Fabrication of O-enriched macroporous polymer for the efficient adsorption organic acid from aqueous solution

Herein, an oxygen-rich polymer, namely, β-CD-PS was gained according to one-step nucleophilic substitution, and it was used to adsorb organic acids from aqueous solution. The nucleophilic substitution brought abundant functional -OH groups (the oxygen content was 9.04 wt%) to the polymer, and increased the hydrogen bonding between the polymer and the adsorbate. The adsorption results showed that the capacities of organic acids on β-CD-PS were much greater than chloromethylated polystyrene (CMPS). The maximum adsorption capacities of salicylic acid (SA), pyrogallic acid (PA), β-naphthol (NAP), 1,1'-bi-2-naphthol (BNAP) and gallic acid (GA) were 407.47 mg/g, 312.42 mg/g, 246.39 mg/g, 320.75 mg/g and 254.40 mg/g, respectively. Langmuir model was more fit for the adsorption of BNAP, PA, and GA, and Freundlich model was more suited to the adsorption of PHE, NAP, and SA. Thermodynamic analysis showed that the adsorption was spontaneous process, furthermore, the exothermic occurred between the adsorption site and SA, NAP, and phenol (PHE) and the endothermic occurred between the adsorption site and BNAP, PA and GA. The adsorption kinetics results indicated that the time for the equilibrium of SA, PA, GA, and NAP was about 100 min, while BNAP required more time. Moreover, the adsorption of SA on β-CD-PS could achieve most adsorption at high concentrations and complete removal at 100 mg/L. The organic acids adsorbed on the polymer can be eluted with a mixture of anhydrous ethanol and 0.01mol/L NaOH. The β-CD-PS exhibited superior adsorption efficiency, reproducibility, and reusability, demonstrating their excellent performance for the adsorption of organic acids, and analysis of the adsorption mechanism revealed that the -OH groups played a significant role due to the strong hydrogen bonding interaction.