Recent Submissions

  • 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.
  • Illuminating Initial Carbon-Carbon Bond Formation during the Early Stages of Methane Dehydroaromatization.

    Caglayan, Mustafa; Paioni, Alessandra Lucini; Abou-Hamad, Edy; Shterk, Genrikh; Pustovarenko, Alexey; Baldus, Marc; Chowdhury, Abhishek Dutta; Gascon, Jorge (Angewandte Chemie (International ed. in English), Wiley, 2020-06-11) [Article]
    Still in 2020, methane dehydroaromatization (MDA) is among the most challenging processes in catalysis science due to the inherent harsh reaction conditions and fast catalyst deactivation. To improve it further, understanding the initial C-C bond formation mechanism is sine qua non. However, consensus about the actual reaction mechanism is still to be achieved. In this work, using advanced magic angle spinning (MAS) solid-state NMR spectroscopy, we study in detail the early stages of the reaction over a well-dispersed Mo/H-ZSM-5 catalyst. Simultaneous detection of acetylene (i.e., presumably the direct C-C bond forming product from methane), methylidene, allenes, acetal and surface-formate species along with the typical olefinic/aromatic species allow us to conclude the existence of two independent C-H activation pathways. Moreover, this study emphasizes the significance of mobility-dependent host-guest chemistry between inorganic zeolite and its organic trapped species during heterogeneous catalysis.
  • Lattice deformation in epitaxial Fe3O4 films on MgO substrate studied by polarized Raman spectroscopy∗

    Yang, Yang; Zhang, Qiang; Mi, Wenbo; Zhang, Xixiang (Chinese Physics B, IOP Publishing, 2020-05-25) [Article]
    The lattice structures of epitaxial Fe3O4 films deposited on MgO were studied systematically using polarized Raman spectroscopy as a function of film thickness, where interesting phenomena were observed. Firstly, the spectral conflict to the Raman selection rules (RSRs) was observed under cross sectional configuration, which can be attributed to the tetragonal deformation in the growth direction due to the lattice mismatch between Fe3O4 and MgO. Secondly, the blue-shift and broadening of Raman peaks evidenced the decrease of the tensile strain in Fe3O4 film with decreased thickness. Thirdly, distinct from the other Raman modes, the lowest T 2g mode exhibited asymmetric lineshape, which can be interpreted using the spatial correlation model. The increased correlation length introduced in the model can well explain the enhanced peak asymmetry feature with decreasing thickness. These results provide useful information for understanding the lattice structure of epitaxial Fe3O4 film.
  • Impact of small promoter amounts on coke structure in dry reforming of methane over Ni/ZrO2

    Franz, Robert; Kühlewind, Tobias; Shterk, Genrikh; Abou-Hamad, Edy; Parastaev, Alexander; Uslamin, Evgeny; Hensen, Emiel J.M.; Kapteijn, Freek; Gascon, Jorge; Pidko, Evgeny A. (Catalysis Science & Technology, Royal Society of Chemistry (RSC), 2020-05-22) [Article]
    Coke deposition is one of the main challenges in the commercialisation of dry reforming of methane over supported Ni catalysts. Besides the coke quantity, the structure of the deposits is also essential for the catalyst lifetime. Accordingly, in this study, we analysed the effect of Na, K, and Cs promoters on both these variables over Ni/ZrO2 catalysts. Besides blocking the most active coke-forming sites already at low loading, the promoting effect of the alkali metals is also contributed to by their coke gasification activity. To evaluate the additional impact of the latter, the behaviour of alkali-doped catalysts was compared to that for Mn-doped catalysts, exclusively featuring the site-blocking promotion mechanism. While the conversion is barely affected by the type of promoter, it has a profound effect on the amount and the composition of carbon deposits formed during the reaction. Promoting with K or Mn reduces the coke content to a similar degree but with less carbon fibres observed in the case of K. The promotion by Cs and Na results in the lowest coke content. The superior performance of Cs and Na-doped Ni/ZrO2 catalysts is attributed to the enhanced coke gasification via carbonate species on top of the site blocking effects.
  • Piezotronic AlGaN nanowire Schottky junctions grown on a metal substrate

