Novel I−-doped BiOBr composites: Modulated valence bands and largely enhanced visible light phtotocatalytic activities

Visible-Light-Active Iodide-Doped BiOBr Coatings for Sustainable Infrastructure

The search for efficient materials for sustainable infrastructure is an urgent challenge toward potential negative emission technologies and the global environmental crisis. Pleasant, efficient sunlight-activated coatings for applications in self-cleaning windows are sought in the glass industry, particularly those produced from scalable technologies. The current work presents visible-light-active iodide-doped BiOBr thin films fabricated using aerosol-assisted chemical vapor deposition. The impact of dopant concentration on the structural, morphological, and optical properties was studied systematically. The photocatalytic properties of the parent materials and as-deposited doped films were evaluated using the smart ink test. An optimized material was identified as containing 2.7 atom % iodide dopant. Insight into the photocatalytic behavior of these coatings was gathered from photoluminescence and photoelectrochemical studies. The optimum photocatalytic performance could be explained from a balance between photon absorption, charge generation, carrier separation, and charge transport properties under 450 nm irradiation. This optimized iodide-doped BiOBr coating is an excellent candidate for the photodegradation of volatile organic pollutants, with potential applications in self-cleaning windows and other surfaces.

Anchoring bismuth oxybromo-iodide solid solutions on flexible electrospun polyacrylonitrile nanofiber mats for floating photocatalysis

Constructing floating photocatalysts with highly efficient visible-light utilization is a promising approach for practical photocatalytic wastewater treatment. In this study, we anchored bismuth oxybromo-iodide (BiOBr_xI_1-x (0 ≤ x ≤ 1)) on flexible electrospun polyacrylonitrile (PAN) nanofiber mats to create BiOBr_xI_1-x@PAN nanofibers with tunable light absorption properties as floating photocatalysts at room temperature. As x increased, the photocatalytic activity of the BiOBr_xI_1-x@PAN nanofibers with similar loading content initially increased, and then decreased, for the degradation of bisphenol A (BPA) and methyl orange (MO) under visible-light irradiation (λ > 420 nm) conditions. The BiOBr_xI_1-x@PAN (0 < x < 1) nanofibers exhibited better photocatalytic performance compared to the BiOBr@PAN and BiOI@PAN nanofibers. Under visible-light irradiation, the BPA degradation rate of the BiOBr_0.5I_0.5@PAN nanofibers was 1.9 times higher than that of the BiOI@PAN nanofibers, while the BiOBr@PAN nanofibers had no noticeable degradation performance. The MO degradation rate of the BiOBr_0.5I_0.5@PAN nanofibers was 2.5 and 3.2 times higher than that of the BiOBr@PAN and BiOI@PAN nanofibers, respectively. The enhanced performance possibly originated from a balance between the light absorption and redox capabilities, along with efficient separation of electron-hole pairs in the BiOBr_0.5I_0.5@PAN nanofibers, as determined by ultraviolet-visible diffuse reflectance spectroscopy, X-ray photoelectron spectra analysis of the valence bands, and photocurrent response characterization. Compared to the powder structures, the BiOBr_xI_1-x@PAN nanofibers showed enhanced performance due to the excellent dispersion and immobilization of the BiOBr_xI_1-x solid solution, which provided more active sites during photocatalytic degradation. In addition, their flexible self-supporting structures allowed for floating photocatalysis near the water surface. They could be reused directly without separation and maximized the absorption of visible light during the photocatalytic reaction. Therefore, these solid-solution-based floatable nanofiber photocatalysts are good potential candidates for wastewater treatment applications.

Enhanced photocatalytic degradation of glyphosate over 2D CoS/BiOBr heterojunctions under visible light irradiation

Two-dimensional (2D) heterojunction photocatalysts can shorten the carrier transfer pathway. In this study, CoS nanoparticles were deposited on the surface of 2D BiOBr nanosheets to fabricate novel ultrathin and intimate-contact 2D heterojunction photocatalysts by a two-step solvothermal route. Under visible-light (λ > 400 nm) irradiation, the apparent reaction rate constant of glyphosate degradation over 10%CoS/BiOBr reaches 0.0074 min^-1 (74.7% glyphosate was degraded within 3 h), which is about 5.3 times that of pure BiOBr (0.0014 min^-1). The extraordinary photocatalytic performance is attributed to the strong visible-light absorption, the effective charge separation and low charge transfer resistance. The possible photocatalytic reaction process and mechanism over CoS/BiOBr heterojunctions are proposed. Moreover, the 10%CoS/BiOBr sample shows good reusability and stability. This work could provide a new insight for the design and development of 2D heterojunction photocatalysts.

