Evaluating the adsorptivity of organo-functionalized silica nanoparticles towards heavy metals: Quantitative comparison and mechanistic insight.

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.

Optimization of adsorption configuration by DFT calculation for design of adsorbent: A case study of palladium ion-imprinted polymers.

Trial-and-error method is widely used to seek an efficient adsorbent, although it is time- and money-consuming. Rationally design of functional materials via theoretical calculation is an emerging and appealing strategy in material science. However, exploiting of theoretical calculation for assistance of adsorbent design is rarely to be attempted despite it is usually utilized to explore the adsorption mechanism. In this work, density functional theory (DFT) calculation is exploited to design an adsorbent with high adsorption capacity and selectivity. The well-known palladium ion-imprinted polymer (IIP) was used as a model adsorbent. Then, three types of given adsorption configurations (a-Pd-IIP, b-Pd-IIP and c-Pd-IIP) were optimized. Further, their adsorption energies were calculated by DFT, which were -13.978 eV for b-Pd-IIP, -8.764 eV for a-Pd-IIP and -3.587 eV for c-Pd-IIP, respectively. The correlation coefficient (R2) between the theoretical adsorption energy and the experimental adsorption capacity reached to as high as 0.985. In addition, the dynamics and selectivity experimental results further consolidated the tendency of the calculation result. All these results demonstrate that the adsorption energy derived from DFT calculations is an important factor in guiding the design of IIPs.