Xiancai Jiang

Template synthesis of CoSe2/Co3Se4 nanotubes: tuning of their crystal structures for photovoltaics and hydrogen evolution in alkaline medium

Tubular-structured nanomaterials with tailorable crystal structures and shell architectures whose properties can be tuned without changing their chemical compositions are attractive in electrochemical energy conversion and storage fields. Herein, we report the fabrication of tubular-structured orthorhombic CoSe2 (o-CoSe2) and cubic CoSe2 (c-CoSe2) by calcining monoclinic Co3Se4 nanotubes (Co3Se4 NTs) prepared by a facile precursor transformation method. Benefiting from advantageous structural features, including functional shells and well-defined interior voids, the tubular-structured o-CoSe2 showed a high power conversion efficiency of 9.34% as a counter electrode catalyst for dye-sensitized solar cells (DSSCs), superior to that of a Pt counter electrode (8.15%), under AM 1.5 G irradiation. In addition, the o-CoSe2 nanotubes also demonstrated excellent electrocatalytic activity in terms of low onset overpotential (∼54 mV) and small Tafel slope (∼65.9 mV per decade) as a hydrogen evolution reaction (HER) catalyst in alkaline medium. Hence, this work provides a promising strategy to selectively design and synthesize highly active electrocatalysts for energy conversion.

The effect of glycerol on properties of chitosan/poly(vinyl alcohol) films with AlCl3·6H2O aqueous solution as the solvent for chitosan.

The AlCl3·6H2O aqueous solution was used to dissolve chitosan (CS) and the CS/poly(vinyl alcohol) (PVA) blend films were prepared at the absence of acetic acid. AlCl3·6H2O was retained in CS/PVA film and glycerol was added to form the complex plasticizer with AlCl3·6H2O. The effect of glycerol on the water sorption, crystalline, thermal and mechanical properties of AlCl3·6H2O doped CS/PVA film was studied by atomic force microscopy, X-ray diffraction, thermal gravity analysis and tensile testing, respectively. The experimental results showed that glycerol had a significant positive effect on the properties of AlCl3·6H2O doped CS/PVA films. With the synergism effect of AlCl3·6H2O and glycerol, the prepared CS/PVA films showed excellent mechanical properties. With the addition of 30wt% glycerol, the AlCl3·6H2O doped CS/PVA films behave the tensile strength of 39MPa and elongation at break of 120%, respectively.

Studies of the plasticizing effect of different hydrophilic inorganic salts on starch/poly (vinyl alcohol) films.

The effects of different inorganic salts LiCl, MgCl2·6H2O, CaCl2, and AlCl3·6H2O on the crystalline, thermal, water vapor barrier, and tensile properties of starch/PVA films were studied. The high plasticizing efficiency of all these four inorganic salts for starch/PVA film was confirmed by the obtained results. These four salts all had a good compatibility with starch/PVA within the content of 15 wt% and starch/PVA became completely miscible with the addition of 15 wt% inorganic salts. All these four salts had a strong destroying effect on the crystals of starch and PVA. Among these four salts, AlCl3·6H2O had the largest negative effect on the thermal stability of starch/PVA and LiCl had the largest improving effect on the water sorption rate of starch/PVA film. On the whole MgCl2·6H2O and CaCl2 were the more suitable plasticizer for starch/PVA film among these four inorganic salts. With the addition of 15 wt% MgCl2·6H2O and CaCl2, the elongation at break of starch/PVA film could reach to 418.83% and 434.80%, respectively.

Hierarchical Porous Co9S8/Nitrogen-Doped Carbon@MoS2 Polyhedrons as pH Universal Electrocatalysts for Highly Efficient Hydrogen Evolution Reaction

The development of highly active and stable earth-abundant electrocatalysts to reduce or eliminate the reliance on noble-metal based ones for hydrogen evolution reaction (HER) over a broad pH range remains a great challenge. Herein, hierarchical porous Co9S8/N-doped carbon@MoS2 (Co9S8/NC@MoS2) polyhedrons have been synthesized by a facile hydrothermal approach using highly conductive Co/NC polyhedrons composed of cobalt nanoparticles embedded in N-doped carbon matrices as both the structural support and cobalt source. The Co/NC polyhedrons were prepared by direct carbonization of Co-based zeolitic imidazolate framework (ZIF-67) in Ar atmosphere. Benefiting from the prominent synergistic effect of N-doped carbon enhancing the conductivity of the hybrid, MoS2 and Co9S8 providing abundant catalytically active sites as well as the well-defined polyhedral structure promoting mechanical stability, the as-synthesized Co9S8/NC@MoS2 shows excellent HER activity and good stability over a broad pH range, with onset overpotentials of 4, 38, and 45 mV, Tafel slopes of 60.3, 68.8, and 126.1 mV dec-1, and overpotentials of 67, 117, and 261 mV at 10 mA cm-2 in 1.0 M KOH, 0.5 M H2SO4, and 1.0 M phosphate buffer solution (PBS), respectively. This work provides a general and promising approach for the design and synthesis of inexpensive and efficient pH-universal HER electrocatalysts.

