A novel 0D/2D WS2/BiOBr heterostructure with rich oxygen vacancies for enhanced broad-spectrum photocatalytic performance

Fabrication of a Novel Z-Scheme AgBiO3/BiOCl Heterojunction with Excellent Photocatalytic Performance towards Organic Pollutant

A novel and highly efficient photocatalyst of a AgBiO3/BiOCl heterojunction has been developed via a facile water bath and in situ precipitation method. The photocatalytic activities of the catalysts were investigated by the degradation of ciprofloxacin (CIP) under visible-light irradiation (>420 nm). The experiment results revealed that the photocatalytic performance of the optimized AgBiO3/BiOCl heterojunction was much higher than pure AgBiO3 and BiOCl. The degradation efficiency of the as-prepared AgBiO3/BiOCl heterojunction (ABC-30) for CIP could reach 88% within 160 min, with 2.89 and 3.76 times higher activity than pure AgBiO3 and BiOCl, respectively. The improved photocatalytic performance of AgBiO3/BiOCl was attributed to the synergistic effect of the enhanced light absorption range and effective separation and transfer of the photo-induced charge carrier. The optimized heterojunction showed broad-spectrum catalytic activities towards various organic contaminants. The degradation efficiencies varied with the nature of the pollutant and decreased in the following order: Lanasol Red 5B (100%) > methyl orange (99%) > methylene blue (98%) > tetracycline (92%) > ciprofloxacin (88%) > ofloxacin (85%) > norfloxacin (78%) > rhodamine B (59%) > metronidazole (43%) > phenol (40%) > carbamazepine (20%). Furthermore, the trapping experiments and ESR indicated that superoxide radicals and holes were the main reactive species.

Hydrophilicity and Pore Structure Enhancement in Polyurethane/Silk Protein-Bismuth Halide Oxide Composite Films for Photocatalytic Degradation of Dye

Polyurethane/silk protein-bismuth halide oxide composite films were fabricated using a blending-wet phase transformationin situsynthesis method. The crystal structure, micromorphology, and optical properties were conducted using XRD, SEM, and UV-Vis DRS characterize techniques. The results indicated that loaded silk protein enhanced the hydrophilicity and pore structure of the polyurethane composite films. The active species BiOX were observed to grow as nanosheets with high dispersion on the internal skeleton and silk protein surface of the polyurethane-silk protein film. The photocatalytic efficiency of BiOX/PU-SF composite films was assessed through the degradation of Rhodamine B under visible light irradiation. Among the tested films, the BiOBr/PU-SF composite exhibited the highest removal rate of RhB at 98.9%, surpassing the removal rates of 93.7% for the BiOCl/PU-SF composite and 85.6% for the BiOI/PU-SF composite. Furthermore, an active species capture test indicated that superoxide radical (•O2-) and hole (h+) species played a predominant role in the photodegradation process.

In situ Mo-doped ZnIn2S4/Ni-Ni Hofmann-type coordination polymer composites for photocatalytic hydrogen evolution reaction

Solar energy-assisted hydrogen production technology is an essential tool for exploring hydrogen energy. To date, semiconductors have been used as the primary photocatalyst to generate hydrogen via photocatalytic water splitting. However, the high photogenerated electron-hole recombination rate of semiconductor photocatalysts results in a low hydrogen production rate. Herein, the synergistic effect of Mo-ion doping and the incorporation of Ni-based Hofmann-type coordination polymer (Ni-Ni HCP) on the photocatalytic performance of ZnIn2S4 (ZIS) is investigated. The hydrogen production rate of the prepared in-situ Mo doped ZnIn2S4 wrapped Ni-Ni HCP (Ni-Ni HCP/Mo-ZIS) sample under visible-light irradiation is 26.7 mmol g-1h-1, which is 10 times that of pure ZIS. Hydrogen production rate test, microscopic characterization, and density functional theory calculation confirm that the proposed dual modulation approach (combined ion doping and heterogeneous structure construction) could effectively increase the photocatalytic efficiency of ZIS. The stability of prepared samples is also examined by four-cycle photocatalytic hydrogen production tests. The proposed integrated method opens a new route for advancing renewable energy technology towards a sustainable future.

