A mechanistic study of selective propane dehydrogenations on MoS2 supported single Fe atoms

On-purpose propane dehydrogenation (PDH) has emerged as a profitable alternative to the traditional cracking of oil products for propylene production. By means of density functional theory (DFT) calculations, the present work demonstrates that Fe atoms may atomically disperse on MoS₂ (Fe₁/MoS₂) and serve as a promising single-atom catalyst (SAC) for PDH. The catalytic activity of Fe₁/MoS₂ is attributed to the highly exposed d orbitals of single Fe atoms, while the propylene selectivity is originated from the kinetic inhibition of propylene dehydrogenation resulting from fast propenyl hydrogenation. The unique catalytic selectivity of Fe₁/MoS₂ may inspire further investigations of on-purpose dehydrogenations of propane on SACs.     

Facile preparation of α-MnO2 nanowires for assembling free-standing membrane with efficient Fenton-like catalytic activity

Assembling MnO₂ nanowires into macroscopic membrane is a promising engineered technology for catalyst separation and enhancement of Fenton-like reaction activity, yet its development is limited by the deficiencies in preparation and property modulation of the MnO₂ nanowires. In this work, we developed a facile method using C₂H₅OH and CH₃COOK as reductive and vital control reagents to react with KMnO₄ by hydrothermal reaction at 140 °C for 12 h, to prepare the ultralong α-MnO₂ nanowires up to tens of micrometers with high purity and aspect ratio. Such strategy not only had the advantages of being mild, easily controlled and environmental pollution-free, but also endowed α-MnO₂ nanowires with excellent ability as a Fenton catalyst when assembled into free-standing membrane for degrading phenolic compounds (k_obs = 0.0738 ～ 0.1695 min^?1) in a continuous flow reaction. The reactive oxygen species (i.e., ^?OH) from Fenton-like reaction were enriched within this α-MnO₂ nanowire membrane via nanoconfinement effect, which further enhanced the mass transportation of ^?OH available for phenolic contaminants. MnO₂ nanowire membrane using our method possessed the high practical potential for water purify due to its easy-preparation and enhanced catalytic performances.     

Tough and transparent blends of polylactide with block copolymers of ethylene glycol and propylene glycol

In order to modify its physical properties, particularly the drawability and toughness, polylactide (PLA) was melt blended with a set of PEG-b-PPG-b-PEG block copolymers with varying ratio of the hydrophilic (PEG) and hydrophobic (PPG) blocks. Miscibility of the copolymers with PLA depended on their molar mass and PEG content. Interestingly, the best drawability was achieved in the case of partially miscible blends, in which fine liquid inclusions of the modifier were dispersed in PLA rich matrix with glass transition temperature only moderately decreased, to about 50 °C. About 37 fold increase of the elongation at break and about 1.5 fold increase of the tensile impact strength with respect to neat PLA were reached at small content (10 wt.%) of the modifier. Despite the phase separation, the blends remained transparent. In addition, the barrier properties for oxygen were improved.     

Altering the Position of Phenyl Substitution to Adjust Film Morphology and Memory Device Performance

In this study, two structural isomers α‐PBT and β‐PBT, which only differ in the phenyl substituent position on the quinoline chromophore, have been designed and successfully synthesized. The influences of substituent position on the film morphology and the storage performance of the devices were investigated. Both molecules employed in the memory devices exhibited same nonvolatile binary (write‐once‐read‐many‐times; WORM) characteristics, but the switch threshold voltage (Vth) of the β‐PBT‐based device was clearly lower than that of the α‐PBT‐based device. Simulation results demonstrate that the variation of the phenyl substituent position led to different intermolecular stacking styles and thus to varied grain sizes for each film morphology. This work illustrates that altering the phenyl substituent position on the molecular backbone could improve the quality of the film morphology and reduce power consumption, which is good for the rational design of future advanced organic memory devices (OMDs).     

Preparation of electrically enhanced forward osmosis (FO) membrane by two-dimensional MXenes for organic fouling mitigation

In this work, a conductive thin film composite forward osmosis (TFC-FO) membrane was firstly prepared via vacuum filtering MXenes nanolayer on the outer surface of polyethersulfone membrane followed by interfacial polymerization in the other side. Moreover, its feasibility of mitigating organic fouling under electric field was evaluated. Results indicated that the addition of MXenes greatly reduced the electric resistance of membrane from 2.1 × 10¹² Ω to 46.8 Ω, enhanced the membrane porosity and promoted the membrane performance in terms of the ratio of water flux to reverse salt flux. The modified TFC-FO membrane presented the optimal performance with 0.47 g/m² loading amount of MXenes. Organic fouling experiments using sodium alginate (SA) and bovine serum albumin (BSA) as representative demonstrated that the introduction of MXenes could effectively enhance the anti-fouling ability of TFC-FO membrane under the electric field of 2 V. The interelectron repulsion hindered organic foulants attaching into membrane surface and thus effectively alleviated the membrane fouling. More importantly, the modified TFC-FO membrane showed good stability during the fouling experiment of 10 h. In all, our work proved that introducing MXenes into the porous layer of support is feasible to alleviate organic fouling of FO membrane.     