    Al-Maghrabi, Latifah; Huang, Chen; Priante, Davide; Tian, Meng; Min, Jung-Wook; Zhao, Chao; Zhang, Huafan; Subedi, Ram Chandra; Alhashim, Hala H.; Sun, Haiding; Ng, Tien Khee; Ooi, Boon S. (AIP Advances, AIP Publishing, 2020-05-11) [Article]
    The non-centrosymmetric crystal structures of polar-semiconductors comprising GaN, InN, AlN, and ZnO intrigued the scientific community in investigating their potential for a strain-induced nano-energy generation. The coupled semiconducting and piezoelectric properties produce a piezo-potential that modulates the charge transport across their heterostructure interfaces. By using conductive-atomic force microscopy, we investigate the mechanism that gives rise to the piezotronic effect in AlGaN nanowires (NWs) grown on a molybdenum (Mo) substrate. By applying external bias and force on the NWs/Mo structure using a Pt–Ir probe, the charge transport across the two adjoining Schottky junctions is modulated due to the change in the apparent Schottky barrier heights (SBHs) that result from the strain-induced piezo-potential. We measured an increase in the SBH of 98.12 meV with respect to the background force, which corresponds to an SBH variation $\textstyle\frac{\partial\phi}{\partial F}$ of 6.24 meV/nN for the semiconductor/Ti/Mo interface. The SBH modulation, which is responsible for the piezotronic effect, is further studied by measuring the temperature-dependent I–V curves from room temperature to 398 K. The insights gained from the unique structure of AlGaN NWs/Mo shed light on the electronic properties of the metal-semiconductor interfaces, as well as on the potential application of AlGaN NW piezoelectric nanomaterials in optoelectronics, sensors, and energy generation applications.
  • Impact of Small Promoter Amounts on Coke Structure in Dry Reforming over Ni/ ZrO2

    Franz, Robert; Kuehlewind, Tobias; Shterk, Genrikh; Abou-Hamad, Edy; Parastaev, Alexander; Uslamin, Evgeny; Hensen, Emiel J.M.; Kapteijn, Freek; Gascon, Jorge; Pidko, Evgeny (American Chemical Society (ACS), 2020-04-23) [Preprint]
    <jats:p>Coke deposition is one of the main challenges in the commercialization of dry reforming of methane over supported Ni catalysts. Besides the coke quantity, the structure of the deposits is also essential for the catalyst lifetime. Accordingly, in this study, we analysed the effect of different metal promoters on both these variables over Ni/ ZrO<sub>2</sub> catalysts. Alkali metals are known to block the most active coke forming sites already at low loading, leading to an investigation of Na, K and Cs. To analyse the possible contributions of coke gasification activity of the alkali metals, Mn was additionally used as a comparison. While the conversion is barely affected by the type of promoter, it has profound effect on the amount and the composition of carbon deposits formed during reaction: Addition of K or Mn reduces the coke content to a similar degree but with less carbon fibres observed in the case of K. Promotion by Cs and Na results in the lowest coke content, which is attributed to enhanced coke gasification via carbonate species</jats:p>
  • [Cu81(PhS)46(tBuNH2)10(H)32]3+ Reveals the Coexistence of Large Planar Cores and Hemispherical Shells in High-Nuclearity Copper Nanoclusters

