Effect of humic acid on photocatalytic activity of ZnO nanoparticles

• ZnO NPs were synthesized by chemical co-precipitate method.
• The mean diameter was determined to be 55 nm.
• ZnO NPs exhibited excellent photocatalytic activity.
• Presence of HA reduced the photocatalytic efficiency of ZnO NPs.

Zinc oxide nanoparticles (ZnO NPs) are widely used in consumer products including sunscreens, textiles and paints. The indiscriminate use of such materials may leads to its release into the environment. The present study evaluated the photocatalytic effect of ZnO NPs in presence of humic acid (HA), which is an important factor present largely in the environment. ZnO NPs were characterized by using UV–visible spectrophotometer, scanning electron microscopy, particle size analyzer and X-ray diffraction analysis. The mean diameter of the particles was found to be 55 ± 2.1 nm. The XRD patterns exhibited hexagonal structure for ZnO NPs. The photocatalytic activity of ZnO NPs was evaluated based on the change in UV–visible absorption spectra of the methylene blue solution as a function of reaction time under visible light source. The rate of photocatalytic degradation of methylene blue was decreased with increase in HA concentration.