Chunhai Yang

Nitric oxide (NO) is a major air pollutant requiring efficient conversion. Using first-principles calculations, this study investigates the electrocatalytic NO reduction reaction (NORR) as an integrated solution for pollution abatement and value-added synthesis. Among the various metal atom/metal clusters anchored SnS2 nanosheet, Pd3@SnS2 is identified as an efficient single-cluster catalyst (SCC) for NORR to generate NH3 without a limiting potential. Charge transfer analyses reveal that the superior electron-donation capacity of the Pd3 cluster to key intermediates is the critical factor for its catalytic activity, enabling efficient N-O bond activation. The Pd3@SnS2 also demonstrates exceptional selectivity towards NH3 production over N2. Moreover, Ag1@SnS2 exhibits high activity for N-N coupling to reduce the NO into N2, which serves as suitable electrocatalyst for NO remediation.

1,1´‐Dihydroxam‐5,5´‐bisazide (1,1´‐BTO) is the precursor for the well‐known energetic material dihydroxylammonium 5,5´‐bistetrazole‐1,1´‐diolate. It always appears in an anionic state, BTO _anion , and a free radical state, BTO _biradical , depending on the chemical environments during its reactions. To demonstrate their molecular surface reactivity, starting from their electronic structure optimized on the theory level of ωB97XD/def2‐TZVP, theoretical calculations and results discussions were carried out on their atomic dipole moment corrected Hirshfeld population charges, molecular surface electrostatic potential, molecular surface average local ionization energy; to deeply understand thermodynamic stabilities characterized by their aromaticities, nuclear‐independent chemical shift (NICS) along with the direction perpendicular to their molecular plane, its variant free of in‐plane component NICS, magnetically induced current, were calculated from the wave function obtained on the theory level of PBE0/6‐311++G** and discussed. These discussions and conclusions are expected to enrich the deeper understanding of the states presented by 1,1´‐BTO during the reaction process.

To further comprehensively study the intramolecular weak interaction of the gaseous TKX‐50 molecule, the two conformations of the TKX‐50 molecule were analyzed via the Independent Gradient Model based on the Hirshfeld Partition (IGMH) method based on the B3LYP/6‐311 g (d,p) level for geometry optimization and for single point energy. The conclusions manifest that the weak interactions between these fragments are mainly composed of hydrogen bonds and van der Waals interactions. From the strength of inter‐fragment interactions formed by contributing atomic pairs and their percentage contributions, these H bonds, together with dispersion‐dominated weak interactions provided by non‐direct facing atomic pairs near these H bonds, dominate the inter‐fragment interaction resulting in the stability of the molecular structure. Meanwhile, the weak interactions enclosed by end‐atoms of two fragments not only include the contributions provided by inter‐fragment atomic pairs of two fragments but also include the contributions provided by intra‐fragment atomic pairs of fragment 1. For conformation II, due to the H transfer between fragments, a pair of symmetric H bonds at the corresponding regions are extremely strong to reach the level of covalent bond while the two groups −OH at the other end become looser, resulting in conformation II own lower energy. Differences in inter‐fragment interactions between two conformations were essentially brought by the stronger electron‐withdrawing ability of atom O than that of atom N.

Two complexes of dihydroxylammonium 5,5’‐bistetrazole‐1,1’‐diolate (TKX‐50) were employed to evaluate the aromaticity of their tetrazole rings via deep analysis such as the electronic structure, the ZZ component of the natural chemical shielding tensor (NICS_ZZ) and component orbitals, localized orbital locator purely contributed by σ‐orbitals (LOL‐σ) and localized orbital locator purely contributed by π‐orbitals (LOL‐π), the anisotropy of the induced current density (AICD) and the ZZ component of iso‐chemical shielding surface (ICSS_ZZ) of these tetrazole rings thereof. The conclusion shows: that all tetrazole rings and bi‐tetrazole rings in complexes have strong σ and a comparable strength π double aromaticity; all these magnetic shields almost symmetrically increase from the central axis to the tetrazole ring atoms; tetrazole rings in complex II show a little stronger dual aromaticity than that in complex I mainly due to the different orientation of the fragment 2 encompassing two hydroxylamine groups resulting in different effects on the contributions of σ orbitals and π orbitals to total aromaticity of tetrazole rings thereof; the difference in aromaticity is fundamentally caused by the atoms O with stronger electron‐withdrawing than atom N in fragment 2 interact with bi‐tetrazole ring through O in complex I but through N in complex II.

Tetrazole compounds are a category of energetic materials with great potential. Their stability is inherently related to their aromatics. On the basis of research in DFT at b3lyp/6–311^** level on three compounds interested, viz. 5-amino-1 H-tetrazole, 5-carboxyl-1 H-tetrazole, and 2-methyl-5-carboxyl-tetrazole, their aromatic characters are extensively analyzed by virtue of different estimation method. Analyses show that these methods, Nucleus-independent Chemical Shift, iso-chemical shielding surface, adaptive natural density partitioning, π-electrons density, and localized orbital locator of π-electron density are efficient for substituted-tetrazole ring aromaticity estimation. Conclusion denotes that both substituent and substituted position can significantly affect the aromaticity of tetrazole ring of tetrazole compound. Among these given substituents, electro-withdrawing group -COOH significantly increases the aromaticity of the tetrazole rings due to the withdrawing to π-electrons thereof but electro-donating group -NH₂ weakens the one of the tetrazole rings due to the donating to π-electrons thereof. But for 2-methyl-5-carboxyl-tetrazole, the aromaticity increasing of -COOH imposed on π-electrons of tetrazole ring thereof is partially balanced by the existence of the electron-donating group -CH₃ at asymmetric meta-position of tetrazole ring. Consequently, the aromaticity order is 5-Carboxyl-1 H-tetrazole > 2-methyl-5-Carboxyl-tetrazole > 5-amino-1 H-tetrazole.

