Photocatalytic degradation of 2,4-dichlorophenoxyacetic acid in a fluidized bed photoreactor with composite template-free TiO 2 photocatalyst

Abstract

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) was degraded in a photocatalytic fluidized bed reactor with template-free TiO 2 photocatalytic spheres in the presence of UV irradiation at 254 nm. The photocatalyst was prepared by binding together pre-calcined commercial TiO 2 particles (Degussa P-25) in an aqueous sol of TiO 2 nanoparticles (composite sol–gel) by the assistance of a polymeric matrix. The photocatalytic spheres had a considerable degree of consistency in their size and shape. X-ray diffraction (XRD), scanning electron microscopy (SEM), and BET specific surface area were used to characterize the photocatalyst. The effects of the initial contaminant concentration, its adsorption on photocatalyst surface, and the fluence rate on the herbicide degradation were studied. 2,4-D showed significant adsorption on the composite TiO 2 spheres. Depending on the initial concentration of 2,4-D, between 50% and 70% was adsorbed on TiO 2 spheres. In all the cases, adsorption equilibrium was reached within 75 min of contact in the fluidized bed reactor with the UV lamps off. After the UV lamps were turned on, 2,4-D was completely degraded within 45 min of irradiation with a fluence rate of 4.16 mW cm −2. Experimental results were fitted with a simplified kinetic model that takes into account the initial concentration of 2,4-D and the fluence rate. A comparison of photocatalytic degradation of 2,4-D with commercial particulate TiO 2 (Degussa P-25) showed that the composite spheres have a photocatalytic activity 26% higher than that obtained with Degussa P-25. The TiO 2 spheres were mechanically robust and demonstrated a high attrition resistance with only 0.014% of TiO 2 released from the spheres due to attrition after 3 h of continuous operation.