Surface modification of TiO2 photocatalyst for environmental applications

Fabrication of highly efficient ZnO-Pt catalysts assisted by biomass-derived carboxymethyl cellulose for the photodegradation of diverse antibiotics

Antibiotic contamination poses a substantial challenge to environmental, thereby necessitating the development of effective strategies for antibiotic elimination. This study utilized a hydrothermal reaction to incorporate the nano platinum (Pt) onto zinc oxide (ZnO), resulting in the formation of an efficient ZnO-Pt powder photocatalyst. Subsequently, biomass-derived carboxymethyl cellulose (CMC), modified via an acid-assisted freeze-thaw process, was employed as a matrix for fabricating the ZnO-Pt@CMC composite. Characterization of the synthesized materials was conducted using X-ray diffraction (XRD), Raman spectra (Raman), Fourier transform infrared spectrometer (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Afterwards, the photocatalytic performance of both ZnO-Pt and ZnO-Pt@CMC was assessed against a range of simulated antibiotic wastewater including sulfamethoxazole (SMX), ciprofloxacin (CIP), and oxytetracycline (OTC), under various conditions such as solution pH, catalyst dosage, antibiotic concentration, initial solution temperature, and light source. The ZnO-Pt catalyst demonstrated a degradation efficiency of 92.7 % for SMX within 180 min under xenon lamp irradiation, adhering to a pseudo-first-order kinetic model. Otherwise the ZnO-Pt@CMC exhibited degradation efficiencies of 80.6 % and 85.4 % for SMX and OTC over the same duration, while it demonstrated an exceptionally high photodegradation efficiency of 94.9 % for CIP and maintained its activity even after three consecutive cycles of use. Electrochemical impedance spectroscopy (EIS), linear scanning voltammetry (LSV), and radical quenching experiments showed that the introduction of Pt or CMC could increased the transfer and separation rate of ·OH and ·O2- during the photocatalytic degradation, along with a reasonable proposed degradation pathway for SMX.

Lignin and Nanolignin: Next-Generation Sustainable Materials for Water Treatment

Water scarcity, contamination, and lack of sanitation are global issues that require innovations in chemistry, engineering, and materials science. To tackle the challenge of providing high-quality drinking water for a growing population, we need to develop high-performance and multifunctional materials to treat water on both small and large scales. As modern society and science prioritize more sustainable engineering practices, water treatment processes will need to use materials produced from sustainable resources via green chemical routes, combining multiple advanced properties such as high surface area and great affinity for contaminants. Lignin, one of the major components of plants and an abundant byproduct of the cellulose and bioethanol industries, offers a cost-effective and scalable platform for developing such materials, with a wide range of physicochemical properties that can be tailored to improve their performance for target water treatment applications. This review aims to bridge the current gap in the literature by exploring the use of lignin, both as solid bulk or solubilized macromolecules and nanolignin as multifunctional (nano)materials for sustainable water treatment processes. We address the application of lignin-based macro-, micro-, and nanostructured materials in adsorption, catalysis, flocculation, membrane filtration processes, and antimicrobial coatings and composites. Throughout the exploration of recent progress and trends in this field, we emphasize the importance of integrating principles of green chemistry and materials sustainability to advance sustainable water treatment technologies.

Decorated titanium oxide with Ag nanoparticles as an efficient photocatalyst under visible light: a novel synthesis approach

A novel approach for synthesizing Titanium Oxide nanoparticles (NPs) using the rotating electrode in arc discharge method was developed by focusing on enhanced photocatalytic activity. Utilizing a rotating electrode as a third electrode in the arc discharge process enables us to synthesize defective titanium oxide, which facilitates the effective decoration with Ag NPs. Silver-decorated Titanium Oxide (Ag/Titanium Oxide) NPs were synthesized via a photoreduction process, improving visible light response through surface plasmon resonance which introduces new energy levels near the conduction band. The Ag/Titanium Oxide NPs exhibited high degradation of Rhodamine B dye, achieving 98% removal under visible light, attributed to the efficient charge separation. Scanning electron microscopy (SEM) revealed uniform morphology and size distribution and X-ray diffraction (XRD) also identified the crystalline phases (anatase and rutile). X-ray photoelectron spectroscopy (XPS) confirmed the chemical states and successful silver deposition. UV-visible spectroscopy along with photoluminescence (PL) analysis determined the optical properties. BET surface area measurements indicated enhanced surface area, supporting improved photocatalytic efficiency. These results highlight the potential of Ag/Titanium Oxide composite in designing advanced photocatalysts for environmental applications.

Platinum Single Atoms Strongly Promote Superoxide Formation in Titania-Based Photocatalysis - Platinum Nanoparticles Don't

The selective reduction of molecular oxygen to superoxide is one of the key reactions in electrochemistry and photocatalysis. Here the effect of Pt co-catalysts, dispersed on titania, either as single atoms or as nanoparticles, on the photocatalytic superoxide (•O2 -) formation in O2 containing solutions is investigated. The •O2 - formation is traced by nitroblue tetrazolium (NBT) assays and in detail by EPR measurements using TEMPO as •O2 - radical scavenger. The results show that the photocatalytic formation rate of •O2 - on titania can strongly be enhanced by using Pt single atoms as a co-catalyst, whereas Pt nanoparticles hardly exhibit any accelerating effect. This finding is of considerable significance regarding photocatalytic degradation and photocatalytic oxidative synthesis processes.

Effect of photoinduction in PANi/TiO2 heterogeneous structure on conductance of PANi component

A heterostructure consisting of a PANi and a TiO2 layer was chemically deposited consecutively on a glass substrate to investigate the effect of photoinduction in the structure on the conductance of the PANi component. It has been found that in response to the excitation light, the conductance of the PANi component in the PANi/TiO2 heterostructure exhibits a distinct mode to be different from that of a single pristine PANi layer. The features account for the effects of photoelectronic and electrochemical processes that associate with the photoinduction in the PANi/TiO2 heterostructure. The photoelectronic effect involves the appearance of the excess charges photogenerated inside the heterostructure on the depletion region. Due to the thermal diffusion of excess charges across the heterojunction, the width of the depletion is altered, leading to a modification in the conductance of the structure components, including the PANi. The electrochemical effect, on the other hand, relates to the appearance of the reactive oxygen species of O2 •-, OH•- and H+ that are created outside the heterostructure surface due to the photoinduction. Acting as strong oxidants, the species play the role of extra acceptor-like dopants and donor dedoping agents that modify the oxidation state and then the hole density of the p-type semiconductor PANi. The initial modification causes a sudden drop in PANi conductance at the start. As the exposure is further prolonged, the oxidation degree of the PANi component is further altered; the initial PANi emeraldine salt is gradually inverted to the emeraldine base, resulting in a conversion of its conductance. The combination of two modifications is explained for the mixing responses in the conductance of the PANi component and the U-turn shape of its baseline.

