Adsorption of Pb(II) and Cu(II) metal ions on functionalized large-pore mesoporous silica

Adsorption of copper and lead ions in aqueous solutions onto large-pore mesoporous silica materials functionalized with amino and mercapto groups and those with different morphologies including fiber-like, rod-like, and platelet was studied. The synthesized materials were characterized by techniques such as X-ray powder diffraction, nitrogen adsorption–desorption isotherms, scanning electron microscopy, and infrared spectra. Batch experiments were conducted to determine the adsorption processes. The equilibrium adsorption data agreed with Langmuir isotherms and revealed that four amino groups were required to form a stable surface complex with copper ions. Results indicated that initial adsorption rate onto platelet mesoporous adsorbent was rapid and faster than that of rod-like and fibrous morphologies due to its short channeling pores. Thiol-functionalized mesoporous silica adsorbents of all the morphologies have a better affinity for Pb²⁺ than the amino-mesoporous silica. In contrast, aminomesoporous silica has a stronger affinity for Cu²⁺ compared to thiol-mesoporous silica. The optimal Pb²⁺ uptake on thiol-mesoporous silica was in solution with pH in 2–6, while the highest Cu²⁺ uptake on amino-mesoporous silica was at pH 5.

Keywords
Adsorbent; Functionalized silica; Heavy metals; Kinetics; Morphology; Surface complex