Linker Mediated Electronic-State Manipulation of Conjugated Organic Polymers Enabling Highly Efficient Oxygen Reduction.

Conjugated polymers with tailorable composition and microarchitecture are propitious for modulating catalytic properties and deciphering inherent structure-performance relationships. Herein, we report a facile linker engineering strategy to manipulate the electronic states of metallophthalocyanine conjugated polymers and uncover the vital role of organic linkers in facilitating electrocatalytic oxygen reduction reaction (ORR). Specifically, a set of cobalt phthalocyanine conjugated polymers (CoPc-CPs) wrapped onto carbon nanotubes (denoted CNTs@CoPc-CPs) are judiciously crafted via in situ assembling square-planar cobalt tetraaminophthalocyanine (CoPc(NH2)4) with different linear aromatic dialdehyde-based organic linkers in the presence of CNTs. Intriguingly, upon varying the electronic characteristic of organic linkers from terephthalaldehyde (TA) to 2,5-thiophenedicarboxaldehyde (TDA) and then to thieno/thiophene-2,5-dicarboxaldehyde (bTDA), their corresponding CNTs@CoPc-CPs exhibit gradually improved electrocatalytic ORR performance. More importantly, theoretical calculations reveal that the charge transfer from CoPc units to electron-withdrawing linkers (i.e., TDA and bTDA) drives the delocalization of Co d-orbital electrons, thereby downshifting the Co d-band energy level. Accordingly, the active Co centers with more positive valence state exhibit optimized binding energy toward ORR-relevant intermediates and thus a balanced adsorption/desorption pathway that endows significant enhancement in electrocatalytic ORR. This work demonstrates a molecular-level engineering route for rationally designing efficient polymer catalysts and gaining insightful understanding of electrocatalytic mechanisms.

Structural Diversity Design, Four Nucleation Methods Growth and Mechanism of 3D Hollow Box TiO2 Nanocrystals with a Temperature-Controlled High (001) Crystal Facets Exposure Ratio.

Three-dimensional (3D) hollow box TiO2 nanocrystals with structural diversity have been designed and grown by four nucleation methods, including the acid dissolution denucleation method with Fe2O3 as heterogeneous nucleation, the topological phase transition method, the sonic solvothermal method, and the air atmosphere sintering method with TiOF2 as homogeneous nucleation. Through full morphology analysis and structural characterization, reasonable growth mechanisms of 3D hollow box TiO2 nanocrystals were proposed, including nucleation dissolution, Oswald ripening, and hydrolysis reactions. It was found that the high energy (001) crystal facets exposure ratio was closely correlated with reaction temperature of four nucleation-methods, which even reached 92% for the first time. Under simulated sunlight irradiation, their hydrogen production performance and photocatalytic degradation efficiency on model dye molecules rhodamine B (RhB) and methylene blue (MB) were evaluated, and as-prepared hollow box TiO2 nanocrystals prepared by the sonic solvothermal method exhibited the best photocatalytic performance, with a hydrogen production rate of 93.88 µmol/g/h. Within 70 min, the photocatalytic degradation rates of RhB and MB reached 96.59 and 75.25%, respectively, which were 5.74 and 5.54 times that of P25. Their properties are closely connected with the orderly cubic and hierarchy configuration structure of hollow box TiO2 nanocrystals, which have a high exposure ratio of (001) facet controlled by reaction temperatures, thereby greatly improving the photocatalytic activity. This study provides a classic reference for improving the properties of hollow box TiO2 nanocrystals through structural diversity design and various methods of nanocrystal growth.

Predicting Mechanical Properties of Cold-Rolled Steel Strips Using Micro-Magnetic NDT Technologies.

Multiple micro-magnetic non-destructive testing (NDT) technologies are suitable candidates for predicting the mechanical properties of cold-rolled steel strips. In this work, based on magnetic domain dynamics behavior and magnetization theory, the correlation between electromagnetic characteristics extracted by multiple micro-magnetic NDT technologies and the influence factors was investigated. It was found that temperature and tension can subsequently affect the electromagnetic parameters by altering the domain structure and domain walls' motion properties. Pearson's correlation coefficients were employed to reflect the dependence of micromagnetic characteristics on influencing factors. The lift-off was determined as the largest influence factor among influence factors. A pseudo-static detection was reached by polynomial fitting, which could eliminate the influence of lift-off on the detection results. The number of training models was optimized, and the detection accuracy was improved via the improved Generalized Regression Neural Network (GRNN) model, based on the Gaussian Mixture Clustering (GMC) algorithm.

Subpatterns of Thin-Sheet Splash of a Droplet Impact on a Heated Surface.

