Effect of embedded sodium polyacrylate chains on the adsorption mechanism of neutral red by magnetic particles

Monodisperse hollow porous magnetic particles (MHPMs for short) embedded with sodium polyacrylate (PAAS) and the calcinated product of MHPMs (referred to as MHPMs-C, embedded without PAAS) were prepared and evaluated as an adsorbent for the removal of neutral red from water. Both of the adsorption kinetics followed pseudo-second-order model while there was a significant difference between the two rate constants. The second-order rate constant (k₂, 0.775 g mg⁻¹ min⁻¹) for MHPMs was 52 times higher than MHPMs-C and 16 times higher than a similar material on account of stretched PAAS. The maximum adsorption capacity of MHPMs was 61.5 mg g⁻¹. However, the Langmuir isotherm model was not suitable for MHPMs-C. Both of the adsorption equilibrium data of MHPMs and MHPMs-C obeyed the Freundlich isotherm, indicating MHPMs was a better adsorbent. PAAS played a key role in the rapid adsorption process by MHPMs. And rate controlling steps were supposed to be passing through the adsorption equilibrium layers (AELs) and intraparticle diffusion of pollutant molecules. Remarkably, MHPMs could be regenerated for six times by HCl solution (pH 2) without decrease in performance showing good recycling ability. Besides, MHPMs exhibited strong affinity for amino groups in the selective adsorption experiments.