Oxygen-Induced Bi5+-Self-Doped Bi4V2O11 with a p-n Homojunction Toward Promoting the Photocatalytic Performance

In situ growth of BiOBr on copper foam conductive substrate with enhanced photocatalytic performance

Photocatalysis technology based on solar-powered semiconductors is widely recognized as a promising approach for achieving eco-friendly, secure, and sustainable degradation of organic contaminants. Nevertheless, conventional photocatalysts exhibit drawbacks such as a wide bandgap, and rapid recombination of photoinduced electron/hole pairs, in addition to complicated separation and recovery procedures. In this research, we cultivated BiOBr in situ on the surface of copper foam to fabricate a functional photocatalyst (denoted as BiOBr/Cu foam), which was subsequently employed for the photodegradation of Methylene Blue. Based on photodegradation experiments, the 0.3 BiOBr/Cu foam demonstrates superior photocatalytic efficacy compared to other photocatalysts under solar light irradiation. Furthermore, its ease of separation from the solution enhances its potential for reuse. The analysis of charge transfer revealed that the copper foam functions as an effective electron scavenger within the BiOBr/Cu foam, thereby facilitating charge separation and the generation of photo-induced holes. This phenomenon contributes to a significantly enhanced production of hydroxyl radicals. This study provides a valuable perspective on the design and synthesis of photocatalysts with heightened practicality, employing a conductive substrate.

Ball-milling synthesized Bi2VO5.5 for piezo-photocatalytic assessment

The mechanochemical ball milling followed by heating at 650 °C for 5 h successfully produced the single-phase Bi₂VO_5.5 powder. Catalytic activity for methylene blue dye degradation was investigated. Raman spectroscopy and X-ray diffraction were used to confirm the phase formation. The sample's charge carrier transportation behavior was ascertained using time-dependent photocurrent analysis. The piezo-photocatalysis experiment yielded a 63% degradation efficiency for the ball-milled Bi₂VO_5.5 sample. The pseudo-first-order kinetics of the piezo-photocatalytic dye degradation are discerned, and the significant k value of 0.00529 min^-1 is achieved. The scavenger test declares the h⁺ radical is the predominant active species during the piezo-photocatalysis experiment. Vigna radiata seeds were used in a phytotoxicity test to evaluate the germination index. The mechanochemical activation method facilitates reactions by lowering reaction temperature and time. The effect of improved piezo-photocatalytic efficiency on the ball-milled Bi₂VO_5.5 powder is an unexplored area, and we have attempted to investigate it. Here, ball-milled Bi₂VO_5.5 powder achieved improved dye degradation performance.

Mechanochemical Synthesis of Bi2VO5.5 for Improved Photocatalytic Dye Degradation

A single-phase Bi2VO5.5 powder is formed effectively through a mechanochemical ball milling approach at 650 °C in 5 h and its photocatalytic performance on methylene blue dye is explored. X-ray diffraction and Raman spectroscopy analytical instruments are utilized to confirm the phase formation. The evident presence of irregular-shaped grains is affirmed using a scanning electron microscope. To ascertain the chemical condition of the components present, the Bi2VO5.5 powdered sample undergo an X-Ray photoelectron spectroscopy investigation. The sample is analyzed using a time-dependent photocurrent to discern its charge carrier transportation behavior. A photocatalytic study using Bi2VO5.5 powder produced through the mechanochemical ball milling method has not been explored till now. The efficacy of the ball-milled Bi2VO5.5 powder to attain enhanced photocatalytic efficiency which hasn't been investigated till now, is explored. The ball-milled Bi2VO5.5 sample achieved 70% degradation efficiency when performing the photocatalysis investigation. The photocatalytic dye degradation discerns pseudo-first-order kinetics and achieves a notable k value of 0.00636 min-1. The scavenger test indicates that h+ radicals are the prominent active species during the photocatalysis experiment. The germination index is determined by conducting a phytotoxicity test with the use of Vigna radiata seeds. Here ball-milled Bi2VO5.5 powder attains enhanced dye degradation efficiency.

