Special Issue "Recent Advances in TiO2 Photocatalysts"

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

Deadline for manuscript submissions: 30 November 2020.

Special Issue Editors

Prof. Dr. Marta Gmurek
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Guest Editor
Lodz University of Technology Faculty of Process and Environmental Engineering, Lodz, Poland
Interests: Scientific: photochemistry, water and wastewater treatment, advanced oxidation processes, photodegradation, disinfection, solar disinfection, toxicity, mass spectroscopy, reactions of reactive oxygen species
Special Issues and Collections in MDPI journals
Dr. Anna Malankowska
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Guest Editor
University of Gdansk Faculty of Chemistry, Gdansk, Poland
Interests: heterogeneous photocatalysis, environmental remediation technologies, nanotechnology, nanomaterials, nanobiomedicine, environmental protection, synthesis of quantum dots, metallic and semiconductors nanoparticles
Dr. Rui C. Martins
Website
Guest Editor
Department of Chemical Engineering, Faculty of Sciences and Technology, University of Coimbra, Rua Sílvio Lima, 3030-790 Coimbra, Portugal
Interests: chemical reaction engineering; effluents treatment; advanced oxidation processes; ozonation and photocatalytic ozonation; ecotoxicology and environmental chemistry; product recovery
Special Issues and Collections in MDPI journals
Dr. Ewa Borowska
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Guest Editor
Karlsruhe Institute of Technology Engler-Bunte-Institut, Water Chemistry and Water Technology, Karlsruhe, Germany
Interests: fate of micropollutants in aquatic environment, solar-driven degradation processes, identification of transformation products, wastewater treatment using photochemical processes

Special Issue Information

Dear Colleagues,

Chemical processes, such as advanced oxidation processes (AOPs), receive a lot of attention with respect to their application for water treatment purposes. Among these processes, semiconductor photocatalysis, especially with titanium dioxide (TiO2), has been studied in detail, also with regard to the elimination of selected micropollutants in water. This inexpensive, stable and non-toxic catalyst provides very good removal efficiencies. TiO2 photocatalysts have a great potential for application in the decontamination of wastewater, exhaust gases and disinfection. High-efficiency TiO2-based photocatalysts are also successfully used in photocatalytic water splitting and photoconversion, providing low cost and environmentally-friendly production of clean fuels. However, due to the energy band gap, the practicality of natural solar light employment is limited. Nowadays, the application of visible light in TiO2 photocatalysis is the main goal of research.

This Special Issue aims to report on recent progress and developments in methods promoting the visible light photocatalytic activity of TiO2, including metal and non-metal doping, surface deposition of noble metals, semiconductor coupling, and dye sensitizing. Furthermore, research into understanding the mechanism of photocatalysis, photocatalytic ozonation, as well as the photoconversion and water splitting will be important subjects for this Special Issue.

Prof. Dr. Marta Gmurek
Dr. Anna Malankowska
Prof. Dr. Rui C. Martins
Dr. Ewa Borowska
Guest Editors

Manuscript Submission Information

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Keywords

  • homogeneous and heterogeneous photocatalysis
  • photocatalytic ozonation
  • visible light application
  • mechanism investigation
  • structure modification
  • structure characterization
  • water splitting
  • hydrogen production
  • photoconversion

Published Papers (18 papers)

