Recent advances in BiOBr-based photocatalysts for environmental remediation

Lignin and Nanolignin: Next-Generation Sustainable Materials for Water Treatment

Water scarcity, contamination, and lack of sanitation are global issues that require innovations in chemistry, engineering, and materials science. To tackle the challenge of providing high-quality drinking water for a growing population, we need to develop high-performance and multifunctional materials to treat water on both small and large scales. As modern society and science prioritize more sustainable engineering practices, water treatment processes will need to use materials produced from sustainable resources via green chemical routes, combining multiple advanced properties such as high surface area and great affinity for contaminants. Lignin, one of the major components of plants and an abundant byproduct of the cellulose and bioethanol industries, offers a cost-effective and scalable platform for developing such materials, with a wide range of physicochemical properties that can be tailored to improve their performance for target water treatment applications. This review aims to bridge the current gap in the literature by exploring the use of lignin, both as solid bulk or solubilized macromolecules and nanolignin as multifunctional (nano)materials for sustainable water treatment processes. We address the application of lignin-based macro-, micro-, and nanostructured materials in adsorption, catalysis, flocculation, membrane filtration processes, and antimicrobial coatings and composites. Throughout the exploration of recent progress and trends in this field, we emphasize the importance of integrating principles of green chemistry and materials sustainability to advance sustainable water treatment technologies.

Room temperature synthesis of one-dimensional hierarchical hollow BiOBr with tunable photocatalysis reaction pathway for RhB under visible light

One-dimensional (1D) hierarchical photocatalyst has the advantages of 1D materials and hierarchical materials, which is a kind of potential high performance photocatalytic materials. However, how to efficiently synthesize 1D hierarchical BiOBr is still a huge challenge. Herein, 1D rod-like Bi6O5(OH)3(NO3)5·3H2O, the hydrolysis product of Bi(NO3)3·5H2O, was acted as both the template and Bi source to synthesize 1D hierarchical hollow BiOBr (1DHHBr) through a facile solution stirring method at room temperature, using KBr as Br source. As compared with lamellar-like BiOBr, 1DHHBr has larger specific surface areas and abundant mesoporous pores. The superiorities of morphology and texture for 1DHHBr not only improve the adsorption capability for RhB molecules, but also raise the separation efficiency of photogenerated charges. Therefore, 1DHHBr exhibits much higher photocatalytic degradation performance of RhB under visible light through an initial N-deethylation process followed by the disruption conjugated chromophore groups pathway, based on the combination of photocatalytic mechanism of 1DHHBr and photosensitization mechanism of RhB. The active species trapping tests prove that •O2- is the major active species for the N-deethylation of RhB, while h+ is the main active species for the cleavage of conjugated chromophore structures of RhB and its deethylated derivatives. Importantly, the visible light photocatalysis reaction pathway for RhB over 1DHHBr can be tuned by the addition of benzoquinone and sodium oxalate, respectively. Moreover, this facile approach can be easily expanded to fabricate other 1D hierarchical hollow BiOX (e.g., BiOCl and BiOI) and therefore justify its usefulness in rationally designing the 1D hierarchical hollow bismuth-based layered photocatalysts.

Effectively Enhanced Photocatalytic Performance of BP/BiOBr 2D/2D Z-Scheme Heterojunction

Black phosphorus (BP) is a novel two-dimensional (2D) material with remarkable potential for use in environmental remediation and energy conversion. However, the practical application of BP is significantly limited by its low catalytic efficiency and poor structural stability. In this study, a Z-scheme BP/BiOBr 2D/2D heterojunction was fabricated using a simple solution reaction method at room temperature. The BP/BiOBr heterojunction exhibited significantly enhanced photocatalytic performance in the degradation of various organic pollutants and the production of hydrogen under visible light irradiation. This improved activity can be attributed to the efficient separation of photogenerated charges and the extended lifetime of charge carriers within the heterojunction. The durability and structural stability of the BiP-10 heterojunction were demonstrated through cycling tests, which maintained high photocatalytic efficiency over multiple uses. This study presents a promising approach to the development of BP-based photocatalytic materials for sustainable environmental and energy applications.

