Recent Submissions

  • Investigating the Catalytic Active Sites of Mo/HZSM-5 and Their Deactivation During Methane Dehydroaromatization

    Wang, Ning; Dong, Xinglong; Liu, Lingmei; Cai, Dali; Wang, Jianjian; Hou, Yilin; Emwas, Abdul-Hamid M.; Gascon, Jorge; Han, Yu (SSRN Electronic Journal, Elsevier BV, 2020-10-09) [Article]
    Molybdenum supported on zeolite HZSM-5 (Mo/HZSM-5) is the most studied catalyst for methane dehydroaromatization (MDA). However, the nature of its catalytic active sites and their deactivation mechanisms remain unclear and controversial. Here we report new insights into this system, on the basis of advanced characterization and a rational design of experiments. We find that it is the size of the HZSM-5 crystal that determines the form and location of the catalytic active molybdenum carbide (MoCx) species, and thus the performance of Mo/HZSM-5; we also find that MoCx sites are preferentially deactivated over acid sites, when supported on nano-sized HZSM-5. These findings lead us to develop an “encapsulation” strategy, which effectively reconciles the deactivation rates at the MoCx sites and the acid sites, enabling a full utilization of both sites, and consequently leading to a 10-fold increase in catalyst lifetime and aromatics yield. Our results indicate that MoCx particles formed outside the micropores of HZSM-5, which are traditionally considered detrimental to the reaction, can serve as active sites for MDA, provided that they are properly protected from direct exposure to coke deposition. These findings allow us to design control experiments to answer an open question whether the acid sites, in addition to promoting the dispersion of Mo species, play a catalytic role in the MDA reaction, and the results show that acid sites are indeed essential for the conversion of methane.
  • Diels-Alder Polymer Networks with Temperature-Reversible Cross-Linking-Induced Emission Yu Jiang*, and Nikos Hadjichristidis*

    Hadjichristidis, Nikos; Jiang, Yu (Angewandte Chemie, Wiley, 2020-10-08) [Article]
    A novel synthetic strategy toward reversible cross-linked polymeric materials with tunable fluorescence properties is presented. Dimaleimide-substituted tetraphenylethene (TPE-2MI), which is nonemissive due to the photo-induced electron transfer (PET) between maleimide (MI) and tetraphenylethene (TPE) groups, was used to cross-link random copolymers of methyl (MM), decyl (DM) or lauryl (LM) with furfuryl methacrylate (FM). The mixture of copolymer and TPE-2MI in DMF showed reversible fluorescence with “on/off” behavior depending on the Diels-Alder (DA)/retro-DA process, which is easily adjusted by temperature. At high temperatures, the retro-DA reaction of polymer networks is dominant, and the fluorescence is quenched by the PET mechanism. In contrast, at low temperatures, the emission recovers as the DA reaction takes over. Based on these results, a transparent PMFM/TPE-2MI film was prepared, and the emission behavior was investigated. It was found that the polymer film shows an accurate response to the external temperature and exhibited tunable fluorescent “turn on/off” behavior. These excitingresults suggest the possible application of this type of reversible cross-linked materials in many areas, including information security and transmission. An example of invisible/visible writing is given.
  • In silico design of novel NRR electrocatalysts: cobalt-molybdenum alloys.

    Castellano-Varona, Blanca; Harb, Moussab; Araña, Javier; Cavallo, Luigi; Azofra Mesa, Luis (Chemical communications (Cambridge, England), Royal Society of Chemistry (RSC), 2020-10-07) [Article]
    Metals are amongst the most efficient developed electrocatalysts for nitrogen reduction reaction (NRR) with iron and ruthenium presenting the best catalytic indicators. However, the potential use of metal alloys as NRR electrocatalysts is still underdeveloped. While Co has demonstrated poor electrocatalytic activity for NRR, alloying Co with Mo exhibits an improvement in both N2 physisorption and the stabilisation of the elusive N2H as the first reduced intermediate species. This stabilisation occurs on surface Mo or Co atoms with a high connectivity with Mo. Herein, we report a complete DFT study analysing the potential application of CoMo alloys as catalysts for N2-into-NH3 conversion given the low theoretical overpotentials that they present.
  • Titanium methyl tamed on silica: synthesis of a well-defined pre-catalyst for hydrogenolysis of n-alkane

