Hydrogen dissociation and diffusion on Ni- and Ti-doped Mg(0001) surfaces

It is well-known, both theoretically and experimentally, that alloying MgH(2) with transition elements can significantly improve the thermodynamic and kinetic properties for H(2) desorption, as well as the H(2) intake by Mg bulk. Here, we present a density functional theory investigation of hydrogen dissociation and surface diffusion over a Ni-doped surface and compare the findings to previously investigated Ti-doped Mg(0001) and pure Mg(0001) surfaces. Our results show that the energy barrier for hydrogen dissociation on the pure Mg(0001) surface is high, while it is small/null when NiTi are added to the surface as dopants. We find that the binding energy of the two H atoms near the dissociation site is high on Ti, effectively impeding diffusion away from the Ti site. By contrast, we find that on Ni, the energy barrier for diffusion is much reduced. Therefore, although both Ti and Ni promote H(2) dissociation, only Ni appears to be a good catalyst for Mg hydrogenation, allowing diffusion away from the catalytic sites. Experimental results corroborate these theoretical findings, i.e., faster hydrogenation of the Ni-doped Mg sample as opposed to the reference Mg- or Ti-doped Mg.     

Experimental and theoretical studies of elemental site preferences in quasicrystalline approximants (R-phases) within the Li-Mg-Zn-Al system

A series of ternary and quaternary R-phase compounds in the Li-Mg-Zn-Al system are synthesized from pure elements in sealed Ta tubes with starting compositions based on the suggestions from electronic structure calculations using relative Mulliken populations to quantify the site preferences for the various elements. Single-crystal structural analyses reveal new R-phase compounds with various Li/Mg and Zn/Al ratios. The space group of all compounds is Im3 (No. 204). Five quaternary phases [Li1.00(1)Mg0.63(2)Zn1.23(1)Al2.14(1) (1), a = 14.073(3) A; Li1.00(1)Mg0.63(1)Zn1.42(1)Al1.96(1) (2), a = 14.088(3) A; Li1.01(1)Mg0.62(1)Zn1.31(1)Al2.06(1) (3), a = 14.096(5) A; Li1.03(1)Mg0.60(1)Zn1.78(3)Al1.59(3) (4), a = 13.993(5) A; Li0.78(2)Mg0.85(2)Zn2.47(1)Al0.94(1) (5), a = 13.933(2) A] and four ternary compounds [Li1.63Zn0.81(1)Al2.56(1) (6), a = 14.135(3) A; Li1.63Zn1.42(1)Al1.95(1) (7), a = 13.966(5) A; Li1.63Zn1.59(1)Al1.78(1) (8), a = 13.947(2) A; and Li1.63Zn1.77(1)Al1.60(1) (9), a = 13.933(4) A] are identified. The crystal structure exhibits an Al/Zn (M sites) network constructed from M12 icosahedra and M60 buckyball-type clusters. Li/Mg atoms (A sites) fill cavities within the Al/Zn network to give pentagonal dodecahedra (A20). The site-potential studies (relative Mulliken populations) indicate two groups of atomic sites (positively and negatively polarized), which are consistent with the single-crystal studies. Further differentiation of site potentials among the various electropositive sites leads to segregation of Li and Mg, which is also verified experimentally. The analysis of relative Mulliken populations in an intermetallic framework provides a useful method for elucidating elemental site preferences when diffraction techniques cannot unequivocally solve the site preference problem.     

