Porous ionic liquids for oxidative desulfurization influenced by electrostatic solvent effect.

Developing a highly efficient strategy for the stabilization of the solid-liquid interface is a persistent pursuit for researchers. Herein, porous ionic liquids based on UiO-66 (Zr) porous materials were synthesized and applied to the selective desulfurization catalysis, which integrates the permanent pores of porous solids with the exceptional properties of ionic liquids. Results show that porous ionic liquids possess high activity and selectivity for dibenzothiophene. Experimental analysis and density functional theory calculations revealed that the ionic liquids moiety served as an extractant to enrich dibenzothiophene into the porous ionic liquids phase through the π···π and CH···π interactions. Additionally, the electrostatic solvent effect in the porous ionic liquids contributes to the stabilization solid-liquid interface, which was favorable for UiO-66 moiety to catalytically activate hydrogen peroxide (H2O2) to generate ·OH radicals, and subsequently oxidized dibenzothiophene to the corresponding sulfone. It is hoped that the development of porous ionic liquids could pave a new route to the stabilization of the solid-liquid interface for catalytic oxidation.

Defect Engineering on Boron Nitride for O2 Activation and Subsequent Oxidative Desulfurization.

The rational design of highly active hexagonal boron nitride (h-BN) catalysts at the atomic level is urgent for aerobic reactions. Herein, a doping impurity atom strategy is adopted to increase its catalytic activities. A series of doping systems involving O, C impurities and B, N antisites are constructed and their catalytic activities for molecular O2 have been studied by density functional theory (DFT) calculations. It is demonstrated that O2 is highly activated on ON and BN defects, and moderately activated on CB and CN defects, however, it is not stable on NB and OB defects. The subsequent application in oxidative desulfurization (ODS) reactions proves the ON and C-doped (CB , CN ) systems to be good choice for sulfocompounds oxidization, especially for dibenzothiophene (DBT). While the BN antisite is not suitable for such aerobic reaction due to the extremely stable B-O* -B species formed during the oxidation process.

Theoretical prediction of the SO2 absorption by hollow silica based porous ionic liquids.

As an acid gas, sulfur dioxide (SO2) has caused serious pollution to the environment. Therefore, SO2 capture is crucial. The silica-based porous ionic liquid possesses not only the porosity and high specific surface area of hollow silica, but also the fluidity of the liquid. The absorption mechanism of SO2 absorption by porous ionic liquids through density functional theory (DFT) was systematically studied in this paper. First six kinds of absorption sites were predicted, and then various analyses such as structure, energy, and electrostatic potential analysis (ESP) were employed after optimization. The results show that SO2 has the strongest adsorptive interaction between the canopy and the silica sphere. In addition, the main force between the porous ionic liquid and SO2 is hydrogen bonding and π-hole bonding. Finally, by increasing the degree of polymerization of the canopy, that is, increasing the number of ether groups, will be beneficial to the absorption of SO2.

Rational design of the carbon doping of hexagonal boron nitride for oxygen activation and oxidative desulfurization.

The doping of hexagonal boron nitride (h-BN) materials has a great influence on their catalytic oxidation performance, but the mechanism of doping has still not been studied in depth to date. Herein, carbon-doped h-BN materials were systematically investigated. Three different doping modes were established, and their performance for O2 activation and oxidative desulfurization (ODS) were explored. DFT calculation showed that not all carbon-doped forms of the h-BN surface could activate O2. Specifically, two of the dispersed doping forms could activate O2, whereas the π-doping form could not activate O2, and thus the ODS reaction could not be carried out. For the two dispersed doping forms, the O2 adsorption on the CB-doped h-BN surface (C-doped in B position) was too strong, which hampered its ODS performance; whereas the O2 adsorption on the CN-doped h-BN surface (C-doped in the N position) was moderate, resulting in good catalytic activity for ODS. Therefore, to design effective BN-based catalysts by C doping, it is suggested that the C dopant should be dispersed to substitute the N atom of h-BN, and CN-doped h-BN will play an important role in ODS with moderate O2 activation. This study can be used as a reference for the catalytic oxidation of boron nitride.

