Phosphomolybdic acid–reduced graphene oxide (PMoA–rGO) nanocomposites are fabricated by a photochemical reduction method. They are characterized by ultraviolet-visible spectra, scanning electron microscope images, Fourier transform infrared spectroscopy, Raman spectra and X-ray photoelectron spectroscopy in order to confirm that oxygen-containing functional groups on GO are replaced by PMoA and that GO is reduced to rGO in the photo-reduction process. The electrochemical properties of PMoA–rGO are investigated by cyclic voltammetry, which shows that the PMoA–rGO modified glassy carbon electrode has high electrocatalytic activity in acid solution via a fast, surface-controlled electron transfer process. The results indicate that the use of rGO not only increases the electroactive surface area, but also facilitates electron transfer due to its high electric conductivity.

New hybrid films were synthesized by Fe2+ doping into polyoxometalates acid (POMs)/polyacrylamide (PAM) system, and the effect of Fe2+ doping on microstructure and photochromic properties was studied via transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), ultraviolet–visible spectra (UV–vis) and X-ray photoelectron spectroscopy (XPS). The shape of molybdenumphosphoric acid (PMoA) particles changed from well dispersed sphere to irregular conglomeration. The vibrational spectra of FT-IR verified that the hydrogen bonding between PMoA and PAM was weakened after Fe2+ doping. The hybrid films exhibited a good photochromic property, which changed from colorless to blue under UV irradiation. The color change intensity of PMoA/PAM film was 2.56 times stronger than that of Fe2+/PMoA/PAM under the same condition. XPS results indicated that the amount of PMoA in photo-reductive reaction was decreased after Fe2+ doping, which resulted in the photochromic efficiencies weakened.Highlights► Fe2+ doping had a great effect on the microstructure and photochromic properties. ► The absolute absorbency of irradiated PMoA/PAM films was stronger than Fe2+/PMoA/PMA films. ► The competition with Fe2+ resulted in decrease of PMoA in photoreductive reaction.

The electrochemical properties of anthraquinone monosulfonate (AQS) adsorbed on the basal plane of chemically-reduced graphene oxide (RGO) by π–π stacking interaction were investigated. The AQS/RGO nanocomposites were synthesized via a simple reduction–adsorption method and characterized with various techniques, and the surface concentration of AQS on the basal plane of RGO was estimated to be 1.72 × 10−12 mol cm−2. Electrochemical tests showed that the AQS/RGO nanocomposites accelerated the heterogeneous electron transfer, when ferro/ferricyanide was used as a redox probe, and RGO facilitated the electron transfer between AQS and the surface of glassy carbon electrode, producing a well-defined redox couple centered at −0.490 V versus SCE at neutral medium. Compared with AQS and RGO modified glassy carbon (GC) electrode, the AQS/RGO nanocomposites showed better electrocatalytic activity towards oxygen reduction reaction. Rotating disk electrode data showed that the reduction of O2 on AQS/RGO/GC electrode underwent a two-electron process to H2O2 at low overpotential and shifted to four-electron reduction to H2O at relatively high overpotential. The present work demonstrates that AQS can be an efficient catalyst when noncovalently functionalized on the basal plane of RGO for electrochemical applications.

Anthraquinone/graphene nanocomposite was synthesized via a facile two-step electroreduction process and was characterized with various techniques. The electrocatalytic activity of the as-prepared anthraquinone/graphene nanocomposite towards O2 reduction was studied in neutral medium. Results show that most of oxygen-containing functional groups on graphene oxide were removed after electroreduction. Anthraquinone/graphene nanocomposite exhibits excellent electrocatalytic performance for two-electron reduction of oxygen, suggesting its potential as metal-free electrocatalysts for oxygen reduction reaction.Highlights► Anthraquinone/graphene (AQ/GE) nanocomposite was prepared by two-step electroreduction method. ► Raman, FT-IR and XPS spectra indicate vanishing of most oxygen functionalities on graphene oxide via electroreduction. ► GE is an excellent support for grafting AQ electrocatalysts. ► AQ/GE nanocomposite showed high catalytic activity for 2e− reduction of oxygen in neutral medium.