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Open AccessArticle
Large-Area Patterning of Oil-Based Inks on Superhydrophobic TiO2 Nanotubular Layers by Photocatalytic Wettability Conversion
Catalysts 2020, 10(10), 1203; https://doi.org/10.3390/catal10101203 - 17 Oct 2020
Abstract
Patterning an oil-based ink on a solid surface based on a wettability difference is of significant importance for the application of offset printing. Herein, we describe a large-area patterning of oil-based ink on a self-organized TiO2 nanotubular layer based on a photocatalytic [...] Read more.
Patterning an oil-based ink on a solid surface based on a wettability difference is of significant importance for the application of offset printing. Herein, we describe a large-area patterning of oil-based ink on a self-organized TiO2 nanotubular layer based on a photocatalytic wettability conversion. The TiO2 nanotubular layer was fabricated by electrochemical anodization, which demonstrated a superhydrophobic wettability after modification with a self-assembled molecular layer. Subsequently, area-selective ultraviolet (UV) irradiation through a pre-designed pattern of water-based UV-resistant ink formed by an ink-jet technique was used to form a wettability difference. After removing the water-based ink, an oil-based ink was capable of depositing selectively on the superhydrophobic area to form the same pattern as the pre-designed pattern of water-based ink. This large-area patterning of an oil-based ink based on the photocatalytic wettability conversion is potentially applicable in offset printing. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Open AccessFeature PaperArticle
Exploring the Photothermo-Catalytic Performance of Brookite TiO2-CeO2 Composites
Catalysts 2020, 10(7), 765; https://doi.org/10.3390/catal10070765 - 09 Jul 2020
Cited by 1
Abstract
The thermocatalytic, photocatalytic and photothermo-catalytic oxidation of some volatile organic compounds (VOCs), 2-propanol, ethanol and toluene, was investigated over brookite TiO2-CeO2 composites. The multi-catalytic approach based on the synergistic effect between solar photocatalysis and thermocatalysis led to the considerable decrease [...] Read more.
The thermocatalytic, photocatalytic and photothermo-catalytic oxidation of some volatile organic compounds (VOCs), 2-propanol, ethanol and toluene, was investigated over brookite TiO2-CeO2 composites. The multi-catalytic approach based on the synergistic effect between solar photocatalysis and thermocatalysis led to the considerable decrease in the conversion temperatures of the organic compounds. In particular, in the photothermo-catalytic runs, for the most active samples (TiO2-3 wt% CeO2 and TiO2-5 wt% CeO2), the temperature at which 90% of VOC conversion occurred was about 60 °C, 40 °C and 20 °C lower than in the thermocatalytic tests for 2-propanol, ethanol and toluene, respectively. Furthermore, the addition of cerium oxide to brookite TiO2 favored the total oxidation to CO2 already in the photocatalytic tests at room temperature. The presence of small amounts of cerium oxide allowed to obtain efficient brookite-based composites facilitating the space charge separation and increasing the lifetime of the photogenerated holes and electrons as confirmed by the characterization measurements. The possibility to concurrently utilize the photocatalytic properties of brookite and the redox properties of CeO2, both activated in the photothermal tests, is an attractive approach easily applicable to purify air from VOCs. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Open AccessArticle
Enhanced Photocatalytic CO2 Reduction over TiO2 Using Metalloporphyrin as the Cocatalyst
Catalysts 2020, 10(6), 654; https://doi.org/10.3390/catal10060654 - 11 Jun 2020
Abstract
The photocatalytic reduction of carbon dioxide (CO2) into CO and hydrocarbon fuels has been considered as an ideal green technology for solar-to-chemical energy conversion. The separation/transport of photoinduced charge carriers and adsorption/activation of CO2 molecules play crucial roles in photocatalytic [...] Read more.
The photocatalytic reduction of carbon dioxide (CO2) into CO and hydrocarbon fuels has been considered as an ideal green technology for solar-to-chemical energy conversion. The separation/transport of photoinduced charge carriers and adsorption/activation of CO2 molecules play crucial roles in photocatalytic activity. Herein, tetrakis (4-carboxyphenyl) porphyrin (H2TCPP) was incorporated with different metal atoms in the center of a conjugate macrocycle, forming the metalloporphyrins TCPP-M (M = Co, Ni, Cu). The as-obtained metalloporphyrin was loaded as a cocatalyst on commercial titania (P25) to form [email protected] (M = Co, Ni, Cu) for enhanced CO2 photoreduction. Among all of the [email protected] (M = Co, Ni, Cu), [email protected] exhibited the highest evolution rates of CO (13.6 μmol⋅g−1⋅h−1) and CH4 (1.0 μmol⋅g−1⋅h−1), which were 35.8 times and 97.0 times those of bare P25, respectively. The enhanced photocatalytic activity could be attributed to the improved photogenerated electron-hole separation efficiency, as well as the increased adsorption/activation sites provided by the metal centers in TCPP-M (M = Co, Ni, Cu). Our study indicates that metalloporphyrin could be used as a high-efficiency cocatalyst to enhance CO2 photoreduction activity. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Open AccessArticle
Industrial Textile Wastewater Ozone Treatment: Catalyst Selection
Catalysts 2020, 10(6), 611; https://doi.org/10.3390/catal10060611 - 01 Jun 2020
Abstract
One of the recent trends in textile wastewater treatment has become catalytic ozonation. The necessity of effective color removal in a short treatment time is a standard during industrial implementation. At the same time, efficient chemical oxygen demand (COD), total organic carbon (TOC), [...] Read more.
One of the recent trends in textile wastewater treatment has become catalytic ozonation. The necessity of effective color removal in a short treatment time is a standard during industrial implementation. At the same time, efficient chemical oxygen demand (COD), total organic carbon (TOC), and toxic by-product removal are highly expected. This study presents the results of a catalytic ozonation treatment. Three types of catalysts: a metal oxide (TiO2 as P25 by Degussa), activated carbon (nano-powder by Sigma, AC), and metal particles (platinum, 1% wt. supported on AC matrix by Sigma, Pt–AC) have been applied. The investigations were conducted for real industrial wastewater originated in textile dyeing with Reactive Black 5 dye (RB5). The experiments ran for the raw wastewater (without pretreatment), exposed blocking of the catalytic action by all used catalysts. The catalytic effect could be observed when catalytic ozonation was used as a polishing step after electrocoagulation (EC). Although the catalytic effect could be observe for all catalysts then, especially in the removal of colorless by-products, the AC was exposed as the most effective. This contributed to 35% and 40% of TOC and COD removal. While only 18% and 23% of TOC and COD were removed in the same process without AC. The decrease in toxicity was 30%. The results of the study revealed the complexity of the issue and resulted in an extensive discussion devoted to the basis of the catalytic activity of each catalyst. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Open AccessArticle
Synthesis of Conducting Bifunctional [email protected]2 Nanocomposites for Supercapacitor Electrode and Visible Light Driven Photocatalysis
Catalysts 2020, 10(5), 546; https://doi.org/10.3390/catal10050546 - 14 May 2020
Cited by 3
Abstract
We report a polyaniline-wrapped, manganese-doped titanium oxide (PANi/Mn-TiO2) nanoparticle composite for supercapacitor electrode and photocatalytic degradation. The PANi/Mn-TiO2 nanoparticles were synthesized using a solvothermal process, followed by oxidative polymerization of aniline. The structural properties of studied materials were confirmed by [...] Read more.
