Metallically gradated silicon nanowire and palladium nanoparticle composites as robust hydrogenation catalysts

Advances and Challenges in Development of Transition Metal Catalysts for Heterogeneous Hydrogenation of Organic Compounds

Actual problems of development of catalysts for hydrogenation of heterocyclic compounds by hydrogen are summarized and discussed. The scope of review covers composites of nanoparticles of platinum group metals and 3d metals for heterogeneous catalytic processes. Such problems include increase of catalyst activity, which is important for reduction of precious metals content; development of new catalytic systems which do not contain metals of platinum group or contain cheaper analogues of Pd; control of factors which make influence on the selectivity of the catalysts; achievement of high reproducibility of the catalyst's performance and quality control of the catalysts. Own results of the authors are also summarized and described. The catalysts were prepared by decomposition of Pd0 and Ni0 complexes, pyrolysis of Ni2+ and Co2+ complexes deposited on aerosil and reduction of Ni2+ in pores of porous support in situ. The developed catalysts were used for hydrogenation of multigram batches of heterocyclic compounds.

Circularizing PET-G Multimaterials: Life Cycle Assessment and Techno-Economic Analysis

The recycling of multimaterials such as payment or access cards poses significant challenges. Building on previous experimental work demonstrating the feasibility of chemically recyclable payment cards made from glycol-modified poly(ethylene terephthalate) (PET-G), we use life cycle assessment and techno-economic analysis to investigate two chemical recycling scenarios and evaluate their potential environmental and economic benefits. Recovering all components from the depolymerized products (Scenario 1) achieves substantial environmental benefits across most categories, reducing global warming by up to 67% compared to only recovering major components (Scenario 2). However, the environmental benefits in Scenario 1 incur 69% higher total annualized costs, causing its profitability to be dependent on a minimum selling price of £13.4/kg for cyclohexanedimethanol and less than a 10% discount rate. In contrast, Scenario 2 is less sensitive to discount rate variation and thus a lower risk and more economically feasible option, albeit less environmentally sustainable.

Wastewater treatment: A universal, scalable and recyclable catalyst with adjustable activity for diverse dyes degradation

The growing concern over water shortage and pollution is propelling and accelerating the development of sewage treatment technologies. Among them, the catalytic hydrogenation method is highly recommended from a sustainable perspective, because it can turn toxic pollutants into valuable raw materials. The catalyst with excellent activity and stability plays a critical role in this "trash to treasure" approach. Herein, we proposed a novel economical, scalable and recyclable candidate catalyst, i.e., the copper nanoparticles supported on zinc oxide nanowire array (Cu-ZnO NWA), for realizing efficient and stable dye wastewater treatment. The salix argyracea-shaped Cu-ZnO NWA displays very outstanding universality and controllability towards the catalytic hydrogenation reactions of diverse dyes, owing to the fact that ZnO nanowire array not only offers a platform to realize stable and homogeneous dispersion of Cu nanoparticles, but also provides a large quantity of catalytically active sites. More attractively, its synthetic method can be facilely extended to various conductive substrates through combined electrodeposition and hydrothermal technique, showing its general applicability for the surface assembly of sewage treatment facilities. Benefiting from above advantages, this proposal offers an attractive approach for large-scale and continuous decolorization of dye wastewater, and presents a broad application prospect in the textile printing industry.

Green synthesis silver nanoparticles Bougainvillea glabra Choisy/LED light with high catalytic activity in the removal of methylene blue aqueous solution

