Reaction of Vinyl Selenides with Secondary Phosphines and Elemental Selenium: One‐Pot Selective Synthesis of a New Family of Diselenophosphinic Se‐Esters

Alkyl vinyl selenides react with diverse secondary phosphines and elemental selenium in a 1.1:1:2 molar ratio (120–124°C, 20–40 min, 1,4‐dioxane) to afford selectively earlier unknown diselenophosphinic Se‐esters, R₂P(Se)SeCH(Me)SeR´, in 82–99% yield. This three‐component atom‐economic reaction proceeds via intermediate formation of diselenophosphinic acid R₂P(Se)SeH (generated from secondary phosphine and selenium), which adds to the double bond of vinyl selenide in a Markovnikov manner to give the target products.     

Heat-Induced Precipitation and Light-Induced Dissolution of Metal (Ag & Au) Nanoparticles in Hybrid Film

Metal nanoparticle-doped materials have attracted much attention because of their enhanced third-order nonlinear optical susceptibility. In their application, (1) controllable precipitation and (2) stability against photo-irradiation are essential concerns. Silver or gold nanoparticle-doped films were made from hybrid sol containing metal ions with their stabilizer on silica glass substrates by the sol-gel dip-coating technique and their heat-induced precipitation and photo-stability were investigated. The heat-induced precipitation up to 1000°C was remarkably different in Ag and Au nanoparticles. After 120–500°C heating, Ag nanoparticles with a wide range of radii were formed in the hybrid films. Above 500°C, organic groups were completely evacuated and at 800°C, mono-dispersed Ag nanoparticles with radii of 2–4 nm were precipitated in the resultant film. On the other hand, Au nanoparticles of 10 nm average radius precipitated at 120°C and showed no drastic change in subsequent heating up to 1000°C. Since Ag nanoparticle-doped film showed the photosensitive change, their photostability was investigated by irradiating them under Xenon lamp light. The 800°C-heating sample showed no decrease in the plasma absorption band at around 420 nm wavelength after 20 h light irradiation, but the band intensities in the 120–500°C-heating films decreased noticeably.     

Selenium electrochemistry in choline chloride–urea deep eutectic electrolyte

The electrochemical behaviour of selenium in the deep eutectic solvent made of a 1:2 molar ratio of choline chloride and urea (ChCl–U) has been investigated at a polycrystalline gold electrode by voltammetry and chronoamperometry. In order to favour the deposition of grey selenium, selenium oxide was chosen as the solution precursor and a temperature range from 70 to 110 °C was selected. Cyclic voltammograms recorded in the 1:2 choline chloride–urea liquid containing 10 mM SeO₂ are strongly affected by the temperature. At 110 °C, three main cathodic responses are evidenced around ?0.075, ?0.2 and ?0.7 V. These cathodic peaks have been attributed respectively to the underpotential deposition (upd) of Se, the bulk deposition of Se and the cathodic stripping of selenium associated to the formation of Se(?II). Potentiostatic current transients obtained at 110 °C are indicative of a nucleation with diffusion-controlled growth mechanism for the selenium electrodeposition and support the formation of a upd layer preceding the bulk deposition. The dissolution transients triggered by double potential step perturbations could however not be interpreted on the basis of a similar formalism.     

Hydrothermal Synthesis of Platinum‐Group‐Metal Nanoparticles by Using HEPES as a Reductant and Stabilizer

Platinum‐group‐metal (Ru, Os, Rh, Ir, Pd and Pt) nanoparticles are synthesized in an aqueous buffer solution of 4‐(2‐hydroxyethyl)‐1‐piperazineethanesulfonic acid (HEPES) (200 mM , pH 7.4) under hydrothermal conditions (180 °C). Monodispersed (monodispersity: 11–15 %) metal nanoparticles were obtained with an average particle size of less than 5 nm (Ru: 1.8±0.2, Os: 1.6±0.2, Rh: 4.5±0.5, Ir: 2.0±0.3, Pd: 3.8±0.4, Pt: 1.9±0.2 nm). The size, monodispersity, and stability of the as‐obtained metal nanoparticles were affected by the HEPES concentration, pH of the HEPES buffer solution, and reaction temperature. HEPES with two tertiary amines (piperazine groups) and terminal hydroxyl groups can act as a reductant and stabilizer. The HEPES molecules can bind to the surface of metal nanoparticles to prevent metal nanoparticles from aggregation. These platinum‐group‐metal nanoparticles could be deposited onto the surface of graphite, which catalyzed the aerobic oxidation of alcohols to aldehydes.     

