Ammonia gas sensing characteristics of V2O5 nanostructures: a combined experimental and ab initio density functional theory approach

Abstract

A combined experimental and density functional theory of α-V2O5 for ammonia gas sensing have been investigated. The material was synthesized from hydrated NH4VO3 in CVD at 400 °C in N2 atmosphere for different time (12 h and 24 h). Highly crystalline orthorhombic α-V2O5 nano-rods with dominant (001) and (110) planes/facets nano-rods were observed from XRD, SEM and TEM characterizations. Using VSM technique, para-to ferro-magnetic transition was observed in the α-V2O5 nanoparticles synthesized at 24 h. Improved gas sensing was observed in case of the paramagnetic α-V2O5 nano-rods (nanoparticles synthesized at 12 h) compared with the one synthesized at 24 h. Additionally, significant rise in gas sensing response was observed around the metal to insulator transition temperature. Calculation of adsorption of NH3 molecule(s) on (001), (110), (200) and (400) facets showed that (001), (200) and (400) possessed more active sites than (110) surface. However, at higher concentration of NH3 molecules, the number of adsorbed molecules was found to be limited by the available adsorption sites in the case of (001) thereby causing the surface to be unstable. DFT calculations were also used to investigate NH3 adsorption on (110) surface of α-V2O5 with the analysis showing exponential decrease in the electronic band gap of the material’s surface with the increasing numbers of NH3 loadings