TiO2 photocatalysis: Design and applications

Antibacterial activity of photocatalytic titanium dioxide (TiO2) thin films for Listeria monocytogenes biofilms disinfection

The presence of microbial biofilms on equipment surfaces is a recurrent problem in the food industry. To reduce the risk of biofilm development, a preventive method based on photoactive antibacterial surfaces is proposed. In the present study, crystalline rutile form titanium dioxide (TiO2) thin layers are deposited on stainless steel substrates by RF sputtering under reactive plasma. Such layers are assessed for their bactericidal activity on two strains of Listeria monocytogenes. After 1 h of irradiation under UV-A at 365 nm, a decrease of 2 log of the number of adherent Listeria cells is observed. Analysis with scanning electron microscopy suggests damages to the bacterial walls. Moreover, the peroxidation of the membrane lipids of L. monocytogenes by the radical species formed by photocatalysis is confirmed since malondialdehyde was detected after irradiation. Furthermore, the present work investigates the role of the redox species generated by photocatalysis. Indeed, experiments carried out in the presence of scavenger molecules (DMSO, EDTA-2Na, superoxide dismutase) show that holes are the main redox species involved in the antibacterial activity of the deposited layers. These results allow a better understanding of the role of the redox species generated by the photocatalytic activity of the rutile TiO2 thin layers.

Photocatalytic Hydrogen Production Using Semiconductor (CdSe)13 Clusters

Atomically precise (CdSe)13 clusters, the smallest CdSe semiconductors, represent a unique class of materials at the boundary between nanocrystals and molecules. Despite their promising potential, low structural stability limits their applications as photocatalysts. Herein, we report photocatalytic hydrogen production using atomically precise (CdSe)13 clusters. To improve stability in aqueous environments, we induce self-assembly into suprastructures, making them suitable for water splitting. Our findings demonstrate that Co2+ doping enhances the electrical properties of these clusters, while bipyridine serves as cocatalyst by interacting with Co2+ dopants and providing catalytic active sites. Through the synergistic effects of Co2+ doping and bipyridine, Co2+-doped (CdSe)13 suprastructures achieve promising hydrogen evolution activity, surpassing those of undoped suprastructures or nanoclusters. Theoretical calculations confirm that Co2+ doping and bipyridine incorporation lower the hydrogen adsorption energy, consistent with the experimental results. These results highlight the potential of semiconductor (CdSe)13 clusters as photocatalysts for sustainable hydrogen production.

Biomimetic Superwetting Phenomena for Antifogging Surfaces

Fog formation on transparent windows compromises the visual clarity of these surfaces and brings hidden safety dangers, which underscores the importance of research into antifogging coatings. In recent years, biomimetic superwetting coatings have garnered significant attention as a key technology for addressing fogging issues. This review outlines the latest advancements in the design and fabrication of superwetting antifogging materials. Initially, the antifogging mechanism of superwetting surfaces was introduced briefly. Subsequently, contemporary developments in superhydrophobic antifogging surfaces inspired by organisms and superhydrophilic antifogging coatings with a variety of material systems have been emphatically discussed. The amphiphilic and heat-assisted antifogging surfaces, including photothermal and electrothermal surfaces, were also overviewed. Finally, a summary and future perspective on antifogging coating from its functionality, durability, and availability were discussed.

A novel three-dimensional TiO2-sponge cascade photocatalytic system for enhanced removal of non-steroidal anti-inflammatory drugs from wastewater

This study introduces a novel, bio-inspired photocatalytic system utilizing a TiO2-sponge in a cascade configuration, optimized for the efficient degradation of non-steroidal anti-inflammatory drugs such as naproxen and ketoprofen. Comprehensive characterization of the photocatalyst was performed, including alignment of the photocatalyst's absorption spectrum with the light source's emission spectrum. Operational parameters like flow rates and cascade configuration were meticulously optimized to enhance degradation efficiency. Real-world testing using municipal sewage demonstrated a high removal efficiency, achieving about 80 % for the targeted drugs within 240 min. Physicochemical analyses, including XPS and FTIR, confirmed the photocatalyst's durability across five catalytic cycles without surface degradation from photo-oxidation processes. The system's energy efficiency, evidenced by an electrical energy per order value of 8.69 kWh/m3, highlights its potential for scalable and sustainable wastewater treatment. This innovative approach not only demonstrates the practical application of bio-based materials in environmental remediation but also significantly contributes to advancing sustainable wastewater management practices.

3D Self-Supported Visible Light Photochemical Nanocatalysts

This work focuses on 3D, self-supported, nanofibrous TiO2 structures (nanogrids) prepared using blend electrospinning. The presence of anatase and brookite phases in Cu-doped TiO2 nanogrids significantly enhances the photocatalytic properties of the titania system. The absorption edge in Cu-doped TiO2 shifts to the visible due to the narrowed bandgap and efficient separation of photogenerated charge carriers facilitated by Cu doping. The presence of the brookite phase further contributes to the enhanced performance, by reducing electron-hole recombination. A wide range of characterization techniques, including cyclic voltammetry and chronoamperometry studies which show that the Cu doped TiO₂ sample generates a significant photocurrent under visible light, are employed to elucidate the role of Cu doping in enhancing the visible light photocatalytic efficiency of TiO2 nanogrids, offering valuable insights for developing advanced photochemical catalysts for environmental and energy applications. The nanogrids studied here are far superior to P25 Degussa and are activated by natural sunlight and do not require a filtration system to remove nanoparticles from the water. These self-supported nanofibrous photochemical catalysts offer all the benefits of nanomaterials while suffering from none of their drawbacks.

Pd single atoms on g-C3N4 photocatalysts: minimum loading for maximum activity

Noble metal single atoms (SAs) on semiconductors are increasingly explored as co-catalysts to enhance the efficiency of photocatalytic hydrogen production. In this study, we introduce a "spontaneous deposition" approach to anchor Pd SAs onto graphitic carbon nitride (g-C3N4) using a highly dilute tetraaminepalladium(ii) chloride precursor. Maximized photocatalytic activity and significantly reduced charge transfer resistance can be achieved with a remarkably low Pd loading of 0.05 wt% using this approach. The resulting Pd SA-modified g-C3N4 demonstrates a remarkable hydrogen production efficiency of 0.24 mmol h-1 mg-1 Pd, which is >50 times larger than that of Pd nanoparticles deposited on g-C3N4 via conventional photodeposition. This significant enhancement in catalytic performance is attributed to improved electron transfer facilitated by the optimal coordination of Pd SAs within the g-C3N4 structure.

Photo-induced degradation of toxic recalcitrant compounds from surface water: Insights into advanced nanomaterials, hybrid photocatalytic systems, and real applications

The rapid increase in toxic recalcitrant organic compounds (ROCs) from various industrial, residential, and agricultural sources poses a significant public health concern and threatens environmental preservation. The presence of these toxic ROCs weakens the effectiveness of conventional water and wastewater treatment systems. As a result, numerous physicochemical and biological treatment processes have been explored, each demonstrating varying removal efficiencies depending on experimental conditions. Given the limitations of existing treatment methods, research has increasingly focused on advanced oxidation processes, particularly photocatalysis. Photocatalysis is a prominent treatment technique due to its low sludge production, non-toxic nature, reusable characteristics, and ability to harness visible light. This review comprehensively examines the ecotoxicological effects of ROCs, existing biological and physicochemical treatment methods, advancements in photocatalyst synthesis, the transition from conventional to advanced photocatalysts, and hybrid treatment systems. In the context of photocatalytic removal of ROCs, the review also addresses several influencing parameters, including initial pollutant concentration, solution pH, light intensity, catalyst dose, and catalyst type. Global case studies focusing on the mechanisms of photocatalytic degradation of ROCs are highlighted. The documented photocatalysts for removing ROCs from water and wastewater have shown promising results. Moreover, integrating photocatalysis with advanced physicochemical and biological processes has effectively removed various dissolved (e.g., ROCs) and suspended impurities, showcasing its practical applications. Thus, this study could serve as a valuable resource for researchers and engineers working on the treatment of various micropollutants, such as ROCs, in real wastewater.

