Special Issue "Commemorative Issue in Honor of Professor Akira Fujishima"

A special issue of Catalysts (ISSN 2073-4344).

Deadline for manuscript submissions: closed (15 January 2021).

Special Issue Editors

Prof. Dr. Chiaki Terashima
E-Mail Website
Guest Editor
Photocatalysis International Research Center, Research Institute for Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
Interests: Plasma Chemistry, Diamond Materials
Prof. Dr. Hideki Sakai
E-Mail Website
Guest Editor
Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
Interests: Applied Interfacial Chemistry, Interfacial Photoelectrochemistry
Dr. Ken-ichi Katsumata
E-Mail Website
Guest Editor
Department of Materials Science and Technology, Faculty of Industrial Science and Technology, Tokyo University of Science, 6-3-1 Niijuku, Katsushika-ku, Tokyo 125-8585, Japan
Special Issues and Collections in MDPI journals
Dr. Norihiro Suzuki
E-Mail Website
Guest Editor
Photocatalysis International Research Center, Research Institute for Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
Interests: Functional Inorganic Materials

Special Issue Information

Dear Colleagues,

Our journal is pleased to publish a Special Issue in honor of Distinguished Professor Akira Fujishima at Tokyo University of Science (TUS). Prof. Fujishima retired from the University of Tokyo in 2003, and then moved to Kanagawa Academy of Science & Technology as Chairman. Later, he joined as President of TUS from 2010 to 2018. Presently, Prof. Fujishima is working as a Director of Photocatalysis International Research Center (PIRC) at TUS, which opened in 2013. This distinguished scientist was the first to report the unusual photo-induced oxidation of water on the surface of titanium dioxide.  First, this result, together with his subsequent work, provided the foundation for the photoelectrochemical splitting of water to produce oxygen and hydrogen on semiconducting materials.  Through his work, as well as that of many others, a large number of new materials have been developed for photoelectrochemical solar energy conversion.

In honor and recognition of Professor Akira Fujishima’s outstanding career contributions to the fields of photocatalysis, heterogeneous catalysis, and catalytic reaction engineering, this Special Issue of Catalysts welcomes the submission of original research manuscripts or reviews in these areas. We plan to receive submissions from now to 15th December 2020. Manuscripts will be published online on an ongoing basis after being processed.

Prof. Dr. Chiaki Terashima
Prof. Dr. Hideki Sakai
Dr. Ken-ichi Katsumata
Dr. Norihiro Suzuki
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 papers will be 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 2000 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

  • Photocatalysis
  • Nano-sized Structural and Functional Materials
  • Photochemical Energy Storage and Conversion
  • Electrophotonic Materials for Information Storage and Transmission
  • Molecular Electronics
  • Photo-functional Materials
  • Photoelectrochemistry
  • Photochromic Materials

Published Papers (18 papers)

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Research

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Open AccessFeature PaperArticle
Visible Light-Assisted Photocatalysis Using Spherical-Shaped BiVO4 Photocatalyst
Catalysts 2021, 11(4), 460; https://doi.org/10.3390/catal11040460 - 01 Apr 2021
Viewed by 358
Abstract
In this research work, we reported the synthesis of a spherical-shaped bismuth vanadate (BiVO4) photocatalyst using a cost-effective, simple, chemical hydrothermal method and studied the effect of deposition temperatures on the structural, morphological, optical properties, etc. The XRD result confirmed the [...] Read more.
In this research work, we reported the synthesis of a spherical-shaped bismuth vanadate (BiVO4) photocatalyst using a cost-effective, simple, chemical hydrothermal method and studied the effect of deposition temperatures on the structural, morphological, optical properties, etc. The XRD result confirmed the monoclinic scheelite phase of BiVO4. An XPS study confirmed the occurrence of Bi, V, and O elements and also found that Bi and V exist in +3 and +5 oxidation states, respectively. SEM micrographs revealed the spherical-shaped morphology of the BiVO4 photocatalyst. Optical investigation showed that the bandgap of the BiVO4 photocatalyst varied between 2.25 and 2.32 eV. The as-synthesized BiVO4 photocatalyst was used to study the photocatalytic degradation of crystal violet (CV) dye under visible light illumination. The photocatalytic degradation experiment showed that the degradation percentage of crystal violet dye using BiVO4 reached 98.21% after 120 min. Mineralization of crystal violet dye was studied using a chemical oxygen demand analysis. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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Open AccessFeature PaperArticle
Direct Dimethyl Carbonates Synthesis over CeO2 and Evaluation of Catalyst Morphology Role in Catalytic Performance
Catalysts 2021, 11(2), 223; https://doi.org/10.3390/catal11020223 - 08 Feb 2021
Viewed by 671
Abstract
In recent years, direct synthesis of dimethyl carbonate (DMC) from carbon dioxide (CO2) has received considerable attention due to green and sustainable technology. Here, we report a production of DMC from major greenhouse gases and CO2 using various morphologies of [...] Read more.