Coordination solids derived from Cp*M(CN)3- (M = Rh,Ir)

Solutions of Rh2(OAc)4 and Et4N[Cp*Ir(CN)3] react to afford crystals of the one-dimensional coordination solid [Et4N[Cp*Ir(CN)3][Rh2(OAc)4]]. This reaction is reversed by coordinating solvents such as MeCN. The structure of the polymer consists of helical anionic chains containing Rh2(OAc)4 units linked via two of the three CN ligands of Cp*Ir(CN)3-. Use of the more Lewis acidic Rh2(O2CCF3)4 in place of Rh2(OAc)4 gave purple [(Et4N)2[Cp*Ir(CN)3]2[Rh2(O2CCF3)4]3], whose insolubility is attributed to stronger Rh-NC bonds as well as the presence of cross-linking. The species [[Cp*Rh(CN)3][Ni(en)n](PF6)] (n = 2, 3) crystallized from an aqueous solution of Et4N[Cp*Rh(CN)3] and [Ni(en)3](PF6)2; [[Cp*Rh(CN)3][Ni(en)2](PF6)] consists of helical chains based on cis-Ni(en)(2)2+ units. Aqueous solutions of Et4N[Cp*Ir(CN)3] and AgNO3 afforded the colorless solid Ag-[Cp*Ir(CN)3]. Recrystallization of this polymer from pyridine gave the hemipyridine adduct [Ag[Ag(py)][Cp*Ir(CN)3]2]. The 13C cross-polarization magic-angle spinning NMR spectrum of the pyridine derivative reveals two distinct Cp* groups, while in the pyridine-free precursor, the Cp*'s appear equivalent. The solid-state structure of [Ag[Ag(py)][Cp*Ir(CN)3]2] reveals a three-dimensional coordination polymer consisting of chains of Cp*Ir(CN)3- units linked to alternating Ag+ and Ag(py)+ units. The network structure arises by the linking of these helices through the third cyanide group on each Ir center.     

Synthesis and structural characterization of porphyrinic enediynes: geometric and electronic effects on thermal and photochemical reactivity

We report the preparation of [5,10,15,20-tetraphenyl-2,3,7,8,12,13,17,18-octakis(phenylethynyl)porphinato] complexes of Ni(II), H(2), Zn(II), Mg(II), and Cu(II), as well as select trimethylsilanylethynyl derivatives. The X-ray structures of the octakis(phenylethynyl) compounds show systematic deviations from planarity (Ni(II), 0.2851 A; Zn(II), 0.0304 A) as a function of the central cation. These geometric distortions are reflected in bathochromic shifts of the Soret and Q bands (Ni(II), 497, 604, and 650 nm; Mg(II), 515, 595, 642, and 705 nm) which loosely correlate with increasing planarity of the structure. Similarly, vibrational modes involving the octasubstituted porphyrin core exhibit shifts to lower frequency as a function of increasing planarity in the solution-state resonance Raman spectra (lambda(exc) = 501.7 nm) of these compounds. Analogous trends are also observed in their solid-state electronic and resonance Raman spectra, indicating that the structural distortions within the octakis(phenylethynyl) series are preserved in solution. Comparison of the saddle distortion of the octasubstituted Ni(II) compound with the ruffle/saddle distortions of the pentakis and hexakis Ni(II) derivatives reveals some influence of asymmetric peripheryl substitution on geometric structure. These Ni(II) derivatives also exhibit systematic red shifts in their electronic spectra as a function of the number of conjugated alkyne units ( approximately 13 nm/alkyne), revealing participation of the enediyne units in the electronic ground and excited states. The solid-state Bergman cyclization temperatures of the phenylethynyl compounds vary markedly as a function of planarity, and correlate loosely with alkyne termini separation (Ni(PA)(8), 4.00 A, 281 degrees C; MgP(PA)(8), 3.77 A, 244 degrees C). In solution, both thermal and photochemical activation of the free-base octakis(phenylethynyl) compound lead to formal reduction of the porphyrin backbone via H-atom addition at opposing meso-positions. Generation of a common product suggests that both thermal and photochemical pathways to Bergman cyclization in solution contain significant activation barriers to formation of the 1,4-phenyl diradical intermediate, and under these solution conditions, alternate reaction channels are more thermodynamically favorable.     

