Haihui Zhou

Studies of heavy metal ion adsorption on Chitosan/Sulfydryl-functionalized graphene oxide composites

Chitosan/Sulfydryl-functionalized graphene oxide composite (CS/GO-SH) was successfully synthesized via covalent modification and electrostatic self-assembly. A facile diazonium chemical process was developed to fabricate sulfydryl-functionalized graphene oxide (GO-SH) by introducing sulfydryl compounds to the graphene oxide sheets (GO), and the GO-SH was used to self-assemble with chitosan via an electrostatic interaction. The chemical structure and morphology of the CS/GO-SH composite were characterized by Fourier transformed infrared, Raman spectroscopy, scanning electron microscopy, X-ray powder diffraction and thermogravimetric examination. The results indicated that the CS/GO-SH was a new type of with multifunctional groups such as -OH, -COOH, -SH and -NH2. Simultaneously, the self-assembly of chitosan with GO-SH sheets changed the blocky structure of the CS to the loosely packed structure which is analogous to graphene oxide sheets. The resulting CS/GO-SH was used as an adsorbent material for removal of Cu (II), Pb (II) and Cd (II) in single- and multi-metal ions systems. It was found that the CS/GO-SH has potential applications in fields of adsorptive materials due to its superiority of the chemical characteristic and the specific surface area.

Facile Preparation of High‐Quality Graphene Scrolls from Graphite Oxide by a Microexplosion Method

Figure 1 . a) Structure diagrams of GS, MWCNT, and GSS. b) Sketch showing the preparation steps of GSS based on a microexplosion method. Owing to their 1D structure and remarkable mechanical, physical, and electrical properties, carbon nanotubes (CNTs) have attracted considerable interest in various applications over the past decades. [ 1 ] In recent years, graphene sheets (GS), the ideal 2D sp 2 hybridized structure, are the basic building blocks for other carbon allotropes, such as 0D fullerenes, 1D CNTs, and 3D graphite (G). GS have been actively developed because of their superb characteristics, such as high chemical stability, excellent electrical conductivity, and large surface area. [ 2 ] However, monolayer GS tends to form irreversible agglomerates during the drying process, which severely restricts the development of further researches. [ 3 ]

Effects of conductive polyaniline (PANI) preparation and platinum electrodeposition on electroactivity of methanol oxidation

A modified galvanostatic method, termed the ‘pulse galvanostatic method’ (PGM) was used to synthesize nanofibular polyaniline (PANI). In contrast to granular PANI prepared by the conventional galvanostatic method (GM), nanofibular PANI has better conductivity and higher specific surface area. The nanofibular PANI electrode modified by Pt microparticles, at the same Pt loading, exhibits a considerably higher electrocatalytic activity on the methanol oxidation than that of the granular PANI electrode modified by Pt microparticles. Furthermore, the PGM method can be used as a good method for Pt microparticle electrodeposition. The composite electrode composed of PANI and Pt microparticles has the best electrocatalytic activity in the experimental range. The effects of Pt loading and methanol concentration, on the electrocatalytic activity for methanol oxidation have also been researched.

Preparation of well-dispersed PdAu bimetallic nanoparticles on reduced graphene oxide sheets with excellent electrochemical activity for ethanol oxidation in alkaline media

Chemically reduced graphene oxide sheets-supported PdAu (PdAu/CRG) nanocomposites were prepared facilely by co-reduction of graphene oxide sheets, PdCl2 and HAuCl4. Then the PdAu/CRG nanocomposites were characterized by using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results reveal that PdAu bimetallic nanoparticles with an average diameter of 6 nm are dispersed uniformly on the chemically reduced graphene oxide sheets (CRG). The electrocatalytic performance of the PdAu/CRG catalyst was studied by cyclic voltammetric and chronoamperometric measurements. Electrochemical experiments show that the PdAu/CRG catalyst has excellent catalytic activity and good stability for ethanol oxidation, indicating that the readily available CRG is an outstanding catalyst carrier for ethanol oxidation in alkaline media.

Graphene covalently functionalized with poly(p-phenylenediamine) as high performance electrode material for supercapacitors

A reduced graphene oxide–poly(p-phenylenediamine) (RGO–PPD) composite was prepared from p-phenylenediamine (PD) and chlorinated graphene oxide (GO–COCl) sheets through amidation and polymerization processes. Then the RGO–PPD composite was characterized by using scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy. The results show that PPD nanoparticles were wrapped within or on the surface of graphene sheets uniformly. The RGO–PPD composite displayed a layered-stacking structure and had a large surface area (674.22 m2 g−1) and a high pore volume (0.43 cm3 g−1). Capacitive properties of the RGO–PPD composite were studied using cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS) in an electrolyte of 0.5 M H2SO4 aqueous solution. The RGO–PPD exhibits a high specific capacitance of 347 F g−1 at a discharge rate of 1 A g−1 and excellent cycling stability with 90.1% of its initial capacitance at a large current density of 10 A g−1 after 1000 charge/discharge cycles. The energy density and specific power density of the present supercapacitor are 48.2 W h kg−1 and 1.0 kW kg−1, respectively. The results suggest that the RGO–PPD is a promising material for high-performance supercapacitor applications.

