A robust PHDI-crosslinked cellulose aerogel loaded with CaCO3 for Congo red removal

Abstract

Cellulose acetate (CA) aerogels suffer from poor water stability and limited active sites, hindering their practical use in dye wastewater treatment. To overcome this, we developed a robust CA aerogel using a novel synergistic strategy of covalent crosslinking with polyisocyanate (PHDI) followed by in situ precipitation of calcium carbonate (CaCO₃). The resulting CaCO₃/CA-PHDI composite aerogel exhibits exceptional adsorption performance for Congo red, achieving a high removal efficiency of 97.8%, a maximum capacity of 191.6 mg g⁻¹, and stable operation across a wide pH (3–11) and temperature (25–65 °C) range. The adsorption follows pseudo-second-order kinetics and the Langmuir isotherm, indicative of monolayer chemisorption. The primary mechanism is identified as coordination between Ca²⁺ and sulfonate groups, synergized by hydrogen bonding and electrostatic interactions. Furthermore, the aerogel maintains over 73% removal after five regeneration cycles. This work provides a high-performance adsorbent and elucidates the organic–inorganic synergistic enhancement mechanism, offering a new design strategy for functional biomass materials in practical wastewater remediation.