Single-source materials for metal-doped titanium oxide: syntheses, structures, and properties of a series of heterometallic transition-metal titanium oxo cages

Titanium dioxide (TiO(2)) doped with transition-metal ions (M) has potentially broad applications in photocatalysis, photovoltaics, and photosensors. One approach to these materials is through controlled hydrolysis of well-defined transition-metal titanium oxo cage compounds. However, to date very few such cages have been unequivocally characterized, a situation which we have sought to address here with the development of a simple synthetic approach which allows the incorporation of a range of metal ions into titanium oxo cage arrangements. The solvothermal reactions of Ti(OEt)(4) with transition-metal dichlorides (M(II)Cl(2), M = Co, Zn, Fe, Cu) give the heterometallic transition-metal titanium oxo cages [Ti(4)O(OEt)(15)(MCl)] [M = Co (2), Zn (3), Fe (4), Cu (5)], having similar MTi(4)(μ(4)-O) structural arrangements involving ion pairing of [Ti(4)O(OEt)(15)](-) anion units with MCl(+) fragments. In the case of the reaction of MnCl(2), however, two Mn(II) ions are incorporated into this framework, giving the hexanuclear Mn(2)Ti(4)(μ(4)-O) cage [Ti(4)O(OEt)(15)(Mn(2)Cl(3))] (6) in which the MCl(+) fragments in 2-5 are replaced by a [ClMn(μ-Cl)MnCl](+) unit. Emphasizing that the nature of the heterometallic cage is dependent on the metal ion (M) present, the reaction of Ti(OEt)(4) with NiCl(2) gives [Ti(2)(OEt)(9)(NiCl)](2) (7), which has a dimeric Ni(μ-Cl)(2)Ni bridged arrangement arising from the association of [Ti(2)(OEt)(9)](-) ions with NiCl(+) units. The syntheses, solid-state structures, spectroscopic and magnetic properties of 2-7 are presented, a first step toward their applications as precursor materials.     

Rhodium/iridium-titanium azaheterometallocubanes

Treatment of [[Ti(eta5-C5Me5)(mu-NH)]3(mu3-N)] (1) with the diolefin complexes [[MCl(cod)]2] (M = Rh, Ir; cod = 1,5-cyclooctadiene) in toluene afforded the ionic complexes [M-(cod)(mu3-NH)3Ti3(eta5-C5Me5)3(mu3-N)]Cl [M = Rh (2), Ir (3)]. Reaction of complexes 2 and 3 with [Ag(BPh4)] in dichloromethane leads to anion metathesis and formation of the analogous ionic derivatives [M(cod)(mu3-NH)3Ti3-(eta5-C5Me5)3(mu3-N)][BPh4] [M = Rh (4), Ir (5)]. An X-ray crystal structure determination for 5 reveals a cube-type core [IrTi3N4] for the cationic fragment, in which 1 coordinates in a tripodal fashion to the iridium atom. Reaction of the diolefin complexes [[MCl(cod))2] (M = Rh, Ir) and [[RhCl(C2H4)2]2] with the lithium derivative [[Li(mu3-NH)2(mu3-N)-Ti3(eta5-C5Me5)3(mu3-N)]2] x C7H8 (6 C7H8) in toluene gave the neutral cube-type complexes [M(cod)(mu-NH)2(mu3-N)Ti3-(eta5-C5Me5)3(mu3-N)] [M = Rh (7), Ir (8)] and [Rh(C2H4)2(mu3-NH)2(mu3-N)Ti3(eta5-C5Me5)3(mu3-N)] (9), respectively. Density functional theory calculations have been carried out on the ionic and neutral azaheterometallocubane complexes to understand their electronic structures.     

