Recent advances on Bi2WO6-based photocatalysts for environmental and energy applications

Engineering a staggered type-II Bi2WO6/WO3 heterojunction with improved photocatalytic activity in wastewater treatment

In recent years, the removal organic pollutants from wastewater by advanced oxidation processes, especially photocatalysis, has become a meaningful approach due to its eco-friendliness and low cost. Herein, staggered type-II Bi2WO6/WO3 heterojunction photocatalysts were prepared by a facile hydrothermal route and investigated by modern physicochemical methods (X-ray diffraction, scanning electron microscopy, low-temperature nitrogen adsorption-desorption, and diffuse reflectance spectroscopy). The optimized BWOW-5 photocatalyst exhibited a H2O2-assisted photocatalytic methylene blue removal efficiency of 94.1% (k = 0.01414 min-1) within 180 min under optimal reaction conditions, which is much higher than that of unmodified Bi2WO6 and WO3 due to efficient separation of the photogenerated charge carriers. The trapping experiments demonstrated that photogenerated hydroxyl radicals and holes play a key role in the photodegradation reaction. Moreover, the optimized BWOW-5 heterojunction photocatalyst exhibited excellent activity in the H2O2-assisted degradation of other pollutants, namely phenol, isoniazid, levofloxacin, and dibenzothiophene with the removal rate of 63.1, 73.6, 95.0, and 72.4%, respectively. This investigation offers a design strategy for Bi2WO6-based multifunctional photocatalytic composites with improved activity for organic pollutant degradation.

Efficient photodegradation of antibiotics by g-C3N4 and 3D flower-like Bi2WO6 perovskite structure: Insights into the preparation, evaluation, and potential mechanism

Antibiotics are emerging organic pollutants that have attracted huge attention owing to their abundant use and associated ecological threats. The aim of this study is to develop and use photocatalysts to degrade antibiotics, including tetracycline (TC), ciprofloxacin (CIP), and amoxicillin (AMOX). Therefore, a novel Z-scheme heterojunction composite of g-C3N4 (gCN) and 3D flower-like Bi2WO6 (BW) perovskite structure was designed and developed, namely Bi2WO6/g-C3N4 (BW/gCN), which can degrade low-concentration of antibiotics in aquatic environments under visible light. According to the Density Functional Theory (DFT) calculation and the characterization results of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FITR), Scanning electron microscopy - energy spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS), this heterojunction was formed in the recombination process. Furthermore, the results of 15 wt%-BW/gCN photocatalytic experiments showed that the photodegradation rates (Rp) of TC, CIP, and AMOX were 92.4%, 90.1% and 82.3%, respectively, with good stability in three-cycle photocatalytic experiments. Finally, the quenching experiment of free radicals showed that the holes (h+) and superoxide radicals (·O2-) play a more important role than the hydroxyl radicals (·OH) in photocatalysis. In addition, a possible antibiotic degradation pathway was hypothesized on the basis of High performance liquid chromatography (HPLC) analysis. In general, we have developed an effective catalyst for photocatalytic degradation of antibiotic pollutants and analyzed its photocatalytic degradation mechanism, which provides new ideas for follow-up research and expands its application in the field of antibiotic composite pollution prevention and control.

CAZ Composite Photocatalysts for H2 Production and Degradation under Visible Light

g-C3N4/Ag-ZnO (CAZ) composite photocatalysts were synthesized successfully by the hydrothermal method. The photocatalytic performance of photocatalysts was assessed through experiments measuring both hydrogen (H2) production and the degradation of methylene blue (MB). The H2 production rate of 60% CAZ reached 2.450 mmol·g-1·h-1, which was 8.5 times that of g-C3N4. 25% CAZ degraded 99.14% of MB dye within 40 min, and its degradation rate constant was 12.4 times that of g-C3N4. CAZ composite photocatalysts have good synergistic properties in degradation and hydrogen production and exhibit better photocatalytic performance. A Z-scheme photocatalytic system mechanism of CAZ has been proposed for the enhanced H2 production and photocatalytic degradation rate.

UV-Vis-NIR Broadband Self-Powered CuInS2/SnO2 Photodetectors and the Application in Encrypted Optical Communication

Photodetectors (PDs) with broadband photoresponse can meet the demand for multiband detection in complex environments, overcoming the technological complexity issue of integrated narrow-band PDs. Self-powered heterojunction PDs having ultraviolet-visible-near-infrared broadband photoresponse were constructed by using SnO2 nanopillars and CuInS2 nanoflakes. The dimension, crystalline quality, and energy level structure of the SnO2 nanopillars were regulated by changing the concentration of Sn ions in the precursor solution. The optimized interfacial energy band structure of the heterojunction can increase the transfer ability of the photogenerated carrier. The optimum performance is achieved for the CuInS2/SnO2(0.025M) PD prepared at 0.025 M Sn ion concentration in the precursor solution with the responsivities of 1.15, 6.13, and 1.02 mA/W, and detectivities of 1.19 × 1010, 6.35 × 1010, and 1.02 × 1010 Jones under 254 nm solar-blind ultraviolet light, 475 nm visible light, and 940 nm near-infrared light. Furthermore, a proof-of-concept solar-blind ultraviolet-visible-near-infrared encrypted communication system utilizing a broadband self-powered CuInS2/SnO2 PD as the receiving terminal and solar-blind ultraviolet light, ultraviolet light, visible light, and near-infrared light as the carrier and encryption protocol is proposed. The PD has great potential for applications in the field of encrypted optical communication.

Constructing a 3D Bi2WO6/ZnIn2S4 direct Z-scheme heterostructure for improved photocatalytic CO2 reduction performance

Developing efficient heterojunction photocatalysts with enhanced charge transfer and reduced recombination rates of photogenerated carriers is crucial for harnessing solar energy in the photocatalytic CO2 reduction into renewable fuels. This study employed electrostatic self-assembly techniques to construct a 3D Bi2WO6/ZnIn2S4 direct Z-scheme heterojunctions. The unique 3D structure provided abundant active sites and facilitated CO2 adsorption. Moreover, the optimized Bi2WO6/ZnIn2S4 composite demonstrated an impressive CH4 yield of 19.54 μmol g-1 under 4 h of simulated sunlight irradiation, which was about 8.73 and 16.30-fold higher than pure ZnIn2S4 and Bi2WO6. The observed enhancements in photocatalytic performance are attributed to forming a direct Z-scheme heterojunction, which effectively promotes charge transport and migration. This research introduces a novel strategy for constructing photocatalysts through the synergistic effect of morphological interface modifications.

