A simple hydrothermal approach to modify palygorskite for high-efficient adsorption of Methylene blue and Cu(II) ions

Silicate materials have been frequently used as stable, low-cost and efficient adsorbents for the removal of dyes and heavy metal ions from aqueous solution. Herein, at the aim of designing new adsorbent with higher adsorption capacity, natural palygorskite (PAL) was modified via a one-step hydrothermal process by introducing sodium silicate and magnesium salts. The effect of Si/Mg dosage ratio on the structure and physico-chemical features of the adsorbent was investigated, and its adsorption capability for Methylene blue (MB) and Cu(II) ions was intensively evaluated. It was found that Si/Mg dosage ratio is the key to control the adsorption properties of the adsorbent. The active magnesium silicate could be formed around PAL at the moderate Si/Mg dosage ratio, and even the undesirable quartz impurities without adsorption activity in the natural PAL minerals may transform as amorphous magnesium silicate with higher adsorption activity in this process. The adsorbent shows greater BET specific surface areas (407.3 m(2)/g), ideal surface charge distribution and superior adsorption capacity to MB and Cu(II) ions, with the maximum adsorption capacity of 527.22 mg/g for MB and 210.64 mg/g for Cu(II) ions at the Si/Mg dosage ratio of 2:1. The MB molecules and Cu(II) ion could be almost completely removed from 100 mg/L of MB solution and 25 mg/L of Cu(II) solution by the adsorbent, respectively, which is far away higher than that of raw PAL. The electrostatic attraction, ion exchange and chemical association of -Si-O- groups contribute to the enhanced adsorption for MB or Cu(II) ions. (C) 2014 Elsevier B.V. All rights reserved.