Room temperature gas sensing mechanism of SnO2 towards chloroform: Comparing first principles calculations with sensing experiments

Abstract

Herein, room temperature sensing of chloroform (CHCl3) gas using SnO2 nanostructured thin films synthesized via a single-step aerosol chemical vapor deposition (ACVD) process is demonstrated. The sensing mechanism is investigated by means of dispersion-corrected density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations of chloroform’s adsorption on the (110) facet of rutile SnO2. Theoretical calculations demonstrate that direct adsorption of chloroform on the stoichiometric and the oxygen defective SnO2 surface is thermodynamically favorable. Upon adsorption, chloroform molecules donate charge to the surface inducing a drop in the surface resistance, thus promoting a sensing response. Calculated adsorption energies are in the range of (0.7–1.0 eV) per chloroform molecule, which is noticeably larger than the previously calculated adsorption energies on graphene and graphene oxide (0.2–0.4 eV), suggesting a stronger binding on metal-oxides compared to carbon-based materials. Long-range dispersive interactions are found to account for>50% of the calculated adsorption energies. AIMD simulations in the canonical ensemble at room temperature show that chloroform molecules minimally interact with the ionosorbed oxygen species (O2-) suggesting that the room temperature sensing mechanism is mainly attributed to the direct binding of chloroform molecules on the sensor surface.