Reduction Reaction Of P-nitrophenol Research Articles

A general protocol for precise syntheses of ordered mesoporous intermetallic nanoparticles.

Intermetallic nanomaterials consist of two or more metals in a highly ordered atomic arrangement. There are many possible combinations and morphologies, and exploring their properties is an important research area. Their strict stoichiometry requirement and well-defined atom binding environment make intermetallic compounds an ideal research platform to rationally optimize catalytic performance. Making mesoporous intermetallic materials is a further advance; crystalline mesoporosity can expose more active sites, facilitate the mass and electron transfer, and provide the distinguished mesoporous nanoconfinement environment. In this Protocol, we describe how to prepare ordered mesoporous intermetallic nanomaterials with controlled compositions, morphologies/structures and phases by a general concurrent template strategy. In this approach, the concurrent template used is a hybrid of mesoporous platinum or palladium and Korea Advanced Institute of Science and Technology-6 (KIT-6) (meso-Pt/KIT-6 or meso-Pd/KIT-6) that can be transformed by the second precursors under reducing conditions. The second precursor can either be a second metal or a metalloid/non-metal, e.g., boron/phosphorus. KIT-6 is a silica scaffold that is removed using NaOH or HF to form the mesoporous product. Procedures for example catalytic applications include the 3-nitrophenylacetylene semi-hydrogenation reaction, p-nitrophenol reduction reaction and electrochemical hydrogen evolution reaction. The synthetic strategy for preparation of ordered mesoporous intermetallic nanoparticles would take almost 5 d; the physical characterization by electron microscope, X-ray diffraction and inductively coupled plasma-mass spectrometry takes ~2 days and the function characterization depends on the research question, but for catalysis it takes 1-5 h.

Effective Mn Doping of Co3O4 to Improve the Catalytic Performance of Co3O4/N-doped Carbon toward Hydrogenation Reduction Reaction of p-Nitrophenol

Abstract This work reports that 5% Mn doping of Co3O4 can greatly improve catalytic performance of Co3O4/N-doped carbon (Co3O4/NC) catalysts toward hydrogenation reaction of p-nitrophenol by using NaBH4 as reducing agent. Mn doping can cause formation of cobalt or oxygen vacancies without changing the crystalline structure of Co3O4. The 5%Mn-doped Co3O4/NC has a high activity parameter of 173 s−1·g−1 when the molar ratio of NaBH4:p-nitrophenol is 100:1, while the un-doped Co3O4/NC catalyst has a low parameter of 37.0 s−1·g−1.

PEPPSI-Type Pd(II)—NHC Complexes on the Base of p-tert-Butylthiacalix[4]arene: Synthesis and Catalytic Activities

The creation of effective catalytic systems for cross-coupling reactions, reduction, etc., capable of working in water-organic or pure aqueous media is in great demand. The article presents the synthesis of NHC-palladium complexes of the PEPPSI type based on monoimidazolium derivatives of thiacalix[4]arene. The structure of the imidazolium precursors, obtained in 81–88% yields and the complexes themselves, obtained in 40–50% yields, is established using modern methods, including X-ray structural analysis and high-resolution mass spectrometry. It is shown that the obtained complex with bulk substituents near the palladium atom is not inferior to the well-known PEPPSI-type Organ’s catalyst in the catalysis of Suzuki-Miyaura coupling and is four times superior to the latter in the p-nitrophenol reduction reaction. Given the presence of free phenolic hydroxyl groups in the macrocycle, the obtained complexes are of interest for further post-modification or for immobilization on a carrier.