Highly Dispersed TiO(6) Units in a Layered Double Hydroxide for Water Splitting

A family of photocatalysts for water splitting into hydrogen was prepared by distributing TiO(6) units in an MTi-layered double hydroxide matrix (M=Ni, Zn, Mg) that displays largely enhanced photocatalytic activity with an H(2) -production rate of 31.4?μmol?h(-1) as well as excellent recyclable performance. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) mapping and XPS measurement reveal that a high dispersion of TiO(6) octahedra in the layered doubled hydroxide (LDH) matrix was obtained by the formation of an M(2+) -O-Ti network, rather different from the aggregation state of TiO(6) in the inorganic layered material K(2) Ti(4) O(9) . Both transient absorption and photoluminescence spectra demonstrate that the electron-hole recombination process was significantly depressed in the Ti-containing LDH materials relative to bulk Ti oxide, which is attributed to the abundant surface defects that serve as trapping sites for photogenerated electrons verified by positron annihilation and extended X-ray absorption fine structure (EXAFS) techniques. In addition, a theoretical study on the basis of DFT calculations demonstrates that the electronic structure of the TiO(6) units was modified by the adjacent MO(6) octahedron by means of covalent interactions, with a much decreased bandgap of 2.1?eV, which accounts for its superior water-splitting behavior. Therefore, the dispersion strategy for TiO(6) units within a 2D inorganic matrix can be extended to fabricate other oxide or hydroxide catalysts with greatly enhanced performance in photocatalysis and energy conversion.     

Ti and Ni tubes combined in thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) for the determination of copper in biological samples

This study presents an evaluation of Cu determination in thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) using Ni and Ti metal tube atomizers. The TS-FF-AAS system was equipped with Ti tubes inserted inside Ni tubes (called Ni/Ti), and also different configurations of Ti tube atomizers placed on an oxidizing air/acetylene flame. This new arrangement combining both tubes permitted an increased sensitivity (approximately 4 times) when it was compared with single Ni or Ti tubes. This high sensitivity is due to the formation of TiO₂ inside the Ti tubes (shown by X-ray diffractometry and microanalyses), improving the Cu atomization through the corresponding oxide. The estimated gaseous phase temperatures for the tubes (Ni, Ti and Ni/Ti) were of the same magnitude (varied from 1400 to 1800 °C). Tests with concomitants (Na, K, Ca and Mg) showed similar behavior of Ni and Ni/Ti tubes. The differences between Ni and Ni/Ti tube atomizers for Cu sensitivity were not related to differences between the tube atomizers' internal volumes. The method accuracy was verified using certified reference materials (CRM's) of biological samples prepared with a closed-vessel microwave system using diluted HNO₃. A 2 µg L^− 1 Cu detection limit was obtained using a Ni/Ti tube atomizer. The recoveries for Cu from the CRM's were about 100%. Finally, the use of a Ti tube inside a Ni tube increased the Ti tube lifetime.     

NiTi过渡金属团簇的结构和芳香性的理论研究

在B3PW91/6-311+G(d)计算水平上, 计算并讨论了Ni₄Ti₂, [Ni₄Ti₂]²⁺, [Ni₄Ti₂]^2-与Ni₄Ti₄, [Ni₄Ti₄]²⁺, [Ni₄Ti₄]^2-团簇的几何结构和芳香性. 在构型优化过程中得到了Ni₄Ti₂(D_4h), [Ni₄Ti₂]²⁺(D_4h), [Ni₄Ti₂]^2-(D_4h)和Ni₄Ti₄(D_2h)4个稳定构型, 发现当引入上下2个Ti原子后, Ni₄环成为了平面正方形构型. 核无关化学位移(NICS)计算结果表明, Ni₄Ti₂(D_4h)与Ni₄Ti₄(D_2h)的NICS值为正, 而[Ni₄Ti₂]²⁺(D_4h)和[Ni₄Ti₂]^2-(D_4h)的NICS值为负, 且[Ni₄Ti₂]^2-(D_4h)的NICS值更负. 同时还发现, 由s与d轨道参与形成的反磁性环流是引起[Ni₄Ti₂]²⁺(D_4h)和[Ni₄Ti₂]^2-(D_4h)具有较大芳香性的主要原因; 其中Ti原子主要提供d_z²与s轨道, 而Ni原子主要利用其d_z²与d_x²-y²轨道形成正方形环, 它们之间构成了球状的d轨道环流, 且[Ni₄Ti₂]²⁺(D_4h)和[Ni₄Ti₂]^2-(D_4h)中还有非常明显的π轨道环流.     

