Poly(hydromethylsiloxane)-derived high internal phase emulsion-templated materials (polyHIPEs) containing palladium for catalytic applications

Journal of Materials Science - Cross-linking of poly(hydromethylsiloxane) (PHMS) with 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane (D4Vi) in water-in-oil high internal phase emulsion...     

Visualizing Thermally Activated Memristive Switching in Percolating Networks of Solution-Processed 2D Semiconductors

Memristive systems present a low-power alternative to silicon-based electronics for neuromorphic and in-memory computation. 2D materials have been increasingly explored for memristive applications due to their novel biomimetic functions, ultrathin geometry for ultimate scaling limits, and potential for fabricating large-area, flexible, and printed neuromorphic devices. While the switching mechanism in memristors based on single 2D nanosheets is similar to conventional oxide memristors, the switching mechanism in nanosheet composite films is complicated by the interplay of multiple physical processes and the inaccessibility of the active area in a two-terminal vertical geometry. Here, the authors report thermally activated memristors fabricated from percolating networks of diverse solution-processed 2D semiconductors including MoS₂, ReS₂, WS₂, and InSe. The mechanisms underlying threshold switching and negative differential resistance are elucidated by designing large-area lateral memristors that allow the direct observation of filament and dendrite formation using in situ spatially resolved optical, chemical, and thermal analyses. The high switching ratios (up to 10³) that are achieved at low fields (≈4 kV cm⁻¹) are explained by thermally assisted electrical discharge that preferentially occurs at the sharp edges of 2D nanosheets. Overall, this work establishes percolating networks of solution-processed 2D semiconductors as a platform for neuromorphic architectures.     

Smart polyion complex micelles for targeted intracellular delivery of PEGylated antisense oligonucleotides containing acid-labile linkages

A novel pH-sensitive and targetable antisense ODN delivery system based on multimolecular assembly into polyion complex (PIC) micelles of poly(L-lysine) (PLL) and a lactosylated poly(ethylene glycol)-antisense ODN conjugate (Lac-PEG-ODN) containing an acid-labile linkage (beta-propionate) between the PEG and ODN segments has been developed. The PIC micelles thus prepared had clustered lactose moieties on their peripheries and achieved a significant antisense effect against luciferase gene expression in HuH-7 cells (hepatoma cells), far more efficiently than that produced by the nonmicelle systems (ODN and Lac-PEG-ODN) alone, as well as by the lactose-free PIC micelle. In line with this pronounced antisense effect, the lactosylated PIC micelles showed better uptake than the lactose-free PIC micelles into HuH-7 cells; this suggested the involvement of an asialoglycoprotein (ASGP) receptor-mediated endocytosis process. Furthermore, a significant decrease in the antisense effect (27 % inhibition) was observed for a lactosylated PIC micelle without an acid-labile linkage (thiomaleimide linkage); this suggested the release of the active (free) antisense ODN molecules into the cellular interior in response to the pH decrease in the endosomal compartment is a key process in the antisense effect. Use of branched poly(ethylenimine) (B-PEI) instead of the PLL for PIC micellization led to a substantial decrease in the antisense effect, probably due to the buffer effect of the B-PEI in the endosome compartment, preventing the cleavage of the acid-labile linkage in the conjugate. The approach reported here is expected to be useful for the construction of smart intracellular delivery systems for antisense ODNs with therapeutic value.     

How to control the selectivity in the reduction of NOx with H2 over Pt-Ba/Al2O3 Lean NOx Trap catalysts

The reduction process of NO_x species stored over Pt-Ba/Al₂O₃ Lean NO_x Trap systems is analysed in this paper when H₂ is used as a reductant. The effect of different experimental conditions (temperature, reductant concentration, adsorption lengths, etc.) is addressed and discussed in relation to the selectivity and the efficiency of the reduction process.     

Sol–Gel Synthesis of λ–Na2O·xAl2O3 Films

Na₂O· x Al₂O₃ ( x = 9, 11)films have been obtained by sol–gel method. Crystallization processes during heat treatments have been investigated by X–ray diffraction analysis. A metastable phase with the mullite structure, λ–Na₂O· x Al₂O₃, has been observed starting from 800°C. Films remained stable after a heat treatment at 1000°C for 250 h. Impedance spectroscopy measurements showed that the films of λ-Na₂O· x Al₂O₃ possess a large three–dimensional ionic conductivity at 400°C.     

Dynamics and Selectivity of N<Subscript>2</Subscript>O Formation/Reduction During Regeneration Phase of Pt-Based Catalysts

