Chemical Investigation of the NO_x Detection Mechanisms by Semiconductor Metal Oxide Nanoparticles

This work reports an FTIR study of the NO_x adsorption/desorption cycles on tin oxide nanosized particles under the operating conditions of real sensors (150℃,in presence of O_2).The chemical reactions are monitored in situ and correlated with the variations of the SnO_2 electrical conductivity.On the basis of the FTIR spectra,two contributing mechanisms for the NO_x detection are suggested.The first one presents the formation of bridged nitrate groups bound to the SnO_2 surface via oxygen vacancies acting as electron donor sites.The second mechanism also involves surface oxygen vacancies in the coordination of NO_x,but this time the formation of NO_x anionic species is considered.Both mechanisms lead to the decrease of the electrical conductivity under NO_x adsorption.However,the bridged nitrate groups are not reversible under gas desorption and thus irreversibly contaminate the surface after the first NO_x adsorption.On the contrary,the nitrosyl anionic species are reversible and,from the second NO_x adsorption/desorption cycle,ensure the reproducibility of the sensor response.

Zn-Cu-codoped SnO_2 nanoparticles: Structural, optical, and ferromagnetic behaviors

Zn-Cu-codoped SnO2 nanoparticles have been synthesized by chemical precipitation method. All nanoparticles are crystalline, with the average size increases from 2.55 nm to 4.13 nm as the calcination temperature increases from 400℃ to 600℃. The high calcination temperature can enhance the crystalline quality and grain growth. The oxygen content decreases with decreasing calcination temperature; at a low temperature of 400℃, Zn-Cu-codoped SnO2 nanoparticles are in a rather oxygen-poor state having many oxygen vacancies. The optical band gap energies of Zn-Cu-codoped SnO2 nanoparticles calcined at 400℃ and 600℃ are decreased from 3.93 eV to 3.62 eV due to quantum confinement effects. Both samples exhibit room-temperature ferromagnetism, with a larger saturation magnetization at 400℃ due to the presence of large density of defects such as oxygen vacancies. Zn-Cu-codoped SnO2 nanoparticles exhibit large optical band gap energies and room temperature ferromagnetism, which make them potential candidates for applications in optoelectronics and spintronics.

Dielectric and magnetic properties of(Zn, Co) co-doped SnO_2 nanoparticles

Polycrystalline samples of（Zn, Co） co-doped SnO2 nanoparticles were prepared using a co-precipitation method. The influence of（Zn, Co） co-doping on electrical, dielectric, and magnetic properties was studied. All of the（Zn, Co） co-doped SnO2 powder samples have the same tetragonal structure of SnO2. A decrease in the dielectric constant was observed with the increase of Co doping concentration. It was found that the dielectric constant and dielectric loss values decrease, while AC electrical conductivity increases with doping concentration and frequency. Magnetization measurements revealed that the Co doping SnO2 samples exhibits room temperature ferromagnetism. Our results illustrate that（Zn, Co） co-doped SnO2 nanoparticles have an excellent dielectric, magnetic properties, and high electrical conductivity than those reported previously, indicating that these（Zn, Co） co-doped SnO2 materials can be used in the field of the ultrahigh dielectric material, high frequency device, and spintronics.

Effect of Nanoparticle Size on Gas-sensing Properties of Tin Dioxide Sensors

Sn（OH）4 was prepared by the conventional solution precipitate method,followed by supercritical CO2 drying.The resultant Sn（OH）4 was divided into three aliquots and calcined at 400,600 and 800 °C,respectively,thus SnO2 nanoparticles with average crystallite sizes of 5,10 and 25 nm were obtained.Furthermore,three SnO2 thick film gas sensors（denoted as sensors S-400,S-600 and S-800） were fabricated from the above SnO2 nanoparticles.The adhesion of sensing materials on the surface of alumina tube is good.Compared to the sensors S-600 and S-800,sensor S-400 showed a much higher sensitivity to 1000 μL/L ethanol.On the other hand,sensor S-800 showed a much lower intrinsic resistance and improved selectivity to ethanol than sensors S-400 and S-600.X-Ray diffraction（XRD）,transmission electron microscopy（TEM） and selective area electron diffraction（SAED） measurements were used to characterize the SnO2 nanoparticles calcined at different temperatures.The differences in the gas sensing performance of these sensors were analyzed on the basis of scanning electron microscopy（SEM）.

Photoluminescence and thermoluminescence properties of SnO_2 nanoparticles embedded in Li_2O-K_2O-B_2O_3 with Cu-doping

Cu-doped borate glass co-doped with SnO2nanoparticles is fabricated by melt quenching.The structure and morphology of the samples are examined by X-ray diffraction and field emission scanning electron microscopy.Up-conversion enhancement is observed in the photoluminescence（PL） and thermoluminescence（TL） intensities of the glass.PL emission spectra are identified in the blue and green regions,and a fourfold increase in emission intensity may be observed in the presence of embedded SnO2nanoparticles.The glow curve is recorded at 215 C,and fourfold increases in TL intensity are obtained by addition of 0.1 mol% SnO2nanoparticles to the glass.Higher TL responses of the samples are observed in the energy range of 15-100 KeV.At energy levels greater than;.1 MeV,however,flat responses are obtained.The activation energy and frequency factor of the second-order kinetic reaction are calculated by the peak shape method.