Bismuth Oxyhalides Research Articles

Sonochemically Synthesized Bismuth Oxyiodide Nanocrystal for Wastewater Remediation through Visible‐Light Photocatalysis

AbstractIt has been demonstrated that bismuth oxyhalides [BiOX (X = Cl, Br, and I)] nano‐crystals can efficiently behave as photocatalysts both under visible light and UV light. Different types of dyes, phenols, etc. can be degraded by bismuth oxyhalides materials efficiently, for the purification of wastewater. The raw materials used in the synthesis of bismuth oxyiodide (BiOI) are pure Bi2O3, halide salt, and capping agent (poly‐vinyl‐pyrrolidone). A variety of characterization techniques are used to characterize the as‐synthesized samples, including X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV–Vis diffuse reflection spectroscopy (UV–Vis DRS), photoluminescence (PL), Mott–Schottky, field emission scanning electron microscopy (FESEM), energy dispersive X‐ray spectroscopy (EDX), and high resolution transmission electron microscopic (HRTEM), etc. A potential application in environmental remediation is achieved through 95.25% degradation of organic Rhodamine B (RhB) dye within 100 min using the synthesized materials under visible light irradiation.

Oxygen Vacancy Defect Enhanced NIR-II Photothermal Performance of BiOxCl Nanosheets for Combined Phototherapy of Cancer Guided by Multimodal Imaging.

Narrow photo-absorption range and low carrier utilization are significant barriers that restrict the antitumor efficiency of 2D bismuth oxyhalide (BiOX, X = Cl, Br, I) nanosheets (NSs). Introducing oxygen vacancy (OV) defects can expand the absorption range and improve carrier utilization, which are crucial but also challenging. In this study, a series of BiOxCl NSs with different OV defect concentrations (x = 1, 0.7, 0.5) is developed, which shows full spectrum absorption and strong absorption in the second near-infrared region (NIR-II). Density functional theory calculations are utilized to calculate the crystal structure and density states of BiOxCl, which confirm that part of the carriers is separated by OV enhanced internal electric field to improve carrier utilization. The carriers without redox reaction can be trapped in the OV, leading to great majority of photo-generated carriers promoting the photothermal performance. Triggered by single NIR-II (1064nm), BiOxCl NSs' bidirectional efficient utilization of carriers achieves synchronously combined phototherapy, leading to enhanced tumor ablation and multimodal diagnostic in vitro and vivo. It is thus believed that this work provides an innovative strategy to design and construct nanoplatforms of indirect band gap semiconductors for clinical phototheranostics.

Design and synthesis of a UV–vis-NIR response heterostructure system: For efficient solar energy conversion and BPA photocatalytic degradation

Combining upconversion materials with narrow-wide bandgap semiconductors to construct heterostructured composite photocatalysts effectively improves solar energy conversion efficiency. NYF:Ln3+(Ln = Yb,Er,Tm)@BiOX(X = Cl,Br,I) heterostructures were prepared by a two-step hydrothermal method. This work explores the effects of different lanthanide ion doping and narrow-wide bandgap bismuth oxyhalides on the performance of the heterostructures system. Under near-infrared (NIR) light irradiation, NYF:Yb,Er,Tm@BiOI degraded 94 % BPA within 160 min. Significantly, compared with NYF:Yb,Er@BiOCl, NYF:Yb,Er@BiOBr and the NYF:Yb,Er,Tm/BiOI mechanical mixtures, the photocatalytic activity of NYF:Yb,Er,Tm@BiOI was increased by 9.4 times, 3.7 times and 1.8 times, respectively. The enhanced photocatalytic activity is attributed to the doping of Er-Tm double-activated ions, which provides multiple upconversion emissions and forms more overlap in the narrow bandgap BiOI absorption spectrum, making it advantageous to utilize upconversion light fully. Eventually, an underlying mechanism was proposed that the existence of FRET in the NYF:Yb,Er,Tm@BiOI heterostructure leads to enhanced photocatalytic activity. This work provides new insights into the design of advanced structures for NIR-responsive photocatalysts.

