Room temperature NH3 sensing properties and humidity influence of Ti3C2Tx and Ag-Ti3C2Tx in an oxygen-free environment

Ti3C2Tx is a new two-dimensional material with attractive characteristics, but the disadvantage of easy oxidation hinders its practical application. In this paper, single/few-layer Ti3C2Tx (ST) and multilayer Ti3C2Tx (MT) are fabricated from severely oxidized Ti3C2Tx by TMAOH intercalation. Simultaneously most TiO2 nanoparticles are removed. This is a useful path to fabricate Ti3C2Tx with oxygen-rich functional groups by reusing the oxidized Ti3C2Tx. Ag-loaded Ti3C2Tx (AgT) is then successfully synthesized by the self-reduction of AgNO3 on MT. The morphology, surface functional groups, oxidation degree, and oxidation derived defects are characterized by XRD, SEM, TEM, XPS, and FTIR. The gas sensing test results illustrate that MT and AgT are more sensitive to NH3 than ST. These sensors perform best in 40% RH N2 and worst in dry N2, significantly related to humidity. In comparison, AgT exhibits the best humidity resistance due to its minor response degradation from 40% RH N2 to dry N2. The DFT calculation results reveal that with pre-adsorbed H2O, the adsorption capacity of Ti3C2O2 and Ag-Ti3C2O2 for NH3 is considerably enhanced. In the absence of H2O, the adsorption of NH3 by Ag-Ti3C2O2 is much more effective than that of Ti3C2O2, indicating that Ag-Ti3C2O2's response decays less with humidity changes. The enhanced scattering of carriers by the Ti atom at the adsorption site on the Ti3C2O2 surface also contributes to the gas sensing performance. These simulation results are consistent with the experimental results. In addition, the formation of heterojunction between Ag and Ti3C2Tx is beneficial to improving its gas-sensing response to NH3.