Self-assembly L-cysteine based 2D g-C3N4 nanoflakes for light-dependent degradation of rhodamine B and tetracycline through photocatalysis

Abstract Background Rhodamine B (RhB) is generally used as a fluorescent dye and colorant in the textile and food industries. Tetracycline (TC) is another most frequently detected antibiotic in surface water, sludge, and effluents from hospitals, and may have a critical impact on the aquatic environment. In this study, self-assembly L-cysteine (L-Cys)-based 2D g-C3N4 nanoflakes (CN_Sx; x = 2, 5, and 10) with a porous structure were employed for the visible-light photocatalytic degradation of rhodamine B (RhB) and tetracycline (TC). Methods Upon introduction of L-Cys, the g-C3N4 nanoflakes underwent folding and contained more wrinkles and pinholes than the parent g-C3N4, thus forming porous structures that provided more active sites for the reaction. The COO‒ group of the L-Cys residue could react with either the ‒NH2 of melamine or g-C3N4 to undergo an addition reaction. An excess of L-Cys might induce unwanted defects and distort the structure to enhance the charge recombination, thus hindering the photocatalytic activity. Significant findings Self-assembly L-cysteine (L-Cys)-based 2D g-C3N4 nanoflakes exhibited a light-dependent photocatalytic activity; the CN_S5 showed up to 90 and 70% removal efficiency for RhB (5 ppm) and TC (20 ppm), respectively, within 180 min under irradiation. The enhanced photocatalytic activity could be attributed to its mesoporosity, abundant photoexcited electrons, and few structure defects. These results suggested that self-assembly L-Cys-assisted synthesis is an effective and facile method for the preparation of 2D g-C3N4 nanoflakes for environmental remediation.