In recent years, direct synthesis of dimethyl carbonate (DMC) from carbon dioxide (CO2) has received considerable attention due to green and sustainable technology. Here, we report a production of DMC from major greenhouse gases and CO2 using various morphologies of cerium oxide (CeO2). Time-dependent synthesis of CeO2, with controlled morphology having various shapes including sphere, nanorods and spindle shape, along with its formation mechanism is proposed. The experimental results indicate the morphology of CeO2 was mostly dependent on the reaction time where crystal growth occurred through Ostwald ripening. The morphology, size and shape of CeO2 were observed using transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM).The crystallographic analysis using X-ray diffraction (XRD) shows cubic fluorite phase of CeO2 with crystallite size ~72.0 nm using the Debye–Scherrer equation. The nitrogen adsorption desorption technique suggested the formation of the highly mesoporous framework of CeO2 and the excellent surface area around 104.5 m2/g obtained for CeO2 spindles by Brunauer–Emmett–Teller (BET) method. The DMC synthesis reactions were studied over CeO2 catalyst with different morphologies. The results of catalytic reactions specify that the morphology of catalyst plays an important role in their catalytic performances, where spindle shape CeO2 was the most active catalyst producing of up to13.04 mmol of DMC. Furthermore, various dehydrating agents were used to improve the DMC production at optimized reaction parameters. The overall results reveal that the higher surface area and spindle shape of CeO2 makes it a useful, reusable catalyst for one-pot DMC synthesis. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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Open AccessFeature PaperArticle
Hydrophilic/Hydrophobic Silane Grafting on TiO2 Nanoparticles: Photocatalytic Paint for Atmospheric Cleaning
Catalysts 2021, 11(2), 193; https://doi.org/10.3390/catal11020193 - 02 Feb 2021
Viewed by 760
Abstract
In this study, anatase titania was utilized to prepare a durable photocatalytic paint with substantially enhanced photoactivity towards NO oxidation. Consequently, to alleviate the choking effect of photocatalytic paint and incorporate self-cleaning properties, the parent anatase titania was modified with Al(OH)3 and [...] Read more.
In this study, anatase titania was utilized to prepare a durable photocatalytic paint with substantially enhanced photoactivity towards NO oxidation. Consequently, to alleviate the choking effect of photocatalytic paint and incorporate self-cleaning properties, the parent anatase titania was modified with Al(OH)3 and a number of organosilane (tetraethyl orthosilicate, propyltrimethoxysilane, triethoxy(octadecyl)silane, and trimethylchlorosilane) coatings. A facile hydrolysis approach in ethanol was employed to coat the parent titania. To facilitate uniform dispersion in photocatalytic paint and strong bonding with the prevailing organic matrix, it is necessary to avail both hydrophobic and hydrophilic regions on the titania surface. Therefore, during the preparation of modified titania, the weight proportion of the total weight of alkyl silane and trimethylchlorosilane was adjusted to a ratio of 1:1. As the parent titania has few hydrophilic portions on the surface, tetraethyl orthosilicate was coated with an organic silane having an extended alkyl group as a hydrophobic group and tetraethyl orthosilicate as a hydrophilic group. When these two silane mixtures are hydrolyzed simultaneously and coated on the surface of parent titania, a portion containing a large amount of tetraethyl orthosilicate becomes hydrophilic, and a part containing an alkyl silane becomes hydrophobic. The surface morphology and the modified titania’s optical attributes were assessed using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), UV-Vis diffuse reflectance spectroscopy (DRS), and electrochemical impedance spectroscopy (EIS) analysis. Based on the advanced characterizations, the NO removal mechanism of the modified titania is reported. The modified titania coated at 20 wt.% on the ceramic substrate was found to remove ~18% of NO under one h of UV irradiation. An extensive UV durability test was also carried out, whereby the coated surface with modified titania was exposed to 350 W/m2 of UV irradiance for 2 weeks. The results indicated that the coated surface appeared to preserve the self-cleaning property even after oil spraying. Hence, facile hydrolysis of multiple organosilane in ethanol could be a viable approach to design the coating on anatase titania for the fabrication of durable photoactive paint. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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Open AccessCommunication
Synthesis of Au or [email protected] Nanocrystals via Interfacial Photoreduction
Catalysts 2021, 11(2), 174; https://doi.org/10.3390/catal11020174 - 27 Jan 2021
Viewed by 505
Abstract
The surface modification of perovskite nanocrystals (NCs) (i.e., their decoration with noble metals) holds great promise with respect to the tailoring of their properties but has remained a challenge because perovskite NCs are extremely sensitive to water and alcohols. In this study, Au [...] Read more.
