Yuhong Zheng

Green biosynthesis and characterization of zinc oxide nanoparticles using Corymbia citriodora leaf extract and their photocatalytic activity

ABSTRACT We reported a green and simple method for biosynthesizing zinc oxide nanoparticles (ZnO NPs) using Corymbia citriodora leaf extract as reducing and stabilizing agent. SEM, EDX, XRD, UV–VIS spectroscopy, Raman spectroscopy and TGA have been used for characterizing the biosynthesized ZnO NPs. The results indicating the ZnO NPs synthesized by C. citriodora leaf extract have high purity and the average size is 64 nm. The photocatalytic activity of the ZnO NPs has been investigated by degradation methylene blue under visible light irradiation. Due to the smaller size, the biosynthesized ZnO NPs showed an excellent photocatalytic performance.

A sensitive electrochemical sensor for direct phoxim detection based on an electrodeposited reduced graphene oxide–gold nanocomposite

The principal objective of this study was to develop a sensitive and selective electrochemical sensor for phoxim detection based on a reduced graphene oxide–gold nanocomposite (RGO–Au) modified grassy carbon electrode (GCE). The proposed sensor was fabricated by pulsed electrodeposition of reduced graphene oxide followed by chronoamperometric deposition of Au nanoparticles, and applied for the electrochemical detection of phoxim. The modified electrode was characterized by SEM, UV-vis spectroscopy, Raman spectroscopy and XRD. The electrocatalytic activity of RGO–Au/GCE towards reduction of phoxim was evaluated using cyclic voltammetry and differential pulse voltammetry. The results showed that the RGO–Au nanocomposite could greatly enhance the electrochemical reduction of phoxim. Under optimal conditions, the reduction peak current was proportional to phoxim concentration over a wide range between 0.01 and 10 μM, and the detection limit was 0.003 μM (S/N = 3). The proposed phoxim biosensor also exhibited excellent stability and reproducibility. In addition, the sensor was successfully employed for determining phoxim in a variety of food samples.

High-resolution electron microscopy study on the substructure of Ti-Ni-Hf B19' Martensite

The substructure of martensite in the Ti,,Ni,,Hf,, alloy has been investigated by high-resolution electron microscopy (HREM) and discussed within the framework of a phenomenological theoretical analysis. The (001) compound twins and (001) stacking faults were confirmed to be the main substructure inside a martensite variant with some (011) stacking faults infrequently observed. The (001) twinning boundary was straight with some blurred regions and (001) faults existing near the interface. The (001) compound twin alone is shown to be unable to produce the lattice invariant shear necessary for the martensitic transformation

Sensitive determination of quinoline yellow using poly (diallyldimethylammonium chloride) functionalized reduced graphene oxide modified grassy carbon electrode.

A novel poly (diallyldimethylammonium chloride) functionalized reduced graphene oxide (PDDA-RGO) nanocomposite modified electrode was fabricated, and applied for the electrochemical determination of quinoline yellow (QY). The formation of PDDA-RGO nanocomposite was confirmed by SEM, FTIR and Raman spectroscopy. The electrocatalytic activity of PDDA-RGO nanocomposite to the oxidation of QY was evaluated using cyclic voltammetry and differential pulse voltammetry. Under the optimal conditions, the proposed sensor exhibited excellent electrochemical performance towards detection of QY. The linear range is from 0.01 to 10 μM, and the detection limit is down to 0.002 μM (S/N=3). The proposed sensor also exhibited excellent anti-interference property, repeatability and stability. In addition, the proposed electrochemical sensor was successfully applied to determination of QY in soft drink.

HREM studies of twin boundary structure in deformed martensite in the cold-rolled TiNi shape memory alloy

The microstructural aspects and interfacial characteristics of deformed martensite variants in TiNi alloy, cold-rolled to different extents, have been investigated by TEM and HREM techniques. With the increasing reduction of thickness, the following phenomena happen: the dominant deformation mechanism changes from coalescence of the martensite variant to coalescence of the substructural bands and the introduction of secondary twinning plates; the quantities of (100) compound twins and [011] Type II twins are reduced, with an increase of (11 (1) over bar) Type I, (001) compound twins and (011) Type I twins and the introduction of (111) Type I twins; the (100) intervariant boundary gradually loses its mobility and becomes wavy, the (011) Type II twin boundary changes from gradually and randomly curved to the distorted shape, the (11 (1) over bar) Type I, (001) compound and (011) Type I twin boundaries become stepped, and the (111) Type I twin boundaries exhibit a wavy morphology

