Hollow and porous octacalcium phosphate superstructures mediated by the polyelectrolyte PSS: a superior removal capacity for heavy metal and antibiotics

We report an efficient method for synthesis of hollow and porous octacalcium phosphate (OCP) superstructures composed of ultrathin nanosheets controlled by the negatively charged polyelectrolyte of poly(sodium 4-styrene sulfonate). They possess high specific surface areas, regulated pore structure and surface property, facilitating high adsorption of various pollutants, such as Cu(II), Cd(II) and tetracycline (TC), with the maximum adsorption capacities of 135.69, 147.28 and 52.63 mg g⁻¹, respectively. Strikingly, the hollow OCP superstructures exhibit superhigh Pb(II) adsorption capacity of 1868.6 mg g⁻¹ owing to the well matching between crystal lattices before and after the ion exchange process. The kinetic and isotherm processes fit well with the pseudo-second-order model and the Langmuir model, respectively. The results demonstrated that the adsorption of heavy metal ions mainly attributes to the cation exchange and that the adsorption of TC is caused by the formation of TC-Ca complexion. The mineral-based adsorbents prepared via the biomimetic approach may have a very broad application for water pollution treatment.