Photocatalytic properties of PVDF membranes modified with g-C3N4 in the process of Rhodamines decomposition

Abstract

The PVDF membrane modification was performed utilizing the graphitic carbon nitride (g-C3N4) in order to generate photocatalytic properties under visible light irradiation. Graphitic carbon nitride was synthesized via heating of melamine. Commercial PVDF ultrafiltration membranes with cut-off of 150 kDa were activated with a carbonate buffer and g-C3N4 was subsequently attached by terminal amino groups. The structural and morphological properties of g-C3N4 and membrane materials have been characterized using TEM, SEM-EDX, FTIR and EDX analysis. The adsorption of Rhodamine B and Rhodamine 6G on modified membranes and their subsequent degradation of dyes were studied. Membranes with immobilized g-C3N4 possessed 10 times higher adsorption rate of Rhodamine 6G compared to Rhodamine B. The highest photocatalytic activity of modified membranes has been observed in alkaline media. Using isopropanol, tert-butylhydroquinone, potassium iodine and Cr(VI) as OH, O2−, h+ and ē scavengers, it has been shown that the generated holes have been responsible for dyes degradation in acidic media and superoxide radicals in alkaline media, and both of them at neutral conditions. The transport through PVDF-g-C3N4 membranes have been characterized by the volumetric flux of 320–350 L/(m2·h) during the ultrafiltration of dyes. Rejection of Rhodamine B and Rhodamine 6G was of 96 and 94%, respectively. The yield of dyes decomposition was about 80% and 85% for Rhodamine B and Rhodamine 6G, correspondingly, within the range of dye concentration from 5 to 50 mg/L. PVDF-g-C3N4 membranes were characterized with high stability and reusability in process of dyes ultrafiltration in the crossflow mode. The loss of membrane activity after 5 cycles of ultrafiltration (total duration equal to 50 h) was approximately 15%.