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By virtue of the hydroxyl and carboxyl groups on the graphene oxide (GO) plane, three-dimensional tremella-like Zn–Al–Zr-layered double-hydroxide/GO (Zn–Al–Zr LDH/GO) nanocomposites have been successfully prepared via the self-assembly process. As compared to Zn–Al–Zr LDH, the Zn–Al–Zr LDH/GO nanocomposite (LDH/GO-4) possesses a hierarchical pore structure; it shows an enlarged pore width which endows it with enhanced phosphorus (P) adsorption capacity, and the fitting of nonlinear Langmuir showed that the maximum adsorption capacity reaches 36.86 ± 0.76 mg-P/g. The fitting of the kinetic model confirmed that the adsorption process was predominantly chemisorption. Meanwhile, fitting of the thermodynamic model indicated that the adsorption process was endothermic, stochastic, and spontaneous. For LDH/GO-4, the [−C–O–Zn-(OH)x] and [−COO–ZrO-(OH)x] groups are its chief active sites to chemically absorb P. In this study, LDH/GO-4 can make the total phosphorus (TP) concentration of the real river water decline from 0.28 mg/L to near zero in 24 h, while the Phoslock commercial product only achieves a TP removal rate of 46.43% under the same conditions. Moreover, LDH/GO-4 also has good reusability in a steady recovery of P, and the removal rate of TP was still over 95% after it experienced the adsorption–desorption of P for five cycles. Thus, LDH/GO-4 shows great potential for application in the sustainable P recovery field. [ABSTRACT FROM AUTHOR]

The phase transition of the β-HMX crystal has been widely studied under high pressure, but the microscopic transition mechanism is not sufficiently understood. In this article, we perform a series of ab initio molecular dynamics simulations focusing on structure deformation and the corresponding vibration spectra resolution of β-HMX at 0–40 GPa. Several typical pressure-induced phase transition processes are confirmed by analyzing the chemical bond, dihedral angle, charge transfer, and IR and Raman spectra. The corresponding relationship between molecular structure and spectral signal is constructed through the partial spectra calculations of special functional groups within the HMX molecule. The anisotropic effects of different groups on the initial structural phase transition are uncovered. The equatorial C–N and axial N–N bonds have the largest compression ratio as pressure increases, which is the intrinsic factor for the initiation of structure transformation. The C–N molecular ring plays an important role in the entire phase transition process. In addition, the phase transition of β → ζ is also closely related to the deformation of NO2, while that of ζ → ε is induced by the axial N–NO2 group. Regarding the higher-pressure phase transition, the synergetic effect of N–NO2, CH2 groups, and molecular rings becomes more considerable. [ABSTRACT FROM AUTHOR]

The structure and properties of nano-carbon materials formed in explosives detonation are always a challenge, not only for the designing and manufacturing of these materials but also for clearly understanding the detonation performance of explosives. Herein, we study the dynamic evolution process of condensed-phase carbon involved in 2,4,6-Triamino-1,3,5-trinitrobenzene (TATB) detonation using the quantum-based molecular dynamics method. Various carbon structures such as, graphene-like, diamond-like, and "diaphite", are obtained under different pressures. The transition from a C sp2- to a sp3-hybrid, driven by the conversion of a hexatomic to a non-hexatomic ring, is detected under high pressure. A tightly bound nucleation mechanism for diamond-like carbon dominated by a graphene-like carbon layer is uncovered. The graphene-like layer is readily constructed at the early stage, which would connect with surrounding carbon atoms or fragments to form the tetrahedral structure, with a high fraction of sp3-hybridized carbon. After that, the deformed carbon layers further coalesce with each other by bonding between carbon atoms within the five-member ring, to form the diamond-like nucleus. The complex "diaphite" configuration is detected during the diamond-like carbon nucleation, which illustrates that the nucleation and growth of detonation nano-diamond would accompany the intergrowth of graphene-like layers. [ABSTRACT FROM AUTHOR]

Plastic-bonded explosives (PBXs) consisting of explosive grains and a polymer binder are commonly synthesized to improve mechanical properties and reduce sensitivity, but their intrinsic chemical behaviors while subjected to stress are not sufficiently understood yet. Here, we construct three composites of β-HMX bonded with the HTPB binder to investigate the reaction characteristics under shock loading using the quantum-based molecular dynamics method. Six typical interactions between HMX and HTPB molecules are detected when the system is subjected to pressure. Although the initial electron structure is modified by the impurity states from HTPB, the metallization process for HMX does not significantly change. The shock decompositions of HMX/HTPB along the (100) and (010) surface are initiated by molecular ring dissociation and hydrogen transfer. The initial oxidations of C and H within HTPB possess advantages. As for the (001) surface, the dissociation is started with alkyl dehydrogenation oxidation, and a stronger hydrogen transfer from HTPB to HMX is detected during the following process. Furthermore, considerable fragment aggregation is observed, which mainly derives from the formation of new C−C and C−N bonds under high pressure. The effect of cluster evolution on the progression of the following reaction is further studied by analyzing the bonded structure and displacement rate. [ABSTRACT FROM AUTHOR]

The thermal decomposition of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) is studied using a quantum-based molecular dynamics (MD) method at several temperatures, to uncover its fundamental reaction mechanism and kinetic properties. The primary decomposition pathways, key intermediate products and their population evolutions are systematically investigated. For the first time, we uncover four sequential reaction stages during the thermal dissociation of TATB: (1) C–NO2 bond cleavage and amino dehydrogenation; (2) hydrogen transfer to nitro or NO2, with further conversion to NO and H2O; (3) carbon oxidation and molecular ring deep fission to generate CO and small –CN fragments; (4) final formation of gaseous N2 and CO2. The fission and formation rate constants and reaction energy barriers of the main chemical bonds are obtained by exploring the kinetic process. We confirm that C–NH2 bond breaking is the rate-controlling step for carbon oxidation, while N–N bond formation is the rate-controlling step for N2 generation. Besides, we obtain the global exothermic reaction rate and reaction heat based on an analysis of the changes in potential energy. The results not only give a deep insight into the chemical performance of TATB, but also provide prerequisite parameters for improving the macroscopic physical models for explosive reactivity. [ABSTRACT FROM AUTHOR]