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The broad application of highly electrocatalytic SnO2–Sb electrodes for wastewater treatment is limited by their short service lifetime. Herein, a novel substrate structure, tubular porous titanium, was applied to prepare a TiO2-NT/SnO2–Sb electrode, which could greatly improve the stability of the electrode for electrochemical oxidation process. Based on the analysis conducted using a field emission scanning electron microscope (FE-SEM), linked with an energy dispersive spectrometer (EDS), it was demonstrated that a solid solution between Sn and Sb presented a smooth surface of the tubular porous electrode. The crystalline structure and chemical composition of the electrode coating are determined by X-ray diffraction (XRD). Accelerated service life test reveals that under the 0.2 A cm−2 current density in a 0.5 M H2SO4 solution, the TiO2-NT/SnO2–Sb tubular porous electrode has the longest accelerated service lifetime of 68.9 h, which is 10.9 times that of the TiO2-NT/SnO2–Sb plate electrode. Cyclic voltammetry curves (CVs) and linear sweep voltammetry curves (LSVs) reveal the enhanced electroactive surface area and higher oxygen evolution potential (OEP = 1.85 V vs. Ag/AgCl) of the electrode. Moreover, the TiO2-NT/SnO2–Sb tubular porous electrode has the larger outer voltammetric charge q*. During the electrochemical oxidation of pyrimidine, the tubular system constructed using the TiO2-NT/SnO2–Sb tubular porous electrode as the anode also exhibited best electrocatalytic performance, and 97.9% pyridimine removal efficiency and 79.4% COD removal efficiency at 6 h were achieved.

A novel composite porous Sb-doped SnO2 (TiO2-NTs/m-SnO2-Sb) electrode with high specific surface area and excellent electrochemical oxidation performance was fabricated through the electrodeposition method with Pluronic F127 as a templating agent. The effect of calcination temperature on the structure and electrochemical performance of the composite porous SnO2-Sb electrodes has been studied. The microstructure and composition of the electrodes were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and N2 adsorption–desorption. The results revealed that the electrodeposition processes with a template can improve the coating structure effectively, and an appropriate calcination temperature can improve the mesostructure and crystallinity of the SnO2. Electrochemical measurements showed that the TiO2-NTs/m-SnO2-Sb electrode had a high oxygen evolution overpotential and large electrochemical active area. The electrocatalytic performance of the TiO2-NTs/m-SnO2-Sb electrode was further analyzed in the removal of a model pollutant (benzoic acid). The corresponding kinetic constant for benzoic acid removal was greatly enhanced, and the mesostructure significantly promoted the adsorption and diffusion of benzoic acid in the TiO2-NTs/m-SnO2-Sb electrode. The effects of initial benzoic acid concentration, supporting electrolyte concentration, current density and pH on the electrochemical degradation by the TiO2-NTs/m-SnO2-Sb electrode were investigated.

A series of iron–copper bimetallic nanoparticles supported on hollow mesoporous silica spheres with different Fe/Cu ratios were prepared using a simple post-impregnation and sodium borohydride reduction strategy. Different Fe/Cu ratios were obtained by addition of various amounts of ferric and copper salts. The catalysts were characterized by XRD, XPS, nitrogen physisorption, SEM and TEM. To explore the difference of catalytic reactivity among the various FeCu/HMS composites, Fenton-like catalytic oxidation of orange II was chosen as the model catalysis reaction. The catalytic results showed that the catalytic activity depended highly upon the Fe/Cu ratio. Particularly, 1/3 (2Fe6Cu/HMS) is the optimum Fe/Cu mass ratio to achieve the best catalytic activity. Based on the results of detection of ˙OH radicals and cyclic voltammograms, the important origin of the synergetic effect in 2Fe6Cu/HMS is considered as the combination of iron and copper species, which can accelerate the interfacial electron transfer in redox cycles of Fe3+/Fe2+ and Cu2+/Cu+ pairs, followed by the increase in the ˙OH radical generation. The 2Fe6Cu/HMS also possesses less pH dependence and maintains its high activity even under alkaline conditions. The optimal parameters in the degradation of 100 mg L−1 orange II are 27.4 mM of H2O2 with 1.0 g L−1 of catalyst, performed at a pH of 7.0 and 30 degree celsius. It is worth noting that 2Fe6Cu/HMS also possesses potential to treat a high concentration of dye pollutants. 77.7% of orange II was removed when conducted at 1000 mg L−1 initial dye concentration. The stability and recoverability of the composite catalyst were assessed it exhibited a good performance after 5 consecutive runs. The as-synthesized composite catalyst proved to be an attractive alternative for dye wastewater treatment applications.