Sludge reduction and hydrogen production in a microbial photoelectrochemical cell with a g-C3N4/CQDs/BiOBr composite photocathode

Hydrogen (H2) remains a pivotal clean energy source, and the emergence of Solar-powered Microbial Photoelectrochemical Cells (MPECs) presents promising avenues for H2 production while concurrently aiding organic matter degradation. This study introduces an MPEC system employing a g-C3N4/CQDs/BiOBr photocathode and a bioanode, successfully achieving simultaneous H2 production and sludge reduction. The research highlights the effective formation of a Z-type heterojunction in the g-C3N4/CQDs/BiOBr photocathode, substantially enhancing the photocurrent response under light conditions. Operating at - 0.4 V versus RHE, it demonstrated a current density of - 3.25 mA·cm-2, surpassing that of g-C3N4/BiOBr (-2.25 mA·cm-2) by 1.4 times and g-C3N4 (-2.04 mA·cm-2) by 1.6 times. When subjected to visible light irradiation and a 0.8 V applied bias voltage, the MPEC system achieved a current density of 1.0 mA·cm-2. The cumulative H2 production of the MPEC system reached 8.9 mL, averaging a production rate of 0.13 mL·h-1. In the anode chamber, the degradation rates of total chemical oxygen demand (TCOD), soluble chemical oxygen demand (SCOD), total suspended solids (TSS), volatile suspended solids (VSS), proteins, polysaccharides, and volatile fatty acids (VFA) in the sludge were recorded at 57.18%, 82.64%, 64.98%, 86.39%, 42.81%, 67.34%, and 29.01%, respectively.

Bismuth oxybromide nanosheets as an efficient photocatalyst for dye degradation

The contamination of water resources by organic pollutants presents significant environmental and health challenges. Therefore, it is urgent to develop highly efficient and green approach for treating organic water pollutants. Bismuth oxybromide (BiOBr) has gained attention due to its high photoactivity. In this work, we report a modification to improve its photocatalytic activity. BiOBr were prepared using a capping agent, benzene-1,3,5-tricarboxylic acid, to tune the morphology of the compound. The resulting BiOBr shows nanosheet morphology, which provides a high surface-to-volume ratio and a larger conduction band compared to bulk BiOBr. As a result, the BiOBr nanosheets show the highest efficiency for photodegradation of Rhodamine B, compared to benchmark TiO2 and bulk BiOBr catalysts.

Achieving high photocatalytic NOx removal activity using a Bi/BiOBr/TiO2 composite photocatalyst

Fossil fuel combustion generates nitrogen oxides (NO + NO2 = NOx), which pose threats to the environment and human health. Although commercial products containing titanium dioxide (TiO2) can remedy NOx pollution by photocatalysis, they only function in the ultraviolet (UV). On the other hand, bismuth oxybromide (BiOBr) is active in the visible. BiOBr is stable, affordable, and non-toxic, making it an appealing alternative. In addition, nanoparticulate Bi metal can further enhance visible light absorption through its surface plasmon properties and charge carrier lifetime by spatially separating charge. In this study, to enhance the visible-light activity of TiO2-based photocatalysts for NOx pollution, a composite of Bi-decorated BiOBr/TiO2 was synthesised using a solvothermal method across varying the Ti/Bi atomic ratio (0.2, 2.2, 4.4, and 6.6), and synthesis duration (6h, 12h, and 18h). The photocatalytic performance of the synthesised composites for NO gas removal was investigated using an adapted ISO method (22197-1:2016). Analysis showed that the preferential growth of the (010) crystal facet in BiOBr and the presence of Bi metal both play an important role in the superior photocatalytic activity seen in our Bi-decorated BiOBr/TiO2 composite. The composites were characterised using X-ray diffraction (XRD), attenuated total reflectance - Fourier transform infrared spectroscopy (ATR-FTIR), high-resolution scanning electron microscopy (HR-SEM), UV-Vis diffuse reflectance (DRS) spectroscopy, transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Brunauer-Emmett-Teller (BET) analysis, thermogravimetric analysis (TGA), and diffuse reflectance transient absorption spectroscopy (DR-TAS). Our research shows that the Bi/BiOBr-TiO2 composite synthesised through a 12h solvothermal method with a Ti/Bi atomic ratio of 4.4 exhibits the highest photocatalytic performance towards both NO and NO2 oxidation; with 32.8% and 54.9% NO removal and 15.1% and 29.5% NO2 under visible and UV lamps, respectively.