Surface termination modulation for superior S-Scheme Bi2WO6/BiOI heterojunction photocatalyst: a hybrid density functional study

The prevailing theoretical frameworks indicate that depending on the growth conditions, the Bi2WO6(001) surface can manifest in three distinct terminations-DL-O-Bi (DL: double layers), O-Bi, and O-W. In this study, we conduct a comprehensive examination of the interplay between these terminations on Bi2WO6(001) and the 1I-terminated BiOI(001) facet, especially focusing on their impact on the photocatalytic activity of Bi2WO6/BiOI heterostructure, applying hybrid functional calculations. The models formulated for this research are designated as Bi2WO6(O-Bi)/BiOI(1I), Bi2WO6(DL-O-Bi)/BiOI(1I), and Bi2WO6(O-W)/BiOI(1I). Our findings reveal that Bi2WO6(O-Bi)/BiOI(1I) shows a type II band alignment, which facilitates the spatial separation of photo-generated electrons and holes. Notably, the Bi2WO6(DL-O-Bi)/BiOI(1I) configuration has the lowest binding energy and results in an S-scheme (or Step-scheme) heterostructure. In contrast to the type II heterostructure, this particular configuration demonstrates enhanced photocatalytic efficiency due to improved photo-generated carrier separation, augmented oxidation capability, and better visible-light absorption. Conversely, Bi2WO6(O-W)/BiOI(1I) presents a type I projected band structure, which is less conducive for the separation of photo-generated electron-hole pairs. In summation, this investigation points out that one could significantly refine the photocatalytic efficacy of not only Bi2WO6/BiOI but also other heterostructure photocatalysts by modulating the coupling of different terminations via precise crystal synthesis or growth conditions.

Construction of built-in correction photoelectrochemical sensing platform for diagnosis of Alzheimer's disease

The occurrence of Alzheimer's disease (AD) is strongly associated with the progressive aggregation of a 42-amino-acid fragment derived from the amyloid-β precursor protein (Aβ1-42). Therefore, it is crucial to establish a versatile platform that can effectively detect Aβ1-42 to aid in the early-stage preclinical diagnosis of AD. Herein, we introduce a specialized split-type analytical platform that enables sensitive and accurate monitoring of Aβ1-42 based on a self-corrected photoelectrochemical (PEC) sensing system. To realize this design, gelatinized Ti3C2@Bi2WO6 Schottky heterojunctions were prepared and served as photoelectrodes for tackling the photoinduced charge carriers. Functionalized CaCO3@CuO2 nanocomposites were used as signal converters to detect Aβ1-42 and amplify the signal further. Benefiting from the glucose oxidation induced acid microenvironment and H2O2 output, the nanocomposites are able to rapidly decompose, producing Ca2+ and Fenton-like catalyst Cu2+. The Cu2+-driven Fenton-like reaction generated ·OH, which accelerated the 3,3',5,5'-tetramethylbenzidine (TMB) oxidation. Additionally, Ca2+ was cross-linked with alginate inducing gelation on the surface of Ti3C2@Bi2WO6 Schottky heterojunctions, influencing mass transfer and light absorption. Eventually results in the shift of photocurrent, allowing for precise quantification with a detection limit of 0.06 pg mL-1. The combination of colorimetric variation and the photoelectric effect provide a more accurate and reliable result. This research opens up new possibilities for constructing PEC platforms and beyond.

Research progress, trends, and updates on pollutants removal by Bi2WO6-based photocatalysts under visible light irradiation

In recent years, extensive research has been conducted on bismuth tungstate (Bi2WO6) in the field of photocatalysis owing to its unique crystal structure and favorable bandgap. This study offers a comprehensive review of the research on Bi2WO6-based photocatalysts from 2007 to 2022 using bibliometric analysis. The analysis utilized the Web of Science Core Collection Database and encompassed a dataset of 2064 publications. The bibliometric analysis and science mapping were carried out using the bibliometix R-package and CiteSpace software. This analysis examined and discussed the network of relationships among countries, journals, organizations, authors, and keywords pertaining to the topic and subtopics under investigation. The findings demonstrate that China has played a significant role in this research area and has formed close collaborations with other countries. The identification of highly-cited emerging terms suggests that enhancing the photocatalytic performance of Bi2WO6-based nanomaterials is a primary research focus. Moreover, there has been increasing interest in exploring the synergistic effects of photocatalysis and adsorption as a means to improve catalytic efficiency. This study provides valuable insights for researchers seeking a deeper understanding of Bi2WO6-based photocatalysts.

UV-light-responsive Ag/TiO2/PVA nanocomposite for photocatalytic degradation of Cr, Ni, Zn, and Cu heavy metal ions

The rapid growth of industrialization has led to the uncontrolled pollution of the environment, and rapid action is needed. This study synthesized Ag/TiO2/polyvinyl alcohol (PVA) nano photocatalyst for promising light-derived photocatalytic removal of heavy metal ions. The design of experiment (DOE) was used to study the effect of important factors (pH, reaction time, and photocatalyst dosage) to maximize the final performance of the photocatalyst. In the optimized condition, the Ag/TiO2/PVA nano-photocatalyst removed more than 94% of Cr6+ in 180 min, and the efficiency was more than 70% for Cu2+, Zn2+, and Ni2+ metal ions. The adsorption of the heavy metal ions on the photocatalyst was described well with the Langmuir isotherm, while the pseudo-second-order linear kinetic model fitted with the experimental data. The nano-photocatalyst's stability was confirmed after maintaining its performance for five successive runs. The enhanced photocatalytic activity for the heavy metal ions removal can be attributed to the presence of metallic silver nanoparticles (electron transfer and plasmonic fields mechanisms) and PVA, which delayed the recombination of electron-hole. The synthesized ternary Ag/TiO2/PVA nano-photocatalyst showed promising performance for the elimination of heavy metal ions and can be used for environmental remediation purposes.

Immobilization of Bi2WO6 on Polymer Membranes for Photocatalytic Removal of Micropollutants from Water - A Stable and Visible Light Active Alternative

In this work, bismuth tungstate Bi2WO6 is immobilized on polymer membranes to photocatalytically remove micropollutants from water as an alternative to titanium dioxide TiO2. A synthesis method for Bi2WO6 preparation and its immobilization on a polymer membrane is developed. Bi2WO6 is characterized using X-ray diffraction and UV-vis reflectance spectroscopy, while the membrane undergoes analysis through scanning electron microscopy, X-ray photoelectron spectroscopy, and degradation experiments. The density of states calculations for TiO2 and Bi2WO6, along with PVDF reactions with potential reactive species, are investigated by density functional theory. The generation of hydroxyl radicals OH• is investigated via the reaction of coumarin to umbelliferone via fluorescence probe detection and electron paramagnetic resonance. Increasing reactant concentration enhances Bi2WO6 crystallinity. Under UV light at pH 7 and 11, the Bi2WO6 membrane completely degrades propranolol in 3 and 1 h, respectively, remaining stable and reusable for over 10 cycles (30 h). Active under visible light with a bandgap of 2.91 eV, the Bi2WO6 membrane demonstrates superior stability compared to a TiO2 membrane during a 7-day exposure to UV light as Bi2WO6 does not generate OH• radicals. The Bi2WO6 membrane is an alternative for water pollutant degradation due to its visible light activity and long-term stability.

