The selectivity for sulfur removal from oils is an important topic. In this work, the selectivity for different sulfur removal methods has been studied by conceptual density functional theory (CDFT) at the B3LYP/6-31111G(3df,2p) level of theory. In principle, the selectivity is directly related to the mechanisms of sulfur removal. It cannot be precisely elucidated until the mechanisms are totally known. However, current work shows that relationships can be constructed between CDFT and the selectivity. That is, for hydrodesulfurization, good descriptors will be ionization energy, hardness, and bond lengths of SAC; for adsorptive desulfurization, the hardness is a good descriptor; for oxidative desulfurization, good descriptors are electron density and Fukui function. And for extractive desulfurization (nonmetal-based ionic liquids), electron affinity and electrophilicity may be good descriptors. In addition, structures and frontier orbitals of various sulfides have also been discussed. It is hoped that these relationships between CDFT and selectivity can give useful information to develop highly efficient sulfur removal methods for specific sulfides, like 4,6-dimethyldibenzothiophene, and 4-methyldibenzothiophene.

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The chemical hardness of adsorbents is an important physicochemical property in the process of adsorption based on the hard and soft acids and bases (HSAB) theory. Tuning chemical hardness of adsorbents modulated by their concomitants is a promising approach to enhance the adsorptive capacity in principle. In the present work, we report an efficient strategy that the adsorption capacity for aromatic sulfocompounds can be enhanced by tuning the chemical hardness. This strategy is first theoretically explored by introducing C element into the network of hexagonal boron nitride (h-BN) based on a series of model materials (model_ x C, x = 1–5). Computational results show that the chemical hardness is reduced after gradually C-doping, which may lead to an enhancement of adsorption capacity according to the HSAB theory. Then, a series of C-doped h-BN materials (BCN- x , x = 10–50) were controlled synthesized. All of the as-prepared materials show better adsorption capacities (e.g., 27.43 mg g –1 for BCN-50) than pure h-BN. Experiment results show that the adsorption capacity correlates well with the C content in the BCN- x , which is consistent with the results predicted by theoretical calculation. This strategy may be helpful to rationally design highly efficient adsorbents in separation engineering and may be expanded to similar two-dimensional materials, where the π–π interaction is the dominant driven force.

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