Abstract: The limitations of the loading of the porous metalorganic framework [Zn4O(bdc)3] (bdc = benzene-1,4-dicarboxylate; MOF-5 or IRMOF-1) with Pd nanoparticles was investigated. First, the volatile organometallic precursor [Pd(5-C5H5)(3-C3H5)] was employed to get the inclusion compound [Pd(5-C5H5)(3-C3H5)]x@MOF-5 via gas-phase infiltration at 10-3 mbar. A loading of four molecules of [Pd(5-C5H5)(3-C3H5)] per formula unit of MOF-5 (x = 4) can be reached (35 wt.% Pd). Second, the metalorganic precursor [Pd(acac)2] (acac = 2,4-pentanedionate) was used and the inclusion materials [Pd(acac)2]x@MOF-5 of different Pd loadings were obtained by incipient wetness infiltration. However, the maximum loading was lower as compared with the former case with about two precursor molecules per formula unit of MOF-5. Both loading routes are suitable for the synthesis of Pd nanoparticles inside the porous host matrix. Homogeneously distributed nanoparticles with diameter of 2.4(±0.2) nm can be achieved by photolysis of the inclusion compounds [Pd(5-C5H5)(3-C3H5)]x@MOF-5 (x 4), while the hydrogenolysis of [Pd(acac)2]x@MOF-5 (x 2) leads to a mixture of small particles inside the network (< 3 nm) and large Pd agglomerates (40 nm) on the outer surface of the MOF-5 specimens. The pure Pdx@MOF-5 materials proved to be stable under hydrogen pressure (2 bar) at 150 °C over many hours. Neither hydrogenation of the bdc linkers nor particle growth was observed. The new composite materials were characterized by 1H/13C-MAS-NMR, powder XRD, ICP-AES, FT-IR, N2 sorption measurements and high resolution TEM. Raising the Pd loading of a representative sample Pd4@MOF-5 (35 wt.% Pd) by using [Pd(5-C5H5)(3-C3H5)] as precursor in a second cycle of gas-phase infiltration and photolysis was accompanied by the collapse of the long-range crystalline order of the MOF.

Abstract: Successful encapsulation of polyoxometalate (POM) within the framework of a mesoporous iron trimesate MIL-100(Fe) sample has been achieved by direct hydrothermal synthesis in the absence of fluorine. XRPD, 31P MAS NMR, IR, EELS, TEM and 57Fe Mössbauer spectrometry corroborate the insertion of POM within the cavities of the MOF. The experimental Mo/Fe ratio is 0.95, in agreement with the maximum theoretical amount of POM loaded within the pores of MIL-100(Fe), based on steric hindrance considerations. The POM-MIL-100(Fe) sample exhibits a pore volume of 0.373 cm3 g−1 and a BET surface area close to 1000 m2 g−1, indicating that small gas molecules can easily diffuse inside the cavities despite the presence of heavy phosphomolybdates. These latter contribute to the decrease in the overall surface area, due to the increase in molar weight, by 65%. Moreover, the resulting Keggin containing MIL-100(Fe) solid is stable in aqueous solution with no POM leaching even after more than 2 months. In addition, no exchange of the Keggin anions by tetrabutylammonium perchlorate in organic media has been observed.

Abstract: The synthesis, electron diffraction (ED), synchrotron X-ray and neutron structure, X-ray absorption spectroscopy (XAS) and magnetic property studies of La2MnVO6 double perovskite are described. Analysis of the synchrotron powder X-ray diffraction data for La2MnVO6 indicates a disordered arrangement of Mn and V at the B-site of the perovskite structure. Absence of super-lattice reflections in the ED patterns for La2MnVO6 supports the disordered cation arrangement. Room temperature time-of-flight (TOF) neutron powder diffraction (NPD) data show no evidence of cation ordering, in corroboration with the ED and synchrotron studies (orthorhombic Pnma, a = 5.6097(3), b = 7.8837(5) and c = 5.5668(3) ; 295 K, NPD). A comparison of XAS analyses of La2TVO6 with T = Ni and Co shows T2+ formal oxidation state while the T = Mn material evidences a Mn3+ admixture into a dominantly Mn2+ ground state. V-K edge measurements manifest a mirror image behavior with a V4+ state for T = Ni and Co with a V3+ admixture arising in the T = Mn material. The magnetic susceptibility data for La2MnVO6 show ferromagnetic correlations; the observed effective moment, µeff (5.72 µB) is much smaller than the calculated moment (6.16 µB) based on the spin-only formula for Mn2+ (d5, HS) /V4+ (d1), supportive of the partly oxidized Mn and reduced V scenario (Mn3+/V3+).