Novel Ag-Bridged Z-Scheme CdS/Ag/Bi2WO6 Heterojunction: Excellent Photocatalytic Performance and Insight into the Underlying Mechanism

The construction of semiconductor heterojunction photocatalysts that improve the separation and transfer of photoinduced charge carriers is an effective and widely employed strategy to boost photocatalytic performance. Herein, we have successfully constructed a CdS/Ag/Bi2WO6 Z-scheme heterojunction with an Ag-bridge as an effective charge transfer channel by a facile process. The heterostructure consists of both CdS and Ag nanoparticles anchored on the surface of Bi2WO6 nanosheets. The photocatalytic efficiency of the CdS/Ag/Bi2WO6 system was studied by the decontamination of tetracycline (TC) and Rhodamine B (RhB) under visible light irradiation (λ ≥ 420). The results exhibited that CdS/Ag/Bi2WO6 shows markedly higher photocatalytic performance than that of CdS, Bi2WO6, Ag/Bi2WO6, and CdS/Bi2WO6. The trapping experiment results verified that the •O2- and h+ radicals are the key active species. The results of photoluminescence spectral analysis and photocurrent responses indicated that the CdS/Ag/Bi2WO6 heterojunctions exhibit exceptional efficiency in separating and transferring photoinduced electron-hole pairs. Based on a series of characterization results, the boosted photocatalytic activity of the CdS/Ag/Bi2WO6 system is mostly due to the successful formation of the Ag-bridged Z-scheme heterojunction; these can not only inhibit the recombination rate of photoinduced charge carriers but also possess a splendid redox capacity. The work provides a way for designing a Z-scheme photocatalytic system based on Ag-bridged for boosting photocatalytic performance.

Optimizing physico-chemical properties of hierarchical ZnO/TiO2 nano-film by the novel heating method for photocatalytic degradation of antibiotics and dye

The design of semiconductor catalysts with excellent photocatalytic properties, stability, recyclability, and good separation for the treatment of polluted water is still challenging. In this paper, the ZnO/TiO2 nano-thin films were fabricated using the magnetron sputtering technique and then heating the underlying ZnO layer and the upper TiO2 layer for their respective optimal heating time, i. e. heating ZnO for 3 h and heating TiO2 for 2 h. The as-prepared films were characterized. The results show that the preferred growth of TiO2 grains along the [001] axis, relatively large specific surface area, and increased amounts of surface oxygen vacancies (OVs) were induced to the heterojunction catalysts through this optimized heating strategy, which boosts the photocatalytic activity of ZnO/TiO2 nano-film. The degradation experiment inndicates that the ciprofloxacin (CIP) removal efficiency can reach 97.3% in 2 h duration, which was higher than that of the samples annealed for the same periods. Meanwhile, the prepared ZnO/TiO2 photocatalytic film exhibited favorable stability of 95.5% degradation efficiency after the fourth run and general applicability for the photodegradation of various contantains, whih removed 99.5% of ofloxacin (OFX) and 77.6% of tetracycline (TC) in 2 h and 94.1% of Rhodamine B (RhB) in 1 h. This work is expected to yields a novel insight into the production of heterojunction photocatalysts with excellen ability for photocatalytic degradation of pollutants in the practical industry.

Recent Progress in Photocatalytic Degradation of Water Pollution by Bismuth Tungstate

Photocatalysis has emerged as a highly promising, green, and efficient technology for degrading pollutants in wastewater. Among the various photocatalysts, Bismuth tungstate (Bi2WO6) has gained significant attention in the research community due to its potential in environmental remediation and photocatalytic energy conversion. However, the limited light absorption ability and rapid recombination of photogenerated carriers hinder the further improvement of Bi2WO6's photocatalytic performance. This review aims to present recent advancements in the development of Bi2WO6-based photocatalysts. It delves into the photocatalytic mechanism of Bi2WO6 and summarizes the achieved photocatalytic characteristics by controlling its morphology, employing metal and non-metal doping, constructing semiconductor heterojunctions, and implementing defective engineering. Additionally, this review explores the practical applications of these modified Bi2WO6 photocatalysts in wastewater purification. Furthermore, this review addresses existing challenges and suggests prospects for the development of efficient Bi2WO6 photocatalysts. It is hoped that this comprehensive review will serve as a valuable reference and guide for researchers seeking to advance the field of Bi2WO6 photocatalysis.

Outstanding photo-thermo synergy in aerobic oxidation of cyclohexane by bismuth tungstate-bismuth oxychloride high-low heterojunction

The difficulty of achieving both high conversion rate and high selectivity is a huge challenge in the catalytic aerobic oxidation of cyclohexane. In this paper, bismuth tungstate-bismuth oxychloride (Bi2WO6-BiOCl) nanoflower heterojunctions prepared via a one-step solvothermal process were applied in the photo-thermo synergetic catalytic oxidation of cyclohexane in the dried air. With the addition of little water at different reaction temperature, the ratio of bismuth to tungsten and the mass ratio of Bi2WO6 to BiOCl can be precisely tailored in the nanoflower sphere composites with thin nanosheets. Their microscopic morphology, elemental composition, crystal structure, and photoelectrochemical characteristics were explored by different characterization methods. The Bi2WO6-BiOCl composites possessed poor photocatalytic and thermal performances with the low conversion rates of 1.43% and 2.68%, respectively. However, through the photo-thermo catalytic oxidation process, an exceptional conversion rate of 13.32% was achieved with excellent selectivity of 99.22% for cyclohexanone and cyclohexanol (KA oil) using the same Bi2WO6-BiOCl composites. This superior performance outstrips Bi2WO6 flowers, BiOCl nanosheets and Bi2WO6-BiOCl composites with other compounding ratios. The creation of a high-low heterojunction in the Bi2WO6-BiOCl composite was confirmed by band energy analysis. The opto-electronic analysis, band energy analysis, sacrifice experiments, and active radical analysis were employed to elucidate the mechanism for the exceptional photo-thermo catalytic performance in detail. This work offers an exploratory solution to the challenges of high energy consumption and the difficulty in simultaneously achieving high selectivity and high conversion rates in cyclohexane oxidation, thus holding significant value.

