Fabrication of cubic Co3O4-hexagonal ZnO disk/rGO as a two-phase benzaldehyde sensor via a sequential nucleation strategy

Heterogeneous materials with scientific design have drawn widespread attention for their morphology-dependent properties and synergistic effects in the application of volatile organic compound (VOC) sensing. Here, we report a sequential nucleation strategy to prepare a Co3O4-ZnO/reduced graphene oxide (rGO) heterogeneous composite via the electrostatic adsorption process, chemical coordination step and crystal nucleation procedure. In this approach, the volatility and alkalescence of ammonia effectively avoids spontaneous diffusion and exchange reactions among metal ions with similar radii. Benefitting from the stepwise pathways, the post-generated ZnO exhibits oriented growth along the < 2 <(1)over bar> (1) over bar 0 > face and a hexagonal morphology, which favors the VOC sensing. Based on this, the synthesized Co3O4-ZnO/rGO ternary composite shows an enhanced response (Ra/Rg) of 3.0 and a faster response/recovery of 19/12 s towards 5 ppm benzaldehyde in the gas phase than the individual and binary ZnO-based systems. Furthermore, it also presents a comparable sensitivity of 7.98 mu Acm(-2) mM(-1) towards benzaldehyde in the liquid phase. These superior sensing abilities of the Co3O4-ZnO/rGO sensor can be attributed to the enhanced oxygen adsorption capacity by the large sensing area of hexagonal ZnO disk, the p-n effects of Co3O4-ZnO on rGO sheets, as well as the excellent characteristics of rGO sheets.

Automated summary

The synthesized Co3O4-ZnO/rGO ternary composite displayed superior sensing abilities towards benzaldehyde in both gas and liquid phases, with enhanced response and faster response/recovery compared to individual and binary ZnO-based systems. This was attributed to the oriented growth and hexagonal morphology of ZnO, the p-n effects of Co3O4-ZnO on rGO sheets, and the excellent characteristics of rGO sheets.