Abstract: 1D CuO/ZnO nanocomposites were grown on Si(100) substrates by means of an original two-step synthetic strategy. ZnO nanorod (NR) arrays were initially deposited by plasma enhanced-chemical vapor deposition (PE-CVD) from an ArO2 atmosphere. Subsequently, tailored amounts of CuO were dispersed over zinc oxide matrices by radio frequency (RF)-sputtering of Cu from Ar plasmas, followed by thermal treatment in air. A thorough characterization of the obtained systems was carried out by X-ray photoelectron and X-ray excited-Auger electron spectroscopies (XPS and XE-AES), glancing incidence X-ray diffraction (GIXRD), field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDXS), atomic force microscopy (AFM), transmission electron microscopy (TEM), electron diffraction (ED) and energy filtered-TEM (EF-TEM). Pure and highly oriented CuO/ZnO NR arrays, free from ternary ZnCuO phases and characterized by a copper(II) oxide content controllable as a function of the adopted RF-power, were successfully obtained. Interestingly, the structural relationships between the two oxides at the CuO/ZnO interface were found to depend on the overall CuO loading. The obtained nanocomposites displayed promising photocatalytic performances in H2 production by reforming of ethanolwater solutions under simulated solar illumination, paving the way to the sustainable conversion of solar light into chemical energy.

Abstract: Highly homogeneous mullite-type solid solutions Bi2Fe4-xCrxO9 (x = 0.5, 1, 1.2) were synthesized using a soft chemistry technique followed by a solid-state reaction in Ar. The crystal structure of Bi2Fe3CrO9 was investigated using X-ray and neutron powder diffraction, transmission electron microscopy and Fe-57 Mossbauer spectroscopy (S.G. Pbam, a = 7.95579(9) angstrom , b = 8.39145(9) angstrom, c = 5.98242(7) angstrom, R-F(X-ray) = 0.022, R-F(neutron) = 0.057). The ab planes in the structure are tessellated with distorted pentagonal loops built up by three tetrahedrally coordinated Fe sites and two octahedrally coordinated Fe/Cr sites, linked together in the ab plane by corner-sharing forming a pentagonal Cairo lattice. Magnetic susceptibility measurements and powder neutron diffraction show that the compounds order antiferromagnetically (AFM) with the Neel temperatures decreasing upon increasing the Cr content from T-N similar to 250 K for x = 0 to T-N similar to 155 K for x = 1.2. The magnetic structure of Bi2Fe3CrO9 at T = 30 K is characterized by a propagation vector k = (1/2,1/2,1/2). The tetrahedrally coordinated Fe cations form singlet pairs within dimers of corner-sharing tetrahedra, but spins on the neighboring dimers are nearly orthogonal. The octahedrally coordinated (Fe, Cr) cations form antiferromagnetic up-up-down-down chains along c, while the spin arrangement in the ab plane is nearly orthogonal between nearest neighbors and collinear between second neighbors. The resulting magnetic structure is remarkably different from the one in pure Bi2Fe4O9 and features several types of spin correlations even on crystallographically equivalent exchange that may be caused by the simultaneous presence of Fe and Cr on the octahedral site.

Abstract: In recent years there is increased interest in plasma-based CO2 conversion. Several plasma setups are being investigated for this purpose, but the most commonly used ones are a dielectric barrier discharge (DBD), a microwave (MW) plasma and a gliding arc (GA) reactor. In this proceedings paper, we will show results from our experiments in a (packed bed) DBD reactor and in a vortex-flow GA reactor, as well as from our model calculations for the detailed plasma chemistry in a DBD, MW and GA, for pure CO2 as well as mixtures of CO2 with N-2, CH4 and H2O.