Assisted assembling of Bi2WO6/rGO composites: A 3D/2D Hierarchical nanostructures for enhanced photocatalytic water remediation and photo-(electro)catalytic water splitting proficiency

The current study explores the possibility of effectively improving Bi2WO6 (BWO) nanostructures in photocatalytic clean H2 generation and treating water from pharmaceutical wastes. BWO nanoparticles (NPs) hybridized with carbon-derived materials proved to be an efficient candidate in the field of photocatalysis. In this work, BWO nanostructures have been synthesized via the facile co-precipitation technique. The reduced graphene oxide (r-GO) was used as the carbon derivative for the hybridization process. Furthermore, different weight percentages of rGO were loaded with BWO NPs through the wet impregnation technique. The structural, and morphological analysis confirmed the formation of BWO/x% rGO composites. UV-DRS analysis showcased the reduction in bandgap in annexure with increased light absorbance region upon rGO inclusion. Time-resolved photoluminescence (TRPL) proved a prolonged lifetime for BWO/15% rGO composite. In addition, their photocatalytic abilities were put to the test, and BWO/15% rGO nano-hybrid demonstrated a superior degradation of pharmaceutical wastes like tetracycline hydrochloride (TCH) and levofloxacin (LVX) from water in 15 min. Furthermore, photo-electrochemical measurements showed the lowest onset potential and better charge transfer for efficient splitting of water. The photocatalytic water splitting was performed in the presence of sacrificial agents and in the absence of sacrificial agents, where BWO/15% rGO exhibited maximum H2 evolution.

Achieving Enhanced Visible-Near-Infrared Light Absorption in Stable Lead-Free Vanadium-Based Perovskite Nanocrystals via Structural Regulation

Lead-free halide perovskites are promising materials for solar energy applications. However, their efficiency is hindered by poor light absorption in the visible-near-infrared region. Herein, we introduce vanadium (V) with low-lying ground/excited-state energy levels to form two types of stable lead-free V-based perovskite (Cs2NaVCl6 and Cs3V2Cl9) colloidal nanocrystals (NCs) with strong light absorption covering the ultraviolet to near-infrared region. We find the absorption can be further enhanced by structural regulation, in which the zero-dimensional (0D) Cs3V2Cl9 NCs show stronger and red-shifted (up to 1400 nm) light absorption compared to the three-dimensional Cs2NaVCl6 NCs. In 0D Cs3V2Cl9 NCs, [V2Cl9]3- dimers play a vital role in governing strong visible-near-infrared light absorption. We demonstrated their application for photocatalytic CO2 reduction. Our work sheds light on the structure-property relationship governing the absorption behavior, providing a novel route for tuning the light absorption ability of lead-free halide perovskites.

An Emerging Family of Piezocatalysts: 2D Piezoelectric Materials

Piezocatalysis is an emerging technique that holds great promise for the conversion of ubiquitous mechanical energy into electrochemical energy through piezoelectric effect. However, mechanical energies in natural environment (such as wind energy, water flow energy, and noise) are typically tiny, scattered, and featured with low frequency and low power. Therefore, a high response to these tiny mechanical energies is critical to achieving high piezocatalytic performance. In comparison to nanoparticles or 1D piezoelectric materials, 2D piezoelectric materials possess characteristics such as high flexibility, easy deformation, large surface area, and rich active sites, showing more promise in future for practical applications. In this review, state-of-the-art research progresses on 2D piezoelectric materials and their applications in piezocatalysis are provided. First, a detailed description of 2D piezoelectric materials are offered. Then a comprehensive summary of the piezocatalysis technique is presented and examines the piezocatalysis applications of 2D piezoelectric materials in various fields, including environmental remediation, small-molecule catalysis, and biomedicine. Finally, the main challenges and prospects of 2D piezoelectric materials and their applications in piezocatalysis are discussed. It is expected that this review can fuel the practical application of 2D piezoelectric materials in piezocatalysis.

Aurivillius-layered Bi2WO6 nanoplates with CoOx cocatalyst as high-performance piezocatalyst for hydrogen evolution

Developing a high-performance piezocatalyst that directly transforms mechanical energy into hydrogen is highly desirable in the field of new energy. Herein, the Aurivillius-layered Bi2WO6 (BWO) nanoplates are prepared through a hydrothermal reaction at a moderate temperature of 160 °C, and exhibit strong piezoelectric properties, enabling them to catalyze water splitting through ultrasonic-induced piezocatalysis effect. The hydrogen evolution reaction (HER) and H2O2 generation efficiencies are measured to be 0.43 and 0.36 mmol g-1 h-1, respectively. To further boost piezocatalytic performance, cobalt oxide nanoparticles are intentionally photo-deposited onto these nanoplates as cocatalyst. This configuration results in a significantly boosted HER performance with an efficiency of 3.59 mmol g-1 h-1, which is 2.8 times higher than that of pristine nanoplates and demonstrates strong competitiveness compared to other reported piezocatalysts. The cobalt oxide cocatalyst plays a crucial role in facilitating efficient charge separation and migration, increasing the charge concentration, and ultimately enhancing piezocatalytic HER activity. Overall, this work highlights the potential of Aurivillius-layered bismuth oxide compounds as efficient piezocatalysts and provides valuable insights for designing high-performance piezocatalysts in the field of new energy.

Photoelectrochemical Methods for the Determination of the Flat-Band Potential in Semiconducting Photocatalysts: A Comparison Study

In addition to the band gap of a semiconducting photocatalyst, its band edges are important because they play a crucial role in the analysis of charge transfer and possible pathways of the photocatalytic reaction. The Mott-Schottky method using electrochemical impedance spectroscopy is the most common experimental technique for the determination of the electron potential in photocatalysts. This method is well suited for large crystals, but in the case of nanocatalysts, when the thickness of the charged layer is comparable with the size of the nanocrystals, the capacitance of the Helmholtz layer can substantially affect the measured potential. A contact between the electrolyte and the substrate, used for deposition of the photocatalyst, also affects the impedance. Application of other photoelectrochemical methods may help to avoid concerns in the interpretation of impedance data and improve the reliability of measurements. In this study, we have successfully prepared five visible-light active photocatalysts (i.e., N-doped TiO2, WO3, Bi2WO6, CoO, and g-C3N4) and measured their flat-band potentials using four (photo)electrochemical methods. The potentials are compared for all methods and discussed regarding the type of semiconducting material and its properties. The effect of methanol as a sacrificial agent for the enhanced transfer of charge carriers is studied and discussed for each method.

