Y.; Li, Y.; Lu, Y. AuPd bimetallic nanoparticles decorated Cd0.5Zn0.5S photocatalysts with enhanced visible-light photocatalytic H2 production activity. Int. J. Hydrogen Energy 2016, 41, 14704–14712. [Google Scholar] [CrossRef]
  75. **a, Y.; Li, Q.; Lv, K.; Tang, D.; Li, M. Superiority of graphene over carbon analogs for enhanced photocatalytic H2-production activity of ZnIn2S4. Appl. Catal. B Environ. 2017, 206, 344–352. [Google Scholar] [CrossRef]
  76. **n, Y.; Lu, Y.; Han, C.; Ge, L.; Qiu, P.; Li, Y.; Fang, S. Novel NiS cocatalyst decorating ultrathin 2D TiO2 nanosheets with enhanced photocatalytic hydrogen evolution activity. Mater. Res. Bull. 2017, 87, 123–129. [Google Scholar] [CrossRef]
  77. **ng, Z.; Zong, X.; Zhu, Y.; Chen, Z.; Bai, Y.; Wang, L. A nanohybrid of CdTe@ CdS nanocrystals and titania nanosheets with p–n nanojunctions for improved visible light-driven hydrogen production. Catal. Today 2016, 264, 229–235. [Google Scholar] [CrossRef]
  78. Yan, J.; Li, X.; Yang, S.; Wang, X.; Zhou, W.; Fang, Y.; Zhang, S.; Peng, F.; Zhang, S. Design and preparation of CdS/H-3D-TiO2/Pt-wire photocatalysis system with enhanced visible-light driven H2 evolution. Int. J. Hydrogen Energy 2017, 42, 928–937. [Google Scholar] [CrossRef]
  79. Yan, Q.; Wu, A.; Yan, H.; Dong, Y.; Tian, C.; Jiang, B.; Fu, H. Gelatin-assisted synthesis of ZnS hollow nanospheres: The microstructure tuning, formation mechanism and application for Pt-free photocatalytic hydrogen production. CrystEngComm 2017, 19, 461–468. [Google Scholar] [CrossRef]
  80. Yang, L.; Guo, S.; Li, X. Au nanoparticles@ MoS2 core-shell structures with moderate MoS2 coverage for efficient photocatalytic water splitting. J. Alloys Compd. 2017, 706, 82–88. [Google Scholar] [CrossRef]
  81. Yang, Y.; Zhang, Y.; Fang, Z.; Zhang, L.; Zheng, Z.; Wang, Z.; Feng, W.; Weng, S.; Zhang, S.; Liu, P. Simultaneous Realization of Enhanced Photoactivity and Promoted Photostability by Multilayered MoS2 Coating on CdS Nanowire Structure via Compact Coating Methodology. ACS Appl. Mater. Interfaces 2017, 9, 6950–6958. [Google Scholar] [CrossRef]
  82. Yu, X.; Shi, J.; Wang, L.; Wang, W.; Bian, J.; Feng, L.; Li, C. A novel Au NPs-loaded MoS2/RGO composite for efficient hydrogen evolution under visible light. Mater. Lett. 2016, 182, 125–128. [Google Scholar] [CrossRef]
  83. Yuan, Y.J.; Chen, D.Q.; Huang, Y.W.; Yu, Z.T.; Zhong, J.S.; Chen, T.T.; Tu, W.G.; Guan, Z.J.; Cao, D.P.; Zou, Z.G. MoS2 Nanosheet-Modified CuInS2 Photocatalyst for Visible-Light-Driven Hydrogen Production from Water. ChemSusChem 2016, 9, 1003–1009. [Google Scholar] [CrossRef]
  84. Yuan, Y.-J.; Tu, J.-R.; Ye, Z.-J.; Chen, D.-Q.; Hu, B.; Huang, Y.-W.; Chen, T.-T.; Cao, D.-P.; Yu, Z.-T.; Zou, Z.-G. MoS2-graphene/ZnIn2S4 hierarchical microarchitectures with an electron transport bridge between light-harvesting semiconductor and cocatalyst: A highly efficient photocatalyst for solar hydrogen generation. Appl. Catal. B Environ. 2016, 188, 13–22. [Google Scholar] [CrossRef]
  85. Yue, Z.; Liu, A.; Zhang, C.; Huang, J.; Zhu, M.; Du, Y.; Yang, P. Noble-metal-free hetero-structural CdS/Nb2O5/N-doped-graphene ternary photocatalytic system as visible-light-driven photocatalyst for hydrogen evolution. Appl. Catal. B Environ. 2017, 201, 202–210. [Google Scholar] [CrossRef]
  86. Zhang, J.; Yao, W.; Huang, C.; Shi, P.; Xu, Q. High efficiency and stable tungsten phosphide cocatalysts for photocatalytic hydrogen production. J. Mater. Chem. A 2017, 5, 12513–12519. [Google Scholar] [CrossRef]
  87. Zhang, N.; Chen, D.; Cai, B.; Wang, S.; Niu, F.; Qin, L.; Huang, Y. Facile synthesis of CdS ZnWO4 composite photocatalysts for efficient visible light driven hydrogen evolution. Int. J. Hydrogen Energy 2017, 42, 1962–1969. [Google Scholar] [CrossRef]
  88. Zhang, S.; Wang, L.; Zeng, Y.; Xu, Y.; Tang, Y.; Luo, S.; Liu, Y.; Liu, C. CdS-Nanoparticles-Decorated Perpendicular Hybrid of MoS2 and N-Doped Graphene Nanosheets for Omnidirectional Enhancement of Photocatalytic Hydrogen Evolution. ChemCatChem 2016, 8, 2557–2564. [Google Scholar] [CrossRef]
  89. Zhang, Y.; Han, L.; Wang, C.; Wang, W.; Ling, T.; Yang, J.; Dong, C.; Lin, F.; Du, X.-W. Zinc-Blende CdS Nanocubes with Coordinated Facets for Photocatalytic Water Splitting. ACS Catal. 2017, 7, 1470–1477. [Google Scholar] [CrossRef]
