Hydroxyl modified hypercrosslinked polymers: targeting high efficient adsorption separation towards aniline

Abstract

The removal of aniline from aqueous solution has a major environmental impact and attracted increasing attention in last few years. In this work, four hypercrosslinked polymers (HCPs) bearing phenolic hydroxyl groups were one-step synthesized via specifically choosing phenol (PH) or 2,2′-dihydroxybiphenyl (DBP) as building units and 1,4-bis(chloromethyl)benzene (DCX) or 4,4′-bis(chloromethyl)-1,1′-biphenyl (BCMBP) as crosslinkers. The hydroxyl-modified benzene rings knitted with each other via the linkage of crosslinkers, which potentially produces the extended π-conjugated structure. Herein, DBP-B, derived from DBP and BCMBP, exhibits the highest surface area of up to 752 m² g⁻¹ with a predominantly microporous structure and allows for the maximum adsorption capacity (q_max = 227.690 mg g⁻¹) toward aniline. The aniline adsorption yields the negative changes in Gibbs free energy and enthalpy, corresponding to an exothermic and spontaneous process. Such excellent aniline adsorption properties were likely attributed to this HCP having an extended π-conjugated structure and abundant hydroxyl functional groups. More intriguingly, this HCP displays a rapid adsorption rate and a superior aniline processing capacity, namely that (i) the adsorption time of 60 min can reach the adsorption equilibrium; (ii) only an applied amount of 20 mg could reduce the concentration of 5 mL aniline solution from 39.40 mg L⁻¹ to 4.36 mg L⁻¹, meeting the discharge requirement of Chinese environmental protection authorities (<5 mg L⁻¹). This finding indicates that such a HCP has excellent potential to be a viable alternative to currently investigated materials applied in wastewater treatment.