Nanostructured Hybrids Based on Tantalum Bromide Octahedral Clusters and Graphene Oxide for Photocatalytic Hydrogen Evolution.

The generation of hydrogen (H2) using sunlight has become an essential energy alternative for decarbonization. The need for functional nanohybrid materials based on photo- and electroactive materials and accessible raw materials is high in the field of solar fuels. To reach this goal, single-step synthesis of {Ta6Bri12}@GO (GO = graphene oxide) nanohybrids was developed by immobilization of [{Ta6Bri12}Bra2(H2O)a4]·4H2O (i = inner and a = apical positions of the Ta6 octahedron) on GO nanosheets by taking the advantage of the easy ligand exchange of the apical cluster ligands with the oxygen functionalities of GO. The nanohybrids were characterized by spectroscopic, analytical, and morphological techniques. The hybrid formation enhances the yield of photocatalytic H2 from water with respect to their precursors and this is without the presence of precious metals. This enhancement is attributed to the optimal cluster loading onto the GO support and the crucial role of GO in the electron transfer from Ta6 clusters into GO sheets, thus suppressing the charge recombination. In view of the simplicity and versatility of the designed photocatalytic system, octahedral tantalum clusters are promising candidates to develop new and environmentally friendly photocatalysts for H2 evolution.

Tuning the Catalytic Performance of Cobalt Nanoparticles by Tungsten Doping for Efficient and Selective Hydrogenation of Quinolines under Mild Conditions.

Non-noble bimetallic CoW nanoparticles (NPs) partially embedded in a carbon matrix (CoW@C) have been prepared by a facile hydrothermal carbon-coating methodology followed by pyrolysis under an inert atmosphere. The bimetallic NPs, constituted by a multishell core-shell structure with a metallic Co core, a W-enriched shell involving Co7W6 alloyed structures, and small WO3 patches partially covering the surface of these NPs, have been established as excellent catalysts for the selective hydrogenation of quinolines to their corresponding 1,2,3,4-tetrahydroquinolines under mild conditions of pressure and temperature. It has been found that this bimetallic catalyst displays superior catalytic performance toward the formation of the target products than the monometallic Co@C, which can be attributed to the presence of the CoW alloyed structures.

Enhanced Photocatalytic Activity and Stability in Hydrogen Evolution of Mo6 Iodide Clusters Supported on Graphene Oxide.

Catalytic properties of the cluster compound (TBA)2[Mo6Ii8(O2CCH3)a6] (TBA = tetrabutylammonium) and a new hybrid material (TBA)2Mo6Ii8@GO (GO = graphene oxide) in water photoreduction into molecular hydrogen were investigated. New hybrid material (TBA)2Mo6Ii8@GO was prepared by coordinative immobilization of the (TBA)2[Mo6Ii8(O2CCH3)a6] onto GO sheets and characterized by spectroscopic, analytical, and morphological techniques. Liquid and, for the first time, gas phase conditions were chosen for catalytic experiments under UV-Vis irradiation. In liquid water, optimal H2 production yields were obtained after using (TBA)2[Mo6Ii8(O2CCH3)a6] and (TBA)2Mo6Ii8@GO) catalysts after 5 h of irradiation of liquid water. Despite these remarkable catalytic performances, "liquid-phase" catalytic systems have serious drawbacks: the cluster anion evolves to less active cluster species with partial hydrolytic decomposition, and the nanocomposite completely decays in the process. Vapor water photoreduction showed lower catalytic performance but offers more advantages in terms of cluster stability, even after longer radiation exposure times and recyclability of both catalysts. The turnover frequency (TOF) of (TBA)2Mo6Ii8@GO is three times higher than that of the microcrystalline (TBA)2[Mo6Ii8(O2CCH3)a6], in agreement with the better accessibility of catalytic cluster sites for water molecules in the gas phase. This bodes well for the possibility of creating {Mo6I8}4+-based materials as catalysts in hydrogen production technology from water vapor.

Polyvinylidene Fluoride-Graphene Oxide Membranes for Dye Removal under Visible Light Irradiation.

In this study, polyvinylidene fluoride (PVDF)-graphene oxide (GO) membranes were obtained by employing triethyl phosphate (TEP) as a solvent. GO nanosheets were prepared and characterized in terms of scanning and transmission electron microscopy (SEM and TEM, respectively), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), chemical analysis and inductively coupled plasma mass spectroscopy (ICP). Two different phase inversion techniques, Non-Solvent Induced Phase Separation (NIPS) and Vapour-Induced Phase Separation (VIPS)/NIPS, were applied to study the effect of fabrication procedure on the membrane structure and properties. Membranes were characterized by SEM, AFM, pore size, porosity, contact angle and mechanical tests, and finally tested for photocatalytic methylene blue (MB+) degradation under visible light irradiation. The effect of different pH values of dye aqueous solutions on the photocatalytic efficiency was investigated. Finally, the influence of NaCl salt on the MB+ photodegradation process was also evaluated.