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.

Advancing nonadiabatic molecular dynamics simulations in solids with E(3) equivariant deep neural hamiltonians

Non-adiabatic molecular dynamics (NAMD) simulations have become an indispensable tool for investigating excited-state dynamics in solids. In this work, we propose a general framework, N2AMD (Neural-Network Non-Adiabatic Molecular Dynamics), which employs an E(3)-equivariant deep neural Hamiltonian to boost the accuracy and efficiency of NAMD simulations. Distinct from conventional machine learning methods that predict key quantities in NAMD, N2AMD computes these quantities directly with a deep neural Hamiltonian, ensuring excellent accuracy, efficiency, and consistency. N2AMD not only achieves impressive efficiency in performing NAMD simulations at the hybrid functional level within the framework of the classical path approximation (CPA), but also demonstrates great potential in predicting non-adiabatic coupling vectors and suggests a method to go beyond CPA. Furthermore, N2AMD demonstrates excellent generalizability and enables seamless integration with advanced NAMD techniques and infrastructures. Taking several extensively investigated semiconductors as the prototypical system, we successfully simulate carrier recombination in both pristine and defective systems at large scales where conventional NAMD often significantly underestimates or even qualitatively incorrectly predicts lifetimes. This framework offers a reliable and efficient approach for conducting accurate NAMD simulations across various condensed materials.

Oxygen Vacancies on Hydrated Anatase (101) Surfaces: Insights from Classical and Ab Initio Molecular Dynamics Simulations

Hydrated anatase (101) titanium dioxide surfaces with oxygen vacancies have been studied using a combination of classical and ab initio molecular dynamics simulations. The reactivity of surface oxygen vacancies was investigated using ab initio calculations, showing that water molecules quickly adsorb to oxygen vacancy sites upon hydration. The oxygen vacancy then quickly reacts with the adsorbed water, forming a protonated bridging oxygen atom at the vacancy site and at a neighboring oxygen bridge. Ab initio simulations also revealed that this occurs via a short-lived hydronium ion intermediate. It was investigated how this reaction affects the structure and dynamics of water near the anatase surface. Classical molecular dynamics simulations of surfaces with and without oxygen vacancies showed that vacancies disrupt the second solvation shell, consisting of water molecules hydrogen bonded to the surface, thereby changing the local water density and diffusion as well as the binding modes for hydrogen bonding. Our findings support the hydroxylation of oxygen vacancies on anatase (101) surfaces, rather than stabilization by molecular adsorption or subsurface diffusion. The work gives new atomistic insight into water structure and surface chemistry on the catalytically relevant anatase (101) titanium dioxide surface.

Encapsulation of perovskite quantum dots in CAU-17 organic frameworks for stable photocatalysis

In this study, MAPbBr3 was encapsulated within a porous metal-organic framework (CAU-17) via ligand-assisted reprecipitation, which enhanced the perovskite's photocatalytic stability. This encapsulation approach not only stabilises the photocatalytic performance of MAPbBr3 but also enables further enhancement of its catalytic efficiency through halogen anion group modification. Results from various characterisation demonstrate that the CAU-17/MAPbBr2Cl composites possess excellent properties, achieving a tetracycline degradation efficiency of up to 92%.

Defect physics investigations in bulk NaBiO3 photocatalysts via Heyd-Scuseria-Ernzerhof hybrid density functional theory calculations

This study employs Heyd-Scuseria-Ernzerhof hybrid density functional theory calculations to thoroughly investigate the n-type and p-type conductivity mechanisms of NaBiO3 photocatalysts. The results reveal that the intrinsic interstitial defect Na1+i is dominant under most growth conditions because of its lower formation energy. It is an excellent donor because of its shallower charge transition level. This makes it easily reach and even exceed the significant concentration of 1021 cm-3 with Na chemical potential regulation. Thus, in most circumstances, the intrinsic n-type conductivity of NaBiO3 found in experiments should primarily originate from the contribution of the interstitial defect Na1+i. The anti-site defect Bi2+Na also contributes to the unintentional n-type conductivity behavior. Especially under Na-poor and Bi-rich growth conditions, Bi2+Na becomes the dominant defect and is most responsible for the intrinsic n-type conductivity. The two major intrinsic defects, including Na1+i and Bi2+Na defects, can act as the photocatalytic reaction active sites or as a hole capture center (Bi2+Na) rather than as the recombination centers of the photo-generated electrons and holes in NaBiO3. On the other hand, based on thermodynamic simulation, the study examines the impacts of n-type and p-type doping at a fixed donor D+ or acceptor A- concentration on the conductive properties of NaBiO3 under different chemical potential conditions. It is indicated that p-type doping can convert the intrinsic n-type NaBiO3 into a p-type semiconductor only under non-thermal equilibrium growth conditions (quenching method). In contrast, n-type doping can easily enhance its n-type carrier concentration. Our results can guide optimizing the growth conditions to achieve high donor doping and high photocatalytic performance in NaBiO3 or NaBiO3-based materials.

Photoelectrochemical water splitting with In2O3-x nanofilm/black Ti-Si-O composite photoanode

Fabricating TiO2 with heterostructures is one of the important ways to enhance its photocatalytic activity. In this work, we fabricated black Si-doped TiO2 nanotubes (Ti-Si-O) through anodization and Sn reduction, and constructed In2O3-x nanofilm/black Ti-Si-O composite photoanode through electrochemical deposition and Ar annealing. The composition evolution, morphology, optical properties and photoelectrochemical performance of the composite photoanode were investigated. The In2O3-x /black Ti-Si-O composite photoanode exhibited excellent PEC hydrogen production performance, with a high photocurrent density of 3.76 mA cm-2 at 0 V Ag/AgCl, which was 2.16 times that of the black Ti-Si-O photoanode. The synergistic effects of Si doping, Ti3+/O vacancies and the modification with In2O3-x nanofilms provide a beneficial approach to design of high-efficiency photoanodes.

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.

Recent advances in synthesis and application of Magnéli phase titanium oxides for energy storage and environmental remediation

High-temperature reduction of TiO2 causes the gradual formation of structural defects, leading to oxygen vacancy planar defects and giving rise to Magnéli phases, which are substoichiometric titanium oxides that follow the formula Ti n O2n-1, with 4 ≤ n ≤ 9. A high concentration of defects provides several possible configurations for Ti4+ and Ti3+ within the crystal, with the variation in charge ordered states changing the electronic structure of the material. The changes in crystal and electronic structures of Magnéli phases introduce unique properties absent in TiO2, facilitating their diverse applications. Their exceptional electrical conductivity, stability in harsh chemical environments and capability to generate hydroxyl radicals make them highly valuable in electrochemical applications. Additionally, their high specific capacity and corrosion resistance make them ideal for energy storage facilities. These properties, combined with excellent solar light absorption, have led to their widespread use in electrochemical, photochemical, photothermal, catalytic and energy storage applications. To provide a complete overview of the formation, properties, and environmental- and energy-related applications of Magnéli phase titanium suboxides, this review initially highlights the crystal structure and the physical, thermoelectrical and optical properties of these materials. The conventional and novel strategies developed to synthesise these materials are then discussed, along with potential approaches to overcome challenges associated with current issues and future low-energy fabrication methods. Finally, we provide a comprehensive overview of their applications across various fields, including environmental remediation, energy storage, and thermoelectric and optoelectronic technologies. We also discuss promising new directions for the use of Magnéli phase titanium suboxides and solutions to challenges in energy and environment-related applications, and provide guidance on how these materials can be developed and utilised to meet diverse research application needs. By making use of control measures to mitigate the potential hazards associated with their nanoparticles, Magnéli phases can be considered as versatile materials with potential for next generation energy needs.

