One-step preparation of hydroxyapatite-loaded magnetic Polycaprolactone hollow microspheres for malachite green adsorption by Pickering emulsion template method

In this study, hydroxyapatite (HAp) nanorods were prepared by a simple hydrothermal method and hydro-phobically modified with lauric acid (LA). Modified HAp and magnetic triiron tetraoxide (Fe3O4) nanoparticles as emulsifiers were loaded on polycaprolactone (PCL) microspheres by Pickering emulsion template method. The structure, composition and morphology of prepared HAp and m-RHAp-PCL microspheres were characterized by IR, XRD, SEM and TGA. Furthermore, the adsorption capacity of pure HAp and m-RHAp-PCL microspheres was investigated by malachite green (MG) as a model dye. The results showed that the adsorption processes of pure HAp and m-RHAp-PCL microspheres correlated better with the Langmuir isothermal adsorption curve. The maximum adsorption capacity of m-RHAp-PCL microspheres was 609 mg/g, and the relative adsorption capacity of HAp on microspheres was higher than that of pure HAp, indicating its greater adsorption potential for MG. The values of R-L and 1/n indicated that the adsorption process was spontaneous. The adsorption kinetic data of samples was in good agreement with the pseudo-second-order kinetic model. In addition, the adsorbent could be easily recovered under magnetic fields. The removal ability of MG was retained after four cycles, which demonstrated the excellent reusability and stability of m-RHAp-PCL microspheres for MG adsorption from aqueous as a potential adsorbent candidate material.