168 results found
Trott G, Garden JA, Williams CK, 2019, Heterodinuclear zinc and magnesium catalysts for epoxide/CO2 ring opening copolymerizations, CHEMICAL SCIENCE, Vol: 10, Pages: 4618-4627, ISSN: 2041-6520
Lim JYC, Yuntawattana N, Beer PD, et al., 2019, Isoselective Lactide Ring Opening Polymerisation using Rotaxane Catalysts, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, Vol: 58, Pages: 6007-6011, ISSN: 1433-7851
Pankhurst JR, Paul S, Zhu Y, et al., 2019, Polynuclear alkoxy-zinc complexes of bowl-shaped macrocycles and their use in the copolymerisation of cyclohexene oxide and CO2, DALTON TRANSACTIONS, Vol: 48, Pages: 4887-4893, ISSN: 1477-9226
Zhu Y, Poma A, Rizzello L, et al., 2019, Metabolically Active, Fully Hydrolysable Polymersomes, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, Vol: 58, Pages: 4581-4586, ISSN: 1433-7851
Kennedy OW, White ER, Howkins A, et al., 2019, Mapping the origins of luminescence in ZnO nanowires by STEM-CL, Journal of Physical Chemistry Letters, Vol: 10, Pages: 386-392, ISSN: 1948-7185
In semiconductor nanowires, understanding both the sources of luminescence (excitonic recombination, defects, etc.) and the distribution of luminescent centers (be they uniformly distributed, or concentrated at structural defects or at the surface) is important for synthesis and applications. We develop scanning transmission electron microscopy-cathodoluminescence (STEM-CL) measurements, allowing the structure and cathodoluminescence (CL) of single ZnO nanowires to be mapped at high resolution. Using a CL pixel resolution of 10 nm, variations of the CL spectra within such nanowires in the direction perpendicular to the nanowire growth axis are identified for the first time. By comparing the local CL spectra with the bulk photoluminescence spectra, the CL spectral features are assigned to internal and surface defect structures. Hyperspectral CL maps are deconvolved to enable characteristic spectral features to be spatially correlated with structural features within single nanowires. We have used these maps to show that the spatial distribution of these defects correlates well with regions that show an increased rate of nonradiative transitions.
Raman SK, Raja R, Arnold PL, et al., 2019, Waste not, want not: CO2 (re)cycling into block polymers, Chemical Communications, ISSN: 1359-7345
<p>A new catalysis combining two different polymerisation mechanisms but using a single catalyst allows the efficient recycling of CO<sub>2</sub> and block polymer formation.</p>
Stoesser T, Mulryan D, Williams CK, 2018, Switch Catalysis To Deliver Multi-Block Polyesters from Mixtures of Propene Oxide, Lactide, and Phthalic Anhydride, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, Vol: 57, Pages: 16893-16897, ISSN: 1433-7851
Deacy AC, Durr CB, Garden JA, et al., 2018, Groups 1, 2 and Zn(II) Heterodinuclear Catalysts for Epoxide/CO2 Ring-Opening Copolymerization, INORGANIC CHEMISTRY, Vol: 57, Pages: 15575-15583, ISSN: 0020-1669
Durr CB, Williams CK, 2018, New Coordination Modes for Modified Schiff Base Ti(IV) Complexes and Their Control over Lactone Ring-Opening Polymerization Activity, INORGANIC CHEMISTRY, Vol: 57, Pages: 14240-14248, ISSN: 0020-1669
Regoutz A, Kerherve G, Villar-Garcia I, et al., 2018, The influence of oxygen on the surface interaction between CO2 and copper studied by ambient pressure X-ray photoelectron spectroscopy, SURFACE SCIENCE, Vol: 677, Pages: 121-127, ISSN: 0039-6028
Chen TTD, Zhu Y, Williams CK, 2018, Pentablock Copolymer from Tetracomponent Monomer Mixture Using a Switchable Dizinc Catalyst, MACROMOLECULES, Vol: 51, Pages: 5346-5351, ISSN: 0024-9297
Thevenon A, Cyriac A, Myers D, et al., 2018, Indium Catalysts for Low-Pressure CO2/Epoxide Ring-Opening Copolymerization: Evidence for a Mononuclear Mechanism?, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 140, Pages: 6893-6903, ISSN: 0002-7863
