Designing biomimetic porous celery: TiO₂/ZnO nanocomposite for enhanced CO₂ photoreduction

The nanostructured heterojunction photocatalysts are considered promising in photocatalytic reduction in the carbon dioxide. Herein, we demonstrate a simple sol–gel and hydrolysis process to design nanostructured TiO₂/ZnO heterojunction, by using the biological template celery stalk. The nanostructured photocatalyst consists of anatase TiO₂ and wurtzite ZnO nanoparticles. A well-connected heterojunction, with uniformly distributed nanoparticles, on the pores and folds of celery stems, is obtained. The enhanced specific surface area of 55.5 m²/g is achieved. The crystal structure, morphology and surface composition are investigated by electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. Furthermore, we demonstrate the photocatalytic performance of as-synthesized nanostructure TiO₂/ZnO heterojunction. The photocatalytic yield, of CO₂ reduction into CH₄, exhibits a five times increase, from 0.55 to 2.56 µmol h⁻¹ g⁻¹, for the nanocomposite as compared to the pure TiO₂. This enhanced performance corresponds to the efficient charge transfer and hindrance in the recombination of electron–hole pairs due to the optimum band positions of ZnO and TiO₂. This study demonstrates the potential of using biotemplates to design efficient photocatalysts to convert CO₂ into useful solar fuels.