Straightforward Solvent‐Free Synthesis of Tertiary Phosphine Chalcogenides from Secondary Phosphines,Electron‐Rich Alkenes,and Elemental Sulfur or Selenium

A series of tertiary phosphine sulfides and selenides have been synthesized in excellent yields (88‐99%) via a three‐component reaction between secondary phosphines, electron‐rich alkenes (styrene, vinyl chalcogenides), and elemental sulfur or selenium, proceeding under solvent‐free conditions (80‐82°C, 4–44 h). The interaction occurs via initial oxidation of secondary phosphines with elemental sulfur or selenium followed by noncatalyzed anti‐Markovnikov addition of the generated R₂P(E)H (E = S, Se) species to alkenes to afford the corresponding adducts with high chemo‐ and regioselectivity.     

Surfactant enhanced lipase containing films characterized by confocal laser scanning microscopy

An environmentally benign method for the synthesis of noble metal nanoparticles has been reported using aqueous solution of gum kondagogu (Cochlospermum gossypium). Both the synthesis, as well as stabilization of colloidal Ag, Au and Pt nanoparticles has been accomplished in an aqueous medium containing gum kondagogu. The colloidal suspensions so obtained were found to be highly stable for prolonged period, without undergoing any oxidation. SEM–EDXA, UV–vis spectroscopy, XRD, FTIR and TEM techniques were used to characterize the Ag, Au and Pt nanoparticles. FTIR analysis indicates that –OH groups present in the gum matrix were responsible for the reduction of metal cations into nanoparticles. UV–vis studies showed a distinct surface plasmon resonance at 412 and 525 nm due to the formation of Au and Ag nanoparticles, respectively, within the gum network. XRD studies indicated that the nanoparticles were crystalline in nature with face centered cubic geometry. The noble metal nanoparticles prepared in the present study appears to be homogeneous with the particle size ranging between 2 and 10 nm, as evidenced by TEM analysis. The Ag and Au nanoparticles formed were in the average size range of 5.5 ± 2.5 nm and 7.8 ± 2.3 nm; while Pt nanoparticles were in the size range of 2.4 ± 0.7 nm, which were considerably smaller than Ag and Au nanoparticles. The present approach exemplifies a totally green synthesis using the plant derived natural product (gum kondagogu) for the production of noble metal nanoparticles and the process can also be extended to the synthesis of other metal oxide nanoparticles.     

Structural Evolution of Anatase-Supported Platinum Nanoclusters into a Platinum-Titanium Intermetallic Containing Platinum Single Atoms for Enhanced Catalytic CO Oxidation

Strong metal-support interactions characteristic of the encapsulation of metal particles by oxide overlayers have been widely observed on large metal nanoparticles, but scarcely occur on small nanoclusters (<2 nm) for which the metal-support interactions remain elusive. Herein, we study the structural evolution of Pt nanoclusters (1.5 nm) supported on anatase TiO₂ upon high-temperature H₂ reduction. The Pt nanoclusters start to partially evolve into a CsCl-type PtTi intermetallic compound when the reduction temperature reaches 400 °C. Upon 700 °C reduction, the PtTi nanoparticles are exclusively formed and grow epitaxially along the TiO₂ (101) crystal faces. The thermodynamics of the formation of PtTi via migration of reduced Ti atoms into Pt cluster is unraveled by theoretical calculations. The thermally stable PtTi intermetallic compound, with single-atom Pt isolated by Ti, exhibits enhanced catalytic activity and promoted catalytic durability for CO oxidation.     

