Synthesis of poly(N-vinyl-2-pyrrolidone) adsorbed-AuPt/C bimetallic nanoparticles and their unusual electrocatalytic activity towards methanol tolerant oxygen reduction reaction

Journal of Solid State Electrochemistry - It has been suggested that the presence of adsorbed impurities, such as capping agent or organic reaction products adsorbed on the metallic nanoparticles,...     

Pt-decorated PdCo@Pd/C core-shell nanoparticles with enhanced stability and electrocatalytic activity for the oxygen reduction reaction

A simple method for the preparation of PdCo@Pd core-shell nanoparticles supported on carbon based on an adsorbate-induced surface segregation effect has been developed. The stability of these PdCo@Pd nanoparticles and their electrocatalytic activity for the oxygen reduction reaction (ORR) were enhanced by decoration with a small amount of Pt deposited via a spontaneous displacement reaction. The facile method described herein is suitable for large-scale, lower-cost production and significantly lowers the Pt loading and thus the cost. The as-prepared PdCo@Pd and Pd-decorated PdCo@Pd nanocatalysts have a higher methanol tolerance than Pt/C in the ORR and are promising cathode catalysts for fuel cell applications.     

Synthesis and crystal structure of bis(O-methyl hydrogenato carbonodithioate)-Pb(II): structural,optical and photocatalytic studies of PbS nanoparticles from the complex

Abstract

Lead(II) methyl xanthate [Pb(S₂COMe)₂] was synthesized and characterized by single crystal X-ray crystallography. The molecular structure showed a distorted tetrahedral geometry around Pb(II) with each monomeric unit linked with another through Pb···S interactions. The compound was used to prepare hexadecylamine capped PbS (HDA-PbS) and oleylamine capped PbS (OLA-PbS) nanoparticles. The PbS nanoparticles were indexed to the cubic PbS crystalline phase with particle sizes of 4.5 – 34.5?nm. The estimated optical bandgaps obtained from the tauc’s plots were 3.47 and 3.30?eV for HDA-PbS and OLA-PbS, respectively, which are blue shifted in comparison to bulk PbS. The photodegradation of methylene blue using PbS as photocatalyst shows that HDA-PbS have the best degradation efficiency of 77.70% after 240?min.     

Site selectivity in the reactions of the hexanuclear platinum cluster [Pt6(mu-PtBu2)4(CO)6][CF3SO3]2

The previously reported hexanuclear cluster [Pt(6)(mu-PtBu(2))(4)(CO)(6)](2+)[Y](2) (1-Y(2): Y=CF(3)SO(3) (-)) contains a central Pt(4) tetrahedron bridged at each of the opposite edges by another platinum atom; in turn, four phosphido ligands bridge the four Pt-Pt bonds not involved in the tetrahedron, and, finally, one carbonyl ligand is terminally bonded to each metal centre. Interestingly, the two outer carbonyls are more easily substituted or attacked by nucleophiles than the inner four, which are bonded to the tetrahedron vertices. In fact, the reaction of 1-Y(2) with 1 equiv of [nBu(4)N]Cl or with an excess of halide salts gives the monochloride [Pt(6)(mu-PtBu(2))(4)(CO)(5)Cl](+)[Y], 2-Y, or the neutral dihalide derivatives [Pt(6)(mu-PtBu(2))(4)(CO)(4)X(2)] (3: X=Cl; 4: X=Br; 5: X=I). Moreover, the useful unsymmetrically substituted [Pt(6)(mu-PtBu(2))(4)(CO)(4)ICl] (6) was obtained by reacting equimolar amounts of 2 and [nBu(4)N]I, and the dicationic derivatives [Pt(6)(mu-PtBu(2))(4)(CO)(4)L(2)](2+)[Y](2) (7-Y(2): L=(13)CO; 8-Y(2): L=CNtBu; 9-Y(2): L=PMe(3)) were obtained by reaction of an excess of the ligand L with 1-Y(2). Weaker nitrogen ligands were introduced by dissolving the dichloride 3 in acetonitrile or pyridyne in the presence of TlPF(6) to afford [Pt(6)(mu-PtBu(2))(4) (CO)(4)L(2)](2+)[Z](2) (Z=PF(6) (-), 10-Z(2): L=MeCN; 11-Z(2): L=Py). The "apical" carbonyls in 1-Y(2) are also prone to nucleophilic addition (Nu(-): H(-), MeO(-)) affording the acyl derivatives [Pt(6)(mu-PtBu(2))(4)(CO)(4)(CONu)(2)] (12: Nu=H; 13: Nu=OMe). Complex 12 is slowly converted into the dihydride [Pt(6)(mu-PtBu(2))(4)(CO)(4)H(2)] (14), which was more cleanly prepared by reacting 3 with NaBH(4). In a unique case we observed a reaction involving also the inner carbonyls of complex 1, that is, in the reaction with a large excess of the isocyanides R-NC, which form the corresponding persubstituted derivatives [Pt(6)(mu-tPBu(2))(4)(CN-R)(6)](2+)[Y](2), (15-Y(2): R=tBu; 16-Y(2) (2-): R=-C(6)H(4)-4-C triple bond CH). All complexes were characterized by microanalysis, IR and multinuclear NMR spectroscopy. The crystal and molecular structures of complexes 3, 5, 6 and 9-Y(2) are also reported. From the redox viewpoint, all complexes display two reversible one-electron reduction steps, the location of which depends both upon the electronic effects of the substituents, and the overall charge of the original complex.     

