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Integrating pseudocapacitive materials with a conductive carbonaceous matrix is an efficient method to improve their capacitive deionization (CDI) performance. However, it remains a challenge to optimize the structure and chemical component of each part and strengthen the internal bonding between them for the further improvement of salt adsorption capacity (SAC). Herein, we report an ultrafine anatase TiO2/carbon nanocomposite confined into N-doped mesoporous carbon (TiO2/C@NMC) via a mesostructured polydopamine (mPDA) coated MOF strategy and subsequent pyrolysis. During the pyrolysis process, the mPDA shell could construct a spatially confined environment to effectively limit the aggregation of TiO2 nanoparticles and restrain their transformation into the rutile phase, contributing to the abundant faradaic active sites and strong interaction with a conductive carbon matrix. Moreover, the mPDA shell-derived N-doped mesoporous carbon provides abundant ion diffusion channels and alleviates the volume variation of the inner faradaic materials during the adsorption/desorption process. As a result, TiO2/C@NMC delivers an excellent SAC of 27.73 mg g−1 and stable regeneration properties over 50 cycles, demonstrating its great potential as a superior pseudocapacitive electrode for hybrid CDI (HCDI). This work offers a promising strategy to regulate the properties of pseudocapacitive materials for designing advanced HCDI devices.

Carbon-based electrodes play important roles in constructing efficient capacitive deionization (CDI) devices. Therefore, the rational design of carbon materials with optimized structure, composition, and morphology is crucial for further improving the CDI performance. Herein, a novel N, P co-doped eave-like hierarchical porous carbon (NP-EHPC) for CDI is reported. To prepare the NP-EHPC, the core–shell ZIF-8@AF particles are first prepared through the kinetically-controlled growth of zeolitic imidazolate framework-8 (ZIF-8) and polymerization of p-aminophenol and formaldehyde (AF), followed by subsequent pyrolysis and post-doping with phosphorus. Owing to the unique eave-like morphology, presence of abundant mesopores, and co-doping of P and N, the NP-EHPC exhibits a high desalination capacity of 24.14 mg g−1 in 500 mg L−1 NaCl solution at 1.2 V and long cycling stability of over 150 cycles. Moreover, the density functional theory (DFT) calculation results reveal that the co-doping of N and P atoms can greatly enhance the binding energies for Na and Cl atoms and lead to superior electrosorption capacity. This work provides a new insight into the design of high-performance carbon materials for the desalination of brackish water.

Defect-engineered UiO-66-NH2 was introduced into a polyamide layer to form a thin film nanocomposite (TFN) membrane. Simultaneous enhancements in permeance and selectivity to Na2SO4 solution were achieved.

A phenolic resin (PR)-assisted strategy to transform the zeolitic imidazolate framework (ZIF-67) into hierarchical Co/N-doped carbon rhombic dodecahedra for electrocatalysis is proposed for the first time. The hierarchical ZIF-67@PR composite carbon (HZPC) is obtained by coordinating the kinetic rate of precursors: nucleation/growth of ZIF-67 and polymerization of PR. The introduction of the PR polymer prevents agglomeration of cobalt nanoparticles, creates the well-distributed hierarchical porous structure and optimizes the composition. The advantages of the structure and composition endow HZPC with excellent oxygen reduction reaction (ORR) activity and long-term durability.

A polydopamine (PDA)-assisted interface-induction strategy is proposed to transform Zn, Co-zeolitic imidazolate frameworks (ZIFs) into hollow cactus-like carbon sheet/carbon nanotubes (CS/CNTs) for electrocatalysis for the first time. The precursor Zn, Co-ZIFs@PDA was obtained by the coordination between Co2+ (from ZIFs) and N atoms (from PDA). The introduction of PDA achieves simultaneous rational optimization of the composition (N-doping) and structure (2D/1D) by the interface-induction and confinement effect. The advantageous structure and composition endow CS/CNTs with outstanding oxygen reduction reaction activity and durability in alkaline solution.