We report a polyaniline-wrapped, manganese-doped titanium oxide (PANi/Mn-TiO2) nanoparticle composite for supercapacitor electrode and photocatalytic degradation. The PANi/Mn-TiO2 nanoparticles were synthesized using a solvothermal process, followed by oxidative polymerization of aniline. The structural properties of studied materials were confirmed by XRD, FTIR, HRTEM, FESEM, and UV visible spectroscopy. The as-prepared PANi/Mn-TiO2 nanoparticles revealed admirable electrochemical performance with a specific capacitance of 635.87 F g−1 at a current density of 1 A g−1 with a notable life cycle retention of 91% after 5000 charge/discharge cycles. Furthermore, the asymmetric cell with PANi/Mn-TiO2 as a positive electrode exhibited energy density of 18.66 W h kg−1 with excellent stability. Moreover, the PANi/Mn-TiO2 had promising photocatalytic activity for methylene blue degradation. The improved performance of PANi/Mn-TiO2 nanoparticles is attributed to the well-built synergetic effect of components that lead to significant reduction of band gap energy and charge transfer resistance, as revealed by UV visible spectroscopy and electrochemical impedance spectroscopy. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Open AccessArticle
Biomorphic Fibrous TiO2 Photocatalyst Obtained by Hydrothermal Impregnation of Short Flax Fibers with Titanium Polyhydroxocomplexes
Catalysts 2020, 10(5), 541; https://doi.org/10.3390/catal10050541 - 13 May 2020
Abstract
A biomimetic solution technology for producing a photocatalytic material in the form of biomorphic titanium oxide fibers with a hierarchical structure using short flax fiber as a biotemplate is proposed. The impregnation of flax fibers intensified under hydrothermal conditions with a precursor was [...] Read more.
A biomimetic solution technology for producing a photocatalytic material in the form of biomorphic titanium oxide fibers with a hierarchical structure using short flax fiber as a biotemplate is proposed. The impregnation of flax fibers intensified under hydrothermal conditions with a precursor was performed in an autoclave to activate the nucleation of the photoactive TiO2 phases. The interaction between precursor and flax fibers was studied by using infrared spectroscopy (IR) and differential scanning calorimetry/thermogravimetry analysis (DSC/TG). The morphology, structure, and textural properties of the TiO2 fibers obtained at annealing temperatures of 500–700 °C were determined by X-ray diffraction analysis, scanning electron microscopy, and nitrogen adsorption/desorption. It is shown that the annealing temperature of the impregnated biotemplates significantly affects the phase composition, crystallite size, and porous structure of TiO2 fiber samples. The photocatalytic activity of the obtained fibrous TiO2 materials was evaluated by using the decomposition of the cationic dye Rhodamine B in an aqueous solution (concentration 12 mg/L) under the influence of ultraviolet radiation (UV). The maximum photodegradation efficiency of the Rhodamine B was observed for TiO2 fibers annealed at 600 °C and containing 40% anatase and 60% rutile. This sample ensured 100% degradation of the dye in 20 min, and this amount significantly exceeds the photocatalytic activity of the commercial Degussa P25 photocatalyst and TiO2 samples obtained previously under hydrothermal conditions by the sol-gel method. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Open AccessArticle
Photocatalytic Oxidative Degradation of Carbamazepine by TiO2 Irradiated by UV Light Emitting Diode
Catalysts 2020, 10(5), 540; https://doi.org/10.3390/catal10050540 - 13 May 2020
Cited by 2
Abstract
Here, ultraviolet light-emitting diodes (UV-LED) combined with TiO2 was used to investigate the feasibility of carbamazepine (CBZ) degradation. The effects of various factors, like crystal form of the catalyst (anatase, rutile, and mixed phase), mass concentration of TiO2, wavelength and [...] Read more.
Here, ultraviolet light-emitting diodes (UV-LED) combined with TiO2 was used to investigate the feasibility of carbamazepine (CBZ) degradation. The effects of various factors, like crystal form of the catalyst (anatase, rutile, and mixed phase), mass concentration of TiO2, wavelength and irradiation intensity of the UV-LED light source, pH of the reaction system, and coexisting anions and cations, on the photocatalytic degradation of CBZ were studied. The mixed-phase (2.8 g/L) showed the best degradation efficiency at 365 nm among three kinds of TiO2, wherein CBZ (21.1 µM) was completely oxidized within 1 h. The results of batch experiments showed that: (i) CBZ degradation efficiency under UV-LED light at 365 nm was higher than 275 nm, due to stronger penetrability of 365 nm light in solution. (ii) The degradation efficiency increased with increase in irradiation intensity and pH, whereas it decreased with increase in initial CBZ concentration. (iii) The optimal amount of mixed-phase TiO2 catalyst was 2.8 g/L and excessive catalyst decreased the rate. (iv) The co-existence of CO32−, HCO3, and Fe3+ ions in water significantly accelerated the degradation rate of photocatalytic CBZ, whereas Cu2+ ions strongly inhibited the degradation process of CBZ. ·OH was found to be the main active species in the UV-LED photocatalytic degradation of CBZ. UV-LED is more environmentally friendly, energy efficient, and safer, whereas commercial TiO2 is economical and readily available. Therefore, this study provides a practically viable reference method for the degradation of pharmaceuticals and personal care products (PPCPs). Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Open AccessArticle
Shape-Selective Mesoscale Nanoarchitectures: Preparation and Photocatalytic Performance
Catalysts 2020, 10(5), 532; https://doi.org/10.3390/catal10050532 - 12 May 2020
Abstract
We create ordered arrays of shape-selective gold-titania composite nanomaterials at the mesoscale (100 µm to 5 mm) by a combination of both bottom-up and top-down approaches for exquisite control of the size, shape, and arrangement of nanomaterials. Lithographic techniques along with wet chemical [...] Read more.
We create ordered arrays of shape-selective gold-titania composite nanomaterials at the mesoscale (100 µm to 5 mm) by a combination of both bottom-up and top-down approaches for exquisite control of the size, shape, and arrangement of nanomaterials. Lithographic techniques along with wet chemical synthetic methods were combined to create these composite nanomaterials. The photocatalytic activity of these TiO2, TiO2-Au and SiO2-TiO2-Au nano-composite mesoscale materials was monitored by the photodegradation of a model analyte, methyl orange, under UV and visible (Vis) illumination. Bare TiO2- and SiO2-TiO2-coated pillar arrays showed significant activity toward methyl orange in UV light with degradation rates on the order of 10−4–10−3 min−1. The photocatalytic activity of these arrays was also found to depend on the nanoparticle shape, in which particles with more edges and corners were found to be more reactive than spherical particles (i.e., the photocatalytic activity decreased as follows: diamonds > squares > triangles > spheres). SiO2-TiO2-Au nano-composite pillar arrays were tested in both UV and Vis light and showed increased activity in Vis light but decreased activity in UV light as compared to the bare semiconductor arrays. Additionally, the Au nanorod-functionalized nanoarrays exhibit a strong shape-dependence in their photocatalytic activity toward methyl orange degradation in Vis light. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Open AccessArticle
Investigation of the Synergistic Effect of Sonolysis and Photocatalysis of Titanium Dioxide for Organic Dye Degradation
Catalysts 2020, 10(5), 500; https://doi.org/10.3390/catal10050500 - 02 May 2020
Cited by 2
Abstract
Herein, we report the effect of sonoluminescence and an initial dye concentration on the sonophotocatalysis of TiO2 for the degradation of eosin B, a textile dye. We first investigated the light illuminated during ultrasound irradiation (sonoluminescence) by photographic images, a radical indicator [...] Read more.