Single-Atom Catalysts on C3N4: Minimizing Single Atom Pt Loading for Maximized Photocatalytic Hydrogen Production Efficiency

The use of metal single atoms (SAs) as co-catalysts on semiconductors has emerged as a promising technology to enhance their photocatalytic hydrogen production performance. In this study, we describe the deposition of very low amounts of Pt SAs (<0.1 at %) on exfoliated graphitic carbon nitride (C3N4) by a direct Pt-deposition approach from highly dilute chloroplatinic acid precursors. We find that - using this technique-a remarkably low loading of highly dispersed Pt SAs (0.03 wt %) on C3N4 is sufficient to achieve a drastic decrease in the overall charge transfer resistance and a maximized photocatalytic efficiency. The resulting low-loaded Pt SAs/C3N4 provides a H2 production rate of 1.66 m mol/h/mg Pt, with a remarkable stability against agglomeration; even during prolonged photocatalytic reactions no sign of light-induced Pt agglomerations can be observed. We ascribe the high performance and stability to the site-selective, stable coordination of Pt within the C3N4 structure. Notably the H2 production rate of the low-loaded Pt SAs surpasses the activity of Pt SAs deposited by other techniques or nanoparticles at comparable or even higher loading - the optimized Pt SAs decorated C3N4 show ≈5.9 times higher rate than Pt NP decorated C3N4.

Investigating the thermal and mechanical properties of novel LDPE/TiO2 and LDPE/TiO2/CNT composites for 3D printing applications

The development of new materials is essential for advancing technology and improving the quality of life. With new materials, we can create products that are stronger, more durable, and more efficient. The ongoing research and development of new materials for 3D printing applications continue to drive innovation in various fields, leading to improved products and processes with great benefits. The main goal of this work was to produce a functional filament with a 1.75-mm diameter that may be used for 3D printing. Composite materials were prepared using a low-density polyethylene (LDPE) resin as polymer matrix, and titanium dioxide (TiO2) and carbon nanotubes (CNT) as fillers in various ratios. Up to 15 wt% of TiO2 and 0.25 wt% of CNT were added. Some of the greatest difficulties with high filler content composites are achieving good homogeneity, and in the case of the 3D printing, greatest difficulties are producing the filament with a specific and stable filament diameter. During the 3D printing itself, the fillers can also often cause the nozzle clogging. This paper reports findings of thermal and mechanical properties of the LDPE/TiO2/CNT composites which are significant for the 3D printing process and the applicability of the composite materials. All of the planed composite materials are successfully prepared and 3D printed into the tensile test specimens. The melting point shift caused by the addition of fillers did not show consistent pattern at differential scanning calorimetry, as all of the samples had melting temperatures around 113.5 ± 1.4 °C. The addition of filler, according to the TGA, increased the threshold temperature for the material decomposition, in case of TiO2 5.4 °C increase, while TiO2 and CNT combination increased the threshold temperature for 6.8 °C. The results of the tensile test show a general increase trend with addition of TiO2 filler but do not show to a trend for the tensile strength as a result of the addition of CNT filler. The sample with highest TiO2 filler ratio of 15% (LDPE 15T0C) showed the greatest tensile strength of 14.5 MPa, compared to the 13.0 MPa of pure LDPE. The sample with 5% of TiO2 filler and 0.1% of CNT filler (LDPE 5T0.1C) showed the greatest elongation of 73.9%, compared to the 68.9% of pure LDPE.

Photocatalytic production and biological activity of D-arabino-1,4-lactone from D-fructose

Lactones play crucial roles in various fields, such as pharmaceuticals, food, and materials science, due to their unique structures and diverse biological activities. However, certain lactones are difficult to obtain in large quantities from natural sources, necessitating their synthesis to study their properties and potential. In this study, we investigated the photocatalytic conversion of D-fructose, a biomass-derived and naturally abundant sugar, using a TiO2 photocatalyst under light irradiation in ambient conditions. The resulting products were identified using HPLC, LCMS, MALDI TOF MS, and 1H NMR. The results confirmed the successful production of D-arabino-1,4-lactone as a key product, along with the formation of other valuable compounds, including rare sugars such as erythrose and glyceraldehyde. Analysis of the reaction mechanism revealed that D-arabino-1,4-lactone can be directly produced by the α scission (C1-C2 position cleavage) of D-fructose. Furthermore, erythrose and glyceraldehyde, as rare sugars, can be produced from the decomposition of D-arabino-1,4-lactone, which means that D-arabino-1,4-lactone can be used as a source of rare sugars. Furthermore, to investigate the biological activity of D-arabino-1,4-lactone, it was administered to Bifidobacterium. The results showed that Bifidobacterium proliferated and produced more lactic acid than when cultured in a medium without D-arabino-1,4-lactone, suggesting that Bifidobacterium can utilize D-arabino-1,4-lactone.

Bottom-up approaches to prepare ultrathin TiO2 nanosheets

Atomically thin two-dimensional (2D) materials are promising platforms to explore the unusual physical and chemical properties in surface chemistry, various catalysis, and devices. Most 2D materials derive from inherently layer-structured compounds through top-down exfoliation, but it is usually challenging to directly prepare ultrathin nanosheets of non-layered materials. TiO2 contains at least 8 non-layered polymorphs, and some of them have found wide applications in heterogeneous catalysis, photocatalysis, solar cells, lithium-ion batteries, etc. In this review, we summarize typical bottom-up wet-chemistry synthetic systems of atomically thin TiO2 nanosheets. The synthesis protocols are discussed in groups of different phases, and the growth mechanisms are classified into three approaches of strong ligand confinement, layered intermediate, and templated synthesis.

Defect-Mediated Crystallization of the Particulate TiO2 Photocatalyst Grown by Atomic Layer Deposition

Nanopowders or films of pure and mixed oxides in nanoparticulate form have gained specific interest due to their applicability in functionalizing high-surface-area substrates. Among various other applications, our presented work primarily focuses on the behavior of TiO2 as a photocatalyst deposited by atomic layer deposition (ALD) on a quartz particle. The photocatalytic activity of TiO2 on quartz particles grown by ALD was studied in terms of ALD growth temperature and post-treatment heating rate. Amorphous TiO2 thin films (30 nm) were grown from tetrakis(dimethylamido)titanium (TDMAT) at 100 and 200 °C on quartz particles (0.35-3.5 μm) and crystallized using oxidative heat treatment at 500 °C with variable heating rates. The growth temperature was found to affect the TiO2 defect structure: TiO2 grown at 200 °C is black due to Ti3+ defects, whereas the film grown at 100 °C is white but contains some traces of the TDMAT ALD precursor. During the oxidative heat treatment, precursor traces desorbed and Ti3+ defects were oxidized. ALD TiO2 grown at 100 °C crystallized as anatase, whereas the rutile-to-anatase ratio of 200 °C grown TiO2 increased with the heating rate. The hydrogen production rate of mixed-phase TiO2 was found to outperform that of anatase TiO2.

Enhanced Photocatalytic Oxidative Coupling of Methane over Metal-Loaded TiO2 Nanowires

The photocatalytic oxidative coupling of methane (OCM) on metal-loaded one-dimensional TiO2 nanowires (TiO2 NWs) was performed. With metal loading, the electric and optical properties of TiO2 NWs were adjusted, contributing to the improvement of the activity and selectivity of the OCM reaction. In the photocatalytic OCM reaction, the 1.0 Au/TiO2 NW catalyst exhibits an outstanding C2H6 production rate (4901 μmol g-1 h-1) and selectivity (70%), alongside the minor production of C3H8 and C2H4, achieving a total C2-C3 hydrocarbon selectivity of 75%. In contrast, catalysts loaded with Ag, Pd, and Pt show significantly lower activity, with Pt/TiO2 NWs producing only CO2, indicating a propensity for the deep oxidation of methane. The O2-TPD analyses reveal that Au facilitates mild O2 adsorption and activation, whereas Pt triggers excessive oxidation. Spectroscopic and kinetic studies demonstrate that Au loading not only enhances the separation efficiency of photogenerated electron-hole pairs, but also promotes the generation of active oxygen species in moderate amounts, which facilitates the formation of methyl radicals and their coupling into C2H6 while suppressing over-oxidation to CO2. This work provides novel insights and design strategies for developing efficient photocatalysts.

