**4. Conclusions**

In this study, the photochemical behaviors of GO and the degradation of SMZ were quantitatively analyzed. GO could promote the degradation of SMZ under UV light. ·OH and 1O2 were the main free radicals participating in the cotransformation between GO and SMZ. High pH, Cl<sup>−</sup>, and SO4<sup>2</sup>− improved the degradation of SMZ by affecting the formation of ·OH. However, the presence of HA consumed ·OH, leading to less degradation of SMZ. As for GO, its color changed from light yellow to dark brown under UV illumination. However, the absorption peak did not shift significantly, and the ratio of *I*D/*I*G was slightly smaller, which indicated that GO was somewhat reduced. The findings of this work may have significant implications for predicting the fate and assessing the potential risks of environmental pollutants and nanoparticles. However, to better understand the environmental behaviors of nanoparticles, long-term experiments under natural solar radiation are still needed.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/2079-499 1/11/8/2134/s1, Figure S1: Figure S1. Photolysis kinetics of SMZ (5 μM) under UV light without GO (a) and the adsorption of SMZ (5 μM) by GO (10 and 100 mg/L) in the dark within 6 h (b), Figure S2: Pseudo first-order fitting results for SMZ degradation kinetics under various GO concentrations (10-50 mg/L), Figure S3: Pseudo first-order kinetics fitting for kinetics of SMZ degradation with L-histidine and KI, Figure S4: Pseudo first-order kinetics fitting for kinetics of SMZ degradation at pH 3.0-9.0, Figure S5: Changes in the color of GO under UV light as a function of irradiation time, Figure S6: Variation of GO absorbance with time under light, Figure S7: Raman spectra of GO before and after UV illumination.

**Author Contributions:** Conceptualization, F.-F.L. and G.-Z.L.; methodology, M.-R.L.; software, M.- R.L. and S.-C.W.; validation, F.-F.L., M.-R.L., S.-C.W., Y.-X.Z. and G.-Z.L.; formal analysis, F.-F.L., Y.-X.Z. and J.-L.F.; investigation, M.-R.L.; resources, M.-R.L. and Y.-X.Z.; data curation, M.-R.L.; writing—original draft preparation, F.-F.L., M.-R.L. and Y.-X.Z.; writing—review and editing, F.- F.L., G.-Z.L. and J.-L.F.; visualization, F.-F.L. and M.-R.L.; supervision, F.-F.L. and G.-Z.L.; project administration, F.-F.L. and G.-Z.L.; funding acquisition, F.-F.L., G.-Z.L. and J.-L.F. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the National Natural Science Foundation of China-Shandong Joint Fund (U1906224), the Natural Science Foundation of Shandong Province (ZR2020MD114, ZR2019MEE026), the Key Research and Development Program of Shandong Province (2019JZZY010333), the Young Scholars Program of Shandong University, and Shandong University Interdisciplinary Research and Innovation Team of Young Scholars (2020QNQT20).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

**Acknowledgments:** We thank the anonymous reviewers for their valuable comments.

**Conflicts of Interest:** The authors declare no conflict of interest.
