Intercalation of [Cr(C2O4)3]3 - complex in mg,al layered double hydroxides

A Mg,Al layered double hydroxide (LDH) with [Cr(C(2)O(4))(3)](3)(-) anions in the interlayer has been synthesized following two different routes: reconstruction from a mildly calcined Mg,Al-carbonate LDH, and anion exchange from a Mg,Al-nitrate LDH. The solids prepared have been characterized by elemental chemical analysis, powder X-ray diffraction, FT-IR and UV-vis/DR (diffuse reflectance) spectroscopies, thermal methods, nitrogen adsorption at -196 degrees C, and FT-IR monitoring of pyridine adsorption. The results obtained indicate that the most appropriate method is anion exchange, leading to a well crystallized LDH with an interlayer spacing of 10 A. Due to the high pH value (>8) of the solution in the reconstruction method, however, a polyphasic system is obtained, where, in addition to a phase with the LDH structure, amorphous magnesium oxalate and chromium oxohydroxides are also formed due to hydrolysis of the complex. The interlayer complex is stable up to 200 degrees C, but the layered structure is stable up to 330 degrees C, probably because of the presence of interlayer oxalate anions formed during decomposition of the complex. Calcination leads to oxidation of Cr(3+) ions to the six-valent state, which reverts to Cr(3+) when the calcination temperature is further increased.     

Synthesis and characterization of new Mg(2)Al-paratungstate layered double hydroxides

Layered double hydroxides (LDHs, or hydrotalcites) with Mg(2+) and Al(3+) cations in the mixed metal hydroxide layer and paratungstate anions in the interlayer have been prepared. Different methods have been followed: anion exchange with Mg,Al LDHs originally containing nitrate or adipate, reconstruction of the LDH structure from a mildly calcined Mg(2)Al-CO(3) LDH, and coprecipitation. In all cases, the tungsten precursor salt was (NH(4))(10)H(2)W(12)O(42). The prepared solids have been characterized by elemental chemical analysis, powder X-ray diffraction (PXRD), FT-IR spectroscopy, thermogravimetric (TG) and differential thermal (DTA) analyses, scanning electron microscopy (SEM) with EDX (energy-dispersive X-ray analysis), and nitrogen adsorption at -196 degrees C for surface area and surface texture. Most of the synthesis methods used, especially anion exchange starting from a Mg(2)Al-NO(3) precursor at low temperature and short reaction times, lead to formation of a hydrotalcite with a gallery height of 9.8 A; increasing the reaction temperature to 70-100 degrees C and maintaining short contact times leads to a solid with a gallery height of 7.8 A. Both phases have been identified as a result of the intercalation of W(7)O(24)(6)(-) species in different orientations in the interlayer space. If the time of synthesis or the temperature is increased, a more stable phase, with a gallery height of 5.2 A corresponding to a solid with intercalated W(7)O(24)(6)(-), is formed, probably with grafting of the interlayer anion on the brucite-like layers. All systems are microporous. Calcination at 300 degrees C leads to amorphous species, and crystallized MgWO(4) is observed at 700 degrees C.     

Preparation of porous solids composed of layered niobate walls from colloidal mixtures of niobate nanosheets and polystyrene spheres

Macroporous solids with crystalline layered walls were fabricated from colloidal mixtures of size-controlled niobate nanosheets and polystyrene spheres. The macroporous solids, obtained after burning off the spheres, were characterized by scanning electron microscopy and X-ray diffraction. The obtained structures strongly depended on the lateral dimension L of the nanosheets used. When small nanosheets (L=100 nm) were used, partly ordered macroporous solids with interconnected pores were obtained, whereas sponge-like random macroporous structures were obtained with larger nanosheets (L=190 and 270 nm). Peapod-like hollow structures were obtained when we used small (L=190 nm) and very large (L=3 microm) nanosheets at the same time. The microstructure of the pore walls was controllable by changing the calcination conditions. The walls were composed of propylammonium/K(4)Nb(6)O(17) intercalation compound which has a layered structure with exchangeable cations in the interlayer space, stable up to 350 degrees C for 6 h on calcination. The walls were converted to crystalline K(8)Nb(18)O(49) after calcination at 500 degrees C for 6 h.     

