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Metals are often used in environments that are conducive to corrosion, which leads to a reduction in their mechanical properties and durability. Coatings are applied to corrosion-prone metals such as aluminum alloys to inhibit the destructive surface process of corrosion in a passive or active way. Standard anticorrosive coatings function as a physical barrier between the material and the corrosive environment and provide passive protection only when intact. In contrast, active protection prevents or slows down corrosion even when the main barrier is damaged. The most effective industrially used active corrosion inhibition for aluminum alloys is provided by chromate conversion coatings. However, their toxicity and worldwide restriction provoke an urgent need for finding environmentally friendly corrosion preventing systems. A promising approach to replace the toxic chromate coatings is to embed particles containing nontoxic inhibitor in a passive coating matrix. This work presents the development and optimization of effective anticorrosive coatings for the industrially important aluminum alloy, AA2024-T3 using this approach. The protective coatings were prepared by dispersing mesoporous silica containers, loaded with the nontoxic corrosion inhibitor 2-mercaptobenzothiazole, in a passive sol-gel (SiOx/ZrOx) or organic water-based layer. Two types of porous silica containers with different sizes (d ≈ 80 and 700 nm, respectively) were investigated. The studied robust containers exhibit high surface area (≈ 1000 m² g-1), narrow pore size distribution (dpore ≈ 3 nm) and large pore volume (≈ 1 mL g-1) as determined by N2 sorption measurements. These properties favored the subsequent adsorption and storage of a relatively large amount of inhibitor as well as its release in response to pH changes induced by the corrosion process. The concentration, position and size of the embedded containers were varied to ascertain the optimum conditions for overall anticorrosion performance. Attaining high anticorrosion efficiency was found to require a compromise between delivering an optimal amount of corrosion inhibitor and preserving the coating barrier properties. This study broadens the knowledge about the main factors influencing the coating anticorrosion efficiency and assists the development of optimum active anticorrosive coatings doped with inhibitor loaded containers.
Two examples of our biophotonic research utilizing nanoparticles are presented, namely laser-based fluoroimmuno analysis and in-vivo optical oxygen monitoring. Results of the work include significantly enhanced sensitivity of a homogeneous fluorescence immunoassay and markedly improved spatial resolution of oxygen gradients in root nodules of a legume species.
Functional nanoporous carbon-based materials derived from oxocarbon-metal coordination complexes
(2017)
Nanoporous carbon based materials are of particular interest for both science and industry due to their exceptional properties such as a large surface area, high pore volume, high electroconductivity as well as high chemical and thermal stability. Benefiting from these advantageous properties, nanoporous carbons proved to be useful in various energy and environment related applications including energy storage and conversion, catalysis, gas sorption and separation technologies. The synthesis of nanoporous carbons classically involves thermal carbonization of the carbon precursors (e.g. phenolic resins, polyacrylonitrile, poly(vinyl alcohol) etc.) followed by an activation step and/or it makes use of classical hard or soft templates to obtain well-defined porous structures. However, these synthesis strategies are complicated and costly; and make use of hazardous chemicals, hindering their application for large-scale production. Furthermore, control over the carbon materials properties is challenging owing to the relatively unpredictable processes at the high carbonization temperatures.
In the present thesis, nanoporous carbon based materials are prepared by the direct heat treatment of crystalline precursor materials with pre-defined properties. This synthesis strategy does not require any additional carbon sources or classical hard- or soft templates. The highly stable and porous crystalline precursors are based on coordination compounds of the squarate and croconate ions with various divalent metal ions including Zn2+, Cu2+, Ni2+, and Co2+, respectively. Here, the structural properties of the crystals can be controlled by the choice of appropriate synthesis conditions such as the crystal aging temperature, the ligand/metal molar ratio, the metal ion, and the organic ligand system. In this context, the coordination of the squarate ions to Zn2+ yields porous 3D cube crystalline particles. The morphology of the cubes can be tuned from densely packed cubes with a smooth surface to cubes with intriguing micrometer-sized openings and voids which evolve on the centers of the low index faces as the crystal aging temperature is raised. By varying the molar ratio, the particle shape can be changed from truncated cubes to perfect cubes with right-angled edges.
These crystalline precursors can be easily transformed into the respective carbon based materials by heat treatment at elevated temperatures in a nitrogen atmosphere followed by a facile washing step. The resulting carbons are obtained in good yields and possess a hierarchical pore structure with well-organized and interconnected micro-, meso- and macropores. Moreover, high surface areas and large pore volumes of up to 1957 m2 g-1 and 2.31 cm3 g-1 are achieved, respectively, whereby the macroscopic structure of the precursors is preserved throughout the whole synthesis procedure.
Owing to these advantageous properties, the resulting carbon based materials represent promising supercapacitor electrode materials for energy storage applications. This is exemplarily demonstrated by employing the 3D hierarchical porous carbon cubes derived from squarate-zinc coordination compounds as electrode material showing a specific capacitance of 133 F g-1 in H2SO4 at a scan rate of 5 mV s-1 and retaining 67% of this specific capacitance when the scan rate is increased to 200 mV s-1.
In a further application, the porous carbon cubes derived from squarate-zinc coordination compounds are used as high surface area support material and decorated with nickel nanoparticles via an incipient wetness impregnation. The resulting composite material combines a high surface area, a hierarchical pore structure with high functionality and well-accessible pores. Moreover, owing to their regular micro-cube shape, they allow for a good packing of a fixed-bed flow reactor along with high column efficiency and a minimized pressure drop throughout the packed reactor. Therefore, the composite is employed as heterogeneous catalyst in the selective hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran showing good catalytic performance and overcoming the conventional problem of column blocking.
Thinking about the rational design of 3D carbon geometries, the functions and properties of the resulting carbon-based materials can be further expanded by the rational introduction of heteroatoms (e.g. N, B, S, P, etc.) into the carbon structures in order to alter properties such as wettability, surface polarity as well as the electrochemical landscape. In this context, the use of crystalline materials based on oxocarbon-metal ion complexes can open a platform of highly functional materials for all processes that involve surface processes.
Conventional energy sources are diminishing and non-renewable, take million years to form and cause environmental degradation. In the 21st century, we have to aim at achieving sustainable, environmentally friendly and cheap energy supply by employing renewable energy technologies associated with portable energy storage devices. Lithium-ion batteries can repeatedly generate clean energy from stored materials and convert reversely electric into chemical energy. The performance of lithium-ion batteries depends intimately on the properties of their materials. Presently used battery electrodes are expensive to be produced; they offer limited energy storage possibility and are unsafe to be used in larger dimensions restraining the diversity of application, especially in hybrid electric vehicles (HEVs) and electric vehicles (EVs). This thesis presents a major progress in the development of LiFePO4 as a cathode material for lithium-ion batteries. Using simple procedure, a completely novel morphology has been synthesized (mesocrystals of LiFePO4) and excellent electrochemical behavior was recorded (nanostructured LiFePO4). The newly developed reactions for synthesis of LiFePO4 are single-step processes and are taking place in an autoclave at significantly lower temperature (200 deg. C) compared to the conventional solid-state method (multi-step and up to 800 deg. C). The use of inexpensive environmentally benign precursors offers a green manufacturing approach for a large scale production. These newly developed experimental procedures can also be extended to other phospho-olivine materials, such as LiCoPO4 and LiMnPO4. The material with the best electrochemical behavior (nanostructured LiFePO4 with carbon coating) was able to delive a stable 94% of the theoretically known capacity.