Fabrication of Unique Mixed-Valent CoCo and CuCu Metal-Organic Frameworks (MOFs) for Desulfurization of Fuels: A Combined Experimental and Theoretical Approach toward Green Fuel.

Herein, metal-organic framework (MOF)-based adsorbents are designed with distinct hard and soft metal building units, namely, [CoCo(PD)(BP)] () and [CuCu(PD)(BP)] (), where HPD = pyrazine-1,4-diide-2,3-dicarboxylic acid and BP = 4,4'-bipyridine. The designed MOFs were characterized via spectral and SCXRD techniques, which confirm the mixed-valent states (+1 and +2) of the metal ions. Topological analysis revealed the rare and topologies for Co MOF, while Cu-MOF exhibits a unique topology in the 8-c net (point symbol for net: {4·6}). Moreover, severe environmental issues can be resolved by effectively removing heterocyclic organosulfur compounds from fuels via adsorptive desulfurization. Further, the developed MOFs were investigated for sulfur removal via adsorptive desulfurization from a model fuel consisting of dibenzothiophene (DBT), benzothiophene (BT), and thiophene (T) in the liquid phase using -octane as a solvent. The findings revealed that effectively removes the DBT with a removal efficiency of 86% at 300 ppm and an operating temperature of 25 °C, with a recyclability of up to four cycles. The adsorption kinetic analysis showed that the pseudo-first-order model could fit better with the experimental data indicating the physisorption process. Further, the studies revealed that adsorption capacity increased with the increasing initial DBT concentration with a remarkable capacity of 70.5 mg/g, and the adsorption process was well described by the Langmuir isotherm. The plausible reason behind the enhanced removal efficiency shown by as compared to could be the soft-soft interactions between soft sulfur and soft Cu metal centers. Interestingly, density functional theory (DFT) studies were done in order to predict the mechanism of binding of thiophenic compounds with , which further ascertained that along with other interactions, the S···π and S···Cu interactions predominate, resulting in a high uptake of DBT as compared to others. In essence, turns out to be a promising adsorbent in the field of fuel desulfurization for the benefit of mankind.