Synthesis and adsorption properties of halloysite/carbon nanocomposites and halloysite-derived carbon nanotubes

• Halloysite/carbon composites are synthesized by hydrothermal method.
• Cellulose can carbonize as a carbon layer deposited on the surface of halloysite.
• Amorphous carbon nanotubes are obtained by removing halloysite.
• The phenol removal rate is greatly increased due to the covered carbon layer.

Halloysite/carbon nanocomposites are synthesized via a hydrothermal route using halloysite as the template and cellulose as the carbon precursor. Cellulose carbonized as a carbon layer deposited on the surface of halloysite. High-resolution transmission electron microscopy, field-emission scanning electron microscopy, X-ray diffraction, X-ray photo electron spectroscopy, and Fourier-transform infrared spectrometry are employed to study the morphological and structural changes of the halloysite/carbon nanocomposites. The results indicate that the thickness of the carbon layer coated on the halloysite surface ranges from 15 nm to 25 nm and contains CH2, CH3, CO and other organic groups. Amorphous carbon nanotubes with lengths of 0.5–1 μm and diameters of 20–80 nm are obtained by removing the halloysite template using hydrofluoric acid. After the activation treatment, the BET surface area of the activated halloysite/carbon and carbon nanotube are obviously enhanced, which values are 1150 and 1288 m2/g, respectively. The values are higher than that of the common activated carbon. The adsorption properties of phenol on different materials are compared. In comparison of unmodified halloysite, the phenol removal rate on halloysite/carbon, carbon nanotube, activated halloysite/carbon can be increased by 25-fold, 30-fold and 49-fold, respectively. The phenol removal rate on the activated halloysite/carbon and carbon nanotube are higher than that of common activated carbon. A Freundlich adsorption model well describes the adsorption behavior of phenol onto the halloysite/carbon nanocomposite and carbon nanotube.