Single Photocatalyst Research Articles

Internal electric field driven BiOBr homojunction to accelerate O2 reduction reaction for the photodegradation of tetracycline

Oxygen reduction reaction (ORR) in photocatalysis process can generate large quantities of superoxide radicals (•O2–) and hydroxyl radicals (•OH), so as to degrade contaminants efficiently and rapidly. However, the electrons and holes (e-/h+) of single photocatalysts are easy to combine, which limits the ORR efficiency. In this paper, BiOBr microplate (BiOBr-P)/BiOBr nanoflower (BiOBr-F) homojunction with the molar ratio of 1:1 (which was labeled as BPF-1/1) was constructed to enhance the e-/h+ separation and drive the ORR, which can be ascribed to the different work function values between BiOBr-P and BiOBr-F, thereby resulting in the generation of internal electric field (IEF) and band bending. Meanwhile, •O2–, •OH and hydrogen peroxide (H2O2) were analyzed quantitatively, which illustrated that the BPF-1/1 homojunction could accelerate the ORR, producing more •O2– and •OH than BiOBr-P and BiOBr-F. Furthermore, tetracycline (TC) was utilized as the model contaminant to assess the photocatalytic performance of the studied materials. It was proved that BPF-1/1 homojunction displayed the optimum photocatalytic performance compared with BiOBr-P and BiOBr-F. Moreover, the photocatalytic reaction mechanism of BPF-1/1 homojunction photocatalyst for TC degradation was put forward under the visible light. This research offers a feasible strategy for the preparation of effective homojunctions to raise the ORR efficiency and improve the photocatalytic activity.

Magnetically guidable single TiO2 nanotube photocatalyst: Structure and photocatalytic properties

The influence of annealing temperature, the crystallinity, textural properties of magnetically guidable anodic TiO2 nanotubes in form of single tube powders on the photocatalytic decomposition of model organic dye is investigated for the first time. The powders were prepared from self-organized anodic TiO2 nanotube layers (grown on Ti) by etching in piranha solution, detaching them from the Ti substrate, and annealing in a wide range of temperatures (400–900 °C). The nanotubular shape was preserved up to 800 °C. Powders annealed up to 800 °C did not contain any detectable rutile phase, which is unique among other TiO2 nanomaterials at this temperature. Part of the obtained TiO2 ST-NT powders was decorated with Fe3O4 nanoparticles using an oleic acid-based synthesis. The TiO2 ST-NT and TiO2 ST-NT@Fe3O4NPs powders were characterized in terms of morphology, crystallinity, and specific surface area. Finally, all materials were exploited for the photocatalytic decomposition of a model dye. The best photocatalytic performance of TiO2 ST-NT and TiO2 ST-NT@Fe3O4NPs powders were obtained at annealing temperatures of 600 and 700 °C, respectively. The synergy resulting from annealing, crystallite size, and specific surface area enhances the photocatalytic activity of TiO2 ST-NT and TiO2 ST-NT@Fe3O4NPs powders under UV light. This approach goes beyond the classical Kasuga alkaline hydrothermal approach, enabling the preparation of large quantity of TiO2 nanotubes without any impurities (such as e.g. Na or Ca content resulting from the Kasuga approach).

Spatiotemporal imaging of charge transfer in photocatalyst particles.

The water-splitting reaction using photocatalyst particles is a promising route for solar fuel production1-4. Photo-induced charge transfer from a photocatalyst to catalytic surface sites is key in ensuring photocatalytic efficiency5; however, it is challenging to understand this process, which spans a wide spatiotemporal range from nanometres to micrometres and from femtoseconds to seconds6-8. Although the steady-state charge distribution on single photocatalyst particles has been mapped by microscopic techniques9-11, and the charge transfer dynamics in photocatalyst aggregations have been revealed by time-resolved spectroscopy12,13, spatiotemporally evolving charge transfer processes in single photocatalyst particles cannot be tracked, and their exact mechanism is unknown. Here we perform spatiotemporally resolved surface photovoltage measurements on cuprous oxide photocatalyst particles to map holistic charge transfer processes on the femtosecond to second timescale at the single-particle level. We find that photogenerated electrons are transferred to the catalytic surface quasi-ballistically through inter-facet hot electron transfer on a subpicosecond timescale, whereas photogenerated holes are transferred to a spatially separated surface and stabilized through selective trapping on a microsecond timescale. We demonstrate that these ultrafast-hot-electron-transfer and anisotropic-trapping regimes, which challenge the classical perception of a drift-diffusion model, contribute to the efficient charge separation in photocatalysis and improve photocatalytic performance. We anticipate that our findings will be used to illustrate the universality of other photoelectronic devices and facilitate the rational design of photocatalysts.

