Synthesis of Pb9(PO4)6/Ag3PO4 Composite Photocatalysts with Enhanced Visible Light Photocatalytic Activity

Pb₉(PO ₄)₆/Ag₃PO ₄ photocatalysts with different amounts of Pb₉(PO ₄)₆ were successfully synthesised by the ion exchange method. The catalysts were characterized by X‐ray diffractometry (XRD ), High‐resolution transmission electron microscopy (HRTEM ), X‐ray photoelectron spectroscopy (XPS ), Brunauer– Emmett–Teller (BET ), Fourier transform infrared spectrometry (FT ‐IS ), and ultraviolet‐visible (UV ‐vis) spectroscopy. All Pb₉(PO ₄)₆/Ag₃PO ₄ photocatalysts show much higher photocatalytic activities than pure Ag₃PO ₄ under visible light irradiation in the methyl‐orange (MO ) decomposition. Especially, the 3.0 wt% Pb₉(PO ₄)₆/Ag₃PO ₄ photocatalyst shows the highest photoactivity and also high stability after five cycles. The MO degradation rate during each cycle is almost maintained at 97%. Photo‐electrochemical measurement of photocatalysts verified that the enhancing photocatalytic activity was resulted from the electron‐hole pair high separation. The photocatalytic activity enhancement of Pb₉(PO ₄)₆/Ag₃PO ₄ is closely related to , the main active oxygen species.     

Study of intercalated Ti atom in tetrahedral or octahedral sites of titanium disulfide (001) surfaces: theoretical scanning tunneling microscopy images

We have performed ab initio linear combination of atomic orbitals-density functional theory calculations on biperiodic supercells to model the electronic and geometrical involvements of Ti intercalated atom in either octahedral or tetrahedral sites of the (001) TiS2 surfaces. For each type of defect, both the relaxed atomic structure and the electronic properties of the defect states were carefully analyzed. For the titanium atom in the van der Waals gap, the partial filling of the conduction band is in agreement with the metallic behavior reported by experimental studies and the last filled states in the bottom of the conduction band--mainly developed on titanium 3d orbitals--permit us to explain the dark defects observed on the scanning tunneling microscopy image of the (001) TiS2 surfaces. On the other hand, the intercalated titanium atom in the tetrahedral site which is just below the top sulfur atom plane governs the electronic density detected by the tip. It permits us to explain the triangular defect with a clear maximum of intensity in its center and dark sides.     

Effect of temperature on the extraction of octahedral and tetrahedral cobalt(II) by 8-hydroxyquinoline and/or dibenzo-18-crown-6 or dibenzylamine

The extraction behavior of octahedral and tetrahedral cobalt(II) complexes from aqueous nitrate medium was studied in the system 8-hydroxyquinoline (HOX) and dibenzo-18-crown-6 (Db 18C6) or dibenzylamine (DBA) in chloroform at different temperatures to evaluate the thermodynamic functions as well as the equilibrium constants of each reaction. The stoichiometry of the extracted organic phase species were established to be Co(OX)₂·Db18C6 for the octahedral cobalt and Co(OX)₂·DBA for the tetrahedral cobalt.     

Bioactive Ca10(PO4)6(OH)2−TiO2 composite coating prepared by sol-gel process

The sol-gel prepared titania (TiO₂) has recently been demonstrated with a promising bioactivity [1]. It forms a chemical bond with the living bone in the body, although the bonding is not very strong. The present study is intended to improve the bone-bonding ability of the titania gel. The goal is achieved by impregnating the titania with hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂). The processing route includes the following steps: (1) the titania sol solution was prepared; (2) the solution was mixed with fine hydroxyapatite (HA) powders; (3) the mixture was used to produce a coating on a commercial pure titanium (c.p. Ti) or Ti6A14V plate by a dip coating technique; (4) the coating was fired at 400–600°C. The resulting coating is a composite consisting of hydroxyapatite embedded in the matrix of the titania gel. Such HA-TiO₂ composite coating is capable of inducing the hydroxyapatite precipitation from a simulated body fluid. When implanted in femurs of goat, the composite coating shows a bonding with bone. Its bone-bonding strength is twice as high as that of the pure titania gel coating. The results indicate that impregnating with hydroxyapatite is a promising way to increase the bioactivity of the titania gel.     

Platium Film Electrodes (1) Platium Film on Ti or TiO2-Covered Ti

A platium film was formed on a Ti(Pt-Ti) and on a TiO₂(Pt-TiO₂-Ti) substrate by the conventional electroplating method (ELP) and by the electroless plating technique (ELSP). The effective minimum film thickness was found to be 0.5 μm judging from the maximum electrocatalytic capablity in alkaline (1 M NaOH) water electrolysis. The film obtained from ELP is superior to that obtained from ELSP, being more tightly bound to the substrate, showing better coverage of the subsrate surface, and also being mechanically stronger. Comparisons with bright Pt and with Pt-black electrodes were made and it is concluded that the electrodes newly prepared using ELP will work as well as Pt-black electrods. The electrodes from ELSP are useful only as cathodes, and are not suitable as anodes.     

