Sorption of Cr, Pb, Cu, Zn, Cd, Ni, and Co to nano-TiO₂ in seawater

In this study, the role of nanoparticles in complex aqueous matrices such as the Baltic Sea was investigated in batch-mode experiments in which titanium dioxide nanoparticles (nano-TiO₂) were tested for their ability to remove heavy metals (Cr, Pb, Cu, Zn, Cd, Ni, Co) from multicomponent spiked and non-spiked Baltic Sea water. The experimental data were analyzed using different isotherms (Langmuir, Freundlich, Dubinin–Kaganer–Radushkevich (DKR)) and models (pseudo-first-order and pseudo-second-order models, the double-exponential model, and the Weber–Morris model). The equilibria and kinetic investigations showed that metal sorption to nano-TiO₂ occurs in a two-step, multilayer process and that there is strong competition for sorption sites. The results of the DKR isotherm and dilution experiment indicated weak electrostatic bonds, except for Pb. The distribution coefficient values (1.8 × 10³ to 2.8 × 10⁵ ml g⁻¹) were consistent with the good sorbent properties of nano-TiO₂ and supported the use of the particles in seawater purification technologies. However, metal-enriched nano-TiO₂ may also act as an effective carriers of metals to marine sediments, which could increase their availability to benthic organisms.