Fabrication of the hyper-crosslinked polymers chemically functionalized by 8-hydroxyquinoline and their efficient adsorptive removal of 2-naphthol from water

Hyper-crosslinked polymers (HCPs) chemically functionalized with plentiful heteroatoms are of great importance for the adsorptive removal of polar aromatic substances from water, while their facile fabrication is of great challenge, and the adsorptive removal of the 2-naphthol from water remains a bottleneck. Herein, 8-hydroxyquinoline (HQ) was employed as the chemical modifier and firstly uploaded on the polymers according to the nucleophilic substitution, thereafter several external crosslinking agents were employed and the Friedel-Crafts alkylation was performed for the intermediate polymer, and hence the HCPs chemically functionalized by HQ, namely, PS-HQ-HCPs, were successfully fabricated. The nucleophilic substitution supplied the intermediate polymer with plentiful ether oxygen (O, 4.81%) and pyridine nitrogen (N, 6.39%). The Friedel-Crafts alkylation constructed predominant micro-porosity and meso-porosity for the final polymers with high Brunauer-Emmett-Teller (BET) surface area (SBET, 384-618 m2/g) and pore volume (Vtotal, 0.36-0.63 cm3/g). 2-Naphthol was utilized as the adsorbate to investigate the batch adsorption, and the predicted maximum capacity (qmax) on the final polymer, namely, PS-HQ-DCX was 828 mg/g at 318 K, higher than most synthetic materials. Meanwhile, the adsorption attained the equilibrium within 360 min, and the kinetic data can be described by the micro-pore diffusion model. As the initial 39.5 mg/L of 2-naphthol was fed for the adsorption, the final concentration reduced to 1.9 mg/L, less than the discharge standard in China (GB 8978-19962, mg/L). The dynamic adsorption revealed that the saturated capacity was 632 mg/g, approaching to the fitted qmax (688 mg/g) by the Langmuir model, and 232 mL anhydrous ethanol completely desorbed 2-naphthol from the polymers. This universal synthetic protocol is of great importance for the fabrication of some other functionalized HCPs, and this strategy was universal for some other phenolic compounds and external cross-linking agents.