•MWCNTs/Fe3O4 composites were synthesized by a hydrothermal process.•MWCNTs/Fe3O4 magnetic composites with adsorption and catalytic ozonation performance for BPA.•MWCNTs/Fe3O4 showed enhanced activity due to hollow tube structure and surface oxygen-containing groups.•BPA removal efficiency could be promoted in co-existence of humic acid due to increased OH radicals.MWCNTs/Fe3O4 magnetic composites, combined adsorption and catalytic ozonation behavior, were synthesized by a hydrothermal process. The synthesized MWCNTs/Fe3O4 composites were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), element analysis and Brunauer-Emmett-Teller (BET) surface area. The adsorption performance and catalytic activity of MWCNTs/Fe3O4 for BPA removal in aqueous solution were evaluated. The results showed that the synthesized MWCNTs/Fe3O4 exhibited an excellent adsorption ability and catalytic ozonation activity owning to its large specific surface areas, hollow tube channels and abundant surface oxygen-containing groups, leading to high adsorption for BPA and O3, high retention and utilization of O3 molecules on the composites. In addition, the catalytic ozonation performance of MWCNTs/Fe3O4 could be improved by increasing surface oxygen-containing groups to accelerate O3 decomposition, thus producing more OH radicals. Moreover, BPA removal efficiency could be improved by increasing dose of catalyst, pH value and the concentration of humic acid (HA). The fluorescence spectra and OH radicals measurement displayed that HA could greatly increase OH radicals via inducing more surface oxygen-containing groups on the catalyst, thus, promoting BPA removal. Furthermore, MWCNTs/Fe3O4 showed the great stability and durability during several reaction recycles.Download high-res image (260KB)Download full-size image

•NTHPC is successfully synthesized via the MnO2-introduced-tunnels strategy.•The nanotunnels are successfully introduced into hierarchical-porous carbon.•NTHPC shows a higher specific surface area and moderate pore volume.•NTHPC displays excellent supercapacitive performance.•This work provides a novel way for preparing hierarchical-porous carbon materials.Nanotunnels inserted hierarchical-porous carbon (NTHPC) have been synthesized successfully via a MnO2-introduced-tunnels strategy using MnO2 nanorods as template, with agar and β-cyclodextrin serving as hybrid carbon precursors. The as-prepared NTHPC possesses a higher specific surface area of 1441 m2 g−1, a moderate pore volume of 1.23 cm3 g−1, and the hierarchical-porous structure with inserted nanotunnels. Transmission electron microscopy has demonstrated that the width of the nanotunnels is between 20 and 100 nm, and the length ranges from 0.2 to 2.0 μm. Tests in a three-electrode system showed that the NTHPC has high specific capacitance (253.1 F g−1, 5 mV s−1), as well as good rate capability (203.3 F g−1, 100 mV s−1) and excellent cycling stability. More importantly, an assembled symmetric supercapacitor with NTHPC electrodes delivered an outstanding energy density of up to 34.9 Wh kg−1 with power density of 755.2 W kg−1. The remarkable electrochemical performance of the NTHPC is ascribed to the nanotunnels, which act as ion reservoirs and liquid transfer channels that can increase the ion transport rate and shorten the ion transfer distance. This study provides a novel method for the preparation of high-performance hierarchical-porous carbon and guidance for its potential applications in supercapacitors.Download high-res image (276KB)Download full-size image

The remarkable electrochemical performance of graphene-based materials has drawn a tremendous amount of attention for their application in supercapacitors. Inspired by supramolecular chemistry, the supramolecular hydrogel is prepared by linking β-cyclodextrin to graphene oxide (GO). The carbon nanoparticles-anchored graphene nanosheets are then assembled after the hydrothermal reduction and carbonization of the supramolecular hydrogels; here, the β-cyclodextrin is carbonized to carbon nanoparticles that are uniformly anchored on the graphene nanosheets. Transmission electron microscopy reveals that carbon nanoparticles with several nanometers are uniformly anchored on both sides of graphene nanosheets, and X-ray diffraction spectra demonstrate that the interlayer spacing of graphene is enlarged due to the anchored nanoparticles among the graphene nanosheets. The as-prepared carbon nanoparticles-anchored graphene nanosheets material (C/r-GO-1:3) possesses a high specific capacitance (310.8 F g–1, 0.5 A g–1), superior rate capability (242.5 F g–1, 10 A g–1), and excellent cycle stability (almost 100% after 10 000 cycles, at the scan rate of 50 mV s–1). The outstanding electrochemical performance of the resulting C/r-GO-1:3 is mainly attributed to (i) the presence of the carbon nanoparticles, (ii) the enlarged interlayer spacing of the graphene sheets, and (iii) the accelerated ion transport rates toward the interior of the electrode material. The supramolecule-inspired approach for the synthesis of high-performance carbon nanoparticles-modified graphene sheets material is promising for future application in graphene-based energy storage devices.Keywords: electrochemical behavior; graphene; supercapacitors; supramolecular; β-cyclodextrin

