In this work, pyridinium-functionalized silica nanoparticles adsorbent (PC/SiO 2 /Fe 3 O 4 ) was synthesized for phosphate removal from aqueous solutions. The removal efficiency of phosphate on the PC/SiO 2 /Fe 3 O 4 was carried out and investigated under various conditions such as pH, contact temperature and initial concentration. The results showed that the adsorption equilibrium could be reached within 10 min, which fitted a Langmuir isotherm model, with maximum adsorption capacity of 94.16

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... g/g, and the kinetic data were fitted well by pseudo-second-order and intra-particle diffusion models. Phosphate loaded on the adsorbents could be easily desorbed with 0.2 mol/L of NaOH, and the adsorbents showed good reusability. The adsorption capacity was still around 50 mg/g after 10 times of reuse. All the results demonstrated that this pyridinium-functionalized mesoporous material could be used for the phosphate removal from aqueous solution and it was easy to collect due to its magnetic properties. Key words | adsorption, desorption, magnetic separation, phosphate, pyridinium-functionalized adsorbent Recently, magnetic nanoparticles (MNPs) have attracted more attention in water treatment, due to their convenient separation from water with a simple magnetic process and low cost (Tang & Lo ). Several studies have reported that heavy metals, phenolic compounds, drugs, and others are adsorbed onto MNPs (Lin et al. ). We also notice that exchange quaternary ammonium cations can adsorb anions from water. For example, Qiu et al. () prepared an anion phase with N-methylimidazolium immobilized on silica to separate common inorganic anions. Qiu et al. () reported poly(ionicliquid)-grafted silica hybrid