Sequential adsorption - Photocatalytic oxidation process for wastewater treatment using a composite material TiO2/activated carbon

Abstract

A composite material was tested to eliminate phenol in aqueous solution combining adsorption on activated carbon and photocatalysis with TiO2 in two different ways. A first implementation involved a sequential process with a loop reactor. The aim was to reuse this material as adsorbent several times with in situ photocatalytic regeneration. This process alternated a step of adsorption in the dark and a step of photocatalytic oxidation under UV irradiation with or without H2O2. Without H2O2, the composite material was poorly regenerated due to the accumulation of phenol and intermediates in the solution and on TiO2 particles. In presence of H2O2, the regeneration of the composite material was clearly enhanced. After five consecutive adsorption runs, the amount of eliminated phenol was twice the maximum adsorption capacity. The phenol degradation could be described by a pseudo first-order kinetic model where constants were much higher with H2O2 (about tenfold) due to additional •OH radicals. The second implementation was in a continuous process as with a fixed bed reactor where adsorption and photocatalysis occurred simultaneously. The results were promising as a steady state was reached indicating stabilized behavior for both adsorption and photocatalysis.