•Three-dimensional N-doped graphene hydrogels were synthesized using a hydrothermal method.•The hydrogels exhibited strong mechanical properties.•The synthesized NG-3:3 showed excellent capacitance (387.2 F g−1 at 1 A g−1).Three-dimensional nitrogen-doped graphene hydrogel (3D NG) samples are successfully synthesized via a hydrothermal method. The synthesized 3D NG exhibits excellent mechanical properties, including the support of approximately 1165 g with three NG cylinders. The morphology, structure, component and electrochemical performance of the NG samples are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscope, X-ray photoelectron spectroscopy, thermogravimetric analysis, N2 adsorption-desorption, cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy, respectively. X-ray photoelectron spectroscopy indicates that N is present in the graphene as pyrrolic N, pyridinic N and quaternary/graphitic N, with pyrrolic N being the predominant species in all of the samples. The electrochemical results demonstrate that the 3D NG with a nitrogen content of 7.7 wt% shows excellent capacitive behavior (387.2 F g−1 at 1 A g−1) in 6 M KOH. In addition, the specific capacitance value of this sample remains at approximately 90.5% of the maximum value (298.5 F g−1 at 5 A g−1) after 5500 cycles. The main reason for the excellent electrochemical behavior is the incorporation of the pyrrolic and pyridinic N in the graphene, enhancing the pseudo-capacitance of this material. It indicates that the 3D NG can be used as an electrode material for high-performance supercapacitors.

•A three-dimensional porous graphene layers was prepared via a gas foaming method.•Melamine was the nitrogen source to synthesize the N-doped 3D graphene layers.•The specific surface area of 3D N-doped graphene material is as high as 1196 m2 g−1.•The 3D N-doped graphene specific capacitance is 335 F g−1 in three-electrode system.•The energy density of 3D N-doped graphene reaches 58.1 Wh kg−1 in a symmetric cell.A porous graphene layers with a three-dimensional structure (3DG) was prepared via a gas foaming method based on a polymeric predecessor. This intimately interconnected 3DG structure not only significantly increases the specific surface area but also provides more channels to facilitate electron transport. In addition, 3D N-doped (3DNG) layers materials were synthesized using melamine as a nitrogen source. The nitrogen content in the 3DNG layers significantly influenced the electrochemical performance. The sample denoted as 3DNG-2 exhibited a specific capacitance of 335.2 F g−1 at a current density of 1 A g−1 in a three-electrode system. Additionally, 3DNG-2 exhibited excellent electrochemical performance in aqueous and organic electrolytes using a two-electrode symmetric cell. An energy density of 58.1 Wh kg−1 at a power density of 2500 W kg−1 was achieved, which is approximately 3 times that (19.6 Wh kg−1) in an aqueous electrolyte in a two-electrode system. After 1000 cycles, the capacity retention in aqueous electrolyte was more than 99.0%, and this retention in organic electrolytes was more than 89.4%, which demonstrated its excellent cycle stability. This performance makes 3DNG-2 a promising candidate as an electrode material in high-power and high-energy supercapacitor applications.

