Photocatalytic solar energy conversion is a clean technology for producing renewable energy sources, but its efficiency is greatly hindered by the kinetically sluggish oxygen evolution reaction. Herein, confined defects in atomically-thin BiOCl nanosheets were created to serve as a remarkable platform to explore the relationship between defects and photocatalytic activity. Surface defects can be clearly observed on atomically-thin BiOCl nanosheets from scanning transmission electron microscopy images. Theoretical/experimental results suggest that defect engineering increased states of density and narrowed the band gap. With combined effects from defect induced shortened hole migratory paths and creation of coordination-unsaturated active atoms with dangling bonds, defect-rich BiOCl nanosheets displayed 3 and 8 times higher photocatalytic activity towards oxygen evolution compared with atomically-thin BiOCl nanosheets and bulk BiOCl, respectively. This successful application of defect engineering will pave a new pathway for improving photocatalytic oxygen evolution activity of other materials.

Graphitic carbon nitride/bismuth oxyiodine (g-CN/BiOI) composites with excellent photoelectrochemical (PEC) performance have been designed for a facile and sensitive PEC monitoring platform of bisphenol A (BPA) for the first time. The g-CN/BiOI composites were synthesized by a facile microwave method with 1-butyl-3-methylimidazolium iodine ([Bmim]I) as precursor. The heterojunction comprising g-CN and BiOI has been fabricated. The internal electric field formed at the interface of the heterojunction contributed to the separation of photogenerated electron–hole pairs. Consequently, the g-CN/BiOI composites achieved a greatly improved photocurrent density (∼2-fold) compared to the pure BiOI. In addition, the photocurrent of g-CN/BiOI composites can be further enhanced by introducing BPA into the aqueous solution. The increased photocurrent was applied as the PEC detection signal to trace the concentration of BPA sensitively and effectively. The self-constructed BPA PEC sensor displayed a satisfactory sensing performance with a rapid response, a wide linear range (80–3200 ng mL−1) and a low detection limitation (26 ng mL−1, S/N = 3). Moreover, the BPA PEC sensor exhibited an agreeable anti-interference capacity and outstanding stability, and provided a promising analytical method to detect BPA in the environment.

In this work, two kinds of self-assembled hierarchical BiOBr microcrystals were rapidly synthesized through a simple microwave-assisted route in the presence of reactable ionic liquid 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br). These porous and hollow BiOBr microspheres were obtained via a facile solvothermal method with or without polyvinyl pyrrolidone (PVP), respectively. During the synthetic process, ionic liquid [C16mim]Br played as solvent, reactant and template at the same time. Moreover, the BiOBr hollow and porous microspheres exhibited outstanding photocatalytic activities for the degradation of rhodamine B (RhB) under visible light irradiation. A possible photocatalytic mechanism was also discussed in detail. It can be assumed that the higher photocatalytic activities of BiOBr porous microspheres materials could be ascribed to the novel structure, larger specific surface area, narrower band gap structure and smaller particle size.Hollow and porous BiOBr microcrystals were rapidly synthesized through a microwave-assisted route in the presence of ionic liquid [C16mim]Br and exhibited outstanding photocatalytic activities for the degradation of Rhodamine B (RhB) under visible light irradiation.Download high-res image (322KB)Download full-size image

•An ionic liquid induced strategy for the synthesis of porous perovskite-like PbBiO2Br materials.•Porous PbBiO2Br structures exhibited the maximum BET and showed the highest photocatalytic activity.•The superoxide radical (O2−) and hole (h+) are the dominant species for the degradation of pollutants.A novel perovskite-like PbBiO2Br uniform porous microspheres photocatalyst was successfully prepared via ethanol glycol (EG)-assisted solvothermal method in the presence of reactable ionic liquid 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br) and polyvinyl-pyrrolidone (PVP) system. During the synthetic process, the ionic liquid-PVP complex system acts as the solvent, reactant and template simultaneously, and demonstrates excellent control capability for PbBiO2Br porous microstructure. The photocatalytic activity of the PbBiO2Br materials was evaluated by colorless antibiotic agent ciprofloxacin (CIP), endocrine disrupter bisphenol A (BPA), and colored rhodamine (RhB), methylene blue (MB) as target pollutants under visible light irradiation. After several characterizations, the influencing factor of the promotional photocatalytic activity for PbBiO2Br photocatalysts was discussed in detail. Through the ESR and trapping experiment verification, the superoxide radical (O2−) and hole (h+) were the main active species for the photocatalysis process.Download high-res image (324KB)Download full-size image

•Various strategies for synthesis and performance improvement of layered bismuth oxyhalides materials have been surveyed.•The application of photocatalytic layered bismuth oxyhalides materials in energy and environment has been proposed.•Insight the structure-activity relationship from light harvesting, interfacial reactions and charge separation.Photocatalytic solar energy conversion is considered one of the most promising pathways to address the global energy shortage and environmental crisis. Layered bismuth oxyhalides are a new class of photocatalytic materials with a strong light response to boost solar energy conversion due to their appealing energy band structure and unique layered structure. This critical review summarizes recent progress in designing and tuning new bismuth oxyhalide materials to boost solar energy conversion. We start with methods to prepare and tune bismuth oxyhalides to enhance photocatalysis: structural engineering via control of the bismuth-rich state, elemental doping, defect control, interface engineering, solid solutions, inner coupling, and heterojunction construction. Then advancements in versatile photocatalytic applications of bismuth oxyhalide–based photocatalysts in the areas of oxygen evolution, hydrogen evolution, CO2 reduction, nitrogen fixation, organic syntheses, disinfection, and pollutant removal are discussed. Finally, the major challenges and opportunities regarding the future exploration of bismuth oxyhalide–based materials in photocatalysis are presented. The present review will deepen understanding regarding bismuth oxyhalides and open new directions in designing and optimizing advanced bismuth oxyhalide–based materials for energy and environmental applications.Download high-res image (197KB)Download full-size image

•Strategies for preparation of atomically-thin 2D materials have been surveyed.•Insight the structure-activity relationship from light harvesting, charge separation and interfacial reactions.•Various activity improvement strategies for atomically-thin 2D materials have been proposed.Atomically-thin two-dimensional materials can afford promising opportunities for various photocatalytic applications thanks to its unique structure and fascinating properties. However, the understanding of their clear relationship between structure and activity is difficult and insufficient. In this review, various strategies for preparation of atomically-thin 2D materials have been surveyed. Then, the structure-activity relationship insights have been highlighted from three crucial factors of photocatalysis namely light harvesting, charge separation and interfacial reactions, by surveying the recent developed freestanding atomically-thin photocatalysts. Various activity improvement strategies for atomically-thin 2D materials, such as element doping, defect engineering, active sites enlarging, etc. have been proposed. Finally, the opportunities and challenges of atomically-thin two-dimensional materials for photocatalysis has been presented to satisfy people's requirement of potential applications.Download high-res image (328KB)Download full-size image

