Dopant effect on the optical and thermal properties of the 2D organic-inorganic hybrid perovskite (HDA)2PbBr4.

Lead-based two-dimensional organic-inorganic hybrid perovskites (2D HOIPs) are popular materials with various optical properties, which can be tuned through metal ion doping. Due to the size and valence misfit, metal ion dopants in 2D lead-based HOIPs are still limited. In this work, Mn2+, Sb3+ and Bi3+ are doped into 2D (HDA)2PbBr4 (HDA = protonated dopamine) successfully. As a result, the dopants in 2D (HDA)2PbBr4 can induce their characteristic optical spectra, which is studied at different temperatures and excitation powers. The temperature-dependent energy transfer in the Mn-doped sample has been clarified, in which abnormal phenomena including negative thermal quenching have been observed. In addition, the dopant ions can impact the phase transition temperatures of the samples, especially lowering their crystallization temperatures greatly. The mussel-inspired organic cation, feasible metal ion regulation, and superior stability provide (HDA)2PbBr4 potential for further applications.

Decomposition mechanism of 1,3,5-trinitro-2,4,6-trinitroaminobenzene under thermal and shock stimuli using ReaxFF molecular dynamics simulations.

To obtain atomic-level insights into the decomposition behavior of 1,3,5-trinitro-2,4,6-trinitroaminobenzene (TNTNB) under different stimulations, this study applied reactive molecular dynamics simulations to illustrate the effects of thermal and shock stimuli on the TNTNB crystal. The results show that the initial decomposition of the TNTNB crystal under both thermal and shock stimuli starts with the breakage of the N-NO2 bond. However, the C6 ring in TNTNB undergoes structural rearrangement to form a C3-C5 bicyclic structure at a constant high temperature. Then, the C3 and C5 rings break in turn. The main final products of TNTNB under shock are N2, CO2, and H2O, while NO,  N2, H2O and CO are formed instead at 1 atm under a constant high temperature. Pressure is the main reason for this difference. High pressure promotes the complete oxidation of the reactants.

Mussel-Inspired Two-Dimensional Halide Perovskite Facilitated Dopamine Polymerization and Self-Adhesive Photoelectric Coating.

Polydopamine (PDA) is a good adhesion agent for lots of gels inspired by the mussel, whereas hybrid organic-inorganic perovskites (HOIPs) usually exhibit extraordinary optoelectronic performance. Herein, mussel-inspired chemistry has been integrated with two-dimensional HOIPs first, leading to the preparation of new crystal (HDA)2PbBr4 (1) (DA = dopamine). The organic cation dopamine can be introduced into PDA resulting in a thin film of (HPDA)2PbBr4 (PDA-1). The dissolved inorganic components of layered perovskite in DMF solution together with H2O2 addition can facilitate DA polymerization greatly. More importantly, PDA-1 can inherit an excellent semiconductor property of HOIPs and robust adhesion of the PDA hydrogel resulting in a self-adhesive photoelectric coating on various interfaces.

Atomic perspective revealing for combustion evolution of nitromethane/nano-aluminum hydride composite.

Adding aluminum hydride (AlH3) into energetic materials (EMs) can improve their combustion and energy performance effectively. However, the potential mechanism of AlH3 on EMs is still unclear. Based on the ReaxFF-lg method, the thermal decomposition of nitromethane/nano-aluminum hydride (NM/nano-AlH3) composites were studied. The addition of AlH3 reduces the energy barrier and increases the energy release during the decomposition of NM, accelerates the decomposition of NM. The main way of AlH3 oxidation involves the capture of O atoms from NM. The results show that AlH3 content and passivated layer affect the oxidation and hydrogen release of AlH3. The explosion of small particle size AlH3 leads to rapid oxidation and hydrogen release. The oxidation of large particle size AlH3 is dominated by the inward and outward diffusion of O and Al atoms. The products of NM/nano-AlH3 composites are H2O, CO2, N2 gases, and Al clusters. This work is expected to guide the application of AlH3 in EMs.

Enantioselective synthesis of 3-aryl-phthalides through a nickel-catalyzed stereoconvergent cross-coupling reaction.