•RGO/CoAl-LDHs nanocomposites were prepared by a electrostatic self-assembly method.•Face-to-face contact between CoAl-LDHs and GO nanosheets can be observed from TEM.•The nanocomposite exhibited a higher specific capacitance and rated capability.•Self-agglomeration of the nanosheets can be avoided by electrostatic self-assembly.Graphene oxide/CoAl-layered double hydroxide (GO/CoAl-LDHs) composites were successfully prepared by a face-to-face electrostatic self-assembly method. Positively charged colloidal CoAl-LDHs nanosheets (CoAl-LDH-NS) and negatively charged colloidal GO nanosheets were uniformly mixed; then CoAl-LDH-NS were assembled on GO nanosheets via electrostatic attraction to prepare GO/CoAl-LDHs composites. The GO/CoAl-LDHs composites were then transformed to the reduced graphene oxide/CoAl-layered double hydroxide (RGO/CoAl-LDHs) composites with a hydrothermal method. The results showed that the content of RGO has a remarkable influence on the capacitive properties of composites. Among the composites with different RGO content, the RGO/CoAl-LDHs composite containing 12.0 wt% RGO displayed a maximum specific capacitance of 825 F g−1 at low current density of 1 A g−1, while that of pure CoAl-LDHs was 552 F g−1. The capacitance retention of the RGO/CoAl-LDHs composite from 1 A g−1 to 8 A g−1 is found to be 62.3%, whereas that of pure CoAl-LDHs is only 31.9%. Face-to-face self-assembling between positively charged CoAl-LDH-NS and negatively charged GO nanosheets can effectively reduce the self-agglomeration of GO nanosheets and avoid CoAl-LDH-NS stacking together, which lead to improvement of the capacitive performance.

Inspired by baking bread, our research group demonstrates a novel method for baking three-dimensional (3D) graphene layers with an open porous network, pore size in the range of dozens of nanometers to several hundred nanometers, and a pore wall thickness of about 10 nm. Such continuously cross-linking structures not only effectively overcome the restacking and agglomeration of graphene nanosheets but also possess more channels between nanosheets to lower the resistance for electron access to the inter-space. Compared with reduced graphene oxide (rGO) prepared at the same temperature, the unique 3D porous-structured graphene layers also contain 4.3 at.% nitrogen. When the 3D graphene layers are employed as an active electrode material for a supercapacitor, a high specific capacitance (SC) of 231.2 F g−1 at 1 A g−1 is displayed after electrochemical activation, approximately two times that of rGO. Only <1.0% of the capacitance degrades after 8000 cycles, exhibiting its excellent cycle stability; furthermore, it liberates a high energy density of 32.1 Wh kg−1 at a power density of 500 W kg−1. The attractive performances of 3D graphene layers make them a promising candidate as an electrode material for supercapacitors.

•The negative electrode sheets are prepared by simulating manufacture condition of negative plates.•The effect of carbon additives on negative electrode sheets is studied by electrochemical method.•Carbon additives in NAM enhance electrochemical properties of the negative sheets.•The negative sheets with 0.5 wt% carbon additive exhibit better electrochemical performance.•The charge-discharge mechanism is discussed in detail according to the experimental results.In this study, carbon additives such as activated carbon (AC) and carbon black (CB) are introduced to the negative electrode to improve its electrochemical performance, the negative electrode sheets are prepared by simulating the negative plate manufacturing process of lead-acid battery, the types and contents of carbon additives in the negative electrode sheets are investigated in detail for the application of lead-carbon battery. The electrochemical performance of negative electrode sheets are measured by chronopotentiometry, galvanostatic charge-discharge and electrochemical impedance spectroscopy, the crystal structure and morphology are characterized by X-ray diffraction and scanning electron microscopy, respectively. The experimental results indicate that the appropriate addition of AC or CB can enhance the discharge capacity and prolong the cycle life of negative electrode sheets under high-rate partial-state-of-charge conditions, AC additive exerts more obvious effect than CB additive, the optimum contents for the best electrochemical performance of the negative electrode sheets are determined as 0.5wt% for both AC and CB. The reaction mechanism of the electrochemical process is also discussed in this paper, the appropriate addition of AC or CB in negative electrode can promote the conversion of PbSO4 to Pb, suppress the sulfation of negative electrode sheets and reduce the electrochemical reaction resistance.

