Efficient removal of heavy metal from aqueous solution by sulfonic acid functionalized nonporous silica microspheres

Abstract Nonporous thiol-functionalized silica spheres (SiO2 SH) were prepared by hydrolysis of 3-mercaptopropyltrimethoxysilane. Then, sulfonic acid functionalized silica microspheres (SiO2 SO3H) were prepared through direct oxidization of SiO2 SH by H2O2 and used as adsorbent. The structure and surface of the adsorbent were investigated by field emission scanning electron microscopy, N2 adsorption–desorption isotherm, Fourier transform infrared spectroscopy and electron diffraction spectroscope. The BET surface area of the particles is only 1.58 m2/g. However, the content of thiol group on particle surface was as high as 36% (wt%). It was found that the SiO2 SO3H could effectively remove heavy metal ions (Pb2+, Cd2+, and Cu2+) in solution through electrostatic interaction. When SiO2 SO3H with the particle size of 0.95 μm was used as adsorbent, the adsorption capacity for Pb2+, Cd2+, and Cu2+ reaches 635, 499, and 260 mg/g, respectively. The strong adsorption ability of SiO2 SO3H can be attributed to the nonporous particles with rich sulfonic group facilitating the mass transport of metal ions to the active sites. The adsorption isotherm data obey the Freundlich model. Kinetics of the metal ions removal was found to follow pseudo-second-order rate equation. pH values have only small influence on the adsorption capacity in the studied pH range. Consecutive adsorption–desorption experiments showed that SiO2 SO3H could be reused with only a slight loss in the adsorption capacity.