The surface modification of perovskite nanocrystals (NCs) (i.e., their decoration with noble metals) holds great promise with respect to the tailoring of their properties but has remained a challenge because perovskite NCs are extremely sensitive to water and alcohols. In this study, Au or [email protected]3 NCs were successfully synthesized by photoreduction at the water/hexane interface. First, Cs4PbBr6 NCs were synthesized through the hot-injection method. Then, Cs4PbBr6 was transformed into CsPbBr3 and subjected to noble metal modification, both at the interface. The synthesized CsPbBr3 NCs exhibited a cubic perovskite phase and had an average size of approximately 13.5 nm. The deposited Au and Pt nanoparticles were crystalline, with a face-centered cubic lattice and average diameters of approximately 3.9 and 4.4 nm, respectively. The noble metal modification process had almost no effect on the steady-state photoluminescence (PL) emission wavelength but affected the charge-recombination kinetics of the CsPbBr3 NCs. Time-resolved PL decay spectral analysis indicated that the fluorescence lifetimes of the Au and [email protected]3 NCs were shorter than those of the pure CsPbBr3 NCs, probably owing to the quenching of the free charges because of electron transfer from the perovskite to the noble metal nanoparticles. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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Open AccessArticle
The Role of Adsorption in the Photocatalytic Decomposition of Dyes on APTES-Modified TiO2 Nanomaterials
Catalysts 2021, 11(2), 172; https://doi.org/10.3390/catal11020172 - 27 Jan 2021
Viewed by 431
Abstract
This work investigated for the first time the role of adsorption in the photocatalytic degradation of methylene blue and Orange II dyes in the presence of 3-aminopropyltriethoxysilane (APTES)-modified TiO2 nanomaterials. It has been demonstrated that the decrease in adsorption has a detrimental [...] Read more.
This work investigated for the first time the role of adsorption in the photocatalytic degradation of methylene blue and Orange II dyes in the presence of 3-aminopropyltriethoxysilane (APTES)-modified TiO2 nanomaterials. It has been demonstrated that the decrease in adsorption has a detrimental effect on photocatalytic activity. APTES/TiO2 photocatalysts were successfully prepared by solvothermal modification of TiO2 in a pressure autoclave, followed by heat treatment in an inert gas atmosphere at the temperature range from 300 °C to 900 °C. It was observed that functionalization of TiO2 via APTES effectively suppressed the anatase-to-rutile phase transformation, as well as the growth of crystallites size during calcination, and reduction of specific surface area (APTES modification inhibits sintering of crystallites). The noted alterations in the adsorption properties, observed after the calcination, were generally related to changes in the surface characteristics, mainly surface charges expressed by the zeta potential. Positively charged surface enhances adsorption of anionic dye (Orange II), while negatively charged surface was better for adsorption of cationic dye (methylene blue). The adsorption process substantially affects the efficiency of the photocatalytic oxidation of both dyes. The methylene blue decomposition proceeded according to the pseudo-first and pseudo-second-order kinetic models, while the degradation of Orange II followed the zero, pseudo-first, and pseudo-second order kinetic models. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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Open AccessArticle
Analyses of the Effect of Peptidoglycan on Photocatalytic Bactericidal Activity Using Different Growth Phases Cells of Gram-Positive Bacterium and Spheroplast Cells of Gram-Negative Bacterium
Catalysts 2021, 11(2), 147; https://doi.org/10.3390/catal11020147 - 20 Jan 2021
Viewed by 386
Abstract
We conducted photocatalytic experiments focusing on the peptidoglycan layer to elucidate the details of the mechanism of photocatalytic sterilization. The previous study of our laboratory suggested that the presence of the peptidoglycan layer increases the bactericidal effect. To further verify it, the following [...] Read more.