•The G/MnO2 composites were prepared by an electrostatic self-assembly method.•The graphene was obtained by an electrochemical exfoliation method.•Opposite charges were preconditions for the electrostatic self-assembly process.•The face-to-face contact style improved effectively the conductivity of MnO2.•95.6% of maximum capacitance was retained after 10000 cycles in the G-2/MnO2.Layered graphene/manganese oxide (G/MnO2) nanocomposites for supercapacitor applications were prepared with a face-to-face electrostatic self-assembly method using high-quality graphene, which was obtained from the one-step electrochemical exfoliation of graphite. The results reveal that the graphene and MnO2 nanaosheets need to be oppositely charged for the electrostatic self-assembly process. The face-to-face contact between the MnO2 nanosheets and graphene can effectively improve the conductivity of MnO2 and prevent the restacking and agglomeration of graphene. In addition, the composites exhibit an electrochemical-activation behavior, and the ratio of MnO2/graphene in composites significantly influences the electrochemical performance. The G-2/MnO2 composite displays a specific capacitance of 319 F g−1 at 0.2 A g−1, and only 4.4% of the capacitance degrades after 10,000 cycles, which demonstrates the composite's excellent cycle stability. Furthermore, the composite features a high energy density of 31.5 Wh kg−1 at a power density of 100 W kg−1. This attractive performance makes it a promising candidate as an electrode material for supercapacitors. Remarkably, although the graphene content in G-4/MnO2 composite is the same, the specific capacitance reduced to 186 F g−1 due to the different mixing times.

•ZVI-mediated advanced oxidation was applied to degrade acid orange II (AOII).•Lower pH in aqueous media was favorable for AOII degradation in ZVI/O2 system.•The measurement of H2O2 and Fe2+ demonstrated role of Fenton reaction in ZVI/O2 system at low pH.•OH produced via Fenton reaction was reactive species to degrade AOII in ZVI/O2 system.In this study, zero-valent iron (ZVI)-mediated advanced oxidation was applied to degrade the acid orange II (AOII) in the presence of oxygen. The effect of pH value, ZVI dosage, O2 concentration and added Fe2+ ions on the degradation efficiency was investigated. It was found that the increases of acidity in aqueous solution, ZVI dosage and O2 concentration were favorable to the oxidation reaction of AOII in ZVI-mediated advanced oxidation processes. The lower pH value in aqueous medium was favorable for AOII degradation in ZVI/O2 system. The AOII degradation efficiency and COD removal efficiency system could achieve more than 95% and 65% within 3 h in the ZVI/O2 at initial pH 3.0, respectively. The AOII degradation in ZVI/O2 system followed the first-order reaction kinetics at pH range of 3.0–7.0, while AOII degradation followed the zero-order reaction kinetics at pH range of 9.0–11.0. The measurements of H2O2 and Fe2+ in ZVI/O2 system, and the characterization for used ZVI particles demonstrated the role of Fenton reaction in the ZVI/O2 system, which occurred favorably at low pH to generate H2O2 and Fe2+, followed by a likely species OH to degrade AOII. The involvement of OH in oxidizing AOII was examined by determining the degradation rates using OH scavenger. Moreover, the coexistence ions had no significantly influence the oxidation process, indicating the true application process. Finally, organic compounds as intermediates of the degradation process were identified by LC/MS.

•TMA+ intercalated MnO2 was synthesized via an exfoliation and self-assembly process.•The as-prepared self-assembled MnO2 exhibits an ordered layered structure.•The as-prepared MnO2 possesses a large interlayer spacing of 0.67 nm.•The maximum specific capacitance of self-assembled MnO2 is 180 F g−1 at 0.5 A g−1.•The specific capacitance of self-assembled MnO2 decreased 10% after 10,000 cycles.Layered birnessite-type manganese oxide is exfoliated into single-layer manganese oxide nanosheets. Then, the exfoliated manganese oxide nanosheets are spontaneously restacked by a self-assembly process, which is driven mainly by electrostatic interactions between the negatively charged manganese oxide nanosheets and the positively charged tetramethylammonium (TMA+) ions, yielding a new ordered layered structure of MnO2 (self-assembled MnO2) with a large interlayer spacing of 0.67 nm, suggesting the formation of a layered hybrid form, intercalated with TMA+ ions in residence between the manganese oxide nanosheets. The large interlayer spacing facilitates rapid ion exchange and the intercalation and deintercalation of electrolyte cations. The supercapacitive behavior of the as-prepared self-assembled MnO2 is evaluated by cyclic voltammetry (CV), galvanostatic charge–discharge (CD) experiments and electrochemical impedance spectroscopy (EIS). The specific capacitance value is 180 F g−1 at a current density of 0.5 A g−1. After 10,000 cycles, the specific capacitance is still approximately 90% of the maximum specific capacitance. In addition, the intercalation of TMA+ ions between the manganese oxide nanosheets leads to a low charge-transfer resistance. These experimental results demonstrate that this self-assembled MnO2 is a promising candidate for use as electrode material in supercapacitor applications.