Polyaniline (PANI) film in the form of emeraldine salt (ES) doped with anthraquinone-2-sulfonate (AQS) was synthesized by a novel electrochemical doping-dedoping-redoping method on pre-activated spectroscopically pure graphite electrode surface. SEM showed the highly porous microstructure with sponge-like morphology of the AQS/PANI hybrid film, which has more available active sites for facilitating electron transfer and energy efficiency of redox reactions. FTIR and UV-vis spectra demonstrated the incorporation of AQS into the conductive PANI matrix. Cyclic voltammetric (CV), electrochemical impedance spectroscope (EIS), rotating ring-disk electrode (RRDE) and chronoamperometry (CA) techniques indicated that the AQS/PANI composite has high electrocatalytic activity and remarkable stability for the two-electron reduction of oxygenvia an electrochemical–chemical mechanism at the base of the porous PANI film. The acid centers of PANI (protonated imine group) played an important role not only in two internal redox transform processes, but also in an external charge transfer reaction during the electrocatalytic reduction of oxygen. The incorporation of anionic AQS groups into PANI matrix to prepare electroactive PANI using the electrochemical doping-dedoping-redoping method is conceptually new, and may be extended to the development of new functional materials from many other conducting polymers and quinonoid compounds for wide applications in catalysis, sensors, molecular electronics, and so on.

This study focuses on the preparation of a new type of Prussian Blue/polyaniline (PB/PANI)-modified electrode as oxygen reduction cathode, and its availability in microbial fuel cell (MFC) for biological power generation. The PB/PANI-modified electrode was prepared by electrochemical and chemical methods, both of which exhibited good electrocatalytical reactivity for oxygen reduction in acidic electrolyte. The MFC with PB/PANI-modified cathode aerated by either oxygen or air was shown to yield a maximum power density being the same with that of the MFC with liquid-state ferricyanide cathode, and have an excellent duration as indicated by stable cathode potential for more than eight operating circles. This study suggests a promising potential to utilize this novel electrode as an effective alternative to platinum for oxygen reduction in MFC system without losing sustainability.

So far, membrane fouling in membrane bioreactors (MBRs) is still not fully understood due to the complex nature of membrane foulants. The challenge to the study of membrane fouling behavior and membrane fouling mechanisms calls for the use and/or development of novel approaches for clearer understanding of membrane foulants such as structure and configuration of fouling layer, physicochemical and biological nature of membrane foulants, and deposition behavior of microorganisms on membranes. As such, MBR fouling can be characterized by the following: (i) visualization of cake morphology, (ii) analysis of chemical composition and, (iii) identification of microbial community structure. The state-of-the-art approaches used for membrane fouling study are critically reviewed in this paper. The advantages and limitations of currently used approaches are discussed as well. Lastly, potential approaches that can be applied for the characterization of membrane fouling in MBRs in the future are mentioned.

To reduce the amount of phosphate buffer currently used in Microbial Fuel Cell's (MFC's), we investigated the role of biological nitrification at the cathode in the absence of phosphate buffer. The addition of a nitrifying mixed consortia (NMC) to the cathode compartment and increasing ammonium concentration in the catholyte resulted in an increase of cell voltage from 0.3 V to 0.567 V (external resistance of 100 Ω) and a decrease of catholyte pH from 8.8 to 7.05. A large fraction of ammonium was oxidized to nitrite, as indicated by an increase of nitrate-nitrogen (NO3−–N). An MFC inoculated with an NMC and supplied with 94.2 mgN/l ammonium to the catholyte could generate a maximum power of 2.1 ± 0.14 mW (10.94 ± 0.73 W/m3). This compared favorably to an MFC supplied with either buffered or non-buffered solution. The buffer-free NMC inoculated cathodic chamber showed the smallest polarization resistance, suggesting that nitrification resulted in improved cathode performance. The improved performances of the phosphate buffer-free cathode and cell are positively related to biological nitrification, in which we suggest additional protons produced from ammonium oxidation facilitated electrochemical reduction of oxygen at cathode.

