An overview of semiconductor photocatalysis

Size Dependent Photocatalytic Activity of Mesoporous ZnIn2S4 Nanocrystal Networks

Understanding of the band-edge electronic structure and charge-transfer dynamics in size-confined nanostructures is vital in designing new materials for energy conversion applications, including green hydrogen production, decomposition of organic pollutants and solar cells. In this study, a series of mesoporous materials comprising continuous networks of linked zinc indium sulfide (ZnIn2S4) nanocrystals with a tunable diameter (ranging from 4 to 12 nm) is reported. These nanomaterials demonstrate intriguing size-dependent electronic properties, charge-transfer kinetics and photocatalytic behaviors. Our extensive characterizations uncover strong size effects on the catalytic activity of constituent ZnIn2S4 nanocrystals in the photochemical hydrogen evolution reaction. As an outcome, the optimized single-component ZnIn2S4 mesostructure produces hydrogen at a 7.8 mmol gcat -1 h-1 release rate under ultraviolet (UV)-visible light irradiation associated with an apparent quantum yield (AQY) of 17.2% at 420 ± 10 nm, far surpassing its microstructured counterpart by a factor of 10.7×. These findings provide a valuable perspective for the rational design of semiconductor nanostructures through synthetic engineering, aiming at the development of high-performance catalysts for zero-carbon energy-related applications.

Self-sensitized photodegradation and adsorption of aqueous malachite green dye using one-dimensional titanium oxide nanofilaments

Truly one-dimensional titanium oxide nanofilaments with a lepidocrocite structure (1DLs) were explored in the adsorption and photocatalytic degradation of aqueous malachite green (MG), a toxic polluting dye. Decolorization is monitored by ultraviolet-visible spectroscopy, and mineralization is confirmed by total organic carbon analysis. The 1DL/MG flocs are characterized by scanning electron microscopy and X-ray diffraction. 1DLs, a colloidal nanomaterial, exhibit flocculating behavior while demonstrating high affinity for MG, with a maximum uptake of >680 mg/g rapidly via ion exchange. Additionally, 1DLs decolorize MG under visible light only, unlike most available titania products, via a self-sensitization effect. MG is decolorized by 1DLs by >70% in 30 min under 1 sun exposure of visible light. Counterintuitively, dye adsorption increases as the normalized concentration by mass of 1DL decreases. Demonstrating high adsorption capacity and dye mineralization supports the use of 1DLs in water treatment and self-sensitization for photoelectrochemical devices, like solar cells.

Synthesis and Photo/Radiation Chemical Characterization of a New Redox-Stable Pyridine-Triazole Ligand

Photocatalysis using transition-metal complexes is widely considered the future of effective and affordable clean-air technology. In particular, redox-stable, easily accessible ligands are decisive. Here, we report a straightforward and facile synthesis of a new highly stable 2,6-bis(triazolyl)pyridine ligand, containing a nitrile moiety as a masked anchoring group, using copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction. The reported structure mimics the binding motif of uneasy to synthesize ligands. Pulse radiolysis under oxidizing and reducing conditions provided evidence for the high stability of the formed radical cation and radical anion 2,6-di(1,2,3-triazol-1-yl)-pyridine compound, thus indicating the feasibility of utilizing this as a ligand for redox active metal complexes and the sensitization of metal-oxide semiconductors (e. g., TiO2 nanoparticles or nanotubes).

Perspectives for Photocatalytic Decomposition of Environmental Pollutants on Photoactive Particles of Soil Minerals

The literature shows that both in laboratory and in industrial conditions, the photocatalytic oxidation method copes quite well with degradation of most environmental toxins and pathogenic microorganisms. However, the effective utilization of photocatalytic processes for environmental decontamination and disinfection requires significant technological advancement in both the area of semiconductor material synthesis and its application. Here, we focused on the presence and "photocatalytic capability" of photocatalysts among soil minerals and their potential contributions to the environmental decontamination in vitro and in vivo. Reactions caused by sunlight on the soil surface are involved in its normal redox activity, taking part also in the soil decontamination. However, their importance for decontamination in vivo cannot be overstated, due to the diversity of soils on the Earth, which is caused by the environmental conditions, such as climate, parent material, relief, vegetation, etc. The sunlight-induced reactions are just a part of complicated soil chemistry processes dependent on a plethora of environmental determinates. The multiplicity of affecting factors, which we tried to sketch from the perspective of chemists and environmental scientists, makes us rather skeptical about the effectiveness of the photocatalytic decontamination in vivo. On the other hand, there is a huge potential of the soils as the alternative and probably cheaper source of useful photocatalytic materials of unique properties. In our opinion, establishing collaboration between experts from different disciplines is the most crucial opportunity, as well as a challenge, for the advancement of photocatalysis.

Wavelength-Dependent Activity of Oxygen Species in Propane Conversion on Rutile TiO2(110)

Photocatalytic oxidative dehydrogenation of propane (C3H8) into propene (C3H6) under mild conditions holds great potential in the chemical industry, but understanding how active species participate in C3H8 conversion remains a significant challenge. Here, the wavelength-dependent activities of bridging oxygen (Ob2-) and the Ti5c-bound oxygen adatom (OTi2-) of model rutile (R) TiO2(110) in C3H8 conversion have been investigated. Under 257 and 343 nm irradiation, hole-trapped OTi- and Ob- can abstract the hydrogen atom of C3H8, forming the CH3CH•CH3 radical and C3H6. However, the rate of C3H8 conversion with hole-trapped Ob- is strongly dependent on the wavelength, primarily producing the C3H7• radical. In the case of hole-trapped OTi-, C3H6 is the main product, which is nearly independent of wavelength. The differences in the wavelength-dependent activity and product selectivity are likely due to dynamic control rather than thermodynamic control. The result provides a deeper understanding of the dynamic processes involved in the conversion of light alkanes in TiO2 photocatalysis.

