Mechanistic study of the increased phototoxicity of titanium dioxide nanoparticles to Chlorella vulgaris in the presence of NOM eco-corona

Ziruo Liu; Subhasis Ghoshal; Audrey Moores; Saji George

doi:10.1016/j.ecoenv.2023.115164

Mechanistic study of the increased phototoxicity of titanium dioxide nanoparticles to Chlorella vulgaris in the presence of NOM eco-corona

Ecotoxicol Environ Saf. 2023 Jun 22:262:115164. doi: 10.1016/j.ecoenv.2023.115164. Online ahead of print.

Authors

Ziruo Liu¹, Subhasis Ghoshal², Audrey Moores³, Saji George⁴

Affiliations

¹ Department of Food Science and Agricultural Chemistry, Macdonald Campus, McGill University, 21,111 Lakeshore, Ste Anne de Bellevue, Quebec H9X 3V9, Canada; Department of Materials Engineering, McGill University, 3610 University Street, Montreal, Quebec H3A 0C5, Canada; Centre in Green Chemistry and Catalysis, Department of Chemistry, McGill University, 801 Sherbrooke St. West, Montreal, QC, H3A 0B8, Canada.
² Department of Civil Engineering, McGill University, Montreal, Quebec H3A 0C3, Canada.
³ Department of Materials Engineering, McGill University, 3610 University Street, Montreal, Quebec H3A 0C5, Canada; Centre in Green Chemistry and Catalysis, Department of Chemistry, McGill University, 801 Sherbrooke St. West, Montreal, QC, H3A 0B8, Canada. Electronic address: audrey.moores@mcgill.ca.
⁴ Department of Food Science and Agricultural Chemistry, Macdonald Campus, McGill University, 21,111 Lakeshore, Ste Anne de Bellevue, Quebec H9X 3V9, Canada. Electronic address: saji.george@mcgill.ca.

PMID: 37356401
DOI: 10.1016/j.ecoenv.2023.115164

Abstract

Widespread applications and release of photoactive nanoparticles (NPs) such as titanium dioxide (TiO₂) into environmental matrices warrant mechanistic investigations addressing toxicity of NPs under environmentally relevant conditions. Accordingly, we investigated the effects of surface adsorbed natural organic matters (NOMs) such as humic acid, tannic acid and lignin on the band gap energy, abiotic reactive oxygen species (ROS) generation, surface chemistry and phototoxicity of TiO₂ NPs. Initially, a liquid assisted grinding method was optimized to produce TiO₂ NPs with a NOM layer of defined thickness for further analysis. Generally, adsorption of NOM reduced the band-gap energy of TiO₂ NPs from 3.08 eV to 0.56 eV with humic acid, 1.92 eV with tannic acid and 2.48 eV with lignin. Light activated ROS generation by TiO₂ NPs such as hydroxyl radicals, however, was reduced by 4, 2, 9 times in those coated with humic acid, tannic acid and lignin, respectively. This reduction in ROS despite decrease in band gap energy corroborated with the decreased surface oxygen vacancy (as revealed by X-ray Photoelectron Spectroscopy (XPS)) and quenching of ROS by surface adsorbed NOM. Despite the reduced ROS generation, the NOM-modified TiO₂ NPs exhibited an increased phototoxicity to Chlorella vulgaris in comparison to pristine TiO₂ NPs. Further analysis suggested that photoactivation of NOM modified TiO₂ NPs releases toxic degradation products. Findings from our studies thus provide mechanistic insight into the ecotoxic potential of NOM-modified TiO₂ NPs when exposed to light in the environment.

Keywords: Band gap energy; Chlorella vulgaris; Eco-corona; Natural organic matters; Phototoxicity; Surface oxygen vacancy; Titanium dioxide.