A Palladium-Nanoparticle and Silicon-Nanowire-Array Hybrid: A Platform for Catalytic Heterogeneous Reactions

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.

Photoisomerization of Sulindac and Ozagrel Hydrochloride by Vitamin B2 Catalyst Under Visible Light Irradiation

PURPOSE

Photoisomerization of the E/Z-alkene structures of drugs is a matter of concern as it could result in potency loss and adverse side effects. This study focused on light-induced isomerization of sulindac and ozagrel hydrochloride catalyzed by concomitant vitamin B₂ under light-emitting diode (LED) or fluorescent light.

METHODS

In the presence of 0.05/0.03 equivalents of vitamin B₂/flavin adenine dinucleotide (FAD), sulindac or ozagrel hydrochloride was irradiated with LED light (405 nm) or fluorescent light. The photoisomerization in CD₃OD and D₂O was monitored by ¹H NMR spectroscopy.

RESULTS

Sulindac and ozagrel hydrochloride isomerized in the presence of a catalytic amount of vitamin B₂ or FAD under irradiation of 405 nm LED light and fluorescent light. Irradiation with LED light was found to be more effective than fluorescent light irradiation. The rate of photoisomerization was affected by the solvent, and the reaction in CD₃OD proceeded faster than in D₂O. Furthermore, ozagrel hydrochloride was more prone to isomerization than sulindac.

CONCLUSION

The catalytic activity of vitamin B₂ or FAD was demonstrated in the photoisomerization reaction of sulindac and ozagrel hydrochloride. Considering that the rate of photoisomerization in D₂O is very slow, the possibility of the occurrence of photoisomerization during clinical use is low. However, this study suggests that the interfusion of vitamin B₂ or FAD under excessive light exposure should be avoided as a caution during intravenous administration of sulindac or ozagrel hydrochloride.

Replacing Metals with Oxides in Metal-Assisted Chemical Etching Enables Direct Fabrication of Silicon Nanowires by Solution Processing

Metal-assisted chemical etching (MACE) has emerged as an effective method to fabricate high aspect ratio nanostructures. This method requires a catalytic mask that is generally composed of a metal. Here, we challenge the general view that the catalyst needs to be a metal by introducing oxide-assisted chemical etching (OACE). We perform etching with metal oxides such as RuO₂ and IrO₂ by transposing materials used in electrocatalysis to nanofabrication. These oxides can be solution-processed as polymers exhibiting similar capabilities of metals for MACE. Nanopatterned oxides can be obtained by direct nanoimprint lithography or block-copolymer lithography from chemical solution on a large scale. High aspect ratio silicon nanostructures were obtained at the sub-20 nm scale exclusively by cost-effective solution processing by halving the number of fabrication steps compared to MACE. In general, OACE is expected to stimulate new fundamental research on chemical etching assisted by other materials, providing new possibilities for device fabrication.

Microfluidic synthesis of high-valence programmable atom-like nanoparticles for reliable sensing

Synthesis of programmable atom-like nanoparticles (PANs) with high valences and high yields remains a grand challenge. Here, a novel synthetic strategy of microfluidic galvanic displacement (μ-GD) coupled with microfluidic DNA nanoassembly is advanced for synthesis of single-stranded DNA encoder (SSE)-encoded PANs for reliable surface-enhanced Raman scattering (SERS) sensing. Notably, PANs with high valences (e.g., n-valence, n = 12) are synthesized with high yields (e.g., >80%) owing to the effective control of interfacial reactions sequentially occurring in the microfluidic system. On the basis of this, we present the first demonstration of a PAN-based automatic analytical platform, in which sensor construction, sample loading and on-line monitoring are carried out in the microfluidic system, thus guaranteeing reliable quantitative measurement. In the proof-of-concept demonstration, accurate determination of tetracycline (TET) in serum and milk samples with a high recovery close to 100% and a low relative standard deviation (RSD) less than 5.0% is achieved by using this integrated analytical platform.

The Hydrophobic Effect Applied to Organic Synthesis: Recent Synthetic Chemistry "in Water"

Recent developments over the past few years in aqueous micellar catalysis are discussed. Applications to problems in synthesis are highlighted, enabled by the use of surfactants that self-aggregate in water into micelles as nanoreactors. These include amphiphiles that have been available for some time, as well as those that have been newly designed. Reactions catalyzed by transition metals, including Pd, Cu, Rh, and Au, are of particular focus.