Synergistic Bonding of Poly(N-isopropylacrylamide)-Based Hybrid Microgels and Gold Nanoparticles Used for Temperature-Responsive Controllable Catalysis of p-Nitrophenol Reduction

Stimuli-responsive hybrid nanoparticles used for controllable catalysis have been attracting increasing attention. This study aims to prepare hybrid microgels with excellent temperature-sensitive colorimetric and catalytic properties through combining the surface plasmon resonance properties of gold nanoparticles (AuNPs) with the temperature-sensitive properties of poly(N-isopropylacrylamide) (PNIPAM)-based microgels. Microgels with hydroxy groups (MG-OH) were prepared by soap-free emulsion polymerization, using N-isopropylacrylamide as the main monomer, hydroxyethyl methylacrylate as the functional monomer, N,N'-methylene bisacrylamide as the crosslinker, and 2,2'-azobis(2-methylpropionamidine) dihydrochloride as an initiator to ensure the microgels are positively charged. Furthermore, chemical modification on the surface of MG-OH was carried out by 3-mercaptopropyltriethoxysilane to obtain thiolated microgels (MG-SH). Two kinds of hybrid nanoparticles, AuNPs@MG-OH and AuNPs@MG-SH, were self-assembled, through electrostatic interaction between positive MG-OH and negative citrate-stabilized AuNPs as well as through synergistic bonding of electrostatic interaction and Au-S bonding between positive MG-SH and negative AuNPs. The morphology, stability, temperature-sensitive colorimetric properties, and catalytic properties of hybrid microgels were systematically investigated. Results showed that although both AuNPs@MG-OH and AuNPs@MG-SH exhibit good temperature-sensitive colorimetric properties and controllable catalytic properties for the reduction reaction of p-nitrophenol, AuNPs@MG-SH with synergistic bonding has better stability and higher catalytic performance than AuNPs@MG-OH. This work has good competitiveness against known PNIPAM-based materials and may provide an effective method for preparing smart catalysts by self-assembly with stimuli-responsive polymers, which has a great potential application for catalyzing a variety of reactions.

Activity and reusability of immobilized gold nanoparticles for the catalysis of both oxidation and reduction reactions

Colloidal gold nanoparticles (AuNP) are well-known to present a catalytic activity. However, they are characterized by certain limitations, as a rather poor stability and lack of both handling and reusability. Their immobilization on surfaces could help to overcome these drawbacks. This work evaluated the impact of the immobilization of AuNP towards their catalytic activity on reduction and oxidation reactions. Colloidal AuNP stabilized with citrate ions were synthesized, characterized, and immobilized by the dip-coating method, the obtained immobilized AuNP (iAuNP) were characterized. The catalytic activity of AuNP and iAuNP was evaluated and compared to each other through the p-nitrophenol reduction reaction. The kinetic of the catalytic activity of iAuNP was slower than colloidal AuNP. The catalytic activity appeared to be impacted by the less available surface of iAuNP. The reduction efficiency of iAuNP was also evaluated with the DPPH•/DPPH2 reduction reaction. The capacity of iAuNP to catalyze the reduction of DPPH• in DPPH2 was shown even after 130 days and 20 reuses of the nanostructured surface on the contrary to non-reusable colloidal AuNP. The oxidation efficiency of iAuNP was measured by the ability to catalyze the auto-oxidation of curcumin (HPLC-UV/vis). For all these experiments, the addition of 4-mercapto-phenol on the surface of iAuNP passivated the surface, decreasing the catalytic activity of the materials. In conclusion, iAuNP are redox catalysts with both anti- and pro-oxidant effects and high reusability over a very long period.

Catalytic activity of gold nanoparticles protected by quaternary ammonium salt-based gemini surfactants with different spacer structures.

The protection and stabilization of metal nanoparticles with gemini surfactants can greatly improve their catalytic and reductive activities as well as stability, expanding their practical applicability. In this study, gold nanoparticles were prepared using three quaternary ammonium salt-based gemini surfactants with different spacer structures (2C12(Spacer)) as protective agents, and their structures and catalytic activities were investigated. The size of the 2C12(Spacer)-protected gold nanoparticles decreased as the ratio of [2C12(Spacer)] to [Au3+] ([2C12(Spacer)] : [Au3+]) increased from 1 : 1 to 4 : 1. Furthermore, the stability of the gold nanoparticles was affected by the spacer structure and surfactant concentration. The gold nanoparticles protected by 2C12(Spacer) with a diethylene chain and oxygen atom in the spacer were stable even at low surfactant concentrations because the gemini surfactants sufficiently covered the surface of the gold nanoparticles, and the aggregation between the nanoparticles was suppressed. In addition, the gold nanoparticles protected by 2C12(Spacer) with an oxygen atom in the spacer exhibited high catalytic activities for the reduction reaction of p-nitrophenol and 1,1-diphenyl-2-picrylhydrazyl radical scavenging reaction because of their small size. Thus, we elucidated the effect of spacer structure and surfactant concentration on the structure and catalytic activities of gold nanoparticles.