Solvent-Free Ball Milling Synthesis of Water-Stable Tin-Based Pseudohalide Perovskites for Photocatalytic CO2 Reduction

A pseudohalide (SCN-) tin-based perovskite material using a solvent-free ball milling method is developed. The synthesized perovskite exhibits long-term water stability and demonstrated significant photocatalytic activity in reducing CO2 to CO under light irradiation. The structural transition from nanoparticles to planar perovskites is achieved by varying the ratios of dimethylammonium (DMA) and formamidinium (FA) cations, which is confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. The surface elemental distribution, absorption spectra, band gap and energy levels estimations using energy-dispersive X-ray spectroscopy (EDS), Kubelka-Munk function, and ultraviolet photoelectron spectroscopy (UPS) are thoroughly investigated. These findings indicated that the incorporation of DMA cations increased the band gap and shifted the absorption spectra toward the blue region. The optimal photocatalytic performance is observed for the perovskite composition with a 50% DMA cation ratio (DMA0.5FA0.5SnI(SCN)2), achieving a CO production yield of 285 µmol g-1 with 12 hours irradiation in humid environment. The efficiency is critically dependent on the ball milling speed and duration, with 400 rpm and 1 hour being the optimal conditions. This research highlights the potential of environmentally friendly synthesis methods in developing stable and efficient lead-free perovskites as photocatalytic materials, contributing to the goal of net-zero carbon emissions.

Preparation of Red TiO2 with Excellent Visible Light Absorption from Industrial TiOSO4 Solution for Photocatalytic Degradation of Dyes

At present, it is still difficult to significantly reduce the bandgap of TiO2 to promote its visible light absorption. Herein, we first synthesized sulfur-doped TiO2 from industrial TiOSO4 and then successfully synthesized red TiO2 nanoparticles by calcination with the N source melamine. Theoretical calculations show that predoped S could markedly decrease the formation energy and substitution energy of N-doped TiO2, especially in high N/Ti ratios. The red TiO2 nanoparticles have a low bandgap (2.10 eV) and exhibit remarkable visible light absorption capacity. Electron paramagnetic resonance measurements show that the red TiO2 has abundant oxygen vacancies and Ti3+. The synergetic effect of Ti3+, oxygen vacancies, and nonmetallic element doping leads to the bandgap of TiO2 significantly being reduced. In addition, the red TiO2 exhibits great photocatalytic activity in the visible light degradation of rhodamine B (Rh.B) and methylene blue (MB). This study provides a new idea for the preparation of TiO2 with high visible light absorption.

In situ hydrothermal synthesis of visible light active sulfur doped TiO2 from industrial TiOSO4 solution

A cost-effective industrial TiOSO4 solution was employed to fabricate visible light active sulfur-doped titanium dioxide (S-TiO2) via a facile hydrothermal method. The effect of calcination temperature on morphology, particle size, crystallinity, and photocatalytic property of S-TiO2 was systematically investigated. Successful incorporation of sulfur into TiO2 was confirmed by carbon-sulfur analysis, X-ray photoelectron spectroscopy (XPS), and Energy dispersive spectrometer (EDS). The research results demonstrated that calcination temperature significantly impacted the crystallinity, specific surface area, sulfur content, and light absorption properties of S-TiO2. The catalyst calcined at 400 °C revealed the highest photocatalytic activity, with a rate constant of 0.02408 min-1, approximately 25 times higher than commercial P25 catalyst. The higher activity was attributed to the synergistic effect of well-crystallized anatase phase, specific surface area, and red shift of spectral absorption.

UV and Visible Light-Induced Photocatalytic Efficiency of Polyaniline/Titanium Dioxide Heterostructures

The concept of using polyaniline/titanium dioxide heterostructures as efficient photocatalysts is based on the synergistic effect of conducting polymer and metal oxide semiconductors. Due to inconclusive literature reports, the effect of different polyaniline/TiO2 ratios on photocatalytic activity under UV and visible light was investigated. In most papers, non-recommended dyes are used as model compounds to evaluate visible light activity. Therefore, colorless phenol was used instead of dyes in this study to clarify the real visible light-induced photocatalytic activity of polyaniline/TiO2 composites. This publication also includes a discussion of whether materials derived from bulk (non-nanostructured) polyaniline and TiO2 by the standard in situ oxidative polymerization method are suitable candidates for promising photocatalytic materials. The evaluation of photocatalytic activity was performed in both UV and visible light systems. X-ray diffraction and UV-Vis diffuse reflectance spectroscopy methods were applied to characterize the obtained samples. Obtained polyaniline (pure and in composites) was identified as emeraldine salt. In the UV system, none of the prepared samples with different polyaniline-titania ratios had activity better than reference P25 titania. It has been observed that the presence of polyaniline adversely affects the photocatalytic properties, as the polyaniline layer covering the titania surface can shield the UV light transmission by blocking the contact between the TiO2 surface and organic molecules. In the case of using visible light, no synergies have been observed between polyaniline and titania either. The photodegradation efficiencies of the most active samples were similar to those of pure polyaniline. In conclusion, in order to obtain efficient polyaniline/titania photocatalysts active in UV and/or visible light, it is necessary to take into account the morphological and surface properties of both components.

Gels in Heterogeneous Photocatalysis: Past, Present, and Future

Photocatalysis has attracted more and more attention as a possible solution to environmental, water, and energy crises. Although some photocatalytic materials have already proven to perform well, there are still some problems that should be solved for the broad commercialization of photocatalysis-based technologies. Among them, cheap and easy recycling, as well as stability issues, should be addressed. Accordingly, the application of gels, either as a photocatalytic material or as its support, might be a good solution. In this review, various propositions of gel-based photocatalysts have been presented and discussed. Moreover, an easy nanoarchitecture design of gel-based structures enables fundamental studies, e.g., on mechanism clarifications. It might be concluded that gels with their unique properties, i.e., low density, high specific surface area, great porosity, and low-cost preparation, are highly prospective for solar-energy-based reactions, water treatment, photodynamic cancer therapies, and fundamental research.

Photonic Band Gap Engineering by Varying the Inverse Opal Wall Thickness

We demonstrate the band gap programming of inverse opals by fabrication of different wall thickness by atomic layer deposition (ALD). The opal templates were synthesized using polystyrene and carbon nanospheres by the vertical deposition method. The structure and properties of the TiO2 inverse opal samples were investigated using Scanning Electron Microscope (SEM) and Focused Ion Beam Scanning Electron Microscopy (FIB-SEM), Energy Dispersive X-ray analysis (EDX), X-ray Diffraction (XRD) and Finite Difference Time Domain (FDTD) simulations. The photonic properties can be well detected by UV-Vis reflectance spectroscopy, while diffuse reflectance spectroscopy appears to be less sensitive. The samples showed visible light photocatalytic properties using Raman microscopy and UV-Visible spectrophotometry, and a newly developed digital photography-based detection method to track dye degradation. In our work, we stretch the boundaries of a working inverse opal to make it commercially more available while avoiding fully filling and using cheaper, but lower-quality, carbon nanosphere sacrificial templates.

nano-TiO2 reduces bioavailability and biotransformation responses to crude oil WAF-associated PAHs in the European sea bass Dicentrachus labrax

The present study investigates the potential interaction between nano‑titanium dioxide (nano-TiO2) and the water accommodated fraction (WAF) of crude oil and associated chemicals on bioavailability and biotransformation responses in the European sea bass (Dicentrarchus labrax). An in vivo (48-h) waterborne exposure with nano-TiO2 (10 mgL-1), crude oil WAF (0.068 gL-1), alone and in combination was performed. Combined exposure significantly reduced levels of polycyclic aromatic hydrocarbons (PAH) in either seawater and fish fillets compared to WAF alone. A significant reduction in the expression of several biotransformation genes (cyp1a, gsta, erβ2, elmod2, abcb1 and abcc1) when nano-TiO2 was combined with WAF was observed in fish liver, compared to WAF alone. EROD and GST enzyme activities were also significantly reduced. Nano-TiO2 can reduce PAHs bioavailability in seawater and biological responses in European sea bass, suggesting a potential safe application of nano-TiO2 for the remediation of crude oil WAF in the marine environment.

