Photocatalytic degradation of methyl orange by TiO2-coated activated carbon and kinetic study

TiO2-coated activated carbon (AC) grain (TiO2/AC) was prepared through hydrolytic precipitation of TiO2 from Tetrabutylorthotitanate and following heat treatment. The TiO2/AC was characterized by BET, SEM, XRD and optical absorption spectroscopy. The samples were employed as catalysts for methyl orange photocatalytic oxidation degradation in aqueous suspension, used as probe reaction. The kinetics of methyl orange photodegradation was analyzed. The results indicate that BET surface area of TiO2-coated ACs decreased drastically in comparison with the original AC with increasing TiO2 coatings by more than 1 doped cycle. Nano-TiO2 particles were dispersed on the AC with the size of 20–40 nm. Crystalline TiO2 doped onto AC was from anatase to rutile with increase of heat-treatment temperature. The TiO2/AC was shown high photoactivity for the photodegradation of methyl orange (MO) dyestuff in aqueous solution under UV irradiation. The kinetics of photocatalytic MO dyestuff degradation was found to follow a pseudo-first-order rate law. It was observed that the presence of the AC enhanced the photoefficiency of the titanium dioxide catalyst. Different amount of TiO2 coatings induced different increases in the apparent first-order rate constant of the process. The kinetic behavior could be described in terms of a modified Langmuir–Hinshelwood model. The values of the adsorption equilibrium constants for the organic molecules, KC, and for the rate constants, kc, were certainly dependent on TiO2 content. At 47 wt% TiO2 coatings with the highest rate constant, the KC and kc was 0.1116 l mmol−1 and 0.1872 mmol l−1 min−1, respectively. The mechanism of methyl orange degradation was discussed in terms of the titanium dioxide photosensitization by the AC.