Synthesis of p-Aminophenol from p-Nitrophenol Using CuO-Nanoleaf/g-Al2O3 Catalyst

The CuO-nanoleaf/g-Al2O3 catalyst was synthesized through wet chemical impregnation and had promising catalytic activity in reducing p-Nitrophenol (PNP) into p-Aminophenol (PAP). The synthesis was conducted in situ with Ethylene Glycol as a stabilizer agent of the CuO-nanoleaf structure and g-Al2O3 as catalyst support with high adsorption ability. Furthermore, the crystal phase, morphology, element composition, and specific surface area were investigated by X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), and N2 adsorption-desorption, respectively. The XRD pattern showed the crystal phase of CuO and g-Al2O3 in the composite, and the morphology was successfully reported using FESEM. The increase in the specific surface area of the catalyst indicates that the CuO material was well composited in g-Al2O3. The catalyst has good activity in reducing PNP to PAP with 93.53% PNP conversion within 4 min. In addition, the reduction reaction of PNP with excess NaBH4 could be categorized as pseudo-first order kinetic with a constant rate of 0.6935 min−1 for CuO-nanoleaf/g-Al2O3 catalyst. The loading catalyst and temperature reaction effect on PNP conversion were also investigated. The results showed that 94.18% PNP conversion was obtained within only 2.5 min under the optimized conditions. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

The synthesis of size-controlled hollow spherical covalent organic frameworks and its application in photocatalysis and Suzuki coupling reactions

Here, we reported the self-templated preparation of an allyl-containing, internally hollow, spherical COFs. Various factors affecting the formation of hollow spherical COFa-2 were investigated using diverse spectroscopic and microscopic techniques. Detailed time-dependent studies revealed a continuous transition of COFa-2 catalyst from an initial solid spherical structure to a homogeneous hollow spherical system by an Ostwald maturation mechanism. In addition, the effects of precursors with different structures on the photoelectric properties and photocatalytic degradation of RhB of the prepared COFa-1, COFa-2 and COFa-3 were also studied. Results have shown that allyl can effectively improve the response of COFa-2 to visible light and the degradation ability of RhB. Furthermore, allyl-palladium (COFa-2@Pd2+) formed by the coordination of palladium ions with allyl can effectively catalyze the Suzuki coupling (TOF = 16 × 10-4) and the reduction reaction of p-nitrophenol (Kapp = 1.56 min−1). More importantly, the catalysts COFa-2 and COFa-2@Pd2+ showed high stability after being recycled 10 times.

Metal-organic framework grown in situ on chitosan microspheres as robust host of palladium for heterogeneous catalysis: Suzuki reaction and the p-nitrophenol reduction

In this study, the metal-organic framework ZIF-8 has been successfully planted on the surface of chitosan microspheres (CS/PDA@ZIF-8) using polydopamine as connecting material for the first time, which avoids the use of expensive, non-renewable, and non-biodegradable polystyrene microspheres commonly used as templates to prepare core-shell structures. Moreover, the metal-organic framework ZIF-8 was prepared specially by three different methods and all characterized by SEM, TEM, and BET, and the ZIF-8 shell prepared at room temperature presents a regular morphology, uniform size, large specific surface area (353.1 m2/g) than the shells prepared by the other methods including. The CS/PDA@ZIF-825@Pd with high catalytic activity and high stability was especially prepared by encapsulating Pd nanoparticles into the pores of CS/PDA@ZIF-825. Notably, the fabricated catalyst performed well in an array of reactions, for example the Kapp value of the p-nitrophenol reduction reaction reached 0.0426 s−1, and the TOF of the Suzuki coupling reaction reached 128 h−1. In addition, the ZIF-67, UiO-66, UiO-66-NH2, HKUST-1, and NH2-MIL-53(Al) were also grown on chitosan microcapsules successively to prepare the core-shell microspheres, which prove the universal applicability of this strategy. And beyond that, the introduction of chitosan microspheres endows the material with biodegradable properties and excellent recycling properties.