Preparation and characterization of poly(vinyl alcohol)/sodium alginate hydrogel with high toughness and electric conductivity

Development of bio-based hydrogels with good mechanical properties and high electrical conductivity is of great importance for their excellent biocompatibility and biodegradability. Novel electrically conducive and tough poly(vinyl alcohol)/sodium alginate (PVA/SA) composite hydrogel was obtained by a simple method in this paper. PVA and SA were firstly dissolved in distilled water to form the composite solution and the pure PVA/SA hydrogel was obtained through the freezing/thawing process. The pure PVA/SA hydrogels were subsequently immersed into the saturated NaCl aqueous solution to increase the gel strength and conductivity. The effect of the immersing time on the thermal and mechanical properties of PVA/SA hydrogel was studied. The swelling properties and the antiseptic properties of the obtained PVA/SA hydrogel were also studied. This paper provided a novel way for the preparation of tough hydrogel electrolyte.

Preparation and characterization of novel magnetic Fe 3 O 4 /chitosan/Al(OH) 3 beads and its adsorption for fluoride

A novel magnetic bioadsorbent beads composed of Fe3O4, chitosan, and Al(OH)3 (Fe3O4/CS/Al(OH)3) was synthesized by a modified solvothermal and in-situ reaction. The composite adsorbent was characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and vibrating sample magnetometer, respectively. Adsorption toward F- onto Fe3O4/CS/Al(OH)3 was investigated as a function of Fe3O4 concentration, initial solution pH, adsorbent dosage, initial fluorion concentration, co-existing ions in water and initial temperature. The addition of Fe3O4 could enhance the adsorption properties of CS/Al(OH)3. The saturated adsorption capacity of magnetic Fe3O4/CS/Al(OH)3 calculated from the Langmuir isotherm model was 76.63mg/g at 298K. The adsorption isotherm of F- followed Langmuir isotherm model and the adsorption kinetics fitted better to the pseudo-second order kinetic model. The influence of temperature confirmed that the adsorption was spontaneous and endothermic. The magnetic Fe3O4/CS/Al(OH)3 beads could be easily separated from water under a low magnetic field.

Preparation and characterization of quaternized poly(vinyl alcohol)/chitosan/MoS2 composite anion exchange membranes with high selectivity

In this study, a series of novel quaternized poly(vinyl alcohol)/chitosan/molybdenum disulfide (QPVA/CS/MoS2) anion exchange membranes (AEMs) were prepared for direct methanol alkaline fuel cell (DMAFC). The composite membrane was synthesized by adding different amounts of MoS2 nanosheets (0, 0.1, 0.2, 0.5 and 1wt%) into QPVA/CS mixture solution and using the solution casting method. The crystallinity, thermal and mechanical properties, ion conductivity and resistance to methanol of the QPVA/CS/MoS2 membranes were characterized by X-ray diffraction, thermogravimetric analysis, tensile testing, ion exchange capacity, and methanol permeability measurements, respectively. The MoS2 was homogeneously dispersed in the membranes. The mechanical strength of the composite membranes was enhanced with the addition of MoS2. With the addition of 1.0wt% MoS2, the QPVA/CS/MoS2 composite membrane has the lowest methanol permeability of 0.210×10-7cm2·s-1. This study confirmed that the novel QPVA/CS/MoS2 membrane would be a potential candidate for the application in DMAFCs.

Influences of nonsolvent on the morphologies and electrochemical properties of carbon nanofibres from electrospun polyacrylonitrile nanofibres

The influences of nonsolvent on the morphologies and electrochemical properties of carbon nanofibres (CNFs) obtained via pre-oxidation and carbonization of electrospun polyacrylonitrile (PAN) nanofibres were mainly studied. Volatile methanol (MeOH) and acetonitrile (MeCN) were introduced into PAN solutions as the nonsolvent for PAN, which may produce porous structures via inducement of phase separation. The morphologies of the prepared nanofibres were observed via scanning electron microscopy. It was found that PAN nanofibres possessed corrugated and rough surfaces. PAN fibres obtained in the presence of nonsolvent showed larger diameters and wider distributions than those obtained without nonsolvent. After thermal treatments, inter-bonded CNFs were prepared. The structures of CNFs were confirmed by X-ray diffraction and Raman spectrometry. Then the electrochemical properties of CNFs were examined by an electrochemical method in a three-electrode system. Based on chronopotentiometry, CNFs exhibited the highest capacity up to

Metal-organic framework-derived Ni–Co alloy@carbon microspheres as high-performance counter electrode catalysts for dye-sensitized solar cells

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