Metal/Covalent Organic Framework Encapsulated Lead-Free Halide Perovskite Hybrid Nanocatalysts: Multifunctional Applications, Design, Recent Trends, Challenges, and Prospects

Perovskites are bringing revolutionization in a various fields due to their exceptional properties and crystalline structure. Most specifically, halide perovskites (HPs), lead-free halide perovskites (LFHPs), and halide perovskite quantum dots (HPs QDs) are becoming hotspots due to their unique optoelectronic properties, low cost, and simple processing. HPs QDs, in particular, have excellent photovoltaic and optoelectronic applications because of their tunable emission, high photoluminescence quantum yield (PLQY), effective charge separation, and low cost. However, practical applications of the HPs QDs family have some limitations such as degradation, instability, and deep trap states within the bandgap, structural inflexibility, scalability, inconsistent reproducibility, and environmental concerns, which can be covered by encapsulating HPs QDs into porous materials like metal-organic frameworks (MOFs) or covalent-organic frameworks (COFs) that offer protection, prevention of aggregation, tunable optical properties, flexibility in structure, enhanced biocompatibility, improved stability under harsh conditions, consistency in production quality, and efficient charge separation. These advantages of MOFs-COFs help HPs QDs harness their full potential for various applications. This review mainly consists of three parts. The first portion discusses the perovskites, halide perovskites, lead-free perovskites, and halide perovskite quantum dots. In the second portion, we explore MOFs and COFs. In the third portion, particular emphasis is given to a thorough evaluation of the development of HPs QDs@MOFs-COFs based materials for comprehensive investigations for next-generation materials intended for diverse technological applications, such as CO2 conversion, pollutant degradation, hydrogen generation, batteries, gas sensing, and solar cells. Finally, this review will open a new gateway for the synthesis of perovskite-based quantum dots.

TEMPO/O2 Synergistically Mediated BiBrO-Photocatalyzed Decarboxylative Phosphorylation of N-Arylglycines

With both TEMPO and O2 (in air) as the homogeneous redox mediators, BiBrO as the heterogeneous semiconductor photocatalyst, the first example of semi-heterogeneous photocatalytic decarboxylative phosphorylation of N-arylglycines with diarylphosphine oxides was established. A series of α-amino phosphinoxides were efficiently synthesized.

A novel GO hoisted SnO2-BiOBr bifunctional catalyst for the remediation of organic dyes under illumination by visible light and electrocatalytic water splitting

It is imperative to develop affordable multi-functional catalysts based on transition metals for various applications, such as dye degradation or the production of green energy. For the first time, we propose a simple chemical bath method to create a SnO2-BiOBr-rGO heterojunction with remarkable photocatalytic and electrocatalytic activities. After introducing graphene oxide (GO) into the SnO2-BiOBr nanocomposite, the charge separation, electron mobility, surface area, and electrochemical properties were significantly improved. The X-ray diffraction results show the successful integration of GO into the SnO2-BiOBr nanocomposite. Systematic material characterization by scanning and transmission electron microscopy showed that the photocatalysts are composed of uniformly distributed SnO2 nanoparticles (∼11 nm) on the regular nanosheets of BiOBr (∼94 nm) and rGO. The SnO2-BiOBr-rGO photocatalyst has outstanding photocatalytic activity when it comes to reducing a variety of organic dyes like rhodamine B (RhB) and methylene blue (MB). Within 90 minutes of visible light illumination, degradation of a maximum of 99% for MB and 99.8% for RhB was noted. The oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performance was also tested for the ternary nanocomposite, and significantly lower overpotential values of 0.34 and -0.11 V (vs. RHE) at 10 mA cm-2 were observed for the OER and HER, respectively. Furthermore, the Tafel slope values are 34 and 39 mV dec-1 for the OER and HER, respectively. The catalytic degradation of dyes with visible light and efficient OER and HER performance offer this work a broad spectrum of potential applications.

WO3/BiOBr S-Scheme Heterojunction Photocatalyst for Enhanced Photocatalytic CO2 Reduction

The photocatalytic CO2 reduction strategy driven by visible light is a practical way to solve the energy crisis. However, limited by the fast recombination of photogenerated electrons and holes in photocatalysts, photocatalytic efficiency is still low. Herein, a WO3/BiOBr S-scheme heterojunction was formed by combining WO3 with BiOBr, which facilitated the transfer and separation of photoinduced electrons and holes and enhanced the photocatalytic CO2 reaction. The optimized WO3/BiOBr heterostructures exhibited best activity for photocatalytic CO2 reduction without any sacrificial reagents, and the CO yield reached 17.14 μmol g-1 after reaction for 4 h, which was 1.56 times greater than that of BiOBr. The photocatalytic stability of WO3/BiOBr was also improved.