Particles-involved photochemical processes: A review for the case of mercury reduction in relation to aquatic mercury cycling

Mercury (Hg) is one of the toxic metals of global and environmental concern, with aquatic Hg cycling being central in determining the production of highly toxic methylmercury and the air-water Hg exchange influencing the long-range intercontinental atmospheric Hg transport. Both inorganic and organic forms of Hg can be bound by suspended particles, including inorganic minerals (in particular metal oxides/sulfides) and particulate organic matter. Photochemical transformation is a critical process in surface water, and the role of suspended particles in Hg redox photoreactions has increasingly emerged, albeit in limited studies in comparison to extensive studies on aqueous (homogeneous) photoreactions of Hg. The lack of understanding of what roles suspended particles play might result in inaccurate estimation of how Hg species transform and/or cycle in the environment. In view of this gap, this paper critically reviews and synthesizes information on the studies conducted on different natural surface waters with respect to the potential roles of suspended particles on Hg photo-redox reactions. It robustly discusses the various possible pathways and/or mechanisms of particle-mediated Hg (II) reduction, in enhancing or lowering the production of dissolved gaseous mercury. These processes include photo hole-electron pair formation and reactive oxygen species generation from particle excitation and their involvement in Hg photoreduction, in addition to the light attenuation effect of particles. This paper highlights the necessity of future studies exploiting these particles-mediated Hg photoreactions pathways and the implications of including these heterogeneous photoreactions (together with particulate elemental Hg species) on the air-water Hg exchange estimation.

High power illumination system for uniform, isotropic and real time controlled irradiance in photoactivated processes research

In the study of photocatalytic and photoactivated processes and devices a tight control on the illumination conditions is mandatory. The practical challenges in the determination of the necessary photonic quantities pose serious difficulties in the characterization of catalytic performance and reactor designs and configurations, compromising an effective comparison between different experiments. To overcome these limitations, we have designed and constructed a new illumination system based in the concept of the integrating sphere (IS). The system provides uniform and isotropic illumination on the sample, either in batch or continuous flow modes, being these characteristics independent of the sample geometry. It allows direct, non-contact and real time determination of the photonic quantities as well as versatile control on the irradiance values and its spectral characteristics. It can be also scaled up to admit samples of different sizes without affecting its operational behaviour. The performance of the IS system has been determined in comparison with a second illumination system, mounted on an optical bench, that provides quasi-parallel beam (QPB) nearly uniform illumination in tightly controlled conditions. System performance is studied using three sample geometries: a standard quartz cuvette, a thin straight tube and a microreactor by means of potassium ferrioxalate actinometry. Results indicate that the illumination geometry and the angular distribution of the incoming light greatly affect the absorption at the sample. The sample light absorption efficiency can be obtained with statistical uncertainties of about 3% and in very good agreement with theoretical estimations.

Unraveling the Impact of Adsorbed Molecules on Photocatalytic Processes: Advancements in Understanding Facet-Controlled Semiconductor Photocatalysts

This work aims to demonstrate that the Fe2O3 nanocrystals' adsorptive and photocatalytic properties can be adjusted by exposing the crystal facets that are functionalized. To this end, cube- and disc-like structures were synthesized using a metal ion-mediated hydrothermal route. Thereafter, some of the samples were annealed at 500 °C for 3 h. Our paper combines the experimental part with theoretical calculations of the obtained materials' band edge positions. The results reveal that-aside from hematite-the as-synthesized discs also contain γ-FeOOH and β-Fe2O3 phases, which transform into α-Fe2O3 during annealing. The hydrodynamic diameter, zeta potential, and adsorption kinetics measurements show that the cube-like samples exhibit the highest affinity for cationic, whereas the discs have an affinity for anionic dye. Measurements of the wall zeta potential also reveal that annealing the discs modifies their surface state and ability to adsorb molecules. Photocatalytic tests show that the as-synthesized powders have better photocatalytic performance toward methylene blue decomposition than the annealed ones. The observed small changes in the concentration of the MO during illumination result from the energy band structure of the cube-like crystal orientation.

Photocatalytic activity enhancement of nanostructured metal-oxides photocatalyst: a review

Nanostructured metal oxide semiconductors have emerged as promising nanoscale photocatalysts due to their excellent photosensitivity, chemical stability, non-toxicity, and biocompatibility. Enhancing the photocatalytic activity of metal oxide is critical in improving their efficiency in radical ion production upon optical exposure for various applications. Therefore, this review paper provides an in-depth analysis of the photocatalytic activity of nanostructured metal oxides, including the photocatalytic mechanism, factors affecting the photocatalytic efficiency, and approaches taken to boost the photocatalytic performance through structure or material modifications. This paper also highlights an overview of the recent applications and discusses the recent advancement of ZnO-based nanocomposite as a promising photocatalytic material for environmental remediation, energy conversion, and biomedical applications.

Anti-Environmental Aging Passive Daytime Radiative Cooling

Passive daytime radiative cooling technology presents a sustainable solution for combating global warming and accompanying extreme weather, with great potential for diverse applications. The key characteristics of this cooling technology are the ability to reflect most sunlight and radiate heat through the atmospheric transparency window. However, the required high solar reflectance is easily affected by environmental aging, rendering the cooling ineffective. In recent years, significant advancements have been made in understanding the failure mechanisms, design strategies, and manufacturing technologies of daytime radiative cooling. Herein, a critical review on anti-environmental aging passive daytime radiative cooling with the goal of advancing their commercial applications is presented. It is first introduced the optical mechanisms and optimization principles of radiative cooling, which serve as a basis for further endowing environmental durability. Then the environmental aging conditions of passive daytime radiative cooling, mainly focusing on UV exposure, thermal aging, surface contamination and chemical corrosion are discussed. Furthermore, the developments of anti-environmental aging passive daytime radiative cooling materials, including design strategies, fabrication techniques, structures, and performances, are reviewed and classified for the first time. Last but not the least, the remaining open challenges and the insights are presented for the further promotion of the commercialization progress.

