Purification of phenol-contaminated water by adsorption with quaternized poly(dimethylaminopropyl methacrylamide)-grafted PVBC microspheres

Abstract

Cross-linked poly(vinylbenzyl chloride) (PVBC) microspheres tethered with polymer brushes containing quaternary ammonium ions were developed as an anionic adsorbent for the efficient removal of phenol from aqueous solutions. The terminal alkyl chlorine groups on the PVBC microspheres served as anchor sites for the grafting of poly(dimethylaminopropyl methacrylamide) (PDMAPMA) brushes via surface-initiated atom transfer radical polymerization (ATRP). The pendent tertiary amino groups of the PDMAPMA chains were converted into quaternary ammonium ions by N-alkylation reaction to produce anionic adsorption functionality. Success for each reaction step was ascertained by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Batch adsorption results demonstrated that solution pH values in a wide range of 3.0–11.0 had no evident effect on phenol adsorption by the quaternized PDMAPMA-grafted PVBC (i.e., PVBC-g-QPDMAPMA) microspheres, and that the adsorption capacity of the microspheres increased with the grafting density of the quaternized PDMAPMA brushes within 6 h. The so-synthesized anionic adsorbents had a rapid pseudo-first-order-adsorption kinetic (equilibrium achieved within 60 min), and the Langmuir model-fitted maximum adsorption capacity of phenol was approximately 2.23 mmol g⁻¹ at pH 6.5 with an initial concentration of 1.05–5.31 mmol L⁻¹ (i.e., 100–500 mg L⁻¹). The calculated thermodynamic parameters revealed an exothermic and spontaneous adsorption process of phenol onto the quaternized QPDMAPMA-grafted microspheres. Desorption and adsorption cycle experiments demonstrated that the anionic adsorbents loaded with phenol were found to be readily regenerated in a 0.1 mol L⁻¹ NaOH solution, and that the adsorption capacity decreased by less than 10% upon five cycles.