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New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production
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New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production

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

Deadline for manuscript submissions: closed (30 April 2020) | Viewed by 84571

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editor

Prof. Dr. Simonetta Palmas

E-Mail Website
Guest Editor
Department of Mechanical, Chemical and Materials Engineering, University of Cagliari, Via Marengo 3, I-09123 Cagliari, Italy
Interests: preparation and characterization of catalysts for redox processes; synthesis and characterization of semiconductor nanostructured materials; synthesis of TiO2 nanotubes; advanced oxidation processes for the demolition of biorefractory organics and wastewater treatment; application of photoelectrocatalytic processes in the energetic and environmental field
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Remediation of wastewater, up to a level acceptable for discharge into receiving waterbodies, involves an ever-growing demand of energy, so effective and low energy use demand treatment processes that are highly desirable

Among the others, photo and photo-electrochemical treatment processes may be considered as advanced oxidation processes (AOP), which are based on the generation of OH radicals, strong oxidizing agents able to indiscriminately degrade even the most persistent organic compounds.

Photocatalysis, which exploits the semiconductor material’s ability to generate electron-hole coupling, under the irradiation of a suitable wavelength, can be considered as an effective method for organic degradation, especially when the semiconductor is active in the range of visible light.

Greater efficiencies may be obtained in photo-electrocatalytic processes, thanks to the application of an electric field, which assists the displacement of electrons within the semiconductor structure, thus reducing the recombination between photo-generated charges, which represents one of the main drawbacks of this process.

This Special Issue aims to focus on new trends in photo-electrocatalysis, not only for aspects related to possible advances in materials science, but also to new possible applications of the technology. Actually, we may consider the different philosophies that have been prevailing in these last few years: rather than considering the wastewater treatment process as just a way to destroy or remove organics from waste, the pollutants may be considered as a source of energy, so that the electrons produced by the oxidative process could be recovered and possibly used to obtain new chemicals and fuels.

Thus, research on new morphologies and structures, which allow more photoactive, visible responsive, and stable materials will be welcome, as well as studies on combined processes in which photo- or photo-electrochemistry contributes to an increase in the sustainability of the whole process, in terms of lowering costs and achieving the most valuable final products.

Prof. Simonetta Palmas
Guest Editor

Manuscript Submission Information

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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

  • Photoelectrocatalytic wastewater treatment
  • Photoelectrocatalytic degradation of organics
  • Nanostructured semiconductors
  • Visible light sensitive semiconductors
  • Wastewater sustainable combined processes
  • Advanced electrochemical oxidation processes
  • Bioelectricity
  • Photoelectrosyntesis
  • H2 production

Published Papers (16 papers)

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Editorial

Jump to: Research, Review

2 pages, 170 KiB  
Editorial
Special Issue: New Trends in Photo (Electro)catalysis: From Wastewater Treatment to Energy Production
by Simonetta Palmas
Catalysts 2021, 11(5), 586; https://doi.org/10.3390/catal11050586 - 30 Apr 2021
Cited by 2 | Viewed by 1251
Abstract
This Special Issue aimed at focusing on photo- and photo-electrocatalytic processes specifically devoted to present both new catalytic materials and possible applications in environmental and energetic fields [...] Full article
(This article belongs to the Special Issue New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production)

