Jianhua Hou

Hierarchical Porous Nitrogen-Doped Carbon Nanosheets Derived from Silk for Ultrahigh-Capacity Battery Anodes and Supercapacitors

Hierarchical porous nitrogen-doped carbon (HPNC) nanosheets (NS) have been prepared via simultaneous activation and graphitization of biomass-derived natural silk. The as-obtained HPNC-NS show favorable features for electrochemical energy storage such as high specific surface area (SBET: 2494 m(2)/g), high volume of hierarchical pores (2.28 cm(3)/g), nanosheet structures, rich N-doping (4.7%), and defects. With respect to the multiple synergistic effects of these features, a lithium-ion battery anode and a two-electrode-based supercapacitor have been prepared. A reversible lithium storage capacity of 1865 mA h/g has been reported, which is the highest for N-doped carbon anode materials to the best of our knowledge. The HPNC-NS supercapacitors electrode in ionic liquid electrolytes exhibit a capacitance of 242 F/g and energy density of 102 W h/kg (48 W h/L), with high cycling life stability (9% loss after 10,000 cycles). Thus, a high-performance Li-ion battery and supercapacitors were successfully assembled for the same electrode material, which was obtained through a one-step and facile large-scale synthesis route. It is promising for next-generation hybrid energy storage and renewable delivery devices.

From Rice Bran to High Energy Density Supercapacitors: A New Route to Control Porous Structure of 3D Carbon

Controlled micro/mesopores interconnected structures of three-dimensional (3D) carbon with high specific surface areas (SSA) are successfully prepared by carbonization and activation of biomass (raw rice brans) through KOH. The highest SSA of 2475 m2 g−1 with optimized pore volume of 1.21 cm3 g−1 (40% for mesopores) is achieved for KOH/RBC = 4 mass ratio, than others. The as-prepared 3D porous carbon-based electrode materials for supercapacitors exhibit high specific capacitance specifically at large current densities of 10 A g−1 and 100 A g−1 i.e., 265 F g−1 and 182 F g−1 in 6 M KOH electrolyte, respectively. Moreover, a high power density ca. 1223 W kg−1 (550 W L−1) and energy density 70 W h kg−1 (32 W h L−1) are achieved on the base of active material loading (~10 mg cm2) in the ionic liquid. The findings can open a new avenue to use abundant agricultural by-products as ideal materials with promising applications in high-performance energy-storage devices.

Enhanced electrochemical performance of ball milled CoO for supercapacitor applications

In the present work, we report the enhanced electrochemical performance of ball milled CoO nanoparticles for supercapacitor applications. The mechanical ball milling provides clean physical processes to prepare nanoparticles from CoO micropowders for excellent electrochemical performances. The performances of CoO samples at different milling times have been researched. With the increase of milling time the specific capacitance of CoO samples increases. The average size of CoO nanoparticles which have been milled for 96 h is estimated to be 5–20 nm by Transmission Electron Microscopy (TEM) analysis showing clear edges having superior boundary crystallinity. This clear edge superior boundary crystalline shape favours rapid electron and ion transport. The electrochemical behaviour is analyzed in a three electrode system using 1 M KOH solution as the electrolyte in terms of cyclic voltammetry, cyclic charge–discharge, and electrochemical impedance spectra. The CoO nanoparticle electrode exhibits a specific capacitance of 600 F g−1 at 0.5 A g−1 constant discharge current density. The high specific capacitance and the stability of the CoO nanoparticle electrode are attributed to good crystallinity and large specific surface area. The specific capacity retention is 96.6% at a current density of 2 A g−1 and 95.3% at a current density of 4 A g−1 over 2000 charge–discharge cycles. The excellent cyclic stability indicates that nanocrystalline CoO is an excellent supercapacitor electrode material.

Facile synthesis of novel Nb3O7F nanoflowers, their optical and photocatalytic properties

Novel nanoflowers (NNF) of Nb3O7F have been synthesized by a facile template free route without using any surfactant. The evolution of these NNF have been studied by varying different reaction parameters. Using the UV-Vis spectra absorption peak the calculated bandgap was 2.9 eV. Organic dye rhodamine B (RhB) was degraded with average photodegradation efficiency of 87.8%, 94.23% and 99.7% with higher rate constant k = 1.1559, 1.9011 and 3.8862 for 0.005 g, 0.01 g and 0.1 g respectively. The rate constant for 0.1 g was found to be larger than for Nb2O5, commercial TiO2 Degussa P25, carbon modified Nb2O5/TiO2, g-C3N4, Fe2O3/g-C3N4 composites and SnNb2O6.

Floating photocatalyst of B-N-TiO2/expanded perlite: a sol-gel synthesis with optimized mesoporous and high photocatalytic activity.