Photocatalytic hydrocarbon production from aqueous acetic acid using TiO2 with simultaneous photodeposition of Cu

Photocatalytic techniques are considered clean, sustainable and cost-effective in energy conversion and environmental restoration. The large band gap, light harvesting limitation and rapid electron-hole pair recombination can suppress the photocatalytic efficiency in photocatalytic applications. Metal deposition has become one of the most important technical means to improve photocatalytic efficiency. This study has dealt with photocatalytic hydrocarbon and hydrogen production from the acetic acid solution with simultaneous in situ Cu deposition on TiO2 photocatalyst surface. Due to having favorable redox potential and work function values, the photodeposition and Schottky junction formation of Cu occurred smoothly on the TiO2 surface, which further contributed to accelerating the interfacial charge transfer and photocatalytic activity. The reaction conditions (Cu2+ loading, reaction pH and initial concentration of acetic acid) were optimized to enhance photocatalytic methane production. Under the optimum condition, the Cu/TiO2 photocatalytic hydrocarbon production was maximum (4136 μmol g-1), approximately 9 times better than those obtained with pure TiO2 (450 μmol g-1). The surface morphological and optical properties of photodeposited Cu/TiO2 samples were characterized before and after the photocatalytic reaction with utmost precision and thoroughness using a TEM, XPS, DRS, PL, N2 adsorption-desorption isotherm and BET surface area analysis. The DRS and PL study confirm that in situ Cu-deposition on TiO2 reduced the energy bandgap and improved the light-harvesting area, photogenerated electron-hole pair separation and migration efficiency, respectively. Cycle experiments disclose that the simultaneous Cu-deposited photocatalyst has excellent stability and reusability. A reaction mechanism was proposed for the photocatalytic hydrocarbon formation from the acetic acid by Cu/TiO2 photocatalytic reaction.

Photocatalytic degradation of polycyclic aromatic hydrocarbons under visible light irradiation in water using TiO2/MgO nanocomposites

An extensive class of pollutants found in soil, water, and bottom sediments are categorized as polycyclic aromatic hydrocarbons. A possible method of breaking down polycyclic aromatic hydrocarbons is thought to be the photochemical approach. The potential application of mesoporous nanocomposites on TiO2/MgO as catalysts for the photooxidation of polycyclic aromatic hydrocarbons under the influence of visible light was assessed in this work. TiO2/MgO nanocomposites were successfully obtained by the self-propagating high-temperature synthesis using methotitanic acid and magnesium nitrate as metal precursors. An important step in the synthesis was the conversion of the titanium precursor into a water-soluble form with the subsequent addition of glycine and citric acid at a carbon/nitrogen (C/N) molar ratio of 0.25. This synthesis via solutions allowed the target materials with major phases of magnesium metatitanate MgTiO3, magnesium dititanate MgTi2O5, and magnesium titanate Mg2TiO4 to be obtained after heat treatment at 750 °C. Heterostructured mesoporous TiO2/MgO powders with a specific surface area of 22.0-28.4 m2/g had an average diameter of the predominant pores of 10-30 nm. The greatest degree of photocatalytic oxidation of fluorene, pyrene, and benzpyrene (80, 68, and 53%, respectively) was obtained when it was combined with the TiO2/MgTi2O5/MgTiO3 nanocomposite under visible light irradiation. This study showed that mesoporous TiO2/MgO nanocomposites could be used as photooxidation catalysts for polycyclic aromatic hydrocarbons. The maximum level of photocatalytic oxidation of polycyclic aromatic hydrocarbons in TiO2/MgO nanocomposites occurred at pH 7 and a photocatalyst dose of 1 mg/L under the influence of normal solar radiation.

Comparative Toxicity of TiO2 and Sn-Doped TiO2 Nanoparticles in Zebrafish After Acute and Chronic Exposure

This study was conducted to assess the toxicological potential of synthesized pure and Sn-doped TiO2 NPs (Sn-TiO2 NPs) in zebrafish after acute and chronic exposure. The pure TiO2 NPs, 4%, and 8% Sn-TiO2 NPs were synthesized and characterized using X-ray diffraction, Scanning Electron Microscope, diffuse reflectance spectra, dynamic light scattering, and zeta potential analyses. The pure TiO2 NPs, 4%, and 8% Sn-TiO2 NPs were spherical with average sizes of about 40, 28, and 21 nm, respectively, indicating significant size reduction of TiO2 NPs following Sn doping. According to our results, the LC50-96h increased in the order of 8% Sn-TiO2 NPs (45 mg L-1) < 4% Sn-TiO2 NPs (80.14 mg L-1) < pure TiO2 NPs (105.47 mg L-1), respectively. Exposure of fish to Sn-TiO2 NPs after 30 days resulted in more severe histopathological alterations in gills, liver, intestine, and kidneys than pure TiO2 NPs. Furthermore, Sn-doping significantly elevated malondialdehyde levels and micronuclei frequency, indicating increased oxidative stress and genotoxicity. Expression analysis revealed altered expression of various genes, including upregulation of pro-apoptotic Bax gene and downregulation of anti-apoptotic Bcl-2 gene, suggesting potential induction of apoptosis in response to Sn-doped NPs. Additionally, antioxidant genes (Gpx, Sod, Cat, and Ucp-2) and stress response gene (Hsp70) showed altered expression, suggesting complex cellular responses to mitigate the toxic effects. Overall, this study highlights the concerning impact of Sn-doping on the toxicity of TiO2 NPs in zebrafish and emphasizes the need for further research to elucidate the exact mechanisms underlying this enhanced toxicity.

Photocatalytic Hydrogen Production Using TiO2-based Catalysts: A Review

Photocatalytic water splitting is an environmentally friendly hydrogen production method that uses abundant renewable resources such as water and sunlight. While Titanium dioxide (TiO2) photocatalyst exhibits excellent properties, its high band gap limits absorption to ultraviolet (UV) irradiation, resulting in low photo conversion efficiency. This review explores various modification techniques aimed at enhancing the efficiency of TiO2 under visible light irradiation. Factors influencing the photocatalytic water splitting reaction, such as catalyst structure, morphology, band gap, sacrificial reagents, light intensity, temperature, and potential of Hydrogen (pH) are examined. This review also summarizes different catalyst synthesis methods, and types of photocatalytic reactors, and provides insights into quantum yield. Finally, the review addresses the challenges and future outlook of photocatalytic water splitting.

Efficient electro-oxidation-based degradation of per- and polyfluoroalkyl (PFAS) persistent pollutants by using plasma torch synthesized pure-Magnéli phase-Ti4O7 anodes

Pure Magnéli-phase Ti4O7 were prepared by means of a Plasma Torch (PT) coating method and integrated into an advanced electro-catalytic oxidation (AEO) process in order to degrade perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) persistent pollutants present in waters. The X-ray diffraction analysis confirmed the polycrystalline nature of the pure Magnéli phase PT-Ti4O7 coatings (∼100 μm thick)). The Raman spectra of the PT-Ti4O7 coatings also exhibited the two characteristic peaks (at 138 and 183 cm-1) of the PT-Ti4O7 Magnéli phase. Scanning electron microscopy revealed the nanostructured hierarchical morphology of the PT-Ti4O7 thus conferring them high surface area. The PT-Ti4O7 anodes are shown to achieve higher degradation efficiencies towards PFOA and PFOS in comparison with the conventional boron-doped diamond anodes. By investigating several AEO parameters (including current density, treatment time, nature of the anode material), we were able to optimise the AEO process. Thus, for both PFOA and PFOS (at an initial concentration of 500 ppb in synthetic wastewaters), degradation efficiencies as high as 96.6% and 99.7% were achieved, respectively, with a current density of 20 mA/cm2, a treatment time of 120 min and PT-Ti4O7 mesh-type anodes. PFOA and PFOS can be degraded by both direct anodic electrochemical oxidation (•OH radicals) and indirect electrochemical oxidation via mediators, such as persulphate acid (H2S2O8) generated by sulphate anodic oxidation. The degradation of both compounds followed pseudo-first-order kinetics. The reaction rate constant (k) for PFOS removal was 4.63 × 10-2 min-1, whereas 2.76 × 10-2 min-1 was recorded for PFOA removal. Subsequently, we have used the above optimal AEO operating conditions to treat real wastewater effluents (containing 17 types of PFAS molecules with a total content of 8500 ppb) and achieved a degradation rate of 39.1%-87.4% for eight of the 17 PFAS compounds. The degradation rate was found to be dependent on the chemical structure and chain length of each PFOA/PFOS component.

