Effect of pH and temperature on photocatalytic oxidation of methyl orange using black sand as photocatalyst

Abstract

Azo dyes are considered hazardous compounds for the environment and human health. Methyl orange is one type of azo dyes and it is widely used in textile, leather, and other chemical industries. The degradation of this compound is a challenge for traditional treatments. Advanced oxidation processes such as heterogeneous photocatalysis, sonolysis, radiolysis, etc., become an alternative for mineralizing organic compounds by producing a highly oxidant agent (OH•). Nowadays, a great number of research studies have tried to modify TiO2 with metals in order to improve the degradation of hazardous pollutants such as azo dyes. This study used black sand as an alternative photocatalyst, evaluating the influence of pH (2, 5, 3 and 8) and temperature (20, 25, 30 and 35°C) on the photocatalytic oxidation of methyl orange. Black sand was magnetically separated. The fraction that showed the best characteristics for dye degradation was used. Experimental results allowed establishing that methyl orange photocatalytic oxidation is best performed at pH 2 and 30°C, with a degradation percentage of 96.93%. The reaction follows a pseudo-first order kinetic. In addition, the kinetic coefficient found at different temperatures was correlated using Arrhenius equation in order to determinate changes in the kinetic coefficient depending on the temperature. The equation pre-exponential coefficient was 374782115.1 and energy activation was -58,104.4 J mol-1 K-1.