Polydopamine-assisted polyethyleneimine functionalization of bacterial cellulose aerogel for efficient adsorptive removal of Cu(II) and organic dyes.

Abstract

Direct functionalization of biopolymer aerogels often encounters steric agglomeration and pore blockage, which can significantly limit the accessibility of active sites for water purification. To address this challenge, a robust composite aerogel (BC-PDA-PEI) was engineered via a stepwise assembly strategy, utilizing polydopamine (PDA) as an interfacial adhesion layer to uniformly anchor polyethyleneimine (PEI) onto a bacterial cellulose skeleton. Structural characterization demonstrated that the PDA intermediate effectively suppresses the phase separation of PEI, thereby preventing bulk agglomeration and facilitating a thin, nanoscale coating. The resulting composite exhibited broad-spectrum removal performance, achieving maximum adsorption capacities (q_m) of 93.52 mg/g for Cu(II) (as a model heavy metal), 615.02 mg/g for the anionic dye Congo Red, and 92.22 mg/g for the cationic dye Methylene Blue. Adsorption kinetics and isotherms were best described by the pseudo-second-order and Langmuir models, respectively, suggesting a monolayer-type adsorption mechanism. Post-adsorption FTIR/XPS analyses, together with the surface-charge trend, suggested pollutant-dependent interaction pathways: abundant amine groups contribute to the capture of Cu(II) via strong coordination, while the net positive surface character of BC-PDA-PEI favors the electrostatic removal of anionic dyes. This work presents a practical interfacial modification route to address agglomeration and pore occlusion issues in biopolymer aerogel functionalization, leading to the development of a sustainable adsorbent for the efficient removal of heavy metal ions and organic dyes from wastewater.