  90. Zhao, H.; Sun, R.; Li, X.; Sun, X. Enhanced photocatalytic activity for hydrogen evolution from water by Zn0.5Cd0.5S/WS2 heterostructure. Mater. Sci. Semicond. Process. 2017, 59, 68–75. [Google Scholar] [CrossRef]
  91. Zhou, X.; Huang, J.; Zhang, H.; Sun, H.; Tu, W. Controlled synthesis of CdS nanoparticles and their surface loading with MoS 2 for hydrogen evolution under visible light. Int. J. Hydrogen Energy 2016, 41, 14758–14767. [Google Scholar] [CrossRef]
  92. Jiang, D.; Chen, X.; Zhang, Z.; Zhang, L.; Wang, Y.; Sun, Z.; Irfan, R.M.; Du, P. Highly efficient simultaneous hydrogen evolution and benzaldehyde production using cadmium sulfide nanorods decorated with small cobalt nanoparticles under visible light. J. Catal. 2018, 357, 147–153. [Google Scholar] [CrossRef]
  93. Kumar, D.P.; Park, H.; Kim, E.H.; Hong, S.; Gopannagari, M.; Reddy, D.A.; Kim, T.K. Noble metal-free metal-organic framework-derived onion slice-type hollow cobalt sulfide nanostructures: Enhanced activity of CdS for improving photocatalytic hydrogen production. Appl. Catal. B Environ. 2018, 224, 230–238. [Google Scholar] [CrossRef]
  94. Lv, J.-X.; Zhang, Z.-M.; Wang, J.; Lu, X.-L.; Zhang, W.; Lu, T.-B. In situ synthesis of CdS/graphdiyne heterojunction for enhanced photocatalytic activity of hydrogen production. ACS Appl. Mater. Interfaces 2019, 11, 2655–2661. [Google Scholar] [CrossRef]
  95. Feng, C.; Chen, Z.; Hou, J.; Li, J.; Li, X.; Xu, L.; Sun, M.; Zeng, R. Effectively enhanced photocatalytic hydrogen production performance of one-pot synthesized MoS2 clusters/CdS nanorod heterojunction material under visible light. Chem. Eng. J. 2018, 345, 404–413. [Google Scholar] [CrossRef]
  96. Liu, Y.; Ma, Y.; Liu, W.; Shang, Y.; Zhu, A.; Tan, P.; **ong, X.; Pan, J. Facet and morphology dependent photocatalytic hydrogen evolution with CdS nanoflowers using a novel mixed solvothermal strategy. J. Colloid Interface Sci. 2018, 513, 222–230. [Google Scholar] [CrossRef]
  97. Wang, L.; Xu, N.; Pan, X.; He, Y.; Wang, X.; Su, W. Cobalt lactate complex as a hole cocatalyst for significantly enhanced photocatalytic H2 production activity over CdS nanorods. Catal. Sci. Technol. 2018, 8, 1599–1605. [Google Scholar] [CrossRef]
  98. Abe, R. Recent progress on photocatalytic and photoelectrochemical water splitting under visible light irradiation. J. Photochem. Photobiol. C Photochem. Rev. 2010, 11, 179–209. [Google Scholar] [CrossRef]
  99. Ahmed, A.Y.; Kandiel, T.A.; Ivanova, I.; Bahnemann, D. Photocatalytic and photoelectrochemical oxidation mechanisms of methanol on TiO2 in aqueous solution. Appl. Surf. Sci. 2014, 319, 44–49. [Google Scholar] [CrossRef]
  100. Al-Ahmed, A.; Mukhtar, B.; Hossain, S.; Javaid Zaidi, S.; Rahman, S. Application of Titanium dioxide (TiO2) based photocatalytic nanomaterials in Solar and Hydrogen Energy: A Short Review. Mater. Sci. Forum 2012, 712, 25–47. [Google Scholar] [CrossRef]
  101. Amao, Y. Solar fuel production based on the artificial photosynthesis system. ChemCatChem 2011, 3, 458–474. [Google Scholar] [CrossRef]
  102. An, X.; Jimmy, C.Y. Graphene-based photocatalytic composites. RSC Adv. 2011, 1, 1426–1434. [Google Scholar] [CrossRef]
  103. Ashokkumar, M. An overview on semiconductor particulate systems for photoproduction of hydrogen. Int. J. Hydrogen Energy 1998, 23, 427–438. [Google Scholar] [CrossRef]
  104. Babu, V.J.; Vempati, S.; Uyar, T.; Ramakrishna, S. Review of one-dimensional and two-dimensional nanostructured materials for hydrogen generation. Phys. Chem. Chem. Phys. 2015, 17, 2960–2986. [Google Scholar] [CrossRef] [Green Version]
  105. Bai, S.; Yin, W.; Wang, L.; Li, Z.; **ong, Y. Surface and interface design in cocatalysts for photocatalytic water splitting and CO2 reduction. RSC Adv. 2016, 6, 57446–57463. [Google Scholar] [CrossRef]
  106. Bowker, M. Sustainable hydrogen production by the application of ambient temperature photocatalysis. Green Chem. 2011, 13, 2235–2246. [Google Scholar] [CrossRef]
  107. Chen, X.; Li, C.; Grätzel, M.; Kostecki, R.; Mao, S.S. Nanomaterials for renewable energy production and storage. Chem. Soc. Rev. 2012, 41, 7909–7937. [Google Scholar] [CrossRef]
