Photocatalytic Decolorization of Methylene Blue in Aqueous TiO 2 Suspension

Abstract

ABSTRACT

A series of experiments were carried out to study the photocatalytic decolorization of methylene blue in a thermostatic reactor. The methylene blue solution for the experiment was synthetic, and all of the experiments were performed in a 2-L reactor with UV lamps, a wavelength at 365 nm, in combination with a TiO₂ powder as the catalyst. The results indicated that the optimal tentative conditions were developed in a solution with 0.25 g/L of TiO₂ at a pH of 3.0, and the irradiation flux of an intensity of 2.83 mW/cm² to achieve approximately 98.2% color removal from the methylene blue solution (initial 10 μM) during a reaction time of 60 min. The reaction can be expressed as pseudo first-order kinetics with the observed rate constant, K_obs, 0.067 min₋₁. The addition of H₂O₂ as an oxidation agent in the reaction system results in shortening the reaction time, because the reaction efficiency is increased. However, three kinds of anions (CO₃=, Cl⁻, and SO₄=) can inhibit the reaction progress. A higher temperature is significantly helpful to diminish the TOC of the wastewater during a photocatalysis process. The higher the reaction temperature, the more TOC removal is achieved. The experimental data estimates the activation energy of photocatalysis for methylene blue to be 14.45 KJ/mol, which can be reduced to ∼12.1 KJ/mol by adding 5 mM H₂O₂ into the solution.

Key words:

TiO₂/UV; methylene blue; Langmuir-Hinshelwood model; photocatalysis