Photocatalytic Nanocomposite Based on Titanate Nanotubes Decorated with Plasmonic Nanoparticles for Enhanced Broad-Spectrum Antibacterial Activity

Infections resulting from microorganisms pose an ongoing global public health challenge, necessitating the constant development of novel antimicrobial approaches. Utilizing photocatalytic materials to generate reactive oxygen species (ROS) presents an appealing strategy for combating microbial threats. In alignment with this perspective, sodium titanate nanotubes were prepared by scalable hydrothermal method using TiO2 and NaOH. Ag, Au, and Ag/Au-modified titanate nanotubes (TNTs) were prepared by a cost-effective and simple ion-exchange method. All samples were characterized by XRD, FT-IR, HRTEM, and DLS techniques. HRTEM images indicated that the tubular structure was preserved in all TNTs even after the replacement of Na+ with Ag+ and/or Au3+ ions. The antibacterial activity in dark and sunlight conditions was evaluated using different bacterial strains, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. The results showed that while a low bacterial count (∼log 5 cells per well) was used for inoculation, the TNTs exhibited no antibacterial activity against the three bacterial strains, regardless of whether they were tested under light or dark conditions. However, the plasmonic nanoparticle-decorated TNTs showed remarkable activity in the dark. Additionally, Ag/Au-TNTs demonstrated significantly higher activity in the dark compared with either Ag-TNTs or Au-TNTs alone. Notably, under dark conditions, the Au/Ag-TNTs achieved log reductions of up to 4.5 for P. aeruginosa, 5 for S. aureus, and 3.7 for E. coli. However, when exposed to sunlight, Au/Ag-TNTs resulted in a complete reduction (log reduction ∼9) for P. aeruginosa and E. coli. The combination of two plasmonic nanoparticles (Ag/Au) decorated on the surface of TNTs showed synergetic bactericidal activity under both dark and light conditions. Ag/Au-TNTs could be explored to design surfaces that are responsive to visible light and exhibit antimicrobial properties.

Thioxanthone Functionalized NanoTiO2 Composites as Photocatalyst for Degradation of Organic Dyes

Titanium dioxide (TiO2) photocatalytic technology has the advantages of high catalytic activity, high chemical stability, nontoxicity, and low cost. Therefore, it finds widespread applications in the degradation of organic pollutants in water, antibacterial, environmental purification, and other fields. In this study, we have obtained a photocatalyst by modifying nanoTiO2 with the photosensitizer thioxanthone. The light-harvesting units of thioxanthone and nanoTiO2 can work synergistically to capture light energy. As a heterogeneous photocatalytic material, it can efficiently degrade organic dyes such as Rhodamine B, methyl blue and methyl orange. Specifically, the degradation rate of 0.1 mmol/L Rhodamine B can reach 97% after 35 min of irradiation, and methyl blue and methyl orange can also reach 98 and 56%, respectively.

Embracing heterogeneous photocatalysis: evolution of photocatalysts in annulation of dimethylanilines and maleimides

Recent advances in visible-light-promoted construction of tetrahydroquinolines from dimethylanilines and maleimides are documented. Homogeneous and heterogeneous photocatalytic systems, as well as the reaction mechanism, are emphasized. The mechanism of this photocatalytic annulation reaction is quite clear, i.e., dimethylanilines and maleimides serve as the radical precursors and radical acceptors, respectively. This annulation reaction could serve as an excellent platform for evaluating novel oxidative heterogeneous photocatalytic systems, which could further inspire chemists in this field to develop more efficient photocatalytic systems. Significant opportunities are expected in the future for heterogeneous photocatalysis strategies.

Enhanced photocatalytic removal of bromate in drinking water by Au/TiO2 under ultraviolet light

The photo-reduction of bromate (BrO3 -) has attracted much attention due to the carcinogenesis and genotoxicity of BrO3 - in drinking water. In this study, a heterojunction photocatalyst was developed by depositing Au nanoparticles (NPs) onto P25 TiO2 NPs through a one-pot, solvent-thermal process. Due to the unique properties of Au, the Au NPs deposited on the TiO2 surface created a Schottky barrier between the metal and the semiconductor, leading to an effective separation of photo-generated charge carriers as the Au nanoparticles served as electron sinks. The Au/TiO2 photocatalyst demonstrated efficient reduction of BrO3 - under UV light illumination without the need for sacrificial agents. The effect of different Au loading of Au/TiO2 was systematically investigated for its influence on the generation of electrons and the reduction ability of BrO3 -. The results indicate that the 1% Au/TiO2 catalyst exhibited a higher concentration of localized electrons, rendering it more effective in BrO3 - removal. The photocatalytic efficiency for BrO3 - reduction decreased upon the addition of K2S2O8 as an electron quencher, suggesting that the primary factor in this photo-reduction process was the availability of electrons. These findings hold promise for the potential application of the Au/TiO2 catalyst in the removal of BrO3 - from drinking water through photo-reduction.

Continuously Adjustable Thickness of Bi2MoO6 Nanosheets Enhances Photocatalytic Oxidation

In this study, two-dimensional (2D) nanosheet photocatalysts of Bi2MoO6 with varying thicknesses were synthesized by adjusting the temperature during the hydrothermal reaction. The thinnest Bi2MoO6 nanosheet reached an approximate thickness of ∼4 nm, while the thickest nanosheet measured only ∼16 nm. The photocatalytic performance for Rhodamine B (RhB) degradation was found to be the most effective for the thinnest Bi2MoO6 nanosheet, displaying a degradation rate constant of 0.11 min-1. This rate was 2.5 times higher than that observed for the ∼16 nm thick Bi2MoO6 photocatalyst. The enhanced performance of the thinner two-dimensional nanostructure can be attributed to improved separation and migration of photogenerated charges. Additionally, the study identified hydroxyl radicals (•OH) and superoxide radicals (•O2-) as crucial oxidative species, contributing to the efficient mineralization of RhB dye. This work highlights the controllable synthesis of 2D materials with varying thicknesses and their specific applications in photocatalytic oxidation.

BODIPY-Based Macrostructures: A Design Strategy toward Enhancing the Efficiency of Dye-Sensitized Solar Cells

Among the metal-free dyes, boron dipyrromethene (BODIPY) has attracted much attention in the solar cell industry due to its thermal stability and tunable electronic and photophysical properties. However, the low power conversion efficiency of dye-sensitized solar cells based on BODIPY has limited their widespread application. Accordingly, different types of structural modifications have already been proposed to improve the photophysical properties of the BODIPY dyes. In this study, we used the strategy of constructing BODIPY-based covalent macrostructures by integrating two BODIPY subunits via a π-linker in linear and cyclic configurations. To this end, various types of the π-linkers including butadiyne, phenyl, and thiophene derivatives are considered. The structural, electronic, and optical properties as well as the photovoltaic performance of BODIPY dimers are theoretically calculated within DCM solvent. The results indicate that for a given linker, the BODIPY dimers with a linear configuration show better performance as compared to their macrocyclic counterparts. The reason is the enhancement of π-conjugation length, higher light harvesting ability, and proper charge carrier separation in linearly linked BODIPYs. In the cyclic series, the dyes incorporating phenyl linkers exhibit greater power conversion efficiency of up to 9%. For the dyes with a linear configuration, the involvement of a thienyl-thiophene bridge results in lower charge recombination and enhances the efficiency by up to 15%, which are expected to be potential candidates for organic dyes applied in DSSCs.