Photocatalysis Meets Piezoelectricity in a Type-I Oxygen Vacancy-Rich BaTiO3/BiOBr Heterojunction: Mechanism Insights from Characterizations to DFT Calculations

It is a challenging task to design a piezoelectric photocatalyst with excellent performance under mechanical agitation instead of ultrasonic irradiation. Integrating vacancy defects into a heterojunction seems to be an effective strategy for synergistically increasing its piezo-photocatalytic performance. For this goal, a two-step hydrothermal method was adopted to architect a type-I oxygen-vacancy-rich BaTiO3/BiOBr heterojunction to surge the degradation of Rhodamine B (RhB) under the combined action of simulated sunlight irradiation and mechanical agitation. Various instrumental techniques demonstrated the formation of a BaTiO3/BiOBr heterojunction with high crystallinity. The existence of surface oxygen vacancies was confirmed by XPS and EPR tests. PFM results manifested that this heterojunction had excellent piezoelectric properties, with a piezoelectric response value of 30.31 pm V-1. Comparative experiments indicated that RhB degradation efficiency under piezo-photocatalysis over this heterojunction largely exceeded the total sum of those under piezocatalysis and photocatalysis. h+, ·O2-, and 1O2 were the dominant reactive species for RhB degradation. The improved separation efficiency of photogenerated charges was verified by electrochemical measurements. DFT calculations indicated that the polarization of BaTiO3 could affect the electronic band structure of BiOBr. This work will provide comprehensive insights into piezo-photocatalytic mechanism at a microcosmic level and help to develop new-styled piezoelectric photocatalysts.

Multisite Cocatalysis: Single atomic Pt2+/Pt0 active sites synergistically improve the simulated sunlight driven H2O-to-H2 conversion performance of Sb2S3 nanorods

Single atomic metal (SAM) cocatalysis is a potential strategy to improve the performance of photocatalytic materials. However, the cocatalytic mechanism of SAM sites in different valence states is rarely reported. Herein, single atomic Pt2+/Pt0 active sites were anchored on Sb2S3 nanorods to synergistically improve the photoactivity for hydrogen production under simulated sunlight. Experimental results and density functional theory calculations indicated that the coexistence of single atomic Pt2+/Pt0 sites synergistically improves the broadband light harvesting and promotes the Sb2S3-to-Pt electron transfer following inhibited photoexciton recombination kinetics and enhanced H proton adsorption capacity, resulting higher and more durable photoactivity for hydrogen production. Therefore, the optimal Sb2S3-Pt0.9‰ composite catalyst achieved remarkably enhanced hydrogen evolution rate of 1.37 mmol∙g-1∙h-1 (about 105-fold greater of that of Sb2S3 NRs) under faintly alkaline condition, and about 5.41 % of apparent quantum yield (AQY700 nm) was achieved, which shows obvious superiority in hydrogen production by contrasting with the reported Sb2S3-based photocatalysts and conventional semiconductor photocatalytic materials modified with noble metals. This study elucidate a well-defined mechanism of multisite cocatalysis for photoactivity improvement.

Construction of Z-scheme AgCl/BiOCl heterojunction with oxygen vacancies for improved pollutant degradation and bacterial inactivation

A facile Z-scheme AgCl/BiOCl heterojunction photocatalyst with oxygen vacancies was fabricated by a water-bath method. The structural, morphological, optical and electronic properties of as-synthesized samples were systematically characterized. The oxygen vacancies were confirmed by EPR, which could optimize the band-gap of the AgCl/BiOCl heterojunction and improve the photo-induced electron transfer. The optimized AgCl/BiOCl heterojunction showed excellent photocatalytic degradation efficiency (82%) for tetracycline (TC). Simultaneously, E. coli was completely inactivated within 60 min due to the AgCl/BiOCl heterojunction. The elevated catalytic activity of the optimal AgCl/BiOCl heterojunction was ascribed to the synergistic effect of the enhanced light absorption and effective photoinduced charge carrier separation and transfer. Moreover, the degradation efficiency of the AgCl/BiOCl heterojunction towards ofloxacin, norfloxacin and Lanasol Red 5B was 73%, 74% and 96%, respectively. The experimental factors for the degradation efficiency of TC were also studied. Furthermore, active species trapping experiments indicated that superoxide radicals (˙O2-) were the main reactive species, and the Z-scheme charge transfer mechanism helped to improve the photocatalytic activity.

Rational design of full-spectrum visible-light-responsive bimetallic sulfide Bi2S3/CoS2 composites for high-efficiency photocatalytic degradation of naproxen and bacterial inactivation

