Room-temperature efficient NO2 sensors based on Cr-modified ZnO@graphene-like UC composites

The design of high-performance NO2 sensors that work at room-temperature is particularly important for expanding the range of NO2 detection applications. To improve the detection sensitivity of ZnO to NO2 at room-temperature, Cr-modified ZnO@ graphene-like UC (ultrahigh-surface-area carbon matrix) composite sensors were prepared by a two-step wet-impregnation strategy. Transition metal Cr was used to modify ZnO to improve its catalytic properties. The modified ZnO was composited with the nanopores of UC to improve the specific surface area of the material and prevent the agglomeration of ZnO. The sensor exhibits superior NO2 sensing performance at room-temperature, and the response value reaches 2.7 at a NO2 concentration of 1 ppm. Density functional theory (DFT) was used to calculate the adsorption model of nitrogen dioxide on the sensor surface, and the mechanism of enhanced sensing was revealed. The enhanced NO2 gas sensing performance is attributable to Cr modification decreasing the band gap width and enhancing the electron transition ability. Moreover, an impurity energy level is introduced after Cr modification, causing the formation of new chemical bonds, and the orbital hybridization of O, Cr, and ZnO results in the redistribution of electrons and enhanced electron transfer.