A thin-sheet splash of a droplet impact on a solid surface typically appears as secondary droplets are ejected from a levitated liquid lamella. A recent work (Qin, M.; Tang, C.; Guo, Y.; Zhang, P.; Huang, Z., Langmuir 2020, 36 (18), 4917-4922) identified three subpatterns of a thin-sheet splash on a smooth wall at room temperature (T0). In the present work concerning the high-temperature (TW) surface, we show that subpatterns of the thin-sheet splash can be unified in the three-dimensional phase diagram of Oh-We-TW, where Oh is the Ohnesorge number and We is the Weber number. As TW is sufficiently high, the Leidenfrost effect becomes so prominent that both deposition and thin-sheet splash make a transition to Leidenfrost breakup. For the transition surface temperature TW,cr from thin-sheet splash to deposition, a scaling correlation of TW,cr/T0 ∼ We3/2 is derived based on the analysis of the temperature-dependent destabilizing force on the levitated lamella and agrees well with our experimental data.

Protective Effect of Lemon Peel Extract on Oxidative Stress in H9c2 Rat Heart Cell Injury.

AIM: Lemon peel, a traditional Chinese medicine, was tested in this study for its novel application in inhibiting cellular oxidative stress, and the effect of lemon peel extract (LPE) on protecting H9c2 rat heart cells from oxidative stress was investigated. METHODS: The scavenging effects of LPE on 1,1-diphenyl-2-picryhydrazyl (DPPH) and 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) free radicals were measured in extracellular experiments. The 3-(4,5-dimethyl-2-thiazolinyl)-2,5-diphenyl-2-h-tetrazolylammonium bromide (MTT) assay was used to detect the cell survival rate. The cell supernatant and intracellular oxidation-related indicators were detected by a kit, and the mRNA expression in H9c2 cells was detected by quantitative polymerase chain reaction (qPCR). The chemical substances of LPE were analyzed by high-performance liquid chromatography (HPLC). RESULTS: The results showed that LPE exhibited better DPPH and ABTS free radical scavenging abilities than vitamin C. Compared with the cells in the normal state (control group), the cell survival rate in the model group decreased, and the level of lactate dehydrogenase (LDH) increased, the levels of superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) decreased, and the content of malondialdehyde (MDA) increased. Compared with the control group, the expression of Bcl-2-related X protein (Bax), caspase-3, nuclear factor erythroid 2-related factor 2 (Nrf2), and heme oxygenase-1 (HO-1) in the model group was increased, and the expression of B-cell lymphoma-2 (Bcl-2) was reduced. Compared with the model group, LPE treatment improved the cell survival rate, reduced the levels of LDH and MDA, increased the levels of SOD, CAT, and GSH, downregulated the expression of Bax, caspase-3, Nrf2 and HO-1, and upregulated the expression of Bcl-2. The composition analysis showed that LPE contained catechin, rutin, naringin, quercetin, and hesperidin. CONCLUSION: The results indicated that LPE could protect H9c2 cells from oxidative stress through five active components. LPE has the potential to be developed into natural medicine or health food for the inhibition of cell oxidative damage.

Theoretical studies on the initial reaction kinetics and mechanisms of p-, m- and o-nitrotoluene.

The potential energy surfaces (PESs) of three nitrotoluene isomers, such as p-nitrotoluene, m-nitrotoluene, and o-nitrotoluene, have been theoretically built at the CCSD(T)/CBS level. The geometries of reactants, transition states (TSs) and products are optimized at the B3LYP/6-311++G(d,p) level. Results show that reactions of -NO2 isomerizing to ONO, and C-NO2 bond dissociation play important roles among all of the initial channels for p-nitrotoluene and m-nitrotoluene, and that the H atom migration and C-NO2 bond dissociation are dominant reactions for o-nitrotoluene. In addition, there exist pathways for three isomer conversions, but with high energy barriers. Rate constant calculations and branching ratio analyses further demonstrate that the isomerization reactions of O transfer are prominent at low to intermediate temperatures, whereas the direct C-NO2 bond dissociation reactions prevail at high temperatures for p-nitrotoluene and m-nitrotoluene, and that H atom migration is a predominant reaction for o-nitrotoluene, while C-NO2 bond dissociation becomes important by increasing the temperature.

On the Second Explosion Limits of Hydrogen, Methane, Ethane, and Propane.

In this work, we have first investigated the explosion limit behaviors from hydrogen to propane through numerical simulations and validated with the available experimental data. The shape of the explosion limit curves and the possible turning points (P 1-2, T 1-2), first to second limit transition, and (P 2-3, T 2-3), second to third limit transition that bound the second explosion limit as a function of the fuel carbon number, have been examined. Results show that with an increase of methane mole fraction in the hydrogen/methane system, the upper turning point (P 1-2, T 1-2) remains almost unchanged and the lower transition point (P 2-3, T 2-3) rotates counterclockwise around (P 1-2, T 1-2). With a further increase of carbon number, (P 1-2, T 1-2) moves to the lower-pressure and -temperature region and (P 2-3, T 2-3) gradually moves to the lower-pressure and higher-temperature region. The slope of the second explosion limit is inversely proportional to the carbon number, k PT = 0.0069 - 0.005/(X c - 0.7), approximately. Second, a sensitivity analysis has been conducted to study the elementary reaction on the second explosion limits. The results show that the chain branching and termination reactions governing the explosion limit of hydrogen have a little effect on the second explosion limit of methane. The C2H5O2H decomposition to form OH radicals is dominant in controlling the nonmonotonic behavior of the second explosion limit of C2H6. The second explosion limit behavior of propane is governed by three sets of reactions in the low-temperature oxidation process.