Stoesser T, Williams CK, 2018, Selective Polymerization Catalysis from Monomer Mixtures: Using a Commercial Cr-Salen Catalyst To Access ABA Block Polyesters, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, Vol: 57, Pages: 6337-6341, ISSN: 1433-7851
Zhu Y, Radlauer MR, Schneiderman DK, et al., 2018, Multiblock polyesters demonstrating high elasticity and shape memory effects, Macromolecules, Vol: 51, Pages: 2466-2475, ISSN: 0024-9297
Polyester block polymers containing polylactide have garnered significant attention as renewable, degradable alternatives to traditional elastomers. However, the low glass transition of the PLA blocks limits the upper-use temperatures of the resulting elastomers. To improve the thermal performance, we explore a series of multiblock polyesters composed of poly(ε-decalactone) (PDL) and poly(cyclohexene phthalate) (PCHPE). These materials are prepared using switchable polymerization catalysis followed by chain extension. The strategy involves (i) alternating ring-opening copolymerization (ROCOP) of cyclohexene oxide and phthalic anhydride, (ii) ε-decalactone ring-opening polymerization (ROP), and (iii) diisocyanate coupling of the telechelic triblocks to increase molar mass. The resulting multiblock polyesters are amorphous, and the blocks are phase separated; glass transition temperatures are ∼−45 and 100 °C. They show thermal resistance to mass loss with Td5% ∼ 285 °C and higher upper use temperatures compared to alternative aliphatic polyesters. The nanoscale phase behavior and correlated mechanical properties are highly sensitive to the block composition. The sample containing PCHPE = 26 wt % behaves as a thermoplastic elastomer with high elongation at break (εb > 2450%), moderate tensile strength (σb = 12 MPa), and low residual strain (εr ∼ 4%). It shows elastomeric behavior from −20 to 100 °C and has a processing temperature range of ∼170 °C. At higher PCHPE content (59 wt %), the material has shape memory character with high strain fixation (250%) and recovery (96%) over multiple (25) recovery cycles. The multiblock polyesters are straightforward to prepare, and the methods presented here can be extended to produce a wide range of new materials using a other epoxides, anhydrides, and lactones. This first report on the thermal and mechanical properties highlights the significant
Leung AHM, Pike SD, Clancy AJ, et al., 2018, Layered zinc hydroxide monolayers by hydrolysis of organozincs, CHEMICAL SCIENCE, Vol: 9, Pages: 2135-2146, ISSN: 2041-6520
2D inorganic materials and their exfoliated counterparts are both of fundamental interest and relevant for applications including catalysis, electronics and sensing. Here, a new bottom-up synthesis route is used to prepare functionalised nanoplatelets, in apolar organic solvents, via the hydrolysis of organometallic reagents; the products can be prepared in high yield, at room temperature. In particular, a series of layered zinc hydroxides, coordinated by aliphatic carboxylate ligands, were produced by the hydrolysis of diethyl zinc and zinc carboxylate mixtures, optimally at a molar ratio of [COOR]/[Zn] = 0.6. Layered zinc hydroxides coordinated by oleate ligands form high concentration solutions of isolated monolayers (3 nm thick x ∼ 26 nm) in apolar organic solvents (up to 23 mg mL−1 in toluene), as confirmed by both atomic force and transmission electron microscopies of deposited species. The high solubility of the product allows the synthetic pathway to be monitored directly in situ through 1H NMR spectroscopy. The high solubility also provides a route to solution deposition of active functional materials, as illustrated by the formation of nanoporous films of optically transparent porous zinc oxide (1 μm thickness) after annealing at 500 °C. This new organometallic route to 2D materials obviates common complications of top-down exfoliation syntheses, including sonochemical-degradation and low yields of aggregated polydispersed layers, and may potentially be extended to a wide range of systems.
