Designed synthesis of ZnO/Pd@ZIF-8 hybrid structure for highly sensitive and selective detection of methane in the presence of NO2

Abstract

The selectivity of low-temperature CH4 sensing based on metal oxides remains a challenge, especially in the presence of NO2, a typical concomitant gas with CH4 in coal mines at ppm level. In this work, a novel strategy was provided to realize the low-temperature CH4 sensing with excellent selectivity against NO2 based on the core-shell structured ZnO/Pd@ZIF-8 via a self-templating method. The sensor based on the ternary hybrid exhibited a response of 16.9 % to 0.1 % CH4 under 470 nm light illumination at 80 °C with a response/recovery time of 3.5/4.8 min. The sensor demonstrated the features of full reversibility, long-term stability and good resistance to humidity. The sensor also showed a good selectivity against NO2, where a response of 13.1 % to the mixed gas containing 0.1 % CH4 and 1 ppm NO2. The CH4 sensing at 80 °C was attributed to the photoactivated Pd nanoparticles as well as its catalytic promotion effect to CH4. ZIF-8 with an effective aperture size of 4.0–4.2 Å reduced the diffusion of NO2 due to its larger kinetic molecular of 4.5 Å, while the diffusion of CH4 (3.8 Å) was less affected. The present novel strategy to improve the selectivity of low-temperature CH4 sensing may pave the way to improving the selectivity of other types of metal oxide-based gas sensors.