Gas Adsorption Thermodynamics Deduced from the Electrical Responses in Gas-Gated Field-Effect Nanosensors

Understanding the underlying physical chemistry governing the nanomaterial-based electrical gas sensing process is pivotal for the rational design of high-performance gas sensors. Herein, using a remarkable ppb-level NO₂-gated field-effect nanosensor that is based on a reduced graphene oxide rGO/TiO₂ nanoparticle heterojunction, as an exploratory platform, we have established a generic physical chemistry model to quantitatively gain insight into the correlation between the measured source-drain (S-D) current and the gas sorption thermodynamics in this NO₂ nanosensor. Based on thin-film field-effect transistor theory, the measured S-D current leads to the solution to the gas-induced gate voltage, which further solves the surface charge density using the Graham surface potential vs surface charge density function. Consequently, based on the Van’t Hoff equation, key thermodynamic information can be obtained from this model including adsorption equilibrium constants and adsorption enthalpy of NO₂ on TiO₂ nanoparticles. The acquisition of gas adsorption enthalpy provides a generic and nonspecific method to identify the nature of the adsorbed molecules