A Tight-Connection g-C3N4/BiOBr (001) S-Scheme Heterojunction Photocatalyst for Boosting Photocatalytic Degradation of Organic Pollutants

The efficient separation of photogenerated charge carriers and strong oxidizing properties can improve photocatalytic performance. Here, we combine the construction of a tightly connected S-scheme heterojunction with the exposure of an active crystal plane to prepare g-C3N4/BiOBr for the degradation of high-concentration organic pollutants. This strategy effectively improves the separation efficiency of photogenerated carriers and the number of active sites. Notably, the synthesized g-C3N4/BiOBr displays excellent photocatalytic degradation activity towards various organic pollutants, including methylene blue (MB, 90.8%), congo red (CR, 99.2%), and tetracycline (TC, 89%). Furthermore, the photocatalytic degradation performance of g-C3N4/BiOBr for MB maintains 80% efficiency under natural water quality (tap water, lake water, river water), and a wide pH range (pH = 4-10). Its excellent photocatalytic activity is attributed to the tight connection between g-C3N4 and BiOBr in the S-scheme heterojunction interface, as well as the exposure of highly active (001) crystal planes. These improve the efficiency of the separation of photogenerated carriers, and maintain their strong oxidation capability. This work presents a simple approach to improving the separation of electrons and holes by tightly combining two components within a heterojunction.

Decorating of 2D indium oxide onto 2D bismuth oxybromide to enhance internal electric field and stimulate artificial photosynthesis

CO2 photocatalytic reduction is an excellent strategy for promoting solar-to-chemical energy conversion and alleviating the severe environmental crisis. In this study, 2D indium oxide (IO) is decorated on 2D bismuth oxybromide (BOB) nanosheets to gain BOB/IO (BxIy) heterojunction. The optimal B3I1 composite affords a CO production rate of 54.2 μmol⋅g-1, about 2.2 times and 11.3 times higher than those of the pristine BOB and IO, respectively. The introduction of IO significantly enhances the internal electric field (IEF), leading to accelerated charge transfer and prolonged lifetime of the photogenerated carriers. In the BxIy composite, the BOB and IO serve as the electron acceptor and donor, respectively, facilitating the reduction of CO2 and oxidation of H2O. In-situ DRIFTs spectra are used to confirm the catalytic active sites and provide insights into the mechanism of CO2 photoreduction. The results suggest *COOH and *CO2- species played a crucial role in the formation of CO. This work presents a valuable perspective on understanding the charge transfer route and developing highly efficient photocatalysts for CO2 photoreduction.

2D/2D heterojunctions for rapid and self-cleaning removal of antibiotics via visible light-assisted peroxymonosulfate activation: Efficiency, synergistic effects, and applications

Developing eco-friendly and efficient technologies for treating antibiotic wastewater is crucial. Traditional methods face challenges in incomplete removal, high costs, and secondary pollution. Heterogeneous peroxymonosulfate (PMS) activation assisted by visible light shows promise, but suitable activators remain a huge challenge. Here, we synthesized cost-effective carbon nitride/bismuth bromide oxide (CN/BiOBr) heterojunctions. Such a heterojunction achieved rapid PMS activation, achieving over 90.00% tetracycline (TC) removal only within 1 min (kobs of 2.23 min-1), surpassing previous systems by nearly 1-2 orders of magnitude and even remarkably superior to the popular single-atom catalysts. The system exhibited self-cleaning properties, maintaining activity after 8 cycles and stability across a wide pH range (3.01 to 9.03). Quenching experiments and theoretical calculations elucidated the exclusive •O2- species involvement and removal pathways. Eco-toxicity assessment and total organic carbon results confirmed simultaneous degradation, detoxification, and mineralization. This system also showed excellent resistance to environmental factors, e.g., coexisting anions, varying pH, and water sources, and demonstrated potential in coking and medical wastewater purification. This study presents a novel technique for rapidly decontaminating antibiotic wastewater through visible light-assisted PMS activation and introduces innovative bionic catalytic oxidation combining light and darkness for practical applications.

