Synthesis, characterization, and application of date palm leaf waste-derived biochar to remove cadmium and hazardous cationic dyes from synthetic wastewater

The adsorption of methylene blue (MB) dye and cadmium (Cd2+) onto biochar derived from date palm leaf waste (DPbc) was evaluated and modeled using adsorption kinetics and different isotherm models; further, the batch process parameters were optimized. Surface characterization techniques revealed rough and porous surfaces on the biochar matrices. Additionally, the sorption of Cd2+ and MB dye onto DPbc altered its surface morphology and elemental composition. Equilibrium contact time of 60 and 30 min are proposed for Cd2+ and the MB dye, respectively, and a strong correlation to the experimental data was seen using the pseudo-second-order kinetic model. The removal efficiency and the sorption capacity of Cd2+ increased upon increasing the initial pH from 2.5 to 5.5, while a decreasing trend was observed for the MB dye when the solution pH was increased from 2 to 10. The removal efficiency of Cd2+ and MB dyes increased by 70% and 20% when the DPbc dose increased from 0.5 to 2.0 g and 0.3 to 1.0 g, respectively. The adsorption capacity increased, while the removal efficiency decreased for both Cd2+ and the MB dye as the initial pollutant concentration increased due to a rapid saturation of the sorption sites. The adsorption capacity and removal efficiency increased upon increasing the solution temperature from 30 to 60 °C, indicating an endothermic reaction. A spontaneous nature is proposed for the adsorption process as the Gibbs free energy is negative. Experimental adsorption could be modeled better using the Freundlich isotherm model compared to other isotherm models for both Cd2+ and the MB dye.