Facile synthesis of mesoporous ZnO sheets assembled by small nanoparticles for enhanced NO2 sensing performance at room temperature

Here we demonstrate a facile synthesis of nanoparticle-assembled mesoporous ZnO sheets by calcination of a novel sheet-like δ-Zn(OH)2 precursor at low temperature (100 °C). The mesoporous ZnO sheets were assembled by ultrasmall ZnO nanoparticles with an average crystal size less than 10 nm, having a high specific surface area of 87.63 m2 g−1. The high specific surface area, rich mesopores and oxygen vacancies, and the small crystal size of the ZnO nanoparticles contributed to the good NO2 sensing performance of the sensors. The comparison study indicated that the mesoporous ZnO sheets assembled by the smallest nanoparticles exhibited the highest response to ppm level of NO2 at room temperature (the response to 1 ppm of NO2 was 135%). Moreover, the sensor exhibited high response/recovery rates, full reversibility and good selectivity to NO2. Based on the surface depletion model, the higher response of the mesoporous ZnO sheets assembled by the smaller nanoparticles was attributed to their more significant narrowing of the conduction channel upon exposure to NO2.