Halide and Oxide Double Perovskites As Promising Semiconductor Photocatalysts Candidates for Artificial Photosynthesis of Solar Fuels

Artificial photosynthesis of solar fuels is deemed as one of the Holy grails of renewable energy technology for simultaneously solving energy and environmental issues. At the present, it is one of the most involved programs in the international Mission Innovation Challenge for Accelerating the Clean Energy Revolution. Solar-driven water splitting and CO2 conversion are the main research application of artificial photosynthesis. However, these reactions are extremely challenging due to energetically uphill (G>0) and non-spontaneous multi-electron transfer processes, which are difficult to be understood by traditional knowledge of catalysis. An efficient solar energy conversion system must simultaneously deal well with light absorption, charge separation and transfer, surface redox reactions. Particularly, efficient charge separation and transfer by retarding back electron transfer, are often regarded as the key determining steps for overall solar energy conversion. To solve the high recombination rates of photogenerated electron-hole pairs and their low reduction and oxidation abilities in a single photocatalyst, heterojunction manipulation is urgently required. Two mainstream heterojunctions—type-II and Z-scheme heterojunctions have been widely acknowledged [1].Recently, lead halide perovskites (LHPs) with the chemical formula of ABX3, where A is an organic or inorganic cation (A= Cs+, MA+, FA+), B is Pb2+, and X is a halogen anion (Br-, Cl-, I-), such as CH3NH3PbI3,FAPbI3, and CsPbBr3 have been widely investigated as auspicious semiconductor photocatalysts for photocatalytic H2 production and photocatalytic CO2 reduction owing to their impressive photoelectrochemical properties, facile to synthesize, high carrier mobility, low exciton binding energy, and long carrier lifetime [2]. However, the high toxicity and notorious instability upon exposure to light, moisture, and high temperature are the major obstacles to their practical use.Therefore, developing alternative lead-free semiconductor photocatalysts with similar optoelectronic properties to the LHPs is highly needed.Inorganic halide double-perovskites and analogous oxide double-perovskites with the chemical formula of A2B'B"X6 and A2B'B"O6, respectively, are layered 3D materials, which have been considered as a novel ecofriendly visible light responsive semiconductor photocatalysts to replace the toxic lead-halide perovskite. The main feature of the halide and oxide double-perovskites is that their structures can be accommodated with different transition metal combinations on B' and B" site cations to tune their intrinsic properties such as light absorption, carrier mobilities, chemical diversity, and so on. Theoretically, an auspicious photocatalytic activity can be realized from them owing to their impressive photophysical properties. However, poor charge separation and severe charge recombination have restricted their practical photocatalytic application. Recently, several halides and oxides double perovskites have been demonstrated as visible light-responsive photocatalysts for photocatalytic CO2 reduction and photocatalytic half-reaction (oxygen and hydrogen evolution reactions) such as Cs2AgBrBr6, Cs2AgSbBr6, Sr2CoTaO6, Sr2CoWO6, etc. [3-5]. However, for oxide double perovskites even though they have shown bifunctional photocatalytic oxygen and hydrogen two half-reactions with visible light but their potential as photocatalytic CO2 reduction and one-step overall water splitting have not been achieved so far. Therefore, further improvement of the material design and synthesis by assembling heterostructure based on two eco-friendly halide and oxide double perovskites may play a key role in achieving high efficient photocatalytic performance under visible-light-irradiation. Thought is a challenging task, but holds great potential in advancing science and technology in photocatalysis. References Liao, C. Li, S.-Y. Liu, B. Fang, H. Yang, Emerging frontiers of Z-scheme photocatalytic systems, Trends in Chemistry. 4 (2022) 111–127.-C. Wang, N. Li, A.M. Idris, J. Wang, X. Du, Z. Pan, Z. Li, Surface Defect Engineering of CsPbBr3 Nanocrystals for High Efficient Photocatalytic CO2 Reduction, Solar RRL. 5 (2021) 2100154.Idris, A. M.; Liu, T.; Shah, J. H.; Zhang, X.; Ma, C.; Malik, A. S.; Jin, A. Solar RRL 2020, 4 (3), 1900456.Idris, A. M.; Liu, T.; Hussain Shah, J.; Han, H.; Li, C. ACS Sustainable Chemistry&Engineering 2020, 8 (37), 14190-14197.Wang, H. Huang, Z. Zhang, C. Wang, Y. Yang, Q. Li, D. Xu, Lead-free perovskite Cs2AgBiBr6@g-C3N4 Z-scheme system for improving CH4 production in photocatalytic CO2 reduction, Applied Catalysis B: Environmental. 282 (2021).

