Stability of nTiO(2) particles and their attachment to sand: Effects of humic acid at different pH

作者：Wu Yang; Cheng Tao^*

来源：Science of the Total Environment, 2016, 541: 579-589.

DOI：10.1016/j.scitotenv.2015.09.116

• nTiO(2)
• Particle stability
• Particle attachment to sand
• Humic acid adsorption
• Fe oxyhydroxide coating
• DLVO interaction energy

The fate and transport of nano-scale or micro-scale titanium dioxide particles (nTiO(2)) in subsurface environments are strongly influenced by the stability of nTiO(2) and their attachment to sediment grains. nTiO(2) may carry either positive or negative charges in natural water, therefore, environmental factors such as pH, humic substances, and Fe oxyhydroxide coatings on sediment grains, which are known to control the stability and transport of negatively-charged colloids, may influence nTiO(2) in different manners. The objective of this study is to investigate the effects of pH and humic acid (HA) on the stability and attachment of nTiO(2) to sand at HA concentrations that are relevant to typical groundwater conditions, so that mechanisms that control nTiO(2) immobilization and transport in natural systems can be elucidated. Stability and attachment of nTiO(2) to quartz sand and Fe oxyhydroxide coated quartz sand are experimentally measured under a range of HA concentrations at pH 5 and 9. Results show that at pH 5, negatively-charged HA strongly adsorbs to positively-charged nTiO(2) and Fe oxyhydroxide, which, at low HA concentrations, partially neutralizes the positive charges on nTiO(2) and Fe oxyhydroxide, and therefore decreases the repulsive electrostatic forces between the surfaces, resulting in nTiO(2) aggregation and attachment. At high HA concentrations, adsorbed HA reverses the surface charges of nTiO(2) and Fe oxyhydroxide, and makes nTiO(2) and Fe oxyhydroxide strongly negatively charged, resulting in stable nTiO(2) suspension and low nTiO(2) attachment. At pH 9, HA, nTiO(2), and Fe oxyhydroxide are all negatively charged, and HA adsorption is low and does not have a strong impact on the stability and attachment of nTiO(2). Overall, this study shows that changes in surface charges of nTiO(2) and Fe oxyhydroxide coating caused by HA adsorption is a key factor that influences the stability and attachment of nTiO(2).

• 出版日期2016-1-15