Photocatalytic water decontamination has emerged as a highly promising technology for efficient and rapid water treatment, harnessing sustainable solar energy as its driving force. In this study, we prepared visible-light active Bi2S3/CoS2 composites for the degradation of naproxen (NPX) and the inactivation of Escherichia coli (E. coli). The homogeneous dispersion of CoS2 was stably integrated with Bi2S3, resulting in a significant enhancement of the specific surface area, efficient utilization of visible light, and effective separation of photogenerated charge carriers. Consequently, this synergistic photocatalytic system greatly facilitated the successful degradation of NPX and the inactivation of E. coli under visible-light irradiation. Compared to the pure Bi2S3 and CoS2 catalysts, the Bi2S3/CoS2 (1:2) composites displayed significantly enhanced photodegradation activity, achieving 96.46% (k = 0.2847 min-1) degradation of NPX within 90 min and maintaining good recyclability with no significant decline after six successive cycles. Additionally, the photocatalytic inactivation of E. coli results indicated that Bi2S3/CoS2 composites exhibited excellent performance, leading to the inactivation of 7 log10 cfu mL-1 of bacterial cells after 150 min of visible-light exposure. Scanning Electron Microscopy (SEM) and K+ ions leakage tests demonstrated that the destruction of the E. coli cell membrane structure resulted in cell death. The outcomes of this work suggest that Bi2S3/CoS2 composites hold significant potential for treating water contaminated with antibiotic and microbial pollutants.

Trends and prospects of 2-D tungsten disulphide (WS2) hybrid nanosystems for environmental and biomedical applications

Recently, 2D layered transition metal dichalcogenides (TMDCs) with their ultrathin sheet nanostructure and diversified electronic structure have drawn attention for various advanced applications to achieve high-performance parameters. Unique 2D TMDCs mainly comprise transition metal and chalcogen element where chalcogen element layers sandwich the transition metal element layer. In such a case, various properties can be enhanced and controlled depending on the targeted application. Among manipulative 2D TMDCs, tungsten disulphide (WS2) is one of the emerging nano-system due to its fascinating properties in terms of direct band gap, higher mobility, strong photoluminescence, good thermal stability, and strong magnetic field interaction. The advancement in characterization techniques, especially scattering techniques, can help in study of opto-electronic properties of 2D TMDCs along with determination of layer variations and investigation of defect. In this review, the fabrication and applications are well summarized to optimize an appropriate WS2-TMDCs assembly according to focused field of research. Here, the scientific investigations on 2D WS2 are studied in terms of its structure, role of scattering techniques to study its properties, and synthesis routes followed by its potential applications for environmental remediation (e.g., photocatalytic degradation of pollutants, gas sensing, and wastewater treatment) and biomedical domain (e.g., drug delivery, photothermal therapy, biomedical imaging, and biosensing). Further, a special emphasis is given to the significance of 2D WS2 as a substrate for surface-enhanced Raman scattering (SERS). The discussion is further extended to commercial and industrial aspects, keeping in view major research gaps in existing research studies.

PVP encapsulated MXene coated on PET surface (PMP)-based photocatalytic materials: A novel photo-responsive assembly for the removal of tetracycline

Tetracycline (TC) antibiotic that is effective against wide-range micro-organisms, thereby used to control bacterial infection. The partial metabolism of TC antibiotics in humans and animals leads to the contamination of TC in the environments like water bodies. Thus, requirements to treat/remove/degrade TC antibiotics from the water bodies to control environmental pollution. In this context, this study focuses on fabricating PVP-MXene-PET (PMP) based photo-responsive materials to degrade TC antibiotics from the water. Initially, MXene (Ti2CTx) was synthesized using a simple etching process from the MAX phase (Ti3AlC2). The synthesized MXene was encapsulated using PVP and cast onto the surface of PET to fabricate PMP-based photo-responsive materials. The rough surface and micron/nano-sized pores within the PMP-based photo-responsive materials might be improved the photo-degradation of TC antibiotics. The synthesized PMP-based photo-responsive materials were tested against the photo-degradation of TC antibiotics. The band gap value of the MXene and PMP-based photo-responsive materials was calculated to be ∼1.23 and 1.67 eV. Incorporating PVP within the MXene increased the band gap value, which might be beneficial for the photo-degradation of TC, as the minimum band gap value should be ∼1.23 eV or more for photocatalytic application. The highest photo-degradation of ∼83% was achieved using PMP-based photo-degradation at 0.1 mg/L of TC. Furthermore, ∼99.71% of photo-degradation of TC antibiotics was accomplished at pH ∼10. Therefore, the fabricated PMP-based photo-responsive materials might be next-generation devices/materials that efficiently degrade TC antibiotics from the water.

