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This paper describes the effects of doped metals on hydrogen evolution reaction (HER) electrocatalyzed by atomically controlled MAu24 and M2Au36 nanoclusters, where M = Pt and Pd. HER performances, such as onset potential ( Eonset), catalytic current density, and turnover frequency (TOF), are comparatively examined with respect to the doped metals. Doping Pt or Pd into gold nanoclusters not only changes the electrochemical redox potentials of nanoclusters but also considerably improves the HER activities. Eonset is found to be controlled by the nanocluster's reduction potential matching the reduction potential of H+. The higher catalytic current and TOF are observed with the doped nanoclusters in the order of PtAu24 > PdAu24 > Au25. The same trend is observed with the Au38 group (Pt2Au36 > Pd2Au36> Au38). Density functional theory calculations have revealed that the hydrogen adsorption free energy (Δ GH) is significantly lowered by metal-doping in the order of Au25 > PdAu24 > PtAu24 and Au38 > Pd2Au36 > Pt2Au36, indicating that hydrogen adsorption on the active site of nanocluster is thermodynamically favored by Pd-doping and further by Pt-doping. The doped metals, albeit buried in the core of the nanoclusters, have profound impact on their HER activities by altering their reduction potentials and hydrogen adsorption free energies.

Compared to fluorescence, electrogenerated chemiluminescence (ECL) can be a superior analytical tool in terms of sensitivity and signal-to-noise ratios due to the absence of background emissions from unwanted photoexcitation. Semiconductor nanoparticles (NPs) are highly promising in many analytical applications, because they can produce stable ECL and possess surface-dependent, tuneable ECL properties. This minireview deals with the brief overview of ECL energetics and processes; the current progress of ECL of semiconductor NPs; and recent advances in biological sensing based on ECL of semiconductor NPs. The current challenges and perspectives on ECL of semiconductor NPs and their biological sensing applications are also discussed.

This paper describes the effects of doped metals on hydrogen evolution reaction (HER) electrocatalyzed by atomically controlled MAu

We report a carbon-based, three-dimensional nanofluidic transport membrane that enables gated, or on/off, control of the transport of organic molecular species and metal ions using an applied electrical potential. In the absence of an applied potential, both cationic and anionic molecules freely diffuse across the membrane via a concentration gradient. However, when an electrochemical potential is applied, the transport of ions through the membrane is inhibited.

We report reactivity of the gold nanoparticle [TOA+] [Au25(SC2Ph)18]1− (TOA+ = tetraoctylammonium; SC2Ph = phenylethanethiolate = L; [Au25(SC2Ph)18]1− = Au25L181−) with Ag+, Cu2+, and Pb2+ ions. Titration of solutions of Au25L181− in CH2Cl2 with one and two equivalents of Ag+ produces changes in absorbance spectra with isosbestic points, and a titration curve break at 1:1 mol ratio, indicating a stoichiometric interaction. Similar effects are seen with Cu2+ and Pb2+ additions, but the break occurs at 0.5:1 mol ratio metal/nanoparticle. Changes in Au25L181− absorbance and fluorescence spectra are qualitatively similar to those accompanying oxidation of the Au25L181− nanoparticle anion, but the spectra of the stoichiometric products differ slightly according to the metal ion. Addition of higher excess of Ag+ or Cu2+ causes loss of characteristic [Au25(SC2Ph)18]1− UV−vis spectral fine structure and apparent irreversible refining into larger nanoparticles. Voltammetric currents for nanoparticle 0/-1 and +1/0 ...