Photocatalytic degradation of Congo red dye using magnetic silica-coated Ag2WO4/Ag2S as Type I heterojunction photocatalyst: Stability and mechanisms studies

In the present study, magnet silica-coated Ag2WO4/Ag2S nanocomposites (FOSOAWAS) were fabricated via a multistep method to address the drawbacks related to single photocatalysts (pure Ag2WO4 and pure Ag2S) and to clarify the significant influence of semiconductor heterojunction on the enhancement of visible-light-driven organic degradation. Different techniques were performed to investigate the elemental composition, morphology, magnetic and photoelectrochemical properties of the fabricated FOSOAWAS photocatalyst. The FOSOAWAS photocatalyst (1 g/L) exhibited excellent photodegradation efficiency (99.5%) against Congo red dye (CR = 20 ppm) after 140 min of visible-light illumination. This result confirmed the ability of the heterojunction between Ag2WO4 and Ag2S species to improve the efficiency of the photogenerated electron/hole pair separation and to reduce their recombination. The kinetics studies of CR photoreaction suggested that the photodegradation rate of the FOSOAWAS photocatalyst was 3.26 and 2.94 times higher than that of pure Ag2WO4 and Ag2S NPs, respectively. The CR dye was investigated under various operating conditions (FOSOAWAS dosage, CR concentration, and pH of solution). The trapping experiments proved the significant roles of H2O2, •OH, and h+ oxidants in the photoreaction of CR dye. The proposed mechanism explains that the Type I heterojunction between Ag2WO4 and Ag2S semiconductors was responsible for the improved photocatalytic activity of the FOSOAWAS nanocomposite. Finally, the reusability and stability experiments proved the sufficient stability and facile separation of FOSOAWAS heterojunction, which may be employed in practical applications.

Single-atom zinc catalyst for co-production of hydrogen and fine chemicals in soluble biomass solution

Single-atom photocatalysts (SAPCs) have attracted great interests due to their remarkable atom utilization efficiency, excellent activity, and selectivity, yet no application in synchronous biorefinery and water splitting. Here, efficient SAPCs based on atomically dispersed Zn atoms on carbon nitride (named Zn−mCN) were produced. Experiments verified that Zn−mCN has widened adsorption range of visible-light and lowered ability of electron−hole recombination, leading to excellent photocatalytic redox activity for synchronous biorefinery and water splitting to co-produce lactic acid (selectivity up to 91.0%) and hydrogen (∼15898.8 ​μmol ​g − 1 ​h − 1 ). This system has excellent universality for small- molecule monosaccharides and macromolecular xylan. Poisoning experiments showed that h + , 1 O 2 , ·O 2 − and ·OH can promote the simultaneous production of lactic acid and hydrogen. This work realized full utilization of whole redox reaction and provided a novel strategy for efficient and concomitant production of hydrogen and value-added chemicals from biomass-derived feedstocks aqueous solutions. The Zn@mCN single atom photocatalyst with Zn-N6 coordination has widened adsorption range of visible light and lowered ability of electron-hole recombination, leading to excellent photocatalytic redox activity for synchronous biorefinery and water splitting to co-produce lactic acid and hydrogen. Meanwhile, this system presents excellent universality for small molecule monosaccharides and macromolecular xylan.

