Now showing items 1-20 of 2012

    • Alternating Gyroid Network Structure in an ABC Miktoarm Terpolymer Comprised of Polystyrene and Two Polydienes

      Moschovas, Dimitrios; Manesi, Gkreti-Maria; Karydis-Messinis, Andreas; Zapsas, Georgios; Ntetsikas, Konstantinos; Zafeiropoulos, Nikolaos E.; Piryazev, Alexey A.; Thomas, Edwin L.; Hadjichristidis, Nikos; Ivanov, Dimitri A.; Avgeropoulos, Apostolos (Nanomaterials, MDPI AG, 2020-07-31) [Article]
      The synthesis, molecular and morphological characterization of a 3-miktoarm star terpolymer of polystyrene (PS, M¯n = 61.0 kg/mol), polybutadiene (PB, M¯n = 38.2 kg/mol) and polyisoprene (PI, M¯n = 29.2 kg/mol), corresponding to volume fractions (φ) of 0.46, 0.31 and 0.23 respectively, was studied. The major difference of the present material from previous ABC miktoarm stars (which is a star architecture bearing three different segments, all connected to a single junction point) with the same block components is the high 3,4-microstructure (55%) of the PI chains. The interaction parameter and the degree of polymerization of the two polydienes is sufficiently positive to create a three-phase microdomain structure as evidenced by differential scanning calorimetry and transmission electron microscopy (TEM). These results in combination with small-angle X-ray scattering (SAXS) and birefringence experiments suggest a cubic tricontinuous network structure, based on the I4132 space group never reported previously for such an architecture.
    • Methanol as the Hydrogen Source in the Selective Transfer Hydrogenation of Alkynes Enabled by a Manganese Pincer Complex

      Sklyaruk, Jan; Zubar, Viktoriia; Borghs, Jannik C.; Rueping, Magnus (Organic Letters, American Chemical Society (ACS), 2020-07-28) [Article]
      The first base metal-catalyzed transfer hydrogenation of alkynes with methanol is described. An air and moisture stable manganese pincer complex catalyzes the reduction of a variety of different alkynes to the corresponding (Z)-olefins in high yields. The reaction is stereo- and chemoselective and scalable.
    • Model-Based Design of Graphite-Compatible Electrolytes in Potassium-Ion Batteries

      Zhang, Jiao; Cao, Zhen; Zhou, Lin; Liu, Gang; Park, Geon-Tae; Cavallo, Luigi; Wang, Limin; Alshareef, Husam N.; Sun, Yang-Kook; Ming, Jun (ACS Energy Letters, American Chemical Society (ACS), 2020-07-24) [Article]
      Potassium-ion batteries (KIBs) are attractive alternatives to lithium-ion batteries (LIBs) because of their lower cost and global potassium sustainability. However, designing compatible electrolytes with graphite anode remains challenging. This is because the electrolyte decomposition and/or graphite exfoliation (due to K+–solvent co-insertion) always exist, which is much harder to overcome compared to the case of LIBs because of the higher activities of K+. Herein, we report a general principle to design compatible electrolytes with the graphite anode, where the K+ can be reversibly (de)intercalated. We find that the electrolyte composition is critical to determining the graphite performance, which can be tuned by the kind of solvent, anion, additives, and concentration. We present a new interfacial model to understand the variation in performance (i.e., K+ (de)intercalation or K+–solvent co-insertion or decomposition). Our model is distinctly different from the solid electrolyte interphase interpretation. This work offers new opportunities to design high-performance KIBs and potassium-ion sulfur batteries. Particularly, we present new guideline to design electrolytes for KIBs and other advanced mobile (ion) batteries.
    • Recycling Borate Complex for Synthesis of Polycarbonate Polyols: Towards an Environmentally Friendly and Cost-Effective Process.

