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排序方式： 共有189条查询结果，搜索用时 15 毫秒
41.
Dr. Maja Budanovic Dr. Dejan Urbančok Jasmine Y. H. Er Dr. Malcolm E. Tessensohn Prof. Dr. Richard D. Webster 《ChemElectroChem》2021,8(11):2075-2086
Pyridinium (the protonated form of pyridine) and related compounds have been proposed to be promising homogenous electrocatalysts in the electrochemical reduction of CO2 to methanol due to the low overpotential required to achieve faradaic yields of about 20 %, although the percentage yields vary dramatically between different research groups. In this study, experimental conditions were varied during the electrolysis of CO2 at a platinum electrode in the presence of pyridinium to determine the reasons for the discrepancies in the yields of methanol reported between different research groups. Two other vitamin-based and environmentally friendly nitrogen-containing heterocyclic compounds (nicotinamide and nicotinic acid) which have structural similarities to the promising but toxic pyridine homogeneous electrocatalyst, were also investigated as alternative electrocatalysts for the reduction of CO2 in aqueous acidic media. Cyclic voltammetry studies suggest that nicotinamide and nicotinic acid (forms of vitamin B3) follow a similar reaction mechanism as pyridine in the reduction of CO2. Relatively low faradaic yields of methanol were obtained during controlled potential electrolysis experiments for all the electrocatalysts (0.4–1.9 %) which can be attributed to the low solubility of CO2 along with the competing hydrogen evolution reaction. It was found that adventitious sources of methanol were responsible for greatly inflating the apparent yields of methanol unless scrupulous care was taken in controlling the experimental conditions. The problem with background methanol is particularly difficult to control due to the electrochemical reactions typically generating products in the parts per million range, considerably lower than normal synthetic reactions. 相似文献
42.
A fast automated system for rapid electrophoretic separations in short conventional capillaries employing contactless conductivity detection is presented. The instrument is based on pneumatic pressurization and does not require a conventional pump. The required pressures and flow rates for the different steps of the injection and flushing processes are produced with the help of two flow restrictors. The device is implemented on a microfluidic breadboard with dimensions of ca. 13 × 20 cm and employs miniature valves. Nine inorganic cations, namely NH4+, K+, Na+, Ca2+, Mg2+, Mn2+, Sr2+, Li+, and Ba2+, could be separated in a capillary of 10 μm inner diameter and 6 cm effective length within 25 s. Following a reduction of the effective length to 4 cm, still five inorganic cations could be separated in a time span of 12 s. The repeatability of peak areas was better than 3.1 % and limits of detection between 3.5 and 5.5 μM were achieved. 相似文献
43.
Fangzhou Liu Christopher Chang Sing Chan Chao Ma Ho Won Tam Tik Lun Leung Jingyang Lin Aleksandra B. Djuri&#x;i&#x; Kam Sing Wong Jasminka Popovi&#x; Alan Man Ching Ng Wai Kin Chan Wei Chen Zhubing He Ayotunde Emmanuel Adesina Yishu Foo Juan Antonio Zapien 《Advanced Optical Materials》2019,7(19)
Significant enhancement of the light emission in Ruddlesden–Popper organic–inorganic halide perovskites is obtained by antisolvent induced spontaneous formation of nanocrystals in an amorphous matrix. This morphology change results in the passivation of defects and significant enhancement of light emission and 16 times higher photoluminescence quantum yield (PLQY), and it is applicable to different spacer cations. The use of trioctylphosphine oxide results in further defect passivation leading to an increase in PLQY (≈2.3 times), the suppression of lower energy emission in low temperature photoluminescence spectra, the dominance of radiative recombination, and the disappearance of thermal quenching of the luminescence. The proposed method offers a reproducible, controllable, and antisolvent‐insensitive alternative to energy landscape engineering to utilize energy funneling phenomenon to achieve bright emission. Instead of facilitating fast energy transfer from lower to higher number of perovskite sheets to prevent nonradiative losses, it is demonstrated that defects can be effectively passivated via morphology control and the use of a passivating agent, so that bright emission can be obtained from single phase nanocrystals embedded in amorphous matrix, resulting in light emitting diodes with a maximum external quantum efficiency of 2.25%. 相似文献
44.
Jasmine Viger‐Gravel Claudia E. Avalos Dominik J. Kubicki David Gajan Moreno Lelli Olivier Ouari Anne Lesage Lyndon Emsley 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(22):7327-7331
The introduction of high‐frequency, high‐power microwave sources, tailored biradicals, and low‐temperature magic angle spinning (MAS) probes has led to a rapid development of hyperpolarization strategies for solids and frozen solutions, leading to large gains in NMR sensitivity. Here, we introduce a protocol for efficient hyperpolarization of 19F nuclei in MAS DNP enhanced NMR spectroscopy. We identified trifluoroethanol‐d3 as a versatile glassy matrix and show that 12 mm AMUPol (with microcrystalline KBr) provides direct 19F DNP enhancements of over 100 at 9.4 T. We applied this protocol to obtain DNP‐enhanced 19F and 19F–13C cross‐polarization (CP) spectra for an active pharmaceutical ingredient and a fluorinated mesostructured hybrid material, using incipient wetness impregnation, with enhancements of approximately 25 and 10 in the bulk solid, respectively. This strategy is a general and straightforward method for obtaining enhanced 19F MAS spectra from fluorinated materials. 相似文献
45.
