Eggshell‐Based Biochar for Superior Adsorption of Crystal Violet Dye and Fluoride From Wastewater

ABSTRACT Present study investigates the efficiency of eggshell biochar as a low‐cost and ecofriendly adsorbent for the simultaneous removal of fluoride ions and crystal violet (CV) dye from wastewater. The eggshell waste was pyrolyzed to produce biochar, which was thoroughly characterized and subsequently employed for contaminant adsorption. The effects of key process parameters including the initial pollutant concentration, adsorbent dosage, solution pH, and contact time on adsorption efficiency were examined. The adsorption mechanism was studied using Langmuir, Freundlich, and Temkin isotherms, and the models were compared using the Akaike information criterion (AIC), which indicated that the Langmuir model provided the best fit. The Langmuir isotherm model demonstrated the maximum adsorption capacities of 821.11 and 522.31 mg/g, respectively, for CV dye and fluoride ions maintaining the contact time of 120 min at the agitation speed of 150 rpm. The adsorption mechanism was primarily governed by the solution pH, electrostatic interactions, physisorption, and pore filling. The functional groups present in eggshell biochar including C=O, –COOH, and –OH played a substantial role in the adsorption of selected pollutants. Moreover, the pseudo‐second‐order kinetic model accurately described the adsorption process providing the best fit. Overall, the study confirmed that the biochar derived from waste eggshell has the potential to serve as a sustainable adsorbent in water purification.