      Gnanou, Yves; Patil, Naganath; Bhoopathi, Senthil; Chidara, Vamshi Krishna; Hadjichristidis, Nikos; Feng, Xiaoshuang (ChemSusChem, Wiley, 2020-07-22) [Article]
      In this investigation, we unveil a metal-free process that warrants the synthesis of poly(propylene carbonate) (PPC) diols/polyols by copolymerization of carbon dioxide (CO 2 ) with propylene epoxide (PO) under environmentally-friendly, and cost-effective conditions; this process implies the recycling of triethylborane (TEB) and of ammonium salts that both enter in the composition of the initiators used to copolymerize CO 2 and PO. In complement to the above approach, a polymeric support poly(diallyl dimethylammonium chloride) (PDADMAC), was synthesized and modified to carry ammonium carboxylate salts along its chain; the prepared polymeric initiator was utilized to copolymerize CO 2 with PO under heterogeneous conditions. Not only were the polymerization results similar to the samples obtained under homogeneous conditions, but the polymer substrate could easily be recovered by simple filtration. The integrity of the polycarbonate diols/polyols, the recycling process were followed by 1 H, 11 B NMR, GPC, and MALDI-TOF.
    • Noncovalent Supramolecular Diblock Copolymers: Synthesis and Microphase Separation

      Bhaumik, Saibal; Ntetsikas, Konstantinos; Hadjichristidis, Nikos (Macromolecules, American Chemical Society (ACS), 2020-07-22) [Article]
      Supramolecular block copolymers (PS-DAT-sb-PI-Thy) were synthesized via noncovalent hydrogen bonding between well-defined thymine end-functionalized polyisoprene (PI-Thy) and diaminotriazine (DAT) end-functionalized polystyrene (PS-DAT). Three covalently linked block copolymers were also synthesized for comparison with the noncovalent supramolecular block copolymers. The complementary DAT/Thy interaction resulted in the microphase separation of the supramolecular block copolymer system. Detailed characterization of all functionalized homopolymers and block copolymers was carried out via proton nuclear magnetic resonance (1H NMR) spectroscopy, gel permeation chromatography, matrix-assisted laser desorption/ionizationtime of flight mass spectrometry, and differential scanning calorimetry. The self-assembly process of supramolecular block copolymers was evidenced by transmission electron microscopy. Small-angle X-ray scattering was also performed to study the microphase separation of supramolecular and covalently linked block copolymers. Comparison of microphase separation images of supramolecular block copolymers and the corresponding covalently linked analogues reveals differences in d-spacing and microdomain shape.
    • Controlling N-doping type in carbon to boost single-atom site Cu catalyzed transfer hydrogenation of quinoline

      Zhang, Jian; Zheng, Caiyan; Zhang, Maolin; Qiu, Yajun; Xu, Qi; Cheong, Weng Chon; Chen, Wenxing; Zheng, Lirong; Gu, Lin; Hu, Zhengpeng; Wang, Dingsheng; Li, Yadong (Nano Research, Springer Science and Business Media LLC, 2020-07-20) [Article]
      Single-atom site (SA) catalysts on N-doped carbon (CN) materials exhibit prominent performance for their active sites being M-Nx. Due to the commonly random doping behaviors of N species in these CN, it is a tough issue to finely regulate their doping types and clarify their effect on the catalytic property of such catalysts. Herein, we report that the N-doping type in CN can be dominated as pyrrolic-N and pyridinic-N respectively through compounding with different metal oxides. It is found that the proportion of distinct doped N species in CN depends on the acidity and basicity of compounded metal oxide host. Owing to the coordination by pyrrolic-N, the SA Cu catalyst displays an enhanced activity (two-fold) for transfer hydrogenation of quinoline to access the valuable molecule tetrahydroquinoline with a good selectivity (99%) under mild conditions. The higher electron density of SA Cu species induced by the predominate pyrrolic-N coordination benefits the hydrogen transfer process and reduces the energy barrier of the hydrogenation pathway, which accounts for the improved catalytic effeciency. [Figure not available: see fulltext.].
    • The role of noncovalent interactions in olefin polymerization catalysis: a further look to the fluorinated ligand effect

      Falivene, Laura; Cavallo, Luigi; Talarico, Giovanni (Molecular Catalysis, Elsevier BV, 2020-07-14) [Article]
      The noncovalent interactions and remote ligand effects in catalysis have attracted a large attention in the last years. The rationalization of such interactions is tricky and often their role can be elucidated only with a detailed mechanistic study. Here we report the case of fluorinated ligand systems showing a very peculiar behavior in the catalysis of olefin polymerization. The results reported aim to clarify the origin of such behavior underlying the nature of the control of the fluorinated groups on the key steps of the polymerization. These insights can offer new cues to rationalize similar evidences in other reaction fields.
    • Interface Matters: Enhanced Photoluminescence and Long-Term Stability of Zero-Dimensional Cesium Lead Bromide Nanocrystals via Gas-Phase Aluminum Oxide Encapsulation.

