46 research outputs found

    Combination of natural betanidin dye with synthetic organic sensitiser towards dye-sensitised solar cell application

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    A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Materials Science and Engineering of the Nelson Mandela African Institution of Science and TechnologyBetanidins belong to natural red-purple pigments betacyanins, which experimentally demonstrated good light adsorption in a visible range and might be suitable for the dye sensitised solar cell (DSSCs). Instability is a well-known drawback of natural dyes, which impedes their use for DSSCs. A thermodynamic approach helps to understand the betanidin (Bd) instability which occurs due to spontaneous decarboxylation reaction with decarboxylated betanidin (dBd) formation. The study considers the improvement of the sensitiser’s functionality via combination of natural Bd/dBd dyes and synthetic 4- (Diphenylamino)phenylcyanoacrylic acid (L0) dye. Novel complex D–π–A organic dyes, L0–Bd and L0–dBd with structural isomers, have been designed via esterification reactions. The DFT/B3LYP5/6‒31G(d,p) approach has been used to compute geometry, vibrational spectra and thermodynamic characteristics of the individual isomers and their complexes with L0. Implementation of TD–DFT method aids in obtaining optoelectronic properties. The broader coverage of the solar spectrum with greater light-harvesting efficiency was achieved for the complexes compared to individual dyes. The dyes attachment to the semiconductor TiO2 was simulated in terms of different adsorption modes to hydrogenated (TiO2)6 cluster. Binding energies and electronic spectra of the dye@TiO2 systems were computed, and electron density distributions over frontier molecular orbitals analysed. Binding energy magnitudes varied within 15‒21 eV for the dye@TiO2 systems

    Density Functional Theory

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    Density Functional Theory (DFT) is a powerful technique for calculating and comprehending the molecular and electrical structure of atoms, molecules, clusters, and solids. Its use is based not only on the capacity to calculate the molecular characteristics of the species of interest but also on the provision of interesting concepts that aid in a better understanding of the chemical reactivity of the systems under study. This book presents examples of recent advances, new perspectives, and applications of DFT for the understanding of chemical reactivity through descriptors forming the basis of Conceptual DFT as well as the application of the theory and its related computational procedures in the determination of the molecular properties of different systems of academic, social, and industrial interest

    Carbon Ligands

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    Homogeneous catalysis owes its success, in large part, to the development of a wide range of ligands with well-defined electronic and steric properties, which have thus made it possible to adjust the behavior of many organometallic complexes. However, ligands used in catalysis have long been centered on elements of group 15, and it is only more recently that carbon ligands have proved to be valuable alternatives with the emergence of cyclic diaminocarbenes (NHC).This Special Issue aims to provide a contemporary overview of the advances in carbon ligand chemistry from fundamental aspects to applications

    Aspects of the chemistry of lead in multiphase soil model systems and the environment

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    Synthetic model soils were used to evaluate redistribution of Pb in both the three-stage sequential extraction procedure proposed by the Commission of the European Communities Bureau of Reference (BCR, now Standards, Measurements and Testing Programme) (1993) and the commonly-applied procedure of Tessier et al. (1979). Redistribution of Pb in both schemes was found to be substantial, sufficient to render meaningless any attempts to quantify the original phase associations of Pb in cases where these are not known. In the model systems, the manganese oxide (hausmannite) and humic acid phases were found to be responsible for most of this redistribution in both schemes. Despite the fact that both schemes allow severe Pb redistribution to occur, differences are apparent in the manner in which this occurs. Whereas Tessier et al.’s procedure in all cases yielded the highest recovery of Pb at the reducing step, the three-stage BCR procedure released the most Pb at the oxidizing step, in both cases irrespective of where it originated. These differences are attributable to a combination of high temperature (96 °C) and the presence of 25% v/v acetic acid in Tessier et al.’s reducing step. These conditions were found to reduce the sorptive capacity of humic acid by more than 50%, in addition to retaining more of the Pb in solution by complexation with acetate ions. Extensive redistribution in the three-stage BCR procedure was also observed in systems where natural soils were mixed with Pb-spiked synthetic phases. In keeping with the results relating to synthetic soil models, the organic matter and Fe/ Mn oxide fractions of the natural soils appear to dominate the redistribution of Pb during the extraction. Two approaches were tested in terms of their ability to counteract the redistribution of Pb. Each approach was applied to the first extraction step of the BCR scheme, which underwent a range of modifications. These involved the use of 6 distinct solid sequestering materials, and 5 dissolved complexing agents. The most promising of all the approaches are those which involve the two soluble structurally-distinct complexing agents cryptand 2.2.2 (a macrobicyclic ligand) and nitrilotriacetic acid (NT A). The addition of each ligand generally improved the percentages of Pb recovered from the multi-phase model soils, with Pb originally spiked on calcite. However, the effectiveness of the cryptand and NTA at inhibiting redistribution (at concentrations of 9 x 10⁻³ and 1 x 10⁻⁎ M, respectively) was dependent on the percentages (by weight) of the hausmannite and humic acid in each model system. In the presence of no more than 2% hausmannite, both cryptand and NTA could satisfactorily recover about 60% of the Pb, provided that the percentages of humic acid in the systems were not higher than 10% and 5%, respectively. The preliminary criteria for selecting a potentially useful soluble complexing agent suggested by the results of this study are that the ligand possess (a) a high stability constant for the ion involved, and (b) a semi-encapsulated metal binding site (which appears to inhibit direct surface extraction from occurring). It is desirable in the case of Pb to decrease the extraction time of the first step in the BCR scheme to minimize opportunity for redistribution. The modified extraction solution using the cryptand successfully recovered Pb from a mixture of Pb-spiked calcite and a “clean” natural soil. However, when applied to contaminated roadside soil and dust samples (in the absence of a spiked phase), the modified extraction solution did not significantly alter the recovery pattern of Pb, relative to the conventional extraction solution. This result may reflect the natural distribution of Pb in these samples. Four parks in the City of Hamilton were selected as monitoring sites for assessment of levels of Pb in roadside soil and street dust during the removal of leaded-petrol from the New Zealand market. Samples were collected every 2 - 3 months during November 1995 to September 1996. The mean concentrations of Pb in top 2 cm kerbside soil from all the parks reveal a slight downward trend (statistically significant in three parks) whereas those of the fine and coarse fractions of kerbside dust were oscillating

