Biosorption of Hexavalent Chromium Over Modified Terrestrial Moss: Experimental, Kinetic, and Isotherm Studies

In this research, activated carbon was prepared from terrestrial moss and utilized as a low-cost adsorbent to remove hexavalent chromium [Cr(VI)] from aqueous solution. The study examined important biosorption factors including initial pH (1–3), contact time (0.5–24 h), initial Cr(VI) concentration (20–400 mg/L), and biosorbent dosage (0.05–0.4 g) to assess their impact on the efficiency of modified terrestrial moss (MAC) in eliminating Cr(VI) from water. The biosorbent capacity was evaluated using different kinetic models and isotherms. The highest removal efficiency of Cr(VI) onto MAC was ascertained as 97.8% at an initial solution pH of 1, MAC dose of 0.2 g, initial Cr(VI) concentration of 50 mg. L⁻¹, and contact time of 15 h. The FTIR analysis revealed the interactions of certain functional groups in the adsorption of chromium ions. The biosorption occurred through the anionic adsorption mechanism and followed the pseudo-second order kinetic model. The experimental data was best fitted with Freundlich isotherm. Furthermore, the thermodynamic studies suggest that the biosorption process is both spontaneous and exothermic. The positive entropy change implied the randomness at the solid–liquid interface. In light of these compelling results, the study recommends the consideration of MAC as an efficient and practical solution for the removal of Cr (VI) from aqueous environments.