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The Application of Microwave-Assisted Technology in Chemical Reaction

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Microwave Chemistry".

Deadline for manuscript submissions: 31 July 2024 | Viewed by 7883

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Special Issue Editors

Prof. Dr. Yong Nie

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Guest Editor

College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
Interests: microwave; biomass energy; process intensification; biodiesel; reactor development

Dr. Qinglong **e

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Guest Editor

College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
Interests: microwave; biodiesel; glycerol; process intensification; fixed-bed reactor; numerical simulation

Special Issue Information

Dear Colleagues,

Compared with conventional heating, microwave heating offers many advantages, including rapid and uniform heating, ease of set-up and operation, and low cost. The microwave-assisted technology has been applied in various organic and inorganic reactions, which can enhance the processes. An exploration of the thermal and non-thermal intensification effects of the microwave irradiation, especially at the molecular scale, will help us understand the microwave technology more deeply and promote its applications. This Special Issue aims to collect original research papers and review articles focused on the abovementioned aspects of microwave-assisted chemical reactions. Manuscripts presenting research on the application of microwave technology in chemical reactions, heat and mass transfer in microwave-assisted reactions, numerical simulation of microwave-heated processes, and intensification mechanism of microwave irradiation are all welcome.

Prof. Dr. Yong Nie
Dr. Qinglong **e
Guest Editor

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Keywords

microwave
process intensification
numerical simulation
thermal effect
non-thermal effect
reaction kinetics
heat transfer
microwave catalysis

Published Papers (6 papers)

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Research

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14 pages, 8192 KiB

Open AccessArticle

Effects of TiO₂ Nanoparticles Synthesized via Microwave Assistance on Adsorption and Photocatalytic Degradation of Ciprofloxacin

by Debora Briševac, Ivana Gabelica, Davor Ljubas, Arijeta Bafti, Gordana Matijašić and Lidija Ćurković

Molecules 2024, 29(12), 2935; https://doi.org/10.3390/molecules29122935 - 20 Jun 2024

Viewed by 351

Abstract

In this study, the optimal microwave-assisted sol-gel synthesis parameters for achieving TiO₂ nanoparticles with the highest specific surface area and photocatalytic activity were determined. Titanium isopropoxide was used as a precursor to prepare the sol (colloidal solution) of TiO₂. Isopropanol was used as a solvent; acetylacetone was used as a complexation moderator; and nitric acid was used as a catalyst. Four samples of titanium dioxide were synthesized from the prepared colloidal solution in a microwave reactor at a temperature of 150 °C for 30 min and at a temperature of 200 °C for 10, 20, and 30 min. The phase composition of the TiO₂ samples was determined by X-ray diffraction analysis (XRD) and Fourier-transform infrared spectroscopy (FTIR). Nitrogen adsorption/desorption isotherms were used to determine the specific surface area and pore size distributions using the Brunauer–Emmett–Teller (BET) method. The band-gap energy values of the TiO₂ samples were determined by diffuse reflectance spectroscopy (DRS). The distribution of Ti and O in the TiO₂ samples was determined by SEM-EDS analysis. The effects of adsorption and photocatalytic activity of the prepared TiO₂ samples were evaluated by the degradation of ciprofloxacin (CIP) as an emerging organic pollutant (EOP) under UV-A light (365 nm). The results of the photocatalytic activity of the synthesized TiO₂ nanoparticles were compared to the benchmark Degussa P25 TiO₂. Kinetic parameters of adsorption and photocatalysis were determined and analyzed. It was found that crystalline TiO₂ nanoparticles with the highest specific surface area, the lowest energy band gap, and the highest photocatalytic degradation were the samples synthesized at 200 °C for 10 min. The results indicate that CIP degradation by all TiO₂ samples prepared at 200 °C show a synergistic effect of adsorption and photocatalytic degradation in the removal process. Full article

(This article belongs to the Special Issue The Application of Microwave-Assisted Technology in Chemical Reaction)

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14 pages, 1411 KiB

Open AccessArticle

Microwave Heating for Synthesis of Carbonaceous Adsorbents for Removal of Toxic Organic and Inorganic Contaminants

by Aleksandra Bazan-Wozniak, Katarzyna Machelak, Agnieszka Nosal-Wiercińska and Robert Pietrzak

Molecules 2023, 28(19), 6825; https://doi.org/10.3390/molecules28196825 - 27 Sep 2023

