Huiping Bi

Graphene-based 3D composite hydrogel by anchoring Co3O4 nanoparticles with enhanced electrochemical properties

Three-dimensional (3D) graphene-based composite materials have attracted increasing attention, owing to their specific surface area, high conductivity and electronic interactions. Here, we report a convenient route to fabricate a 3D Co3O4/Graphene Hydrogel (CGH) composite as an electrode material for supercapacitors. Utilizing the gelation of a graphene oxide dispersion enables the anchoring of Co3O4 nanoparticles on the graphene sheet surfaces and formation of the hydrogel simultaneously. Remarkably, the spherical Co3O4 particles can serve as spacers to keep the neighboring graphene sheets separated. The CGH exhibits a high specific capacitance (Cs) of 757.5 F g(-1) at a current density of 0.5 A g(-1), indicating its potential application as an electrode material for supercapacitors.

Cobalt Sulfide/Graphene Composite Hydrogel as Electrode for High-Performance Pseudocapacitors.

Graphene and its composite hydrogels with interconnected three-dimensional (3D) structure have raised continuous attention in energy storage. Herein, we describe a simple hydrothermal strategy to synthesize 3D CoS/graphene composite hydrogel (CGH), which contains the reduction of GO sheets and anchoring of CoS nanoparticles on graphene sheets. The formed special 3D structure endows this composite with high electrochemical performance. Remarkably, the obtained 3D CGH exhibits high specific capacitance (Cs) of 564 F g−1 at a current density of 1 A g−1 (about 1.3 times higher than pure CoS), superior rate capability and high stability. It is worth mentioning that this methodology is readily adaptable to decorating CoS nanoparticles onto graphene sheets and may be extended to the preparation of other pseudocapacitive materials based on graphene hydrogels for electrochemical applications.

Reduced graphene oxide decorated with CuO-ZnO hetero-junctions: towards high selective gas-sensing property to acetone

The development of an efficient gas sensor device with high sensitivity, good selectivity and excellent stability is necessary to satisfy future societal and environmental needs. Herein, a one-step hydrothermal strategy is developed for the synthesis of a CuO–ZnO/reduced graphene oxide (rGO) ternary composite. Compositional, morphological and structural analyses demonstrate the successful anchoring of nanoscale p–n junctions between CuO and ZnO nanoparticles on rGO sheets. The obtained CuO–ZnO/rGO ternary composite exhibits outstanding sensing properties to acetone (the gas response value reaches from 9.4 to 10 ppm of acetone), almost 1.5 times and 2.0 times higher than CuO–ZnO and ZnO/rGO, respectively. More significantly, the ternary composite presents weaker sensing performance to ethanol and showing superior performance for effectively distinguishing acetone and ethanol. Moreover, the ternary composite exhibits good selectivity towards acetone vapor (about 6–41 times greater than that of other tested vapors). These findings highlight beneficial synergistic effects originated from large numbers of valid p–n junctions of CuO–ZnO and superior substrate characteristics of rGO sheets.

Self-assembled hydrothermal synthesis for producing a MnCO3/graphene hydrogel composite and its electrochemical properties

As ultrathin and flexible materials, graphene sheets are versatile building blocks for fabricating graphene-based functional composite materials for widespread applications. In this paper, we demonstrated a facile approach to prepare MnCO3/graphene hydrogel (MGH) composites via a hydrothermal process. The MnCO3 nanoparticles are 50–100 nm in size and are deposited on graphene sheets’ surfaces as spacers to prevent graphene sheets from restacking. A combination of deposited MnCO3 nanoparticles and hydration of the hydrogel could effectively keep the neighboring graphene sheets separated. The obtained MGH nanocomposite presents a high specific capacitance (Cs) of 645.5 F g−1 at 0.5 A g−1 in a three-electrode system, suggesting that it is a robust candidate as a supercapacitor electrode material.

Graphene-based cobalt sulfide composite hydrogel with enhanced electrochemical properties for supercapacitors

The three-dimensional cobalt sulfides/graphene hydrogel (CoSGH) nanocomposites were fabricated via a facile one-step hydrothermal route in a water–isopropanol system. The structural, morphological and physical properties of the as-fabricated composites were investigated, and the results confirm that amorphous cobalt sulfide particles were successfully anchored onto graphene sheets. As electrode materials for supercapacitors, the composites exhibit a maximum specific capacitance (Cs) of 435.7 F g−1 at a current density of 0.5 A g−1 measured in 6 M KOH electrolyte, which is significantly higher than that of cobalt sulfides and graphene. Furthermore, the CoSGH nanocomposites have also shown excellent cycling stability with 82.3% capacitance retention over 3000 cycles which is higher than that of pure cobalt sulfides. The enhanced electrochemical properties exhibited by CoSGH highlight the special hydrogel structure and synergistic effects between cobalt sulfides and graphene.

Three-dimensional nickel hydroxide/graphene composite hydrogels and their transformation to NiO/graphene composites for energy storage

Graphene and its functionalized derivatives like graphene oxide (GO) have become handy and convenient building blocks for self-assembly to fabricate graphene-based functional materials with three-dimensional (3D) macroscopic structures. Herein, a convenient one-step hydrothermal method for preparing Ni(OH)2/graphene composite hydrogels (NGHs) with interconnected networks is described. This procedure includes the reduction of GO sheets by hydrazine and the in situ deposition of Ni(OH)2 nanoplates on graphene sheets. Notably, the obtained NGH7.5 (the calculated mass ratio of formed Ni(OH)2 with GO is 7.5 : 1) can offer a high specific capacitance of 1125.4 F g−1 at a charge/discharge rate of 0.5 A g−1, which is almost 2.2 times and 8.1 times higher than Ni(OH)2 and graphene, respectively. Meanwhile, the NGHs also present stable cycling performances with 87.3% capacitance retention after 1000 cycles, which are significantly higher than that of its counterparts of Ni(OH)2. More interestingly, the 3D structure of the NGH can be easily transmitted to NiO/graphene (NiO/G) composites utilizing a facile thermal treatment procedure. The electrode based on the NiO/G composite delivers a discharge capacity of 1349 mA h g−1 and a charge capacity of 992 mA h g−1 at the 1st cycle with a coulombic efficiency of about 73.5%. This work opens a considerable way to fabricate functional graphene-based 3D structures and their composite materials, and makes a significant contribution to energy storage/conversion from alternative energy sources.

Selective removal of nitroaromatic compounds from wastewater in an integrated zero valent iron (ZVI) reduction and ZVI/H2O2 oxidation process

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.

A controllable synthetic route for preparing graphene-Cu and graphene-Cu2O nanocomposites using graphene oxide-Cuo as a precursor

The development of convenient method to obtain graphene-based nanocomposites is a key issue for their application. Herein, we described a facile route for synthesizing graphene-Cu and graphene-Cu2O nanocomposites using graphene oxide-CuO as a precursor. Remarkably, the different nanocomposites could be formed just by varying the reaction temperature and time. This work provides a feasible route for the preparation of graphene-based nanocomposites with various constituents.

Synthesis of hollow anatase nanospheres with excellent adsorption and photocatalytic performances

Hollow anatase nanospheres have been synthesized. The silica template makes anatase more stable and its subsequent removal results in the formation of hollow structures, which significantly improves its surface area and active sites. The as-synthesized hollow anatase nanospheres show excellent adsorption and photocatalytic performance to solid anatase nanospheres and P25.