Stosser T, Chen TTD, Zhu Y, et al., 2018, 'Switch' catalysis: from monomer mixtures to sequence-controlled block copolymers, PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 376, ISSN: 1364-503X
Garcia-Trenco A, Regoutz A, White ER, et al., 2018, PdIn intermetallic nanoparticles for the hydrogenation of CO2 to methanol, Applied Catalysis B: Environmental, Vol: 220, Pages: 9-18, ISSN: 0926-3373
Direct hydrogenation of CO2 to methanol could offer significant environmental benefits, if efficient catalysts can be developed. Here, bimetallic Pd-In nanoparticles show good performance as catalysts for this reaction. Unsupported nanoparticles are synthesised by the thermal decomposition of Pd(acetate)2 and In(acetate)3 precursors in a high boiling point solvent (squalane), followed by reduction using dilute H2 gas (210 °C). Adjusting the ratio of the two metallic precursors allow access to 5–10 nm nanoparticles with different phase compositions, including metallic Pd(0), In2O3 and intermetallic PdIn. Liquid phase methanol synthesis experiments (50 bar, 210 °C, H2:CO2 = 3:1) identify the intermetallic PdIn nanoparticles as the most efficient. The catalysts exhibit around 70% higher methanol rates (normalised to the overall molar metal content) compared to the conventional heterogeneous Cu/ZnO/Al2O3 catalyst (900 and 540 μmol mmolPdInorCuZnAl−1 h−1, respectively). In addition, the optimum Pd/In catalyst shows an improved methanol selectivity over the whole temperature range studied (190–270 °C), reaching >80% selectivity at 270 °C, compared to only 45% for the reference Cu/ZnO/Al2O3 catalyst. Experiments showed an improvement in stability; the methanol production rate declined by 20% after 120 h run for the optimum PdIn-based compared with 30% for the Cu/ZnO/Al2O3 catalyst (after 25 h). The optimum catalyst consists of ∼8 nm nanoparticles comprising a surface In-enriched PdIn intermetallic phase as characterised by XRD, HR-TEM, STEM-EDX and XPS. Post-catalysis analysis of the optimum catalyst shows that the same PdIn bimetallic phase is retained with only a slight increase in the nanoparticle size.
Stosser T, Li C, Unruangsri J, et al., 2017, Bio-derived polymers for coating applications: comparing poly(limonene carbonate) and poly (cyclohexadiene carbonate), POLYMER CHEMISTRY, Vol: 8, Pages: 6099-6105, ISSN: 1759-9954
Myers D, Witt T, Cyriac A, et al., 2017, Ring opening polymerization of macrolactones: high conversions and activities using an yttrium catalyst, POLYMER CHEMISTRY, Vol: 8, Pages: 5780-5785, ISSN: 1759-9954
Pike SD, Garcia-Trenco A, White ER, et al., 2017, Colloidal Cu/ZnO catalysts for the hydrogenation of carbon dioxide to methanol: investigating catalyst preparation and ligand effects, Catalysis Science and Technology, Vol: 7, Pages: 3842-3850, ISSN: 2044-4753
The production of methanol from CO2 hydrogenation is a promising potential route to a renewable liquid fuel and renewable energy vector. Herein, three distinct routes to make colloidal catalysts based on mixtures of Cu(0) and ZnO nanoparticles (NPs) and using low-temperature organometallic procedures are reported. The colloids are surface coordinated by a phosphinate ligand: dioctylphosphinate ([DOPA]−), which delivers a high solubility in organic solvents. Further, the synthetic routes allow fine control of the ZnO:Cu and ligand loadings. The catalysts are prepared by mixing small NPs (2 nm) of either Cu(0) or air-stable Cu2O NPs with ZnO NPs (3 nm), or by the synthesis of Cu(0) in presence of ZnO NPs (ZnO: 2 nm, Cu: 6 nm). The resulting colloidal catalysts are applied in the liquid phase hydrogenation of CO2 to methanol (210 °C, 50 bar, 3 : 1 molar ratio of CO2 : H2). The catalysts typically exhibit 3 times higher rates when compared to a heterogeneous Cu–ZnO–Al2O3 commercial catalyst (21 vs. 7 mmolMeOH gCuZnO−1 h−1). The characterisation of the post-catalysis colloids show clear Cu/ZnO interfaces (HR-TEM), which are formed under reducing conditions, as well as differences in the Cu(0) NP size (from 3 to 7 nm) and nanoscale restructuring of the catalysts. The combination of characterisation and catalytic results indicate that the activity is mostly dictated by the Cu(0) particle size and ligand loading. Smaller Cu(0) NPs exhibited lower turnover frequency (TOF) values, whereas higher ligand loadings ([DOPA]−:(Cu + Zn) of 0.2–1.1) lead to smaller Cu(0) NPs and reduce the formation of Cu/ZnO interfaces. UV-vis spectroscopy reveals that the Cu(0) NPs are more stable to oxidation under air after catalysis than beforehand, potentially due to migration of ZnO onto the Cu surface whilst under catalytic conditions.