Ultrathin CuBi2O4 on a bipolar Bi2O3 nano-scaffold: a self-powered broadband photoelectrochemical photodetector with improved responsivity and response speed

CuBi₂O₄ is a promising photoactive material for photoelectrochemical (PEC) broadband photodetectors due to its suitable band structure, but its photo-responsivity is severely limited by the short carrier diffusion length and long light penetration depth. To address the trade-off between light absorption and charge separation, a nano-structured bipolar Bi₂O₃ host scaffold was coupled with an ultrathin CuBi₂O₄ light absorbing layer to construct a host-guest Bi₂O₃/CuBi₂O₄ photocathode. The work function of the bipolar Bi₂O₃ scaffold lies in between FTO and CuBi₂O₄, making Bi₂O₃ a suitable back contact layer for hole transport. Compared with the flat CuBi₂O₄ and Bi₂O₃ scaffold counterpart, the nanostructured Bi₂O₃/CuBi₂O₄ exhibits significantly improved light absorption and enhanced charge separation efficiency. The Bi₂O₃/CuBi₂O₄ PEC photodetector can be self-powered and demonstrates a broad photo-response ranging from ultraviolet (UV) to near infrared (NIR). It shows a high responsivity of 75 mA W^-1 and a remarkable short response time of 0.18 ms/0.19 ms. Bi₂O₃/CuBi₂O₄ prepared by magnetron sputtering demonstrates great potential for rapid PEC photodetection in a wide optical domain.

Rich Indium-Vacancies In2 S3 with Atomic p-n Homojunction for Boosting Photocatalytic Multifunctional Properties

Design and development of highly efficient photocatalytic materials are key to employ photocatalytic technology as a sound solution to energy and environment related challenges. This work aims to significantly boost photocatalytic activity through rich indium vacancies (V_In ) In₂ S₃ with atomic p-n homojunction through a one-pot preparation strategy. Positron annihilation spectroscopy and electron paramagnetic resonance reveal existence of V_In in the prepared photocatalysts. Mott-Schottky plots and surface photovoltage spectra prove rich V_In In₂ S₃ can form atomic p-n homojunction. It is validated that p-n homojunction can effectively separate carriers combined with photoelectrochemical tests. V_In decreases carrier transport activation energy (CTAE) from 0.64 eV of V_In -poor In₂ S₃ to 0.44 eV of V_In -rich In₂ S₃ . The special structure endows defective In₂ S₃ with multifunctional photocatalysis properties, i.e., hydrogen production (872.7 µmol g^-1 h^-1 ), degradation of methyl orange (20 min, 97%), and reduction in heavy metal ions Cr(VI) (30 min, 98%) under simulated sunlight, which outperforms a variety of existing In₂ S₃ composite catalysts. Therefore, such a compositional strategy and mechanistic study are expected to offer new insights for designing highly efficient photocatalysts through defect engineering.

Bi-doped graphitic carbon nitride nanotubes boost the photocatalytic degradation of Rhodamine B

Polymeric carbon nitride (PCN) is an emerging metal-free photocatalyst with high stability but is plagued by low photocatalytic efficiency due to the rapid charge carrier recombination behavior.

Generation of 2D nonlayered ferromagnetic VO2(M) nanosheets induced by strain engineering of CO2

Two-dimensional (2D) nonlayered ferromagnets displaying high Curie temperatures, sizable magnetic anisotropy levels, and large spin polarizations are emerging as promising 2D ferromagnetics. However, the difficulties in synthesizing 2D nonlayered intrinsic ferromagnets have largely limited their development. Herein, defect-rich 2D nonlayered VO₂(M) nanosheets have been fabricated by deploying straining engineering of CO₂ on the metal-insulator transition (MIT) of VO₂. Above T_MIT, the strong strain engineering of CO₂ in the R phase of VO₂ generated a very large number of atomic defects in its 3D crystal structure, and as a result facilitated conversion of the defective 3D network to 2D nanosheets along the c-axis. The as-prepared 2D defective VO₂(M) nanosheets displayed unique room-temperature ferromagnetism, attributed to the symmetry breaking triggered by the disordered atomic structure combined with the 3D-to-2D transformation.