  108. Colmenares, J.C.; Luque, R. Heterogeneous photocatalytic nanomaterials: Prospects and challenges in selective transformations of biomass-derived compounds. Chem. Soc. Rev. 2014, 43, 765–778. [Google Scholar] [CrossRef] [PubMed]
  109. Colón, G. Towards the hydrogen production by photocatalysis. Appl. Catal. A Gen. 2016, 518, 48–59. [Google Scholar] [CrossRef]
  110. Fang, W.; **ng, M.; Zhang, J. Modifications on reduced titanium dioxide photocatalysts: A review. J. Photochem. Photobiol. C Photochem. Rev. 2017, 32, 21–39. [Google Scholar] [CrossRef]
  111. Fornasiero, P.; Christoforidis, K.C. Photocatalytic Hydrogen production: A rift into the future energy supply. ChemCatChem 2017, 9, 1523–1544. [Google Scholar]
  112. Fresno, F.; Portela, R.; Suárez, S.; Coronado, J.M. Photocatalytic materials: Recent achievements and near future trends. J. Mater. Chem. A 2014, 2, 2863–2884. [Google Scholar] [CrossRef]
  113. Gholipour, M.R.; Dinh, C.-T.; Béland, F.; Do, T.-O. Nanocomposite heterojunctions as sunlight-driven photocatalysts for hydrogen production from water splitting. Nanoscale 2015, 7, 8187–8208. [Google Scholar] [CrossRef]
  114. Grabowska, E. Selected perovskite oxides: Characterization, preparation and photocatalytic properties—A review. Appl. Catal. B Environ. 2016, 186, 97–126. [Google Scholar] [CrossRef]
  115. Guo, L.; **g, D.; Liu, M.; Chen, Y.; Shen, S.; Shi, J.; Zhang, K. Functionalized nanostructures for enhanced photocatalytic performance under solar light. Beilstein J. Nanotechnol. 2014, 5, 994–1004. [Google Scholar] [CrossRef] [Green Version]
  116. Han, B.; Hu, Y.H. MoS2 as a co-catalyst for photocatalytic hydrogen production from water. Energy Sci. Eng. 2016, 4, 285–304. [Google Scholar] [CrossRef]
  117. Hisatomi, T.; Kubota, J.; Domen, K. Recent advances in semiconductors for photocatalytic and photoelectrochemical water splitting. Chem. Soc. Rev. 2014, 43, 7520–7535. [Google Scholar] [CrossRef] [PubMed]
  118. Jiao, W.; Shen, W.; Rahman, Z.U.; Wang, D. Recent progress in red semiconductor photocatalysts for solar energy conversion and utilization. Nanotechnol. Rev. 2016, 5, 135–145. [Google Scholar] [CrossRef]
  119. Junge, H.; Rockstroh, N.; Fischer, S.; Brückner, A.; Ludwig, R.; Lochbrunner, S.; Kühn, O.; Beller, M. Light to Hydrogen: Photocatalytic Hydrogen Generation from Water with Molecularly-Defined Iron Complexes. Inorganics 2017, 5, 14. [Google Scholar] [CrossRef]
  120. Kagkoura, A.; Skaltsas, T.; Tagmatarchis, N. Transition metal chalcogenides/graphene ensembles for light-induced energy applications. Chem. Eur. J. 2017, 23, 12967–12979. [Google Scholar] [CrossRef]
  121. Kitano, M.; Tsujimaru, K.; Anpo, M. Hydrogen production using highly active titanium oxide-based photocatalysts. Top. Catal. 2008, 49, 4. [Google Scholar] [CrossRef]
  122. Kudo, A.; Miseki, Y. Heterogeneous photocatalyst materials for water splitting. Chem. Soc. Rev. 2009, 38, 253–278. [Google Scholar] [CrossRef]
  123. Kumar, P.S.; Sundaramurthy, J.; Sundarrajan, S.; Babu, V.J.; Singh, G.; Allakhverdiev, S.I.; Ramakrishna, S. Hierarchical electrospun nanofibers for energy harvesting, production and environmental remediation. Energy Environ. Sci. 2014, 7, 3192–3222. [Google Scholar] [CrossRef] [Green Version]
  124. Leung, D.Y.; Fu, X.; Wang, C.; Ni, M.; Leung, M.K.; Wang, X.; Fu, X. Hydrogen Production over Titania-Based Photocatalysts. ChemSusChem 2010, 3, 681–694. [Google Scholar] [CrossRef] [PubMed]
  125. Li, C.; Xu, Y.; Tu, W.; Chen, G.; Xu, R. Metal-free photocatalysts for various applications in energy conversion and environmental purification. Green Chem. 2017, 19, 882–899. [Google Scholar] [CrossRef]
  126. Francesco, P.; Fabrizio, S.; Marco, M.; Claudio, M.; Valter, M. The Role of Surface Texture on the Photocatalytic H2Production on TiO2. Catalysts 2019, 9, 32. [Google Scholar]
  127. Zhang, X.; Wang, Y.; Liu, B.; Sang, Y.; Liu, H. Heterostructures construction on TiO2 nanobelts: A powerful tool for building high-performance photocatalysts. Appl. Catal. B Environ. 2017, 202, 620–641. [Google Scholar] [CrossRef]