We conducted photocatalytic experiments focusing on the peptidoglycan layer to elucidate the details of the mechanism of photocatalytic sterilization. The previous study of our laboratory suggested that the presence of the peptidoglycan layer increases the bactericidal effect. To further verify it, the following experiments were performed: experiments on cells with different peptidoglycan layer thickness used Lactobacillus plantarum cells with different growth phases, experiments on cells with the thin peptidoglycan layer used Escherichia coli cells and spheroplast cells from which the peptidoglycan layer was removed from E. coli cells. The bactericidal effects increased as the growth progresses of L. plantarum. It was confirmed by TEM that the thickness of the peptidoglycan layer increased with cell growth. The survival rates of E. coli intact cells were significantly lower than those of spheroplast cells. These results strongly suggest that the peptidoglycan layer enhances the photocatalytic bactericidal effect. As a result of allowing the photocatalytic reaction to act on peptidoglycan, the amount of hydroxyl radical was smaller, and the amount of hydrogen peroxide was higher than in the absence of peptidoglycan. It is suggested that peptidoglycan may convert produced hydroxyl radical to hydrogen peroxide. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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Open AccessFeature PaperArticle
Preparation of Nanoparticle Porous-Structured BiVO4 Photoanodes by a New Two-Step Electrochemical Deposition Method for Water Splitting
Catalysts 2021, 11(1), 136; https://doi.org/10.3390/catal11010136 - 18 Jan 2021
Cited by 1 | Viewed by 556
Abstract
In the synthesis method of a BiVO4 photoanode via BiOI flakes, a BiOI film is formed by electrochemical deposition in Step 1, and a vanadium (V) source solution is placed by drop-casting on the BiOI film in Step 2. Following this, BiVO [...] Read more.
In the synthesis method of a BiVO4 photoanode via BiOI flakes, a BiOI film is formed by electrochemical deposition in Step 1, and a vanadium (V) source solution is placed by drop-casting on the BiOI film in Step 2. Following this, BiVO4 particles are converted from the BiOI–(V species) precursors by annealing. However, it is challenging to evenly distribute vanadium species among the BiOI flakes. As a result, the conversion reaction to form BiVO4 does not proceed simultaneously and uniformly. To address this limitation, in Step 2, we developed a new electrochemical deposition method that allowed the even distribution of V2O5 among Bi–O–I flakes to enhance the conversion reaction uniformly. Furthermore, when lactic acid was added to the electrodeposition bath solution, BiVO4 crystals with an increased (040) peak intensity of the X-ray diffractometer (XRD) pattern were obtained. The photocurrent of the BiVO4 photoanode was 2.2 mA/cm2 at 1.23 V vs. reversible hydrogen electrode (RHE) under solar simulated light of 100 mW/cm2 illumination. The Faradaic efficiency of oxygen evolution was close to 100%. In addition, overall water splitting was performed using a Ru/SrTiO3:Rh–BiVO4 photocatalyst sheet prepared by the BiVO4 synthesis method. The corresponding hydrogen and oxygen were produced in a 2:1 stoichiometric ratio under visible light irradiation. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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Open AccessFeature PaperArticle
Synthesis of N-Doped TiO2 for Efficient Photocatalytic Degradation of Atmospheric NOx
Catalysts 2021, 11(1), 109; https://doi.org/10.3390/catal11010109 - 14 Jan 2021
Viewed by 617
Abstract
Titanium oxide (TiO2) is a potential photocatalyst for removing toxic NOx from the atmosphere. Its practical application is, however, significantly limited by its low absorption into visible light and a high degree of charge recombination. The overall photocatalytic activity of [...] Read more.
