One-step synthesis of mesoporous ZnO@ZIF-8 composites for CO2, CH4, N2 adsorption and separation with potential application for industrial biogas

The separation of CO₂ and N₂ from CH₄ is essential for improving natural gas quality, while capturing and eliminating CO₂ and CH₄ from the air is crucial for reducing greenhouse gas emissions. This study investigates the performance of a mesoporous ZnO@ZIF-8 composite for these purposes by examining its adsorption equilibrium for CO₂, CH₄, and N₂. The composite was prepared through a mechanical grinding technique utilizing a mortar and pestle and characterized by various analytical methods, including X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and nitrogen adsorption/desorption measurements. Adsorption isotherms for CO₂, CH₄, and N₂ were recorded at temperatures of 283, 298, 308, and 318 K and pressures up to 100 kPa, with the data being modeled using the Langmuir model. Additionally, separation selectivities for binary mixtures of CO₂/N₂, CO₂/CH₄, and CH₄/N₂, as well as biogas-like mixtures, were evaluated using the Ideal Adsorbed Solution Theory (IAST) model. At 298 K and 100 kPa, the selectivities for equimolar mixtures were found to be 9.13 for CO₂/N₂, 2.51 for CO₂/CH₄, and 3.63 for CH₄/N₂. Notably, the composite exhibited a CO₂ selectivity of 0.1086 at 283 K, which decreased to 0.0953 at 318 K, indicating the influence of temperature on CO₂ adsorption efficiency. Under these conditions, the adsorption capacities were measured at 3.0 mmol/g for CO₂ and 1.3 mmol/g for CH₄. These findings demonstrate the potential of the ZnO@ZIF-8 composite for efficient gas separation, particularly for enhancing biogas quality and contributing to greenhouse gas reduction through selective CO₂ capture. • ZnO@ZIF-8, synthesized eco-friendly, shows high CO 2 (3.0 mmol/g) and CH 4 (1.3 mmol/g) adsorption capacities. • CO 2 , CH 4 , and N 2 adsorption isotherms fit the Langmuir model across various temperatures and pressures. • CO 2 /N 2 selectivity is 9.13, CO 2 /CH 4 is 2.51, and CH 4 /N 2 is 3.63 at 298 K and 100 kPa, indicating effective separation. • ZnO@ZIF-8 enhances biogas quality by effectively separating CO 2 from CH 4 , with selectivity varying with temperature.