Investigation of the formation of nickel and cobalt nanoparticles upon thermal decomposition of Ni,Al-and Co,Al-layered double hydroxides pillared with complexes [Ni(edta)]<Superscript>2−</Superscript> and [Co(edta)]<Superscript>2−</Superscript>

Double layered hydroxides [M_0.7Al(OH)_3.6] [M(edta)]_0.4·nH₂O (M,Al-M(edta), M = Ni, Co) containing nickel or cobalt edta complexes in the interlayer space were obtained for the first time. Vacuum thermal decomposition of these compounds results in the formation of metal nanoparticles dispersed in an amorphous matrix. Thermal decomposition products were studied by powder X-ray diffraction and ferromagnetic resonance technique. The scheme of structural rearrangements occurring during heating was derived from the data obtained. According to this scheme, below 200°C the interlayer and absorbed water escapes, and at 200–325°C metal-hydroxide layers undergo dehydration. At higher temperatures organic fragment of the complex suffers destruction to yield metal. It is shown that thermal decomposition of Ni, Al-Ni(edta) at 325–340°C gives isotropic nickel nanoparticles, while at higher temperatures the metal consists of a mixture of isotropic and anisotropic particles. Isotropic particles of β-Co formed at 350°C and above are of size 3–4 nm, no anisotropic particles being observed.     

A General and High‐Yield Galvanic Displacement Approach to Au?M (M=Au,Pd, and Pt) Core–Shell Nanostructures with Porous Shells and Enhanced Electrocatalytic Performances

In this work, we utilize the galvanic displacement synthesis and make it a general and efficient method for the preparation of Au? M (M=Au, Pd, and Pt) core–shell nanostructures with porous shells, which consist of multilayer nanoparticles. The method is generally applicable to the preparation of Au? Au, Au? Pd, and Au? Pt core–shell nanostructures with typical porous shells. Moreover, the Au? Au isomeric core–shell nanostructure is reported for the first time. The lower oxidation states of Au^I, Pd^II, and Pt^II are supposed to contribute to the formation of porous core–shell nanostructures instead of yolk‐shell nanostructures. The electrocatalytic ethanol oxidation and oxygen reduction reaction (ORR) performance of porous Au? Pd core–shell nanostructures are assessed as a typical example for the investigation of the advantages of the obtained core–shell nanostructures. As expected, the Au? Pd core–shell nanostructure indeed exhibits a significantly reduced overpotential (the peak potential is shifted in the positive direction by 44 mV and 32 mV), a much improved CO tolerance (I_f/I_b is 3.6 and 1.63 times higher), and an enhanced catalytic stability in comparison with Pd nanoparticles and Pt/C catalysts. Thus, porous Au? M (M=Au, Pd, and Pt) core–shell nanostructures may provide many opportunities in the fields of organic catalysis, direct alcohol fuel cells, surface‐enhanced Raman scattering, and so forth.     

Reaction of CO oxidation on platinum,rhodium, a platinum-rhodium alloy,and a heterophase bimetallic platinum/rhodium surface

The reaction of CO oxidation on thin metal films of platinum, rhodium, and their alloy and on a heterophase bimetallic Pt/Rh surface that consisted of platinum particles of size 10–20 nm on the surface of rhodium was studied in the region of low reactant pressures (lower than 2 × 10^?5 mbar). At low temperatures (T < 200°C), the activity of samples increased in the order Rh > Pt/Rh > Pt-Rh alloy > Pt. Above 200°C, the rate of reaction on the heterophase Pt/Rh surface was almost twice as high as the sum of the rates of reaction on the individual metals; this fact is indicative of a synergistic effect. The nature of this effect is considered.     

