A metal-free photocatalytically active hybrid fiber as a novel self-cleaning adsorbent for enhanced tetracycline removal

Abstract

Metal-free photocatalytic degradation of pollutants is an eco-friendly green method for wastewater remediation. Herein we reported using amine modified alginate as an anchor line, as well as graphene oxide (GO) and carbon nanotubes (CNT) as photoactive units to fabricate a recyclable metal-free photocatalytically active hybrid fiber via facile carbodiimine-mediated amide coupling and calcium ion crosslinking. The results show that the photoactive fiber with unique microporosity and enhanced thermal stability has been successfully prepared. The prepared fiber presented a significantly photo-enhanced removal effect on tetracycline (TC). The efficiency of TC removal promoted by the fiber under solar irradiation is 10 times higher than that under dark. In the photocatalytic treatment of TC, the fiber also showed higher TC removal efficiency than that of GO and CNTs alone due to the synergistic effect of GO/CNT. Electron spin resonance analysis confirmed that the fiber under solar irradiation induced the generation of ¹O₂ and holes (h⁺) which degraded TC. UV-vis spectra analysis indicated that GO and CNT components in the fiber promoted TC to undergo oxidative degradation. Major transformation products during TC removal were identified with liquid chromatography mass spectrometry. Finally, such photoactivity of the fiber can be utilized to develop a convenient irradiation/agitation regeneration approach to make the fiber adsorbent reusable. The recycled fiber maintained an excellent level of TC removal performance after multiple recycling steps. Overall, this study provides a new strategy of preparing a recyclable metal-free photocatalytic material for water treatment, and is of great reference value for research in this field.