Facile preparation of functionalized carbon nanotubes with tannins through mussel-inspired chemistry and their application in removal of methylene blue

Since their first discovery, the carbon nanotubes (CNTs) have attracted great research attention owing to their great mechanical properties, high chemical stability, unique electronic properties and diameter ratio. The CNTs have been extensively applied as adsorbents to remove various environmental pollutants for their large surface areas. Nevertheless, the performance of pristine CNTs for removal of cationic dye methylene blue (MB) is largely limited for their poor dispersibility and lack of functional groups. In this work, the functionalized CNTs have been synthetized through the self-polymerization of tannins under alkaline solution. The obtained samples, including pristine CNTs and CNT-TA composites, were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The effects of adsorption factors, including contact time, initial MB concentration, solution pH and temperature, were scientifically investigated. Results indicate that the adsorption capacity of functionalized CNTs at room temperature could reach up to 105 mg/g, which is much higher than that of pristine CNTs in the same experimental condition. According to the results of adsorption kinetics, isotherms and thermodynamics, the adsorption of MB onto CNT-TA follows the pseudo-first-order model and Freundlich isotherm model, and the MB adsorption process is exothermic and spontaneous. These results indicate the functionalized CNTs could be applied as high-performance adsorbents with great potential of adsorbing the cationic dye pollutants from aqueous solution.