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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. (C) 2012 Elsevier Ltd. All rights reserved.