    Saidi, Aya; Almaksoud, Walid; Samantaray, Manoja K.; Abou-Hamad, Edy; Basset, Jean-Marie (Chemical Communications, Royal Society of Chemistry (RSC), 2020-10-05) [Article]
    Alkylation of Ti(CH3)2Cl2 1 by MeLi gives the homoleptic Ti(CH3)42 for the first time in the absence of any coordinating solvent. The reaction of 2 with silica pretreated at 700 8C (SiO2–700) gives two inequivalent silica-supported Ti-methyl species 3. Complex 3 was characterized by IR, microanalysis (ICP-OES, CHNS, and gas quantification), and advanced solid-state NMR spectroscopy (1H, 13C, DQ, TQ, and HETCOR). The catalytic activity of the precatalyst 3 is investigated in low-temperature hydrogenolysis of propane and n-butane with TONs of 419 and 578, respectively
  • Polyurethanes from Direct Organocatalytic Copolymerization of p-Tosyl Isocyanate with Epoxides.

    Gnanou, Yves; Jia, Mingchen; Hadjichristidis, Nikos; Feng, Xiaoshuang (Angewandte Chemie (International ed. in English), Wiley, 2020-09-29) [Article]
    The direct copolymerization of p -tosyl isocyanate (TSI) with epoxides, initiated by onium salts in the presence of trialkylborane, to produce polyurethanes is reported. The rate of copolymerization and the (regio)selectivity were investigated in relation to the trialkylborane and initiator used. Under optimized conditions such copolymerizations have been successfully performed for a wide range of epoxides, including ethylene oxide, propylene oxide, 1-octene oxide, cyclohexene oxide, and allyl glycidyl ether. These copolymerizations afford a new category of polyurethanes, clear of side products such as cyclic oxazolidinone, isocyanurate, and poly(isocyanate) linkages. The experimental conditions used in this work are compatible with those for the organocatalytic (co)polymerization of other oxygenated monomers and CO 2 , holding the potential for their terpolymerization with p -tosyl isocyanate and the development of new materials with unprecedented properties.
  • Methane Dry Reforming on Supported Cobalt Nanoparticles Promoted by Boron

    Al Abdulghani, Abdullah; Park, Jung-Hyun; Kozlov, Sergey; Kang, Dong-Chang; Al-Sabban, Bedour E.; Pedireddy, Srikanth; Aguilar-Tapia, Antonio; Ould-Chikh, Samy; Hazemann, Jean-Louis; Basset, Jean-Marie; Cavallo, Luigi; Takanabe, Kazuhiro (Journal of Catalysis, Elsevier BV, 2020-09-26) [Article]
    Stable operations for catalytic dry reforming of methane (DRM) is essential for industrial applications. High stability for the syngas production can be achieved via a kinetic balance between formation of carbon species and their removal by oxygen species on the metal surface, which clears the surface for further reaction steps. This study reports highly stable performances by a boron-doped cobalt catalyst as a non-noble-metal, coking-free catalyst. Although the precise location of doped boron could not be identified experimentally because of its low concentration, density functional theory (DFT) calculations suggested that interstitial boron (B) is most likely present in the subsurface region of cobalt (Co) surfaces. B-doping was shown both experimentally and computationally to increase the reactivity of Co catalysts toward both methane (CH4) and carbon dioxide (CO2). Moreover, B-doping was found to balance the amounts of surface C and O and maintain the reduced state of Co surfaces while in a steadystate. Nevertheless, a negative kinetic order with respect to CO2 partial pressure indicates that steady-state surface coverage of oxygen species originating from CO2 dissociation was prevalent on B-doped Co, consistent with the coking-free nature of the catalyst. This study introduces a promising Co-B catalyst design for controlling metal surface reactivity toward DRM and relevant catalytic reactions.
  • All-Perovskite Tandem Solar Cells: A Roadmap to Uniting High Efficiency with High Stability

