•One-pot synthesis of Bi2S3/SnS2/Bi2O3 ternary heterojunction was presented.•Bi2S3/SnS2/Bi2O3 showed higher photocatalytic performance than that of bare Bi2S3.•This improvement was attributed to the construction of a double Z-scheme system.•The interface between microstructure and dye is a factor to enhance degradation.The construction of solid-state Z-scheme heterojunction photocatalytic system to efficiently tailor the photoinduced charge separation is of great significance to water purification. In this study, we reported for the first time the controlled preparation of Bi2S3/SnS2/Bi2O3 double Z-scheme heterojunction photocatalyst by a simple one-pot solvothermal route. The experimental results with regard to rhodamine B (RhB) degradation showed that the as-fabricated heterojunctions can significantly enhance photocatalytic activity in comparison with pure Bi2S3. In addition, the optimized BiS-4 sample possessed good simulated-sunlight photocatalytic efficiency towards the degradation of other types of dyes, including methyl orange (MO), methylene blue (MB), orange IV (OG IV) and crystal violet (CV). By further probing the charge separation and migration behaviors, studying the band structure, as well as conducting the active species trapping experiments, a possible double Z-scheme photocatalytic mechanism was proposed, which not only benefited the efficient photogenerated electron-hole pair separation but also demonstrated advanced capacity for the removal of organic dyes. This work would pave the route towards the design of novel Z-scheme photocatalytic systems for energy conversion and environmental remediation.Download high-res image (231KB)Download full-size image

•BDE-209 and BEH-TEBP dominated in the road dust samples.•BFR abundance in road dust declined as traffic density increased.•Traffic was deduced to be an important outdoor emission source of BFRs.•BFRs associated with road dust in China were estimated up to be 4980 kg year−1.The distribution of brominated flame retardants (BFRs) including ∑8PBDEs, DBDPE, BTBPE, EH-TBB, BEH-TEBP and PBEB in road dust (RD) collected in Xinxiang, China was characterized. Analysis of RD samples indicated that the BFR abundance declined as traffic density decreased, with total mean levels of 292, 184, 163, 104 and 70 ng g−1 dust at sites from traffic intersections, main roads, collector streets, bypasses and parks, respectively. A possible explanation for this phenomenon is that the majority of BFRs may be emitted from the interior of vehicles via their ventilation systems. Of the 13 analyzed substances, BDE-209 and BEH-TEBP were the most abundant components in RD from Xinxiang. Similar amounts of ∑BDEs excluding BDE-209 were found at different types of sampling sites, and thus, atmospheric deposition is also a probable source of BFRs in RD which can be subject to air transportation. The main PBDE sources were traced to commercial products including DE-71, Bromkal 79-8DE, Saytex 201E and Bromkal 82 DE mixtures. Our results confirm that the use of deca-BDE commercial mixture is a major source of PBDE contamination in RD. Risk assessment indicated the concentrations of BFRs in RD in this study do not constitute a non-cancer or cancer risk to humans through ingestion. Annual emission fluxes of the commonly detected BFRs via RD in China were estimated to be up to 4980 kg year−1.Download high-res image (337KB)Download full-size image

•One-pot synthesis of sphere-shaped BiVO4/RGO composite was presented.•The composite showed improved direct sunlight-driven photocatalytic activity.•The origin of the enhanced photocatalytic performances was discussed.•h+ directly oxidation of substrates suppressed the formation rate of OH.Sphere-shaped bismuth vanadate (BiVO4) was synthesized by a simple and cost-effective low temperature hydrothermal method. In order to improve the photo-response of the prepared sphere-shaped BiVO4 in natural sunlight, the as-synthesized BiVO4 incorporated with graphene oxide (GO) was assembled into sphere-shaped BiVO4/reduced graphene oxide (RGO) composites. For studying their morphological, physical, optical, and photo-chemical properties, the obtained composites were well characterized with the aid of various physicochemical techniques, such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible diffuse reflectance, N2 adsorption/desorption and electrochemical measurements. In addition, the photocatalytic performance of the prepared BiVO4 and BiVO4/RGO composites were evaluated by monitoring the degradation of Rhodamine B (RhB)-contained wastewater under natural sunlight irradiation, where the highest photocatalytic degradation efficiency can be achieved for the BiVO4/RGO composites with 3 wt% RGO dosage (approx. 68.85% increase compared with that of pure sphere-shaped BiVO4) The improved photocatalytic activity of BiVO4/RGO composite is attributed to the formation of well-defined BiVO4-RGO interfaces, which greatly enhances the charge separation efficiency.

