Palygorskite-template amorphous carbon nanotubes as a superior adsorbent for removal of dyes from aqueous solutions

Abstract

The carbon-coated palygorskite (Pal@C) was prepared by impregnation and carbonization using modified palygorskite (Pal) as a hard template and glucose as the carbon source. The amorphous carbon nanotubes (ACNTs) could be finally obtained by removing Pal template using acid and alkali treatment. In comparison with pure Pal@C nanocomposite, the maximum adsorption capacity of Congo red dye onto the ACNTs could be improved by over 13-fold (467.97 mg/g vs. 34.40 mg/g, ACNTs vs. Pal@C), which was attributed to the larger specific surface area (877.09 m2/g) and more mesoporous pores (average pore diameter is 7.62 nm) that ACNTs possess. The effects of different dyes molecules such as Congo red and methyl orange on the adsorption properties of ACNTs were investigated. The maximum adsorption capacity of Congo red was 467.97 mg/g more than that of methyl orange (253.26 mg/g) due to differences in molecular structure and size. Furthermore, Langmuir model can be used to predict the adsorption isotherm of Congo red dye by ACNTs. Our kinetic study showed that the quasi-second-order kinetic model could describe the adsorption behavior of ACNTs for Congo red. In particular, the ACNTs presented a higher adsorption capacity for adsorption of Congo red, regardless of pH.