Microwave-Field-Optimized GO/TiO2 Nanomaterials for Enhanced Interfacial Charge Transfer in Photocatalysis

The swift recombination of photo-induced electrons and holes is a major obstacle to the catalytic efficiency of TiO2 nanomaterials, but the incorporation of graphene oxide and out-field modification is considered a potent method to augment photocatalytic properties. In this work, a series of GO/TiO2 photocatalysts were successfully optimized by a microwave field. As determined by transient photocurrent response and electrochemical impedance spectroscopy (EIS) tests, microwave irradiation at 600 W for 5 min on the GO/TiO2 photocatalyst promoted interfacial charge transfer and suppressed charge recombination. Through systematic characterizations, GT(600/5) exhibited the highest photooxidation rate (81.5%, 60 min) of Rhodamine B under visible light compared to other homologous samples, owing to the minimum grain size (16.914 nm), enlarged specific surface area (151 m2/g), maximum light response wavelength (510 nm), narrowest bandgap width (2.90 eV), and stronger oxidized hydroxyl radicals (•OH). Given the environmental friendliness, greenness, and sustainability, this study could present an efficient and economical strategy for synthesizing and fine-tuning photocatalysts.

Photocatalytic Mechanisms of Organic Thermally Activated Delayed Fluorescence Compounds

Reverse intersystem crossing (RISC) has become possible by minimizing the energy gap between the first excited singlet (S1) and triplet state (T1), which facilitates the thermally activated delayed fluorescence (TADF). Due to the small singlet-triplet energy gap, the S1 and T1 states exhibit comparable redox reactivity, leading organic TADF compounds to be potent photocatalysts. Here, we report such TADF compounds with multiple donor units designed as an efficient photocatalyst for the direct C(sp3)-H carbamoylation of saturated aza-heterocycles. The results obtained by photophysical investigations and chemical calculations confirm that both the S1 and T1 states are involved in the photocatalysis cycle, with the fast spin-flip from the S1 to triplet states being a crucial factor in the enhancement of catalytic performance. The findings will be beneficial for the design of novel, efficient organic photocatalysis with TADF characteristics and aid in the development of organic photocatalysis.

Identification of large polarons and exciton polarons in rutile and anatase polymorphs of titanium dioxide

Titanium dioxide (TiO2) is a wide-gap semiconductor with numerous applications in photocatalysis, photovoltaics, and neuromorphic computing. The unique functional properties of this material critically depend on its ability to transport charge in the form of polarons, namely narrow electron wavepackets accompanied by local distortions of the crystal lattice. It is currently well established that the most important polymorphs of TiO2, the rutile and anatase phases, harbor small electron polarons and small hole polarons, respectively. However, whether additional polaronic species exist in TiO2, and under which conditions, remain open questions. Here, we provide definitive answers to these questions by exploring the rich landscape of polaron quasiparticles in TiO2 via recently developed ab initio techniques. In addition to the already known small polarons, we identify three species, namely a large hole polaron in rutile, a large quasi-two-dimensional electron polaron in anatase, and a large exciton polaron in anatase. These findings complete the puzzle on the polaron physics of TiO2 and pave the way for systematically probing and manipulating polarons in a broad class of complex oxides and quantum materials.

"Sunlight-driven catalytic degradation of MB dye and multi-cycle Re-usability analysis of Cu2-xSe nanoparticles"

One of the best ways to remove organic dyes based contaminant from water resources and industrial waste water is the sunlight driven photo-catalytic degradation method. The theme of the present investigation is the photocatalytic degradation of methylene blue (MB) dye using economically produced Cu2-XSe nanoparticles (NPs) catalyst under solar radiations. The Cu2-XSe NPs crystallized in the cubic structural phase with an average crystallite size around 19 nm. The direct band gap was found to be 2.1 eV. The PL spectra and corresponding CIE diagram show the Cu2-xSe NPs emitted yellow color. The SEM micrographs show that the small grains staked over others to form large grains or patches. The FTIR and EDX spectra confirmed the formation of Cu2-XSe NPs. The obtained optimum photocatalytic degradation efficiency for Cu2-XSe NPs is 90.3 %. For first cycle analysis. The pseudo-first order and second order models were used to analyze the kinetic data of Cu2-XSe NPs for varying concentrations. The multiple-cycle degradation analysis by catalyst of MB dye in one day spam for continuous four cycles were also analysed and discussed. The sun light driven multi-cycle catalytic degradation confirms the re-usability of Cu2-xSe NPs for the treatment of industrial waste water and other contaminated water bodies for the survival of aquatic life and for saving environment.

Combined Role of {001} Facet-Enriched Morphology and Gold Nanoparticle Deposition on Anatase TiO2 Photoactivity

The interplay on anatase TiO2 photoactivity between particle morphology and gold nanoparticles (NPs) deposition, via either deposition-precipitation (DP) or photodeposition (P), is here investigated by evaluating the photoactivity of Au modified anatase (Au/TiO2) nanocrystals with either a pseudospherical shape or a nanosheet structure in both reduction and oxidation test reactions. The presence of Au NPs on the anatase surface only slightly affects its photoactivity in Cr(VI) reduction, which is kinetically limited by the anodic half-reaction, whereas a larger exposure of highly oxidant {001} facets is beneficial for overcoming this rate-determining step. In the photocatalytic oxidation of both formic acid, proceeding through a direct mechanism, and rhodamine B (RhB) on surface fluorinated photocatalysts, occurring through a hydroxyl-radical-mediated mechanism, the presence of gold NPs produces a significant photoactivity increase only with spherically shaped photocatalysts, mainly exposing {101} facets. These results are rationalized in light of the preferential migration of photogenerated, oppositely charged carriers toward different crystal facets. In fact, when the Au/TiO2 material mainly exposes the more oxidant {001} facets, where photoproduced holes preferentially migrate, recombination between these latter and the electrons captured by Au NPs is favored. Instead, Au NPs on {101} facets efficiently capture photopromoted electrons, preferentially migrating toward such facets with a consequent improvement of photoproduced charge separation.

Arsenite removal by using ZnAlFe mixed metal oxides derived from layered double hydroxides

ZnAlFe mixed metal oxides (ZnAlFe-MMOs) were synthesized from layered double hydroxides (LDHs) prepared by the coprecipitation method at pH 9 using an initial weight composition of Zn2+ = 75%, Al3+ = 15% and Fe3+ = 10%, with or without the addition of citric or oxalic acid. The solids were calcined at 400 °C to obtain the respective MMOs, which exhibited relatively high specific surface areas (165.3-63.8 m2 g-1) and semiconductor properties active in the visible region (bandgap values (Eg) of 2.42-1.77 eV). The synthesized materials were tested for the removal of trivalent arsenic by adsorption and by photocatalysis under visible light irradiation (λ ≥ 420 nm). The best removal of As(III) by adsorption (65.9%) and by photocatalysis (99.9%) was obtained with the ZnAlFe-MMOs prepared in the absence of organic acids. The XPS results indicate the coexistence of As3+ and As5+ over ZnAlFe-MMOs after the photocatalytic reaction and also confirm the formation of Fe2+ sites on the hematite surface that enhances the removal of As(III). Raman measurements confirmed that, in the photocatalytic experiments, As is largely retained as As(V) on ZnAlFe-MMOs, bound to Fe. The results of fluorescence of 7-hydroxycoumarin suggest that the photocatalyst produces HO•, which can be the main species for As(III) oxidation under UV-Vis irradiation. Moreover, ZnAlFe-MMOs exhibited a good reusability after regeneration making ZnAlFe-MMOs a promising material for arsenic decontamination in polluted water.

