Influences of As(v), Sb(iii), and Hg(ii) ions on the nucleation and growth of akaganeite†
The physico-chemical properties of akaganeite are known to be modified when formed in the presence of ions, but there are no reports on these effects for arsenic, antimony and mercury. In this work, akaganeites are precipitated via hydrolysis of FeCl3 solutions in the absence and in the presence of varying concentrations of As5+, Sb3+ and Hg2+. All co-precipitated akaganeites exhibit an acicular morphology, and the increase of ion concentration greatly reduces the particle sizes and induces a transformation from nanostructured powders to nanoparticle morphologies. The variation of the mean crystallite size versus ion concentration is fitted to an exponential function, and the derived parameters suggest that the energy for particle growth is greater for akaganeite co-precipitated with As5+. The analysis of infrared, Raman and Mössbauer spectra suggests the replacement of OH⋯Cl groups by ionic species located at the surface and tunnel sites. The 77 K hyperfine data suggest that the iron ions in the vicinity of unoccupied chloride sites and on the surface are the most affected ones. One can unambiguously conclude that these ions do not replace iron in the lattice but are adsorbed at the surface and possibly to tunnel sites as ionic species during nucleation and growth of the particles, altering the surface tension of the nucleus and also the growth energy.