Influence of Perfluorinated End Groups on the SFRD of [Pt(cod)Me(CnF2n+1)] onto Porous Al2O3 in CO2 under Reductive Conditions

The optimized synthesis of a range of cyclooctadiene‐stabilized Pt complexes that contained different perfluoro‐alkane chains, [Pt(cod)Me(C_nF_2n+1)], is presented. These metal–organic compounds were employed in the so‐called supercritical fluid reactive deposition (SFRD) in CO₂ under reductive conditions to generate metallic nanoparticles on aluminum oxide as a porous support. Thus, Al₂O₃‐supported Pt nanoparticles with a narrow particle‐size distribution were obtained. At a reduction pressure of 15.5 MPa and a temperature of 353 K, particle diameters of d₅₀=2.3–2.8 nm were generated. Decreasing the pressure during the reduction reaction led to slightly larger particles whilst decreasing the amount of organometallic precursor in CO₂ yielded a decrease in the particle size from x₅₀=3.2 nm to 2.6 nm and a particle‐size distribution of 2.2 nm. Furthermore, substitution of the CH₃ end group by the C_nF_2n+1 end groups led to a significant drop in Pt loading of about 50 %. Within the series of perfluorinated end groups that were considered, the Pt complex that contained a branched perfluoro‐isopropyl group showed the most‐interesting results when compared to the control precursor, [Pt(cod)Me₂] ( 1 ).     

Electronic structure and chain-length effects in diplatinum polyynediyl complexes trans,trans-[(X)(R3P)2Pt(C triple bond C)(n)Pt(PR3)2(X)]: a computational investigation

Structure and bonding in the title complexes are studied using model compounds trans,trans-[(C6H5)(H3P)2Pt(C triple bond C)(n)Pt(PH3)2(C6H5)] (PtCxPt; x = 2n = 4-26) at the B3LYP/LACVP* level of density functional theory. Conformations in which the platinum square planes are parallel are very slightly more stable than those in which they are perpendicular (DeltaE = 0.12 kcal mol(-1) for PtC8Pt). As the carbon-chain length increases, progressively longer C triple bond C triple bonds and shorter triple bond C-C triple bond single bonds are found. Whereas the triple bonds in HCxH become longer (and the single bonds shorter) as the interior of the chain is approached, the PtC triple bond C triple bonds in PtCxPt are longer than the neighboring triple bond. Also, the Pt-C bonds are shorter at longer chain lengths, but not the H-C bonds. Accordingly, natural bond orbital charge distributions show that the platinum atoms become more positively charged, and the carbon chain more negatively charged, as the chain is lengthened. Furthermore, the negative charge is localized at the two terminal C triple bond C atoms, elongating this triple bond. Charge decomposition analyses show no significant d-pi* backbonding. The HOMOs of PtCxPt can be viewed as antibonding combinations of the highest occupied pi orbital of the sp-carbon chain and filled in-plane platinum d orbitals. The platinum character is roughly proportional to the Pt/Cx/Pt composition (e.g., x = 4, 31 %; x = 20, 6 %). The HOMO and LUMO energies monotonically decrease with chain length, the latter somewhat more rapidly so that the HOMO-LUMO gap also decreases. In contrast, the HOMO energies of HCxH increase with chain length; the origin of this dichotomy is analyzed. The electronic spectra of PtC4Pt to PtC10Pt are simulated. These consist of two pi-pi* bands that redshift with increasing chain length and are closely paralleled by real systems. A finite HOMO-LUMO gap is predicted for PtCinfinityPt. The structures of PtCxPt are not strictly linear (average bond angles 179.7 degrees -178.8 degrees ), and the carbon chains give low-frequency fundamental vibrations (x = 4, 146 cm(-1); x = 26, 4 cm(-1)). When the bond angles in PtC12Pt are constrained to 174 degrees in a bow conformation, similar to a crystal structure, the energy increase is only 2 kcal mol(-1). The above conclusions should extrapolate to (C triple bond C)(n) systems with other metal endgroups.     

