A complex study of photocatalytic oxidation pathways of antibiotics with graphitic carbon nitride-The way towards continuous flow conditions

Abstract

The release of pharmaceuticals and their metabolites into the environment poses pollution risks with consequences in fauna and flora that are not yet fully known nor understood. Photocatalysis with graphitic carbon nitride (g-C3N4) using solar light could potentially contribute to reducing these risks. In this work, g-C3N4 in two different forms was investigated for photooxidative degradation of three chosen antibiotics: tetracycline, trimethoprim, and sulfamethoxazole. The emphasis was put on investigation of degradation pathways description, mechanism modeling, and comparison of two photoreactor systems. g-C3N4 in powder form was studied in a batch photoreactor, while g-C3N4 in the form of a photocatalytic film was studied in a photomicroreactor with a slit geometry. It was found that during the photooxidative processes mainly oxidation products of starting material were prevaling in the reaction mixture, while the degradation products of smaller molecular mass were apparently directly mineralized. The comparison of batch and micro protoreactor has shown that the latter was substantially better performing thanks to the more efficient photocatalytic film irradiation and narrow internal space. It was found that the microphotoreactor with a photocatalytic film based on g-C3N4 is a promising concept that provides a high scalability potential and deserves further investigation and development.The release of pharmaceuticals and their metabolites into the environment poses pollution risks with consequences in fauna and flora that are not yet fully known nor understood. Photocatalysis with graphitic carbon nitride (g-C3N4) using solar light could potentially contribute to reducing these risks. In this work, g-C3N4 in two different forms was investigated for photooxidative degradation of three chosen antibiotics: tetracycline, trimethoprim, and sulfamethoxazole. The emphasis was put on investigation of degradation pathways description, mechanism modeling, and comparison of two photoreactor systems. g-C3N4 in powder form was studied in a batch photoreactor, while g-C3N4 in the form of a photocatalytic film was studied in a photomicroreactor with a slit geometry. It was found that during the photooxidative processes mainly oxidation products of starting material were prevaling in the reaction mixture, while the degradation products of smaller molecular mass were apparently directly mineralized. The comparison of batch and micro protoreactor has shown that the latter was substantially better performing thanks to the more efficient photocatalytic film irradiation and narrow internal space. It was found that the microphotoreactor with a photocatalytic film based on g-C3N4 is a promising concept that provides a high scalability potential and deserves further investigation and development.