Theoretical prediction of F-doped hexagonal boron nitride: A promising strategy to enhance the capacity of adsorptive desulfurization.

Hexagonal boron nitride (h-BN) has been used as adsorbent for many chemical applications. The doping strategy is an efficient way to enhance the adsorptive capacity. In the present work, the F-doped h-BN material was investigated by density functional theory (DFT). Five possible F doping h-BNF adsorbents were firstly considered. Results show that only the F_e_B and F_t_B models are thermodynamically favorable. The adsorptive energies of DBT for these five h-BNF materials are all enhanced as compared to the pristine h-BN. Then 2F doping h-BNF adsorbents were also explored. Results show that the combinations of F_e_B and F_t_B are still thermodynamically favorable. Moreover, adsorbents which contain F_t_B exhibits better adsorptive performance, especially the combination of F_t_B + F_t_B. Last, several quantum analysis schemes have been employed to analyze the interaction nature between h-BNF and DBT. Results show that F⋯H-C hydrogen bond, the π-π interaction, and strong electrostatic F⋯S-C interaction plays important roles during adsorptive desulfurization (ADS) process. This work proposed a promising strategy to enhance the capacity of ADS.

The interaction nature between hollow silica-based porous ionic liquids and CO2: A DFT study.

Carbon dioxide (CO2) is one of the main factors leading to the greenhouse effect, so the capture of CO2 gas is currently a hot spot of research. Hollow silica-based porous ionic liquids (HS-liquids) are porous liquids containing cavities that are not only fluid but also have a high specific surface area and were used for the capture of CO2. However, the mechanism of CO2 absorption by HS-liquids has not been studied. In this work, the mechanism of CO2 absorption by HS-liquids was systematic studied by density functional theory (DFT). First, five possible models for absorbing CO2 in HS-liquids were constructed and optimized. The interaction energies between HS-liquids and CO2 at different sites were obtained. Moreover, the effects of HS-liquids with different degrees of polymerization of polyethylene glycol and different alkyl chain lengths on CO2 absorption were also investigated. Results show that the strongest absorption site locates near the polyethylene glycol unit. Then, the electrostatic potential (ESP) and reduced density gradient (RDG) methods were employed to further understand the interaction nature between them. The results show that hydrogen bonding dominates the weak interaction between the HS-liquid and CO2.

Unraveling the mechanism of CO2 capture and separation by porous liquids.

Carbon dioxide (CO2) emissions intensify the greenhouse effect so much that its capture and separation are needed. Porous liquids, possessing both the porous properties of solids and the fluidity of liquids, exhibit a wide range of applications in absorbing CO2, but the mechanism of gas capture and separation demands in-depth understanding. To this end, we provide a molecular perspective of gas absorption in a porous liquid composed of porous organic cages dissolved in a size-excluded solvent, hexachloropropene, by density functional theory for the first time. In this work, different conformations were considered comprehensively for three representative porous organic cages and molecules. Results show that chloroform, compared to CO2, tends to enter the cage due to stronger C-H⋯π interaction and the optimal capacity of each cage to absorb CO2 through hydrogen bonding and π-π interaction is 4, 2 and 4 equivalents, respectively. We hope that these discoveries will promote the synthesis of similar porous liquids that are used to capture and separate gases.

The electronic structure and physicochemical property of boron nitridene.

Inspired by searching new forms of Boron Nitride (BN) compounds, the electronic structure and physicochemical property of a graphyne-like BN compound was explored by density functional theory with cluster models as well as periodic models. This graphyne-like BN compound is named Boron Nitridene in this work, based on geometry and bond order analysis as its B-N linking units take on double bond characteristics. Different cluster models of Boron Nitridene-x (x = 1-5) were constructed. Results show that the geometric parameters and molecular orbitals are similar for these models. The chemical stability of Boron Nitridene was estimated by the concept of heats of formation, vibrational frequency, and ab initio molecular dynamics. In addition, the IR and Raman spectra were predicted and the unique stretching modes were assigned to give a reference with experimental synthesis. Last, the adsorption strength of small molecules was calculated, and the results show the boron nitridene interacts stronger than hexagonal boron nitride (h-BN).