PEI doped In2O3 nanospheres based gas sensor for high-performance formaldehyde detection

Doping metal oxides with proper polymers would be another effective strategy to address their gas sensing shortcomings, such as low sensitivity and unsatisfactory detection limits in certain applications. Herein, polyethyleneimine (PEI) with its high thermal stability and special functional groups was employed to dope In2O3 using a facile hydrothermal method followed by calcination. The resultant In2O3/PEI nanospheres (PIn) composites sensors exhibited improved selectivity and sensitivity to formaldehyde. Specifically, the PIn composite sensor with 5 wt% PEI (PIn-5%) showed a high response value of 420.1 to 105 ppm formaldehyde at 110 degrees C, which was about four times higher than that of bare In2O3 and twice that of the mixture of In2O3 and PEI. The composite sensor also demonstrated good response linearity, low detection limit and fast response. To demonstrate its potential application in food quality inspection, the composite sensor was employed in rapid detection of low concentrations of residual formaldehyde on vegetables, revealing that formaldehyde might be misused as a preservative in some cases. Finally, the gas sensing mechanism of PIn composites was discussed, and their improved formaldehyde sensing performance was attributed to the heterojunctions formed between PEI and In2O3, the specific selective interaction of PEI with formaldehyde, the increased oxygen vacancy, and the porous structure with an enlarged surface area and small In2O3 nanoparticle size. These results suggested a promising approach to enhancing the gas sensing performance of metals oxides using appropriate polymers.