Romain C, Garden JA, Trott G, et al., 2017, Di-Zinc-Aryl Complexes: CO2 Insertions and Applications in Polymerisation Catalysis, CHEMISTRY-A EUROPEAN JOURNAL, Vol: 23, Pages: 7367-7376, ISSN: 0947-6539
Marafie JA, Bradley DDC, Williams CK, 2017, Thermally Stable Zinc Disalphen Macrocycles Showing Solid-State and Aggregation-Induced Enhanced Emission, INORGANIC CHEMISTRY, Vol: 56, Pages: 5688-5695, ISSN: 0020-1669
Myers D, White AJP, Forsyth CM, et al., 2017, Phosphasalen Indium Complexes Showing High Rates and Isoselectivities in rac-Lactide Polymerizations, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, Vol: 56, Pages: 5277-5282, ISSN: 1433-7851
Saini PK, Fiorani G, Mathers RT, et al., 2017, Zinc versus Magnesium: Orthogonal Catalyst Reactivity in Selective Polymerizations of Epoxides, Bio-derived Anhydrides and Carbon Dioxide, CHEMISTRY-A EUROPEAN JOURNAL, Vol: 23, Pages: 4260-4265, ISSN: 0947-6539
Pike SD, White ER, Regoutz A, et al., 2017, Reversible Redox Cycling of Well-Defined, Ultrasmall Cu/Cu2O Nanoparticles, ACS Nano, Vol: 11, Pages: 2714-2723, ISSN: 1936-0851
Exceptionally small and well-defined copper (Cu) and cuprite (Cu2O) nanoparticles (NPs) are synthesized by the reaction of mesitylcopper(I) with either H2 or air, respectively. In the presence of substoichiometric quantities of ligands, namely, stearic or di(octyl)phosphinic acid (0.1–0.2 equiv vs Cu), ultrasmall nanoparticles are prepared with diameters as low as ∼2 nm, soluble in a range of solvents. The solutions of Cu NPs undergo quantitative oxidation, on exposure to air, to form Cu2O NPs. The Cu2O NPs can be reduced back to Cu(0) NPs using accessible temperatures and low pressures of hydrogen (135 °C, 3 bar H2). This striking reversible redox cycling of the discrete, solubilized Cu/Cu(I) colloids was successfully repeated over 10 cycles, representing 19 separate reactions. The ligands influence the evolution of both composition and size of the nanoparticles, during synthesis and redox cycling, as explored in detail using vacuum-transfer aberration-corrected transmission electron microscopy, X-ray photoelectron spectroscopy, and visible spectroscopy.
