Oxygen Vacancy-Enhanced Ultrathin Bi2O3-Bi2WO6 Nanosheets' Photocatalytic Performances under Visible Light Irradiation

The oxygen vacancy caused by ultrathin structures would be introduced into the semiconductor photocatalyst to boost its photocatalytic activity. Herein, ultrathin Bi₂O₃-Bi₂WO₆ nanosheet composites have been successfully synthesized via a facile hydrothermal method. Compared to pure Bi₂WO₆ nanosheets, the Bi₂O₃-Bi₂WO₆ nanosheet composites possess abundant oxygen vacancies, which was confirmed by the positron annihilation spectra. The ultrathin Bi₂O₃-Bi₂WO₆ nanosheet composites exhibited remarkable photocatalytic degradation performance for oxytetracycline compared with that of pure Bi₂WO₆ nanosheets. The excellent photocatalytic activities of Bi₂O₃-Bi₂WO₆ composites could be attributed to the heterojunction structure and the oxygen vacancies caused by ultrathin structures.

Visible-LED-light-driven photocatalytic degradation of ofloxacin and ciprofloxacin by magnetic biochar modified flower-like Bi2WO6: The synergistic effects, mechanism insights and degradation pathways

Bi₂WO₆ possesses good stability but poor photocatalytic activity under visible light. Herein, the coupling of Bi₂WO₆, Fe₃O₄ and biochar (Bi₂WO₆/Fe₃O₄/BC) was investigated to enhance the photocatalytic performance of Bi₂WO₆ through facile hydrothermal method, which almost completely degraded ofloxacin (OFL) and ciprofloxacin (CIP) within 30 min under energy-saving visible LED irradiation. The superior photocatalytic activity of Bi₂WO₆/Fe₃O₄/BC was ascribed to the stronger visible light adsorption capacity and the lower recombination of electron-hole pairs. O₂^- played a major role during the photocatalytic reaction. The characterization results suggested that the introduction of biochar avoided the agglomeration of Bi₂WO₆ microspheres and Fe₃O₄ nanoparticles, at the same time, the biochar participated in OFL and CIP photodegradation by consuming different oxygen-containing functional groups. In order to further evaluate the application potential of Bi₂WO₆/Fe₃O₄/BC, the effects of environment factors and the application in different actual water were carefully investigated. Various transformation products and the possible degradation pathways of OFL and CIP were analyzed based on high resolution mass spectrometry (HRMS) results, moreover, the toxicity evaluation results of Escherichia coli indicated these intermediates products were less toxic compared OFL and CIP. Overall, Bi₂WO₆/Fe₃O₄/BC can provide a potential way for the application of photocatalytic technology in ambient wastewater purification.

Near-Infrared-Responsive Photocatalysts

Broadening the absorption of light to the near-infrared (NIR) region is important in photocatalysis to achieve efficient solar-to-fuel conversion. NIR-responsive photocatalysts that can utilize diffusive solar energy are attractive for alleviating the energy crisis and environmental pollution. Over the past few years, considerable progress on the component and structural design of NIR-responsive photocatalysts have been reported. This study aims to systematically summarize recent progress toward the material design and mechanism optimization of NIR-responsive photocatalysts in this area. Depending on the main strategies for harvesting NIR photons, NIR-responsive photocatalysts can be categorized as direct NIR-light photocatalysts, indirect NIR-light photocatalysts, and photothermal photocatalysts. Furthermore, the construction and application of different NIR-responsive photocatalytic systems are summarized. Conclusions and perspectives are presented to further explore the potential of NIR-responsive photocatalysts in this field.

Remarkable phosphate recovery from wastewater by a novel Ca/Fe composite: Synergistic effects of crystal structure and abundant oxygen-vacancies