•Bi self-doping BiOCl composites were synthesized with glucose as reducing agent.•The introduction of Bi contributed to the high PEC performance.•The PEC performance of Bi/BiOCl was evaluated by monitoring ciprofloxacin.Metallic Bi, as a typical semimetal, has attracted significant attentions due to the highly anisotropic Fermi surface, long carrier mean free path, low carrier density, and small band gap. In this work, metallic Bi self-doping BiOCl (Bi/BiOCl) composites with high photoelectrochemical performance have been synthesized by a facile solvothermal method. A series of characterization methods have confirmed that the metallic Bi has been uniformly distributed on the surface of BiOCl. The introduction of metallic Bi can contribute to enhancing electron transport and separation of photoexcited electrons and holes. As a result, the Bi/BiOCl composites can exhibit superior photocurrent response compared to the pure BiOCl. In addition, ciprofloxacin has been used as target analyte to demonstrate the photoelectrochemical performance of the Bi/BiOCl composites. The Bi/BiOCl modified ITO can display outstanding stability and a wide linear range toward the detection of ciprofloxacin. The Bi/BiOCl composites can act as outstanding photoelectrochemical materials for application in photoelectrochemical field.Download high-res image (97KB)Download full-size image

•g-C3N4/Bi4O5Br2 composite material has been prepared via an ionic liquid assisted solvothermal method.•g-C3N4/Bi4O5Br2 composites showed the enhanced photocatalytic activity under visible light irradiation.•The increased light harvseting ability and photogenerated charge carriers separation efficiency contribute to the improved photocatalytic performance.A novel visible-light-driven g-C3N4/Bi4O5Br2 composite material has been prepared via an ionic liquid 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br) assisted solvothermal method. In this process, the ionic liquid [C16mim]Br played an important role as the solvent, dispersing agent and reactant at the same time. Colorless antibiotic ciprofloxacin (CIP) was chosen as the target pollutant to evaluate the as-prepared photocatalyst. Compared with the pure Bi4O5Br2, the as-prepared g-C3N4/Bi4O5Br2 composites showed the enhanced photocatalytic activity under visible light irradiation. 10 wt% g-C3N4/Bi4O5Br2 composite exhibited the best photodegradation performance among the g-C3N4/Bi4O5Br2 composites. The increased light harvseting ability and photogenerated charge carriers separation efficiency contribute to the improved photocatalytic performance for the as-prepared composites. Holes were determined to be the main active specie during the photocatalytic degradation.A novel visible-light-driven g-C3N4/Bi4O5Br2 composite material has been prepared via an ionic liquid 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br) assisted solvothermal method. Colorless antibiotic ciprofloxacin (CIP) was chosen as the target pollutant to evaluate the as-prepared photocatalyst. Compared with the pure Bi4O5Br2, the as-prepared g-C3N4/Bi4O5Br2 composites showed the enhanced photocatalytic activity under visible light irradiation. 10 wt% g-C3N4/Bi4O5Br2 composite exhibited the best photodegradation performance among the g-C3N4/Bi4O5Br2 composites. The increased light harvseting ability and photogenerated charge carriers separation efficiency contribute to the improved photocatalytic performance for the as-prepared composites. Holes were determined to be the main active specie during the photocatalytic degradation.Download high-res image (133KB)Download full-size image

Sustainable mesoporous graphitic carbon nitride (mpg-C3N4) modified PbBiO2Br porous microsphere (mpg-C3N4/PbBiO2Br) had been successfully synthesized via solvothermal process. Multiple techniques were applied to explore the structure, morphology, optical and electronic properties of the as-prepared photocatalysts. It could be found that the mpg-C3N4 was uniformly distributed on the surface of the PbBiO2Br porous microsphere. Compared with the pure PbBiO2Br, the mpg-C3N4/PbBiO2Br exhibited superior photocatalytic activity for the degradation of organic pollutants under visible light irradiation. When the mass fraction of mpg-C3N4 was 3%, the mpg-C3N4/PbBiO2Br composite materials exhibited the highest photocatalytic performance. The results indicated that the introduction of mpg-C3N4 could effectively enhance the electron mobility to promote the catalytic activity. The enhanced photocatalytic activity of the mpg-C3N4/PbBiO2Br materials can be attributed to the stronger optical trapping capability and the more effective separation efficiency of photogenerated electron-hole pairs. During the process of photocatalysis, the main active species of the photocatalysts were determined to be the and hole under visible light irradiation. Based on the relative band positions of mpg-C3N4 and PbBiO2Br, a possible photocatalytic mechanism of mpg-C3N4/PbBiO2Br composite catalyst was proposed.Download high-res image (194KB)Download full-size image

Oxygen reduction (ORR), oxygen evolution (OER), and hydrogen evolution (HER) reactions are extremely important electrochemical reactions for electrochemical energy conversion and storage. The development of highly efficient, low-cost, durable, and sustainable electrocatalysts is required for these three crucial electrochemical reactions. Herein, an effective tri-functional electrocatalyst, Co3O4 nanoparticle-modified N-doped hollow hierarchical porous carbon microtubes (Co3O4/NCMTs), was successfully prepared via the pyrolysis of metal cobalt(II) complex willow catkin biomass under an argon–ammonia atmosphere. The obtained carbon materials inherit the original micron tubular structure of the willow catkin and form a hollow micro/mesoporous hierarchical construction. Ammonia can hugely elevate the content of doped nitrogen in the carbon skeleton. The doped N and Co3O4 nanoparticles contribute to form more active sites for the electrochemical reactions. When compared with the Pt/C catalyst, the Co3O4/NCMT-800 electrocatalyst with a positive onset potential (E0 = 0.906 V) and half-wave potential (E1/2 = 0.778 V) exhibit superior catalytic stability and tolerance to methanol in the ORR. The optimal Co3O4/NCMT-800 material exhibit high activity with a low overpotential of 0.35 V for the OER and 0.21 V for the HER to achieve a current density of 10 mA cm−2. The enhanced OER and HER performance of the Co3O4/NCMTs contribute to improve the overall water splitting ability. The excellent tri-functional electrocatalytic activity can be ascribed to the doped N and Co3O4 nanoparticles loaded into the hollow hierarchical porous carbon microtubes that accelerate electron transport and enhance charge delocalization. Due to the abundant biomass precursor with a unique structure, the advanced non-noble metal-doped hollow porous carbon materials exhibit outstanding application prospects in the electrocatalysis field.