Support based metal incorporated layered nanomaterials for photocatalytic degradation of organic pollutants

An effective approach to producing sophisticated miniaturized and nanoscale materials involves arranging nanomaterials into layered hierarchical frameworks. Nanostructured layered materials are constructed to possess isolated propagation assets, massive surface areas, and envisioned amenities, making them suitable for a variety of established and novel applications. The utilization of various techniques to create nanostructures adorned with metal nanoparticles provides a secure alternative or reinforcement for the existing physicochemical methods. Supported metal nanoparticles are preferred due to their ease of recovery and usage. Researchers have extensively studied the catalytic properties of noble metal nanoparticles using various selective oxidation and hydrogenation procedures. Despite the numerous advantages of metal-based nanoparticles (NPs), their catalytic potential remains incompletely explored. This article examines metal-based nanomaterials that are supported by layers, and provides an analysis of their manufacturing, procedures, and synthesis. This study incorporates both 2D and 3D layered nanomaterials because of their distinctive layered architectures. This review focuses on the most common metal-supported nanocomposites and methodologies used for photocatalytic degradation of organic dyes employing layered nanomaterials. The comprehensive examination of biological and ecological cleaning and treatment techniques discussed in this article has paved the way for the exploration of cutting-edge technologies that can contribute to the establishment of a sustainable future.

Eco-Friendly Photocatalytic Solutions: Synthesized TiO2 Nanoparticles in Cellulose Membranes for Enhanced Degradation of Indigo Carmine Dye

This study focuses on comparing the efficiency of commercially available TiO2 (P25) with synthesized TiO2 nanoparticles (TiO2NP) impregnated in nonmodified cellulose membranes, specifically targeting the degradation of Indigo Carmine (IC) dye. We developed a novel method to enhance the interaction between cellulose and TiO2, thereby improving efficiency and reusability. This involves dissolving microcrystalline cellulose in 1-butyl-3-methylimidazolium chloride (BMImCl) and dispersing the TiO2 samples within this solution. The resulting cellulose membrane embedded with TiO2 nanoparticles (TiO2NP) exhibited a higher adsorption capacity and greater photocatalytic efficiency against IC compared to that of P25. This improvement is attributed to the larger surface area and increased reactivity of the synthesized TiO2NPs. Furthermore, the CEL_TiO2NP membranes demonstrated excellent stability and reusability, maintaining their catalytic efficiency over multiple cycles. This study presents new opportunities for developing efficient, reusable photocatalytic materials for environmental remediation using eco-friendly cellulose.

Design and Preparation of Heterostructured Cu2O/TiO2 Materials for Photocatalytic Applications

The extensive use of fossil fuels has sped up the global development of the world economy and is accompanied by significant problems, such as energy shortages and environmental pollution. Solar energy, an inexhaustible and clean energy resource, has emerged as a promising sustainable alternative. Light irradiation can be transformed into electrical/chemical energy, which can be used to remove pollutants or transform contaminants into high-value-added chemicals through photocatalytic reactions. Therefore, photocatalysis is a promising strategy to overcome the increasing energy and environmental problems. As is well-known, photocatalysts are key components of photocatalytic systems. Among the widely investigated photocatalysts, titanium dioxide (TiO2) has attracted great attention owing to its excellent light-driven redox capability and photochemical stability. However, its poor solar light response and rapid recombination of electron-hole pairs limit its photocatalytic applications. Therefore, strategies to enhance the photocatalytic activity of TiO2 by narrowing its bandgap and inhibiting the recombination of charges have been widely accepted. Constructing heterojunctions with other components, including cuprous oxide (Cu2O), has especially narrowed the bandgap, providing a promising means of solving the present challenges. This paper reviews the advances in research on heterostructured Cu2O/TiO2 photocatalysts, such as their synthesis methods, mechanisms for the enhancement of photocatalytic performance, and their applications in hydrogen production, CO2 reduction, selective synthesis, and the degradation of pollutants. The mechanism of charge separation and transfer through the Cu2O/TiO2 heterojunctions and the inherent factors that lead to the enhancement of photocatalytic performance are extensively discussed. Additionally, the current challenges in and future perspectives on the use of heterostructured Cu2O/TiO2 photocatalysts are also highlighted.

Facile synthesis of TiO2-carbon composite doped nitrogen for efficient photodegradation of noxious methylene blue dye

The present work shows that the degrading ability of TiO2 is significantly improved when exposed to light, particularly in relation to the organic dye methylene blue (MB), following the introduction of a carbon framework through sol-hydrothermal synthesis approach. The newly prepared TiO2-C@N composite had the ability to function as both an adsorbent and a photocatalyst to eliminate MB from contaminated wastewater. The outcomes show the removal efficiency of MB amounts to 99.87% upon the application of UV radiation, which is much higher than the rate achieved under dark conditions (28.9%). As ascertained by the kinetic study, the degradation of methylene blue (MB) under UV light through photocatalysis using the TiO2-C@N photocatalyst conformed to the widely recognized pseudo-first order (PFO) model. TiO2-C@N photocatalyst showed outstanding reliability and reusability, maintaining consistent degradation efficiency over five consecutive cycles without any obvious decline. The materials were characterized by XRD, XPS, FE-SEM, EDS, and N2 adsorption-desorption measurements. Nanometer-sized particles, a unique surface dominance, high surface area, large pore volume ratios, low band gap, high oxygen vacancies, increased pollution absorptivity, and reduced electron-hole pair recombination characterize the monolithic TiO2-C@N photocatalyst over TiO2. These unique features render TiO2-C@N a promising catalyst in effectively breaking down noxious MB organic pollutants through photodegradation.

Clay Minerals/TiO2 Composites-Characterization and Application in Photocatalytic Degradation of Water Pollutants

TiO2 used for photocatalytic water purification is most active in the form of nanoparticles (NP), but their use is fraught with difficulties in separation from solution or/and a tendency to agglomerate. The novel materials designed in this work circumvent these problems by immobilizing TiO2 NPs on the surface of exfoliated clay minerals. A series of TiO2/clay mineral composites were obtained using five different clay components: the Na-, CTA-, or H-form of montmorillonite (Mt) and Na- or CTA-form of laponite (Lap). The TiO2 component was prepared using the inverse microemulsion method. The composites were characterized with X-ray diffraction, scanning/transmission electron microscopy/energy dispersive X-ray spectroscopy, FTIR spectroscopy, thermal analysis, and N2 adsorption-desorption isotherms. It was shown that upon composite synthesis, the Mt interlayer became filled by a mixture of CTA+ and hydronium ions, regardless of the nature of the parent clay, while the structure of Lap underwent partial destruction. The composites displayed high specific surface area and uniform mesoporosity determined by the size of the TiO2 nanoparticles. The best textural parameters were shown by composites containing clay components whose structure was partially destroyed; for instance, Ti/CTA-Lap had a specific surface area of 420 m2g-1 and a pore volume of 0.653 cm3g-1. The materials were tested in the photodegradation of methyl orange and humic acid upon UV irradiation. The photocatalytic activity could be correlated with the development of textural properties. In both reactions, the performance of the most photoactive composites surpassed that of the reference commercial P25 titania.

