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Journals
Catalysts
Special Issues
Understanding the Molecular Mechanisms of Photocatalysis
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Understanding the Molecular Mechanisms of Photocatalysis

A special issue of Catalysts (ISSN 2073-4344). This special issue belongs to the section "Photocatalysis".

Deadline for manuscript submissions: closed (31 March 2021) | Viewed by 16982

Special Issue Editors

Prof. Dr. Maria Luisa Marin

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Guest Editor
Instituto de Tecnología Química, Universitat Politècnica de València-Consejo Superior de Investigaciones Científicas, Avenida de los Naranjos s/n, 46022 Valencia, Spain
Interests: photocatalysis; photochemistry; mechanisms and photobiology
Special Issues, Collections and Topics in MDPI journals
Dr. Francisco Boscá

E-Mail Website
Guest Editor
Instituto Universitario Mixto de Tecnología Química (ITQ-UPV), Universitat Politècnica de València, Av. de los Naranjos s/n, 46022 Valencia, Spain
Interests: photocatalysis; photochemistry; mechanisms and photobiology

Special Issue Information

Dear Colleagues,

Photocatalysis includes those processes that use light to activate a substance (photocatalyst) that subsequently modifies the rate of a chemical reaction without being altered or consumed. Upon absorption of light, photocatalysts in their excited electronic states are susceptible to accepting and donating electrons under very mild conditions. One of the advantages of photocatalytic redox processes over conventional ones is that the photocatalysts are almost inert until the desired oxidizing and/or reducing species is generated in situ upon application of the appropriate light source. However, although these reactive species are easy to generate, their short lifetime makes controlling subsequent steps and, therefore, product formation challenging. This reason may be why, although photocatalysis has already had a technological impact in specialized industrial applications, little attention has been paid to rationalizing the molecular mechanisms underlying these kind of reactions. A postulated overall mechanism should consider, on one hand, a thermodynamic analysis of all the steps involved in the photocatalytic cycle, and, on the other hand, an examination of the kinetic feasibility of the postulated processes. Hence, a deeper mechanistic understanding of every step in the photocatalytic process is still necessary, since it will allow us to determine the nature of the involved reactive species and their role in the operating photochemical pathways, providing the fundamentals for tailored photocatalytic treatments designed to undertake specific families of compounds.

This Special Issue, “Understanding the Molecular Mechanisms of Photocatalysis”, expects to contribute to progress in reaction discovery and inspire the invention of improved photocatalysts, regardless of whether they are organic (supported or not) or semiconductor-based photocatalysts, for future technological applications. We welcome contributions on (but not limited to):

  • photocatalytic processes for wastewater remediation;
  • photocatalytic processes for wastewater disinfection;
  • new photocatalytic materials for light-harvesting applications;
  • synthetic processes mediated by photocatalysis;
  • photocatalysis for radical mediated organic synthesis;
  • mechanisms and kinetics of organic reactions mediated by light;
  • the use of visible light for (enantio)selective organic transformations
  • catalytic mechanisms of heterogeneous photoredox catalysis;
  • photocatalytic materials for photodynamic therapy; and
  • fundamental understanding of reactive oxygen species (ROS) actions.

Prof. Dr. Maria Luisa Marin
Dr. Francisco Boscá
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Catalysts is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • band-gap
  • excited states
  • kinetic analysis
  • oxidation
  • reaction mechanisms
  • reduction
  • semiconductors
  • spectroscopy
  • time-resolved techniques
  • visible light

Published Papers (5 papers)

