Phototransformation of zinc oxide nanoparticles and coexisting pollutant: Role of reactive oxygen species

Meng-Ru Li; Fei-Fei Liu; Su-Chun Wang; Xin Cheng; Huan Zhang; Tian-Yuan Huang; Guang-Zhou Liu

doi:10.1016/j.scitotenv.2020.138335

Phototransformation of zinc oxide nanoparticles and coexisting pollutant: Role of reactive oxygen species

Sci Total Environ. 2020 Aug 1:728:138335. doi: 10.1016/j.scitotenv.2020.138335. Epub 2020 Apr 23.

Authors

Meng-Ru Li¹, Fei-Fei Liu², Su-Chun Wang¹, Xin Cheng¹, Huan Zhang¹, Tian-Yuan Huang¹, Guang-Zhou Liu³

Affiliations

¹ Institute of Marine Science and Technology, Shandong University, Qingdao 266237, PR China.
² Institute of Marine Science and Technology, Shandong University, Qingdao 266237, PR China. Electronic address: liufeifei@sdu.edu.cn.
³ Institute of Marine Science and Technology, Shandong University, Qingdao 266237, PR China. Electronic address: liuguangzhou@sdu.edu.cn.

PMID: 32361107
DOI: 10.1016/j.scitotenv.2020.138335

Abstract

In this study, the photochemistry of ZnO NPs and their effect on phototransformation of coexisting pollutants (sulfamethazine, SMZ) were systematically investigated under UV illumination. SMZ (40 μM) degradation was accelerated by ZnO NPs, as the observed reaction rate constant (k_obs) increased from 0.0809 h^-1 to 0.7982 h^-1 at the concentration of 5-50 mg/L ZnO NPs. Free radical quenching and quantification experiments indicated the reactive oxygen species, especially the hydroxyl radicals (OH) and singlet oxygen (¹O₂), made great contributions to SMZ degradation. Moreover, SMZ was prone to be degraded at high pH with k_obs reaching upto 0.5734 h^-1 at pH 12.0. The presence of Cl^- (1000 mM) reduced the SMZ decomposition greatly by 2.4-fold while the effects of SO₄^2- (30 mM) were very limited. Natural organic matter including humic acid and tannic acid both inhibited the degradation of SMZ with k_obs decreasing by 35.4-fold and 132-fold, respectively. During the photoreaction process, ZnO NPs fragmented into relative small size pieces obviously along with the release of Zn²⁺. Finally, the possible cotransformation pathways of ZnO NPs and SMZ were proposed based on SMZ degradation intermediates and the above results. These findings of the present study suggested that the photoreactions of ZnO NPs greatly influenced the transformation of contaminants and ZnO NPs themselves in aquatic environment, which may have significant implications for the fate assessment of NPs and environmental pollutants.

Keywords: Free radicals; Phototransformation; Sulfamethazine; Zinc oxide nanoparticles.