Multicomponent Photocatalytic-Dispersant System for Oil Spill Remediation

In the present work, the potential application of a fabricated halloysite nanotubes-Ag-TiO2 (HNT-Ag-TiO2) composite loaded with a binary surfactant mixture made up of lecithin and Tween 80 (LT80) in remediating oil spillages was examined. The as-prepared Ag-TiO2 that was used in the fabrication of the HNT-Ag-TiO2-LT80 composite was characterized by X-ray diffraction, Raman spectroscopy, UV-vis and diffuse reflectance spectroscopy, CV analyses, and SEM-EDX. The synthesized composite was also characterized by thermogravimetric analysis, Fourier-transform infrared spectroscopy, and scanning electron microscopy-energy dispersive X-ray spectroscopy. The synthesized composite was active in both the UV and visible light regions of the electromagnetic spectrum. The oil-remediating potential of the as-prepared composite was examined on crude oil, and aromatics and asphaltene fractions of crude oil. The composite was able to reduce the surface tension, form stable emulsions and smaller oil droplet sizes, and achieve a high dispersion effectiveness of 91.5%. A mixture of each of the crude oil and its fractions and HNT-Ag-TiO2-LT80 was subjected to photodegradation under UV light irradiation. The results from the GC-MS and UV-vis analysis of the photodegraded crude oil revealed that the photocatal composite was able to photodegrade the crude oil, aromatics, and asphaltene fractions of crude oil with the formation of intermediate photodegradation products depicting that the HNT-Ag-TiO2-LT80 has a potential as an oil spill remediation material.

Effluent toxicity study using biomarkers for ciprofloxacin photoelectrocatalytic degradation by bismuth-doped titanium dioxide nanotubes

Ciprofloxacin hydrochloride (CIP) is a broad-spectrum synthetic antibiotic often found in domestic sewage and industrial waste due to the inefficiency of conventional treatments. Given the potential risk of drug accumulation, this study presents coatings of titanium dioxide nanotubes (TiO2) doped with different bismuth (Bi) concentrations to degrade CIP through photocatalytic and photoelectrochemical processes. Characterization studies revealed that bismuth (Bi) doping affected the morphology of the materials, with concentrations of 0.01 and 0.05 mol L-1, resulting in collapsed materials with a smaller active surface area. Photocatalysis tests for all the materials exhibited a similar degree of efficiency to photolysis, approximately 33%. Ecotoxicity tests using the biomarkers Lactuca sativa L., Lemna minor, and Artemia salina indicated that, although they were similar to photolysis in terms of efficiency, the effluents generated when employing the doped catalysts showed lower levels of toxicity, with the best results achieved for the material doped with 0.005 mol L-1 of Bi, with a toxicity level approximately 40% lower. Photoelectrocatalysis proved to be the most efficient CIP degradation technique. The highest degradation rate was observed for materials doped with 0.005 mol L-1 of Bi, with an efficiency of 46%, which is 1.4 times more efficient than photolysis. These results demonstrate that materials doped with low amounts of Bi can be effectively used as photoanodes for drug degradation, as their performance is superior, and the final product generated exhibits low toxicity to living organisms.

Photodegradation of MC-LR using a novel Au-decorated Ni metal-organic framework (Au/Ni-MOF)

Microcystins (MCs) are toxins produced by cyanobacteria commonly found in harmful algal blooms (HAB) occurring in many surface waters. Conventional methods for removing MC-LR such as membrane filtration and activated carbon are only phase change removal methods and are often expensive in operation and maintenance. It is urgent to develop a rapid, easy-to-use, and cost-effective method for the degradation of MC-LR. In this study, a novel Au-decorated Ni-metal-organic framework (Au/Ni-MOF) was newly developed on a hydrophilic carbon fiber paper (2 cm × 2 cm) using an air spraying method. The Au/Ni-MOF was then applied for the photodegradation of MC-LR in water under UV-Vis. The addition of Au onto the surface of the Ni-MOF resulted in a nearly fivefold enhancement in the reaction rate coefficient (k), reaching a value of 0.0599 min-1 for the photodegradation of MC-LR (initial concentration of 20 ppb). It was found that 94.2% of MC-LR removal was attributed to photodegradation, with the remaining 5.8% from adsorption. The rate coefficient of 20 ppb of MC-LR in the surface water sample (pH 6.0) was 0.06 min-1 likely due to the presence of other contaminates including scavenger agents within the sample which inhibits the degradation reaction of the MC-LR. Overall, this study demonstrated the potential for the novel Au/Ni-MOF to effectively reduce the concentration of the MC-LR toxin in the contaminated water.

Emergence of CuInS2 derived photocatalyst for environmental remediation and energy conversion

Hydrogen production, catalytic organic synthesis, carbon dioxide reduction, environmental purification, and other major fields have all adopted photocatalytic technologies due to their eco-friendliness, ease of use, and reliance on sunlight as the driving force. Photocatalyst is the key component of photocatalytic technology. Thus, it is of utmost importance to produce highly efficient, stable, visible-light-responsive photocatalysts. CIS stands out among other visible-light-response photocatalysts for its advantageous combination of easy synthesis, non-toxicity, high stability, and suitable band structure. In this study, we took a brief glance at the synthesis techniques for CIS after providing a quick introduction to the fundamental semiconductor features, including the crystal and band structures of CIS. Then, we discussed the ways doping, heterojunction creation, p-n heterojunction, type-II heterojunction, and Z-scheme may be used to modify CIS's performance. Subsequently, the applications of CIS towards pollutant degradation, CO2 reduction, water splitting, and other toxic pollutants remediation are reviewed in detail. Finally, several remaining problems with CIS-based photocatalysts are highlighted, along with future potential for constructing more superior photocatalysts.

