Show Abstract ▼

Abstract: The formation of different nickel, cobalt and copper layered hydroxide phases by a variety of solution and solid-state synthesis methods have been investigated. Initially, the preparative conditions were varied to generate single-phase products from metal(II) nitrate hexahydrate that were characterised by powder X-ray diffraction, vibrational spectroscopy and thermogravimetric analysis. As well as the β-M(OH)2 and α-M(OH)2 phases (where M = Ni, Co) two different hydroxynitrate phases with the generic formula M(OH)2-x(NO3)x materials were isolated with x = 0.67 and 1.0 (where M = Ni, Co). The reduction of symmetry of the nitrate anion from D3h to C2v can allow the alpha-phase to be distinguished from the two layered hydroxynitrate phases in both infrared and Raman spectroscopy. The symmetric N-O stretch enables the two hydroxynitrate phases to be distinguished through the sharp absorptions at ca. 1000 cm-1 (x = 0.67) and ca. 1050 cm-1 (x = 1.0). The TGA data of the pure phases showed key differences between the layered hydroxides, with anhydrous phases having singular weight losses over short temperature ranges while hydrated phases have multiple losses over larger ranges. Short-range characterisation techniques were used to characterise the poorly crystalline alpha-phases of nickel and cobalt together with beta-phase copper hydroxide, and the results compared with the three copper hydroxide minerals malachite, azurite and georgeite. Two synthetic forms of georgeite were also analysed, prepared by supercritical antisolvent precipitation with carbon dioxide and sodium carbonate precipitation. The alpha-phases and georgeite were both shown through infrared spectroscopic analysis to have uncoordinated nitrate and carbonate with D3h symmetry incorporated into the structures. Synchrotron X-ray pair distribution function analysis showed only short-range order (<15 Å) in the alpha-phases with only intralayer atom pair distances present. Shorter atom pair distances were observed for georgeite phases (<5 Å), but were matched to intralayer bond distances expected of alpha-phase type layered hydroxides of 2.0 Å and 3.0 Å. This redefines georgeite as an alpha-phase hydroxide for the first time contrary to the literature definition of a hydroxysalt phase. The disordering of beta-phase nickel hydroxide through the formation of stacking faults and interstratification was investigated by varying temperature and time using nickel(II) nitrate. Stacking faulted materials were formed at low temperature and identified by broadening of the 00l reflections while interstratified materials were identified through the splitting of the 001 into two lines. In contrast to interstratified materials presented in previous studies as alpha-phase and beta-phase layering, this work has shown through vibrational spectroscopy that layered hydroxysalts can also undertake the interstratification process. Standard mixtures of hydroxynitrate and beta-phase were prepared to investigate if the intensity of particular vibrational bands could be correlated with the proportion of the particular phases in mixtures. The intensity of the infrared bands at 990 cm-1 and the Raman bands at 1315 cm-1 were shown to correlate with content, theoretically providing a method to determine mixture compositions.

Show Abstract ▼

Abstract: Several organic–inorganic hybrid materials from the metal–organic framework (MOF) family have been shown to form stable liquids at high temperatures. Quenching then results in the formation of melt-quenched MOF glasses that retain the three-dimensional coordination bonding of the crystalline phase. These hybrid glasses have intriguing properties and could find practical applications, yet the melt-quench phenomenon has so far remained limited to a few MOF structures. Here we turn to hybrid organic–inorganic perovskites—which occupy a prominent position within materials chemistry owing to their functional properties such as ion transport, photoconductivity, ferroelectricity and multiferroicity—and show that a series of dicyanamide-based hybrid organic–inorganic perovskites undergo melting. Our combined experimental–computational approach demonstrates that, on quenching, they form glasses that largely retain their solid-state inorganic–organic connectivity. The resulting materials show very low thermal conductivities (~0.2 W m−1 K−1), moderate electrical conductivities (10−3–10−5 S m−1) and polymer-like thermomechanical properties.

Show Abstract ▼

Abstract: Current industrial production of ammonia from the Haber-Bosch process and its transport concomitantly produces a large quantity of CO2. Herein, we successfully synthesize inorganic-structure-based catalysts with [Fe-S2-Mo] motifs with a connecting structure similar to that of FeMoco (a cofactor of nitrogenase) by placing iron atoms on a single molecular layer of MoS2 at various loadings. This type of new catalytic material functionally mimics the nitrogenase to convert N2 to ammonia and hydrogen in water without adding any sacrificial agent under visible-light illumination. Using the elevated temperature boosts the ammonia yield and the energy efficiency by one order of magnitude. The solar-to-NH3 energy-conversion efficiency can be up to 0.24% at 270°C, which is the highest efficiency among all reported photocatalytic systems. This method of ammonia production and the photocatalytic materials may open up an exciting possibility for the decentralization of ammonia production for fertilizer provision to local farmlands using solar illumination.

Open Access

Show Abstract ▼

Abstract: A general method to carry out the fluorination of metal oxides with poly(tetrafluoroethylene) (PTFE, Teflon) waste by spark plasma sintering (SPS) on a minute scale with Teflon is reported. The potential of this new approach is highlighted by the following results. i) The tantalum oxyfluorides Ta3O7F and TaO2F are obtained from plastic scrap without using toxic or caustic chemicals for fluorination. ii) Short reaction times (minutes rather than days) reduce the process time the energy costs by almost three orders of magnitude. iii) The oxyfluorides Ta3O7F and TaO2F are produced in gram amounts of nanoparticles. Their synthesis can be upscaled to the kg range with industrial sintering equipment. iv) SPS processing changes the catalytic properties: while conventionally prepared Ta3O7F and TaO2F show little catalytic activity, SPS‐prepared Ta3O7F and TaO2F exhibit high activity for photocatalytic oxygen evolution, reaching photoconversion efficiencies up to 24.7% and applied bias to photoconversion values of 0.86%. This study shows that the materials properties are dictated by the processing which poses new challenges to understand and predict the underlying factors.

Open Access

Show Abstract ▼

Abstract: Defect engineering is a powerful tool that can be used to tailor the properties of metal–organic frameworks (MOFs). Here, we incorporate defects through ball milling to systematically vary the porosity of the giant pore MOF, MIL-100 (Fe). We show that milling leads to the breaking of metal–linker bonds, generating additional coordinatively unsaturated metal sites, and ultimately causes amorphisation. Pair distribution function analysis shows the hierarchical local structure is partially retained, even in the amorphised material. We find that solvents can be used to stabilise the MIL-100 (Fe) framework against collapse, which leads to a substantial retention of porosity over the non-stabilised material.