Bromine Ion-Intercalated Layered Bi2WO6 as an Efficient Catalyst for Advanced Oxidation Processes in Tetracycline Pollutant Degradation Reaction

The visible-light-driven photocatalytic degradation of pharmaceutical pollutants in aquatic environments is a promising strategy for addressing water pollution problems. This work highlights the use of bromine-ion-doped layered Aurivillius oxide, Bi2WO6, to synergistically optimize the morphology and increase the formation of active sites on the photocatalyst's surface. The layered Bi2WO6 nanoplates were synthesized by a facile hydrothermal reaction in which bromine (Br-) ions were introduced by adding cetyltrimethylammonium bromide (CTAB)/tetrabutylammonium bromide (TBAB)/potassium bromide (KBr). The as-synthesized Bi2WO6 nanoplates displayed higher photocatalytic tetracycline degradation activity (~83.5%) than the Bi2WO6 microspheres (~48.2%), which were obtained without the addition of Br precursors in the reaction medium. The presence of Br- was verified experimentally, and the newly formed Bi2WO6 developed as nanoplates where the adsorbed Br- ions restricted the multilayer stacking. Considering the significant morphology change, increased specific surface area, and enhanced photocatalytic performance, using a synthesis approach mediated by Br- ions to design layered photocatalysts is expected to be a promising system for advancing water remediation.

A machine learning-based nano-photocatalyst module for accelerating the design of Bi2WO6/MIL-53(Al) nanocomposites with enhanced photocatalytic activity

It is a great challenge to acquire novel Bi2WO6/MIL-53(Al) (BWO/MIL) nanocomposites with excellent catalytic activity by the trial-and-error method in the vast untapped synthetic space. The degradation rate of Rhodamine B dye (DRRhB) can be used as the main parameter to evaluate the catalytic activity of BWO/MIL nanocomposites. In this work, a machine learning-based nano-photocatalyst module was developed to speed up the design of BWO/MIL with desirable performance. Firstly, the DRRhB dataset was constructed, and four key features related to the synthetic conditions of BWO/MIL were filtered by the forward feature selection method based on support vector regression (SVR). Secondly, the SVR model with radical basis function for predicting the DRRhB of BWO/MIL was established with the key features and optimal hyperparameters. The correlation coefficients (R) between predicted and experimental DRRhB were 0.823 and 0.884 for leave-one-out cross-validation (LOOCV) and the external test, respectively. Thirdly, potential BWO/MIL nanocomposites with higher DRRhB were discovered by inverse projection, the prediction model, and virtual screening from the synthesis space. Meanwhile, an online web service (http://1.14.49.110/online_predict/BWO2) was built to share the model for predicting the DRRhB of BWO/MIL. Moreover, sensitivity analysis was brought into boosting the model's explainability and illustrating how the DRRhB of BWO/MIL changes over the four key features, respectively. The method mentioned here can provide valuable clues to develop new nanocomposites with the desired properties and accelerate the design of nano-photocatalysts.

2D/2D Biochar/Bi2WO6 Hybrid Nanosheets with Enhanced Visible-Light-Driven Photocatalytic Activities for Organic Pollutants Degradation

In this work, a novel two-dimensional/two-dimensional (2D/2D) hybrid photocatalyst consisting of Bi2WO6 (BWO) nanosheets and cotton fibers biochar (CFB) nanosheets was successfully prepared via a facile hydrothermal process. The as-prepared photocatalysts were characterized by a variety of techniques, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectroscopy. It was revealed that amorphous CFB nanosheets were uniformly immobilized on the surface of crystalline BWO nanosheets, and an intimate contact between CFB and BWO was constructed. The photocatalytic activities of the prepared BWO and CFB-BWO photocatalysts were evaluated by photocatalytic degradation of rhodamine B (RhB) and tetracycline hydrochloride (TC-HCl) in aqueous solutions under visible-light irradiation. Compared to the pristine BWO, the CFB-BWO composite photocatalysts exhibited significant enhancement in photocatalytic activities. Among all CFB-BWO samples, the 9CFB-BWO sample with the CFB mass ratio of 9% exhibited optimal photocatalytic activities for RhB or TC-HCl degradation, which was ca. 1.8 times or 2.4 times that of the pristine BWO, respectively. The improvement in photocatalytic activities of the CFB-BWO photocatalysts could be ascribed to the enhanced migration and separation of photogenerated charge carriers due to the formation of a 2D/2D interfacial heterostructure between CFB and BWO. Meanwhile, the possible mechanism of CFB-BWO for enhanced photocatalytic performance was also discussed. This work may provide a new approach to designing and developing novel BWO-based photocatalysts for the highly efficient removal of organic pollutants.

Ionic liquids assisted preparation of BiPO4 photocatalyst with enhanced photocatalytic activity for tetracycline and rhodamine B removal

In this work, BiPO4 (BPO)-based photocatalyst was successfully synthesized by a conventional hydrothermal strategy using bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) and 1-ethyl-3-methylimidazolium dihydro phosphate ([EMIm]H2PO4). [EMIm]H2PO4 can serve as a phosphorus source and surfactant. Photocatalytic activities of the photocatalysts prepared were evaluated by the destruction of rhodamine B (RhB) and tetracycline (TC) under UV light irradiation, respectively. The results reveal that the sample (IL-BPO) synthesized with the assistance of ionic liquid exhibits enhanced photocatalytic activity in comparison with the reference BiPO4. The significantly improved photocatalytic activity of IL-BPO can be mainly attributed to the boosted separation of photoinduced electron-hole pairs (e-/h+) and richer oxygen vacancies (OVs).

Bismuth tungstate Bi2WO6: a review on structural, photophysical and photocatalytic properties

This review paper provides a comprehensive overview of the recent trends in bismuth tungstate (Bi₂WO₆) research, covering its structural, electrical, photoluminescent, and photocatalytic properties. The structural characteristics of bismuth tungstate are explored in detail, including its different allotropic crystal structures with respect to its isotypic materials. The electrical properties of bismuth tungstate, such as its conductivity and electron mobility, are also discussed, along with its photoluminescent properties. The photocatalytic activity of bismuth tungstate is a particular focus, with recent advances in doping and co-doping strategies with metals, rare earth and other elements summarized. The limitations and challenges of using bismuth tungstate as a photocatalyst are also examined, such as its low quantum efficiency and susceptibility to photodegradation. Finally, recommendations for future research directions are provided, including the need for further studies on the underlying mechanisms of photocatalytic activity, the development of more efficient and stable bismuth tungstate-based photocatalysts, and the exploration of new applications in fields such as water treatment and energy conversion.