Synthesis of Ag/GO nanocomposite with promising photocatalytic ability for reduction reaction of p-nitrophenol

p-Aminophenol (PAP) is an important intermediate reagent in the synthesis of paracetamol, widely used as an analgesic and antipyretic drug. Therefore, finding an effective catalyst to improve PAP synthesis efficiency is worth studying. Among those studies, nanocomposite is the most promising material. In this study, Ag/GO nanocomposites were synthesized by reducing silver nitrate on graphene oxide (GO) with sodium borohydride as a reducing agent and characterized by SEM, EDX, XRD and UV–vis methods. The catalytic ability was investigated based on the hydrogenation reaction of p-nitrophenol (PNP). We successfully synthesized Ag/GO nanocomposite with relatively homogeneous distributions and similar particle sizes. The results showed that Ag/GO nanocomposite has an excellent catalytic activity with the yield of reduction reaction at 97%, 3 min. Moreover, this photocatalyst can easily be recovered and reused three times without any reaction efficiency reduction. We also successfully synthesized and crystallized PAP with high purity and the total yield of 45.82%. The results show that Ag/GO nanocomposite is an excellent catalyst for high-performance reactions with many useful properties, such as easily recovered and repetitive used. On top of that, Ag/GO nanocomposite is safe, less toxic and environmentally friendly.

Rapid visual detection for nitroreductase based on the copper ions-induced and NADH-mediated aggregation of gold-silver alloy nanoparticles

Hypoxia refers to the lack of oxygen supply to cells or tissues. The overexpression of nitroreductase has been shown to be closely related to the degree of hypoxia, which leads to the level of nitroreductase (NTR) being used as an indicator of hypoxia. We reported a facile visual detection of NTR based on the aggregation of gold and silver alloy nanoparticles. Compared with gold nanoparticles (AuNPs), the aggregation behavior of Au80Ag20 NPs caused a more prominent color change. Copper ions (Cu2+) can be rapidly reduced by nicotinamide adenine dinucleotide (NADH) under the catalysis of Au80Ag20 NPs. But NADH is consumed as an electron donor during the catalytic reduction reaction of p-nitrophenol (pNP) by NTR. A decrease of NADH amount results in the aggregation of Au80Ag20 NPs by the excess Cu2+ and different aggregation degrees of Au80Ag20 NPs lead to observable color change. A linear correlation of A600/A505 = 0.0285 [NTR]+0.361 (R2 = 0.980) was obtained with a limit of detection (LOD) of 0.23 μg/mL for UV–vis spectrophotometer. For visual detection, the values of R/B against the concentration of NTR obtains a calibration curve of R/B = −0.031 [NTR]+ 1.54 (R2 = 0.985) with a LOD of 0.76 μg/mL, which is of the same order of magnitude as the UV–vis spectrophotometer analysis. As a comparison, Au80Ag20 NPs was replaced by several different composition nanoparticles (Au NPs, Au70Ag30 NPs, Au50Ag50 NPs) to be a chromogenic substrate, and the results suggest the Au80Ag20 NPs is the most sensitive substrate in our assay. Selectivity tests showed that the detection system did not respond to other common substances, and the reaction mechanism was verified by inhibitor research. Finally, the assay was used on the human serum samples with spiking NTR, and the recovery rates of this assay with UV–vis spectrophotometer were basically consistent with RGB analysis.

Synthesis and Crystal-Phase Engineering of Mesoporous Palladium-Boron Alloy Nanoparticles.