A nickel-catalyzed asymmetric Suzuki-Miyaura cross-coupling of racemic 3-bromo-phthalides and arylboronic acids was realized for the synthesis of diverse chiral 3-aryl-phthalides in moderate to excellent reaction yields. The reaction proceeded in a stereoconvergent manner and high enantioselectivities were observed for most examined examples. A number of functional groups like aldehyde, ester and bromide were well tolerated. Heteroaromatic boronic acids were also competent coupling partners in this reaction.

Encapsulating aluminum nanoparticles into carbon nanotubes for combustion: a molecular dynamics study.

Metal nanoparticles are easily deactivated by migration-aggregation in combustion. Encapsulated nanoparticles are one of the tools for coping with the stability challenges of metal nanoparticles. The self-assembly details of aluminum nanoparticles (ANPs) encapsulated into carbon nanotubes (CNTs) were demonstrated by molecular dynamics simulations. The simulation results show that ANPs can completely self-roll into CNTs to form a stable core-shell structure by inertial force and van der Waals force. Inside the tubes, ANPs move toward the cap at a velocity of 2.27 Å ps-1. However, it increases to 3.17 Å ps-1 when near the cap of CNTs. The initiation of the ANPs' oxidation and degradation can be effectively checked by coating CNTs. The diffusion of the Al atoms in the encapsulated ANPs occurred earlier than their oxidation in combustion, verified by using ReaxFF molecular dynamics simulations. The morphological evolutions of the nanostructures in the initial combustion of the encapsulated ANPs are predicted. The interplay between the encapsulated ANPs' responses and external stimuli is classified into core-shell separation, shell damage, and core-shell burst, which provides insights into the oxidation mechanism of encapsulated nanoparticles.

Clinical significance of signet ring cells in surgical esophageal and esophagogastric junction adenocarcinoma: A systematic review and meta-analysis.

BACKGROUND: The clinical significance of signet ring cells (SRCs) in surgical esophageal and esophagogastric junction adenocarcinoma (EEGJA) remains unclear now. AIM: To explore the association between the presence of SRCs and the clinicopathological and prognostic characteristics in surgical EEGJA patients by combining and analyzing relevant studies. METHODS: The PubMed, Web of Science, and EMBASE electronic databases were searched for the relevant literature up to March 28, 2021. The relative risk (RR) with 95% confidence interval (CI) was calculated to assess the relationship between SRCs and clinicopathological parameters of surgical EEGJA patients, and the hazard ratio (HR) with 95%CI was calculated to explore the impact of SRC on the prognosis. All statistical analyses were conducted with STATA 12.0 software. RESULTS: A total of ten articles were included, involving 30322 EEGJA patients. The pooled results indicated that the presence of SRCs was significantly associated with tumor location (RR: 0.76, 95%CI: 0.61-0.96, P = 0.022; I 2 = 49.4%, P = 0.160) and tumor-node-metastasis stage (RR: 1.30, 95%CI: 1.02-1.65, P = 0.031; I 2 = 73.1%, P = 0.002). Meanwhile, the presence of SRCs in surgical EEGJA patients predicted a poor overall survival (HR: 1.36, 95%CI: 1.12-1.65, P = 0.002; I 2 = 85.7%, P < 0.001) and disease-specific survival (HR: 1.86, 95%CI: 1.55-2.25, P < 0.001; I 2 = 63.1%, P = 0.043). CONCLUSION: The presence of SRCs is related with advanced tumor stage and poor prognosis and could serve as a reliable and effective parameter for the prediction of postoperative survival and formulation of therapy strategy in EEGJA patients. However, more high-quality studies are still needed to verify the above findings.

Reactive molecular dynamics simulation of thermal decomposition for nitromethane/nano-aluminum composites.

