Enhanced toluene sensing performances over commercial Co3O4 modulated by oxygen vacancy via NaBH4-assisted reduction approach

Abstract

Toluene is widely used as a solvent and reactant in a wide range of industrial fields; however, gaseous toluene is toxic to humans, causing severe acute respiratory effects. In this case, Co₃O₄-based chemiresistive gas sensors are promising candidates for monitoring toluene. However, it is challenging to prepare Co₃O₄-based sensing materials with good toluene sensing performances on a large-scale. In this study, oxygen vacancy-rich Co₃O₄ materials were successfully synthesized via the reduction of commercial Co₃O₄ using NaBH₄ as the reducing agent (designated as Co₃O₄-R), and the oxygen vacancy concentrations in Co₃O₄-R materials were effectively modulated by regulating the NaBH₄ concentration. With an increase in oxygen vacancies, the optimal Co₃O₄-R-5 samples displayed better sensing performances toward 100 ppm toluene at 190 °C than that of the pristine commercial Co₃O₄, including an enhanced response value of 3.18 (vs. 1.22 for commercial Co₃O₄) and fast response time of 48 s and recovery time of 38 s. The combination of band structure analysis and chemisorption analysis indicated that the enhanced toluene sensing performances of Co₃O₄-R is attributed to the synergistic effect of reducing the band gap and activating the surface oxygen species. This work demonstrates the first utilization of commercial Co₃O₄ for toluene sensing applications, providing a universal and high-throughput preparation method to prepare gas sensing materials using commercial metal oxides.