Revolutionizing the Role of Solar Light Responsive BiVO4/BiOBr Heterojunction Photocatalyst for the Photocatalytic Deterioration of Tetracycline and Photoelectrocatalytic Water Splitting

In this study, a series of BiVO4/BiOBr composites with varying mole ratios were successfully synthesized using a hydrothermal method. The in-situ synthesis strategy facilitated the formation of a close interfacial contact between BiVO4 and BiOBr at the depletion zone, resulting in improved charge segregation, migration, reduced charge recombination, enhanced solar light absorption capacity, promoting narrow band gap, and large surface area. This study investigates the influence of different mole ratios of BiVO4 and BiOBr in a BiVO4/BiOBr nanocomposite on the photocatalytic degradation of tetracycline (TC), a pharmaceutical pollutant, and photoelectrocatalytic water splitting (PEC) under solar light irradiation. Maximum decomposition efficiency of ~90.4% (with a rate constant of 0.0159 min-1) for TC was achieved with 0.5 g/L of 3:1 BiVO4: BiOBr (31BVBI) photocatalyst within 140 min. The degraded compounds resulting from the TC abatement were analyzed using GC-MS. Furthermore, TC standards exhibited 78.2% and 87.7% removal of chemical oxygen demand (COD) and total organic carbon (TOC), respectively, while TC tablets showed 64.6% COD removal and 73.8% TOC removal. The PEC water splitting experiments demonstrated that the 31BVBI photoanode achieved the highest photocurrent density of approximately 0.2198 mA/cm2 at 1.23 V vs. RHE, resulting in the generation of approximately 1.864 mmolcm-2 s-1 of hydrogen, while remaining stable for 21,600 s. The stability of the photocatalyst was confirmed by post-degradation characterizations, which revealed intact crystalline planes, shape, and surface area. Comparisons with existing physicochemical methods used in industries indicate that the reported photocatalyst possesses strong surface catalytic properties and has the potential for application in industrial wastewater treatment and hydrogen generation, offering an advantageous alternative to costly and time-consuming processes.

Porous Rod-like NiTiO3-BiOBr Heterojunctions with Highly Improved Visible-Light Photocatalytic Performance

NiTiO₃-BiOBr heterostructured photocatalysts were constructed via precipitation, calcination and hydrothermal treatments. Various characterizations demonstrated that BiOBr nanosheets were decorated on NiTiO₃ nanoparticals, forming porous rod-like heterojunctions. Compared with independent NiTiO₃ and BiOBr, the composites with optimal BiOBr content presented highly improved visible-light photocatalytic efficiency. The degradation rates of Rhodamine B (RhB) and tetracycline (TC) reached 96.6% in 1.5 h (100% in 2 h) and 73.5% in 3 h, which are 6.61 and 1.53 times those of NiTiO₃, respectively. The result is an improved photocatalytic behavior from the formation of heterojunctions with a large interface area, which significantly promoted the separation of photogenerated carriers and strengthened the visible-light absorption. Based on the free radical capture experiments and band position analysis, the photodegradation mechanism of type-II heterojunction was deduced. This study provides a new way to fabricate highly efficient NiTiO₃-based photocatalysts for degrading certain organics.

Significantly activated persulfate by novel carbon quantum dots-modified N-BiOCl for complete degradation of bisphenol-A under visible light irradiation

The practical application of bismuth-based photocatalysts in the field of micropollutant photodegradation is limited due to their weak light absorption and rapid charge recombination. Herein, we have developed a novel carbon quantum dots-modified N-BiOCl (CDs-N-BiOCl) photocatalyst to activate persulfate (PS) for the complete elimination of endocrine-disruptor bisphenol A (BPA) under visible light irradiation. The photoelectric properties characterization shows that N atoms could replace Cl atoms or adsorb on Bi atoms to form local N 1s states in the BiOCl lattice, accompanied by the introduction of doping energy levels that shorten the electron migration distance. Meanwhile, the decorated CDs could effectively accept the photoinduced electrons from N-BiOCl conduction band to facilitate the charge separation. Thus, the 7%CDs-N-BiOCl (7CNB) nanocomposite synergistically activated PS realized rapid and effective degradation of BPA within 20 min (degradation efficiency and mineralization reached 100 % and 66.4 % respectively). Moreover, the 7CNB/PS system displayed favorable adaptability, durability, and interference resistance. Furthermore, the biotoxicity experiments demonstrated that the photodegradation intermediates promoted the growth of Escherichia coli which indicates its eco-friendliness for practical application. Finally, the electron transfer mechanism and the formation of reactive oxygen species in the photodegradation process were interpreted. In short, this work will present a promising strategy for bismuth-based photocatalysts to be used for the efficient treatment of real water bodies under visible light irradiation.

A novel S-scheme Ws2/BiYWO6 electrostatic heterostructure for enhanced photocatalytic degradation performance towards the degradation of Rhodamine B

Constructing S-scheme heterojunction between two semiconductor materials is an effective route to increase the photocatalytic degradation efficiency. Here, a novel S-scheme WS₂/BiYWO₆ heterojunction photocatalyst was prepared by wet chemical route. At the same time, the photocatalytic degradation performance of the fabricated materials was analyzed by the degradation of Rhodamine B under visible light. Of all prepared WS₂/BiYWO₆ composites, the 20 wt.% WS₂ loaded WS₂/BiYWO₆ composite exhibited an enhanced photocatalytic degradation ability than other prepared photocatalysts. Here, O₂^·- and ^·OH radicals are performing a pivotal role in the Rhodamine B degradation and the optimized composite shows greater photocurrent intensity than pure BiYWO₆ and WS₂, respectively. Also, the synthesized photocatalyst maintains its stability with negligible changes even after three cycles. Thereby, the constructed S-scheme WS₂/BiYWO₆ heterojunction is a potential material for the wastewater remediation.

