Solution Combustion Systhesis Of SnO₂ Nanorod Arrays And Their Gas Sensing Properties

SnO₂,a high-performance semiconductor,is the most frequent and promising gas-sensing material since it has unique surface characterastic and can provide high response,good selectivity for flammable,explosive,toxic and noxious gases with low preparation cost as well as stable thermal and chemical properties.However,the extremely low responses to certain gases,such as aldehydes,ethers and benzene,are obtained for it.Additionally,with the continuous improvement of gas monitoring requirements,the higher goals are put forward for sensors.Therefore,it is a very valuable project to improve the performance of gas sensor by modifying SnO₂ materials with morphology regulation,surface modification and doping.In this thesis,a simple,fast and novel solution combustion method was employed to realize the controllable synthesis of twin-layered SnO₂ nanorod arrays by adjusting the synthesis parameters without adding templates,surfactants,catalysts,growth substrates and pre-deposited SnO₂ seed layers.Then,SnO₂ nanorod arrays were modified by Pt modification of precious metal and La doping of rare-earth element,respectively,and the gas sensing properties of SnO₂ nanorod arrays before and after modification were studied.The specific results are as follows:?1?By adjusting the synthesis parameters,such as tin source,urea and cotton fiber,it was found that a relatively complete double-layer SnO₂ nanorod array structure could be obtained when the calcination temperature was 650 ? and the holding time was for 1 h.?2?The controlled synthesis of twin-layered SnO₂ nanorod arrays was realized by summarnzing the influence rule of various synthesis parameters of the combustion system on the controllability of solution combustion and the morphology of the twin-layered SnO₂ nanorod array.The crystal growth and formation mechanism of the twin-layered SnO₂ nanorod array was proposed.In the process of preparing twin-layered SnO₂ nanorod arrays by solution combustion,the guidance and dispersion of SnO₂ sheets by cotton fiber through inhomogeneous nucleation,the kinetic characteristics of combustion method itself and the intrinsic anisotropy of crystal structure were complementary to each other,which jointly promoted the formation of twin-layered SnO₂ nanorod arrays.?3?The gas sensing properties of SnO₂ materials which were be obtained at the calcination temperatures of 600 ?,650?,700 ? and 800 ? for 1 h,respectively,when other experimental parameters remain optimum were tested.The results revealed that SnO₂ nanorod array sensor had the best gas sensitivity to acetaldehyde when the calcination temperature was 650 ?.The response of the sensor to 200 ppm of acetaldehyde reached 178.77 at the optimal heating voltage of 3.75 V with a fair selectivity?K>1.6?,good response-recovery characteristics and the detection as low as ppb level.?4?The above SnO₂ nanorod arrays obtained by calcination at 650 ? for 1 h were modified by precious metal Pt.It was found that the presence of Pt as metallic nanoparticles on the surface of SnO₂ nanorod?nanoparticles?inhibited the growth of SnO₂ crystal.FESEM results indicated that the addition of Pt destroyed the morphology of SnO₂ nanorod arrays on both sides of SnO₂ lamellar structure and maked the the thickness of nanoparticle layer in the middle of SnO₂ nanoarrays increased sharply.The sensing behaviors suggested that Pt modification can further improved the sensitivities of the SnO₂ samples to acetaldehyde gas,which was the most outstanding with 1.0 at%modifier of Pt.The response of as-prepared sensor based on the SnO₂ decorated with 1.0 at%Pt was exhibited with a value of 863 to 200 ppm of acetaldehyde with a better selectivity?K>1.6?,infinite gas detection range and the detection as low as ppb level at the optimum heating voltage of 3.5 V.However.Pt modification resulted in longer response time of the sensor towards acetaldehyde.?5?The 650 ? calcined SnO₂ nanorod arrays also were modified by rare-earth La doping.It was found that when the doping amount of La increased to 5.0 at%,there was still no impurity phase in the SnO₂ sample.And,La doping prevented SnO₂ crystals from growing while many crystal defects were introduced into the crystal lattice of SnO₂.Like Pt modification,the architecture of SnO₂ nanorod arrays also was be damaged by La incorporation.The performance testing results manifested that La doping effectively activated the sensitivity of SnO₂ for ether.The the sensor based on La-doped SnO₂ materials displyed the best gas-sensitive performance for ether with 5.0 at%La.Its response achieved 386 towards ether with superior selectivity?K=2.4?,ampliative ether detection range and the detection as low as ppb level at the relatively low and optimum heating voltage of 3.0 V.However,the response and recovery times of the sensor for ether were extended after La incorporation.