Polymeric Carbon Nitride/Mesoporous Silica Composites as Catalyst Support for Au and Pt Nanoparticles

Small and homogeneously dispersed Au and Pt nanoparticles (NPs) were prepared on polymeric carbon nitride (CN_x)/mesoporous silica (SBA‐15) composites, which were synthesized by thermal polycondensation of dicyandiamide‐impregnated preformed SBA‐15. By changing the condensation temperature, the degree of condensation and the loading of CN_x can be controlled to give adjustable particle sizes of the Pt and Au NPs subsequently formed on the composites. In contrast to the pure SBA‐15 support, coating of SBA‐15 with polymeric CN_x resulted in much smaller and better‐dispersed metal NPs. Furthermore, under catalytic conditions the CN_x coating helps to stabilize the metal NPs. However, metal NPs on CN_x/SBA‐15 can show very different catalytic behaviors in, for example, the CO oxidation reaction. Whereas the Pt NPs already show full CO conversion at 160 °C, the catalytic activity of Au NPs seems to be inhibited by the CN_x support.     

Ptshell–Aucore/C electrocatalyst with a controlled shell thickness and improved Pt utilization for fuel cell reactions

Nanoscale Pt_shell–Au_core/C with a controlled shell thickness was successfully synthesized based on a successive reduction strategy. With a Au core size of 4.8 nm, a complete Pt shell of thickness ∼0.6 nm was formed at Pt/Au mole ratio 1:1. The complete coverage of Au core with Pt shell was suggested by various techniques including TEM, UV–vis and cyclic voltammetry. A higher specific activity compared to conventional Pt/C was demonstrated using the probe reaction of methanol electro-oxidation, proving the improved Pt utilization with this core-shell structure.     

PtM/C (M = Ni,Cu, or Ag) electrocatalysts: effects of alloying components on morphology and electrochemically active surface areas

The microstructures of Pt/C and PtM/C (M?=?Ni, Cu, or Ag) electrocatalysts were studied using X-ray diffraction and transmission electron microscopy (TEM). The electrochemically active surface areas of the prepared materials were estimated by cyclic voltammetry in 1 M H₂SO₄. The materials, with metal contents ranging from 30 to 35 wt.%, were synthesized by chemically reducing the metal precursors in water–ethylene glycol solutions. The actual composition of the bimetallic nanoparticles corresponds to a theoretical (1:1) composition for the PtAg/C catalysts, whereas in the PtNi/C and PtCu/C materials, a portion of the alloying component exists in an oxide form. Decreasing the average metallic crystallite sizes from 3.5 to 1.6 nm does not increase the electrochemically active surface area. This apparent contradiction is because a majority of the PtNi and PtCu nanoparticles consist of 2–4 disordered crystallites. In addition, a portion of the PtNi or PtCu nanoparticle surface is covered by nickel or copper oxides, respectively. PtAg nanoparticles, which have a smaller size relative to other bimetallic particles according to the TEM data, are characterized by an intense platinum surface segregation. The agglomeration processes are lowest for the PtAg nanoparticles.     

A facile synthesis and characterization of Ag, Au and Pt nanoparticles using a natural hydrocolloid gum kondagogu (Cochlospermum gossypium)

An environmentally benign method for the synthesis of noble metal nanoparticles has been reported using aqueous solution of gum kondagogu (Cochlospermum gossypium). Both the synthesis, as well as stabilization of colloidal Ag, Au and Pt nanoparticles has been accomplished in an aqueous medium containing gum kondagogu. The colloidal suspensions so obtained were found to be highly stable for prolonged period, without undergoing any oxidation. SEM-EDXA, UV-vis spectroscopy, XRD, FTIR and TEM techniques were used to characterize the Ag, Au and Pt nanoparticles. FTIR analysis indicates that -OH groups present in the gum matrix were responsible for the reduction of metal cations into nanoparticles. UV-vis studies showed a distinct surface plasmon resonance at 412 and 525 nm due to the formation of Au and Ag nanoparticles, respectively, within the gum network. XRD studies indicated that the nanoparticles were crystalline in nature with face centered cubic geometry. The noble metal nanoparticles prepared in the present study appears to be homogeneous with the particle size ranging between 2 and 10 nm, as evidenced by TEM analysis. The Ag and Au nanoparticles formed were in the average size range of 5.5±2.5 nm and 7.8±2.3 nm; while Pt nanoparticles were in the size range of 2.4±0.7 nm, which were considerably smaller than Ag and Au nanoparticles. The present approach exemplifies a totally green synthesis using the plant derived natural product (gum kondagogu) for the production of noble metal nanoparticles and the process can also be extended to the synthesis of other metal oxide nanoparticles.     

