Layered double hydroxides (LDHs), also known as hydrotalcite-like materials or anionic clays, are an important class of layered materials. Various studies show that LDHs have a wide range of applications in industry, e.g., catalyst precursors, ion exchangers, adsorbents for environmental contaminants, and substrates for the immobilization of biological material. [1][2][3][4] However, for the purpose of developing novel innovative applications of LDHs as materials for chemical sensors, [5,6] clay-modified electrodes, [7,8] corrosion-resistant coatings, [9,10] membrane catalysis, or components in optical and magnetic devices, intensive studies have been conducted aimed at organizing LDH microcrystals into large uniformly aligned 2D arrays or films. Several methods have been employed to fabricate LDH films on different substrates thus far. For example, LDH microcrystals have been deposited on indium-doped SnO 2 coated glass, platinum disks, and gold electrode surfaces from colloidal suspensions in order to prepare LDH films for electrode modification by deposition [11,12] and Langmuir-Blodgett methods. [8] Most of the films obtained, however, were not oriented or uniformly aligned as it is hard to control the LDH crystallite orientation using these methods. Recently, new techniques have been reported for the fabrication of oriented LDH films. Pinnavaia and co-workers found that colloidal suspensions of LDHs obtained through hydrolysis of LDH/methoxide were able to form transparent and smooth films, [13] in which the LDH microcrystals were extremely well oriented. By employing ultrasonification, Jung and co-workers obtained a monolayer of LDH films with a high packing density and a preferred orientation with the c-axis perpendicular to the substrate surface (ab-face parallel). [14,15] However, this route did not allow control of the orientation of the LDH microcrystals with respect to the substrate plane because of the intrinsic propensity of the microcrystals to align in an orientation that leads to maximum faceto-face contact between the crystals and the substrate. In spite of the progress made during the last decade in research on LDH films and their crystal orientation, there has been no synthetic method for directly growing uniformly aligned LDH polycrystalline films from a substrate. Growing thin films directly from a substrate considerably improves the adherence and the mechanical stability of the resulting thin film, compared to colloidal-deposition techniques (for example, spin-coating, dip-coating, and screen-printing).[16] Therefore, the exploration of new approaches to fabricate oriented LDH films on substrates is of significant importance. Among the existing synthetic methods to fabricate inorganic films, hydrothermal synthesis shows high flexibility in terms of control of the structure and morphology of the resulting inorganic materials. It is also a well-known pathway for fabricating inorganic films with the desired micro-or nanostructure and controlled crystal orientation. Our group has recently repor...
Shiga toxin (Stx) is the key virulent factor in Shiga toxin-producing Escherichia coli (STEC). To date, three Stx1 subtypes and seven Stx2 subtypes have been described in E. coli, which differed in receptor preference and toxin potency. Here, we identified a novel Stx2 subtype designated Stx2h in E. coli strains isolated from wild marmots in the Qinghai-Tibetan plateau, China. Stx2h shares 91.9% nucleic acid sequence identity and 92.9% amino acid identity to the nearest Stx2 subtype. The expression of Stx2h in type strain STEC299 was inducible by mitomycin C, and culture supernatant from STEC299 was cytotoxic to Vero cells. The Stx2h converting prophage was unique in terms of insertion site and genetic composition. Whole genome-based phylo- and patho-genomic analysis revealed STEC299 was closer to other pathotypes of E. coli than STEC, and possesses virulence factors from other pathotypes. Our finding enlarges the pool of Stx2 subtypes and highlights the extraordinary genomic plasticity of E. coli strains. As the emergence of new Shiga toxin genotypes and new Stx-producing pathotypes pose a great threat to the public health, Stx2h should be further included in E. coli molecular typing, and in epidemiological surveillance of E. coli infections.
Solar-driven carbonylation with CO2 replacing toxic CO as a C1 source is of considerable interest; however it remains a great challenge due to the inert CO2 molecule. Herein, we integrate cobalt single-site and ultrafine CuPd nanocluster catalysts into a porphyrin-based metal–organic framework to construct composite photocatalysts (Cu1Pd2) z @PCN-222(Co) (z = 1.3, 2.0, and 3.0 nm). Upon visible light irradiation, excited porphyrin can concurrently transfer electrons to Co single sites and CuPd nanoclusters, providing the possibility for coupling CO2 photoreduction and Suzuki/Sonogashira reactions. This multicomponent synergy in (Cu1Pd2)1.3@PCN-222(Co) can not only replace dangerous CO gas but also dramatically promote the photosynthesis of benzophenone in CO2 with over 90% yield and 97% selectivity under mild condition. Systematic investigations clearly decipher the function and collaboration among different components in these composite catalysts, highlighting a new insight into developing a sustainable protocol for carbonylation reactions by employing greenhouse gas CO2 as a C1 source.
in Wiley InterScience (www.interscience.wiley.com).Activated layered double hydroxides (LDHs) with high crystallinity, obtained by calcination/rehydration of LDH precursors synthesized by urea decomposition, have higher catalytic activity in acetone self-condensation and Knoevenagel reactions than less crystalline materials obtained from LDH precursors synthesized by titration coprecipitation. The activated LDHs possess both basic and acidic sites. High resolution transmission electron microscopy (HRTEM) confirms that the highly crystalline activated LDHs retain the lattice structure of the LDH precursors with lattice parameters a ¼ b ¼ 0.31 6 0.01 nm and a ¼ 60 6 28. An acid-base catalytic mechanism has been proposed to interpret the catalytic behavior based on the fact that acid-base hydroxyl group pairs on the activated LDH surface have a separation of 0.31 nm. It is proposed that the active sites are mainly located on the ordered array of hydroxyl sites on the basal surfaces rather than on the edges, as has been previously suggested.
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