Research

Jump to: Editorial, Review

10 pages, 1608 KiB  
Article
Enhanced Photocatalytic Activity of Semiconductor Nanocomposites Doped with Ag Nanoclusters Under UV and Visible Light
by Jorge González-Rodríguez, Lucía Fernández, Yanina B. Bava, David Buceta, Carlos Vázquez-Vázquez, Manuel Arturo López-Quintela, Gumersindo Feijoo and Maria Teresa Moreira
Catalysts 2020, 10(1), 31; https://doi.org/10.3390/catal10010031 - 26 Dec 2019
Cited by 15 | Viewed by 3405
Abstract
Emerging contaminants (ECs) represent a wide range of compounds, whose complete elimination from wastewaters by conventional methods is not always guaranteed, posing human and environmental risks. Advanced oxidation processes (AOPs), based on the generation of highly oxidizing species, lead to the degradation of [...] Read more.
Emerging contaminants (ECs) represent a wide range of compounds, whose complete elimination from wastewaters by conventional methods is not always guaranteed, posing human and environmental risks. Advanced oxidation processes (AOPs), based on the generation of highly oxidizing species, lead to the degradation of these ECs. In this context, TiO2 and ZnO are the most widely used inorganic photocatalysts, mainly due to their low cost and wide availability. The addition of small amounts of nanoclusters may imply enhanced light absorption and an attenuation effect on the recombination rate of electron/hole pairs, resulting in improved photocatalytic activity. In this work, we propose the use of silver nanoclusters deposited on ZnO nanoparticles (ZnO–Ag), with a view to evaluating their catalytic activity under both ultraviolet A (UVA) and visible light, in order to reduce energetic requirements in prospective applications on a larger scale. The catalysts were produced and then characterized by scanning electron microscopy (SEM), X-ray diffractometry (XRD) and inductively coupled plasma-optical emission spectrometry (ICP-OES). As proof of concept of the capacity of photocatalysts doped with nanoclusters, experiments were carried out to remove the azo dye Orange II (OII). The results demonstrated the high photocatalytic efficiency achieved thanks to the incorporation of nanoclusters, especially evident in the experiments performed under white light. Full article
(This article belongs to the Special Issue New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production)
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15 pages, 4299 KiB  
Article
Niobium Oxide Catalysts as Emerging Material for Textile Wastewater Reuse: Photocatalytic Decolorization of Azo Dyes
by Alexsandro Jhones dos Santos, Luana Márcia Bezerra Batista, Carlos Alberto Martínez-Huitle, Ana Paula de Melo Alves and Sergi Garcia-Segura
Catalysts 2019, 9(12), 1070; https://doi.org/10.3390/catal9121070 - 14 Dec 2019
Cited by 36 | Viewed by 4376
Abstract
Niobium-based metal oxides are emerging semiconductor materials with barely explored properties for photocatalytic wastewater remediation. Brazil possesses the greatest reserves of niobium worldwide, being a natural resource that is barely exploited. Environmental applications of solar active niobium photocatalysts can provide opportunities in the [...] Read more.
Niobium-based metal oxides are emerging semiconductor materials with barely explored properties for photocatalytic wastewater remediation. Brazil possesses the greatest reserves of niobium worldwide, being a natural resource that is barely exploited. Environmental applications of solar active niobium photocatalysts can provide opportunities in the developing areas of Northeast Brazil, which receives over 22 MJ m2 of natural sunlight irradiation annually. The application of photocatalytic treatment could incentivize water reuse practices in small and mid-sized textile businesses in the region. This work reports the facile synthesis of Nb2O5 catalysts and explores their performance for the treatment of colored azo dye effluents. The high photoactivity of this alternative photocatalyst makes it possible to quickly obtain complete decolorization, in less than 40 min of treatment. The optimal operational conditions are defined as 1.0 g L−1 Nb2O5 loading in slurry, 0.2 M of H2O2, pH 5.0 to treat up to 15 mg L−1 of methyl orange solution. To evaluate reutilization without photocatalytic activity loss, the Nb2O5 was recovered after the experience and reused, showing the same decolorization rate after several cycles. Therefore, Nb2O5 appears to be a promising photocatalytic material with potential applicability in wastewater treatment due to its innocuous character and high stability. Full article
