Cr-doped Co₃O₄ nanorods as chemiresistor for ultraselective monitoring of methyl benzene

Ultrasensitive and selective detection of methyl benzenes was achieved for Co₃O₄ nanorods through Cr-doping. Pure and 1.17-1.89 at% Cr-doped Co₃O₄ nanorods were synthesized by a solvothermal reaction, followed by calcination at 400 °C for 2 h. The gas-sensing properties of the nanorods were tested to methyl benzene (toluene and xylene) and compared with interfering gases (benzene, ethanol, ammonia, CO and NO ₂) at various concentrations (0.25-5 ppm) and temperatures (250-350 °C). The results demonstrated that Cr-doping significantly enhanced the response to methyl benzenes while suppressing cross-responses to interfering gases, resulting in selectivity for methyl benzene. The ultraselectivity to methyl benzene in the Cr-doped Co₃O₄ nanorods was attributed to catalytic activity and the abundant adsorbed oxygen of the Cr oxides and Co₃O₄ for the partial oxidation of methyl benzenes to more active chemical species.