Removal of Heavy Metals from Aqueous Solution Using Novel Nanoengineered Sorbents: Self‐Assembled Carbamoylphosphonic Acids on Mesoporous Silica

Abstract

Self‐assembled monolayers of carbamoylphosphonic acids (acetamide phosphonic acid and propionamide phosphonic acid) on mesoporous silica supports were studied as potential absorbents for heavy and transition metal ions in aqueous wastes. The adsorption capacity, selectivity, and kinetics of the materials in sequestering metal ions, including Cd^2 +, Co^2 +, Cu^2 +, Cr^3 +, Pb^2 +, Ni^2 +, Zn^2 +, and Mn^2 +, were measured in batch experiments with excess sodium ion. The solution pH ranged from 2.2 to 5.5. The kinetics study shows that the adsorption reached equilibrium in seconds, indicating that there is little resistance to mass transfer, intraparticle diffusion, and surface chemical reaction. The competitive adsorption study found the phosphonic acid‐SAMMS to have an affinity for divalent metal ions in decreasing order of Pb^2 + > Cu^2 + > Mn^2 + > Cd^2 + > Zn^2 + > Co^2 + > Ni^2 +. The measured Cd^2 +adsorption isotherm was of the Langmuirian type and had a saturation binding capacity of 0.32 mmol/g.

Keywords:

• Self‐assembled monolayers on mesoporous silica
• MCM‐41
• Carbamoylphosphonic acid
• Kinetics
• Equilibrium
• Adsorption

Acknowledgments

This work was supported by a LDRD program at Pacific Northwest National Laboratory (PNNL) and in part by SEDRP. PNNL is operated by Battelle for the U.S. Department of Energy. The work was partially performed at the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the U.S. DOE Office of Biological and Environmental Research, located at PNNL. The authors thank Mr. Christian D. Johnson for reviewing the manuscript.