The Precision Defect Engineering with Nonmetallic Element Refilling Strategy in g-C3 N4 for Enhanced Photocatalytic Hydrogen Production

Traditional defect engineering and doping strategies are considered effective means for improving H₂ evolution, but the uncontrollability of the modification process does not always lead to efficient activity. A defect-induced heteroatom refilling strategy is used here to synthesize heteroatoms introduced carbon nitride by precisely controlling the "introduction" sites on efficient N1 sites. Density functional theory calculations show that the refilling of B, P, and S sites have stronger H₂ O adsorption and dissociation capacity than traditional doping, which makes it an optimal H₂ production path. The large internal electric field strength of heteroatom-refilled catalysts leads to fast electron transfer and the hydrogen production of the best sample is up to 20.9 mmol g^-1  h^-1 . This work provides a reliable and clear insight into controlled defect engineering of photocatalysts and a universal modification strategy for typical heteroatom and co-catalyst systems for H₂ production.

Bismuth-based nanostructured photocatalysts for the remediation of antibiotics and organic dyes

A serious threat to human health and the environment worldwide, in addition to the global energy crisis, is the increasing water pollution caused by micropollutants such as antibiotics and persistent organic dyes. Nanostructured semiconductors in advanced oxidation processes using photocatalysis have recently attracted a lot of interest as a promising green and sustainable wastewater treatment method for a cleaner environment. Due to their narrow bandgaps, distinctive layered structures, plasmonic, piezoelectric and ferroelectric properties, and desirable physicochemical features, bismuth-based nanostructure photocatalysts have emerged as one of the most prominent study topics compared to the commonly used semiconductors (TiO₂ and ZnO). In this review, the most recent developments in the use of photocatalysts based on bismuth (e.g., BiFeO₃, Bi₂MoO₆, BiVO₄, Bi₂WO₆, Bi₂S₃) to remove dyes and antibiotics from wastewater are thoroughly covered. The creation of Z-schemes, Schottky junctions, and heterojunctions, as well as morphological modifications, doping, and other processes are highlighted regarding the fabrication of bismuth-based photocatalysts with improved photocatalytic capabilities. A discussion of general photocatalytic mechanisms is included, along with potential antibiotic and dye degradation pathways in wastewater. Finally, areas that require additional study and attention regarding the usage of photocatalysts based on bismuth for removing pharmaceuticals and textile dyes from wastewater, particularly for real-world applications, are addressed.

Bismuth-doped g-C3N4/ZIF-8 heterojunction photocatalysts with enhanced photocatalytic performance under visible light illumination

In this work, g-C₃N₄/ZIF-8 heterojunction photocatalysts were synthesised by the process by which the metal-organic framework ZIF-8 nanoparticles were grown onto the g-C₃N₄ layer in situ. Bismuth element was doped into the as-prepared g-C₃N₄/ZIF-8 material and a new type of Bi@g-C₃N₄/ZIF-8 composite photocatalysts was manufactured, in which the doping element acts in adjusting the bandgap in the photocatalysts. The prepared photocatalysts were characterised by XRD, FESEM, TEM, FTIR, XPS, UV-VIS DRS, photoluminescence and photo-electrochemical experiments. The results show that the ZIF-8 nanoparticles grown in situ were well-formed onto the g-C₃N₄ layer, and bismuth was evenly doped into the gaps of the g-C₃N₄/ZIF-8 framework. The degradation rate of methylene blue by CNZ-1.5(Bi)-12, which was a photocatalyst composed of 12% Bi-doped with g-C₃N₄/ZIF-8 material (the mass ratio of g-C₃N₄: ZIF-8 = 1:1.5), reached 86.6% under visible light irradiation within 60 min. The free radical scavenging experiment and electron spin resonance spectroscopy showed that ∙OH was the main active substance. Bismuth doping into the photocatalytic system promotes the excitation of electrons from the valence band to the conduction band and provides a good channel for the transmission of photogenerated carriers as well. It is achieved that intensive visible light absorption, the enhanced separation efficiency of photogenerated carriers, and excellent thermal stability and high recyclability in the novel composite photocatalyst, owing to the synergistic effect of the introduced bismuth with the heterostructure of g-C₃N₄/ZIF-8. Therefore, the synthesised Bi@g-C₃N₄/ZIF-8 heterojunction photocatalysts may be used as a good photocatalyst for purifying and degrading organic matter in sewage.

Novel Bi2WO6/ZnSnO3 heterojunction for the ultrasonic-vibration-driven piezocatalytic degradation of RhB

This study designed and prepared a new piezoelectric catalytic nanomaterial, Bi₂WO₆/ZnSnO₃, and applied it in piezocatalytic water purification. Results indicated that the composite had superior piezocatalytic efficiency and stability in rhodamine B (RhB) degradation under ultrasonic vibration. The Bi₂WO₆/ZnSnO₃ sample with 10% Bi₂WO₆ had the optimum activity with a degradation rate of 2.15 h^-1, which was 7.4 and 11.3 times that of ZnSnO₃ and Bi₂WO₆, respectively. Various characterizations were conducted to study the morphology, structure, and piezoelectric properties of the Bi₂WO₆/ZnSnO₃ composites and reveal the reasons for their improved piezocatalytic performance. Results showed that ZnSnO₃ cubes were dispersed throughout the surface of Bi₂WO₆ nanosheets, which enhanced the specific surface area and facilitated the piezocatalytic reaction. Additionally, type-II heterojunction structures formed at the contact interface of Bi₂WO₆ and ZnSnO₃, driving the migration of piezoelectric-induced electrons and holes. Accordingly, the separation efficiency of charge carriers improved, and the piezoelectric catalytic activity was significantly enhanced. This study may provide a potential composite catalyst and a promising idea for the design of highly efficient piezoelectric catalyst.

Enhanced photocatalytic degradation of tetracycline by a H2O2-assisted Bi3NbO7/Bi2Sn2O7 composite under visible light

A Z-scheme BNO/BSO composite photocatalyst has been successfully prepared using an in situ solvothermal method. The phase component, microstructure and optical properties of the as-prepared samples were characterized using X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy and other means. The photocatalytic performance of the BNO/BSO composite was evaluated via the degradation of the typical antibiotic tetracycline (TC) under hydrogen peroxide assistance and visible light irradiation. The "cata + H₂O₂ + vis" system shows the best photocatalytic activity, and its apparent rate constant reaches 0.03164 min^-1, which is 4.9 times and 5.7 times that of the "cata + vis" system and the "cata + H₂O₂" system, respectively. Compared with pristine that of BSO alone, the reaction rate constant of the 15% BNO/BSO composite increases 1.8 times. The enhanced photocatalytic activity is attributed to the construction of a unique Z-scheme-type heterojunction, which effectively suppresses the recombination of electron-hole pairs. In addition, the addition of H₂O₂ promotes the generation of more active species. Moreover, a possible photocatalytic degradation mechanism is also further proposed.