Calcium-based materials are considered to be promising adsorbents for phosphate removal in the water environment due to their environmental friendliness and low price. However, improving the efficiency and rate of P adsorption of calcium-based materials still needs further exploration. In this study, a high-efficiency and eco-friendly Ca/Fe composite was rationally designed and fabricated by a co-precipitated method. Batch adsorption experiments showed that Ca/Fe composites with a Ca: Fe molar ratio of 3: 1 exhibited a remarkable phosphate sorption capacity of 161.4 mg P/g. Furthermore, the phosphate adsorption capacity of Ca/Fe-3/1 composite was maintained relatively high at pH 3-11 due to the ligand exchange, electrostatic and chemical precipitation. In addition, the experiment performed to determine the effect of coexisting ions shows that only carbonate ions slightly inhibit the phosphate adsorption effect of the Ca/Fe-3/1 composite. The newly prepared Ca/Fe composites have a fast phosphate removal efficiency. The XPS and EPR analysis showed that a large number of oxygen vacancies were formed on Ca/Fe composites due to the introduction of magnetic Fe. This is the first time to introduction oxygen vacancies into Ca/Fe composites by co-precipitation. The existence of oxygen vacancies can promote electron transfer rate and reduce the bonding energy barrier for phosphate adsorption, thereby increasing the phosphate absorption rate of the Ca/Fe composites. The enhanced phosphate removal by Ca/Fe composites with abundant oxygen vacancies provides a new strategy for the preparation of commercial phosphate -controlling materials.

Near-Infrared-Driven Photocatalysts: Design, Construction, and Applications

Photocatalysts, which utilize solar energy to catalyze the oxidation or reduction half reactions, have attracted tremendous interest due to their great potential in addressing increasingly severe global energy and environmental issues. Solar energy utilization plays an important role in determining photocatalytic efficiencies. In the past few decades, many studies have been done to promote photocatalytic efficiencies via extending the absorption of solar energy into near-infrared (NIR) light. This Review comprehensively summarizes the recent progress in NIR-driven photocatalysts, including the strategies to harvest NIR photons and corresponding photocatalytic applications such as the degradation of organic pollutants, water disinfection, water splitting for H₂ and O₂ evolution, CO₂ reduction, etc. The application of NIR-active photocatalysts employed as electrocatalysts is also presented. The subject matter of this Review is designed to present the relationship between material structure and material optical properties as well as the advantage of material modification in photocatalytic reactions. It paves the way for future material design in solar energy-related fields and other energy conversion and storage fields.

Constructing Surface Plasmon Resonance on Bi2WO6 to Boost High-Selective CO2 Reduction for Methane

Plasmonic Bi₂WO₆ with strong localized surface plasmon resonance (LSPR) around the 500-1400 region is successfully constructed by electron doping. Oxygen vacancies on W-O-W (V1) and Bi-O-Bi (V2) sites are precisely controlled to obtain Bi₂WO₆-V₁ with LSPR and Bi₂WO₆-V₂ with defect absorption. Density functional theory (DFT) calculation demonstrates that the V1-induced energy state facilitates photoelectron collection for a long lifetime, resulting in LSPR of Bi₂WO₆. Photoelectron trapping on V1 sites is demonstrated by a single-particle photoluminescence (PL) study, and 93% PL quenching efficiency is observed. With strong LSPR, plasmonic Bi₂WO₆-V₁ exhibits highly selective methane generation with a rate of 9.95 μmol g^-1 h^-1 during the CO₂ reduction reaction (CO₂-RR), which is 26-fold higher than 0.37 μmol g^-1 h^-1 of BiWO₃-V₂ under UV-visible light irradiation. LSPR-dependent methane generation is confirmed by various photocatalytic results of plasmonic Bi₂WO₆ with tunable LSPR and different light excitations. Furthermore, the DFT-simulated pathway of CO₂-RR and in situ Fourier transform infrared spectra on the surface of Bi₂WO₆ prove that V1 sites facilitate CH₄ generation. Our work provides a strategy to obtain nonmetallic plasmonic materials by electron doping.

Unique 1D/2D Bi2O2CO3 nanorod-Bi2WO6 nanosheet heterostructure: synthesis and photocatalytic performance

A novel 1D/2D Bi2O2CO3–Bi2WO6 heterostructure was synthesized by high temperature calcination. These 1D/2D Bi2O2CO3–Bi2WO6 heterostructures displayed an outstanding photocatalytic activity to degrade organic compounds.

