Oxygen Reduction Reaction with Manganese Oxide Nanospheres in Microbial Fuel Cells.

Operating microbial fuel cells (MFCs) under extreme pH conditions offers a substantial benefit. Acidic conditions suppress the growth of undesirable methanogens and increase redox potential for oxygen reduction reactions (ORRs), and alkaline conditions increase the electrocatalytic activity. However, operating any fuel cells, including MFCs, is difficult under such extreme pH conditions. Here, we demonstrate a pH-universal ORR ink based on hollow nanospheres of manganese oxide (h-Mn3O4) anchored with multiwalled carbon nanotubes (MWCNTs) on planar and porous forms of carbon electrodes in MFCs (pH = 3-11). Nanospheres of h-Mn3O4 (diameter ∼ 31 nm, shell thickness ∼ 7 nm) on a glassy carbon electrode yielded a highly reproducible ORR activity at pH 3 and 10, based on rotating disk electrode (RDE) tests. A phenomenal ORR performance and long-term stability (∼106 days) of the ink were also observed with four different porous cathodes (carbon cloth, carbon nanofoam paper, reticulated vitreous carbon, and graphite felt) in MFCs. The ink reduced the charge transfer resistance (R ct) to the ORR by 100-fold and 45-fold under the alkaline and acidic conditions, respectively. The current study promotes ORR activity and subsequently the MFC operations under a wide range of pH conditions, including acidic and basic conditions.

Diffusion doping of cobalt in rod-shape anatase TiO2 nanocrystals leads to antiferromagnetism.

Cobalt(ii) ions were adsorbed to the surface of rod-shape anatase TiO2 nanocrystals and subsequently heated to promote ion diffusion into the nanocrystal. After removal of any remaining surface bound cobalt, a sample consisting of strictly cobalt-doped TiO2 was obtained and characterized with powder X-ray diffraction, transmission electron microscopy, UV-visible spectroscopy, fluorescence spectroscopy, X-ray photoelectron spectroscopy, SQUID magnetometry, and inductively-coupled plasma atomic emission spectroscopy. The nanocrystal morphology was unchanged in the process and no new crystal phases were detected. The concentration of cobalt in the doped samples linearly correlates with the initial loading of cobalt(ii) ions on the nanocrystal surface. Thin films of the cobalt doped TiO2 nanocrystals were prepared on indium-tin oxide coated glass substrate, and the electrical conductivity increased with the concentration of doped cobalt. Magnetic measurements of the cobalt-doped TiO2 nanocrystals reveal paramagnetic behavior at room temperature, and antiferromagnetic interactions between Co ions at low temperatures. Antiferromagnetism is atypical for cobalt-doped TiO2 nanocrystals, and is proposed to arise from interstitial doping that may be favored by the diffusional doping mechanism.

Quantitative Attachment of Bimetal Combinations of Transition-Metal Ions to the Surface of TiO2 Nanorods.

We report the sequential, quantitative loading of transition-metal ions (Cr3+, Mn2+, Fe2+, Co2+, Ni2+, and Cu2+) onto the surface of rod-shaped anatase TiO2 nanocrystals in bimetallic combinations (6 C2 = 15) to form M,M'-TiO2 nanocrystals. The materials were characterized with transmission electron microscopy (TEM), powder X-ray diffraction (XRD), elemental analysis, X-ray photoelectron spectroscopy (XPS), and UV-visible spectroscopy. TEM and XRD data indicate that the sequential adsorption of metal ions occurs with the retention of the phase and morphology of the nanocrystal. Atomistic models of the M,M'-TiO2 nanocrystals were optimized with density functional theory calculations. Calculated UV-visible absorption spectra and partial charge density maps of the donor and acceptor states for the electronic transitions indicate the importance of metal-to-metal charge transfer (MMCT) processes.

Direct arylation catalysis with chloro[8-(dimesitylboryl)quinoline-κN]copper(I).

We report direct arylation of arylhalides with unactivated sp2 C-H bonds in benzene and naphthalene using a copper(I) catalyst featuring an ambiphilic ligand, (quinolin-8-yl)dimesitylborane. Direct arylation could be achieved with 0.2 mol % catalyst and 3 equivalents of base (KO(t-Bu)) at 80 °C to afford TON ≈160-190 over 40 hours.