Mg1-xTixNi(0≤x≤0.4)系列合金的合成及性能研究

采用机械合金化法成功制备了Mg1-xTixNi(0≤x≤0.4)系列三元合金.XRD结构分析表明,不同成分的合金在相同的球磨时间下非晶化程度有所区别,并且合金的非晶化程度随着球磨时间的增加而趋于完全.少量Ti的加入使得该系列合金的电化学性能及循环稳定性都有所提高.在球磨120h的该系列合金中,Mg0.9Ti0.1Ni合金的最大初始放电容量达到356.85mA·h·g-1(100mA·g-1,-0.5Vvs.Hg/HgO),而Mg0.7Ti0.3Ni合金的循环稳定性最好.Ti的加入亦提高了合金的抗腐蚀性能,使其腐蚀电位正移.     

Syntheses, structure, and bonding of Rb14(Mg1-xInx)30. A nonstoichiometric phase with an unusual substitution in the anion framework

The title compound Rb(14)(Mg(1-x)In(x))(30) (x = 0.79-0.88) has been obtained from high-temperature reactions of the elements in welded Ta tubes. There is no analogous binary compound without Mg. The crystal structure established by single-crystal X-ray diffraction means (space group P2m (No. 189), Z = 1 and a = b = 10.1593(3) Angstroms, c = 17.783(1) Angstroms for x = 0.851) features two distinct types of anionic layers: isolated pentacapped trigonal prismatic In(11)(7-) clusters and condensed [(Mg(x)In(1-x))(5)In(14)](7-) layers. The latter consists of analogous M(11) (M = Mg/In) fragments that share prismatic edges and are interbridged by trigonal M(3) units. The structure shows substantial differences from related A(15)Tl(27) (A = Rb, Cs) in which the cation A that centers a six-membered ring of Tl(11) fragments is replaced by M(3.) Both linear muffin-tin orbital and extended Hückel calculations are used to analyze the observed phase width and site preferences. We further utilize the results to rationalize the distortion of the M(11) fragment in the condensed layer and also to correlate with electrical properties. An isomorphous phase region (Rb(y)K(1-)(y))(14)(Mg(1-x)In(x))(30) (y = 0.52, 0.66 for x = 0.79) is also formed.     

Preparation, characterization and metal sorption studies of a Chrome-Azurol-S-loaded anion-exchange resin

Chrome Azurol S (CS) was mobilized on an strongly basic anion-exchange resin (Dowex 2 x 4, in Cl(-) form) by batch equilibration. The modified resin was stable in acetate buffer solution and in 0.1 M HCl and H(2)SO(4), but it was readily degraded with 2-6 M HCl and HNO(3). Retention of Ba(II), Sr(II), Ca(II), Mg(II), Al(III), Cr(III), Zn(II), Fe(III), Ti(IV), Mn(II), Co(II), Ni(II), Cu(II), Cd(II) and Pb(II) was studied using the batch equilibration method. The uptake and recovery yields were determined by using inductively-coupled plasma atomic emission spectroscopy (for Mg, Al, Cr, Ti, Fe, Mn, Ni, Zn, Cu, Cd and Pb) and atomic absorption spectrophotometry (for Ba, Sr, Ca and Co). The optimum pH value was established for performing a selective separation of Al(III) from the other metal ions. The sorption capacities of the CS-loaded resing for Al(III), Cr(III), Mg(II) (at pH 6), Fe(III) (at pH 5) and Ti(IV) (at pH 4) were 14, 2.9, 0.3, 3 and 3.9 mumoles g(-1) respectively. On this basis a method for separating Al(III) from other cations was established.     

