Formation of Iron(III) (Hydr)oxides on Polyaspartate- and Alginate-Coated Substrates: Effects of Coating Hydrophilicity and Functional Group.

To better understand the transport of contaminants in aq. environments, we need more accurate information about heterogeneous and homogeneous nucleation of Fe(III) hydroxide nanoparticles in the presence of orgs. We combined synchrotron-based grazing incidence small-angle x-ray scattering (GISAXS) and SAXS and other nanoparticle and substrate surface characterization techniques to observe Fe(III) (hydr)oxide [10-4M Fe(NO3)3 in 10mM NaNO3] pptn. on quartz and on polyaspartate- and alginate-coated glass substrates and in soln. (pH =3.7±0.2). Polyaspartate was detd. to be the most neg. charged substrate and quartz the least; however, after 2 h, total nanoparticle vol. calcns.-from GISAXS-indicate that pos. charged pptn. on quartz is twice that of alginate and 10 times higher than on polyaspartate, implying that electrostatics do not govern Fe(III) (hydr)oxide nucleation. On the basis of contact angle measurements and surface characterization, we concluded that the degree of hydrophilicity may control heterogeneous nucleation on quartz and org.-coated substrates. The arrangement of functional groups at the substrate surface (-OH and -COOH) may also contribute. These results provide new information for elucidating the effects of polymeric org. substrate coatings on the size, vol., and location of nucleating Fe hydroxides, which will help predict nanoparticle interactions in natural and engineered systems. [on SciFinder(R)]