    Cornerstones in Contemporary Inorganic Chemistry

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    A collection of essential research articles and scientific reviews covering some of the most pertinent and topical areas of study that currently constitute Inorganic Chemistry in the early 21st century

    Microorganisms in the Deterioration and Preservation of Cultural Heritage

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    This open access book offers a comprehensive overview of the role and potential of microorganisms in the degradation and preservation of cultural materials (e.g. stone, metals, graphic documents, textiles, paintings, glass, etc.). Microorganisms are a major cause of deterioration in cultural artefacts, both in the case of outdoor monuments and archaeological finds. This book covers the microorganisms involved in biodeterioration and control methods used to reduce their impact on cultural artefacts. Additionally, the reader will learn more about how microorganisms can be used for the preservation and protection of cultural artefacts through bio-based and eco-friendly materials. New avenues for developing methods and materials for the conservation of cultural artefacts are discussed, together with concrete advances in terms of sustainability, effectiveness and toxicity, making the book essential reading for anyone interested in microbiology and the preservation of cultural heritage

    On the Predictive Power of Chemical Concepts

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    Many chemical concepts can be well defined in the context of quantum chemical theories. Examples are the electronegativity scale of Mulliken and Jaffe and the hard and soft acids and bases concept of Pearson. The sound theoretical basis allows for a systematic definition of such concepts. However, while they are often used to describe and compare chemical processes in terms of reactivity, their predictive power remains unclear. In this work, we elaborate on the predictive potential of chemical reactivity concepts, which can be crucial for autonomous reaction exploration protocols to guide them by first-principles heuristics that expoit these concepts.Comment: 23 pages, 1 figure, 1 tabl

    Synthesis, crystal structures and molecular modelling of rare earth complexes with bis(2-pyridylmethyl)amine and its derivatives : a quantum chemical investigation of ligand conformational space, complex intramolecular rearrangement and stability

