Tianmo Liu

Enhanced gas sensing properties by SnO2 nanosphere functionalized TiO2 nanobelts

We report synthesis of hierarchical nanostructures of SnO2 nanosphere functionalized TiO2 nanobelts as a novel sensing material by a simple hydrothermal technique. A systematic comparison study reveals an enhanced gas sensing performance for the sensor made of SnO2 and TiO2 toward volatile organic compounds of several species over that of the commonly applied undecorated TiO2 nanobelts. The improved gas sensing properties are attributed to the pronounced electron transfer between the hierarchical nanostructures and the absorbed oxygen species as well as to the heterojunctions of the SnO2 nanospheres to the TiO2 nanobelts which provide additional reaction rooms. The results represent an advance of hierarchical nanostructures in further enhancing the functionality of gas sensors, and this facile method could be applicable to many sensing materials.

Selective Detection of Formaldehyde Gas Using a Cd-Doped TiO(2)-SnO(2) Sensor.

We report the microstructure and gas-sensing properties of a nonequilibrium TiO2-SnO2 solid solution prepared by the sol-gel method. In particular, we focus on the effect of Cd doping on the sensing behavior of the TiO2-SnO2 sensor. Of all volatile organic compound gases examined, the sensor with Cd doping exhibits exclusive selectivity as well as high sensitivity to formaldehyde, a main harmful indoor gas. The key gas-sensing quantities, maximum sensitivity, optimal working temperature, and response and recovery time, are found to meet the basic industrial needs. This makes the Cd-doped TiO2-SnO2 composite a promising sensor material for detecting the formaldehyde gas.

Growth-controlled NiCo2S4 nanosheet arrays with self-decorated nanoneedles for high-performance pseudocapacitors

We report a synthesis of NiCo2S4 nanosheet arrays with self-decorated nanoneedles on nickel foams by a facile and efficient two-step hydrothermal approach. We demonstrate that the morphologies of various three-dimensional nanostructures such as nanoneedle arrays, nanosheet arrays, and nanoneedle-decorated nanosheet arrays can be manipulated by tuning the amount of additive ammonium fluoride alone in the reaction. The unusual nanostructure of nanoneedles grown on the surface of NiCo2S4 nanosheet arrays shows a large electroactive surface area and superior electrochemical properties. The electrode made of the NiCo2S4 nanosheet arrays with self-decorated nanoneedles shows greatly improved electrochemical performances with an ultrahigh specific capacitance of 2617.6 F g−1 at a current density of 15 mA cm−2 and of 2051.0 F g−1 even at a current density of 30 mA cm−2. The electrode also exhibits an excellent cycling stability by retaining 93.2% of its original state after 5000 cycles, rendering the NiCo2S4 nanosheet arrays with self-decorated nanoneedles a potential electrode material for high-performance supercapacitors.

Hydrothermal synthesis of different TiO2 nanostructures: structure, growth and gas sensor properties

A type of titanium precursor, H-exchanged titanate nanobelts, was used to prepare nanosized anatase titanium dioxide (TiO2) with various morphologies by hydrothermal method. Nanorods, nanobelts, nano-polyhedrons and nanoparticles were successfully synthesized. We found that CTAB and EDTA-4Na+ play critical roles in synthesizing the nanorods and nano-polyhedrons. All the samples exhibit rapid response and recovery time to ethanol, but Nanorods, nanobelts and nano-polyhedrons show lager response than nanoparticles.

Crystal structure and strain state of molecular beam epitaxial grown Gd2O3 on Si(1 1 1) substrates: a diffraction study

In this work, Gd2O3 thin films grown by molecular beam epitaxy on Si(1?1?1) substrates were investigated by various diffraction methods. The Gd2O3 layers exhibit a highly perfect cubic bixbyite structure with a single domain orientation, low lattice mismatch with Si and good crystallinity. Threefold in-plane symmetry and bright streaky patterns were observed during the oxide growth by in situ high-energy electron diffraction. X-ray diffraction results demonstrate that Gd2O3 on Si(1?1?1) is fully epitaxial with a single domain orientation with aandepitaxial relationship. The lattice parameter of Gd2O3 is slightly smaller than the one of the Si substrate. In the in-plane direction, the Gd2O3 layer is only ?0.1% mismatched with the Si substrate (relative to 2aSi). This indicates a pseudomorphic growth of Gd2O3 on Si(1?1?1), where the Gd2O3 layer experiences tensile strain in the in-plane direction and compressive strain in the out-of-plane direction.