Cited by 3 | Viewed by 721

Abstract

The residues obtained from the extraction of Inonotus obliquus fungus were used to produce carbonaceous adsorbents. The initial material was subjected to pyrolysis in a microwave oven. The adsorbents were characterized through elemental analysis, low-temperature nitrogen adsorption/desorption isotherms, and Boehm titration. The carbonaceous adsorbents were tested for the removal of NO₂, methylene blue, and malachite green. The results indicated that the obtained carbonaceous adsorbents exhibited basic characteristics and possessed specific surface areas of 372 and 502 m²/g. The adsorption process of liquid contaminants was modeled using the single-layer Langmuir model. The maximum adsorption capacities were found to be 101 and 109 mg/g for methylene blue, and 75 and 77 mg/g for malachite green. The kinetic study demonstrated that the adsorption of methylene blue and malachite green was better described by a pseudo-second order model. The study affirmed that the adsorption of organic dyes onto the resultant carbonaceous adsorbents was both spontaneous and endothermic. The study also demonstrated that the presence of an air stream during the NO₂ adsorption process and prehumidization of the adsorbent with humid air had a beneficial effect on the obtained sorption capacities. In conclusion, the study demonstrated that pyrolysis of the extraction residues from the fungus Inonotus obliquus yields highly effective, environmentally friendly, and cost-efficient carbonaceous adsorbents for the removal of both gaseous and liquid pollutants. Full article

(This article belongs to the Special Issue The Application of Microwave-Assisted Technology in Chemical Reaction)

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16 pages, 5277 KiB

Open AccessArticle

Efficient Treatment of Oily Sludge via Fast Microwave-Assisted Pyrolysis, Followed by Thermal Plasma Vitrification

by Qinglong **e, Zhen Chen, Yuqiang Zhou, Tongbo Pan, Ying Duan, Shangzhi Yu, **aojiang Liang, Zhenyu Wu, Weirong Ji and Yong Nie

Molecules 2023, 28(10), 4036; https://doi.org/10.3390/molecules28104036 - 11 May 2023

Cited by 1 | Viewed by 1463

Abstract

Oily sludge, as a critical hazardous waste, requires appropriate treatment for resource recovery and harmfulness reduction. Here, fast microwave-assisted pyrolysis (MAP) of oily sludge was conducted for oil removal and fuel production. The results indicated the priority of the fast MAP compared with the MAP under premixing mode, with the oil content in solid residues after pyrolysis reaching below 0.2%. The effects of pyrolysis temperature and time on product distribution and compositions were examined. In addition, pyrolysis kinetics can be well described using the Kissinger-Akahira-Sunose (KAS) and the Flynn-Wall-Ozawa (FWO) methods, with the activation energy being 169.7–319.1 kJ/mol in the feedstock conversional fraction range of 0.2–0.7. Subsequently, the pyrolysis residues were further treated by thermal plasma vitrification to immobilize the existing heavy metals. The amorphous phase and the glassy matrix were formed in the molten slags, resulting in bonding and, hence, immobilization of heavy metals. Operating parameters, including working current and melting time, were optimized to reduce the leaching concentrations of heavy metals, as well as to decrease their volatilization during vitrification. Full article

(This article belongs to the Special Issue The Application of Microwave-Assisted Technology in Chemical Reaction)

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11 pages, 10211 KiB

Open AccessCommunication

Effect of Europium Addition on the Microstructure and Dielectric Properties of CCTO Ceramic Prepared Using Conventional and Microwave Sintering

by Gecil Evangeline T, Raja Annamalai A and Pavel Ctibor

Molecules 2023, 28(4), 1649; https://doi.org/10.3390/molecules28041649 - 8 Feb 2023