In Situ Observation of the Thermally Induced Growth of Platinum‐Nanoparticle Catalysts Using High‐Temperature X‐ray Diffraction

Fundamental understanding about the thermal stability of nanoparticles and deliberate control of structural and morphological changes under reactive conditions is of general importance for a wide range of reaction processes in heterogeneous and electrochemical catalysis. Herein, we present a parametric study of the thermal stability of carbon‐supported Pt nanoparticles at 80 °C and 160 °C, with an initial particle size below 3 nm, using in situ high‐temperature X‐ray diffraction (HT‐XRD). The effects on the thermal stability of carbon‐supported Pt nanoparticles are investigated with control parameters such as Brunauer–Emmet–Teller (BET) surface area, metal loading, temperature, and gas environment. We demonstrate that the growth rate exhibits a complex, nonlinear behavior and is largely controlled by the temperature, the initial particle size, and the interparticle distance. In addition, an ex situ transmission electron microscopy study was performed to verify our results obtained from the in situ HT‐XRD study.     

Bovine Serum Albumin Nanospheres Synchronously Encapsulating “Gold Selenium/Gold” Nanoparticles and Photosensitizer for High-Efficiency Cancer Phototherapy

Gold nanostructures have generated significant attention in biomedical areas because of their major role in cancer photothermal therapeutics. In order to conveniently combine gold nanostructures and drugs into one nanocomposite, Au₂Se/Au core–shell nanostructures with strong near-infrared-absorbing properties were synthesized using a simple method and embedded inside bovine serum albumin (BSA) nanospheres by using a spray dryer equipped with an ultrasonic atomizer followed by thermal denaturation. The nanospheres with narrow size distribution mainly ranging from 450 to 600 nm were obtained. The Au₂Se/Au-loaded BSA nanospheres (1 mg) adsorbed at least 0.01 mg of water-insoluble zinc phthalocyanine (ZnPc) photosensitizer. After irradiation with a 655-nm laser (20 min), the temperature of the Au₂Se/Au-loaded BSA nanospheres [200 μL, 2 mg/mL, BSA/Au₂Se/Au 10:1 (w/w)] increased by over 20 °C from the initial temperature of 24.82?±?0.15 °C, and the release of ZnPc was improved compared with a corresponding sample without irradiation. After being incubated with cancer cells (human esophageal carcinoma Eca-109), the nanospheres exhibited photothermal and photodynamic therapy with a synergistic effect upon laser irradiation. This work provides novel Au₂Se/Au-loaded polymer nanospheres prepared by a high-efficiency strategy for incorporating drugs for improving the efficiency in killing cancer cells.     

Sorption-luminescence determination of gold,silver, and platinum with the use of silica gel chemically modified with <Emphasis Type="Italic">N</Emphasis>-(1,3,4-thiodiazole-2-thiol)-<Emphasis Type="Italic">N</Emphasis>′-propylurea groups