    Huang, Renwu; Yin, Jun; Dong, Chunwei; Ghosh, Atanu; Alhilaly, Mohammad Jaber; Dong, Xinglong; Hedhili, Mohamed N.; Abou-Hamad, Edy; Alamer, Badriah Jaber; Nematulloev, Saidkhodzha; Han, Yu; Mohammed, Omar F.; Bakr, Osman (Journal of the American Chemical Society, American Chemical Society (ACS), 2020-04-21) [Article]
    Copper-based nanomaterials have attracted tremendous interest due to their unique properties in the fields of photoluminescence and catalysis. As a result, studies on the correlation between their molecular structure and their properties are of great importance. Copper nanoclusters are a new class of nanomaterials that can provide an atomic-level view of the crystal structure of copper nanoparticles. Herein, a high-nuclearity copper nanocluster with 81 copper atoms, formulated as [Cu81(PhS)46(tBuNH2)10(H)32]3+ (Cu81), was successfully synthesized and fully studied by X-ray crystallography, X-ray photoelectron spectroscopy, hydrogen evolution experiments, electrospray ionization mass spectrometry, nuclear magnetic resonance spectroscopy, and density functional theory calculations. Cu81 exhibits extraordinary structural characteristics, including (i) three types of novel epitaxial surface-protecting motifs; (ii) an unusual planar Cu17 core; (iii) a hemispherical shell, comprised of a curved surface layer and a planar surface layer; and (iv) two distinct, self-organized arrangements of protective ligands on the curved and planar surfaces. The present study sheds light on structurally unexplored copper nanomaterials and paves the way for the synthesis of high-nuclearity copper nanoclusters.
  • Effect of surface roughness on the anomalous Hall effect in Fe thin films

    Zhang, Qiang; Zheng, Dongxing; Wen, Yan; Zhao, Yuelei; Mi, Wenbo; Manchon, Aurelien; Boulle, Olivier; Zhang, Xixiang (Physical Review B, American Physical, 2020-04-01) [Article]
    Surface roughness plays an important role on the magnetotransport properties of thin films, especially in ultrathin films. In this work, we prepared Fe thin films with various surface roughness by using different seed layers and studied the electrical transport and anomalous Hall effect. By tuning surface roughness scattering, the longitudinal resistivity (ρxx) measured at 5 K increases by one order of magnitude and the corresponding anomalous Hall resistivity (ρAHE) increases by three times with increasing roughness. The intrinsic, skew-scattering, and side-jump contributions to ρAHE were separated from our data. The anomalous Hall angle depends on the surface roughness, which may be of importance to the material engineering for achieving large spin Hall angle.
  • Ligand-free gold nanoclusters confined in mesoporous silica nanoparticles for styrene epoxidation

    Alshankiti, Buthainah; Almaksoud, Walid; Habeeb Muhammed, Madathumpady Abubaker; Anjum, Dalaver H.; Moosa, Basem; Basset, Jean-Marie; Khashab, Niveen M. (Nanoscale Advances, Royal Society of Chemistry (RSC), 2020-03-18) [Article]
    We present a novel approach to produce gold nanoclusters (Au NCs) in the pores of mesoporous silica nanoparticles (MSNs) by sequential and controlled addition of metal ions and reducing agents. This impregnation technique was followed to confine Au NCs inside the pores of MSNs without adding external ligands or stabilizing agents. TEM images show a uniform distribution of monodisperse NCs with an average size of 1.37 ± 0.4 nm. Since the NCs are grown in situ in MSN pores, additional support and high temperature calcination are not required to use them as catalysts. The use of Au NC/MSNs as a catalyst for the epoxidation of styrene in the presence of tert-butyl hydroperoxide (TBHP) as a terminal oxidant resulted in an 88% conversion of styrene in 12 h with a 74% selectivity towards styrene epoxide. Our observations suggest that this remarkable catalytic performance is due to the small size of Au NCs and the strong interaction between gold and the MSNs. This catalytic conversion is environmentally friendly as it is solvent free. We believe our synthetic approach can be extended to other metal NCs offering a wide range of applications.
  • Spray-coated graphene oxide hollow fibers for nanofiltration