  128. Li, X.; Yu, J.; Wageh, S.; Al-Ghamdi, A.A.; **e, J. Graphene in photocatalysis: A review. Small 2016, 12, 6640–6696. [Google Scholar] [CrossRef] [PubMed]
  129. Li, Y.; Li, Y.-L.; Sa, B.; Ahuja, R. Review of two-dimensional materials for photocatalytic water splitting from a theoretical perspective. Catal. Sci. Technol. 2017, 7, 545–559. [Google Scholar] [CrossRef]
  130. Low, J.; Jiang, C.; Cheng, B.; Wageh, S.; Al-Ghamdi, A.A.; Yu, J. A Review of Direct Z-Scheme Photocatalysts. Small Methods 2017, 1, 1700080. [Google Scholar] [CrossRef]
  131. Maeda, K. Photocatalytic water splitting using semiconductor particles: History and recent developments. J. Photochem. Photobiol. C Photochem. Rev. 2011, 12, 237–268. [Google Scholar] [CrossRef]
  132. Martha, S.; Sahoo, P.C.; Parida, K. An overview on visible light responsive metal oxide based photocatalysts for hydrogen energy production. RSC Adv. 2015, 5, 61535–61553. [Google Scholar] [CrossRef]
  133. Matsuoka, M.; Kitano, M.; Takeuchi, M.; Tsujimaru, K.; Anpo, M.; Thomas, J.M. Photocatalysis for new energy production: Recent advances in photocatalytic water splitting reactions for hydrogen production. Catal. Today 2007, 122, 51–61. [Google Scholar] [CrossRef]
  134. Morales-Torres, S.; Pastrana-Martínez, L.M.; Figueiredo, J.L.; Faria, J.L.; Silva, A.M. Design of graphene-based TiO2 photocatalysts—A review. Environ. Sci. Pollut. Res. 2012, 19, 3676–3687. [Google Scholar] [CrossRef] [PubMed]
  135. Nguyen-Phan, T.-D.; Baber, A.E.; Rodriguez, J.A.; Senanayake, S.D. Au and Pt nanoparticle supported catalysts tailored for H2 production: From models to powder catalysts. Appl. Catal. A Gen. 2016, 518, 18–47. [Google Scholar] [CrossRef]
  136. Ni, M.; Leung, M.K.; Leung, D.Y.; Sumathy, K. A review and recent developments in photocatalytic water-splitting using TiO2 for hydrogen production. Renew. Sustain. Energy Rev. 2007, 11, 401–425. [Google Scholar] [CrossRef]
  137. Nurlaela, E.; Ziani, A.; Takanabe, K. Tantalum nitride for photocatalytic water splitting: Concept and applications. Mater. Renew. Sustain. Energy 2016, 5, 18. [Google Scholar] [CrossRef]
  138. Pasternak, S.; Paz, Y. On the similarity and dissimilarity between photocatalytic water splitting and photocatalytic degradation of pollutants. ChemPhysChem 2013, 14, 2059–2070. [Google Scholar] [CrossRef]
  139. Preethi, V.; Kanmani, S. Photocatalytic hydrogen production. Mater. Sci. Semicond. Process. 2013, 16, 561–575. [Google Scholar] [CrossRef]
  140. Primo, A.; Corma, A.; García, H. Titania supported gold nanoparticles as photocatalyst. Phys. Chem. Chem. Phys. 2011, 13, 886–910. [Google Scholar] [CrossRef]
  141. Protti, S.; Albini, A.; Serpone, N. Photocatalytic generation of solar fuels from the reduction of H2O and CO2: A look at the patent literature. Phys. Chem. Chem. Phys. 2014, 16, 19790–19827. [Google Scholar] [CrossRef]
  142. Puga, A.V. Photocatalytic production of hydrogen from biomass-derived feedstocks. Coord. Chem. Rev. 2016, 315, 1–66. [Google Scholar] [CrossRef]
  143. Ran, J.; Zhang, J.; Yu, J.; Jaroniec, M.; Qiao, S.Z. Earth-abundant cocatalysts for semiconductor-based photocatalytic water splitting. Chem. Soc. Rev. 2014, 43, 7787–7812. [Google Scholar] [CrossRef]
  144. Samokhvalov, A. Hydrogen by photocatalysis with nitrogen codoped titanium dioxide. Renew. Sustain. Energy Rev. 2017, 72, 981–1000. [Google Scholar] [CrossRef]
  145. Serrano, D.P.; Coronado, J.M.; Víctor, A.; Pizarro, P.; Botas, J.Á. Advances in the design of ordered mesoporous materials for low-carbon catalytic hydrogen production. J. Mater. Chem. A 2013, 1, 12016–12027. [Google Scholar] [CrossRef]
  146. Sharma, P.; Kolhe, M.L. Review of sustainable solar hydrogen production using photon fuel on artificial leaf. Int. J. Hydrogen Energy 2017, 42, 22704–22712. [Google Scholar] [CrossRef]
  147. Shi, J.; Guo, L. ABO3-based photocatalysts for water splitting. Prog. Nat. Sci. Mater. Int. 2012, 22, 592–615. [Google Scholar] [CrossRef]
  148. Shimura, K.; Yoshida, H. Heterogeneous photocatalytic hydrogen production from water and biomass derivatives. Energy Environ. Sci. 2011, 4, 2467–2481. [Google Scholar] [CrossRef]
