Shedding Light Onto the Nature of Iron Decorated Graphene and Graphite Oxide Nanohybrids for CO₂ Conversion at Atmospheric Pressure

We report on the design and testing of new graphite and graphene oxide‐based extended π‐conjugated synthetic scaffolds for applications in sustainable chemistry transformations. Nanoparticle‐functionalised carbonaceous catalysts for new Fischer Tropsch and Reverse GasWater Shift (RGWS) transformations were prepared: functional graphene oxides emerged from graphite powders via an adapted Hummer's method and subsequently impregnated with uniform‐sized nanoparticles. Then the resulting nanomaterials were imaged by TEM, SEM, EDX, AFM and characterised by IR, XPS and Raman spectroscopies prior to incorporation of Pd(II) promoters and further microscopic and spectroscopic analysis. Newly synthesised 2D and 3D layered nanostructures incorporating carbon‐supported iron oxide nanoparticulate pre‐catalysts were tested, upon hydrogen reduction in situ, for the conversion of CO2 to CO as well as for the selective formation of CH4 and longer chain hydrocarbons. The reduction reaction was also carried out and the catalytic species isolated and fully characterised. The catalytic activity of a graphene oxide‐supported iron oxide pre‐catalyst converted CO2 into hydrocarbons at different temperatures (305, 335, 370 and 405 °C), and its activity compared well with that of the analogues supported on graphite oxide, the 3‐dimensional material precursor to the graphene oxide. Investigation into the use of graphene oxide as a framework for catalysis showed that it has promising activity with respect to reverse gas water shift (RWGS) reaction of CO2 to CO, even at the low levels of catalyst used and under the rather mild conditions employed at atmospheric pressure. Whilst the γ‐Fe2O3 decorated graphene oxide‐based pre‐catalyst displays fairly constant activity up to 405 °C, it was found by GC‐MS analysis to be unstable with respect to decomposition at higher temperatures. The addition of palladium as a promoter increased the activity of the iron functionalised graphite oxide in the RWGS. The activity of graphene oxide supported catalysts was found to be enhanced with respect to that of iron‐functionalised graphite oxide with, or without palladium as a promoter, and comparable to that of Fe@carbon nanotube‐based systems tested under analogous conditions. These results display a significant step forward for the catalytic activity estimations for the iron functionalised and rapidly processable and scalable graphene oxide. The hereby investigated phenomena are of particular relevance for the understanding of the intimate surface morphologies and the potential role of non‐covalent interactions in the iron oxide‐graphene oxide networks, which could inform the design of nano‐materials with performance in future sustainable catalysis applications

Radio- and nano-chemistry of aqueous Ga(iii) ions anchored onto graphene oxide-modified complexes

The gallium-68 radiolabelling of new functional graphene oxide composites is reported herein along with kinetic stability investigations of the radio-nanohybrids under different environments and insights into their surface characteristics by SEM and XPS. The present work highlights the potential of graphene oxides as nanocarriers for small molecules such as bis(thiosemicarbazonato) complexes to act as multifunctional platforms for rapid and effective radioimaging agent incorporation

Synthesis of a new zwitterionic cyclopentadienyl-imidazolium compound and isolation of the 3,3'-(trans-3,5-cyclopentenyl)-di(1-tert-butylimidazolium)bromide intermediate

The new zwitterionic compound 1-tert-butylimidazolium-cyclopentadienylide, shown to have a polar ground state and a non-polar fulvene-like excited state, has been synthesised and the intermediate 3,3'-(trans-3,5-cyclopentenyl)di(1-tert-butylimidazolium)bromide isolated and structurally characterised. (C) 2004 Elsevier Ltd. All rights reserved

Synthesis of a new bidentate ferrocenyl N-heterocyclic carbene ligand precursor and the palladium (II) complex trans-[PdCl2(C over cap fc over cap C)], where (C over cap fc over cap C)=1,1 `-di-tert-butyl-3,3 ` (1,1 `-dimethyleneferrocenyl)-diimidazol-2-ylidene

A new ferrocenyl-N-heterocyclic carbene ligand precursor 1,1′-bis[(1-tert-butylimidazolium)-3-methyl]ferrocene dichloride has been synthesised and structurally characterised. The imidazolium salt was readily deprotonated in situ with KN(SiMe3)2 and reacted with [PdCl2 (cod)] to afford the structurally characterised palladium (II) complex trans-[PdCl2(C∧fc∧C)], where (cod) = 1,5-cyclooctadiene and (C∧fc∧C) = 1,1′-di-tert-butyl-3,3′-(1,1′-dimethyleneferrocenyl)-diimidazol-2-ylidene

Silicon containing ferrocenyl phosphane ligands

New ferrocenyl phosphane ligands incorporating Si-P linkages, [(eta-C5H4SiMe2PR2)(2)Fe], where R= Ph and Me, and the corresponding metal complexes [Mo(CO)(4)(L)] have been prepared and characterised. The molecular structures of [(eta-C5H4SiMe2PR2)(2)Fe], where R =Ph and Me have been determined by single crystal X-ray diffraction. (C) 2003 Elsevier B.V. All rights reserved

Noncovalent interactions within a synthetic receptor can reinforce guest binding

Structural and thermodynamic data are presented on the binding properties of anion receptors containing two covalently linked cyclopeptide subunits that bind sulfate and iodide anions with micromolar affinity in aqueous solution. A synchrotron X-ray crystal structure of the sulfate complex of one receptor revealed that the anion is bound between the peptide rings of the biscyclopeptide. Intimate intramolecular contacts between the nonpolar surfaces of the proline rings of the individual receptor moieties in the complex suggest that hydrophobic interactions within the receptor that do not directly involve the guest contribute to complex stability. This finding is supported by a microcalorimetric analysis of the solvent dependence of complex stability, which showed that increasing the water content of the solvent has only a weak influence on the Gibbs energy of binding. Hence, the increasing amount of energy required for desolvating the binding partners in solutions containing more water is almost compensated by the increasingly favorable hydrophobic interactions. Further observations that suggest that guest-induced intra-receptor interactions contribute to guest binding are (i) anion binding of a monomeric cyclopeptide lacking the covalent linkage between the two rings leads to the formation of 2:1 complexes; (ii) in the crystal structure of the 2:1 iodide complex of this monotopic receptor, a similar arrangement of the two cyclopeptide rings has been found as in the sulfate complex of the biscyclopeptide; (iii) complex formation of the monomeric cyclopeptide in aqueous solution is highly cooperative with a large stability constant corresponding to the formation of the 2:1 complexes from relatively instable 1:1 complexes; (iv) the monomeric cyclopeptide forms only 1:1 anion complexes in DMSO where hydrophobic interactions do not take place; and (v) introducing polar hydroxy groups on the proline rings of the monomeric cyclopeptide disrupts cooperativity causing the formation of only 1:1 complexes even in aqueous solution. Taken together these observations demonstrate that, in addition to direct receptor-substrate interactions, noncovalent interactions between the two subunits of such biscyclopeptides contribute significantly to anion complex stability. Reinforcement of molecular recognition through intra-receptor interactions should be an attractive new strategy to boost host-guest affinities