In-situ construction of Z-scheme 2D/2D g-C3N4/BiOBr heterojunction with enhanced photocatalytic CO2 reduction

A novel series of g-C3N4/BiOBr (CN/BOB) Z-scheme heterojunction catalysts with two-dimensional/two-dimensional (2D/2D) morphology were synthesized by an in-situ hydrolysis method for photocatalytic CO2 reduction. Without adding any sacrificial agents or co-catalysts, the optimal CN/BOB heterostructure exhibits a boosted CO generation rate of 20.1 μmol·g-1·h-1 under the simulated solar light irradiation, severally being 1.7 and 3.7 times that of pristine BiOBr and g-C3N4. The enhanced performance principally benefit from the 2D/2D microstructure and Z-scheme heterojunction of photocatalysts. The intimate contact of 2D/2D morphology signifies more transmission channels and shorter transfer interface distance of photogenerated charges. While relevant characterizations and first-principles calculations jointly demonstrate that the Z-scheme heterojunction could significantly accelerate the spatial separation and transfer of photo-induced carriers, and evidently promote the redox ability of photocatalysts. The research furnishes a novel strategy to construct a promising bismuth oxyhalide based heterojunction catalyst for the application of photocatalytic CO2 reduction.

Optimizing CO2 photoreduction on bismuth oxyhalides via intrinsic and extrinsic techniques

Intrinsic and extrinsic techniques that have been applied to BiOX photocatalysts for optimizing CO2 photoreduction are concisely summarized.

Insights into the nucleation and growth of BiOCl nanoparticles by in situ X-ray pair distribution function analysis and in situ liquid cell TEM.

The synthesis of bismuth oxyhalides as defined nanostructures is hindered by their fast nucleation and growth in aqueous solutions. Using our recently developed single-source precursor, the formation of bismuth oxychloride in such solutions can be slowed significantly. As reported herein, this advance enables BiOCl formation to be investigated by in situ X-ray total scattering and in situ liquid cell transmission electron microscopy. In situ pair distribution function analysis of X-ray total scattering data reveals the local order of atomic structures throughout the synthesis, while in situ liquid cell transmission electron microscopy allows for tracking the growth of individual nanoparticles. Through this work, the precursor complex is shown to give rise to BiOCl upon heating in solution without the observation of structurally distinct intermediates. The emerging nanoparticles have a widened interlayer spacing, which moderately decreases as the particles grow. Mechanistic insights into the formation of bismuth oxyhalide nanoparticles, including the absence of distinct intermediates within the available time resolution, will help facilitate future design of controlled BiOX nanostructures.

Enhanced pollutant photodegradation activity of graphitic carbon nitride on via bismuth oxyhalide graphene hybridization and the mechanism study

Addressing the degradation of persistent organic pollutants like Bisphenol A (BPA) and Rhodamine B (RhB) with a photocatalyst that is both cost-effective and environmentally friendly is a notable challenge. This...

Promoting oxygen electrode reaction kinetics in photo-assisted Li-O2 batteries through heterostructure design and built-in electric field construction.

Li-O2 batteries (LOBs) boast an exceptionally high theoretical energy density; however, the slow kinetics of the oxygen electrode reaction have been a significant hurdle in their advancement and practical application. In this study, a composite of bismuth oxyhalide heterojunction incorporated with metal-organic frameworks (MOFs) was engineered on carbon cloth (Zr-MOF/BiOIBr/CC) as an efficient bifunctional catalyst to enhance the oxygen electrode reaction in photo-assisted LOBs. Compared to Zr-MOF/CC, Zr-MOF/BiOIBr/CC significantly expands the light absorption spectrum of the catalyst. Furthermore, the built-in electric field in the heterojunction aids in the separation and directional movement of photogenerated carriers, thereby expediting the reaction kinetics of LOBs. Consequently, the photo-assisted LOBs with Zr-MOF/BiOIBr/CC as the cathodes display a discharge potential of 3.05 V, a low charge potential of 3.20 V, and an energy efficiency of up to 95.3%, and can sustain an extended cycle life of over 255 cycles. This study underscores the potential application of MOFs/semiconductor heterostructural materials in photo-assisted LOBs and offers insights into the systematic design of photo-assisted air batteries and other advanced semiconductors.

