Evaluating the adsorptivity of organo-functionalized silica nanoparticles towards heavy metals: Quantitative...

Organo-functionalized SiO₂ nanoparticles are regarded as promising adsorbents for capture of heavy metals. However, actual adsorptivity of a specific functional group onto SiO₂ surface is unclear, thus extending a debate on which type of organic group possesses a better affinity toward heavy metals. Herein, surface functionalization of SiO₂ with different groups (i.e., -EDTA (ethylenediamine triacetic acid), -COOH, -SO₃H, -SH and -NH₂) were achieved by a facile silylating reaction. Batch experiments indicated that adsorption capacity of SiO₂ was remarkably improved by surface functionalization. Quantitative analysis manifested that one mole of EDTA grafted onto SiO₂ surface can adsorb 1.51 mol of Pb(II) ions, which was 7.7, 17.1, 28.4 and 50.2-fold larger than those of COOH-, SO₃H-, SH- and NH₂-functionalized SiO₂, respectively. This is first time to evaluate adsorptivity of functionalized SiO₂ on the basis of per effective functional group, which may repair deficiency of conventional assessment method that calculated on the basis of per unit mass. Further, adsorption mechanism of these functionalized SiO₂ were identified and uncovered by experimental and theoretical studies. This work not only develops an efficient adsorbent for heavy metal remediation but also provides a valuable insight for evaluation and design of novel SiO₂-based materials.