Rational design and synthesis of noble metal nanomaterials with desired crystal phases (atomic level) and controllable structures/morphologies (mesoscopic level) are paramount for modulating their physiochemical properties. However, it is challenging to simultaneously explore atomic crystal-phase structures and ordered mesoscopic morphologies. Here, we report a simple synergistic templating strategy for the preparation of palladium–boron (Pd–B) nanoparticles with precisely controllable crystal-phases and highly ordered mesostructures. The engineering of crystal-phase structures at atomic levels is achieved by interstitially inserting metallic B atoms into face-centered cubic mesoporous Pd (fcc-mesoPd) confined in a mesoporous silica template. With the gradual insertion of B atoms, fcc-mesoPd is transformed into fcc-mesoPd5B, hcp-mesoPd2B with randomly distributed B atoms (hcp-mesoPd2B-r), and hcp-mesoPd2B with an atomically ordered B sequence (hcp-mesoPd2B-o) while preserving well-defined mesostructures. This synergistic templating strategy can be extended to engineer crystal-phase structures with various mesostructures/morphologies, including nanoparticles, nanobundles, and nanorods. Moreover, we investigate the crystal-phase-dependent catalytic performance toward the reduction reaction of p-nitrophenol and find that hcp-mesoPd2B-o displays much better catalytic activity. This work thus paves a new way for the synthesis of hcp-Pd2B nanomaterials with mesoscopically ordered structure/morphology and offers new insights of fcc-to-hcp evolution mechanisms which could be applied on other noble metal-based nanomaterials for various targeted applications.

Fabrication of multifunctional Guar gum-silver nanocomposite hydrogels for biomedical and environmental applications

Poly(acrylamide-co-acrylamidoglycolic acid)/guar gum@ Ag-nanocomposite (AgNC@PAAG) hydrogels has been fabricated by a green protocol utilizing rhubarb stem-extract as bioreductant. The prepared nanocomposites (NCs) are formulated by varying guar gum (GG) polymer and cross-linker content, and used remarkably to study the release of an anticancer drug, 5-fluorouracil (FU). The AgNC@PAAG has demonstrated its potential in bacterial inactivation and p-nitrophenol (PNP) reduction. The AgNC@PAAG hydrogels showed extended FU release time, which was up to 23 h in pH 7.4. The higher zone of inhibition was documented for AgNC@PAAG against B. subtilis and E. coli. It was noticed that, the inhibition activity of AgNC@PAAG, was directly proportional to cross-linker content than the GG polymer. The efficiency of AgNC@PAAG as a nanocatalyst was evaluated for a model reduction reaction of p-nitrophenol (PNP) reduction by aqueous sodium borohydride (NaBH4), with an apparent rate constant of 121.8 × 10−3 min−1 at ambient temperature. The proposed nanocatalysts are reliable and recyclable, demonstrated its catalytic recycle efficacy of 85% after the third successive run. These NCs robust its biological and catalytic activity after embedding silver nanoparticles (AgNPs) by the bioreduction process; these optimized nanocatalysts can be remarkably used in biomedical healthcare sectors and industrial catalysis.

Two-Step Mediated Electrosynthesis and Catalytic Activity of Au/Cu2O@poly(N-vinylpyrrolidone) Nanocomposite

Efficient two-step methylviologen (MV2+) — mediated electrosynthesis of a nanocomposite of gold nanoparticles with copper(I) oxide stabilized by a shell of poly(N-vinylpyrrolidone) (Au/Cu2O@PVP) was performed in DMF at room temperature at the potentials of MV.+ radical cation generation. At the first step, the mediated reduction of Cu2+ ions, generated in situ by dissolution of the copper anode, in the presence of dissolved oxygen or with subsequent oxidation with oxygen, leads to Cu2O@PVP composite containing Cu(0) and Cu2O in a different ratio. In the latter case, the resulting composite is in the form of stable nanoroses. When AuCl is added into the resulting solutions of Cu2O@PVP, the partial chemical reduction of AuCl by Cu(0) occurs to form Au(0) and CuCl. At the second step, the electrochemical reduction of AuCl leads to Au/Cu2O@PVP nanocomposite not containing Cu(0), but nanoroses are preserved. Cu2O@PVP nanoparticles are catalytically inactive in the reduction reaction of p-nitrophenol with sodium borohydride in water, and Au/Cu2O@PVP nanocomposites exhibit catalytic activity. In the presence of cetyltrimethylammonium chloride, the catalytic activity of both types of particles sharply increases; in the case of Cu2O@PVP, the increase is so high that the catalytic activity becomes the same as for Au/Cu2O@PVP.