Hydrothermal carbonization carbon induced synthesis of flower-like C/Bi/BiOI heterojunction with heightened photocatalytic Cr(VI) reduction

Modification with metallic Bi and formation heterojunction with carbon material are considered as the compelling strategies to address the shortcoming of bismuth oxyhalide in photocatalytic Cr(VI) reduction. However, the simultaneous and in-situ synthesis of metallic Bi and hydrothermal carbonization carbon (HC) on BiOI to fabricate a ternary heterojunction photocatalyst remains a challenge yet, and the synergistic mechanism between the localized surface plasmon resonance (LSPR) effect and HC is still indistinct. Herein, a ternary heterojunction photocatalyst comprising metallic Bi, HC, and flower-like BiOI was designed and synthesized through the in-situ induction of HC. During the solvothermal synthesis, a portion of Bi3+ was reduced to metallic Bi nanoparticles, and simultaneously gauzy HC was formed. In the ternary heterojunction, the metallic Bi nanoparticles displayed strong LSPR effect, and the coated HC was conducive to transferring photogenerated electrons and enriching Cr(VI). Due to the synergistic effect of metallic Bi and HC, multiple channels for photogenerated carrier transfer were constructed. Deriving from the excellent light-harvesting, accelerated transfer/separation, and restrained recombination of photogenerated carriers, the ternary heterojunction of flower-like C/Bi/BiOI showed superior photocatalytic Cr(VI) reduction. The reaction rate constant of photocatalytic Cr(VI) reduction was about 26 times higher than that of BiOI.

PH-Dependent photocatalytic performance of faceted BiOBr semiconductor particles in degradation of dyes

Bismuth oxyhalides, such as bismuth-oxy-bromide (BiOBr), show high performance in photocatalytic oxidation of water pollutants. Process conditions, and in particular the pH of the solution, largely affect the photocatalytic efficacy, which is fundamentally poorly understood. We prepared {001} faceted bismuth-oxy-bromide (BiOBr), and determined by advanced AFM analysis that the surface charge of the {001} facet of BiOBr is slightly positive at acidic pH (pH 3) and significantly negative and increasing in negative surface charge in the order pH 6 < pH 9. Decomposition of MB or RhB by illumination of BiOBr is strongly favored by basic conditions (pH 9-10), as evident from discoloration experiments, and determination of the TOC as a function of time of illumination. Reference experiments show the pH dependent degradation profiles cannot be explained by differences in quantities of adsorption of the dye, but rather by the lifetime and/or quantity of BiOBr related photoexcited (surface) charge carriers (holes and electrons) – correlating with surface charge. Using MeOH and other scavengers, we show oxidation of MB or RhB is mainly induced by superoxide anions (•O2− radicals) at low pH and by holes or hydroxyl radicals at high pH – in agreement with surface charge induced band bending. This study provides novel understanding of the pH dependence of the rates of photocatalytic degradation of dyes using BiOBr photocatalysts.

Facile construction of 2D Ni2P/Bi12O17Cl2 composite to reinforce photocatalytic degradation performance of antibiotics in water

Utilizing highly efficient and stable photocatalysts to remove residual organic pollutants in wastewater has been deemed to be a promising and green technique for environmental management. Herein, novel 2D Ni2P/Bi12O17Cl2 composites have been prepared by a facile deposition-precipitation method, and the structure, morphology, optical, photo-electrochemical and photoluminescence properties were characterized particularly. Oxytetracycline (OTC), phenol and methyl orange (MO) were selected as target pollutants to evaluate the photocatalytic performance of the Ni2P/Bi12O17Cl2. Under visible light illumination (λ > 420 nm), the Ni2P/Bi12O17Cl2 photocatalyst possesses outstanding photocatalytic properties for the degradation of OTC, phenol and MO than those of Bi12O17Cl2. The enhanced photocatalytic activity of the Ni2P/Bi12O17Cl2 is attributed to Ni2P acting as photogenerated electrons trappers to reinforce photoinduced charges separation. Furthermore, the Ni2P/Bi12O17Cl2 photocatalyst owns outstanding stability. This study might shed light on the enhanced photocatalytic capacities of bismuth oxyhalide by means of embellishing transition metal phosphides in environment remediation fields.