Photocatalytic degradation of organic pollutants in the presence of selected transition metal nanoparticles: review

Photocatalysis has attracted a lot of attention in recent years due to its potential in solving energy and environmental issues. Efficient light absorption and charge separation are two of the key factors for the exploration of high-performance photocatalytic systems, which are generally difficult to obtain from a single photocatalyst. The combination of various materials to form heterojunctions provides an effective way to better harvest solar energy and facilitate charge separation and transfer, thus enhancing photocatalytic activity and stability. This review concisely summarizes the recent development of visible light responsive heterojunctions, including the preparation and performance of semiconductor/semiconductor junctions and semiconductor/metal junctions and their mechanism for enhancing light harvesting and charge separation/transfer. In this regard, this review presents some unitary, binary and ternary CeO2 photocatalysts used for the degradation of organic pollutants. We expect this review to provide the type of guidelines for readers to gain a clear picture of nanotechnology and the fabrication and application of different types of heterostructured photocatalysts.

Hydrolytically stable mixed ditopic linker based zirconium metal organic framework as a robust photocatalyst towards Tetracycline Hydrochloride degradation and hydrogen evolution

In the existing eco-crisis, designing and engineering an efficient as well as water stable photocatalyst for energy conversion and pollutant abatement remains crucial. In this regard, a mixed linker type zirconium metal organic framework (Zr-MOF) with terepthalic acid based ditopic linkers were utilized to design a single component photocatalyst through single step solvothermal method to utilize photons from visible light illumination towards hydrogen energy (H2) production and Tetracycline Hydrochloride (TCH) degradation. The one pot synthesized mixed linker based Zr-MOF displays visible light absorption through band gap tuning, superior exciton segregation and oxygen vacancy that cumulatively supports the enhancement in the photocatalytic output with respect to their pristine counterparts. Additionally, the X-ray photoelectron spectroscopy, optical and electrochemical studies strongly reinforces the above claims. The prepared mixed linker Zr-MOF showed superior photocatalytic H2 evolution performance of 247.88 µmol h−1 (apparent conversion efficiency; ACE = 1.9%) that is twice than its pristine Zr-MOFs. Moreover, in TCH degradation, the mixed linker MOF displays an enhanced efficacy of 91.8 % and adopts pseudo-first order type kinetics with a rate constant value of 0.032. Typically, the active species participating for the TCH photo-degradation follows the order of hydroxyl (OH.) < superoxide (O2.-) radicals. Consequently, the mixed linker Zr-MOF could be effectively used as a robust photocatalyst exhibiting boosted TCH degradation and H2 production.

Polymeric Carbon Nitride-based Single Atom Photocatalysts for CO2 Reduction to C1 Products

Polymeric Carbon Nitride-based Single Atom Photocatalysts for CO2 Reduction to C1 Products

Enhancing the Photoinduced Interlayer Charge Transfer and Spatial Separation in Type-II Heterostructure of WS2 and Asymmetric Janus-MoSSe with Intrinsic Self-Build Electric Field

Two-dimensional heterostructure manipulation is promising to overcome the high recombination rates and limited redox abilities of photogenerated electron-hole pairs in a single photocatalyst. The built-in electric field (Ehetero) in the type-II heterojunction is normally unfavorable for the desired charge transfer, which is an important but easily neglected issue that needs to be solved. Here, on the basis of the density functional theory (DFT) and the nonadiabatic molecular dynamics (NAMD) calculations, we obtain a type-II band alignment in Janus-MoSSe/WS2 heterostructure, which meets the band-edge position requirement for water splitting. Importantly, the intrinsic self-build electric field (Eself) of Janus-MoSSe can effectively weaken the hindrance effect of Ehetero for charge transfer by constructing a suitable Se-S stacking configuration, improving charge separation efficiency in the Janus-MoSSe/WS2 heterostructure. Our work provides a materials-by-design paradigm and interlayer charge-transfer dynamics understanding of heterostructure engineering against asymmetric structures lacking reflection symmetry.