•2D-2D graphene-like g-C3N4/ultrathin Bi4O5Br2 materials have been prepared.•With matched energy band structure, the effective charge separation can be achieved.•The holes and O2− are determined to be the main active species.A novel visible-light-driven 2D-2D graphene-like g-C3N4/ultrathin Bi4O5Br2 photocatalyst was prepared via a facile solvothermal method in the presence of reactable ionic liquid 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br) for the first time. FT-IR, XPS and TEM analysis results demonstrated the successful introduction of the 2D graphene-like g-C3N4 material to the Bi4O5Br2 system. DRS and BET analysis results indicated the existence of the g-C3N4 could lead to the broaden absorption edge and larger surface area of the ultrathin Bi4O5Br2 nanosheets. The electrochemical analysis implied a fast transfer of the interfacial electrons and low recombination rate of photogenerated charge carriers in g-C3N4/Bi4O5Br2, which could be assigned to the sufficient and tight contact between ultrathin Bi4O5Br2 and graphene-like g-C3N4. The quinolone antibiotic ciprofloxacin (CIP) was chosen as the target pollutant to evaluate the photocatalytic performance of the as-prepared samples under visible light irradiation. 1 wt% g-C3N4/Bi4O5Br2 composite exhibited the highest photocatalytic degradation performance among all of the as-prepared photocatalysts. The enhancement of photocatalytic activity was attributed to the maximum contact between graphene-like g-C3N4 and ultrathin Bi4O5Br2 material with matched energy band structure, which enable the efficient charge seperation. A possible photocatalytic mechanism also was proposed.Download high-res image (145KB)Download full-size image

•Novel La ions doped BiOBr microspheres have been synthesized in the present of [C16mim]Br.•Ionic liquid played the role of solvent, reactant and template at the same time.•The materials have enhanced photocatalytic activities due to the reduced band gap and improved separation efficiency of electron–hole pairs.In this work, La3+ doped BiOBr microspheres have been prepared via 1-hexadecyl-3-methy-limidazolium bromine ([C16mim]Br) assisted solvothermal process. In this process, [C16mim]Br acted not only as the template but also the Br source and was good for the even dispersion of La3+. The morphology and compositional characteristics of the La3+ doped BiOBr microspheres were investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The photocatalytic activity of the La3+ doped BiOBr microspheres was evaluated by the degradation of rhodamine B (RhB), colorless antibiotic agent ciprofloxacin (CIP) under visible light irradiation. The as-prepared La3+ doped BiOBr microspheres exhibited much higher photocatalytic activity than pure BiOBr, and the 1 wt% La3+ doped BiOBr showed the highest photocatalytic activity. The enhanced photocatalytic activities were ascribed to the narrowed band gap and the efficient separation of electron hole pairs. The free radical trapping experiments suggested that the holes were the main active specie for the photocatalytic degradation. A possible photocatalytic mechanism of La3+ doped BiOBr has been proposed.Lanthanum ions doped BiOBr microspheres have been prepared via 1-hexadecyl-3-methy-limidazolium bromine ([C16mim]Br) assisted solovthermal process.

Nitrogen-doped carbon quantum dots (N-CQDs) modified atomically-thin BiOI nanosheets nanojunctions have been controllably prepared. The obtained BiOI consisted of 1–2 [Bi–O–I] units, which is the thinnest BiOX material reported so far. The atomically-thin structure was designed to accelerate carrier transfer among the BiOI nanosheet interior while the N-CQDs were constructed to facilitate surface charge carrier separation. Bidirectional acceleration of carrier separation can be achieved via this unique structure for both the materials interior and the surface. After the N-CQDs were modified on the BiOI, the photocatalytic activity of the N-CQDs/BiOI material greatly improved under visible light and UV irradiation. Through multiple characterizations, it can be found that the active species during the photocatalytic process can be manipulated. The modified N-CQDs could activate molecular oxygen via single electron reduction under visible light irradiation. Both ˙OH and O2˙− can be obtained from N-CQDs/BiOI materials under UV irradiation and N-CQDs could further increase the active species concentration. This study provides an approach to tune the active species for pollutant removal, selective organic synthesis or donating abundant hot electrons for CO2 photoreduction.

The porous ultrathin graphitic carbon nitride (g-C3N4) with confined surface carbon defects was obtained via the twice thermal treatment of bulk g-C3N4. The as-prepared porous ultrathin g-C3N4 sample displayed the average thickness of about 0.9 nm. The porous ultrathin g-C3N4 with confined surface carbon defects was designed to bidirectional acceleration of carrier separation for both the bulk and the surface. Multiple characterizations have been employed to determine the structure, morphology, surface feature, defect, and electronic structure of the obtained samples. The photocatalytic activity of the obtained porous ultrathin g-C3N4 materials was evaluated for the degradation of rhodamine B under the visible light irradiation. The structure-activity relationship of the porous ultrathin g-C3N4 materials was studied in details. The free radicals during the photocatalysis process was determined and analyzed by electron spin resonance and X-ray photoelectron spectroscopy valence band spectra technique, in which the main free radicals would be changed from superoxide radical for bulk g-C3N4 to both superoxide radical and hydroxyl radical for porous ultrathin g-C3N4. This ideal material model disclosing atomic-level insights into the role of porous ultrathin structure with confined carbon defects in the enhanced photocatalytic activity.

In this study, carbon quantum dots (CQDs)/bismuth oxyiodide (BiOI) materials have been synthesized via a reactable ionic liquid (IL) 1-hexyl-3-methyl-imidazolium iodine assisted solvothermal method. The introduction of IL was beneficial to construct the tight junctions between CQDs and BiOI. Based on the initial formation of strong-coupling between CQDs and IL, the tight junctions between CQDs and BiOI can be constructed as the iodide ions in the IL react with bismuth nitrate to in situ form BiOI during solvothermal treatment. The photocatalytic activity of the as-prepared CQDs/BiOI materials was evaluated using rhodamine B (RhB) as target pollutant. The CQDs/BiOI materials displayed the enhanced photocatalytic performance than pure BiOI while the 6 wt% CQDs/BiOI materials showed the highest activity. The enhanced photocatalytic activity can be ascribed to the cooperation effect of the excellent contact interface between BiOI and CQDs, while the effective separation of charge carriers via CQDs and the CQDs acted as photocatalytic reaction centers. The main active species during the photodegradation process was determined and photocatalytic mechanism was proposed based on the X-ray photoelectron spectroscopy valence band spectra, active species trapping experiments and electron spin resonance analysis.