Simple synthesis of BiOI/ZnO/rGO for efficient photocatalytic degradation of antibiotic chloramphenicol under visible light

BiOI/ZnO/rGO (reduced graphene oxide) composite photocatalyst was fabricated using a simple one-step hydrothermal process and applied to the degradation of antibiotic chloramphenicol (CAP). By tuning the Bi/Zn ratios, the structure and photoelectric properties of the catalyst were investigated and characterized in terms of their morphological, structural, optical and photoelectrochemical properties. The as-synthesized composite photocatalysts are well-crystalline, uniform dispersion and exhibit good photocatalytic properties. The photocatalytic degradation rate of CAP by BiOI/ZnO/rGO composite is 8.1 times and 1.8 times that of BiOI and ZnO, respectively. The photocatalytic mechanism studies revealed that the synergistic effect between rGO and BiOI/ZnO can effectively separate photogenerated electron-hole, enhance photocurrents and conductivity, and improve charge carrier densities. Moreover, BiOI/ZnO/rGO possesses good stability and reusability that the degradation efficiency remained above 80% even after 5 recycling. This study reveals that both the introduction of rGO and heterostructure construction between BiOI and ZnO play a crucial role in their photoelectrochemical and photocatalytic properties.

Ultrafast many-body bright-dark exciton transition in anatase TiO2

The momentum-forbidden dark excitons can have a pivotal role in quantum information processing, Bose-Einstein condensation, and light-energy harvesting. Anatase TiO2 with an indirect band gap is a prototypical platform to study bright to momentum-forbidden dark exciton transition. Here, we examine, by GW plus the real-time Bethe-Salpeter equation combined with the nonadiabatic molecular dynamics (GW + rtBSE-NAMD), the many-body transition that occurs within 100 fs from the optically excited bright to the strongly bound momentum-forbidden dark excitons in anatase TiO2. Comparing with the single-particle picture in which the exciton transition is considered to occur through electron-phonon scattering, within the GW + rtBSE-NAMD framework, the many-body electron-hole Coulomb interaction activates additional exciton relaxation channels to notably accelerate the exciton transition in competition with other radiative and nonradiative processes. The existence of dark excitons and ultrafast bright-dark exciton transitions sheds insights into applications of anatase TiO2 in optoelectronic devices and light-energy harvesting as well as the formation process of dark excitons in semiconductors.

Fabrication of Co3O4/Co3S4/CNTs for photocatalytic treatment of wastewater under xenon lamp

The current study is about the synthesis of nanoparticles (NPs) of cobalt oxide (CO) and cobalt sulfide (CS) followed by their nanocomposites as CO/CS and CO/CS/CNT by ultrasonication approach. The addition of carbon-based materials in the oxides and sulfides enhances their performance by developing physico-chemical interactions. Prepared NPs were utilized for the photodegradation of organic contaminants. The characteristics, as well as the efficiency of the prepared samples, have been systematically examined by X-ray diffraction (XRD) technique, Fourier transform infrared spectroscopy (FTIR), and UV-vis spectroscopy. Photocatalytic activities of bare samples and synthesized nanocomposites were tested for the degradation of methyl orange (MO) using a xenon lamp. The percentage degradation of dye was 24.14%, 57.94%, 71.66%, and 85.04% in the presence of CO, CS, CO/CS, and CO/CS/CNT, respectively. Crystal violet (CV), Rhodamine B (rho-B), and industrial wastewater were also degraded by the ternary composite. The comparative studies showed the best performance of CO/CS/CNT, which enhanced the generation of electron-hole pairs by absorption of photons of incoming radiations, increased charge separation, and maximum surface area for adsorption.

Principles of Photocatalysts and Their Different Applications: A Review

Human existence and societal growth are both dependent on the availability of clean and fresh water. Photocatalysis is a type of artificial photosynthesis that uses environmentally friendly, long-lasting materials to address energy and environmental issues. There is currently a considerable demand for low-cost, high-performance wastewater treatment equipment. By changing the structure, size, and characteristics of nanomaterials, the use of nanotechnology in the field of water filtration has evolved dramatically. Semiconductor-assisted photocatalysis has recently advanced to become among the most promising techniques in the fields of sustainable energy generation and ecological cleanup. It is environmentally beneficial, cost-effective, and strictly linked to the zero waste discharge principle used in industrial effluent treatment. Owing to the reduction or removal of created unwanted byproducts, the green synthesis of photoactive nanomaterial is more beneficial than chemical synthesis approaches. Furthermore, unlike chemical synthesis methods, the green synthesis method does not require the use of expensive, dangerous, or poisonous ingredients, making it a less costly, easy, and environmental method for photocatalyst synthesis. This work focuses on distinct greener synthesis techniques utilized for the production of new photocatalysts, including metals, metal doped-metal oxides, metal oxides, and plasmonic nanostructures, including the application of artificial intelligence and machine learning to the design and selection of an innovative photocatalyst in the context of energy and environmental challenges. A brief overview of the industrial and environmental applications of photocatalysts is also presented. Finally, an overview and recommendations for future research are given to create photocatalytic systems with greatly improved stability and efficiency.