Optimized mesoporous photocatalyst endowed with high specific surface area and large pore size was synthesized by sol–gel method. These large pore mesoporous materials (33.39 nm) were conducive to the movement of larger molecules or groups in pore path and for effective use of active sites. The high specific surface area (SBET, 99.23 m2 g−1) was beneficial to catalytic oxidation on the surface. Moreover, B and N co-doped anatase TiO2 in the presence of Ti–O–B–N and O–Ti–B–N contributed to the pore structure optimization and enhanced photoresponse capacity with a narrow band gap and red shift of absorption. The obtained materials with floating characteristics based on expanded perlite (EP) showed favorable features for photocatalytic activity. The best RhB photodegration rate of B–N–TiO2/EP (6 mg/g, 24 wt% TiO2) reached 99.1% after 5 h in the visible region and 99.8% after 1 h in the UV region. The findings can provide insights to obtain floatable photocatalysts with simple preparation method, optimized mesoporous, co-doping agents, as well as good photocatalytic performance, coverable and reusability. B–N–TiO2/EP has potential applications for practical environmental purification.

Micro and nano hierachical structures of BiOI/activated carbon for efficient visible-light-photocatalytic reactions

Constructing the heterojunctions or designing the novel nanostructures are thought as effective methods to improve photocatalytic activities of semiconductors. Herein, a one-step green route was developed to fabricate bismuth oxyiodide/activated carbon (BiOI/C) composite. The prepared BiOI/C exhibit obviously red shifts and increased absorption range of visible light. The presence of Bi-C bonds confirms the heterojunction, on account of which the BiOI nanosheets tightly grew on the surface of carbon and subsequently provided the hierarchical structure, sufficient interfacial interaction and high specific surface area. Significantly, the sufficient interracial interaction is beneficial to the detachment of electrons (e−)-holes (h+) pairs and the Bi-C bonds work like a bridge to rapidly transmit the e− from BiOI to carbon. What’s more, the hierarchical structure of BiOI/C efficiently shortened the diffusion pathways of pollutants and the high SBET provided more exposed reaction sites. Benefiting from multiple synergistic effects, the as-prepared BiOI/C exhibited enhanced photocatalytic activities in degrading Rhodamine B (RhB) solution under visible light irradiation. The degradation rate of optimized BiOI/C reaches up to 95% in 120 min, and the efficiency is 3.36 times higher than pure BiOI. This study provides a promising strategy that activated carbon can be utilized in highly-efficiency photocatalysts.

Preparation and application synthesis of magnetic nanocomposite using waste toner for the removal of Cr(VI)

In this study, a novel magnetic nanocomposite was prepared using waste toner (WT) through high temperature decomposition, and calcination was conducted in different atmospheres (air, ammonia, and vacuum). WT calcined in ammonia (WT(NH3)), and it was then utilized as an efficient absorbent for the reduction of Cr(VI) in aqueous solutions; a batch experiment with different conditions was performed to investigate its Cr(VI) removal ability. The effects of two pH-regulating acid (HCl and H2SO4) treatments were also studied. It was found that WT(NH3) could remove about 99% Cr(VI) at pH 2 under H2SO4 treatment. The XRD and TEM results coupled with VSM results confirmed that WT(NH3) is an Fe3O4/Fe2N nanohybrid, which possesses excellent water-dispersibility and remarkable magnetic properties. XPS analysis showed the presence of Cr(VI) and Cr(III) on the surface of WT(NH3), which indicated that Cr(VI) was reduced to Cr(III). Furthermore, H2SO4 regulation also promoted the reduction of Cr(VI) by WT(NH3), and this reduction was higher than that obtained by HCl regulation.

Adsorption and reduction of hexavalent chromium on magnetic greigite (Fe3S4)-CTAB: leading role of Fe(II) and S(−II)

In this study, a facile one-step route was used to synthesize a novel magnetic mesoporous greigite (Fe3S4)-CTAB composite, which was utilized to remove hexavalent chromium (Cr(VI)). The optimized Fe3S4-CTAB0.75 composite with a CTAB dosage of 0.75 g possessed the maximum specific surface, showing the highest Cr(VI) adsorption capacity of 330.03 mg g−1. The mechanism analysis revealed that Fe(II) and S(−II) were critical for the reduction of Cr(VI). CTAB can promote the removal of Cr(VI) by Fe3S4-CTAB composites, possibly due to increased S(−II) concentration, better dispersion of nanoparticles, and greater zeta potential. Besides, there is mild effect of Fe0 on Cr(VI) removal, which is confirmed by the disappearance of the Fe0 peak from the XPS analysis. The pseudo-second-order kinetic model could explain the Cr(VI) removal processes well. The adsorption of Cr(VI) at different initial concentrations was more consistent with a Langmuir isotherm. The existence of H+ was beneficial for Cr(VI) removal by Fe3S4-CTAB0.75. Our work confirmed that the obtained Fe3S4-CTAB0.75 composites exhibit considerable potential for Cr(VI) removal from aqueous solution.