(This article belongs to the Special Issue New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production)
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16 pages, 6923 KiB  
Article
Preparation and Analysis of Ni–Co Catalyst Use for Electricity Production and COD Reduction in Microbial Fuel Cells
by Paweł P. Włodarczyk and Barbara Włodarczyk
Catalysts 2019, 9(12), 1042; https://doi.org/10.3390/catal9121042 - 08 Dec 2019
Cited by 13 | Viewed by 2703
Abstract
Microbial fuel cells (MFCs) are devices than can contribute to the development of new technologies using renewable energy sources or waste products for energy production. Moreover, MFCs can realize wastewater pre-treatment, e.g., reduction of the chemical oxygen demand (COD). This research covered preparation [...] Read more.
Microbial fuel cells (MFCs) are devices than can contribute to the development of new technologies using renewable energy sources or waste products for energy production. Moreover, MFCs can realize wastewater pre-treatment, e.g., reduction of the chemical oxygen demand (COD). This research covered preparation and analysis of a catalyst and measurements of changes in the concentration of COD in the MFC with a Ni–Co cathode. Analysis of the catalyst included measurements of the electroless potential of Ni–Co electrodes oxidized for 1–10 h, and the influence of anodic charge on the catalytic activity of the Ni–Co alloy (for four alloys: 15, 25, 50, and 75% concentration of Co). For the Ni–Co alloy containing 15% of Co oxidized for 8 h, after the third anodic charge the best catalytic parameters was obtained. During the MFC operation, it was noted that the COD reduction time (to 90% efficiency) was similar to the reduction time during wastewater aeration. However, the characteristic of the aeration curve was preferred to the curve obtained during the MFC operation. The electricity measurements during the MFC operation showed that power equal to 7.19 mW was obtained (at a current density of 0.47 mA·cm−2). Full article
(This article belongs to the Special Issue New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production)
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13 pages, 6265 KiB  
Article
Wastewater Treatment and Electricity Production in a Microbial Fuel Cell with Cu–B Alloy as the Cathode Catalyst
by Paweł P. Włodarczyk and Barbara Włodarczyk
Catalysts 2019, 9(7), 572; https://doi.org/10.3390/catal9070572 - 28 Jun 2019
Cited by 28 | Viewed by 5254
Abstract
The possibility of wastewater treatment and electricity production using a microbial fuel cell with Cu–B alloy as the cathode catalyst is presented in this paper. Our research covered the catalyst preparation; measurements of the electroless potential of electrodes with the Cu–B catalyst, measurements [...] Read more.
The possibility of wastewater treatment and electricity production using a microbial fuel cell with Cu–B alloy as the cathode catalyst is presented in this paper. Our research covered the catalyst preparation; measurements of the electroless potential of electrodes with the Cu–B catalyst, measurements of the influence of anodic charge on the catalytic activity of the Cu–B alloy, electricity production in a microbial fuel cell (with a Cu–B cathode), and a comparison of changes in the concentration of chemical oxygen demand (COD), NH4+, and NO3– in three reactors: one excluding aeration, one with aeration, and during microbial fuel cell operation (with a Cu–B cathode). During the experiments, electricity production equal to 0.21–0.35 mA·cm−2 was obtained. The use of a microbial fuel cell (MFC) with Cu–B offers a similar reduction time for COD to that resulting from the application of aeration. The measured reduction of NH4+ was unchanged when compared with cases employing MFCs, and it was found that effectiveness of about 90% can be achieved for NO3– reduction. From the results of this study, we conclude that Cu–B can be employed to play the role of a cathode catalyst in applications of microbial fuel cells employed for wastewater treatment and the production of electricity. Full article