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Research

14 pages, 4088 KiB  
Article
An Accurate Growth Mechanism and Photocatalytic Degradation Rhodamine B of Crystalline Nb2O5 Nanotube Arrays
by Wei Guo, Libin Yang, Jinghao Lu, Peng Gao, Wenjing Li and Zhiying Feng
Catalysts 2020, 10(12), 1480; https://doi.org/10.3390/catal10121480 - 17 Dec 2020
Cited by 1 | Viewed by 2046
Abstract
To effectively improve photocatalytic activity, the morphology and crystallinity of semiconductor photocatalysts must be precisely controlled during the formation process. Self-aligned Nb2O5 nanotube arrays have been successfully fabricated using the electrochemical anodization method. A novel growth mechanism of Nb2 [...] Read more.
To effectively improve photocatalytic activity, the morphology and crystallinity of semiconductor photocatalysts must be precisely controlled during the formation process. Self-aligned Nb2O5 nanotube arrays have been successfully fabricated using the electrochemical anodization method. A novel growth mechanism of Nb2O5 nanotubes has been proposed. Starting from the initial oxidation process, the “multi-point” corrosion of fluoride ions is a key factor in the formation of nanotube arrays. The inner diameter and wall thickness of the nanotubes present a gradually increasing trend with increased dissociative fluorine ion concentration and water content in the electrolyte. With dehydroxylation and lattice recombination, the increased crystallinity of Nb2O5 represents a reduction of lattice defects, which effectively facilitates the separation and suppresses the recombination of photo-generated carriers to enhance their catalytic degradation activity. Full article
(This article belongs to the Special Issue Understanding the Molecular Mechanisms of Photocatalysis)
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15 pages, 5918 KiB  
Article
Photocatalytic Degradation of Quinoline Yellow over Ag3PO4
by Asma Tab, Mohamed Dahmane, Belabed Chemseddin, Bachir Bellal, Mohamed Trari and Claire Richard
Catalysts 2020, 10(12), 1461; https://doi.org/10.3390/catal10121461 - 14 Dec 2020
Cited by 14 | Viewed by 2442
Abstract
In this study, the ability of Ag3PO4 to achieve the photocatalytic degradation of quinoline yellow (QY) a hazardous and recalcitrant dye, under UVA and visible light was investigated. The photocatalyst Ag3PO4 was synthesized through a precipitation method, [...] Read more.
In this study, the ability of Ag3PO4 to achieve the photocatalytic degradation of quinoline yellow (QY) a hazardous and recalcitrant dye, under UVA and visible light was investigated. The photocatalyst Ag3PO4 was synthesized through a precipitation method, and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), BET Brunauer–Emmett-Teller (BET) analysis, UV-Differential Reflectance Spectroscopy (DRS) and Fourier transform infrared spectroscopy (FTIR). Ag3PO4 could successfully induce the photocatalytic degradation of QY under UVA and visible light. Optimal parameters were 0.5 g·L−1 of the catalyst, 20 ppm of QY and pH~7. Ag3PO4 was 1.6-times more efficient than TiO2 Degussa P25 under UVA light in degrading QY. Total organic carbon (TOC) analyses confirmed the almost complete QY mineralization. At least eight intermediate degradation products were identified by liquid chromatography coupled to high resolution mass spectrometry. The stability of Ag3PO4 was satisfactory as less than 5% Ag metal appeared in XRD analyses after 3 reuse cycles. These results show that under optimized conditions Ag3PO4 can efficiently achieve quinolone yellow mineralization. Full article
(This article belongs to the Special Issue Understanding the Molecular Mechanisms of Photocatalysis)
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17 pages, 4284 KiB  
Article
Enhanced Photodegradation of Synthetic Dyes Mediated by Ag3PO4-Based Semiconductors under Visible Light Irradiation
by Alice Pavanello, Alejandro Blasco, Peter F. Johnston, Miguel A. Miranda and Maria Luisa Marin
Catalysts 2020, 10(7), 774; https://doi.org/10.3390/catal10070774 - 11 Jul 2020
Cited by 19 | Viewed by 2579
Abstract
Four silver phosphate-based materials were successfully synthesized, characterized, and evaluated, together with TiO2, in the photodegradation of synthetic dyes (tartrazine, Orange II, rhodamine, and Brilliant Blue FCF) under two irradiation sources centered at 420 and 450 nm. Scanning Electron Microscopy (SEM) [...] Read more.