The thermal decomposition of pure nitromethane (NM) and NM/nano-aluminum (Al) composites was simulated by reactive molecular dynamics with ReaxFF-lg corrected force field parameters. The initial decomposition pathway of NM molecules in pure NM is C-N bond rupture. However, NM is decomposed early by the initial pathway of N-O bond rupture when it mixes with nano-Al because of the strong attraction of Al to O. The decomposition process of NM/nano-Al can be divided into three stages: adsorption, slow decomposition, and rapid decomposition. The addition of nano-Al particles decreases the energy barrier in decomposition, increases the released energy, and reduces the decomposition temperature of NM. Adding 3% Al to the explosive can make the detonation pressure 3.083% higher than that of pure system. Compared with pure NM, the energy barrier of 16% Al composite is 25.63 kcal/mol lower and the energy released is 22.99 kcal/mol more. There is an optimal amount of Al contents being added to the NM composite by which the largest total numbers of gaseous products (N2, H2O, and CO2) are released. The effect of Al additives on CO2 production is the most obvious. The maximum detonation pressure can be achieved by adding an appropriate amount of nano-Al, which is similar to the experimental results. Graphical abstract.

Thermal Decomposition Mechanism of 1,3,5,7-Tetranitro-1,3,5,7-tetrazocane Accelerated by Nano-Aluminum Hydride (AlH3): ReaxFF-Lg Molecular Dynamics Simulation.

ReaxFF-low-gradient reactive force field with CHONAl parameters is used to simulate thermal decomposition of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) and AlH3 composite. Perfect AlH3 and surface-passivated AlH3 particles were constructed to mix with HMX. The simulation results indicate HMX is adsorbed on the surface of particles to form O-Al and N-Al bonds. The decomposition of HMX and AlH3 composite is an exothermic reaction without energy barrier, but the decomposition of pure HMX needs to overcome the energy barrier of 133.57 kcal/mol. Active nano-AlH3 causes HMX to decompose rapidly at low temperature, and the primary decomposition pathway is the rupture of N-O and C-N bonds. Adiabatic simulation shows that the energy release and temperature increase of HMX/AlH3 is much larger than those of the HMX system. Surface-passivated AlH3 particles only affect the initial decomposition rate of HMX. In HMX and AlH3 composites, the strong attraction of Al in AlH3 to O and the activation of the intermediate reaction by H2 cause HMX to decompose rapidly. The final decomposition products of pure HMX are H2O, N2, and CO2, and those of HMX/AlH3 are H2O, N2, and Al-containing clusters dominated by C-Al. The final gas production shows that the specific impulse of HMX/AlH3 is larger than that of HMX.

Crystal morphology prediction of 2,2',4,4',6,6'-hexanitrostilbene (HNS) by molecular scale simulation.

The spiral growth model was applied to predict the crystal morphology of 2,2',4,4',6,6'-hexanitrostilbene (HNS). We selected solvents of N,N-dimethylformamide (DMF), N-methyl pyrrolidone (NMP), and nitric acid (NA) to control the crystal morphologies of HNS. Molecular dynamic simulations were used to relax the constructed interface model. The relative growth rate of important face is calculated by the spiral growth expression. The predicted crystal shapes are flaky in three solvents. Only (100), (001), and (011) faces are generated in DMF, NMP, and NA. The aspect ratios of the predicted HNS crystal morphologies in DMF, NMP, and NA are 23.00, 15.45, and 4.85, respectively. In addition, we analyzed the properties on each face using periodic bond chain, molecular arrangement, and roughness model. The excellent agreement between the predicted morphologies and the experimental images is clearly evident. These simulation results can provide guidance for the recrystallization of HNS. Graphical abstract.

Crystal Morphology Prediction and Anisotropic Evolution of 1,1-Diamino-2,2-dinitroethylene (FOX-7) by Temperature Tuning.

Temperature-induced morphological changes are one of the strategies for designing crystal shapes, but the role of temperature in enhancing or inhibiting crystal growth is not well understood yet. To meet the requirements of high density and low sensitivity, we need to control the crystal morphology of the energetic materials. We studied the crystal morphology of 1,1-diamino-2,2-dinitroethylene (FOX-7) in dimethyl sulfoxide/water mixed solvent by using the modified Hartman-Perdok theorem. Molecular dynamics simulations were used to determine the interaction of FOX-7 and solvents. The results showed that the crystal shape of FOX-7 is hexagonal, the (101) face is the largest exposed face and is adjacent to six crystal faces at 354 K. As the temperature goes down, the area of the (001) face is significantly reduced. The crystal morphology of FOX-7 at 324 K has a smaller aspect ratio of 4.72, and this temperature is suitable for tuning the morphology from slender hexagon into diamond. The prediction results are in remarkable agreement with the experiments. Moreover, we predicted the evolution path of FOX-7 morphology by Gibbs-Curie-Wulff theorem and explained the variation of crystal shape caused by different external conditions in the actual crystallization process.

