Flexible humidity-tolerant γ-Fe2O3-rGO-based nanohybrids for energy efficient selective NO2 gas sensing

Abstract

The present manuscript reports an energy efficient γ-Fe₂O₃-rGO-based humidity tolerant nanohybrids, fabricated on flexible tempered glass (FTG), for NO₂ gas sensing at room temperature. An interaction between n-type γ-Fe₂O₃ and p-type rGO semiconductors assisted in forming a p–n heterojunction at their interface, creating oxygen vacancies (O_v) in the γ-Fe₂O₃ phase, as revealed by XPS analysis. The O₂ adsorbed on these sites produced O₂⁻ species, which facilitated the charge-transfer from O₂⁻ to NO₂ to eventually reduce the resistivity. The voltage at 0.3 volt restricted the effect of humidity on NO₂ gas sensing in a wide RH range (15–97%), making it not only humidity tolerant but also energy efficient. The bending of the FTG up to about 150° resulted in a negligible change in %response (from 56% to 50%) with a minor increase in recovery time, suggesting its potential for usage in flexible electronic devices. Its high selectivity for NO₂ gas sensing is manifested by a minor decrease in %response from 56% to 49% in the presence of common air pollutant gases like Cl₂, NO₂, CO, NH₃, C₃H₆O, H₂S, and C₂H₅OH at 10-ppm of each. The role of rGO in the nanohybrids towards enhancing the conductivity is corroborated by the significantly lower %response observed (9%) for bare γ-Fe₂O₃ film on FTG. The efficient sensing of NO₂ gas has been correlated based on the comparison of the electron affinity (eV) values with other probe gases, following the order: NO₂ (2.30) > CO (1.32) > H₂O (1.3) > NH₃ (0.16) > C₃H₆O (0.00152) > H₂S (−1.16). Thus, the as-designed γ-Fe₂O₃-rGO-based NO₂ gas sensor, operating at 0.3 V at RT, demonstrating selective sensing with rapid response/recovery times (0.08 min/0.25 min) for 0.5 ppm NO₂, having high %response, reproducibility, humidity tolerance in a wide RH range and long-term stability (>52 weeks), is suggested to be a novel NO₂ gas sensing device.