Optimizing the physical-chemical properties of carbon nanotubes (CNT) and graphene nanoplatelets (GNP) on Cu(II) adsorption.

Systematic experiments of copper adsorption on 10 different commercially available nanomaterials were studied for the influence of physical-chemical properties and their interactions. Design of experiment and response surface methodology was used to develop a polynomial model to predict maximum copper adsorption (initial concentration, Co=10mg/L) per mass of nanomaterial, qe, using multivariable regression and maximum R-square criterion. The best subsets of properties to predict qe in order of significant contribution to the model were: bulk density, ID, mesopore volume, tube length, pore size, zeta-charge, specific surface area and OD. The highest experimental qe observed was for an alcohol-functionalized MWCNT (16.7mg/g) with relative high bulk density (0.48g/cm(3)), ID (2-5nm), 10-30µm long and OD<8nm. Graphene nanoplatelets (GNP) showed poor adsorptive capacity associated to stacked-nanoplatelets, but good colloidal stability due to high functionalized surface. Good adsorption results for pristine SWCNT indicated that tubes with small diameter were more associated with good adsorption than functionalized surface. XPS and ICP analysis explored surface chemistry and purity, but pHpzc and zeta-charge were ultimately applied to indicate the degree of functionalization. Optimum CNT were identified in the scatter plot, but actual manufacturing processes introduced size and shape variations which interfered with final property results.

Effect of acid and alcohol network forces within functionalized multiwall carbon nanotubes bundles on adsorption of copper (II) species.

The adsorptive capacity of multiwall CNTs for copper species in water depends on the type of functional group present on their surface. The alcohol (OH) and acid (COOH) network forces formed by van der Waals bonds within the CNT bundles can define their aggregate state and available sites for copper adsorption. Copper is attracted to different oxygen radicals on the surface and within the bundles of CNTs. The effect of initial concentration shown on isotherm curves was investigated as an impact of different network forces and the presence of impurities leached from as-received CNTs. Deprotonation of CNTs reduced the COOH network forces, improved adsorption capacity and removed the effect of initial concentration. Impurities leached from CNTs under the effect of pH were less than 1 mg g(-1) for each metal, which was insignificant compared to copper in solution. Pristine CNTs were acid washed and purified (Ox-CNTs), improving their adsorption capacity, but the effect of initial concentration was still present. Adsorption of copper is stronger for OH-functionalized CNTs, followed by deprotonated COOH-functionalized CNTs, as-received COOH-functionalized CNT, Ox-CNTs and finally pristine CNTs. FTIR, XPS and zeta potential measurements were used to identify and quantify the different surface functional groups present on CNTs.