Lars Robben

Bi2WO6 Inverse Opals: Facile Fabrication and Efficient Visible‐Light‐Driven Photocatalytic and Photoelectrochemical Water‐Splitting Activity

Photonic crystals have attracted extensive interest for their potential applications in manipulating light in nontraditional ways based on photonic band-structure concepts. [ 1 ] In a photonic crystal, light with certain frequencies is forbidden to propagate due to a photonic stop band arising from the periodic modulation of the refractive index. [ 2 ] Slow light propagation near this stop band is a unique property of photonic crystals, and is of particular interest for enhancing the light energy-conversion effi ciency in solar cells, the hydrogen production through photocatalytic water splitting, and photocatalytic processes for environmental remediation. [ 3 ] It has been reported that TiO 2 inverse-opal fi lms exhibit signifi cantly increased photocatalytic effi ciencies as compared with conventional TiO 2 fi lms. This enhancement of the effi ciency is generally attributed to the improved interaction of light with TiO 2 due to the low group velocities of light near the stop-band edge, improved light harvesting due to the multiple scattering effect in the inverse-opal structure, and continuous pore channels that facilitate the transfer of reactant molecules. [ 3 a,c,d]

Study of the Efficiency of UV and Visible-Light Photocatalytic Oxidation of Methanol on Mesoporous RuO2–TiO2 Nanocomposites

Mesoporous RuO(2)-TiO(2) nanocomposites at different RuO(2) concentrations (0-10 wt%) are prepared through a simple one-step sol-gel reaction of tetrabutyl orthotitanate with ruthenium(III) acetylacetonate in the presence of an F127 triblock copolymer as structure-directing agent. The thus-formed RuO(2)-TiO(2) network gels are calcined at 450 °C for 4 h leading to mesoporous RuO(2)-TiO(2) nanocomposites. The photocatalytic CH(3)OH oxidation to HCHO is chosen as the test reaction to examine the photocatalytic activity of the mesoporous RuO(2)-TiO(2) nanocomposites under UV and visible light. The photooxidation of CH(3)OH is substantially affected by the loading amount and the degree of dispersion of RuO(2) particles onto the TiO(2), which indicates the exclusive effect of the RuO(2) nanoparticles on this photocatalytic reaction under visible light. The measured photonic efficiency ξ=0.53% of 0.5 wt% RuO(2)-TiO(2) nanocomposite for CH(3)OH oxidation is maximal and the further increase of RuO(2) loading up to 10 wt% gradually decreases this value. The cause of the visible-light photocatalytic behavior is the incorporation of small amounts of Ru(4+) into the anatase lattice. On the other hand, under UV light, undoped TiO(2) shows a very good photonic efficiency, which is more than three times that for commercial photocatalyst, P-25 (Evonik-Degussa); however, addition of RuO(2) suppresses the photonic efficiency of TiO(2). The proposed reaction mechanism based on the observed behavior of RuO(2)-TiO(2) photocatalysts under UV and visible light is explored.

Ease synthesis of mesoporous WO3-TiO2 nanocomposites with enhanced photocatalytic performance for photodegradation of herbicide imazapyr under visible light and UV illumination.

Herein, we report the ease synthesis of mesoporous WO3-TiO2 nanocomposites at different WO3 contents (0-5wt%) together with their photocatalytic performance for the degradation of the imazapyr herbicide under visible light and UV illumination. XRD and Raman spectra indicated that the highly crystalline anatase TiO2 phase and monoclinic and triclinic of WO3 were formed. The mesoporous TiO2 exhibits large pore volumes of 0.267cm(3)g-1 and high surface areas of 180m(2)g(-1) but they become reduced to 0.221cm(3)g(-1) and 113m(2)g(-1), respectively upon WO3 incorporation, with tunable mesopore diameter in the range of 5-6.5nm. TEM images show WO3-TiO2 nanocomposites are quite uniform with 10-15nm of TiO2 and 5-10nm of WO3 sizes. Under UV illumination, the overall photocatalytic efficiency of the 3% WO3-TiO2 nanocomposite is 3.5 and 6.6 times higher than that of mesoporous TiO2 and commercial UV-100 photocatalyst, respectively. The 3% WO3-TiO2 nanocomposite is considered to be the optimum photocatalyst which is able to degrade completely (100% conversion) of imazapyr herbicide along 120min with high photonic efficiency ∼8%. While under visible light illumination, the 0.5% WO3-TiO2 nanocomposite is the optimum photocatalyst which achieves 46% photocatalytic efficiency.

Li Ion Dynamics in Al-Doped Garnet-Type Li7La3Zr2O12 Crystallizing with Cubic Symmetry

Abstract Lithium-ion dynamics in the garnet-type solid electrolyte “Li7La3Zr2O12” (LLZ) crystallizing with cubic symmetry was probed by means of variable-temperature 7Li NMR spectroscopy and ac impedance measurements. Li jump rates of an Al-containing sample follow Arrhenius behaviour being characterized by a relatively high activation energy of 0.54(3) eV and a pre-exponential factor of 2.2(5) × 1013 s-1. The results resemble those which were quite recently obtained for an Al-free LLZ sample crystallizing, however, with tetragonal symmetry. Hence, most likely, the significantly higher Li conductivity previously reported for a cubic LLZ sample cannot be ascribed solely to the slight structural distortions accompanying the change of the crystal symmetry. Here, even Al impurities, acting as stabilizer for the cubic polymorph at room temperature, do not lead to the high ion conductivity reported previously.