The facile synthesis and engineering of highly active catalysts is an urgent requirement for the practical application of environmental remediation. In this report, we demonstrate the convenient synthesis of Co3O4-incorporated carbon composite (Co3O4/CC) by pyrolysis of a cobalt complex modified cotton cloth, which can be extended to other cellulose products (cotton, filter paper). Benefitting from the ultrafine Co3O4 particles with a mean particle size of ∼7.4 nm, the Co3O4/CC catalyst exhibits excellent performance for biphenol A (BPA) removal based on the sulfate radical (SO4˙−) process. Notably, as a proof-of-concept application, the Co3O4/CC packed column as a microreactor was designed and used in the continuous-flow reaction. Leveraging on the long half-life time period and high oxidability of SO4˙−, the degradation rate of BPA could increase above 95% at a flow rate of 2 mL min−1 when the total BPA solution reached to 1400 mL. The convenient synthesis of a high-performance catalyst and its efficient application to a continuous-flow reaction represent a further step towards practical application of SO4˙− based advanced oxidation processes.

The simultaneous rational optimization of structure and composition is extremely important for improving the catalytic performance of yolk–shell nanoreactors, but has been rarely achieved so far. In this work, yolk–shell Co3O4/C@SiO2 nanoreactors (YSCCSs) are facilely synthesized by coordinating the growth of Co-zeolitic imidazole framework (ZIF-67) crystals with the hydrolysis/condensation of tetraethoxysilane (TEOS). In this process, the preliminarily formed ZIF-67 crystals play an essential role in the final structure of YSCCSs, which can be used as the template for silicon hydroxide growth and the precursors for carbon and cobalt species. To present the advantages of YSCCSs as a catalyst, sulfate-radical-based advanced oxidation processes (SR-AOPs) for bisphenol A (BPA) degradation were chosen as the model reaction. For comparison, three other catalysts, including yolk–shell Co3O4@SiO2 nanoreactors (YSCSs), and Co3O4 and ZIF-67 derived Co3O4/C nanoparticles, were also tested. The results show that YSCCSs exhibit significant BPA degradation performance over YSCSs, and CO3O4 and Co3O4/C nanoparticles. This outstanding catalytic performance is ascribed to the rational optimization of the catalyst from the following two aspects: (i) confinement effect of yolk–shell nanostructure and the improved dispersity of carbon supported Co3O4 species enhance the catalytic activity and stability (structure optimization); and (ii) the existence of graphitized carbon accelerates the electron transport from the catalyst to peroxymonosulfate (PMS) and thus increases the reaction kinetics (composition optimization). The results of this research show that metal–organic framework (MOF)-derived nanoreactors with a rational structure and composition have a promising application prospect for environmental remediation.

A novel single-step approach, named phase transformation interfacial growth (PTIG), was developed for the fabrication of metal-organic framework membranes on polymeric substrates. Both the separation layer and the substrate were formed within the PTIG process. This innovative methodology paves a way for fabricating high-quality MOF membranes.

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.

The inherently granular nature of nitrogen and metal co-doped carbons derived from metal–organic frameworks (MOFs) hinders their practical application in the oxygen reduction reaction (ORR). In this work, we have developed a novel N, Co-containing MOF-based hierarchical carbon fiber as an ORR catalyst. The products (ZCP-CFs) are synthesized by the incorporation of a Zn, Co-zeolitic imidazolate framework (Zn, Co-ZIF) with electrospun Co2+/poly(acrylonitrile) fiber, followed by carbonization and acid leaching treatment. The effects of the pyrolysis temperature and precursor on the ORR performance of the final samples were systematically studied. The results indicated that the material prepared at 900 °C (ZCP-CFs-9) was identified as the best ORR catalyst in the series of samples. Further comparison among samples obtained from different catalyst precursors also demonstrated the superior performance of ZCP-CFs-9, with its more positive half-wave potential (−0.135 V vs. Ag/AgCl), higher diffusion-limited and kinetic-limiting currents and higher selectivity (number of electrons transferred n = ∼3.97) than Zn, Co-ZIF derived carbon and Zn, Co-ZIF free carbon fiber. Notably, the ZCP-CFs-9 catalyst exhibited very close activity to a commercial Pt/C catalyst with better durability and stronger tolerance to methanol crossover. The remarkable ORR performance may be ascribed to its unique structure, such as its large surface area and hierarchical porosity, the dispersed and protected Co nanoparticles and N functionalized carbon framework, as well as the abundant graphitic carbon and its 1D fibrous structure. Considering the diversity of MOFs and electrospinnable polymer precursors, this strategy may be further extended to other MOF-based carbon fibers for energy storage and conversion.

