Solid Phase Extraction of Cesium from Aqueous Solution Using Sol-Gel Encapsulated Cobalt Hexacyanoferrate

The synthesis and evaluation of silica sol-gels doped with cobalt hexacyanoferrate (CoHCF) for solid phase extraction of Cs⁺ from aqueous solution is described. The CoHCF is formed by first introducing K₄Fe(CN)₆ (HCF) into the sol-gel and subsequently contacting the porous solid to a solution containing Co²⁺. Generally, sols contain alcohol as a co-solvent, which limits the solubility of HCF. Inclusion of generation-4 polyamidoamine (G4-PAMAM) dendrimer in the sol-gel increases the level of HCF and, in turn, the CoHCF. The uptake capacity of this composite was 0.43±0.01mmolCs⁺g^–1. A second approach to increasing the level of HCF silica is to exclude alcohol from the sol and use ultrasound to obtain a homogeneous suspension; HCF concentrations up to 0.17M in the sol were thereby achieved. After gelation and reaction with Co²⁺, the resulting composite had a capacity of 0.61±0.01mmolCs⁺g^–1. With 0.5mMCs⁺ as the sample, the presence of either 0.5–100mM Na⁺ or 10mMCa²⁺ did not change that value at the 95% confidence level.