Selective Photocatalytic Reduction of CO2 to CH4 Modulated by Chloride Modification on Bi2WO6 Nanosheets

Solar-driven photocatalytic CO₂ reduction into CH₄ with H₂O is considered to be a promising way to alleviate the energy crisis and greenhouse effect. However, current CO₂ photoreduction technologies tend to overlook the role of photooxidation half reaction as well as the effect of the protons produced by water oxidation on CH₄ generation, resulting in low CO₂ conversion efficiency and poor CH₄ selectivity. In the present study, a series of chloride-modified Bi₂WO₆ nanosheets were constructed in view of chloride-assisted photocatalytic water oxidation. The results show that the CH₄ yield of the synthesized sample can be enhanced up to about 10 times compared to that with no Cl^- modification. Besides, the selectivity of CH₄ can be regulated by the loading amount of chloride, varying from 51.29% for Bi₂WO₆ to 94.98% for the maximum. The increase of product yield is attributed to chloride modification, which not only changed the morphology of the catalyst, but also modified the pathway of water oxidation. Further studies on intermediate products and the density functional theory calculation confirm that the Cl^- ions on Bi₂WO₆ nanosheets not only promote H₂O oxidation, but also lower the energy barrier for intermediate *CHO generation, thus facilitating CH₄ production. The results gained herein may provide some illuminating insights into the design of a highly selective photocatalyst for efficient CO₂ reduction.

Bi and oxygen defects improved visible light photocatalysis with BiOBr nanosheets

Bi metal attached BiOBr with oxygen defect (BiOBr(3)-Bi(x%, x = 10, 20, 30)) nanosheets was prepared via the hydrothermal process in this study. The different characterization techniques of x-ray diffraction, x-ray photoelectron spectrometer, electron spin resonance (ESR), field emission scanning electron microscope, and high resolution transmission electron microscope were used to distinguish the composition, crystal structure, and morphology of the samples. Under visible light irradiation, the BiOBr(3)-Bi(x%, x = 10, 20, 30) samples exhibited improved photocatalytic activity for the degradation of colored dyes (RhB) and colorless tetracycline hydrochloride. Such an improvement was ascribed to the widened visible light absorption and enhanced separation of the photogenerated electron-hole pairs because of the synergistic effect of oxygen vacancies and Bi metal with plasmon resonance effects. A possible photocatalytic mechanism of the quasi Z-scheme process was proposed on the basis of ESR measurements and radical-trapping experiments.

Optimizing the Carbon Dioxide Reduction Pathway through Surface Modification by Halogenation

Facilitating the charge separation of semiconductor photocatalysts to increase the photocatalytic CO₂ reduction activity has become a great challenge for sustainable energy conversion. Herein, the surface halogen-modified defect-rich Bi₂ WO₆ nanosheets have been successfully prepared to address the aforementioned challenge. Importantly, the modification of surface with halogen atoms is beneficial for the adsorption and activation for CO₂ molecules and charge separation. These properties have been analyzed by experimental and theoretical methods. DFT calculations revealed that the modification of the Bi₂ WO₆ surface with Br atoms can decrease the formation energy of the *COOH intermediate, which accelerates CO₂ conversion. All halogen-modified defect-rich Bi₂ WO₆ nanosheets showed an enhanced photocatalytic CO₂ reduction activity. Specifically, Br-Bi₂ WO₆ exhibited the best CO generation rate of 13.8 μmol g^-1 h^-1 , which is roughly 7.3 times as high as the unmodified defect-rich Bi₂ WO₆ (1.9 μmol g^-1 h^-1 ). Moreover, in the presence of a cocatalyst (cobalt phthalocyanine) and a sacrificial agent (triethanolamine), Br-Bi₂ WO₆ exhibited an even further improved CO generation rate of 187 μmol g^-1  h^-1 . This finding provides a new approach to optimize the CO₂ reduction pathway of semiconductor photocatalysts, which is beneficial to develop highly efficient CO₂ reduction photocatalysts.