  149. Stroyuk, A.; Kryukov, A.; Kuchmii, S.Y.; Pokhodenko, V. Semiconductor photocatalytic systems for the production of hydrogen by the action of visible light. Theor. Exp. Chem. 2009, 45, 209. [Google Scholar] [CrossRef]
  150. Wang, H.; Yuan, X.; Wu, Y.; Huang, H.; Peng, X.; Zeng, G.; Zhong, H.; Liang, J.; Ren, M. Graphene-based materials: Fabrication, characterization and application for the decontamination of wastewater and wastegas and hydrogen storage/generation. Adv. Colloid Interface Sci. 2013, 195, 19–40. [Google Scholar] [CrossRef]
  151. Wang, H.; Zhang, L.; Chen, Z.; Hu, J.; Li, S.; Wang, Z.; Liu, J.; Wang, X. Semiconductor heterojunction photocatalysts: Design, construction, and photocatalytic performances. Chem. Soc. Rev. 2014, 43, 5234–5244. [Google Scholar] [CrossRef]
  152. Wang, L. Strategies for efficient solar water splitting using carbon nitride. Chem. Asian J. 2017, 12, 1421–1434. [Google Scholar]
  153. Wang, M.; Han, K.; Zhang, S.; Sun, L. Integration of organometallic complexes with semiconductors and other nanomaterials for photocatalytic H2 production. Coord. Chem. Rev. 2015, 287, 1–14. [Google Scholar] [CrossRef]
  154. Watanabe, M. Dye-sensitized photocatalyst for effective water splitting catalyst. Sci. Technol. Adv. Mater. 2017, 18, 705–723. [Google Scholar] [CrossRef]
  155. Wen, M.; Mori, K.; Kuwahara, Y.; An, T.; Yamashita, H. Design and architecture of metal organic frameworks for visible light enhanced hydrogen production. Appl. Catal. B Environ. 2017, 218, 555–569. [Google Scholar] [CrossRef]
  156. **ao, F.X.; Miao, J.; Tao, H.B.; Hung, S.F.; Wang, H.Y.; Yang, H.B.; Chen, J.; Chen, R.; Liu, B. One-Dimensional Hybrid Nanostructures for Heterogeneous Photocatalysis and Photoelectrocatalysis. Small 2015, 11, 2115–2131. [Google Scholar] [CrossRef]
  157. **e, G.; Zhang, K.; Guo, B.; Liu, Q.; Fang, L.; Gong, J.R. Graphene-Based Materials for Hydrogen Generation from Light-Driven Water Splitting. Adv. Mater. 2013, 25, 3820–3839. [Google Scholar] [CrossRef]
  158. **ng, J.; Fang, W.Q.; Zhao, H.J.; Yang, H.G. Inorganic photocatalysts for overall water splitting. Chem. Asian J. 2012, 7, 642–657. [Google Scholar] [CrossRef]
  159. Xu, Y.; Xu, R. Nickel-based cocatalysts for photocatalytic hydrogen production. Appl. Surf. Sci. 2015, 351, 779–793. [Google Scholar] [CrossRef]
  160. Xu, Y.; Zhang, B. Hydrogen photogeneration from water on the biomimetic hybrid artificial photocatalytic systems of semiconductors and earth-abundant metal complexes: Progress and challenges. Catal. Sci. Technol. 2015, 5, 3084–3096. [Google Scholar] [CrossRef]
  161. Ye, S.; Wang, R.; Wu, M.-Z.; Yuan, Y.-P. A review on gC3N4 for photocatalytic water splitting and CO2 reduction. Appl. Surf. Sci. 2015, 358, 15–27. [Google Scholar] [CrossRef]
  162. Yin, S.; Han, J.; Zhou, T.; Xu, R. Recent progress in gC3N4 based low cost photocatalytic system: Activity enhancement and emerging applications. Catal. Sci. Technol. 2015, 5, 5048–5061. [Google Scholar] [CrossRef]
  163. Yuan, Y.J.; Lu, H.W.; Yu, Z.T.; Zou, Z.G. Noble-Metal-Free Molybdenum Disulfide Cocatalyst for Photocatalytic Hydrogen Production. ChemSusChem 2015, 8, 4113–4127. [Google Scholar] [CrossRef]
  164. Zhang, P.; Zhang, J.; Gong, J. Tantalum-based semiconductors for solar water splitting. Chem. Soc. Rev. 2014, 43, 4395–4422. [Google Scholar] [CrossRef]
  165. Zhang, Q.; Gangadharan, D.T.; Liu, Y.; Xu, Z.; Chaker, M.; Ma, D. Recent advancements in plasmon-enhanced visible light-driven water splitting. J. Mater. 2017, 3, 33–50. [Google Scholar] [CrossRef]
  166. Zhang, X.; Peng, T.; Song, S. Recent advances in dye-sensitized semiconductor systems for photocatalytic hydrogen production. J. Mater. Chem. A 2016, 4, 2365–2402. [Google Scholar] [CrossRef]
  167. Zhao, X.; Wang, P.; Long, M. Electro- and Photocatalytic Hydrogen Production by Molecular Cobalt Complexes with Pentadentate Ligands. Comments Inorg. Chem. 2017, 37, 238–270. [Google Scholar] [CrossRef]
  168. Zhao, Z.; Sun, Y.; Dong, F. Graphitic carbon nitride based nanocomposites: A review. Nanoscale 2015, 7, 15–37. [Google Scholar] [CrossRef] [PubMed]
  169. Zou, X.; Zhang, Y. Noble metal-free hydrogen evolution catalysts for water splitting. Chem. Soc. Rev. 2015, 44, 5148–5180. [Google Scholar] [CrossRef] [PubMed]