Herein, we report the effect of sonoluminescence and an initial dye concentration on the sonophotocatalysis of TiO2 for the degradation of eosin B, a textile dye. We first investigated the light illuminated during ultrasound irradiation (sonoluminescence) by photographic images, a radical indicator (luminol), and photoluminescence spectra of the detection range of 300–1050 nm. Next, we examined the synergistic effect of sonolysis on photocatalysis by comparing the dye degradation of sonophotocatalysis to that of individual contributions of sonolysis and photocatalysis. Since it was found that the synergist effect is highly engaged with a dye concentration and sonication power, we conducted the comparison test in different concentrations of eosin B (5 and 20 mg/L) and ultrasound powers (35.4, 106.1, and 176.8 W/cm2). When the concentration of dyes was low, negative synergistic effects were found at all ultrasound powers, whereas at the high concentration, positive synergistic effects were observed at high ultrasound power. This difference in synergistic effects was explained by the influence of ultrasound on dynamics of dye adsorption on the TiO2 surface. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Open AccessArticle
Enhancement of Photocatalytic Oxidation of Glucose to Value-Added Chemicals on TiO2 Photocatalysts by A Zeolite (Type Y) Support and Metal Loading
Catalysts 2020, 10(4), 423; https://doi.org/10.3390/catal10040423 - 13 Apr 2020
Cited by 2
Abstract
TiO2-based photocatalysts synthesized by the microwave-assisted sol-gel method was tested in the photocatalytic glucose conversion. Modifications of TiO2 with type-Y zeolite (ZeY) and metals (Ag, Cu, and Ag-Cu) were developed for increasing the dispersion of TiO2 nanoparticles and increasing [...] Read more.
TiO2-based photocatalysts synthesized by the microwave-assisted sol-gel method was tested in the photocatalytic glucose conversion. Modifications of TiO2 with type-Y zeolite (ZeY) and metals (Ag, Cu, and Ag-Cu) were developed for increasing the dispersion of TiO2 nanoparticles and increasing the photocatalytic activity. Effects of the TiO2 dosage to zeolite ratio (i.e., TiO2/ZeY of 10, 20, 40, and 50 mol %) and the silica to alumina ratio in ZeY (i.e., SiO2:Al2O3 of 10, 100, and 500) were firstly studied. It was found that the specific surface area of TiO2/ZeY was 400–590 m2g−1, which was higher than that of pristine TiO2 (34.38 m2g−1). The good properties of 20%TiO2/ZeY photocatalyst, including smaller particles (13.27 nm) and high surface area, could achieve the highest photocatalytic glucose conversion (75%). Yields of gluconic acid, arabinose, xylitol, and formic acid obtained from 20%TiO2/ZeY were 9%, 26%, 4%, and 35%, respectively. For the effect of the silica to alumina ratio, the highest glucose conversion was obtained from SiO2:Al2O3 ratio of 100. Interestingly, it was found that the SiO2:Al2O3 ratio affected the selectivity of carboxylic products (gluconic acid and formic acid). At a low ratio of silica to alumina (SiO2:Al2O3 = 10), higher selectivity of the carboxylic products (gluconic acid = 29% and formic acid = 32%) was obtained (compared with other higher ratios). TiO2/ZeY was further loaded by metals using the microwave-assisted incipient wetness impregnation technique. The highest glucose conversion of 96.9 % was obtained from 1 wt. % Ag-TiO2 (40%)/ZeY. Furthermore, the bimetallic Ag-Cu-loaded TiO2/ZeY presented the highest xylitol yield of 12.93%. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Open AccessFeature PaperArticle
The Effect of AgInS2, SnS, CuS2, Bi2S3 Quantum Dots on the Surface Properties and Photocatalytic Activity of QDs-Sensitized TiO2 Composite
Catalysts 2020, 10(4), 403; https://doi.org/10.3390/catal10040403 - 07 Apr 2020
Abstract
The effect of type (AgInS2, SnS, CuS2, Bi2S3) and amount (5, 10, 15 wt%) of quantum dots (QDs) on the surface properties and photocatalytic activity of QDs-sensitized TiO2 composite, was investigated. AgInS2, [...] Read more.
The effect of type (AgInS2, SnS, CuS2, Bi2S3) and amount (5, 10, 15 wt%) of quantum dots (QDs) on the surface properties and photocatalytic activity of QDs-sensitized TiO2 composite, was investigated. AgInS2, SnS, CuS2, Bi2S3 QDs were obtained by hot-injection, sonochemical, microwave, and hot-injection method, respectively. To characterize of as-prepared samples high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-Vis spectroscopy and photoluminescence (PL) emission spectroscopy were applied. The size of AgInS2, SnS, CuS2, Bi2S3 QDs were 12; 2–6; 2–3, and 1–2 nm, respectively. The QDs and QDs-sensitized TiO2 composites obtained have been tested in toluene degradation under LEDs light irradiation (λmax = 415 nm and λmax = 375 nm). For pristine QDs the efficiency of toluene degradation increased in the order of AgInS2 < Bi2S3 < CuS < SnS under 375 nm and AgInS2 < CuS < Bi2S3 < SnS under 415 nm. In the presence of TiO2/SnS QDs_15% composite, 91% of toluene was degraded after 1 h of irradiation, and this efficiency was about 12 higher than that for pristine QDs under 375 nm. Generally, building the TiO2/AgInS2 and TiO2/SnS exhibited higher photoactivity under 375 nm than the pristine TiO2 and QDs which suggests a synergistic effect between QDs and TiO2 matrix. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Open AccessArticle
Selective Oxidation of Crude Glycerol to Dihydroxyacetone in a Biphasic Photoreactor
Catalysts 2020, 10(4), 360; https://doi.org/10.3390/catal10040360 - 26 Mar 2020
Abstract
In this paper, the first biphasic photoreactor was introduced and utilized for the conversion of glycerol to glyceraldehyde (GAD) and dihydroxyacetone (DHA) using water and ethyl acetate as dispersed (active) and continuous (inactive) phases, respectively. Increasing the ethyl acetate content in the reactor [...] Read more.
In this paper, the first biphasic photoreactor was introduced and utilized for the conversion of glycerol to glyceraldehyde (GAD) and dihydroxyacetone (DHA) using water and ethyl acetate as dispersed (active) and continuous (inactive) phases, respectively. Increasing the ethyl acetate content in the reactor improved the DHA yield; however, the optimal DHA selectivity was obtained at an ethyl acetate to water ratio of 90:10 (vol/vol). Compared to a monophasic photoreactor containing only water and identical amounts of glycerol and photocatalyst, the biphasic reactor containing 90 vol % ethyl acetate increased the DHA yield by a factor of 2.9 (from 4.5% to 13%) and the concentration of DHA by approximately 14 times (from 0.08 mM to 1.1 mM) after 240 min. Additionally, photocatalytic conversion of crude glycerol extracted using a 90:10 (vol/vol) ethyl acetate-water mixture showed a similar DHA conversion and yield to that of pure glycerol. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Open AccessArticle
Synergistic Effect of Dielectric Barrier Discharge Plasma and TiO2-Pillared Montmorillonite on the Degradation of Rhodamine B in an Aqueous Solution
Catalysts 2020, 10(4), 359; https://doi.org/10.3390/catal10040359 - 25 Mar 2020
Abstract
Photocatalytic, plasma and combined plasma–photocatalytic processes were applied for the destruction of a model pollutant, Rhodamine B dye, in an aqueous solution (concentration of 40 mg/L). For this purpose TiO2-pillared montmorillonite was used as a photocatalyst (characterized by X-ray analysis and [...] Read more.
Photocatalytic, plasma and combined plasma–photocatalytic processes were applied for the destruction of a model pollutant, Rhodamine B dye, in an aqueous solution (concentration of 40 mg/L). For this purpose TiO2-pillared montmorillonite was used as a photocatalyst (characterized by X-ray analysis and low-temperature nitrogen adsorption/desorption). It was prepared by the method of intercalation of titanium hydroxocomplexes, including hydrothermal activation of the process and preliminary mechanical treatment of the layered substrate. The dielectric barrier discharge (DBD) plasma in the presence of photocatalysts increases the efficiency of dye degradation (100%, 8 s) compared to plasmolysis (94%) and UV photolysis (92%, 100 min of UV irradiation); in contrast to photolysis, destructive processes are more profound and lead to the formation of simple organic compounds such as carboxylic acids. The plasma–catalytic method enhances by 20% the energetic efficiency of the destruction of Rhodamine B compared to DBD plasma. The efficiency of dye destruction with the plasma–catalytic method increases with the improvement of the textural properties of the photocatalyst. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Open AccessArticle
Core-Shell Nanostructures of Graphene-Wrapped CdS Nanoparticles and TiO2 ([email protected]@TiO2): The Role of Graphene in Enhanced Photocatalytic H2 Generation