Novel nitrogen-doped carbon quantum dots (N-CQDs)/BiOBr ultrathin nanosheets photocatalysts have been prepared via reactable ionic liquid assisted solvothermal process. The one-step formation mechanism of the N-CQDs/BiOBr ultrathin nanosheets was based on the initial formation of strong coupling between the ionic liquid and N-CQDs as well as subsequently result in tight junctions between N-CQDs and BiOBr with homodisperse of N-CQDs. The photocatalytic activity of the as-prepared photocatalysts was evaluated by the degradation of different pollutants under visible light irradiation such as ciprofloxacin (CIP), rhodamine B (RhB), tetracycline hydrochloride (TC), and bisphenol A (BPA). The improved photocatalytic performance of N-CQDs/BiOBr materials was ascribed to the crucial role of N-CQDs, which worked as photocenter for light harvesting, charge separation center for separating the charge carriers, and active center for degrading the pollutants. After the modification of N-CQDs, the molecular oxygen activation ability of N-CQDs/BiOBr materials was greatly enhanced. A possible photocatalytic mechanism based on experimental results was proposed.Keywords: BiOBr; Ionic liquid; Molecular oxygen; N-CQDs; Photocatalytic;

Novel Bi4O5Br2 photocatalysts were synthesized by a one-pot solvothermal method in the presence of reactable ionic liquid 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br). X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (DRS) and other characterizations were applied to investigate their structures, morphologies, optical and electronic properties. Bisphenol-A (BPA) was chosen to evaluate the photocatalytic activity of Bi4O5Br2 nanosheets. After the visible light irradiation, about 91.2% of BPA were removed by Bi4O5Br2 after 3.5 h with the reaction rate constant of 0.01086, which is much higher than that of the pure BiOBr (24.4%). Liquid chromatography combined with mass spectrometry (LC-MS) technique was used to track the intermediates species, showing the photocatalytic mechanism is related to photogenerated holes instead of hydroxyl radicals. The as-prepared Bi4O5Br2 also exhibited excellent stability as well as reusability, implying a great promising practical application for the photodegradation of organic pollutants.Novel photocatalysts Bi4O5Br2 ultrathin nanosheets were synthesized by a one-pot solvothermal method in the presence of reactable ionic liquid 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br). Bisphenol-A (BPA) were chosen to evaluate the photocatalytic activity of Bi4O5Br2 nanosheets. After the visible light irradiation, about 91.2% of BPA could be removed by Bi4O5Br2, which was much higher than that of the pure BiOBr material. In addition, the intermediate was identified by liquid chromatography combined with mass spectrometry (LC-MS) technique. A possible photocatalytic mechanism is proposed. Furthermore, Bi4O5Br2 could primely mineralize BPA and exhibit good stability and reusability, implying a great promising practical application in the photodegradation of organic pollutants.

In this study, novel visible-light-driven carbon quantum dots (CQDs)/Bi4O5I2 material has been prepared via a reactable ionic liquid 1-hexyl-3-methylimidazolium iodide ([Hmim]I) assisted bidirectional regulation solvothermal method. This is the first time for the preparation of CQDs/Bi4O5I2 material with halogen and CQDs bidirectional regulation at the same time. With CQDs modified on the surface of Bi4O5I2, fast transfer of photogenerated charges and low recombination of photo-induced electron-hole pairs facilitated the enhancement of photodegradation activity. At the same time, the introduction of CQDs made the electrons occupied in high-energy potential on the conduction band of Bi4O5I2 transfer to the reaction center CQDs and the molecular oxygen can be thus activated. The enhanced mechanisms for the active species (holes, hydroxyl and superoxide radicals) during the photocatalytic reaction under visible irradiation were analyzed using DRS analysis, electron spin resonance (ESR) technique and free radicals trapping experiments.Novel CQDs/Bi4O5I2 materials have been prepared via a reactable ionic liquid assisted bidirectional regulation solvothermal method. This is the first time for the preparation of CQDs/Bi4O5I2 material with halogen and CQDs bidirectional regulation at the same time.

•BiPO4 photocatalyst have been synthesized in the presence of ionic liquids [Omim]H2PO4.•Ionic liquid played the role of solvent, reactant and template at the same time.•The different photocatalytic activities of BiPO4 samples is mainly attributed to the different morphologies and microstructures.Bismuth phosphate (BiPO4) has been researched as one of the important bismuth-containing salts with high-efficient photocatalytic activity under UV light irradiation. However, the morphologies and microstructures of BiPO4 photocatalyst on photocatalytic activity have not been clearly investigated. Herein, BiPO4 photocatalyst with various morphologies and microstructures have been synthesized via a facile reactable ionic liquid [Omim]H2PO4 assisted solvothermal process in H2O, ethanol, ethylene glycol (EG) and ethylene glycol monomethyl ether (EGME), respectively. The photocatalytic ability of the as-prepared samples was evaluated using ciprofloxacin (CIP) as target pollutant. The result implied that different photocatalytic activities for CIP degradation is mainly attributed to different morphologies and microstructures of BiPO4 samples prepared in different solvents. The BiPO4 sample which was prepared under H2O condition showed the highest photocatalytic activity. In addition, inorganic salt NaH2PO4·2H2O was utilized to prepare BiPO4 samples instead of [Omim]H2PO4. It can be found that the photocatalytic efficiency of BiPO4 prepared via ionic liquid exhibited higher photocatalytic activity than that of inorganic salt for the degradation of CIP under UV light irradiation.

•Novel Er ions doped BiOBr microspheres have been synthesized in the present of [C16mim]Br.•The Er/BiOBr composites exhibited higher visible light photocatalytic activity than pure BiOBr on the degradation of CIP.•The enhanced photocatalytic performance could be attributed to the improved separation efficiency of electron–hole pairs and reduced band gap.Erbium (Er)-doped BiOBr with different Er ions doping concentrations has been synthesized through a solvothermal method in the presence of reactive ionic liquid 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br). The as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform spectrophotometer (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and UV–vis diffuse reflectance spectroscopy (DRS). The photocatalytic activities of the Er ions doped BiOBr samples were evaluated by the degradation of ciprofloxacin (CIP) under visible-light irradiation. The results assumed that doping of Er ions over BiOBr led to the increase of the photocatalytic activity under visible light irradiation and 3 wt% Er/BiOBr showed the highest photocatalytic activity. The enhanced photocatalytic performance could be attributed to the improved separation efficiency of electron–hole pairs and reduced band gap.Erbium ions doped BiOBr has been synthesized through a solvothermal method in the presence of reactable ionic liquid 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br). The sphere-like Er/BiOBr hierarchical structures were formed with an average diameter of 2–3 μm. The photocatalytic activities of pure BiOBr and Er/BiOBr samples were evaluated by the degradation of ciprofloxacin (CIP) under visible-light irradiation, in which 3 wt% Er/BiOBr showed the highest photocatalytic activity. The enhanced photocatalytic performance could be attributed to the improved separation efficiency of electron–hole pairs and reduced band gap.