Proton nuclear magnetic resonance (NMR) was used to measure the rate constant and activation energy barrier for electron self-exchanges of the phenylethanethiolate-protected nanoparticle couple [Au25(SC2Ph)18]0/1−. The thiolate ligand α-methylene proton resonances of electrolytically prepared CD2Cl2 solutions of the oxidized (Au250) and reduced (Au251−) nanoparticles exhibit characteristic chemical shifts and line-shapes. That for the α-CH2 protons in Au250 is shifted ∼2 ppm downfield from Au251− and has an increased line-width reflecting the odd electron count of the nanoparticle core. Solution mixtures of Au250 and Au251− exhibit further peak broadening and intermediate values of α-CH2 proton chemical shifts, effects quantitatively consistent with an electron self-exchange process in the fast-exchange regime. Analysis of changes in peak broadening at varied total nanoparticle concentration and at varied temperatures produces a rate constant for [Au25(SC2Ph)18]0/1− self-exchange of 3.0(±0.1) × 107 M−1s−1...

The electron-transport properties of unlinked and linked solid-state films of very small “Au38” nanoparticles (monolayer protected clusters, or MPCs) remarkably change in opposing directions upon contact with increasing pressures of CO2 gas (0∼6.6 MPa). Electronic conductivities (σEL) of dropcast, unlinked Au MPC films increase up to 31-fold with increasing CO2 pressure, while σEL of dithiol-linked Au MPC films decreases with increasing CO2 pressure. In conductivity by electron hopping between electron donor and acceptor Au MPC cores, the organic protecting ligands serve as a solvent shell whose properties influence the dynamics of electron transport. Exposure of Au MPC films to CO2 and consequent swelling by CO2 (or organic vapor) sorption into the monolayers changes two key factors: core edge-to-edge electron tunneling distances (dHOP) and a previously underappreciated effect of dimension and/or frequency of local core thermal motions. Swelling induces increases in both, but depending on which factor i...

Hydrogen peroxide (H2O2) can be used as a coreactant to generate reductive-oxidation ECL of Tris(2,2′-bipyridine)ruthenium(II), Ru(bpy)32+ (bpy = 2,2′-bipyridine), in pH 7.5 phosphate buffer solution (PBS). Although Ru(bpy)3+ is adsorbed and precipitated on the electrode upon reduction of Ru(bpy)32+ in aqueous solutions, ECL can still be generated and scanning electrochemical microscopy (SECM) experiments verified the presence of some dissolved Ru(bpy)3+ in the solution. When H2O2 is electrochemically reduced, it produces hydroxyl radical ( OH). ECL is generated by an energetic electron transfer (ET) reaction between Ru(bpy)3+ and OH. The ECL intensity depends on both the Ru(bpy)32+ and H2O2 concentrations. However, a relatively high concentration of H2O2 (>1 mM H2O2 with 0.1 mM Ru(bpy)32+) quenches ECL significantly. H2O2 also quenches the photoluminescence of Ru(bpy)32+ with a quenching rate constant of 5.7 × 106 M−1 s−1.

We characterized the acid–base properties, electrochemistry, and electrogenerated chemiluminescence (ECL) of neutral red in acetonitrile (MeCN). To determine the acid–base properties, the basic form (NR) of neutral red was prepared and titrated with anhydrous HClO 4 , yielding p K a = 6.5 in MeCN. NR showed three irreversible electrochemical oxidations and a one-electron reversible reduction. However, the acid form (NRH + ) was reduced at more positive potentials than NR in a two-electron transfer reaction. Benzoyl peroxide (BPO) was used as a co-reactant to generate ECL on reduction of NR because it produces a strong oxidizing agent ( C 6 H 5 CO 2 ) on reduction. A high concentration of BPO quenched ECL. NRH + did not produce ECL because its reduction was by the transfer of two electrons and the energy available in the ECL reaction was not sufficient to generate an excited state. However, the NR ECL showed a maximum intensity at 610 nm, which corresponds to the λ max of NRH + fluorescence rather than that of NR. The ECL intensity of NR depended strongly on the concentration of NR, BPO, and trifluoroacetic acid (TFA). The integrated ECL intensity of NR, compared with that of Ru ( bpy ) 3 2 + , yielded a relative ECL intensity ratio, I NR / I Ru(II) of ∼0.05.