Synthesis of 3‐Amino‐1‐(difluoromethylidene)tetralins via Relay Photocatalytic Cascade Reactions of Arylalanines and 2‐Bromo‐3,3,3‐trifluoropropene

AbstractA relay photocatalytic cascade reaction for the synthesis of 3‐amino‐1‐(difluoromethylidene)tetralins was described. The reaction used readily available N‐Boc protected arylalanines and bulk industrial chemical 2‐bromo‐3,3,3‐trifluoropropene (BTP) as the starting materials combining two photoredox catalytic cycles with a single photocatalyst. In the first catalytic cycle, the defluorinative coupling of N‐Boc arylalanines with BTP provided 2‐bromo‐1,1‐difluoroalkenes. In the second catalytic cycle, 2‐bromo‐1,1‐difluoroalkenes underwent intramolecular radical cyclization by photoredox activation of C(sp2)−Br bond, affording the desired 3‐amino‐tetralins bearing an exo‐difluoroethylene unit in good yields. Moreover, the reactions of 3‐aryl propanoic acids and BTP for the construction of 1‐(difluoromethylidene)tetralins were also demonstrated.magnified image

Photocatalytic degradation of organic pollutants by Ag2O/AgSiOx

Silver silicate (AgSiOx) is a visible-driven photocatalyst. However, the efficiency of single component photocatalysts can be improved by coupling with other compounds. In this work, AgSiOx was coupled with different amounts of Ag2O using a co-precipitation method. Ratios of Ag2O:AgSiOx were controlled by varying the concentrations of Na2SiO3.9H2O and NaOH. All prepared products were characterized by X-ray diffractometry, transmission electron microscopy, X-ray photoelectron spectroscopy, surface analysis, and UV–vis diffuse reflectance spectroscopy. Under visible light irradiation, the Ag2O/AgSiOx composite could degrade rhodamine B, reactive orange, and bisphenol A solutions. The Ag2O/AgSiOx exhibited greater photocatalytic activity than AgSiOx and Ag2O because this composite improved visible light absorption and inhibited charge recombination. The Ag2O/AgSiOx prepared from 0.012 mol NaOH exhibited the highest photocatalytic activity. Photocatalytic degradation of all pollutant models to low mass species was studied by electrospray ionization mass spectrometry and the cytotoxicity of pollutant model solutions before and after photocatalytic processes was evaluated on L929 mouse fibroblast cells using the MTT assay.

Recent advances on Z-scheme engineered BiVO4-based semiconductor photocatalysts for CO2 reduction: A review

The designs of two or more absorber materials in a Z-scheme charge transfer configuration have paved the way for efficient CO2 photoreduction to high-value chemicals and fuels using the artificial photosynthesis approach. Under visible light irradiation or natural solar illumination, semiconductors that themselves do not satisfy minimum thermodynamic requirements for CO2 reduction or accompanying oxidation reactions can be used for targeted specific half-reactions. In this context, BiVO4 has been extensively investigated for water oxidation showing promising activity under visible-light illumination but is restricted as a single reduction photocatalyst since its conduction band is not negative enough. This review provides an overview of the basic principles and fundamentals of CO2 photoreduction and highlights the recent advances in the literature using BiVO4-based Z-scheme photocatalysts. We show that using BiVO4 as the oxidation photocatalyst, together with a reduction photocatalyst (Cu2O, CdZnS, ZnIn2S4, CuGaS2, g-C3N4, others) and under the Z-scheme charge transfer, is strategic for increasing visible-light absorption and facilitating charge separations while keeping the high redox potentials of the individual semiconductor components. This approach additionally helps to avoid undesired photocorrosion reactions triggered by trapped charges. Finally, some critical comments are raised for future research directions to improve CO2 capture and photocatalytic conversion to green fuels and chemicals.

Photocatalytic Degradation of Rhodamine B Dye by Nanocomposites: A Review

Pollution by textile dyes on waterbodies is an issue for both human health and the environment. To remove/degrade dyes, many approaches (coagulation, membrane separation, and adsorption) have been investigated. However, the use of semiconductor-assisted materials in conjunction with sustainable solar energy has emerged as a possible solution to the problem. Although single component photocatalysts have been tested, composites of semiconductor materials are being employed owing to their low efficiency and stability due to the high recombination rate electron-hole pair and inefficient visible light absorption. By combining two or more semiconductor components, semiconductor heterojunction systems are created. Overall stability is increased by the synergistic impact of their features, such as adsorption and better charge carrier movement. This paper discusses current advances in advanced nanocomposite materials utilized as photocatalysts, as well as the utilization of heterojunctions, crystallinity, and doping to improve photocatalytic characteristics. The conclusion includes a summary, research gaps, and a forecast for the future. This study will aid in the development of efficient heterostructure photodegradation systems by providing a comprehensive appraisal of recent advances in demonstrating effective nanocomposites for photodegradation of Rhodamine B dye under ideal circumstances.