Four silver phosphate-based materials were successfully synthesized, characterized, and evaluated, together with TiO2, in the photodegradation of synthetic dyes (tartrazine, Orange II, rhodamine, and Brilliant Blue FCF) under two irradiation sources centered at 420 and 450 nm. Scanning Electron Microscopy (SEM) images showed different topologies of the synthesized materials, whereas diffuse reflectance spectra demonstrated that they display absorption up to 500 nm. Degradation experiments were performed in parallel with the silver materials and TiO2. Upon irradiation centered at 420 nm, the abatement of the dyes was slightly more efficient in the case of TiO2—except for Orange II. Nevertheless, upon irradiation centered at 450 nm, TiO2 demonstrated complete inefficiency and silver phosphates accomplished the complete abatement of the dyes—except for Brilliant Blue FCF. A careful analysis of the achieved degradation of dyes revealed that the main reaction mechanism involves electron transfer to the photogenerated holes in the valence band of silver photocatalysts, together with the direct excitation of dyes and the subsequent formation of reactive species. The performance of TiO2 was only comparable at the shorter wavelength when hydroxyl radicals could be formed; however, it could not compete under irradiation at 450 nm since the formed superoxide anion is not as reactive as hydroxyl radicals. Full article
(This article belongs to the Special Issue Understanding the Molecular Mechanisms of Photocatalysis)
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11 pages, 1678 KiB  
Article
Characterization and Comparative Performance of TiO2 Photocatalysts on 6-Mercaptopurine Degradation by Solar Heterogeneous Photocatalysis
by Luis A. González-Burciaga, Cynthia M. Núñez-Núñez, Miriam M. Morones-Esquivel, Manuel Avila-Santos, Adela Lemus-Santana and José B. Proal-Nájera
Catalysts 2020, 10(1), 118; https://doi.org/10.3390/catal10010118 - 14 Jan 2020
Cited by 14 | Viewed by 4910
Abstract
The crystallographic properties of two titanium dioxide (TiO2) photocatalysts, P25, and commercial C1-TiO2 reactive grade, were analyzed by X-ray diffraction (XRD) and the band-gap was calculated with UV–Vis spectrometry with integration sphere. Then, their performance was tested in the degradation [...] Read more.
The crystallographic properties of two titanium dioxide (TiO2) photocatalysts, P25, and commercial C1-TiO2 reactive grade, were analyzed by X-ray diffraction (XRD) and the band-gap was calculated with UV–Vis spectrometry with integration sphere. Then, their performance was tested in the degradation of 6-mercaptopurine (6-MP) by heterogeneous photocatalysis with solar radiation under different pH conditions and the addition of hydrogen peroxide (H2O2); the degradation efficiency was monitored by UV–Vis spectrophotometry. The XRD analysis showed that both photocatalysts studied have anatase phase, while only P25 contains rutile; the band gap values were lower, in both catalysts, than those reported for catalysts obtained by the sol-gel method. With both photocatalysts, degradation experiments showed efficiency greater than 98% in experiments in the presence of H2O2 regardless of pH. The properties of the photocatalysts, along with the data obtained from the experimentation, helped determine the best semiconductor for the degradation of 6-MP with these operating conditions in this work. Full article
(This article belongs to the Special Issue Understanding the Molecular Mechanisms of Photocatalysis)
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12 pages, 2517 KiB  
Article
Surface-Doped Graphitic Carbon Nitride Catalyzed Photooxidation of Olefins and Dienes: Chemical Evidence for Electron Transfer and Singlet Oxygen Mechanisms
by Apostolos Chatzoudis, Vasileios Giannopoulos, Frank Hollmann and Ioulia Smonou
Catalysts 2019, 9(8), 639; https://doi.org/10.3390/catal9080639 - 27 Jul 2019
Cited by 7 | Viewed by 4304
Abstract
A new photocatalytic reactivity of carbon-nanodot-doped graphitic carbon nitride (CD-C3N4) with alkenes and dienes, has been disclosed. We have shown that CD-C3N4 photosensitizes the oxidation of unsaturated substrates in a variety of solvents according to two [...] Read more.
A new photocatalytic reactivity of carbon-nanodot-doped graphitic carbon nitride (CD-C3N4) with alkenes and dienes, has been disclosed. We have shown that CD-C3N4 photosensitizes the oxidation of unsaturated substrates in a variety of solvents according to two competing mechanisms: the energy transfer via singlet oxygen (1O2) and/or the electron transfer via superoxide (O·−2). The singlet oxygen, derived by the CD-C3N4 photosensitized process, reacts with alkenes to form allylic hydroperoxides (ene products) whereas with dienes, endoperoxides. When the electron transfer mechanism operates, cleavage products are formed, derived from the corresponding dioxetanes. Which of the two mechanisms will prevail depends on solvent polarity and the particular substrate. The photocatalyst remains stable under the photooxidation conditions, unlike the most conventional photosensitizers, while the heterogeneous nature of CD-C3N4 overcomes usual solubility problems. Full article
(This article belongs to the Special Issue Understanding the Molecular Mechanisms of Photocatalysis)
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