Interfacial engineering of hierarchical ZnO Tetrapod/Co3O4/Ag heterostructures for room-temperature VOC sensing and photocatalytic dye degradation

Engineering functional metal oxide heterostructures capable of operating under ambient conditions remains a key challenge for gas sensing and photocatalytic applications. This study thus demonstrates the development of a hierarchically structured ZnO tetrapod–based Co₃O₄/Ag heterostructure aimed at enabling gas sensing and photocatalytic applications under ambient conditions. A simplified, scalable synthesis method was used to create an open, three-dimensional architecture incorporating p–n heterojunctions and noble-metal species. Structural and surface analyses (SEM, Raman spectroscopy, XPS, Kelvin probe techniques) confirm the successful decoration of ZnO tetrapod arms with spinel Co₃O₄ nanoparticles and dispersed Ag species, forming nanoscale interfaces of n-type ZnO, p-type Co₃O₄, and metallic Ag, thus inducing interfacial band bending, enhanced oxygen activation, and enhanced charge transfer kinetics. Consequently, the heterostructure is demonstrated to exhibit a stable and reproducible p-type response to ethanol vapor at room temperature without external heating, surpassing pure ZnO and binary counterparts. Additionally, the composite shows significantly improved photocatalytic activity, achieving up to 97.8% methyl orange degradation under ultraviolet light irradiation within 120 minutes, which this study attributes to efficient charge separation and reduced electron–hole recombination at heterointerfaces, thereby demonstrating the potential of hierarchical interface engineering for practical, low-power, room-temperature gas sensing and photocatalytic applications.