In this study, we evaluated, in a pioneering way, the influence of wavelengths from the decomposition of white light on the production and physicochemical properties of silver nanoparticles (AgNPs). Bearing in mind a process of green synthesis, an extract of the bracts of Bougainvillea glabra Choisy (BgC) was used, a species native to tropical and subtropical regions and frequently used in ornamentation, possessing in its photochemical composition, biomolecules capable of acting as reducing agents for convert Ag⁺ to Ag⁰. We used light-emitting diodes (LED) to obtain the desired wavelengths (violet, blue, green, yellow, orange, and red) in the test called rainbow, and we evaluated the obtaining of AgNPs compared to white LED light, nature, and absence of light. In the rainbow assay, we obtained a gradual increase in the intensity of the plasmonic band resonance from the red wavelength (0.124 ± 0.067 a.u.) to violet (0.680 ± 0.199 a.u.), indicating a higher reaction yield in obtaining AgNPs. Smaller hydrodynamic sizes (approximately 150 nm) at more energetic wavelengths (violet, blue, and green) about less energetic wavelengths (yellow, orange, and red) (approximately 400 nm) were obtained. Analysis by SEM microscopy, FTIR spectroscopy, and X-ray diffraction indicates the presence of silver nanoparticles in all LED colors used together with white LED light and Laboratory light (natural light). Due to the high environmental demand to remove pollutants from water sources, including textile dyes, we applied AgNPs/BgC to remove methylene blue (MB) dye from an aqueous solution. A minimum removal percentage greater than 65%, with emphasis on formulations synthesized by the colors of violet LED (84.27 ± 2.65%) and orange LED (85.91 ± 1.95%), was obtained.

Solvated electron-induced synthesis of cyclodextrin-coated Pd nanoparticles: mechanistic, catalytic, and anticancer studies

Herein, using in situ generated solvated electrons in the reaction media, a highly time-efficient, one-pot green approach has been employed to synthesize palladium (Pd) nanoparticles (NPs) coated with a molecular assembly of α-cyclodextrin (α-CD). The appearance of a shoulder peak at 280 nm in the UV-Vis absorption spectra indicated the formation of Pd NPs, which was further confirmed from their cubic phase XRD pattern. The nanomorphology varied considerably as a function of the dose rate, wherein sphere-shaped NPs (average size ∼ 7.6 nm) were formed in the case of high dose rate electron-beam assisted synthesis, while nanoflakes self-assembled to form nanoflower-shaped morphologies in a γ-ray mediated approach involving a low dose rate. The formation kinetics of NPs was investigated by pulse radiolysis which revealed the formation of Pd-based transients by the solvated electron-induced reaction. Importantly, no interference of α-CD was observed in the kinetics of the transient species, rather it played the role of a morphology directing agent in addition to a biocompatible stabilizing agent. The catalytic studies revealed that the morphology of the NPs has a significant effect on the reduction efficiency of 4-nitrophenol to 4-aminophenol. Another important highlight of this work is the demonstration of the morphology-dependent anticancer efficacy of Pd NPs against lung and brain cancer cells. Notably, flower-shaped Pd NPs exhibited significantly higher cancer cell killing as compared to spherical NPs, while being less toxic towards normal lung fibroblasts. Nonetheless, these findings show the promising potential of Pd NPs in anticancer treatment.

Ultrahigh Metal Content Carbon-Based Catalyst for Efficient Hydrogenation of Furfural: The Regulatory Effect of Glycerol

The development of high-content non-noble metal nanocatalysts is important for multiphase catalysis applications. However, it is a challenge to solve the agglomeration in the preparation of high-content metal catalysts. In this paper, a carbon-based catalyst (Co@CN-G-600) with 71.28 wt % cobalt metal content was prepared using a new strategy of gas-phase carbon coating assisted by glycerol. The core of this strategy is to maintain the spacing of metallic cobalt by continuous replenishment of dissociated ligands during pyrolysis over gas-phase glycerol. This approach is also applicable to other non-noble metals. When Co@CN-G-600 was further used as a catalyst for the selective hydrogenation of furfural (FF) to prepare furfuryl alcohol (FOL), the yield of FOL was >99.9% under mild conditions of 80 °C, compared to only 8.23% catalytic yield at up to 130 °C for Co@CN-600 without glycerol. The excellent catalytic performance mainly lies in the fact that the introduction of glycerol modulates the size effect, electronic effect, and acidic site intensity of the high-content Co catalyst, which promotes the activation of FF and hydrogen. Meanwhile, the optimized specific surface area and pore structure by glycerol improve the accessibility of high-density active sites and promote more efficient mass transfer. In addition, the introduction of glycerol produced a graphitic carbon layer encapsulation structure relative to Co@CN-600, which substantially improved the cycling stability of the catalyst. This study resolves the paradox of high content and high dispersion of non-noble metal catalysts in the synthesis process and provides a general pathway and example for the preparation of stable high-content metal catalysts.

