Ligand exchange in zirconocene dichloride–diethylzinc bimetallic systems

The reaction between zirconocene dichloride and excess diethylzinc in d-6-benzene solution was studied. It was found that the exchange reaction between Cp2ZrCl2 and Et2Zn is accompanied by the formation of such complexes as bis-(cyclopentadienyl)ethylzirconium chloride (EtZrCp2Cl), a zirconium-organozinc complex, and bis-(cyclopentadienyl)diethylzirconium (Et2ZrCp2). It was also found that as a result of ligand exchange in zirconocene dichloride–diethylzinc bimetallic systems, the zirconium-organozinc complex is formed in minor amounts. An assessment of the thermodynamic stability of the obtained products is given based on the results of DFT analysis. The description of the NMR spectral data of the obtained organozirconium complexes is carried out.

Ligand exchange in zirconocene dichloride–diethylzinc bimetallic systems

The reaction between zirconocene dichloride and excess diethylzinc in d-6-benzene solution was studied. It was found that the exchange reaction between Cp2ZrCl2 and Et2Zn is accompanied by the formation of such complexes as bis-(cyclopentadienyl)ethylzirconium chloride (EtZrCp2Cl), a zirconium-organozinc complex, and bis-(cyclopentadienyl)diethylzirconium (Et2ZrCp2). It was also found that as a result of ligand exchange in zirconocene dichloride–diethylzinc bimetallic systems, the zirconium-organozinc complex is formed in minor amounts. An assessment of the thermodynamic stability of the obtained products is given based on the results of DFT analysis. The description of the NMR spectral data of the obtained organozirconium complexes is carried out.

Shape and Size Control of Bimetallic PtX (X = Au, Ni, Sn) Nanoparticles

<p>Nanoparticles show interesting and novel properties compared to their bulk materials. These properties range from optical, magnetic, electronic to catalytic and can be influenced by shape, size and elemental composition. As the ability to control nanoparticle morphology is important in materials science these particles are actively researched. Moreover, by combining different metals multiple properties intrinsic to those elements can be accessed within a single system. This thesis describes general synthetic approaches and underlying theory in the formation of nanoparticles. Focusing on organic solution phase synthesis, pathways to control both size and shape of nanoparticles are discussed. The concept behind the formation and possible structures of bimetallic nanoparticles are explained. Additionally, a brief overview about used characterisation techniques such as transmission electron microscopy and x-ray diffraction are given. Metallic nanoparticles were formed using the organic solution phase synthesis within Fischer-Porter bottles. Elevated temperatures and the presence of hydrogen lead to thermal decomposition of the metallic precursor, reduction of formed metal ions and subsequent build-up of nanoparticles. For bimetallic nanoparticles the seed mediated growth technique is commonly used. By utilizing this technique bimetallic AuPt nanoparticles were formed. The impact of different surfactants, hydrogen pressure, precursors and reaction time upon the size, elemental composition and morphology of these bimetallic AuPt nanoparticles is investigated. The bimetallic structure is evaluated and experiments to control the growth of platinum onto the seed structures are conducted. Further research deals with the formation of hexagonal close packed (hcp) nickel nanoparticles. By altering the surfactant type and concentration nickel favours to crystallise in its hcp modification rather than its most common face-centred cubic (fcc) phase. It was found that nickel packing in this hcp crystal system is forming hourglass-shaped nanoparticles. These particles are further used in seed mediated growth experiments with a platinum precursor to achieve bimetallic nanoparticles to both exploit the catalytic activity of platinum as well as the magnetic moment of nickel. It is shown that the choice of reaction conditions is crucial to achieve growth onto the nickel surface. Moreover, it was found that these nanoparticles are only selectively coated by platinum on hcp {001} facets leading to exposure of both nickel and platinum surfaces. The key results are summarised and the exploited parameters evaluated. Also, perspectives for future research are discussed and a brief outlook for the application of the investigated bimetallic systems is given. Bimetallic tin-platinum nanoparticles were formed by coreduction of the respective tin and platinum containing metal precursors. Several metal sources for both tin and platinum were investigated upon their decomposition and the resulting nanoparticle shape and elemental composition. The formation of a bimetallic precursor containing a Pt-Sn bond is discussed. Further reaction parameters such as temperature and time are also investigated to eludicate their impact on the formed nanoparticles. Finally, the key results are summarised and the exploited parameters evaluated. Also, perspectives for future research are discussed and a brief outlook for the application of the investigated bimetallic systems is given. The discussion in Chapter 4 about selectively obtaining hcp Ni nanoparticles is shortened and a major focus is given on the platinum coating of these hourglass-shaped nanoparticles, as Lee et al. published a paper on "Shaped Ni nanoparticles with an unconventional hcp crystalline structure" (Chemical Communications, 2014, 50, 6353-6356) during the course of these studies, describing similar methods and findings as observed in this research.</p>

