| With the accelerating of industrialization, gas sensors have been widely used in many areas, such as environmental monitoring (SO2、NO2、CO and so on), domestic safety, public security and automotive applications, etc. Moreover, for low-cost and portable applications, semiconducting metal oxides gas sensors have been received more attention from all walks of life. Metal oxides are typically used as gas-sensing materials, which plays an important role in gas sensing detection. At present, it is strongly needed to develop new type advanced gas sensing materials in order to improve sustainability of our society and quality of life.As an n-type semiconductor, SnO2 has been widely studied for applications as gas sensing material. Compared with other metal oxide semiconductors, SnO2 is the earliest to be used into a commercial gas sensor, due to its unique sensing abilities. However their properties are still limited by some shortcomings such as high operating temperature, low sensitivity, poor selectivity and stability. In this work, we firstly prepared porous SnO2 hollow spheres, and then functionalized their surfaces by using second components, including metal oxide (NiO) and noble metal (Au), to enhance their sensing properties. In addition, mechanisms of their microstructural formation and gas sensing properties enhancement were studied comprehensively.1. Facile synthesis and high formaldehyde-sensing performance of nickel oxide-SnO2 hybrid nanospheres.A formaldehyde gas sensor based on multi-hierarchy hybrid composite was simply fabricated by modifying SnO2 nanospheres with nickel oxide dopants. This hybrid composite provided an indoor air monitoring sensor to achieve ultraselective, sensitive, and reliable detection towards formaldehyde. Compared with pure SnO2 nanospheres, the merged oxides exhibit superior sensing properties at 100℃, opening up an additional avenue to further manipulate individual oxides of interest for gas sensors on demand. The enhanced sensor properties can be attributed to the following factors:(ⅰ) The addition of nickel oxide dopants results in an extensive increase in the value of Ra especially when the temperatures below 200℃; (ⅱ) the Ni ions can easy aggregate a full monolayer of oxygen ions which can be oxidized into a higher oxidation state; and (ⅲ) the formation of P-N junction by adding the nickel oxide.2. Fabrication of highly sensitive ethanol gas sensor based on porous SnO2 nanospheres sensitized with nanosized Au particles.Porous SnO2 hollow spheres were employed as a unique platform to deposit Au nanoparticles and the as-prepared Au-decorated porous SnO2 hollow spheres were further investigated as a novel model for chemical gas sensors by using ethanol and acetone as the probe molecule. The obtained results show that the gas sensor exhibits excellent sensing properties, such as high response(response value of ethanol increases from 38.8 to 109.5 and response value of acetone increases from 10.6 to 23.8), fast response-recovery, lower detectable threshold(0.5ppm) and good stability. The enhanced sensor properties can be attributed to the following factors:(ⅰ) The large surface-to-volume ratio and porous structure of the hollow spheres are beneficial for gas diffusion and mass transport in sensing layer; (ⅱ) The porous shells can provide abundant channels for gas molecules to diffuse into the interior of hollow spheres, thus generating two electron depletion layers on both the outer and inner surfaces of sphere shells; and (ⅲ) The Au nanoparticles supported on the SnO2 shells can serve as catalysts to promote the kinetics of surface reactions between gas molecules and the sensing layer. |
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