Rapid and selective removal of aromatic diamines from the polyurethane bio-hydrolysate by β-cyclodextrin appended hyper-cross-linked porous polymers

During the degradation and recycling process of polyurethane (PU) through biotechnology, it is essential to remove toxic and hazardous aromatic diamines (4,4′-methylene dianiline (MDA), 2,4-toluene diamine (TDA)) selectively and rapidly before the biorefinery of residues in the PU hydrolysate. In this study, β-cyclodextrin (β-CD) appended hyper-cross-linked polymers (HCPs) with high porosity were constructed via the Friedel-Crafts alkylation reaction. In particular, with partial hydroxyl groups on β-CD units, the hydrophilicity of HCP-BCDOH was drastically improved, contributing to fast adsorption equilibrium for TDA (1 min) and MDA (15 min). Besides, the isothermal experiments demonstrate high maximum theoretical adsorption capacities of HCP-BCDOH upon MDA (2.27 mmol·g−1) and TDA (1.53 mmol·g−1). Moreover, spectral analysis and thermodynamic experiments revealed the adsorption mechanism of aromatic diamines by HCP-BCDOH, which is mainly controlled by weak interactions, involving "host–guest" interaction, hydrophobic interaction, and π-π stacking. These interactions endow HCP-BCDOH with high selectivity and removal efficiencies towards MDA and TDA. Owing to the exceptional adsorption properties and high reusability of HCP-BCDOH, it may offer a promising and efficient adsorbent for the removal of aromatic amines from the PU bio-hydrolysate.