An alternative hydrothermal route to amorphous carbon nanotubes for treatment of organic pollutants in water

Abstract

Ultralong and uniform amorphous carbon nanotubes (ACNTs) were prepared by using a simple and environmental friendly hydrothermal method at low temperature. Factors affecting the growth of the ACNTs were systematically studied. A reasonable Ostwald ripening growth mechanism was proposed for the formation of the ACNTs. The as-prepared ACNTs were used as an adsorbent for the removal of methylene blue (MB) from aqueous solutions in two modes, batch and fixed bed. In the batch mode, the removal efficiency for MB was improved remarkably by increasing the contact time and the adsorbent dosage. High pH values were in favor of the adsorption for MB. The adsorption isotherm of the ACNTs was well fitted with Langmuir model, with square of correlation coefficient r² > 0.9996. The maximum adsorption capacity (q_m = 46.21 mg g⁻¹) of the ACNTs was higher than that of the multi-walled carbon nanotubes (q_m = 35.83 mg g⁻¹). In addition, the adsorption kinetics results presented two adsorption stages. The rapid and the slow adsorption stages resulted from the adsorption of the external and the inner surface of the ACNTs, respectively. In the fixed-bed mode, the MB removal percentage increased with decreasing the flow rate and the concentration of MB. The results reveal that the as-prepared ACNTs can be employed as an adsorbent for the removal of organic pollutants from wastewater.