Novel Visible Light-Driven Photocatalytic Chlorine Activation Process for Carbamazepine Degradation in Drinking Water

Photolysis of free chlorine (HOCl/ClO^-) is an advanced oxidation process (AOP) to produce hydroxyl (HO^•) and other radicals for refractory micropollutant degradation. However, HOCl/ClO^- is only conducive to activation and production of radicals by ultraviolet (UV) light. For the first time, we show the use of visible light (>400 nm) to produce HO^• and ClO^•, through use of graphitic carbon nitride (g-C₃N₄) and photogenerated h_vb⁺, e_cb^-, and O₂^•- in the presence of HOCl/ClO^-, which was termed visible light g-C₃N₄-enabled chlorine AOP (VgC-AOP). The VgC-AOP increased the pseudo first-order degradation rate constant of a model micropollutant, carbamazepine, by 16 and 7 times higher than that without g-C₃N₄ and HOCl/ClO^-, respectively, and remained active over multiple use cycles. Effects of water quality [pH, alkalinity, Cu(II), and natural organic matter (NOM)] and the operational conditions (g-C₃N₄ and HOCl/ClO^- concentrations, irradiation wavelength, and dose) were investigated. Of particular significance is its superior performance in the presence of NOM, which absorbs less light at visible light wavelengths and scavenges less surface-bonded reactive species, compared against UV/TiO₂ or UV/chlorine AOPs. The VgC-AOP is practically relevant, feasible, and easily implementable and it expands the potential types of light sources (e.g., LEDs and solar light).

Facile polyol-triggered anatase-rutile heterophase TiO2-x nanoparticles for enhancing photocatalytic CO2 reduction

Solar-driven CO₂ photoreduction into fuels has great potential in addressing the environmental and energy crisis. Heterophase TiO₂ has attracted increasing attention in photoenergy applications owing to its fascinating properties, but much more attention has been paid on photodegradation and photocatalytic water splitting than that of photocatalytic CO₂ reduction. Herein, anatase-rutile heterophase TiO₂ nanoparticles with oxygen vacancy (TiO_2-x) were successfully synthesized by involving proper amounts of polyols (EG, DEG, TEG, etc.) into the reaction system. The heterophase TiO_2-x nanoparticles could accelerate the electron-hole separation and exhibit superior photocatalytic activity for reducing CO₂ into methane. This work offers an alternative approach to simply fabricate TiO_2-x-based heterophase photocatalyst towards efficient CO₂ photoreduction.

Recent advances in engineering active sites for photocatalytic CO2 reduction

The photocatalytic conversion of green-house gas CO₂ into high value-added carbonaceous fuels and chemicals through harvesting solar energy is a great promising strategy for simultaneously tackling global environmental issues and the energy crisis. Considering the vital role of active sites in determining the activity and selectivity in photocatalytic CO₂ reduction reactions, great efforts have been directed toward engineering active sites for fabricating efficient photocatalysts. This review highlights recent advances in the strategies for engineering active sites on surfaces and in open frameworks toward photocatalytic CO₂ reduction, referring to surface vacancies, doped heteroatoms, functional groups, loaded metal nanoparticles, crystal facets, heterogeneous/homogeneous single-site catalysts and metal nodes/organic linkers in metal organic frameworks.

Topotactic Transformation of Bismuth Oxybromide into Bismuth Tungstate: Bandgap Modulation of Single-Crystalline {001}-Faceted Nanosheets for Enhanced Photocatalytic CO2 Reduction

The photocatalytic conversion of CO₂ to energy-rich CH₄ solar fuel is an ideal strategy for future energy generation as it can resolve global warming and the imminent energy crisis concurrently. However, the efficiency of this technology is unavoidably hampered by the ineffective generation and utilization of photoinduced charge carriers. In this contribution, we report a facile in situ topotactic transformation approach where {001}-faceted BiOBr nanosheets (BOB-NS) were employed as the starting material for the formation of single-crystalline ultrathin Bi₂WO₆ nanosheets (BWO-NS). The as-obtained BWO-NS not only preserved the advantageous properties of the 2D nanostructure and predominantly exposed {001} facets but also possessed enlarged specific surface areas as a result of sample thickness reduction. As opposed to the commonly observed bandgap broadening when the particle sizes decrease to an ultrathin nanoscale owing to the quantum size effect, the developed BWO-NS exhibited a fascinating bandgap narrowing compared to those of pristine Bi₂WO₆ nanoplates (BWO-P) synthesized from a conventional one-step hydrothermal approach. Moreover, the electronic band positions of BWO-NS were modulated as a result of ion exchange for the reconstruction of the energy bands, where BWO-NS demonstrated significant upshifting of CB and VB levels; these are beneficial for photocatalytic reduction applications. This propitious design of BWO-NS through integrating the merits of BOB-NS caused BWO-NS to exhibit substantial 2.6 and 9.3-fold enhancements of CH₄ production over BOB-NS and BWO-P, respectively.

