Promoting the surface catalytic oxidation activity of MOF-derived Co3O4 rectangular rods via Cr-doping for ppb-level xylene detection

Abstract

Promoting the surface catalytic oxidation activity of Co₃O₄ can contribute to the efficient detection of trace reactive gas (e.g. xylene), yet certain challenges remain. In this work, a strategy where Cr³⁺ is incorporated into metal–organic framework (MOF)-templated Co₃O₄ rectangular rods to substitute Co²⁺ to create a sensing material is proposed. The optimized sample (Co₃O₄ with 3 at% Cr-doping) features an increased Co³⁺/Co²⁺ ratio, a high total percentage of reactive oxygen species (surface chemisorbed oxygen and oxygen vacancies), and a high surface area relative to pure Co₃O₄. In situ DRIFTS analysis also demonstrates that the Cr-doping can accelerate the fast catalytic oxidation of xylene over the Co₃O₄ surface. Consequently, this 3 at% Cr–Co₃O₄ gas sensor presents a high response (R_g/R_a = 33.2@100 ppm), and obvious selectivity to xylene at a low working temperature of 130 °C. Moreover, the sensor attains a detection threshold as low as 0.1 ppm, surpassing many recent reports. This study presents a robust strategy involving an active catalytic oxide for ppb-level low reactivity gas detection for early warning in practical applications.