Modulating interleaved ZnO assembly with CuO nanoleaves for multifunctional performance: perdurable CO2 gas sensor and visible light catalyst

Abstract

Herein, we report the preparation of well characterized hierarchical CuO/ZnO heterostructures and demonstrate the versatility of this composite as a CO₂ gas sensor and a visible light catalyst for methylene blue (MB) degradation. 3D hierarchical ZnO spheres were decorated with CuO nanoleaves to form the interleaved p-CuO/n-ZnO hetero-surfaces. Subsequently, silver (Ag) functionalized composites were tested for their sensitivity and selectivity towards CO₂ gas as a core application. The nanostructured Ag@CuO/ZnO composite demonstrated an improved sensor response of 34% at 320 °C with response/recovery times of 76 and 265 s compared to the CuO/ZnO composite and control samples. Additionally, the Ag@CuO/ZnO composite displayed excellent recovery (97%), repeatability (96%), accuracy (86%), and lower baseline drifts with a co-efficient of variation (COV) of 4.5% measured over an extended period of 40 days towards 1000 ppm CO₂ gas for 10 individually tested sensors. In a parallel application as a photocatalyst, the CuO/ZnO composite was observed to degrade 98% methylene blue in 180 min with the first order rate constant (κ_app) found to be 6- and 75-fold greater, respectively, when compared to the ZnO and CuO samples under visible light irradiation. The gas sensing mechanism substantiated from in situ diffuse reflectance infra-red Fourier transform spectroscopy (DRIFTS) confirmed the formation of copper carbonate in the presence of CO₂. Interleaved assembly ensured the high mobility of electron–hole pairs with concerted efforts from a high effective surface area, multi-interleaved p/n nano-interfaces and the catalytic role of Ag. The confluence of these factors resulted in an improved CO₂ sensor response and photocatalytic performance.