Built-in electric field for photocatalytic overall water splitting through a TiO2/BiOBr P-N heterojunction

Photocatalytic overall water splitting to simultaneously obtain abundant hydrogen and oxygen is still the mountain that stands in the way for the practical applications of hydrogen energy, in which composite semiconductor photocatalysts are critical for providing both electrons and holes to promote the following redox reaction. However, the interface between different components forms a deplete layer to hinder the charge transfer to a large extent. In order to enhance the charger transfer from an interface to the surface and promote the spatial separation of electron-hole pairs, a built-in electric field induced by a p-n heterojunction emerges as the best choice. As a touchstone, a p-n heterojunction of TiO2/BiOBr with a strong built-in electric field has been constructed, which presents a wide spectrum response owing to its interleaved band gaps after composition. The built-in electric field greatly enhances the separation and transportation of photogenerated carriers, resulting in fluorescence quenching due to the carrier recombination. The sample also displayed exceptional photoelectron responses: its photocurrent density (43.3 μA cm-2) was over 10 times that of TiO2 (3.5 μA cm-2) or BiOBr (4.2 μA cm-2). In addition, the sample with a molar ratio of 3 : 1 between TiO2 and BiOBr showed the best photocatalytic overall water splitting performance under visible light (λ > 420 nm): the hydrogen and oxygen production rate were 472.7 μmol gcat.-1 h-1 and 95.7 μmol gcat.-1 h-1, respectively, which are the highest values under visible light without other cocatalysts to have been reported in literature for the photocatalyst.

Co2+-Doped BiOBrxCl1-x hierarchical microspheres display enhanced visible-light photocatalytic performance in the degradation of rhodamine B and antibiotics and the inactivation of E. coli

In this article, we have synthesized Co²⁺-doped BiOBr_xCl_1-x hierarchical nanostructured microspheres, featuring different degrees of Co²⁺ doping, displaying excellent photocatalytic performance. X-ray diffraction and Raman spectroscopy indicated that the Co²⁺ ions were successfully doped into the BiOBr_xCl_1-x nanocrystals. The photodegradation rate of rhodamine B mediated by a doped BiOBr_xCl_1-x was 150 % greater than that of the non-doped BiOBr. We ascribe the improved photocatalytic capability of the Co²⁺-doped BiOBr_xCl_1-x to a combination of its superior degree of light absorption, more efficient carrier separation, and faster interfacial charge migration. The major active species involved in the photodegradation of RhB also has been investigated. Moreover, the doped BiOBr_xCl_1-x possessed excellent cellular biocompatibility and displayed remarkable performance in the photocatalytic bacterial inactivation.

First-principles investigation of nonmetal doped single-layer BiOBr as a potential photocatalyst with a low recombination rate

Nonmetal doping is an effective approach to modify the electronic band structure and enhance the photocatalytic performance of bismuth oxyhalides.

Core-shell structured Fe3O4@GO@MIL-100(Fe) magnetic nanoparticles as heterogeneous photo-Fenton catalyst for 2,4-dichlorophenol degradation under visible light

A novel core-shell structured Fe₃O₄@GO@MIL-100(Fe) magnetic catalyst was successfully synthesized and used as heterogeneous photo-Fenton catalyst for 2,4-dichlorophenl (2,4-DCP) degradation. The catalyst was fully characterized by X-ray diffraction pattern (XRD), Raman spectroscopy, Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Brunner-Emmet-Teller (BET) and magnetic hysteresis loops measurements. The effects of initial pH, H₂O₂ concentration, catalyst load and irradiation intensity on 2,4-DCP degradation were also investigated. The results showed that Fe₃O₄@GO@MIL-100(Fe) exhibited excellent photo-Fenton catalytic activity, achieving almost 100% of 2,4-DCP degradation within 40 min at reaction condition of 3 mmol/L H₂O₂, 50 mg/L 2,4-DCP, pH 5.5 and irradiation intensity of 500 W. The high catalytic activity of Fe₃O₄@GO@MIL-100(Fe) can be attributed to the efficient transfer of photo-generated electrons between MIL-100(Fe) and Fe₃O₄ by GO. The recycling experiments displayed that Fe₃O₄@GO@MIL-100(Fe) catalyst possessed good stability and could be easily recovered under an applied magnetic field. Finally, the possible mechanism of 2,4-DCP degradation in the photo-Fenton system catalyzed by Fe₃O₄@GO@MIL-100(Fe) was also proposed according to the analyses of reactive species, photoluminescence (PL) emission spectra and the photocurrent responses.