Modeling spin interactions in a cyclic trimer and a cuboidal Co4O4 core with Co(II) in tetrahedral and octahedral environments

The X-ray crystallographic structures, the magnetic susceptibilities from 2 to 300 K, and a theoretical analysis of the magnetism for a triangular and a tetranuclear molecule consisting of linked high-spin cobalt(II) centers are described. The interpretation of the magnetic data for the triangular compound [Co(depa)Cl](3) (depa is the anion of 2,2'-(bis-4-ethylpyridyl)amine), which has tetrahedrally coordinated Co(2+) ions, entails isotropic antiferromagnetic exchange interaction and antisymmetric exchange acting within the two low-lying spin doublets. Two strong isotropic ferromagnetic interactions have been modeled in the cuboidal compound Co(4)(DPM)(4)(CH(3)O)(4)(CH(3)OH)(4) (DPM represents the anion of dipivaloylmethane), which has octahedral coordination, and the system can be approximately considered as two weakly coupled S = 3 species.     

The crystal structure of Na4Ni7(PO4)6

Na₄Ni₇(PO₄)₆ crystallizes in the space group Cm with a = 10.550(2), b = 13.985(5), and c = 6.398(2)Å; β = 104.87(2)°. For Z = 2 the calculated density is 3.906 g/cm³ (V = 912.4 ų). Structure determination and refinement (R = 0.041, R_W = 0.045) were carried out on flux (NaF) grown crystals. The structure consists of layers of nickel-containing octahedra and phosphorus-containing tetrahedra interconnected to form a pseudocentrosymmetric framework. A layer consisting of parallel tunnels which run along the a direction contains the sodium ions in a noncentrosymmetric arrangement.     

Dinuclear [Co(II)(NCMe)5Co(II)(NCS)4] possessing octahedral and tetrahedral Co(II) sites

The structural and magnetic properties of dinuclear [Co(II)(NCMe)(5)Co(II)(NCS)(4)]·MeCN have been investigated. The structure consists of an octahedral Co(II)(NCMe)(5) center connected to a tetrahedral Co(II)(NCS)(4) center bridged by a μ(1,3)-NCS(-) ligand. The bridging NCS(-) weakly couples the pair of S = (3)/(2) Co(II) spin sites, as evidenced by the magnetic data being best fit by the Curie-Weiss expression with θ = -15.5 K.     

Design, formation and properties of tetrahedral M(4)L(4) and M(4)L(6) supramolecular clusters

The rigid tris- and bis(catecholamide) ligands H(6)A, H(4)B and H(4)C form tetrahedral clusters of the type M(4)L(4) and M(4)L(6) through self-assembly reactions with tri- and tetravalent metal ions such as Ga(III), Fe(III), Ti(IV) and Sn(IV). General design principles for the synthesis of such clusters are presented with an emphasis on geometric requirements and kinetic and thermodynamic considerations. The solution and solid-state characterization of these complexes is presented, and their dynamic solution behavior is described. The tris-catecholamide H(6)A forms M(4)L(4) tetrahedra with Ga(III), Ti(IV), and Sn(IV); (Et(3)N)(8)[Ti(4)A(4)] crystallizes in R3(-)c (No. 167), with a = 22.6143(5) A, c = 106.038(2) A. The cluster is a racemic mixture of homoconfigurational tetrahedra (all Delta or all Lambda at the metal centers within a given cluster). Though the synthetic procedure for synthesis of the cluster is markedly metal-dependent, extensive electrospray mass spectrometry investigations show that the M(4)A(4) (M = Ga(III), Ti(IV), and Sn(IV)) clusters are remarkably stable once formed. Two approaches are presented for the formation of M(4)L(6) tetrahedral clusters. Of the bis(catecholamide) ligands, H(4)B forms an M(4)L(6) tetrahedron (M = Ga(III)) based on an "edge-on" design, while H(4)C forms an M(4)L(6) tetrahedron (M = Ga(III), Fe(III)) based on a "face-on" strategy. K(5)[Et(4)N](7)[Fe(4)C(6)] crystallizes in I43(-)d (No. 220) with a = 43.706(8) A. This M(4)L(6) tetrahedral cluster is also a racemic mixture of homoconfigurational tetrahedra and has a cavity large enough to encapsulate a molecule of Et(4)N(+). This host-guest interaction is maintained in solution as revealed by NMR investigations of the Ga(III) complex.     