Electron Beam Induced Enhancement of the Catalytic Properties of Ion-Track Membranes Supported Copper Nanotubes in the Reaction of the P-Nitrophenol Reduction

This study considers the effect of various doses of electron irradiation on the crystal structure and properties of composite catalysts based on polyethylene terephthalate track-etched membranes and copper nanotubes. Copper nanotubes were obtained by electroless template synthesis and irradiated with electrons with 3.8 MeV energy in the dose range of 100–250 kGy in increments of 50 kGy. The original and irradiated samples of composites were investigated by X-ray diffraction technique (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The improved catalytic activity of composite membranes with copper nanotubes was demonstrated by the example of the reduction reaction of p-nitrophenol in the presence of sodium borohydride. Irradiation with electrons at doses of 100 and 150 kGy led to reaction rate constant increases by 35 and 59%, respectively, compared to the non-irradiated sample. This enhancing catalytic activity could be attributed to the changing of the crystallite size of copper, as well as the surface roughness of the composite membrane.

Structure and Catalytic Activities of Gold Nanoparticles Protected by Homogeneous Polyoxyethylene Alkyl Ether Type Nonionic Surfactants.

Gold nanoparticles were prepared in aqueous solutions containing four homogeneous polyoxyethylene (EO) alkyl ether type nonionic surfactants: octaoxyethylene dodecyl ether (C12EO8), methoxyoctaoxyethylene dodecyl ether (C12EO8OMe), ethoxyoctaoxyethylene dodecyl ether (C12EO8OEt), and trioxypropylene-octaoxyethylene dodecyl ether (C12EO8PO3). The sizes of obtained gold nanoparticles were almost independent of the terminal group in the EO surfactants; and the average sizes of nanoparticles prepared by surfactants with hydroxy, methoxy, ethoxy, and trioxypropylene terminal groups at [surfactant]:[Au3+] = 1:1 were 5.1 ± 1.2, 8.1 ± 1.4, 6.4 ± 2.1, and 8.6 ± 2.9 nm, respectively. The gold nanoparticles easily aggregated together according to the increasing hydrophobicity of hydroxy < methoxy ethoxy < trioxypropylene terminal groups. Highly stable dispersed nanoparticles were observed with hydroxy group in the EO terminal group. On the other hand, introducing hydrophobic moiety to the hydroxy group resulted in aggregated nanoparticles because of the interaction between the hydrophobic groups of a protective agent for the gold nanoparticles. For the reduction reaction of p-nitrophenol and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging reaction, catalytic activities of the prepared gold nanoparticles decreased by the introduction of methoxy, ethoxy, or trioxypropylene to the hydroxy group of the EO type surfactant. Thus, a significant correlation was observed between the structure of gold nanoparticles and their catalytic activities.

Controlled synthesis of metal-organic frameworks coated with noble metal nanoparticles and conducting polymer for enhanced catalysis

The combination of noble metal nanoparticles (NM NPs) and metal-organic frameworks (MOFs) for enhanced properties in catalysis is a rapidly developing interdisciplinary research field. Herein we report a facile one-step approach to the deposition of functional nanocomposite shell composed of NM NPs and conducting polymer on the surface of particulate UiO-66. Our approach is based on the recently developed double solvents method involving a hydrophobic solvent (n-hexane) and a hydrophilic solvent (water). Particularly, the n-hexane was used in a large amount to suspend the UiO-66 particles with hydrophilic inner pores and promoted the enrichment of the water containing the palladium chloride (PdCl2) inside the pores of UiO-66 particles, because these two solvents are immiscible and the volume of water is smaller than the pore volume of the UiO-66 particles. After the introduction of hydrophobic pyrrole into the n-hexane, the UiO-66 particles are successfully coated with a nanocomposite shell, composed of Pd NPs and polypyrrole (PPy) resulting from the interfacial polymerization of pyrrole on the external surface of UiO-66 particles initiated by PdCl2 presented within the UiO-66 particles. Significantly, in such a unique structure, the prepared hybrid particles noted as UiO-66/Pd@PPy nanocomposite particles are demonstrated to be an excellent catalyst with both high activity and stability in the reduction reaction of p-nitrophenol and sodium borohydride. Furthermore, this synthetic method not only effectively controls the mass loading of Pd NPs and PPy on the UiO-66 particles but also enables the deposition of Au@PPy and Ag@PPy nanocomposite shells onto the surface of the UiO-66 particles.