To fully and deeply understand the weak interactions in the gaseous structure of the TKX-50 molecule, two conformations I and II of the TKX-50 molecule confirmed in a crystal cell were optimized at the B3LYP/6-311g(d,p) level in the gas state, and the single point energy of the optimized structure was calculated at the M06-2X/ma-TZVPP level. Analyzing methods for weak interactions such as the interaction region indicator (IRI), topological basin analysis, and the extended transition state-natural orbitals for chemical valence (ETS-NOCV) theory with the help of Multiwfn code were employed to reveal the corresponding intramolecular weak interactions. The results showed that there were 5 kinds of intramolecular weak interaction in both conformations. They are two types of H bond, two types of intra-ring weak interaction, and one type of O–N bond within the molecular fragment containing the bis-tetrazole ring. The combined effect of all these weak interactions holds the bis-tetrazole ring of TKX-50 retaining an almost coplanar configuration. Meanwhile, the strength of these weak interactions is significantly different in conformation I and conformation II. The most obvious difference is that conformation II has a significant H transfer between intramolecular fragments due to the mirror rotation of almost 180° of cations (NH₃OH)⁺ perpendicular to the N–O bond axis thereof as compared to the reference conformation I. This conformational difference not only makes the weak interaction between the two conformations very different but also forms a quasi-covalent bond in conformation II with much larger bonding energy than other H bonds, thus resulting in conformation II having lower electron energy and more stable geometry. In addition, the order of breaking various H bonds in the combustion decomposition process of TKX-50 is deduced by comparing various H bonds.

Bubble volume and bubble geometry are key parameters that affect the movement and acoustic radiation performance of bubble columns. This paper proposes an image processing method to study the movement and acoustic radiation characteristics of the rising bubbles originating from the combustion of a pyrotechnic composition based on high-speed photography. Results showed that during the rise of bubbles, their shape gradually changed from spherical to irregular, and their rising trajectory presented a curvilinear form. After the rising velocities of the bubbles in the z and x directions were compared, the results revealed that the rising velocity of the bubbles was unstable. The velocity of the rising bubbles in the direction of the z axis was much higher than that of the x axis. Meanwhile, the acceleration of bubble volume decreased first and then increased. This process was repeated; however, the amplitude of increase or decrease was inconsistent, which led to the generation of a certain amount of acoustic radiation effect, and it had a similar trend of change with the acceleration of bubble volume.

In this work, microwave (MW) irradiation was employed to enhance the zero-valent iron (ZVI)-dominated de-contamination of chromite ore processing residue (COPR). A coupling system and the traditional two-step procedure were both conducted to evaluate the effects of MW irradiation on the reduction and the incorporation of COPR into the composite materials-based geopolymers. The factors including the ratios of liquid to solid, the mass ratios of ZVI to COPR, and the acid dosage had some obvious influence on the reduction of COPR in the MW system. The compressive strengths of 31.54 and 41.56 MPa were determined from the two-step procedure and the coupling system at the COPR dosage of 10% (mass ratio), respectively. The employment of MW irradiation not only strengthened the formation of the geopolymer matrices but also improved the chemical stabilization of Cr species in the solidified blocks. The coupled process was more conducive to incorporating the treated COPR into the geopolymer-based crystalline microstructures compared with the subsequent usage of ZVI reduction and MW irradiation.

A simple physical method was developed for the surface modification and the solubilization of MWNTs in water by Congo red. The resulting water‐soluble MWNTs (MWNTs‐CR) can form stable and uniform films on solid supports when dried, which was used to fabricate MWNTs‐CR modified glassy carbon electrodes (MWNTs‐CR/GCE). Voltammetric studies showed that MWNTs‐CR/GCE exhibited a strong enhancement effect on the electrooxidation of ofloxacin. MWNTs‐CR films were also proved to possess overwhelming advantages as electrochemical sensing films over other commonly used MWNTs composite films (e.g., MWNTs‐DHP and MWNTs‐Nafion), reflected by the higher oxidation current, lower background and stronger accumulation capacity towards less soluble species. The sensitive oxidation of ofloxacin at MWNTs‐CR/GCE was used for the determination of ofloxacin. Under optimal conditions, the oxidation current was proportional to ofloxacin concentration in the ranges of 5×10⁻⁸–3.0×10⁻⁵ M. The detection limit of 9×10⁻⁹ M was obtained for 350 s accumulation at open circuit (S/N=3). This method was applied to the determination of ofloxacin in human urine and the result was satisfying.