Preparation And Gas Sensing Properties Based On Multi-stage Structure Of Zinc Stannate

Hydrogen sulfide（H₂S）,as a toxic and corrosive gas,is very harmful to the environment and life.Therefore,real-time detection for the low concentration H₂S is necessary due to the acceptable concentration of H₂S in the environment being less than83 ppb.In contrast to the simple oxides,the ternary oxides,such as Zn₂SnO₄,were relatively less concerned on their gas sensing properties towards H₂S.The present Zn₂SnO₄ sensors exhibited high optimum temperature（>260℃）,lowest detection（≥1ppm）,and poor selectivity.In order to detect ppb-level H₂S at low temperature,in this thesis,Zn₂SnO₄ micro-or nano-materials with different morphologies were synthesized by hydrothermal method by utilizing deionized water and ethylenediamine as solvents,which were characterized by FT-IR,TG,XRD,SEM,TEM,BET,and XPS.The thick film sensors were fabricated to test their gas sensitivity towards H₂S and other gases.Meanwhile,the sensitive mechanism of the materials to H₂S was also discussed.The main contents of this thesis are as follows:（1）The reaction of 1.2 mmol Zn（CH₃COO）₂,0.6 mmol SnCl₄ and 7.2 mmol NaOH at 200℃for 24 h gave rise to white precursors.After calcined at 600℃for 2 h in air,Zn₂SnO₄ micro-spheres with diameter of¹μm were obtained which comprise of nanosheets with thickness of⁸5nm.The response of the microsphere sensor towards 100 ppm H₂S is 65.13 while the lowest detection limit is 50 ppb at optimum working temperature of 170℃;（2）The precursors obtained from the reaction of 2 mmol Zn（NO₃）₂,0.6 mmol SnCl₄ and 7mmol NaOH at 200℃for 24 h were calcined at 600℃for 2 h in air.Subsequently,the octahedral Zn₂SnO₄ materials with the size of 0.37-0.88μm were obtained.Its BET specific surface area is 21.8 m²·g^-1.With the same optimum working temperature of170℃,its response to 100 ppm H₂S is 172.50 and the lowest detection limit reduces to5 ppb;（3）Hydrothermal reaction of 2 mmol Zn（CH₃COO）₂,0.6 mmol SnCl₄ and 7mmol NaOH at 220℃for 24 h followed by calcining at 600℃for 2 h in air led to the formation of the Zn₂SnO₄ hierarchical micro-spheres with the size of about 2μm.The microspheres were composed of nanosheets with the thickness of 100 nm and octahedra with the size of 0.32-0.95μm,respectively.The optimum working temperature of the micro-sphere sensor fell to 133℃,at which the response to 100 ppm H₂S is 144.33 and the lowest detection limit reduces to 1 ppb.Furthermore,the selectivity and response-recovery characteristics were also improved.In addition,the gas sensing mechanism of these materials was speculated according to the XPS results,which indicated that the redox reaction engenders between H₂S and the surface adsorbed oxygen,and generates the product of SO₂ and H₂O.