Efficient BiVO4-Based Photoanode with Chemically Precipitated Hierarchical Cobalt Borate (Co-Bi) Oxygen Evolution Reaction Catalysts.

The integration of cobalt borate OER catalysts with electrodeposited BiVO4-based photoanodes through a simple drop casting technique was shown to provide an improvement of the photoelectrochemical performance of electrodes under simulated solar light. Catalysts were obtained by chemical precipitation mediated by NaBH4 at room temperature. Scanning electron microscopy (SEM) investigation of precipitates showed a hierarchical structure with globular features covered in nanometric thin sheets providing a large active area, whereas X-ray diffraction (XRD) and Raman spectroscopy highlighted their amorphous structure. The photoelectrochemical behavior of samples was investigated by linear scan voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) techniques. The amount of particles loaded onto BiVO4 absorbers was optimized by variation of the drop cast volume. The enhancement of photocurrent generation by Co-Bi-decorated electrodes with respect to bare BiVO4 was observed with an increase from 1.83 to 3.65 mA/cm2 at 1.23 V vs RHE under AM 1.5 simulated solar light, corresponding to a charge transfer efficiency of 84.6%. The calculated maximum applied bias photon-to-current efficiency (ABPE) value for optimized samples was 1.5% at 0.5 V applied bias. Under constant illumination at 1.23 V vs RHE, a depletion of photoanode performances was observed within an hour, likely due to the detachment of the catalyst from the electrode surface.

Flexible Perfluoropolyethers-Functionalized CNTs-Based UHMWPE Composites: A Study on Hydrogen Evolution, Conductivity and Thermal Stability.

Flexible conductive composites based on ultra-high molecular weight polyethylene (UHMWPE) filled with multi-walled carbon nanotubes (CNTs) modified by perfluoropolyethers (PFPEs) were produced. The bonding of PFPE chains, added in 1:1 and 2:1 weight ratios, on CNTs influences the dispersion of nanotubes in the UHMWPE matrix due to the non-polar nature of the polymer, facilitating the formation of nanofillers-rich conductive pathways and improving composites' electrical conductivity (two to five orders of magnitude more) in comparison to UHMWPE-based nanocomposites obtained with pristine CNTs. Electrochemical atomic force microscopy (EC-AFM) was used to evaluate the morphological changes during cyclic voltammetry (CV). The decrease of the overpotential for hydrogen oxidation peaks in samples containing PFPE-functionalized CNTs and hydrogen production (approximately -1.0 V vs. SHE) suggests that these samples could find application in fuel cell technology as well as in hydrogen storage devices. Carbon black-containing composites were prepared for comparative study with CNTs containing nanocomposites.

Thermodynamics of aqueous perfluorooctanoic acid (PFOA) and 4,8-dioxa-3H-perfluorononanoic acid (DONA) from DFT calculations: Insights into degradation initiation.

Modern fluorosurfactants introduced during and after perfluoroalkyl carboxylates/sulfonates phase-out present chemical features designed to facilitate abatement, hence reducing persistence. However, the implications of such features on environmental partitioning and stability are yet to be fully appreciated, partly due to experimental difficulties inherent to the handling of their (diluted) aqueous solutions. In this work, rigorous quantum chemistry calculations were carried out in order to provide theoretical insights into the thermodynamics of hydroperfluorosurfactants in aqueous medium. Estimates of acid dissociation constant (pKa), standard reduction potential (E0), and bond dissociation enthalpy (BDE) and free energy (BDFE) were computed for perfluorooctanoic acid (PFOA), 4,8-dioxa-3H-perfluorononanoic acid (DONA) and their anionic forms via ensemble averaging at density functional theory level with implicit solvent models. A a> in the neighborhood of zero and a E0 of about 2.2 V were obtained for PFOA. Predictions for the acidic function of DONA compare well with PFOA's, with a pKa of 0.8-1.5 and a E0 of 2.07-2.15 V. Deprotonation thus represents the dominant phenomenon at environmental conditions. Calculations indicate that H-abstraction of the aliphatic proton of DONA by a hydroxyl radical is the thermodynamically favored reaction path in oxidative media, whereas hydrolysis is not a realistic scenario due to the high dissociation constant. Short intramolecular interactions available to the peculiar hydrophobic tail of DONA were also reviewed, and the relevance of the full conformational space of the fluorinated side chain discussed.

Comparison of Branched and Linear Perfluoropolyether Chains Functionalization on Hydrophobic, Morphological and Conductive Properties of Multi-Walled Carbon Nanotubes.

The functionalization of multi-walled carbon nanotubes (MW-CNTs) was obtained by generating reactive perfluoropolyether (PFPE) radicals that can covalently bond to MW-CNTs' surface. Branched and linear PFPE peroxides with equivalent molecular weights of 1275 and 1200 amu, respectively, have been thermally decomposed for the production of PFPE radicals. The functionalization with PFPE chains has changed the wettability of MW-CNTs, which switched their behavior from hydrophilic to super-hydrophobic. The low surface energy properties of PFPEs have been transferred to MW-CNTs surface and branched units with trifluoromethyl groups, CF3, have conferred higher hydrophobicity than linear units. Porosimetry discriminated the effects of PFPE functionalization on meso-porosity and macro-porosity. It has been observed that reactive sites located in MW-CNTs mesopores have been intensively functionalized by branched PFPE peroxide due to its low average molecular weight. Conductivity measurements at different applied pressures have showed that the covalent linkage of PFPE chains, branched as well as linear, weakly modified the electrical conductivity of MW-CNTs. The decomposed portions of PFPE residues, the PFPE chains bonded on carbon nanotubes, and the PFPE fluids obtained by homo-coupling side-reactions were evaluated by mass balances. PFPE-modified MW-CNTs have been characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), static contact angle (SCA), surface area, and porosity measurements.

Halogen bonding: a general route in anion recognition and coordination.

This critical review describes how halocarbons can function as effective binding sites of anions via halogen bonding, the noncovalent interaction whereby halogen atoms accept electron density. The focus is on the binding and coordination of oxyanions, by far the most numerous class of anions in organic chemistry. It is shown how a large variety of inorganic and organic oxyanions can form discrete adducts and 1D, 2D, or 3D supramolecular networks with chloro-, bromo-, and iodocarbons. Specific examples are discussed in order to identify new supramolecular synthons based on halogen bonding and to outline some general principles for the design of effective and selective receptors based on this interaction. The interaction allows for several other anions to self-assemble with halocarbons and mention is also given to the halogen bonding-based coordination of halides, polycyano- and polyoxometallates (72 references).