In situ polymerization of the 4-vinylbenzenesulfonic anion in Ni-Al-layered double hydroxide and its molecular dynamic simulation

This paper describes a systematic study on the thermal polymerization of both pristine 4-vinylbenzenesulfonic anion (VBS) and intercalated VBS in the two-dimensional (2D) gallery of Ni-Al layered double hydroxide (VBS/Ni-Al-LDH), by virtue of combining experimental and theoretical investigations. In situ FT-IR, in situ high-temperature X-ray diffraction (HT-XRD), UV-vis absorption spectroscopy, TG-DTA and elemental analysis were used to study the polymerization process, and it was found that the polymerization of VBS/Ni-Al-LDH occurs at ca. 150-170 degrees C, at least 40 degrees C lower than that of the pristine VBS, indicating that the layered structure of LDH is favorable for thermal polymerization of VBS. Therefore, this layered inorganic material may have potential application as a "molecular reactor" for enhancing the efficiency of polymerization reaction. Furthermore, the sheet-like polymerization product was obtained with the LDHs lamella as template. For better understanding the structure and arrangement of intercalated VBS and the polymerization product between the layers of Ni-Al-LDH, molecular dynamics (MD) simulation method was employed. The simulation results of hydration energies show that there are two relatively stable stages upon the increase of the number of interlayer water molecules. VBS molecules exhibit a tendency from tilted to vertical orientation with respect to the layers as the interlayer water content increases. Compared with the experimental results, the calculated interlayer spacing is more severely affected by interlayer water content. Finally, a typical tetramer product of VBS intercalated LDH was studied and the simulated equilibrium interlayer spacing is consistent with the experimental result of in situ HT-XRD. Based on the combination of experimental and theoretical studies on the interlayer polymerization system, the aim of this work is to deeply investigate the differences in thermal polymerization process between pristine monomers and intercalated ones in the gallery of LDHs, and to give detailed information of the arrangement and swelling behavior of guest molecules confined between the sheets of host layers.     

Molecular dynamics simulation of thermomechanical properties of montmorillonite crystal. 3. montmorillonite crystals with PEO oligomer intercalates

We present the results of molecular dynamics (MD) simulation of the structure and thermomechanical behavior of Wyoming-type Na+-montmorillonite (MMT) with poly(ethylene oxide) (PEO) oligomer intercalates. Periodic boundary conditions in all three directions and simulation cells containing two MMT lamellae [Si248Al8][Al112Mg16]O640[OH]128 oriented parallel to the XY-plane were used. The interlamellar space, or gallery, between neighboring MMT lamellae was populated by 24 Na+ counterions and PEO macromolecules of different lengths, ranging from 2 up to 240 repeat units. We considered three different loadings of PEO within the gallery: 80, 160, and 240 repeat units, corresponding to 13, 23, and 31 wt % PEO based on total mass of the nanocomposite, respectively. In the cases of 13 and 23 wt %, the polymer chains formed one or two well-defined amorphous layers with interlayer distances of 1.35 and 1.8 nm, respectively. We have observed also formation of a wider monolayer gallery with interlayer distances of 1.6 nm. Three-layer PEO films formed in the case of 31 wt % loading. The thermal properties were analyzed over the range 300-400 K, and the isothermal linear compressibility, transversal moduli, and shear moduli were calculated at 300 K. These properties are compared with the results of our simulation of thermal and mechanical properties of MMT crystal with galleries filled by one or two water layers as well as with those of an isolated clay nanoplate.     

Interlayer esterification of layered silicic acid-alcohol nanostructured materials derived from alkoxytrichlorosilane

Layered silicic acid-organic nanohybrid materials consisting of long-chain alkoxy groups attached to thin silica layers have been prepared via esterification of a layered silicic acid-alcohol nanostructured material derived from hexadecoxytrichlorosilane (C(16)H(33)OSiCl(3)). The esterification reaction was performed by heating the layered composite. The detailed characterization of the product heated at 80 degrees C revealed that the interlayer alcohol molecules partly ( approximately 50%) reacted with the interlayer surface silanol groups to form alkoxy groups. Unreacted alcohol molecules were removed by tetrahydrofuran (THF) treatment to form a novel alkoxylated layered silica material. This product retains its structure up to 120 degrees C and has a higher stability in organic solvents if compared with the layered silicic acid-alcohol nanocomposite before esterification, whose structure collapsed over 100 degrees C. Furthermore, various alcohols can be adsorbed into the esterified nanohybrid with the expansion of the interlayer spacing.     

