An investigation into the simultaneous influence of withdrawal speed and number of coated layers on photocatalytic activity of ZnO thin films

Abstract

In this context, an investigation into the influence of withdrawal speed and number of coated layers of ZnO thin films on their photocatalytic activity has been performed, to study simultaneous effect of the two parameters. Zinc acetate dehydrate, isopropanol and monoethanol amine were used as starting materials and the films were deposited on soda lime glass substrates from a sol prepared through sol–gel route. Three levels of speeds (withdrawal speed = 3, 6, and 12 cm/min) and four levels of number of layers (number of coated layers = 10, 20, 30, and 40) have been applied, using a dip-coating technique, in deposition process. The structural properties of the samples have been studied using an X-ray diffractometer, field emission scanning electron microscope, and scanning probe microscopy. Estimation of coatings porosity has also been made using image analysis of large-scale field emission scanning electron microscope images. Photocatalytic dye degradation experiments revealed that, both parameters are of great significance. It was observed that, at constant number of coated layers of 10, the films prepared by withdrawal speed = 3 cm/min revealed a noticeably better removal of 39 % than the ones prepared by withdrawal speed = 12 cm/min. However, as the number of coated layers grew to 40, the significance of the withdrawal speed decreased. Therefore, at number of coated layers = 40 the difference of performance for thin films prepared by the highest and lowest withdrawal speed was found to be only 2 %, which indicates the dominant role of number of coated layers at higher withdrawal speeds. Since higher speeds are more convenient to be achieved, by improving the number of coated layers, thin films with better photocatalytic performance could be obtained more easily.