In view of the importance of water quality and environmental aspect, zeolitic imidazolate framework-8 (ZIF-8) adsorbent was synthesized via a solvothermal approach for oil removal from water. Response surface methodology-central composite design approach (RSM-CCD) using a statistical software (Design expert, version 8.0.6) was employed to identify the influence of three independent variables of ZIF-8 synthesis procedure including ligand/salt molar ratio, solvent/salt molar ratio, and synthesis temperature on the oil adsorption capacity and yield of adsorbent as RSM responses. The optimum conditions for preparing ZIF-8 were found as follows: ligand/salt molar ratio of 10.4, solvent/salt ratio of 702.7, and temperature of 52.9 °C, which resulted in 1120 mg/g of olive oil uptake and 43% of ZIF-8 yield. Morphological and structural properties of the prepared adsorbent were characterized by N2 adsorption-desorption, XRD, FE-SEM, and FTIR analyses. Batch equilibrium adsorption experiments were conducted under varied system parameters expected to affect the ZIF-8 adsorption capacity including oil concentration, ZIF-8 dosage, contact time, and temperature. The isotherm and kinetic of olive oil adsorption onto ZIF-8 followed the Freundlich and pseudo-first-order models, respectively. The evaluation of thermodynamic parameters demonstrated that olive oil adsorption onto optimized ZIF-8 was spontaneous and exothermic in nature. In addition, the used ZIF-8 can be recovered effectively using a simple ethanol-washing method. Based on experimental results, the ZIF-8 prepared in this study can be successfully used in oil/water emulsion separation.
Keywords: Adsorption; Emulsion; Oil/water emulsion; Olive oil; Response surface methodology; ZIF-8.