Spin-gap formation and thermal structural studies in reduced hybrid layered vanadates

Reduced layered M(C4H4N2)V4O10 ((I, M = Co; II, M = Ni; III, M = Zn); C4H4N2 = pyrazine, pyz) hybrid solids were synthesized via hydrothermal reactions at 200-230 degrees C, and their structures determined by single-crystal X-ray diffraction (Cmcm, No. 63, Z = 4; a = 14.311(2), 14.2372(4), 14.425(1) A; b = 6.997(1), 6.9008(2), 6.9702(6) A; and c = 11.4990(8), 11.5102(3), 11.479(1) A; for I, II, and III, respectively). All three solids are isostructural and contain V4O102- layers condensed from edge- and corner-shared VO5 square pyramids. A single symmetry-unique V atom is reduced by 1/2 electron (on average) and bonds via its apical oxygen atom to interlayer Mpyz2+ chains. Magnetic susceptibility measurements show a strong temperature dependence and a Curie constant that is consistent with two randomly localized spins per V4O10(2-) formula for III. Further, the unusual discovery of a remarkably well-defined transition to a singlet ground state, as well as formation of a spin gap, is found for III at 22(1) K. The temperature-dependent electrical conductivities show apparent activation energies of 0.36 (I), 0.46 (II), and 0.59 eV (III). During heating cycles in flowing N2, the samples exhibit weight losses corresponding to the removal of predominantly pyrazine, pyrazine fragments, and CO2 via reaction of pyrazine with the vanadate layer. The complete removal of pyrazine without loss of crystallinity is found for well-ground samples of I and III. The SEM images of I and II after heating at 400-500 degrees C show relatively intact crystals, but at 600 degrees C further structural collapse results in the formation of macropores at the surfaces.     

Layered Double Hydroxides Intercalated by Polyoxometalate Anions with Keggin (alpha-H(2)W(12)O(40)(6)(-)), Dawson (alpha-P(2)W(18)O(62)(6)(-)), and Finke (Co(4)(H(2)O)(2)(PW(9)O(34))(2)(10)(-)) Structures

The pillaring of Mg(3)Al layered double hydroxides (LDHs) by the title polyoxometalates (POMs) was accomplished by ion exchange reaction of the LDH-hydroxide and -adipate precursors with the POM anion at ambient or refluxing temperatures. The structural, thermal and textural properties of the LDH-POM intercalates were elucidated based on XRD, FTIR, TEM, EDS, and N(2) adsorption-desorption studies. A gallery height of approximately 10 ? was observed for the LDH intercalated by the symmetrical Keggin POM, whereas two different gallery heights were found for the cylindrical Dawson (14.5 and 12.8 ?) and Finke (13.3 and 12.6 ?) anions, depending on the preparation temperature. The differences in POM orientations were rationalized in terms of different electrostatic and hydrogen-bonding interactions between the POM pillars and the LDH layers. Upon thermal treatment at >/=100 degrees C, the intercalated Dawson and Finke POM ions exhibited only one gallery orientation, regardless of synthesis conditions. The crystalline microporous structures were retained upon heating each LDH-POM intercalate in N(2) to 200 degrees C. Pillaring in all cases was accompanied by the formation of a poorly ordered Mg(2+)/Al(3+) salt impurity that formed on the external surfaces of the LDH crystals.     

层状双金属氢氧化物的剥离方法及其应用

层状双金属氢氧化物(LDHs)是由带结构正电荷的片层和层间阴离子有序组装而成的层状无机化合物, 近期其剥离研究受到关注. 剥离后的LDHs纳米片可被看做“无机高分子”, 具有纳米尺度的开放结构, 既可作为理论研究模型, 又可作为新型基元组装功能复合纳米结构或材料, 具有显著的应用潜力. 本文对LDHs的剥离方法、剥离产物的表征方法及其应用研究现状进行了综述, 并对今后的研究方向进行了展望.     

