Degradation of cosmetic ingredient methylparaben by zinc oxide nanoparticles, aided by sonication, light or a combination of sonication and light

Abstract

Parabens are frequently used in cosmetics and their high quantities in wastewater are detrimental to the ecosystem. The effect of sonication, light aid and a combination of both on nano-sized zinc oxide-mediated degradation of methylparaben (MP) was investigated using electronic spectroscopy and differential conductometry. The time-dependent absorption at λmax of MP (i.e. 254 nm) was used to monitor the system. The degradation process that followed pseudo-first-order kinetics was augmented by the presence of ZnO. Light exposure gave better results than sonication; however, a negative synergy was observed under the combined catalysis. This limitation was overcome using constant sonication time, a high amount of catalyst and variable light exposure duration. Conductivity measurements revealed an excess of free radical or neutral species. X-ray diffraction analysis (XRD) indicated a wurtzite hexagonal structure and crystallite size of 39 nm for ZnO NPs. In Fourier transform infrared spectrum, the Zn-O band was observed at 618 cm−1.

Keywords

• Zinc oxide nanoparticles
• methylparaben degradation
• photosono-catalytic effects
• conductometry
• electronic spectroscopy