A hydration-layered structure of buserite-type manganese oxide (Mg–buserite) was successfully synthesized by an ion exchange method. The as-prepared Mg–buserite possesses a large basal spacing of 10 Å, and contains Mg2+ ions and two sheets of water molecules in the interlayer region. The supercapacitive behaviors of Mg–buserite were systematically investigated by cyclic voltammetry (CV), galvanostatic charge–discharge (CD) experiments and electrochemical impedance spectroscopy (EIS). The results showed that the specific capacitance of the Mg–buserite electrode sharply increased during the initial 500 cycles and reached a maximum of 164 F g−1 at approximately the 500th cycle at a scan rate of 1 mV s−1, and then it remained an almost constant value and decreased slightly upon prolonged cycling. After 22,000 cycles, the specific capacitance decreased by approximately 6% of the maximum specific capacitance. The superior capacitive behavior and excellent cycling stability of the as-prepared Mg–buserite are attributed to the large basal spacing, which can accommodate a larger amount of electrolyte cations and provide more favorable pathways for electrolyte cations intercalation and deintercalation. The experimental results demonstrate that Mg–buserite is a promising candidate as an electrode material for supercapacitors.Highlights► Mg–buserite with a large basal spacing of 10 Å was successfully synthesized. ► Mg2+ and two sheets of H2O molecules occupy the interlayer region of Mg–buserite. ► The maximum specific capacitance of Mg–buserite is 164 F g−1 at 1 mV s−1. ► The specific capacitance of Mg–buserite decreased only 6% after 22,000 cycles. ► The superior capacitive behaviors are attributed to the large basal spacing.

A todorokite-type manganese oxide (T-MnOx) with a 3 × 3 large tunnel structure was successfully synthesized by a hydrothermal method and employed as an active electrode material for a supercapacitor. The todorokite structure of the as-prepared manganese oxide was confirmed by X-ray diffraction (XRD), and the fragmented platelets were observed by scanning electron microscopy (SEM). The electrochemical performances of the as-prepared T-MnOx were evaluated by cyclic voltammetry (CV), galvanostatic charge–discharge (CD) experiments and electrochemical impedance spectroscopy (EIS) in 1 M Na2SO4 electrolyte. The specific capacitance of the T-MnOx electrode sharply increased during the initial 1000 cycles and then continued improving gradually. It reached a maximum of 220 F g−1 at approximately the 4000th cycle at a scan rate of 2 mV s−1, and further studies showed that the morphology and structure of the T-MnOx were maintained after 4000 cycles, indicating that an electrochemical activation process occurred during the initial thousands of cycles. The electrochemical activation mechanism is discussed in detail. The specific capacitance remained an almost constant value and decreased slightly upon prolonged cycling. After 23,000 cycles, it decreased by 6% of the maximum specific capacitance. The experimental results demonstrate that T-MnOx is a promising candidate as an electrode material for supercapacitors.Highlights► The electrochemical capacitance behavior of todorokite (T-MnOx) was studied. ► The T-MnOx with 3 × 3 large tunnels was successfully synthesized. ► The maximum specific capacitance of the T-MnOx electrode is 220 F g−1 at 2 mV s−1. ► The as-prepared T-MnOx exhibits excellent cycle stability. ► The electrochemical activation mechanism is discussed in detail.