Laves phases, gamma-brass, and 2x2x2 superstructures: a new class of quasicrystal approximants and the suggestion of a new quasicrystal

Of the most common cubic intermetallic structure types, several (MgCu(2), Cu(5)Zn(8), Ti(2)Ni, and alpha-Mn) have superstructures with unusual symmetry properties. These superstructures (Be(5)Au, Li(21)Si(5), Sm(11)Cd(45), and Mg(44)Ir(7)) have the unusual property of pairs of perpendicular pseudo fivefold axes, most apparent in their X-ray diffraction patterns. The current work shows that an 8D to 3D projection method cleanly describes most (and in one case, all) of the atomic positions in the four superstructures mentioned above. This type of projection, which maps the E(8) lattice (a mathematically simple 8D crystal) into 3D space, combines the desired higher dimensional point group's perpendicular fivefold rotations with 3D translational symmetry-exactly what we see in the experimental crystal structures. The projection method successfully accounts for all heavy atom positions in the four superstructures, and at least 60-70 % of the light atom positions. The results suggest that all of these structures, previously known to be connected only by qualitative similarities in their atomic "clusters", are approximants of a single, as-yet unknown, class of quasicrystal.     

Ab initio thermodynamics examination of sulfur species present on Rh, Ni, and binary Rh-Ni surfaces under steam reforming reaction conditions

The stable form of adsorbed sulfur species and their coverage were investigated on Rh, Ni, and Rh-Ni binary metal surfaces using density functional theory calculations and the ab initio thermodynamics framework. S adsorption, SO(x) (x = 1-4) adsorption, and metal sulfide formation were examined on Rh(111) and Ni(111) pure metals. Both Rh and Ni metals showed a preference for S surface adsorption rather than SO(x) adsorption under steam reforming conditions. The transition temperature from a clean surface (<(1)/(9) ML) to S adsorption was identified on Rh(111), Ni(111), Rh(1)Ni(2)(111), and Rh(2)Ni(1)(111) metals at various P(H(2))/P(H(2)S) ratios. Bimetallic Rh-Ni metals transition to a clean surface at lower temperatures than does the pure Rh metal. Whereas Rh is covered with (1)/(3) ML of sulfur under the reforming conditions of 4-100 ppm S and 800 °C, Rh(1)Ni(2) is covered with (1)/(9) ML of sulfur at the lower end of this range (4-33 ppm S). The possibility of sulfate formation on Rh catalysts was examined by considering higher oxygen pressures, a Rh(221) stepped surface, and the interface between a Rh(4) cluster and CeO(2)(111) surface. SO(x) surface species are stable only at high oxygen pressure or low temperatures outside those relevant to the steam reforming of hydrocarbons.     

Effects of Ti and Zr Substituted on the Electrochemical Characteristics of MgNi-Based Alloy Electrodes

Mg-based hydrogen storage alloys MgNi, Mg0.9Ti0.1Ni, and Mg0.9Ti0.06Zr0.04Ni were successfully prepared by means of mechanical alloying （MA）. The structure and the electrochemical characteristics of these Mg-based materials were studied. The X-ray diffraction （XRD） result shows that the main phases of the alloys exhibit amorphous structure. The scanning electron microscopy （SEM） photograph shows that the particle size of Ti and Zr substituted alloys was about 2-4 μm in diameter. The cycle lives of the alloys were prolonged by adding Ti and Zr. After 50 charge-discharge cycles, the discharge capacity of Mg0.9Ti0.06Zr0.04Ni was 91.74% higher than that of MgNi alloy and 37.96% higher than that of Mg0.9Ti0.1Ni alloy. The main reason for the electrode capacity decay is the formation of Mg（OH）2 （product of Mg corrosion） at the surface of alloy. The potentiodynamic polarization result indicates that Ti and Zr doping improves the anticorrosion in an alkaline solution. The electrochemical impedance spectroscopy （EIS） results suggest that proper amount of Ti and Zr doping improves the electrochemical catalytic activity significantly.     

Photocatalytic activity of R3MO7 and R2Ti2O7 (R=Y, Gd, La; M=Nb, Ta) for water splitting into H2 and O2

The photocatalytic activities of R3MO7 and R2Ti2O7 (R=Y, Gd, La; M=Nb, Ta) strongly depended on the crystal structure. Overall, photocatalytic water splitting into H2 and O2 proceeded over La3TaO7 and La3NbO7, which have an orthorhombic weberite structure, Y2Ti2O7 and Gd2Ti2O7, which have a cubic pyrochlore structure, and La2Ti2O7, which has a monoclinic perovskite structure. All of these materials are composed of a network of corner-shared octahedral units of metal cations (TaO6, NbO6, or TiO6); materials without such a network were inactive. The octahedral network certainly increased the mobility of electrons and holes, thereby enhancing photocatalytic activity.     

