Adsorption, aggregation and sedimentation of titanium dioxide nanoparticles and nanotubes in the presence of different sources of humic acids

Tianhui Zhao; Mengyuan Fang; Zhi Tang; Xiaoli Zhao; Fengchang Wu; John P Giesy

doi:10.1016/j.scitotenv.2019.07.312

Adsorption, aggregation and sedimentation of titanium dioxide nanoparticles and nanotubes in the presence of different sources of humic acids

Sci Total Environ. 2019 Nov 20:692:660-668. doi: 10.1016/j.scitotenv.2019.07.312. Epub 2019 Jul 20.

Authors

Tianhui Zhao¹, Mengyuan Fang², Zhi Tang³, Xiaoli Zhao⁴, Fengchang Wu⁴, John P Giesy⁵

Affiliations

¹ College of Water Sciences, Beijing Normal University, Beijing 100875, China; State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
² State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; Faculty of Environmental Science and Engineering, Kunming University of Science and Technology, Kunming, Yunnan 650550, China.
³ State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China. Electronic address: tzwork@hotmail.com.
⁴ State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
⁵ Department of Veterinary Biomedical Sciences and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada; Department of Environmental Science, Baylor University, Waco, TX, United States.

PMID: 31539974
DOI: 10.1016/j.scitotenv.2019.07.312

Abstract

Environmental behavior, bioavailability and risks posed by TiO₂, nanomaterials (TiO₂ NMs) in surface waters are affected by morphologies of the particles and geochemistry, including pH, inorganic and organic matter. Here, the adsorption, aggregation and sedimentation of TiO₂ nanoparticles (TiO₂ NPs) and nanotubes (TiO₂ NTs) were investigated in the presence of Elliott Soil humic acid (HA_E) and Suwannee River humic acids (HA_S). The adsorption amount of HA on TiO₂ NMs was inversely proportional to pH of solution. Maximum adsorption amount of HA on the surface of TiO₂ NMs follows the order TiO₂ NPs + HA_E (236.05 mg/g) > TiO₂ NTs + HA_E (146.05 mg/g) > TiO₂ NTs + HA_S (70.66 mg/g) > TiO₂ NPs + HA_S (37.48 mg/g). Stability of TiO₂ NPs and TiO₂ NTs largely depended on their isoelectric point, morphology and solution pH in the absence of HA. Dispersion of TiO₂ NMs was enhanced with solution pH deviated from the isoelectric point of nanomaterials due to electrostatic repulsion. Moreover, tubular structures of TiO₂ NTs with higher length-diameter ratio seem to aggregate more easily than dose sphere-like TiO₂ NPs. This might be due to their spherical structure enhancing steric repulsion. Notably, the adsorption of HA led to disagglomeration and significant stability of TiO₂ NPs and TiO₂ NTs due to steric hindrance under varying solution pH. In addition, adsorption time, concentration and sources of HA also influenced suspension/sedimentation behavior of TiO₂ NPs and TiO₂ NTs, and aromatic-rich HA_E stabilized TiO₂ NMs suspension more aggressively than aliphatic-rich HA_S.

Keywords: Adsorption; Aggregation; Humic acid; Nanotubes; Sedimentation; Titanium dioxide nanoparticles.