Materials and methods Chemicals and reagents

2. Materials and methods 2.1. Chemicals and reagents Table 1. Physicochemical properties of three different CNTs.CNTs typeOD (nm)Length (μm)PurityAshSSA (m2/g)Metal impurities constants (μg/g)CdCoCuNiPbZnMWCNTs36±212±2>973±0.5275±120.017105.443N.D.11.4321.8750.56OH-MWCNTs36±24±1.5>972±0.3103±4N.D.0.1011.754.7832.9890.101COOH-MWCNTs36±24±1.5>972±0.3115±5N.D.0.186N.D.0.156N.D.N.D.N.D.: not detected;OD: outer diameter;SSA: specific surface area.Full-size tableTable optionsView in workspaceDownload as CSV Fig. 1. FE-SEM (A–C) image of CNTs (A: MWCNTs; B: OH-MWCNTs; C: COOH-MWCNTs) deposited on copper grid with carbon film and TEM (D–F) image of MG-132 same CNTs (D MWCNTs; E OH-MWCNTs; F: COOH-WCNTs) with bar scale 100 nm.Figure optionsDownload full-size imageDownload as PowerPoint slide Aqueous suspensions of different MWCNTs were prepared based on the methods of Alpatova et al. (2010), 5 mg CNTs were added to 50 mL of ultrapure water in a semilunar valve 100 mL glass beaker with sonication for 12 h (80 W, 32 kHz) in an ultrasonic cell disruptor (Nanjing Emmanuel Instrument Equipment Co., Ltd. Nanjing, China) until the absorbance at 400 nm was unchanged. The absorbance was measured by UV–vis spectrometry (TU-1800, Persee, China). Before each use, the suspensions of CNTs were diluted to 0.5 mg/L and a 30 min sonication was carried out. The metal stock solution was prepared by dissolving a defined amount of ZnSO4·7H2O into 0.1 L of ultrapure water.