The single metal atom (Ni, Pd, Pt) anchored on defective hexagonal boron nitride for oxidative desulfurization.

Single-atom catalysts (SACs) have attracted great attention for various chemical reactions because of their strong activity, high metal utilization ratio, and low cost. Here, by using the density functional theory (DFT) method, the stability of a single VIII-group metal atom (M = Ni, Pd, Pt) anchored on the defective hexagonal boron nitride (h-BN) sheet and its possible application in oxidative desulfurization (ODS) are investigated. Calculations show that the stability of the single M atom embedded in the h-BN surface with B and N vacancies is strikingly enhanced compared to that on the perfect h-BN surface. The catalytic activities of the defective h-BN-supported single metal atom are further studied by the activation of molecular oxygen and subsequent oxidation of dibenzothiophene (DBT). O2 is activated to the super-oxo state with large interaction energies on three M/VN surfaces. However, among the three M/VB surfaces, only Pt/VB performs efficient activation of O2. The oxidation of DBT proceeds in two steps; the rate-determining step is the initial step, in which activated O2 oxidizes DBT to produce sulfoxide. By comparing the energy barrier in the first reaction step, both Ni/VN and Pt/VB are revealed as promising candidates for the ODS reaction.

Group IIIA Single-Metal Atoms Anchored on Hexagonal Boron Nitride for Selective Adsorption Desulfurization via S-M Bonds.

Single-atom adsorbents (SAAs) featuring maximized atom utilization and uniform isolated adsorption sites have aroused extensive research interest in recent years as a novel class of adsorption materials research. Nevertheless, it is still challenging to gain a fundamental understanding of the complicated behaviors of SAAs for adsorbing thiophenic compounds (THs). Herein, this work systematically investigated the mechanisms of adsorption desulfurization (ADS) over a single group IIIA metal atom (Ga, In, and Tl) anchored on hexagonal boron nitride nanosheets (BNNSs) via density functional theory (DFT) calculations. First, all the possible doping sites have been considered and their stabilities have been evaluated by the doped energy. DFT calculations reveal that metal atoms prefer to substitute B atoms on BNNSs rather than N atoms. Additionally, SAAs all exhibit considerably enhanced adsorption capacity for THs primarily by the sulfur-metal (S-M) bond with π-π interactions maintained. Among them, In-atom-based SAAs would be adequate to provide the highest adsorption energy (In_cen_B, -40.1 kcal mol-1). Furthermore, from the perspective of adsorption energy, the SAAs show superior selectivity to THs than aromatic compounds due to the newly formed S-M bond. We hope that our work will manifest the design and application of SAAs in the field of ADS and shed light on a new strategy for fabricating SAAs based on BNNSs.

Ag Atom Anchored on Defective Hexagonal Boron Nitride Nanosheets As Single Atom Adsorbents for Enhanced Adsorptive Desulfurization via S-Ag Bonds.

Single atom adsorbents (SAAs) are a novel class of materials that have great potential in various fields, especially in the field of adsorptive desulfurization. However, it is still challenging to gain a fundamental understanding of the complicated behaviors on SAAs for adsorbing thiophenic compounds, such as 1-Benzothiophene (BT), Dibenzothiophene (DBT), and 4,6-Dimethyldibenzothiophene (4,6-DMDBT). Herein, we investigated the mechanisms of adsorptive desulfurization over a single Ag atom supported on defective hexagonal boron nitride nanosheets via density functional theory calculations. The Ag atom can be anchored onto three typical sites on the pristine h-BN, including the monoatomic defect vacancy (B-vacancy and N-vacancy) and the boron-nitrogen diatomic defect vacancy (B-N-divacancy). These three Ag-doped hexagonal boron nitride nanosheets all exhibit enhanced adsorption capacity for thiophenic compounds primarily by the S-Ag bond with π-π interaction maintaining. Furthermore, from the perspective of interaction energy, all three SAAs show a high selectivity to 4,6-DMDBT with the strong interaction energy (-33.9 kcal mol-1, -29.1 kcal mol-1, and -39.2 kcal mol-1, respectively). Notably, a little charge transfer demonstrated that the dominant driving force of such S-Ag bond is electrostatic interaction rather than coordination effect. These findings may shed light on the principles for modeling and designing high-performance and selective SAAs for adsorptive desulfurization.

The Cyclobutanocucurbit[5-8]uril Family: Electronegative Cavities in Contrast to Classical Cucurbituril while the Electropositive Outer Surface Acts as a Crystal Packing Driver.

The structural parameters for the cyclobutanoQ[5-8] family were determined through single crystal X-ray diffraction. It was found that the electropositive cyclobutano methylene protons (CH2) are important in forming interlinking crystal packing arrangements driven by the dipole-dipole interactions between these protons and the portal carbonyl O of a near neighbor. This type of interaction was observed across the whole family. Electrostatic potential maps also confirmed the electropositive nature of the cyclobutano CH2 but, more importantly, it was established that the cavities are electronegative in contrast to classical Q[5-8], which are near neutral.

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.

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.

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 mechanism of thiophene oxidation on metal-free two-dimensional hexagonal boron nitride.

Hexagonal boron nitride (h-BN) as an outstanding catalyst has been applied in oxidative desulfurization (ODS). In order to increase its catalytic performance, deep insight into the catalytic mechanism is urgent. In this work, DFT calculations were carried out to explore thiophene oxidation on the h-BN surface sites, involving the perfect and zigzag B, zigzag N, and armchair edge sites, and B- or N-monovacancy site. The calculated results show that O2 is easily activated on defect sites such as the edge sites and N-vacancy sites. For the thiophene oxidation mechanism, our results show that the zigzag N edge site is the most favorable active site, followed by the armchair and zigzag B edge sites. For the vacancy sites, although they are active for O2 dissociation, the dissociated O is trapped in the vacancy site, and they are not active for eventual sulfone formation.