Shape and Size Control of Bimetallic PtX (X = Au, Ni, Sn) Nanoparticles

<p>Nanoparticles show interesting and novel properties compared to their bulk materials. These properties range from optical, magnetic, electronic to catalytic and can be influenced by shape, size and elemental composition. As the ability to control nanoparticle morphology is important in materials science these particles are actively researched. Moreover, by combining different metals multiple properties intrinsic to those elements can be accessed within a single system. This thesis describes general synthetic approaches and underlying theory in the formation of nanoparticles. Focusing on organic solution phase synthesis, pathways to control both size and shape of nanoparticles are discussed. The concept behind the formation and possible structures of bimetallic nanoparticles are explained. Additionally, a brief overview about used characterisation techniques such as transmission electron microscopy and x-ray diffraction are given. Metallic nanoparticles were formed using the organic solution phase synthesis within Fischer-Porter bottles. Elevated temperatures and the presence of hydrogen lead to thermal decomposition of the metallic precursor, reduction of formed metal ions and subsequent build-up of nanoparticles. For bimetallic nanoparticles the seed mediated growth technique is commonly used. By utilizing this technique bimetallic AuPt nanoparticles were formed. The impact of different surfactants, hydrogen pressure, precursors and reaction time upon the size, elemental composition and morphology of these bimetallic AuPt nanoparticles is investigated. The bimetallic structure is evaluated and experiments to control the growth of platinum onto the seed structures are conducted. Further research deals with the formation of hexagonal close packed (hcp) nickel nanoparticles. By altering the surfactant type and concentration nickel favours to crystallise in its hcp modification rather than its most common face-centred cubic (fcc) phase. It was found that nickel packing in this hcp crystal system is forming hourglass-shaped nanoparticles. These particles are further used in seed mediated growth experiments with a platinum precursor to achieve bimetallic nanoparticles to both exploit the catalytic activity of platinum as well as the magnetic moment of nickel. It is shown that the choice of reaction conditions is crucial to achieve growth onto the nickel surface. Moreover, it was found that these nanoparticles are only selectively coated by platinum on hcp {001} facets leading to exposure of both nickel and platinum surfaces. The key results are summarised and the exploited parameters evaluated. Also, perspectives for future research are discussed and a brief outlook for the application of the investigated bimetallic systems is given. Bimetallic tin-platinum nanoparticles were formed by coreduction of the respective tin and platinum containing metal precursors. Several metal sources for both tin and platinum were investigated upon their decomposition and the resulting nanoparticle shape and elemental composition. The formation of a bimetallic precursor containing a Pt-Sn bond is discussed. Further reaction parameters such as temperature and time are also investigated to eludicate their impact on the formed nanoparticles. Finally, the key results are summarised and the exploited parameters evaluated. Also, perspectives for future research are discussed and a brief outlook for the application of the investigated bimetallic systems is given. The discussion in Chapter 4 about selectively obtaining hcp Ni nanoparticles is shortened and a major focus is given on the platinum coating of these hourglass-shaped nanoparticles, as Lee et al. published a paper on "Shaped Ni nanoparticles with an unconventional hcp crystalline structure" (Chemical Communications, 2014, 50, 6353-6356) during the course of these studies, describing similar methods and findings as observed in this research.</p>

Effect of pH and Al Cations on Chromate Inhibition of Galvanic-Induced Corrosion of AA7050-T7451 Macro-Coupled to 316SS

The performance of chromate in protecting AA7050-T7451 coupled to 316SS in simulated fastener environments, including those representative of the boldly exposed surfaces and downhole conditions, was investigated utilizing a number of electrochemical and surface characterization techniques. The influence of pH and Al3+ on the galvanic coupling behavior and damage evolution on AA7050 as a function of chromate concentration were assessed. The degree of chromate inhibition was observed to decrease as pH decreased, owing to chromate speciation and reduced capacity to suppress the hydrogen evolution reaction (HER) compared to the oxygen reduction reaction (ORR). The addition of 0.1 M Al3+ significantly increased HER kinetics and produced a large buffer effect which overwhelmed the ability of chromate to slow damage propagation on AA7050. Assessment of cathodes indicated that Cu was more important than 316SS in driving damage initiation, but less active than 316SS in supporting high-rate damage propagation in simulated crevice environments. The implications of this study for actual bimetallic systems are discussed.