      Bose, Riya; Zheng, Yangzi; Guo, Tianle; Yin, Jun; Hedhili, Mohamed N.; Zhou, Xiaohe; Veyan, Jean-Francois; Gereige, Issam; Al-Saggaf, Ahmed; Gartstein, Yuri N.; Bakr, Osman; Mohammed, Omar F.; Malko, Anton V. (ACS applied materials & interfaces, American Chemical Society (ACS), 2020-07-09) [Article]
      Cesium lead halide perovskite nanocrystals (PNCs), while possessing facile chemical synthesis routes and high photoluminescence (PL) properties, are still challenged by issues of instability and degradation. Although atomic layer deposition (ALD) of metal oxides has been one of the common encapsulation approaches for longer term stability, its application inevitably resulted in severe loss of emission efficiency and at times partial loss of structural integrity of perovskites, creating a bottleneck in its practical viability. We demonstrate a nondestructive modified gas-phase technique with codeposition of both precursors trimethylaluminum and water to dramatically enhance the PL emission in zero-dimensional (0D) Cs4PbBr6 PNCs via alumina encapsulation. X-ray photoelectron spectroscopy analysis of Cs4PbBr6 films reveals the alumina deposition to be accompanied by elemental composition changes, particularly by the reduction of the excessive cesium content. Ab initio density functional theory simulations further unfold that the presence of excess Cs on the surface of PNCs leads to decomposition of structural [PbBr6]4- octahedra in the 0D perovskite lattice, which can be prevented in the presence of added hydroxyl groups. Our study thus unveils the pivotal role of the PNC surface composition and treatment in the process of its interaction with metal oxide precursors to control the PL properties as well as the stability of PNCs, providing an unprecedented way to use the conventional ALD technique for their successful integration into optoelectronic and photonic devices with improved properties.
    • Chemoselective Hydrogenation of Alkynes to (Z)-Alkenes Using an Air-Stable Base Metal Catalyst

      Zubar, Viktoriia; Sklyaruk, Jan; Brzozowska, Aleksandra; Rueping, Magnus (Organic Letters, American Chemical Society (ACS), 2020-07-08) [Article]
      A highly selective hydrogenation of alkynes using an air-stable and readily available manganese catalyst has been achieved. The reaction proceeds under mild reaction conditions and tolerates various functional groups, resulting in (Z)-alkenes and allylic alcohols in high yields. Mechanistic experiments suggest that the reaction proceeds via a bifunctional activation involving metal–ligand cooperativity.
    • Thermochemistry of 5,10,15,20-tetraphenylporphyrin

      Kudin, Lev S.; Dunaev, Anatoly M.; Motalov, Vladimir B.; Cavallo, Luigi; Minenkov, Yury (Journal of Chemical Thermodynamics, Elsevier BV, 2020-07-08) [Article]
      Saturated vapor pressure of 5,10,15,20-tetraphenylporphyrin (TPP) was determined by Knudsen effusion mass spectrometry technique. The temperature dependence of the vapor pressure is described by the equation ln (p/Pa) = −(23.45 ± 0.26)⋅103/T + (37.32 ± 0.47) in the temperature range 490–615 K. The molar heat capacity measurements of TPP were performed in the temperature range 169–568 K. Quantum-chemical calculations of the structure and force field of the TPP molecule were carried out. These data were used to calculate thermodynamic functions of TPP in the solid and gas states. The enthalpy of sublimation of triclinic form of TPP was determined by the second and third laws of thermodynamics. The value ΔsH° (298.15 K) = 220 ± 12 kJ⋅mol−1 was recommended. The reaction based Feller-Peterson-Dixon approach predicts the gas phase TPP formation enthalpy ΔfH° (298.15 K) = 1004 ± 10 kJ⋅mol−1. A combination of the two last values results in the formation enthalpy of the TPP triclinic form ΔfH° (298.15 K) = 784 ± 15 kJ⋅mol−1.
    • Unrealistic energy and materials requirement for direct air capture in deep mitigation pathways