A case study of different bismuth oxyhalides BiOX (X = F, Cl, Br, and I)/biochar-derived rice husk@graphitic carbon nitride for the robustness of H2O2 photoproduction and antibiotic photodegradation

In this study, the heterojunction photocatalyst bismuth oxyhalides/rice husk-derived biochar@graphitic carbon nitride (BiOX (X = F, Cl, Br, and I)/BC@CN) was successfully synthesized through calcination and hydrothermal self-assembly synthesis. The photo-absorption range of CN was expanded by coupling of biochar and BiOX, which also improved electron production and increased the number of active sites for O2 and H+ adsorption. This structure modification produced good H2O2 production performance with the H2O2 photoproduction of BiOI/BC@CN reaching 2.89 mM·g−1 under visible light illumination. Besides, the highest photodegradation of ciprofloxacin (CIP) of BiOBr/BC@CN was given at pH 7.5, catalyst dose 30 mg, and CIP concentration 20 mg·L−1 (99.79 %), in which the photodegradation kinetics followed the pseudo-first-order model with a rate constant of 0.03098 min−1. This work provides an innovative and practical modification method that utilizes agricultural by-products from rice husks to promote the advancement of semiconducting catalysts in the photo-activities of H2O2 generation and antibiotic removal.

A comprehensive review on tailoring factors of porous bismuth oxyhalide photocatalysts for wastewater treatment application

BackgroundPhotocatalysis is a green, environmentally friendly approach for converting organic contaminants into harmless byproducts. Especially, Bismuth oxyhalides (BiOX, where X = Cl, Br and I) have emerged as promising photocatalysts for wastewater treatment due to their layered-by-layered structure, strong chemical stability and nontoxicity in compare to other metal oxides, which makes the photocatalyst advantageous for photocatalytic application. MethodsThis review provides an overview of recent developments in the synthesis and application of BiOX-based porous photocatalysts for the removal of organic contaminants from wastewater. Firstly, morphology-controlled synthesis of BiOX in degradation of organic contaminants. Then, modulation of electronic structure through doping, facet engineering and surface engineering has been highlighted for better photocatalytic applications. Furthermore, fabrication of diverse heterojunctions and co-catalyst loading upon BiOX are introduced, which can vary photocatalytic activity towards the degradation of organic contaminants. Significant findingsFinally, this review ended on the future trend and prospects of BiOX for the creation of potential high-performance photocatalysts in the near future. The porous structure of BiOX improved photocatalytic activity, pollutant degradation efficiency, visible light response charge carrier separation, and stability. Overall, bismuth oxyhalide photocatalysts have a lot of potential for effective and long-term wastewater treatment, and their development represents an important step towards addressing the global water pollution crisis.

The Tunable Electronic and Optical Properties of Two-Dimensional Bismuth Oxyhalides.

Two-dimensional (2D) bismuth oxyhalides (BiOX) have attracted much attention as potential optoelectronic materials. To explore their application diversity, we herewith systematically investigate the tunable properties of 2D BiOX using first-principles calculations. Their electronic and optical properties can be modulated by changing the number of monolayers, applying strain, and/or varying the halogen composition. The band gap shrinks monotonically and approaches the bulk value, the optical absorption coefficient increases, and the absorption spectrum redshifts as the layer number of 2D BiOX increases. The carrier transport property can be improved by applying tensile strain, and the ability of photocatalytic hydrogen evolution can be obtained by applying compressive strain. General strain engineering will be effective in linearly tuning the band gap of BiOX in a wide strain range. Strain, together with halogen composition variation, can tune the optical absorption spectrum to be on demand in the range from visible to ultraviolet. This suggests that 2D BiOX materials can potentially serve as tunable novel photodetectors, can be used to improve clean energy techniques, and have potential in the field of flexible optoelectronics.

Evaluation of photocatalytic activity of heterojunctions between bismuth oxyhalides and hematite in the degradation of organic compounds in liquid phases under visible light