Syntheses and Characterizations of Luminescent Complexes [(BINAP)Pt(C≡CC6H4R-p)2] (R = H, 1; CH3, 2) (BINAP = 2,2''-Bis(diphenylphosphino)-1,1''-binaphthyl)

[(BINAP)Pt(C≡CC6H4R-p)2] (R = H, 1; CH3, 2) (BINAP = 2,2'-bis(diphenylphos- phino)-1,1'-binaphthyl) were synthesized and characterized by X-ray crystallography. Complex 1 crystallizes in triclinic, space group P with a = 11.699(3), b = 12.512(3), c = 15.611(4)(A), α = 93.277(3),β= 97.626(2), γ = 97.375(14)o, V = 2239.9(9)(A)3, Mr = 1014.92, Z = 2, Dc = 1.505 g/cm3, F(000) = 1010, μ(MoKα) = 3.244 mm-1, the final R = 0.0338 and wR = 0.0905 for 7738 observed reflections (I > 2σ(I)). Complex 2 crystallizes in monoclinic, space group P21/n with a = 18.03690 (10), b = 13.06060(10), c = 21.6913(3)(A), β= 96.5430(10)o, V = 5076.60(9)(A)3, Mr = 1132.94, Z = 4, Dc = 1.482 g/cm3, F(000) = 2272, μ(MoKα) = 2.973 mm-1, the final R = 0.0481 and wR = 0.0893 for 8916 observed reflections (I > 2σ(I)). Both complexes emit intensively photoluminescence in both solid state and fluid solution due to MLCT (Pt→-C≡CC6H4R-p) emissive state.     

1H, 13C, 195Pt and 15N NMR structural correlations in Pd(II) and Pt(II) chloride complexes with various alkyl and aryl derivatives of 2,2'-bipyridine and 1,10-phenanthroline

(1)H, (13)C, (195)Pt and (15)N NMR studies of platinide(II) (M = Pd, Pt) chloride complexes with such alkyl and aryl derivatives of 2,2'-bipyridine and 1,10-phenanthroline as LL = 6,6'-dimethyl-bpy, 5,5'-dimethyl-bpy, 4,4'-di-tert-butyl-bpy, 2,9-dimethyl-phen, 2,9-dimethyl-4,7-diphenyl-phen, 3,4,7,8-tetramethyl-phen, having the general [M(LL)Cl(2)] formula were performed and the respective chemical shifts (δ(1H), δ(13C), δ(195Pt), δ(15N)) reported. (1)H high-frequency coordination shifts (Δ(coord)(1H) = δ(complex)(1H)-δ(ligand)(1H)) mostly pronounced for nitrogen-adjacent protons and methyl groups in the nearest adjacency of nitrogen, as well as (15)N low-frequency coordination shifts (Δ(coord)(15H) = δ(complex)(15H)-δ(ligand)(15H)) were discussed in relation to the molecular structures.     

Immobilization of Au nanoparticles on poly(glycidyl methacrylate)-functionalized magnetic nanoparticles for enhanced catalytic application in the reduction of nitroarenes and Suzuki reaction

We report a novel strategy for the synthesis of magnetic nanocomposite for highly efficient catalysis. Poly(glycidyl methacrylate) (PGMA) chains were grafted to the surface of magnetic nanoparticles (MNPs) through surface-initiated reversible addition-fragmentation chain transfer polymerization. Then, the oxirane rings in the PGMA chains were opened with 2,6-diamino pyridine (DAP) molecules as ligands to prepare the solid support. Finally, this magnetic nanocomposite was used for the immobilization of gold nanoparticles. Fourier-transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, transmission electron microscopy, scanning electron microscopy, gel permeation chromatography, vibrating sample magnetometry, and atomic absorption spectroscopy were used for characterization of the catalyst. The loading of gold nanoparticles on the solid support was 0.52 mmol/g. The catalytic activity of the prepared catalyst (MNP@PGMA@DAP@Au) was evaluated for the reduction of nitro compounds and C–C coupling reaction in water. The catalyst can be easily recovered and reused seven times without significant loss of catalytic activity.     