Enhanced generation of oxysulfur radicals by the BiOBr/Montmorillonite activated sulfite system: Performance and mechanism

The easily synthesized, cost-effective, and stable photocatalysts for sulfite activation are always required for the enhancement of organic contaminants degradation. Herein, the facile coprecipitation synthesis of Bismuth oxybromide (BiOBr)/Montmorillonite (MMT) was reported, which could activate sulfite (SO32-/HSO3-) under sunlight and accelerate the catalytic performance more effectively than pristine BiOBr. After adding sulfite to the photocatalysis system, the photodegradation efficiency of atrazine (ATZ) achieved 73.7% ± 1.5% after 5 min and 94.4% ± 1.6% after 30 min of sunlight irradiation with BiOBr/MMT. The BiOBr/MMT-sulfite system also presented remarkable photocatalytic performance to eliminate various contaminants, including ciprofloxacin, sulfadiazine, tetracycline, and carbamazepine. The various features of the photocatalyst materials were studied, including their surface morphology, structure, optical properties, and composition. The results illustrated that by adding MMT, the bandgap of the pristine BiOBr was reduced and the surface area was increased, which led to an increased ability to adsorb materials. Results of various influence factors showed this enhanced system had satisfactory and stable removal performance of ATZ in the pH range of 3.0-6.5, but HPO42- had a strong negative effect on the system performance. Oxysulfur radicals (SO5·- and SO4·-), h+, and 1O2 were discovered as the prevailing active species in the BiOBr/MMT-sulfite system. The proposed degradation mechanism of this photocatalyst-enhanced system revealed that sulfite adsorption on the surface of the photocatalyst played a vital role during the initial phase, and the degradation pathway of ATZ was discussed. This study provides a new synthesis strategy of a photocatalyst for sulfite activation and expands the potential uses of Bi-based photocatalysts in degrading difficult-to-remove organic pollutants.

Electrocatalytic Synthesis of Pyridine Oximes using in Situ Generated NH2 OH from NO species on Nanofiber Membranes Derived from NH2 -MIL-53(Al)

Pyridine oximes produced from aldehyde or ketone with hydroxylamine (NH2 OH) have been widely applied in pharmaceutics, enzymatic and sterilization. However, the important raw material NH2 OH exhibits corrosive and unstable properties, leading to substantial energy consumption during storage and transportation. Herein, this work presents a novel method for directly synthesizing highly valuable pyridine oximes using in situ generated NH2 OH from electrocatalytic NO reduction with well-design nanofiber membranes (Al-NFM) derived from NH2 -MIL-53(Al). Particularly, 2-pyridinealdoxime, the precursor of antidote pralidoxime (2-PAM) for nerve agents suffering from scarcity and high cost, was achieved with a Faraday efficiency up to 49.8 % and a yield of 92.1 %, attributing to the high selectivity of NH2 OH production on Al-NFM, further easily reacted with iodomethane to produce 2-PAM. This study proposes a creative approach, having wide universality for synthesizing pyridine and other oximes with a range of functional groups, which not only facilitates the conversion of exhaust gas (NO) and waste water (NO2 - ) into valuable chemicals especially NH2 OH production and in situ utilization through electrochemistry, but also holds significant potential for synthesis of neuro detoxifying drugs to humanity security.

Regulation of friction pair to promote conversion of mechanical energy to chemical energy on Bi2WO6 and realization of enhanced tribocatalytic activity to degrade different pollutants

Recently, friction-induced tribocatalysis has received tremendous attention through converting mechanical energy to chemical energy. However, its efficiency is much lower than those of photocatalysis and piezocatalysis, and its environmental application is limited in dye degradation. Herein, we developed a facile approach to improve the tribocatalytic activity of Bi2WO6 via adding trace polymer powders to form friction pairs with Bi2WO6. Among various polymers, PTFE was demonstrated to be the best counterpart of Bi2WO6. Subsequently, the PTFE dosage, stirring rate, magnetic bar size and number, and stirring mode were further optimized. The PTFE-promoted Bi2WO6 tribocatalysis was verified to possess excellent performance not only for removing different dyes, but also for degrading chlorophenols that are typical persistent organic pollutants. Multiple uses of the recycled catalysts indicated its good stability and prominent tribocatalytic durability. EPR measurements suggested the generation of hydroxyl radical and superoxide radical, which were determined to be continuously generated within 12 h at the rates of 0.88 μM h-1 and 85 μM h-1, respectively. Subsequently, a possible mechanism was proposed to explain the enhanced performance of the PTFE-promoted Bi2WO6 tribocatalysis. Finally, on basis of the detected intermediates, the degradation pathways of Rhodamine B and 2,4-Dichlorophenol during tribocatalysis were suggested.

