Hydrogels of poly(vinyl alcohol) (PVA) and alginate that are cross-linked with boric acid (PVA-B) hydrogels can be stable in water when they are further cross-linked with a nucleophile complex that replaces the boron complex. The B(OH)(3) dimer cores, rather than the BO4- cores, constitute the skeleton of the PVA-B matrix under neutral or acidic conditions. The nucleophiles SO42-, NO3- and H2PO4- can substitute up to 52, 44, and 59% of the boron cores in the PVA-B matrix to form shape-stable PVA hydrogels with isotactic segments at d:B ratios of 3.0:1, 2.6:1, and 3.5:1, respectively. The boron substitution is proposed to be achieved by allowing nucleophiles to attack carbon atoms that are linked to the B3 complex and replace one B(OH)(3) from the dimer core via Walden inversion mechanisms at 1:1 stoichiometry. Shape-stable PVA-S immobilized copper hexacyanoferrate (CuHCF) hydrogels were synthesized to effectively adsorb cesium (Cs) ions from a water.