Halloysite aluminosilicate nanotubes loaded with ruthenium particles were used as reactors for Fischer–Tropsch synthesis. To load ruthenium inside clay, selective modification of the external surface with ethylenediaminetetraacetic acid, urea, or acetone azine was performed. Reduction of materials in a flow of hydrogen at 400 °C resulted in catalysts loaded with 2 wt.% of 3.5 nm Ru particles, densely packed inside the tubes. Catalysts were characterized by N2-adsorption, temperature-programmed desorption of ammonia, transmission electron microscopy, X-ray fluorescence, and X-ray diffraction analysis. We concluded that the total acidity and specific morphology of reactors were the major factors influencing activity and selectivity toward CH4, C2–4, and C5+ hydrocarbons in the Fischer–Tropsch process. Use of ethylenediaminetetraacetic acid for ruthenium binding gave a methanation catalyst with ca. 50% selectivity to methane and C2–4. Urea-modified halloysite resulted in the Ru-nanoreactors with high selectivity to valuable C5+ hydrocarbons containing few olefins and a high number of heavy fractions (α = 0.87). Modification with acetone azine gave the slightly higher CO conversion rate close to 19% and highest selectivity in C5+ products. Using a halloysite tube with a 10–20-nm lumen decreased the diffusion limitation and helped to produce high-molecular-weight hydrocarbons. The extremely small C2–C4 fraction obtained from the urea- and azine-modified sample was not reachable for non-templated Ru-nanoparticles. Dense packing of Ru nanoparticles increased the contact time of olefins and their reabsorption, producing higher amounts of C5+ hydrocarbons. Loading of Ru inside the nanoclay increased the particle stability and prevented their aggregation under reaction conditions.
A scalable and efficient photocatalyst is a key factor for sustainable hydrogen production. For the first time, clay nanotube-templated mesoporous silica of MCM-41 type was used as an efficient carrier for photocatalytic nanoparticles. 4–5 nm CdS quantum dots (QDs) were synthesized in situ on the surface of this hierarchical aluminosilicate. The influence of the QD composition on the structural, spectral, and photocatalytic properties was investigated. A series of photocatalysts with various QD sizes (3.2–4.8 nm) and band gaps (2.46–2.66 eV) were obtained. Optimization of the CdS and cocatalyst (Ru) concentration resulted in an efficient visible light photocatalyst for hydrogen production. The photocatalytic activity was tested in an aqueous solution of Na2S/Na2SO3 under 30 W 450 nm diode illumination. The hydrogen evolution rate reached 2600 μmol/gcat·h (apparent quantum efficiency of 15%) for the system with 15.0 wt % of CdS doped with 0.2 wt % of Ru, which corresponds to the rate of hydrogen production of 17.1 mmol per hour counting on the active phase. The material demonstrated almost 100% efficiency of the catalytically active phase. It showed better catalytic activity in comparison to MCM-41 due to the hierarchical structure and presence of Al that stimulated electron transfer during the photocatalytic reaction.
Following nanoarchitectural approach, mesoporous halloysite nanotubes with internal surface composed of alumina were loaded with 5–6 nm RuCo nanoparticles by sequential loading/reduction procedure. Ruthenium nanoclusters were loaded inside clay tube by microwave-assisted method followed by cobalt ions electrostatic attraction to ruthenium during wetness impregnation step. Developed nanoreactors with bimetallic RuCo nanoparticles were investigated as catalysts for the Fischer-Tropsch process. The catalyst with 14.3 wt.% of Co and 0.15 wt.% of Ru showed high activity (СO conversion reached 24.6%), low selectivity to methane (11.9%), CO 2 (0.3%), selectivity to C 5+ hydrocarbons of 79.1% and chain growth index (α) = 0.853. Proposed nanoreactors showed better selectivity to target products combined with high activity in comparison to the similar bimetallic systems supported on synthetic porous materials. It was shown that reducing agent (NaBH 4 or H 2 ) used to obtain Ru nanoclusters at first synthesis step played a very important role in the reducibility and selectivity of resulting RuCo catalysts.
Inactivation of bacteria under the influence of visible light in presence of nanostructured materials is an alternative approach to overcome the serious problem of the growing resistance of pathogenic bacteria to antibiotics. Cadmium sulfide quantum dots are superefficient photocatalytic material suitable for visible light transformation. In this work, CdS nanoparticles with size of less than 10 nm (QDs) were synthesized on the surface of natural and synthetic mesoporous aluminosilicates and silicates (halloysite nanotubes, MCM-41, MCM-41/Halloysite, SBA-15). Materials containing 5–7 wt.% of CdS were characterized and tested as agents for photocatalytic bacteria degradation of Gram-positive S. aureus and Gram-negative E. coli with multiple antibiotic resistance. Eukaryotic cell viability tests were also conducted on the model cancer cells A 459. We found that the carrier affects prokaryotic and eukaryotic toxicity of CdS quantum dots. CdS/MCM-41/HNTs were assumed to be less toxic to eukaryotic cells and possess the most prominent photocatalytic antibacterial efficiency. Under visible light irradiation, it induced 100% bacterial growth inhibition at the concentration of 125 μg/mL and the bacteriostatic effect at the concentration of 63 μg/mL. CdS/MCM-41/HNTs showed 100% E. coli growth inhibition in the concentration of 1000 μg/mL under visible light irradiation.
The Fischer–Tropsch process is considered one of the most promising eco-friendly routes for obtaining synthetic motor fuels. Fischer–Tropsch synthesis is a heterogeneous catalytic process in which a synthesis gas (CO/H2) transforms into a mixture of aliphatic hydrocarbons, mainly linear alkanes. Recently, an important direction has been to increase the selectivity of the process for the diesel fraction. Diesel fuel synthesized via the Fischer–Tropsch method has a number of advantages over conventional fuel, including the high cetane number, the low content of aromatic, and the practically absent sulfur and nitrogen impurities. One of the possible ways to obtain a high yield of diesel fuel via the Fischer–Tropsch process is the development of selective catalysts. In this review, the latest achievements in the field of production of diesel via Fischer–Tropsch synthesis using catalysts are reviewed for the first time. Catalytic systems based on Al2O3 and mesoporous silicates, such as MCM-41, SBA-15, and micro- and mesoporous zeolites, are observed. Together with catalytic systems, the main factors that influence diesel fuel selectivity such as temperature, pressure, CO:H2 ratio, active metal particle size, and carrier pore size are highlighted. The motivation behind this work is due to the increasing need for alternative processes in diesel fuel production with a low sulfur content and better exploitation characteristics.
Fly ash by-products are emerging biocompatible fillers for a number of construction materials. The value of fly ash as a filler is higher if the content of hollow cenospheres is increased. Here we describe a new method for detection and sizing of fly ash spheres based on darkfield microscopy with hyperspectral image capture to perform white light interferometry. Our method is cost-effective and can provide rapid means for evaluating cenosphere content during the enrichment process. We show that fly ash cenospheres produce a strong oscillation over wavelength in optical recordings. The phenomenon is easiest to observe using microscope imaging techniques that preserve both spatial and spectral information. Frequency is observed to increase in direct proportion to the sphere diameter. The oscillation appears in light recorded from any focal plane on the sphere which indicates that the entire sphere is involved in sustaining the signal, making the detection of cenospheres of different size and displacement within a recording volume productive. There is no oscillation from nonspherical particles of fly ash or other material, so this detection method is highly selective for the cenospheres.
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