Reduction from p-nitrophenol (PNP) to p-aminophenol (PAP) was studied in the cathodes of self-driven microbial fuel cells (MFCs), and the influence of electron donor (CH3COONa) & acceptor concentration, external resistance and electrolyte conductivity were investigated. The results showed that PNP reduction efficiencies reached 100% when initial concentrations were lower than 50 mg L−1. PAP formation efficiencies were promoted from 31.7 ± 2.1% to 76.4 ± 4.1%, by increasing CH3COONa concentration from 2000 mg L−1 to 4000 mg L−1. Decreasing the external resistance from 1000 Ω to 240 Ω improved the PAP formation by 4–5 times for higher currents. Increasing the electrolyte conductivity (controlled by total dissolved solids, TDS) could accelerate the PNP degradation process within 24 h. Illumina high-throughput sequencing showed the dominating bacteria on the biocathodes were: Ignavibacterium 14.37%, Ottowia 4.04%, Pseudomonas 3.66%, Proteiniphilum 2.50%, Chlorobaculum 1.67%, Nitrospira 1.62% (at the genera level). The bacteria might play vital roles in more efficient nitrophenol degradation in biocathode MFCs. Compared to the abiotic control, the main advantages of PNP degradation in biocathodes are higher PNP reduction & PAP formation efficiencies, less electron donor consumption and higher system efficiency. The self-driven MFC system could be a promising way to deal with nitroaromatic pollutants.

Sulfide-modified nanoscale zerovalent iron (S-nZVI) was effectively utilized for the reduction of various contaminants, despite its applicability being limited due to agglomeration, oxidation and electron loss. In this study, biochar (BC)-supported S-nZVI was prepared to enhance the reactivity of S-nZVI for nitrobenzene (NB) reduction. Scanning electron microscopy images showed that the S-nZVI particles were well-dispersed on the BC surface as well as in the channels. NB removal and aniline formation could be significantly enhanced by using S-nZVI@BC, as compared to S-nZVI and blank BC. NB removal by S-nZVI@BC followed the pseudo second-order kinetics model and Langmuir isotherm model, suggesting hybrid chemical reaction-sorption was involved. Furthermore, a possible reaction mechanism for enhanced NB removal by S-nZVI@BC was proposed, including chemical adsorption of NB onto S-nZVI@BC, direct reduction by S-nZVI and enhanced electron transfer. The high reducibility of S-nZVI@BC as well as its excellent antioxidation ability and reusability demonstrated its promising prospects in remediation applications.

In this study, a membrane-free bio-contact coupled bioelectrochemical system (BC-BES) was established for the enhanced reductive transformation of p-nitrophenol (PNP). The results showed that the electric field played a key role in both PNP reduction and p-aminophenol (PAP) formation. The vast majority of PNP was reductively transformed to PAP in the biocathode of BC-BES. At a cathode potential of −1000 mV vs. Ag/AgCl and hydraulic retention time (HRT) of 8.9 h, PNP removal rate as high as 18.95 ± 0.10 mol per m3 per day could be achieved in the BC-BES with acetate as the electron donor. High PNP removal and PAP formation could be achieved at low acetate dosage, high initial PNP concentration and short HRT, indicating the strong ability of the BC-BES to resist shock loading. Furthermore, partial mineralization of PAP was observed in the anode of the BC-BES, which was beneficial for the further polishing of the BC-BES effluent. Considering the advantages of high loading rate, low acetate consumption and high system stability, it is hoped that the application of this BC-BES will enhance the reductive removal of nitrophenols from wastewaters.

