Remarkable adsorptive denitrogenation of indole and quinoline from model fuel oil by CuCl/UiO-66 metal-organic framework

Environmental pollution, driven by the increasing consumption of fossil fuels, is a critical concern, mainly due to the harmful effects of nitrogen-containing compounds (NCCs). NCCs must be deleted from model fuel because of negative results on the stability of the catalyst. A novel adsorbent was developed by reducing CuCl₂ on a zirconium-based metal organic framework (MOF) with sodium sulfite under ambient conditions to produce CuCl(x)/UiO-66(Zr). This material was then applied for the first time to remove harmful NCCs from model fossil fuels. This study found that CuCl improved adsorptive denitrogenation (ADN) effectiveness through π-complexation, defining a crucial role for the Cu(I) species. The adsorbents analyzed using XRD, FTIR, FE-SEM, EDX, BET, and TGA techniques. Characterization analyses showed that CuCl was well distributed on UiO-66. Although the adsorbent porosity decreased after modification, however, the adsorption of NCCs enhanced. Adsorption results showed that CuCl(2.0)/UiO-66 removed 200 ppm of quinoline (QUI) and indole (IND) in 360 min at 0.05 g adsorbent dose, 5 ml solution, 25 °C, and pH 8. Also, it was found that the adsorption of NCCs by CuCl(2.0)/UiO-66 had a sufficient fit for IND and QUI with the maximum adsorption capacities of 227.27 and 188.68 mg/g, respectively, by the Langmuir isotherm. Also, the pseudo-second-order model showed the proper fit for QUI and IND with linear regression (R²) of 0.9997 and 0.9997, respectively, over CuCl(2.0)/UiO-66. The adsorbent used after five cycles still had a good performance in removing NCCs. The improved removal of NCCs by CuCl(2.0)/UiO-66 may be explained by a π-complexation mechanism, where copper(I) ions form selective complexes with the adsorbates. The newly presented adsorption process can be performed as a method for refining of fuel, which is drastically beneficial, environmentally friendly, and cost-effective.