Composite aerogels of TEMPO-oxidized pineapple leaf pulp and chitosan for dyes removal

Recycling agricultural and aquacultural by-products into high-value engineering aerogels is a sustainable solution to minimize the negative impacts of these wastes on the environment in case of improper treatment. For the first time, discarded pineapple leaves are processed by a novel two-step procedure involving strong alkali and alkali/hydrogen peroxide treatments to generate cellulose-rich pulp containing 91.66 wt% cellulose. The mediated oxidation catalyzed by 2,2,6,6-tetramethylpiperidinyloxy is performed to introduce more carboxylate groups in the pulp for further physically interacting with amino groups on shrimp-based chitosan to synthesize unique composite aerogels without consuming any crosslinkers. The composite aerogels are ultra-lightweight and exhibit a significant rise in their compressive modulus from 2.46 to 27.25 kPa due to the chitosan addition. At the same initial dye concentration of 300 mg/L, the composite aerogels composed of 0.6 wt% chitosan achieve the equilibrium methyl orange adsorption capacity of 136.64 mg/g in only 6 min, while the highest equilibrium methylene blue adsorption uptake of 31.56 mg/g is witnessed in the samples having the lowest chitosan content (0.2 wt%). The developed composite aerogels display the notable porous structure, remarkable mechanical properties, and high removal efficiency for the two typical dyes, demonstrating the effectiveness of combining the world’s two largest natural sources by a simple and green fabrication. The approach in this study is directed towards multiple goals such as addressing the accumulation and underutilization of solid waste, dealing with water pollution caused by harmful dyes in many developing countries, and providing another solution for the cleaner production of renewable materials.