Subpatterns of Thin-Sheet Splash on a Smooth Surface.

When a droplet impacts a smooth solid surface with a sufficiently high inertia, a thin sheet is created and the whole droplet fluid then breaks apart. Latka, A. [Thin-sheet creation and threshold pressures in drop splashing. Soft Matter 2017, 13, 740-747] defined it as thin-sheet splash. In this work, we used a high-speed camera with a long-distance microscope and experimentally showed that thin-sheet splash can be subdivided into three distinct patterns in terms of breakup location. Specifically, pattern 1 is characterized by the breakup of the rim with the thin sheet being intact, pattern 2 by the almost simultaneous breakup of both the rim and the thin sheet, and pattern 3 by the breakup of the thin sheet followed by the breakup of the rim. The effects of the Weber number and the Ohnesorge number on the transitions of these subpatterns were determined over large ranges of their values, and a regime nomogram in the parametric space of We-Oh was obtained.

Auto-ignition behaviors of nitromethane in diluted oxygen in a rapid compression machine: Critical conditions for ignition, ignition delay times measurements, and kinetic modeling interpretation.

In this work, the weakest thermodynamic conditions for the auto-ignition of mixtures containing nitromethane were experimentally determined by using the rapid compression machine facility. Results show there is a narrow weak ignition region between ignition and non-ignition. The weak ignition region would disappear with the increase of the EOC (end of compression) pressure and nitromethane concentration. In addition, the ignition delay times for successful auto-ignition for different nitromethane concentrations and equivalence ratio mixtures were measured and compared. Results show that the dependence of nitromethane ignition on the equivalence ratio is weak. Subsequently, the measured ignition delay time data were employed to validate several kinetic models in literature and our previous model shows better agreement with experimental results, as well as other available literature data. Sensitivity analysis for the model reveals the importance of unimolecular decomposition and H-abstraction reactions for the ignition delay times in the temperature range studied herein. Finally, critical conditions for nitromethane ignition under extended conditions that are beyond the ability of the experimental facility were predicted.

Kinetics of Hydrogen Abstraction and Addition Reactions of 3-Hexene by ȮH Radicals.

Rate coefficients of H atom abstraction and H atom addition reactions of 3-hexene by the hydroxyl radicals were determined using both conventional transition-state theory and canonical variational transition-state theory, with the potential energy surface (PES) evaluated at the CCSD(T)/CBS//BHandHLYP/6-311G(d,p) level and quantum mechanical effect corrected by the compounded methods including one-dimensional Wigner method, multidimensional zero-curvature tunneling method, and small-curvature tunneling method. Results reveal that accounting for approximate 70% of the overall H atom abstractions occur in the allylic site via both direct and indirect channels. The indirect channel containing two van der Waals prereactive complexes exhibits two times larger rate coefficient relative to the direct one. The OH addition reaction also contains two van der Waals complexes, and its submerged barrier results in a negative temperature coefficient behavior at low temperatures. In contrast, The OH addition pathway dominates only at temperatures below 450 K whereas the H atom abstraction reactions dominate overwhelmingly at temperature over 1000 K. All of the rate coefficients calculated with an uncertainty of a factor of 5 were fitted in a quasi-Arrhenius formula. Analyses on the PES, minimum reaction path and activation free Gibbs energy were also performed in this study.

Exploiting hydrophobic borohydride-rich ionic liquids as faster-igniting rocket fuels.

A family of hydrophobic borohydride-rich ionic liquids was developed, which exhibited the shortest ignition delay times of 1.7 milliseconds and the lowest viscosity (10 mPa s) of hypergolic ionic fluids, demonstrating their great potential as faster-igniting rocket fuels to replace toxic hydrazine derivatives in liquid bipropellant formulations.

High methane natural gas/air explosion characteristics in confined vessel.

The explosion characteristics of high methane fraction natural gas were investigated in a constant volume combustion vessel at different initial conditions. Results show that with the increase of initial pressure, the peak explosion pressure, the maximum rate of pressure rise increase due to a higher amount (mass) of flammable mixture, which delivers an increased amount of heat. The increased total flame duration and flame development time result as a consequence of the higher amount of flammable mixture. With the increase of the initial temperature, the peak explosion pressures decrease, but the pressure increase during combustion is accelerated, which indicates a faster flame speed and heat release rate. The maximum value of the explosion pressure, the maximum rate of pressure rise, the minimum total combustion duration and the minimum flame development time is observed when the equivalence ratio of the mixture is 1.1. Additionally, for higher methane fraction natural gas, the explosion pressure and the maximum rate of pressure rise are slightly decreased, while the combustion duration is postponed. The combustion phasing is empirically correlated with the experimental parameters with good fitting performance. Furthermore, the addition of dilute gas significantly reduces the explosion pressure, the maximum rate of pressure rise and postpones the flame development and this flame retarding effect of carbon dioxide is stronger than that of nitrogen.