Titanium oxide (TiO2) is a potential photocatalyst for removing toxic NOx from the atmosphere. Its practical application is, however, significantly limited by its low absorption into visible light and a high degree of charge recombination. The overall photocatalytic activity of TiO2 remains too low since it can utilize only about 4–5% of solar energy. Nitrogen doping into the TiO2 lattice takes advantage of utilizing a wide range of solar radiation by increasing the absorption capability towards the visible light region. In this work, N-doped TiO2, referred to as TC, was synthesized by a simple co-precipitation of tri-thiocyanuric acid (TCA) with P25 followed by heat treatment at 550 degrees C. The resulting nitrogen doping increased the visible-light absorption and enhanced the separation/transfer of photo-excited charge carriers by capturing holes by reduced titanium ions. As a result, TC samples exhibited excellent photocatalytic activities of 59% and 51% in NO oxidation under UV and visible light irradiation, in which the optimum mass ratio of TCA to P25 was found to be 10. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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Open AccessFeature PaperArticle
Low Temperature Deposition of TiO2 Thin Films through Atmospheric Pressure Plasma Jet Processing
Catalysts 2021, 11(1), 91; https://doi.org/10.3390/catal11010091 - 11 Jan 2021
Viewed by 495
Abstract
Titanium dioxide (TiO2) has been widely used as a catalyst material in different applications such as photocatalysis, solar cells, supercapacitor, and hydrogen production, due to its better chemical stability, high redox potential, wide band gap, and eco-friendly nature. In this work [...] Read more.
Titanium dioxide (TiO2) has been widely used as a catalyst material in different applications such as photocatalysis, solar cells, supercapacitor, and hydrogen production, due to its better chemical stability, high redox potential, wide band gap, and eco-friendly nature. In this work TiO2 thin films have been deposited onto both glass and silicon substrates by the atmospheric pressure plasma jet (APPJ) technique. The structure and morphological properties of TiO2 thin films are studied using different characterization techniques like X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and field emission scanning electron microscopy. XRD study reveals the bronze-phase of TiO2. The XPS study shows the presence of Ti, O, C, and N elements. The FE-SEM study shows the substrate surface is well covered with a nearly round shaped grain of different size. The optical study shows that all the deposited TiO2 thin films exhibit strong absorption in the ultraviolet region. The oleic acid photocatalytic decomposition study demonstrates that the water contact angle decreased from 80.22 to 27.20° under ultraviolet illumination using a TiO2 photocatalyst. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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Open AccessArticle
Promoting Photoelectrochemical Water Oxidation on Ti-Doped Fe2O3 Nanowires Photoanode by O2 Plasma Treatment
Catalysts 2021, 11(1), 82; https://doi.org/10.3390/catal11010082 - 09 Jan 2021
Viewed by 388
Abstract
Surface electron traps on semiconductor photoanodes mediate surface recombination and deteriorate the photoelectrochemical (PEC) water oxidation performance of the photoanode. Developing convenient methods to reduce surface electron traps is therefore essential for high efficiency PEC water oxidation on semiconductor photoanodes, particularly for nanostructured [...] Read more.
Surface electron traps on semiconductor photoanodes mediate surface recombination and deteriorate the photoelectrochemical (PEC) water oxidation performance of the photoanode. Developing convenient methods to reduce surface electron traps is therefore essential for high efficiency PEC water oxidation on semiconductor photoanodes, particularly for nanostructured photoanodes with large surface area. Herein, we employ a O2 plasma treatment to boost the PEC water oxidation performance of Ti-doped Fe2O3 (Ti-Fe2O3) nanowires photoanodes, aiming to reduce surface oxygen vacancies, the dominant electron traps on Ti-Fe2O3 surface. X-ray diffraction (XRD), scanning electron microscopy and spectroscopic analyses show that the oxygen plasma treatment changes the structural, morphological and optical properties negligibly, but it does reduce the content of surface oxygen vacancies, as estimated from O1s X-ray photoelectron spectroscopy spectra. An optimal O2 plasma treatment (200 W, 70 s) increases the photocurrent density of the Ti-Fe2O3 nanowire photoanode to 2.14 mA·cm−2 (1.23 V vs. RHE) under air mass 1.5G simulated solar light, which is 1.95 times higher than the pristine Ti-Fe2O3 nanowire photoanode. The surface hole transfer efficiency is also improved by 1.66 times due to the reduced surface recombination. The work suggests that O2 plasma treatment is a convenient but effective method to boost the PEC water oxidation performance of Ti-Fe2O3 photoanode and might be applicable to other semiconducting oxide photoanodes for high efficiency PEC water splitting. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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Open AccessArticle
Wastewater Contaminated with Hydrazine as Scavenger Agent for Hydrogen Production by Cu/Ti Nanostructures
Catalysts 2021, 11(1), 74; https://doi.org/10.3390/catal11010074 - 07 Jan 2021
Viewed by 367
Abstract
Cu/Ti photocatalysts were prepared by the sol-gel process with different copper loadings (1.0, 2.5, and 5.0 wt.%) and then thermally treated at several calcination temperatures from 400 to 600 °C. The materials were characterized by X-ray diffraction (XRD), N2 physisorption, Scanning Electronic [...] Read more.
