Embedding Group VIII Elements into a 2D Rigid pc-C3N2 Monolayer to Achieve Single-Atom Catalysts with Excellent OER Activity: A DFT Theoretical Study

Under DFT calculations, a systematic investigation is carried out to explore the structures and oxygen evolution reaction (OER) catalytic activities of a series of 2D single-atom catalyst (SAC) systems, which are constructed by doping the transition metal (TM) atoms in group VIII into the cavities of rigid phthalocyanine carbide (pc-C₃N₂). We can find that when Co, Rh, Ir and Ru atoms are doped in the small or large cavities of a pc-C₃N₂ monolayer, they can be used as high-activity centers of OER. All these four new TM@C₃N₂ nanostructures can exhibit very low overpotential values in the range of 0.33~0.48 V, even smaller than the state-of-the-art IrO₂ (0.56 V), which indicates considerably high OER catalytic activity. In particular, the Rh@C₃N₂ system can show the best OER performance, given that doped Rh atoms can uniformly serve as high-OER-active centers, regardless of the size of cavity. In addition, a detailed mechanism analysis was carried out. It is found that in these doped pc-C₃N₂ systems, the number of outer electrons, the periodic number of doped TM atoms and the size of the embedded cavity can be considered the key factors affecting the OER catalytic activity, and excellent OER catalytic performance can be achieved through their effective cooperation. These fascinating findings can be advantageous for realizing low-cost and high-performance SAC catalysts for OER in the near future.     

共价有机框架材料催化研究进展

共价有机框架材料(COFs)是一类具有高比表面积、高孔隙率、高结晶度的结构多样性多孔材料.由于COFs具有可设计性、易功能化的特点,可通过"自上而下"或者后修饰策略将具有催化活性的官能团或金属颗粒嵌入到材料骨架当中,从而设计出高效催化剂. COFs已逐渐在多相催化及其它催化领域展现出非常大的应用价值.本文综述了COFs作为催化剂载体在多种催化反应中的合成策略与应用,对COFs催化剂的现状进行了总结与展望,同时指出该领域面临的问题与挑战.     

焙烧温度对费托合成铁基催化剂还原动力学的影响

采用沉淀法和喷雾干燥技术制备了一个典型的费托合成铁基催化剂(100Fe/3K/6SiO_2,质量比)所得样品在不同温度下焙烧5 h.分别利用N_2吸附和穆斯保尔谱表征了催化剂的织构和物相性质,同时利用热重分析仪记录了催化剂在H2气氛中的还原过程,并利用气固反应模型对还原曲线进行了动力学模拟.结果表明,300~600℃焙烧后催化剂的还原过程可用相同的模型拟合,其中由α-Fe_2O_3还原为Fe_3O_4的过程可用一维晶相形成与生长模型或三维相界面反应模型描述,Fe_3O_4还原为α-Fe的过程受二维晶相形成与生长模型控制.而对于700℃焙烧后的催化剂,其还原过程可能受晶相形成与生长模型和收缩核模型共同影响.随着焙烧温度的提高,催化剂的还原能力减弱,还原过程活化能升高.这可能是由于焙烧温度的提高导致晶粒尺寸增大和晶格缺陷减少所致.     

Numerical investigation on the rotating detonation critical mode for a methane–air mixture in an annular tube using reactive Navier–Stokes equations

Journal of Thermal Analysis and Calorimetry - Previous experimental studies show that gaseous detonation propagation in an annular tube can be divided into three categories, i.e., stable mode,...     

Nanofiber Configuration of Electrospun Scaffolds Dictating Cell Behaviors and Cell-scaffold Interactions

Electrospun nanofibers are of the same length scale as the native extracellular matrix and have been extensively reported to facilitate adhesion and proliferation of cells and to promote tissue repair and regeneration. With a primary focus on tissue repair and regeneration using electrospun scaffolds, only a few studies involved electrospun nanofiber scaffolds directing cell behaviors have been reported. In this study, we prepared electrospun nanofiber scaffolds with distinct fiber configurations, namely, random and aligned orientations of nanofibers, as well as oriented yarns, and investigated their effects on cell behaviors. Our results showed that these scaffolds supported good proliferation and viability of murine fibroblasts. Fiber configuration profoundly influenced cell morpho-logy and orientation but showed no effects on cell proliferation rate. The yarn scaffold had comparable total protein accumulation with the random and aligned scaffolds, but it supported a greater pro-liferation rate of fibroblasts with significantly elevated collagen de-position due to its porous fibrous configuration. Cell-seeded yarn scaffolds showed a greater Young's modulus compared with cell-free controls as early as 1 week. Together with its unique fiber configuration similar to the native extracellular matrix of the myocardium, the yarn scaffold might be a suitable matrix material for modeling cardiac fibrotic disorders.     