In this study, an effective photocatalytic disinfection of E. coli 8099 using Ag/BiOI composites under visible light irradiation (λ > 420 nm) was studied. The nanostructured Ag/BiOI composites were synthesized in the presence of ethylene glycol by a solvothermal process and subsequent photodeposition method. The prepared Ag/BiOI photocatalysts were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), energy dispersive spectrometer (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectra (DRS) measurement. The experimental results showed that the photocatalytic disinfection efficiency of E. coli (∼5 × 107 cfu mL−1) using 2.09%Ag/BiOI was almost 99.99% within 10 min irradiation, and significantly higher than that of BiOI. The determination of cell structure destruction by TEM microscopy and the measurement of released K+ further confirmed that the cell membranes of E. coli were ruptured in the photocatalytic disinfection. It was found that the deposited Ag can facilitate the surface-adsorbed O2 to scavenge the photogenerated electrons. The main active species OH for the photocatalytic disinfection performance of E. coli   was produced by two pathways, that is, hvb+ oxidized water molecules to form OH (oxidative pathway), and O2 captured the photogenerated electron to generate O2- and subsequently produce OH (reductive pathway).Highlights► Photocatalytic disinfection of E. coli using Ag/BiOI under visible light was studied. ► Ag/BiOI had a higher photocatalytic disinfection activity than BiOI under visible light. ► Deposited Ag can facilitate surface-adsorbed O2 to scavenge photogenerated electrons. ► OH was the reactive species for photocatalytic disinfection performance of E. coli.

Polyaniline (PANI) and manganese dioxide (MnO2) composite (PANI/MnO2) was synthesized via a simultaneous-oxidation route. In this route, all reactants were dispersed homogenously in precursor solution and existed as ions and molecules, and involved reactions of ions and molecules generating PANI and MnO2 simultaneously. In this way, PANI molecule and MnO2 molecule contact each other and arrange alternately in the composite. The inter-molecule contact improves the conductivity of the composite. The alternative arrangement of PANI molecules and MnO2 molecules separating each other, and prevents the aggregation of PANI and cluster of MnO2 so as to decrease the particle size of the composite. The morphology, structure, porous and capacitive properties are characterized by scanning electron microscopy, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, Branauer–Emmett–Teller test, thermogravimetric analysis, Fourier transform infrared spectroscopy, cyclic voltammetry, charge–discharge test and the electrochemical impedance measurements. The results show that MnO2 is predominant in the PANI/MnO2 composite and the composite exhibits larger specific surface area than pure MnO2. The maximum specific capacitance of the composite electrode reaches up to 320 F/g by charge–discharge test, 1.56 times higher than that of MnO2 (125 F/g). The specific capacitance retains approximately 84% of the initial value after 10,000 cycles, indicating the good cycle stability.Highlights► PANI/MnO2 composite was synthesized by the simultaneous-oxidation route. ► Good contact in inter-molecule level between PANI and MnO2 improves the conductivity. ► The separation between PANI and MnO2 prevents the aggregation of nano-composite. ► The maximum specific capacitance of the PANI/MnO2 electrode is 320 F/g. ► The as-prepared PANI/MnO2 exhibits excellent cycle stability of 84% capacitance retention after 10,000 cycles.

An organic nitridizing reagent was employed in the preparation of nanocrystalline VN at 800 °C under a N2 atmosphere. The prepared VN was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), and its supercapacitive behavior was studied by cyclic voltammetry (CV) in three different types of aqueous electrolyte, 0.5 M H2SO4, 2.0 M NaNO3 and 1.0 M KOH. The XRD results indicate that prepared VN has a cubic structure with space group Fm3m and a lattice parameter of 4.139 Å. The nanocrystalline structure of VN with a low degree of crystallinity was confirmed by TEM imaging. The presence of oxygen on the VN surface was detected by FTIR and XPS, and its molecular composition was determined to be VN1.02O0.1. The specific capacitances of nanocrystalline VN were determined to be 114, 45.7 and 273 F g−1 in 0.5 M H2SO4, 2.0 M NaNO3 and 1.0 M KOH, respectively. Thus, the KOH solution was considered the best aqueous electrolyte for the capacitive performance of VN. The supercapacitive mechanism and the factor that influenced the specific capacitance are also analyzed in this paper.Highlights► Organic nitridizing agent was employed for preparation of nanocrystalline VN. ► The supercapacitive behavior of VN was studied by electrochemical method. ► The supercapacitive behavior of VN was studied in three kinds of electrolyte. ► The specific capacitance of VN was determined as 273 F g−1 in 1.0 M KOH. ► The supercapacitive mechanism and involved factor on capacitance were analyzed.

