Titanium Carbide MXene as NH3 Sensor: Realistic First-Principles Study

This work presents a more realistic study on the potential of titanium carbide MXene (Ti3C2Tx) for gas sensing, by employing first principle calculations. The effects of different ratios of different functional groups on the adsorption of NH3, NO, NO2, N2O, CO, CO2, CH4, and H2S gas molecules on Ti3C2Tx were analyzed. The results indicated that Ti3C2Tx is considerably more sensitive to NH3, among the studied gas molecules, with a charge transfer of -0.098 e and an adsorption energy of -0.36 eV. By analyzing the electrostatic surface potential (ESP) and the projected density of states (PDOS), important physical and mechanical properties that determine the strength and nature of gas-substrate interactions were investigated, and also, the significant role of electrostatic effects on the charge transfer mechanism was revealed. Further, the Bader charge analysis for the closest oxygen and fluorine atoms to NH3 molecule showed that oxygen atoms have 60% to 180% larger charge transfer than fluorine atoms, supporting that Ti3C2Tx substrate with a relatively lower ratio of fluorine surface terminations has a stronger interaction with NH3 gas molecules. The calculations show that in the presence of water molecules, approximately 90% smaller charge transfer between NH3 molecule and the Ti3C2Tx occurs. Ab initio molecular dynamics simulations (AIMD) were also carried out to evaluate the thermal stabilities of Mxenes. The comprehensive study presented in this work provides insights and paves the way for realizing sensitive NH3 sensors based on Ti3C2Tx that can be tuned by the ratio of surface termination groups

Impact of Different Ratios of Fluorine, Oxygen, and Hydroxyl Surface Terminations on Ti3C2T x MXene as Ammonia Sensor: A First-Principles Study

A first-principles study was successfully employed to investigate the impact of different ratios of functional groups such as fluorine (-F), oxygen (-O), and hydroxyl (-OH) on ammonia (NH3) sensing of titanium carbide Mxene. Density functional theory (DFT) calculations were performed for studying the adsorption energy (Eads) and charge transfer (CT) between different gases (NH3, CO 2 , NO, H2S and SO 2 ) and TbC2T x material with a high ratio of fluorine surface functional groups, TbC2(OH)o.44Fo.ssO0.66. DFT calculations showed more sensitivity to NH3, with the highest CT (0.098 e) and the lowest Eads (-0.36 eV) among the mentioned gases. The adsorption of NH3 on TbC2T x MXene with a high and low ratios of fluorine surface functional groups, TbC2(OH)o.44Fo.ssOO.66 (Substrate 1) and TbC2(OH)o.66Fo.2201.11 (Substrate 2) respectively, resulted in adsorption energies of -0.36 eV and -0.49 eV, revealing a stronger adsorption of NH3 on Substrate 2 with low ratios of fluorine. In addition, the isosurfaces representation of charge difference illustrated that fluorine atoms have smaller charge transfer than oxygen atoms when interacting with NH3 molecules. The Bader charge difference for the closest oxygen and fluorine atoms to NH3 molecule showed that oxygen atoms have 60% to 180% larger Bader charge difference, when compared to fluorine atoms, supporting that TbC2T x sensor with a lower ratio of fluorine surface termination has a stronger interaction with NH3 gas molecules

Humidity Sensing Properties of Halogenated Graphene: A Comparison of Fluorinated Graphene and Chlorinated Graphene

This work presents a comparison of humidity sensing properties of fluorinated graphene (FG) and chlorinated graphene (ClG), using experimental data and atomic-level ab-initio simulations. The fabrication of the humidity sensor included drop-casting FG and ClG suspensions on silver (Ag)based interdigitated electrodes (IDEs) to form the sensing layer. The sensitivity of FG and ClG to humidity variations was investigated by measurement of relative resistance change (\u394 R/Rb) of the fabricated humidity sensors when the relative humidity (RH) was changed from 20% to 80%, in steps of 10%, at a constant temperature of 24\ub0 C. For RH transition from 20% to 80%, the \u394 R/Rb of the FG-based and the ClG-based humidity sensors were measured as 13.3% and 10.8%, respectively, resulting in a sensitivity of 0.22%/%RH and 0.18%/%RH, respectively. Density functional theory (DFT) calculations showed adsorption energy (Eads) of-0.50 eV and-0.43 eV for the physisorption of water molecules on the FG and ClG, respectively, demonstrating the higher sensitivity of the FG to humidity. The density of states (DOS) calculations showed that the water-adsorbed FG has a larger DOS near the Fermi level when compared to water-adsorbed ClG, which can be attributed to the stronger interaction and more effective charge transfer between the FG and the water molecule