Polycarbonate track etched membrane filter

CNTs (diameters 10-20 nm, length 5-20 µm) were purchased from Arry Nano (Frechen Königsdorf, Germany). Covalent functionalization or oxidation was achieved by a modified procedure, as previously described. 29 CNTs were dispersed in a 3 : 1 volume ratio mixture of sulphuric acid (H 2 SO 4 , 10 M) and nitric acid (HNO 3 , 10 M) by water bath sonication for 1 h (Transsonic t460 water bath sonicator, 85 Watt, 35 kHz), followed by probe sonication using QSonica sonicator (30 effective minutes with 50% on-50% off cycles, amplitude 100%, 25 watts) on ice. For non-covalent functionalization, the CNTs were dispersed in a 1 mg ml -1 solution of carboxymethyl cellulose (CMC) (Sigma) in a 1 : 2 mass ratio by probe sonication. Aggregates and clusters were removed by centrifugation at 8000g. Excess CMC was washed away using a 0.2 µm pore size polycarbonate track-etched membrane filter (Whatman) (Fig. 1a). For covalent functionalization, the strongly acidic mixture was refluxed at 120 °C for 48 h. The oxidised CNTs (Ox-CNTs) were washed extensively (3 cycle of centrifugation, 11 000g, 30 min) and re-dispersed in water. Amorphous carbon residues were removed by overnight stirring of the Ox-CNTs in 10 mM NaOH 30 and filtration washings with water using a 0.1 µm pore size polycarbonate track-etched membrane filter (Whatman) (Fig. 1b).