Waste-treating-waste: A compressible shrimp-shell-derived chitin/polyethyleneimine aerogel for efficient adsorption of Cr(VI) and Congo red from simulated wastewater

Given the need to achieve the Global Sustainable Development Goals (SDGs), water and wastewater treatment, alongside waste valorization, are recognized as some of the most critical objectives. Thus, wastewater treatment via sustainable and environmentally friendly adsorbents is imperative. Herein, compressible hierarchical shrimp-shell-derived chitin (Ch)/polyethyleneimine (PEI) hybrid aerogels (denoted as ChP) were developed. The prepared hybrid bio-based aerogel exhibited excellent reversible compressibility with abundant water-transport pathways to accelerate Cr(VI) and Congo red adsorption. The Langmuir monolayer maximum adsorption capacities of ChP1@1 at 298 K were found to be 329.97 mg/g for Cr(VI) at pH 3 and 1495.31 mg/g for CR at pH 5. Interestingly, the incorporation of PEI not only enhanced the adsorption capacity but also tailored the network of the aerogels. Kinetic and thermodynamic studies revealed that the process followed the pseudo-second-order and Elovich kinetic models, with a spontaneous and endothermic adsorption behavior. Additionally, the fabricated aerogel demonstrated exceptional selectivity and removal efficiency even in the presence of various interfering elements, with stable performance of up to 5 cycles. Mechanistic insights elucidated by FTIR and XPS demonstrate that Cr(VI) initially adsorbed through electrostatic interaction followed by partial reduction, whereas CR is mainly captured by electrostatic interaction and hydrogen bonding. Overall, this eco-friendly aerogel offers promising potential for sustainable wastewater remediation and circular waste reutilization.