Facile fabrication of BUC‐21/g‐C3N4 composites and their enhanced photocatalytic Cr(VI) reduction performances under simulated sunlight

A series of BUC‐21/g‐C₃N₄ composites were facilely fabricated from two‐dimensional metal–organic framework BUC‐21 and two‐dimensional metal‐free polymer semiconductor graphitic carbon nitride (g‐C₃N₄) through ball‐milling, and characterized via powder X‐ray diffraction, Fourier transform infrared spectrometry, thermogravimetric analysis, transmission electron microscopy, and UV–visible diffuse reflectance, X‐ray photoelectron and photoluminescence emission spectrometry. The photocatalytic activities of B100G100 (weight ratio of BUC‐21 to g‐C₃N₄ being 1:1) towards Cr(VI) reduction were investigated upon the irradiation of simulated sunlight and real sunlight, in which the influences of various organic compounds (tartaric acid, citric acid and oxalic acid) as hole scavengers, pH values (2, 3, 4, 5, 6, 7 and 8) and foreign ions (ions in tap water and real surface water) were also investigated. The results revealed that B100G100 exhibited more outstanding photocatalytic Cr(VI) reduction than individual BUC‐21 and g‐C₃N₄, resulting from enhanced separation of photogenerated electrons and holes, which were confirmed via both photoluminescence emission and electrochemical determination. The B100G100 composite exhibited good reusability and stability after several experimental runs. Also, the corresponding mechanism of photocatalytic reaction was proposed.     

The ball-shaped heteropolytungstates [[Sn(CH3)2(H2O)]24[Sn(CH3)2]12(A-XW9O34)12]36- (X=P, As): stability, redox and electrocatalytic properties in aqueous media

The electrochemical behavior of the ball-shaped heteropolytungstates [[Sn(CH(3))(2)(H(2)O)](24)[Sn(CH(3))(2)](12)(A-XW(9)O(34))(12)](36-) (X=P, 1; As, 2) was examined in aqueous electrolytes by redissolution of their respective mixed cesium-sodium salts Cs(14)Na(22)[[Sn(CH(3))(2)(H(2)O)](24)[Sn(CH(3))(2)](12) (A-PW(9)O(34))(12)]149 H(2)O (Cs(14)-1) and Cs(14)Na(22)[[Sn(CH(3))(2)(H(2)O)](24)[Sn(CH(3))(2)](12)(A-AsW(9)O(34))(12)]149 H(2)O (Cs(14)-2). In the studied media, Cs(14)-2 is readily soluble in contrast to the significantly less soluble Cs(14)-1. The solubility of Cs(14)-1 is increased by the presence of Li(+) ions in solution. Gel filtration studies with 1 and 2 rule out a decay of the dodecameric spherical assemblies to Keggin-based monomers on the timescale of the experiment. By UV/Vis spectroscopy and cyclic voltammetry, 2 was found to be significantly less stable than 1 and both polyanions also show rather different decomposition pathways. Polyanion 1 collapses first into Keggin-type monomers which might contain the trilacunary [A-alpha-PW(9)O(34)](9-). The final monomeric species obtained from 1 appears to be very similar to [PW(11)O(39)](7-), which is the final transformation product of [A-alpha-PW(9)O(34)](9-) in the same media. In contrast, 2 does not seem to follow an analogous transformation pathway as that of the trilacunary [A-alpha-AsW(9)O(34)](9-). Importantly, stabilization of 1 is observed in chloride media. The fairly long-term stability of 1 in 1 M LiCl, pH 3, has allowed for its electrochemical study to be carried out. The solid-state cyclic voltammogram of 1 entrapped in a carbon paste electrode shows the same characteristics as 1 dissolved in chloride solutions, thus supporting the conclusion that the polyanion is stable in these environments. Controlled potential coulometry on 1 indicates that the number of electrons consumed in the first wave is larger than twenty. To our knowledge, 1 constitutes the first example of a molecule that can take up such a large number of electrons resulting in a chemically reversible W-wave. These properties show promise for future fundamental and applied studies. Polyanion 1 is also efficient in the electrocatalytic reduction of NO(x), including nitrate. Finally, a remarkable interaction was found between 1 and NO, a highly promising feature for biomimetic applications.     

Electrochemistry of the two-dimensional heteronuclear [Fe3Pt3(CO)15] n clusters (n=2-, 1-, 0): MO treatment of the skeletal adjustments in 86-84e − congeners

Electrochemical studies show that it is possible to move step-wise and reversibly between the redox congeners of the series [Fe₃Pt₃(CO)₁₅] ⁿ ,n=2-/1-/0. By contrast, a multielectron reduction of the dianion leads to an irreversible demolition of the species. When [Fe₃Pt₃(CO)₁₅]^2– is treated with one or two equimolar amounts of the oxidant [Fe(C₅H₅)₂]⁺, the oxidized species (n=1- andn=0) can be also obtained. It can be established or extrapolated from the already known structures of the dianion and the monoanion that the successive oxidations strengthen the inner Pt-Pt linkages of the overall quasiplanar Fe₃Pt₃ skeleton. MO analysis, by establishing the antibonding nature of the frontier level from which the electrons are added or subtracted, allows the correlation of the bonding features of the inner Pt₃ skeleton with the redox propensities of the system.     