Bismuth-Based Multi-Component Heterostructured Nanocatalysts for Hydrogen Generation

Developing a unique catalytic system with enhanced activity is the topmost priority in the science of H2 energy to reduce costs in large-scale applications, such as automobiles and domestic sectors. Researchers are striving to design an effective catalytic system capable of significantly accelerating H2 production efficiency through green pathways, such as photochemical, electrochemical, and photoelectrochemical routes. Bi-based nanocatalysts are relatively cost-effective and environmentally benign materials which possess advanced optoelectronic properties. However, these nanocatalysts suffer back recombination reactions during photochemical and photoelectrochemical operations which impede their catalytic efficiency. However, heterojunction formation allows the separation of electron–hole pairs to avoid recombination via interfacial charge transfer. Thus, synergetic effects between the Bi-based heterostructured nanocatalysts largely improves the course of H2 generation. Here, we propose the systematic review of Bi-based heterostructured nanocatalysts, highlighting an in-depth discussion of various exceptional heterostructures, such as TiO2/BiWO6, BiWO6/Bi2S3, Bi2WO6/BiVO4, Bi2O3/Bi2WO6, ZnIn2S4/BiVO4, Bi2O3/Bi2MoO6, etc. The reviewed heterostructures exhibit excellent H2 evolution efficiency, ascribed to their higher stability, more exposed active sites, controlled morphology, and remarkable band-gap tunability. We adopted a slightly different approach for reviewing Bi-based heterostructures, compiling them according to their applicability in H2 energy and discussing challenges, prospects, and guidance to develop better and more efficient nanocatalytic systems.

Construction of Bi2WO6 with double active sites of tunable metallic Bi and oxygen vacancies for photocatalytic oxidation of cyclohexane to cyclohexanone

Oxygen-containing organics, which are generated from the selective oxidation of their corresponding hydrocarbons, have high value in the chemical and pharmaceutical industries. However, their oxidation reactions are very challenging as the products are more active than the substrates, especially for the oxidation of cyclohexane (CHA). Herein, we focused on the one-step preparation of Bi₂WO₆ with double active sites of tunable metallic Bi and oxygen vacancies (OV-Bi/Bi₂WO₆) by a facile solvothermal treatment. Then, OV-Bi/Bi₂WO₆ was used as an efficient photocatalyst for the partial oxidation of CHA to cyclohexanone (CHA-one) for the first time in air as an oxidant under solvent-free and room temperature conditions. The Bi : Bi₂WO₆ ratio in the as-prepared OV-Bi/Bi₂WO₆ heterojunction could be tailored from 0.08 to 8.43 by controlling the solvothermal temperature, and the synergistic effect between DMF and EG could increase the reduction of MDF/EG and promote the production of Bi. Moreover, OV-Bi/Bi₂WO₆-160 yielded 4.4 and 8.8 times more CHA-one (128.8 μmol) than pure Bi₂WO₆ and metallic Bi, respectively, and achieved 93.6% selectivity to CHA-one in air as an oxidant under solvent-free conditions. The results revealed that the highly enhanced photocatalytic activity was mainly attributed to the superior specific surface area, outstanding photo-absorption, abundant oxygen vacancies, and efficient electron-hole separation. Moreover, for the unique double active sites in OV-Bi/Bi₂WO₆, oxygen vacancies can enhance the adsorption and activation capacity of Bi₂WO₆ for O₂, while metallic Bi can improve the adsorption and activation capacity of Bi₂WO₆ for CHA. Meanwhile, OV-Bi/Bi₂WO₆ also exhibited excellent durability due to the strong interaction between metallic Bi and Bi₂WO₆. The present work provides a flexible approach for tailoring the Bi : Bi₂WO₆ ratio and outlines an effective method for producing CHA-one from CHA under mild conditions.

Tuning oxygen vacancy in Bi2WO6 by heteroatom doping for enhanced photooxidation-reduction properties

Heteroatom doping was recently regarded as an effective method to tune the band gap and improve the separation and transfer of photogenerated electron-hole pairs in semiconductor photocatalysts. Herein, a novel S,F-codoped Bi2WO6 (S,F-Bi2WO6) with suitable oxygen vacancies was synthesized via the hydrothermal-calcination and post-sulfurization, for efficient Cr(VI) reduction and methyl orange (MO) degradation under visible light. The amount of surface oxygen vacancies could be controlled by adjusting the S/F ratio during the doping process, which modulated the band structure and photogenerated charge behavior of Bi2WO6. The optimal S0.10F-Bi2WO6 exhibited an excellent photooxidation-reduction performance, which Cr(VI) reduction and MO degradation efficiencies were 1.6 and 2.6 times than those of the pristine Bi2WO6 without oxygen vacancy under visible-light, respectively. The enhanced photooxidation-reduction performance was because the right amount of oxygen vacancies could effectively narrow the bandgap and improve the separation efficiency of electron-hole pairs. Thus, this work offered a mild and simply approach for preparing heteroatom doped Bi2WO6 and a potential to be extended to the synthesis of other doped materials for environmental remediation.

Degradation of Dye Wastewater by a Novel mBT-MPR Visible Light Photocatalytic System

The high efficiency and low consumption green wastewater treatment technology has important practical significance for the recycling of printing and dyeing wastewater. The efficiency of visible light catalytic degradation of organics is greatly affected by the performance of the catalyst and the photo reactor. Therefore, Bi₂WO₆/TiO₂/Fe₃O₄ (mBT) visible light photocatalyst was accurately prepared by the ammonia iron double drop method. In order to improve the photodegradation efficiency, a tubular magnetic field-controlled photocatalytic reactor (MPR) was developed. The novel mBT-MPR visible light photocatalytic system was proposed to treat RhB simulated wastewater. The experimental results showed that when the dosage of mBT catalyst was 1 g/L and visible light was irradiated for 60 min, the average removal rate of rhodamine B (RhB) with initial an concentration of 10 mg/L in the simulated wastewater for four times was 91.7%. The mBT-MPR visible light photocatalysis system is a green and efficient treatment technology for organic pollutants in water with simple operation, low energy consumption, and no need for catalyst separation.