    Zheng, Xiaopeng; Alsalloum, Abdullah Yousef; Hou, Yi; Sargent, E.; Bakr, Osman (Accounts of Materials Research, American Chemical Society (ACS), 2020-09-25) [Article]
    Organic−inorganic halide perovskite photovoltaics (PVs)only a decade-old fieldhave reached impressive power conversion efficiencies (PCEs) and passed industrial stability requirements (IEC 61215:2016 Damp Heat and Humidity Freeze tests), solidifying their status among candidates for next generation PVs. Among the various perovskite PV technologies, all-perovskite tandem solar cells (PTSCs) are frontrunners for commercialization. PTSCs unite a narrow-bandgap (NBG; Eg ≈1.2 eV) perovskite back cell with a wide-bandgap (WBG; Eg ≈1.7−1.9 eV) perovskite front cell. Despite their nascency, PTSCs have achieved certified PCEs of 24.8% and 24.2% for small-area (0.049 cm2) and large-area devices (1.041 cm2), respectively. With further advances in materials development, PTSCs are capable of moving beyond the PCE limits of single-junction cells due to reduced thermalization losses and improved utilization of the solar spectrum. By contrast, the PCE of single-junction perovskite devices is already approaching its saturation level, which is already very close to the device’s Shockley−Queisser limit for a bandgap of around 1.55 eV. The tandem architecture, thus, provides the most viable path forward to further exploiting the potential of perovskite solar cells. However, PTSC technology faces a set of challenges distinct from those in perovskite single-junction devices because (i) NBG perovskitestypically achieved by Pb−Sn alloyingare prone to oxidation (Sn2+ to Sn4+), which results in a high density of Sn vacancies that degrade the optoelectronic performance of NBG perovskite films, (ii) practically complete photon absorption and charge extraction require thick, NBG perovskite films having long carrier diffusion lengths, and (iii) WBG perovskites with high Br/(I + Br) ratio experience large voltage losses and inferior light stability due to surface trap states and phase segregation. In this Account, we discuss how to manage these considerations and maximize the power output in PTSCs via light management. We then review strategies, including composition- and additive-engineering, defect passivation, and matching charge transport layers, for enhancing the carrier diffusion length of NBG perovskite cells and mitigating voltage losses in WBG perovskite cells. We also summarize the advances made in the fabrication of PTSCs on the device level, especially the evolution of tunnel recombination junctions and tandem device architectures. Finally, we highlight further research efforts needed to overcome roadblocks to commercialization (e.g., improving the environmental, thermal, and operating stability of these devices) and offer our perspective on the future development of this rapidly advancing field.
  • Polymer nano-rings with uranium specific clefts for selective recovery of uranium from acidic effluents via reductive adsorption

    Kushwaha, Shilpi; Mane, Manoj Vasisht; Ravindranathan, Sapna; Das, Amitava (ACS Sensors, American Chemical Society (ACS), 2020-09-25) [Article]
    Nanostructured polymeric materials, functionalized with appropriate receptor have opened up newer possibilities for designing a reagent that shows analyte-specific recognition and efficient scavenging of an analyte that has either detrimental influence for human physiology and environment or for its recovery for further value addition. Higher active surface area, morphological diversity, synthetic tuneability for desired surface functionalization, and the ease of regeneration of nanostructured material for further use have provided such material with a distinct edge over conventional reagents. Use of biodegradable polymeric backbone has an added significance owing to the recent concern over the impact of polymer on the environment. Functionalization of biodegradable sodium alginate with AENA (6.85 % grafting) as the receptor functionality led to a unique open framework nanoring (NNRG) morphology with a favourable spatial orientation for specific recognition and efficient binding to uranyl ions (U) in an aqueous medium over a varied pH range. Nanoring morphology was confirmed by TEM and AFM images. The nano-scale design maximizes the surface area for the molecular scavenger. A combination of all these features along with the reversible bindingphenomenon has made NNRG as a superior reagent for specific, efficient uptake of UO2 2+ species from an acidic (pH 3-4) solution and compares better than all existing UO22+-scavengers reported till date. This could be utilized for recovery of uranyl species from a synthetic acidic effluent of the nuclear power. Results of the U uptake experiments reveal a maximum adsorption capacity of 268 mg of U per g of NNRG in synthetic nuclear effluent. XPS studies revealed a reductive complexation process and stabilization of U(IV)-species in adsorbed uranium species (U@NNRG).
  • The influence of arm composition on the self-assembly of low-functionality telechelic star polymers in dilute solutions