Accelerated reduction of typical multi-substituted nitroaromatic compounds (NACs), i.e., 2,4-dinitroanisole (DNAN), was achieved in an anaerobic system coupled with zero valent iron (ZVI), with the underlying role of ZVI in this process elucidated. Both removal of DNAN and formation of its final reductive product 2,4-diaminoanisole (DAAN) were notably improved in the ZVI coupled biosystem. In the ZVI coupled biosystem and biotic control system, complete removal of DNAN could be achieved within 4 h and 20 h, respectively. However, only 28.71 ± 5.06% of DNAN could be removed in the ZVI control system after 20 h. Correspondingly, the formation efficiencies of DAAN in the ZVI coupled biosystem, biotic control system and ZVI control system were 99.66 ± 0.70%, 16.99 ± 1.73% and 0.00 ± 0.00%, respectively. The increased DNAN removal and DAAN formation in the ZVI coupled biosystem was linked to the high accumulation of formate, low oxidation–reduction potential (ORP) and great pH self-buffering capability, which was provided by the addition of ZVI. Compared with the biotic control system, the production of CH4 was significantly accelerated in the ZVI coupled biosystem, indicating that a favorable environment for methanogens was created at the presence of ZVI. Especially, the ZVI coupled biosystem displayed a more stable performance in terms of DNAN reduction with the coexistence of the competitive electron acceptors, such as nitrate and sulfate. Therefore, the ZVI coupled biosystem could be a promising alternative to the conventional anaerobic reduction process for the removal of multi-substituted NACs from wastewater.

In this study, an integrated system comprised of zero-valent iron (ZVI) reduction and ZVI-based Fenton oxidation processes (ZVI-ZVI/H2O2) was applied for the selective removal of nitroaromatic compounds (NACs) from 2,4-dinitroanisole (DNAN) producing wastewater. For the ZVI reduction process, at a hydraulic retention time (HRT) of 6 h and neutral pH of 7.2, removal efficiencies of 2,4-dinitroanisole (DNAN), 2,4-dinitrophenol (DNP) and 2,4-dinitrochlorobenzene (DNCB) were as high as 81.3 ± 3.6%, 80.6 ± 1.8% and 90.9 ± 3.5%, respectively, demonstrating the excellent performance of ZVI. For the ZVI/H2O2 oxidation process, the optimal pH and H2O2 dosage were found to be 3.0 and 100 mmol L−1, respectively. Under these optimal conditions, NACs and their degradation intermediates could be removed selectively and effectively in the coupled ZVI reduction and ZVI/H2O2 oxidation process, as was indicated by the low UV254 value of 0.104 ± 0.003 and the low TOC removal efficiency of 32.4 ± 0.7% in the effluent. Ferrous ions could be generated in situ through the corrosion of the metal iron in both the ZVI reduction process and the ZVI/H2O2 oxidation process, giving rise to a potent Fenton-type reaction. In addition, the enhanced Fenton reaction with the aid of reaction between Fe0 and Fe3+ was probably due to the presence of Fe0 in the ZVI/H2O2 oxidation process, which promoted the utilization efficiency of the Fenton catalyst, i.e., Fe2+. Compared to the sequential ZVI reduction and homogeneous Fenton oxidation process (ZVI-Fe2+/H2O2), the low consumption of iron shavings, the reduced H2O2 consumption and the low yield of ferric sludge made the integrated ZVI-ZVI/H2O2 process promising for the treatment of NAC containing wastewater.

Ultrafiltration (UF) is an emerging membrane-based water separation process with potential application in drinking water treatment and for wastewater reuse. Nevertheless, membrane fouling decreases membrane performance and increases the frequency and cost of chemical cleaning. In this work, we present a method for loading ZnO nanoparticles into a polyethersulfone (PES) UF membrane to improve its fouling resistance. ZnO nanoparticles were synthesized with a sol–gel process using cost-effective precursors, resulting in particles with an average radius of 10 nm and ZnO content between 0.25 and 0.75 wt%. The hydrophilicity of the membrane surface was improved by the integration of ZnO nanoparticles, leading to a reduction in membrane contact angle (75.5 to 62.6°) and an increase in permeability (46.4 to 365.8 L m−2 h−1). Sodium alginate (SA), bovine serum albumin (BSA) and humic acid (HA) were chosen as model organic foulants to investigate fouling behavior of the fabricated membranes. Reduced fouling was conspicuously observed for ZnO/PES composite membranes compared to control membranes in all fouling cases. In order to better understand the fouling mechanism, atomic force microscopy (AFM) was used to quantify the intermolecular adhesion forces between the foulant and the clean or fouled membrane. Lower adhesion forces were observed for the modified membranes, indicating that the addition of sol–gel formed ZnO nanoparticles endows the PES UF membrane with an improved antifouling performance.