Theoretical investigations of optoelectronic properties, photocatalytic performance as a water splitting photocatalyst and band gap engineering with transition metals (TM = Fe and Co) of K3VO4, Na3VO4 and Zn3V2O8: a first-principles study

First-principles density functional investigations of the structural, electronic, optical and thermodynamic properties of K3VO4, Na3VO4 and Zn3V2O8 were performed using generalized gradient approximation (GGA) via ultrasoft pseudopotential and density functional theory (DFT). Their electronic structure was analyzed with a focus on the nature of electronic states near band edges. The electronic band structure revealed that between 6% Fe and 6% Co, 6% Co significantly tuned the band gap with the emergence of new states at the gamma point. Notable variations were highlighted in the electronic properties of Na3V(1-x)Fe x O4, Na3V(1-x)Co x O4, K3V(1-x)Fe x O4, K3V(1-x)Co x O4, Zn3(1-x)V2(1-x)Co x O8 and Zn3(1-x)V2(1-x)Fe x O8 (where x = 0.06) due to the different natures of the unoccupied 3d states of Fe and Co. Density of states analysis as well as α (spin up) and β (spin down) magnetic moments showed that cobalt can reduce the band gap by positioning the valence band higher than O 2p orbitals and the conduction band lower than V 3d orbitals. Mulliken charge distribution revealed the presence of the 6s2 lone pair on Zn, greater population and short bond length in V-O bonds. Hence, the hardness and covalent character develops owing to the V-O bond. Elastic properties, including bulk modulus, shear modulus, Pugh ratio and Poisson ratio, were computed and showed Zn3V2O8 to be mechanically more stable than Na3VO4 and K3VO4. Optimal values of optical properties, such as absorption, reflectivity, dielectric function, refractive index and loss functions, demonstrated Zn3V2O8 as an efficient photocatalytic compound. The optimum trend within finite temperature ranges utilizing quasi-harmonic technique is illustrated by calculating thermodynamic parameters. Theoretical investigations presented here will open up a new line of exploration of the photocatalytic characteristics of orthovanadates.

Superhydrophobicity, Photocatalytic Self-Cleaning and Biocidal Activity Combined in a Siloxane-ZnO Composite for the Protection of Limestone

The erosion phenomena of the natural stone in cultural heritage are induced by various sources. Consequently, the development of multifunctional protective materials that combine two or more useful properties is an effective strategy in addressing the synergistic effects of various erosion mechanisms. A multifunctional coating, consisting of a silane-based precursor and zinc oxide (ZnO) nanoparticles (NPs), is produced and tested for the protection of limestone. The hybrid coating combines the following three properties: superhydrophobicity, including water-repellency, photocatalytic self-cleaning and biocidal activity. The relative concentration of the NPs (0.8% w/w), used for the suggested composite coating, is carefully selected according to wetting studies, colourimetric measurements and durability (tape peeling) tests. The non-wetting state is evidenced on the surface of the composite coating by the large contact angle of water drops (≈153°) and the small contact angle hysteresis (≈5°), which gives rise to a physical self-cleaning scenario (lotus effect). The photocatalytic chemical self-cleaning is shown with the removal of methylene blue, induced by UV-A radiation. Moreover, it is shown that the suggested coating hinders the incubation of E. coli and S. aureus, as the inhibitions are 94.8 and 99.9%, respectively. Finally, preliminary studies reveal the chemical stability of the suggested coating.

Synthesis of Fe2O3/TiO2 Photocatalytic Composites for Methylene Blue Degradation as a Novel Strategy for High-Value Utilisation of Iron Scales

In this study, novel Fe2O3/TiO2 photocatalytic composites were synthesised by combining traditional oxidation roasting with the sol-gel method, using low-cost metallurgical waste (iron scales) as the raw material. The characterisation results revealed that the oxidised iron scales could be transformed into high-purity and porous Fe2O3 particles through oxidation roasting, thereby providing additional sites for the adsorption process and thus serving as an effective carrier for TiO2-based photocatalytic materials. During the sol-gel process, TiO2 was loaded onto the synthesised Fe2O3 particles, generating core-shell heterostructure Fe2O3/TiO2 photocatalytic composites. Under visible light irradiation for 90 min, the Fe2O3/TiO2 photocatalytic composites achieved a remarkable methylene blue removal rate (97.71%). This reaction process followed the quasi-first-order kinetic model with a rate constant of 0.038 min-1. The results have demonstrated that this combination of various components in the Fe2O3/TiO2 photocatalytic composites improved the adsorption, light utilisation, and charge separation effect of the photocatalysts. Moreover, the material exhibited favourable stability and recyclability, making it a decent candidate for the treatment of wastewater from the biochemical industry. Therefore, this study provides a new strategy for improving the photocatalytic activity of TiO2 and expanding the high value-added utilisation of iron scales.

Easy and green synthesis of nano-ZnO and nano-TiO2 for efficient photocatalytic degradation of organic pollutants

As the textile industry expands, more industrial waste effluents are released into natural water streams, prompting the research and development of innovative materials for the remediation of environmental issues. In this research, a direct precipitation and hydrolysis method were used to synthesize ZnO and TiO2 nanoparticles, respectively that were utilized to investigate the photocatalytic activity of Congo Red (CR) dye. Afterward, the crystallite size was computed from the data of the X-ray diffractometer (XRD), and utilizing several models (Scherrer equation, LSLMSE, Monshi-Scherrer equation, Williamson-Hall model, Size-strain plot method, Halder-Wagner model, Sahadat-Scherrer model). Among these models, the size-strain plot model yields the most accurate crystal size (45.31 nm) for ZnO nanoparticles and the Halder-Wagner model (2.44 nm) for TiO2 nanoparticles. Scanning Electron Microscope exhibited the spherical shape of nanoparticles (ZnO, and TiO2) with particle size (less than 151 nm). The absorption spectrum from Fourier transform infrared (FTIR) spectroscopy confirmed the formation of nanoparticles (ZnO, and TiO2). Thereafter, the photocatalytic activity of the ZnO-TiO2 nanocomposite was evaluated by using Congo Red (CR) dye under different process variables, such as catalyst dose, time, initial dye concentration, pH, radical scavenging ability, and reusability. The best degradation (90 %) was recorded at 180 min time intervals using a 0.2 g catalyst dose with a 20 ppm CR concentration at pH 9.

Ba2+-doping introduced piezoelectricity and efficient Ultrasound-Triggered bactericidal activity of brookite TiO2 nanorods

Exploring highly efficient ultrasound-triggered catalysts is pivotal for various areas. Herein, we presented that Ba2+ doped brookite TiO2 nanorod (TiO2: Ba) with polarization-induced charge separation is a candidate. The replacement of Ba2+ for Ti4+ not only induced significant lattice distortion to induce polarization but also created oxygen vacancy defects for facilitating the charge separation, leading to high-efficiency reactive oxygen species (ROS) evolution in the piezo-catalytic processes. Furthermore, the piezocatalytic ability to degrade dye wastewater demonstrates a rate constant of 0.172 min-1 and achieves a 100 % antibacterial rate at a low dose for eliminating E. coli. This study advances that doping can induce piezoelectricity and reveals that lattice distortion-induced polarization and vacancy defects engineering can improve ROS production, which might impact applications such as water disinfection and sonodynamic therapy.

Impact of LED radiation intensity on gold nanoparticles photodeposition on TiO2 with physicochemical and photocatalytic characterization

This study investigates the influence of LED radiation intensity on the photodeposition of gold nanoparticles onto TiO2 substrates, examining their physicochemical properties and photocatalytic activities. Utilizing a range of radiation intensities and wavelengths, TiO2-Au composites were synthesized and characterized through techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS). The deposition process, markedly enhanced by shorter wavelengths and higher intensities, efficiently formed gold nanoparticles. This research distinctly highlights observable morphological changes in the nanoparticles; increased radiation intensity not only augmented the size but also altered their shape from spherical to hexagonal. These morphological transformations significantly improve the composites' light absorption and catalytic properties due to the surface plasmon resonance of the gold nanoparticles. Photocatalytic assessments, using metronidazole as a model pollutant, demonstrated that composites prepared with higher LED intensities showed significantly enhanced degradation capabilities compared to those synthesized with lower intensities. The findings underscore that manipulating photodeposition parameters can critically influence the structural and functional properties of TiO2-Au composites, potentially advancing their applications in environmental remediation and solar energy utilization.

