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 m(2)/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 A mu mol 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.