Catalysts 2020, 10(4), 358; https://doi.org/10.3390/catal10040358 - 25 Mar 2020
Cited by 2
Abstract
Aiming to achieve enhanced photocatalytic activity and stability toward the generation of H2 from water, we have synthesized noble metal-free core-shell nanoparticles of graphene (G)-wrapped CdS and TiO2 ([email protected]@TiO2) by a facile hydrothermal method. The interlayer thickness of G [...] Read more.
Aiming to achieve enhanced photocatalytic activity and stability toward the generation of H2 from water, we have synthesized noble metal-free core-shell nanoparticles of graphene (G)-wrapped CdS and TiO2 ([email protected]@TiO2) by a facile hydrothermal method. The interlayer thickness of G between the CdS core and TiO2 shell is optimized by varying the amount of graphene quantum dots (GQD) during the synthesis procedure. The most optimized sample, i.e., [email protected]@TiO2 generated 1510 µmole g−1 h−1 of H2 (apparent quantum efficiency (AQE) = 5.78%) from water under simulated solar light with air mass 1.5 global (AM 1.5G) condition which is ~2.7 times and ~2.2 time superior to pure TiO2 and pure CdS respectively, along with a stable generation of H2 during 40 h of continuous operation. The increased photocatalytic activity and stability of the [email protected]@TiO2 sample are attributed to the enhanced visible light absorption and efficient charge separation and transfer between the CdS and TiO2 due to incorporation of graphene between the CdS core and TiO2 shell, which was also confirmed by UV-vis, photoelectrochemical and valence band XPS measurements. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Open AccessArticle
Development and Validation of a LC-MS/MS Method for Determination of Multi-Class Antibiotic Residues in Aquaculture and River Waters, and Photocatalytic Degradation of Antibiotics by TiO2 Nanomaterials
Catalysts 2020, 10(3), 356; https://doi.org/10.3390/catal10030356 - 24 Mar 2020
Cited by 2
Abstract
This study presents a multi-residue method for simultaneous qualitative and quantitative analysis of eight antibiotics from some common classes, including beta-lactam, tetracyclines, lincosamides, glycopeptides, and sulfonamides in 39 aquaculture and river water samples from the Mekong Delta (Vietnam) using liquid chromatography-tandem mass spectrometry [...] Read more.
This study presents a multi-residue method for simultaneous qualitative and quantitative analysis of eight antibiotics from some common classes, including beta-lactam, tetracyclines, lincosamides, glycopeptides, and sulfonamides in 39 aquaculture and river water samples from the Mekong Delta (Vietnam) using liquid chromatography-tandem mass spectrometry (LC-MS/MS). As a result, doxycycline (DXC), oxytetracycline (OTC), lincomycin (LCM), sulfamethoxazole (SMX), and sulfamethazine (SMZ) were detected with high frequency over 65% and an average concentration of 22.6–76.8 ng·mL−1. The result suggests that antibiotic residues in the aquaculture and river waters are considered as an emerging environmental problem of the region. To address this issue, we fabricated the well-defined TiO2 nanotube arrays (TNAs) and nanowires on nanotube arrays (TNWs/TNAs) using the anodization method. The TNAs had an inner tube diameter of ~95 nm and a wall thickness of ~25 nm. Meanwhile, the TNWs/TNAs had a layer of TiO2 nanowires with a length of ~6 µm partially covering the TNAs. In addition, both TNAs and TNWs/TNAs had pure anatase phase TiO2 with (101) and (112) dominant preferred orientations. Moreover, the TNAs and TNWs/TNAs effectively and rapidly degraded the antibiotic residues under UV-VIS irradiation at 120 mW/cm2 and obtained over 95% removal at 20 min. Indeed, the photocatalytic reaction rate constants (k) were in the range of 0.14–0.36 min−1 for TNAs, and 0.15–0.38 min−1 for TNWs/TNAs. Noticeably, the k values of TNWs/TNAs were slightly higher than those of TNAs for LCM, DXC, OTC, SMZ, and SMX that could be attributed to the larger surface area of TNWs/TNAs than TNAs when TNWs/TNAs had an additional ~6μm TNWs top layer. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Open AccessArticle
The Use of Tunable Optical Absorption Plasmonic Au and Ag Decorated TiO2 Structures as Efficient Visible Light Photocatalysts
Catalysts 2020, 10(1), 139; https://doi.org/10.3390/catal10010139 - 20 Jan 2020
Cited by 5
Abstract
Exploring solar-excited heterogeneous photocatalysts by taking advantage of surface plasmon resonance (SPR) has drawn growing research attention. As it could help to pave the way for global sustainable development. The decoration of TiO2 particles with noble metals possessing SPR effects is regarded [...] Read more.
Exploring solar-excited heterogeneous photocatalysts by taking advantage of surface plasmon resonance (SPR) has drawn growing research attention. As it could help to pave the way for global sustainable development. The decoration of TiO2 particles with noble metals possessing SPR effects is regarded as one of the most effective solutions. The perfect match of the SPR absorption band with the spectrum of incident light is an essential factor for plasmonic enhancement. However, modifying with sole noble metal is often limited as it tunes wavelength of only several nanometers. To overcome this drawback, an alternative approach can be offered by decoration with more than one noble metal. For instance, Au-Ag co-decoration displays greatly adjustable, composition-dependent SPR agent over a broad range of the visible light spectrum (ca. from 415 to 525 nm). Hence Au-Ag complex is a remarkable candidate for tuning the photo adsorption of TiO2 from UV to visible light. This study presents a novel and tailored method for the fabrication of Au-Ag co-modified TiO2 particles, and how Au-Ag dependent SPR was applied as the visible light-responsive TiO2 based photocatalysts in a simple but reliable way. The fabricated Au-Ag co-decorated TiO2 (AuxAg(1−x)/TiO2) was characterized and proved to own excellent stability and large specific surface area. The optimization of these particles against the wavelength of maximal solar light intensity was confirmed by photo degradation of methylene blue under visible light radiation. This work may provide further insight into the design of TiO2-based composites with improved photocatalytic properties for environmental remediation and renewable energy utilization. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Open AccessArticle
Solar Photocatalytic Degradation of Sulfamethoxazole by TiO2 Modified with Noble Metals
Catalysts 2019, 9(6), 500; https://doi.org/10.3390/catal9060500 - 30 May 2019
Cited by 10
Abstract
Application of solar photocatalysis for water treatment is intensively studied. In this work, we investigated TiO2 modified with platinum (Pt/TiO2) and palladium (Pd/TiO2) using sulfamethoxazole (SMX) as the model contaminant. We considered the following parameters: (i) level of [...] Read more.
Application of solar photocatalysis for water treatment is intensively studied. In this work, we investigated TiO2 modified with platinum (Pt/TiO2) and palladium (Pd/TiO2) using sulfamethoxazole (SMX) as the model contaminant. We considered the following parameters: (i) level of TiO2 modification with Pt/Pd, (ii) initial concentration of photocatalysts, (iii) geographic location where processes were conducted, and (iv) natural water matrix. The catalysts characterized by SEM, EDX, DRS, and XRD techniques showed successful deposition of Pd and Pt atoms on TiO2 surface that enabled light absorption in the visible (Vis) range, and therefore caused efficient SMX removal in all tested conditions. A comparison of the rate constants of SMX degradation in various conditions revealed that modification with Pd gave better results than modification with Pt, which was explained by the better optical properties of Pd/TiO2. The removal of SMX was higher with Pd/TiO2 than with Pt/TiO2, independent of the modification level. In the experiments with the same modification level, similar rate constants were achieved when four times the lower concentration of Pd/TiO2 was used as compared with Pt/TiO2. Formation of four SMX transformation products was confirmed, in which both amine groups are involved in photocatalytic oxidation. No toxic effect of post-reaction solutions towards Lepidium sativum was observed. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Review