Strategies for enhancing performance of perovskite bismuth ferrite photocatalysts (BiFeO3): A comprehensive review

Organic pollutants pose a significant threat to water safety, and their degradation is of paramount importance. Photocatalytic technology has emerged as a promising approach for environmental remediation, and Bismuth ferrite (BiFeO3) has been shown to exhibit remarkable potential for photocatalytic degradation of water pollutants, with its excellent crystal structure properties and visible light photocatalytic activity. This review presents an overview of the crystal properties and photocatalytic mechanism of perovskite bismuth ferrite (BiFeO3), as well as a summary of various strategies for enhancing its efficiency in photocatalytic degradation of organic pollutants. These strategies include pure phase preparation, microscopic modulation, composite modification of BiFeO3, and the integration of Fenton-like reactions and external field-assisted methods to improve its photocatalytic performance. The review emphasizes the impact of each strategy on photocatalytic enhancement. By providing comprehensive strategies for improving the efficiency of BiFeO3 photocatalysis, this review inspires new insights for efficient degradation of organic pollutants using BiFeO3 photocatalysis and contributes to the development of photocatalysis in environmental remediation.

Magnetic-field-induced simultaneous charge separation and oxygen transfer in photocatalytic oxygen activation for algae inactivation

Photocatalytic oxygen activation is an excellent strategy for algae control in water. However, the fast recombination of photogenerated charge and slow rate of oxygen transfer limit the reactive oxygen species generation efficiency for algae inactivation. Herein, to solve above issues, magnetic field was introduced to the BiO_2-x/Bi₃NbO₇ system to effectively covert oxygen into reactive radicals. The electrochemical experiment and DFT calculation results indicated the charge separation could be accelerated by the Lorentz force generated by the magnetic field, resulting in increase of electron concentration. Meanwhile, the value of volumetric gas-liquid mass transfer coefficient was increased by 59.79 % with magnetic field, thus more oxygen could be reduced to superoxide radical. Photocatalytic algae inactivation rate by BiO_2-x/Bi₃NbO₇ with magnetic field could be increased by 2.07 times than that without magnet filed. This work further extends the strategy of using magnetic field to simultaneously facilitate the charge separation and oxygen transfer rate.

Recent progress in semiconductor/graphene photocatalysts: synthesis, photocatalytic applications, and challenges

The presence of an increasing number of organic pollutants in water now poses serious risks to both human health and ecological systems. Many of these pollutants are persistent and non-biodegradable. The contamination of fresh water by harmful substances has compelled researchers to develop innovative, efficient, and cost-effective water remediation techniques and materials. Thus, photocatalysis has long been recognized as a promising approach to tackle both environmental remediation and the energy crisis. However, semiconductor photocatalysts frequently suffer from defects such as photo-generated charge carrier recombination, poor visible light response, and slow surface reaction kinetics, which can be remedied by modifications with appropriate co-catalysts. Therefore, graphene and its derivatives have widely been used as supports for semiconductors and photocatalysts due to their distinctive optical, physicochemical, and electrical features. This critical review addresses the current progress in the design and synthesis of graphene/semiconductor photocatalysts, as well as their use in photocatalytic degradation of organic pollutants and hydrogen production. Several influencing parameters are addressed, including pH, photocatalyst loading, initial pollutant concentration, light wavelength, and oxidizing species, all of which could have a significant impact on the rate of organic pollutant's degradation. Furthermore, the recyclability of the catalyst and its photocatalytic activity mechanisms are thoroughly discussed. Numerous case studies are systematically presented. Moreover, future prospects and major challenges are highlighted.