(This article belongs to the Special Issue New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production)
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16 pages, 6775 KiB  
Article
Porous Ni Photocathodes Obtained by Selective Corrosion of Ni-Cu Films: Synthesis and Photoelectrochemical Characterization
by Laura Mais, Simonetta Palmas, Michele Mascia, Elisa Sechi, Maria Francesca Casula, Jesus Rodriguez and Annalisa Vacca
Catalysts 2019, 9(5), 453; https://doi.org/10.3390/catal9050453 - 16 May 2019
Cited by 10 | Viewed by 2927
Abstract
In this work, a dealloying technique is proposed as a synthesis method to obtain highly porous Nickel electrodes starting from Ni-Cu co-deposit: pulsed corrosion is applied adopting different corrosion and relaxation times. Different morphologies, pore size distribution and residual copper amount were obtained [...] Read more.
In this work, a dealloying technique is proposed as a synthesis method to obtain highly porous Nickel electrodes starting from Ni-Cu co-deposit: pulsed corrosion is applied adopting different corrosion and relaxation times. Different morphologies, pore size distribution and residual copper amount were obtained depending on the corrosion conditions. For the developed electrodes, the surface roughness factor, Rf, was evaluated by electrochemical impedance spectroscopy (EIS). The hydrogen evolution reaction (HER) on these electrodes was evaluated by means of steady-state polarization curves, and the related parameters were derived by Tafel analysis. Finally, a thin layer of NiO on the porous structures was obtained to exploit the semiconductor characteristic of the oxide, so that an extra-photopotential was obtained by the simulated solar light action. Results demonstrate greater apparent activity of the developed electrodes towards HER in comparison with commercial smooth Ni electrode, which can be mainly attributed to the large Rf obtained with the proposed technique. Full article
(This article belongs to the Special Issue New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production)
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13 pages, 3122 KiB  
Article
Effect of the Degree of Inversion on the Photoelectrochemical Activity of Spinel ZnFe2O4
by Luis I. Granone, Konstantin Nikitin, Alexei Emeline, Ralf Dillert and Detlef W. Bahnemann
Catalysts 2019, 9(5), 434; https://doi.org/10.3390/catal9050434 - 09 May 2019
Cited by 18 | Viewed by 2909
Abstract
Physicochemical properties of spinel ZnFe2O4 (ZFO) are known to be strongly affected by the distribution of the cations within the oxygen lattice. In this work, the correlation between the degree of inversion, the electronic transitions, the work function, and the [...] Read more.
Physicochemical properties of spinel ZnFe2O4 (ZFO) are known to be strongly affected by the distribution of the cations within the oxygen lattice. In this work, the correlation between the degree of inversion, the electronic transitions, the work function, and the photoelectrochemical activity of ZFO was investigated. By room-temperature photoluminescence measurements, three electronic transitions at approximately 625, 547, and 464 nm (1.98, 2.27, and 2.67 eV, respectively) were observed for the samples with different cation distributions. The transitions at 625 and 547 nm were assigned to near-band-edge electron-hole recombination processes involving O2- 2p and Fe3+ 3d levels. The transition at 464 nm, which has a longer lifetime, was assigned to the relaxation of the excited states produced after electron excitations from O2- 2p to Zn2+ 4s levels. Thus, under illumination with wavelengths shorter than 464 nm, electron-hole pairs are produced in ZFO by two apparently independent mechanisms. Furthermore, the charge carriers generated by the O2− 2p to Zn2+ 4s electronic transition at 464 nm were found to have a higher incident photon-to-current efficiency than the ones generated by the O2− 2p to Fe3+ 3d electronic transition. As the degree of inversion of ZFO increases, the probability of a transition involving the Zn2+ 4s levels increases and the probability of a transition involving the Fe3+ 3d levels decreases. This effect contributes to the increase in the photoelectrochemical efficiency observed for the ZFO photoanodes having a larger cation distribution. Full article