Wide spectral degradation of Norfloxacin by Ag@BiPO4/BiOBr/BiFeO3 nano-assembly: Elucidating the photocatalytic mechanism under different light sources

Metallic Ag deposited BiPO₄/BiOBr/BiFeO₃ ternary nano-hetero-structures were rationally designed and synthesized by a simple precipitation-wet impregnation-photo deposition method. The plasmonic junction possesses an excellent wide spectrum photo-response and makes best use of BiPO₄ which is otherwise a poor photocatalyst. Ag@BiPO₄/BiOBr/BiFeO₃ showed superior photocatalytic activity for degradation of norfloxacin (NFN) under visible, ultra-violet, near-infra-red and natural solar light. Especially catalyst APBF-3 (0.3 wt% Ag@BiPO₄/BiOBr/BiFeO₃) shows 98.1% degradation of NFN (20 mg/L) in 90 min under visible light and 99.1% in less than 45 min under UV exposure. Free radical scavenging experiments and electron spin resonance (ESR) results has been used for explanation of charge transfer, photocatalytic mechanism and role of radicals for binary, ternary and Ag deposited ternary junctions for UV and visible exposure. Metallic Ag in addition to its surface plasmon resonance helps in protection of high conduction band and valence band in the three semiconductors. A dual Z-scheme mechanism has been predicted by comparing with possibilities of double charge and vectorial charge transfer.

Efficient photocatalytic reactions of Cr(vi) reduction and ciprofloxacin and RhB oxidation with Sn(ii)-doped BiOBr

Efficient photocatalytic reactions of Cr(VI) reduction, ciprofloxacin and RhB oxidation with Sn(II) doped BiOBr.

Application of BiOX Photocatalysts in Remediation of Persistent Organic Pollutants

Bismuth oxyhalides have recently gained attention for their promise as photocatalysts. Due to their layered structure, these materials present fascinating and highly desirable physicochemical properties including visible light photocatalytic capability and improved charge separation. While bismuth oxyhalides have been rigorously evaluated for the photocatalytic degradation of dyes and many synthesis strategies have been employed to enhance this property, relatively little work has been done to test them against pharmaceuticals and pesticides. These persistent organic pollutants are identified as emerging concerns by the EPA and effective strategies must be developed to combat them. Here, we review recent work directed at characterizing the nature of the interactions between bismuth oxyhalides and persistent organic pollutants using techniques including LC-MS/MS for the determination of photocatalytic degradation intermediates and radical scavenging to determine active species during photocatalytic degradation. The reported investigations indicate that the high activity of bismuth oxyhalides for the breakdown of persistent organic pollutants from water can be largely attributed to the strong oxidizing power of electron holes in the valence band. Unlike conventional catalysts like TiO2, these catalysts can also function in ambient solar conditions. This suggests a much wider potential use for these materials as green catalysts for industrial photocatalytic transformation, particularly in flow chemistry applications.

Intensive photocatalytic activity enhancement of Bi5O7I via coupling with band structure and content adjustable BiOBrxI1-x

Band structure and component content are the key factors for determining the activity of semiconductor heterojunction. In this study, a novel Bi₅O₇I/BiOBr_xI_1-x heterostructure was synthesized by a simple hydrobromic (HBr) acid etching method through transforming partial of Bi₅O₇I to I^- ion doped BiOBr (BiOBr_xI_1-x) at room temperature without adding extra dopant. Both the band structure and component content of Bi₅O₇I/BiOBr_xI_1-x alter with the additive HBr acid. The Bi₅O₇I/BiOBr_xI_1-x (S3.0) sample exhibits the best photocatalytic activity, 6 times higher than that of pure Bi₅O₇I, for the degradation of methyl orange under visible-light (λ > 420 nm). The activity enhancement of Bi₅O₇I/BiOBr_xI_1-x is primarily ascribed to the improved separation efficiency of photocharges, originated from the adjustable band structure and component content. The significant findings of this paper provide a facile way to construct highly efficient semiconductor heterojunction via playing the synergetic effect of adjustable band structure and component content for purifying organic pollutants in wastewater.