      Chatterjee, Sudipta; Huang, Kuo-Wei (Nature Communications, Springer Science and Business Media LLC, 2020-07-03) [Article]
      The increasing global atmospheric CO2 concentration due to heavy reliance on fossil fuels as the primary energy sources (~410 ppm in 2019)1 has made direct extraction or removal of CO2 from ambient air (direct air carbon capture (DACC)) the most logical alternative over traditional modes of carbon capture from large stationary sources because of many of the perceived advantages and compelling arguments2. With the current level of CO2 emissions (32.6 gigatons (Gt)-CO2/year2017)1, Realmonte and co-workers recently imposed the global capacity at 30 Gt-CO2/year as a case study for DACC, and concluded that “in theory DACCS can be an enabling factor for the Paris Agreement objectives” and recommended the policy makers to “support an acceleration in development and deployment of DACCS”3. While challenges of large-scale CO2 utilization and sequestration were recognized and these approaches were deemed impractical4,5, our analysis further showed that the energy and materials requirements for DACC are unrealistic even when the most promising technologies are employed. Thus, DACC is unfortunately only an energetically and financially costly distraction in effective mitigation of climate changes at a meaningful scale before we achieve the status of a significant surplus of carbon-neutral/low-carbon energy.
    • Evidence for Silica Surface Three- and Five-Membered Metallacycle Intermediates in the Catalytic Cycle of Hydroaminoalkylation of Olefins Using Single-Ti-Metal Catalysts

      Yaacoub, Layal F.; Aljuhani, Maha A.; Jedidi, Abdesslem; Al-Harbi, Manal S.; Almaksoud, Walid; Wackerow, Wiebke; Abou-Hamad, Edy; Pelletier, Jeremie; El Eter, Mohamad; Cavallo, Luigi; Basset, Jean-Marie (Organometallics, American Chemical Society (ACS), 2020-06-30) [Article]
      The single-site silica-supported group IV metal amido complex [Ti(NMe2)4] gives the tris(amido)-supported fragment [(=Si−O−)Ti(−NMe2)3], which transforms into a three-membered metallacycle (called a metallaaziridine) by an αH transfer between two amido ligands. When the three-membered metallacycle reacts with 1-octene, it gives a five-membered metallacycle by insertion of the double bond into the M−C bond of the metallaziridine. These two metallacycles, key intermediates in the catalytic cycle of the hydroaminoalkylation of terminal olefins, were isolated and fully characterized following the surface organometallic chemistry (SOMC) concept and procedures. This paper shows that surface organometallic chemistry can be used to identify and fully characterize three- and five-membered metallacycles of Ti in the hydroaminoalkylation of olefins.
    • All-Polycarbonate Thermoplastic Elastomers Based on Triblock Copolymers Derived from Triethylborane-Mediated Sequential Copolymerization of CO2 with Various Epoxides

      Jia, Mingchen; Zhang, Dongyue; de Kort, Gijs W.; Wilsens, Carolus H. R. M.; Rastogi, Sanjay; Hadjichristidis, Nikos; Gnanou, Yves; Feng, Xiaoshuang (Macromolecules, American Chemical Society (ACS), 2020-06-29) [Article]
      Various oxirane monomers including alkyl ether or allyl-substituted ones such as 1-butene oxide, 1-hexene oxide, 1-octene oxide, butyl glycidyl ether, allyl glycidyl ether, and 2-ethylhexyl glycidyl ether were anionically copolymerized with CO2 into polycarbonates using onium salts as initiator in the presence of triethylborane. All copolymerizations exhibited a “living” character, and the monomer consumption was monitored by in situ Fourier-transform infrared spectroscopy. The various polycarbonate samples obtained were characterized by 1H NMR, GPC, and differential scanning calorimetry. In a second step, all-polycarbonate triblock copolymers demonstrating elastomeric behavior were obtained in one pot by sequential copolymerization of CO2 with two different epoxides, using a difunctional initiator. 1-Octene oxide was first copolymerized with CO2 to form the central soft poly(octene carbonate) block which was flanked by two external rigid poly(cyclohexene carbonate) blocks obtained through subsequent copolymerization of cyclohexene oxide with CO2. Upon varying the ratio of 1-octene oxide to cyclohexene oxide and their respective ratios to the initiator, three all-polycarbonate triblock samples were prepared with molar masses of about 350 kg/mol and 22, 26, and 29 mol % hard block content, respectively. The resulting triblock copolymers were analyzed using 1H NMR, GPC, thermogravimetric analysis, differential scanning calorimetry, and atomic force microscopy. All three samples demonstrated typical elastomeric behavior characterized by a high elongation at break and ultimate tensile strength in the same range as those of other natural and synthetic rubbers, in particular those used in applications such as tissue engineering.
    • Facile Green Synthesis of New Copper-Based Metal–Organic Frameworks: Experimental and Theoretical Study of the CO2 Fixation Reaction

