Alan Meng

ZnO/Ag micro/nanospheres with enhanced photocatalytic and antibacterial properties synthesized by a novel continuous synthesis method

A series of ZnO/Ag micro/nanospheres (MNSs) with different Ag contents have been successfully synthesized via a self-design concentric impinging stream microreactor combined with microwave technique. Various characterization results showed that Ag nanoparticles with an average diameter of about 15 nm were successfully deposited upon ZnO microspheres with sizes ranging from 300–700 nm which are composed of ZnO nanoparticles with diameters of less than 10 nm. The photocatalytic performance of a series of ZnO/Ag MNSs was evaluated against methyl orange, and the antibacterial properties were tested against Escherichia coli. All of the results showed that the photocatalytic and antibacterial activities of ZnO/Ag MNSs loaded with different Ag contents are superior to that of the pure ZnO. The optimal loading Ag content is approximately 7.5 atom% as the MO is almost completely degraded after irradiating for 30 min and the MIC value is 100 μg mL−1. The possible mechanisms of the enhanced photocatalytic and antibacterial properties of ZnO/Ag MNSs were proposed. This fabrication method has the inherent advantages of simplicity, continuous production and low cost, so it is more appropriate for a large-scale continuous production with higher yields of ZnO/Ag MNSs in industry.

Mechanically exfoliated g-C3N4 thin nanosheets by ball milling as high performance photocatalysts

g-C3N4 with a layered structure has been proven as an outstanding metal-free organic photocatalyst because of its appropriate bandgap, abundant building elements, and excellent chemical stability. Here, a simple one-step ball milling method is presented for synthesis of mechanically exfoliated g-C3N4 (MECN) thin nanosheets at large scales for the first time. Characterization results showed that gradual size reduction, accompanied by a continual bandgap absorption shift, occurred with increasing grinding time. The obtained MECN thin nanosheets showed significantly enhanced simulated sun light driven photocatalytic activity toward organic degradation compared to their bulk counterpart, highlighting the crucial role of morphology and surface area on the photocatalytic performance.

A glassy carbon electrode modified with a composite consisting of reduced graphene oxide, zinc oxide and silver nanoparticles in a chitosan matrix for studying the direct electron transfer of glucose oxidase and for enzymatic sensing of glucose

AbstractThe authors describe the fabrication of a nanocomposite consisting of reduced graphene oxide, zinc oxide and silver nanoparticles by microwave-assisted synthesis. The composite was further reduced in-situ with hydrazine hydrate and then placed, along with the enzyme glucose oxidase, on a glassy carbon electrode. The synergistic effect of the materials employed in the nanocomposite result in excellent electrocatalytic activity. The Michaelis-Menten constant of the adsorbed GOx is 0.25 mM, implying a remarkable affinity of the GOx for glucose. The amperometric response of the modified GCE is linearly proportional to the concentration of glucose in 0.1 to 12.0 mM concentration range, and the detection limit is 10.6 µM. The biosensor is highly selective, well reproducible and stable. Graphical abstractA nanocomposite consisting of graphene oxide, zinc oxide and silver nanoparticles was prepared by microwave-assisted synthesis and further reduced with 85 % hydrazine hydrate (HAA). The material was incorporated, along with glucose oxidase, into a chitosan (CS) matrix on a glassy carbon electrode to give a glucose biosensor with a 10.6 µM detection limit.

Amorphous carbon coating for improving the field emission performance of SiC nanowire cores

Decorating silicon carbide nanowires with a low work function material is a simple and effective strategy to improve their field emission performance. In the present work, amorphous carbon (a-C) coatings have been successfully decorated onto the surface of SiC nanowires via chemical vapor reaction (CVR) using the Fe–Ni bibasic catalyst. Field emission measurements suggest that the resultant products have an excellent performance with a low turn-on field of 0.5 V μm−1 and a low threshold field of 2.1 V μm−1, indicating their enormous potential for applications in electron emitter fields. A novel electronic transport mechanism was first proposed to explain the improvement in the field emission performances, and the method and growth mechanism could be an effective clue and example for the synthesis of other coaxial nanostructures.

Rapid synthesis of a flower-like ZnO/rGO/Ag micro/nano-composite with enhanced photocatalytic performance by a one-step microwave method

Flower-like ZnO/rGO/Ag micro/nano-composites (MNCs) have been engineered by a one-step microwave technique using graphene oxide, AgNO3 and Zn(CH3COO)2 as raw materials without adding any external toxic reagent. This is a facile and rapid process requiring only low power microwave irradiation (120 W). Various characterization results showed that the flower-like ZnO/rGO/Ag MNCs consisted of a ZnO nanosheet and Ag nanoparticles and reduced graphene oxide (rGO) deposited on ZnO nanosheet surface. The composite shows an enhanced and faster ultraviolet and simulated daylight photocatalytic property, i.e. 92.73% and 70.43% degradation of methyl orange in 20 minutes as compared to the values of 70.91% and 60.82%, 55.48% and 50.61% by bare ZnO and rGO/ZnO, respectively. The enhanced photocatalytic property is attributed to an efficient charge transfer process from ZnO to both Ag and rGO. This method would be beneficial for synthesizing efficient ZnO-based ternary photocatalysts with a combination of metal and rGO.

