Titanium dioxide mediated photo-degradation of methyl orange by ultraviolet light

Abstract

The photo-degradation of an aqueous solution containing the azo dye methyl orange (MO) is reported. Disappearance of color and substrate together with decreases in chemical oxygen demand (COD) and total organic carbon (TOC) content were observed. The effects of some auxiliary dyeing additives were also evaluated. The photo-decomposition followed pseudo-first-order kinetics. Some by-products and their photo-degradation pathways were identified. In addition, the toxicity and phytotoxicity of some by-products were tested using the earthworm (Eisenia andrei) avoidance test and the Bromus ramosus seed germination test. High sensitivity of E. andrei towards soil wetted with MO solution was observed, and germination of B. ramosus seeds was inhibited by MO solution, while no effects were seen for the same solution after photocatalytic oxidation.

Keywords:

• TiO₂
• methyl orange
• photo-decomposition
• intermediate products
• toxicity

Acknowledgements

The authors are indebted to Ms. Hajer Rebai for her kind help in brushing the English of the manuscript.