Crystal structure of bis-(3-bromo-mesit-yl)(quino-lin-1-ium-8-yl)boron(III) tribromide.

The title compound, C27H26.82BBr2.18N(+)·Br3 (-), is a cationic tri-aryl-borane isolated as its tribromide salt. The aryl substituents include a protonated 8-quinolyl group and two 3-bromo-mesityl groups. The mol-ecule was prepared on combination of 3:1 Br2 and dimesit-yl(quinolin-8-yl)borane in hexa-nes. The refinement of the structure indicated a degree of 'over-bromination' (beyond two bromine atoms) for the cation. There are two tribromide ions in the asymmetric unit, both completed by crystallographic inversion symmetry.

Self-limiting adsorption of Eu³âº on the surface of rod-shape anatase TiO2 nanocrystals and post-synthetic sensitization of the europium-based emission.

The surface of oleic acid stabilized rod-shape anatase TiO2 nanocrystals was modified by adsorption of Eu(3+) ions. The Eu(3+) attachment showed Langmuir adsorption behavior, thus the loading of Eu(3+) could be controlled precisely up to surface saturation coverage. The Eu(3+)-TiO2 nanorods show weak Eu(3+) based luminescence. However, addition of thenoyltrifluoroacetone (TTFA) leads to coordination of the ligand to the Eu(3+) centers and the TTFA-Eu(3+)-TiO2 materials exhibit strong Eu(3+) fluorescence sensitized by the TTFA ligand.

Chloro({2-[mesityl(quinolin-8-yl-κN)boryl]-3,5-dimethyl-phenyl}methyl-κC)palladium(II) as a catalyst for Heck reactions.

We recently reported an air and moisture stable 16-electron borapalladacycle formed upon combination of 8-quinolyldimesitylborane with bis(benzonitrile)dichloropalladium(II). The complex features a tucked mesityl group formed upon metalation of an ortho-methyl group on a mesityl; however it is unusually stable due to contribution of the boron pz orbital in delocalizing the carbanion that gives rise to an η4-boratabutadiene fragment coordinated to Pd(II), as evidenced from crystallographic data. This complex was observed to be a highly active catalyst for the Heck reaction. Data of the catalyst activity are presented alongside data found in the literature, and initial comparison reveals that the borapalladacycle is quite active. The observed catalysis suggests the borapalladacycle readily undergoes reductive elimination; however the Pd(0) complex has not yet been isolated. Nevertheless, the ambiphilic ligand 8-quinolyldimesitylborane may be able to support palladium in different redox states.

Crystal structure of 8-iodo-quinolinium tetra-chlorido-aurate(III).

The structure of the title salt, (C9H7IN)[AuCl4], is comprised of planar 8-iodo-quinolinium cations (r.m.s. deviation = 0.05 Å) and square-planar tetra-chlorido-aurate(III) anions. The asymmetric unit contains one 8-iodo-quinolinium cation and two halfs of [AuCl4](-) anions, in each case with the central Au(III) atom located on an inversion center. Inter-molecular halogen-halogen contacts were found between centrosymmetric pairs of I [3.6178 (4) Å] and Cl atoms [3.1484 (11), 3.3762 (13), and 3.4935 (12) Å]. Inter-molecular N-H⋯Cl and C-H⋯Cl hydrogen bonding is also found in the structure. These inter-actions lead to the formation of a three-dimensional network. Additionally, there is an intra-molecular N-H⋯I hydrogen bond between the aromatic iminium and iodine. There are no aurophilic inter-actions or short contacts between I and Au atoms, and there are no notable π-stacking inter-actions between the aromatic cations.

Facile method to attach transition metal ions to the surface of anatase TiO(2) nanorods.

We report a robust, low-cost method to attach transition metal ions directly to the surface of anatase TiO2 rod-shaped nanocrystals with preservation of the host nanocrystal morphology and phase. The procedure has been optimized to achieve quantitative control of metal ion loading on the surface of the nanorods. The metal ion can be attached to the nanocrystal surface up to fullmonolayer coverage, after which the surface becomes saturated and there is no further addition.

