Highly efficient green-activated carbon/ZIF-8 nanocomposites from walnut hulls and date kernels for superior dye pollutant removal in water purification

This study introduces the green synthesis and adsorption performance of activated carbon/zeolitic imidazolate framework-8 (ZIF-8) nanocomposites derived from walnut hulls and date kernels for efficient dye removal from aqueous solutions. Activated carbon (AC) was produced from agro-waste precursors of walnut hull powder and date kernel powder and was used as a support for the in situ growth of ZIF-8 to create eco-friendly nanocomposites (Z@ACW and Z@ACD) at various weights (0.01, 0.02, and 0.04). Structural and surface characterizations using FE-SEM, FT-IR, XRD, EDX, and BET confirmed the successful integration of ZIF-8 with AC, resulting in highly porous materials with large surface areas (up to 1250.3 m 2 /g for ZW-0.04). Batch adsorption experiments with methylene blue (MB) and methyl orange (MO) dyes showed maximum uptake capacities of 341.30 mg/g and 862.07 mg/g, respectively, under optimized conditions. The maximum removal efficiency was achieved through the optimization of adsorption parameters such as pH, adsorbent dosage, initial concentration, contact time, and temperature. Kinetic analysis followed the pseudo-second-order model, while equilibrium data best fit the Langmuir isotherm, indicating chemisorption as the dominant mechanism and monolayer adsorption behavior. Thermodynamic parameters indicated a spontaneous and endothermic process. The nanocomposites displayed excellent reusability and structural stability over multiple adsorption-desorption cycles. The primary removal mechanisms involved hydrogen bonding, pore filling, surface complexation, π-π stacking, and electrostatic attraction. These findings demonstrate that Z@ACW and Z@ACD nanocomposites are promising, sustainable adsorbents for effective dye remediation and the valorization of biomass waste in water purification systems. • Synthesized green-activated carbon/ZIF-8 nanocomposites from walnut hulls powder and date kernels powder using an eco-friendly method for dyes removal. • Nanocomposites exhibited high surface areas and showed superior adsorption capacity for methylene blue (341.30 mg/g) and methyl orange (862.07 mg/g). • Linear fits were followed by PSO kinetics adsorption and Langmuir isotherm models, indicating chemisorption and monolayer adsorption with endothermic thermodynamics. • Demonstrated excellent reusability, stability, and multiple dyes removal mechanisms such as hydrogen bonding, surface complexation, pore filling, π-π stacking, and electrostatic attraction.