      Kurisingal, Jintu Francis; Rachuri, Yadagiri; Gu, Yunjang; Chitumalla, Ramesh Kumar; Vuppala, Srimai; Jang, Joonkyung; Bisht, Kamal Kumar; Suresh, Eringathodi; Park, Dae-Won (ACS Sustainable Chemistry & Engineering, American Chemical Society (ACS), 2020-06-29) [Article]
      Two new entangled Cu(II)-based metal–organic frameworks (MOFs) have been synthesized, namely [Cu(BDC)(BPDB)0.5]n (PNU-25) and [Cu(NH2-BDC)(BPDB)0.5]n (PNU-25-NH2), using a H2O-MeOH solvent mixture. Both the PNU-25 and PNU-25-NH2 MOF materials were characterized by various analytical techniques and their catalytic potential of CO2 fixation into cyclic carbonates at an atmospheric pressure, a low reaction temperature, and in the neat conditions were demonstrated. The amine-functionalized PNU-25-NH2 exhibited a significant high conversion of epichlorohydrin (ECH) at the 1 bar of CO2 pressure, at 55 °C, and a moderate catalyst amount (1 mol%), with over 99% selectivity toward the corresponding cyclic carbonate of ECH. The superior catalytic activity of PNU-25-NH2 may be attributed to its high amount of acidic-basic sites and large BET surface area in comparison with the PNU-25. The PNU-25-NH2 catalyst could be reused up to four cycles without compromising its structural integrity and the ECH conversion. The reaction mechanism of CO2 and ECH cycloaddition reaction mediated by the PNU-25-NH2 was investigated in detail based on the experimental inferences and periodic calculations of density functional theory (DFT). The energy barrier of the rate-determining step of the PNU-25-NH2/TBAB-catalyzed reaction was significantly lower than those of the rate-determining steps of un-catalyzed and TBAB-catalyzed reactions.
    • Racemic alcohols to optically pure amine precursors enabled by catalyst dynamic kinetic resolution: experiment and computation

      Azofra, Luis Miguel; Tran, Mai Anh; Zubar, Viktoriia; Cavallo, Luigi; Rueping, Magnus; El-Sepelgy, Osama (Chemical Communications, Royal Society of Chemistry (RSC), 2020-06-29) [Article]
      <p>An unprecedented base metal catalysed asymmetric synthesis of α-chiral amine precursors from racemic alcohols is reported. This redox-neutral reaction utilises a bench-stable manganese complex and Ellman’s sulfinamide as versatile ammonia...</p>
    • Significant Impact of Exposed Facets on the BiVO4 Material Performance for Photocatalytic Water Splitting Reactions

      Lardhi, Sheikha F.; Cavallo, Luigi; Harb, Moussab (The Journal of Physical Chemistry Letters, American Chemical Society (ACS), 2020-06-26) [Article]
      The impact of the four predominant (010), (110), (001), and (121) exposed facets obtained experimentally for monoclinic BiVO4 on its photocatalytic performance for water splitting reactions is investigated on the basis of the hybrid density functional theory including the spin–orbit coupling. Although their electronic structure is similar, their transport and redox properties reveal anisotropic characters based on the crystal orientation and termination. The particular role of each facet in proton reduction was correlated with the surface Bi coordination number and their geometrical distribution. Our work predicts the (001) facet as the only good candidate for both HER and OER, while the (010) facet is a fitting candidate for OER only. The (110) and (121) surfaces are acceptable candidates only for OER but less potential than (001) and (010). These outcomes will efficiently conduct experimentalists for an attentive design of facet-oriented BiVO4 samples toward improving water oxidation and proton reduction.
    • Using sodium acetate for the synthesis of [Au(NHC)X] complexes

      Scattolin, Thomas; Tzouras, Nikolaos V.; Falivene, Laura; Cavallo, Luigi; Nolan, Steven P. (Dalton Transactions, Royal Society of Chemistry (RSC), 2020-06-26) [Article]
      <p>Sodium acetate enables the synthesis of [Au(NHC)Cl] complexes, as well as their Au-alkynyl and -thiolato derivatives in high yields, under air and in technical grade, green solvents. The mild synthetic methods are also investigated computationally.</p>
    • Structurally Tunable Two-Dimensional Layered Perovskites: From Confinement and Enhanced Charge Transport to Prolonged Hot Carrier Cooling Dynamics.

