Towards Low Temperature VOCs Chemoresistors : Graphene Oxide versus Porphyrin-based Materials

The sensing of gas molecules is of fundamental importance for environmental monitoring, control of chemical processes, and non-invasive medical diagnostics based on human’s breath analysis [1,2]. In recent years, graphene-based gas sensors have attracted much attention and different materials have been developed [2]. However, they still suffer from several problems, which could be overcome by covering the graphene surface with metal oxides (MOS). Besides, thanks to the high chemical versatility, promising results could be also obtained by coupling porphyrin-based macrocycles to MOS. As such, boosted potentialities, especially in terms of tuned selectivity and low water interference, may be obtained. Therefore, the present work is aimed at evaluating and comparing the sensing at both mild temperatures (also exploiting the UV light) of SnO2 matrix coupled with different porphyrins and graphene oxide (GO, in a fixed SnO2/GO weight ratio [4]) materials towards the sensing of acetone molecules. Specifically, three zinc porphyrins were adopted: zinc tetraphenylporphyrin (ZnTPP) and two perfluorinated derivatives of ZnTPP. The sensor responses at 150 °C of the latter resulted about ten times more intense than those of ZnTPP@Sn and Sn32@GO, whose intensities are similar. By computing the response and recovery times, it can be stated that the former for the three hybrids is comparable, whereas the recovery time of SnO2–porphyrins are significantly longer. Switching the UV lamp on, the samples ability to sense acetone drastically changed: the LOD reached the 200 ppb for all the materials, while perfluorinated derivatives can still guarantee the more intense response. A possible explanation of the role of both GO and porphyrins in boosting the SnO2 sensing of oxidizing molecules (as acetone) is reported, according to the recent literature related to hybrid chemoresistors [3,4] and DSSC devices [5].