Preparation of RHgCl via transmetalation of (8-quinolyl)SnMe3 and redistribution to R2Hg (R = 8-quinolyl): a highly distorted diorganomercury(II) with 84 degree C-Hg-C angle.

Transmetalation occurs upon addition of HgCl2 to (8-quinolyl)SnMe3 to yield (8-quinolyl)HgCl. The molecule features a frustrated Hg-N Lewis pair; however the mercury(II) center showed low affinity for sulfur Lewis bases, S8 or thiophene. In the presence of NH4SCN, ligand redistribution led to R2Hg. The molecule was found as linear or bent polymorphs, depending on the solvent of recrystallization. The geometry about Hg(II) in the bent polymorph is distorted trigonal prismatic that features a C-Hg-C angle of 84°, weak intramolecular Hg-N contacts, and two intermolecular η(2)-quinoline contacts in which the neighboring R2Hg molecule participates as a bis-η(2)-bidentate ligand.

Photoinduced Charge Transfer from Titania to Surface Doping Site.

We evaluate a theoretical model in which Ru is substituting for Ti at the (100) surface of anatase TiO2. Charge transfer from the photo-excited TiO2 substrate to the catalytic site triggers the photo-catalytic event (such as water oxidation or reduction half-reaction). We perform ab-initio computational modeling of the charge transfer dynamics on the interface of TiO2 nanorod and catalytic site. A slab of TiO2 represents a fragment of TiO2 nanorod in the anatase phase. Titanium to ruthenium replacement is performed in a way to match the symmetry of TiO2 substrate. One molecular layer of adsorbed water is taken into consideration to mimic the experimental conditions. It is found that these adsorbed water molecules saturate dangling surface bonds and drastically affect the electronic properties of systems investigated. The modeling is performed by reduced density matrix method in the basis of Kohn-Sham orbitals. A nano-catalyst modeled through replacement defect contributes energy levels near the bottom of the conduction band of TiO2 nano-structure. An exciton in the nano-rod is dissipating due to interaction with lattice vibrations, treated through non-adiabatic coupling. The electron relaxes to conduction band edge and then to the Ru cite with faster rate than hole relaxes to the Ru cite. These results are of the importance for an optimal design of nano-materials for photo-catalytic water splitting and solar energy harvesting.

1,2-Nucleophilic addition of 2-(picolyl)organoboranes to nitrile, aldehyde, ketone, and amide.

A series of 2-(picolyl)borane molecules were synthesized as products of the reaction between 2-(picolyl)lithium and R(2)BOMe (R = ethyl, 9-BBN, phenyl, 9-borafluorenyl). The 2-(picolyl)boranes were dimeric; whereas, monomers coordinated to LiOMe could be isolated when the synthesis was carried out in the presence of TMEDA and THF. The 2-(picolyl)boranes undergo reaction with nitriles, ketones, aldehydes, and amides with apparent 1,2-addition of the B-C(picolyl) bond to the unsaturated bond. Theoretical models reveal the presence of a donor orbital on the 2-(picolyl)borane with significant electron density at the benzylic carbon that we conclude was involved in nucleophilic attack on the electrophilic center of unsaturated organic functional groups.

Reactivity of the bifunctional ambiphilic molecule 8-(dimesitylboryl)quinoline: hydrolysis and coordination to Cu(I), Ag(I) and Pd(II).

The ambiphilic molecule 8-(dimesitylboryl)quinoline (1) was synthesized by treatment of 8-bromoquinoline or 8-iodoquinoline with n-BuLi followed by dimesitylboronfluoride. Hydrolysis of 1 is unusually rapid compared to bulky triorganoboranes with the sequential loss of mesitylene and formation of mesityl(quinolin-8-yl)borinic acid (2) and 8-quinoline boronic acid dimer (3). Cooperativity within the bifunctional ambiphilic site leads to water activation and protodeboronation of the B-C(Mes) bonds. Blocking of the ambiphilic site of 1 by methylation of the quinoline nitrogen atom leads to an air-stable N-methyl-quinolinium salt. Coordination complexes were formed by reaction of 1 with CuCl, Ag(OTf), and PdCl(2)(PhCN)(2) with coordination of the quinolinyl nitrogen to the metal ion. The Cu(I) and Ag(I) centers are stabilized by η(3)-BC(ipso)C(ortho)π-interaction. The isolated Pd(II) complex is a product of cyclometalation, resulting from elimination of HCl upon deprotonation of the ortho-methyl group of nearby mesityl. The bonding in 7 could be understood as a 16-electron Pd complex that features an anionic η(3)-C(ipso)-C(ortho)-C(benzyl) allylic ligand fragment plus a Pd→B bond, or an η(4)-BC(ipso)-C(ortho)-C(benzyl) boratabutadiene anion fragment.

