Ag-SnO ₂ Heterogeneous Nanoparticle/rGO Nanosheet Composites with Porous and Fine-Grained Features for Low-Temperature Detection of ppb-Level NO Gas

Silver-tin oxide heterogeneous nanoparticle/reduced graphene oxide sheet (Ag-SnO₂/rGO) ternary composites were synthesized via a one-step microwave-assisted method to enhance the gas-sensing performance toward NO gas. The morphologies and structure of the Ag-SnO₂/rGO composites were characterized using XRD, SEM, TEM, XPS, and EPR. The Ag-SnO₂/rGO composite exhibits a porous, layered stacking structure. The Ag-SnO₂ nanoparticles formed in situ are homogeneously wrapped on the surfaces of rGO. These nanoparticles range in size from 12 to 33 nm, with a mean value of 19 nm. Also, the Ag-SnO₂/rGO composite possesses enormous heterojunction interfaces and oxygen vacancy defects. Systematic gas-sensing performance tests were conducted on Ag-SnO₂/rGO composites with different Ag contents. The 0.5Ag-SnO₂/rGO sensor demonstrated excellent NO sensing performance with a strong response, a relatively low testing temperature (50-180 °C), and a relatively low detection limit (100 ppb). In particular, the 0.5Ag-SnO₂/rGO sensor exhibited the greatest sensitivity and excellent selectivity for NO gas in the concentration range of 0.1-50 ppm at 100 °C. The responses reach 78, 221, 327, 432, 842, 1032, and 1502 toward NO gases with concentrations of 0.1, 0.5, 1, 5, 10, 25, and 50 ppm, respectively. The improvement in the NO-sensing performance should result from the synergistic effect of Ag, SnO₂, and rGO species, along with massive oxygen vacancies and heterojunctions.