This paper describes a facile approach for the surface modification of polypropylene non-woven fabric (NWF) by PVA (polyvinyl alcohol) to determine its filterability. The NWF surface modification involved the physical adsorption of PVA to immobilize PVA on the NWF surface. Chemical structures and morphological changes of the PVA-modified NWF sample surfaces were characterized in details by attenuated total reflectance Fourier transform infrared (FTIR/ATR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron micrograph (SEM), and water contact angle measurements. Results reveal that PVA concentration has significant effects on the immobilization degree of PVA, and pure water contact angle on the NWF surface decreases with the increase in PVA concentration indicating an enhanced hydrophilicity for the modified NWF. Coomassie brilliant blue G250 method was utilized to quantify the static bovine serum albumin solution adsorption on the NWF surface. This adsorption was used to indicate the protein fouling property of the modified NWF with PVA. The results showed that after PVA modification, the polar groups such as C–O, C–O–C were introduced to the NWF surface, hydrophilicity was improved, and water static contact angles were decreased from 86 ± 1° to 43 ± 3°, the amount of bovine serum albumin (BSA) static adsorption on modified NWF was decreased by 83.4%. Membrane bioreactor was used for the treatment of a pharmaceutical wastewater to determine the filterability of modified NWF. The results revealed that flux declination of modified NWF was only 12%, in comparison of the original NWF of 40%. The anti-fouling property for the modified NWF was enhanced greatly.

Conducting polypyrrole (PPy) films with anthraquinonedisulfonate (AQDS) incorporated as dopants were prepared by electropolymerization of the pyrrole monomer in the presence of anthraquinone-2,6-disulfonic acid, disodium salt on a graphite electrode from aqueous solution. Cyclic voltammetry (CV), scanning electron microscope (SEM), and Fourier transfer infrared spectroscopy (FTIR) technologies were used to characterize the resulting AQDS/PPy composite film. The electrocatalytic activities of the bare graphite and the AQDS/PPy/graphite cathodes toward oxygen reduction and Fe2+ regeneration were studied by using cyclic voltammetry and cathodic polarization technologies. In addition, the electron-Fenton degradation of amaranth azo dye was also studied with the potentiostatic electrolysis mode, using the bare graphite and the AQDS/PPy/graphite as cathode and Fe3+ as catalyst. The results show that (i) H2O2 generation and Fe2+ regeneration mainly depend on the cathode materials utilized, (ii) solution pH, cathodic potential, and oxygen flow rate influence H2O2 accumulation and current efficiency greatly, while the effect of AQDS doping concentration is insignificant, and (iii) Fe3+ concentration influences the electro-Fenton oxidation ability and efficiency; the main oxidizing species is hydroxyl radical (•OH) formed in the reaction solution from Fenton’s reagent electrogenerated concurrently at the cathode.

Poly (vinylidene fluoride) (PVDF)/graphene oxide (GO) ultrafiltration (UF) membranes are prepared via immersion precipitation phase inversion process. Raman spectra results indicate the existence of GO in PVDF/GO UF membranes. SEM pictures show that the PVDF/GO UF membranes present developed finger-like pore substructure along with the increased porosity and mean pore size. As revealed by FT-IR spectra, large amount of OH groups are appeared due to the introduction of GO nanosheets that improve the surface hydrophilicity of the modified membrane. In permeation experiment, the water flux is improved after blending GO. With 2 wt% GO content, the pure water flux and permeation flux reach peak values of 26.49 L/m2 h and 14.21 L/m2 h, increasing 79% and 99% respectively. Furthermore, the flux recovery ratio (FRR) and the fouling resistance results suggest that PVDF/GO UF membranes have better antifouling properties than pure PVDF due to the changes of surface hydrophilicity and membrane morphologies. AFM images show that UF membranes have a smoother surface with a higher efficient filtration area, which would enhance antifouling properties.

•The storage of anammox bacteria at 4 °C was better than that at room temperature.•The cell membrane of bacteria was not damaged by sharp edges of the GO nanowalls.•Adding 0.1 g/L GO enhanced the activity of anammox and shortened the start-up time.•GO can be used as a scaffold for anammox bacteria to promote the granular process.In this study, the reactivation of three kinds of anammox sludge was investigated, including the sludge stored at room temperature (sludge A), at 4 °C without and with 0.1 g/L graphene oxide (GO) (sludge B and C). The reactors were operated for about 5 weeks. The reactivation of anammox bacteria was evaluated by measuring the total nitrogen removal rate, special anammox activity (SAA) and extracellular polymeric substances (EPS). The characterization of microorganisms was observed by using scanning electron microscope (SEM) and fluorescence in situ hybridization (FISH). The activity and properties of sludge C were optimal. The final total nitrogen removal rate of reactor B and C achieved about 1200 mg/L/day, while reactor A achieved only 773.6 mg/L/day. According to Mastersizer, the particle size of reactor A, B and C increased to 153, 189 and 230 μm, respectively. The time reaching the original NRR (700 mgN/L/day) was 35 days, 21 days and 12 days, and the specific anammox activity (SAA) eventually fixed at 0.30, 0.42, 0.44 g N (g VSS day)−1, respectively. The total EPS, the polymers carbohydrate and proteins in the extracted EPS decreased individually. Scanning electron microscope (SEM) showed the granulation process and the change of particle size in the cultivated sludge. FISH analysis confirmed the existence of other bacteria and anammox bacteria became the dominant population. All results indicated that the sludge stored at 4 °C was easier to reactivate, and the addition of 0.1 g/L GO would further promote the reactivation of anammox.