Bis(µ-dimesitylborinato-κO:O)bis-[(2-methyl-pyridine-κN)lithium].

The title compound, [Li(2)(C(18)H(22)BO)(2)(C(6)H(7)N)(2)], is a lithium dimesitylboroxide dimer in which the lithium cation is also coordinated by one mol-ecule of 2-methyl-pyridine. At the core of the structure is an Li(2)O(2) four-membered ring. The structure is centrosymmetric with an inversion centre midway between two Li atoms. Inter-molecular C-H⋯π inter-actions and π-π inter-actions between the 2-methyl-pyridine rings exist [centroid-centroid distance = 3.6312 (16) Å].

Oxybis(dimesitylborane) dichloro-methane hemisolvate.

The title compound, C(36)H(44)B(2)O·0.5CH(2)Cl(2), contains an almost linear O-B-O linkage [177.23 (15)°] and approximately orthogonal [interplanar angles 89.49 (5) and 80.77 (4)°] trigonal planar B centers, consistent with the previously reported non-solvated structure [Cardinet al. (1983). J. Chem. Res. (S), p. 93]. Inter-molecular C-H⋯π inter-actions exist between mesityl groups, with a C-H⋯centroid separation of 3.6535 (18) Å. The dichloromethane mol-ecules lie on twofold rotation axes.

Fluoride ion complexation by a B(2)/Hg heteronuclear tridentate Lewis acid.

The reaction of [Li(THF)(4)][1,8-mu-(Mes(2)B)C(10)H(6)] with HgCl(2) affords [1,1'-(Hg)-[8-(Mes(2)B)C(10)H(6)](2)] () or [1-(ClHg)-8-(Mes(2)B)C(10)H(6)] (), depending on the stoichiometry of the reagents. These two new compounds have been characterized by (1)H, (13)C, (11)B and (199)Hg NMR, elemental analysis and X-ray crystallography. The cyclic voltammogram of in THF shows two distinct waves observed at E(1/2) -2.31 V and -2.61 V, corresponding to the sequential reductions of the two boron centers. Fluoride titration experiments monitored by electrochemistry suggest that binds tightly to one fluoride anion and more loosely to a second one. Theses conclusions have been confirmed by a UV-vis titration experiment which indicates that the first fluoride binding constant (K(1)) is greater than 10(8) M(-1) while the second (K(2)) equals 5.2 (+/- 0.4) x 10(3) M(-1). The fluoride binding properties of have been compared to those of [1-(Me(2)B)-8-(Mes(2)B)C(10)H(6)] () and [1-((2,6-Me(2)-4-Me(2)NC(6)H(2))Hg)-8-(Mes(2)B)C(10)H(6)] (). Both experimental and computational results indicate that its affinity for fluoride anions is comparable to that of but significantly lower than that of the diborane . In particular, the fluoride binding constants of , and in chloroform are respectively equal to 5.0 (+/- 0.2) x 10(5) M(-1), 1.0 (+/- 0.2) x 10(3) M(-1) and 1.7 (+/- 0.1) x 10(3) M(-1). Determination of the crystal structures of the fluoride adducts [S(NMe(2))(3)][-mu(2)-F] and [S(NMe(2))(3)][-mu(2)-F] along with computational results indicate that the higher fluoride binding constant of arises from a strong chelate effect involving two fluorophilic boron centers.

8-Iodo-quinolinium chloride dihydrate.

