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Location determination of metal nanoparticles relative to a metal-organic framework
No full textMetal nanoparticles (NPs) stabilized by metal-organic frameworks (MOFs) have been intensively studied in recent decades, while investigations on the location of guest metal NPs relative to host MOF particles remain challenging and very rare. In this work, we have developed several characterization techniques, including high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) tomography, hyperpolarized Xe-129 NMR spectroscopy and positron annihilation spectroscopy (PAS), which are able to determine the specific location of metal NPs relative to the MOF particle. The fine PdCu NPs confined inside MIL-101 exhibit excellent catalytic activity, absolute selectivity and satisfied recyclability in the aerobic oxidation of benzyl alcohol in pure water. As far as we know, the determination for the location of metal NPs relative to MOF particles and pore structure information of metal NPs/MOF composites by Xe-129 NMR and PAS techniques has not yet been reported
Development of a bismuth-based metal-organic framework for photocatalytic hydrogen production
No full textA novel 3D bismuth-organic framework (called Bi-TBAPy) single crystal was synthesized by employing 1,3,6,8-tetrakis(p-benzoic acid)pyrene (H(4)TBAPy) as an organic linker. The study demonstrates that the Bi-TBAPy not only possesses good chemical stability and suitable band edge positions for promising photocatalytic H-2 evolution, but it also exhibits a typical ligand-to-metal charge transfer for favorable charge separation. The photocatalytic H-2 evolution rates on the as-obtained Bi-TBAPy with different cocatalysts modified were examined with triethanolamine as the sacrificial reagent. Based on this, the hydrogen evolution rate of 140 mu mol h(-1) g(-1) was obtained on the optimized sample with a loading of 2 w% Pt as a cocatalyst. To the best of our knowledge, this is the first bismuth-based metal-organic framework (MOF) that functions as an effective photocatalyst for photocatalytic water reduction. Our study not only adds a new member to the family of photocatalyst materials, but also reveals the importance of cocatalyst modification in improving photocatalytic activity of MOFs. (C) 2019, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved
Enhanced reactivity of fluorine with para-hydrogen in cold interstellar clouds by resonance-induced quantum tunnelling
No full textChemical reactions are important in the evolution of low-temperature interstellar clouds, where the quantum tunnelling effect becomes significant. The F + para-H-2 -> HF + H reaction, which has a significant barrier of 1.8 kcal mol(-1), is an important source of HF in interstellar clouds; however, the dynamics of this quantum-tunnelling-induced reactivity at low temperature is unknown. Here, we show that this quantum tunnelling is caused by a post-barrier resonance state. Quantum-state-resolved crossed-beam scattering measurements reveal that this resonance state has a collision energy of similar to 5 meV and a lifetime of similar to 80 fs, which are in excellent agreement with a recent anion photoelectron spectroscopic study. Accurate quantum reactive scattering calculations on the new iCSZ-LWAL potential energy surfaces provides a detailed explanation of the experimental results. The reaction rate for this system was also theoretically determined accurately at temperatures as low as 1K
A Photoexcitation-Induced Twisted Intramolecular Charge Shuttle
No full textCharge transfer and separation are important processes governing numerous chemical reactions. Fundamental understanding of these processes and the underlying mechanisms is critical for photochemistry. Herein, we report the discovery of a new charge-transfer and separation process, namely the twisted intramolecular charge shuttle (TICS). In TICS systems, the donor and acceptor moieties dynamically switch roles in the excited state because of an approximately 90 degrees intramolecular rotation. TICS systems thus exhibit charge shuttling. TICSs exist in several chemical families of fluorophores (such as coumarin, BODIPY, and oxygen/carbon/silicon-rhodamine), and could be utilized to construct functional fluorescent probes (i.e., viscosity- or biomolecule-sensing probes). The discovery of the TICS process expands the current perspectives of charge-transfer processes and will inspire future applications
Application of an in situ CO2-bicarbonate system under nitrogen depletion to improve photosynthetic biomass and starch production and regulate amylose accumulation in a marine green microalga Tetraselmis subcordiformis
No full textBackground: Microalgal starch is regarded as a promising alternative to crop-based starch for biorefinery such as the production of biofuels and bio-based chemicals. The single or separate use of inorganic carbon source, e.g., CO2 and NaHCO3, caused aberrant pH, which restricts the biomass and starch production. The present study applied an in situ CO2-NaHCO3 system to regulate photosynthetic biomass and starch production along with starch quality in a marine green microalga Tetraselmis subcordiformis under nitrogen-depletion (-N) and nitrogen-limitation (+/- N) conditions.
