Ultrathin Bi2WO6 Research Articles

Ultrathin Bi2WO6 nanosheets loaded g-C3N4 quantum dots: A direct Z-scheme photocatalyst with enhanced photocatalytic activity towards degradation of organic pollutants under wide spectrum light irradiation

A novel ultrathin Bi2WO6 nanosheets loaded g-C3N4 quantum dots (CNQDs/BWO) photocatalyst was successfully fabricated, and used to catalyze two representative organic pollutants, rhodamine B (RhB) and tetracycline (TC) under wide spectrum light irradiation. The degradation experiments showed that CNQDs/BWO exhibited enhanced photocatalytic activities towards degradation of organic pollutants. Under visible light irradiation, the 5% CNQDs/BWO exhibited the best degradation efficiency with 87% and 92.51% removal of TC and RhB within 60 min, respectively. And under near-infrared (NIR) light, the 5% CNQDs/BWO still showed the best performance, its degradation efficiency to TC were ∼2 times than pure BWO. The upconversion behaviors of CNQDs might contribute to the enhanced photocatalysis. According to similar degradation trend, it is inferred that the catalytic mechanism in NIR light is consistent with that in visible light. The enhanced photocatalytic activity of CNQDs/BWO under wide spectrum light irradiation can be ascribed to a Z-scheme mechanism based on the calculated the lowest unoccupied molecular orbital (LUMO) of CNQDs and CB position of BWO, the free radical quenching experiment, and ESR characterization results. The composites have prominent light absorption, high stability and excellent photocatalysis efficiency, which would be used as a promising strategy for organic pollutants degradation.

Photocatalytic reduction of CO2 to methane over PtOx-loaded ultrathin Bi2WO6 nanosheets

Solar CO2 photoreduction into hydrocarbons is promising and significative. However, many conventional catalysts reported usually suffer from poor photocatalytic activities. Herein, ultrathin Bi2WO6 nanosheets with a thickness of about 4.8 nm have been synthesized by hydrothermal method, which exhibited a CH4 production rate of 19 ppm g−1 h−1 under a low CO2 concentration of 400 ppm. PtOx nanoparticles with a size of about 2 nm were then loaded on the Bi2WO6 nanosheets as excellent co-catalysts by photoreduction in aqueous solution, and an optimal CH4 yield of 108.8 ppm g−1 h−1 was achieved, which was about 5.7 times than that of pristine Bi2WO6 nanosheets. Further analyses of photocurrent curves, electrochemical impedance spectroscopy and polarization curves of water oxidation indicated that the improved photocatalytic activity was suggested to result from the enhanced carrier separation and accelerated water oxidation by PtOx nanoparticles. The work will likely give a deeper insight of PtOx nanoparticles and provide a new idea to design catalysts for CO2 photoreduction to CH4.

Ultra-thin Bi2WO6 porous nanosheets with high lattice coherence for enhanced performance for photocatalytic reduction of Cr(VI)

Bi2WO6 porous nanosheets (PNS) with different thickness were synthesized via one-pot hydrothermal method. The thickness of Bi2WO6 nanosheets could be well controlled from ∼27 nm to ∼16 nm by adjusting the precursor concentration. In addition, the PNS exhibited porous structures, high surface area and high lattice coherence, which increased the number of catalytic sites and facilitated the charge migration within the sheet structure. The Cr(VI) reduction experiments showed that the photocatalytic activity was greatly affected by the thickness of the product and the optimal photocatalytic activity under visible light irradiation was achieved by BWO-3 with thickness of ∼18 nm. The photocatalytic ratio of Cr(VI) reduction for BWO-3 reached to ∼99.5% after 100 min visible light irradiation, which was higher than that of BWO (∼78%). Based on the optical and electrochemical measurements, BWO-3 had upshifted conduction band of 0.05 V, prolonged carriers’ lifetime of 2.03 ns and decreased carriers' recombination efficiency compared to BWO. These results endowed BWO-3 with high photoreduction ability, increased transfer and separation efficiency of carriers, and thus enhanced the photoreduction activity.

Ultrathin Bi2WO6 nanosheet decorated with Pt nanoparticles for efficient formaldehyde removal at room temperature

Two-dimensional (2D) ultrathin bismuth tungstate (Bi2WO6) nanosheets (BWO-NS) with a thickness of approximately 4.0 nm were synthesized by a one-step hydrothermal method, and decorated with platinum (Pt) nanoparticles (NPs) via an impregnation/borohydride-reduction approach. The as-prepared ultrathin Pt-BWO-NS exhibited superior catalytic activity for removing gaseous formaldehyde (HCHO) at ambient temperature, in comparison with bulk counterpart with Bi2WO6 sheet thickness of tens of nanometers. The ultrathin structure endowed the Pt-BWO-NS sample with larger specific surface area, which can provide abundant surface active sites for HCHO adsorption and facilitate the homogeneous dispersion of Pt NPs. X-ray photoelectron spectroscopy and hydrogen temperature-programmed reduction analyses revealed the interaction between the Bi2WO6 support and Pt species, which is crucial for activating surface oxygen atoms to participate in the catalytic HCHO oxidation process. By conducting in situ diffuse reflectance infrared Fourier transform spectroscopy under different atmospheres, i.e., gaseous HCHO in nitrogen or oxygen (O2), the reaction mechanism and the role of O2 were elucidated, with dioxymethylene, formate and linearly adsorbed carbon monoxide identified as the main reaction intermediates. This study may provide new enlightenment on fabricating novel 2D nanomaterials for efficient indoor air purification and potentially other environmental applications.