Cited by 8 | Viewed by 1702

Abstract

In this work, Eu₂O₃-doped (CaCu₃Ti₄O₁₂)_x of low dielectric loss have been fabricated using both conventional (CS) and microwave sintering (MWS), where x = Eu₂O₃ = 0.1, 0.2, and 0.3, respectively. According to X-ray diffraction (XRD) and scanning electron microscope (SEM) reports, increasing the concentration of Eu³⁺ in the CCTO lattice causes the grain size of the MWS samples to increase and vice versa for CS. The X-ray photoelectron spectroscopy (XPS) delineated the binding energies and charge states of the Cu²⁺/Cu⁺ and Ti⁴⁺/Ti³⁺ transition ions. Energy dispersive spectroscopy (EDS) analysis revealed no Cu-rich phase along the grain boundaries that directly impacts the dielectric properties. The dielectric characteristics, which include dielectric constant (ε) and the loss (tan δ), were examined using broadband dielectric spectrometer (BDS) from 10 to 10⁷ Hz at ambient temperature. The dielectric constant was >10⁴ and >10² for CS and MWS samples at x > 0.1, respectively, with the low loss being constant even at high frequencies due to the effective suppression of tan δ by Eu³⁺. This ceramic of low dielectric loss has potential for commercial applications at comparatively high frequencies. Full article

(This article belongs to the Special Issue The Application of Microwave-Assisted Technology in Chemical Reaction)

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7 pages, 235 KiB

Open AccessCommunication

Degree of Coupling in Microwave-Heating Polar-Molecule Reactions

by ** Huang, Linsen Yang and Kama Huang

Molecules 2023, 28(3), 1364; https://doi.org/10.3390/molecules28031364 - 31 Jan 2023

Cited by 1 | Viewed by 1122

Abstract

Microwave-assisted chemical reactions have been widely used, but the overheating effect limits further applications. The aim of this paper is to investigate the coupling degree of the electromagnetic field and thermal field in microwave-heating chemical reactions whose polarization changes as the reactions proceed. First, the entropy-balance equation of microwave-heating polar-molecule reactions is obtained. Then, the coupling degree of the electromagnetic field and the thermal field in microwave-heating polar-molecule reactions is derived, according to the entropy-balance equation. Finally, the effects of reaction processes on the degree of coupling are discussed. When the time scale of the component-concentration variation is much greater than the wave period during the chemical processes, the degree of coupling is sufficiently small, and the electric and thermal fields are considered as weakly coupled. On the other hand, the degree of coupling may change during the reactions. If the absolute value of the coupling degree becomes larger, due to the change in component concentration, this will lead to a transition from weak coupling to strong coupling. Full article

(This article belongs to the Special Issue The Application of Microwave-Assisted Technology in Chemical Reaction)

Review

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23 pages, 1350 KiB

Open AccessReview

A Systematic Review on Biomass Treatment Using Microwave-Assisted Pyrolysis under PRISMA Guidelines

by Neyha Rubab Syed, Bo Zhang, Stephen Mwenya and Awsan Shujaa Aldeen

Molecules 2023, 28(14), 5551; https://doi.org/10.3390/molecules28145551 - 20 Jul 2023

Cited by 2 | Viewed by 1947

Abstract

Biomass as a renewable energy resource is a major topic on a global scale. Several types of biomass heat treatment methods have been introduced to obtain useful byproducts via pyrolysis. Microwaves are a practical replacement for conventional stoves and ovens to perform pyrolysis of biomass. Their rapid heating rate and user-friendliness make them a good choice for the pyrolysis process over conventional methods. The current study reviewed research articles that used microwaves for the pyrolysis process on different types of biomass. This study primarily provides comprehensive details about the pyrolysis process, especially microwave-assisted pyrolysis (MAP) and its feasibility for treating biomass. A systematic literature review, according to the PRISMA guidelines, was performed to find research articles on biomass treatment using MAP technology. We analyzed various research studies (n = 32), retrieved from different databases, that used MAP for pyrolysis on various types of biomass, and we achieved good results. The main goal of this study was to examine the usefulness of the MAP technique, comparing its effects on distinguished types of biomass. We found MAP’s effective parameters, namely, temperature, concentration of microwave absorber, moisture percentage of starting material and flow rate, microwave power and residence time of the initial sweep gas that control the pyrolysis process, and effect quality of byproducts. The catalytic agent in MAP pyrolysis was found to be useful for treating biomass, and that it has great potential to increase (nearly double) the production yield. Although MAP could not be used for all types of materials due to some challenges, it produced good results compared to conventional heating (pyrolysis) methods. We concluded that MAP is an effective method for reducing pyrolysis reaction time and improving the quality of value-added products. Also, MAP eliminates the shredding requirement for biomass and improves heating quality. Therefore, it is a viable method for reducing pyrolysis processing costs and should be applied on a larger scale than lab scale for commercialization. Full article

(This article belongs to the Special Issue The Application of Microwave-Assisted Technology in Chemical Reaction)

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