Blue/red light-triggered reversible color switching based on CeO2-x nanodots for constructing rewritable smart fabrics

Photoreversible color switching systems (PCSSs) have attracted increasing attention in various applications, but in most PCSSs the discoloration process usually relies on harmful UV light as a stimulus and the recoloration requires high temperature. To solve these problems, we have designed and prepared CeO2-x nanodots as novel photocatalytic components in PCSSs that respond to two kinds of visible light. CeO2-x nanodots are prepared by a solvothermal reaction with l-ascorbic acid as the reducing agent. CeO2-x nanodots with a size of ∼2 nm have a high concentration of oxygen vacancies, which confers a broadened photoabsorption with an edge at 500 nm, as well as a weak photoabsorption tail in the visible region (500-800 nm). To realize the color switching, both the CeO2-x/Dye/H2O solution and CeO2-x/dye/hydroxyethyl cellulose (HEC)-coated fabrics have been prepared. Under blue (450 nm) light irradiation, both the solution and fabric show a rapid discoloration in 30 s and 150 s, respectively, due to the efficient photocatalytic reduction of the redox dye by CeO2-x. Conversely, red (630 nm) light irradiation with air confers a rapid recoloration in 35 s for the solution and 200 s for the fabric, resulting from CeO2-x-mediated self-catalyzed oxidation. In particular, the required images and letters can be remotely printed on CeO2-x/Dye/HEC-coated T-shirts with a 450 nm laser pen, and then erased with 630 nm light, with high reversibility and stability. Therefore, the present CeO2-x/Dye/HEC PCSSs have great potential to construct rewritable smart fabrics for various applications.

Plasma treated Bi2WO6 ultrathin nanosheets with oxygen vacancies for improved photocatalytic CO2 reduction

Ar-plasma treatment quickly and effectively increased the amount of oxygen vacancies on the surface of Bi₂WO₆. In photocatalytic CO₂ reduction, the CO generation rate of Bi₂WO₆ with abundant surface oxygen vacancies increased by 2.4 times.

In situ assembly of CQDs/Bi2WO6 for highly efficient photocatalytic degradation of VOCs under visible light

A facile strategy of the assembly of CQD/Bi₂WO₆ hybrid materials, which exhibit highly efficient photocatalytic degradation of pollutants under visible light.

Self-assembled CoTiO3 nanorods with controllable oxygen vacancies for the efficient photochemical reduction of CO2 to CO

CoTiO₃ with oxygen vacancies was used as a cocatalyst for the photochemical reduction of CO₂ to CO. The bond length of the double bond between C and O in CO₂ increases from 1.17 Å to 1.25 Å in the activation step.

Challenges and implication of full solar spectrum-driven photocatalyst

Conventional metal oxide and its composites embrace the long-standing problem of using the combined visible and near-infrared (NIR) light. Doping with suitable impurities of metal, nonmetal, or its combinations for visible light enhancement is very well studied. However, the quantum efficiency of these photocatalysts does not produce an exciting appearance toward visible and NIR light when irradiated through either artificial or natural light. Furthermore, owing to the limited availability of solar light, challenges arise from the implication of these developed nano-photocatalysts. Therefore, the hybridized concept was developed for the effective use of either full or partial solar spectrum, even functioning in dark conditions. The present review focuses on the challenges of hybridized photocatalysts in storing and discharging the harvested photons obtained from the solar spectrum. The review vividly emphasizes the evolution of light-driven nanomaterials since its innovation and significant breakthroughs in brief, while a detailed presentation of the implications of hybrid photocatalysts for full solar applications, including the mechanistic features, charging-discharging characteristics, work function, charge carrier mobility, and interactions, follows. The article also delivers the substantial contribution of these materials in regard to energy and environmental application.

