Fengyun Wang

A study of the solvent effect on the morphology of RDX crystal by molecular modeling method

Abstract Molecular dynamics simulations have been performed to investigate the effect of acetone solvent on the crystal morphology of RDX. The results show that the growth morphology of RDX crystal in vacuum is dominated by the (111), (020), (200), (002), and (210) faces using the BFDH laws, and (111) face is morphologically the most important. The analysis of surface structures of RDX crystal indicates that (020) face is non-polar, while (210), (111), (002), and (200) faces are polar among which (210) face has the strongest polarity. The interaction between acetone solvent and each RDX crystal face is different, and the order of binding energy on these surfaces is (210) > (111) > (002) > (200) > (020). The analysis of interactions among RDX and acetone molecules reveal that the system nonbond interactions are primary strong van der Waals and electrostatic interactions containing π-hole interactions, the weak hydrogen bond interactions are also existent. The effect of acetone on the growth of RDX crystal can be evaluated by comparing the binding energies of RDX crystalline faces. It can be predicted that compared to that in vacuum, in the process of RDX crystallization from acetone, the morphological importance of (210) face is increased more and (111) face is not the most important among RDX polar surfaces, while the non-polar (020) face probably disappears. The experimentally obtained RDX morphology grown from acetone is in agreement with the theoretical prediction.

Solvent effect on the crystal morphology of 2,6-diamino-3,5-dinitropyridine-1-oxide: a molecular dynamics simulation study.

The attachment energy (AE) calculations were performed to predict the growth morphology of 2,6-diamino-3,5-dinitropyridine-1-oxide (ANPyO) in vacuum. The molecular dynamics (MD) method was applied to simulate the interaction of trifluoroacetic acid solvent with the habit faces and the corrected AE model was adopted to predict the growth habit of ANPyO in the solvent. The results indicate that the growth morphology of ANPyO in vacuum is dominated by (110), (100), (10-1) and (11-2) faces. The corrected AE energies change in the order of (110)>(10-1)>(11-2)>(100), which causes the crystal morphology to become very close to a flake in trifluoroacetic acid solvent and accords well with the results obtained from experiments. The radial distribution function analysis shows that the solvent molecules adsorb on the ANPyO faces mainly via the solvent-crystal face interactions of hydrogen bonds, Coulomb and Van der Waals forces. In addition to the above results, the analysis of diffusion coefficient of trifluoroacetic acid molecules on the crystal growth faces shows that the growth habit is also affected by the diffusion capacity of trifluoroacetic acid molecules. These suggestions may be useful for the formulation design of ANPyO.

A study of the solvent effect on the crystal morphology of hexogen by means of molecular dynamics simulations

In this work, molecular dynamics simulations have been performed to study the solvent effect on the crystal morphology of hexogen. The hexogen growth habits in a vacuum predicted by the AE model are dominated by the (111), (020), (200), (002), and (210) faces. Hexogen surfaces–acetone solvent micro interface models are constructed to study the adsorption behavior of acetone on these habit planes. The modified attachment energy model considering both the solvent–surface adsorption interactions and surface structures is proposed to predict the crystal morphology of hexogen in the acetone solvent. The calculations of the modified attachment energies suggest that via the effect of acetone solvent, the (210) face has the largest morphology importance and the morphological importance of the (111), (002) and (200) faces reduces, whereas the (020) face disappears. The predicted result is in reasonable agreement with the observed experiment shape. Furthermore, the diffusion coefficients of acetone solvent toward the different RDX surfaces suggests that the (210) and (111) faces are the dominate growth faces on the final RDX crystal habits, whereas the (020) face probably disappears, which validates the reliability of the modified attachment energy model.

Prediction of crystal morphology of cyclotrimethylene trinitramine in the solvent medium by computer simulation: a case of cyclohexanone solvent.

The crystal morphology of the energetic material cyclotrimethylene trinitramine (also known as RDX) influenced by the solvent effect was investigated via molecular dynamics simulation. The modified attachment energy (MAE) model was established by incorporating the growth parameter-solvent term. The adsorption interface models were used to study the adsorption interactions between solvent and RDX surfaces. The RDX crystal morphology grown from the cyclohexanone (CYC) solvent as a case investigation was calculated by the MAE model. The calculation results indicated that, due to the effect of CYC solvent, (210) and (111) faces had the greatest morphological importance on the final RDX crystal, while the morphological importance of (020), (002), and (200) faces were reduced. The predicted RDX morphology was in reasonable agreement with the observed experiment result.

Modeling the interaction of seven bisphosphonates with the hydroxyapatite(100) face

The interaction of seven pamidronate bisphosphonate (Pami-BPs) and its analogs with the hydroxyapatite (HAP) (100) surface was studied using density functional theory (DFT) and molecular dynamic (MD) methods. Partial Mulliken oxygen atomic charges in protonated structures were calculated at the level of B3LYP/6-31G*. The MD simulation was performed using the Discover module of Material Studio by compass force field. The results indicate the abilities of donating electrons of the oxygen atoms of the phosphate groups that are closely associated with the antiresorptive potency. The binding energies, including vdw and electrostatic, are used to discuss the mechanism of antiresorption. The results of calculations show that the strength of interaction of the HAP (100) face with the bisphosphonates is N4 > N6 > N7 > N5 > N3 > N2 > N1 according to their experimental pIC50 values.