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    Limited research has been performed on the coordination behaviour of hybrid aliphatic and heterocyclic polyamines with trivalent rare earth elements. The rare earth coordination properties of several Nalkylated derivatives of the tridentate ligand bis(2-pyridylmethyl)amine (DPA, HL1) backbone - involving the rare earth elements Y, La-Nd, Sm, Eu and Tb-Lu - have been investigated in this study However, the structural and energetic characteristics of DPA coordination with rare earth elements (REE) have not been studied thus far. Potential applications of DPA-based rare earth complexes are primarily dependent on their electronic and magnetic characteristics, which are affected weakly by the coordination environment, where potential applications may include use as Lanthanide Shift Reagents (LSR), Luminescence probes and small-molecule magnets (SMM). A systematic conformational search of DPA was carried out in this study in order to identify the global minimum conformer and for comparison of the free and coordinated geometries, using the M06(D3) functional belonging to the Density Functional Theory (DFT) family of model chemistries. An understanding of the aforementioned would play an important role in analysis of bulk characterization and the prediction of the reactivity of DPA. Final geometries and electronic energies were obtained from the ‘domain based local pair natural orbital’ (DLPNO)-Mþller-Plesset and -coupled cluster theoretical methods, as follows: DLPNO-CCSD(T0)/aug-cc-pVQZ//DLPNO-MP2/aug-cc-pVTZ. Fifteen Single-crystal X-ray diffractometer (SC-XRD) crystal structures of mononuclear rare earth chloride coordination complexes with DPA (RE = La-Nd, Sm, Eu, Tb-Lu and Y) were obtained and geometrically analysed in this study. Three isostructural series of constitutional isomers were identified, consisting of one series of nine-coordinate molecule (M1) and two series of eight-coordinate ion pairs (M2 and M3). This conformational diversity is most likely due the flexible nature of the DPA backbone, as well as the additional stability gained from reduced coordination spheres as a function of decreasing rare earth ionic radii across the lanthanide series (Lanthanide contraction). A Quantum Theory of Atoms-in-Molecules (QTAIM) topological analysis was performed in order to identify and characterise potential hydrogen bonding interactions in H-optimised crystal structures. The crystal structures of five dinuclear (RE = Tb-Tm) and two tetranuclear (RE = Yb and Lu) rare earth chloride complexes with DPA have also been structurally analysed. Furthermore, one mononuclear (RE = Dy), two dinuclear complexes (RE = Dy and Lu) with EtDPA, and one mononuclear complex with the DPA-derivative HL4 (RE = Dy) were structurally characterised. A DFT study of the theoretical interconversion of one real- and two hypothetical- mononuclear lanthanum containing isostructural series (cf. aforementioned crystal structures) was undertaken in order to gain a deeper understanding of the processes involved, in terms of the participating minimum energy paths (MEPs), intermediates and transition states – as determined via the Nudged-Elastic Band (NEB) procedure. This hypothesis is supported by the well-known conformational lability of rare earth complexes, due to the weak/minor covalency of their coordination bonds. An attempt was made to determine the respective energies of one real- and two hypothetical diamagnetic or ‘closed-shell’ constitutional isomers containing the rare earth ions La3+(M1), Y3+(M2) and Lu3+ (M3). It was assumed that the most stable isomers have a greater probability of being observed as the asymmetric unit of the complex crystal structure – assuming weak contributions of lattice or intermolecular interactions towards the geometry of the asymmetric unit

    Abstracts of the XL QUITEL Congress

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    Abstracts of the XL QUITEL Congres

    Dipicolinamide Ligands and Analogs for Lanthanides (Ln), Actinides (An) and Mercury (Hg) for Application to Nuclear Fuel Cycle Separations and Waste Management

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    Spent nuclear fuel (SNF) – or used nuclear fuel (UNF) – contains long-lived minor actinides such as 241Am, 245Cm, and 237Np, together with fission products that include lanthanides. Minor actinides are responsible for much of the radiotoxicity and heat generation that limits the capacity of geological repositories. Thus, removing minor actinides from UNF can reduce storage time required for decay to natural levels of activity by several orders of magnitude. Actinide(An)/Lanthanide(Ln) separation processes via solvent extraction by selective complexation with organic or aqueous ligands have to overcome difficulties due to similarities in their ionic radii for the +3 oxidation state. Actinide valence orbitals (5f) allow for a stronger covalent component in metal-ligand interactions with soft-donor ligands, as compared to the 4f orbitals in lanthanides. Therefore, we have synthesized ligands with soft-donor sites that can take advantage of slight differences in hardness between An(III) and Ln(III) for selective An3+ separations. We have investigated the binding and extraction properties of An and Ln with ligands that contain the C=O vs. the C=S group, specifically dipicolinamides vs. dithiopicolinamides. The S-donor thioamide ligand did not show strong binding towards Ln(III) in the UV-visible and NMR spectra in CH3CN, yet it was shown to extract Am(III) over Ln(III) from highly acidic solutions. Gas-phase studies and theoretical DFT calculations both showed stronger binding of An(III) vs. Ln(III) for the thioamide vs. the amide ligand in agreement with extraction results. Moreover, a dipyridine-dipicolinamide ligand was also used on an aqueous environment as a holdback reagent that keeps Am(III) selectively in the aqueous phase while HDEHP complexes Ln(III) in the organic phase, taking advantage of the difference on hardness between An(III) and Ln(III). Our dipicolinamide and dithiopicolinamide results open new possibilities for efficient waste transmutation processes and for minor actinide recycling that can increase uranium utilization. Aside from SNF, dithiopicolinamide ligands also showed promise for addressing the presence of mercury in cold war nuclear waste. As Hg is present in the nuclear waste tanks at the Savannah River Site in several forms, including organic Hg, the mercury problem has been of concern
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