Preparation And Gas Sensing Properties For Rare-earth Vanadate Nanomaterials With Specific Morphology

Due to the multi-valence,layered structure,wide band gap,good chemical and thermal stability,vanadium oxide has good prospects for development.The surface of vanadate cerium(CeVO4)and vanadate neodymium(NdVO4)is with efficient catalytic performance and gas sensing properties as important vanadium oxide semiconductor materials,due to the specific electrons structural of 4f and varied electronic transitions modes of rare.earth elements.In this work,the' preparation of CeVO4 nanorods(CeVO4 NRs),NdVO4 NRs and CexNd1-xVO4 NRs with specific morphology by hydrothermal synthesis were performed,and their morphology and structure,gas properties and gas sensing mechanism were further researched.It includes three aspects as follow.(1)CeVO4 NRs with square-section were successfully synthesized via a one-step hydrothermal method using EDTA as a chelating agent,and the length and sectional size are found to be 1.5f?m and 100nm,respectively.The(010)or(004)lattice facets of CeVO4 NRs with high activity reach an exposed percentage of 96.77%.The vanadium ions on the surface of sample exhibit a mixture valence states,i.e.,V5+ and V3+.As V3+ dangling bonds,there are a large number of oxygen vacancies(V0)nearby of V3+,which were induced by EDTA desorption during hydrothermal process.Based on the nature of CeVO4 NRs,the gas sensor prepared by CeVO4 NRs,exhibits a good sensitivity,fast response time(0.5s)and recovery time(80s)with high selectivity to acetone at the optimum working temperature(108?).It is confirmed that the adsorbed oxygen(Oads)are easily formed on the Vo of(010)or(004)lattice planes for CeVO4 NRs occurred by the identification of experiment.And the redox reaction of Oads occured is reversible.The reactive intermediates(O-ads etc.)were generated by Oads,inducing the gas-sensitive response to acetone through the redox reaction with the hydrogen bond of acetone molecules.(2)NdVO4 NRs with rectangular-section were prepared via a one-step hydrothermal method using EDTA as a chelating agent,adjusting pH=9 of the precursor solution.The cross-sectional area and length for NdV04 NRs are found to be approximately 45×130nm2 and 2.?m,respectively.A gas sensor based on NdV04 NRs exhibits a good gas sensing performance and rapid response time(2.5s)to ethanol gas at the operating temperature(115?),due to a large number of active sites(Nd0,V4+)and V0 on the surface of sensors,forming reactive intermediates,O-ads,etc.And O-add,and-OH of ethanol molecules can combined with each other easily on the surface of(010)or(004)lattice planes for NdVO4 NRs with high activity,thus facilitating the redox reaction and gas-sensitive response.(3)On the basis of gas-sensing properties for NdVO4 NRs,Ce3+ doped to the NdVO4 NRs was carried out,and then a seriers of CexNd1-x,VO4 NRs were synthesized.From their gas sensing results,it shows that the n-type semiconductor for CexNd1-xVO4 NRs(x=0.2)were translated to p-type semiconductor,and it also exhibits good gas sensing properties to acetone gas at optimum operating temperature(105?),which superior to the sensitivity of nanorods with the other components(x=0.3,0.5,1).Its response time and response time were 10s and 50s,respectively.Compared with NdVO4 NRs,the sensitivity of Ce?Nd1-xVO4 NRs(x=0.2)increased by 7.5%to acetone gas at operating temperature(115?),which mainly due to the increase of Oads on the surface for CexNd1-xVO4 NRs(x=0.2)by the doping.Based on oxidation of Oads,the gas properties are effectively improved as to the reducing gas.