Exploring structural and optical properties of iodine-doped TiO2 nanoparticles in Rhodamine-B dye degradation: Experimental and theoretical investigation

Energy conversion and pollutant degradation are critical for advancing sustainable technologies, yet they often encounter challenges related to charge recombination and efficiency limitations. This study explores iodine-doped TiO2 nanoparticles as a potential solution for enhancing both energy conversion and pollutant degradation. The nanoparticles were synthesized via the sol-gel method with varying iodine precursor concentrations (0.025-0.1 M) and were characterized for their structural, compositional, and optical properties, particularly in relation to their photocatalytic performance in Rhodamine-B dye degradation. X-ray diffraction confirmed a tetragonal anatase crystal structure, with the average crystallite size decreasing from 10.06 nm to 8.82 nm with increase in iodine concentration. Selected area electron diffraction patterns verified the polycrystalline nature of the nanoparticles. Dynamic light scattering analysis showed hydrodynamic radii ranging from 95 to 125 nm. Fourier-transform infrared spectroscopy identified metal-oxygen vibrations at 441 cm⁻1, and electron microscopy confirmed the spherical morphology of the nanoparticles. Elemental analysis detected the presence of Ti, O, and I in the samples. Diffuse reflectance spectroscopy indicated the optical absorption edges for the doped samples in the visible region from which the corresponding band gap values were deduced. Photoluminescence spectroscopy revealed that the sample with 0.1 M iodine exhibit the lowest emission intensity, suggesting reduced charge recombination. Notably, 0.1 M iodine doped TiO2 samples demonstrated the highest photocatalytic efficiency, achieving 82.36% degradation of Rhodamine-B dye within 140 min under visible light. Additionally, ab-initio density functional theory calculations were performed to investigate the structural, optical, and adsorption properties of TiO2, iodine-doped TiO2, Rhodamine-B, and their composites, providing further insight into the enhanced photocatalytic activity observed in the experiments.

Photostability evaluation of manidipine tablets and structural determination of its photoproducts

Manidipine (MP) is a dihydropyridine drug, which is treated for the reduction of high blood pressure. The aim of this study is to clarify the photochemical behavior of MP in the case of ultraviolet light (UV) irradiation for MP tablets (Calslot® tablets). The tablets and its altered forms (powders and suspensions) were UV-irradiated using a black light, and residual amounts of active pharmaceutical ingredients (APIs) were monitored by high-performance liquid chromatography (HPLC). Due to the photoproducts of MP were detected in HPLC chromatograms, the elucidation of their chemical structures was carried out utilizing electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). As a result, APIs in Calslot® tablets were almost completely photodegraded in the case that Calslot® tablets were suspended in an aqueous media along with the generation of some MP photoproducts. LC-ESI-MS/MS analysis clarified the chemical structures of three MP photoproducts, indicating that they were a pyridine analogue, benzophenone and a hydrolysate. Benzophenone was a main MP photoproduct. It was possible that MP might be firstly oxidized to form its pyridine analogue, followed by the oxidation of a dimethyl methylene moiety. This moiety seemed to be eliminated as a benzophenone, and the cleavage of an ester bond of the residual moiety resulted in the generation of a hydrolysate. Finally, toxicological potencies of MP and its photoproducts were predicted in silico toxicity evaluation, suggesting some of biological effects of the photoproducts might be altered compared with MP.

Hydrothermally Grown Globosa-like TiO2 Nanostructures for Effective Photocatalytic Dye Degradation and LPG Sensing

The rapid expansion of industrial activities has resulted in severe environmental pollution manifested by organic dyes discharged from the food, textile, and leather industries, as well as hazardous gas emissions from various industrial processes. Titanium dioxide (TiO2)-nanostructured materials have emerged as promising candidates for effective photocatalytic dye degradation and gas sensing applications owing to their unique physicochemical properties. This study investigates the development of a photocatalyst and a liquefied petroleum gas (LPG) sensor using hydrothermally synthesized globosa-like TiO2 nanostructures (GTNs). The synthesized GTNs are then evaluated to photocatalytically degrade methylene blue dye, resulting in an outstanding photocatalytic activity of 91% degradation within 160 min under UV light irradiation. Furthermore, these nanostructures are utilized to sense liquefied petroleum gas, which attains a superior sensitivity of 7.3% with high response and recovery times and good reproducibility. This facile and cost-effective hydrothermal method of fabricating TiO2 nanostructures opens a new avenue in photocatalytic dye degradation and gas sensing applications.

Metal oxide-based photocatalysts for the efficient degradation of organic pollutants for a sustainable environment: a review

Photocatalytic degradation is a highly efficient technique for eliminating organic pollutants such as antibiotics, organic dyes, toluene, nitrobenzene, cyclohexane, and refinery oil from the environment. The effects of operating conditions, concentrations of contaminants and catalysts, and their impact on the rate of deterioration are the key focuses of this review. This method utilizes light-activated semiconductor catalysts to generate reactive oxygen species that break down contaminants. Modified photocatalysts, such as metal oxides, doped metal oxides, and composite materials, enhance the effectiveness of photocatalytic degradation by improving light absorption and charge separation. Furthermore, operational conditions such as pH, temperature, and light intensity also play a crucial role in enhancing the degradation process. The results indicated that both high pollutant and catalyst concentrations improve the degradation rate up to a threshold, beyond which no significant benefits are observed. The optimal operational conditions were found to significantly enhance photocatalytic efficiency, with a marked increase in degradation rates under ideal settings. Antibiotics and organic dyes generally follow intricate degradation pathways, resulting in the breakdown of these substances into smaller, less detrimental compounds. On the other hand, hydrocarbons such as toluene and cyclohexane, along with nitrobenzene, may necessitate many stages to achieve complete mineralization. Several factors that affect the efficiency of degradation are the characteristics of the photocatalyst, pollutant concentration, light intensity, and the existence of co-catalysts. This approach offers a sustainable alternative for minimizing the amount of organic pollutants present in the environment, contributing to cleaner air and water. Photocatalytic degradation hence holds tremendous potential for remediation of the environment.

Fabrication of a highly efficient CuO/ZnCo2O4/CNTs ternary composite for photocatalytic degradation of hazardous pollutants

In the current study, CuO, ZnCo2O4, CuO/ZnCo2O4, and CuO/ZnCo2O4/CNTs photocatalysts were prepared to remove crystal violet (CV) and colorless pollutants (diclofenac sodium and phenol) from wastewater. Herein, sol-gel and co-precipitation methods were used to synthesize CuO and ZnCo2O4, respectively. The sonication method was used to synthesize CuO/ZnCo2O4 and a CNTs-based composite (CuO/ZnCo2O4/CNTs). From the UV-Vis spectra of CuO, ZnCo2O4, CuO/ZnCo2O4, and CuO/ZnCo2O4/CNTs, the optical band gap value was calculated to be 2.11, 2.18, 1.71 and 1.63 eV respectively. The photocatalytic results revealed that CuO/ZnCo2O4/CNTs exhibited higher degradation of 87.7% against CV dye, 82% against diclofenac sodium, and 72% against phenol as compared to other prepared photocatalysts. The OH˙ radical is identified as the active species in the photocatalytic process over CuO/ZnCo2O4/CNTs. The impact of several parameters, such as pH, concentration, and catalyst dosage, has also been investigated. The better activity of the CNTs-based composite was due to the synergic effect of both CuO/ZnCo2O4 nanocomposite and carbon nanotubes. Therefore, the synthesized CuO/ZnCo2O4/CNTs photocatalyst has the potential to degrade organic wastewater effluents effectively.