(This article belongs to the Special Issue New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production)
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21 pages, 5009 KiB  
Article
Integrated Au/TiO2 Nanostructured Photoanodes for Photoelectrochemical Organics Degradation
by Roberto Matarrese, Michele Mascia, Annalisa Vacca, Laura Mais, Elisabetta M. Usai, Matteo Ghidelli, Luca Mascaretti, Beatrice R. Bricchi, Valeria Russo, Carlo S. Casari, Andrea Li Bassi, Isabella Nova and Simonetta Palmas
Catalysts 2019, 9(4), 340; https://doi.org/10.3390/catal9040340 - 05 Apr 2019
Cited by 18 | Viewed by 3490
Abstract
In this work, hierarchical Au/TiO2 nanostructures were studied as possible photoanodes for water splitting and bisphenol A (BPA) oxidation. TiO2 samples were synthetized by Pulsed Laser Deposition (PLD), while Au nanoparticles (NPs) were differently dispersed (i.e., NPs at the bottom or [...] Read more.
In this work, hierarchical Au/TiO2 nanostructures were studied as possible photoanodes for water splitting and bisphenol A (BPA) oxidation. TiO2 samples were synthetized by Pulsed Laser Deposition (PLD), while Au nanoparticles (NPs) were differently dispersed (i.e., NPs at the bottom or at the top of the TiO2, as well as integrated TiO2/Au-NPs assemblies). Voltammetric scans and electrochemical impedance spectroscopy analysis were used to correlate the morphology of samples with their electrochemical properties; the working mechanism was investigated in the dark and in the presence of a light radiation, under neutral pH conditions towards the possible oxidation of both bisphenol A (BPA) and water molecules. Different behavior of the samples was observed, which may be attributed mainly to the distributions of Au NPs and to their dimension as well. In particular, the presence of NPs at the bottom seems to be the crucial point for the working mechanism of the structure, thanks to scattering effects that likely allow to better exploit the radiation. Full article
(This article belongs to the Special Issue New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production)
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13 pages, 2752 KiB  
Article
The Role of Mediated Oxidation on the Electro-irradiated Treatment of Amoxicillin and Ampicillin Polluted Wastewater
by Fernando L. Silva, Cristina Sáez, Marcos R.V. Lanza, Pablo Cañizares and Manuel A. Rodrigo
Catalysts 2019, 9(1), 9; https://doi.org/10.3390/catal9010009 - 24 Dec 2018
Cited by 20 | Viewed by 2704
Abstract
In this work, the electrolysis, photoelectrolysis and sonoelectrolysis with diamond electrodes of amoxicillin (AMX) and ampicillin (AMP) solutions were studied in the context of the search for technologies capable of removing antibiotics from liquid wastes. Single-irradiation processes (sonolysis and photolysis) were also evaluated [...] Read more.
In this work, the electrolysis, photoelectrolysis and sonoelectrolysis with diamond electrodes of amoxicillin (AMX) and ampicillin (AMP) solutions were studied in the context of the search for technologies capable of removing antibiotics from liquid wastes. Single-irradiation processes (sonolysis and photolysis) were also evaluated for comparison. Results showed that AMX and AMP are completely degraded and mineralized by electrolysis in both chloride and sulfate media, although the efficiency is higher in the presence of chloride. The effect of the current density on mineralization efficiency is not relevant and this may be related to the role of mediated oxidation. Irradiation by ultraviolet light or ultrasound (US) waves does not produce a synergistic effect on the mineralization of AMX and AMP solutions. This indicates that the massive formation of radicals during the combined processes can favor their recombination to form stable and less reactive species. Full article
(This article belongs to the Special Issue New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production)
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19 pages, 11119 KiB  
Article
Ag/Ag2O as a Co-Catalyst in TiO2 Photocatalysis: Effect of the Co-Catalyst/Photocatalyst Mass Ratio