Hydrothermal preparation of reduced graphene oxide–silver nanocomposite using Plectranthus amboinicus leaf extract and its electrochemical performance

Graphene based nanocomposites are receiving increasing attention in many fields such as material chemistry, environmental science and pharmaceutical science. In this study, a facial synthesis of a reduced graphene oxide-silver nanocomposite (RGO-Ag) was carried out from Plectranthus amboinicus leaf extract. The synthesized nanocomposite was characterized by using X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscope and UV-vis spectroscopy for structural confirmation. The reduction of graphene oxide and silver ions was achieved simultaneously due to the reducibility of the Plectranthus amboinicus leaf extract. We further investigated the electrochemical properties of the biosynthesized RGO-Ag nanocomposite. A nonenzymatic H2O2 electrochemical sensor was shown to be successfully fabricated by using biosynthesized RGO-Ag nanocomposite. Moreover, the fabricated electrochemical sensor also showed good selectivity.

Ascorbic acid amperometric sensor using a graphene-wrapped hierarchical TiO2 nanocomposite

An ascorbic acid (AA) amperometric sensor was fabricated based on a glassy carbon electrode (GCE) modified with a reduced graphene oxide-wrapped hierarchical TiO2 (RGO—TiO2) nanocomposite. The RGO—TiO2 nanocomposite was synthesized via the facial wet chemical method and characterized by scanning electron microscopy and X-ray diffraction. Cyclic voltammetry and amperometric techniques were employed to investigate its electrocatalytic performance towards the AA oxidation. The combined advantages of RGO and TiO2 provide the electrode with higher current response and lower oxidation potential compared with those of bare GCE and TiO2 modified GCE. The proposed electrode can be used for the determination of AA in the wide concentration range from 1 to 1500 µM with the detection limit of 0.5 µM. The proposed electrode was successfully used to determine AA in vitamin C tablets and spiked fruit juice.

High resolution electron microscopy studies on the interface structure of deformed stress induced martensite variants in a Ti-Ni-Nb shape memory alloy

Abstract The interfacial structure of deformed stress induced martensite variants in the Ti-44.7 at.% Ni-9 at.% Nb alloy have been investigated by high resolution electron microscopy. Bands conversions were revealed to happen inside the martensite variants to accommodate the macroscopic strain. The evolution of twinning modes from ( 11 1 ) Type I to (001) compound Type, Type II and (111) Type I were found. These newly formed (001) deformation twins nucleate and grow inside the substructural bands to perform the coalescence of substructural bands. It also causes the rearrangement of the unfavorably oriented bands. The appearance of the Type II twinning plate seems to eliminate the stress concentration during the coalescence of martensite bands. The (111) Type I twinning plate is also introduced to accommodate the shape deformation in different directions.

HREM studies on the microstructure of severely cold-rolled TiNi alloy after reverse martensitic transformation

The microstructure of Ti — 49.8 at.% Ni alloy, which was cold rolled to about 30% reduction in thickness in its martensitic condition and subsequently heated up to 200°C for half an hour, has been studied by high resolution electron microscopy. The newly-formed parent phase has an orientation relationship with the residual martensite: [111]P[110]M, (101)P 6.5° away from (001)M. The parent phase-martensite interface is not smooth and well coherent. The boundary between two subgrains of the parent phase is not straight and perfectly coherent, with partial dislocation observed at the interface. Inside some parent phase grains, thin plate-like {114} and spear-like {112} twin-related parent phase variant pairs are observed. The {114} twinning boundary is relatively straight, but with two or three atomic-height blurred layers existing near the interface.

Thickness-Controllable Silica Coating of CdTe QDs by Reverse Microemulsion Method for the Application in the Growth of Rice

Herein, we report the synthesis and surface modification of CdTe quantum dots (QDs) and the application in the rice growth. Water-soluble thioglycolic acid (TGA) stabilized CdTe quantum dots were synthesized firstly and then the surface modification was conducted. II–VI semiconductor nanocrystals prefer to be coated with silica as inert materials to improve their chemical properties. The toxicity of QDs reduced after the modification. Silica coated QDs were used in the growth of rice seed and the effect was discussed. In our knowledge it is the first time we report that the silica coated QDs had nice effect on the growth of rice.