Ultrasonic-assisted adsorption of eriochrome black T and celestine blue dyes onto Ipomoea batatas-derived biochar

ABSTRACT

In a bid to develop efficient biochars, we prepared new biochar by the pyrolysis of Ipomoea batatas feedstock for the ultrasonic-aided adsorption of eriochrome black T (EBT) and celestine blue (CB) dyes. The characterisation of the Ipomoea batatas-derived biochar (IBBC) showed potent functional groups, good thermal stability, porous structure and a point of zero charge of 6.41. The pH of 2.0 and 7.0 was found to be optimum for the uptake of anionic EBT and cationic CB onto IBBC, respectively. A decrease in the surface area of IBBC from 96.35 m²/g to 48.43 m²/g and 32.11 m²/g was obtained after the adsorption of EBT and CB, respectively. Thermogravimetric analysis revealed high thermal stability of IBBC up to 350°C. The Energy dispersive X-ray (EDX) spectrum revealed carbon (52.6%), oxygen (24.5%) and potassium (7.1%) as the major component of the biochar. The elemental analysis showed carbon, hydrogen and nitrogen compositions of 55.4%. 2.6% and 1.2%, respectively. Moreover, a biochar yield of 36.2% was obtained. The adsorption of both dye molecules was well correlated by the Freundlich isotherm, supported by the Scatchard model analysis. Kinetics was well fitted to the film diffusion and pseudo-second-order models, while thermodynamics showed an endothermic and spontaneous dye uptake on IBBC. The adsorption capacity of the biochar for EBT and CB was 59.24 mg/g and 63.69 mg/g respectively. Percentage desorption of 87.5% for EBT and 82.3% for CB was achieved during regeneration of the dye-loaded biochar. Moreover, IBBC showed good potentials to be reused for adsorption. The results revealed the potentials of the novel biochar for efficient adsorption of both cationic and anionic dye species.

KEYWORDS:

• Adsorption
• biochar
• dye
• celestine blue
• eriochrome black T

Acknowledgments

The authors are grateful to the University of the Free State, South Africa for the postdoctoral support granted to Dr. K. G. Akpomie.

Disclosure statement

No potential conflict of interest was reported by the author(s).