Enhanced photocatalytic performance of rhodamine B and enrofloxacin by Pt loaded Bi4V2O11: boosted separation of charge carriers, additional superoxide radical production, and the photocatalytic mechanism

Photocatalytic performance is influenced by two contradictory factors, which are light absorption range and separation of charge carriers. Loading noble metals with nanosized interfacial contact is expected to improve the separation and transfer of photo-excited charge carriers while enlarging the light absorption range of the semiconductor photocatalyst. Therefore, it should be possible to improve the photocatalytic performance of pristine nontypical stoichiometric semiconductor photocatalysts by loading a specific noble metal. Herein, a series of novel Pt-Bi4V2O11 photocatalysts have been successfully prepared via a surface reduction technique. The crystal structure, morphology, and photocatalytic performance, as well as photo-electron properties of the as-synthesized samples were fully characterized. Moreover, the series of Pt-Bi4V2O11 samples were evaluated to remove typical organic pollutants, rhodamine B and enrofloxacin, from aqueous solutions. The photoluminescence, quenching experiments and the electron spin resonance technique were utilized to identify the effective radicals during the photocatalytic process and understand the photocatalytic mechanism. The photocatalytic performance of Pt-Bi4V2O11 was tremendously enhanced compared with pristine Bi4V2O11, and there was additional ˙O2- produced during the photocatalytic process. This study deeply investigated the relation between the separation of charge carriers and the light harvesting, and revealed a promising strategy for fabricating efficient photocatalysts for both dyes and antibiotics.

In-situ fabrication of 3D hierarchical flower-like β-Bi2O3@CoO Z-scheme heterojunction for visible-driven simultaneous degradation of multi-pollutants

Development of an efficient heterojunction catalyst with a superior visible-light driven activity is regarded as a promising strategy to decontaminate organic wastewater. Herein, a novel direct Z-scheme β-Bi₂O₃@CoO heterojunction was well designed and successfully fabricated by in situ incorporating the two energy band-matched semiconductors. The obtained β-Bi₂O₃@CoO hybrid presented a unique 3D hierarchical structure with a mass of open channels and mesoporous, which afforded not only rapid mass transfer of targets but also good light-harvesting in view of the multiple reflections. Compared to the pristine β-Bi₂O₃ and CoO, the β-Bi₂O₃@CoO hybrid exhibited remarkably improved photocatalytic activity towards the simultaneous degradation of chlorotetracycline (CTC), tetracycline hydrochloride (TCH), oxytetracycline (OTC) and nitrobenzene (NB) under visible-light irradiation. The possible intermediates and degradation pathways were also tracked by mass spectra (MS) analysis. Moreover, a direct Z-scheme charge transfer mechanism in the intimate contact interface between β-Bi₂O₃ and CoO was verified for the improved catalytic activity, endowing the effective separation/transportation of the photo-excited charge carriers and maintenance of the strong redox ability in β-Bi₂O₃@CoO heterojunction. The present work affords a simple approach to design and construct 3D hierarchical direct Z-scheme photocatalysts with promising applications in water environment remediation.

Atomic Level Interface Control of SnO2-TiO2 Nanohybrids for the Photocatalytic Activity Enhancement

This review article highlights atom-level control of the heterojunction and homojunction in SnO2-TiO2 nanohybrids, and the effects on the photocatalytic property. Firstly, a comprehensive description about the origin for the SnO2-TiO2 coupling effect on the photocatalytic activity in the conventional SnO2-TiO2 system without heteroepitaxial junction is provided. Recently, a bundle of thin SnO2 nanorods was hetero-epitaxially grown from rutile TiO2 seed nanocrystals (SnO2-NR#TiO2, # denotes heteroepitaxial junction). Secondly, the heterojunction effects of the SnO2-NR#TiO2 system on the photocatalytic activity are dealt with. A novel nanoscale band engineering through the atom-level control of the heterojunction between SnO2 and TiO2 is presented for the photocatalytic activity enhancement. Thirdly, the homojunction effects of the SnO2 nanorods on the photocatalytic activity of the SnO2-NR#TiO2 system and some other homojunction systems are discussed. Finally, we summarize the conclusions with the possible future subjects and prospects.

