The adsorption of cobalt ions from aqueous solution using multiwalled carbon nanotube/polypyrrole modified with NaBH4: Batch and fixed-bed studies

Abstract

In this study, the adsorption of cobalt and the performance of polypyrrole-modified carbon nanotubes as adsorbents were investigated. The reducing agent sodium borohydride (NaBH4) was used to improve the surface modification. The adsorption percentages of adsorbents in the absence/presence of sodium borohydride were 32.5 % and 97.5 %, respectively. The adsorption was carried out in continuous and batch stages. Factors such as operating conditions, adsorbent dosing, the effects of pH, temperature and initial concentration, ionic strength, acidity on desorption were studied in batch mode. The Langmuir isotherm has the best prediction of the adsorption behavior of multiwalled carbon nanotubes/polypyrrole modified by sodium borohydride. The maximum capacity of 20.11 mg/g each at pH 8 and 25 °C was reached. The pseudo-second-order models was the best kinetic model fitted with the results of the studied adsorbent. Thermodynamic studies showed that the adsorption of the adsorbent took place in the form of endotherms and that the capacity increased with increasing temperature. Subsequently, modeling studies of breakthrough curves in a fixed bed column were examined in continuous experiments. The optimal conditions for fixed bed column performance were 0.66 mL/min, 60 mg/L concentration and 0.30 g mass, which corresponded to a final breakthrough time of 2.34 h at an adsorption capacity of 26.29 mg/g. The Yan model was in better agreement with the packed-bed column data than the Thomas model, and its model prediction of maximum column capacity was very close to the Langmuir isotherm of the batch study.