Photoinduced properties of anodized Ti alloys for biomaterial applications

The photocatalytic properties of anodic oxides on a newly developed TiNbSn and commonly used Ti6Al4V alloys as biomaterials were investigated. The alloys were anodized in an electrolyte of sodium tartrate acid with H2O2 at a high voltage and the mechanism of the photocatalytic and antiviral activities was studied. The anodized TiNbSn and Ti6Al4V exhibited highly crystallized rutile TiO2 and poorly crystallized anatase TiO2, respectively. X-ray photoelectron spectroscopy analysis revealed the presence of oxides of the alloying elements in addition to TiO2. The anodized TiNbSn exhibited higher activities than Ti6Al4V, and electron spin resonance spectra indicated that the number of hydroxyl radicals (⋅OH) generated from the anodized TiNbSn was higher than that from the anodized Ti6Al4V. The results can be explained by two possible mechanisms: the higher crystallinity of TiO2 on TiNbSn than that on the Ti6Al4V reduces the number of charge recombination sites and generates abundant ⋅OH; charge separation in the anodic oxide on TiNbSn due to the electronic band structure between TiO2 and the oxides of alloying elements enhances photo activities. The excellent photoinduced characteristics of the anodized TiNbSn are expected to contribute to the safe and reliable implant treatment.

Recent Developments in Semiconductor-Based Photocatalytic Degradation of Antiviral Drug Pollutants

The prevalence of antiviral drugs (ATVs) has seen a substantial increase in response to the COVID-19 pandemic, leading to heightened concentrations of these pharmaceuticals in wastewater systems. The hydrophilic nature of ATVs has been identified as a significant factor contributing to the low degradation efficiency observed in wastewater treatment plants. This characteristic often necessitates the implementation of additional treatment steps to achieve the complete degradation of ATVs. Semiconductor-based photocatalysis has garnered considerable attention due to its promising potential in achieving efficient degradation rates and subsequent mineralization of pollutants, leveraging the inexhaustible energy of sunlight. However, in recent years, there have been few comprehensive reports that have thoroughly summarized and analyzed the application of photocatalysis for the removal of ATVs. This review commences by summarizing the types and occurrence of ATVs. Furthermore, it places a significant emphasis on delivering a comprehensive summary and analysis of the characteristics pertaining to the photocatalytic elimination of ATVs, utilizing semiconductor photocatalysts such as metal oxides, doped metal oxides, and heterojunctions. Ultimately, the review sheds light on the identified research gaps and key concerns, offering invaluable insights to steer future investigations in this field.

Composite of graphitic carbon nitride and TiO2 as photo-electro-catalyst in microbial fuel cell

The widespread application of surfactants and their subsequent discharge in the receiving water bodies is a very common issue in developing countries. In the present investigation, a composite of graphitic carbon nitride (GCN) and TiO₂ was used as a photo-electro-catalyst in a microbial fuel cell (MFC)-based hybrid system for bio-electricity production and simultaneous pollutant removal (organic matter and sodium dodecyl sulphate, SDS). The GCN: TiO₂ composite with a ratio of 70:30 (by wt. %) revealed a better electrochemical response; thus, it was used as a photo-electro-catalyst in MFC. Additionally, the photochemical characterization indicated a decrease in the band gap and charge recombination of GCN-TiO₂ composite compared to standalone TiO₂, which indicated a conducive effect of GCN addition. Further, on the actual use as a photo-electro-catalyst, the GCN-TiO₂ catalysed MFC attained 58.2 ± 9.6% and 86.5 ± 7.1% of COD and SDS removal; while simultaneously harvesting a maximum power density of 1.07 W m^-3, which was higher than standalone TiO₂-catalysed MFC. The follow-up treatment in the charcoal bio-filter and photo-cathodic chamber of the hybrid system further improved the overall COD and SDS removal efficiency to 92.1 ± 2.7 and 95.6 ± 1.5%, respectively. The electro-catalytic performance of the GCN-TiO₂ can be attributed to the presence of nitrogen-active species in the composite. The results of this investigation demonstrated a potential MFC-based hybrid system for the simultaneous secondary and tertiary treatment of municipal wastewater. Consequently, the outcome of this investigation indicates an innovative research direction in the field of photo-electro-catalyst, which can fit into the role of a photo-catalyst as well as an electro-catalyst.

Modeling the Interaction of Coronavirus Membrane Phospholipids with Photocatalitically Active Titanium Dioxide

The outbreak of viral infectious diseases urges airborne droplet and surface disinfection strategies, which may rely on photocatalytic semiconductors. A lipid bilayer membrane generally encloses coronaviruses and promotes the anchoring on the semiconductor surface, where, upon photon absorption, electron-hole pairs are produced, which can react with adsorbed oxygen-containing species and lead to the formation of reactive oxygen species (ROSs). The photogenerated ROSs may support the disruptive oxidation of the lipidic membrane and pathogen death. Density functional theory calculations are employed to investigate adsorption modes, energetics, and electronic structure of a reference phospholipid on anatase TiO2 nanoparticles. The phospholipid covalently bound on TiO2, engaging a stronger adsorption on the (101) than on the (001) surface. The energetically most stable structure involves the formation of four covalent bonds through phosphate and carbonyl oxygen atoms. The adsorbates show a reduction of the band gap compared with standalone TiO2, suggesting a significant interfacial coupling.