Catalytic activity of TiO2 nanoparticles in the synthesis of some 2,3-disubstituted dihydroquinazolin-4（1H）-ones

Green chemistry is playing an important role for synthesizing organic compounds, due to its eco-friendly nature and low cost. In green chemistry, metal nanoparticles exhibited some useful physical and chemical properties （catalytic activity）. Due to its diverse properties, nanoparticles can be utilized as a catalyst in various organic reactions. Recent research has been directed towards the utilization of eco- friendly and bio-friendly plant materials in nanoparticles synthesis. In our present work, TiO2 nanoparticles （TiO2 NPs） were synthesized using Annona squamosa peel extract and their catalytic applications were studied on the 2,3-disubstituted dihydroquinazolin-4（l1H）-one synthesis. Synthesized compounds were confirmed using FT-IR.1H NMR, 13C NMR and GC-MS analyses.     

One-step solvothermal synthesis of N-doped TiO2 nanoparticles with high photocatalytic activity in the reduction of aqueous Cr（Ⅵ）

N-doped TiO2 （N-TiO2） nanoparticles were synthesized via a one-step low temperature （180℃） solvothermal route, which adopted NH4NO3 as the nitrogen source. The structure, composition, BET specific surface area, and optical properties of the as-synthesized product were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, N2 adsorption- desorption isotherms, and UV-vis diffuse reflectance spectroscopy. In addition, its photocatalytic properties were tested by the reduction of aqueous Cr（VI） under UV and visible light （x 〉 420 rim） irradiation. It was observed that for the reduction of aqueous Cr（VI）, the as-synthesized N-TiO2 nanoparticles not only exhibited much higher photocatalytic activity than P25 TiO2 under UV light, but also exhibited remarkably high photocatalytic activity under visible light （λ 〉 420 nm）.     

Mechanistic analysis of the oxygen reduction reaction at (La,Sr)MnO3 cathodes in solid oxide fuel cells

The primary aim of this work was to establish the mechanism of the oxygen reduction reaction (ORR) at (La(0.8)Sr(0.2))0.98MnO3 (LSM)-based cathodes in solid oxide fuel cells. Rate equations, based on the Butler-Volmer equation and employing either Langmuir or Temkin adsorption conditions for reactant and intermediate species, were derived, yielding predicted reaction orders and transfer coefficients. Experimental data were collected using half-cell cyclic voltammetry in a variable pO2 atmosphere (0.03 to 1 atm) at 600 to 900 degrees C, using both dense and porous LSM-based cathodes, employed to establish the impact of the accessibility of the active site on cathode activity. The rate of the ORR at dense LSM has been found to be limited by the dissociation of O(2ads)- at low currents and by the first electron-transfer step, reducing O(2ads) to O(2ads)-, at high currents. However, at porous LSM cathodes, the reaction mechanism is more difficult to deduce because the electrode morphology impacts significantly on the measured kinetic and mechanistic parameters, giving anomalous transfer coefficients of <0.5.     

Preparation of monometallic (Pd,Ag) and bimetallic (Pd/Ag,Pd/Ni,Pd/Cu) nanoparticles via reversed micelles and their use in the Heck reaction

The metal nanoparticles (NPs) have been prepared using a water-in-oil microemulsion system of water/dioctyl sulfosuccinate sodium salt (aerosol-OT, AOT)/isooctane at 25 °C. Since the NPs produced in this system can endure forcing conditions (100 °C), this system has been used for the synthesis of nano-catalysts in the Heck reactions. FE-SEM, DLS, and UV/vis analyses have been used to characterize the surface morphology, size, and proof of the formation of all the prepared metal NPs, respectively. In addition, the effects of some reaction parameters (here, bases and solvents) were optimized. Differences in the catalytic properties of the synthesized NPs have also been investigated. Consequently, the Pd/Cu (4:1) bimetallic NP showed the highest activity in the C–C coupling reaction of the iodobenzene with the styrene, thus it is employed as the superior catalyst in this study. Therefore, the Pd/Cu (4:1) bimetallic NPs were further investigated using TEM and XRD analyses. This catalyst system is also reusable for six runs with very negligible reduction in the efficiency.