Tuning J-aggregates of tetra(p-hydroxyphenyl)porphyrin by the headgroups of ionic surfactants in acidic nonionic micellar solution

J-aggregates of the diacid form of tetra(p-hydroxyphenyl)porphyrin (THPP) were found to be stable in nonionic micellar solution in the presence of trace ionic surfactant with an oxyacid headgroup. The excitation energy of exciton coupling depends systematically on the headgroups of the ionic surfactant, by which strong and weak coupling can be accomplished in the J-aggregates. The J-aggregates have two strong exciton bands corresponding to the B- and Q-bands of the protonated monomers. The total fluorescence of THPP is quenched through aggregate formation. A strong and sharply peaked resonance light-scattering signal that suggests a delocalized excitonic state was observed just slightly to the red of the absorption maximum of the J-aggregates. The overall resonance Raman intensities appeared to be stronger in the aggregates than in the monomers. In the kinetics of aggregation induced by sodium dodecyl sulfate (SDS), no characteristics of autocatalyzed reactions were observed, and there was only a logarithmic phase that lasted only several seconds.     

NMR Crystallography of an Oxovanadium(V) Complex by an Approach Combining Multinuclear Magic Angle Spinning NMR,DFT, and Spin Dynamics Simulations

Bioinorganic vanadium(V) solids are often challenging for structural analysis. Here, we explore an NMR crystallography approach involving multinuclear ¹³C/⁵¹V solid‐state NMR spectroscopy, density functional theory (DFT), and spin dynamics numerical simulations, for the spectral assignment and the 3D structural analysis of an isotopically unmodified oxovanadium(V) complex, containing 17 crystallographically inequivalent ¹³C sites. In particular, we report the first NMR determination of C–V distances. So far, the NMR observation of ¹³C–⁵¹V proximities has been precluded by the specification of commercial NMR probes, which cannot be tuned simultaneously to the close Larmor frequencies of these isotopes (100.6 and 105.2 MHz for ¹³C and ⁵¹V, respectively, at 9.4 T). By combining DFT calculations and ¹³C–⁵¹V NMR experiments, we propose a complete assignment of the ¹³C spectrum of this oxovanadium(V) complex. Furthermore, we show how ¹³C–⁵¹V distances can be quantitatively estimated.     

Single-Molecule Redox-Targeting Reactions for a pH-Neutral Aqueous Organic Redox Flow Battery

Aqueous organic redox flow batteries (AORFBs) have received considerable attention for large-scale energy storage. Quinone derivatives, such as 9,10-anthraquinone-2,7-disulphonic acid (2,7-AQDS), have been explored intensively owing to potentially low cost and swift reaction kinetics. However, the low solubility in pH-neutral electrolytes restricts their application to corrosive acidic or caustic systems. Herein, the single molecule redox-targeting reactions of 2,7-AQDS anolyte are presented to circumvent its solubility limit in pH-neutral electrolytes. Polyimide was employed as a low-cost high-capacity solid material to boost the capacity of 2,7-AQDS electrolyte to 97 Ah L⁻¹. Through in situ FTIR spectroscopy, a hydrogen-bonding mediated reaction mechanism was disclosed. In conjunction with NaI as catholyte and nickel hexacyanoferrate as the catholyte capacity booster, a single-molecule redox-targeting reaction-based full cell with energy density up to 39 Wh L⁻¹ was demonstrated.     

Femtosecond transient absorption, nanosecond time-resolved resonance Raman, and density functional theory study of fenofibric acid in acetonitrile and isopropyl alcohol solvents

Hydrogen abstraction reaction of fenofibric acid (FA) in acetonitrile and isopropyl alcohol solvents was studied by femtosecond transient absorption (fs-TA) and nanosecond time-resolved resonance Raman (ns-TR(3)) spectroscopy experiments. The singlet excite state ((1)FA) (nπ*) with a maximum transient absorption at 352 nm observed in the fs-TA experiments undergoes efficient intersystem crossing (ISC) to convert into a nπ* triplet state FA ((3)FA) that exhibits two transient absorption bands at 345 and 542 nm. The nπ* (3)FA species does not decay obviously within 3000 ps. In the ns-TR(3) experiments, the nπ* (3)FA is also observed and completely decays by 120 ns. Compared with the triplet states of benzophenone (BP) and ketoprofen (KP), the nπ* (3)FA species seems to have a much higher hydrogen abstraction reactivity so that (3)FA decays fast and generates a FA ketyl radical like species. In isopropyl alcohol solvent, the nπ* (3)FA exhibits similar reactivity and promptly abstracts a hydrogen from the strong hydrogen donor isopropyl alcohol solvent to generate a ketyl radical intermediate. With the decay of the FA ketyl radical, no light absorption transient (LAT) intermediate is observed in isopropyl alcohol solvent although such a LAT species was observed after similar experiments for BP and KP. Comparison of the ns-TR(3) spectra for the species of interest with results from density functional theory calculations were used to elucidate the identity, structure, properties, and major spectral features of the intermediates observed in the ns-TR(3) spectra. This comparison provides insight into the structure and hydrogen abstraction reactivity of the triplet states of BP derivatives.