Reactive molecular dynamics simulation of the high-temperature pyrolysis of 2,2',2'',4,4',4'',6,6',6''-nonanitro-1,1':3',1''-terphenyl (NONA).

2,2',2'',4,4',4'',6,6',6''-Nonanitro-1,1':3',1''-terphenyl (NONA) is currently recognized as an excellent heat-resistant explosive. To improve the atomistic understanding of the thermal decomposition paths of NONA, we performed a series of reactive force field (ReaxFF) molecular dynamics simulations under extreme conditions of temperature and pressure. The results show that two distinct initial decomposition mechanisms are the homolytic cleavage of the C-NO2 bond and nitro-nitrite (NO2 → ONO) isomerization followed by NO fission. Bimolecular and fused ring compounds are found in the subsequent decomposition of NONA. The product identification analysis under finite time steps showed that the gaseous products are CO2, N2, and H2O. The amount of CO2 is energetically more favorable for the system at high temperature or low density. The carbon-containing clusters are a favorable growth pathway at low temperatures, and this process was further demonstrated by the analysis of diffusion coefficients. The increase of the crystal density accelerates the decomposition of NONA judged by the analysis of reaction kinetic parameters and activation barriers. In the endothermic and exothermic stages, a 20% increase in NONA density increases the activation energies by 3.24 and 0.48 kcal mol-1, respectively. The values of activation energies (49.34-49.82 kcal mol-1) agree with the experimental data in the initial decomposition stage.

Molecular Modeling on Morphology of 3,4-Bis(3-nitrofurazan-4-yl)furoxan Crystals in Dichloroethane or Benzene Mixture Solvents.

According to the experiments, DNTF crystallizes in benzene/methylbenzene (1:1), benzene/methylbenzene/ethanol (2:3:5), and sym-dichloroethane solvents into two similar crystal shapes, namely strip and tetrahedral. There is a possibility that solvent changes the crystal morphology. In order to explain this phenomenon, the DNTF growth interface model was constructed according to the actual solution environment. The interaction energy between the solvent phase and the DNTF crystal face was studied by means of molecular dynamics simulation. The crystal morphology of DNTF was predicted using the classical modified attachment energy model (MAE) in benzene, methylbenzene, benzene/methylbenzene (1:1), benzene/methylbenzene/ethanol (2:3:5), and sym-dichloroethane. The results show that the DNTF growths are mainly dominated by the (011), (001), (101), (110), (111), and (11[Formula: see text]) faces in vacuum. However, only a few faces will remain in the solvents, of which the (011) and (101) faces are exposed in benzene, methylbenzene, and benzene/methylbenzene (1:1), and only the (111) faces constitute the crystal shape of the DNTF in benzene/methylbenzene/ethanol (2:3:5) and sym-dichloroethane. The predicted results successfully explained the observed phenomena in the experiment. The simulation results can provide some guidance for the crystallization process of DNTF.

Uncovering the action of ethanol controlled crystallization of 3,4-bis(3-nitrofurazan-4-yl)furoxan crystal: A molecular dynamics study.

A computational strategy in consideration of attachment energy, temperature, solubility and supersaturation unravels details of the solvent effect on the crystal morphology. The crystal morphologies were predicted by the advanced screw dislocation growth model. This research sheds much light on the crystal growth mechanisms with the example of 3,4-bis(3-nitrofurazan-4-yl)furoxan (DNTF) in ethanol. The solvation model based on the experiment situation was established into periodic supercell. Molecular dynamics simulation was performed for obtaining the adsorption energy at the equilibrium state of the interface layer. The growth characteristics of relevant growth faces are introduced. At the same time, a periodic bond chains analysis can be applied to the existence and evolution of crystal growth units. The prediction results are in remarkable agreement with the experimental results. We found that crystal morphology of DNTF is composed of (002), (111), (111¯) and (101) faces in ethanol. As the saturation temperature rises, the (101) face becomes smaller and eventually disappears.

