Porous Lanthanide Metal-Organic Frameworks Using Pyridine-2,4-dicarboxylic Acid as a Linker: Structure, Gas Adsorption, and Luminescence Studies.

Two types of new lanthanide coordination networks, [Ln3(pdc)4(Hpdc)(H2O)3]·8H2O [H2pdc = pyridine-2,4-dicarboxylic acid; Ln = Ce (1), Pr (2), Sm (3), Eu (4); type A) and [Tb5(pdc)4(Hpdc)]·3H2O (type B), have been synthesized using a hydrothermal synthetic method. The former type A compound has an unfamiliar architecture, even basically comprised of primitive cubic (pcu) topology, and demonstrate porous gas adsorption behavior, giving several hundreds of square meters per gram surface areas after evacuation of the water molecules, while the latter type B compound does not show any porous properties. Most interestingly, the solvothermal synthetic method using N,N-dimethylformamide (DMF) as a solvent gives compounds that crystallize in a structure analogous to that of type A for Ln = La-Ho, probably formulated as [Ln3(pdc)4(Hpdc)·(DMF)m]·nDMF. These compounds also exhibit large surface areas after evacuation of the DMF molecules and also moderate amounts of hydrogen gas uptake at 77 K. The luminescence properties were investigated for Eu and Tb analogues at elevated temperatures, at which an unusual increase in the emission intensity was observed upon the release of solvents, and discussed based on their porous structure.

Bio-inspired honeycomb-like graphitic carbon nitride for enhanced visible light photocatalytic CO2 reduction activity.

Graphitic carbon nitride (g-C3N4) is paying attention lately owing to its interesting characteristics and substantial application in improving environmental and energy concerns. Nevertheless, the photocatalytic activity of g-C3N4 is constrained by the inertness of the surface and particle aggregation during photocatalytic activity. Herein, we report the preparation of g-C3N4 with honeycomb-like morphology (HC-C3N4) via thermal condensation of prepared SiO2 templates and dicyandiamide. The etching out of the SiO2 templates by NH4HF2 created hollow or macropores in the C3N4 matrix resulting in its structural changes. Similar, to the bulk C3N4, the HC-C3N4 exhibited higher photocatalytic CO2 reduction in hydrocarbons. This improved photocatalytic achievement is associated with higher specific surface area, excellent visible light absorption capability, higher electron donor density, easy mass diffusion of materials for surface reaction, and effective segregation of photogenerated charge carriers. Furthermore, the HC-C3N4 honeycomb structure was deposited with Ni(OH)2 clusters which showed remarkable CO2 reduction activity of 1.48 µmolh-1 g-1 of CH4 and 0.73 µmolh-1 g-1 of CH3OH generation which is 3.5 and 4.3 times higher CO2 reduction activity compared with bulk C3N4 clustered with Ni(OH)2 particles. This comprehensive study demonstrated that HC-C3N4 nanostructured polymeric semiconductor is envisaged to have great potential in the application of a variety of fields such as photocatalysis, sensor technology, and nanotechnology.

Rare-earth-free white emitting Ba2TiP2O9 phosphor: revealing its crystal structure and photoluminescence properties.

A high intensity bluish-white emitting Ba2TiP2O9 phosphor was synthesized by a conventional solid-state reaction method and the precise crystal structure was investigated for the first time by Rietveld refinement analysis. Ba2TiP2O9 has a monoclinic crystal structure with a space group C2/c (no. 15), which is built out of PO4 tetrahedra and TiO5 pyramidal polyhedra connected to form a chain structure along the c-axis. The emission of Ba2TiP2O9 is due to a charge transfer transition between Ti(4+)-O(2-) in the pyramidal TiO5. The obtained Ba2TiP2O9 was excited efficiently by UV and VUV and displayed a bright bluish-white luminescence.

Hydrothermal synthesis of meso/macroporous BiVO4 hierarchical particles and their photocatalytic degradation properties under visible light irradiation.

An ordered hierarchical meso/macroporous monoclinic bismuth vanadate (BiVO4) particle was fabricated for the first time by a simple two-step melamine template hydrothermal method followed by calcination. The physiochemical parameters of as-prepared porous materials were characterized by means of X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Raman, Barrett-Emmett-Teller, and UV-vis techniques. The nitrogen adsorption-desorption measurement and pore size distribution curve suggest that meso/macropores exist in these hierarchical microarchitectures. Further, it is found that melamine plays a significant role in the formation of porous BiVO4 particles, and when a known amount of melamine was added, the surface area and pore size of such porous BiVO4 particles were increased. The photocatalytic activities of the as-prepared hierarchical BiVO4 samples were measured for the photodegradation of Congo red aqueous dye solution under visible light irradiation. Surprisingly, the porous BiVO4 particles showed outstanding photocatalytic activities than polycrystalline BiVO4 sample. The possible enhancement of such catalytic performance has also been further discussed.

Long phosphorescent Ca2SnO4 with minuscule rare earth dopant concentration.

Rare-earth doped Ca2SnO4 phosphors were synthesized using a conventional solid state reaction method. The red phosphorescence of Eu(3+) was observed in this system with persistence time. In the as-prepared samples, the doped rare earth ions occupied both Ca and Sn sites in the host lattice. The longest phosphorescent persistence property can be achieved for the Ca2SnO4 phosphors with a 0.1% Eu dopant. Depending on the doped rare earth ions, afterglow emissions of various colors were observed.

Redetermination of the low-temperature polymorph of Li(2)MnSiO(4) from single-crystal X-ray data.

Crystals of dilithium manganese(II) silicate were grown under high-temperature hydro-thermal conditions in the system LiOH-MnO(2)-SiO(2). The title compound crystallizes in the ß(II)-Li(3)PO(4) structure type. The coordination polyhedra of all cations are slightly distorted tetra-hedra (m symmetry for MnO(4) and SiO(4)), which are linked by corner-sharing to each other. The vertices of the tetra-hedra point to the same direction perpendicular to the distorted hexa-gonal close-packed (hcp) array of O atoms within which half of the tetra-hedral voids are occupied by cations. In comparison with the previous refinement from powder X-ray data [Dominko et al. (2006 ▶). Electrochem. Commun.8, 217-222], the present reinvestigation from single-crystal X-ray data allows a more precise determination of the distribution of the Li(+) and Mn(2+) cations, giving a perfectly site-ordered structure model for both Li(+) and Mn(2+).

Combinatorial synthesis of phosphors using arc-imaging furnace.

We have applied a novel 'melt synthesis technique' rather than a conventional solid-state reaction to rapidly synthesize phosphor materials. During a synthesis, the mixture of oxides or their precursors is melted by light pulses (10-60 s) in an arc-imaging furnace on a water-cooled copper hearth to form a globule of 1-5 mm diameter, which is then rapidly cooled by turning off the light. Using this method, we synthesized several phosphor compounds including Y3Al5O12:Ce(YAG) and SrAl2O4:Eu,Dy. Complex phosphor oxides are difficult to produce by conventional solid-state reaction techniques because of the slow reaction rates among solid oxides; as a result, the oxides form homogeneous compounds or solid solutions. On the other hand, melt reactions are very fast (10-60 s) and result in homogeneous compounds owing to rapid diffusion and mixing in the liquid phase. Therefore, melt synthesis techniques are suitable for preparing multi component homogeneous compounds and solid solutions.