Si-H Surface Groups Inhibit Methacrylic Polymerization: Thermal Hydrosilylation of Allyl Methacrylate with Silicon Nanoparticles

Hydrogen-terminated silicon nanoparticles (H-SiNPs) inhibit anerobic thermal autopolymerization of methacrylates. When heated to 100 °C under an inert atmosphere, allyl methacrylate (AMA) was stable for at least 95 h in the presence of 1.2 wt % H-SiNPs, exhibiting less than 0.15% conversion, whereas the neat monomer solidified within 24 h (over 10% conversion after 34 h). A mechanism is proposed that is based on H-transfer from SiNPs to the thermally activated methacrylic dimer biradical, quenching autopolymerization. An analysis of SiNPs isolated after heating in AMA reveals the grafting of ester groups. Thermal hydrosilylation offers a facile way to attach an allyl group to the surface of SiNPs.

Supercritical Carbon Dioxide Treatment of Porous Silicon Increases Biocompatibility with Cardiomyocytes

Porous silicon is of current interest for cardiac tissue engineering applications. While porous silicon is considered to be a biocompatible material, it is important to assess whether post-etching surface treatments can further improve biocompatibility and perhaps modify cellular behavior in desirable ways. In this work, porous silicon was formed by electrochemically etching with hydrofluoric acid, and was then treated with oxygen plasma or supercritical carbon dioxide (scCO2). These processes yielded porous silicon with a thickness of around 4 μm. The different post-etch treatments gave surfaces that differed greatly in hydrophilicity: oxygen plasma-treated porous silicon had a highly hydrophilic surface, while scCO2 gave a more hydrophobic surface. The viabilities of H9c2 cardiomyocytes grown on etched surfaces with and without these two post-etch treatments was examined; viability was found to be highest on porous silicon treated with scCO2. Most significantly, the expression of some key genes in the angiogenesis pathway was strongly elevated in cells grown on the scCO2-treated porous silicon, compared to cells grown on the untreated or plasma-treated porous silicon. In addition, the expression of several apoptosis genes were suppressed, relative to the untreated or plasma-treated surfaces.

Catalytic Reductive Alkylation of Amines in Batch and Microflow Conditions Using a Silicon-Wafer-Based Palladium Nanocatalyst

We describe the development of the catalytic reductive alkylation of amines with aldehydes under the atmospheric pressure of H2 using a brush-like silicon-nanostructure-supported palladium nanoparticle composite (SiNS-Pd) as a silicon-wafer-based reusable heterogeneous catalyst. The present reaction of primary and secondary amines with various aliphatic and aromatic aldehydes in the presence of the catalyst (0.02-0.05 mol % Pd) gave the corresponding secondary and tertiary amines including Lomerizine and Aticaprant in a 68% quantitative yield without overalkylation. We also designed and fabricated a flow device equipped with SiNS-Pd for microflow reactions, which was applied to the gas-liquid-solid triphasic reaction system (i.e., H2 gas, a substrate solution, and a solid catalyst). A multigram-scale reaction of aniline and benzaldehyde was demonstrated to obtain N-benzylaniline (ca. 4 g/day), in which the internal volume of the flow channel was 43 μL, the residence time was approximately 1 s, and the turnover number (TON) reached 4.0 × 104 in a continuous 24 h run (1.7 × 103 h-1; 0.50 s-1).