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.

Recent advances in nanomaterials for water protection and monitoring

Nanomaterials (NMs) for adsorption, catalysis, separation, and disinfection are scrutinized. NMs-based sensor technologies and environmental transformations of NMs are highlighted.

HCl post-processing BiOBr photocatalyst: structure, morphology, and composition and their impacts to activity

This work reports a systematic investigation on the structure, morphology, and composition, and their impacts on photocatalytic performance, for a HCl post-processing BiOBr photocatalyst.

Novel I-BiOBr/BiPO4 heterostructure: synergetic effects of I− ion doping and the electron trapping role of wide-band-gap BiPO4 nanorods

Outstanding activity of I-BiOBr/BiPO₄ was displayed due to the synergetic effects of doped I⁻ ions in I-BiOBr and I-BiOBr/BiPO₄ interface.

Tunable photocatalytic and photoelectric properties of I−-doped BiOBr photocatalyst: dramatic pH effect

Dramatic effect of synthesis pH was discovered for expediently tuning photocatalytic and photoelectric properties of I⁻-doped BiOBr photocatalyst.

Room temperature synthesis of Bi4O5I2 and Bi5O7I ultrathin nanosheets with a high visible light photocatalytic performance

Bi₄O₅I₂ and Bi₅O₇I ultrathin nanosheets with a high visible-light photocatalytic activity for phenol degradation are prepared via a facile route at room temperature.

Construction of amorphous TiO₂/BiOBr heterojunctions via facets coupling for enhanced photocatalytic activity

Facets coupled BiOBr with amorphous TiO2 composite photocatalysts are synthesized via an in situ direct growth approach under microwave irradiation. XRD, SEM and HRTEM characterizations indicate that the heterointerface between BiOBr and amorphous TiO2 occurs mainly on the {001} facets of BiOBr. BET and TEM verify that the heterojunctions possess higher specific surface areas and smaller amorphous TiO2 particle size than bare BiOBr and amorphous TiO2, exhibiting the inhibition function of BiOBr on the growth of TiO2 particles. XPS verifies the interaction between the two components. The degradation of methyl orange (MO) and phenol are used as the objective reaction to evaluate the photocatalytic activity of the as-prepared samples. The reaction rate constant of 15% TiO2/BiOBr composite is 3.4 times greater than that of pure BiOBr, which is attributed to its higher surface area, and efficient separation of photo-generated electron-hole pairs between BiOBr and amorphous TiO2.

Fabrication of multiple heterojunctions with tunable visible-light-active photocatalytic reactivity in BiOBr-BiOI full-range composites based on microstructure modulation and band structures

The fabrication of multiple heterojunctions with tunable photocatalytic reactivity in full-range BiOBr-BiOI composites based on microstructure modulation and band structures is demonstrated. The multiple heterojunctions are constructed by precipitation at room temperature and characterized systematically. Photocatalytic experiments indicate that there are two types of heterostructures with distinct photocatalytic mechanisms, both of which can greatly enhance the visible-light photocatalytic performance for the decomposition of organic pollutants and generation of photocurrent. The large separation and inhibited recombination of electron-hole pairs rendered by the heterostructures are confirmed by electrochemical impedance spectra (EIS) and photoluminescence (PL). Reactive species trapping, nitroblue tetrazolium (NBT, detection agent of (•)O2(-)) transformation, and terephthalic acid photoluminescence (TA-PL) experiments verify the charge-transfer mechanism derived from the two types of heterostructures, as well as different enhancements of the photocatalytic activity. This article provides insights into heterostructure photocatalysis and describes a novel way to design and fabricate high-performance semiconductor composites.

Synthesis and characterization of a CuS–WO3 composite photocatalyst for enhanced visible light photocatalytic activity

WO₃ nanorods and flower-like CuS were synthesized by a hydrothermal process.