Hierarchical three-dimensional (3D) flower-like n-ZnO/p-NiO heterostructures with various Zn_xNi_y molar ratios (Zn₅Ni₁, Zn₂Ni₁, Zn₁Ni₁, Zn₁Ni₂ and Zn₁Ni₅) were synthesized by a facile hydrothermal method. Their crystal phase, surface morphology, elemental composition and chemical state were comprehensively investigated by XRD, SEM, EDS, TEM and XPS techniques. Gas sensing measurements were conducted on all the as-developed Zn_xNi_y-based sensors toward ammonia (NH₃) detection under various working temperatures from 160 to 340 °C. In particular, the as-prepared Zn₁Ni₂ sensor exhibited superior NH₃ sensing performance under optimum working temperature (280 °C) including high response (25 toward 100 ppm), fast response/recovery time (16 s/7 s), low detection limit (50 ppb), good selectivity and long-term stability. The enhanced NH₃ sensing capabilities of Zn₁Ni₂ sensor could be attributed to both the specific hierarchical structure which facilitates the adsorption of NH₃ molecules and produces much more contact sites, and the improved gas response characteristics of p-n heterojunctions. The obtained results clear demonstrated that the optimum n-ZnO/p-NiO heterostructure is indeed very promising sensing material toward NH₃ detection for different applications.

A hierarchically-nanostructured active material composed of nanoparticles, micro-sized dodecahedron and nanowires has been successfully fabricated and used for glucose oxidation, in which the NiCo ₂ O ₄ nanowires (NWs) were grown in situ on the carbon paper (CP) and used for supporting the ZIF-67 derived Co ₃ O ₄ dodecahedron, with the Au nanoparticles (Au-Np) being further electrodeposited on their surface (Au-Np/Co ₃ O ₄ /NiCo ₂ O ₄ NWs/CP). The nanowires effectively avoid the agglomeration of Co ₃ O ₄ , thus providing greater surface area for loading the Au nanoparticles. The introduction of Au can decrease the oxidation potential and enhance the catalytic current, which is beneficial towards the electrocatalytic oxidation of glucose. The Au-Np/Co ₃ O ₄ /NiCo ₂ O ₄ NWs/CP-based non-enzymatic glucose sensor exhibits good sensing performance, including high sensitivity of 15.3 μA/μM/cm ² , outstanding response/recovery times of 2.5/4.0 s (toward 180 μM glucose), good reproducibility, and excellent selectivity. Therefore, constructing hierarchical nanocomposite is a promising strategy to develop non-enzymatic electrochemical glucose sensor.