In-situ halloysite functionalization of anionic hybrid gels possessing easily implemented site-specific (alkyl)amide and carboxyl groups

Design of functional materials with tunable properties based on anionically-modified copolymer network of poly (N-isopropyl acrylamide-co-methacrylic acid) P(NIPA-co-MA) containing linear polyacrylamide and various amounts of Halloysite nanotubes (Hal) was presented using a facile route of solution casting. The organic/ inorganic nanostructures based on thermo-responsive PNIPA were constructed to create hybrid materials via in situ polymerization with different Hal-loading and then used for the removal of cationic methylene blue (MB) dye from aqueous solutions. To achieve the desired mechanical property, the optimum composition of hybrids was determined following a simple and cost-effective synthesis procedure. In situ one-pot polymerization was promoted by semi-IPN formation, following a much simpler route than traditional preparation approaches for stable cross-linked hybrid formation. The swelling of hybrids decreased by 2.9-fold with loading of 5.40 % Hal, confirming the hydrogen bonding interactions between Hal and PAAm/P(NIPA-co-MA) network. The mechanical properties of Hal-doped hybrid gels showed an increase-decrease tendency with increase of Hal-content from 0.80 to 5.40 % (w/v) due to the high aspect ratio of Hal and strong secondary interactions between Hal and PAAm/P(NIPA-co-MA) chains. The effective cross-link density for Hal-doped hybrids was expressed by a cubic polynomial as a function of Hal concentration. Temperature-sensitive swelling results showed that the advantage of sustained release property of Hal can be combined with excellent controllability of PNIPA-based network. Adsorption results of MB onto Hal-doped hybrids bearing methacrylic acid moieties demonstrated their potential as efficient adsorbents for the removal of cationic dyes. A new route offered by the proposed procedure for design of hybrids containing "green" one-dimensional nanofillers creates an innovative perspective on robust hybrid structures for practical applications.