A review on the progress of the photocatalytic removal of refractory pollutants from water by BiOBr-based nanocomposites

Organic matters from various sources such as the manufacturing, agricultural, and pharmaceuticals industries is continuously discharged into water bodies, leading to increasingly serious water pollution. Photocatalytic technology is a clean and green advanced oxidation process, that can successfully decompose various organic pollutants into small inorganic molecules such as carbon dioxide and water under visible light irradiation. Bismuth oxybromide (BiOBr) is an attractive visible light photocatalyst with good photocatalytic performance, suitable forbidden bandwidth, and a unique layered structure. However, the rapid combination of the electron-hole pairs generated in BiOBr leads to low photocatalytic activity, which limits its photocatalytic performance. Due to its unique electronic structure, BiOBr can be coupled with a variety of different functional materials to improve its photocatalytic performance. In this paper, We present the morphologically controllable BiOBr and its preparation process with the influence of raw materials, additives, solvents, synthesis methods, and synthesis conditions. Based on this, we propose design synthesis considerations for BiOBr-based nanocomplexes in four aspects: structure, morphology and crystalline phase, reduction of electron-hole pair complexation, photocorrosion resistance, and scale-up synthesis. The literature on BiOBr-based nanocomposites in the last 10 years (2012-2022) are summarized into seven categories, and the mechanism of enhanced photocatalytic activity of BiOBr-based nanocomposites is reviewed. Moreover, the applications of BiOBr-based nanocomposites in the fields of degradation of dye wastewater, antibiotic wastewater, pesticide wastewater, and phenol-containing wastewater are reviewed. Finally, the current challenges and prospects of BiOBr-based nanocomposites are briefly described. In general, this paper reviews the construction of BiOBr-based nanocomposites, the mechanism of photocatalytic activity enhancement and its research status and application prospects in the degradation of organic pollutants.

Ultrahigh-efficient BiOBr-x%La@y%CNQDs nanocomposites with enhanced generation and separation of photogenerated carriers towards bisphenol A degradation and toxicity reduction

In this study, a series of hierarchical flower-like La-doped BiOBr composites modified with carbon nitride quantum dots (BiOBr-x%La@y%CNQDs) was synthesized using a microwave solvothermal method in combination with a calcination method. It was found that La doping and CNQDs co-decorated with BiOBr showed much better photoreactivity for bisphenol A (BPA) degradation than pure BiOBr. The best degradation and mineralization efficiencies of BPA were 100% and 77% within 12 min at La and CNQDs contents of 1% and 1.25%, respectively. Various characterization results demonstrated that this synergistic effect on BiOBr-1%La@1.25%CNQDs was attributed to its improved light-harvesting properties, enhanced photogenerated electron and holes pairs separation and interfacial charge transfer. Degradation pathways were proposed based on active species analysis, identification of nine intermediates, and density functional theory (DFT) calculations. Furthermore, a bioluminescence assay of the inhibition rate of the luminescent bacterium Vibrio qinghaiensis sp. Q67 showed that BiOBr-1%La@1.25%CNQDs have superior detoxification ability. The present study provides some insight into the design of ultrahigh-efficiency nanojunction photocatalysts with a broadened photoabsorption range and improved separation efficiency of photogenerated carriers to enhance the degradation and detoxification performance of BPA.

Photocatalytic degradation of tetracycline antibiotic over a flower-like S-doped BiOBr: Performance, mechanism insight and toxicity assessment

A new catalyst of S-BiOBr flower-like morphology was synthesized by simple pyrolysis and further used for photocatalytic degradation of TC. Phase structure analysis, elemental analysis and micromorphological analysis confirmed that S doping has a reinforcing effect on the polarization between the [Bi2O2S]2+ and [Br2]2- layers and is conducive to interlayer polarization and rapid charge transfer. In addition, its unique petal morphology is more favorable to the adsorption of contaminants on its surface and accelerates the reaction of catalyst surfactant with contaminants. It was also found that S-BiOBr degrades TC significantly better than single BiOBr@HCs, with up to 99.1% in 60 min illumination. In addition, the S-BiOBr catalyst has good reusability in antibiotic degradation. The results of photocatalytic mechanism analysis show that free radical O2− plays a major role in the photodegradation of organic model pollutants. Intermediates in TC degradation were identified, and their potential degradation pathways were prospected, and the toxicity development of TC in the degradation process was analyzed by toxicity assessment software. The S-BiOBr photocatalytic system developed in this paper provides a new idea for effective modification of bismuth-based semiconductors and has important guiding significance for future water purification.

