Abstract:The electrochemical behavior of fac- [Mn(pdbpy) (CO)3Br] (pdbpy = 4-phenyl-6-(phenyl-2,6-diol)-2,2'-bipyridine), 1, in acetonitrile under Ar and its catalytic performances for CO2 reduction with added water, 2,2',2''-trifluoroethanol (TFE) and phenol are discussed in detail. Preparative-scale electrolysis experiments, carried out at -1.5 V vs. SCE in CO2-saturated acetonitrile solutions, reveal that the process selectivity is extremely sensitive to the acid strength, providing CO and formate in different faradaic yields. A detailed spectroelectrochemical (IR and UV-Vis) study under Ar and CO2 atmospheres shows that 1 undergoes fast solvolysis; however dimer formation in acetonitrile is suppressed, providing an atypical reduction mechanism in comparison with other reported Mn I catalysts. Spectroscopic evidence of Mn hydride formation supports the existence of different electrocatalytic CO2 reduction pathways. Furthermore, a comparative investigation performed on the new fac-[Mn(ptbpy)(CO)3Br] (ptbpy = 4-phenyl-6-(phenyl-3,4,5-triol)-2,2'-bipyridine) catalyst, 2, bearing a bipyridyl derivative with OH groups in different positions to those in 1, provides complementary information about the role that the local proton source plays during the electrochemical reduction of CO2.

The effect of a local proton source on the activity of a bromotricarbonyl Mn redox catalyst for CO2 reduction has been investigated. The electrochemical behaviour of the novel complex [fac-Mn(dhbpy)(CO)3Br] (dhbpy = 4-phenyl-6-(1,3-dihydroxybenzen-2-yl) 2,2'-bipyridine), containing two acidic OH groups in the proximity of the metal centre, under a CO2 atmosphere showed a sustained catalysis in homogeneous solution even in the absence of Brønsted acids.

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The study of the photocatalytic activity of TiO(2) inverse opals showed that these structures behave as metamaterials: their properties arise principally from the 3D periodic structure of the material and marginally from porosity, reflectivity and scattering.

We report the hydrothermal synthesis of graphene (GNP)-TiO2 nanoparticle (NP) hybrids using COOH and NH2 functionalized GNP as shape controller. Anatase was the only TiO2 crystalline phase nucleated on the functionalized GNP, whereas traces of rutile were detected on unfunctionalized GNP. X-Ray Photoelectron spectroscopy (XPS) showed C-Ti bonds on all hybrids, thus confirming heterogeneous nucleation. GNP functionalization induced the nucleation of TiO2 NPs with specific shape and crystalline facets exposed. COOH functionalization directed the synthesis of anatase truncated bipyramids, bonded to graphene sheets via the {101} facets, while NH2 functionalization induced the formation of belted truncated bipyramids, bonded to graphene via the {100} facets. Belted trunc ated bipyramids formed on unfuctionalized GNP too, however the NPs were more irregular and rounded. These effects were ascribed to pH variations in the proximity of the functionalized GNP sheets, due to the high density of COOH or NH 2 groups. Because of the different reactivity of anatase {100} and {101} crystalline facets, we hypothesize that the hybrid materials will behave differently as photocatalysts, and that the COOH-GNP-TiO2 hybrids will be better photocatalysts for water splitting and H2 production .