Adsorptive Denitrogenation of Fuels onto Mixed-Linker Metal Organic Frameworks (ML-MOF) and ML-MOF Derived Carbon-based Nanocomposites

This study presents a comprehensive investigation into the preparation, characterization, and adsorption performance of mixed-linker UiO-67 (ML-UiO-67) and their carbon derivatives. ML-UiO-67 was synthesized via solvothermal methods using biphenyl 4,4'-dicarboxylic acid and terephthalic acid as organic linkers. Thermal treatments at 400 °C and 600 °C under nitrogen atmosphere yielded carbon-based nanocomposites (400 °C-2H-6H and 600 °C-2H-6H) with varying durations (2 and 6 h). The structures of synthesized materials were analyzed using thermogravimetric analysis (TGA), X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR), to interpret structural, thermal, and functional properties. The adsorption behavior of indole, a nitrogenous compound in model fuel, was assessed under varying parameters, including adsorbent quantity, temperature, initial indole concentration, and reaction time. Adsorption capacities were quantified, and kinetic and equilibrium isotherm equations were applied to elucidate adsorption mechanisms. The results showed rapid adsorption occur in the first 20 min, with adsorption equilibrium reached in 90–120 min. The pseudo-first-order kinetic model is appropriate for explaining the mechanism of adsorption process, indicating diffusion-controlled behavior. Dubinin-Radushkevich and Freundlich isotherms were successfully applied, highlighting multilayer adsorption and physical adsorption mechanisms. Among the tested adsorbents, 400 °C-2H exhibited the highest adsorption capacity (16.8 mg/g) at 1 mg dosage. Desorption experiments did not show promising results, only 600 °C-6H nanoparticles can desorb 59% of the adsorbed indole. The experimental results indicate important information on the design and use of ML-UiO-67 based adsorbents for effective adsorption of nitrogen-containing compounds in fuels.