•A simple and sensitive PEC strategy based on the Au/BiOCl composites is designed for 4-chlorophenol detection.•The Au/BiOCl composites have been prepared in the [C16mim]Cl by a facile one-pot solvothermal reaction.•The PEC detection method shows wide detectable range and low detection limit.The Au/BiOCl composites have been prepared by a facile one-pot ethylene glycol (EG) assisted solvothermal reaction in the presence of ionic liquid 1-hexadecyl-3-methylimidazolium chloride ([C16mim]Cl). During the synthesis procedure, the [C16mim]Cl has been used as Cl source, solvent of this system, and dispersing agent to effectively disperse Au on the surface of BiOCl. The as-prepared samples have been systematically characterized by multiple instruments to investigate the structure, morphology, and photoelectrochemical properties. According to the photoelectrochemical data, the Au/BiOCl composites exhibit better photoelectrochemical performance toward the detection of 4-chlorophenol than that of the pure BiOCl. The photocurrent response of Au/BiOCl modified electrode is high and stable under light irradiation. The proposed Au/BiOCl modified electrode shows a wide linear response ranging from 0.16 to 20 mg L−1 with detection limit of 0.05 mg L−1. It indicates a dramatically promising application of bismuth oxyhalides in photoelectrochemical detection. It will be expected that the present study may be lightly extended to the monitor of other organic pollutants by photoelectrochemical detection of the Au/BiOCl composites.

•MWCNT/Bi4O5Br2 materials with strong coupling have been prepared via reactable ionic liquid assisted solvothermal method.•The MWCNT/Bi4O5Br2 exhibited the increased photocatalytic activity for the degradation of tetracycline hydrochloride.•The hole and O2− were determined to be the main active species.•The modified MWCNT could improve molecular oxygen activation ability of Bi4O5Br2 under the visible light irradiation.Multiwalled carbon nanotube (MWCNT)/Bi4O5Br2 materials have been prepared with the Bi4O5Br2 ultrasmall nanosheets in situ strong coupling to MWCNT via the ionic liquid (IL) assisted solvothermal method. The formation mechanism was based on the original formation of strong coupling between the IL and MWCNT, and then the tight junctions between Bi4O5Br2 and MWCNT can be established as the bromine ions in the IL react with bismuth source to in situ produce Bi4O5Br2 during solvothermal process. The structures, morphologies, surface features, optical properties, electronic structures and photocatalytic properties were investigated in detail. The MWCNT/Bi4O5Br2 materials exhibited increased photocatalytic activity than pure Bi4O5Br2 for the degradation of antibiotic agent tetracycline hydrochloride and rhodamine B. Meanwhile, the 0.1 wt% MWCNT/Bi4O5Br2 materials displayed the highest activity. The hole and O2− were determined to be the main active species during the photodegradation process under visible light irradiation by the electron spin resonance, X-ray photoelectron spectroscopy valence band spectra and active species trapping experiments. After the introduction of MWCNT, the molecular oxygen activation capacity of Bi4O5Br2 greatly improved, which was believed to be responsible for the increased photocatalytic activity.

Carbon quantum dots (CQDs) induced ultrasmall BiOI nanosheets with assembled hollow microsphere structures were prepared via ionic liquids 1-butyl-3-methylimidazolium iodine ([Bmim]I)-assisted synthesis method at room temperature condition. The composition, structure, morphology, and photoelectrochemical properties were investigated by multiple techniques. The CQDs/BiOI hollow microspheres structure displayed improved photocatalytic activities than pure BiOI for the degradation of three different kinds of pollutants, such as antibacterial agent tetracycline (TC), endocrine disrupting chemical bisphenol A (BPA), and phenol rhodamine B (RhB) under visible light, light above 580 nm, or light above 700 nm irradiation, which showed the broad spectrum photocatalytic activity. The key role of CQDs for the improvement of photocatalytic activity was explored. The introduction of CQDs could induce the formation of ultrasmall BiOI nanosheets with assembled hollow microsphere structure, strengthen the light absorption within full spectrum, increase the specific surface areas and improve the separation efficiency of the photogenerated electron–hole pairs. Benefiting from the unique structural features, the CQDs/BiOI microspheres exhibited excellent photoactivity. The h+ was determined to be the main active specie for the photocatalytic degradation by ESR analysis and free radicals trapping experiments. The CQDs can be further employed to induce other nanosheets be smaller. The design of such architecture with CQDs/BiOI hollow microsphere structure can be extended to other photocatalytic systems.

•Few-layered MoS2/BiOI heterostructures had been synthesized by one-pot solvothermal process.•The intimate interfacial contact between MoS2 nanosheets and BiOI nanosheets promoted the charge separation efficiency.•MoS2/BiOI photocatalysts displayed greatly improved photocatalytic performance under visible light.Highly efficient few-layered MoS2/BiOI photocatalysts were successfully prepared by one-step solvent thermal process. The photocatalytic performance of MoS2/BiOI was evaluated by using rhodamine B (RhB) as the target pollution to degrade under visible light irradiation. After the introduction of MoS2 nanosheet, the MoS2/BiOI composites showed excellent photocatalytic performance. The optimal content of MoS2 was 0.5 wt%, and the composites exhibited a higher photocatalytic activity than the pure BiOI and MoS2/BiOI composites with different MoS2 weight ratios. The primary cause of the enhanced photocatalytic activity of MoS2/BiOI was the formation of heterojunction between BiOI and MoS2, which could promote the electron-hole pairs separation ability. The main active species during the photocatalytic process was discussed by the radicals trapping experiments with the addition of different scavengers. Meanwhile, a possible mechanism was proposed to explicate the improvement of photocatalytic activity upon visible light irradiation.Highly efficient few-layer MoS2/BiOI photocatalysts were successfully synthesized by a one-pot solvothermal process. The MoS2/BiOI exhibited a significant enhanced photocatalytic performance for the degradation of RhB under visible light irradiation.