    Moghimi, Esmaeel; Chubak, Iurii; Founta, Dimitra; Ntetsikas, Konstantinos; Polymeropoulos, Georgios; Hadjichristidis, Nikos; Likos, Christos N.; Vlassopoulos, Dimitris (Colloid and Polymer Science, Springer Science and Business Media LLC, 2020-09-25) [Article]
    We combine synthesis, physical experiments, and computer simulations to investigate self-assembly patterns of low-functionality telechelic star polymers (TSPs) in dilute solutions. In particular, in this work, we focus on the effect of the arm composition and length on the static and dynamic properties of TSPs, whose terminal blocks are subject to worsening solvent quality upon reducing the temperature. We find two populations, single stars and clusters, that emerge upon worsening the solvent quality of the outer block. For both types of populations, their spatial extent decreases with temperature, with the specific details (such as temperature at which the minimal size is reached) depending on the coupling between inter- and intra-molecular associations as well as their strength. The experimental results are in very good qualitative agreement with coarse-grained simulations, which offer insights into the mechanism of thermoresponsive behavior of this class of materials.
  • In-chain functionalized poly( ε -caprolactone): A valuable precursor towards the synthesis of 3-miktoarm star containing hyperbranched polyethylene

    Al-Sulami, Ahlam; Ladelta, Viko; Hadjichristidis, Nikos (Journal of Polymer Science, Wiley, 2020-09-23) [Article]
    Well-defined 3-miktoarm star copolymer 3μ-HBPE(PCL)2 (HBPE: hyperbranched polyethylene, PCL: poly[ε-caprolactone]) was synthesized by combining chain walking polymerization (CWP), ring-opening polymerization (ROP), and “click” chemistry. The synthetic methodology includes the following steps: (a) synthesis of in-chain ethynyl-functionalized PCL, (PCL)2-C ≡ CH by ROP of ε-caprolactone (CL) with ethylene-functionalized solketal (3-[prop-2-yn-1-yloxy] propane-1,2-diol) as difunctional initiator and phosphazene superbase t-BuP2 as catalyst; (b) synthesis of azido-functionalized hyperbranched PE (HBPE-N3) by CWP of ethylene with α-diimine-Pd(II) catalyst, followed by quenching with excess 4-vinylbenzyl chloride and transformation of chloro to azide group with sodium azide; and (c) “clicking” HBPE-N3 and (PCL)2-C ≡ CH using copper(I)-catalyzed azide–alkyne cycloaddition. 1H NMR spectroscopy, gel permeation chromatography, Fourier-transform infrared spectroscopy, and differential scanning calorimetry were used to determine the molecular characteristics and thermal properties of the polymers. Self-assembly behavior of 3μ-HBPE (PCL)2 in petroleum ether, a selective solvent for HBPE, was investigated by dynamic light scattering, atomic force microscopy, and transmission electron microscopy. The in-chain alkyne-functionalized poly(ε-caprolactone) is a valuable precursor for PCL-based complex macromolecular architectures.
  • Metathesis of Classical and Functionalized Olefins Catalyzed by Silica-Supported Single-Site Well-Defined W and Mo Pre-catalysts

    Saidi, Aya; Samantaray, Manoja; Poater, Albert; Tretiakov, Mykyta; Cavallo, Luigi; Basset, Jean-Marie (ChemCatChem, Wiley, 2020-09-17) [Article]
    Olefin metathesis of α-olefins (C 6 , C 8 , C 10 ), α, β-unsaturated ester, α, β- unsaturated acetate and cross-metathesis of 1-octene and ethyl 6-heptenoate were carried out using well-defined [(≡Si-O-)W(CH 3 ) 5 ] and [(≡Si-O-)Mo(≡C t Bu)(CH 2 t Bu) 2 ] pre-catalysts. During the reaction, it was observed that irrespective of the chain length, linear α-olefins are almost showing similar TON. We observed that Mo pre-catalyst performs better with TONs between 700 and 1478 as compared to W with TONs between 213 and 962 at room temperature. Both the pre-catalysts performed equally at 70 ᴼ C, with almost similar activity as well as TON (≈ 1700). We also carried out self-metathesis of functionalized olefins using both silica-supported W and Mo pre-catalysts. It was observed that W pre-catalyst performs much better than Mo pre-catalyst for functionalized olefin metathesis reaction in our conditions. Additionally, we noticed that W pre-catalyst provides selective metathesis product, whereas Mo pre-catalyst gives a range of products due to the isomerization of the olefinic bond.
  • Nanoporous GaN/n-type GaN: a cathode structure for ITO-free perovskite solar cells

