Optimized mercapto-modified resorcinol formaldehyde xerogel for adsorption of lead and copper ions from aqueous solutions

Resorcinol formaldehyde (RF) xerogel was modified by mercapto functional groups for removal of Pb(II) and Cu(II) ions from aqueous solutions. The chemical structure of the mercapto-modified resorcinol formaldehyde xerogel (MRFX) was compared with the RF xerogel via Fourier transform infrared spectra (FTIR), X-ray photoelectric spectroscopy (XPS), and energy dispersive X-ray (EDX) mapping to characterize the functional groups and their dispersion in the xerogel. The results showed that the MRFX included not only thiol groups, but also sulfonic groups with higher adsorption affinity sites. The functional groups were fully dispersed in the xerogel and made a homogeneous composition. X-ray diffraction (XRD) patterns were also employed to show the effect of modifier on the phase structure of the xerogels. Moreover, the morphologies of the xerogels were observed by scanning electron microscope (SEM) and transmission electron microscopy (TEM) techniques. According to the TEM micrographs, the MRFX included more nanopores than the unmodified xerogel. The MRFX was studied for adsorption tests. According to the results, the optimal pH to adsorb maximum Pb(II) and Cu(II) ions was 6. Adsorption kinetics study revealed that the adsorption process followed the pseudo-second-order kinetic equations and the adsorption equilibrium agreed much more with Langmuir rather than Freundlich model. Resorcinol formaldehyde xerogel was modified by mercaptopropyl-trimethoxysilane during a sol-gel process. After the aging step, the wet gel was treated with pure acetone to exchange the pore liquid. As a result, the porosity of the xerogel was not terminated after drying. The xerogel was then used to adsorb Cu(II) and Pb(II) ions from aqueous solutions. According to the results, thiol and sulfonic groups were the major active sites with high adsorption affinities in the adsorption process. [GRAPHICS] .