A flexible 3D hybrid PC/Ag surface-enhanced Raman scattering (SERS) substrate was fabricated through the combination of electrospinning and in situ chemical reduction. Due to the rough surface morphology and the intricate 3D structure, a high density of Raman "hotspots" was formed at the junctions of cross-linked nanofibers, resulting in excellent sensitivity to a probe molecule (4-aminothiophenol). The nanofibers were modified with l-cysteine to capture TNT molecules by the formation of a Meisenheimer complex, after which positively charged 4-ATP-labelled AgNPs were introduced to the system, which both generated more hotspots and led to a linear relationship between the TNT concentration and the SERS intensity of the labelled molecules. As a result, a good linear response ranging from 10-8 to 10-12 M was achieved, and the detection limit for TNT was as low as 2.05 × 10-13 M. This strategy demonstrates an ultra-sensitive approach for the detection of trace amounts of TNT, and a promising method for the detection of many other analogous explosives.

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.

Reductive degradation of three typical multi-substituted nitroaromatic pollutants by zero valent iron was comprehensively compared in terms of performance, kinetics, toxicity and mechanisms in this study. The results showed that 0.5 mM 2,4-dinitrochlorobenzene (DNCB), 2,4-dinitroanisole (DNAN) and 2,4-dinitrophenol (DNP) could be completely removed in the ZVI reduction system within 75 min, 90 min and 210 min, respectively. The pseudo first-order kinetics could well describe the reduction process of the three NACs by ZVI. The reduction rates of the three NACs follow the order of DNCB > DNAN > DNP, which was further confirmed by density functional theory computational analysis. Moreover, the acute toxicity of the three NAC effluents significantly decreased after treatment with ZVI. In addition, the mechanistic investigation revealed that the selective reduction of nitro groups on the three NACs was closely related to the characteristics of the functional groups on the benzene rings. The results of this study would increase the comprehensive understanding in terms of their performance, kinetics, toxicity and mechanisms involved in the reduction of multi-substituted NACs by ZVI, thus benefiting the effective treatment of wastewaters containing multi-substituted nitroaromatic pollutants due to ZVI.

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.

Ordered mesoporous carbon (OMC) membranes have broad applications such as size exclusion separation of molecules. In this work, a new method to prepare OMC hollow fiber membranes through a confined soft templating route is developed. In this method, commercialized polymeric hollow fiber ultrafiltration membranes were immersed in an ethanol solution containing a phenolic resin and a Pluronic triblock copolymer. Upon solvent evaporation, the phenolic resin and the surfactant self-assembled into the confined voids of the ultrafiltration membrane. After drying and pyrolysis, OMC hollow fiber membranes were obtained. The OMC hollow fiber membranes possess continuous membrane walls with an average thickness of 113 μm. The membrane wall has a hierarchical pore structure: one coming from hexagonally ordered mesoporous carbon with a pore diameter of ∼4.3 nm and the other being disordered defect holes with a size of 8–50 nm randomly distributed inside the OMC matrix. The gas permeance results indicate that the OMC hollow fiber membranes exhibit Knudsen diffusion behavior confirming their good quality.