    Lee, Kwangjae; Min, Jung-Wook; Turedi, Bekir; Alsalloum, Abdullah Yousef; Min, Jung-Hong; Kim, Yeong Jae; Yoo, Young Jin; Oh, Semi; Cho, Namchul; Subedi, Ram Chandra; Mitra, Somak; Yoon, Sang Eun; Kim, Jong Hyun; Park, Kwangwook; Chung, Tae-Hoon; Jung, Sung Hoon; Baek, Jong-Hyeob; Song, Young Min; Roqan, Iman S.; Ng, Tien Khee; Ooi, Boon S.; Bakr, Osman (ACS Energy Letters, American Chemical Society (ACS), 2020-09-17) [Article]
    Introducing suitable electron/hole transport layers and transparent conductive layers (TCLs) into perovskite solar cells (PSCs) is key to enhancing the selective extraction of charge carriers and reducing surface recombination losses. Here, we introduce nanoporous gallium nitride (NP GaN)/n-type GaN (n-GaN) as a dual-function cathode structure for PSCs, acting as both the TCL and the electron transport layer (ETL). We demonstrate that the hierarchical NP GaN structure provides an expanded interfacial contact area with the perovskite absorber, while the n-GaN under the NP GaN displays high transmittance in the visible spectrum as well as higher lateral electric conductivity than that of a conventional ITO film. Prototype MAPbI3 PSCs based on this NP GaN/n-GaN cathode structure (without an extra ETL) show a power conversion efficiency of up to 18.79%. The NP GaN/n-GaN platform demonstrated herein paves the way for PSCs to take advantage of the widely available heterostructures of mature III-nitride-based technologies.
  • The CASP13-CAPRI targets as case studies to illustrate a novel scoring pipeline integrating CONSRANK with clustering and interface analyses

    Barradas Bautista, Didier; Cao, Zhen; Cavallo, Luigi; Oliva, Romina (BMC Bioinformatics, Springer Science and Business Media LLC, 2020-09-16) [Article]
    Abstract Background Properly scoring protein-protein docking models to single out the correct ones is an open challenge, also object of assessment in CAPRI (Critical Assessment of PRedicted Interactions), a community-wide blind docking experiment. We introduced in the field CONSRANK (CONSensus RANKing), the first pure consensus method. Also available as a web server, CONSRANK ranks docking models in an ensemble based on their ability to match the most frequent inter-residue contacts in it. We have been blindly testing CONSRANK in all the latest CAPRI rounds, where we showed it to perform competitively with the state-of-the-art energy and knowledge-based scoring functions. More recently, we developed Clust-CONSRANK, an algorithm introducing a contact-based clustering of the models as a preliminary step of the CONSRANK scoring process. In the latest CASP13-CAPRI joint experiment, we participated as scorers with a novel pipeline, combining both our scoring tools, CONSRANK and Clust-CONSRANK, with our interface analysis tool COCOMAPS. Selection of the 10 models for submission was guided by the strength of the emerging consensus, and their final ranking was assisted by results of the interface analysis. Results As a result of the above approach, we were by far the first scorer in the CASP13-CAPRI top-1 ranking, having high/medium quality models ranked at the top-1 position for the majority of targets (11 out of the total 19). We were also the first scorer in the top-10 ranking, on a par with another group, and the second scorer in the top-5 ranking. Further, we topped the ranking relative to the prediction of binding interfaces, among all the scorers and predictors. Using the CASP13-CAPRI targets as case studies, we illustrate here in detail the approach we adopted. Conclusions Introducing some flexibility in the final model selection and ranking, as well as differentiating the adopted scoring approach depending on the targets were the key assets for our highly successful performance, as compared to previous CAPRI rounds. The approach we propose is entirely based on methods made available to the community and could thus be reproduced by any user.
  • A New Synthetic Methodology of Site-Specific Functionalized Polypeptides: Metal-Free, Highly Active and Selective at Room Temperature

    Zhao, Wei; Lv, Yanfeng; Li, Ji; Feng, Zihao; Ni, Yonghao; Hadjichristidis, Nikos (Angewandte Chemie International Edition, Wiley, 2020-09-16) [Article]
    Functionalized polypeptides have attracted tremendous interest in recent years and found many stimulating applications due to their tunable physicochemical characteristics including hydrophilicity and stimuli-responsive behavior. The development of new strategies to produce these polymers without metallic contaminants is crucial for their applications in high-value and sensitive domains, such as biomedical, microelectronic, food packaging and personal beauty care fields. Herein, a highly efficient strategy to access well-defined site-specific functionalized polypeptides is developed by combining Michael reaction with hydrogen-bonding organocatalytic ROP of NCA. A library of chain-end and chain-middle functionalized polypeptides (14 examples) with predesigned molecular weights and low polydispersities are readily prepared with this approach. Specifically, the whole synthetic process is metal-free, fulfilling high activity and selectivity at room temperature.
  • The anticancer activity of an air-stable Pd(I)-NHC (NHC = N-heterocyclic carbene) dimer.

