Xiumei Xu

In2O3 nanoplates: preparation, characterization and gas sensing properties

In this work, a simple route for the synthesis of irregular In2O3 nanoplates in the presence of oleic acid and urea is described. The structure and morphology of the as-obtained product were characterized using X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The results indicate that the synthesized In2O3 nanostructures are composed of irregular nanoplates. The gas sensing properties of the as-obtained product were investigated. The sensor based on the In2O3 irregular nanoplates exhibits a remarkably enhanced response and a fast response/recovery time towards NO2.

Synthesis, characterization and gas sensing properties of porous flower-like indium oxide nanostructures

In this work, flower-like In2O3 nanostructures were prepared with a solvothermal method in the presence of K3C6H5O7·H2O. The as-synthesized samples were characterized by using X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The results indicate that the synthesized flower-like In2O3 nanostructures were constructed by porous nanosheets. The gas sensing properties of the as-obtained products were investigated. It was found that the sensor based on such flower-like In2O3 nanostructures exhibited high response and good selectivity to NO2.

Protein-directed synthesis of highly monodispersed, spherical gold nanoparticles and their applications in multidimensional sensing

An in-situ reduction method has been reported to prepare gold nanoparticles (GNPs) of 40–110 nm by using the green reducing agents of proteins, which are activated by H2O2 and the superoxide anion (). The protein of collagen turns HAuCl4 to the aqueous Au(I) ainions, which are further reduced by other proteins to be highly monodispersed and spherical GNPs of different sizes. The GNPs reduced by different proteins are found to be with the exposed {100} facets, the distinctive UV-vis absorption spectra and various colors (See Fig. 1). By means of extracting the color responses, such as red, green and blue (RGB) alterations, an in-situ reduction method-based multidimensional sensing platform is fabricated in the process of GNPs synthesis. Without further modification of GNPs, nine common proteins are found to be well detected and discriminated at different concentrations. Moreover, this sensing platform also demonstrates great potentials in qualitative and semiquantitative analysis on the individuals of these proteins with high sensitivity. Furthermore, the validation of this multidimensional sensing platform has been carried out by analysis on the spiked proteins in human urine and the target proteins in complex matrix (e.g. lysozyme in human tear).

Synthesis and NO2 sensing properties of indium oxide nanorod clusters via a simple solvothermal route

In this work, a low-cost and environmentally friendly solvothermal route to the synthesis of indium oxide nanorod clusters was described in the presence of sodium chlorate and urea. The morphologies and structures of the as-prepared samples were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The results clearly revealed that the as-prepared indium oxide was composed of nanorods with a diameter of about 15 nm. The gas sensing properties of the as-prepared indium oxide samples were tested towards various gases. The indium oxide nanorod cluster based sensor showed high response and good selectivity toward NO2 at an operating temperature of 150 °C, giving a response of about 41 to 500 ppb.

One-step synthesis and gas sensing properties of hierarchical SnO2 materials

Hierarchical tin oxide(SnO2) architectures were synthesized with a facile hydrothermal method. In the hydrothermal synthesis, sodium dodecyl benzene sulfonate(SDBS) surfactant plays an important role as structure-directing reagent. The synthesized samples were characterized by powder X-ray diffraction(XRD), field emission scanning electron microscopy(FESEM), transmission electron microscopy(TEM) and high-resolution transmission electron microscopy(HRTEM). The results clearly reveal that the hierarchical architectures of SnO2 were composed of aggregated nanosheets with a thickness of about 100 nm. A possible mechanism for the formation of the SnO2 hierarchical architectures was proposed. In addition, the gas sensing properties of the as-prepared products were investigated and it was found that the sensor based on the special SnO2 hierarchical architectures exhibited a high response and good selectivity to NO2 at the optimal working temperature of 160 °C.

One-step synthesis and upconversion luminescence properties of hierarchical In2O3:Yb3+,Er3+ nanorod flowers

In2O3:Yb3+,Er3+ nanorod flowers (NRFs) are prepared by a simple hydrothermal method, where sucrose was used as a ligand. The obtained In2O3:Yb3+,Er3+ NRFs were carefully characterized by scanning electron microscopy (SEM), power X-ray diffraction (XRD), transmission electron microscopy (TEM) and steady/transient spectroscopy. The dependence of the upconversion luminescence (UCL) of In2O3:Yb3+,Er3+ NRFs on morphology, Yb3+ concentration and excitation power was carefully discussed. It is found that the luminescence intensity ratio of the red emission to green emission (R/G) depended on the morphology and Yb3+ concentration, and the green emissions are dominantly resulting from a three-photon populating process with higher Yb3+ doping concentration. More importantly, the concentration quenching in the In2O3:Yb3+,Er3+ NRFs was greatly suppressed due to boundary effects, and is beneficial for lighting and photon energy conversion devices.

Fine-tuning of multiple upconversion emissions by controlling the crystal phase and morphology between GdF3:Yb3+,Tm3+ and GdOF:Yb3+,Tm3+ nanocrystals

Fine-tuning of multi-color emission characteristics of upconversion lanthanide-ion-doped nanocrystals is of high importance for 3-D color displays, multi-color bio-imaging, and multiplexed cellular labeling. Here, we report a strategy enabling crystal phase transition and morphology transformation between GdF3:Yb3+,Tm3+ and GdOF:Yb3+,Tm3+ nanocrystals for fine-tuning of upconversion multi-color emissions. By controlling the ratio between oleylamine (OM)/octadecene (ODE), the orthorhombic phase of rhombic nanoplates (GdF3:Yb3+,Tm3+) was transformed to the cubic phase of nanospheres (GdOF:Yb3+,Tm3+), along with their upconversion color change from blue to red. Broadband upconversion emission was observed from GdOF:Yb3+,Tm3+ nanocrystals at a high excitation power, which is expected to originate from oxygen defects. Multi-color upconversion nanocrystals providing broadband emission are expected to find their applications in broad band multi-color biomolecular imaging requiring a high imaging resolution.