A facile slow-gel method for bulk Al-doped carboxymethyl cellulose aerogels with excellent flame retardancy

Bulk Al-doped carboxymethyl cellulose aerogels were obtained via a facile slow-gel method and freeze-drying technology. In this method, the cross-linker Al³⁺ was released slowly and completely with enough d-(+)-gluconic acid δ-lactone as a sustained-release agent. Depended on controlled releasing of Al³⁺, the reaction speed between Al³⁺ and carboxyl groups was controlled and Al³⁺ was well-distributed in the aerogels. The coordination type between Al³⁺ and carboxymethyl cellulose was the bidentate bridging coordination. By adjusting the amount of Al³⁺ and the degree of substitution of carboxymethyl cellulose, interconnected network and closely packed sheet-like structure presented, respectively. According to the nitrogen adsorption-desorption isotherms, the aerogels were a kind of mesoporous material with pore blocking or cavitation. In addition, the aerogels exhibited outstanding weight-bearing capacity and excellent flame retardancy. This work provided a valuable reference for doping metal ions into polysaccharide aerogels and expanding the application fields of aerogels.