The iron phosphate K3Fe5(PO4)6

The crystal structure of tripotassium pentairon hexaphosphate has been determined by single‐crystal X‐ray diffraction. The structure contains one Fe atom on a center of symmetry, one K, two Fe and two P atoms on twofold axes, and one Fe, two P and one K atom in general positions. The K₃Fe₅(PO₄)₆ structure consists of a complex three‐dimensional framework of corner‐sharing between iron polyhedra, and corner‐ and edge‐sharing between PO₄ tetrahedra and iron polyhedra (FeO₅ and FeO₆). This linkage between iron and phosphorus forms intersecting channels containing the K atoms.     

Microanalytical investigations on optical phase gratings in K(TiO)PO4 single crystals

The Rb/K ion exchange in micro-structured K(TiO)PO₄ single crystals in contact with Rb containing nitrate melts results in ion-exchanged zones with enlarged refractive index which works as an optical phase grating. The knowledge of the diffusion behavior was the prerequisite for the generation of optimum refractive index profiles. Therefore, the local Rb/K concentration of ion-exchanged single crystals was determined with an electron probe microanalyzer (EPMA). The observed degree of ion exchange and the calculated Rb/K counterdiffusion coefficients were used to estimate the optimum ion exchange conditions. The diffusion-generated optical phase gratings show very narrow and deep ion-exchanged zones. The ratio of the ion penetration depths results in an extreme diffusion anisotropy D_Rb/K(c):D_Rb/K(b) ≈ 500:1.

     

Study of the ionic conductivity of Ca6La4(PO4)2(SiO4)4F2 and Ca4La6(SiO4)6F2

In order to enhance our knowledge about the Ca_10−xLa_x(PO₄)_6−x(SiO₄)_xF₂ (0 ≤ x ≤ 6) series, whose chemical stability decreases as the substitution degree increases, Ca₆La₄(PO₄)₂(SiO₄)₄F₂ and Ca₄La₆(SiO₄)₆F₂ compounds were prepared through a solid-state reaction. Their ionic conductivity was measured by impedance spectroscopy. The results indicate that the conductivity increases with substitution, and fits the Arrhenius equation over the investigated temperature range. At high temperatures, a change in the activation energy has been observed, which has been related to the nature of the Ca/La–F bond, i.e. to the polarizability of lanthanum.     

Hydrothermal synthesis and characterization of (Na,K)Ti2(PO4)3 solid solutions

Na_1?x K_xTi₂(PO₄)₃ (0 ≤ x ≤ 1) solid solutions are synthesized through ion exchange under hydrothermal conditions and a sol-gel process. The unit cell parameters are calculated for (Na,K) titanium phosphates. Cation-exchange reactions in the NaTi₂(PO₄)₃-KTi₂(PO₄)₃-NaCl-KCl-H₂O system are studied at T = 973 K and p = 200 MPa. The solid phase with compositions in the range 0 ≤ x ≤ 0.7 is enriched with sodium; in the range 0.7 ≤ x ≤ 1.0, it is enriched with potassium. The excess functions of mixing for the solid solutions are described in terms of the Margules model. Titanium phosphates Na_1?x K_xTi₂(PO₄)₃ show greater nonideality than zirconium phosphates Na_1?x K_xZr₂(PO₄)₃ and lower thermodynamic stability in decay into pure components at high pressures and temperatures.     

Polymorphic transitions in the binary system lead chlorapatite Pb10(PO4)6Cl2 — calcium fluorapatite Ca10(PO4)6F2

Phase dependences in the binary system lead chlorapatite Pb₁₀(PO₄)₆Cl₂ — calcium fluorapatite Ca₁₀(PO₄)₆F₂ with special regard to polymorphic transitions of initial compounds have been examined. Phase diagram of this system over the full temperature and composition range has been provided and the occurrence of solid solutions discovered. The investigations have been carried out by the thermal, microscopic, X-ray and dilatometric analyses.

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Zusammenfassung Es wurde die Phasenabhängigkeit im binären System Bleichlorapatit Pb₁₀(PO₄)₆Cl₂ - Calciumfluorapatit Ca₁₀(PO₄)₆F₂ im besonderen Hinblick auf polymorphe Übergänge der Ausgangsverbindungen untersucht. Das Phasendiagramm dieses Systemes wurde im gesamten Temperatur- und Konzentrationsbereich erstellt und die Existenz von Mischkristallen entdeckt. Die Untersuchungen wurden mittels Thermo-, mikroskopischer, röntgenographischer und dilatometrischer Analyse durchgeführt.

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The author would like to thank Prof. J. Berak for his help and support, and Prof. T. Znamierowska for advice.