Thermal decomposition of dimethyl azo(bisisobutyrate) in a solution containing C(60) produced 1,4- and 1, 16-di(2-carbomethoxy-2-propyl)-1,x-dihydro[60]fullerenes in yields of 21% and 27%, respectively, based on reacted C(60). The structure of this first 1,16-dialkyl-1,16-dihydro[60]fullerene was assigned from (13)C 2D INADEQUATE NMR spectra. The 1,16-isomer has first and second electrochemical reduction potentials shifted positively by 0. 18 V relative to those of the 1,4-isomer. From the close similarity of all spectral, chromatographic, and electrochemical data, the previously unassigned isomer of 1,x-di(2-cyano-2-propyl)-1, x-dihydro[60]fullerene, which was obtained from azo(bisisobutyronitrile) and C(60), is also a 1,16-isomer.

Thermal decomposition of azo(bisisobutyronitrile) in a 1,2-dichlorobenzene solution of C60 gave three regioisomeric 1,x-di(2-cyano-2-propyl)-1,x-dihydro[60]fullerenes in 12, 2, and 4% yields, assig...

Noncovalently linked electron donor-acceptor complexes consisting of either zinc tetraphenylporphyrin, (TPP)Zn, or zinc octaethylporphycene, (OEPc)Zn, as donor and pyridine appended C(60), py approximately C(60), as acceptor, via axial coordination of zinc, are reported. The UV-visible and (1)H NMR spectral studies reveal 1:1 complex formation between the donor and acceptor entities. The determined K values follow the oxidation potential of the employed zinc tetrapyrroles, and the calculated thermodynamic parameters reveal stable complexation. The singlet emission studies show efficient quenching of the investigated zinc tetrapyrrole emission upon axial coordination of pyridine appended C(60). Free-energy calculations indicate that the photoinduced electron transfer from the singlet excited zinc tetrapyrrole to C(60) is exergonic, and the estimated rates of electron transfer are found to be (2.4 +/- 0.3) x 10(8) s(-)(1) for the (TPP)Zn-py approximately C(60) complex and (2.2 +/- 0.3) x 10(8) s(-)(1) for the (OEPc)Zn-py approximately C(60) complex, respectively.

The homogeneous electrocatalytic reduction of 1,2-dihaloethanes by anions of larger fullerenes, C76, C78, and C84, is presented, and structure−reactivity correlations are derived by including our d...

The first report on the homogeneous electrocatalytic reduction of halogenated alkanes by C70 anions is presented. Cyclic voltammetry (CV) measurements indicate that C70n- (n = 2 or 3), electrochemically generated in 0.1 M (TBA)PF6, benzonitrile, catalyzes the dehalogenation of α,ω-dihaloalkanes, X(CH2)mX (X = Cl, Br, or I and m = 2−8). Values of the second-order rate constant, k, for the electrocatalytic dehalogenation of the α,ω-dihaloalkanes by the C70n- anions were determined by using the rotating-disk electrode (RDE) voltammetry under pseudo-first-order conditions with respect to the α,ω-dihaloalkanes. In accordance with Saveant's theory of dissociative reduction, the k values increase in the order Cl < Br < I for the investigated 1,2-dihaloethanes. The k values also decrease with the number of carbon atoms of the alkyl chain for the investigated series of α,ω-diiodoalkanes. The calculated k values for the C70n- (n = 2 or 3) catalysts are generally smaller than those for the C60n- (n = 2 or 3) catalys...