Synthesis of Bi2WO6-x nanodots with oxygen vacancies as an all-in-one nanoagent for simultaneous CT/IR imaging and photothermal/photodynamic therapy of tumors

All-in-one nanoagents with a single-component and all-required functions have attracted increasing attention for the imaging-guided therapy of tumors, but the design and preparation of such nanoagents remain a challenge. Herein, we report the introduction of oxygen vacancies to traditional semiconductors with heavy-metal elements for tuning photoabsorption in the near infrared (NIR) region, by using Bi2WO6 (band-gap: ∼2.7 eV) as a model. Bi2WO6-x nanodots with sizes of ∼3 or ∼8 nm have been prepared by a facile coprecipitation-solvothermal method assisted by citric acid (CA, 0.1-1.5 g) as the reduction agent. CA confers the removal of O atoms from the [Bi2O2]2+ layer during the solvothermal process, resulting in the formation of plenty of oxygen vacancies in the Bi2WO6-x crystal. As a result, NIR photoabsorption of Bi2WO6-x nanodots can be remarkably enhanced with the increase of the CA amount from 0 to 1.0 g. Under irradiation of a single-wavelength (808 nm, 1.0 W cm-2) NIR laser, black Bi2WO6-x-CA1.0 nanodots can not only efficiently produce a sufficient amount of heat with a photothermal conversion efficiency of 45.1% for photothermal therapy, but also generate singlet oxygen (1O2) for photodynamic therapy. Furthermore, due to the presence of heavy-metal (Bi and W) elements, Bi2WO6-x-CA1.0 nanodots have high X-ray attenuation ability for CT imaging. After the Bi2WO6-x-CA1.0 nanodot dispersion is injected into the tumor-bearing mice, the tumor can be imaged by using CT and an IR thermal camera. After irradiation with a single-wavelength (808 nm, 1.0 W cm-2, 10 min) NIR laser, the tumor can be completely suppressed by the synergic photothermal and photodynamic effects of Bi2WO6-x-CA1.0 nanodots, without recurrence and treatment-induced toxicity. Therefore, Bi2WO6-x nanodots have great potential as a novel all-in-one nanoagent for the imaging and phototherapy of tumors.

Direct observation of oxygen-vacancy formation and structural changes in Bi2WO6 nanoflakes induced by electron irradiation

The prominent role of oxygen vacancies in the photocatalytic performance of bismuth tungsten oxides is well recognized, while the underlying formation mechanisms remain poorly understood. Here, we use the transmission electron microscopy to investigate the formation of oxygen vacancies and the structural evolution of Bi₂WO₆ under in situ electron irradiation. Our experimental results reveal that under 200 keV electron irradiation, the breaking of relatively weak Bi-O bonds leads to the formation of oxygen vacancies in Bi₂WO₆. With prolonged electron irradiation, the reduced Bi cations tend to form Bi clusters on the nanoflake surfaces, and the oxygen atoms are released from the nanoflakes, while the W-O networks reconstruct to form WO₃. A possible mechanism that accounts for the observed processes of Bi cluster formation and oxygen release under energetic electron irradiation is also discussed.

Hierarchical Nanostructured Photocatalysts for CO2 Photoreduction

Practical implementation of CO2 photoreduction technologies requires low-cost, highly efficient, and robust photocatalysts. High surface area photocatalysts are notable in that they offer abundant active sites and enhanced light harvesting. Here we summarize the progress in CO2 photoreduction with respect to synthesis and application of hierarchical nanostructured photocatalysts.

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.

Tuning the NIR photoabsorption of CuWO4−x nanodots with oxygen vacancies for CT imaging guided photothermal therapy of tumors

NIR photoabsorption of CuWO_4−x can be tuned, and the resulting CuWO_4−x nanodots can act as efficient all-in-one nanoagent for simultaneous CT/IR imaging and photothermal therapy of tumors.

Engineering surface oxygen defects on tungsten oxide to boost photocatalytic oxygen evolution from water splitting

This study showcases a facile approach for tuning the degree of surface oxygen vacancies in WO₃ and its prominent role in enhancing the performance of WO₃ in photocatalytic O₂ evolution.

