Meijuan Li

Facile fabrication and enhanced photocatalytic performance of Ag/AgCl/rGO heterostructure photocatalyst.

Graphene/reduced graphene oxide (rGO) modification has been demonstrated to be an efficient route to improve the photocatalytic performance of various photocatalysts by promoting the effective separation of photogenerated electrons and holes. It is highly required to develop facile and environmental-friendly methods for the preparation of graphene-based photocatalytic materials. In this study, the Ag/AgCl/rGO heterostructure photocatalyst was fabricated by a mild oxidization reaction of hydrothermally prepared Ag/rGO in FeCl3 solution. It was found that the reduction of graphene oxide (GO) was accompanied with the in situ formation of metallic Ag in a Ag[(NH3)2](+)-immobilized GO solution during hydrothermal treatment, while the following in situ oxidation of metallic Ag by FeCl3 solution resulted in the formation of strongly coupled Ag/AgCl/rGO heterostructure photocatalyst. The photocatalytic experimental results indicated that all the resultant Ag/AgCl/rGO nanocomposite photocatalysts exhibited a much higher photocatalytic activity than the Ag/AgCl and physically mixed Ag/AgCl/rGO composite, and the Ag/AgCl/rGO (3.2 wt % rGO) showed the highest photocatalytic performance. The enhanced photocatalytic performance of Ag/AgCl/rGO heterostructures can be attributed to the cooperation effect of the effective separation of photogenerated carriers via strongly coupled rGO cocatalyst and the enrichment of organic molecules on the rGO nanosheets. Considering the facile preparation and its high photocatalytic activity, it is possible for the present Ag/AgCl/rGO nanocomposites to be widely applied in various fields such as air purification and wastewater treatment.

Preparation and performance enhancements of wear-resistant, transparent PU/SiO2 superhydrophobic coating

ABSTRACT The wear resistance and transparency properties of superhydrophobicity are most important issue essential for the application of superhydrophobic materials in industry. In this paper, we successfully prepared good wear resistance PU/SiO2 (polyurethane/silica) composite superhydrophobic coating with the double-step sol–gel route. The PU and SiO2 coating occurs crosslinking reaction forming composite superhydrophobic coating. The superhydrophobic coating surface is characterised by environmental scanning electron microscope and other testing methods, the results show that the PU/SiO2 composite superhydrophobic coating surface has excellent superhydrophobic properties and the Sa value was 332.5 nm. We used the pressure of 5 KPa to verify the wear resistance which the PU/SiO2 composite superhydrophobic coating surface exhibits good wear resistance, the water contact angle (WCA) still remains 138.7° after the abrasion resistance test. The PU/SiO2 composite superhydrophobic coating has high transparency in the visible light. The largest WCA of PU/SiO2 composite superhydrophobic coating could reach 162.1°.

Fabrication of W@Cu composite powders by direct electroless plating using a dripping method

A direct electroless copper (Cu) coating on tungsten powders method requiring no surface treatment or stabilizing agent and using glyoxylic acid (C2H2O3) as a reducing agent was reported. The effects of copper sulfate concentration and the pH of the plating solution on the properties of the prepared W@Cu composite powders were assessed. The content of Cu in the composite powders was controlled by adjusting the concentration of copper sulfate in the electroless plating solution. A uniform, dense, and consistent Cu coating was obtained under the established optimum conditions (flow rate of C2H2O3 = 5.01 mL/min, solution pH = 12.25 and reaction temperature 45.35 °C) by using central composite design method. In addition, the crystalline Cu coating was evenly dispersed within the W@Cu composite powders and Cu element in the coating existed as Cu0. The formation mechanism for the W@Cu composite powders by electroless plating in the absence of surface treatment and stabilizing agent was also proposed.

Microstructure and electrical conductivity of CNTs/PMMA nanocomposite foams foaming by supercritical carbon dioxide

The carbon nanotubes (CNTs)/ polymethylmethacrylate (PMMA) nanocomposite foams were prepared by the anti-solvent precipitation and supercritical foaming method. The morphology and the electrical conductivity of the foams with different kinds of CNTs were investigated. The experimental results showed that all the foams had uniform cell structure, and the cell size changed from 1.9 to 10 μm when the foaming temperature ranged from 50 °C to 95 °C. With small cell size (1.9–4.0 μm), the conductivities of the foams were 3.34×10−6–4.16×10−6 S/cm compared with the solid matrix since the introduction of micro cells did not destroy the conductive network. However, when the cell size was biger (4.5–10 μm), the aspect ratio of the CNTs played the dominant role of the conductivity. The foams with short CNTs had higher conductivity, since the short CNTs were hard to stretch and snap by the cells and can well-dispersed in the cell wall and cell edges. The results of this work provided a novel material design method for conductive foams based on the rule of both microstructure and aspect ratio of the CNTs.

Preparation of PMMA/graphene oxide microcellular foams using supercritical carbon dioxide

Microcellular foams have a widely applications in many industries due to their superior properties. In this paper, the polymethymethacrylate (PMMA)/graphene oxide (GO) microcellular foams were prepared by supercritical carbon dioxide as a friendly foaming agent. The effect of graphene oxide amount on cellular structure and mechanical strength of foams had been investigated. Microstructure characterization bases on scanning electron microscopy (SEM). The cell size and cell density were calculated via image analysis. It was found that the average foam cell size was decreased from 20.1 μm to 2.2 μm and the cell density was increased from 2.8×108 to 3.3×1010 when 1.5wt.% GO sheets were added into PMMA matrix. In addition, the compression strength of polymeric foams was increased from 13 MPa to 39 MPa.