      El-Ballouli, Ala’a O.; Bakr, Osman; Mohammed, Omar F. (The journal of physical chemistry letters, American Chemical Society (ACS), 2020-06-24) [Article]
      Two-dimensional (2D) layered metal halide perovskites are potential alternatives to three-dimensional perovskites in optoelectronic applications owing to their improved photostabilities and chemical stabilities. Recent investigations of 2D metal halide perovskites have demonstrated interesting optical and electronic properties of various structures that are controlled by their elemental composition and organic spacers. However, photovoltaic devices that utilize 2D perovskites suffer from poor device efficiency due to inefficient charge carrier separation and extraction. In this Perspective, we shed light on confinement control and structural variation strategies that provide better parameters for the efficient collection of charges. The influence of these strategies on the exciton binding energies, charge-carrier mobilities, hot-carrier dynamics, and electron-phonon coupling in 2D perovskites is thoroughly discussed; these parameters highlight unique opportunities for further system optimization. Beyond the tunability of these fundamental parameters, we conclude this Perspective with the most notable strategies for attaining 2D perovskites with reduced bandgaps to better suit photovoltaic applications.
    • Theoretical study of the physicochemical characteristics for Boron-Germanium BGen (n = 1–20) clusters

      Benaida, Meriem; Aiadi, Kamal Eddine; Mahtout, Sofiane; Harb, Moussab (Computational and Theoretical Chemistry, Elsevier BV, 2020-06-16) [Article]
      We present a theoretical study on the equilibrium geometries, energetic, electronic, and magnetic characteristics of BGen (n = 1–20) clusters using the density functional theory (DFT) calculations. The most stable structures display a B atom located at the surface of BGen clusters, except for BGe9, 12, 16, 18, 19, 20. Larger clusters reveal higher binding energy, suggesting their greater stability compared to the corresponding Gen+1 clusters. The calculated fragmentation energy, second-order energy difference, and HOMO-LUMO energy gap reveal that the BGe9, 12 clusters are more stable than other cluster sizes. The calculated magnetic properties of the lowest-energy BGen clusters display a total spin magnetic moment equal to 1 μB, except for the BGe cluster, which takes the value 3 μB. These findings can be useful to the experimentalists in designing new Nano-catalytic systems.
    • Monolayer Perovskite Bridges Enable Strong Quantum Dot Coupling for Efficient Solar Cells

      Sun, Bin; Johnston, Andrew; Xu, Chao; Wei, Mingyang; Huang, Ziru; Jiang, Zhang; Zhou, Hua; Gao, Yajun; Dong, Yitong; Ouellette, Olivier; Zheng, Xiaopeng; Liu, Jiakai; Choi, Min Jae; Gao, Yuan; Baek, Se Woong; Laquai, Frédéric; Bakr, Osman; Ban, Dayan; Voznyy, Oleksandr; García de Arquer, F. Pelayo; Sargent, Edward H. (Joule, Elsevier BV, 2020-06-09) [Article]
      Solution-processed colloidal quantum dots (CQDs) are promising optoelectronic materials; however, CQD solids have, to date, exhibited either excellent transport properties but fusion among CQDs or limited transport when QDs are strongly passivated. Here, we report the growth of monolayer perovskite bridges among quantum dots and show that this enables the union of surface passivation with improved charge transport. We grow the perovskite layer after forming the CQD solid rather than introducing perovskite precursors into the quantum dot solution: the monolayer of perovskite increases interdot coupling and decreases the distance over which carriers must tunnel. As a result, we double the diffusion length relative to reference CQD solids and report solar cells that achieve a stabilized power conversion efficiency (PCE) of 13.8%, a record among Pb chalcogenide CQD solar cells.