Perfluoroalkyl-substituted triazapentadienes and their metal complexes

Triazapentadienides, C(3)F(7)-C(=NR)-N=C(NHR)-C(3)F(7), result from the reaction of primary amines RNH(2) with the fluorinated imine C(3)F(7)-CF=N-C(4)F(9). The aniline derivative (R = Ph) is a weak monoprotic acid in dmso. Its conjugate base exhibits an extensive coordination chemistry. It acts as a bidentate ligand toward the molecular fragments Pd(C(3)H(5)), Rh(c-C(8)H(12)), Ir(c-C(8)H(12)), and Rh(CO)(2). The chelates [C(3)F(7)-C(NPh)-N-C(NPh)-C(3)F(7)](2)M, M = Mg, Mn, Fe, Co, Ni, Cu, Zn, and Pd, were prepared. In the crystallographically characterized Co complex, the metal is 3d(7), S = (3)/(2) and tetrahedrally coordinated. Spin densities at carbon in the C(6)H(5) and C(3)F(7) groups were estimated from the (1)H and (19)F contact shifts. Spin delocalization onto phenyl sp(2) carbons is approximately 10 times greater than onto the fluorinated sp(3) carbons.     

Highly Dispersed TiO6 Units in a Layered Double Hydroxide for Water Splitting

A family of photocatalysts for water splitting into hydrogen was prepared by distributing TiO₆ units in an MTi‐layered double hydroxide matrix (M=Ni, Zn, Mg) that displays largely enhanced photocatalytic activity with an H₂‐production rate of 31.4 μmol h^?1 as well as excellent recyclable performance. High‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) mapping and XPS measurement reveal that a high dispersion of TiO₆ octahedra in the layered doubled hydroxide (LDH) matrix was obtained by the formation of an M²⁺‐O‐Ti network, rather different from the aggregation state of TiO₆ in the inorganic layered material K₂Ti₄O₉. Both transient absorption and photoluminescence spectra demonstrate that the electron–hole recombination process was significantly depressed in the Ti‐containing LDH materials relative to bulk Ti oxide, which is attributed to the abundant surface defects that serve as trapping sites for photogenerated electrons verified by positron annihilation and extended X‐ray absorption fine structure (EXAFS) techniques. In addition, a theoretical study on the basis of DFT calculations demonstrates that the electronic structure of the TiO₆ units was modified by the adjacent MO₆ octahedron by means of covalent interactions, with a much decreased bandgap of 2.1 eV, which accounts for its superior water‐splitting behavior. Therefore, the dispersion strategy for TiO₆ units within a 2D inorganic matrix can be extended to fabricate other oxide or hydroxide catalysts with greatly enhanced performance in photocatalysis and energy conversion.     

电化学合成金属醇盐的研究

纳米材料在生物、电子、能源、化工等各个领域的应用日益广泛 ,已成为当前研究的热点 [1,2 ] ,纳米材料的制备有多种方法 ,其中溶胶 -凝胶 ( Sol- gel) [3 ] 、醇盐热解、化学气相淀积 ( CVD)等方法所使用的前驱体主要为金属醇盐 .传统化学方法合成金属醇盐是用 MXn[X为 Hal,R,H,NR2 ,N( Si Me3 ) 2等 ]与醇进行交换反应 ,过程复杂 ,且原材料不易得到 ,产率低 ,纯度达不到要求 ,后续分离繁琐 ,所以人们一直努力寻找合成金属醇盐的新方法 .有机电解合成一般在常温常压下进行 ,可通过调节电极电位控制电极反应的方向和速度 .据报道 [4] …