Fabrication of W/Cu FGM By Aqueous Tape Casting

Tungsten Copper-based metals (W/Cu) were extensively used as electrical contact materials in switching systems for the electric power industry. In this paper, a novel investigation to prepare Tungsten Copper-based metal composite materials according to functionally graded material (FGM) concept and the method of tape casting was reported. Cu-coated W powders with different Cu weight fraction were synthesized via electricless plain in methanol-water solvent. The green tapes with different composition and thickness were laminated and then sintered to prepare W-Cu functionally graded materials. XRD, EDS, SEM and metallographic analyses were used to characterize the material microstructure and combination between different layers. The results showed that the Cu-coated W powders had grate compressibility leading to wettability of powders. The parallelism and flatness of intermediate layer were good and the combination was tight.

Microstructure and mechanical performance of Cu-SnO2-rGO based composites prepared by plasma activated sintering

A novel chemical technique combined with unique plasma activated sintering (PAS) was utilized to prepare consolidated copper matrix composites (CMCs) by adding Cu-SnO2-rGO layered micro powders as reinforced fillers into Cu matrix. The repeating Cu-SnO2-rGO structure was composed of inner dispersed reduced graphene oxide (rGO), SnO2 as intermedia and outer Cu coating. SnO2 was introduced to the surface of rGO sheets in order to prevent the graphene aggregation with SnO2 serving as spacer and to provide enough active sites for subsequent Cu deposition. This process can guarantee rGO sheets to sufficiently disperse and Cu nanoparticles to tightly and uniformly anchor on each layer of rGO by means of the SnO2 active sites as well as strictly control the reduction speed of Cu2+. The complete cover of Cu nanoparticles on rGO sheets thoroughly avoids direct contact among rGO layers. Hence, the repeating structure can simultaneously solve the wettability problem between rGO and Cu matrix as well as improve the bonding strength between rGO and Cu matrix at the well-bonded Cu-SnO2-rGO interface. The isolated rGO can effectively hinder the glide of dislocation at Cu-rGO interface and support the applied loads. Finally, the compressive strength of CMCs was enhanced when the strengthening efficiency reached up to 41.

Microstructural characterization of the Mg/Cu/Al diffusion bonded joint

A vacuum hot-pressed diffusion bonding method was used to prepare an Mg/Cu/Al laminated composite. Both the Mg/Cu and Al/Cu interfaces were investigated by means of scanning electron microscopy, electron probe microanalysis, X-ray diffraction spectrometer system and Vickers microhardness test. The results showed that two kinds of intermetallic compounds, Al4Cu9 adjacent to the Cu side and Al2Cu adjacent to the Al side, were formed in the interface of Al-Cu. Meanwhile, Mg2Cu was formed at the interface of Mg/Cu. The maximum value of shear strength is 13.1 MPa and the fracture of the joints had taken place at the Mg-Cu interface. The microhardness of the interface increased due to the formation of the intermetallic compounds, which is the main cause leading to poor bond properties.

Synthesis and Compressive Response of Microcellular Foams Fabricated from Thermally Expandable Microspheres

Cellular foams are widely applied as protective and energy absorption materials in both civil and military fields. A facile and simple one-step heating method to fabricate polymeric foams is measured by adopting thermally expandable microspheres (TEMs). The ideal foaming parameters for various density foams were determined. Moreover, a mechanical testing machine and split Hopkinson bar (SHPB) were utilized to explore the quasi-static and dynamic compressive properties. Results showed that the cell sizes of the as-prepared TEMs foams were in the micrometer range of 11 μm to 20 μm with a uniform cell size distribution. All the foams exhibited good compressive behavior under both quasi-static and high strain rate conditions, and were related to both foam densities and strain rates. The compressive strength of the TEMs foams at 8400 s−1 was up to 4 times higher than that at 10−4 s−1. The effects exerted by the strain rate and sample density were evaluated by a power law equation. With increasing density, the strain rate effect was more prominent. At quasistatic strain rates below 3000 s−1 regime, initial cell wall buckling and subsequent cellular structure flattening were the main failure mechanisms. However, in the high strain rate (HSR) regime (above 5000 s−1), the foams were split into pieces by the following transverse inertia force.

Quantitative Analysis of Damping Enhancement and Piezoelectric Effect Mechanism of CNTs/PMN/EP Composites

New types of piezoelectric damping materials, including carbon nanotubes (CNTs)/lead magnesium niobate (PMN)/epoxy (EP) resin, are developed. The tan δ area (TA) analysis method is selected to evaluate the damping properties which obviously clarifies the effect of maximum loss factor (tan δ) and effective temperature range on damping properties. Furthermore, the dominant factor of damping enhancement is quantitatively analyzed via the value of TA. Compared with PMN, the interfacial friction of CNTs acts as the dominant factor for the content less than 0.6 wt.%. The maximum damping percentage of CNTs reaches 29.14%. CNTs form loop circuits gradually with the content of CNTs increasing, and electrical energy generated via piezoelectric effect of PMN is efficiently dissipated through the conductive network. Thus, PMN becomes the dominant factor as the content of CNTs exceeds 0.8 wt.%, and the damping percentage reaches 47.43% at the content of CNTs of 1.0 wt.%.