Results: The CO2 (2%)-NaHCO3 (1 g L-1) system stabilized the pH at 7.7 in the -N cultivation, under which the optimal biomass and starch accumulation were achieved. The biomass and starch productivity under -N were improved by 2.1-fold and 1.7-fold, respectively, with 1 g L-1 NaHCO3 addition compared with the one without NaHCO3 addition. NaHCO3 addition alleviated the high-dCO(2) inhibition caused by the single CO2 aeration, and provided sufficient effective carbon source HCO3- for the maintenance of adequate photosynthetic efficiency and increase in photoprotection to facilitate the biomass and starch production. The amylose content was also increased by 44% under this CO2-bicarbonate system compared to the single use of CO2. The highest starch productivity of 0.73g L(-1)day(-1) under -N cultivation and highest starch concentration of 4.14 g L-1 under +/- N cultivation were both achieved with the addition of 1 g L-1 NaHCO3. These levels were comparable to or exceeded the current achievements reported in studies. The addition of 5 g L-1 NaHCO3 under +/- N cultivation led to a production of high-amylose starch (59.3% of total starch), which could be used as a source of functional food.
Conclusions: The in situ CO2-NaHCO3 system significantly improved the biomass and starch production in T. subcordiformis. It could also regulate the starch quality with varied relative amylose content under different cultivation modes for diverse downstream applications that could promote the economic feasibility of microalgal starch-based biofuel production. Adoption of this system in T. subcordiformis would facilitate the CO2 mitigation couple with its starch-based biorefinery
Comparing the disrupting effects of short-, medium- and long-chain chlorinated Paraffins on cell viability and metabolism
No full textWith the phasing out of short-chain chlorinated paraffins (SCCPs), the production and emissions of medium- and long-chain chlorinated paraffins (MCCPs and LCCPs) are expected to increase. In this study, cell viability assay and pseudotargeted metabolomics approach were adopted to define and compare the toxic effects induced by SCCPs, MCCPs and LCCPs. The dose response curves indicated that three CP mixtures with comparable chlorine contents produced similar inhibitory effects on cell viability. At exposure concentration of 100 mu g/L, three CP mixtures all induced significant increases in levels of reactive oxygen species (ROS) and malondialdehyde (MDA) and a significant reduction in level of adenosine triphosphate production (ATP), and produced similar impact intensities on overall metabolism. A stronger perturbation in phospholipid and fatty add metabolism was observed in all CP exposure groups. In comparison with SCCPs and MCCPs, LCCPs produced a stronger suppressive effect on amino acid transport across cell membrane and induced an opposite effect on purine metabolism. Furthermore, the toxicity mechanism and possible health risks of the three types of CPs were discussed. MCCPs shared the most similar cytotoxicity and metabolic perturbation with SCCPs, suggesting that there should be concern about using MCCPs as alternatives to SCCPs. (C) 2019 Published by Elsevier B.V
Mechanistic Understanding of Size-Dependent Oxygen Reduction Activity and Selectivity over Pt/CNT Nanocatalysts
No full textIdentifying the underlying nature of the structure sensitivity of oxygen reduction reaction (ORR) over carbon supported Pt catalysts is an important but challenging issue in electrochemical system. In this work, we combine experiments, density functional theory calculations with model calculations to clarify the size-dependent ORR activity and selectivity over differently sized Pt/CNT catalysts. HAADF-STEM, HRTEM and XPS measurements show that the Pt nanoparticles supported on CNT possess a well-defined truncated octahedron shape in most cases and similar electronic properties. The observed size-insensitive TOFactive site based on the number of Pt(111) atoms suggests the Pt(111) surface as the dominant active site. Moreover, the Pt(111) surface is also suggested as the dominant active sites for the formation of H2O2, and the catalyst with the higher Pt binding energy facilitates the oxygen reduction to H2O. The insights revealed here could shed new light on the design and optimization of Pt-based ORR catalysts