Graphene oxide as a catalyst for the diastereoselective transfer hydrogenation in the synthesis of prostaglandin derivatives.

Modification of GO by organic molecules changes its catalytic activity in the hydrogen transfer from i-propanol to enones, affecting the selectivity to allyl alcohol and diastereoselectivity to the resulting stereoisomers. It is noteworthy the system does not contain metals and is recyclable.

In†Situ Generation of Active Molybdenum Octahedral Clusters for Photocatalytic Hydrogen Production from Water.

The photocatalytic hydrogen evolution reaction (HER) from water under homogeneous and heterogeneous conditions is explored for the {Mo6 Br(i) 8 }(4+) cluster core based unit starting from (TBA)2 [Mo6 Br(i) 8 F(a) 6 ] (TBA=tetra-n-butylammonium; "i" and "a" refer to the face-capping inner and terminal apical ligand, respectively). The catalytic activity of {Mo6 Br(i) 8 }(4+) is enhanced by the in situ generation of [Mo6 Br(i) 8 F(a) 5 (OH)(a) ](2-) , [Mo6 Br(i) 8 F(a) 3 (OH)(a) 3 ](2-) , and [Mo6 Br(i) 8 (OH)(a) 6 ](2-) , which are identified by ESIMS, luminescence, and NMR techniques. Full substitution of F(-) by OH(-) leads to the formation of (H3 O)2 [Mo6 Br(i) 8 (OH)(a) 6 ]⋅10 H2 O; its structure was determined by single-crystal XRD. The immobilization of the active {Mo6 Br(i) 8 }(4+) onto graphene oxide (GO) surfaces enhances its stability under catalytic conditions. The catalytic activity of the resulting (TBA)2 Mo6 Br(i) 8 @GO material is improved with respect to GO, but is reduced compared to the activity under homogeneous conditions because of changes in the GO semiconducting properties as well as lower activity and/or accessibility of the anchored cluster.

Graphene oxide as a metal-free catalyst for oxidation of primary amines to nitriles by hypochlorite.

Graphene oxide catalyzes oxidation by NaClO of primary benzyl and aliphatic amines to a product distribution comprising nitriles and imines. Nitriles are the sole product for long chain aliphatic amines. Spectroscopic characterization suggests that percarboxylic and perlactone groups could be the active sites of the process.

Copper- and Vanadium-Catalyzed Oxidative Cleavage of Lignin using Dioxygen.

Transition-metal-containing hydrotalcites (HTc) and V(acac)3 /Cu(NO3 )2 ⋅3 H2 O (acac=acetylacetonate) mixtures were tested for their catalytic activity in the cleavage of the lignin model compound erythro-1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-l,3-propanediol (1) with molecular oxygen as oxidant. Both catalytic systems displayed high activity and good selectivity and afforded veratric acid as the main product. The catalyst behavior was studied by EPR spectroscopy, XRD, and Raman spectroscopy. After the catalysts were established for the model system, lignin depolymerization studies were performed with various organsolv and kraft lignin sources. The oxidative depolymerization and lignin bond cleavage were monitored by gel permeation chromatography (GPC), MALDI MS, and 2D-NMR (HSQC). Irrespective of the lignin pretreatment, both HTc-Cu-V and V(acac)3 /Cu(NO3 )2 ⋅3 H2 O were able to cleave the ß-O-4 linkages and the resinol structures to form dimeric and trimeric products.

Cobalt-containing layered or zeolitic silicates as photocatalysts for hydrogen generation.

Layered magadiite and zeolites Y containing framework Co or small CoO clusters in the pores have been synthesized and tested as photocatalysts for water splitting, in the absence and presence of methanol, upon UV or simulated sunlight irradiation; the best performing material was Co-magadiite.

Visible-light photocatalytic hydrogen generation by using dye-sensitized graphene oxide as a photocatalyst.

Dye-sensitized graphene oxide is able to generate hydrogen from water/methanol mixtures (80:20) by using visible or solar light. The most efficient photocatalyst tested contained a tris(2,2-bipyridyl) ruthenium(II) complex incorporated in the interlayer spaces of a few layers of graphene oxide with a moderate degree of oxidation. The graphene oxide-based photocatalyst does not contain noble metals and we have determined that it is two orders of magnitude more active than catalysts based on conventional titania.

ITQ-12: a new microporous silica polymorph potentially useful for light hydrocarbon separations.

The new synthetic form of microporous crystalline silica, denoted as ITQ-12, shows a high potential for the separation of propane and propene from its mixtures.