Novel carbon quantum dot (CQD) modified Bi2MoO6 photocatalysts were prepared via a facile hydrothermal process. The CQD modified Bi2MoO6 materials were characterized by multiple techniques. The CQDs with the average size of about 7 nm were distributed on the surface of Bi2MoO6 nanosheets. The photocatalytic activity of as-prepared CQD modified Bi2MoO6 materials was investigated sufficiently by the photodegradation of four different kinds of pollutants, such as ciprofloxacin (CIP), bisphenol A (BPA), tetracycline hydrochloride (TC), and methylene blue (MB). The improved photocatalytic activity was observed for CQD modified Bi2MoO6 samples compared with pure Bi2MoO6 under visible light irradiation. The CQD modified Bi2MoO6 photocatalysts with a CQD content of 2 wt% exhibited the optimum photocatalytic activity, which was found to increase by about 5 times than that of the pure Bi2MoO6 for the photodegradation of CIP. This improvement was attributed to the crucial role of CQDs, which acted as a photocenter for absorbing solar light, a charge separation center for suppressing charge recombination, and a catalytic center for pollutant photo-degradation. The main active species were determined to be ˙OH and O˙−2 by the ESR technique and analyzed by calculations as well as XPS valence spectra, and a possible photocatalytic mechanism was also proposed.

A novel Bi4O5Br2 photocatalyst was prepared via a reactable ionic liquids-assisted solvothermal method accompanied with facile pH control. A Bi4O5Br2 ultrathin nanosheets material with 8 nm thickness could be obtained. The photocatalytic activity of the Bi4O5Br2 ultrathin nanosheets was evaluated with respect to the photo-degradation of colourless antibiotic agent ciprofloxacin (CIP) under visible light irradiation. The results revealed that the Bi-rich Bi4O5Br2 ultrathin nanosheets exhibited higher photocatalytic activity than BiOBr ultrathin nanosheets for the photo-degradation of CIP. The O2˙− anion was determined to be the main active species for the photo-degradation process by ESR. After multiple characterizations, the variable energy band structure was confirmed to be responsible for the enhanced photocatalytic activity. The more negative conduction band (CB) value of Bi4O5Br2 facilitated the formation of more active species, O2˙−. The upshifting of the CB and the wider valence band favor the higher separation efficiency of electron–hole pairs. It was hoped that this architecture of ultrathin 2D inorganic materials with a suitable band gap can be extended to other systems for high-performance photocatalysis applications.

In this paper, carbon quantum dots (CQDs) modified BiOCl ultrathin nanosheets photocatalyst was synthesized via a facile solvothermal method. The structures, morphologies, optical properties, and photocatalytic properties were investigated in detail. The photocatalytic activity of the obtained CQDs modified BiOCl ultrathin nanosheets photocatalyst was evaluated by the degradation of bisphenol A (BPA) and rhodamine B (RhB) under ultraviolet, visible, and near-infrared light irradiation. The CQDs/BiOCl materials exhibited significantly enhanced photocatalytic performance as compared with pure BiOCl and the 5 wt % CQDs/BiOCl materials displayed the best performance, which showed a broad spectrum of photocatalytic degradation activity. The main active species were determined to be hole and O2•– under visible light irradiation by electron spin resonance (ESR) analysis, XPS valence spectra, and free radicals trapping experiments. The crucial role of CQDs for the improved photocatalytic activity was mainly attributed to the superior electron transfer ability, enhanced light harvesting, and boosted catalytic active sites.Keywords: BiOCl; CQDs; photocatalytic mechanism; ultrathin nanosheets

BiOBr hollow microspheres attached to few-layered molybdenum disulfide (MoS2) were prepared by an ethylene glycol (EG)-assisted microwave process in the presence of 1-hexadecyl-3-methylimidazolium bromine ([C16mim]Br). The as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and UV-vis diffuse reflectance spectroscopy (DRS). During the reaction process, the ionic liquid [C16mim]Br acts as not only a solvent and Br source, but also as a microwave-absorbing agent and template for the fabrication of MoS2/BiOBr hollow microspheres. In addition, the photocatalytic activity of MoS2/BiOBr was evaluated for the degradation of ciprofloxacin (CIP) and Rhodamine B (RhB) under visible light irradiation. The results indicated that 0.2 wt% MoS2/BiOBr microspheres exhibit higher photocatalytic activity than BiOBr. A possible photocatalytic mechanism based on the relative band position of MoS2 and BiOBr was proposed.

Graphitic-carbon nitride/bismuth oxybromide (g-C3N4/BiOBr) porous microspheres have been successfully synthesized by a one-pot ethylene glycol (EG) assisted microwave process in the presence of 1-hexadecyl-3-methylimidazolium bromine ([C16mim]Br). The as-prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and UV–vis diffuse reflectance spectroscopy (DRS). During the reaction process, the ionic liquid acts not only as solvent and Br source but also as a template for fabrication of g-C3N4/BiOBr porous microspheres. In addition, the photocatalytic activity of the g-C3N4/BiOBr is evaluated by degrading Rhodamine B (RhB) and ciprofloxacin (CIP) under visible-light irradiation. It is found that 12.75 wt% g-C3N4/BiOBr microspheres exhibit higher photocatalytic activity than that of the as-prepared BiOBr. A possible photocatalytic mechanism based on the relative band positions of g-C3N4/BiOBr has been proposed.

BiOI hollow microspheres have been rapidly synthesized through a facile reactable ionic liquid 1-butyl-3-methylimidazolium iodine ([Bmim]I)-assisted microemulsion method at room temperature. The formation mechanism of the BiOI hollow microspheres has been investigated. The BiOI hollow microspheres were formed through self-assembly and inside-out Ostwald ripening growth mechanism. During the reactive process, the ionic liquid, which acts as the solvent, reactant and template at the same time, plays a crucial role on the formation of hollow microspheres. In addition, the influencing factors (such as the reactant, the concentration of ionic liquids and the amount of acetic acid) of the formation of BiOI hollow microsphere have also been explored. The photocatalytic ability of the as-prepared photocatalysts was evaluated using rhodamine B (RhB) as a target pollutant. After systematic characterizations, the relationship between the structure of the photocatalyst and the photocatalytic activities were also discussed in detail. It can be assumed that the enhancing photocatalytic activity of BiOI hollow microspheres could be attributed to the improved light harvesting, shortened diffusion pathways, high BET surface area and faster interfacial charge separation. O2˙− and h+ were the main active species for the photocatalytic degradation of RhB. It is hoped that this rapidly synthetic route at room temperature can be extended to the purposive preparation of other hollow microsphere materials.