by Soukaina Akel, Ralf Dillert, Narmina O. Balayeva, Redouan Boughaled, Julian Koch, Mohammed El Azzouzi and Detlef W. Bahnemann
Catalysts 2018, 8(12), 647; https://doi.org/10.3390/catal8120647 - 10 Dec 2018
Cited by 62 | Viewed by 6959
Abstract
Mixtures and composites of Ag/Ag2O and TiO2 (P25) with varying mass ratios of Ag/Ag2O were prepared, employing two methods. Mechanical mixtures (TM) were obtained by the sonication of a suspension containing TiO2 and Ag/Ag2O. Composites [...] Read more.
Mixtures and composites of Ag/Ag2O and TiO2 (P25) with varying mass ratios of Ag/Ag2O were prepared, employing two methods. Mechanical mixtures (TM) were obtained by the sonication of a suspension containing TiO2 and Ag/Ag2O. Composites (TC) were prepared by a precipitation method employing TiO2 and AgNO3. Powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of Ag(0) and Ag2O. The activity of the materials was determined employing methylene blue (MB) as the probe compound. Bleaching of MB was observed in the presence of all materials. The bleaching rate was found to increase with increasing amounts of TiO2 under UV/vis light. In contrast, the MB bleaching rate decreased with increasing TiO2 content upon visible light illumination. XRD and XPS data indicate that Ag2O acts as an electron acceptor in the light-induced reaction of MB and is transformed by reduction of Ag+, yielding Ag(0). As a second light-induced reaction, the evolution of molecular hydrogen from aqueous methanol was investigated. Significant H2 evolution rates were only determined in the presence of materials containing more than 50 mass% of TiO2. The experimental results suggest that Ag/Ag2O is not stable under the experimental conditions. Therefore, to address Ag/Ag2O as a (photo)catalytically active material does not seem appropriate. Full article
(This article belongs to the Special Issue New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production)
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13 pages, 2788 KiB  
Article
TiO2-SiO2-PMMA Terpolymer Floating Device for the Photocatalytic Remediation of Water and Gas Phase Pollutants
by Valentina Sabatini, Luca Rimoldi, Laura Tripaldi, Daniela Meroni, Hermes Farina, Marco Aldo Ortenzi and Silvia Ardizzone
Catalysts 2018, 8(11), 568; https://doi.org/10.3390/catal8110568 - 21 Nov 2018
Cited by 7 | Viewed by 3953
Abstract
Floating photocatalytic devices are highly sought-after as they represent good candidates for practical application in pollutant remediation of large water basins. Here, we present a multilayer floating device for the photocatalytic remediation of contaminants present in water as well as of volatile species [...] Read more.
Floating photocatalytic devices are highly sought-after as they represent good candidates for practical application in pollutant remediation of large water basins. Here, we present a multilayer floating device for the photocatalytic remediation of contaminants present in water as well as of volatile species close to the water surface. The device was prepared on a novel tailored ter-polymer substrate based on methylmethacrylate, α-methylstyrene and perfluoroctyl methacrylate. The ad hoc synthesized support presents optimal characteristics in terms of buoyancy, transparency, gas permeability, mechanical, UV and thermal stability. The adhesion of the TiO2 top layer was favoured by the adopted casting procedure, followed by a corona pre-treatment and by the deposition of an intermediate SiO2 layer, the latter aimed also at protecting the polymer support from photocatalytic oxidation. The device was characterized by contact angle measurement, UV-vis transmittance and scanning electron microscopy. The final device was tested for the photocatalytic degradation of an emerging water pollutant as well as of vapors of a model volatile organic compound. Relevant activity was observed also under simulated solar irradiation and the device showed good stability and recyclability, prospecting its use for the photocatalytic degradation of pollutants in large water basins. Full article
(This article belongs to the Special Issue New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production)
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Review