A membrane aerated biofilm reactor is a promising technology for wastewater treatment. In this study, a carbon-membrane aerated biofilm reactor (CMABR) has been developed, to remove carbon organics and nitrogen simultaneously from one reactor. The results showed that CMABR has a high chemical oxygen demand (COD) and nitrogen removal efficiency, as it is operated with a hydraulic retention time (HRT) of 20 h, and it also showed a perfect performance, even if the HRT was shortened to 12 h. In this period, the removal efficiencies of COD, ammonia nitrogen (NH4+-N), and total nitrogen (TN) reached 86%, 94%, and 84%, respectively. However, the removal efficiencies of NH4+-N and TN declined rapidly as the HRT was shortened to 8 h. This is because of the excessive growth of biomass on the nonwoven fiber and very high organic loading rate. The fluorescence in situ hybridization (FISH) analysis indicated that the ammonia oxidizing bacteria (AOB) were mainly distributed in the inner layer of the biofilm. The coexistence of AOB and eubacteria in one biofilm can enhance the simultaneous removal of COD and nitrogen.

•A2O2 has a better performance in pollutants removal than AOAO process.•Average removal rate of COD was 94% in A2O2 system.•Recycle ratio could strongly affect the nitrification efficiency in A2O2 system.•The best NH4+N removal rate was 90.7% and at recycle ratio was 2.•Refractory organic had a better bio-degradability with co-substrate.In this paper, a pre-denitrification biofilm process was conducted to investigate the degradation of Lurgi coal gasification wastewater (CGW). Under the HRT of 72 h and recycle ratio (R) of 2, 80% of COD and 48.9% of NH4+N could be removed in AOAO system. In order to improve the pollutants removal efficiency, the order of aerobic reactor (O1) and anaerobic tank (A2) was reversed to build the A2O2 system. It was found that A2O2 had a better pollutant removal at the same operation conditions, the maximum removal rates of COD and NH4+N were 94.4% and 90.7%, respectively. Recycle ratio (R) had negligible effect on COD removal, but could strongly affect nitrification efficiency in A2O2. The NH4+N removal rate increased from about 75% at R was 1–90.72% at R was 2, but decreased to 80.31% at R was 3. Batch test results shown that the bio-degradability of nitrogenous heterocyclic compounds (pyridine, pyrrole and imidazole) could be improved as carbon source for denitrification under the condition of cosubstrate (phenol was used in this test) was introduced. Therefore, the results illustrated that the pre-denitrification biofilm process of A2O2 could treat the CGW effectively.

•The preparation conditions of PVDF/GO membranes were optimized by Taguchi design.•The optimal conditions were 12 wt.% PVDF, 5 wt.% PVP and 3 wt.% GO in DMAC.•The solution type was the most effective factor.•The introduction of GO improved antifouling properties of composite membranes.Poly(vinylidene fluoride) (PVDF)/graphene oxide (GO) microfiltration membranes were prepared via phase inversion process. The Taguchi experiments were designed to optimize the preparation conditions of composite membranes. PVDF content, solution type, GO content, and poly-(N-vinyl-2-pyrrolidone) (PVP) content were chosen as important effecting parameters. Membrane filtration resistance was optimized by calculating the signal-to-noise (S/N) ratio of the parameters. The group of PVDF = 12 wt.%, solution type = N, N-dimethylacetamide (DMAC), GO = 3 wt.%, and PVP = 5 wt.% was the optimal combination, and solution type was the most effective factor. Scanning electron microscope (SEM) images showed that all membranes had thicker finger-like substructures. To further investigate the influence of GO on antifouling and mechanical properties, the pure PVDF and PVDF/GO composite membranes (3.0 wt.%) were prepared according to the optimum conditions. The PVDF/GO composite membranes presented better antifouling performances due to the improvement of membrane hydrophilicity. The tensile strength and Young's modulus reached values of 10.33 and 148.47 MPa, which corresponded to a 55.11% and 67.14% increase, respectively.

