Assembly with copper(ii) ions and D-π-A molecules on a graphene surface for ultra-fast acetic acid sensing at room temperature

In this study, a graphene-based composite 4HQ-rGO/Cu2+ was prepared via the supramolecular assembly of graphene nanosheets with 4-hydroxyquinoline (4HQ) and copper(ii) ions. The as-prepared supramolecular assembly exhibited an excellent and enhanced sensing performance towards acetic acid at room-temperature, which was due to the fact that the D-pi-A molecules, i.e. 4HQ, were able to accelerate the charge transfer between the graphene nanosheets and 4HQ molecules when acetic acid was attached. In addition, at room temperature, the copper(ii) ions also played a critical role as the main active site for gas adsorption, and thus the as-fabricated sensor exhibited a high response, outstanding selectivity, and ultra-fast response/recovery time. To examine the selectivity of the Cu2+ ions for the supramolecular assembly, various other transition metal ions such as Mn2+, Fe3+, Co2+, Ni2+, Cu2+, and Cd2+ were attached to the 4HQ-rGO assembly, and their acetic sensing performance was determined. Interestingly, the supramolecular assembly with the Cu2+ ions (4HQ-rGO/Cu2+) exhibited the best sensing performance compared to other metal ion-based 4HQ-rGO materials. Compared with the typical acetic acid gas sensors reported in the literature, it is noteworthy to mention that the as-prepared 4HQ-rGO/Cu2+ supramolecular assembly exhibited the shortest gas response time (within 5 s) at room temperature. The presented study demonstrates that the as-prepared supramolecular assembly is a promising material as a room temperature acetic acid gas sensor in practical applications.