    Mahalingam, Dinesh K.; Falca, Gheorghe; Upadhya, Lakshmeesha; Abou-Hamad, Edy; Batra, Nitinkumar; Wang, Shaofei; Musteata, Valentina-Elena; Da Costa, Pedro M. F. J.; Nunes, Suzana Pereira (Journal of Membrane Science, Elsevier BV, 2020-03-09) [Article]
    Advances in process intensification in the chemical and pharmaceutical industry depends on the availability of more sustainable separation methods. For this progress, membranes with high stability in organic solvents are needed. GO-coated membranes could be advantageous in these applications, being chemically, thermally and mechanically stable. However, simple, scalable, low-cost fabrication methods, particularly for GO deposition on hollow fibers are still in an early phase. We propose here a simple spray-coating method for deposition of GO sheets on crosslinked hollow fiber supports. We first fabricated polyetherimide hollow fiber membranes and crosslinked them with hexamethylene diamine. These supports have strong tolerance to various organic solvents. The amide reaction arising between the imide groups of polyetherimide and the amine groups of hexamethylene diamine provide even higher chemical and mechanical stability. Thereafter, the spray-coating of GO dispersions led to the formation of a stable selective layer on the hollow fibers. An excellent adhesion between GO and the substrate was achieved. The chemical reasons for that were investigated by solid state NMR. Overall, this simple method enables the application of GO hollow fiber membranes in organic solvent nanofiltration, with high performance demonstrated in water and acetone.
  • Highly Stable Phosphonate-Based MOFs with Engineered Bandgaps for Efficient Photocatalytic Hydrogen Production

    Zhu, Yun-Pei; Yin, Jun; Abou-Hamad, Edy; Liu, Xiaokang; Chen, Wei; Yao, Tao; Mohammed, Omar F.; Alshareef, Husam N. (Advanced Materials, Wiley, 2020-03-04) [Article]
    Photoactive metal-organic frameworks (MOFs) represent one of the most promising materials for photocatalytic hydrogen production, but phosphonate-based MOFs have remained largely underdeveloped compared to other conventional MOFs. Herein, a photocatalyst of 1D titanium phosphonate MOF is designed through an easy and scalable stirring hydrothermal method. Homogeneous incorporation of organophosphonic linkers can narrow the bandgap, which is due to the strong electron-donating ability of the OH functional group that can efficiently shift the top of the valence band, moving the light absorption to the visible portion of the spectrum. In addition, the unique 1D nanowire topology enhances the photoinduced charge carrier transport and separation. Accordingly, the titanium phosphonate nanowires deliver remarkably enhanced photocatalytic hydrogen evolution activity under irradiation of both visible light and a full-spectrum simulator. Such concepts of engineering both nanostructures and electronic states herald a new paradigm for designing MOF-based photocatalysts.
  • Constructing Polymorphic Nanodomains in BaTiO 3 Films via Epitaxial Symmetry Engineering

    Peng, Wei; Zorn, Jacob A.; Mun, Junsik; Sheeraz, Muhammad; Roh, Chang Jae; Pan, Jun; Wang, Bo; Guo, Kun; Ahn, Chang Won; Zhang, Yaping; Yao, Kui; Lee, Jong Seok; Chung, Jin-Seok; Kim, Tae Heon; Chen, Long-Qing; Kim, Miyoung; Wang, Lingfei; Noh, Tae Won (Advanced Functional Materials, Wiley, 2020-02-24) [Article]
    Ferroelectric materials owning a polymorphic nanodomain structure usually exhibit colossal susceptibilities to external mechanical, electrical, and thermal stimuli, thus holding huge potential for relevant applications. Despite the success of traditional strategies by means of complex composition design, alternative simple methods such as strain engineering have been intensively sought to achieve a polymorphic nanodomain state in lead-free, simple-composition ferroelectric oxides in recent years. Here, a nanodomain configuration with morphed structural phases is realized in an epitaxial BaTiO3 film grown on a (111)-oriented SrTiO3 substrate. Using a combination of experimental and theoretical approaches, it is revealed that a threefold rotational symmetry element enforced by the epitaxial constraint along the [111] direction of BaTiO3 introduces considerable instability among intrinsic tetragonal, orthorhombic, and rhombohedral phases. Such phase degeneracy induces ultrafine ferroelectric nanodomains (1–10 nm) with low-angle domain walls, which exhibit significantly enhanced dielectric and piezoelectric responses compared to the (001)-oriented BaTiO3 film with uniaxial ferroelectricity. Therefore, the finding highlights the important role of epitaxial symmetry in domain engineering of oxide ferroelectrics and facilitates the development of dielectric capacitors and piezoelectric devices.
  • Effect of Strontium Doping Into CaBi2Nb2O9 Aurivillius Oxide Nanoceramics: Structural and Electrical Properties

