Heyun Zhao

One-pot synthesis of La-doped SnO2 layered nanoarrays with an enhanced gas-sensing performance toward acetone

Lanthanum doped SnO2 well-oriented layered nanorod arrays were synthesized by a substrate-free hydrothermal route of using sodium stannate and sodium hydroxide at 210 °C. The morphology and phase structure of the La-doped SnO2 nanoarrays were investigated by X-ray powder diffraction spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and the BET method. The results showed that the La-doped SnO2 layered nanorod array demonstrated a unique nanostructure combined together with double layers of nanorod arrays and could be indexed to a tetragonal structure. The gas sensing performance of La-doped SnO2 nanoarrays indicated that La doping could enhance the sensing response to acetone. The 3.0 at% La-doped level of the SnO2 sensor not only showed good selectivity and excellent stability, but also exhibited a rapid response and recovery compared to the pristine and other La-doped levels of SnO2 nanoarrays. The gas sensing mechanism of the La-doped SnO2 layered nanoarray was discussed. The La-doped SnO2 sensors are considered to be promising candidates for applications in detecting acetone.

Novel multi-layered SnO2 nanoarray: self-sustained hydrothermal synthesis, structure, morphology dependence and growth mechanism

Novel multi-layered well-oriented SnO2 nanoarray assemblies have been successfully realized via a facile one-step self-sustained hydrothermal route. The morphology and phase structure of the multi-layered SnO2 nanorod arrays were examined using X-ray powder diffraction spectroscopy, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and Raman scattering spectroscopy. The results demonstrate that the multi-layered SnO2 nanoarray structure consists of two storeys of rutile SnO2 nanorods oriented in opposite directions with a diameter of 25 nm and a length of 200–400 nm. The dependence of the morphological evolution process of the layered SnO2 nanorod arrays on the pH value, concentration, reaction temperature and reaction time were investigated. The results show that Sn(OH)62− ions play a key role in the formation of the multi-layered SnO2 nanorod array, and the pH value of the precursor solution is an important parameter for creating the multi-layered structure. A nonclassical crystallization process, i.e. an Ostwald ripening process followed by an in situ oriented growth mechanism, is proposed based on the detailed observations from the morphology dependent crystal evolution process.

2D SnO2 Nanosheets: Synthesis, Characterization, Structures, and Excellent Sensing Performance to Ethylene Glycol

Two dimensional (2D)SnO2 nanosheets were synthesized by a substrate-free hydrothermal route using sodium stannate and sodium hydroxide in a mixed solvent of absolute ethanol and deionized water at a lower temperature of 130 °C. The characterization results of the morphology, microstructure, and surface properties of the as-prepared products demonstrated that SnO2 nanosheets with a tetragonal rutile structure, were composed of oriented SnO2 nanoparticles with a diameter of 6–12 nm. The X-ray diffraction (XRD) and high-resolution transmission electron microscope (FETEM) results demonstrated that the dominant exposed surface of the SnO2 nanoparticles was (101), but not (110). The growth and formation was supposed to follow the oriented attachment mechanism. The SnO2 nanosheets exhibited an excellent sensing response toward ethylene glycol at a lower optimal operating voltage of 3.4 V. The response to 400 ppm ethylene glycol reaches 395 at 3.4 V. Even under the low concentration of 5, 10, and 20 ppm, the sensor exhibited a high response of 6.9, 7.8, and 12.0 to ethylene glycol, respectively. The response of the SnO2 nanosheets exhibited a linear dependence on the ethylene glycol concentration from 5 to 1000 ppm. The excellent sensing performance was attributed to the present SnO2 nanoparticles with small size close to the Debye length, the larger specific surface, the high-energy exposed facets of the (101) surface, and the synergistic effects of the SnO2 nanoparticles of the nanosheets.

The Effect of Eu Doping on Microstructure, Morphology and Methanal-Sensing Performance of Highly Ordered SnO2 Nanorods Array

Layered Eu-doped SnO2 ordered nanoarrays constructed by nanorods with 10 nm diameters and several hundred nanometers length were synthesized by a substrate-free hydrothermal route using alcohol and water mixed solvent of sodium stannate and sodium hydroxide at 200 °C. The Eu dopant acted as a crystal growth inhibitor to prevent the SnO2 nanorods growth up, resulting in tenuous SnO2 nanorods ordered arrays. The X-ray diffraction (XRD) revealed the tetragonal rutile-type structure with a systematic average size reduction and unit cell volume tumescence, while enhancing the residual strain as the Eu-doped content increases. The surface defects that were caused by the incorporation of Eu ions within the surface oxide matrix were observed by high-resolution transmission electron microscope (HRTEM). The results of the response properties of sensors based on the different levels of Eu-doped SnO2 layered nanoarrays demonstrated that the 0.5 at % Eu-doped SnO2 layered nanorods arrays exhibited an excellent sensing response to methanal at 278 °C. The reasons of the enhanced sensing performance were discussed from the complicated defect surface structure, the large specific surface area, and the excellent catalytic properties of Eu dopant.

The alcohol-sensing behaviour of SnO2 nanorods prepared by a facile solid state reaction

SnO2 nanorods with the range of 12-85 nm in diameter were fabricated by a facile solid state reaction in the medium of NaCl-KCl mixture at room temperature and calcined at 600, 680, 760 and 840 oC, respectively. The XRD, TEM and XPS were employed to characterize the structure and morphology of the SnO2 nanorods. The influence of the calcination temperature on the gas sensing behaviour of the SnO2 nanorods with different diameter was investigated. The result showed that all the sensors had good response to alcohol. The response of the gracile nanorods prepared at a low calcined temperature demonstrated significantly better than the thick nanorods prepared at a high calcined temperature. The mechanism was attributed to the nonstoichiometric ratio of Sn/O and larger surface area of the gracile nanorods to enhance the oxygen surface adsorption.

Enhanced ethanol response of La2O3-loaded SnO2 nanorods prepared by an improved solid state reaction

La2O3-loaded SnO2 nanorods with rutile structure were successfully synthesized by an improved solid state reaction with the surfactants in the presence of NaCl-KCl. The indirect-heating sensor was prepared using the products as sensing-material to study the response of the La2O3-loaded SnO2 nanorods. The results showed that the performances of the SnO2 nanorods to ethanol was greatly improved after loading La2O3. The significant improvement could be attributed to the excellent catalytic properties of loaded La2O3 and the high surface area.