Jun Di

Preparation of sphere-like g-C3N4/BiOI photocatalysts via a reactable ionic liquid for visible-light-driven photocatalytic degradation of pollutants

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.

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.

A g-C3N4/BiOBr visible-light-driven composite: synthesis via a reactable ionic liquid and improved photocatalytic activity

g-C3N4/BiOBr composite photocatalysts have been synthesized in the presence of the reactable ionic liquid 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br). The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy, electrochemical impedance spectroscopy (EIS), and photocurrent analysis. During the reaction process, the ionic liquid [C16mim]Br acted as solvent, reactant, template and dispersing agent at the same time, leading the g-C3N4 to disperse well on the surface of the BiOBr flower-like microspheres. The photocatalytic ability of the as-prepared photocatalysts was evaluated using rhodamine B (RhB) as a target pollutant. The photocatalysts exhibited a significantly enhanced photocatalytic performance in the degradation of RhB. The results of PL, EIS, and photocurrent tests indicated that g-C3N4 combined and dispersed well on the surface of BiOBr which facilitated electron–hole separation, and led to the increased photocatalytic activity. The optimal g-C3N4 content for the photocatalytic activity of the g-C3N4/BiOBr composites was determined. Radical trap experiments certified that the hole was the main reactive species for the photocatalytic degradation of RhB. A possible mechanism of g-C3N4 for the enhancement of visible light performance was proposed.

Reactable ionic liquid-assisted rapid synthesis of BiOI hollow microspheres at room temperature with enhanced photocatalytic activity

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.

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.

One-pot solvothermal synthesis of Cu-modified BiOCl via a Cu-containing ionic liquid and its visible-light photocatalytic properties

Novel visible-light-driven Cu-modified BiOCl uniform sphere-like materials have been successfully synthesized through a one-pot ethylene glycol (EG)-assisted solvothermal process in the presence of 1-octyl-3-methylimidazolium copper trichloride ([Omim]CuCl3). The Cu-modified BiOCl materials were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), Raman, photoluminescence (PL) and UV-vis diffuse reflectance spectroscopy (DRS). The results of the XRD, XPS, SEM, EDS, Raman analyses indicated that metal Cu was evenly distributed on the surface of the BiOCl microspheres in the form of Cu2+. During the reaction process, the metal-based ionic liquid acted as the solvent, the template, the Cl source and the Cu source at the same time. It is possible to tune the morphology of the Cu-modified BiOCl materials by varying the amount of ionic liquid used. In addition, the electrochemical and photocatalytic properties of the Cu-modified BiOCl materials were investigated. After the introduction of Cu2+, the photocurrent of the Cu-modified BiOCl materials was higher than that of the pure BiOCl. And the Cu-modified BiOCl materials exhibited higher photocatalytic activity for the degradation of methylene blue (MB) and bisphenol A (BPA) than that of pure BiOCl. The increased photocatalytic activity of the Cu-modified BiOCl materials was attributed to its large adsorption capacity, broad light absorption band and high separation efficiency of photo-generated electrons and holes. On the basis of these findings, the Cu-modified BiOCl materials showed great promise as photocatalysts for degrading organic pollutants and other applications.

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.

Ultrathin 2D Photocatalysts: Electronic‐Structure Tailoring, Hybridization, and Applications

As a sustainable technology, semiconductor photocatalysis has attracted considerable interest in the past several decades owing to the potential to relieve or resolve energy and environmental-pollution issues. By virtue of their unique structural and electronic properties, emerging ultrathin 2D materials with appropriate band structure show enormous potential to achieve efficient photocatalytic performance. Here, the state-of-the-art progress on ultrathin 2D photocatalysts is reviewed and a critical appraisal of the classification, controllable synthesis, and formation mechanism of ultrathin 2D photocatalysts is presented. Then, different strategies to tailor the electronic structure of ultrathin 2D photocatalysts are summarized, including component tuning, thickness tuning, doping, and defect engineering. Hybridization with the introduction of a foreign component and maintaining the ultrathin 2D structure is presented to further boost the photocatalytic performance, such as quantum dots/2D materials, single atoms/2D materials, molecular/2D materials, and 2D-2D stacking materials. More importantly, the advancement of versatile photocatalytic applications of ultrathin 2D photocatalysts in the fields of water oxidation, hydrogen evolution, CO2 reduction, nitrogen fixation, organic syntheses, and removal pollutants is discussed. Finally, the future opportunities and challenges regarding ultrathin 2D photocatalysts to bring about new opportunities for future research in the field of photocatalysis are also presented.