The title compound, C(9)H(7)IN(+)·Cl(-)·2H(2)O, was obtained during the synthesis of 8-iodo-quinoline from 8-amino-quinoline using the Sandmeyer reaction. The 8-iodo-quinolinium ion is almost planar. Solvent water mol-ecules and chloride ions form a hydrogen-bonded chain along the c axis via O-H⋯Cl links. The 8-iodo-quinolinium ions, which are packed along the c axis with cationic aromatic π-π stacking (centroid-centroid distance = 3.624 Å), are linked to the chain via N-H⋯O hydrogen bonds.

8-Iodo-quinolinium triiodide tetra-hydro-furan solvate.

The title compound, C(9)H(7)IN(+)·I(3) (-)·C(4)H(8)O, was synthesized from 8-amino-quinoline using the Sandmeyer reaction. The 8-iodo-quinolinium cation is essentially planar and the triiodide ion is almost linear. N-H⋯O hydrogen bonds, and inter-molecular I⋯I [3.7100 (5) Å] and I⋯H inter-actions, between the cation, anion and solvent mol-ecules result in the formation of sheets oriented parallel to the (03) plane. Between the sheets, 8-iodo-quinolinium and triiodide ions are stacked alternately, with I⋯C distances in the range ∼3.8-4.0 Å.

Adsorption and co-adsorption of ethylene and carbon monoxide on silica-supported monodisperse Pt nanoparticles: volumetric adsorption and infrared spectroscopy studies.

The adsorption of carbon monoxide and ethylene, and their sequential adsorption, was studied over a series of Pt/SBA-15 catalysts with monodisperse particle sizes ranging from 1.7 to 7.1 nm by diffuse-reflectance infrared spectroscopy and chemisorption. Gas adsorption was dependent on the Pt particle size, temperature, and sequence of gas exposure. Adsorption of CO at room temperature on Pt/SBA-15 gives rise to a spectroscopic feature assigned to the C-O stretch: nu(CO) = 2075 cm-1 (1.9 nm); 2079 cm-1 (2.9 nm); 2082 cm-1 (3.6 nm); and 2090 cm-1 (7.1 nm). The intensity of the signal decreased in a sigmoidal fashion with increasing temperature, thereby providing semiquantitative surface coverage information. Adsorption of ethylene on Pt/SBA-15 gave rise to spectroscopic features at approximately 1340, approximately 1420, and approximately 1500 cm-1 assigned to ethylidyne, di-sigma-bonded ethylene, and pi-bonded ethylene, respectively. The ratio of these surface species is highly dependent on the Pt particle size. At room temperature, Pt particles stabilize ethylidyne as well as di-sigma- and pi-bonded ethylene; however, ethylidyne predominated on the surfaces of larger particles. Ethylidyne was the only identifiable species at 403 K, with its formation being more facile on larger particles. Co-adsorption experiments reveal that the composition of the surface layer is dependent on the order of exposure to gases. Exposure of a C2H4-covered Pt surface to CO resulted in an approximately 50% decrease in chemisorbed CO compared to a fresh Pt surface. The nu(CO) appeared at 2050 cm-1 on Pt/SBA-15 pretreated with C2H4 at room temperature. The di-sigma-bonded and pi-bonded species are the most susceptible to displacement from the surface by CO. The formation of ethylidyne appeared to be less sensitive to the presence of adsorbed carbon monoxide, especially on larger particles. Upon exposure of C2H4 to a CO-covered Pt surface, little irreversible uptake occurred due to nearly 100% site blocking. These results demonstrate that carbon monoxide competes directly with ethylene for surface sites, which will have direct implications on the poisoning of the heterogeneously catalyzed conversion of hydrocarbons.

Reverse micelle synthesis of rhodium nanoparticles.

Water-in-oil reverse micelles of butyl ammonium laurate in hexanes that contain sodium hexachlororhodate were reduced with sodium borohydride to yield rhodium nanoparticles. The size of the micelle, determined by dynamic light scattering, was from 3 to 20 nm and varied as the water to surfactant ratio (W) was changed. The rhodium nanoparticles exhibited a Gaussian size distribution (sigma=0.35 nm), with average diameters of 1.5, 2.2, and 2.9 nm. The products were characterized with TEM, HRTEM, and X-ray photoemission spectroscopy.