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The removal of persistent dye pollutants from wastewater streams has drawn a lot of interest from the scienti c community because photocatalysis is the most widely used practical strategy for addressing environmental contamination. Transition-metal oxides are seen to be the most prospective catalysts for e cient and environmental friendly wastewater treatment because of their signi cant photocatalytic activity, excellent solubility, and durability. In this study, we describe the simple, eco-sustainable and cost effective synthesis of ZnO nanoparticles and their use as photocatalysts to break down organic dyes like Congo red (CR) and Malachite Green (MG) in aqueous media. In aqueous solution at ambient temperature, ZnO nanoparticles showed outstanding photocatalytic degradation e ciency of 98.9% for the MG dye and 92.8% for the CR dye. The kinetics of photodegradation were also investigated and followed a pseudo-rst-order mechanism, with rate constants of 0.0204 min − 1 MG and 0.0123 min − 1 for CR in accordance with the Langmuir-Hinshelwood model. Excellent recycling properties were displayed by ZnO nanoparticles for both dyes and the combined effects of their high adsorption capacity and photodegradation of organic dyes make them an extremely effective and affordable catalyst.

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1. INTRODUCTION Nanoparticles are those substances which has a size lower than 100nm at least in 1 dimension. (Batista et al. 2015). Nanoparticles are uniform through out their properties and they are conducting too. At some cases they have special optical properties.(Hewakuruupu Y. L. et al. 2013). Due to their property of having high value of surface area by volume they can be widely used in so many industries, like biomedical, optical, electronic fields etc for applications like fluorescent biological labels, d rug and gene delivery, bio detection of pathogen, detection of proteins, probing of DNA structure, tissue engineering, tumour destruction via heating, separation and purification of biological molecules and cells, MRI contrast enhancement, phagokinetic studies. Also nano-particles are used in the production of food products, cosmetics, medicine, clothing, disinfectants, households, stain-resistant materials, fuel catalysts etc. The nano-particles can be synthesized in so many techniques including chemical as well as using natural raw materials. Like always, the green synthesis of a substance will be highly advanced because of its ore favoured properties. Lilium candidum aka Madonna lily, is a species cominutesg under the true lily family. It is now at the verge of extinction and recorded by IUCN in the list of near threatened species. (Chadbum H 2014). It is a native to Middle East as well as Asia. is used in medical field against carcinogenic factors, ulcers, tumors, external inflammations etc and it is also used in the production of tincture and ointments. And the pollen grain of Lilium candidum is used in the treatment against epilepsy. Ocimum tenuiflorum aka basil, is a perennial plant cominutesg under the family Lamiaceae. It is a native through out Indain sub-continent. (Staples et al. 1999) (Warrier P