Advances in Bi2WO6-Based Photocatalysts for Degradation of Organic Pollutants

With the rapid development of modern industries, water pollution has become an urgent problem that endangers the health of human and wild animals. The photocatalysis technique is considered an environmentally friendly strategy for removing organic pollutants in wastewater. As an important member of Bi-series semiconductors, Bi₂WO₆ is widely used for fabricating high-performance photocatalysts. In this review, the recent advances of Bi₂WO₆-based photocatalysts are summarized. First, the controllable synthesis, surface modification and heteroatom doping of Bi₂WO₆ are introduced. In the respect of Bi₂WO₆-based composites, existing Bi₂WO₆-containing binary composites are classified into six types, including Bi₂WO₆/carbon or MOF composite, Bi₂WO₆/g-C₃N₄ composite, Bi₂WO₆/metal oxides composite, Bi₂WO₆/metal sulfides composite, Bi₂WO₆/Bi-series composite, and Bi₂WO₆/metal tungstates composite. Bi₂WO₆-based ternary composites are classified into four types, including Bi₂WO₆/g-C₃N₄/X, Bi₂WO₆/carbon/X, Bi₂WO₆/Au or Ag-based materials/X, and Bi₂WO₆/Bi-series semiconductors/X. The design, microstructure, and photocatalytic performance of Bi₂WO₆-based binary and ternary composites are highlighted. Finally, aimed at the existing problems in Bi₂WO₆-based photocatalysts, some solutions and promising research trends are proposed that would provide theoretical and practical guidelines for developing high-performance Bi₂WO₆-based photocatalysts.

2D/2D Phosphorus-Doped g-C3N4/Bi2WO6 Direct Z-Scheme Heterojunction Photocatalytic System for Tetracycline Hydrochloride (TC-HCl) Degradation

Bi₂WO₆-based heterojunction photocatalyst for antibiotic degradation has been a research hotspot, but its photocatalytic performance needs to be further improved. Therefore, 2D/2D P-doped g-C₃N₄/Bi₂WO₆ direct Z-scheme heterojunction photocatalysts with different composition ratios were prepared through three strategies of phosphorus (P) element doping, morphology regulation, and heterojunction, and the efficiency of its degradation of tetracycline hydrochloride (TC-HCl) under visible light was studied. Their structural, optical, and electronic properties were evaluated, and their photocatalytic efficiency for TC-HCl degradation was explored with a detailed assessment of the active species, degradation pathways, and effects of humic acid, different anions and cations, and water sources. The 30% P-doped g-C₃N₄/Bi₂WO₆ had the best photocatalytic performance for TC-HCl degradation. Its photocatalytic rate was 4.5-, 2.2-, and 1.9-times greater than that of g-C₃N₄, P-doped g-C₃N₄, and Bi₂WO₆, respectively. The improved photocatalytic efficiency was attributed to the synergistic effect of P doping and 2D/2D direct Z-scheme heterojunction construction. The stability and reusability of the 30% P-doped C₃N₄/Bi₂WO₆ were confirmed by cyclic degradation experiments. Radical scavenging experiments and electron spin resonance spectroscopy showed that the main active species were •O₂^- and h⁺. This work provides a new strategy for the preparation of direct Z-scheme heterojunction catalysts with high catalytic performance.

Facile preparation of visible light-sensitive layered g-C3N4 for photocatalytic removal of organic pollutants

The graphite-phase carbon nitride (g-C₃N₄) photocatalytic materials were prepared by one-step calcination method to degrade methylene blue (MB) and potassium butyl xanthate (PBX) under visible light irradiation. The prepared g-C₃N₄ photocatalytic materials were investigated in detail by various characterizations, and the experiments showed that the graphitic phase carbon nitride photocatalytic materials were successfully prepared by the one-step calcination method. The material possesses excellent optical properties and strong visible light absorption, thus achieving photocatalytic degradation of MB and PBX. The catalyst dosage, pH, the initial concentration of pollutants have important effects on photocatalytic activity of MB and PBX. The photocatalytic degradation efficiency was 98.99% for MB and 96.83% for PBX under the optimal conditions (catalyst dosage, initial pollutant concentration and pH value were 500 mg L^-1, 20 mg L^-1 and 7, respevtively). The photocatalytic mechanisms on MB and PBX were elucidated. ·OH was the key specie for MB, while ·O₂^- was the key specie for PBX. This study advances the development of photocatalytic technology for mineral wastewater.

Self-doping induced oxygen vacancies and lattice strains for synergetic enhanced upconversion luminescence of Er3+ ions in 2D BiOCl nanosheets

Rare earth (RE) ions combined with two-dimensional (2D) semiconductors can exhibit unexpected optical properties. However, fluorescence quenching has always been inevitable due to defects associated with the synthesis and doping of 2D materials. In this work, we reported an efficient upconversion (UC) enhancement of Er³⁺ doped BiOCl nanosheets, utilizing a defect engineering strategy conversely rather than eliminating defects. Experiments and theoretical calculations provide evidence that oxygen vacancies (OVs) and lattice strain are simultaneously formed in the BiOCl:Er³⁺ nanosheets through self-doping of Cl^- ions. Under 980 nm excitation, samples doped with 300 mol% Cl^- ions exhibit the best luminescent emission, and the green and red UC emissions are enhanced 3.5 and 15 times, respectively. We showed that the OVs in the 2D semiconductor can act as energy bridges to transfer charges to the Er³⁺ energy level, enriching the electron population at the excited levels; while, the lattice strain enhances the energy transfer and charge accumulation, which synergistically enhance the UC luminescence. This research provides a new insight into the development of defect engineering for UC PL in 2D nanomaterials.

Enhancing Photocatalysis of Ag Nanoparticles Decorated BaTiO3 Nanofibers through Plasmon-Induced Resonance Energy Transfer Turned by Piezoelectric Field

Revealing the charge transfer path is very important for studying the photocatalytic mechanism and improving photocatalytic performance. In this work, the charge transfer path turned by the piezoelectricity in Ag-BaTiO3 nanofibers is discussed through degrading methyl orange. The piezo-photocatalytic degradation rate of Ag-BaTiO3 is much higher than the photocatalysis of Ag-BaTiO3 and piezo-photocatalysis of BaTiO3, implying the coupling effect between Ag nanoparticle-induced localized surface plasmon resonance (LSPR), photoexcited electron-hole pairs, and deformation-induced piezoelectric field. With the distribution density of Ag nanoparticles doubling, the LSPR field increases by one order of magnitude. Combined with charge separation driven by the piezoelectric field, more electrons in BaTiO3 nanofibers are excited by plasmon-induced resonance energy transfer to improve the photocatalytic property.