Development of P. harmala waste-derived activated carbon for the removal of methylene blue from aqueous solution

Utilization of biomass waste to develop sustainable and efficient adsorbents is a good solution for controlling the contamination of dye waste in aquatic environment. In this work the biomass of Peganum harmala has been carbonized by NaOH and used as activated carbon for adsorption of methylene blue (MB) solution. The effect of the mass ratio of NaOH/precursor on the properties of the prepared materials and their adsorption efficiency was studied. PHC-25, which was prepared by the NaOH-to-precursor mass ratio of 12.5:50 (w/w), had the highest iodine number (877.5 mg g⁻¹), a Brunauer–Emmett–Teller (BET) specific surface area of 989.12 m² g⁻¹ and a total pore volume of 0.4537 cm³ g⁻¹ among the tested samples. The optimum adsorption conditions were found to be pH 8, initial MB concentration of 200 mg L⁻¹ , adsorbent dose of 0.5 g per 50 mL, contact time of 120 min and temperature of 25 °C which gave an adsorption capacity of 138.83 mg g⁻¹ and removal efficiency of 96.52% respectively. The Dubinin – Radushkevich (D–R) model was the best fit adsorption isotherm model among the adsorption isotherm models evaluated, and this model was used to determine the adsorption isotherm parameters. The adsorption isotherm parameters were determined using the Dubinin – Radushkevich (D–R) model which was the best fit adsorption isotherm model among the evaluated adsorption isotherm models. Furthermore, the regeneration experiments showed that the adsorbent could be reused and it still had a reasonable removal ability after five cycles. This study indicates that the activated carbon prepared from Peganum harmala can be considered as a good biomass bio adsorbent for removal of MB from water. Extended regeneration tests are recommended to investigate its practical application for water treatment and further studies with real wastewater are recommended.