Recent advances in photodegradation of antibiotic residues in water

Antibiotics are widely present in the environment due to their extensive and long-term use in modern medicine. The presence and dispersal of these compounds in the environment lead to the dissemination of antibiotic residues, thereby seriously threatening human and ecosystem health. Thus, the effective management of antibiotic residues in water and the practical applications of the management methods are long-term matters of contention among academics. Particularly, photocatalysis has attracted extensive interest as it enables the treatment of antibiotic residues in an eco-friendly manner. Considerable progress has been achieved in the implementation of photocatalytic treatment of antibiotic residues in the past few years. Therefore, this review provides a comprehensive overview of the recent developments on this important topic. This review primarily focuses on the application of photocatalysis as a promising solution for the efficient decomposition of antibiotic residues in water. Particular emphasis was laid on improvement and modification strategies, such as augmented light harvesting, improved charge separation, and strengthened interface interaction, all of which enable the design of powerful photocatalysts to enhance the photocatalytic removal of antibiotics.

Novel Bi2+xWO6 p-n Homojunction Nanostructure: Preparation, Characterization, and Application for a Self-Powered Cathodic Photoelectrochemical Immunosensor

Synthesizing novel cathodic photoactive materials with high photoelectrochemical (PEC) performance is urgently important for the development of photocathodic sensors. Herein, a novel photocathode material, Bi self-doped Bi₂WO₆ (i.e., Bi_2+xWO₆) p-n homojunction, is prepared via a simple ethylene glycol-assisted solvothermal reduction for the first time. Compared with pristine Bi₂WO₆, Bi_2+xWO₆ possesses a narrower band gap and higher light harvesting ability. Among the synthesized materials, Bi_2.1WO₆ exhibits the highest photocurrent response, which is 23 times that of pure Bi₂WO₆ because of the synergistic effect of doped Bi and the p-n homojunction. The open circuit potential, "V-shaped" Mott-Schottky plot, linear sweep voltammetry curve, and transient photocurrent demonstrate the p-n homojunction characteristics of the material well. By using the Bi_2+xWO₆ p-n homojunction as the photocathode for sensing and the plasmonic WO₃/Au composite as the photoanode for signal amplification, a new self-powered membraneless PEC immunosensor is established for a highly sensitive detection of human epididymal protein 4. This study offers a new idea for designing novel photocatalysts with satisfactory performance, and the Bi_2+xWO₆ p-n homojunction is expected to act as a promising PEC platform for developing various self-powered biosensors.

Accurate Control of VS2 Nanosheets for Coexisting High Photoluminescence and Photothermal Conversion Efficiency

In two-dimensional (2D) amorphous nanosheets, the electron-phonon coupling triggered by localization of the electronic state as well as multiple-scattering feature make it exhibit excellent performance in optical science. VS₂ nanosheets, especially single-layer nanosheets with controllable electronic structure and intrinsic optical properties, have rarely been reported owing to the limited preparation methods. Now, a controllable and feasible switching method is used to fabricate 2D amorphous VS₂ and partial crystallized 2D VO₂ (D) nanosheets by altering the pressure and temperature of supercritical CO₂ precisely. Thanks to the strong carrier localization and the quantum confinement, the unique 2D amorphous structures exhibit full band absorption, strong photoluminescence, and outstanding photothermal conversion efficiency.

Sandwich-Nanostructured n-Cu2O/AuAg/p-Cu2O Photocathode with Highly Positive Onset Potential for Improved Water Reduction

An n-Cu₂O layer formed a high-quality buried junction with p-Cu₂O to increase the photovoltage and thus to shift the turn-on voltage positively. Mott-Schottky measurements confirmed that the improvement benefited from a positive shift in flat-band potential. The obtained extremely positive onset potential, 0.8 V_RHE in n-Cu₂O/AuAg/p-Cu₂O, is comparable with measurements from water reduction catalysts. The AuAg alloy sandwiched between the homojunction of n-Cu₂O and p-Cu₂O improved the photocatalytic performance. This alloy both served as an electron relay and promoted electron-hole pair generation in nearby semiconductors; the charge transfer between n-Cu₂O and p-Cu₂O in the sandwich structure was measured with X-ray absorption spectra. The proposed sandwich structure can be considered as a new direction for the design of efficient solar-related devices.