Enhancing air treatment through controlled fabrication of transition metal-doped titanium dioxide nanocomposites for photocatalytic toluene degradation

Rapid industrial growth and urbanization have resulted in a significant rise in environmental pollution issues, particularly indoor air pollutants. As a result, it is crucial to design and develop technologies and/or catalysts that are not only cost-effective but also promising high performance and practical applicability. However, achieving this goal has been so far remained a challenging task. Herein, a series of transition metal M - TiO2 (M = W, Fe, Mn) nanocrystals was prepared for photocatalytic degradation of volatile organic compounds (VOCs), i.e., toluene. Of the nanocomposites tested, W-TiO2 showed significantly improved photocatalytic activity for VOC degradation under UV irradiation compared to the others. In particular, the optimized W dopant amount of 0.5 wt% resulted in the outstanding degradation performance of toluene (96%) for the obtained W-TiO2(0.5%) nanocomposite. Moreover, W-TiO2(0.5%) nanocomposite exhibited good stability for 32 h working under high toluene concentration (10 ppm) compared to the pristine TiO2. The current work demonstrates the potential usage of M - TiO2 nanocrystals, particularly W-TiO2(0.5%), as a promising photocatalyst for efficient VOCs degradation.

Nanocomposite Marvels: Unveiling Breakthroughs in Photocatalytic Water Splitting for Enhanced Hydrogen Evolution

An overview of the significant innovations in photocatalysts for H2 development, photocatalyst selection criteria, and photocatalytic modifications to improve the photocatalytic activity was examined in this Review, as well as mechanisms and thermodynamics. A variety of semiconductors have been examined in a structured fashion, such as TiO2-, g-C3N4-, graphene-, sulfide-, oxide-, nitride-, oxysulfide-, oxynitrides, and cocatalyst-based photocatalysts. The techniques for enhancing the compatibility of metals and nonmetals is discussed in order to boost photoactivity within visible light irradiation. In particular, further deliberation has been carried out on the development of heterojunctions, such as type I, type II, and type III, along with Z-systems, and S-scheme systems. It is important to thoroughly investigate these issues in the sense of visible light irradiations to enhance the efficacy of photocatalytic action. In fact, another advancement in this area may include hiring mediators including grapheme oxide and metals to establish indirect Z-scheme montages with a correct band adjustment. The potential consideration of reaction chemology, mass transfer, kinetics of reactions, restriction of light diffusion, and the process and selection of suitable light and photoreactor also will optimize sustainable hydrogen output efficiency and selectivity.

Facile fabrication of ternary NiTiFe-LDH ultrathin nanosheets for efficient conversion of amines into imines under visible light

Ternary NiTiFe-LDH with an ultrathin nanosheet morphology was successfully fabricated via a facile co-precipitation method, followed by refluxing, and was used as a catalyst for oxidative coupling of amines to produce imines under visible light. The obvious superior activity observed in NiTiFe-LDH ultrathin nanosheets compared with binary NiTi-LDH and bulk NiTiFe-LDH can be ascribed to an enhanced light absorption capability caused by the introduction of Fe3+ ions as well as the ultrathin nanosheets which can minimize the recombination of the photogenerated charge carriers and provide more catalytically active sites for the reaction. As a result, more catalytically active O2˙- radicals are generated over NiTiFe-LDH ultrathin nanosheets, which leads to their superior activity. This study not only shows the possibility of using LDHs in photocatalytic organic transformations but also demonstrates an effective strategy to promote the activity of LDH-based photocatalysts via simultaneous composition and morphology modulation of LDHs.

Photocatalytic microbial disinfection under indoor conditions: Prospects and challenges of near IR-photoactive materials

The accumulation of microbes especially in the air and in water bodies is causing the major disease outbreaks. Indoor environment remediation methods are necessary today to clean up these microbes. Among the remediation methods available, in situ generation of highly reactive and oxidizing radical species by advanced oxidation processes (AOPs) inactivate most of the microbes unselectively. Of these AOPs, photocatalytic microbial disinfection especially under indoor conditions is of great interest to maintain microbe-free indoor environment. For efficient microbes' inactivation under indoor conditions, the near IR and IR response of the photocatalysts must be improved. Though the photocatalytic disinfection of microbes using semiconductor-based photocatalysts has been extensively investigated, most of the photocatalysts that have been investigated are either weekly responsive or totally not irresponsive to IR photons due to inappropriate bandgap energies. Several strategies have been investigated to enhance the light harvesting properties of semiconductor based photocatalysts under indoor conditions and make them active to near IR and IR radiations. This review summarizes the recent progress in the field of materials for photocatalysts employed for microbial removal in indoor environments over the past decade as well as outlines key perspectives to enlighten future researches. The paper details the fundamentals of photocatalysis and basic properties of photocatalytic materials in the disinfection of common microbes under indoor conditions. The applications of photocatalytic materials in the disinfection of microbes in indoor environmental conditions are discussed and reviewed. Finally, the remaining challenges and future strategies/prospects in the design and synthesis of IR (and near IR) responsive photocatalysts are discussed.

Synthesis and Characterization of a Photocatalytic Material Based on Raspberry-like SiO2@TiO2 Nanoparticles Supported on Graphene Oxide

A raspberry-like SiO2@TiO2 new material supported on functionalized graphene oxide was prepared to reduce titania's band gap value. The material was characterized through different analytical methods such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HR-TEM). The band gap value was studied via UV-Vis absorption spectra and determined through the Kubelka-Munk equation. A theoretical study was also carried out to analyze the interaction between the species.

Recent Advances of Doped SnO2 as Electron Transport Layer for High-Performance Perovskite Solar Cells

Perovskite solar cells (PSCs) have garnered considerable attention over the past decade owing to their low cost and proven high power conversion efficiency of over 25%. In the planar heterojunction PSC structure, tin oxide was utilized as a substitute material for the TiO2 electron transport layer (ETL) owing to its similar physical properties and high mobility, which is suitable for electron mining. Nevertheless, the defects and morphology significantly changed the performance of SnO2 according to the different deposition techniques, resulting in the poor performance of PSCs. In this review, we provide a comprehensive insight into the factors that specifically influence the ETL in PSC. The properties of the SnO2 materials are briefly introduced. In particular, the general operating principles, as well as the suitability level of doping in SnO2, are elucidated along with the details of the obtained results. Subsequently, the potential for doping is evaluated from the obtained results to achieve better results in PSCs. This review aims to provide a systematic and comprehensive understanding of the effects of different types of doping on the performance of ETL SnO2 and potentially instigate further development of PSCs with an extension to SnO2-based PSCs.

Supported TiO2-ZnWO4 Photocatalytic Nanofibrous Membranes for Flow-Through and Fixed-Bed Reactors

We developed utilization models of supported electrospun TiO2-ZnWO4 photocatalytic nanofibrous membranes for air and water purifications using a noncomplex system with facile adaptation for large-scale processes. For this uniquely designed and multimode catalyst, ZnWO4 is selected for a visible light activity, while TiO2 is incorporated to enhance physical stability. Morphological structures of the TiO2-ZnWO4 membrane are characterized by scanning electron microscopy and scanning electron microscopy-energy-dispersive X-ray spectroscopy. The distinguished growth of ZnWO4 nanorods at the surface of the TiO2-ZnWO4 membrane is revealed by transmission electron microscopy (TEM). The relaxation process and charge transfer mechanism are proposed following the examination of interface and band gap (2.76 eV) between TiO2 and ZnWO4 particles via HR-TEM and UV-vis spectrophotometry. For the gas-phase reaction, a transparent photocatalytic converter is designed to support the pleated TiO2-ZnWO4 membrane for toluene decomposition under visible light. To obtain a crack-free and homogeneous fiber structure of the pleated TiO2-ZnWO4 membrane, 1 h of nanofibrous membrane fabrication via a Nanospider machine is required. On the other hand, a fiberglass-supported TiO2-ZnWO4 membrane is fabricated as a fixed-bed photocatalyst membrane for methylene blue decomposition under natural sunlight. It is observed that using the calcination temperature at 800 °C results in the formation of metal complexes between fiber glass and the TiO2-ZnWO4 membrane. The TiO2-ZnWO4 membrane successfully decomposes toluene vapor up to 40% under a continuous-flow circumstance in a borosilicate photocatalytic converter and 70% for methylene blue in solution within 3 h. Finally, the mechanically robust and supported TiO2-ZnWO4 nanofibrous membranes are proven for an alternate potential in environmental remediation.