Effect of bismuth tungstate with different hierarchical architectures on photocatalytic degradation of norfloxacin under visible light

Abstract The photocatalytic degradation of norfloxacin by bismuth tungstate (Bi2WO6) with different hierarchical architectures was investigated under visible light irradiation. Bi2WO6 was prepared by hydrothermal method with the reaction solution pH ranging from 4 to11. The relatively ultrathin Bi2WO6 nanoflakes prepared at pH 4 showed excellent adsorption and photodegradation efficiency towards norfloxacin. The characterization results showed that Bi2WO6 prepared at pH 4 had a larger specific area and faster photo-generated carrier separation rate. The decay rate reached the maximum in weak alkaline reaction solution, which could be attributed to the presence of moderate OH− anions. The present study demonstrated that the smaller size of Bi2WO6 could be an efficient photocatalyst on the degradation of norfloxacin in the aquatic environment.

Construction of an all-solid-state artificial Z-scheme system consisting of Bi2WO6/Au/CdS nanostructure for photocatalytic CO2 reduction into renewable hydrocarbon fuel

An all-solid-state Bi2WO6/Au/CdS Z-scheme system was constructed for the photocatalytic reduction of CO2 into methane in the presence of water vapor. This Z-scheme consists of ultrathin Bi2WO6 nanoplates and CdS nanoparticles as photocatalysts, and a Au nanoparticle as a solid electron mediator offering a high speed charge transfer channel and leading to more efficient spatial separation of electron–hole pairs. The photo-generated electrons from the conduction band (CB) of Bi2WO6 transfer to the Au, and then release to the valence band (VB) of CdS to recombine with the holes of CdS. It allows the electrons remaining in the CB of CdS and holes in the VB of Bi2WO6 to possess strong reduction and oxidation powers, respectively, leading the Bi2WO6/Au/CdS to exhibit high photocatalytic reduction of CO2, relative to bare Bi2WO6, Bi2WO6/Au, and Bi2WO6/CdS. The depressed hole density on CdS also enhances the stability of the CdS against photocorrosion.

Harnessing Vis–NIR broad spectrum for photocatalytic CO2 reduction over carbon quantum dots-decorated ultrathin Bi2WO6 nanosheets

The photocatalytic reduction of CO2 to energy-rich hydrocarbon fuels is a promising and sustainable method of addressing global warming and the imminent energy crisis concomitantly. However, a vast majority of the existing photocatalysts are only capable of harnessing ultraviolet (UV) or/and visible light (Vis), whereas the near-infrared (NIR) region still remains unexplored. In this study, carbon quantum dots (CQDs)-decorated ultrathin Bi2WO6 nanosheets (UBW) were demonstrated to be an efficient photocatalyst for CO2 photoreduction over the Vis–NIR broad spectrum. It is noteworthy that the synthesis procedure of the CQDs/UBW hybrid nanocomposites was highly facile, involving a one-pot hexadecyltrimethylammonium bromide (CTAB)-assisted hydrothermal process. Under visible light irradiation, the optimized 1CQDs/UBW (1 wt.% CQD content) exhibited a remarkable 9.5-fold and 3.1-fold enhancement of CH4 production over pristine Bi2WO6 nanoplatelets (PBW) and bare UBW, respectively. More importantly, the photocatalytic responsiveness of CQDs/UBW was successfully extended to the NIR region, which was achieved without involving any rare earth or noble metals. The realization of NIR-driven CO2 reduction could be attributed to the synergistic effects of (i) the ultrathin nanostructures and highly exposed {001} active facets of UBW, (ii) the excellent spectral coupling of UBW and CQDs, where UBW could be excited by the up-converted photoluminescence of CQDs, and (iii) the electron-withdrawing nature of the CQDs to trap the photogenerated electrons and retard the recombination of charge carriers.

Hierarchical nanostructures assembled from ultrathin Bi2WO6 nanoflakes and their visible-light induced photocatalytic property

With the aid of ethylene glycol and sodium dodecylbenzene sulfonate, the hierarchical Bi2WO6 nanoarchitectures assembled from nanoflakes could be attained by a facile solvothermal method. The synthetic strategy is versatile and environmentally friendly and a plausible growth-assembly process was proposed for the formation of the hierarchical nanostructures. The visible-light-irradiated photocatalytic activity was estimated by the degradation of rhodamine B. Compared with the sample prepared by a solid-state reaction, the visible-light-induced photocatalytic efficiency of the nanostructures was enhanced about 6times. The photocatalysis tests show that the nanostructures exhibit excellent photocatalytic activity and recycling performance, which were mainly ascribed to the unique hierarchical nanostructures and are expected to offer promising applications in the field of wastewater treatment.