Cu/Ti photocatalysts were prepared by the sol-gel process with different copper loadings (1.0, 2.5, and 5.0 wt.%) and then thermally treated at several calcination temperatures from 400 to 600 °C. The materials were characterized by X-ray diffraction (XRD), N2 physisorption, Scanning Electronic Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS), Ultraviolet-visible-Diffuse Reflection Spectroscopy, Ultraviolet-visible spectroscopy as a function of the temperature, (Temperature Programmed Reduction) TPR-chemisorption, XPS (X-ray Photoelectron Spectroscopy) and OH determination through DRIFTS (Diffuse reflectance infrared Fourier transform spectroscopy). The Cu/Ti photocatalysts were evaluated for the photocatalytic production of hydrogen using hydrazine as scavenging agent. Moreover, a detailed study of the Cu1+/Cu2+ ratio and the corresponding formation of copper oxide was carried out to understand the correlation between the copper species and the photocatalytic activity. Simultaneously, the OH groups on the TiO2 surface also show insights into the behavior of these materials during the photocatalytic reaction. Despite the low hydrazine concentration (20 mM), the 1.0 (wt.%) Cu/Ti 500 photocatalyst enhanced the hydrogen production three and two times more than photolysis and bare TiO2, respectively. The 1.0 Cu/Ti 500 photocatalyst displayed outstanding stability for at least three continuous cycles of 8 h each, preserving the hydrogen production. The novel ability shown in this work represents an alternative to reduce the hydrazine residues in wastewater to transform it into a hydrogen-producing energy source and must be extended to other reductive pollutants found in wastewater. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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Open AccessFeature PaperArticle
Sulfuric Acid Treated g-CN as a Precursor to Generate High-Efficient g-CN for Hydrogen Evolution from Water under Visible Light Irradiation
Catalysts 2021, 11(1), 37; https://doi.org/10.3390/catal11010037 - 31 Dec 2020
Viewed by 532
Abstract
Modifying the physical, chemical structures of graphitic carbon nitride (g-CN) to improve its optoelectronic properties is the most efficient way to meet a high photoactivity for clean and sustainable energy production. Herein, a higher monomeric precursor for synthesizing improved micro-and electronic structure possessing [...] Read more.
Modifying the physical, chemical structures of graphitic carbon nitride (g-CN) to improve its optoelectronic properties is the most efficient way to meet a high photoactivity for clean and sustainable energy production. Herein, a higher monomeric precursor for synthesizing improved micro-and electronic structure possessing g-CN was prepared by high-concentrated sulfuric acid (SA) treatment of bulk type g-CN (BCN). Several structural analyses show that after the SA treatment of BCN, the polymeric melon-based structure is torn down to cyameluric or cyanuric acid-based material. After re-polycondensation of this material as a precursor, the resulting g-CN has more condensed microstructure, carbon and oxygen contents than BCN, indicating that C, O co-doping by corrosive acid of SA. This g-CN shows a much better visible light absorption and diminished radiative charge recombination by the charge localization effect induced by heteroatoms. As a result, this condensed C, O co-doped g-CN shows the enhanced photocatalytic hydrogen evolution rate of 4.57 µmol/h from water under the visible light (>420 nm) by almost two times higher than that of BCN (2.37 µmol/h). This study highlights the enhanced photocatalytic water splitting performance as well as the provision of the higher monomeric precursor for improved g-CN. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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Open AccessFeature PaperArticle
Polyoxometalate Template-Based Synthetic Strategy to Prepare Ni, Mo Co-Doped CdS for Efficient Photocatalytic Hydrogen Evolution from Water Splitting
Catalysts 2020, 10(12), 1478; https://doi.org/10.3390/catal10121478 - 17 Dec 2020
Cited by 1 | Viewed by 539
Abstract
In this work, a novel polyoxometalate template-based strategy was applied to construct the bi-metal-doped CdS photocatalysts. NiMo6 polyoxometalate template precursor was applied for the preparation of Ni, Mo co-doped CdS photocatalysts (NiMo-CdS). The structures of the materials were explored by XRD, SEM, [...] Read more.