Engineering cuboctahedral N-doped C-coated p-CuO/n-TiO2 heterojunctions toward high-performance photocatalytic cross-dehydrogenative coupling

The low separation efficiency of photogenerated electron-hole (e-h) pairs severely limits the activation of photocatalyts. One brilliant strategy is to construct a p-n type semiconductor heterojunction, which can establish an inner electric field to separate the e-h pairs with high efficiency. Here, for the first time, a cuboctahedral N-doped carbon-coated CuO/TiO2 p-n heterojunction (CuO-TiO2@N-C) was designed and fabricated successfully via direct calcination of a benzimidazole-modulated cuboctahedral HKUST-Cu with titanium-tetraisopropanolate absorbed inside concomitantly. Full structural characterizations incorporating DFT computations demonstrate that the CuO/TiO2 p-n heterostructure can greatly boost the transport and separation of photoinduced e-h pairs. The nitrogen-doped carbon coating, with its excellent conductivity, porosity, stability and surface reaction activity, plays a pivotal role in promoting the overall performance and effectiveness of the reaction. The CuO-TiO2@N-C displays significantly higher photocurrent density (0.042 μA cm-2) than the CuO@N-C (0.014 μA cm-2) and TiO2@N-C (0.03 μA cm-2) electrodes, proving that the p-n heterojunction can improve the e-h generation efficiency. This unique photocatalyst affords superior photocatalytic efficiency, cycle stability and substrate scope towards cross-dehydrogenative coupling reactions.

Hydrothermal synthesis of a photocatalyst based on Byrsonima crassifolia and TiO2 for degradation of crystal violet by UV and visible radiation

This work presents a one-step synthesis methodology for preparing a hydrochar (HC) doped with TiO2 (HC-TiO2) for its application on the degradation of crystal violet (CV) using UV and visible radiation. Byrsonima crassifolia stones were used as precursors along with TiO2 particles. The HC-TiO2 sample was synthesized at 210 °C for 9 h using autogenous pressure. The photocatalyst was characterized to evaluate the TiO2 dispersion, specific surface area, graphitization degree, and band-gap value. Finally, the degradation of CV was investigated by varying the operating conditions of the system, the reuse of the catalyst, and the degradation mechanism. The physicochemical characterization of the HC-TiO2 composite showed good dispersion of TiO2 in the carbonaceous particle. The presence of TiO2 on the hydrochar surface yields a bandgap value of 1.17 eV, enhancing photocatalyst activation with visible radiation. The degradation results evidenced a synergistic effect with both types of radiation due to the hybridized π electrons in the sp2-hybridized structures in the HC surface. The degradation percentages were on average 20% higher using UV radiation than visible radiation under the following conditions: [CV] = 20 mg/L, 1 g/L of photocatalyst load, and pH = 7.0. The reusability experiments demonstrated the feasibility of reusing the HC-TiO2 material up to 5 times with a similar photodegradation percentage. Finally, the results indicated that the HC-TiO2 composite could be considered an efficient material for the photocatalytic treatment of water contaminated with CV.

Effect of Sonication and Ceria Doping on Nanoparticles Fabricated by Laser Marker Ablation of Ti in Water

By employing the laser marker fast ablation technique in water, combined with the innovative inclusion of sonication, we successfully developed Ti-based nanoparticles with improved characteristics. sonication increased the nanoparticle concentration in the colloid, reduced nanoparticle size, and also narrowed size distribution. Our findings also provide valuable insights into the influence of laser parameters, such as wavelength and fluence, on nanoparticle properties. UV laser led to small nanoparticles compared with 1064 nm laser. Additionally, high laser fluence appeared to increase the ablated particle size until a plateau fluence at 28.5 J/cm2; at 38 J/cm2, the particle size decreased. Notably, all synthesized particles exhibited a regular spherical shape, as confirmed by energy dispersive X-ray spectroscopy (EDS) mapping, which also indicated that the majority of Ti-based particles were in an oxidized state. Additionally, the presence of rutile TiO2 in the particles was further confirmed by X-ray diffraction (XRD) analysis. Ceria doping Titania nanoparticles was also attempted.

Direct Interfacial Excitation from TiO2 to Cu(II) Nanoclusters Enables Cathodic Photoresponse for Hydrogen Evolution under Visible-Light Irradiation

The titanium dioxide (TiO₂ ) photocatalyst is only active under UV irradiation due to its wide-gap nature. A novel excitation pathway denoted as interfacial charge transfer (IFCT) has been reported to activate copper(II) oxide nanoclusters-loaded TiO₂ powder (Cu(II)/TiO₂ ) under visible-light irradiation for only organic decomposition (downhill reaction) so far. Here, the photoelectrochemical study shows that the Cu(II)/TiO₂ electrode exhibits a cathodic photoresponse under visible-light and UV irradiation. It originates from H₂ evolution on the Cu(II)/TiO₂ electrode, while O₂ evolution takes place on the anodic side. Based on the concept of IFCT, a direct excitation of electrons from the valence band of TiO₂ to Cu(II) clusters initiates the reaction. This is the first demonstration of a direct interfacial excitation-induced cathodic photoresponse for water splitting without any addition of a sacrificial agent. This study is expected to contribute to the development of abundant visible-light-active photocathode materials for fuel production (uphill reaction).

A novel biosynthesis of MgO/PEG nanocomposite for organic pollutant removal from aqueous solutions under sunlight irradiation

The novel synthesis of MgO from Laurus nobilis L. leaves was prepared using the green synthesis method. It is using direct blending process to decorate MgO/PEG nanocomposite to enhance the photodegradation properties and examine its physical properties using diverse characterization techniques, including XRD, FTIR, SEM, EDX, and UV-Vis. X-ray diffraction reveals a cubic phase of MgO with a 37-nm grain size. SEM images confirm spherical nanoparticles with a diameter size of 22.9 nm. The optical energy gap of MgO NPs was 4.4 eV, and the MgO/PEG nanocomposite was 4.1 eV, which made it an efficient catalyst under sunlight. The photocatalytic activity of Rose Bengal (RB) and Toluidine Blue (TB) dyes at 5 × 10^-5 mol/l dye concentration indicates excellent degradation efficiencies of 98% and 95% in 120 min, respectively, under sunlight irradiation. MgO/PEG is an excellent candidate nanocomposite for applications of photodegradation and could be used for its potential capability to develop conventionally used techniques.

