**Phototransformation of Graphene Oxide on the Removal of Sulfamethazine in a Water Environment**

**Fei-Fei Liu 1,\*, Meng-Ru Li 1, Su-Chun Wang 1, Yu-Xue Zhang 1, Guang-Zhou Liu 1 and Jin-Lin Fan 2**

	- 2Department of Science and Technology Management, Shandong University, Jinan 250100, China; fanjinlin@sdu.edu.cn

**Abstract:** Graphene oxide (GO) is widely used in various fields and has raised concerns regarding its potential environmental fate and effect. However, there are few studies on its influence on coexisting pollutants. In this study, the phototransformation of GO and coexisting sulfamethazine (SMZ) under UV irradiation was investigated, with a focus on the role of reactive oxygen species. The results demonstrated that GO promoted the degradation of SMZ under UV irradiation. The higher the concentration of GO, the higher the degradation rate of SMZ, and the faster the first-order reaction rate. Two main radicals, ·OH and 1O2, both contributed greatly in terms of regulating the removal of SMZ. Cl<sup>−</sup>, SO4<sup>2</sup><sup>−</sup>, and pH mainly promoted SMZ degradation by increasing the generation of ·OH, while humic acid inhibited SMZ degradation due to the reduction of ·OH. Moreover, after UV illumination, the GO suspension changed from light yellow to dark brown with increasing absorbance at a wavelength of 225 nm. Raman spectra revealed that the *I*D/*I*G ratio slightly decreased, indicating that some of the functional groups on the surface of GO were removed under low-intensity UV illumination. This study revealed that GO plays important roles in the photochemical transformation of environmental pollutants, which is helpful for understanding the environmental behaviors and risks of nanoparticles in aquatic environments.

**Keywords:** graphene oxide; sulfamethazine; phototransformation; free radicals
