Fabrication and Application of Low-Cost Thiol Functionalized Coal Fly Ash for Selective Adsorption of Heavy Toxic Metal Ions from Water

A novel thiol modified coal fly ash (CFA-SH) is successfully synthesized by a facile, efficient, and environmentally friendly process using 3-mercaptopropyltrimethoxysilane (MPTS). Various techniques have been used to characterize thoroughly the structure, the surface property, and the presence of the mercaptopropyl groups. The synthesized material proves to be an effective and selective adsorbent for removal of Hg2+ and Cd2+ ions from aqueous solution. The effect of time, pH, sample dose, speed, temperature, and metal ion concentrations were investigated thoroughly to optimize the sorption process. The kinetics data fitted in accordance with the pseudo-second-order model. It is also noticed that the Langmuir equation provides an accurate description of these sorption data, implying that monolayer sorption took place during adsorption. The quick and excellent uptake capacities (q m of 361.01 mg g–1 for Hg2+ within 50 min at pH 8 and 106.38 mg g–1 for Cd2+ within 60 min at pH 8) of the sorbent can be described on the basis of the hard and soft acid–base principle (HSAB) and electrostatic attraction. Moreover, both adsorbents and adsorbates can be reused using concentrated HCl. Finally, the low cost of the developed sorbent is also the prime point of interest in this experiment.