Adsorption of Cr(VI) onto cross-linked chitosan-almond shell biochars: equilibrium, kinetic, and thermodynamic studies

Abstract In this study, to remove Cr(VI) from the solution environment by adsorption, almond shell was pyrolyzed at 400 and 500 °C turned into biochar (ASC400 ASC500) composite adsorbents were obtained coating these biochars with chitosan (Ch-ASC400 Ch-ASC500). The resulting characterized using Fourier transform infrared (FTIR) spectroscopy; Brunauer, Emmett, Teller (BET) surface area; scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX); point of zero charge pH (pH pzc ) analyses. parameters affecting adsorption examined batch experiments optimum for efficient in 55 mg L ?1 determined as follows; adsorbent dosages: 5 g biochars, 1.5 adsorbents, contact time: 120 min, pH: 1.5. It seen that temperature did not affect much. Under conditions, capacities ASC400, ASC500, Ch-ASC400, Ch-ASC500 are 11.33, 11.58, 37.48, 36.65 , respectively, their percentages 95.2%, 97.5%, 94.3%, 94.0%, respectively. Adsorption data applied Langmuir, Freundlich, Scatchard, Dubinin-Radushkevic, Temkin isotherms pseudo-first-order kinetic model, pseudo-second-order intra-particle diffusion film model. fitted well Langmuir isotherm models. From results, it chemical is dominant mechanism. Also, both effective rate. For all proved be most appropriate model adsorption. maximum monolayer calculated 24.15 27.38 54.95 87.86 Ch-ASC500, enthalpy change, entropy free energy changes during process also thermodynamically. As a result, occurs spontaneously adsorbents.