Synthesis of carbon fiber@nickel oxide nanosheet core–shells for high-performance supercapacitors

We report on the design and synthesis of CFs@NiO-NSs and NiO-NSs core–shells by growing nickel oxide nanosheets (NiO-NSs) on carbon fibers (CFs), and test their applications as supercapacitors. We fabricate electrodes based upon the CFs@NiO-NSs core–shell and the NiO-NSs shell and measure their electrochemical performances. In comparison to the NiO-NSs electrode, the CFs@NiO-NSs electrode shows a more enhanced electrochemical performance with a high specific capacitance of 891.1 F g−1 at a current density of 1 A g−1, a good rate capability with 83.3% retention even at a high current density of 20 A g−1, and an excellent cycling stability by retaining 95% even after 5000 cycles. These results make the CFs@NiO-NSs a promising electrode material for high-performance supercapacitors.

Deformation behaviour of hot extruded Mg alloy AZ31 during compressive deformation

Abstract Deformation behaviour of a hot extruded Mg–3Al–1Zn alloy subjected to uniaxial compression at room temperature was investigated. Microstructure evolution showed that the amount of lenticular shaped extension twins increased with the increase in true strain when it was lower than ∼4% but decreased when it was higher than ∼4%. Previous studies indicated that detwinning occurred. However, we have demonstrated in the present paper that no detwinning occurred, but a process of twin growth and coalescence, leading to an analogous detwinning phenomenon observed in the optical micrographs because most of the matrixes were consumed. A strong texture evolution occurred in this process, and the reorientation produced by strong twinning was mainly responsible for strain hardening when compressed along the extrusion direction.

Hydrothermal synthesis and growth mechanisms of different ZnO nanostructures and their gas-sensing properties

ZnO nanostructures with four different morphologies (nanoparticles, nanorods, mixtures of nanoparticles and nanorods as well as nanoflowers aggregated by nanoparticles and nanorods) were synthesized successfully via simple hydrothermal method. The crystalline structures of ZnO samples were characterized by the X-ray diffraction and the microscopic morphologies of ZnO samples were observed by the scanning electron microscopy. Besides, the probable growth mechanisms of ZnO nanostructures with four different morphologies were proposed. We found that Hexamethylenetetramine (HMT), the halogen ion F− and the concentration of OH− played a significant role in the morphology of ZnO nanocrystalline. In addition, further gas sensitivity measurements revealed that all the as-synthesized ZnO performed gas-sensing properties towards the ethanol gas with very low concentration. Furthermore, the gas-sensing properties of nanoflowers were much more excellent than the other three low-dimension nanostructures, which indicated that the splendid gas-sensing properties of ZnO nanoflowers were contributed to their large specific area.

Effect of different structures on the gas sensing property of ZnO

We have successfully reported a new diamond-like morphology of zinc oxide (ZnO) structures via a simple hydrothermal method and discussed its probable growth mechanism. Compared with other morphologies of ZnO structures (microrods and nanosheets), nanodiamonds have excellent gas-sensing property owning to its large specific surface area, holding the perfect promise for ZnO powders as underlying gas-sensing materials. Furthermore, the as-prepared nanosheets assisted with the sodium citrate as an additive were found to show better gas-sensing property due to the smaller size than microrods. We found the positive role of the sodium citrate and reaction time in the growth of nanosheets and nanodiamonds respectively and the corresponding influences on growth mechanism were discussed.

Hydrothermal synthesis and gas sensing properties of different titanate nanostructures

Anatase TiO2 nanoparticles and other three different morphologies of titanate nanostructures such as nanotubes, nanosheets and nanowires were successfully prepared by hydrothermal method. The structures and morphologies of the final products were characterized with field-emission scanning electron microscopy (FE-SEM). Phase analysis was carried out using X-ray diffraction (XRD). A novel formation mechanism from anatase TiO2 nanoparticles to titanate nanowires is proposed based on FE-SEM. The gas sensing properties to ethanol were also investigated. The results indicate that nanotubes, nanosheets, nanowires show much less resistance and larger response than nanoparticles.