Enhanced photoelectrocatalytic decomplexation of Ni-EDTA and simultaneous recovery of metallic nickel via TiO2/Ni-Sb-SnO2 bifunctional photoanode and activated carbon fiber cathode

In order to enhance Ni-EDTA decomplexation and Ni recovery via photoelectrocatalytic (PEC) process, TiO₂/Ni-Sb-SnO₂ bifunctional electrode was fabricated as the photoanode and activated carbon fiber (ACF) was introduced as the cathode. At a cell voltage of 3.5 V and initial solution pH of 6.3, the TiO₂/Ni-Sb-SnO₂ bifunctional photoanode exhibited a synergetic effect on the decomplexation of Ni-EDTA with the pseudo-first-order rate constant of 0.01068 min^-1 with 180 min by using stainless steel (SS) cathode, which was 1.5 and 2.4 times higher than that of TiO₂ photoanode and Ni-Sb-SnO₂ anode, respectively. Moreover, both the efficiencies of Ni-EDTA decomplexation and Ni recovery were improved to 98% from 86% and 73% from 41% after replacing SS cathode with ACF cathode, respectively. Influencing factors on Ni-EDTA decomplexation and Ni recovery were investigated and the efficiencies were favored at acidic condition, higher cell voltage and lower initial Ni-EDTA concentration. Ni-EDTA was mainly decomposed via ·OH radicals which generated via the interaction of O₃, H₂O₂, and UV irradiation in the contrasted PEC system. Then, the liberated Ni²⁺ ions which liberated from Ni-EDTA decomplexation were eventually reduced to metallic Ni on the ACF cathode surface. Finally, the stability of the constructed PEC system on Ni-EDTA decomplexation and Ni recovery was exhibited.

Selective Control and Characteristics of Water Oxidation and Dioxygen Reduction in Environmental Photo(electro)catalytic Systems

ConspectusEmploying semiconductor materials is a popular engineering method to harvest solar energy, which is widely investigated for photocatalysis (PC) and photoelectrocatalysis (PEC) that convert solar light to chemical energy. In particular, environmental photo(electro)catalysis has been extensively studied as a sustainable method for water treatment, air purification, and resource recovery. Environmental PC/PEC processes working in ambient conditions are initiated mainly through hole transfer to water (water oxidation) and electron transfer to dioxygen (O₂ reduction) and the subsequent photoredox transformation of water and dioxygen serves as a base of various PC/PEC systems. Through the redox transformations, different products can be generated depending on the number of transferred electrons and holes. The single electron/hole transfer generates radical species and reactive oxygen species (ROS) which initiate the degradation/transformation of various pollutants in water and air, while the multicharge transfer can generate energy-rich chemicals (e.g., H₂, H₂O₂). Therefore, understanding the characteristics of the photoredox reactions of water and dioxygen on the semiconductor surface is critically important in controlling the selectivity and efficiency of photoconversion processes.In this Account, we describe various environmental PC/PEC conversions with a particular focus on how the phototransformation of dioxygen and water is related to the overall processes occurring on diverse semiconductor materials. The activation of water or dioxygen can be controlled by modifying the properties of semiconductors, changing the kind of counterpart half-reaction and the experimental conditions. If water can be used as a ubiquitous reductant under solar irradiation, many kinds of reductive transformations can be carried out under ambient environmental conditions. For example, various toxic oxyanions (or metal ions) can be reductively transformed to harmless or less harmful species or useful chemicals/fuels can be synthesized under ambient conditions if water can provide electrons and protons via solar water oxidation. On the other hand, dioxygen can turn into reactive oxygen species (ROS) as a versatile oxidant or to a chemical like H₂O₂. There should be many more possibilities of utilizing the photoconversion of water and dioxygen for environmentally significant purposes, which are yet to be further developed and demonstrated. In this Account, we highlight the recent strategies and the novel functional materials for effective activation of water and dioxygen in environmental PC/PEC systems. Design of environmentally functional PC/PEC systems should be based on better understanding of water and dioxygen activation.

Nanomaterials Aspects for Photocatalysis as Potential for the Inactivation of COVID-19 Virus

Coronavirus disease-2019 is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and is the most difficult recent global outbreak. Semiconducting materials can be used as effective photocatalysts in photoactive technology by generating various reactive oxidative species (ROS), including superoxide (•O2−) and hydroxyl (•OH) radicals, either by degradation of proteins, DNA, and RNA or by inhibition of cell development through terminating the cellular membrane. This review emphasizes the capability of photocatalysis as a reliable, economical, and fast-preferred method with high chemical and thermal stability for the deactivation and degradation of SARS-CoV-2. The light-generated holes present in the valence band (VB) have strong oxidizing properties, which result in the oxidation of surface proteins and their inactivation under light illumination. In addition, this review discusses the most recent photocatalytic systems, including metals, metal oxides, carbonaceous nanomaterials, and 2-dimensional advanced structures, for efficient SARS-CoV-2 inactivation using different photocatalytic experimental parameters. Finally, this review article summarizes the limitations of these photocatalytic approaches and provides recommendations for preserving the antiviral properties of photocatalysts, large-scale treatment, green sustainable treatment, and reducing the overall expenditure for applications.

Kinetic Aspects of Benzene Degradation over TiO2-N and Composite Fe/Bi2WO6/TiO2-N Photocatalysts under Irradiation with Visible Light

In this study, composite materials based on nanocrystalline anatase TiO2 doped with nitrogen and bismuth tungstate are synthesized using a hydrothermal method. All samples are tested in the oxidation of volatile organic compounds under visible light to find the correlations between their physicochemical characteristics and photocatalytic activity. The kinetic aspects are studied both in batch and continuous-flow reactors, using ethanol and benzene as test compounds. The Bi2WO6/TiO2-N heterostructure enhanced with Fe species efficiently utilizes visible light in the blue region and exhibits much higher activity in the degradation of ethanol vapor than pristine TiO2-N. However, an increased activity of Fe/Bi2WO6/TiO2-N can have an adverse effect in the degradation of benzene vapor. A temporary deactivation of the photocatalyst can occur at a high concentration of benzene due to the fast accumulation of non-volatile intermediates on its surface. The formed intermediates suppress the adsorption of the initial benzene and substantially increase the time required for its complete removal from the gas phase. An increase in temperature up to 140 °C makes it possible to increase the rate of the overall oxidation process, and the use of the Fe/Bi2WO6/TiO2-N composite improves the selectivity of oxidation compared to pristine TiO2-N.

A combined experimental and theoretical study of RuO2/TiO2 heterostructures as a photoelectrocatalyst for hydrogen evolution

We report a joint experimental and theoretical study of RuO₂/TiO₂ heterostructures. In the experimental section, mesoporous RuO₂/TiO₂ heterostructures were prepared by impregnation of mesoporous TiO₂ nanoparticles which were synthesized from a new precursor, Na₂[Ti(C₂O₄)₃], in an aqueous solution of ruthenium(III) chloride followed by calcination at 300 °C. Using various techniques, the prepared TiO₂ and RuO₂/TiO₂ heterostructures were extensively characterized. The photoelectocatalytic application of the as-prepared heterostructures was then investigated toward the hydrogen evolution reaction (HER). The results illustrated that RuO₂ is dispersed uniformly on the TiO₂ surface. The loading of RuO₂ on TiO₂ decreases the band gap energy and extends the absorption edge to the visible light region. This wide absorption extends the photoelectrocatalytic activity of RuO₂/TiO₂ heterostructures. To obtain a deeper understanding of the increase of the photoelectrocatalytic activity of RuO₂/TiO₂ heterostructures compared to pure TiO₂, theoretical calculations at the density functional theory (DFT) level were performed on some model clusters of pure TiO₂ and the RuO₂/TiO₂ heterostructure. The theoretical results elucidated that the recombination ratio of electron-hole pairs decreases effectively for RuO₂/TiO₂ compared to pure TiO₂.

