锐钛矿型氧化物XO_(2)(X=Ti,Sn,Zr,Ir)表面氧化性对NH_(3)气体光学气敏传感特性的影响

The effect of surface oxidation of anatase oxides XO_(2)(X=Ti,Sn,Zr,Ir)on the characteristics of NH_(3) gas optical gas sensing

锐钛矿相金属氧化物XO_(2)(X=Ti,Sn,Zr,Ir)是具有传感特性的常见材料.光学气敏效应是指气体分子吸附在气敏传感材料上,与表面氧空位发生氧化还原反应,由于光学性质发生改变而检测出气体的成分和浓度,因此,氧化还原反应的强弱是反应传感性能的核心原因.本文采用密度泛函理论(DFT)体系下广义梯度近似(GGA)第一性原理平面波超软赝势方法,分析和计算了含氧空位的锐钛矿相XO_(2)(X=Ti,Sn,Zr,Ir)表面特性.通过以NH_(3)为目标分子,研究分子表面吸附引起的氧化还原反应的机理,分析不相同的氧化物表面的几何结构、吸附能、态密度、差分电荷密度、电荷布居、电荷转移、光学性质等.研究发现:目标分子稳定吸附在氧化物表面后改变材料光学性质.SnO_(2)表面对分子的吸附能最大,IrO_(2)表面与分子的吸附距离最小.NH_(3)分子与表面间存在电荷转移,其转移电子数目大小为:IrO_(2)>TiO_(2)>ZrO_(2)>SnO_(2),氧化物表面氧化性的大小为:IrO_(2)氧空位>TiO_(2)氧空位>ZrO_(2)氧空位>SnO_(2)氧空位;比较吸收谱和反射谱发生变化最为明显的是TiO_(2)表面.结论,在可见光范围内,波长在400~530 nm时,SnO_(2)表面光学气敏传感效应更好.而在530~760 nm范围TiO_(2)表面光学气敏传感效应更好.

Anatase metal oxides XO_(2)(X=Ti,Sn,Zr,Ir)are the common materials with sensing properties.The optical gas-sensing effect means that gas molecules are adsorbed on the gas-sensitive sensing material and undergo redox reactions with oxygen vacancies on the surface.The composition and concentration of the gas are detected due to changes in optical properties.Therefore,the strength of the redox reaction is the core reason for sensing performance.In this paper,the generalized gradient approximation(GGA)first-principles plane wave supersoft pseudopotential method under the density functional theory(DFT)system is used to analyze and calculate the oxygen-containing vacancy anatase phase XO_(2)(X=Ti,Sn,Zr,Ir)surface characteristics.By using NH_(3)as the target molecule,the mechanism of the redox reaction caused after adsorption is studied.The geometric structures,adsorption energies,densities of state,differential charge densities,charge populations,charge transfers,and optical properties of different oxide surfaces are analyzed.The study found that the target molecules can be stably adsorbed on the surface of the oxide,which changes the optical properties of the material surface.After adsorbing molecules,the adsorption energy of SnO_(2)surface to molecules is the largest,and the adsorption distance between IrO_(2)surface and molecules is the smallest.There is a charge transfer between NH_(3)molecules and the surface,and the number of transferred electrons is:IrO_(2)>TiO_(2)>ZrO_(2)>SnO_(2),and the oxide surface oxidation is:IrO_(2)oxygen vacancy>TiO_(2)oxygen vacancy>ZrO_(2)oxygen vacancy>SnO_(2)oxygen vacancy.Comparing the absorption spectra and reflection spectra,the most obvious change is the TiO_(2)surface.In conclusion,in the visible light range,the optical gas sensing effect of SnO_(2)surface in 400~530 nm range is better,and that of TiO_(2)surface in the range of 530~760 nm is better.