A review on the progress of the photocatalytic removal of refractory pollutants from water by BiOBr-based nanocomposites

Organic matters from various sources such as the manufacturing, agricultural, and pharmaceuticals industries is continuously discharged into water bodies, leading to increasingly serious water pollution. Photocatalytic technology is a clean and green advanced oxidation process, that can successfully decompose various organic pollutants into small inorganic molecules such as carbon dioxide and water under visible light irradiation. Bismuth oxybromide (BiOBr) is an attractive visible light photocatalyst with good photocatalytic performance, suitable forbidden bandwidth, and a unique layered structure. However, the rapid combination of the electron-hole pairs generated in BiOBr leads to low photocatalytic activity, which limits its photocatalytic performance. Due to its unique electronic structure, BiOBr can be coupled with a variety of different functional materials to improve its photocatalytic performance. In this paper, We present the morphologically controllable BiOBr and its preparation process with the influence of raw materials, additives, solvents, synthesis methods, and synthesis conditions. Based on this, we propose design synthesis considerations for BiOBr-based nanocomplexes in four aspects: structure, morphology and crystalline phase, reduction of electron-hole pair complexation, photocorrosion resistance, and scale-up synthesis. The literature on BiOBr-based nanocomposites in the last 10 years (2012-2022) are summarized into seven categories, and the mechanism of enhanced photocatalytic activity of BiOBr-based nanocomposites is reviewed. Moreover, the applications of BiOBr-based nanocomposites in the fields of degradation of dye wastewater, antibiotic wastewater, pesticide wastewater, and phenol-containing wastewater are reviewed. Finally, the current challenges and prospects of BiOBr-based nanocomposites are briefly described. In general, this paper reviews the construction of BiOBr-based nanocomposites, the mechanism of photocatalytic activity enhancement and its research status and application prospects in the degradation of organic pollutants.

Fabrication of ternary UiO-66(Ce)/Ag/BiOBr heterojunction for enhanced photocatalytic degradation of ketoprofen via effective electron transfer process: Pathways, DFT calculation and mechanism

Photocatalytic oxidation technique is considered as one of the most prospective approaches to solve the problem of environmental pollution. Herein, the novel ternary nanocomposite UiO-66(Ce)/Ag/BiOBr was fabricated via simple synthetic strategy. The obtained UiO-66(Ce)/Ag/BiOBr exhibited an excellent performance and photocatalytic efficiency of ketoprofen reached 93.5% after 180 min illumination. The ·OH and ·O₂^- were main active species and play an important role during the photocatalytic reaction. Furthermore, intermediate products and degradation pathways of ketoprofen were analyzed based on the 3D-EEM, DFT calculation and LC-MS. The possible reaction mechanism was proposed as follows: (1) the successful construction of heterojunction broadened the light absorption range to the visible light region; (2) the design of Ce-based MOFs provided more chances for electron transfer due to the Ce⁴⁺/Ce³⁺ cycling; (3) the combination of plasmon resonance effect, Schottky junction and effect of Ag bridge was an important strategy to accelerate charge transfer and improve photocatalytic efficiency.

Z-scheme Fe2(MoO4)3/Ag/Ag3PO4 heterojunction with enhanced degradation rate by in-situ generated H2O2: Turning waste (H2O2) into wealth (•OH)

Ag₃PO₄-based photocatalysts have been deeply studied in environmental remediation; however, two problems limited their further application: photocorrosion and quenching effect by in-situ generated H₂O₂. To addressed these two questions simultaneously, Fe₂(MoO₄)₃ was coupled with Ag₃PO₄ to construct Z-scheme Fe₂(MoO₄)₃/Ag/Ag₃PO₄ heterojunction driven by internal-electric-field. The rhodamine B degradation rate of heterojunction was 254 and 7.0 times higher than those of Fe₂(MoO₄)₃ and Ag₃PO₄, respectively. The outstanding photoactivity was due to the high visible-light harvest, low interface resistance, high separation efficiency of charge carriers, long lifetime of hole (h⁺) and electron (e^-), well-preserved oxidation potential of h⁺, and especially photocatalytic produced H₂O₂ inside the system. The in-situ generated H₂O₂ was fully activated to be ^•OH on the Fe₂(MoO₄)₃ surface via a Fenton reaction, leading to the elimination of quenching effect on h⁺ and e^-, and generation of more ^•OH. Additionally, in Z-scheme heterojunction, e^- transferred from Ag₃PO₄ to Fe₂(MoO₄)₃, avoiding the accumulation on Ag₃PO₄ surface, and hence suppressing the photocorrosion. As a result, 91.2% of degradation efficiency remained after 5 cycles. This paper provides a new method to simultaneously increase the degradation rate by utilizing the in-situ generated H₂O₂ and improve the stability of Ag₃PO₄ via constructing a Z-scheme heterojunction.