Jump to: Research

Open AccessReview
Recent Developments of Advanced Ti3+-Self-Doped TiO2 for Efficient Visible-Light-Driven Photocatalysis
Catalysts 2020, 10(6), 679; https://doi.org/10.3390/catal10060679 - 17 Jun 2020
Abstract
Research into the development of efficient semiconductor photocatalytic materials is a promising approach to solving environmental and energy problems worldwide. Among these materials, TiO2 photocatalysts are one of the most commonly used due to their efficient photoactivity, high stability, low cost and [...] Read more.
Research into the development of efficient semiconductor photocatalytic materials is a promising approach to solving environmental and energy problems worldwide. Among these materials, TiO2 photocatalysts are one of the most commonly used due to their efficient photoactivity, high stability, low cost and environmental friendliness. However, since the UV content of sunlight is less than 5%, the development of visible light-activated TiO2-based photocatalysts is essential to increase the solar energy efficiency. Here, we review recent works on advanced visible light-activated Ti3+-self-doped TiO2 (Ti3+–TiO2) photocatalysts with improved electronic band structures for efficient charge separation. We analyze the different methods used to produce Ti3+–TiO2 photocatalysts, where Ti3+ with a high oxygen defect density can be used for energy production from visible light. We categorize advanced modifications in electronic states of Ti3+–TiO2 by improving their photocatalytic activity. Ti3+–TiO2 photocatalysts with large charge separation and low recombination of photogenerated electrons and holes can be practically applied for energy conversion and advanced oxidation processes in natural environments and deserve significant attention. Full article
(This article belongs to the Special Issue Recent Advances in TiO2 Photocatalysts)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Core-shell nanostructures of graphene-wrapped CdS nanoparticles and TiO2 ([email protected]@TiO2): The role of graphene in enhanced photocatalytic H2 generation

Authors: Magnus Rønning
Affiliation: Department of Chemical Engineering, Norwegian University of Science and Technology

Title: The preparation and properties of TiO2-based nanosized photocatalysts
Authors: Ruzimuradov Olim Narbekovich
Affiliation: Turin Polytechnic University in Tashkent

