The designed tough hydrogels, depending on energy dissipation mechanism, possess excellent biocompatibility, stimuli-responsiveness, and outstanding mechanical properties. However, the application of hydrogels is greatly limited in actuators and sensors for the lack of instantaneous recovery and resilience. In this work, we synthesized a double cross-linking poly(acrylic acid) hydrogel via a simple, one-pot, visible-light-trigger polymerization, with carboxymethyl cellulose as initiator and the first cross-linker, N,N'-methylene bis(acrylamide) (MBA) as the second cross-linker. The tensile strength and elastic modulus are in the range of 724-352 kPa and 115-307 kPa, respectively, depending on the MBA content. The swelling ratio of hydrogels dramatically decreased with increasing the MBA content. DMA results indicate that the internal friction between molecules within the hydrogel decreases with the increase of MBA content. Cyclic tensile tests show that after the structure stabilizes, the resilience, maximum stress, and residual strain of Gel-2 maintains over 93% (95% for successive cyclic tensile test), 115 kPa and less than 3%, respectively, at a strain of 125%. The values of resilience and residual strain are almost constant in both successive and intermittent cyclic tensile tests. Moreover, the swollen hydrogel has higher resilience and lower residual strain than the same hydrogel in the as-prepared state.

The cross-linking network of the hydrogel can be rearranged by evaporation-swelling treatment, the obtained hydrogel possesses an excellent vibration absorption ability and high elastic modulus.

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A facile strategy is developed to synthesize the novel attapulgite/poly(acrylic acid) nanocomposite (ATP/PAA) hydrogels via the “one-pot” inverse suspension polymerization with the multifunctionalized attapulgite (org-ATP) as the unique cross-linker. The org-ATP is in situ produced directly in the form of water-in-oil emulsion and then used as prepared for the inverse suspension polymerization without being separated; so the proposed strategy is much simpler compared with the traditional methods. Almost all acrylic acid (AA) monomers have been successfully grafted onto ATP to form the 3-dimensional cross-linking network of the nanocomposite hydrogels, in which the org-ATP nanorods, as cross-linker and structural strengthening agent, drastically improves the mechanical stability of the resulting ATP/PAA hydrogels. The nanocomposite hydrogels exhibit selective adsorption toward the Pb(II) ion with a maximum adsorption capacity of 42 mg/g, and the adsorbed Pb(II) ion could be eluted completely. The optimized nanocomposite hydrogel adsorbent also exhibits an excellent reusability. The adsorption capacity and desorption rate remain unchanged for at least 10 cycles of adsorption–desorption. These strong points make it a potential adsorbent for heavy metal-contaminated water.

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