Dual-functional Z-scheme CdSe/Se/BiOBr photocatalyst: Generation of hydrogen peroxide and efficient degradation of ciprofloxacin

The major challenges of clean energy and environmental pollution have resulted in the development of photocatalysis technologies for energy conversion and the degradation of refractory pollutants. Herein, a novel CdSe/Se/BiOBr hydrangea-like photocatalyst was used to produce hydrogen peroxide (H₂O₂) and degrade ciprofloxacin (CIP). The Z-scheme heterojunction structure of the photocatalyst and the doping of selenium (Se) led to the efficient separation of electron-hole pairs and charge transfer. The optimized sample of 2 wt% CdSe/Se/BiOBr produced 142.15 mg·L^-1 rate of H₂O₂, which was much higher than that produced by pure BiOBr (89.4 mg·L^-1) or CdSe/Se (10.9 mg·L^-1). Additionally, almost 100 % of CIP was degraded within 30 min, with a first order rate constant of nearly 5.35 times that of pure BiOBr and 81.44 times that of pure CdSe/Se. The excellent removal efficiency of CIP from natural water matrices confirmed that the composites are promising for the removal of contaminants from natural waterways. Based on trapping experiments, electron spin resonance spectra (ESR) spectroscopy, and density functional theory (DFT) calculations, the photocatalytic mechanisms of H₂O₂ and CIP degradation by the Z-scheme CdSe/Se/BiOBr composites were proposed. Overall, the dual-functional CdSe/Se/BiOBr composite could potentially be applied for photocatalytic production of H₂O₂ and treatment of organic pollutants in water.

Transformation of phase and heterojunction type by using HAc-adsorbed Bi(NO3)3 as a Bi source

Generally, preparing high-efficiency heterojunction photocatalysts via a facile room-temperature route is attractive from the perspective of energy and labor saving. Herein, by using dried and glacial acetic acid (HAc)-adsorbed bismuth nitrate, instead of Bi(NO₃)₃·5H₂O, as a Bi source, a β-Bi₂O₃/Bi₅O₇I heterojunction with well dispersed flowery hierarchical architecture was synthesized, which endows it with high surface area, open channels and good light harvest. More importantly, the change of the precursor achieved a successful transformation for both of phase and heterojunction type, i.e. from type-Ⅰ BiOI/[Bi₆O₅(OH)₃](NO₃)₅·3H₂O (labeled as BiOI/BBN) to Z-scheme β-Bi₂O₃/Bi₅O₇I heterojunction. Since both β-Bi₂O₃ and Bi₅O₇I are visible light responsive, β-Bi₂O₃/Bi₅O₇I exhibited improved visible-light photocatalytic activity for the degradation of tetracycline (TC) and malachite green (MG) with apparent reactant rate (k_app) values about 10 and 11 times higher than those of BiOI/BBN. Besides, the presence of more oxygen vacancies also contributed to the enhancement in photocatalytic performance.

Construction of oxygen vacancy assisted Z-scheme BiO2-x/BiOBr heterojunction for LED light pollutants degradation and bacteria inactivation

It is well known that the most important task of photocatalytic technology is to synthesize photocatalysts with compact heterojunction structure and high redox ability. To achieve the goal, a novel Z-scheme BiO_2-x/BiOBr heterojunction containing oxygen vacancy was synthesized by an in-situ generation process. Several techniques, X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) have verified the BiO_2-x/BiOBr heterojunction. XPS and electron spin resonance (ESR) reveals the presence of oxygen vacancy in the BiO_2-x/BiOBr composite. As expected, the BiO_2-x/BiOBr composite showed good performance in removing Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Rhodamine B (RhB) and tetracycline (TC). The effects of inorganic ions, pH value and water matrix were investigated with many details. The active species and proposed mechanism were revealed by trapping experiment and related characterizations. The synergistic effect of oxygen vacancy and Z-scheme heterojunction makes the BiO_2-x/BiOBr composite possess excellent photocatalytic activity.