Molecular dynamics simulation on the reaction of nano-aluminum with water: size and passivation effects.

The reaction of aluminum and water is widely used in the field of propulsion and hydrogen production, but its reaction characteristics at the nanometer scale have not been fully studied. In this paper, the effect of particle size and surface passivation of aluminum particle on the reaction mechanism was studied by using reactive molecular dynamics (RMD) simulation. The reduction of aluminum particle size can accelerate the reaction rate in the medium term (20-80 ps) due to the increase of activity, but it also produces an agglomeration effect as the temperature increases. The presence of surface passivation reduces the proportion of active aluminum and the yield of hydrogen decreases by 30% and 33%, respectively, as the particle size decreases from 2.5 nm to 1.6 nm. The addition of AlH3 can overcome these drawbacks when some aluminum powders are replaced by AlH3. The hydrogen yield is increased by the reaction 2AlH3 + 3H2O → Al2O3 + 6H2. In the reaction of surface passivated Al (1.6 nm in diameter) and H2O, when the proportion of AlH3 reaches 25%, the energy release and hydrogen yield increase from 59.47 kJ mol-1 and 0.0042 mol g-1 to 142.56 kJ mol-1 and 0.0076 mol g-1, respectively. This performance even approximates the reaction of pure aluminum with water: 180.67 kJ mol-1 and 0.0087 mol g-1. In addition, the surface passivation affects the reaction mechanism. Before the passivation layer melts, the reaction 4Al + Al2O3 → 3Al2O occurs inside the nanoparticles.

Reactive molecular dynamics simulation of thermal decomposition for nano-aluminized explosives.

Aluminized explosives have important applications in civil construction and military armaments, but their thermal decomposition mechanisms are not well characterized. Here, the thermal decomposition of TNT, RDX, HMX and CL-20 on Al nanoparticles is examined by reactive dynamics simulations using a newly parameterized reactive force field with low gradient correction (ReaxFF-lg). Partially passivated Al nanoparticles were constructed and mixed with TNT, RDX, HMX and CL-20 crystals and then the mixed systems are heated to a high temperature in which the explosives are fully decomposed. The simulation results show that the aluminized explosives undergo three main steps of thermal decomposition, which were denoted "adsorption period" (0-20 ps), "diffusion period" (20-80 ps) and "formation period" (80-210 ps). These stages in sequence are the chemical adsorption between Al and surrounding explosive molecules (R-NO2-Al bonding), the decomposition of the explosives and the diffusion of O atoms into the Al nanoparticles, and the formation of final products. In the first stage, the Al nanoparticles decrease the decomposition reaction barriers of RDX (1.90 kJ g-1), HMX (1.95 kJ g-1) and CL-20 (1.18 kJ g-1), respectively, and decrease the decomposition reaction barrier of TNT from 2.99 to 0.29 kJ g-1. Comparing with the crystalline RDX, HMX and CL-20, the energy releases are increased by 4.73-4.96 kJ g-1 in the second stage. The number of produced H2O molecules increased by 25.27-27.81% and the number of CO2 molecules decreased by 47.73-68.01% in the third stage. These three stages are further confirmed by the evolutive diagram of the structure and temperature distribution for the CL-20/Al system. The onset temperatures (To) of generating H2O for all the aluminized explosives decrease, while those of generating CO2 for aluminized HMX and CL-20 increase, which are in accord with the experiment of aluminized RDX.

Theoretical design of novel energetic salts derived from bicyclo-HMX.

