Chemical and surface modification in graphene oxide for optimum CO₂ gas sensing performance

The level of CO₂ gas sensing is very crucial for applications such as medical and air quality monitoring. The conventional metal oxide-based CO₂ sensors are sensitive but they need additional excitation like high temperature to be operated at room temperature. In this study, the effect of reduction time on the surface functional groups of the graphene-based sensing layer is investigated to achieve high performance of CO₂ gas sensors to be operated at room temperature. Five reduction times (20, 30, 40, 50, 60 min) are examined to synthesize reduced graphene oxide (rGO) from GO precursor material using green reducing agent ascorbic acid. The structural and morphological properties of rGO-based ArGO samples are investigated using FTIR, Raman, and SEM characterization techniques exhibiting the layered, wrinkled structure with apparent folds on the ArGO thin film surface. The highest and the lowest number of oxygen functional groups are shown by the ArGO20 and ArGO60 thin films, respectively. The electrical characterization presents the highest sheet resistance of 786 KΩ sq−1 and the lowest sheet resistance of 103 KΩ sq−1 for ArGO20 and ArGO60 thin films, respectively. Five sensors are fabricated following the reduction time to detect the CO₂ gas at room temperature. Among them, the ArGO40 sensor demonstrated optimum sensing response towards CO₂ gas with high sensitivity, repeatability, selectivity, and long-term stability, revealing that the reduction time of 40 min is optimum to synthesize functionalized graphene sensing material for CO₂ detection.