Study on the structure, morphology and properties of Fe-doped Cu3N films

Fe-doped Cu3N films were prepared by cylindrical magnetron sputtering equipment at room temperature. The doping of Fe with the proper concentration results in a change in the preferred growth orientation from the Cu-rich plane (1 1 1) to the N-rich plane (1 0 0), which relates to the evolution of the surface grain shape from pyramid to sphere. Excessive doping of Fe is not favourable for the crystallization of Cu3N films. The cross-sections of the doped films with preferred growth orientations of [1 0 0] exhibit regular columnar grains. The variation between the lattice constant and the XPS results reveals that Fe probably replaces the position of Cu atoms in the lattice or is segregated in the grain boundaries. Weaker bonding of Cu–N results in a reduction of thermal stability for Fe-doped Cu3N films. And the incorporation of Fe can effectively modify the energy gap. According to the variations in the mean grain size, the peak of N1s and the energy gap, it is inferred that a doping limitation exists around 2.0 at%.

The m-SiCNW/FKM nanocomposites: fabrication, characterization and properties

Nanocomposites consisting of the fluoroelastomer (FKM) matrix and modified SiC nanowires (m-SiCNWs) as strengthening phase (coded as m-SiCNW/FKM nanocomposites) have been prepared for the first time on an open two-roll mill. SiCNWs were modified by simple chemical treatment using fluoroalkylsilane (AC-FAS, CF3(CF2)7CH2CH2Si(OC2H5)3) as modifier. Fourier transform infrared spectroscopy (FTIR) indicated that AC-FAS was successfully grafted to the surface of the SiCNWs. The water contact angle test confirmed that the surface of m-SiCNWs was hydrophobic. Compared with FKM, the tensile strength, stress at 100% strain, tear strength and thermal conductivity at 100 °C of the nanocomposites with 14 phr m-SiCNWs were improved by 15.3%, 102.0%, 17.6% and 56.9%, respectively. The tensile fracture surface morphology of m-SiCNW/FKM nanocomposites shows that m-SiCNWs were uniformly dispersed, and the interfacial adhesion between m-SiCNWs and FKM matrix was strong. Dynamic mechanical analysis shows that the storage modulus (E′) of the m-SiCNW/FKM nanocomposites was improved, and the Tg shifted to a higher temperature by increasing the m-SiCNW content, indicating the greater reinforcing effect of m-SiCNWs. Payne effect, as an important characteristic of rubber materials, was also investigated. The preparation of m-SiCNW/FKM nanocomposites provides a favorable exploration for the application of one-dimensional (1D) nanofiller in polymer composites.

Synthesis, growth mechanism and elastic properties of SiC@SiO2 coaxial nanospring

Herein, a novel coaxial nanospring composed of a helical SiC core and a uniform amorphous SiO2 sheath (SiC@SiO2) has been synthesized via a template/catalyst-free chemical vapor reaction (CVR) approach. An atomic layer dislocation stacking growth model is firstly established for explaining the formation process of the nanospring, which offers a valuable model and an effective clue for understanding the growth of other nonlinear nanostructures. The elastic properties of the products have been investigated by calculating the corresponding spring constant of the SiC@SiO2 coaxial nanospring with a dynamic radius, which makes it a promising candidate for nanomechanical devices, self-sensing resonators and nanoscale elastic energy storage.

A controllable honeycomb-like amorphous cobalt sulfide architecture directly grown on the reduced graphene oxide–poly(3,4-ethylenedioxythiophene) composite through electrodeposition for non-enzyme glucose sensing

A facile, controllable two-step electrodeposition synthesis route was developed, whereby a honeycomb-like amorphous cobalt sulfide architecture was obtained via direct growth on a glassy carbon electrode (GCE) functionalized by a reduced graphene oxide-poly(3,4-ethylenedioxythiophene) (rGO-PEDOT) composite film as an electrode for glucose detection. This electrodeposition method is binder-free, rapid, low-cost and preparation-controlled. The effects of the concentration ratio between CoCl2·6H2O and thiourea, deposition scanning rate and deposition cycles on glucose detection were investigated, and the optimum preparation conditions were determined. The characterization results indicated that the honeycomb-like cobalt sulfide architecture was formed by growing vertically amorphous CoxSy nanosheets with a thickness of about 20-50 nm on the rGO-PEDOT surface, and the morphology of cobalt sulfide could be controlled by regulating the deposition cycles. Under optimal conditions, the sensor exhibited a wide linear range from 0.2 to 1380 μM (R2 = 0.9976), a sensitivity of 113.46 μA mM-1 cm-2, a low detection limit of 0.079 μM and a response time of 3 s. This sensor also displayed good selectivity, reproducibility and repeatability for non-enzyme glucose sensing. More importantly, the sensor was successfully used to determine glucose in human blood serum samples, and the results were consistent with hospital test results.

Excellent high temperature field emission behavior with an ultra-low turn-on field and reliable current emission stability from SiC@SiO2@graphene nanoarray emitters

In the present work, in order to obtain a promising material, SiC@SiO2@graphene nanoarrays with numerous flake-like graphene coatings have been prepared on a Si substrate through a simple chemical vapor deposition (CVD) approach. The field emission (FE) measurements show that the turn-on field (Eto) of the as-synthesized SiC@SiO2@graphene nanoarrays is decreased dramatically from 1.75 V μm−1 to 0.73 V μm−1 when temperature is increased from room temperature (RT) to 500 °C, which is superior to most SiC one-dimensional (1D) nanomaterials. The current fluctuation of the emitters at RT and 200 °C is approximately ±1.3% and ±1.7%, respectively, suggesting remarkable emission efficiency and stability of the sample. The excellent FE behavior is mainly attributed to the distinctly increased number of electron emission sites and the Fermi level (Ef) adjustment caused by the multilayer heterostructure as well as the increased temperatures. Based on the structural components of the nanoarrays, a reasonable “Stripping Reconstruction” mechanism model has been first established. It is believed that not only can the as-synthesized SiC@SiO2@graphene nanoarrays be utilised as promising emitters under high temperatures, but also the proposed mechanism model and the multilayer decoration strategy are valuable for the FE enhancement of other 1D nanomaterials.