Aerobic granular sludge was cultivated adopting internal-circulate sequencing batch airlift reactor. The contradistinctive experiment about short-term membrane fouling between aerobic granular sludge system and activated sludge system were investigated. The membrane foulants was also characterized by Fourier transform infrared (FTIR) spectroscopy technique. The results showed that the aerobic granular sludge had excellent denitrification ability; the removal efficiency of TN could reach 90%. The aerobic granular sludge could alleviate membrane fouling effectively. The steady membrane flux of aerobic granular sludge was twice as much as that of activated sludge system. In addition, it was found that the aerobic granular sludge could result in severe membrane pore-blocking, however, the activated sludge could cause severe cake fouling. The major components of the foulants were identified as comprising of proteins and polysaccharide materials.

This study investigated degradation of azo dyes by using microbial fuel cell (MFC)-Fenton system, in which in-situ production of H2O2 was achieved through two-electron reduction of oxygen in neutral catholyte. Based on sequential operation where H2O2 was synthesized followed by Fenton reaction, the MFC-conventional Fenton system was shown able to remove amaranth (75 mg/L) with the ratio of 82.59% within 1 h when 1 mmol/L Fe2+ was applied. For the MFC-electrochemical Fenton system with 0.5 mmol/L Fe3+ addition, the removal ratio of amaranth (75 mg/L) could reach 76.43% and cathode potential could keep stable for 1 h. Meanwhile, a maximum power density of 28.3 W/m3 was obtained, which was larger than that of 17.2 W/m3 when K3Fe(CN)6 was used as cathodic electron acceptor. This study suggests a proof-in-concept new manner for biorefractory wastewater treatment using the energy produced from biodegradable wastewater along with electrical energy generation simultaneously, which makes dye-containing wastewater treatment a green treatment process and more sustainable.

Phosphomolybdic acid–reduced graphene oxide (PMoA–rGO) nanocomposites are fabricated by a photochemical reduction method. They are characterized by ultraviolet-visible spectra, scanning electron microscope images, Fourier transform infrared spectroscopy, Raman spectra and X-ray photoelectron spectroscopy in order to confirm that oxygen-containing functional groups on GO are replaced by PMoA and that GO is reduced to rGO in the photo-reduction process. The electrochemical properties of PMoA–rGO are investigated by cyclic voltammetry, which shows that the PMoA–rGO modified glassy carbon electrode has high electrocatalytic activity in acid solution via a fast, surface-controlled electron transfer process. The results indicate that the use of rGO not only increases the electroactive surface area, but also facilitates electron transfer due to its high electric conductivity.

Polyaniline (PANI) film in the form of emeraldine salt (ES) doped with anthraquinone-2-sulfonate (AQS) was synthesized by a novel electrochemical doping-dedoping-redoping method on pre-activated spectroscopically pure graphite electrode surface. SEM showed the highly porous microstructure with sponge-like morphology of the AQS/PANI hybrid film, which has more available active sites for facilitating electron transfer and energy efficiency of redox reactions. FTIR and UV-vis spectra demonstrated the incorporation of AQS into the conductive PANI matrix. Cyclic voltammetric (CV), electrochemical impedance spectroscope (EIS), rotating ring-disk electrode (RRDE) and chronoamperometry (CA) techniques indicated that the AQS/PANI composite has high electrocatalytic activity and remarkable stability for the two-electron reduction of oxygenvia an electrochemical–chemical mechanism at the base of the porous PANI film. The acid centers of PANI (protonated imine group) played an important role not only in two internal redox transform processes, but also in an external charge transfer reaction during the electrocatalytic reduction of oxygen. The incorporation of anionic AQS groups into PANI matrix to prepare electroactive PANI using the electrochemical doping-dedoping-redoping method is conceptually new, and may be extended to the development of new functional materials from many other conducting polymers and quinonoid compounds for wide applications in catalysis, sensors, molecular electronics, and so on.