•Flower-like BiOCl/RGO composites were synthesized with a hydrolysis reaction.•SN could be partially degraded by BiOCl/RGO under natural sunlight irradiation.•The mechanism was proved with the help of FTIR, NMR, IC and MS.•The main intermediate product of SN was sulfanilic acid.Flower-like bismuth oxychloride (BiOCl) catalysts were synthesized with a facile hydrolysis reaction, where the synthesized BiOCl products were further decorated with the prepared graphene oxide (GO) to form novel BiOCl/reduced graphene oxide (BiOCl/RGO) composites. The as-synthesized materials were well characterized with the aid of various techniques, before they were used as photocatalysts for the degradation of sulfanilamide (SN) aqueous solution. The BiOCl/RGO composites contained 1 wt% RGO exhibited superior photocatalytic response, where the degradation rate of SN at 82.7% stayed 30% higher than that of pure BiOCl. The enhanced photocatalytic performances of BiOCl/RGO composites were neither related to the surface area values nor the bandgap of the fabricated photocatalysts, but associated with the enhanced visible light absorption and advanced electron transfer ability. On a basis of the analysis on the SN intermediate products by HPLC, IC, FTIR, 1H NMR, 13C NMR and MS, the degradation pathway of SN was speculated, where it was confirmed that the main intermediate product of SN was sulfanilic acid.

Visible light-responsive photocatalytic technology holds great potential in water treatment to enhance purification efficiency, as well as to augment water supply through the safe usage of unconventional water sources. This review summarizes the recent progress in the design and fabrication of visible light-responsive photocatalysts via various synthetic strategies, including the modification of traditional photocatalysts by doping, dye sensitization, or by forming a heterostructure, coupled with π-conjugated architecture, as well as the great efforts made within the exploration of novel visible light-responsive photocatalysts. Background information on the fundamentals of heterogeneous photocatalysis, the pathways of visible light-responsive photocatalysis, and the unique features of visible light-responsive photocatalysts are presented. The photocatalytic properties of the resulting visible light-responsive photocatalysts are also covered in relation to the water treatment, i.e., regarding the photocatalytic degradation of organic compounds and inorganic pollutants, as well as photocatalytic disinfection. Finally, this review concludes with a summary and perspectives on the current challenges faced and new directions in this emerging area of research.

•A dual Bi-based ball-shaped material BiOF/Bi2O3 were facilely synthesized.•The composition effect of BiOF/Bi2O3/RGO hybrid were probed for the first time.•The photocatalytic performances were evaluated upon natural sunlight irradiation.•The composites showed a twofold augmentation in the degradation efficiency.•The hybrid photocatalyst can be easily recycled for three times.A facile and efficient route for the controllable synthesis of BiOF/Bi2O3 nanostructures by hydrolysis method was reported, where the as-prepared BiOF/Bi2O3 was subsequently incorporated with reduced graphene oxide (RGO) sheets to form BiOF/Bi2O3/RGO composites. The obtained BiOF/Bi2O3 and BiOF/Bi2O3/RGO composites were well characterized with the aid of various techniques to probe their crystallographic, morphological, chemical and optical properties. Photocatalytic capacities of the pure BiOF/Bi2O3 and BiOF/Bi2O3/RGO composites have been investigated by the degradation of Rhodamine B (RhB)-contained wastewater under natural sunlight irradiation. A twofold augmentation of degradation efficiency was in turn observed for BiOF/Bi2O3/RGO composites compared with that of pure BiOF/Bi2O3 under the natural sunlight irradiation. The optimum conditions, the effects of the active species and stabilities in photocatalytic performances of the BiOF/Bi2O3/RGO composites have also been probed.

To date, growing interest has been devoted to fabricating graphene–metal oxide hybrid composites for a plethora of applications including photocatalysis. However, controllable synthesis of such composite materials by virtue of facile and rational routes still remains challenging. Herein, we report, for the first time, the design of an in situ, ultrasonic-assisted growth strategy for the tailored production of well-dispersed, rhombus-shaped ZnMoOx/reduced graphene oxide (RGO) composites. The resultant composites exhibit a superior and recyclable natural-sunlight-driven photocatalytic activity toward the degradation of Rhodamine B, where the highest photocatalytic degradation efficiency can be achieved for the ZnMoOx/RGO composites with 3 wt% RGO dosage. In addition, the synthesized hybrids possess a high areal capacitance with a good cycling performance, as well as an interesting noticeable antibacterial activity, offering special insights into the usage of such composites for a wide range of applications.

•Facile fabrication of uniform ZnO nanoclusters and ZnO/RGO nanocomposites was realized.•The photocatalytic properties of ZnO nanoclusters and ZnO/RGO nanocomposites were studied.•ZnO/RGO nanocomposites exhibited superior visible-light-driven photocatalytic activity for the metronidazole degradation.This study reported the first-time fabrication of uniform ZnO nanoclusters through a facile carbon nanosphere template-assisted approach, where the synthesized ZnO products were further decorated with the prepared reduced graphene oxide (RGO) to form novel ZnO/RGO nanocomposites. The as-synthesized materials were well characterized with the aid of various techniques, before they were used as photocatalysts for the degradation of metronidazole in the aqueous environment. Accordingly, the photocatalytic activity of the ZnO nanoclusters could be enhanced by coupling with RGO, where a large improvement (approx. 32.4% increase compared with pure ZnO) in the visible-light-driven degradation of metronidazole was observed on the prepared ZnO/RGO hybrid nanocomposites. Such study may provide insight into the usage of the ZnO/RGO composite in addressing broader environmental issues. The synthetic route employed in this work might also be extended to a useful technique for the preparation of assemblies of other materials based on nanoscale templates via easily-manipulated solution methods.