Co9S8 nanoparticles embedded in a N, S co-doped graphene-unzipped carbon nanotube composite as a high performance electrocatalyst for the hydrogen evolution reaction

In this work, we successfully fabricated a three-dimensional (3D) hierarchical ternary composite by embedding Co9S8 nanoparticles in a nitrogen and sulfur co-doped graphene-unzipped carbon nanotube matrix (Co9S8/NSG-UCNTs) through a facile and controllable one-step pyrolysis method using a graphite oxide/oxidized unzipped carbon nanotubes/cobalt nitrate/thiourea composite as the precursor. The as-prepared 3D ternary composite displays superior catalytic performance for the hydrogen evolution reaction (HER), which outperforms most binary or ternary carbon-based composites in the literature. The HER overpotentials are 65 mV and 86 mV when the current densities reach 10 mA cm−2 and 20 mA cm−2, respectively, and the exchange current density reaches 0.503 mA cm−2. Also, it demonstrates good stability reflected from the negligible activity decrease after 1000 consecutive cycles. The excellent electrocatalytic performance of the Co9S8/NSG-UCNT ternary composite is attributed to the co-effect of the abundant HER active sites induced by Co9S8 nanoparticles, structural defects existing in the carbon support caused by N and S co-doping and outstanding conductivity resulting from the 3D structure.

Synthesis of RuO2 decorated quasi graphene nanosheets and their application in supercapacitors

Multiwalled carbon nanotubes (MWCNTs) are split along the longitudinal direction to form quasi graphene oxide (QGO) by modified Hummers method and quasi graphene nanosheet/RuO2 (QGN/RuO2) composites with 40.0 wt% RuO2 loading are prepared by a one-step hydrothermal synthesis without any reducing agent. The characterization of morphology and structure shows that the amorphous RuO2 nanoparticles are uniformly dispersed on all the surfaces of QGN. The electrochemical measurements show that the QGN/RuO2 composites exhibit good capacitive properties compared to pure RuO2 and pure QGN in acidic, alkaline and even in neutral electrolytes. The specific capacitances of QGN/RuO2 in 1 M KOH, 1 M H2SO4, and 1 M Na2SO4 are 453.7, 415.7, 287.5 F g−1. Significantly, the QGN/RuO2 composites can achieve a high voltage window of 1.6 V and greatly increase the energy density (102.2 W h kg−1) and power density (1600 W kg−1) of supercapacitors in 1 M Na2SO4 (1 A g−1). These results demonstrate that the QGN/RuO2 composites are a promising material for high-performance supercapacitors.

Facile Self‐Assembly Synthesis of PdPt Bimetallic Nanotubes with Good Performance for Ethanol Oxidation in an Alkaline Medium

PdPt bimetallic nanotubes were prepared by the self-assembly of Pt and Pd on Te nanowires at room temperature. The morphologies of the as-prepared PdPt nanotubes were investigated by scanning electron microscopy and transmission electron microscopy, and the results display a large amount of PdPt bimetallic nanotubes with a diameter of 10-20 nm and a length of several micrometers. The composition and structure of the nanotubes were characterized by X-ray diffraction, high-resolution transmission electron microscopy, scanning transmission electron microscopy, and energy spectrum analysis, and the results display uniform compositional distributions of both elements (Pd and Pt). The mechanism of the formation of the nanotube structure was supposed. The electrocatalytic performance of PdPt nanotubes were studied by cyclic voltammetry and chronoamperometry. Electrochemical results show that the as-prepared PdPt nanotube catalysts have not only high activity but also good stability for ethanol oxidation in alkaline medium.

Preparation of anodic films on 2024 aluminum alloy in boric acid-containing mixed electrolyte

Abstract The anodizing oxidation process on 2024 aluminum alloy was researched in the mixed electrolyte with the composition of 30 g/L boric acid, 2 g/L sulfosalicylic acid and 8 g/L phosphate. The results reveal that the pre-treatment and the composition of the mixed electrolyte have influence on the properties of the films and the anodizing oxidation process. Under the condition of controlled potential, the anodizing oxidation current—time response curve displays “saddle” shape. First, the current density reaches a peak value of 8–20 A/dm2 and then decreases rapidly, finally maintains at 1–2 A/dm2. The film prepared in the mixed electrolyte is of porous-type with 20 nm in pore size and 500 μm−2 in porosity. Compared with the conventional anodic film obtained in sulfuric acid, the pore wall of the porous layer prepared in this work is not continuous, which seems to be deposited by small spherical grains. This porous structure of the anodic film may result from the characteristics of the mixed electrolyte and the special anodizing oxidation process. The surface analysis displays that the anodic film is amorphous and composed of O, Al, C, P, S, Si and no copper element is detected.

Catalytic graphitization of PAN-based carbon fibers with electrodeposited Ni-Fe alloy

Ni-Fe alloy was electrodeposited on the surface of polyacrylonitrile (PAN)-based carbon fibers, and catalytic graphitization effect of the heat-treated carbon fibers was investigated by X-ray diffractometry and Raman spectra. It is found that Ni-Fe alloy exhibits significant catalytic effect on the graphitization of the carbon fibers at low temperatures. The degree of graphitization of the carbon fibers coated with Ni-Fe alloy (57.91% Fe, mass fraction) reaches 69.0% through heat treatment at 1 250 °C. However, the degree of graphitization of the carbon fibers without Ni-Fe alloy is only 30.1% after being heat-treated at 2 800 °C. The catalytic effect of Ni-Fe alloy on graphitization of carbon fibers is better than that of Ni or Fe at the same temperature, indicating that Ni and Fe elements have synergic catalytic function. Furthermore, Fe content in the Ni-Fe alloy also influences catalytic effect. The catalytic graphitization of Ni-Fe alloy follows the dissolution-precipitation mechanism.