Effects of humic acids on the aggregation and sorption of nano-TiO2

In this study, humic acids (HAs) from three sources, peat, sediment and straw, used to coat nano-TiO 2 were investigated. The results indicated that HAs isolated from peat were aromatic-rich, whereas those isolated from sediment and straw were aliphatic-rich. The nano-TiO 2 sedimentation experiments indicated that the presence of aromatic-rich HAs was more capable of stabilizing nano-TiO 2 particles than was the presence of aliphatic-rich HAs. This result is because the deionized phenolic groups in the HAs were preferentially adsorbed on the nano-TiO 2 surfaces, which generated a higher charge density on the nano-TiO 2 surfaces and caused stronger repulsive forces among particles. Furthermore, the aromatic-rich TiO 2 -HA complexes exhibited a greater sorption capacity than the aliphatic-rich TiO 2 -HAs complexes and nonlinear phenanthrene sorption because of their higher affinity and the condensed state of aromatic fractions. Note that natural organic matters, such as humic acids, in aquatic environments can not only increase the stability of nanoparticles but can also influence the mobility of hydrophobic organic compounds (HOCs).