Jump to: Editorial, Research

37 pages, 6574 KiB  
Review
A Review on the Pathways of the Improved Structural Characteristics and Photocatalytic Performance of Titanium Dioxide (TiO2) Thin Films Fabricated by the Magnetron-Sputtering Technique
by Yu-Hsiang Wang, Kazi Hasibur Rahman, Chih-Chao Wu and Kuan-Chung Chen
Catalysts 2020, 10(6), 598; https://doi.org/10.3390/catal10060598 - 27 May 2020
Cited by 47 | Viewed by 5442
Abstract
Titanium dioxide (TiO2) thin films are used for a broad range of applications such as wastewater treatment, photocatalytic degradation activity, water splitting, antibacterial and also in biomedical applications. There is a wide range of synthesis techniques for the deposition of TiO [...] Read more.
Titanium dioxide (TiO2) thin films are used for a broad range of applications such as wastewater treatment, photocatalytic degradation activity, water splitting, antibacterial and also in biomedical applications. There is a wide range of synthesis techniques for the deposition of TiO2 thin films, such as chemical vapor deposition (CVD) and physical vapor deposition (PVD), both of which are well known deposition methods. Layer by layer deposition with good homogeneity, even thickness and good adhesive nature is possible by using the PVD technique, with the products being used for photocatalytic applications. This review studies the effects of magnetron sputtering conditions on TiO2 films. This innovative technique can enhance the photocatalytic activity by increasing the thickness of the film higher than any other methods. The main purpose of this article is to review the effects of DC and RF magnetron sputtering conditions on the preparation of TiO2 thin films for photocatalysis. The characteristics of TiO2 films (i.e., structure, composition, and crystallinity) are affected significantly by the substrate type, the sputtering power, the distance between substrate and target, working pressure, argon/oxygen ratio, deposition time, substrate temperature, dopant types, and finally the annealing treatment. The photocatalytic activity and optical properties, including the degree of crystallinity, band gap (Eg), refractive index (n), transmittance (T), and extinction coefficient (k), of TiO2 films are dependent on the above- mentioned film characteristics. Optimal TiO2 films should have a small particle size, a strong degree of crystallinity, a low band gap, a low contact angle, a high refractive index, transmittance, and extinction coefficient. Finally, metallic and nonmetallic dopants can be added to enhance the photocatalytic activity of TiO2 films by narrowing the band gap. Full article
(This article belongs to the Special Issue New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production)
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30 pages, 5150 KiB  
Review
Synthesis and Surface Modification of TiO2-Based Photocatalysts for the Conversion of CO2
by Samar Al Jitan, Giovanni Palmisano and Corrado Garlisi
Catalysts 2020, 10(2), 227; https://doi.org/10.3390/catal10020227 - 14 Feb 2020
Cited by 97 | Viewed by 8405
Abstract
Among all greenhouse gases, CO2 is considered the most potent and the largest contributor to global warming. In this review, photocatalysis is presented as a promising technology to address the current global concern of industrial CO2 emissions. Photocatalysis utilizes a semiconductor [...] Read more.
Among all greenhouse gases, CO2 is considered the most potent and the largest contributor to global warming. In this review, photocatalysis is presented as a promising technology to address the current global concern of industrial CO2 emissions. Photocatalysis utilizes a semiconductor material under renewable solar energy to reduce CO2 into an array of high-value fuels including methane, methanol, formaldehyde and formic acid. Herein, the kinetic and thermodynamic principles of CO2 photoreduction are thoroughly discussed and the CO2 reduction mechanism and pathways are described. Methods to enhance the adsorption of CO2 on the surface of semiconductors are also presented. Due to its efficient photoactivity, high stability, low cost, and safety, the semiconductor TiO2 is currently being widely investigated for its photocatalytic ability in reducing CO2 when suitably modified. The recent TiO2 synthesis and modification strategies that may be employed to enhance the efficiency of the CO2 photoreduction process are described. These modification techniques, including metal deposition, metal/non-metal doping, carbon-based material loading, semiconductor heterostructures, and dispersion on high surface area supports, aim to improve the light absorption, charge separation, and active surface of TiO2 in addition to increasing product yield and selectivity. Full article
(This article belongs to the Special Issue New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production)
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17 pages, 3586 KiB  
Review
Graphitic Carbon Nitride Materials for Photocatalytic Hydrogen Production via Water Splitting: A Short Review
by Seong Jun Mun and Soo-Jin Park
Catalysts 2019, 9(10), 805; https://doi.org/10.3390/catal9100805 - 25 Sep 2019
Cited by 60 | Viewed by 12826
Abstract
The generation of photocatalytic hydrogen via water splitting under light irradiation is attracting much attention as an alternative to solve such problems as global warming and to increase interest in clean energy. However, due to the low efficiency and selectivity of photocatalytic hydrogen [...] Read more.