  170. Shwetharani, R.; Sakar, M.; Fernando, C.; Binas, V.; Balakrishna, R.G. Recent advances and strategies to tailor the energy levels, active sites and electron mobility in titania and its doped/composite analogues for hydrogen evolution in sunlight. Catal. Sci. Technol. 2019, 9, 12–46. [Google Scholar] [CrossRef]
  171. Yuan, Y.-J.; Chen, D.; Yu, Z.-T.; Zou, Z.-G. Cadmium sulfide-based nanomaterials for photocatalytic hydrogen production. J. Mater. Chem. A 2018, 6, 11606–11630. [Google Scholar] [CrossRef]
  172. Yuan, Y.-J.; Ye, Z.-J.; Lu, H.-W.; Hu, B.; Li, Y.-H.; Chen, D.-Q.; Zhong, J.-S.; Yu, Z.-T.; Zou, Z.-G. Constructing anatase TiO2 nanosheets with exposed (001) facets/layered MoS2 two-dimensional nanojunctions for enhanced solar hydrogen generation. ACS Catal. 2015, 6, 532–541. [Google Scholar] [CrossRef]
  173. Liu, S.-H.; Tang, W.-T.; Lin, W.-X. Self-assembled ionic liquid synthesis of nitrogen-doped mesoporous TiO2 for visible-light-responsive hydrogen production. Int. J. Hydrogen Energy 2017, 42, 24006–24013. [Google Scholar] [CrossRef]
  174. Chen, Z.; Jiang, X.; Zhu, C.; Shi, C. Chromium-modified Bi4Ti3O12 photocatalyst: Application for hydrogen evolution and pollutant degradation. Appl. Catal. B Environ. 2016, 199, 241–251. [Google Scholar] [CrossRef]
  175. Yang, S.; Wang, H.; Yu, H.; Zhang, S.; Fang, Y.; Zhang, S.; Peng, F. A facile fabrication of hierarchical Ag nanoparticles-decorated N-TiO2 with enhanced photocatalytic hydrogen production under solar light. Int. J. Hydrogen Energy 2016, 41, 3446–3455. [Google Scholar] [CrossRef]
  176. Silva, L.A.; Ryu, S.Y.; Choi, J.; Choi, W.; Hoffmann, M.R. Photocatalytic hydrogen production with visible light over Pt-interlinked hybrid composites of cubic-phase and hexagonal-phase CdS. J. Phys. Chem. C 2008, 112, 12069–12073. [Google Scholar] [CrossRef]
  177. Qin, N.; **ong, J.; Liang, R.; Liu, Y.; Zhang, S.; Li, Y.; Li, Z.; Wu, L. Highly efficient photocatalytic H2 evolution over MoS2/CdS-TiO2 nanofibers prepared by an electrospinning mediated photodeposition method. Appl. Catal. B Environ. 2017, 202, 374–380. [Google Scholar] [CrossRef]
  178. Gopannagari, M.; Kumar, D.P.; Reddy, D.A.; Hong, S.; Song, M.I.; Kim, T.K. In situ preparation of few-layered WS2 nanosheets and exfoliation into bilayers on CdS nanorods for ultrafast charge carrier migrations toward enhanced photocatalytic hydrogen production. J. Catal. 2017, 351, 153–160. [Google Scholar] [CrossRef]
  179. Wang, M.; Na, Y.; Gorlov, M.; Sun, L. Light-driven hydrogen production catalysed by transition metal complexes in homogeneous systems. Dalton Trans. 2009, 6458–6467. [Google Scholar] [CrossRef] [PubMed]
  180. Linkous, C.A.; Huang, C.; Fowler, J.R. UV photochemical oxidation of aqueous sodium sulfide to produce hydrogen and sulfur. J. Photochem. Photobiol. A Chem. 2004, 168, 153–160. [Google Scholar] [CrossRef]
  181. Huang, C.; Linkous, C.A.; Adebiyi, O.; T-Raissi, A. Hydrogen production via photolytic oxidation of aqueous sodium sulfite solutions. Environ. Sci. Technol. 2010, 44, 5283–5288. [Google Scholar] [CrossRef]
  182. Li, C.; Hu, P.; Meng, H.; Jiang, Z. Role of Sulfites in the Water Splitting Reaction. J. Solut. Chem. 2016, 45, 67–80. [Google Scholar] [CrossRef]
  183. Husin, H.; Adisalamun, S.Y.; Asnawi, T.M.; Hasfita, F. Pt nanoparticle on La0.02Na0.98TaO3 catalyst for hydrogen evolution from glycerol aqueous solution. AIP Conf. Proc. 2017, 1788, 030073. [Google Scholar]
  184. López-Tenllado, F.; Hidalgo-Carrillo, J.; Montes, V.; Marinas, A.; Urbano, F.; Marinas, J.; Ilieva, L.; Tabakova, T.; Reid, F. A comparative study of hydrogen photocatalytic production from glycerol and propan-2-ol on M/TiO2 systems (M = Au, Pt, Pd). Catal. Today 2017, 280, 58–64. [Google Scholar] [CrossRef]
  185. Li, F.; Gu, Q.; Niu, Y.; Wang, R.; Tong, Y.; Zhu, S.; Zhang, H.; Zhang, Z.; Wang, X. Hydrogen evolution from aqueous-phase photocatalytic reforming of ethylene glycol over Pt/TiO2 catalysts: Role of Pt and product distribution. Appl. Surf. Sci. 2017, 391, 251–258. [Google Scholar] [CrossRef]
