High-efficiency sulfur-doped carbon photocatalysts synthesized by carbonization of lignosulfonate at low temperature

Heteroatom-doped carbon photocatalysts have attracted increasing attention since they are inexpensive, envi-ronmentally friendly, and highly efficient. Herein, sulfur-doped carbon photocatalysts were prepared by a one-step low-temperature carbonization method using sodium lignosulfonate (SLS) as a starting material. The physicochemical properties of the carbon photocatalysts were characterized by N2 adsorption-desorption, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS), and so on. Compared with the carbon photocatalyst derived from alkali lignin, the sulfur-doped carbons from SLS can improve the degradation of tetracycline by nearly 40%. Sulfur species, i.e., sulfone and sulfoxide, can reduce the bandgap and promote the separation and transfer of photogenerated charge carriers under visible light irradiation. The recycling experimental results of S-C-N2-12 illustrate that the catalyst is stable without a remarkable loss in photocatalytic degradation of tetracycline after five successive runs, suggesting that the sulfur -containing species coordinated on the carbon surface are relatively stable. The results of radical-assisted electron spin resonance (ESR) and radical scavenger experiments show that h+ plays a major role in the degrading of tetracycline. These findings suggest that the sulfur-doped carbon photocatalysts have a great potential in pollutant degradation and wastewater treatment.