In this work, a novel polyoxometalate template-based strategy was applied to construct the bi-metal-doped CdS photocatalysts. NiMo6 polyoxometalate template precursor was applied for the preparation of Ni, Mo co-doped CdS photocatalysts (NiMo-CdS). The structures of the materials were explored by XRD, SEM, HRTEM, HAADF, element mapping, XPS, Raman spectrum and UV-vis DRS. Moreover, the results of the UV-vis spectrum showed that NiMo-CdS exhibited an enhanced performance on light absorption. The results of photocatalytic hydrogen evolution from water splitting demonstrated that the NiMo-CdS showed higher efficiency on hydrogen evolution than noble-metal Pt-doped CdS. The reason could be ascribed to the enhanced light absorption ability and charge separation after Ni and Mo were introduced, which could also act as co-catalysts. The apparent quantum yield (AQY) efficiency could reach 42% at 365 nm. This work proposed a novel and inexpensive method to synthesize the bi-metal (Ni, Mo) decorated CdS photocatalysts for efficient hydrogen evolution from water splitting. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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Open AccessFeature PaperArticle
Modified Hydrothermal Route for Synthesis of Photoactive Anatase TiO2/g-CN Nanotubes from Sludge Generated TiO2
Catalysts 2020, 10(11), 1350; https://doi.org/10.3390/catal10111350 - 19 Nov 2020
Cited by 1 | Viewed by 649
Abstract
Titania nanotube was prepared from sludge generated TiO2 (S-TNT) through a modified hydrothermal route and successfully composited with graphitic carbon nitride (g-CN) through a simple calcination step. Advanced characterization techniques such as X-ray diffraction, scanning and transmission electron microscopy, infrared spectroscopy, X-ray [...] Read more.
Titania nanotube was prepared from sludge generated TiO2 (S-TNT) through a modified hydrothermal route and successfully composited with graphitic carbon nitride (g-CN) through a simple calcination step. Advanced characterization techniques such as X-ray diffraction, scanning and transmission electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, UV/visible diffuse reflectance spectroscopy, and photoluminescence analysis were utilized to characterize the prepared samples. A significant improvement in morphological and optical bandgap was observed. The effective surface area of the prepared composite increased threefold compared with sludge generated TiO2. The optical bandgap was narrowed to 3.00 eV from 3.18 in the pristine sludge generated TiO2 nanotubes. The extent of photoactivity of the prepared composites was investigated through photooxidation of NOx in a continuous flow reactor. Because of extended light absorption of the as-prepared composite, under visible light, 19.62% of NO removal was observed. On the other hand, under UV irradiation, owing to bandgap narrowing, although the light absorption was compromised, the impact on photoactivity was compensated by the increased effective surface area of 153.61 m2/g. Hence, under UV irradiance, the maximum NO removal was attained as 32.44% after 1 h of light irradiation. The proposed facile method in this study for the heterojunction of S-TNT and g-CN could significantly contribute to resource recovery from water treatment plants and photocatalytic atmospheric pollutant removal. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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Review

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Open AccessFeature PaperReview
Advanced Two-Dimensional Heterojunction Photocatalysts of Stoichiometric and Non-Stoichiometric Bismuth Oxyhalides with Graphitic Carbon Nitride for Sustainable Energy and Environmental Applications
Catalysts 2021, 11(4), 426; https://doi.org/10.3390/catal11040426 - 26 Mar 2021
Viewed by 590
Abstract
Semiconductor-based photocatalysis has been identified as an encouraging approach for solving the two main challenging problems, viz., remedying our polluted environment and the generation of sustainable chemical energy. Stoichiometric and non-stoichiometric bismuth oxyhalides (BiOX and BixOyXz where X [...] Read more.