Acid and redox properties of mixed oxides prepared by calcination of chromate-containing layered double hydroxides

Layered double hydroxides (LDHs) with Mg and Al in the layers and carbonate, nitrate or chloride in the interlayer, or with Zn and Al in the layers and chloride in the interlayer, have been prepared by coprecipitation, and have been used as precursors to prepare chromate-containing LDHs. All these systems, as well as those obtained upon their calcination up to 800 °C, have been characterised by powder X-ray diffraction, FT-IR and vis-UV spectroscopies, temperature-programmed reduction (TPR), nitrogen adsorption at −196 °C for surface texture and porosity assessment, and FT-IR monitoring of pyridine adsorption for surface acidity determination. The results obtained show that the crystallinity of the chromate-containing LDH depends on the precursor used. The layered structure of the Mg, Al systems is stabilised up to 400 °C upon incorporation of chromate; however, the Zn,Al-chromate samples collapse between 200 and 300 °C, with simultaneous formation of ZnO. Calcination of the samples above 400 °C gives rise to a reduction of Cr(VI) to Cr(III), as concluded from vis-UV spectroscopic studies. The TPR profiles show that chromate in ZnAl hydrotalcite is more easily reduced than that incorporated in the magnesium ones. Moderately strong surface Lewis acid sites exist in all samples calcined below 500 °C.     

Polar symmetry and intercalation of new multilayered hybrid molybdates: [M2(pzc)2(H2O)x][Mo5O16] (M = Co, Ni)

The layered molybdate [M2(pzc)2(H2O)x][Mo5O16] (I: M = Ni, x = 5.0; II: M = Co, x = 4.0; pzc = pyrazinecarboxylate) hybrid solids were synthesized via hydrothermal reactions at 160-165 degrees C. The structures were determined by single-crystal X-ray diffraction data for I (Cc, Z = 4; a = 33.217(4) A, b = 5.6416(8) A, c = 13.982(2) A, beta = 99.407(8) degrees , and V = 2585.0(6) A3) and powder X-ray diffraction data for II (C2/c, Z = 4; a = 35.42(6) A, b = 5.697(9) A, c = 14.28(2) A, beta = 114.95(4) degrees , and V = 2614(12) A3). The polar structure of I contains new [Ni2(pzc)2(H2O)5]2+ double layers that form an asymmetric pattern of hydrogen bonds and covalent bonds to stair-stepped [Mo5O16]2- sheets, inducing a net dipole moment in the latter. In II, however, the [Co2(pzc)2(H2O)4]2+ double layers have one less coordinated water and subsequently exhibit a symmetric pattern of covalent and hydrogen bonding to the [Mo5O16]2- sheets, leading to a centrosymmetric structure. Thermogravimetric analyses and powder X-ray diffraction data reveal that I can be dehydrated and rehydrated with from 0 to 6.5 water molecules per formula unit, which is coupled with a corresponding contraction/expansion of the interlayer distances. Also, the dehydrated form of I can be intercalated by approximately 4.3 H2S molecules per formula unit, but the intercalation by pyridine or methanol is limited to less than one molecule per formula unit.     

M(bipyridine)V(4)O(10) (M = Cu, Ag): hybrid analogues of low-dimensional reduced vanadates

