Quantitative Analysis of Flame Instabilities in a Hele-Shaw Burner

We show in this paper that a Hele-Shaw burner can be used for studying the development of premixed flame instabilities in a quasi-two dimensional configuration. It is possible to ignite a plane flame at the top of the cell, and to measure quantitatively the growth rates of the instability by image analysis. Experiments are performed with propane and methane-air mixtures. It is found that the most unstable wavelength, and the maximum linear growth rate of perturbations, directly measured in the present experiments, have the same order of magnitude as those previously measured on flames propagating freely downwards in wide tubes.     

Successive magnetic ordering in two CoⅡ-ladder metal-organic frameworks

Metal-organic frameworks showing successive magnetic ordering are far less common than inorganic compounds.Here,we report two metal-organic frameworks[Co^Ⅱ(ox)(bphy)·0.1(DMF)·0.1(Me OH)]n(1)and[Co3^Ⅱ(ox)3(bphy)2(DMF)2]n(2)comprised of zigzag and necklace Co^Ⅱ-ladders,respectively.Together with a previously reported compound[Co^Ⅱ(ox)(bphy)·0.2(DMF)]n(3)consisting of spiraling zigzag Co^Ⅱ-ladders,these three compounds provide a good system for comparative structural and magnetic studies.Comprehensive magnetic analysis reveals that the three compounds undergo long-range magnetic ordering at^2.6 K but exhibit vastly different short-range magnetic correlations:compound 1 shows short-range spin-canted antiferromagnetism ordering at^14.0 K;compound 2 demonstrates successive short-range antiferromagnetism ordering at^15.5and^12.6 K;compound 3 shows slow magnetic relaxation with Tb≈4.6 K.These results demonstrate long-range magnetic ordering is readily accessible in the frameworks of ox^2-bridging Co^Ⅱ-ladders linked by bphy,where short-range magnetic correlations can be systematicly tuned by the Co^Ⅱ-ladder structures.     

The Role of Sulfur in the S-PtRe/Al2O3 Catalysts: The Endogenous Deposition Effect on the Metal/acid Micro-environment

Alumina is widely used as support in the industrial catalytic process. As a common impurity, the sulfur species, which are often considered a harmful component, play a positive role in some petrochemical reactions. Herein, the S-modified catalysts were fabricated using the exogenous/endogenous deposition method to study the effect of the sulfur induced by introduction approaches. Series characterizations reveal that the exogenous sulfur from the sulfidation treatment affects the active metals by poisoning the low-coordinated sites, leading to the active metal sites decrease. As for the endogenous deposition method, besides the poison effect, the removal of the endogenous sulfur from the S-contain alumina support can produce oxygen vacancies, which can not only act as acid sites but work as an electron acceptor that optimizes the catalyst electronic structure. Benefits from the effect of endogenous sulfur, the catalyst with a suitable catalytic metal/acid micro-environment exhibit the best dehydrocyclization performance.     

Eliminating Concentration Polarization with Cationic Covalent Organic Polymer to Promote Effective Overpotential of Nitrogen Fixation

Electrocatalytic nitrogen reduction reaction offers a sustainable alternative to the conventional Haber-Bosch process. However, it is currently restricted by low effective overpotential due to the concentration polarization, which arises from accumulated products, ammonium, at the reaction interface. Here, a novel covalent organic polymer with ordered periodic cationic sites is proposed to tackle this challenge. The whole network exhibits strong positive charge and effectively repels the positively charged ammonium, enabling an ultra-low interfacial product concentration, and successfully driving the reaction equilibrium to the forward direction. With the given potential unchanged, the suppressed overpotential can be much liberated, ultimately leading to a continuous high-level reaction rate. As expected, when this tailored microenvironment is coupled with a transition metal-based catalyst, a 24-fold improvement is generated in the Faradaic efficiency (73.74 %) as compared with the bare one. The proposed strategy underscores the importance of optimizing dynamic processes as a means of improving overall performance in electrochemical syntheses.     

Nanometer‐Scaled Hollow Spherical Micelles with Hydrophilic Channels and the Controlled Release of Ibuprofen

PS‐b‐PAA spherical micelles with a liquid core and a PAA shell are prepared with the assistance of 1,2‐dichloroethane. During the process of adding a mixture of PNIPAM‐b‐P4VP and PEG‐b‐P4VP, multi‐layered micelles with a mixed corona that consists of both PNIPAM and PEG chains are constructed through the electrostatic interaction and hydrogen bonding between the PAA block and the P4VP block. When heating above the LCST, the PNIPAM chains collapse onto the PAA/P4VP complex layer while the PEG chains still stretch into the solution through the collapsed PNIPAM layer, which leads to the formation of hydrophilic channels around the PEG chains. The ibuprofen encapsulated in the hollow space can diffuse through the channels and its release rate can be controlled by changing the ratio of PEG chains to PNIPAM chains in the corona.