Rapid Microwave-Assisted Synthesis of ZnIn2S4 Nanosheets for Highly Efficient Photocatalytic Hydrogen Production

In this study, a facile and rapid microwave-assisted synthesis method was used to synthesize In₂S₃ nanosheets, ZnS nanosheets, and ZnIn₂S₄ nanosheets with sulfur vacancies. The two-dimensional semiconductor photocatalysts of ZnIn₂S₄ nanosheets were characterized by XRD, FESEM, BET, TEM, XPS, UV-vis diffuse reflectance, and PL spectroscopy. The ZnIn₂S₄ with sulfur vacancies exhibited an evident energy bandgap value of 2.82 eV, as determined by UV-visible diffuse reflectance spectroscopy, and its energy band diagram was obtained through the combination of XPS and energy bandgap values. ZnIn₂S₄ nanosheets exhibited about 33.3 and 16.6 times higher photocatalytic hydrogen production than In₂S₃ nanosheets and ZnS nanosheets, respectively, under visible-light irradiation. Various factors, including materials, sacrificial reagents, and pH values, were used to evaluate the influence of ZnIn₂S₄ nanosheets on photocatalytic hydrogen production. In addition, the ZnIn₂S₄ nanosheets revealed the highest photocatalytic hydrogen production from seawater, which was about 209.4 and 106.7 times higher than that of In₂S₃ nanosheets and ZnS nanosheets, respectively. The presence of sulfur vacancies in ZnIn₂S₄ nanosheets offers promising opportunities for developing highly efficient and stable photocatalysts for photocatalytic hydrogen production from seawater under visible-light irradiation.

Construction of Ag/Ag2S/CdS Heterostructures through a Facile Two-Step Wet Chemical Process for Efficient Photocatalytic Hydrogen Production

We have demonstrated a two-step wet chemical approach for synthesizing ternary Ag/Ag₂S/CdS heterostructures for efficient photocatalytic hydrogen evolution. The CdS precursor concentrations and reaction temperatures are crucial in determining the efficiency of photocatalytic water splitting under visible light excitation. In addition, the effect of operational parameters (such as the pH value, sacrificial reagents, reusability, water bases, and light sources) on the photocatalytic hydrogen production of Ag/Ag₂S/CdS heterostructures was investigated. As a result, Ag/Ag₂S/CdS heterostructures exhibited a 3.1-fold enhancement in photocatalytic activities compared to bare CdS nanoparticles. Furthermore, the combination of Ag, Ag₂S, and CdS can significantly enhance light absorption and facilitate the separation and transport of photogenerated carriers through the surface plasma resonance (SPR) effect. Furthermore, the Ag/Ag₂S/CdS heterostructures in seawater exhibited a pH value approximately 2.09 times higher than in de-ionized water without an adjusted pH value under visible light excitation. The ternary Ag/Ag₂S/CdS heterostructures provide new potential for designing efficient and stable photocatalysts for photocatalytic hydrogen evolution.

Bimodal ionic photomemristor based on a high-temperature oxide superconductor/semiconductor junction

Memristors, a cornerstone for neuromorphic electronics, respond to the history of electrical stimuli by varying their electrical resistance across a continuum of states. Much effort has been recently devoted to developing an analogous response to optical excitation. Here we realize a novel tunnelling photo-memristor whose behaviour is bimodal: its resistance is determined by the dual electrical-optical history. This is obtained in a device of ultimate simplicity: an interface between a high-temperature superconductor and a transparent semiconductor. The exploited mechanism is a reversible nanoscale redox reaction between both materials, whose oxygen content determines the electron tunnelling rate across their interface. The redox reaction is optically driven via an interplay between electrochemistry, photovoltaic effects and photo-assisted ion migration. Besides their fundamental interest, the unveiled electro-optic memory effects have considerable technological potential. Especially in combination with high-temperature superconductivity which, in addition to facilitating low-dissipation connectivity, brings photo-memristive effects to the realm of superconducting electronics.

Halloysite-TiO2 Nanocomposites for Water Treatment: A Review

Halloysite nanotubes (HNTs) are clay minerals with a tubular structure that can be used for many different applications in place of carbon nanotubes. Indeed, HNTs display low/non-toxicity, are biocompatible, and can be easily prepared. Moreover, the aluminum and silica groups present on HNTs' inner and outer surfaces facilitate the interaction with various functional agents, such as alkalis, organosilanes, polymers, surfactants, and nanomaterials. This allows the deposition of different materials, for instance, metal and non-metal oxides, on different substrate types. This review article first briefly presents HNTs' general structure and the various applications described in the last 20 years (e.g., drug delivery, medical implants, and energy storage). Then, it discusses in detail HNT applications for water purification (inorganic and organic pollutants). It focuses particularly on HNT-TiO₂ composites that are considered very promising photocatalysts due to their high specific surface area and adsorption capacity, large pore volume, good stability, and mechanical features.

Enhanced photocatalytic activity of cubic ZnSn(OH)6 by in-situ partial phase transformation via rapid thermal annealing

In this study, a mixed phase ZnSn(OH)₆/ZnSnO₃ photocatalyst was synthesized by calcining ZHS nanostructures via rapid thermal annealing (RTA) process. The composition ratio of ZnSn(OH)₆/ZnSnO₃ was controlled by changing the duration of the RTA process. The obtained mixed-phase photocatalyst was characterized by X-ray diffraction, field emission scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy, ultraviolet photoelectron spectroscopy, photoluminescence, and physisorption analysis. Results showed that ZnSn(OH)₆/ZnSnO₃ photocatalyst obtained by calcining ZHS at 300 °C for 20 s displayed the best photocatalytic performance under UVC light illumination. Under optimized reaction conditions, ZHS-20 (0.125 g) demonstrated nearly complete removal (>99%) of MO dye in 150 min. Scavenger study revealed the predominant role of OH^• in photocatalysis. The enhanced photocatalytic activity of the ZnSn(OH)₆/ZnSnO₃ composites was mainly ascribed to the photosensitization of ZHS by ZTO and effective electron-hole separation at the ZnSn(OH)₆/ZnSnO₃ heterojunction interface. It is expected that this study will provide new research input for the development of photocatalyst through thermal annealing-induced partial phase transformation.