New hybrid layered vanadates, M(bpy)V4O10 (I, M = Cu+; II, M = Ag+; bpy = 4,4'-bipyridine), were prepared from hydrothermal reactions at 220-230 degrees C, and their structures were characterized by single-crystal X-ray diffraction [I, P21/c (No. 14), Z = 4, a = 3.6154(3) A, b = 21.217(1) A, c = 20.267(1) A, and beta = 90.028(3) degrees ; II, P (No. 2), Z = 2, a = 3.5731(4) A, b = 10.429(1) A, c = 21.196(2) A, alpha = 89.031(5) degrees , beta = 89.322(5) degrees , and gamma = 85.546(5) degrees ]. The structures of I and II are closely related, though not isostructurally, with both containing partially reduced V4O10- layers that are constructed from zigzag chains of edge-sharing VO5 tetragonal pyramids. Neighboring zigzag chains within a layer condense via shared vertices and alternate between versions containing V4.5+ and V5+ ions, such that two out of four symmetry-unique V atoms are reduced by a half-electron on average. The interlayer spaces contain unusual M(bpy)+ chains formed from the coordination of two bridging bpy ligands to Ag+/Cu+ in a nearly linear fashion and each with a third bond to a single apical O atom of the reduced (V4.5+) VO5 tetragonal pyramids. Both I and II are stable until approximately 350-400 degrees C in O2, at which point the ligands are liberated to yield the purely inorganic MxV4O10 (M = Ag, Cu) solids. The electrical conductivities of both compounds show a temperature dependence that is consistent with Mott's variable-range-hopping model for randomly localized electrons. Magnetic susceptibilities of both I and II can be fitted to a Curie-Weiss expression (theta = -25 and -31 K, respectively; C approximately 0.40 emu.mol-1.K for both) at higher temperatures and one unpaired spin per formula. However, at below approximately 12-18 K, both show evidence for an antiferromagnetic transition that can be fitted well to the Heisenberg linear antiferromagnetic chain model. These results are analyzed with respect to related reduced vanadates and help to provide new structure-property insights for strongly correlated electron systems.     

Synthesis and Crystal Structures of Two Novel Anionic Aluminophosphates: A One-Dimensional Chain, UT-7 ([Al(3)P(5)O(20)H](5-)[C(7)H(13)NH(3)(+)](5)), and a Layer Containing Two Cyclic Amines, UT-8 ([Al(3)P(4)O(16)](3-)[C(4)H(7)NH(3)(+)](2)[C(5)H(10)NH(2)(+)])

UT-7 and UT-8 (University of Toronto, structure numbers 7 and 8) are two novel aluminophosphate materials prepared under non-aqueous conditions. Their structures, extended in one and two dimensions, respectively, have been solved by single-crystal X-ray diffraction and characterized by a variety of methods including powder X-ray diffraction (PXRD), insitu high-temperature PXRD, thermogravimetric analysis (TGA), energy dispersive X-ray analysis (EDX), and scanning electron microscopy (SEM). UT-7 ([Al(3)P(5)O(20)H](5)(-)[C(7)H(13)NH(3)(+)](5), triclinic space group P&onemacr;, Z = 2, a = 10.118(3) ?, b = 15.691(4) ?, c = 18.117(3) ?, alpha = 72.91(2) degrees, beta = 85.18(2) degrees, gamma = 79.49(2) degrees ) is built of polymeric one-dimensional chain units, hydrogen-bonded into anionic layers that are charge-compensated by interlamellar cycloheptylammonium cations. UT-7 is isostructural to our previously discovered UT-3 chain structure, isolated in the analogous cyclopentylamine system. UT-8 ([Al(3)P(4)O(16)](3-)[C(4)H(7)NH(3)(+)](2)[C(5)H(10)NH(2)(+)], monoclinic space group P2(1), Z = 2, a = 8.993(4) ?, b = 14.884(8) ?, c = 9.799(9) ?, beta = 103.52(3) degrees ) is a two-dimensional net isostructural to several previously reported [Al(3)P(4)O(16)](3)(-) layers. The interlayer region of UT-8 is occupied by two different cyclic organic amine species, namely piperidinium and cyclobutylammonium. To our knowledge, this is the first report of the crystal structure of an aluminophosphate material containing cyclobutylammonium or a mixture of cyclic amines. Interestingly, UT-7 is observed to thermally transform in the solid state to an as yet unknown layered material that can be independently synthesized in a similar synthetic system. In the same way as UT-3 transforms to the UT-4 layered phase, we believe UT-7 transforms to a layered material by means of a chain to layer transformation.     