  186. Oscar, Q.C.; Socorro, O.R.; Solís-Gómezb, A.; Rosendo, L.; Ricardo, G. Enhanced photocatalytic hydrogen production by CdS nanofibers modified with graphene oxide and nickel nanoparticles under visible light. Fuel 2019, 237, 227–235. [Google Scholar]
  187. Andrea, S.; Francesca, G.; Federica, M.; Michela, S.; Daniele, D.; Lorenzo, M.; Antonella, P. Photocatalytic hydrogen evolution assisted by aqueous (waste)biomass under simulated solar light: Oxidized g-C3N4 vs. P25 titanium dioxide. Int. J. Hydrogen Energy 2019, 44, 4072–4078. [Google Scholar]
  188. Tao, C.; Jie, M.; Qingyun, L.; **ao, W.; Jixue, L.; Ze, Z. One-step synthesis of hollow BaZrO3 nanocrystals with oxygen vacancies for photocatalytic hydrogen evolution from pure water. J. Alloys Compd. 2019, 780, 498–503. [Google Scholar]
  189. Bahruji, H.; Bowker, M.; Davies, P.R.; Pedrono, F. New insights into the mechanism of photocatalytic reforming on Pd/TiO2. Appl. Catal. B Environ. 2011, 107, 205–209. [Google Scholar] [CrossRef]
  190. Fu, X.; Wang, X.; Leung, D.Y.; Gu, Q.; Chen, S.; Huang, H. Photocatalytic reforming of C3-polyols for H2 production: Part (I). Role of their OH groups. Appl. Catal. B Environ. 2011, 106, 681–688. [Google Scholar] [CrossRef]
  191. Shkrob, I.A.; Sauer, M.C.; Gosztola, D. Efficient, rapid photooxidation of chemisorbed polyhydroxyl alcohols and carbohydrates by TiO2 nanoparticles in an aqueous solution. J. Phys. Chem. B 2004, 108, 12512–12517. [Google Scholar] [CrossRef]
  192. Shkrob, I.A.; Sauer, M.C. Hole Scavenging and Photo-Stimulated Recombination of Electron—Hole Pairs in Aqueous TiO2 Nanoparticles. J. Phys. Chem. B 2004, 108, 12497–12511. [Google Scholar] [CrossRef]
  193. Du, M.-H.; Feng, J.; Zhang, S. Photo-oxidation of polyhydroxyl molecules on TiO2 surfaces: From hole scavenging to light-induced self-assembly of TiO2-cyclodextrin wires. Phys. Rev. Lett. 2007, 98, 066102. [Google Scholar] [CrossRef]
  194. Wang, B.; Zhang, J.; Huang, F. Enhanced visible light photocatalytic H2 evolution of metal-free g-C3N4/SiC heterostructured photocatalysts. Appl. Surf. Sci. 2017, 391, 449–456. [Google Scholar] [CrossRef]
  195. Zhang, Z.; Zhang, Y.; Lu, L.; Si, Y.; Zhang, S.; Chen, Y.; Dai, K.; Duan, P.; Duan, L.; Liu, J. Graphitic carbon nitride nanosheet for photocatalytic hydrogen production: The impact of morphology and element composition. Appl. Surf. Sci. 2017, 391, 369–375. [Google Scholar] [CrossRef]
  196. Fang, L.J.; Wang, X.L.; Li, Y.H.; Liu, P.F.; Wang, Y.L.; Zeng, H.D.; Yang, H.G. Nickel nanoparticles coated with graphene layers as efficient co-catalyst for photocatalytic hydrogen evolution. Appl. Catal. B Environ. 2017, 200, 578–584. [Google Scholar] [CrossRef]
  197. Yuan, Y.J.; Shen, Z.; Wu, S.; Su, Y.; Pei, L.; Ji, Z.; Ding, M.; Bai, W.; Chen, Y.; Yu, Z.T.; et al. Liquid exfoliation of g-C3N4 nanosheets to construct 2D-2D MoS2/g-C3N4 photocatalyst for enhanced photocatalytic H2 production activity. Appl. Catal. B Environ. 2019, 246, 120–128. [Google Scholar] [CrossRef]
  198. Cai, J.; Shen, J.; Zhang, X.; Ng, Y.H.; Huang, J.; Guo, W.; Lin, C.; Lai, Y. Light-Driven Sustainable Hydrogen Production Utilizing TiO2 Nanostructures: A Review. Small 2019, 3, 1800184. [Google Scholar] [CrossRef]
  199. Wang, C.; Wang, L.; **, J.; Liu, J.; Li, Y.; Wu, M.; Chen, L.; Wang, B.; Yang, X.; Su, B.-L. Probing effective photocorrosion inhibition and highly improved photocatalytic hydrogen production on monodisperse PANI@ CdS core-shell nanospheres. Appl. Catal. B Environ. 2016, 188, 351–359. [Google Scholar] [CrossRef]
  200. Song, J.; Zhao, H.; Sun, R.; Li, X.; Sun, D. An efficient hydrogen evolution catalyst composed of palladium phosphorous sulphide (PdP ~ 0.33 S ~ 1.67) and twin nanocrystal Zn0.5Cd0.5S solid solution with both homo-and hetero-junctions. Energy Environ. Sci. 2017, 10, 225–235. [Google Scholar] [CrossRef]
  201. Ma, S.; **e, J.; Wen, J.; He, K.; Li, X.; Liu, W.; Zhang, X. Constructing 2D layered hybrid CdS nanosheets/MoS2 heterojunctions for enhanced visible-light photocatalytic H2 generation. Appl. Surf. Sci. 2017, 391, 580–591. [Google Scholar] [CrossRef]
  202. Cheng, F.; Yin, H.; **ang, Q. Low-temperature solid-state preparation of ternary CdS/g-C3N4/CuS nanocomposites for enhanced visible-light photocatalytic H2-production activity. Appl. Surf. Sci. 2017, 391, 432–439. [Google Scholar] [CrossRef]