•Dumbbell-shaped BiVO4/RGO hybrid composite was targetedly synthesized.•Dumbbell-shaped BiVO4/RGO composite exhibited augmented photocatalytic activity under natural sunlight irradiation.•The cycle-stabilized photocatalytic performances of the composites were been probed.A simple and efficient route for the controllable synthesis of dumbbell-shaped BiVO4 hierarchical structures at a large scale with uniform size and shape distributions was demonstrated, where the as-synthesized BiVO4 products were then incorporated with prepared reduced graphene oxide (RGO) sheets to form dumbbell-shaped BiVO4/RGO composites. The obtained composites were well characterized with the aid of various techniques to study their morphological, physical, optical, and photo-chemical properties. Photocatalytic capacities of the pure BiVO4 dumbbells and BiVO4/RGO composites have been evaluated by investigating the degradation of Rhodamine B (RhB)-contained wastewater under natural sunlight irradiation, where a noticeable augmentation in the natural-sunlight-driven decolorization efficiency (approx. 26% increase compared with that of pure BiVO4) of RhB could be achieved on the prepared BiVO4/RGO composites under experimentally optimum conditions. The cycle-stabilized photocatalytic performances of the BiVO4/RGO composites have also been probed.Facile synthesis of dumbbell-shaped BiVO4 hierarchical structures/reduced graphene oxide (RGO) hybrid (BiVO4/RGO) composite was reported. The prepared composite exhibited augmented natural-sunlight-driven photocatalytic activity in the degradation of RhB, which could be attributed to the enhanced light absorption efficiency and reduced charge recombination rate within the hybrid structures with the presence of RGO.

Development of highly efficient anode is critical for enhancing the power output of microbial fuel cells (MFCs). The aim of this work is to investigate whether modification of carbon paper (CP) anode with graphene (GR) via layer-by-layer assembly technique is an effective approach to promote the electricity generation and methyl orange removal in MFCs. Using cyclic voltammetry and electrochemical impedance spectroscopy, the GR/CP electrode exhibited better electrochemical behavior. Scanning electron microscopy results revealed that the surface roughness of GR/CP increased, which was favorable for more bacteria to attach to the anode surface. The MFCs equipped with GR/CP anode achieved a stable maximum power density of 368 mW m−2 under 1,000 Ω external resistance and a start time for the initial maximum voltage of 180 h, which were, respectively, 51 % higher and 31 % shorter than the corresponding values of the MFCs with blank anode. The anode and cathode polarization curves revealed negligible difference in cathode potentials but obviously difference in anode potentials, indicating that the GR-modified anode other than the cathode was responsible for the performance improvement of MFC. Meanwhile, compared with MFCs with blank anode, 11 % higher decolorization efficiency and 16 % higher the chemical oxygen demand removal rate were achieved in MFC with GR-modified anode during electricity generation. This study might provide an effective way to modify the anode for enhanced electricity generation and efficient removal of azo dye in MFCs.

•N2O generation was increased with increasing internal recycle ratio in A2O wastewater treatment process.•Nitrous oxide reductase is more sensitive to oxygen than nitrate reductase and nitrite reductase.•Improvements in nitrogen removal and N2O reduction revealed seeming contradiction.•NosZ gene copies reflect the capacity of the system for reducing N2O to N2.To evaluate the effects of internal recycle ratio on nitrous oxide (N2O) generation, we set up three laboratory-scale anaerobic–anoxic–oxic (A2O) wastewater treatment processes, with internal recycle ratios of 100%, 200%, and 300%, respectively. Total nitrogen (TN) removal was markedly enhanced from 45.8% to 61.9%, as the internal recycle ratio increased from 100% to 300%. N2O generation was increased from 3.47 to 9.81 × 10−2 mg/L during the treatment process, with the anoxic section showing the largest N2O increment from denitrification. This phenomenon is attributed to the increased amount of nitrate (NO3−-N) substrate available for denitrification, due to the increased volume of internal recycle liquid, as well as the increased amount of oxygen, which could restrain the activity of nitrous oxide reductase brought to the anoxic section. Nitrous oxide reductase was more sensitive to oxygen than nitrate and nitrite reductases. Microorganism analysis indicated that the population of nosZ gene-containing bacteria was only slightly affected by the recycle ratio. However, the number of nosZ gene copies decreased as the internal recycle ratio increased from 100% to 300%; this result reveals noticeable decreases in the denitrification capacity of the system for reducing N2O to N2.Download full-size image