Exploration of Functionalized Sorbents for Heavy Metal Ions Removal

Abstract

The nano silica spheres are synthesized through sol-gel process. These spheres have very surface area of around 920 m2/g and pore size of about 4.7 nm diameter and are good support material for the preparation of selective sorbent. The silica surface was activated by reacting with an organosilane coupling agent like 3-aminopropyltrimethoxy silane (APTMS) by dispersion in appropriate reaction medium. This process sufficiently activated the inert silica surface for further attachment of organic moitities. Chelating ligands such as 1-napthyl-2-thiourea (ANTU), thiosemicarbazide (TSC) and capryl pyrazolone (CP) were chemically reacted with activated silica surface and functionalized sorbents are synthesized. FTIR, EDX and TGA analysis confirmed the successful immobilization of the organic moieties to the silica surface. After synthesis and characterization, the performance of the materials were tested as sorbents for the separation of heavy metals like Hg(II), Cd(II), Zn(II), Ag(II), and Cr(III) from their aqueous solutions in batch experimental procedures using radiotracer technique. The results showed that the attached functional groups enhanced selectivity of the sorbent towards target metal ions. These functionalized sorbents displayed fast adsorption kinetics and entrapped high percentage of toxic heavy metals from spiked water samples. The adsorption processes were systematically monitored as a function of pH of the medium, agitation time, metal ions concentration and functionalized silica dosage. Effect of various interfering ions on the adsorption of these metals was investigated. Response of the sorbent and sorption process to temperature is also studied and various useful thermodynamic parameters like change in enthalpy (ΔH), entropy (ΔS) and free energy (ΔG) are derived and discussed. An attempt was made in this study to suggest possible mechanism for the uptake of the metal ion and to validate the experimental data by fitting into sorption models such as Langmuir, Freundlich, and Dubinin Radushkevich D-R. Morris Webber, Lagergren and Richenberg‘s equations were applied to follow the kinetics of sorption process. Practical utility and environmental significance of the work was demonstrated. Regeneration of sorbent was carried out to explore the possibility of reuse of these sorbents. These sorbents could be effectively employed for environmental remediation of toxic heavy metals and will greatly improve the conditions of drinking water. Key words: silica nano particles, covalent grafting, adsorption, pollution abatement, radio tracer, Metals preconcentration, heavy metals, organic-inorganic hybrid