From naturally low-grade palygorskite to hybrid silicate adsorbent for efficient capture of Cu(II) ions

A new eco-friendly hybrid Mg, Al-silicate adsorbent with superior adsorption properties for Cu(II) was prepared by a one-step hydrothermal process using earth-abundant low-grade palygorskite (PAL) as the starting materials and non-toxic sodium carbonate as the assistant. The structural characterizations by scanning electronic microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), BET adsorption-desorption isotherms and Zeta potential analyses confirm that part of rod-like PAL crystals were in-situ transformed as smectite sheets, and the hybrid silicate adsorbents with rod/sheet transition formulation were formed. Under the action of alkaline, some inert Si O Si(or M) bonds were broken as –Si–O − groups, which not only make the adsorbent having extremely negative surface charge (−   46.4   mV), but also strengthen the chelating and holding capability of the adsorbent to Cu(II). The silicate adsorbent shows high adsorption capacity of 229.9   mg/g for Cu(II), which can capture 98.95% of Cu(II) from 200   mg/L of Cu(II) solution at the dosage of 2.6   g/L (only 64.5% for raw PAL). The intensified electrostatic attraction , ion-exchange, and chemical association of Si-O − surface groups with Cu(II) primarily contribute to the improved capture capability for Cu(II).