Visible light activity of Bi2WO6@TCNQ with core-shell structure in phenol degradation

Bi2WO6@TCNQ visible light photocatalyst with a core-shell structure was synthesized by adsorption methods. The core-shell structure results in the fast transfer of photogenerated carriers, reduced carrier recombination and photogenerated holes on the HOMO level of TCNQ can be injected into the VB of Bi2WO6 under visible light irradiation, resulting in the direct oxidation of organic pollutants. The photocatalytic activity of Bi2WO6@TCNQ was gradually enhanced with an increasing proportion of TCNQ. When the mass fraction of TCNQ reaches 0.5%, it exhibits the highest visible light activity. The apparent rate constant k of Bi2WO6@TCNQ-0.5% is almost 2.2 times as high as that of pure Bi2WO6.

Significantly enhanced visible light photocatalytic efficiency of phosphorus doped TiO2 with surface oxygen vacancies for ciprofloxacin degradation: Synergistic effect and intermediates analysis

In the present work, we reported a simple method for the simultaneous phosphorus (P) doping and oxygen vacancies creation on TiO₂ in a single step. The obtained P-doped TiO₂ with surface oxygen vacancies (PTSOV) samples exhibited efficient photocatalytic activity for the degradation of fluoroquinolone antibacterial agent (ciprofloxacin) under visible light irradiation. The optimized sample showed a rate constant of 0.065 min^-1 for degradation of ciprofloxacin (CIP) and it was about 16.2 times as high as that of TiO₂ (0.004 min^-1). The transformation products of CIP were identified by liquid chromatography-mass spectrometry (LC-MS), and degradation pathway was tentatively proposed. The doping state of P and the formation of surface oxygen vacancies (SOVs) were investigated by different methods. X-ray diffraction (XRD) and X-ray Photoemission Spectroscopy (XPS) revealed P⁵⁺ doped via formation TiOP bond. Electron paramagnetic resonance (EPR) spectroscopy revealed that SOVs were generated on P-doped TiO₂. It turned out that the synergistic effect between doping P and SOVs on TiO₂ greatly improved transfer and separation efficiency of photogenerated charges, thus significantly enhanced the visible light photocatalytic performance of TiO₂. Our work would provide an effective way to design new photocatalysts with high performance under visible light irradiation.

Mesoporous nanoplate multi-directional assembled Bi2WO6 for high efficient photocatalytic oxidation of NO

Herein, a mesoporous nanoplate multi-directional assembled Bi₂WO₆ architecture was successfully prepared and applied for the photocatalytic removal of NOx pollutants at low concentrations under visible light and simulated solar light irradiation. Bi₂WO₆-180-C synthesized at a hydrothermal temperature of 180 °C with calcination exhibited an excellent conversion efficiency in the photocatalytic oxidation of gaseous NO. The crystallinity, morphology, specific surface area, pore environment, light absorption, and separation of photogenerated electrons and holes were investigated by various techniques; the excellent photocatalytic performance of Bi₂WO₆-180-C was attributed to its special hierarchical mesoporous structure with an appropriate pore size and interconnected porous network, which imparted good gas permeability and fast mass transfer of reaction intermediates and final products of NO oxidation. Furthermore, hierarchical mesoporous Bi₂WO₆ showed excellent photocatalytic durability and reusability.

Efficient solar-driven conversion of nitrogen to ammonia in pure waterviahydrogenated bismuth oxybromide

Solar-driven reduction of dinitrogen to ammonia under mild conditions has attracted widespread interest in recent years. In this study, we first report low-temperature hydrogenated BiOBr for the direct synthesis of ammonia from dinitrogen with high efficiency under solar-light irradiation. In a proof of concept, the hydrogenation treatment can lead to surface disorder due to the strong reducing capacity of hydrogen. Oxygen atoms can be activated, and they can escape from the surface structure to form oxygen vacancies. Then, defect engineering can broaden the photoelectricity absorption window and effectively trigger interfacial electron transfer from the semiconductor to the combined nitrogen. This method exhibits a satisfactory result for photocatalytic nitrogen fixation, yielding about 2.6 times more NH₃ than that obtained from the original sample. The corresponding apparent quantum efficiency can reach a significant value of 2.1% under 380 nm monochromatic light irradiation. These results may pave a new way for the synthesis of highly active photocatalysts for efficient nitrogen fixation under solar light irradiation.

Samples of H-BiOBr use water as reactant which demonstrates efficient nitrogen fixation under sunlight.