    Scattolin, Thomas; Bortolamiol, Enrica; Palazzolo, Stefano; Caligiuri, Isabella; Perin, Tiziana; Canzonieri, Vincenzo; Demitri, Nicola; Rizzolio, Flavio; Cavallo, Luigi; Dereli, Busra; Mane, Manoj Vasisht; Nolan, Steven P.; Visentin, Fabiano (Chemical communications (Cambridge, England), Royal Society of Chemistry (RSC), 2020-09-14) [Article]
    A new dinuclear Pd(i) complex coordinating two bis(NHC) ligands revealed an unsuspected stability despite the unsaturation of the two metal centres. Even more surprisingly, the compound showed high and selective antiproliferative activity against different cancer cell lines and ovarian cancer tumoroids, and the mechanism of action was different from that of cisplatin.
  • Extension of the Surface Organometallic Chemistry to Metal-Organic Framework: development of well-defined single site [(≡Zr-O-)W(=O)(CH2tBu)3] olefin metathesis catalyst.

    Thiam, Zeynabou; Abou-Hamad, Edy; Dereli, Busra; Liu, Lingmei; Emwas, Abdul-Hamid M.; Ahmad, Rafia; Jiang, Hao; Isah, Abdulrahman Adamu; Ndiaye, Papa Birame; Taoufik, Mostafa; Han, Yu; Cavallo, Luigi; Basset, Jean-Marie; Eddaoudi, Mohamed (Journal of the American Chemical Society, American Chemical Society (ACS), 2020-09-09) [Article]
    We report here the first step by step anchoring of a W(≡CtBu)(CH2 tBu)3 complex on a highly crystalline and mesoporous MOF, namely Zr-NU-1000, using Surface organometallic Chemistry (SOMC) concept and methodology. SOMC allowed us to selectively graft the complex on the Zr6 clusters and characterize the obtained single site material by using state of the art experimental methods including extensive solid-state NMR techniques and HAADF-STEM imaging. Further FT-IR spectroscopy revealed the presence of a W=O moiety arising from the in situ reaction of the W≡CtBu functionality with the coordinated water coming from the 8-connected hexanuclear Zr6 clusters. All the steps leading to the final grafted molecular complex have been identified by DFT. The obtained material was tested for gas phase and liquid phase olefin metathesis and exhibited higher catalytic activity than the corresponding catalysts synthesized by different grafting methods. This contribution establishes the importance of applying SOMC to MOF chemistry to get well defined single site catalyst on MOF inorganic secondary building units, in particular the in situ synthesis of W=O alkyl complexes from their W carbyne analogues.
  • Mechanistic Insight into the Photoredox-Nickel-HAT Triple Catalyzed Arylation and Alkylation of α-Amino Csp3–H Bonds

    Maity, Bholanath; Zhu, Chen; Yue, Huifeng; Huang, Long; Harb, Moussab; Minenkov, Yury; Rueping, Magnus; Cavallo, Luigi (Journal of the American Chemical Society, American Chemical Society (ACS), 2020-09-09) [Article]
    We report here a comprehensive computational analysis of the mechanisms of the photoredox-nickel-HAT (HAT: hydrogen atom transfer) catalyzed arylation and alkylation of α-amino Csp3–H bonds developed by MacMillan and coworkers. Different alternatives for the three catalytic cycles were tested to identify unambiguously the operative reaction mechanism. Our analysis indicated that the IrIII photoredox catalyst, upon irradiation with visible light, can be either reduced or oxidized by the HAT and nickel catalysts, respectively, indicating that both reductive and oxidative quenching catalytic cycles can be operative, although the reductive cycle is favored. Our analysis of the HAT cycle indicated that activation of a α-amino Csp3‒H bond of the substrate is facile and selective relative to activation of a β-amino Csp3‒H bond. Finally, our analysis of the nickel cycle indicated that both arylation and alkylation of α-amino Csp3–H bonds occurs via the sequence of nickel oxidation states NiI-NiII-NiI-NiIII, and of elementary steps: radical addition-SET-oxidative addition-reductive elimination.
  • Ledge-directed epitaxy of continuously self-aligned single-crystalline nanoribbons of transition metal dichalcogenides

