Fe(III) Hydroxide Nucleation and Growth on Quartz in the Presence of Cu(II), Pb(II), and Cr(III): Metal Hydrolysis and Adsorption

Fe­(III) hydroxide nanoparticles are an essential carrier for aqueous heavy metals. Particularly, iron hydroxide precipitation on mineral surfaces can immobilize aqueous heavy metals. Here, we used grazing-incidence small-angle X-ray scattering (GISAXS) to quantify nucleation and growth of iron hydroxide on quartz in 0.1 mM Fe­(NO₃)₃ solution in the presence of Na⁺, Cu²⁺, Pb²⁺, or Cr³⁺ at pH = 3.7 ± 0.1. In 30 min, the average radii of gyration (<i>R</i>_g) of particles on quartz grew from around 2 to 6 nm in the presence of Na⁺ and Cu²⁺. Interestingly, the particle sizes remained 3.3 ± 0.3 nm in the presence of Pb²⁺, and few particles formed in the presence of Cr³⁺. Quartz crystal microbalance dissipation (QCM-D) measurements showed that only Cr³⁺ adsorbed onto quartz, while Cu²⁺ and Pb²⁺ did not. Cr³⁺ adsorption changed the surface charge of quartz from negative to positive, thus inhibiting the precipitation of positively charged iron hydroxide on quartz. Masses and compositions of the precipitates were also quantified. This study provided new insights on interactions among quartz, iron hydroxide, and metal ions. Such information is helpful not only for environmental remediation but also for the doping design of iron oxide catalysts