Photocatalysts were synthesized by constructing p-n type heterojunctions between bismuth oxyhalides BiOX (X = I or Br) and hematite (α-Fe2O3) for enhanced visible light photodegradation of pollutants in aqueous medium. BiOX, in this text called precursors, were synthesized using a modified solvothermal method and by coprecipitation. Hematite was added using hydrothermal treatment. Herein the materials prepared using precursors and hematite are being called catalysts. All materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS) and adsorption assays with N2. The characterization of BiOX revealed that the solvothermal methods synthesized precursors with greater surface area and structural uniformity than those obtained by coprecipitation. The BiOI precursors, had observed reaction rate constant, kap, values for rhodamine between 0.0054 and 0.0167 min−1. The BiOBr precursors provided values between 0.1016, and 0.0515 min−1. In order to synthesizing the catalysts, an experimental planning was carried out. It showed that Fe/Bi ratio was the variable with the greatest impact on activity, followed by temperature. The BiOI catalysts had kap maximum values for rhodamine between 0.0419, and 0.0213 min−1, while BiOBr catalysts between 0.1144 and 0.1082 min−1. BiOI and BiOBr catalysts provided kap at least 2.0 and 1.12 times greater than their precursors, respectively. Also, successfully degraded phenol, confirming photocatalytic activity of the catalyst surface.

An enhanced photo(electro)catalytic CO2 reduction onto advanced BiOX (X = Cl, Br, I) semiconductors and the BiOI–PdCu composite

The photoelectrocatalytic reduction of CO2 (CO2RR) onto bismuth oxyhalides (BiOX, X = Cl, Br, I) was studied through physicochemical and photoelectrochemical measurements. The successful synthesis of the BiOX compounds was carried out through a solvothermal methodology and confirmed by XRD measurements. The morphology was analyzed by SEM; meanwhile, area and pore size were determined through BET area measurements. BiOI and BiOCl present a lower particle size (3.15 and 2.71 μm, respectively); however, the sponge-like morphology presented by BiOI results in an increase in the BET area, which can enhance the catalytic activity of this semiconductor. In addition, DRS measurements allowed us to determine bandgap values of 1.9, 2.4, and 3.6 eV for BiOI, BiOBr, and BiOCl, respectively. Such results predict better visible light harvesting for BiOI. Photoelectrochemical measurements indicated that BiOX shows p-type semiconductor behavior, being the holes the majority charge carriers, making BiOI the most active material to carry out photoelectrocatalytic CO2RR. In the second stage, three different composites, BiOI–Pd, BiOI–Cu, and BiOI–PdCu, (BiOI-M; M = Pd, Cu, PdCu), were fabricated to study the influence of active metal nanoparticles (NP's) in the BiOI CO2RR activity. XRD measurements confirmed the interaction between BiOI and the metallic NP's, the three composites overpassed by 20% the BET area of pristine BiOI. Photoelectrochemical measurements indicate that all BiOI-metal composites are suitable materials to perform CO2 reduction in neutral media efficiently; however, the BiOI–PdCu composites surpassed the faradaic current of BiOI–Pd and BiOI–Cu at 0.85 V vs. RHE (3.15, 2.06 and 2.15 mA cm−2, respectively). BiOI–PdCu presented photoactivity to carry out the CO2 reduction evolving formic acid and acetic acid as the main products under visible-light irradiation.

Glycerol photocatalytic oxidation to higher value-added compounds via bismuth oxyhalide photocatalysts

Bismuth oxyhalides (BiOX) including BiOCl, BiOBr, and BiOI, were well synthesized using solvothermal technique and then used in the aqueous phase photooxidation of glycerol as a catalyst. The as-synthesized BiOBr could achieve the highest glycerol transformation of around 85.6% in 8 h under ultraviolet light (UV) irradiation among as-synthesized BiOXs. Moreover, the BiOBr/TiO2 heterojunction was also prepared through an ethylene glycol-assisted solvothermal process. This new BiOBr/TiO2 heterostructure exhibited excellent photocatalytic activity (97.4%) for the oxidation of glycerol compared with pure BiOBr (74%) under ultraviolet light irradiation at 6 h. This obtained behavior was confirmed by more produced OH• radicals of BiOBr/TiO2.