The Shackling Effect in Cyclic Azobenzene Liquid Crystal

We demonstrate here a novel method for the design of liquid crystals (LCs) via the cyclization of mesogens by flexible chains. For two azobenzene-4,4′-dicarboxylate derivatives, the cyclic dimer, cyclic bis(tetraethylene glycol azobenzene-4,4′-dicarboxylate) (CBTAD), shows LC properties with smectic A phase, while its linear counterpart, bis(2-(2′-hydroxyethyloxy)ethyl azobenzene-4,4′-dicarboxylate (BHAD), has no LC phase. The difference is ascribed to the shackling effect from the cyclic topology, which leads to the much smaller entropy change during phase transitions and increases the isotropic temperature greatly for cyclics. In addition, the trans-to-cis isomerization of azobenzene groups under UV-light is also limited in CBTAD. With the reversible isomerization of azobenzene groups, CBTAD showed interesting isothermal phase transition behaviors, where the LC phase disappeared upon photoirradiation of 365 nm UV-light, and recovered when the UV-light was off. Combined with the smectic LC nature, a novel UV-light tuned visible light regulator was designed, by simply placing CBTAD in two glass plates. The scattered phase of smectic LC was utilized as the “OFF” state for light passage, while the UV-light induced isotropic phase was utilized as the “ON” state. The shackling effect outlined here should be applicable for the design of cyclic LC oligomers/polymers with special properties.

     

A study on the direct electrochemistry and electrocatalysis of microperoxidase-11 immobilized on a porous network-like gold film: Sensing of hydrogen peroxide

We have prepared porous and network-like nanofilms of gold by galvanic replacement of a layer of copper particles acting as a template. The films were first characterized by scanning electron microscopy and X-ray diffraction, and then modified with cysteamine so to enable the covalent immobilization of the enzyme microperoxidase-11. The immobilized enzyme undergoes direct electron transfer to the underlying electrodes, and the electrode displays high electrocatalytic activity towards the reduction of oxygen and hydrogen peroxide, respectively, owing to the largely enhanced electroactive surface of the porous gold film. The detection limit of H₂O₂ is 0.4 μM (3 S/N).

On the change in physical properties of Ti4−xFe2 + xOy during hydrogenation II: magnetic data for the ternary oxides Ti4−xFe2 + xOy, β-Ti and the corresponding hydrides

The magnetism of Ti-Fe-based hydrides can be separated into surface and bulk contributions. To distinguish between these properties we performed overall magnetization measurements as well as transmission Mössbauer spectroscopy which is not influenced by small amounts of magnetic surface particles.We examined bulk and powdered specimens of ternary oxides and β-Ti. In all cases we observed the segregation of magnetic particles on heat treatment in a dynamic vacuum of 1 Pa, as used in the activation procedure of TiFe. On severe oxidation the iron Curie point was observed and iron segregation was confirmed by Mössbauer spectroscopy. The change in the magnetic properties of the ternary oxides and of β-Ti on hydrogenation is reported and the role of surface oxides and their magnetic segregation is discussed.     

Laser flash photolytic determination of triplet yields via singlet oxygen generation

The efficiency φ_Δ of the generation of singlet oxygen ¹O₂* via oxygen quenching of triplets of a number of substrates of photochemical and photobiological interest was studied by 337.1 nm laser flash photolysis using 1,3-diphenylisobenzofuran as the monitor for ¹O₂*. For all-trans retinal and two polyenals related to retinal as lower and higher homologues the φ_Δ data agree well with the triplet yields reported in the literature, suggesting that mechanisms involving charge transfer or spin exchange (at twisted configurations) leading to non-production of ¹O₂* are unimportant in the oxygen quenching of the triplets of these polyenes. Similar conclusions are also drawn for pyrene-1-aldehyde and tris(bipyridine)ruthenium(II) triplets where observation of quantitative production of ¹O₂* suggests energy transfer to be the dominant pathway. In support of some previous reports, the singlet oxygen yield in benzophenone triplet quenching by oxygen in benzene is found to be much less than unity (0.4).     

Robust Laminated Anode with an Ultrathin Titanium Nitride Layer for High-Efficiency Top-Emitting Organic Light-Emitting Diodes

The effective reflective anode remains a highly desirable component for the fabrication of reliable top-emitting organic light-emitting diodes (TE-OLEDs) which have the potential to be integrated with complementary metal-oxide-semiconductor (CMOS) circuits for microdisplays. This work demonstrates a novel laminated anode consisting of a Cr/Al/Cr multilayer stack. Furthermore, we implement an ultra-thin titanium nitride (TiN) layer as a protective layer on the top of the Cr/Al/Cr composite anode, which creates a considerably reflective surface in the visible range, and meanwhile improves the chemical stability of the electrode against the atmosphere or alkali environment. Based on [2-(2-pyridinyl-N)phenyl-C](acetylacetonate)iridium(III) as green emitter and Mg/Ag as transparent cathode, our TE-OLED using the TiN-coated anode achieves the maximum current efficiency of 71.2 cd/A and the maximum power efficiency of 66.7 lm/W, which are 81% and 90% higher than those of the reference device without TiN, respectively. The good device performance shows that the Cr/Al/Cr/TiN could function as a promising reflective anode for the high-resolution microdisplays on CMOS circuits.