Fabrication And Investigation Of SnO₂-based Inorganic-organic Composite

With the increasing development of economic and social activities,the environmental pollution is becoming more and more serious,thus the detection and warning of toxic and harmful gases became urgently demanded.It is very important to develop gas sensors with high sensitivity,excellent selectivity,good stability,low working and rapid response-recovery performance.Due to the prospect of combining the merits of both the organic and inorganic moieties,inorganic-organic composite semiconductor gas-sensing materials attracted much attention in recent years.In this thesis,we prepared the novel inorganic-organic composite semiconductor gas sensors by combining the organic semiconductors(Phthalocyanines and P3HT)with SnO2 porous nanosolid(PNS),and their gas-sensing performance towards NO2 was systematically investigated.In comparison with the gas sensors fabricated from pure inorganic or organic semiconductors,the inorganic-organic composite semiconductor devices exhibited high sensitivity,excellent selectivity,low working and rapid response-recovery speeds.Moreover,the gas-sensing mechanism of the inorganic-organic composite semioconductors was further analyzed by the in-situ infrared spectroscopy and Hall Effect measurements.The main results of this thesis were summarized as follows:(1)SnO2 porous nanosolid(PNS)was prepared via a solvothermal hot-press(SHP)process,and the SnO2-SiPc composite semiconductor was prepared by using SiPc and SnO2 PNS,via a new vacuum in-situ composite route.SnO2 PNS with clean surface was obtained by thermal treating SnO2 PNS in vacum,greatly promoted the interaction and bonding between SnO2 PNS and SiPc.The results indicate that SnO2-SiPc composite semiconductor possesses much higher carrier concentration and mobility than both SiPc and SnO2 PNS.In addition,thermal treating SrnO2-SiPc composite semiconductor at 300? resulted in the further increase of both the carrier concentration and mobility.Accordingly,gas-sensing performance of SnO2-SiPc composite sensor was greatly improved.On the other hand,the in-situ Hall Effect measurement results in NO2 atmosphere indicate that SnO2-SiPc composite semiconductor possesses high carrier concentration and mobility.Thus more electrons can be captured by NO2 molecules when the SnO2-SiPc composite semiconductor was exposed to NO2,resulting in much better gas-sensing performance.(2)SnO2 PNS with uniform pores size higher specific surface area was prepared by combining the sol-gel method and SHP route.Furthermore,SnO2-P3HT composite semiconductor was prepared by combining the as-prepared SnO2 PNS and P3HT,via the vacuum in?situ composite route.Because of the well-matched energy levels of SnO2 and P3HT,a snyergetic effect was observed in SnO2-P3HT composite semiconductor,namely,it possesses strikingly higher carrier concentration and mobility than both P3HT and SnO2 PNS,especially the latter.Besides,the SnO2-P3HT composite semiconductor device also exhibite rather higher sensitivity and excellent selectivity towards NO2 gas.The in-situ Hall Effect measurement result reveals that the greatly improved gas-sensing performance of SnO2-P3HT composite semiconductor gas sensor originated from the disappearance and reappearance of the above"synergetic effect" upon the adsorbing and desorbing NO2 molecules on the surface.(3)SnO2-CuPc composite semiconductor was prepared by using the insoluble CuPc and SnO2 PNS,via a enforceable exchange composite driven by pressure difference route.The results indicate that SnO2-CuPc composite semiconductor dispalys much higher carrier concentration and mobility than SnO2 PNS.In addition,the SnO2-CuPc composite semiconductor device exhibited rather higher sensitivity,excellent selectivity,lower working temperature and faster response speed towards NO2 gas.Accordingly,the in-situ Hall Effect measurement results in NO2 atmosphere indicate that SnO2-CuPc composite semiconductor possesses high carrier concentration and mobility,resulting in much better gas-sensing performance.(4)Using the in-situ FTIR spectroscopy,the adsorption and bonding states of NO2,SO2 and NH3 on the surface of SnO2,SiPc,P3HT,SnO2-SiPc and SnO2-P3HT were mornitroed,and the reaction processes of target molecules were analyzed.Furthermore,the differences in both the responsivity and selectivity of these sensing materials was explained.