Novel sphere-like g-C3N4/BiOI composite photocatalysts were prepared by a one-pot EG-assisted solvothermal process in the presence of reactable ionic liquid 1-butyl-3-methylimidazolium iodine ([Bmim]I). The nanostructured heterojunction was formed with g-C3N4 covering the surface of BiOI microspheres uniformly. Multiple techniques were applied to investigate the structure, morphology and photocatalytic properties of as-prepared samples. During the reactive process, the ionic liquid acted as solvent, reactant, template and dispersing agent at the same time, leading to g-C3N4 being uniformly dispersed on the sphere-like BiOI surface. Three different types of dyes rhodamine B (RhB), methylene blue (MB), methyl orange (MO) were chosen as model pollutants to evaluate the photocatalytic activity of g-C3N4/BiOI composite. The as-prepared g-C3N4/BiOI composite exhibited much higher photocatalytic activity than the pure BiOI. At the same time, colourless endocrine disrupting chemical bisphenol A (BPA) and phenols 4-chlorophenol (4-CP) were chosen to further evaluate the photocatalytic activity of g-C3N4/BiOI composite. The g-C3N4/BiOI composite also exhibited much higher photocatalytic activity than the pure BiOI, which showed a broad spectrum of photocatalytic degradation activities. The results indicated that the formed heterojunction of g-C3N4 covers the BiOI microspheres contributed to improved electron–hole separation and enhancement in photocatalytic activity. A photocatalytic mechanism of g-C3N4/BiOI composites is also proposed.

Nitrogen-doped carbon quantum dots (N-CQDs)/BiPO4 materials have been prepared through an ionic liquid assisted solvothermal method. After the introduction of N-CQDs, the N-CQDs/BiPO4 materials exhibited the increased photocatalytic activity for the degradation of four kinds of colorless pollutants under UV irradiation, such as antibiotic ciprofloxacin, enrofloxacin, tetracycline and phenol 4-chlorophenol. Different from roles of carbon quantum dots previous reported, the improved photocatalytic activity was mainly attributed to the molecular oxygen activation ability of N-CQDs, which derived from the oxygen defects on the surface of N-CQDs. The N-CQDs/BiPO4 materials displayed excellent reusability and stability and demonstrated the oxygen defects in N-CQDs could sustainable activate molecular oxygen for organic pollutant removal under UV irradiation. By the electron spin resonance analysis, the main active species was determined to be superoxide radicals rather than hydroxyl radicals. This study presented some new insight for the mode of action of N-CQDs for the increased photocatalytic activity and also provided an approach to enhance the molecular oxygen activation for photocatalytic pollutant removal or selective organic synthesis.Nitrogen-doped carbon quantum dots (N-CQDs)/BiPO4 materials have been prepared. The improved photocatalytic activity was mainly attributed to the molecular oxygen activation ability of N-CQDs, which derived from the oxygen defects on the surface of N-CQDs.

A novel graphene-like BN modified BiPO4 material was prepared for the first time via a simple solvothermal process with the assistance of reactable ionic liquid 1-decyl-3-methylimidazolium dihydrogen phosphate ([Omim]H2PO4). The as-prepared photocatalyst was characterized by XRD, FT-IR, Raman, XPS, TEM, DRS, BET, PL, EIS and ESR to investigate the structure, morphology, optical property, surface area, electrical property and active species. The photocatalytic activities of graphene-like BN/BiPO4 materials were evaluated by the degradation of antibiotic enrofloxacin (ENR) under UV light irradiation and the 1 wt% graphene-like BN/BiPO4 displayed the best activity among the BN/BiPO4 composites. The enhanced photocatalytic activity for the removal of enrofloxacin was attributed to higher separation efficiency of photogenerated electron-hole pairs, and the generated more O2− and OH radicals when the BN was modified on BiPO4. Moreover, a probable degradation mechanism was proposed for the improved photocatalytic activity of BN modified BiPO4.Graphene-like BN has been employed to modify the BiPO4 to acquire higher photocatalytic activity for the removal of enrofloxacin.

In this paper, bismuth oxybromide (BiOBr) nanosquares photocatalysts were synthesized via a facile hydrothermal method with the double regulation of the ionic liquid (IL) 1-hexadecyl-3-methylimidazolium bromide and ammonium bismuth citrate (BCA). To the best of our knowledge, this report is the first to describe the BiOBr material with simultaneous bismuth and halogen bidirectional source regulation. The structures, components, morphologies, optical properties and photocatalytic properties of the as-prepared samples were specifically explored. The photocatalytic ability was assessed using the degradation of rhodamine B under visible light irradiation. The BiOBr-IL + BCA exhibited improved photocatalytic activity compared with the BiOBr materials without double regulation. The primary active species were determined to be holes (h+) and superoxide radicals (O2−) using electron spin resonance (ESR) analysis and free radical trapping experiments. This enhanced activity was attributed to its larger specific surface, the superior electron transfer ability, and the increased negative conduction band position, which favors the photogenerated electrons to trap the molecular oxygen to produce O2−. The production of more O2− can benefit the removal of pollutants.Bismuth and halogen source bidirectional regulation has been employed to prepare the BiOBr nanosquares, which displayed improved photocatalytic activity.

•g-C3N4/BiPO4 heterostructures had been synthesized by one-pot ionic liquid solvothermal process.•The intimate interfacial contact between g-C3N4 nanosheets and BiPO4 promoted the charge separation efficiency.•g-C3N4/BiPO4 photocatalysts displayed greatly improved photocatalytic performance under visible light.The novel g-C3N4/BiPO4 hybrid materials have been synthesized in reactive ionic liquid system via a facile solvothermal process. During the process, the ionic liquid not only plays an important role of solvent, dispersing agent and reactant synchronously in the synthesis of BiPO4 crystal, but also as reactive bridge for the formation of g-C3N4/BiPO4 composites with the hydrogen bond acting force. The g-C3N4/BiPO4 composites showed higher photocatalytic performance for the removal of methylene blue (MB) and antibiotic ciprofloxacin (CIP) after the modification of g-C3N4. The results further indicated the g-C3N4/BiPO4 composite photocatalyst contribute to the separation efficiency of the photo-generated electrons (e−) and holes (h+). As a result, there was synergy role between BiPO4 and g-C3N4 in the g-C3N4/BiPO4 composites, which played a significant role in improving the photocatalytic activity.The novel-type g-C3N4/BiPO4 hybrid materials have been synthesized in reactive ionic liquid system via a facile solvothermal method. During the process, the ionic liquid not only plays an important role of solvent, dispersing agent and reactant synchronously in the synthesis of BiPO4 crystal, but also as reactive bridge for the formation of g-C3N4/BiPO4 composites with the hydrogen bond acting force. The g-C3N4/BiPO4 composites showed higher photocatalytic performance for the removal of methylene blue (MB) and antibiotic ciprofloxacin (CIP) after the modification of g-C3N4. The results further indicated the g-C3N4/BiPO4 composite photocatalyst contribute to the separation efficiency of the photo-generated electrons (e−) and holes (h+).