Recent Trends in Plasmon-Assisted Photocatalytic CO2 Reduction

Direct photocatalytic reduction of CO₂ has become an highly active field of research. It is thus of utmost importance to maintain an overview of the various materials used to sustain this process, find common trends, and, in this way, eventually improve the current conversions and selectivities. In particular, CO₂ photoreduction using plasmonic photocatalysts under solar light has gained tremendous attention, and a wide variety of materials has been developed to reduce CO₂ towards more practical gases or liquid fuels (CH₄ , CO, CH₃ OH/CH₃ CH₂ OH) in this manner. This Review therefore aims at providing insights in current developments of photocatalysts consisting of only plasmonic nanoparticles and semiconductor materials. By classifying recent studies based on product selectivity, this Review aims to unravel common trends that can provide effective information on ways to improve the photoreduction yield or possible means to shift the selectivity towards desired products, thus generating new ideas for the way forward.

Efficient Solar Light Photocatalyst Made of Ag3PO4 Coated TiO2-SiO2 Microspheres

Solar light active photocatalyst was prepared as silver phosphate (Ag₃PO₄) coating on titania-silica (TiO₂-SiO₂) microspheres. Titania-silica microsphere was obtained by spray drying TiO₂-SiO₂ colloidal solutions, whereas Ag₃PO₄ was applied by wet impregnation. XRD on the granules and SEM analysis show that the silver phosphate particles cover the surface of the titania-silica microspheres, and UV-visible diffuse reflectance analysis highlights that Ag₃PO₄/TiO₂-SiO₂ composites can absorb the entire visible light spectrum. BET measurements show higher specific surface area of the composite samples compared to bare Ag₃PO₄. Photocatalytic activity was evaluated by dye degradation tests under solar light irradiation. The prepared catalysts follow a pseudo-first-order rate law for dye degradation tests under solar light irradiation. The composite catalysts with an Ag₃PO₄/TiO₂-SiO₂ ratio of 1:1.6 wt% show better catalytic activity towards both rhodamine B and methylene blue degradation and compared with the results with uncoated TiO₂-SiO₂ microspheres and the benchmark commercial TiO₂ (Evonik-P25) as a reference. The composite photocatalyst showed exceptional efficiency compared to its pristine counterparts and reference material. This is explained as having a higher surface area with optimum light absorption capacity.

Green production of titanium dioxide nanometric particles through electrolytic anodic dissolution of titanium metal

Nanometric titanium derivatives such as hydroxide and dioxide compounds have a great attention because they are significant industrial material of commercial importance and applications in photocatalyst, semiconductors, and wastewater treatment. The present investigation gives the results of anodic dissolution preparation of titanium hydroxide nanometric particles followed by calcination for complete conversion to nanometric titanium dioxide product. The optimum conditions for the anodic dissolution of titanium metal were pH 4, C.D. 65 mA/cm2, 25 °C, 150 rpm, electrode gap distance 3 cm, and NaCl 3 g/l for electrolysis time 240 min and thermally calcinated at 600 °C for 240 min., to reach complete conversion to anatase titanium dioxide nanopowder of main particles size of 77 nm with major percentage of 70%. Chemical and physical characterizations were carried out for evaluation of the obtained products including transmission electron microscope, EDX, XRD, and the scanning advanced electronic diffraction pattern. Preliminary economic indicators were calculated to show that the capital cost of the plant is $1.613 million, with annual operating cost of $0.915 million which means the required investment is $2.528 million. The operating cost for the production of nanometric anatase TiO2 is $30.5/kg with depreciation excluding the land price.

Plasmonic enhanced photocatalytic activity of Ag/TiO2 tube-in-tube fibers

Ag nanoparticle was found to significantly enhance the photocatalytic activity of self-organized TiO₂ nanotube structures. Herein, novel Ag/TiO₂ tube-in-tube fibers have been prepared by a facile electrospinning technology and calcination process. Employed as the photocatalyst, the composite could efficiently catalyze the photodegradation of the model organic pollutant, rhodamine B under visible light irradiation, exhibiting a superior photocatalytic activity than the undoped TiO₂ tube-in-tube fibers. This enhanced activity has been ascribed to plasmonic characteristics of Ag nanoparticles, which promote the light absorption and charge transfer feasibility. The simple, low-cost and green fabrication route of the composite provides a novel means for preparing similar materials, holding great promise for wider application in the future.

More than One Century of History for Photocatalysis, from Past, Present and Future Perspectives

In this review, we analyzed the history and the past and present trends in photocatalysis research, trying to outline possible scenarios for the future in the medium term. The in-depth analysis of the literature reported here—from a mere bibliometric point of view—allowed us to divide the history of photocatalysis into four different periods characterized by different maturity of the topic and different bibliometric features. The turn of the 20th century saw an explosion in scientific production, which is still continuing now and has reached more than 15,000 papers published each year. Research interest is still growing significantly, and the analysis of different keywords suggests that such growth is substantial and not merely due to “publish or perish” behavior. The analysis of the most-investigated topics in the field of photocatalysis highlighted that, during its history, the focus of the research moved from inorganic oxides to carbon and hybrid materials. Concomitantly, the investigation of the “geography” of photocatalysis allowed us to underline its evolution over the years, with the repositioning of its center of mass from the Atlantic Ocean (USA and Europe) to Asia (China and India). Photocatalysis is active as never before but still awaiting major breakthroughs, which would allow a much broader technological and commercial output. Without such breakthroughs in this decade, the growth in scientific interest could level out or even decrease.

