MOF-derived Ag/InPrO sensors with ultra-high sensitivity, quick response and excellent selectivity to formaldehyde gas.

InPrO microtubes are derived from MIL-68, and then Ag nanoparticles are anchored to synthesize Ag/InPrO microtubes. All results indicate that Pr-doping and Ag-loading greatly affect the gas-sensing performance of InO sensor, which InPrO and Ag/InO sensors both exhibit the response value exceeding 900. While Ag/InPrO sensor exhibits the highest response value of 2438.67 to 10 ppm formaldehyde gas, which is about 20 times higher than that of InO sensor (122.59). Furthermore, Ag/InPrO sensor also displays the lower operating temperature (200 °C), shorter response time (12 s), excellent long-term stability, high selectivity, and anti-humidity for formaldehyde gas. According to DFT methods, the adsorption energies of InO, InPrO, and Ag/InPrO sensors for formaldehyde are calculated to be -0.47 eV, -0.63 eV, and -0.94 eV, respectively. These highly-improved gas-sensing properties are due to the synergistic effect of Pr-doping and Ag-loading, which includes the increased surface oxygen from Pr-doping, the electronic and chemical sensitization from Ag nanoparticles. The gas-sensing mechanism of Ag/InPrO sensor provides an effective strategy to achieve an excellent gas sensor for formaldehyde gas.