Nanosheet Array-Like Palladium-Catalysts Pdx/rGO@CoAl-LDH via Lattice Atomic-Confined in Situ Reduction for Highly Efficient Heck Coupling Reaction

A series of novel nanosheet array-like catalysts Pd_x/rGO@CoAl-LDH (x = 0.0098-1.9, refers to Pd loading in wt % on ICP, rGO: reduced graphene oxide, LDH: layered double hydroxide) were first prepared via a simple and green lattice atomic-confined in situ reduction of oxidative Pd precursors by the evenly atomic-dispersed reductive Co²⁺ sites on LDH layers of a nanohybrid rGO@CoAl-LDH with hexagonal LDH nanoplates (∼73 × 7 nm) interdigitated vertical to the surfaces of rGO layer in both sides, fabricated through a simple citric acid-assisted aqueous-phase coprecipitation method. The as-obtained Pd catalysts possess clean Pd nanoclusters (NCs) with tunable sizes in 1.3-1.8 nm on varied Pd loadings. All the Pd_x/rGO@CoAl-LDH catalysts show excellent activities for the Heck reaction, and the Pd_0.0098/rGO@CoAl-LDH with the ultrafine Pd NCs of 1.3 ± 0.2 nm yields a maximum turnover frequency of 160 000 h^-1 over a heterogeneous catalyst so far. The excellent activities can be attributed to the ultrasmall Pd NCs with high dispersion and clean Pd surfaces, increased electron transfer capacity and surface area, and remarkable Pd-CoAl-LDH-rGO three-phase synergistic effect of the present unique nanosheet array-like Pd NCs catalysts. Moreover, the catalyst Pd_0.33/rGO@CoAl-LDH shows a broad range of substrate applicability and can be reused more than five runs without obvious loss of activity, giving the present catalysts long-term stability. These findings make the rGO@CoAl-LDH hybrid prepared by a facile and scalable synthesis route a universal green platform to support other noble or nonprecious metal NCs via lattice atomic-confined in situ reduction strategy to construct more desired heterogeneous catalysts.

Functionalization of silicon nanowire arrays by silver nanoparticles for the laser desorption ionization mass spectrometry analysis of vegetable oils

In this work, novel hybrid nanostructured surfaces, consisting of dense arrays of silicon nanowires (SiNWs) functionalized by Ag nanoparticles (AgNP/SiNWs), were used for the laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF MS) analysis of some typical unsaturated food components (e.g. squalene, oleic acid) to assess their MS performance. The synthesis of the novel platforms is an easy, cost-effective process based on the maskless wet-etching preparation at room temperature of SiNWs followed by their decoration with AgNPs, produced by pulsed laser deposition. No particular surface pretreatment or addition of organic matrixes/ionizers was necessary. Moreover, oil extracts (e.g. extra virgin olive oil, peanut oil) could be investigated on AgNP/SiNWs surfaces, revealing their different MS profiles. It was shown that such substrates operate at reduced laser energy, typically generating intense silver cluster ions and analyte adducts. A comparison with bare SiNWs was also performed, indicating the importance of AgNP density on NW surface. In this case, desorption/ionization on silicon was invoked as probable LDI mechanism. Finally, the influence of SiNW length and surface composition on MS results was assessed. The combination of typical properties of SiNWs (hydrophobicity, antireflectivity) with ionization ability of metal NPs can be a valid methodology for the further development of nanostructured surfaces in LDI-TOF MS applications. Copyright © 2016 John Wiley & Sons, Ltd.

Development of Hierarchical Polymer@Pd Nanowire-Network: Synthesis and Application as Highly Active Recyclable Catalyst and Printable Conductive Ink

A facile one-pot approach for preparing hierarchical nanowire-networks of hollow polymer@Pd nanospheres is reported. First, polymer@Pd hollow nanospheres were produced through metal-complexation-induced phase separation with functionalized graft copolymers and subsequent self-assembly of PdNPs. The nanospheres hierarchically assembled into the nanowire-network upon drying. The Pd nanowire-network served as an active catalyst for Mizoroki-Heck and Suzuki-Miyaura coupling reactions. As low as 500 μmol % Pd was sufficient for quantitative reactions, and the origin of the high activity is ascribed to the highly active sites originating from high-index facets, kinks, and coalesced structures. The catalyst can be recycled via simple filtration and washing, maintaining its high activity owing to the micrometer-sized hierarchical structure of the nanomaterial. The polymer@Pd nanosphere also served as a printable conductive ink for a translucent grid pattern with excellent horizontal conductivity (7.5×10(5) S m(-1)).

The nature of photocatalytic "water splitting" on silicon nanowires

Silicon should be an ideal semiconductor material if it can be proven usable for photocatalytic water splitting, given its high natural abundance. Thus it is imperative to explore the possibility of water splitting by running photocatalysis on a silicon surface and to decode the mechanism behind it. It is reported that hydrogen gas can indeed be produced from Si nanowires when illuminated in water, but the reactions are not a real water-splitting process. Instead, the production of hydrogen gas on the Si nanowires occurs through the cleavage of Si-H bonds and the formation of Si-OH bonds, resulting in the low probability of generating oxygen. On the other hand, these two types of surface dangling bonds both extract photoexcited electrons, whose competition greatly impacts on carrier lifetime and reaction efficiency. Thus surface chemistry holds the key to achieving high efficiency in such a photocatalytic system.

Palladium salt and functional reduced graphene oxide complex: in situ preparation of a generally applicable catalyst for C–C coupling reactions

A simple scheme of Pd²⁺ fixed on FRGO as a highly efficient coupling catalyst.