Fabrication of cerium titanate cellulose fiber nanocomposite materials for the removal of methyl orange and methylene blue from polluted water by photocatalytic degradation

In this study, cellulose fibers (Cf), extracted from sunflower seed husk, and different molar ratios of cerium titanate (Ce-Ti) NPs were prepared from sunflower seed husk extract by a green biosynthesis approach. Cf and Ce-Ti NPs were reacted via cross-linking reaction to synthesize a novel nanocomposite photocatalyst of Ce-Ti/Cf. Using Fourier-transform infrared (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM-EDX) spectroscopy, all manufactured materials were characterized. The results obtained from FTIR and EDX analyses indicated that Cf and its nanocomposites (0.1 Ce-Ti/Cf, 0.3 Ce-Ti/Cf, and 0.5 Ce-Ti/Cf) were successfully prepared by harnessing biomass extract from sunflower seed husk. Furthermore, XRD revealed that the degree of crystallinity of the nanocomposites was enhanced by increasing the molar ratios of the Ce-Ti NPs. The photocatalytic activity of as-fabricated 0.1 Ce-Ti/Cf, 0.3 Ce-Ti/Cf, and 0.5 Ce-Ti/Cf nanocomposite samples was investigated on methylene blue (MB) and methyl orange (MO) dyes as model organic compounds found in wastewaters. The effects of dose, contact time, and pH on the photocatalytic activity of the synthesized nanocomposites, the photodegradation kinetic parameters of MB, and MO degradation with/without the addition of H2O2 were also studied. The results revealed that high photodegradation efficiency could be obtained as the ratio of TiO2 in the Ce-Ti nanocomposite formula increases. Moreover, after sunlight irradiation, the adsorption capacity and the dye decomposition ratio significantly increase during the early contact time and reach equilibrium at about 240 and 120 min for 0.5 Ce-Ti/Cf nanocomposite photocatalyst in the absence and presence of hydrogen peroxide, respectively. In light of the obtained results and the practical wastewater treatment study conducted, the prepared photocatalyst from Ce-Ti/Cf nanocomposites could be a promising material for treating dye wastewater especially collected from Egypt.

Synergy between Sunlight, Titanium Dioxide, and Microbes Enhances Cellulose Diacetate Degradation in the Ocean

Sunlight chemically transforms marine plastics into a suite of products, with formulation─the specific mixture of polymers and additives─driving rates and products. However, the effect of light-driven transformations on subsequent microbial lability is poorly understood. Here, we examined the interplay between photochemical and biological degradation of fabrics made from cellulose diacetate (CDA), a biobased polymer used commonly in consumer products. We also examined the influence of ∼1% titanium dioxide (TiO₂), a common pigment and photocatalyst. We sequentially exposed CDA to simulated sunlight and native marine microbes to understand how photodegradation influences metabolic rates and pathways. Nuclear magnetic resonance spectroscopy revealed that sunlight initiated chain scission reactions, reducing CDA's average molecular weight. Natural abundance carbon isotope measurements demonstrated that chain scission ultimately yields CO₂, a newly identified abiotic loss term of CDA in the environment. Measurements of fabric mass loss and enzymatic activities in seawater implied that photodegradation enhanced biodegradation by performing steps typically facilitated by cellulase. TiO₂ accelerated CDA photodegradation, expediting biodegradation. Collectively, these findings (i) underline the importance of formulation in plastic's environmental fate and (ii) suggest that overlooking synergy between photochemical and biological degradation may lead to overestimates of marine plastic persistence.

Plasmonic Enhanced SERS in Ag/TiO2 Nanostructured Film: An Experimental and Theoretical Study

In this work, we present a new study on the electromagnetic (EM) enhancement properties generated by Ag/TiO₂ toward the finger print of methylene blue (MB) molecules deposited on the surface of Ag nanostructures. SERS intensity generated by MB molecules reflects the interaction between the local electric field and their bonds. A power-dependent SERS study in order to reveal the magnitude effect of a local electric field on the vibration behavior of molecular bonds of MB was performed. A theoretical study using finite element (COMSOL Multiphysics) was performed in order to understand the effect of interparticle distance of Ag nanoparticles on the enhancement properties.

Cu2O/CuS/ZnS Nanocomposite Boosts Blue LED-Light-Driven Photocatalytic Hydrogen Evolution

In the present work, we described the synthesis and characterization of the ternary Cu2O/CuS/ZnS nanocomposite using a facile two-step wet chemical method for blue LED-light-induced photocatalytic hydrogen production. The concentrations of the ZnS precursor and reaction time were essential in controlling the photocatalytic hydrogen production efficiency of the Cu2O/CuS/ZnS nanocomposite under blue LED light irradiation. The optimized Cu2O/CuS/ZnS nanocomposite exhibited a maximum photocatalytic hydrogen evolution rate of 1109 µmolh−1g−1, which was remarkably higher than Cu2O nanostructures. Through the cycle stability it can be observed that the hydrogen production rate of the Cu2O/CuS/ZnS nanocomposite decreased after 4 cycles (1 cycle = 3 h), but it remained at 82.2% of the initial performance under blue LED light irradiation. These reasons are mainly attributed to the introduction of CuS and ZnS to construct a rationally coupled reaction system, which enables the synergistic utilization of photogenerated carriers and the increased absorption of visible light for boosting blue LED-light-driven photocatalytic hydrogen evolution.

ZnO-based antimicrobial coatings for biomedical applications

Rapid transmission of infectious microorganisms such as viruses and bacteria through person-to-person contact has contributed significantly to global health issues. The high survivability of these microorganisms on the material surface enumerates their transmissibility to the susceptible patient. The antimicrobial coating has emerged as one of the most interesting technologies to prevent growth and subsequently kill disease-causing microorganisms. It offers an effective solution a non-invasive, low-cost, easy-in-use, side-effect-free, and environmentally friendly method to prevent nosocomial infection. Among antimicrobial coating, zinc oxide (ZnO) stands as one of the excellent materials owing to zero toxicity, high biocompatibility to human organs, good stability, high abundancy, affordability, and high photocatalytic performance to kill various infectious pathogens. Therefore, this review provides the latest research progress on advanced applications of ZnO nanostructure-based antibacterial coatings for medical devices, biomedical applications, and health care facilities. Finally, future challenges and clinical practices of ZnO-based antibacterial coating are addressed.