Modification of TiO2 by Er3+ and rGO enhancing visible photocatalytic degradation of arsanilic acid

As a typical wide band gap photocatalyst, titania (TiO₂) cannot use the visible light and has fast recombination rate of photogenerated electron-hole pairs. Simultaneous introduction of erbium ion (Er³⁺) and graphene oxide (rGO) into TiO₂ might overcome these two drawbacks. In this study, Er³⁺ and rGO were co-doped on TiO₂ to synthesize Er³⁺-rGO/TiO₂ photocatalyst through a two-step sol-gel method. Based on the UV-visible diffuse reflectance spectra and photoluminescence spectrum, the introduction of Er³⁺ and rGO increased the visible light absorption efficiency and enhanced the migration of photogenerated electron. Pure TiO₂ has almost no photocatalytic activity for arsanilic acid (p-ASA) degradation under visible light irradiation. However, while doping with 2.0 mol% Er³⁺ and 10.0 mol% rGO, the p-ASA could be completely degraded within 50 min by the Er³⁺-rGO/TiO₂ photocatalyst under visible light irradiation, and most of produced inorganic arsenic was in situ removed by adsorption from the solution. The reactive oxygen species (ROS) reacting with p-ASA was determined and superoxide radical (O₂^•-) and singlet oxygen (¹O₂) were the dominant ROS for the oxidation of p-ASA and arsenite. This work provides an approach of introducing Er³⁺ and rGO to enhance the visible light photocatalytic efficiency of TiO₂.

Supported photocatalyst for Cr (VI) conversion and removal of organic pollutants

The photocatalytic property of available semiconductor catalysts still suffers from some urgent problems, such as the high excitation energy, easy agglomeration of powders, or weak recycling property. Therefore, developing novel visible light-supported catalysts and catalyst loading have aroused great attention recently. In this work, a novel Ag₃PO₄/BiVO₄/MWCNTs@Cotton functional fabric was prepared by introducing Ag₃PO₄ as a plasma resonance photocatalyst and MWCNTs with cotton as composite substrates. Not only did the introduction of Ag₃PO₄ and MWCNTs effectively strengthen the application ability of BiVO₄, but also inhibited the recombination of carriers, and promoted the transport of carriers according to spectroscopic and electrochemical tests. Degradation tests remained that Ag₃PO₄/BiVO₄/MWCNTs @cotton retained the high photocatalytic efficiency of the powder catalyst, along with the degradation degree of active blue KN-R (50mg/L) as well as Cr (VI) (20mg/L) could reach more than 90% within 120 min. What's more, the functional fabric has gained excellent performance in degrading pollutants for 5 cycles. Meanwhile, the prepared BiVO₄ is consistent with the band structure and electron density calculated theoretically by the GGA-PBE function. Free radical trapping and scavenging experiments exhibited that functional fabrics could produce active substances such as h⁺,·O₂^-, and·OH, among which the first two are the main active substances in the reaction. To sum up, this study is an effective attempt based on the existing problems of photocatalysts together with providing some study directions for the development of photocatalytic technology in the future.

Long-lifetime water-washable ceramic catalyst filter for air purification

Particulate matter (PM) and volatile organic compounds (VOCs) are recognised as hazardous air pollutants threatening human health. Disposable filters are generally used for air purification despite frequent replacement and waste generation problems. However, the development of a novel regenerable and robust filter for long-term use is a huge challenge. Here, we report on a new class of facile water-washing regenerable ceramic catalyst filters (CCFs), developed to simultaneously remove PM (>95%) and VOCs (>82%) in single-pass and maximized space efficiency by coating the inner and outer filter channels with an inorganic membrane and a Cu₂O/TiO₂ photocatalyst, respectively. The CCFs reveal four-fold increase in the maximum dust loading capacity (approximately 20 g/L) in relation to conventional filters (5 g/L), and can be reused after ten regeneration capability with simple water washing retaining initial PM and VOC removal performances. Thus, the CCFs can be well-suited for indoor and outdoor air purification for 20 years, which shows a huge increase in lifetime compared to the 6-month lifespan of conventional filters. Finally, we believe that the development and implementation of CCFs for air purification can open new avenues for sustainable technology through renewability and zero-waste generation.

Doped and immobilized titanium dioxide photocatalysts as a potential source of nitrosamine formation

Immobilized and visible-light-active titanium dioxide (TiO₂) is widely used for water treatment. However, the accelerated generation of degradation byproducts is a potential risk of TiO₂-based photocatalysis. This study aimed to investigate the structural effect of engineered TiO₂ samples on the formation of major nitrosamines during photocatalysis. The nitrogen-containing impurities and leached metal ions from doped-TiO₂ samples could exacerbate nitrosamine formation potential (FP) in distilled water, secondary effluent, and chloraminated water. Doped-TiO₂ with 2-ethylimidazole, trimethylamine, triethylamine, and N-carbon nanotubes could leach in the range of 47-64 ng L^-1 nitrosamines (including N-nitrosomethylethylamine, N-nitrosodiethylamine, N-nitrosodimethylamine, and N-nitrosopyrrolidine) even under dark conditions. Furthermore, we investigated the role of metal dopants on nitrosamine-FP during the chloramination of precursors such as dimethylamine and microcystin-LR. Metal ions such as Cu that leached from the metal-doped catalysts may catalyze the nitrosamine-FP. Therefore, pre-purification (washing) and immobilization of doped-TiO₂ samples on substrates are suggested to remove a considerable amount of nitrosamines. However, during the prolonged tryout, the selection of substrates was critical. Polymeric supports, such as polyimide and polyvinylpyrrolidone, can produce up to 85 ng L^-1 nitrosamine, whereas TiO₂ immobilized onto steel mesh can remove nitrosamine formation during photocatalytic oxidation followed by chloramination. This study systematically screened a diverse range of dopants, supports, and solvents in engineered TiO₂ photocatalysts, in 61 samples, and provided novel insights into their effect on nitrosamine formation.

Design of biomass-based composite photocatalysts for wastewater treatment: a review over the past decade and future prospects

This investigation applied a systematic review approach on publications covering primary data during 2012-2022 with a focus on photocatalytic degradation of pollutants in aqueous solution by composite materials synthesized with biomass and, at least, TiO₂ and/or ZnO semiconductors to form biomass-based composite photocatalysts (BCPs). After applying a set of eligibility criteria, 107 studies including 832 observations/entries were analyzed. The average removal efficiency and degradation kinetic rate reported for all model pollutants and BCPs were 77.5 ± 21.5% and 0.064 ± 0.174 min^-1, respectively. Principal component analysis (PCA) was applied to analyze BCPs synthesis methods, experimental conditions, and BCPs' characteristics correlated with the removal efficiency and photodegradation kinetics. The relevance of adsorption processes on the pollutants' removal efficiency was highlighted by PCA applied to all categories of pollutants (PCA_pol). The PCA applied to textile dyes (PCA_dyes) and pharmaceutical compounds (PCA_pharma) also indicate the influence of variables related to the composite synthesis (i.e., thermal treatment and time spent on BCPs synthesis) and photocatalytic experimental parameters (catalyst concentration, pollutant concentration, and irradiation time) on the degradation kinetic accomplished by BCPs. Furthermore, the multivariate analysis (PCA_pol) revealed that the specific surface area and the narrow band gap are key characteristics for BCPs to serve as a competitive photocatalyst. The effect of scavengers on pollutants' degradation and the recyclability of BCPs are also discussed, as necessary aspects for scalability trends. Further investigations are recommended to compare the performance of BCPs and commercial catalysts, as well as to assess the costs to treat real wastewater.