    Jalled, Ouissem; Alhassan, Mariah; Alharbi, Seham R.; Alharbi, Zaynab; Al-Hadeethi, Yas; Mohammed, Hiba; Miao, Xiaohe (Journal of Nanoelectronics and Optoelectronics, American Scientific Publishers, 2020-02-14) [Article]
    <jats:p>Herein, we report the synthesis and characterization of Ca<jats:sub>1-<jats:italic>x</jats:italic></jats:sub>Sr<jats:sub><jats:italic>x</jats:italic></jats:sub>Bi<jats:sub>2</jats:sub>Nb<jats:sub>2</jats:sub>O<jats:sub>9</jats:sub> (CSBNO) (0 ≤ <jats:italic>x</jats:italic> ≤ 1) nanoceramics prepared using sucrose-assisted sol–gel combustion methods. The synthesized nanoceramics were characterized by different tools like differential thermal and thermogravimetric analyzer (DTA-TG), high resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FTIR) spectrometer, X-ray powder diffraction (XRD), and impedance analyzer. DTA-TG reveals that the optimum temperature of calcination of CBN is higher than 1000 °C. The FTIR revealed the formation of CaBi<jats:sub>2</jats:sub>Nb<jats:sub>2</jats:sub>O<jats:sub>9</jats:sub> (CBNO) at 614 cm$^{-1}$. The XRD confirmed that all samples exhibited orthorhombic crystal structure. Increased orthorhombic distortion was spotted for doped CBNO and the structure acquires extra orthorhombicity through Sr doping. The TEM measurement inspected the increase of the grain size due to the inclusion of strontium into the orthorhombic crystal structure of CBNO from 56 nm to 76 nm. The dielectric constant measurement demonstrated that the increase in Sr content is associated with steady decrease in Curie temperature from 1207 K up to 720 K. The dielectric loss exhibited a minimum value at <jats:italic>x</jats:italic> = 0.5 and high stability along the temperature range of 300–850 K. Such property may enable this nanocomposite to be used for the application of FeRAM.</jats:p>
  • Direct imaging of an inhomogeneous electric current distribution using the trajectory of magnetic half-skyrmions

    Zhang, Senfu; Zhang, Xichao; Zhang, Junwei; Ganguly, Arnab; Xia, Jing; Wen, Yan; Zhang, Qiang; Yu, Guoqiang; Hou, Zhipeng; Wang, Wenhong; Peng, Yong; Xiao, Gang; Manchon, Aurelien; Kosel, Jürgen; Zhou, Yan; Zhang, Xixiang (Science Advances, American Association for the Advancement of Science (AAAS), 2020-02-08) [Article]
    The direct imaging of current density vector distributions in thin films has remained a daring challenge. Here, we report that an inhomogeneous current distribution can be mapped directly by the trajectories of magnetic half-skyrmions driven by an electrical current in Pt/Co/Ta trilayer, using polar magneto-optical Kerr microscopy. The half-skyrmion carries a topological charge of 0.5 due to the presence of Dzyaloshinskii-Moriya interaction, which leads to the half-skyrmion Hall effect. The Hall angle of half-skyrmions is independent of current density and can be reduced to as small as 4° by tuning the thickness of the Co layer. The Hall angle is so small that the elongation path of half-skyrmion approximately delineates the invisible current flow as demonstrated in both a continuous film and a curved track. Our work provides a practical technique to directly map inhomogeneous current distribution even in complex geometries for both fundamental research and industrial applications.
  • Titanium Carbide MXene Nucleation Layer for Epitaxial Growth of High-Quality GaN Nanowires on Amorphous Substrates