Title: Catalyst Selection for Industrial Textile Wastewater Ozone Treatment
Authors: Lucyna Bilińska 1,*, Kazimierz Blus 1, Marta Gmurek 2 and Stanisław Ledakowicz 2
Affiliation: 1 Bilinski Factory Of Colour, Mickiewicza 29, 95-050 Konstantynow Lodzki, Poland; [email protected] 2 Faculty of Process & Environmental Engineering, Lodz University of Technology, Wolczanska 213, 90-924 Lodz, Poland; [email protected]
Abstract: Catalytic ozonation has appeared as one of the recent trends in textile wastewater treatment. The necessity of effective color removal in short treatment time is a standard when an industrial implementation is planned. At the same time, efficient COD and toxic by-products removal are highly expected. This study presents the results of an ozone treatment supported by three types of catalysts. A metal oxide (TiO2 as P-25 by Degussa), activated carbon (nano-powder by Sigma, AC) and metal particles (platinum, 1% wt. supported on AC matrix by Sigma, Pt-AC). The values of pseudo-first order constants of Reactive Black 5 (RB5) decolorization rate for catalytic ozonation with AC addition were between 0.039 ± 0.001 and 0.121 ± 0.001 min-1 (for pH in the range of 2 - 12). These values were transparently higher than corresponding values of single ozone treatment. Despite, the catalytic effect of AC was shown for the model wastewater (the RB5 solution), the real industrial wastewater revealed opposite behavior. The experiment ran for industrial wastewater, exposed a lack of catalytic action of every investigated catalyst. Additionally, the catalytic effect was not visible in COD removal. Based on these observations, a new mechanism of catalytic ozonation of textile wastewater was proposed.

Title: TiO2 Modified with Metal Sulphides for the Photocatalytic Degradation of Toluene in the Gas Phase
Authors: Anna Malankowska
Affiliation: University of Gdansk Faculty of Chemistry, Gdansk, Poland

Title: Selective Oxidation of Crude Glycerol to Dihydroxyacetone in a Biphasic Photoreactor
Authors: Alexander Imbault; Ramin Farnood
Affiliation: Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, M5S 3E5, Canada
Abstract: In this paper, the first biphasic photoreactor is introduced and utilized for the conversion of glycerol to glyceraldehyde (GAD) and dihydroxyacetone (DHA). Comparing a system containing identical amounts of glycerol and photocatalyst the addition of an inactive phase increased the yield by a factor of 2 (6.5 % to 13 %) and increased the concentration of DHA after 240 min by more than a factor of 18 (0.08 mM to 1.5 mM ). Additionally, the biphasic photoreactor using crude glycerol yielded further benefits by removing impurities from the active phase allowing crude glycerol to have almost identical yield to ‘pure’ glycerol . In past work the yield of DHA from crude glycerol was found to be low due to impurities in crude glycerol poisoning the photocatalyst, the impurities were found to enter the inactive phase in the biphasic reactor. The mechanism of this phenomenon is further investigated to show that the benefits of the biphasic photoreactor do not come from either of the two phases individually. This paper details a widely applicable improvement that could be applied to photoreactors independent of the specific photocatalyst (or photoreaction with no photocatalyst), substrate or which two solvents are used. This opens the door to a host of improvements to a wide array of photoreactions by intelligently picking two immiscible solvents.

Title: Recent Advancement and Development in TiO2 based nanocomposite for degradation of organic pollutants via photocatalysis
Authors: Awais Ahmad1,6, Sobia Tabassum2, J.H.O. Nascimento3, Saad Maroof Saeed4, Abdur Rahim5, Syed Abbas Raza6and Ikram Ahmad1,6*
Affiliation: 1 Department of Chemistry, University of Lahore, 54590 Lahore Pakistan 2 Department of Biological Sciences, International Islamic University, Islamabad 32C2T - Center for Science and Textile Technology, Textile Engineering Department, School of Engineering, Campus Azurem 4Department of Phathalogy, Punjab Medical University Faisalabad,38000 Pakistan 5Interdisciplinary Research Centre in Biomedical Materials (IRCBM), COMSATS University Islamabad, Lahore Campus, Pakistan. 6 Department of Applied Chemistry, Government College University Faisalabad,38000 Pakistan
Abstract: Titanium dioxide had get a very novel interest for scientist due to its promising applications as photcatalyst when any light source exposure on it as well as electrochemical sensor. Due to these potential applications this is the most intensely studied oxide and vastly use in different scientific fields such as in white pigments, degradation of organic pollutants, removal of heavy metals as well as in energy storage, etc. There had been an essential perquisite to remove hazardous materials from water for consumption by living organisms. In this review, we explained that how titanium oxide will work when it surface enhanced via nanotechnology towards photocatalytic activity. This review led to explain some novel recent advancement and development of titanium oxide nanocomposite for degradation of organic pollutants such as methylene blue, cango red, methyl orange, acridine orange etc. via adsorption mechanism under irradiation of light exposure. Titanium oxide had been use with different metals, natural polymer as well synthetic polymer to exhibit its photocatlytic property against pollutants. All the technical scientific issues have been addressed; highlighting the recent advancements.

Title: An Interdisciplinary Approach to Polymers and Photocatalysis - Challenges and their future prospects
Authors: Feroz Shaik1 and Murtuza Ali Syed2
Affiliation: 1* Prince Mohammad Bin Fahd University, Al Khobar, Kingdom of Saudi Arabia 2 National University of Science and Technology, Muscat, Sultanate of Oman
Abstract: Photocatalytic technology is playing a significant role in remediation of pollutants and generation of renewable energy (Hydrogen). Photocatalysts embedded functionalized polymers and their nanocomposites are gaining tremendous attention from academic research as well as industrial applications. Many interesting features allow the photocatalytic embedded polymers to stand out in the field of photocatalytic applications over standalone semi-conductor photocatalysts. This critical review summarizes the development and characterization of photocatalytic polymers, their applications, challenges, recent trends and their future prospects.

