Synthesis of pH, thermally, and shape stable poly(vinyl alcohol) and alginate cross-linked hydrogels for cesium adsorption from water

The poly(vinyl alcohol) (PVA) and alginate hydrogels are non-toxic and biocompatible immobilization matrix with wide applications. The PVA hydrogels crosslinked with boric acid or borate under acidic or alkaline conditions, respectively, were yielded with/without further crosslinking using sulfate. Four types of hydrogels (A-D) were generated and tested. This study aims at exploring the stability of the hydrogels A-D subjected to repeated pH shift to reveal the applicability of these hydrogels in environments with varying pH's. The appearance, structural stability under drying, weight and thermal stability and constituent boron and sulfate ions intake/release rates under pH shifts were characterized for these hydrogels. The PVA hydrogels formed with boric acid, with or without secondary sulfate crosslinking, cannot resist repeated pH challenge. Conversely, the PVA hydrogels formed with borate would have high stability under pH shift, regardless of the implementation of secondary sulfate crosslinking. The clusters with tetraborate ([B₄]) were proposed to be key linkage blocks to establish pH stable PVA hydrogel. The adsorption tests revealed that the boric acid dimer ([B₃][B₃]) or borate–sulfate ([B₃][SO₄]) hydrogels have low intra diffusional resistances and the [B₄] hydrogels are best-performing cesium ion adsorbents.