Garden JA, White AJP, Williams CK, 2017, Heterodinuclear titanium/zinc catalysis: synthesis, characterization and activity for CO2/epoxide copolymerization and cyclic ester polymerization, DALTON TRANSACTIONS, Vol: 46, Pages: 2532-2541, ISSN: 1477-9226
Garcia-Trenco A, White ER, Regoutz A, et al., 2017, Pd2Ga-Based Colloids as Highly Active Catalysts for the Hydrogenation of CO2 to Methanol, ACS Catalysis, Vol: 7, Pages: 1186-1196, ISSN: 2155-5435
Colloidal Pd2Ga-based catalysts are shown to catalyze efficiently the hydrogenation of CO2 to methanol. The catalysts are produced by the simple thermal decomposition of Pd(II) acetate in the presence of Ga(III) stearate, which leads to Pd0 nanoparticles (ca. 3 nm), and the subsequent Pd-mediated reduction of Ga(III) species at temperatures ranging from 210 to 290 °C. The resulting colloidal Pd2Ga-based catalysts are applied in the liquid-phase hydrogenation of carbon dioxide to methanol at high pressure (50 bar). The intrinsic activity is around 2-fold higher than that obtained for the commercial Cu-ZnO-Al2O3 (60.3 and 37.2 × 10–9 molMeOH m–2 s–1), respectively, and 4-fold higher on a Cu or Pd molar basis (3330 and 910 μmol mmolPd or Cu–1 h–1). Detailed characterization data (HR-TEM, STEM/EDX, XPS, and XRD) indicate that the catalyst contains Pd2Ga nanoparticles, of average diameters 5–6 nm, associated with a network of amorphous Ga2O3 species. The proportion of this Ga2O3 phase can be easily tuned by adjusting the molar ratio of the Pd:Ga precursors. A good correlation was found between the intrinsic activity and the content of Ga2O3 surrounding the Pd2Ga nanoparticles (XPS), suggesting that methanol is formed by a bifunctional mechanism involving both phases. The increase in the reaction temperature (190–240 °C) leads to a gradual decrease in methanol selectivity from 60 to 40%, while an optimum methanol production rate was found at 210 °C. Interestingly, unlike the conventional Cu-ZnO-Al2O3, which experienced approximately 50% activity loss over 25 h time on stream, the Pd2Ga-based catalysts maintain activity over this time frame. Indeed, characterization of the Pd/Ga mixture postcatalysis revealed no ripening of the nanoparticles or changes in the phases initially present.
Saini PK, Williams CK, 2017, Polymerisation catalysis using CO<inf>2</inf>: Dinuclear homogeneous catalysts, Modern Developments in Catalysis, Pages: 159-180, ISBN: 9781786341211
zhu Y, romain C, Williams CK, 2016, Sustainable polymers from renewable resources, Nature, Vol: 540, Pages: 354-362, ISSN: 0028-0836
Renewable resources are used increasingly in the production of polymers. In particular, monomers such as carbon dioxide, terpenes, vegetable oils and carbohydrates can be used as feedstocks for the manufacture of a variety of sustainable materials and products, including elastomers, plastics, hydrogels, flexible electronics, resins, engineering polymers and composites. Efficient catalysis is required to produce monomers, to facilitate selective polymerizations and to enable recycling or upcycling of waste materials. There are opportunities to use such sustainable polymers in both high-value areas and in basic applications such as packaging. Life-cycle assessment can be used to quantify the environmental benefits of sustainable polymers.
Pike S, White E, Shaffer M, et al., 2016, Simple Phosphinate Ligands Access New Zinc Clusters Identified in the Synthesis of Zinc Oxide Nanoparticles, Nature Communications, Vol: 7, ISSN: 2041-1723
The bottom-up synthesis of ligand-stabilised functional nanoparticles from molecular precursors is widely applied but difficult to study mechanistically. Here, we use 31P NMR spectroscopy to follow the trajectory of phosphinate ligands during the synthesis of a range of new ligated zinc oxo clusters, containing 4, 6 and 11 zinc atoms. Using an organometallic route, the clusters interconvert rapidly, and self-assemble in solution based on thermodynamic equilibria, rather than nucleation kinetics. These clusters are also identified, in situ, during the synthesis of phosphinate-capped zinc oxide nanoparticles. Unexpectedly, the ligand is sequestered to a stable Zn11 cluster during the majority of the synthesis and only becomes coordinated to the nanoparticle surface, in the final step. As well as a versatile and accessible route to new (optionally doped) zinc clusters, the findings provide a new understanding of the role of well-defined molecular precursors during the synthesis of small (2-4 nm) nanoparticles.
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