Sustainable AC/ZIF-67 hybrid adsorbents derived from agricultural waste for rapid dye removal from water

Activated carbon (AC) derived from a mixture of walnut and almond shells was prepared via phosphoric acid activation (ACA) and subsequently combined with ZIF-67 to fabricate a series of ACA/ZIF-67 composite adsorbents for removing dye contaminants from water. Comprehensive characterization (including FESEM, EDS, FTIR, XRD, and N 2 adsorption–desorption) confirmed the integration of ZIF-67 within the carbon matrix. The results demonstrated that the highest BET surface area (592.43 m 2 . g − 1 ) belongs to the ACA5/ZIF-67 composite with a hierarchical porous structure. The effects of operational parameters, including ACA/ZIF-67 ratio, pH (1–11), amount of adsorbent (0.1–2 g/L), time (5–60 min), initial dye concentration (10–100 mg/L), and operational temperature (25–45 °C), were systematically investigated. Under the optimum conditions of pH 7, temperature of 25 °C, and the amount of adsorbent 1.5 g/L, the ACA5/ZIF-67 composite achieved more than 98% removal of 10 mg/L MB within only 5 min. Equilibrium and kinetic data were satisfactorily well-fitted to the Langmuir isotherm (R² > 0.99) and the pseudo-second-order kinetic (R 2 = 0.9999) models, yielding a maximum adsorption capacity of 35.95 mg/g. This adsorption behavior can be attributed to the combined effects of pore filling, electrostatic attraction, π–π interactions, and hydrogen bonding between dye molecules and the ACA5/ZIF-67 surface. Consequently, these outcomes highlight the potential of biomass-derived AC/ZIF-67 composites as favorable adsorbents for the simulated removal of dyes from aqueous solutions, subject to further assessment in real industrial effluents.