Microwave-assisted Solvothermal Synthesis And Gas Sensitivities Of Nanostructured SnO₂

Nanomaterials are attracting a great deal of attention due to their unique properties andwidely applications. Semiconductor oxides have excellent properties as important functionalmaterials and widely used in technological applications. As an n-type semiconductor with awide band gap, tin oxide is well-known for its potential applications in optoelectronic devices,electrochemical energy stroge for lithium ion batteries, catalysis, transistors, and especially ingas sensors. Material experts have been trying to research and develop SnO₂nanomaterialwith good properties because of the potential development in these applications.It is well-known that the morphology, size, and structure of a specific material canstrongly influence the corresponding chemical, physical properties and its practicalapplications. Hence, in this paper, we used affordable SnCl₄·5H₂O, SnCl₂·2H₂O, urea andcitric acid as raw materials and by microwave-assisted solvothermal method to doexperiments, finally obtained SnO₂nanomaterials with different morphologies and nano-size,the complex of CeO₂/SnO₂. The productions were characterized by XRD, SEM, FTIR and TG,and the gas sensitibities of these productions were measured. There are four parts in thispaper:First, when using SnCl₄·5H₂O as mother salt, SnO₂nanomaterials were obtained throughadding different surfactants and tuning microwave reaction parameters, futhermore, theself-assembly process of SnO₂nanomaterials was also discussed. The results show that, citricacid can coordinate with tin oins and slow down the hydrolysis of solution. Well dispersed tinoxide with20nm in diameter was obtained. Microspheres were formed from nanoparticlesthrough self-assemble process with increasing the microwave hydeothermal temperature.Second, when using SnCl₂·2H₂O as mother salt, SnO₂nanomaterials were obtainedthrough adding different surfactants, tuning microwave reaction parameters, and theconcentration of citric acid and urea. It was also discussed that their effects on the phasestructures and morphologies of products as well as the forming mechanism of precursors andtin oxide. The results show that citric acid can not coordinate with Sn²⁺, and the complex agentis urea, citric acid acts as soft template and dispersing agent in the synthesizing process. Theprecursors were oxidized into SnO₂after being calcined at700℃. The resultant SnO₂can preserve their original shapes of precursors after calcination. With the increasment of thesolvothermal tempreature, rhomb-like plates change into3D network hierarchical structurewhich changes with the hydrothermal temperature and concentration of citric acid and urea.Third, CeO₂/SnO₂nanocomposite materials were obtained using in-situ synthesis method.The grains are6nm-20nm in diameter. When the ration of tin and cerium is1:1, the obtainedgrain size of compound is only6nm.Fourth, the SnO₂thick film gas sensors were fabricated by the traditional preparationprocess of thick film, and using static prepared gas method to detect the alcohol sensitivity.The results show that, there is an optimum working temperature, at this tempreature, thesensor has the best activity and shows the highest sensitivity, this temprature is300℃. Thesample with3D network structure has the best alcohol sensitivity among the samples. It isattributed to the novel hierarchical structure. The hierarchical microspheres result in theformation of3D network, which consists of interconnected SnO₂nanoplatelets andinterconnected voids. The former can improve interconnection of nanosized components andhence shorten the transfer of electrons or signals. The latter is favorable for the target gastransportation and accessibility.