Semiconductor-based photocatalysis has been identified as an encouraging approach for solving the two main challenging problems, viz., remedying our polluted environment and the generation of sustainable chemical energy. Stoichiometric and non-stoichiometric bismuth oxyhalides (BiOX and BixOyXz where X = Cl, Br, and I) are a relatively new class of semiconductors that have attracted considerable interest for photocatalysis applications due to attributes, viz., high stability, suitable band structure, modifiable energy bandgap and two-dimensional layered structure capable of generating an internal electric field. Recently, the construction of heterojunction photocatalysts, especially 2D/2D systems, has convincingly drawn momentous attention practicably owing to the productive influence of having two dissimilar layered semiconductors in face-to-face contact with each other. This review has systematically summarized the recent progress on the 2D/2D heterojunction constructed between BiOX/BixOyXz with graphitic carbon nitride (g-C3N4). The band structure of individual components, various fabrication methods, different strategies developed for improving the photocatalytic performance and their applications in the degradation of various organic contaminants, hydrogen (H2) evolution, carbon dioxide (CO2) reduction, nitrogen (N2) fixation and the organic synthesis of clean chemicals are summarized. The perspectives and plausible opportunities for developing high performance BiOX/BixOyXz-g-C3N4 heterojunction photocatalysts are also discussed. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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Open AccessReview
Titanium Dioxide Derived Materials with Superwettability
Catalysts 2021, 11(4), 425; https://doi.org/10.3390/catal11040425 - 26 Mar 2021
Viewed by 440
Abstract
Titanium dioxide (TiO2) is widely used in various fields both in daily life and industry owing to its excellent photoelectric properties and its induced superwettability. Over the past several decades, various methods have been reported to improve the wettability of TiO [...] Read more.
Titanium dioxide (TiO2) is widely used in various fields both in daily life and industry owing to its excellent photoelectric properties and its induced superwettability. Over the past several decades, various methods have been reported to improve the wettability of TiO2 and plenty of practical applications have been developed. The TiO2-derived materials with different morphologies display a variety of functions including photocatalysis, self-cleaning, oil-water separation, etc. Herein, various functions and applications of TiO2 with superwettability are summarized and described in different sections. First, a brief introduction about the discovery of photoelectrodes made of TiO2 is revealed. The ultra-fast spreading behaviors on TiO2 are shown in the part of ultra-fast spreading with superwettability. The part of controllable wettability introduces the controllable wettability of TiO2-derived materials and their related applications. Recent developments of interfacial photocatalysis and photoelectrochemical reactions with TiO2 are presented in the part of interfacial photocatalysis and photoelectrochemical reactions. The part of nanochannels for ion rectification describes ion transportation in nanochannels based on TiO2-derived materials. In the final section, a brief conclusion and a future outlook based on the superwettability of TiO2 are shown. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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Open AccessFeature PaperReview
Photocatalytic Methane Reforming: Recent Advances
Catalysts 2021, 11(1), 18; https://doi.org/10.3390/catal11010018 - 25 Dec 2020
Viewed by 976
Abstract
Methane reforming is an important potential technology for solving both environmental and energy problems. This technology is important because methane is counted as a greenhouse gas, but on the other hand, it can be reformed into industrially valuable compounds. More research has focused [...] Read more.
Methane reforming is an important potential technology for solving both environmental and energy problems. This technology is important because methane is counted as a greenhouse gas, but on the other hand, it can be reformed into industrially valuable compounds. More research has focused on photocatalytic methane reforming, which has a higher activity than thermal catalysts under dark conditions. The reaction selectivity toward specific products in photocatalytic methane reforming is sometimes different from thermal catalyst systems. Herein, we discuss recent advances in photocatalytic methane reforming to provide various strategies for reforming. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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Open AccessFeature PaperReview
Rational Design of Binary Alloys for Catalytic Growth of Graphene via Chemical Vapor Deposition
Catalysts 2020, 10(11), 1305; https://doi.org/10.3390/catal10111305 - 12 Nov 2020
Cited by 2 | Viewed by 624
Abstract
Chemical vapor deposition is the most promising technique for the mass production of high-quality graphene, in which the metal substrate plays a crucial role in the catalytic decomposition of the carbon source, assisting the attachment of the active carbon species, and regulating the [...] Read more.
Chemical vapor deposition is the most promising technique for the mass production of high-quality graphene, in which the metal substrate plays a crucial role in the catalytic decomposition of the carbon source, assisting the attachment of the active carbon species, and regulating the structure of the graphene film. Due to some drawbacks of single metal substrates, alloy substrates have gradually attracted attention owing to their complementarity in the catalytic growth of graphene. In this review, we focus on the rational design of binary alloys, such as Cu/Ni, Ni/Mo, and Cu/Si, to control the layer numbers and growth rate of graphene. By analyzing the elementary steps of graphene growth, general principles are summarized in terms of the catalytic activity, metal–carbon interactions, carbon solubility, and mutual miscibility. Several challenges in this field are also put forward to inspire the novel design of alloy catalysts and the synthesis of graphene films bearing desirable properties. Full article
(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Akira Fujishima)
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