Internal electric field-mediated sulfur vacancies-modified-In2S3/TiO2 thin-film heterojunctions as a photocatalyst for peroxymonosulfate activation: Density functional theory calculations, levofloxacin hydrochloride degradation pathways and toxicity of intermediates

Photocatalytic activation of peroxymonosulfate is considered an effective method for degrading organic pollutants. However, the difficulty in recovering powder photocatalysts restricts their practical applications. In this study, we hydrothermally generated sulfur-vacancy-modified In2S3/TiO2 thin films on fluorine-doped tin oxide substrates. We further investigated the formation mechanism of heterojunctions and the degradation pathways of levofloxacin hydrochloride by activated PMS using density functional theory calculations. Results from a series of experiments showed that the levofloxacin hydrochloride degradation performance by thin-film catalyst-activated peroxymonosulfate is comparable to that of powder photocatalysts, while the ease of recycling makes the thin film more suitable for applications in a real environment. Furthermore, the construction of heterojunctions and introduction of sulfur vacancies compensated for the poor separation efficiency of photogenerated electron-hole pairs in single photocatalysts. Overall, this study provides novel insights into the degradation of organic pollutants using thin-film photocatalysts in advanced oxidation processes.

Photocatalytic properties of BiOBr/g-C3N4 heterojunctions originated from S-scheme separation and transfer of interfacial charge pairs

Construction of heterojunctions is an available approach to overcome the defects of a single photocatalyst. In this work, BiOBr/g-C3N4 S-scheme heterojunctions were prepared by a microwave hydrothermal approach. The crystal structures, morphologies, and photoinduced charge separation behavior of the BiOBr/g-C3N4 heterojunctions were studied by some analytic techniques. The experimental results reveal that all the BiOBr/g-C3N4 heterojunctions display superior photocatalytic activities to g-C3N4 and BiOBr under visible light exposure, in particular, the sample with 2% molar ratio of BiOBr/g-C3N4 presents the highest photocatalytic performance. The boosted photocatalytic property of BiOBr/g-C3N4 heterojunctions is ascribed to S-scheme segregation and transfer of interfacial charge pairs. Following this mechanism, the efficient segregation of photogenerated carriers can be achieved, at the same time, the robust redox ability of photo-generated e−/h+ pairs can be maintained. This work contributes a reference to develop highly efficiency g-C3N4 based photocatalyst for photocatalytic decomposition of contaminants.

Recent progress on elemental sulfur based photocatalysts for energy and environmental applications

The growing needs of the rising population and blatant misuse of resources have contributed enormously to environmental problems. Among the various methods, photocatalysis has emerged as one of the effective remediation methods. The continuous search for effective photocatalysts that can be made from abundant, cheap, non-toxic materials is going on. Although sulfur is a known insulator, recent sulfur use as a visible light photocatalyst has ushered a new era in this direction. Sulfur is a non-toxic, cheap, and abundant photocatalyst, exhibiting significant photocatalytic properties. But, hydrophobicity, poor light-harvesting and high recombination rate of charge carriers in elemental sulfur photocatalyst are some of the major drawbacks of the elemental sulfur photocatalyst. The photocatalytic activity of sulfur as a single element was low, but various methods such as nanoscaling, heterojunction formation, doping and surface modifications have been used to enhance it. The review highlights sulfur's crystal structure, electronic and optical properties, and morphological changes, making it an excellent visible light photocatalyst. The article points to the limitations of sulfur as a single photocatalyst and various strategies to improve the shortcomings. More recently, there has been an emphasis on the synthesis of metal-free photocatalysts. This review provides its readers with a comprehensive detail of sulfur being used as a dopant in improving the photocatalytic properties of metal-free photocatalysts and their environmental remediation use. Finally, the conclusion and future perspectives for sulfur-based nanostructures are presented.

