Effective elimination of indigo carmine in wastewater using green nanostructured modified biochar: optimization, sorption equilibrium, kinetics, thermodynamics and mechanisms

Abstract

This research examined the application of nano-activated biochar (nMOSAB) produced from Moringa oleifera seeds (MOS) as an adsorbent for the removal of indigo carmine (IC) dye. The synthesis of nMOSAB involved grinding techniques combined with thermal pyrolysis at temperatures exceeding 600 °C, resulting in the formation of nano-sized biochar particles. The adsorption data were evaluated using the Langmuir model for equilibrium and the pseudo-second-order model for kinetics. The nano-biochar exhibited a maximum adsorption capacity of 344.8 mg g⁻¹. In comparison with bulk biochar particles, the adsorption capacity of nMOSAB was found to be 9.5 times greater. The high adsorption capacity can be attributed to various chemical interactions during the adsorption process, such as π–π interactions, hydrogen bonding, and electrostatic interactions. Thermodynamic analyses indicated that the adsorption process is both spontaneous and exothermic. Through traditional batch tests and a packed-bed system, the effectiveness of nMOSAB for the removal of IC from actual wastewater was determined to be 91.6% and 89.6%, respectively. This research clearly demonstrated the capability of nano-biochar derived from M. oleifera seeds to serve as an efficient, eco-friendly, and economical adsorbent for the removal of IC dyes from wastewater.