In the second step, the surface –COOH and –OH moieties on the prepared AT-MWNTs were further modified via condensation of small aminosilane molecules to obtain the amino-functionalized MWNTs (AF-MWNTs). a 5wt% solution. The APTES-acetone solution was then mixed with the prepared AT-MWNT dispersion ataweightratio of 1:10 (APTES/AT-MWNT) and heated at 80 1C for 30min under vigorous stirring. Acetone was selected as the solvent for APTES instead of water to prevent fast polycondensation of –OH groups in aqueous solution [34]. Finally, the reaction solution was ultrasonicated for 60 min, followed by centrifugation at 8000 rpm for 2 m into remove aggregates and particles.The AF-MWNT concentration in the centrifuged dispersion was measured by the drying method aforementioned, normally within the range of 0.6–1wt%.