Synthesis, structure, texture, and CO sensing behavior of nanocrystalline tin oxide doped with scandia

Weakly agglomerated nanocrystalline scandia doped tin oxide powders with high surface area (170-220 m(2)/g) and uniform size (3-4 nm) were synthesized for the first time by a two-step hydrothermal process in the presence of urea, followed by the calcination between 500 and 1200 degrees C. The structure and texture of the binary oxide system were characterized by thermogravimetry and differential thermal analysis, Brunauer-Emmett-Teller-specific surface area analysis, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. A metastable scandium tin oxide solid solution in tetragonal structure was formed for the scandia content lower than 6 mol % as the samples were calcined at 800 degrees C, and the excess Sc atoms were dispersed at the surface of the crystallites above this limit. The solid solution was metastable, so scandium migrated toward the surface region of the crystallites and produced a second phase of Sc(4)Sn(3)O(12) during calcining at high temperatures over 1000-1200 degrees C. In the case of the samples with higher dopant concentration (>15 mol %), the calcination at the temperature between 500 and 800 degrees C caused the precipitation of Sc(2)O(3), and the calcination over 1000-1200 degrees C led to the formation of more Sc(4)Sn(3)O(12). Textural analysis showed that doping an appropriate amount of Sc(2)O(3) into nanosized SnO(2) could effectively inhibit the grain growth and stabilize the surface area against high-temperature calcinations below 1000 degrees C. CO gas-sensing property measurements revealed that the dispersion of Sc at the surfaces of the SnO(2) nanocrystallites could improve the CO sensitivity significantly, and the pellet sample with scandia content of 10 mol % sintered at 800 degrees C showed the best CO gas-sensing property in the operation temperature range of 300-400 degrees C. On the basis of the structural and textural analysis, the correlation between the structure/texture and the sensitivity to CO for the as-calcined (SnO(2))(1-x)(Sc(2)O(3))(x) nanocrystallites has been established and explained.     

Obtention of low oxidation states of copper from Cu2+–Al3+ layered double hydroxides containing organic sulfonates in the interlayer

A series of hydrotalcite-type compounds containing Cu(II) and Al(III) in the layers, and carbonate or different alkylsulfonates in the interlayer, have been prepared and studied. Calcination of these solids gives rise to formation of metallic copper and Cu²⁺ and Cu⁺ oxides or sulfates, depending on the calcination temperature and on the precise nature of the interlayer alkylsulfonate.     

Effect of added zinc on the properties of cobalt-containing ceramic pigments prepared from layered double hydroxides

Layered double hydroxides (LDHs) with the hydrotalcite-type structure containing Co and Al, or Zn, Co and Al in the brucite-like layers and carbonate in the interlayer have been prepared by coprecipitation. The Zn/Co molar ratio was kept to 1 in all samples, while the divalent/trivalent molar ratio was varied from 2/1 to 1/2. The samples have been characterised by element chemical analysis, powder X-ray diffraction, differential thermal and thermogravimetric analysis, temperature-programmed reduction and FT-IR spectroscopy. A single hydrotalcite-like phase is formed for samples with molar ratio 2/1, which crystallinity decreases as the Al content is increased, developing small amounts of diaspore and dawsonite and probably an additional amorphous phase. Calcination at 1200 °C in air led to formation of spinels; a small amount of NaAlO₂ was observed in the Al-rich samples, which was removed by washing. The nature of the spinels formed (containing Co^II, Co^III, Al^III and Zn^II) strongly depends on the cations molar ratio in the starting materials and the calcination treatment, leading to a partial oxidation of Co^II species to Co^III ones. Colour properties (L*a*b*) of the original and calcined solids have been measured. While the original samples show a pink colour (lighter for the series containing Zn), the calcined Co,Al samples show a dark blue colour and the Zn,Co,Al ones a green colour. Changes due to the different molar ratios within a given calcined series are less evident than between samples with the same composition in different series. These calcined materials could be usable as ceramic pigments.     

