Mechanochemical Modification of Nanourchin-like Crystalline ZnO with Ni(OH) ₂ Noncrystals for Acetone Sensing

Rational design of crystalline/amorphous heterostructures is a promising strategy for enhancing the performance of metal oxide semiconductor gas sensors. Herein, a hierarchical urchin-like ZnO/amorphous Ni(OH)2 (c-ZnO/a-Ni(OH)2) composite was synthesized through a facile, room-temperature mechanochemical route. This method enables the direct formation of an amorphous Ni(OH)2 layer on crystalline ZnO microspheres, which are self-assembled from nanoporous nanosheets. Benefiting from this unique c-ZnO/a-Ni(OH)2 heterostructure, the corresponding microelectromechanical system (MEMS)-based sensor demonstrated a remarkable enhancement in acetone sensing. Specifically, the gas response to 5 ppm acetone at 250 °C was approximately twice that of a pristine ZnO sensor. This superior performance is ascribed to the synergistic interplay between the catalytically active amorphous Ni(OH)2, rich in unsaturated coordination sites, and the efficient charge separation at the c-ZnO/a-Ni(OH)2 interface.