    Prabaswara, Aditya; Kim, Hyunho; Min, Jung-Wook; Subedi, Ram Chandra; Anjum, Dalaver H.; Davaasuren, Bambar; Moore, Kalani; Conroy, Michele; Mitra, Somak; Roqan, Iman S.; Ng, Tien Khee; Alshareef, Husam N.; Ooi, Boon S. (ACS Nano, American Chemical Society (ACS), 2020-02-03) [Article]
    Growing III-nitride nanowires on 2D materials is advantageous, as it effectively decouples the underlying growthsubstrate from the properties of the nanowires. As a relatively new family of 2D materials, MXenes are promising candidates as III-nitride nanowire nucleation layers capable of providing simultaneous transparency and conductivity. In this work, we demonstrate the direct epitaxial growth of GaN nanowires on Ti3C2 MXene films. The MXene films consist of nanoflakes spray coated onto an amorphous silica substrate. We observed an epitaxial relationship between the GaN nanowires and the MXene nanoflakes due to the compatibility between the triangular lattice of Ti3C2 MXene and the hexagonal structure of wurtzite GaN. The GaN nanowires on MXene show good material quality and partial transparency at visible wavelengths. Nanoscale electrical characterization using conductive atomic force microscopy reveals a Schottky barrier height of ∼330 meV between the GaN nanowire and the Ti3C2 MXene film. Our work highlights the potential of using MXene as a transparent and conductive preorienting nucleation layer for high-quality GaN growth on amorphous substrates.
  • Enhanced photocatalytic hydrogen evolution from organic semiconductor heterojunction nanoparticles

    Kosco, Jan; Bidwell, Matthew; Cha, Hyojung; Martin, Tyler; Howells, Calvyn Travis; Sachs, Michael; Anjum, Dalaver H.; Gonzalez Lopez, Sandra; Zou, Lingyu; Wadsworth, Andrew; Zhang, Weimin; Zhang, Lisheng; Tellam, James; Sougrat, Rachid; Laquai, Frédéric; DeLongchamp, Dean M.; Durrant, James R.; McCulloch, Iain (Nature Materials, Springer Science and Business Media LLC, 2020-02-03) [Article]
    Photocatalysts formed from a single organic semiconductor typically suffer from inefficient intrinsic charge generation, which leads to low photocatalytic activities. We demonstrate that incorporating a heterojunction between a donor polymer (PTB7-Th) and non-fullerene acceptor (EH-IDTBR) in organic nanoparticles (NPs) can result in hydrogen evolution photocatalysts with greatly enhanced photocatalytic activity. Control of the nanomorphology of these NPs was achieved by varying the stabilizing surfactant employed during NP fabrication, converting it from a core-shell structure to an intermixed donor/acceptor blend and increasing H2 evolution by an order of magnitude. The resulting photocatalysts display an unprecedentedly high H2 evolution rate of over 60,000 µmol h-1 g-1 under 350 to 800 nm illumination, and external quantum efficiencies over 6% in the region of maximum solar photon flux.
  • Coated sulfated zirconia/SAPO-34 for the direct conversion of CO2 to light olefins

    Galilea, Adrian; Chowdhury, Abhishek Dutta; Caglayan, Mustafa; Rodriguez-Gomez, Alberto; Wehbe, Nimer; Abou-Hamad, Edy; Gevers, Lieven; Ould-Chikh, Samy; Gascon, Jorge (Catalysis Science & Technology, Royal Society of Chemistry (RSC), 2020-01-30) [Article]
    The conversion of CO<sub>2</sub> to light olefins <italic>via</italic> bifunctional catalysts (<italic>i.e.</italic> metal oxides/zeolites) is a promising approach to tackle CO<sub>2</sub> emissions and, at the same time, reduce fossil-fuel dependence by closing the carbon cycle.
  • Docking of Tetra-methyl Zirconium to the Surface of Silica: A Well-Defined Pre-catalyst for Conversion of CO2 to Cyclic Carbonates