Synergistic Degradation of Methylene Blue By Novel Fe-Co Bimetallic Catalyst Supported On Waste Silica in Photo-Fenton-Like System

The environment is affected by agricultural, domestic, and industrial activities that lead to drastic problems such as global warming and wastewater generation. Wastewater pollution is of public concern, making the treatment of persistent pollutants in water and wastewater highly imperative. Several conventional treatment technologies have been applied to water and wastewater remediation, but each has numerous limitations. To address this issue, treatment using bimetallic systems has been extensively studied. Synergistic effects between the two metals are highly desirable because they usually offer enhanced activity, selectivity, and stability relative to their monometallic counterparts. In this study, a novel method to fabricate bimetallic Fe-Co catalyst supported on waste silica was investigated for the treatment of methylene blue dye as model pollutant. Under the optimum conditions of pHi 3.0, 3.0 mM H2O2, 1.0 g L-1 Fe-Co/SiO2 catalyst, and 20 mg L-1 initial dye concentration, the maximum response for the decoloration and mineralization efficiencies of methylene blue were 100% and 64.57%, respectively. Superoxide radical was unveiled to be the dominant reactive oxygen species in the photo-Fenton-like system over Fe-Co/SiO2 catalyst. Compared to the contrastive catalyst, the Fe-Co/SiO2 synthesized using fluidized-bed crystallization exhibited comparable decoloration and mineralization efficiencies, and relatively lower metal leaching.

Effect of boron on HEM radiant ignition characteristics

The paper presents the ignition characteristics of high-energy materials (HEMs) containing ammonium perchlorate, butadiene rubber, and a mixture of Al/B nanopowders with different component ratios. Bimetallic systems based on aluminum with boron increase the reactivity and intensify the ignition of boron particles, which helps to decrease the critical ignition conditions of HEMs during heating. It is shown that the use of systems based on aluminum-boron reduces the delay time (by 17–52 %) and the ignition temperature of propellants in comparison with a HEM containing aluminum powder, and increases the activation energy of HEM during radiant heating.

Combining Metal-Metal Cooperativity, Metal-Ligand Cooperativity and Chemical Non-Innocence in Diiron Carbonyl Complexes

Several metalloenzymes, including [FeFe]-hydrogenase, employ cofactors wherein multiple metal atoms work together with surrounding ligands that mediate heterolytic and concerted proton-electron transfer (CPET) bond activation steps. Herein, we report a new dinucleating PNNP expanded pincer ligand, which can bind two low-valent iron atoms in close proximity to enable metal-metal cooperativity (MMC). In addition, reversible partial dearomatization of the ligand’s naphthyridine core enables both heterolytic metal-ligand cooperativity (MLC) and chemical non-innocence through CPET steps. Thermochemical and computational studies show how a change in ligand binding mode can lower the bond dissociation free energy of ligand C(sp3)–H bonds by ~25 kcal mol-1. H-atom abstraction enabled trapping of an unstable intermediate, which undergoes facile loss of two carbonyl ligands to form an unusual paramagnetic (S = 1/2) complex containing a mixed-valent iron(0)-iron(I) core bound within a partially dearomatized PNNP ligand. Finally, cyclic voltammetry experiments showed that these diiron complexes show catalytic activity for the electrochemical hydrogen evolution reaction. This work presents the first example of a ligand system that enables MMC, heterolytic MLC and chemical non-innocence, thereby providing important insights and opportunities for the development of bimetallic systems that exploit these features to enable new (catalytic) reactivity.

Selective heterogeneous hydrodeoxygenation of acetophenone over monometallic and bimetallic Pt–Co catalyst

The hydrodeoxygenation (HDO) of acetophenone was evaluated in liquid phase and gas phase over monometallic Pt/SiO 2 , Co/SiO 2 and bimetallic Pt–Co/SiO 2 catalysts. The influence of reaction time and loading of the catalyst were analysed by following the conversion and products selectivity. Phenylethanol, cyclohexylethanone and cyclohexylethanol are the main products of reaction using the Pt/SiO 2 catalyst. By contrast, ethylbenzene and phenylethanol are the only products formed on the Co/SiO 2 and Pt–Co/SiO 2 catalysts. The bimetallic catalyst is more stable as a function of time and more active towards the HDO process than the monometallic systems. The presence of an organic solvent showed only minor changes in product yields with no effect on the product speciation. Periodic density functional theory analysis indicates a stronger interaction between the carbonyl group of acetophenone with Co than with Pt sites of the mono and bimetallic systems, indicating a key activity of oxophilic sites towards improved selectivity to deoxygenated products. This article is part of the theme issue ‘Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 2)’.