Tuning product selectivity in nitrobenzene reduction over a single Bi2MoO6 photocatalyst in one pot: Mechanisms and roles of reaction compositions

Poor product selectivity of metal oxide photocatalysts is one of crucial issues limiting their application in photocatalytic organic synthesis particularly when multiple parallel reactions as well as several intermediates and products are involved, as in the reduction of nitrobenzene (NB) in this present study. Accordingly, catalyst modification is often needed. Herein, we first demonstrate that without catalyst modification it is feasible to control product selectivity over a single bismuth molybdate photocatalyst to selectively prepare three different valuable compounds including aniline (AN), azobenzene (AZO) and azoxybenzene (AZX) with high efficacy. Two widely used bismuth molybdate photocatalysts, namely Bi2MoO6 and Bi4MoO9, were studied and compared. Bi2MoO6 offers better visible-light-driven photocatalytic performance than Bi4MoO9 partly due to its narrow band gap energy and efficient charge carrier separation and transfer as evidenced from UV–vis DRS, EIS, and transient photocurrent studies. The roles of hydrazine hydrate, alcohol solvent, and KOH additive on the transfer hydrogenation of NB were examined and their concentrations were optimized to solely obtain the three different products with excellent selectivity (>98%). Based on UV–vis DRS and Mott-Schottky analysis, the band energy level of Bi2MoO6 and plausible reactions at solid–liquid interface are proposed. The capability to control product selectivity over a single photocatalyst in one pot demonstrated in this work would make the process more practical especially for continuous flow photochemical systems.

Fabrication of high visible light active LaFeO3/Cl-g-C3N4/RGO heterojunction for solar assisted photo-degradation of aceclofenac

The designing of semiconductor based heterojunction has proved to be an effective strategy for developing more efficient photo-catalyst than single component photo-catalyst. Herein, we report the laboratory scale fabrication of a novel LaFeO3/Cl-g-C3N4/RGO (LCCR) heterojunction with enormous photocatalytic activity. The prepared nano-composite has been characterized using X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM). The LaFeO3/Cl-g-C3N4/RGO (LCCR) nano-heterojunction exhibits excellent photocatalytic activity due to its reduced charge recombination rate. The photocatalytic potential of LCCR was tested for the photo degradation of aceclofenac drug as model pollutant. LCCR with an optimum dosage amount 200 mgL−1 has shown highest degradation of 96.4 % within 90 min of solar light exposure. Various operational parameters such as effect of pH, photocatalyst dosage, pollutant concentration and various ions has been investigated. The photo-degradation outcomes of LCCR nano-composite have been examined in terms of reaction kinetics, active radical identification experiments, high resolution mass spectrometry (HR-MS), chemical oxygen demand (COD) and total organic carbon (TOC) analysis. The photo-degradation experiment followed the pseudo first order kinetics with high rate constant k1 = 0.0461 min−1 and results for TOC and COD analysis shows that 53.2 % of TOC was removed, whereas COD was decreased to 22.4 %. This work shows promising photo-catalyst for treating pharmaceutical effluents.

Nickel single atoms anchored on ultrathin carbon nitride for selective hydrogen peroxide generation with enhanced photocatalytic activity

Photocatalysis technology provides a promising and effective method for hydrogen peroxide (H2O2) production. Nevertheless, the photocatalytic H2O2 production activity is greatly regulated by the two-electron oxygen reduction reaction (2e− O2RR). Herein, we demonstrate a robust single atom photocatalyst (NiCN-x, Ni single atoms anchored on ultrathin g-C3N4) for artificial H2O2 production under visible light irradiation. A high H2O2 generation rate of 27.11 mmol g−1h−1 and an apparent quantum yield (AQY) of 8.56 % at 400 nm are both obtained in the optimal NiCN-4 photocatalytic system. Furthermore, NiCN-4 catalyst shows relatively high selectivity of H2O2 with 87.3 % through using a rotating ring-disk electrode (RRDE) measurement. Furthermore, NiCN-4 shows enhanced photocatalytic TC decomposition with degradation efficiency of 89.4 %. Based on DFT calculation, experimental results and advanced characterizations, we find that the high photocatalytic performance is attributed to the boosting 2e−O2RR process with the formation of Ni-μ-peroxide (Ni-OOH) and the unique electronic feature of Ni-Nx coordination sites. This study offers a new blueprint for the fabrication of single atom catalysts (SACs) to achieve artificial photosynthesis of H2O2 with high selectivity and degradation of organic pollutants.