The generation of photocatalytic hydrogen via water splitting under light irradiation is attracting much attention as an alternative to solve such problems as global warming and to increase interest in clean energy. However, due to the low efficiency and selectivity of photocatalytic hydrogen production under solar energy, a major challenge persists to improve the performance of photocatalytic hydrogen production through water splitting. In recent years, graphitic carbon nitride (g-C3N4), a non-metal photocatalyst, has emerged as an attractive material for photocatalytic hydrogen production. However, the fast recombination of photoexcited electron–hole pairs limits the rate of hydrogen evolution and various methods such as modification, heterojunctions with semiconductors, and metal and non-metal doping have been applied to solve this problem. In this review, we cover the rational design of g-C3N4-based photocatalysts achieved using methods such as modification, metal and non-metal doping, and heterojunctions, and we summarize recent achievements in their application as hydrogen production photocatalysts. In addition, future research and prospects of hydrogen-producing photocatalysts are also reviewed. Full article
(This article belongs to the Special Issue New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production)
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25 pages, 3328 KiB  
Review
Recent Progress on Metal Sulfide Composite Nanomaterials for Photocatalytic Hydrogen Production
by Sher Ling Lee and Chi-Jung Chang
Catalysts 2019, 9(5), 457; https://doi.org/10.3390/catal9050457 - 17 May 2019
Cited by 59 | Viewed by 5674
Abstract
Metal sulfide-based photocatalysts have gained much attention due to their outstanding photocatalytic properties. This review paper discusses recent developments on metal sulfide-based nanomaterials for H2 production, acting as either photocatalysts or cocatalysts, especially in the last decade. Recent progress on key experimental [...] Read more.
Metal sulfide-based photocatalysts have gained much attention due to their outstanding photocatalytic properties. This review paper discusses recent developments on metal sulfide-based nanomaterials for H2 production, acting as either photocatalysts or cocatalysts, especially in the last decade. Recent progress on key experimental parameters, in-situ characterization methods, and the performance of the metal sulfide photocatalysts are systematically discussed, including the forms of heterogeneous composite photocatalysts, immobilized photocatalysts, and magnetically separable photocatalysts. Some methods have been studied to solve the problem of rapid recombination of photoinduced carriers. The electronic density of photocatalysts can be investigated by in-situ C K-edge near edge X-ray absorption fine structure (NEXAFS) spectra to study the mechanism of the photocatalytic process. The effects of crystal properties, nanostructure, cocatalyst, sacrificial agent, electrically conductive materials, doping, calcination, crystal size, and pH on the performance of composite photocatalysts are presented. Moreover, the facet effect and light trapping (or light harvesting) effect, which can improve the photocatalytic activity, are also discussed. Full article
(This article belongs to the Special Issue New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production)
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32 pages, 9086 KiB  
Review
Advanced Design and Synthesis of Composite Photocatalysts for the Remediation of Wastewater: A Review
by Jianlong Ge, Yifan Zhang, Young-Jung Heo and Soo-Jin Park
Catalysts 2019, 9(2), 122; https://doi.org/10.3390/catal9020122 - 30 Jan 2019
Cited by 191 | Viewed by 11048
Abstract
Serious water pollution and the exhausting of fossil resources have become worldwide urgent issues yet to be solved. Solar energy driving photocatalysis processes based on semiconductor catalysts is considered to be the most promising technique for the remediation of wastewater. However, the relatively [...] Read more.
Serious water pollution and the exhausting of fossil resources have become worldwide urgent issues yet to be solved. Solar energy driving photocatalysis processes based on semiconductor catalysts is considered to be the most promising technique for the remediation of wastewater. However, the relatively low photocatalytic efficiency remains a critical limitation for the practical use of the photocatalysts. To solve this problem, numerous strategies have been developed for the preparation of advanced photocatalysts. Particularly, incorporating a semiconductor with various functional components from atoms to individual semiconductors or metals to form a composite catalyst have become a facile approach for the design of high-efficiency catalysts. Herein, the recent progress in the development of novel photocatalysts for wastewater treatment via various methods in the sight of composite techniques are systematically discussed. Moreover, a brief summary of the current challenges and an outlook for the development of composite photocatalysts in the area of wastewater treatment are provided. Full article
(This article belongs to the Special Issue New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production)
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