Silica gel chemically modified with N-(1,3,4-thiodiazole-2-thiol)-N′-propylurea extracted gold(III) from solutions in the range of 6 M HCl-pH 8 and silver(I) from nitric acid solutions in the range of 6 M HNO₃-pH 8 and 1–2 M HCl at 20°C with 99.0–99.9% recovery and a sorption equilibration time of 5 min. Platinum(II) was quantitatively extracted at room temperature from solutions in the range of 4 M HCl-pH 8; the sorption equilibration time was 20 min. For the quantitative extraction of platinum(IV), it should be reduced to platinum(II). The intense yellowish orange luminescence (λ_max (Au) = 575 nm, λ_max (Ag) = 550 nm, and λ_max(Pt) = 620 nm) of surface complexes at 77 K under UV irradiation was used in the development of procedures for the low-temperature sorption-luminescence determination of gold, silver, and platinum. The detection limits were 0.15 (Au), 0.1 (Ag), and 0.05 μg (Pt) per 0.1 g sorbent. The calibration function was linear to 50 (Au, Ag) or 80 μg (Pt) per 0.1 g sorbent. The relative standard deviation in the determination of more than 5 μg of a metal was no higher than 6%. The sorption-luminescence determination procedures were tested in the determination of gold in gold-containing concentrates and their processing products and platinum in alumina-platinum catalysts.     

Platinum–titanium intermetallic nanoparticle catalysts for oxygen reduction reaction with enhanced activity and durability

A facile method to prepare Pt–Ti intermetallic nanoparticles supported on carbon was developed. Starting from a commercial Pt/C catalyst, TiO₂ layers were formed on the Pt/C then thermal annealing under a reducing condition successfully produced intermetallic Pt–Ti nanoparticles with an average size of 4.2 nm. The intermetallic Pt–Ti/C showed enhanced activity and durability for oxygen reduction reaction due to the change in electronic structure and less aggregation.     

Chitosan-mediated synthesis of mesoporous α-Fe2O3 nanoparticles and their applications in catalyzing selective oxidation of cyclohexane

This paper reports the chitosan-mediated synthesis of porous hematite nanoparticles with FeCl₃ as the precursor via a hydrothermal approach at 160 °C. A series of porous chitosan/iron oxide hybrid nanoparticles were obtained via changing the ratio of chitosan to FeCl₃, FeCl₃ concentration and pH value of the reaction solution, and producing porous iron oxide nanoparticles after calcination. The as-prepared samples were characterized by means of X-ray diffraction, transmission electron microscopy, thermal gravimetric analysis, Fourier transform infrared, and N₂ sorption. The particle sizes of these metal oxides were less than 100 nm, and the pore sizes were in the range of 2–16 nm. It was demonstrated that chitosan played a key role in the formation of the porous structures. The resultant α-Fe₂O₃ nanoparticles were used as the support to immobilize Au or Pd nanoparticles, producing Au/α-Fe₂O₃ or Pd/α-Fe₂O₃ nanoparticles. The as-prepared α-Fe₂O₃ nanocatalyst exhibited high selectivity towards cyclohexanone and cyclohexanol for catalyzing cyclohexane oxidation with O₂ at 150°C.     

Nonhydrolytic sol–gel and gram-scale synthesis of surfactant-free maghemite nanoparticles with high surface area

An organic molecule was used as a surfactant for nanoparticle synthesis in liquid phase. However, residual molecules on the surface of the nanoparticles limit their catalytic applications, because the interaction of a reactant with the nanoparticle surface is interrupted. Therefore, it is favorable for catalytic applications that the organic molecule used in the synthesis of nanoparticles only induces a sol–gel reaction of the metal precursors and the formation of nanoparticles and hardly adheres to the resulting nanoparticles. Herein, we report surfactant-free and high-surface area maghemite nanostructures via nonhydrolytic sol–gel reaction. Using Fe(acetylacetonate)₃ as an iron precursor and hexylamine as a solvent and growth inhibitor, Fe₂O₃ nanoparticles were generated by nonhydrolysis of the iron complex and condensation at 140 °C under an air atmosphere. Characterization revealed monodisperse nanoparticles with an average size of 2.3 nm and a crystalline phase of maghemite. Residual hexylamine is hardly observed, and thus their specific surface area is 403.7 m²/g. An experimental comparison of the Fe₂O₃ synthesis with hexylamine and benzylamine indicates that the cone angle of an organic molecule is an important factor in the synthesis of nanoparticles with a small size and high surface area.