    Almaksoud, Walid; Saidi, Aya; Samantaray, Manoja; Abou-Hamad, Edy; poater, albert; Ould-Chikh, Samy; Guo, Xianrong; Guan, Erjia; Ma, Tao; Gates, Bruce C; Basset, Jean-Marie (Chemical Communications, Royal Society of Chemistry (RSC), 2020-01-29) [Article]
    The metal complex (Zr(CH3)4(THF)2) has been fully synthesized, characterized and grafted onto partially dehydroxylated silica to give two surface species -$. / /' $ %3)3(THF)2] (minor) and -$. / /'2Zr(CH3)2(THF)2] $ (major) which have been characterized by SS NMR, IR, elemental analysis. These supported pre-catalysts exhibit the best conversion of CO2 to cyclic carbonates, as compared to the previously reported SOMC catalysts.
  • Edge stabilization in reduced-dimensional perovskites.

    Quan, Li Na; Ma, Dongxin; Zhao, Yongbiao; Voznyy, Oleksandr; Yuan, Haifeng; Bladt, Eva; Pan, Jun; García de Arquer, F Pelayo; Sabatini, Randy; Piontkowski, Zachary; Emwas, Abdul-Hamid M.; Todorović, Petar; Quintero-Bermudez, Rafael; Walters, Grant; Fan, James Z; Liu, Mengxia; Tan, Hairen; Saidaminov, Makhsud I; Gao, Liang; Li, Yiying; Anjum, Dalaver H.; Wei, Nini; Tang, Jiang; McCamant, David W; Roeffaers, Maarten B J; Bals, Sara; Hofkens, Johan; Bakr, Osman; Lu, Zhenghong; Sargent, E. (Nature communications, Springer Science and Business Media LLC, 2020-01-10) [Article]
    Reduced-dimensional perovskites are attractive light-emitting materials due to their efficient luminescence, color purity, tunable bandgap, and structural diversity. A major limitation in perovskite light-emitting diodes is their limited operational stability. Here we demonstrate that rapid photodegradation arises from edge-initiated photooxidation, wherein oxidative attack is powered by photogenerated and electrically-injected carriers that diffuse to the nanoplatelet edges and produce superoxide. We report an edge-stabilization strategy wherein phosphine oxides passivate unsaturated lead sites during perovskite crystallization. With this approach, we synthesize reduced-dimensional perovskites that exhibit 97 ± 3% photoluminescence quantum yields and stabilities that exceed 300 h upon continuous illumination in an air ambient. We achieve green-emitting devices with a peak external quantum efficiency (EQE) of 14% at 1000 cd m-2; their maximum luminance is 4.5 × 104 cd m-2 (corresponding to an EQE of 5%); and, at 4000 cd m-2, they achieve an operational half-lifetime of 3.5 h.
  • Understanding the Origin of Selective Reduction of CO2 to CO on Single-Atom Nickel Catalyst.

    He, Shi; Ji, Dong; Zhang, Junwei; Novello, Peter; Li, Xueqian; Zhang, Qiang; Zhang, Xixiang; Liu, Jie (The journal of physical chemistry. B, American Chemical Society (ACS), 2019-12-27) [Article]
    Electrochemical reduction of CO2 to CO offers a promising strategy for regulating the global carbon cycle and providing feedstock for the chemical industry. Understanding the origin that determines the faradaic efficiency (FE) of reduction of CO2 to CO is critical for developing a highly efficient electrocatalyst. Here, by constructing a single-atom Ni catalyst on nitrogen-doped winged carbon nanofiber (NiSA-NWC), we find that the single-atom Ni catalyst possesses the maximum CO FE of over 95% at -1.6 V vs Ag/AgCl, which is about 30% higher than the standard Ni nanoparticles on the same support. The Tafel analysis reveals that the single-atom Ni catalyst has a preferred reduction of CO2 to CO and a slower rate for the hydrogen evolution reaction. We propose that the domination of singular Ni1+ electronic states and limited hydrogen atom adsorption sites on the single-atom Ni catalyst lead to the observed high FE for CO2 reduction to CO.

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