AACVD-derived ZnO/NiO/Pt heterostructured thin films for photoactivated low-temperature CO₂ sensing

This work reports the synthesis and comprehensive characterization of ZnO, NiO, and ZnO/NiO heterostructured thin films, along with their Pt-decorated counterparts, fabricated by aerosol-assisted chemical vapor deposition (AACVD) for low-temperature CO₂ sensing. Grazing-incidence X-ray diffraction confirmed the formation of hexagonal ZnO and cubic NiO phases, with crystallite sizes in the range of 7–13 nm. The films exhibited compact and homogeneous morphologies, while EDS analysis verified uniform elemental distribution and high reproducibility. Optical measurements revealed direct band gaps of 3.3 eV for ZnO and 3.5 eV for NiO, indicating high-quality films. Gas sensing performance was evaluated under controlled CO₂/N₂ atmospheres (0.1–3%) with and without UV-A irradiation. Photoactivation significantly enhanced the sensor response by promoting charge carrier generation and surface oxygen activation, enabling efficient detection at temperatures below 100 °C. While single-layer ZnO and NiO films exhibited typical n-type and p-type responses, respectively, the ZnO/NiO heterostructure showed superior performance, achieving a maximum response of ∼6.5%, along with improved response (3.6 min) and recovery (3.2 min) times under UV-A illumination. Pt nanoparticle decoration further enhanced sensing performance via catalytic spillover effects, while also modulating adsorption–desorption kinetics. The improved sensing behavior is attributed to the synergistic interplay between photoactivation, heterointerface engineering, and catalytic sensitization. These findings highlight the potential of AACVD-derived ZnO/NiO/Pt heterostructures as low-power, high-performance CO₂ sensors for environmental and industrial applications.