The formation of N₂O has been studied by means of isothermal lean-rich experiments at 150, 180 and 250 °C over Pt–Ba/Al₂O₃ and Pt/Al₂O₃ catalysts with H₂ and/or C₃H₆ as reductants. This allows to provide further insights on the mechanistic aspects of N₂O formation and on the influence of the storage component. Both gas phase analysis and surface species studies by operando FT-IR spectroscopy were performed. N₂O evolution is observed at both lean-to-rich (primary N₂O) and rich-to-lean (secondary N₂O) transitions. The production of both primary and secondary N₂O decreases by increasing the temperature. The presence of Ba markedly decreases secondary N₂O formation. FT-IR analysis shows the presence of adsorbed ammonia at the end of the rich phase only for Pt/Al₂O₃ catalyst. These results suggest that: (i) primary N₂O is formed when undissociated NO in the gas phase and partially reduced metal sites are present; (ii) secondary N₂O originates from reaction between adsorbed NH₃ and residual NO_x at the beginning of the lean phase. Moreover, N₂O reduction was studied performing temperature programming temperature experiments with H₂, NH₃ and C₃H₆ as reducing agents. The reduction is completely selective to nitrogen and occurs at temperature higher than 250 °C in the case of Pt–Ba/Al₂O₃ catalyst, while lower temperatures are detected for Pt/Al₂O₃ catalyst. The reactivity order of the reductants is the same for the two catalysts, being hydrogen the more efficient and propylene the less one. Having H₂ a high reactivity in the reduction of N₂O, it could react with N₂O when the regeneration front is developing. Moreover, also ammonia present downstream to the H₂ front could react with N₂O, even if the reaction with stored NO_x seems more efficient.     

Isotactic polypropylene–vapor grown carbon nanofibers composites: Electrical properties

Nanocomposites have been obtained by dispersing various amounts of vapor grown carbon nanofibers within isotactic polypropylene. Thermal investigations done by differential scanning calorimetry and dynamic mechanical analysis revealed the effect of the vapor grown carbon nanofibers on the melting, crystallization, α, and β relaxations. Direct current electrical features of these nanocomposites have been investigated and related to the thermal features of these nanocomposites. The effect of the loading with carbon nanofibers on the electrical properties of these nanocomposites is discussed within the percolation theory. The percolation threshold was estimated at about 5.5% wt carbon nanofibers. The temperature dependence of the direct current conductivity is analyzed in detail and it is concluded that the electronic hopping is the dominant transport mechanism. A transition from one‐dimensional hopping towards a three‐dimensional hopping was noticed as the concentration of carbon nanofibers was increased from 10% wt to 20% wt carbon nanofiber. The possibility of a differential negative resistivity is suggested. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45297.     

Gold Nanoparticles and g‐C3N4‐Intercalated Graphene Oxide Membrane for Recyclable Surface Enhanced Raman Scattering

Toxic organic pollutants in the aquatic environment cause severe threats to both humans and the global environment. Thus, the development of robust strategies for detection and removal of these organic pollutants is essential. For this purpose, a multifunctional and recyclable membrane by intercalating gold nanoparticles and graphitic carbon nitride into graphene oxide (GNPs/g‐C₃N₄/GO) is fabricated. The membranes exhibit not only superior surface enhanced Raman scattering (SERS) activity attributed to high preconcentration ability to analytes through π–π and electrostatic interactions, but also excellent catalytic activity due to the enhanced electron–hole separation efficiency. These outstanding properties allow the membrane to be used for highly sensitive detection of rhodamine 6G with a limit of detection of 5.0 × 10^?14m and self‐cleaning by photocatalytic degradation of the adsorbed analytes into inorganic small molecules, thus achieving recyclable SERS application. Furthermore, the excellent SERS activity of the membrane is demonstrated by detection of 4‐chlorophenol at less than nanomolar level and no significant SERS or catalytic activity loss was observed when reusability is tested. These results suggest that the GNPs/g‐C₃N₄/GO membrane provides a new strategy for eliminating traditional, single‐use SERS substrates, and expands practical SERS application to simultaneous detection and removal of environmental pollutants.     

Enhanced growth inhibition of hepatic multicellular tumor spheroids by lactosylated poly(ethylene glycol)-siRNA conjugate formulated in PEGylated polyplexes

PEGylated polyplexes (lac-PEGylated polyplexes) composed of poly(L-lysine) and lactosylated poly(ethylene glycol)-small interfering RNA conjugate, which inhibits the RecQL1 gene product, were revealed to show an appreciable growth inhibition of multicellular HuH-7 spheroids (human hepatocarcinoma cell lines) for up to 21 days (IC(50)=6 nM); this system used as an in vitro three-dimensional (3D) model mimicking the in vivo biology of tumors. The PEGylated polyplexes thus prepared had a size of approximately 110 nm with clustered lactose moieties on their periphery as targeting ligands for the asialoglycoprotein-receptor-expressing HuH-7 cells. In contrast, OligofectAMINE/siRNA (cationic lipoplex) was observed to have almost no growth-inhibitory effect against HuH-7 spheroids, even though the lipoplex showed a stronger growth-inhibitory effect than the lac-PEGylated polyplexes on conventional monolayer-cultured HuH-7 cells. The FITC-tagged conjugate in the lac-PEGylated polyplexes showed smooth penetration into the HuH-7 spheroids compared with that in the lipoplexes, as observed by confocal fluorescence-scanning microscopy. This indicates that the small size of approximately 100 nm and the reduced nonspecific interaction due to the nonionic and hydrophilic lactosylated PEG layer contributes to the smooth penetration of the PEGylated polyplexes into the spheroid interior, eventually facilitating their uptake into the cells composing the spheroids. Cellular apoptosis indicating programmed cell death was also observed in the HuH-7 spheroids treated with the PEGylated polyplexes, revealing that the observed growth inhibition was indeed induced by the RNAi of the RecQL1 siRNA. These data suggest that the smart PEGylated polyplexes can indeed penetrate into the multiple cell layers of 3D tumor masses in vivo, exerting therapeutic effects through the RNAi.