Title: Investigation of the Synergistic Effect of Ultraviolet Radiation and Sonocatalysis of Titanium Dioxide in Organic Dye Degradations
Authors: Yunseok Choi a,b, Dain Lee a, Sungje Hong c, Sovann Khan d, Burak Darya a, Jaewon Chung b* and So-Hye Cho a,d*
Affiliation: a Materials Architecturing Research Center, Korea Institute of Science & Technology, 5 Hwarang-ro 14-gil, Seongbuk-gu, Seoul 02792, Republic of Korea b Department of Mechanical Engineering, Korea University, Anam-dong 5-ga, Seongbuk-gu, Seoul 02841, Republic of Korea c Department of Nuclear Engineering, Missouri University of Science and Technology, Rolla, MO, 65409, USA d Photocatalysis International Research Center, Tokyo University of Science, 2641 Yamazaki, Noda-shi, Chiba 278-8510, Japan e Department of Nanomaterials Science and Engineering, Korea University of Science and Technology, 217 Gajeong-ro Yuseong-gu, Daejeon, 34113, Republic of Korea
Abstract: Ultraviolet (UV)-assisted sonocatalysis is one of the powerful advanced oxidation processes (AOPs) for polluted water treatment and titanium dioxide (TiO2) is the most widely used materials in the process. However, UV-assisted sonocatalysis by TiO2 is a very complicated process and hence its mechanism of pollutant degradation is not yet clearly understood. We were interested in the effect of light irradiation on sonocatalysis by TiO2 since TiO2 is renowned for its light-responsive catalytic activity towards dye degradation. We first examined the sonoluminescence generated by ultrasound sonication with various power, which was visible by photographic images in the dark and also a luminol indicator. Next, using eosin B as an organic dye, we compared its decomposition rates by sonocatalysis combined with photocatalysis vs. UV-assisted sonocatalysis (sonophotocatalysis) in the presence of TiO2 nanoparticles (P25) and calculated a synergy effect in percentage. It was found that the synergy effect is highly engaged with dye concentration and sonication power so that we repeated the comparison test in different concentrations of eosin B (0.55 and 2.19 mM) and different sonication powers (35.4, 106.1, and 176.8 W/cm2). At the low concentration of dye, it was found that the synergy effect was negative but at the high concentration, the synergy effect was close to zero, providing activity equal to a sum of each reaction. On the other hand, synergy effects were found highly dependent on sonication powers, which is considered due to different degrees of cavitation and turbulence generated by various powers prevailing the mass transfer of dye molecules to the surface of TiO2.

Title: Antimicrobial Activity Against Methicillin-resistant Staphylococcus Aureus Under Visible Radiation on Zn tetracarboxy-phthalocyanine Sensitized TiO2 Thin Films.
Authors: William Andres Vallejo Lozada
Affiliation: Grupo de Fotoquímica y Fotobiología, Universidad del Atlántico, Puerto Colombia 81007, Colombia.
Abstract: In this work, we determined potential antimicrobial activity of TiO2 thin films sensitized by Zn tetracarboxy-phthalocyanines (TcPcZn). TiO2 thin films were deposited by Doctor Blade method and the sensitization process was carried out by chemisorption process. Properties of compounds were studied trough Fourier Transform infrared spectroscopy (FTIR), UV-Vis spectrophotometry, diffuse reflectance, Raman spectroscopy and scanning electronic microscopy (SEM). Finally, we study antimicrobial effect against Methicillin-resistant Staphylococcus aureus (MRSA) under visible irradiation. Spectroscopy analysis corroborated TcPcZn synthesis and adsorption process. on TiO2 and TcPcZn/TiO2; antimicrobial assay showed TcPcZn/TiO2 thin films reach 76.5% (±0.6) of inhibition of MRSA growth under visible irradiation.

Title: Exploring the photothermo-catalytic performance of Brookite TiO2-CeO2 composites
Authors: Bellardita Marianna, Fiorenza Roberto*, D'Urso Luisa, Scirè Salvatore, Palmisano Leonardo.
Affiliation: (B.M., P. L.) Dipartimento di Ingegneria, Università di Palermo, ed. 6, Viale delle Scienze, 90128 Palermo, Italy. (R.F., D.L., S.S) Dipartimento di Scienze Chimiche, Università di Catania, Viale A. Doria 6, 95125 Catania, Italy.
Abstract: The thermo-catalytic, photo-catalytic and photothermo-catalytic oxidation of VOCs (2-propanol, ethanol and tolune) was investigated on Brookite TiO2-CeO2 composites. The multi-catalytic approach based on the synergistic effect between solar photocatalysis and thermocatalysis led to considerably decrease the conversion temperatures of the organic compounds. The presence of small amounts of cerium oxide allows to obtain efficient brookite-based composites facilitating the space charge separation and increasing the lifetime of the generated photoholes and electrons as confirmed by the characterization measurements. The possibility to concurrently utilize the photocatalytic properties of brookite and the redox properties of CeO2, both activated in the photothermal tests, is an attractive approach easily applicable to purify air from the volatile organic compounds.

Title: TiO2-Graphene Quantum Dot nanohybrids for photocatalysis in biomedical and energy applications
Authors: Anuja Bokare, Sowbaranigha Chinnusamy Jayanthi, Folarin Erogbogbo
Affiliation: San Jose State University
Abstract: Environmental issues like pollution, global warming and abnormal climate changes are causing irreversible damage to the planet. The use of solar energy via photocatalysis contributes towards environmentally harmonious, sustainable and energy efficient technology. TiO2 is one of the most widely used photocatalysts. However, the high band gap (low-usage of visible light) and fast recombination of the photo-generated charge carriers limit its overall photocatalytic activity. Graphene quantum dots are zero-dimensional materials which can act as electron transfer agents in photocatalytic reactions. Hence, when GQDs are combined with TiO2, the resulting hybrid can enhance photocatalytic activity in the visible light range while significantly reducing recombination reaction rates. This review encompasses several advancements made in the field of TiO2-GQD nanohybrid photocatalysis. These include: (1) various structural formulations and synthesis methods of GQD-TiO2 nanohybrids (2) the influence of GQD incorporation on the optical and photoelectrochemical properties of TiO2 nanostructures; (3) discourse about the mechanism behind the overall higher visible light photoactivities of these nanohybrids; and (4) the application of these nanohybrids in biomedical and energy conversion devices. The advances outlined in this review highlight the role that TiO2-GQD nanohybrids may play as an environmentally friendly photocatalyst.

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