Mengxia Ji

Facile fabrication of the visible-light-driven Bi2WO6/BiOBr composite with enhanced photocatalytic activity

Novel Bi2WO6/BiOBr composite photocatalysts were prepared by a one-pot EG-assisted solvothermal process in the presence of reactable ionic liquid 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br). Multiple techniques, such as X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDS), Fourier transform infrared spectroscopy (FT-IR), UV-vis diffuse reflection spectroscopy (DRS), photoluminescence (PL), photocurrent and electrochemical impedance spectroscopy (EIS) were applied to investigate the structures, morphology and photocatalytic properties of as-prepared samples. Compared with bare Bi2WO6 and BiOBr, the Bi2WO6/BiOBr composites exhibited significantly enhanced photocatalytic activity for rhodamine B (RhB) degradation under visible light irradiation. The 50 at% Bi2WO6/BiOBr showed the highest photocatalytic activity under visible light irradiation, which was about 26.6 times and 1.8 times than that of the bare Bi2WO6 and BiOBr, respectively. The Bi2WO6/BiOBr composites also exhibited enhanced photocatalytic activity for bisphenol A (BPA) and methylene blue (MB) degradation under visible light irradiation. The results of PL, photocurrent and EIS indicated that Bi2WO6 and BiOBr could combine well to form a heterojunction structure which facilitated electron–hole separation, and led to the increasing photocatalytic activity. On the basis of the experimental results and estimated energy band positions, the mechanism of enhanced photocatalytic activity was proposed.

Carbon Quantum Dots Modified BiOCl Ultrathin Nanosheets with Enhanced Molecular Oxygen Activation Ability for Broad Spectrum Photocatalytic Properties and Mechanism Insight

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.

Controllable synthesis of Bi4O5Br2 ultrathin nanosheets for photocatalytic removal of ciprofloxacin and mechanism insight

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.

Carbon Quantum Dots Induced Ultrasmall BiOI Nanosheets with Assembled Hollow Structures for Broad Spectrum Photocatalytic Activity and Mechanism Insight

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.

Bidirectional acceleration of carrier separation spatially via N-CQDs/atomically-thin BiOI nanosheets nanojunctions for manipulating active species in a photocatalytic 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.

Microwave-assisted synthesis of few-layered MoS2/BiOBr hollow microspheres with superior visible-light-response photocatalytic activity for ciprofloxacin removal

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.

Ionic liquid-assisted bidirectional regulation strategy for carbon quantum dots (CQDs)/Bi4O5I2 nanomaterials and enhanced photocatalytic properties.

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.

Defect engineering in atomically-thin bismuth oxychloride towards photocatalytic oxygen evolution

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.

Controllable synthesis of perovskite-like PbBiO2Cl hollow microspheres with enhanced photocatalytic activity for antibiotic removal

Novel perovskite-like PbBiO2Cl materials with hollow and porous sphere-like structures were successfully synthesized using a polyvinyl pyrrolidone (PVP) and reactive ionic liquid 1-hexadecyl-3-methylimidazolium chlorine ([C16mim]Cl) complex system. TEM was employed to characterize the hollow-porous structure formed by the double regulation of the ionic liquid and PVP. The achieved hollow-porous PbBiO2Cl sphere-like photocatalyst showed excellent photocatalytic activity towards the degradation of the colorless antibiotic agents ciprofloxacin (CIP) and tetracycline (TC) under visible light irradiation. The enhanced photocatalytic performance of the PbBiO2Cl materials was mainly derived from the porous and hollow structure, which enables a larger specific surface area and faster interfacial charge separation. Moreover, based on the analysis of XPS valence spectra, electron spin resonance (ESR) spectra and free radical trapping experiments, the main active species were determined to be holes and superoxide radicals during the photocatalytic degradation process. According to the results of the characterizations and the comparative tests, possible growth and photocatalytic reaction mechanisms were proposed.

Controlled preparation of MoS 2 /PbBiO 2 I hybrid microspheres with enhanced visible-light photocatalytic behaviour

Novel MoS2/PbBiO2I hybrid microspheres were controllably synthesized via the ionic liquid 1-hexyl-3-methylimidazolium iodide ([Hmim]I) assisted solvothermal method. The morphologies, structures, optical and electronic properties of the materials were explored by XRD, XPS, SEM, TEM, DRS, EIS and photocurrent analysis. The photocatalytic activity of MoS2/PbBiO2I was evaluated by the degradation of rhodamine B (RhB), antibiotic agent ciprofloxacin (CIP) and bisphenol A (BPA) under visible light irradiation. The photodegradation results showed that the activity of MoS2/PbBiO2I was higher than that of pure PbBiO2I because of suitable band alignment, a larger specific surface area, an enhanced light absorption region, and stronger photocurrent intensity arising from the interface interaction between MoS2 and PbBiO2I. The 1.0 wt% MoS2/PbBiO2I showed the best photocatalytic performance. Electron spin resonance (ESR) experiments and free radical trapping experiments showed that the superoxide radicals (O2-) and holes (h+) were determined to be the main active species for the photocatalysis process. A possible mechanism was presented based on the detection and analysis results.