A series of novel Pb–Te binary alloys with different contents of tellurium (0.01–1.0 wt.%) were investigated as the positive grid of a lead acid battery. The microstructure of Pb–Te alloys was observed using a polarizing microscope. The morphology of the corrosion layers and corroded surfaces of Pb and Pb–Te alloy electrodes were analyzed by scanning electron microscopy (SEM) following the corrosion test. The electrochemical properties of Pb–Te alloys and Pb–Te–Sn alloy in sulfuric acid solution were investigated by cyclic voltammetry (CV), open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), alternating current voltammetry (ACV), and linear sweeping voltammetry (LSV). The results indicate that the introduction of tellurium results in grain refinement, increased corrosion resistance, and an accelerated oxygen evolution reaction for the Pb–Te binary alloys. The passive films formed on Pb–Te–Sn alloy shows improved performances in comparison to those on Pb–Ca–Sn alloy.

Vanadium nitride (VN) powder was synthesized by calcining V2O5 xerogel in a furnace under an anhydrous NH3 atmosphere at 400 °C. The structure and surface morphology of the obtained VN powder were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The supercapacitive behavior of VN in 1 M KOH electrolyte was studied by means of cyclic voltammetry (CV), constant current charge–discharge cycling (CD) and electrochemical impedance spectroscopy (EIS). The XRD result indicates that the obtained VN belongs to the cubic crystal system (Fm3m [2 2 5]) with unit-cell parameter 4.15 Å. SEM images show the homogeneous surface of the obtained VN. The CV diagrams illustrate the existence of fast and reversible redox reactions on the surface of VN electrode. The specific capacitance of VN is 161 F g−1 at 30 mV s−1. Furthermore, the specific capacitance remains 70% of the original value when the scan rate increases from 30 to 300 mV s−1. CD experiments show that VN is suitable for CD at high current density, and the slow and irreversible faradic reactions exist during the charge–discharge process of the VN electrode. The experimental results indicate that VN is a promising electrode material for electrochemical supercapacitors.

The effects of three types of fumed silica on the electrochemical properties of gelled electrolytes have been investigated by means of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), transmission electron microscope (TEM) and the Brunauer, Emmett and Teller (BET) technique. The CV and EIS results show that a moderate mechanical dispersion of fumed silica in the H2SO4 solution has important effects on the electrochemical properties of the gelled electrolyte. The optimal mechanical dispersion time is closely related to the operating temperature during preparation of gel, as well as the silica particle size and its distribution. A high stirring rate improves the electrode capacity and decreases the viscosity of the gelled electrolyte. With moderate mechanical dispersion, gelled electrolytes prepared from different fumed silica particles exhibit equal electrode capacities.

•3D MnO2 porous hollow microspheres (PHMSs) are prepared by a self-template process.•MnO2 PHMSs with excellent adsorption and catalytic ozonation performance for BPA.•MnO2 PHMSs show enhanced activity due to hollow-mesoporous shell spherical structure.•O2− and OH are reactive species to induce effective catalytic ozonation of BPA.Three-dimensional (3D) MnO2 porous hollow microspheres (δ- and α- MnO2 PHMSs), with high adsorption and catalytic ozonation performance, were synthesized by a self-template (MnCO3 microspheres) process at room temperature. The synthesized MnO2 PHMSs were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) surface area. The results showed that PHMSs exhibit the excellent adsorption ability and catalytic activity owning to their hollow spherical structure, mesoporous shell and well-defined interior voids, leading to the strong adsorption for bisphenol A (BPA) and the retention of O3 molecules on catalyst. Moreover, the catalytic performance of α-MnO2 PHMSs was better than that of δ-MnO2 PHMSs which was attributed to the richer lattice oxygen of α-MnO2 PHMSs to accelerate O3 decomposition by producing more reactive oxidative species. The degradation efficiency of BPA using 3D α-MnO2 PHMSs was more than 90% in the presence of ozone within 30 min reaction time. The probe tests for reactive oxidative species (ROSs) displayed that BPA degradation by catalytic ozonation is dominated by O2− and OH in our present study. Furthermore, the organic compounds as intermediates of the degradation process were identified by LC/MS.Download high-res image (129KB)Download full-size image