Efficient and stable ZrO2/Fe modified hollow-C3N4 for photodegradation of the herbicide MTSM

Hollow graphitic carbon nitride (HCN) ZrO2/g-C3N4 hybrid composites (HCN–ZR) and the target catalyst Fe/ZrO2/g-C3N4 (HCN–FZR) were prepared successfully by a solvo-thermal method and evaluated for photo-degradation of organic pollutants, i.e. MO, and herbicides, metsulfuron methyl (MTSM). These materials were characterized by a variety of techniques, including Fourier transform infrared spectroscopy, UV-vis spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, HPLC-MS and scanning electron microscopy. The characterization and degradation results showed that FZR particles are well distributed on the surface of HCN to give a photo-catalytically active material. Photodegradation split MTSM completely into a lot of intermediate products, as depicted in the HPLC-MS results. Mooring of FZR on HCN increased the surface-area and light absorption capability of HCN–FZR, due to heterojunction formation between the semiconductors, which retarded electron–hole recombination and enhanced the photo-activity.

Crystal morphology prediction of 1,3,3-trinitroazetidine in ethanol solvent by molecular dynamics simulation.

In order to understand the mechanism of the effect of solvent on the crystal morphology of explosives, and be convenient for the choice of crystallization solvent, the attachment energy (AE) model was performed to predict the growth morphology and the main crystal faces of 1,3,3-trinitroazetidine (TNAZ) in vacuum. The molecular dynamics simulation was applied to investigate the interactions of TNAZ crystal faces and ethanol solvent, and the growth habit of TNAZ in ethanol solvent was predicted using the modified AE model. The results indicate that the morphology of TNAZ crystal in vacuum is dominated by the six faces of [021], [112], [002], [102], [111] and [020], and the crystal shape is similar to polyhedron. In ethanol solvent, The binding strength of ethanol with TNAZ faces changes in the order of [021]>[112]>[002]>[102]>[111]>[020], which causes that [111] and [020] faces disappear and the crystal morphology becomes more regular. The radial distribution function analysis shows that the interactions between solvent and crystal faces mainly consist of coulomb interaction, van der Waals force and hydrogen bonds.

Encapsulating nano rods of copper–biphenylamines framework on g-C3N4 photocatalysts for visible-light-driven organic dyes degradation: promoting charge separation efficiency

For the first time we have successfully constructed semi conductive copper–biphenylamines framework hybrid photocatalysts to degrade organic pollutants. Cu complexes sensitized photocatalysts of g-C3N4, i.e. CN-Cu(BN), CN-Cu(PD) and CN-Cu(BA), have been successfully tested for photocatalytic degradation of organic pollutants under visible light illumination, and a significant enhancement in catalytic activity was observed for CN-Cu(BA) in comparison to pristine g-C3N4. The modified material creates a charge separation with the electrons populating the higher CB and the holes the lower VB, thus enhancing the redox reaction power of the charge carriers. CN-Cu (BA) can easily degrade 99% of RhB in 1.5 hours and 60% of phenol in 2 hours. While the degradation efficiency of CN-Cu(BN), CN-Cu(PD) and g-C3N4 is lower than that of CN-Cu(BA). The kobs for CN-Cu(BN) is 0.01985 min−1, 5.2 times higher than that of g-C3N4, and that of CN-Cu(BA) is 0.0292 min−1 which is 7.55 times greater than that of pristine g-C3N4. These degradation outcomes are favourable for developing a modified catalyst in bulk amount and its application. The strong holes can directly degrade RhB and phenol. Promoting the injection of electrons from g-C3N4 into the copper unit as well as strengthening the electronic interactions between the two units enhanced its activity.

Theoretical studies on a new furazan compound bis[4-nitramino-furazanyl-3-azoxy]azofurazan (ADNAAF).

Bis[4-nitraminofurazanyl-3-azoxy]azofurazan (ADNAAF), synthesized in our previous work [1], contains four furazan units connected to the linkage of the azo-group and azoxy-group. For further research, some theoretical characters were studied by the density functional theoretical (DFT) method. The optimized structures and the energy gaps between the HOMO and LUMO were studied at the B3LYP/6-311++G** level. The isodesmic reaction method was used for estimating the enthalpy of formation. The detonation performances were estimated with Kamlet–Jacobs equations based on the predicted density and enthalpy of formation in the solid state. ADAAF was also calculated by the same method for comparison. It was found that the nitramino group of ADNAAF can elongate the length of adjacent C–N bonds than the amino group of ADAAF. The gas-phase and solid-phase enthalpies of formation of ADNAAF are larger than those of ADAAF. The detonation performances of ADNAAF are better than ADAAF and RDX, and similar to HMX. The trigger bond of ADNAAF is the N–N bonds in the nitramino groups, and the nitramino group is more active than the amino group (–NH2).

Theoretical study of solvent effects on RDX crystal quality and sensitivity using an implicit solvation model.

Density functional theory calculations using an SMD model were performed to investigate the effect of solvents (cyclohexanone, acetone, dimethyl formamide and dimethyl sulphoxide) on the crystal quality and sensitivity of RDX. The results indicate that the N–N bond length of the RDX molecule in solvents differs clearly from that in gas phase. The solvent effect on bond and dihedral angles of RDX molecule is small, however, the RDX molecule still maintains the AEE configuration. Natural population analysis shows that, due to solvation effects, RDX O atoms attract more electrons in solvents than in gas phase, while more positive charge distributes to the molecular skeleton. The calculations of N–NO2 bond BDE and nitro group charge as well as surface electrostatic potential parameters reveal that the solvent effect may be helpful to reduce the sensitivity of RDX, but this effect has an upper limit. Finally, it can be predicted qualitatively that the crystal quality of RDX crystallized from cyclohexanone and dimethyl sulphoxide will be higher than that from acetone and dimethyl formamide. Experimental results support these theoretical predictions.