The Use of Composite TiO2/Activated Carbon Fibers as a Photocatalyst in a Sequential Adsorption/Photocatalysis Process for the Elimination of Ciprofloxacin

Abstract

This work reports the performance of a sequential adsorption/photocatalysis process using activated carbon fibers with deposited TiO2 for the elimination of the antibiotic ciprofloxacin (CIP) in water. A commercial activated carbon fiber (ACF10) was selected as the support, and a TiO2 coating was synthesized using Metal Organic Chemical Vapor Deposition (MOCVD). Experiments were carried out using a photocatalytic reactor irradiated with monochromatic LEDs (365nm). Two different processes have been studied: adsorption/photolysis and adsorption/photocatalysis. The objective was to completely remove the CIP and to evaluate the efficiency of the treatment by following the formation/elimination of aromatic transformation products (ATPs), aliphatic acids, fluoride, and the TOC in the liquid phase. The adsorption kinetic of the CIP by ACF10 was rather slow (71% of CIP adsorbed by 24 h and total adsorption by 20 days). A good fit between the external diffusion limitation model and the experimental curve (kext = 0.0056 h-1) showed an external transfer limitation due to a tight weave of fibers. For the adsorption/photolysis process, a significant decrease of the concentration was achieved (95% after 6 h of irradiation), but ten different ATPs were detected in the liquid phase. To eliminate CIP, 24 h of adsorption and 6 h of irradiation were then necessary, but most of the ATPs remained in solution (total treatment duration: 72 h). With ACF10-TiO2, the same ATPs were present in solution and were eliminated after the 6 h irradiation step (total treatment duration: 30 h). At the end of the treatment, several non-toxic aliphatic acids were found to be present, showing the higher efficiency of this sequential process. The presence of a significant amount of fluorine in the liquid phase suggests some surface photochemical reactions of the adsorbed molecules (CIP and transformation products) and a partial regeneration of the composite material.