Electroreduction of a homologous series of α,ω-diiodoalkanes I(CH2)mI (m = 1−8) is shown to be catalyzed by C60n- anions (n = 2, 3) both in solution and at a C60 film-coated electrode. Solution electrocatalysis occurred for the anions of n = 2 and 3 in 0.1 M (TBA)PF6 in benzonitrile at a platinum working electrode. Electrocatalysis at the film-coated electrode occurred for anions of n = 1 and 2 in 0.1 M (TBA)PF6 in acetonitrile. For solution electrocatalysis, the second-order catalytic rate constants were determined by voltammetry at a rotating disk electrode under pseudo-first-order conditions with respect to the α,ω-diiodoalkanes. The determined k values increase in the order C5 < C8 < C4 < C3 < C6 ≪ C2 for the number of carbon atoms of the alkyl chain of the α,ω-diiodoalkanes. The GC−MS and HPLC product analyses of the constant potential bulk electrolyses revealed that alkanes, alkenes, and monoiodoalkyl derivatives are formed primarily, except for the reaction of C603- with either 1,3-diiodopropane or...

Thermal decomposition of azo(bisisobutyronitrile) in a 1,2-dichlorobenzene solution of C60 gave three regioisomeric 1,x-di(2-cyano-2-propyl)-1,x-dihydro[60]fullerenes in 12, 2, and 4% yields, assig...

The near-infrared photoluminescence of monolayer-protected Au38 and Au140 clusters (MPCs) is intensified with exchange of nonpolar ligands by more polar thiolate ligands. The effect is general and includes as more polar in-coming ligands: thiophenolates with a variety of p-substituents; alkanethiolates omega-terminated by alcohol, acid, or quaternary ammonium groups; and thio-amino acids. Remarkably, place exchanges of the initial phenylethanethiolates on Au38 MPCs by p-substituted thiophenolates and thio-amino acids and of hexanethiolates on Au140 MPCs by omega-quaternary ammonium terminated undecylthiolates result in increases in the near-infrared (NIR) luminescence intensities that are linear with the number of new polar ligands. The increased intensities are systematically larger for thiophenolate ligands having more electron-withdrawing substituents. Analogous effects on intensities are observed in the NIR emission of Au140 MPCs upon place exchange of alkanethiolates with thiolates having short connecting alkanethiolate chains to quaternary ammonium and to omega-carboxylic acid termini, and with oxidative charging of the Au cores. The observations are consistent with sensitivity of the luminescence mechanism to any factor that enhances the electronic polarization of the bonds between the Au core atoms and their thiolate ligands. The luminescence is discussed in terms of a surface electronic excitation, as opposed to a core volume excitation.

The reaction occurring on electrooxidation of Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) and tri-n-propylamine (TPrA) leads to the production of Ru(bpy)(3)(2+) and light emission. The accepted mechanism of this widely used reaction involves the reaction of Ru(bpy)(3)(3+) and a reduced species derived from the free radical of the TPrA. However, this mechanism does not account for many of the observed features of this reaction. A new route involving the intermediacy of TPrA cation radicals (TPrA(*+)) in the generation of Ru(bpy)(3)(2+) was established, based on results of scanning electrochemical microscopy (SECM)-electrogenerated chemiluminescence (ECL) experiments, as well as cyclic voltammetry simulations. A half-life of approximately 0.2 ms was estimated for TPrA(*+) in neutral aqueous solution. Direct evidence for TPrA(*+) in this medium was obtained via flow cell electron spin resonance (ESR) experiments at approximately 20 degrees C. The ESR spectra of the TPrA(*+) species consisted of a relatively intense and sharp septet with a splitting of approximately 20 G and a g value of 2.0038.

Measurements of the core and ligand monolayer compositions of small gold nanoparticles (NPs) using electrospray ionization (ESI) mass spectrometry were performed by incorporating ionization tags, methoxy penta(ethylene glycol) thiolate ligands (-S-PEG), into the ligand monolayers via ligand exchange. During ESI, alkali metal ions (M+) coordinate to the -S-PEG ligands and give the NPs positive charge. Atomically precise, high-resolution measurements show unequivocally that the NP composition is Au25(ligand)18. The predominant ions, M4Au25(ligand)183+ and M5Au25(ligand)184+, have 1− charge on the core. Because ligand exchange is a statistical process, there is a distribution of mixed-monolayer exchange products, which is reflected in the mass spectra.

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