Controlling Shape and Plasmon Resonance of Pt-Etched Au@Ag Nanorods.

Pt-based catalysts with novel structure have attracted great attention due to their outstanding performance. In this work, H2PtCl6 was used as both precursor and etching agent to realize the shape-controlled synthesis of Pt-modified Au@Ag nanorods (NRs). During the synthesis, the as-prepared Ag shell played a crucial role in both protecting the Au NRs from being etched away by PtCl62- and leading to an unusual growth mode of Pt component. The site-specified etching and/or growth depended on the concentration of H2PtCl6, where high-yield core-shell structure or dumbbell-like structure could be obtained. The shape-controlled synthesis also led to a tunable longitudinal surface plasmon resonance from ca. 649 to 900 nm. Meanwhile, the core-shell Pt-modified Au@Ag NRs showed approximately 4-fold enhancement in catalytic reduction reaction of p-nitrophenol than that of the Au NRs, suggesting the great potential for photocatalytic reaction.

In situ prepared nanosized Pt-Ag/PDA/PVA-co-PE nanofibrous membrane for highly-efficient catalytic reduction of p-nitrophenol

Combining highly-active noble metal nanoparticles and unique 3D nanofibrous structure is significant to enhance their intrinsic properties such as catalytic performance. Here, we prepared a poly (vinyl alcohol-co-ethylene) (PVA-co-PE) nanofibrous membrane (NFM) decorated by polydopamine (PDA) via a melt-phase-separated nanofiber-suspension coating followed by in-situ polymerization. The as-prepared PDA modified NFM worked as the in-situ reducing agent to capture silver ions and transfer them to Ag nanoparticles (NPs). Then Ag/PDA/NFM was further coated with Pt NPs by magnetron sputtering technique. The morphology and structure analysis showed that the Ag NPs in diameter from 10 to 200 nm and Pt nanoparticles coating has been successfully immobilized on PDA/NFM. The catalytic rate constant of Pt-Ag/PDA/NFM in the reduction reaction of p-nitrophenol (p-NP) was about 34.43×10-3 s-1 higher than that of Ag/PDA/NFM (30.20×10-3 s-1) and Pt/PDA/NFM (0.188 ×10-3 s-1), respectively, when magnetron sputtering time of Pt was 100 s. It can be attributed to the electronic effect in bimetallic catalyst and the enhancement effect of nanofibrous membrane with high specific surface area. Furthermore, Pt-Ag/PDA/NFM presented an excellent cyclic feature that still about 98% conversion of p-NP after 6 times implying its superiority in reduction degradation of p-nitrophenols.

Preparation of Au@silica Janus nanosheets and their catalytic application

We report the preparation of the Au@silica Janus nanosheets by materialization of the emulsion interface and further functionalization with Au nanoparticles. The amphiphilicity and emulsification property of Au@silica Janus nanosheets were not affected by the grown Au nanoparticles. The catalytic performance of the Au@silica Janus nanosheets was explored using the reduction reaction of p-nitrophenol and p-nitroanisol as model reactions in homogenous reaction and emulsion interfacial reaction, respectively. The results indicated that the Au@silica Janus nanosheets exhibited excellent catalytic activity for the reduction reaction of p-nitrophenol in the homogenous reaction. In emulsion interface, the conversion of p-nitroanisol was 16-fold higher than that of the two-phase interface, which could attribute to the expanded active areas and the favorable mass transfer at the emulsion interface. The recovery of the Au@silica Janus nanosheets was simply realized and could be reused with 100 % catalytic activity. Compared with the particle-like Janus catalyst, the Au@silica Janus nanosheets could achieve better catalytic efficiency with a more low content. The conception of emulsion interfacial catalysis with Janus catalysts provides an avenue for conventional heterogeneous reactions.