抄録
Nanoparticles commonly possess extremely large specific surface areas and surface adsorption capacities for foreign ions. Many intrinsic properties of nanoparticles would be expected to be modified by the adsorption (complexation) process because significant fraction of the atoms are exposed on surface rather than contained in the bulk. However, the theoretical considerations of the processes have been not performed so far. The quantitative prediction of stability of surface complexed nanoparticles is important to model the fate of nanoparticles and the behavior of dissolved element that sorbed to nanoparticles in the surface environments. In this paper, we discussed theoretically the stability of surface complexed nanoparticles. The principle assumption of the theory is that the surface complexation occurs at the bulk of nanoparticles like a solid solution. The surface complexation affects the two aspects to intrinsic stability of nanoparticles. One is the changes in composition of nanoparticles, another is the changes in free energy of formation of surface complexed nanoparticles. The solubility of surface complexed hydrous ferric oxide (HFO) was estimated by using surface complexation modeling coupled with published data of free energy of formation of relevant components. The solubility modeling of surface charged (H+ or OH- sorbed) HFO mechanistically and quantitatively explains the observed non-integral behavior of solubility of HFO. Moreover, the solubility modeling of anion (SO4, PO4 and As(V)) sorbed HFO showed that the sorption process strongly influences on the stability of nanoparticles. This implied that geochemical modeling without considering the effect of sorption process leads to the erroneous prediction of natural system.
