Characterization of network morphology in anion binding hydrogels used for wastewater remediation

This work reports on morphological features of hydrogels, which have been used for the ultimate removal and recovery of nutrient and toxic anions from wastewater effluents. The sorbent used was crosslinked polyamine (PAA·HCl) polymeric hydrogels. The surface topography and morphology of these hydrogels were characterized by tapping mode atomic force microscopy. The change of the gel surface in response to the degree of crosslinking was observed via phase imaging. The crosslinker amount affects both the crosslink density and uniformity. Phase images were recorded at moderate to hard tapping conditions (Asp/A0=0.3-0.6) and related to surface stiffness variations associated with Young's modulus (E) change. Bright ellipse and sponge-like domains of submicrometer scale were found on irregularly crosslinked gels, while the gel topography was uniform in gels that were prepared with a more regular distribution of crosslinks. The observed AFM domain size was strongly affected by the gel's degree of crosslinking.