Oxygen vacancy-rich 2D/0D BiO1-XBr/AgBr Z-scheme photocatalysts for efficient visible light driven degradation of tetracycline

Semiconductor-based photocatalytic technology, as a green and promising avenue in response to the abuse of antibiotic pollution and human health crisis, is restricted by the limited photo-absorption and fast recombination of photogenerated carriers. In this paper, all these challenges were settled by AgBr particles incorporated into oxygen-deficient BiOBr nanosheets, forming novel oxygen vacancy (OV)-rich 2D/0D Z-scheme heterojunctions. Z-scheme photocatalytic system has an effective separation rate of photogenerated carriers and an ability to maintain original redox capacity. Moreover, introducing OVs in the Z-scheme can not only improve the visible light absorption ability, but also serve as recombination centers, thus promoting the separation of electrons and holes. Notably, the photocatalytic activity of 2D/0D BiO_1-XBr/AgBr (2:1) was significantly improved under the irradiation of visible light, removing 81% of tetracycline after 25 min, which was about 2.62 times and 2.03 times as high as those of BiO_1-XBr and AgBr, respectively. In addition, the 2D/0D BiO_1-XBr/AgBr (2:1) indicated high photocatalytic stability and reusability, and its tetracycline degradation efficiency remained stable after five cycles. In summary, this work suggests that the photocatalysts have a great potential to remove TC and provides a possible strategy for purifying water.

Enhanced sunlight driven photocatalytic activity of In2S3 nanosheets functionalized MoS2 nanoflowers heterostructures

Visible light-sensitive 2D-layered based photocatalytic systems have been proven one of the effective recent trends. We report the preparation of a 2D-layered based In₂S₃-MoS₂ nanohybrid system through a facile hydrothermal method, capable of efficiently degrading of organic contaminants with remarkable efficiency. Transmission electron microscopy (TEM) results inferred the attachment of 2D-layered In₂S₃ sheets with the MoS₂ nanoflakes. Field emission SEM studies with chemical mapping confirm the uniform distribution of Mo, In, and S atoms in the heterostructure, affirming sample uniformity. X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy results confirm the appearance of 2H-MoS₂ and β-In₂S₃ in the grown heterostructures. UV-DRS results reveal a significant improvement in the optical absorbance and significant bandgap narrowing (0.43 eV) in In₂S₃-MoS₂ nanohybrid compared to pristine In₂S₃ nanosheets in the visible region. The effective bandgap narrowing facilitates the charge transfer between MoS₂ and In₂S₃ and remarkably improves the synergistic effect. Effective bandgap engineering and improved optical absorption of In₂S₃-MoS₂ nanohybrids are favorable for enhancing their charge separation and photocatalytic ability. The photocatalytic decomposition efficiency of the pristine In₂S₃ nanosheets and In₂S₃-MoS₂ nanohybrids sample is determined by the decomposing of methylene blue and oxytetracycline molecules under natural sunlight. The optimized In₂S₃-MoS₂ nanohybrids can decompose 97.67% of MB and 76.3% of OTC-HCl molecules solution in 8 min and 40 min of exposure of sunlight respectively. 2D-layered In₂S₃-MoS₂ nanohybrids reveal the tremendous remediation performance towards chemical contaminations and pharmaceutical waste, which indicates their applicability in industrial and practical applications.

Selective Bonding Effect of Heterologous Oxygen Vacancies in Z-Scheme Cu2O/SrFe0.5Ta0.5O3 Heterojunctions for Constructing Efficient Interfacial Charge-Transfer Channels and Enhancing Photocatalytic NO Removal Performances

An interfacial structure is crucial to the photoinduced electron transport for a heterostructure photocatalyst. Constructing an interfacial electron channel with an optimized interfacial structure can efficiently improve the electron-transfer efficiency. Herein, the rapid electron-transfer channels were built up in a Cu₂O/SrFe_0.5Ta_0.5O₃ heterojunction (Cu₂O/SFTO) based on the selective bonding effect of heterologous surface oxygen vacancies in the SFTO component. The heterologous surface oxygen vacancies, namely, V_O-Fe and V_O-Ta, respectively, adjacent to Fe and Ta atoms, were introduced into fabricating the Z-scheme Cu₂O/SFTO heterojunction. Compared with sample Cu₂O/SFTO with V_O-Fe, the photocatalytic NO removal efficiency of sample Cu₂O/SFTO with V_O-Fe and V_O-Ta was increased by 22.5%. The enhanced photocatalytic performance originated from the selective bonding effect of heterologous V_O-Fe and V_O-Ta on the interfacial electron-separating and -transfer efficiency. V_O-Fe is the main body to construct the interfacial electron-transfer channels by forming interfacial Fe-O-Cu(I) bonds, which causes lattice distortion at the interface, and V_O-Ta can optimize the structure of interfacial channels by balancing the electron density of SFTO to control the average space of the interface transition zone. This research provides a new cognitive perspective for constructing double perovskite oxide-based heterostructure photocatalysts.