We designed three novel cage energetic anions by introducing ionic bridges containing NΘ, N(OΘ) and N(NΘNO2) into cis-2,4,6,8-tetranitro-1H,5H-2,4,6,8- tetraazabicyclo[3.3.0] octane (bicyclo-HMX or BCMHX). The properties of 21 energetic salts, based on cage anions and ammonium-based cations, were studied by density functional theory (DFT) and volume-based thermodynamics (VBT) calculations. Compared to the parent nonionic BCHMX, most title salts have lower predicted impact sensitivities, higher predicted densities, larger predicted heats of formation (HOFs) and better predicted detonation properties. In particular, 11 energetic salts not only exhibit excellent predicted energetic properties, superior to 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20), but also have lower predicted sensitivity than CL-20. The best salt had a predicted detonation velocity of 10.06 km s-1, a predicted detonation pressure of 48.54 GPa and a predicted sensitivity (h50) of 23.99 cm. By introducing ionic bridges into highly nitrated rings, or modifying the original bridge with ionic bridges, some highly nitrated cage compounds with both excellent performance and low sensitivity can be developed strategically. Graphical abstract Heats of detonation, detonation velocities, and detonation pressures of salts derived from bicyclo-HMX.

Molecular dynamic simulation for thermal decomposition of RDX with nano-AlH3 particles.

Molecular dynamic simulation of a high explosive, RDX, mixed with AlH3 nanoparticles was performed by a newly parameterized ReaxFF force field. Testing of the ReaxFF shows that the mean absolute errors of the densities and bond lengths between calculated and experimental values are less than 7% and 3%, respectively. Using the ReaxFF, effects of AlH3 nanoparticles with different radii on the thermal decomposition of RDX were revealed. A new mechanism of the generation and the consumption of H2 was discovered in the explosion. The H2 is released by AlH3 firstly and then it reacts with NO2 and CO2 from the decomposition of RDX, leading to an increase of H2O, NO and CO. Meanwhile, the size effect of AlH3 upon the reaction was also revealed. As a result, the number of produced H2O and CO2 molecules increases by 10.38% and 56.85%, respectively, when the radius of AlH3 nanoparticles decreases from 1.10 to 0.68 nm. This showed that RDX decomposes more completely with smaller AlH3 nanoparticles, which was further demonstrated by the analysis of reaction residues and diffusion coefficients.

Access to novel graphene-like sheet of hydroboron: first-principles investigation.

We designed a cyclic borane (B6 H12 ) molecule with a benzene-like structure, in which the six B atoms are located in the same plane. Three methods of B3LYP, MP2, and CCSD with the 6-311++G** basis were used to investigate its structure, electronic property, and stability. Next, we calculated the stability and electronic property of three hydroboron derivatives with fused rings of B10 H18 , B14 H24 , and B16 H26 . Finally, we investigated three types of novel two-dimensional infinite hydroboron sheets with diborane as a building block. The results of the phonon spectra ensure the dynamic stability of these predicted structures. Furthermore, the three types of hydroboron sheets are shown to have different band gap energies of less than 3.0 eV. Some investigations on the optical properties have also been performed. The predicted sheets are candidates for semiconductors, whose band gap energy can be tuned by the positions of the bridge hydrogen atoms in the sheets.

Theoretical study of the geometries and decomposition energies of CO2 on Al12X: doping effect of Al12X.

The adsorption and decomposition of CO2 molecule on X-centered icosahedronal Al12X clusters (doping atom X=Al, Be, Zn, Fe, Ni, Cu, B, C, Si, P) were investigated by the DFT methods of PW91 and PWC. Adsorption energies, chemisorption energies and energy barriers of physic- and chemisorptions for CO2 were determined. It was found that the doping atoms and spin states have important influences on the Al12X geometries, electronic properties and energies of the adsorption processes. CO2 chemisorption on the Al12C cluster is energetically and kinetically unfavorable. CO2 decomposition on the metallic doping Al12X (X=Fe, Ni, Cu) clusters has relatively low energy barriers. On contrary, the barriers are large when X=B, C, Si and P. The energy barriers for CO2 chemisorption and decomposition on the Al12Fe cluster are 5.23 kJ/mol and 38.53 kJ/mol, respectively. These values are the lowest among all the clusters being discussed. The adsorption and decomposition of CO2 on the Al12X cluster can be tuned by X doping.