Development of bismuth-rich bismuth oxyhalides based photocatalyst for degradation of a representative antibiotic under simulated solar light irradiation

In this study, the novel 2D/2D S-scheme Bi12O15Cl6/BiOCl heterojunction was fabricated using a facile solvothermal followed by a post-thermal treatment process. The samples were characterized by various modern spectroscopy techniques. A series of Bi12O15Cl6/BiOCl heterojunctions were prepared by adjusting the molar ratio of Bi:Cl and the calcination temperature. The crystalline structure, morphology, elemental composition, and optical properties of nanocomposites strongly depend on the synthesis conditions. The sample prepared with Bi:Cl molar ratio of 2.0:1 and calcined at 400 °C (BOC-2.0-400) containing 29.55 wt% of BiOCl and 70.45 wt% of Bi12O15Cl6, exhibited the highest efficiency in the degradation of CIP solution under simulated solar light irradiation. The reaction rate constant was 2.5 times and 1.8 times higher than that of pristine BiOCl and Bi12O15Cl6, respectively. Under the experimental conditions of catalyst dosage of 0.7 gL-1, initial CIP concentration of 10 mgL-1 and pH8.8, CIP was completely degraded within 150 min of irradiation over the BOC-2.0-400. Furthermore, radical scavenging studies signified that O2●–, h+ are evolved in photocatalytic process. The experimental and characterization results provided evidenc that the excellent photocatalytic performance of Bi12O15Cl6/BiOCl heterojunction was facilitated by the construction of S-scheme charge transfer route with compact interface of 2D/2D morphology. The S-scheme Bi12O15Cl6/BiOCl heterojunction exhibited excellent visible light absorption ability, high photogenerated charge separation efficiency and maintained strong redox capacity for electrons and holes during CIP photodegradation. These findings provide a potential strategy for designing S-scheme heterojunction-based bismuth-rich bismuth oxyhalide photocatalyst to eliminate antibiotic residues.

Mechanistic insights into the deprotonation of methanol by facile synthesized 3D flower-like BiOX (X= Cl, Br, I) catalysts for rapid hydrogen generation from NaBH4 methanolysis: The ‘X’ factor

Bismuth oxyhalides (BiOX, X = Cl, Br, I) have been showing promising catalytic activity in various applications due to their electronic properties and unique layered structure. However, their catalytic potential for hydrogen generation from chemical hydrides is unrevealed. Herein, BiOX (X = Cl, Br, I) catalysts were prepared via a simple co-precipitation method. The physical and chemical characteristics of the as-prepared samples were then duly characterized using various techniques such as X-ray diffractometer spectroscopy (XRD), Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), Nitrogen adsorption-desorption, and Scanning electron microscope (SEM). The catalysts were then applied to NaBH4 methanolysis for the production of hydrogen. Among the BiOX catalysts, BiOCl exhibits excellent performance which is attributed to the highest electronegativity possessed by the Cl− halogens clinging onto the catalytic layers, simply overriding the substitution reactions. Subsequently, superior performances were depicted with rapid generation of hydrogen, High rate of hydrogen generation, HGR = 42,740 mL H2 g−1min−1, and calculated activation energy of Ea = 43.5 kJ/mol with stability for over 5 successive cycles. Withal, a plausible mechanism based on the exchange reactions promoted by the BiOX catalysts, which comprises interlacing [Bi2O2] slabs with double halogen slabs coupled with a strong ionic nature is illustrated in line with the experimental results.

Controlled solvothermal synthesis of Bi5O7I nanoparticles for enhanced photocatalytic degradation of paracetamol

A bismuth oxyiodide photocatalytic material was synthesized using a simple solvothermal method, followed by calcination at temperatures ranging from 340 °C to 500 °C. The multiform bismuth oxyiodides obtained via in situ phase transformation using BiOI as precursors were evaluated by the catalytic degradation of paracetamol under simulated sunlight irradiation in an aqueous solution. Several characterization tools were employed to study the phase structures, morphologies, and optical properties of the samples. The results showed that BiOI was completely transformed into Bi4O5I2 at 410 °C, which was further decomposed into Bi5O7I when the temperature was raised to 500 °C. These bismuth oxyiodides exhibited a distinct band structure that allowed for the adjustment of oxidation and reduction abilities of the band energy levels. The highest photocatalytic activity was achieved by Bi5O7I, which completely degraded paracetamol after 45 min of irradiation. The improvement in catalytic performance activity was attributed to the high ability of holes to oxidize bismuth-rich Bi5O7I, its specific surface area, and the introduction of I vacancies effectively lowers the recombination of photocarrier and changed the band structure of Bi5O7I. Moreover, the Bi5O7I catalyst showed excellent photostability in a five cycle photocatalytic experiment. This study provides a strategy for the development of highly efficient bismuth oxyhalides for the construction of a high performance photocatalyst material for environmental applications.