Novel Covalently Cross-Linked Attapulgite/Poly(acrylic acid-co-acrylamide) Hybrid Hydrogels by Inverse Suspension Polymerization: Synthesis Optimization and Evaluation as Adsorbents for Toxic Heavy Metals

Novel covalently cross-linked microbeads of attapulgite/poly(acrylic acid-co-acrylamide) [ATP/P(AA-AM)] hybrid hydrogels with excellent mechanical stability were synthesized by the inverse suspension copolymerization of acrylic acid (AA) and acrylamide (AM) with multifunctional attapulgite nanorods (MF-ATP) as the sole cross-linker. The synthesis conditions, such as feeding method, neutralization degree of AA, and feed ratio of the comonomers to MF-ATP, were optimized scientifically. The TGA results showed that 96% of the comonomers (AA and AM) were grafted onto the MF-ATP nanorods to form a three-dimensional network skeleton of the hybrid hydrogels, for a feed ratio of MF-ATP nanorods to comonomers of I:S. The ATP/P(AA-AM) hybrid hydrogels exhibited selective adsorption toward toxic heavy-metal ions, especially Pb2+ and Cu2+ ions. In addition, the adsorbed ions could be easily desorbed, indicating the reusability of the ATP/P(AA-AM) hybrid hydrogels. Their use as an adsorbent for toxic heavy-metal ions can therefore be expected to be economically and technically feasible.