Photocatalytic oxidation degradation of tetracycline over La/Co@TiO2 nanospheres under visible light

The oxygen-vacancy-rich La/Co@TiO₂ nanospheres for the photo catalytic degradation of tetracycline were prepared by a simple two-step method. 3 wt%La/Co@TiO₂ nanospheres had better photocatalytic performance of the degradation of tetracycline than that of the other catalysts under visible light may be due to the synergistic effect between La/Co and TiO₂ and nano-confined effect. The catalytic experimental results showed the degradation ratio of tetracycline (40 mg/L) were 100% for 90 min. XPS, Raman, and photoelectrochemical results showed appropriate number of oxygen vacancies existed on the surface of TiO₂, which could improve the activation efficiency of dissolved oxygen in tetracycline solution because they accelerated the electron transfer rate in the system and inhibited the photoelectron-hole pair recombination under visible light. The EPR and radical scavenger tests showed h⁺, O₂^-, and ·OH were the main active species for the degradation of tetracycline. Also, the possible mechanism and intermediates of the tetracycline degradation process were speculated under the visible light. La/Co@TiO₂ nanospheres would be a promising photocatalyst for wastewater treatment.

The Role of Nitrogen-Doped TiO2 Supported by Platinum Catalyst Synthesized via Various Mode Preparations for Photocatalytic Enhancement

The limitations of TiO₂ as a photocatalyst such as the larger bandgap energy, which only activates under the UV region, give a lower photocatalytic activity. This study reports the role of the N and Pt co-dopant on the modification of the TiO₂ photocatalyst for photocatalytic degradation of methylene blue dye under different mode preparations, i.e., sequential and vice-versa modes. The sequential mode preparation of the N and Pt co-dopant TiO₂ photocatalyst consisted of the initial preparation of the N-doped TiO₂ (N-TiO₂) under the calcination method, which was then further doped with platinum (Pt) through the photodeposition process labeled as NP_seq-TiO₂, while the vice-versa mode was labeled as PN_rev-TiO₂. About 1.58 wt.% of N element was found in the NP_seq-TiO₂ photocatalyst, while there was no presence of N element detected in PN_rev-TiO₂, confirmed through an elemental analyzer (CHNS-O) and (EDX) analysis. The optimum weight percentage of Pt for both modes was detected at about ±2.0 wt.%, which was confirmed by inductively coupled plasma-emission spectroscopy (ICP-OES). The photoactivity under methylene blue (MB) dye degradation of the NP_seq-TiO₂ photocatalyst was 2 and 1.5 times faster compared to the unmodified TiO₂ and PN_rev-TiO₂, where the photodegradation rates were, ca., 0.065 min^-1 and 0.078 min^-1, respectively. This was due to the N elements being incorporated with the TiO₂ lattice, which was proven by UV-Vis/DRS where the bandgap energy of NP_seq-TiO₂ was reduced from 3.2 eV to 2.9 eV. In addition, the N generated a stronger PL signal due to the formation of oxygen vacancies defects on the surface of the NP_seq-TiO₂ photocatalyst. The higher specific surface area as well as higher pore volume for the NP_seq-TiO₂ photocatalyst enhanced its photocatalytic activity. Moreover, the NP_seq-TiO₂ showed the lowest COD value, and it was completely mineralized after 7 h of light irradiation. The preparation order did not affect the Pt dopant but did for the N element. Therefore, it is significant to investigate different mode preparations of the N and Pt co-dopant for the modification of TiO₂ to produce a good-quality photocatalyst for photocatalytic study under the photodegradation of MB dye.

Visible-Light-Driven Photocatalysts for Self-Cleaning Transparent Surfaces

Highly transparent photocatalytic self-cleaning surfaces capable of harvesting near-visible (365-430 nm) photons were synthesized and characterized. This helps to address a current research gap in self-cleaning surfaces, in which photocatalytic coatings that exhibit activity at wavelengths longer than ultraviolet (UV) generally have poor optical transparency, because of broadband scattering and the attenuation of visible light. In this work, the wavelength-dependent photocatalytic activity of Pt-modified TiO₂ (Pt-TiO₂) particles was characterized, which exhibited activity for wavelengths up to 430 nm. Pt-TiO₂ nanoparticles were embedded in a mesoporous SiO₂ sol-gel matrix, forming a superhydrophilic surface that allowed for water adsorption and formation of reactive oxide species upon illumination, resulting in the removal of organic surface contaminants. These self-cleaning surfaces only interact strongly with near-visible light (∼365-430 nm), as characterized by photocatalytic self-cleaning tests. Broadband visible transparency was preserved by generating a morphology composed of small clusters of Pt-TiO₂ surrounded by a matrix of SiO₂, which limited diffuse visible light scattering and attenuation. The wavelength-dependent self-cleaning rate by the films was quantified using stearic acid degradation under both monochromatic and AM1.5G spectral illumination. By varying the film morphology, the average transmittance relative to bare glass can be tuned from ∼93%-99%, and the self-cleaning rate can be adjusted by more than an order of magnitude. Overall, the ability to utilize photocatalysts with tunable visible light activity, while maintaining broadband transparency, can enable the use of photocatalytic self-cleaning surfaces for applications where UV illumination is limited, such as touchscreen displays.

Photocatalytic nanohybrid membranes for highly efficient wastewater treatment: A comprehensive review

Wastewater is inevitably generated from human activities as part of the life cycle chain that potentially damages the environment. The integration of photocatalytic reaction and membrane separation for wastewater treatment has gained great attention in recent studies. However, there are still many technical limitations for its application such as toxic metal release, catalyst deactivation, fouling/biofouling, polymer disintegration, and separation performance decline. Different types, combinations, and modifications of photocatalysts material combined with membranes such as semiconductor metal oxides, binary/ternary hybrid metal oxides, elemental doped semiconductors, and metal-organic frameworks (MOFs) for improving the performance and compatibility are presented and discussed. The strategies of incorporating photocatalysts into membrane matrix for pursuing the most stable membrane integrity, high photocatalytic efficiency, and excellent perm-selectivity performance in the very recent studies were discussed. This review also outlines the performance enhancement of photocatalytic membranes (PMs) in wastewater treatment and its potential for water reclamation. Photocatalysts enhanced membrane separation by inducing anti-fouling and self-cleaning properties as well as antibacterial activity. Based on the reviewed study, PMs are possible to achieve complete removal of emerging contaminants and ∼99% reduction of bacterial colony that leading on the zero liquid discharge (ZLD). However, the intensive exposure of photo-induced radicals potentially damages the polymeric membrane. Therefore, future studies should be focused on fabricating chemically stable host-membrane material. Moreover, the light source and the membrane module design for the practical application by considering the hydrodynamic and cost-efficiency should be a concern for technology diffusion to the industrial-scale application.

Visible-Light Activation of a Dissolved Organic Matter-TiO2 Complex Mediated via Ligand-to-Metal Charge Transfer

Given the widespread use of TiO₂, its release into aquatic systems and complexation with dissolved organic matter (DOM) are highly possible, making it important to understand how such interactions affect photocatalytic activity under visible light. Here, we show that humic acid/TiO₂ complexes (HA/TiO₂) exhibit photoactivity (without significant electron-hole activation) under visible light through ligand-to-metal charge transfer (LMCT). The observed visible-light activities for pollutant removal and bacterial inactivation are primarily linked to the generation of H₂O₂via the conduction band. By systematically considering molecular-scale interactions between TiO₂ and organic functional groups in HA, we find a key role of phenolic groups in visible-light absorption and H₂O₂ photogeneration. The photochemical formation of H₂O₂ in river waters spiked with TiO₂ is notably elevated above naturally occurring H₂O₂ generated from background organic constituents due to LMCT contribution. Our findings suggest that H₂O₂ generation by HA/TiO₂ is related to the quantity and functional group chemistry of DOM, which provides chemical insights into photocatalytic activity and potential ecotoxicity of TiO₂ in environmental and engineered systems.