Morphotropy and Temperature-Driven Polymorphism in A2Th(AsO4)2 (A = Li, Na, K, Rb, Cs) Series

A new alkaline thorium arsenate family was obtained and systematically investigated. The structures of A2Th(AsO4)2 (A = Li, Na, K, Rb, Cs) were determined from single crystal X-ray diffraction data. Li2Th(AsO4)2 and either isostructural K2Th(AsO4)2 and Rb2Th(AsO4)2 crystallize in the monoclinic crystal system. Na2Th(AsO4)2 and Cs2Th(AsO4)2 crystallize in the orthorhombic and tetragonal crystal systems, respectively. Li2Th(AsO4)2 consists of [Th(AsO4)2](2-) layers with Li atoms in the interlayer space. The rest of the compounds are based on 3D frameworks. Differences in local environments of ThO8 coordination polyhedra are described in relation to the symmetry. Despite different local environments of ThO8 coordination polyhedra and different structural symmetry, underlying nets of A2Th(AsO4)2 (A = Na, K, Rb, Cs) were shown to be the same. Single-crystal and powder Raman spectra were measured, and bands are assigned. DSC measurements showed phase transitions in K2Th(AsO4)2 and Rb2Th(AsO4)2, which were studied using high-temperature powder X-ray diffraction (HT-PXRD). The data of HT-PXRD demonstrates two high-temperature polymorphic modification of K2Th(AsO4)2 and only one for the isotypic Rb2Th(AsO4)2. The phase transitions in both K and Rb phases are reversible.

Sonic analysis in cut-off grinding of concrete

The machining of concrete with diamond cutting discs is nowadays often done with all-purpose tools and unadjusted machine parameters due to unknown material properties. The inhomogeneous structure of concrete ideally requires continuous process monitoring and real time adjustment of machine parameters. A joined research project of the Institute of Production Engineering and Machine Tools (IFW) and the Institute of Mineralogy (IM) is aimed at enabling process monitoring by means of using acoustic emission (AE) and airborne sound generated by the grinding tools. This paper presents the applied methods and first results. AE and airborne sound measurements show a correlation between the signal intensity and the aggregates present in the concrete. It is shown here that spectral analysis of measured signals can give information about the process and the workpiece structure being cut.

Symmetry reduction due to gallium substitution in the garnet Li6.43(2)Ga0.52(3)La2.67(4)Zr2O12.

Gallium-substituted lithium lanthanum zirconate (LLZO; Li6.62La2.65Ga0.49Zr2O12) belongs to the family of garnets and shows a reduction of the symmetry to space group I 3d compared to Ia d typically observed for these structures.

On the autocorrelation method of external parameter depending data-sets

Abstract The autocorrelation method, proposed at first by [E. K. K. H. Salje, M. I. A. Carpenter, T. H. Malcherek, T. Boffa Ballaran, Eur. J. Min. 2000, 12, 503.] for the evaluation of FTIR data, is an efficient method the evaluation of data depending on external parameters like temperature, pressure, chemical composition etc. In this study a new single parameter value λ′(ω′) is proposed which is computational more efficient with a higher reproducibility than the Δcorr parameter proposed earlier. The method is additionally transferred from Fourier transform infrared (FTIR) spectroscopy to X-ray diffraction data. It is shown that the autocorrelation method has some beneficial properties compared to the often used Pearson’s r-value.

Giant Volume Change and Topological Gaps in Temperature‐ and Pressure‐Induced Phase Transitions: Experimental and Computational Study of ThMo2O8

By applying high temperature (1270 K) and high pressure (3.5 GPa), significant changes occur in the structural volume and crystal topology of ThMo2 O8 , allowing the formation of an unexpected new ThMo2 O8 polymorph (high-temperature/high-pressure (HT/HP) orthorhombic ThMo2 O8 ). Compared with the other three ThMo2 O8 polymorphs prepared at the ambient pressure (monoclinic, orthorhombic, and hexagonal phases), the molar volume for the quenched HT/HP-orthorhombic ThMo2 O8 is decreased by almost 20 %. As a result of such a dramatic structural transformation, a permanent high-pressure quenchable state is able to be sustained when the pressure is released. The crystal structures of the three ambient ThMo2 O8 phases are based on three-dimensional (3D) frameworks constructed from corner-sharing ThOx (x=6, 8, or 9) polyhedra and MoO4 tetrahedra. The HT/HP-orthorhombic ThMo2 O8 , however, crystallizes in a novel structural topology, exhibiting very dense arrangements of ThO11 and MoO4+1 polyhedra connecting along the crystallographic c axis. The phase transitions among all four of these ThMo2 O8 polymorphs are unveiled and fully characterized with regard to the structural transformation, thermal stability, and vibrational properties. The complementary first principles calculations of Gibbs free energies reveal the underlying energetics of the phase transition, which support the experimental findings.

Carbon dioxide uptake in nitrite-sodalite: reaction kinetics and template ordering of the carbonate-nosean formation

Abstract We report on the phase transformation and the reaction kinetics of aluminosilicate nitrite-sodalite |Na8(NO2)2|[AlSiO4]6 crystallizing in space group P4¯3n