Photocatalytic degradation of Rhodamine B by TiO2/ZnO nanofibers under visible-light irradiation

Reduction of contaminants in polluted water can be effectively enhanced by a suitable photocatalyst that utilizes an extended light adsorption spectrum, presents a large surface-to-volume ratio to enhance contact with the contaminants, and reduces the inefficiency from recombination of electron-hole pairs. Based on these objectives, TiO2/ZnO nanofibers are synthesized with small diameter having 10-nm poly-crystallites of large surface area by electrospinning followed by calcination. With different concentrations of zinc acetate in the precursor solutions between 0.15%-0.6%, the diameter of the finished nanofibers ranges from 80 to 130 nm. The photocatalytic activities of nanofibers are studied systematically by the degradation of Rhodamine B dye under the 420-nm visible-light irradiation. Photocatalytical activity can be optimized by introducing an appropriate amount of Zn (0.30 wt.% ZnAc in precursor) to maximize the available hydroxyl radicals for oxidation of the dye. Also, the optimal catalyst loading has been determined to be 2 g of TiO2/ZnO nanofibers per liter of water treated after balancing the enhanced active sites with increasing catalyst and catalyst over-dosage that results in solution opacity and catalyst agglomeration. Therefore, enhanced photodegradation of dyes with photocatalyst nanofiber under visible irradiation can be realized. A kinetic model has been developed to describe successfully the photodegradation of RhB.