Remediation of crystal violet, methyl violet and methylene blue dyes by carbon-based Gundelia tournefortii seed shells: thermochemical activation and desirability function optimization

This study reports the valorization of Gundelia tournefortii (GT) seed shell biomass waste into activated carbon (GTAC) via H3PO4-assisted microwave activation for efficient wastewater remediation. The surface area analysis indicated that GTAC is a mesoporous activated carbon with specific surface area of 315.3 m2/g. Three cationic dyes, namely crystal violet (CV), methyl violet (MV) and methylene blue (MB) were utilized as toxic dyes models in testing the adsorptive performance of GTAC for wastewater remediation. The statistical optimization for the adsorption process of CV, MV, and MB dyes by GTAC was carried out by combination of Box Behnken Design and desirability function approach. The adsorption kinetics of CV, MV, and MB were well fitted to the pseudo second order kinetic model. The adsorption isotherm results show a good fitness of CV to Freundlich isotherm model, while MV and MB were well described by Langmuir isotherm model. The maximum adsorption capacities of GTAC CV = 420.2 mg/g, MV = 252.5 mg/g and for MB = 765.6 mg/g. GTAC retained more than 74% of its adsorption efficiency after five adsorption-desorption cycles, demonstrating good reusability and regeneration performance. Thus, this finding confirms the potential applicability of GTAC for removal of different types of toxic organic dyes from aqueous environment.