Adsorption of BiOBr microspheres to rhodamine B and its influence on photocatalytic reaction

Adsorption and its influence are often neglected during photocatalytic degradation of organic pollutants. To call attention to these issues, a novel bismuth oxybromide (BiOBr) microsphere with hierarchical flower-like structure was fabricated through a facile hydrothermal process using polyvinyl pyrrolidone (PVP) as additive in this work, and then the adsorption of the BiOBr microspheres to RhB and its influence on the photocatalytic degradation of RhB were investigated in detail. Experimental results show that the BiOBr microspheres have a very strong adsorption capacity to RhB. The adsorption behavior follows the Langmuir model and the quasi second order kinetic equation. Tests of the photocatalytic degradation of RhB under visible irradiation verify that the adsorption of the BiOBr microspheres to RhB greatly boosts the degradation of RhB due to the "enriching effect", and a complete degradation of 20 mg L^-1 RhB only requires 37 min.

The spatially separated active sites for holes and electrons boost the radicals generation for toluene degradation

Hydroxyl (⸱OH) and superoxide (⸱O₂^-) radicals are the main drivers for photocatalysis in toluene degradation, but their generation mechanisms are still ambiguous due to the lack of direct evidence. The spatially separated active sites for holes and electrons can help to clarify the dynamic process of radicals generation. By performing theoretical calculations, it is demonstrated that the spatially separated active sites for holes and electrons on the Bi₂O₂CO₃ surface can be constructed by introducing oxygen vacancies in the [Bi₂O₂]²⁺ layer. H₂O and O₂ molecules can be better adsorbed and activated at hole and electron active sites, separately. Accordingly, the pristine and defective Bi₂O₂CO₃ are prepared. The dynamic behavior of H₂O and O₂ molecules at the matching active sites is revealed, which indicates the efficient adsorption of reactants and the substantial production of radicals. Significantly, the specificity of the spatially separated holes and electrons active sites for ⸱OH and ⸱O₂^- radicals generation, respectively, is demonstrated by in situ EPR with the H₂O vapor atmosphere. This work provides a design concept for unraveling reaction mechanisms to realize controllable radicals generation.

Visible-Light-Driven Zr-MOF/BiOBr Heterojunction for the Efficient Synchronous Removal of Hexavalent Chromium and Rhodamine B from Wastewater

With the rapid industrial development, the coexistence of multiple pollutants in wastewater has become a common phenomenon. Thus, developing highly efficient decontamination methods is imperative. In this work, a string of UiO-66-NH₂/BiOBr heterojunctions with varying ratios of BiOBr were prepared and applied to remove hexavalent chromium Cr(VI) and rhodamine B (RhB). The possible growth process of BiOBr nanosheets on UiO-66-NH₂, removal activity of contaminants, and photocatalysis mechanism were investigated. When the mass ratio of UiO-66-NH₂ to BiOBr reaches 1:0.75, the heterojunction (NB-75) shows optimal photocatalytic activity. After 30 min of adsorption, the total removal rates of Cr(VI) (50 mg/L) and RhB (10 mg/L) over NB-75 (0.25 g/L) reaches 96.7% within 120 min of illumination and 98.9% within 80 min of illumination, respectively. For the removal process, there are two factors. The first is the high adsorption capacity for RhB and Cr(VI) owing to the high porosity of UiO-66-NH₂ and interlayer surface positive charge of BiOBr. The second is the improved visible-light photocatalytic performance of the UiO-66-NH₂/BiOBr heterojunction via rapid separation of photoinduced carriers. In addition, the active species capture study reveals that the electrons (e^-) and the superoxide radicals (^•O₂ ^-) play key roles in Cr(VI) reduction, while the holes (h⁺) are major reactive groups participating in the degradation of RhB. This work demonstrated a kind of promising MOF-based photocatalysis material for eliminating Cr(VI) and RhB simultaneously.

Enhanced visible-light photoactivities of porous LaFeO3 by synchronously doping Ni2+ and coupling TS-1 for CO2 reduction and 2,4,6-trinitrophenol degradation

TOC showing the enhanced visible-light photoactivities of porous LaFeO3 by synchronously doping with Ni2+ and coupling with TS-1 for CO2 reduction and 2,4,6-trinitrophenol degradation.