Immobilization of active and stable goethite coated-films by a dip-coating process and its application for photo-Fenton systems

The immobilization of active photo-Fenton heterogeneous catalysts over different materials, mainly polymers, has been studied in the literature to avoid their separation from the reaction solution. However, those materials exhibited a high preparation cost and low stability in the process, being difficult their application in an industrial wastewater treatment plant. In this work, a dip-coating method for the immobilization of goethite film on the wall of a photo-Fenton reactor was studied. The influence of the concentration of the initial goethite suspension as well as the withdrawal speed on the coating process, were evaluated. Both variables have shown to be critical in the homogeneity and the optical properties of the layer and therefore in its activity in the photo-assisted reaction.The immobilized photo-Fenton system was tested in the degradation of a mixture of six selected pharmaceutical compounds (nicotine, 4-acetamidoantipyrine, hydrochlorothiazide, ranitidine, diclofenac sodium and sulfamethoxazole) in aqueous solution. The influence of the goethite layer thickness in the photo-activity of the system was established and the results were compared with those obtained using goethite powder in a slurry photo-reactor. One coating cycle, corresponding to 0.05 g/L of catalyst was enough to obtain 100% degradation of the selected pharmaceutical compounds after 6 h of reaction using a low oxidant concentration, except for the nicotine, that seems to be refractory to the tested photo-Fenton system. The use of a commercial goethite as catalyst and the simplicity of the dip-coating procedure make this process an attractive alternative for the design of wastewater treatments based on the heterogeneous photo-Fenton reaction.

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► Immobilization of a goethite catalyst by a dip-coating procedure.
► Resistant and stable catalyst layers for photo-Fenton processes.
► Activity comparable with that of powder goethite in slurry photo-reactors.
► Degradation and partial mineralization of pharmaceuticals in complex aqueous mixtures.