Facile synthesis of lignosulfonate-derived sulfur-doped carbon materials for photocatalytic degradation of tetracycline under visible-light irradiation

As the only use of 95% of industrial lignin is as a low-value fuel, it is urgent to explore novel approaches to transform lignin into useful materials. Herein, we report the first transformation of lignin into value-added and inexpensive sulfur-doped carbon photocatalysts by one-step carbonization of sodium lignosulfonates in the presence/absence of Na 2 S·9H 2 O. The sulfur-doped carbon photocatalysts were thoroughly characterized by various physicochemical techniques, including N 2 adsorption, X-ray photoelectron spectroscopy (XPS), scanning transmission microscopy (SEM), photocurrent response, photoluminescence (PL) spectroscopy, and electrochemical impedance spectroscopy (EIS). The IR and XPS spectra show that the dominant sulfur species in the prepared carbon materials are thiophene and SO x groups, such as sulfone groups and sulfonic acid groups. Photocatalytic degradation of tetracycline was employed as a model reaction to evaluate the photocatalytic activities of the sulfur-doped carbons. The incorporation of sulfur-containing groups was found to efficiently decrease the band gaps of these carbon materials and enhance photogenerated charge carrier separation and transfer, thus boosting the tetracycline degradation efficiency. The active sulfur species potentially responsible for the photocatalytic degradation of tetracycline and the degradation mechanism of tetracycline were determined. An innovative strategy for the valorization of lignin to produce valuable carbon photocatalysts was developed in this study. • Sulfur-doped carbon photocatalysts have been prepared from lignosulfonate for the first time. • The introduction of sulfur-containing groups can efficiently boost photocatalytic degradation of tetracycline. • Sulfur-containing groups reduce the band gap and suppress charge carrier recombination. • This work offers a new strategy for the high-value utilization of lignin to carbon photocatalysts.