Construction of cerium oxide nanoparticles immobilized on the surface of zinc vanadate nanoflowers for accelerated photocatalytic degradation of tetracycline under visible light irradiation

Construction of Z-scheme heterojunction has been deemed to be an effective and promising approach to boost the photocatalytic activity on account of accelerating the separation efficiency of the photogenerated carriers and maintaining the strong redox ability. Herein, an attractive CeO₂/Zn₃V₂O₈ Z-scheme heterojunction photocatalyst was rationally constructed by zero-dimensional (0D) CeO₂ nanoparticles immobilized on the surface of three-dimensional (3D) Zn₃V₂O₈ nanoflowers using a simple mixing method, and applied to the photocatalytic degradation of tetracycline (TC) under visible light irradiation. As expected, it was observed that the prepared CeO₂/Zn₃V₂O₈ hybrid illustrated significantly boosted the photocatalytic activity for the elimination of TC compared to pure Zn₃V₂O₈. More importantly, the optimized CeO₂(40 wt%)/Zn₃V₂O₈ hybrid owned the largest elimination rate of TC with 1.13 × 10^-2 min^-1, which was around 8.1 and 3.8 times as high as single CeO₂ (0.14 × 10^-2 min^-1) and Zn₃V₂O₈ (0.30 × 10^-2 min^-1), respectively. The appreciable performance improvement was mainly ascribed to the formation of Z-scheme heterojunction between CeO₂ and Zn₃V₂O₈, facilitating the transfer rate of photogenerated carriers and remaining the high reducibility of photoexcited electrons in CeO₂ and strong oxidizability of photoinduced holes in Zn₃V₂O₈. Active species capture experiments and electron spin resonance spectra showed that superoxide radicals and holes were the main active species for TC degradation. Besides, the possible degradation pathways of TC were speculated by identifying degradation intermediates, and the reasonable degradation mechanism including migration and transport behaviors of charge carriers and generation processes of reactive species were revealed in depth. This investigation enriches Zn₃V₂O₈-based Z-scheme heterojunction photocatalytic system and offers a new inspiration for the construction and fabrication of high-efficiency Z-scheme heterojunction photocatalysts to remove the antibiotics from wastewater.

BiOBr/Ag/AgBr heterojunctions decorated carbon fiber cloth with broad-spectral photoresponse as filter-membrane-shaped photocatalyst for the efficient purification of flowing wastewater

The development of recyclable photocatalysts with broad-spectral photoresponse has drawn much attention for the practical application in flowing wastewater treatment. Herein, we have reported the construction of BiOBr/Ag/AgBr junctions on carbon fiber cloth (CFC) as broad-spectral-response filter-membrane-shaped photocatalyst that is efficient and easily recyclable. With CFC as the substrate, BiOBr nanosheets (diameter: 0.5-1 μm) were firstly synthesized by a hydrothermal method, and then Ag/AgBr nanoparticles (size: 100-300 nm) were prepared on the surface of CFC/BiOBr by using a chemical bath deposition route. CFC/BiOBr/Ag/AgBr presents superior flexibility and wide UV-Vis-NIR photoabsorption (from 200 to 1000 nm). Under visible light irradiation, CFC/BiOBr/Ag/AgBr (area: 4 × 4 cm²) can remove 99.8% rhodamine B (RhB), 99.0% acid orange 7 (AO7), and 93.0% tetracycline (TC) after 120 min, better than CFC/BiOBr (95.4% RhB, 55.0% AO7 and 91.2% TC). Interestingly, when CFC/BiOBr/Ag/AgBr is served as a filter-membrane in a photoreactor to purify the flowing sewage (RhB, rate: ~1.5 L h^-1), the degradation rate of RhB goes up to 90.0% after ten filtering grades. Therefore, CFC/BiOBr/Ag/AgBr has great potential to purify the flowing wastewater as a novel filter-membrane-shaped photocatalyst.

The Influence of Photoactive Heterostructures on the Photocatalytic Removal of Dyes and Pharmaceutical Active Compounds: A Mini-Review

The diversification of pollutants type and concentration in wastewater has underlined the importance of finding new alternatives to traditional treatment methods. Advanced oxidation processes (AOPs), among others, are considered as promising candidate to efficiently remove organic pollutants such as dyes or pharmaceutical active compounds (PhACs). The present minireview resumes several recent achievements on the implementation and optimization of photoactive heterostructures used as photocatalysts for dyes and PhACs removal. The paper is focused on various methods of enhancing the heterostructure photocatalytic properties by optimizing parameters such as synthesis methods, composition, crystallinity, morphology, pollutant concentration and light irradiation.