Ashalatha Vazhayil Dr. Linsha Vazhayal Shyamli Ashok C Dr. Jasmine Thomas Dr. Nygil Thomas 《ChemCatChem》2024,16(6):e202301250
For the advancement of electrochemical energy conversion and storage technologies, bifunctional electrocatalysts are crucial for efficiently driving both the oxygen evolution (OER) and reduction reactions (ORR). Cobalt-based spinel oxides are a class of promising bifunctional electrocatalysts. However their low electrical conductivity and stability may hinder further improvement. A novel composite material composed of NiCo2O4 nanoparticles integrated with emerging two dimensional MXene nanosheets (NiCo2O4/MXene) was developed. The successful integration of NiCo2O4 with MXene brings about a number of attractive structural features. This includes synergistic effects between NiCo2O4 and MXene, highly accessible surface areas, complete exposure of numerous active sites, and excellent electronic conductivity, all of which collectively contribute to the desirability of composite material for OER and ORR. The synthesized NiCo2O4/MXene composite showed extraordinary OER electrocatalytic activity with a lower overpotential of 360 mV at a current density of 10 mA/cm2, and a small Tafel slope of 64 mV/dec compared to NiCo2O4, MXene and NiCo2O4+MXene (physically mixed). Additionally, NiCo2O4/MXene displays an ORR limiting current density of −4 mA/cm2 and exhibited highest onset potential and half wave potential of 0.92 V and 0.72 V vs. RHE, respectively, for the ORR in alkaline media compared to NiCo2O4, MXene and NiCo2O4+MXene (physically mixed). 相似文献
46.
Dr. Ilia B. Moroz Dr. Pierre Florian Dr. Jasmine Viger-Gravel Christopher P. Gordon Dr. Anne Lesage Prof. Dr. Christophe Copéret 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(37):16301-16306
A silica-supported monomeric alkylaluminum co-catalyst was prepared via surface organometallic chemistry by contacting tris(neopentyl)aluminum and partially dehydroxylated silica. This system, fully characterized by solid-state 27Al NMR spectroscopy augmented by computational studies, efficiently activates (nBu3P)2NiCl2 towards dimerization of ethene, demonstrating comparable activity to previously reported dimeric diethylaluminum chloride supported on silica. Three types of aluminum surface species have been identified: monografted tetracoordinated Al species as well as two types of bisgrafted Al species—tetra- and pentacoordinated. Of them, only the monografted Al species is proposed to be able to activate the (nBu3P)2NiCl2 complex and generate the active cationic species. 相似文献
47.
Xun Han Benjamin D. Fairbanks Jasmine Sinha Christopher N. Bowman 《Macromolecular rapid communications》2020,41(16)
Through thiol‐ene photopolymerization of presynthesized oligomers, advanced clickable nucleic acids (CNA‐2G) are synthesized with sequence‐controlled repeating units. As examples, poly(thymine‐adenine) (polyTA) CNA‐2G and poly(thymine‐thymine‐cytosine) CNA‐2G are synthesized by polymerizing thiol‐ene heterofunctional dimers with pendant thymine‐adenine nucleobases and trimer with pendant thymine‐thymine‐cytosine nucleobases. Based on size exclusion chromatography (SEC) analysis, polyTA and polyTTC have number average molecular weights of 2000 and 1800, respectively, which contain 7–8 pendant nucleobases. Based on the different behavior of the CNA‐2G monomers and CNA‐2G oligomers with two or more pendant nucleobases in photopolymerization, an unusual thiol‐ene chain‐growth propagation mechanism is observed for the former and a common thiol‐ene step‐growth propagation mechanism for the latter. The uncommon thiol‐ene chain‐growth propagation is hypothesized to rely on a six‐membered ring mediated intramolecular hydrogen atom transfer process. 相似文献
48.
Sie Tiong Ha Teck Leong Lee Siew Ling Lee Guan Yeow Yeap Yip Foo Win Siew Teng Ong 《中国化学快报》2012,23(2):177-180
A homologous series of azomethine esters,4-n-alkanoyloxybenzylidene-4’-bromoanilines possessing even number of carbon atoms at the terminal alkanoyloxy chain(Cn-1H2n-1COO- n = 8,10,12,14,16,18) was synthesized and characterized.Whilst n-octanoyloxy to n-dodecanoyloxy derivatives exhibited enantiotropic smectic A and smectic B phases,n-tetradecanoyloxy to n-octadecanoyloxy derivatives possessed enantiotropic smectic A and monotropic smectic B properties.n-Decanoyloxy derivatives demonstrated the optimum exhibition for both smectic A and smectic B phases.It was found that the length of terminal alkanoyloxy chain has an influence on mesomorphic properties. 相似文献
49.
50.
Yu-Loong Loow Eng Kein New Ge Hoa Yang Lin Yang Ang Luther Yang Wei Foo Ta Yeong Wu 《Cellulose (London, England)》2017,24(9):3591-3618
High reliance on crude oil for energy consumption results in the urgent need to explore and develop alternative renewable sources. One of the most promising routes is the transformation of biomass into biofuels and chemicals. The introduction of deep eutectic solvents in 2004 received a considerable amount of attention across different research fields, particularly in biomass processing. The effectiveness of deep eutectic solvents in breaking down the recalcitrant structure in biomass highlights its impact on the transformation of biomass into various value-added products. In addition, deep eutectic solvents are widely regarded as promising “green” solvents due to their low cost, low toxicity, and biodegradable properties. In this paper, some background information on lignocellulosic biomass and deep eutectic solvents is given. Furthermore, the roles of deep eutectic solvents in biomass processing are discussed, focusing on the impacts of deep eutectic solvents on the selectivity of chemical processes and dissolution of biomass. This review also highlights the advantages and limitations of deep eutectic solvents associated with their usage in biomass valorization. 相似文献