    Aljarb, Areej; Fu, Jui-Han; Hsu, Chih-Chan; Chuu, Chih-Piao; Wan, Yi; Hakami, Mariam; Naphade, Dipti R.; Yengel, Emre; Lee, Chien-Ju; Brems, Steven; Chen, Tse-An; Li, Ming-Yang; Bae, Sang-Hoon; Hsu, Wei-Ting; Cao, Zhen; Albaridy, Rehab; Lopatin, Sergei; Chang, Wen-Hao; Anthopoulos, Thomas D.; Kim, Jeehwan; Li, Lain-Jong; Tung, Vincent (Nature Materials, Springer Science and Business Media LLC, 2020-09-07) [Article]
    Two-dimensional transition metal dichalcogenide nanoribbons are touted as the future extreme device downscaling for advanced logic and memory devices but remain a formidable synthetic challenge. Here, we demonstrate a ledge-directed epitaxy (LDE) of dense arrays of continuous, self-aligned, monolayer and single-crystalline MoS2 nanoribbons on β-gallium (iii) oxide (β-Ga2O3) (100) substrates. LDE MoS2 nanoribbons have spatial uniformity over a long range and transport characteristics on par with those seen in exfoliated benchmarks. Prototype MoS2-nanoribbon-based field-effect transistors exhibit high on/off ratios of 108 and an averaged room temperature electron mobility of 65 cm2 V−1 s−1. The MoS2 nanoribbons can be readily transferred to arbitrary substrates while the underlying β-Ga2O3 can be reused after mechanical exfoliation. We further demonstrate LDE as a versatile epitaxy platform for the growth of p-type WSe2 nanoribbons and lateral heterostructures made of p-WSe2 and n-MoS2 nanoribbons for futuristic electronics applications.
  • Model-based Design of Stable Electrolytes for Potassium Ion Batteries

    Zhang, Jiao; Cao, Zhen; Zhou, Lin; Park, Geon-Tae; Cavallo, Luigi; Wang, Limin; Alshareef, Husam N.; Sun, Yang-Kook; Ming, Jun (ACS Energy Letters, American Chemical Society (ACS), 2020-09-04) [Article]
    Rechargeable potassium (ion) batteries (KIBs) are an emerging energy storage system with many potential advantages over existing battery systems (e.g., Li-ion, Na-ion battery). However, the electrolyte design for KIBs remains challenging because of serious electrolyte decomposition. Particularly, this problem is aggravated when using metal potassium anodes. Herein, we report that the cation-solvent (i.e., K+-solvent) solvation structure which is determined by the electrolyte composition plays a dominant role in the failure of KIBs. We present an analysis of the reaction pathway to understand the behavior of the cation-solvent structure at the surface of metal electrodes (e.g., metal plating or M+-solvent decomposition). The electronegativity change of cation-solvent structure was studied and correlated to the stability of the electrolytes. We find that the electrolyte decomposition can be induced when the K+ -solvent structure accepts one electron from the electrode; however, this process can be suppressed by tuning the electronegativity through varying the solvent chemistry, anions type, and salt concentrations. Our results explain the high stability of existing high-concentration electrolytes, and present a general guideline to design stable electrolytes for KIBs. This approach can pave the way for the realization of high-performance K-ion batteries.
  • High-performance pan-tactic polythioesters with intrinsic crystallinity and chemical recyclability.

    Shi, Changxia; McGraw, Michael L; Li, Zi-Chen; Cavallo, Luigi; Falivene, Laura; Chen, Eugene Y.-X. (Science advances, American Association for the Advancement of Science (AAAS), 2020-09-03) [Article]
    Three types of seemingly unyielding trade-offs have continued to challenge the rational design for circular polymers with both high chemical recyclability and high-performance properties: depolymerizability/performance, crystallinity/ductility, and stereo-disorder/crystallinity. Here, we introduce a monomer design strategy based on a bridged bicyclic thiolactone that produces stereo-disordered to perfectly stereo-ordered polythiolactones, all exhibiting high crystallinity and full chemical recyclability. These polythioesters defy aforementioned trade-offs by having an unusual set of desired properties, including intrinsic tacticity-independent crystallinity and chemical recyclability, tunable tacticities from stereo-disorder to perfect stereoregularity, as well as combined high-performance properties such as high thermal stability and crystallinity, and high mechanical strength, ductility, and toughness.

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