Dual Quantum Dot-Decorated Bismuth Vanadate Photoanodes for Highly Efficient Solar Water Oxidation

Photo-induced charge separation and photon absorption play important roles in determining the performance of the photoelectrocatalytic water splitting process. In this work, we utilize dual quantum dots (QDs), consisting of BiVO₄ and carbon, to fabricate a hybrid homojunction-based BiVO₄ photoanode for efficient and stable solar water oxidation. Formation of homojunctions, by decorating as-prepared BiVO₄ substrate with BiVO₄ QDs, enhances the charge separation efficiency by 1.3 times. This enhancement originates from lattice match, which benefits charge transfer across the interface. Furthermore, the use of carbon QDs as a stable photosensitizer effectively extends the photon absorption limit from 520 nm to over 700 nm, yielding an incident photon-to-electron conversion efficiency of 6.0 %, even at 600 nm at 1.23 V versus RHE. Finally, a remarkable photocurrent density of 6.1 mA cm^-2 at 1.23 V was recorded after depositing FeOOH/NiOOH as cocatalysts, thereby, reaching 82 % of the theoretical efficiency for BiVO₄ .

One-Dimensional/Two-Dimensional Core-Shell-Structured Bi2O4/BiO2- x Heterojunction for Highly Efficient Broad Spectrum Light-Driven Photocatalysis: Faster Interfacial Charge Transfer and Enhanced Molecular Oxygen Activation Mechanism

Deliberate tuning of nanoparticles encapsulated with nanosheet shells can bring about fascinating photocatalytic properties because of the fast charge-transfer characteristics of a nanosized core-shell structure. Herein, a novel core-shell-structured Bi₂O₄/BiO_{2- x} composite was fabricated through a one-step hydrothermal method. The core-shell Bi₂O₄/BiO_{2- x} composite presented distinct optical absorption property, including UV, visible, and near-infrared (NIR) light regions. Compared to Bi₂O₄ and BiO_{2- x}, the Bi₂O₄/BiO_{2- x} composite revealed improved broad spectrum light-responsive molecular oxygen activation into ^•O₂^-, especially achieving ^•O₂^- generation under NIR light irradiation. The achievement that enhanced broad spectrum light-activated molecular oxygen activation could be ascribed to the faster electron transfer confirmed by the electron spin resonance (ESR) spectra, photoluminescence (PL) spectra, photoelectrochemical test, and quantitative analysis of ^•O₂^-. The strong interface effect of the Bi₂O₄/BiO_{2- x} composite was confirmed by X-ray photoelectron spectroscopy analysis. Density functional theory calculated results suggested that the Bi₂O₄/BiO_{2- x} composite revealed increased density of states near the Fermi level, suggesting that it possessed higher carrier mobility as compared to Bi₂O₄ and BiO_{2- x}, contributing to the faster separation of photoinduced carriers and the generation of ^•O₂^-. Benefiting to the heterojunction, the Bi₂O₄/BiO_{2- x} composite showed improved photocatalytic activity and anti-photocorrosion activity during rhodamine B (RhB) and ciprofloxacin (CIP) degradation with the irradiation of UV, visible, and NIR lights. Besides, the possible photocatalytic mechanism and transformation pathway of RhB and CIP degradation by the Bi₂O₄/BiO_{2- x} composite were proposed by the analyses of the liquid chromatography-mass spectrometry. This study furnishes a new strategy for fabricating high-efficient and broad spectrum light-driven heterojunction photocatalysts for environment purification.

Review on nanoscale Bi-based photocatalysts

Nanoscale Bi-based photocatalysts are promising candidates for visible-light-driven photocatalytic environmental remediation and energy conversion. However, the performance of bulk bismuthal semiconductors is unsatisfactory. Increasing efforts have been focused on enhancing the performance of this photocatalyst family. Many studies have reported on component adjustment, morphology control, heterojunction construction, and surface modification. Herein, recent topics in these fields, including doping, changing stoichiometry, solid solutions, ultrathin nanosheets, hierarchical and hollow architectures, conventional heterojunctions, direct Z-scheme junctions, and surface modification of conductive materials and semiconductors, are reviewed. The progress in the enhancement mechanism involving light absorption, band structure tailoring, and separation and utilization of excited carriers, is also introduced. The challenges and tendencies in the studies of nanoscale Bi-based photocatalysts are discussed and summarized.