  203. Tian, F.; Hou, D.; Hu, F.; **e, K.; Qiao, X.; Li, D. Pouous TiO2 nanofibers decorated CdS nanoparticles by SILAR method for enhanced visible-light-driven photocatalytic activity. Appl. Surf. Sci. 2017, 391, 295–302. [Google Scholar] [CrossRef]
  204. Vignesh, K.; Suganthi, A.; Min, B.-K.; Kang, M. Photocatalytic activity of magnetically recoverable MnFe2O4/g-C3N4/TiO2 nanocomposite under simulated solar light irradiation. J. Mol. Catal. A Chem. 2014, 395, 373–383. [Google Scholar] [CrossRef]
  205. Zhen, W.; Ning, X.; Yang, B.; Wu, Y.; Li, Z.; Lu, G. The enhancement of CdS photocatalytic activity for water splitting via anti-photocorrosion by coating Ni2P shell and removing nascent formed oxygen with artificial gill. Appl. Catal. B Environ. 2018, 221, 243–257. [Google Scholar] [CrossRef]
Figure 1. Schematic representation of the water-splitting process on a photocatalyst surface under light irradiation [1]. Reproduced with permission from Ref. [1]. Copyright 2019, Elsevier.
Figure 1. Schematic representation of the water-splitting process on a photocatalyst surface under light irradiation [1]. Reproduced with permission from Ref. [1]. Copyright 2019, Elsevier.
Catalysts 09 00276 g001
Figure 2. Photocatalytic H2 production efficiency of TiO2-p25 using various sacrificial agents.
Figure 2. Photocatalytic H2 production efficiency of TiO2-p25 using various sacrificial agents.
Catalysts 09 00276 g002
Figure 3. Photocatalytic H2 production efficiency of g-C3N4 using various sacrificial agents.
Figure 3. Photocatalytic H2 production efficiency of g-C3N4 using various sacrificial agents.
Catalysts 09 00276 g003
Figure 4. Photocatalytic H2 production efficiency of CdS using various sacrificial agents.
Figure 4. Photocatalytic H2 production efficiency of CdS using various sacrificial agents.
Catalysts 09 00276 g004
Figure 5. H2 production efficiency of sacrificial agents without photocatalyst (photolysis).
Figure 5. H2 production efficiency of sacrificial agents without photocatalyst (photolysis).
Catalysts 09 00276 g005
Figure 6. (a) Schematic and (b) photograph of the reactor used for photocatalytic H2 production.
Figure 6. (a) Schematic and (b) photograph of the reactor used for photocatalytic H2 production.
Catalysts 09 00276 g006
Table 1. Photocatalytic H2 production efficiency of TiO2 using methanol sacrificial agent.
Table 1. Photocatalytic H2 production efficiency of TiO2 using methanol sacrificial agent.
Catalyst Amount (g/L)Concentration of Methanol (%)Light SourceH2 Production Efficiency (μmol/g/h)Reference
110300 W of Xe (without UV cutoff filter)42.00[420]
0.616.66300 W of Xe (with UV cutoff filter)18.47[217]
0.520300 W of Xe (with UV cutoff filter)~20.00[194]
1.2925.8300 W of Xe (with UV cutoff filter)~2.00[421]
Table 2. TOC of solutions after the completion of the photocatalytic reaction.
Table 2. TOC of solutions after the completion of the photocatalytic reaction.
SampleTOC (mg/L)
Blank (Before Light Irradiation)TiO2-P25
Water8.659-
Methanol30,45015,530
Ethanol43,68017,070
Isopropanol55,01017,770
Glycerol54,22018,700
Ethylene glycol59,08017,930
Glucose769911,500
Lactic acid47,31020,440

Share and Cite

MDPI and ACS Style

Kumaravel, V.; Imam, M.D.; Badreldin, A.; Chava, R.K.; Do, J.Y.; Kang, M.; Abdel-Wahab, A. Photocatalytic Hydrogen Production: Role of Sacrificial Reagents on the Activity of Oxide, Carbon, and Sulfide Catalysts. Catalysts 2019, 9, 276. https://doi.org/10.3390/catal9030276

AMA Style

Kumaravel V, Imam MD, Badreldin A, Chava RK, Do JY, Kang M, Abdel-Wahab A. Photocatalytic Hydrogen Production: Role of Sacrificial Reagents on the Activity of Oxide, Carbon, and Sulfide Catalysts. Catalysts. 2019; 9(3):276. https://doi.org/10.3390/catal9030276

Chicago/Turabian Style

Kumaravel, Vignesh, Muhammad Danyal Imam, Ahmed Badreldin, Rama Krishna Chava, Jeong Yeon Do, Misook Kang, and Ahmed Abdel-Wahab. 2019. "Photocatalytic Hydrogen Production: Role of Sacrificial Reagents on the Activity of Oxide, Carbon, and Sulfide Catalysts" Catalysts 9, no. 3: 276. https://doi.org/10.3390/catal9030276

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop