Daria V. Andreeva

Self-Healing Anticorrosion Coatings Based on pH-Sensitive Polyelectrolyte/Inhibitor Sandwichlike Nanostructures

An anticorrosion layer of a smart polymer coating is developed. The nature and properties of the coating simultaneously provide three mechanisms of corrosion protection: passivation of the metal degradation by controlled release of an inhibitor, buffering of pH changes at the corrosive area by polyelectrolyte layers, and self-curing of the film defects due to the mobility of the polyelectrolyte constituents in the layer-by-layer assembly.

Smart self-repairing protective coatings

Nanocontainers with a shell possessing controlled release properties can be used to fabricate a new family of active coatings that can respond quickly to changes in the coating environment or the coatings integrity. The release of corrosion inhibitors encapsulated within nanocontainers is triggered by the corrosion process, which prevents the spontaneous leakage of the corrosion inhibitor out of the coating. Moreover, if different types of nanocontainers loaded with the corresponding active agents are incorporated simultaneously into a coating matrix, the coating can act in several different ways (e.g. antibacterial, anticorrosion and antistatic). This review presents methods for the fabrication of such nanocontainers, how they can encapsulate active material, and their permeability properties.

Cavitation Engineered 3D Sponge Networks and Their Application in Active Surface Construction

The design of the 3D architecture surfaces with both space- and time-dependent functionality (cell attraction, pH-trigged self-cleaning, antiseptic/disinfection) is in the focus. The innovative story includes: sonochemical surface activation, formation of feedback surface component (pH-responsible micelles), proof of responsive activity (time resolved cell adhesion and bacteria deactivation) and space adhesion selectivity (surface patterning).

Buffering polyelectrolyte multilayers for active corrosion protection

Polyelectrolyte multilayers successively deposited on an ultrasonically pre-treated metal surface demonstrate anticorrosion self-healing behaviour by the blocking of the corrosion processes without addition of any other inhibiting species due to their pH-buffering ability.

Efficient three-component coupling catalysed by mesoporous copper-aluminum based nanocomposites

Traditional synthesis methods for propargylamines have several drawbacks. A recently developed alternative route is the so-called “A3 coupling” in which an alkyne, an aldehyde, and an amine are coupled together. Typically, these reactions are catalysed by homogeneous gold salts, organogold complexes or silver salts. But these homogeneous catalysts are expensive and their separation is difficult. Here we report the discovery that solid Cu/Al/oxide mesoporous “sponges” are excellent A3 coupling catalysts. These materials are robust, inexpensive, and easy to make. They give good to excellent yields (87–97%) for a wide range of substrates. Being heterogeneous, these catalysts are also easy to handle and separate from the reaction mixture, and can be recycled with no loss of activity.

Large-Area Organization of pNIPAM-Coated Nanostars as SERS Platforms for Polycyclic Aromatic Hydrocarbons Sensing in Gas Phase

Here, a new surface enhanced Raman spectroscopy (SERS) platform suitable for gas phase sensing based on the extended organization of poly-N-isopropylacrylamide (pNIPAM)-coated nanostars over large areas is presented. This system yields high and homogeneous SERS intensities, and simultaneously traps organic chemical agents as pollutants from the gas phase. pNIPAM-coated gold nanostars were organized into parallel linear arrays. The optical properties of the fabricated substrates are investigated, and applicability for advanced sensing is demonstrated through the detection in the gas phase of pyrene traces, a well-known polyaromatic hydrocarbon.

Layer-by-Layer approaches for formation of smart self-healing materials

This review is focused on the current achievements in application of Layer-by-Layer techniques for formation of materials with self-healing properties. We addressed the questions related to choice of materials for the Layer-by-Layer deposition, general aspects of multilayer formation, deposition techniques, and the mechanisms of self-healing of the multilayers. Layer-by-Layer deposited polyelectrolytes, hydrogels, conducting polymers, inorganic particles, hybrid organic–inorganic particles, and healing agents show great potential in formation of self-healing materials. In general, a non-covalently bonded Layer-by-Layer system exhibits high mobility of its components in response to external stimuli (humidity, T, pH, ionic strength, light, etc.) and, thus, can restore its integrity and heal defects. The review highlights the recent examples of Layer-by-Layer based design of self-healing materials for corrosion protection and biomedical application.

Nanoengineered Metal Surface Capsules: Construction of a Metal‐Protection System

The novel encapsulation system based on a sonochemically formed porous metal layer, which is continuous with the bulk metal is presented. The high surface area of this layer allows the upload of active components (corrosion inhibitors, antiseptics, antibiotics, DNA fragments, etc.). We propose two types of encapsulation systems. According to the Type I system, the spontaneous release of loaded components from the surface capsules can be prevented through chemisorption of the component to the porous metal capsules due to presence of –OH groups. In the Type II encapsulation system, complex formation between an active component and polyelectrolyte can be used. Both encapsulation systems suggested here could solve crucial problems in surface engineering and surface protection: adhesion of a protective system to the surface and release of an active compound on demand.

Ultrasound-assisted design of metal nanocomposites

A one-step method was developed to produce metal nanocomposites from metal alloys under ultrasound irradiation. Systematic investigation of ultrasound effects on various metal particles reveals cavitation-induced recrystallization and oxidation of metals as main factors in the process. The fact that different metals react in dramatically different fashion towards ultrasound irradiation was exploited for the formation of nanoscale composites. Results from the application of ultrasound to formation of nanocatalysts are reported.

Novel and effective copper-aluminum propane dehydrogenation catalysts

The importance of solid catalysts for converting petro- and bulk chemicals is reflected in the sheer magnitude of their market size: catalysts’ sales topped nine billion dollars in 2009.[1] This large value mirrors also the increasing academic interest in heterogeneous catalysis research.[2] As far as bulk chemicals (such as ethene, propene, and their derivatives) are concerned, there is a strong demand for clean and inexpensive catalysts and synthesis processes.[3] There are two types of commonly used dehydrogenation catalysts: supported Cr oxides[4] and Pt-based[5] systems. The problem is that these catalysts are typically either rare and costly, or hazardous. Moreover, they perform well only at high temperatures[6] (typically at 500–600 °C) due to thermodynamic limitations.[7] Optimization studies have led to the inclusion of several promoters of which tin, especially in the combination with platinum as Pt–Sn/Al2O3 is one of the most popular. We report here the discovery of a new alternative catalyst for propane dehydrogenation which does not contain noble or hazardous metals. It is an oxidized porous Cu–Al alloy with a structure that is similar to Raney-type metals.[8] The Raney process, patented by Murray Raney in 1925 and commercialized by W.R. Grace & Co.,[9] is one of the most successful routes for making porous metals. The problem is that this process requires extreme conditions that often restrict the final outcome at the nanometric scale. Here we opted for a different approach, applying a modified version of the ultrasound pore formation method that we have recently reported: high-power ultrasound.[10] In a typical synthesis, Cu and Al beads are melted by using an electric arc. The resulting cake is then pulverized and sonicated in water. This gives a highly porous material containing pores predominantly at the micro-scale (see Figure 1 a and 1 b for a representative example; catalyst D).[11] Figure 1 c and 1 d shows transmission and scanning electron micrographs of such a catalyst. We hypothesize that the sonication creates pores in the Al component followed by surface oxidation (compare the XRD profiles (a) and (b) in Figure 2), whereas Cu supplies the active centers for the catalysis (vide infra). The thickness of the ultra thin oxide layer was estimated by using 3D field ion microscopy as less than 2.0 nm.[10a] Figure 1 Porous Al–Cu alloy D N2 adsorption/desorption isotherms (a), pore size distributions (b), scanning electron micrographs (c) and transmission electron micrograph (d). Figure 2 X-ray diffraction patterns of the porous Al-Cu catalyst D before (a) and after (b) ultrasound treatment (the JCPDS-ICDD standards are also included for ease of comparison). We prepared a series of catalysts with different Cu content (Table 1, entries 1–4), and found that using 25 wt % Cu (catalyst D) gave the most promising results. This catalyst was then activated under different conditions in an effort to optimize the preparation recipe (see entries 4–6). We see a reduction of conversion in the first minutes, probably reflecting some initial sintering and coke deposition (see Figure 3).[7], [12] After this short deactivation period, the catalyst maintains its steady-state activity (all values hereafter refer to the steady-state period). Our catalyst gave reasonable propane consumption rates already at 550 °C (see Table 1). Note that all the reactions gave very good reproducibility (±7 % for different samples from the same catalyst batch). However, if we look at the theoretical phase diagram of Al–Cu, we see that it shows an eutectic point at 548 °C.[13] True, our catalyst is not a pure Al–Cu alloy (since at least its surface is passivated with an oxide layer; see Figure 2). Nevertheless, we hypothesized that a partial melting occurs during the pre-treatment at 600 °C (and possibly even during the reaction at 550 °C). Even if only part of the catalyst were melting, it would be perforce the active part. This is because the first sites that would melt would be the high-energy kinks and breaks where catalysis usually happens.[14] Indeed, when we compared samples A and B that had less Cu but a larger particle size (typically>150 μm), we saw that these were more active than those with more copper but smaller sizes. To check this hypothesis, we prepared another batch of the same catalyst D, but this time activated at 400 °C (all other conditions identical). We then ran the dehydrogenation again, this time 200 degrees lower (i.e. at 350 °C). Excitingly, as Figure 3 shows, this catalyst gave greater conversions, reaching a stable 4 % on stream. This is equivalent to a constant rate of 0.83 mol h−1 g−1. This result is all the more remarkable considering the temperature difference: a 200 °C offset would be expected to slow down the reaction by approximately an order of magnitude (all other known catalysts are inactive under these conditions). For comparison purposes, we tested a standard Pt–Sn/Al2O3 catalyst under similar conditions. This catalyst has been shown in the available literature as the best in terms of activity/selectivity/stability for propane dehydrogenation.[15] Under the same reaction conditions, Pt–Sn/Al2O3 was practically inactive at 350 °C and gave less than 1 % conversion (<0.2 mol h−1 g−1) at 550 °C. Searching the literature, we did not find any reports on propane dehydrogenation over Cu/Al2O3. But, we note the increase in rate quoted by Sokolova et al.[16] when adding Cu to Pt/Al2O3. Table 1 Composition, surface area and initial dehydrogenation rate for Al–Cu catalysts A–D. Figure 3 Temporal propane conversion for catalyst D at 350 °C (•) and 550 °C (○). Inset: relationship between the catalyst space time (i.e. amount of catalyst per propane molar flow pass) and initial propane conversion. Note: the ... In conclusion, we show here that high-power ultrasound is a green chemistry tool for the synthesis of porous copper–aluminum frameworks stabilized by metal oxide. Furthermore, this material is inexpensive (production expenses are approximately 3 € per liter) and the method can be easily scaled-up by using different sonotrodes (or a series of them), as these may vary widely in size and shape. These new porous materials (or “metal sponges”) have an alloy bulk and an oxidized surface, and can catalyze propane dehydrogenation at low temperatures. Thanks to their high activity and because they contain no noble metals, they open exciting opportunities in low-temperature dehydrogenation catalysis for making bulk chemicals.