The effects of bismuth (III) doping and ultrathin nanosheets construction on the photocatalytic performance of graphitic carbon nitride for antibiotic degradation

To further enhance the photocatalytic performance of graphitic carbon nitride (g-C₃N₄), we rationally combined two strategies (foreign metal doping and ultrathin nanosheet construction) to synthesize bismuth (III) (Bi³⁺) doped ultrathin g-C₃N₄ nanosheets (Bi-CNNS) via one-step thermal polymerization method using melamine as the raw material, bismuth nitrate pentahydrate (Bi(NO₃)₃·5H₂O) as the dopant source, and nitric acid (HNO₃) and acetic acid (AC) as soft templates for the ultrathin nanosheets construction. The Bi-CNNS catalysts exhibited an excellent photocatalytic performance in tetracycline (TC) degradation. The TC removal efficiency reached to be 94.1% in 30 min under visible-light irradiation over 0.03Bi-CNNS, which is 6.03 times higher than that of pure g-C₃N₄ (CN). The higher specific surface area, narrower bandgap, the improved photoexcited electron-hole pair transfer and separation efficiency, and prolonged carrier lifetimes in the Bi³⁺-doped ultrathin g-C₃N₄ nanosheets led to a significantly enhanced photocatalytic performance. The main radical species responsible for the degradation of tetracycline over 0.03Bi-CNNS were O₂^- and OH. Moreover, the possible photodegradation intermediate products of TC were detected by gas chromatography-mass spectroscopy (GC-MS), and a possible pathway was proposed.

Wide spectral response photothermal catalysis-fenton coupling systems with 3D hierarchical Fe3O4/Ag/Bi2MoO6 ternary hetero-superstructural magnetic microspheres for efficient high-toxic organic pollutants removal

3D hierarchical Fe₃O₄/Ag/Bi₂MoO₆ magnetic microspheres are fabricated through hydrothermal-photoreduction strategy, which fabricate an advanced photocatalytic-Fenton coupling system. The H₂O₂ produced by photocatalysis could form the photo-Fenton system when combined with Fe₃O₄ under light illumination. The introduction of Ag nanoparticles could induce the localized surface plasmon resonance (LSPR), which provides "hot electrons" for promoting photocatalysis. The addition of Fe₃O₄ achieve the successful coupling of photocatalysis-Fenton, and enhanced the broad spectrum response of the final composite sample. The 3D hierarchical Fe₃O₄/Ag/Bi₂MoO₆ exhibit excellent UV-Vis-NIR-driven photocatalytic performance for mineralization of high-toxic Aatrex and Bisphenol A. The addition of magnetic Fe₃O₄ is conducive to the magnetic separation, which favors practical application. The strategy provides thought-provoking insights for constructing new types of high-performance photocatalytic system.

Facile synthesis of a ZnO-BiOI p-n nano-heterojunction with excellent visible-light photocatalytic activity

In this paper, an efficient method to produce a ZnO/BiOI nano-heterojunction is developed by a facile solution method followed by calcination. By tuning the ratio of Zn/Bi, the morphology varies from nanoplates, flowers to nanoparticles. The heterojunction formed between ZnO and BiOI decreases the recombination rate of photogenerated carriers and enhances the photocatalytic activity of ZnO/BiOI composites. The obtained ZnO/BiOI heterostructured nanocomposites exhibit a significant improvement in the photodegradation of rhodamine B under visible light (λ ≥ 420 nm) irradiation as compared to single-phase ZnO and BiOI. A sample with a Zn/Bi ratio of 3:1 showed the highest photocatalytic activity (≈99.3% after 100 min irradiation). The photodegradation tests indicated that the ZnO/BiOI heterostructured nanocomposites not only exhibit remarkably enhanced and sustainable photocatalytic activity, but also show good recyclability. The excellent photocatalytic activity could be attributed to the high separation efficiency of the photoinduced electron-hole pairs as well as the high specific area.

Mediation of band structure for BiOBrxI1−x hierarchical microspheres of multiple defects with enhanced visible-light photocatalytic activity

The band edge positions are of vital importance due to their direct effect on the redox reactions occurring at the surface of the samples.

Novel two-dimensional Bi4V2O11 nanosheets: controllable synthesis, characterization and insight into the band structure

Novel two-dimensional Bi₄V₂O₁₁ nanosheets were controllably prepared using a stable [Bi(EDTA)]⁻ complex, and their band structures were investigated as well.