Nitrogen-doped carbon quantum dots (N-CQDs) modified atomically-thin BiOI nanosheets nanojunctions have been controllably prepared. The obtained BiOI consisted of 1–2 [Bi–O–I] units, which is the thinnest BiOX material reported so far. The atomically-thin structure was designed to accelerate carrier transfer among the BiOI nanosheet interior while the N-CQDs were constructed to facilitate surface charge carrier separation. Bidirectional acceleration of carrier separation can be achieved via this unique structure for both the materials interior and the surface. After the N-CQDs were modified on the BiOI, the photocatalytic activity of the N-CQDs/BiOI material greatly improved under visible light and UV irradiation. Through multiple characterizations, it can be found that the active species during the photocatalytic process can be manipulated. The modified N-CQDs could activate molecular oxygen via single electron reduction under visible light irradiation. Both ˙OH and O2˙− can be obtained from N-CQDs/BiOI materials under UV irradiation and N-CQDs could further increase the active species concentration. This study provides an approach to tune the active species for pollutant removal, selective organic synthesis or donating abundant hot electrons for CO2 photoreduction.

Novel sphere-like g-C3N4/BiOI composite photocatalysts were prepared by a one-pot EG-assisted solvothermal process in the presence of reactable ionic liquid 1-butyl-3-methylimidazolium iodine ([Bmim]I). The nanostructured heterojunction was formed with g-C3N4 covering the surface of BiOI microspheres uniformly. Multiple techniques were applied to investigate the structure, morphology and photocatalytic properties of as-prepared samples. During the reactive process, the ionic liquid acted as solvent, reactant, template and dispersing agent at the same time, leading to g-C3N4 being uniformly dispersed on the sphere-like BiOI surface. Three different types of dyes rhodamine B (RhB), methylene blue (MB), methyl orange (MO) were chosen as model pollutants to evaluate the photocatalytic activity of g-C3N4/BiOI composite. The as-prepared g-C3N4/BiOI composite exhibited much higher photocatalytic activity than the pure BiOI. At the same time, colourless endocrine disrupting chemical bisphenol A (BPA) and phenols 4-chlorophenol (4-CP) were chosen to further evaluate the photocatalytic activity of g-C3N4/BiOI composite. The g-C3N4/BiOI composite also exhibited much higher photocatalytic activity than the pure BiOI, which showed a broad spectrum of photocatalytic degradation activities. The results indicated that the formed heterojunction of g-C3N4 covers the BiOI microspheres contributed to improved electron–hole separation and enhancement in photocatalytic activity. A photocatalytic mechanism of g-C3N4/BiOI composites is also proposed.

A novel Bi4O5Br2 photocatalyst was prepared via a reactable ionic liquids-assisted solvothermal method accompanied with facile pH control. A Bi4O5Br2 ultrathin nanosheets material with 8 nm thickness could be obtained. The photocatalytic activity of the Bi4O5Br2 ultrathin nanosheets was evaluated with respect to the photo-degradation of colourless antibiotic agent ciprofloxacin (CIP) under visible light irradiation. The results revealed that the Bi-rich Bi4O5Br2 ultrathin nanosheets exhibited higher photocatalytic activity than BiOBr ultrathin nanosheets for the photo-degradation of CIP. The O2˙− anion was determined to be the main active species for the photo-degradation process by ESR. After multiple characterizations, the variable energy band structure was confirmed to be responsible for the enhanced photocatalytic activity. The more negative conduction band (CB) value of Bi4O5Br2 facilitated the formation of more active species, O2˙−. The upshifting of the CB and the wider valence band favor the higher separation efficiency of electron–hole pairs. It was hoped that this architecture of ultrathin 2D inorganic materials with a suitable band gap can be extended to other systems for high-performance photocatalysis applications.

Photocatalytic solar energy conversion is a clean technology for producing renewable energy sources, but its efficiency is greatly hindered by the kinetically sluggish oxygen evolution reaction. Herein, confined defects in atomically-thin BiOCl nanosheets were created to serve as a remarkable platform to explore the relationship between defects and photocatalytic activity. Surface defects can be clearly observed on atomically-thin BiOCl nanosheets from scanning transmission electron microscopy images. Theoretical/experimental results suggest that defect engineering increased states of density and narrowed the band gap. With combined effects from defect induced shortened hole migratory paths and creation of coordination-unsaturated active atoms with dangling bonds, defect-rich BiOCl nanosheets displayed 3 and 8 times higher photocatalytic activity towards oxygen evolution compared with atomically-thin BiOCl nanosheets and bulk BiOCl, respectively. This successful application of defect engineering will pave a new pathway for improving photocatalytic oxygen evolution activity of other materials.

BiOI hollow microspheres have been rapidly synthesized through a facile reactable ionic liquid 1-butyl-3-methylimidazolium iodine ([Bmim]I)-assisted microemulsion method at room temperature. The formation mechanism of the BiOI hollow microspheres has been investigated. The BiOI hollow microspheres were formed through self-assembly and inside-out Ostwald ripening growth mechanism. During the reactive process, the ionic liquid, which acts as the solvent, reactant and template at the same time, plays a crucial role on the formation of hollow microspheres. In addition, the influencing factors (such as the reactant, the concentration of ionic liquids and the amount of acetic acid) of the formation of BiOI hollow microsphere have also been explored. The photocatalytic ability of the as-prepared photocatalysts was evaluated using rhodamine B (RhB) as a target pollutant. After systematic characterizations, the relationship between the structure of the photocatalyst and the photocatalytic activities were also discussed in detail. It can be assumed that the enhancing photocatalytic activity of BiOI hollow microspheres could be attributed to the improved light harvesting, shortened diffusion pathways, high BET surface area and faster interfacial charge separation. O2˙− and h+ were the main active species for the photocatalytic degradation of RhB. It is hoped that this rapidly synthetic route at room temperature can be extended to the purposive preparation of other hollow microsphere materials.