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.