Experimental and modeling study on adsorption of cationic methylene blue dye onto mesoporous biochars prepared from agrowaste

Oak wood, an agrowaste, was activated to prepare biochar and used as an effective biosorbent to remove methylene blue (MB) dye from aqueous solution. The properties of the adsorbent were also characterized using scanning electron microscope, Brunauer–Emmett–Teller, and Fourier Transform Infrared techniques. The adsorption process was studied in a batch system by investigating the effects of different experimental variables such as pH of solution, contact time, adsorbent dosage, initial dye concentration, temperature, and adsorbent particle size. The equilibrium time was obtained as 120 min. The adsorption process was fully described by the Liu equilibrium and pseudo-second-order kinetic models. The maximum adsorption capacity obtained was 97.55 mg/g based on the Langmuir isotherm at 50°C. The activation energy was found to be 24.2 kJ/mol, which indicated the feasibility of the adsorption process. The values of thermodynamic parameters (ΔG°, ΔS°, and ΔH°) showed that the adsorption of MB dye onto the biochar surfaces was spontaneous, feasible, and endothermic. The biochar was also found to enjoy a good performance for the removal of MB in real wastewater samples under optimum experimental conditions. So, it can be concluded that biochar can be utilized as a cost-effective, environmental-friendly, and promising adsorbent for the removal of dyes from colored wastewaters.