Synthesis and Characterization of Poly(ethylene terephthalate)/Modified Lithium‐Aluminum‐Layered Double Hydroxide Nanocomposites Prepared Using In‐situ Polymerization

Layered double hydroxides are a type of layered stacked compound, which can be intercalated with organic‐molecule modifiers. An ion‐exchange process for layered double hydroxide (LDH) was used to intercalate water‐soluble sulfanilic acid salt (SAS) and dimethyl 5‐sulfoisopthalate (DMSI) into lithium aluminum layered double hydroxides (LiAl LDHs). In this work, a hydrothermal process was used to modify LiAl LDHs, and the modified LiAl LDHs were treated with either SAS or DMSI through an ion‐exchange process and were then intercalated using bis‐hydroxyethylene terephthalate (BHET). The results indicate that the modified LiAl LDHs improved the interlayer compatibility between the PET and LiAl LDH layers; thus, enabling the oligomer molecules to more easily enter the gallery of the LiAl LDH layers so that polymer chains could be included between the LDH layers during polymerization of the matrix. The better barrier, mechanical properties, and thermal stability of these new types of PET nanocomposites are discussed.     

WOx/ZrO2 catalysts prepared by anionic exchange: in situ Raman investigation from the precursor solutions to the calcined catalysts

W/ZrO(2) catalysts were prepared using anionic exchange of peroxotungstate species with hydroxyl groups of zirconium hydroxide at low pH. The solids were dried and calcined under air at 700 degrees C. Each step of this novel method of preparation was investigated by Raman spectroscopy. A reference sample was also prepared by incipient wetness impregnation of ZrO(2).n(H2O) with an ammonium tungstate solution and characterized throughout its preparation process. Complementary data were collected from X-ray diffraction, chemical analysis, surface area measurements, and thermal analysis. The Raman spectra of the H2WO4-H2O2 precursor solutions evidenced the presence of (W2O3(O2)4(H2O)2)(2-) dimers. These low-nuclearity species were exchanged with zirconium hydroxide at low pH. The Raman spectra of the dried solids did not reveal peroxotungstate species but were typical of tetrahedral (WO4)(2-) species. A slight agglomeration of W species was observed with an increase in the W content. However, for an equivalent W loading, a higher W dispersion was obtained by anionic exchange, compared to the impregnation method. Furthermore, a remarkable homogeneity of the exchanged samples was evidenced by the micro-Raman spectra. The in situ Raman spectra recorded during calcination characterized both crystalline phases and supported tungsten species. Significant modifications were observed during the calcination process. The exchanged and the impregnated samples, with the same W loading, evidenced a similar type of tungsten species with one W=O bond. However, their behavior during calcination up to 700 degrees C was different. This was attributed to different strengths of interaction with the support. Moreover, the spectra recorded after calcination on various points of the exchanged sample with a high W content revealed a better spatial homogeneity than the impregnated one.     

Preparation of Ni nanoparticles between montmorillonite layers utilizing dimethylaminoborane as reducing agent

Preparation of Ni nanoparticles between montmorillonite layers using dimethylaminoborane (DMAB) as a reducing agent is reported. The DMAB molecules are first intercalated into the interlayer space of Ni-montmorillonite (Ni-mont). Then, as a result of a heating process, the DMAB is decomposed to release electrons for the reduction of the Ni ions. From high-resolution TEM images, it is demonstrated that the deposited Ni nanoparticles with about 1-2 nm in size are formed uniformly over the entire area of the Ni-mont matrix. Considering the gallery height calculated by subtracting the silicate sheet thickness from the basal spacing (1.30 nm), the morphology of the formed Ni nanoparticles in the interlayer space is thought to be disc-like in shape with a thickness of 0.3-0.4 nm and an average lateral size of 1.2 nm.     

Synthesis and characterization of layered double hydroxides (LDH) intercalated with non-steroidal anti-inflammatory drugs (NSAID)

Layered double hydroxides (LDHs) with the hydrotalcite type structure and a Mg:Al ratio of two have been prepared, with salicylate or naproxen in the interlayer. Two synthetic routes have been used: reconstruction from a mildly calcined hydrotalcite-CO₃ precursor, and a coprecipitation method with chlorides of the metals. The solids have been characterized using several physicochemical techniques, i.e., powder X-ray diffraction, FTIR and ¹³C CP/MAS NMR spectroscopies and thermal analysis (thermogravimetric and differential thermal analyses). The gallery height determined is in all cases larger than the size of the drug, 11.5 Å for salicylate and 15.8 and 16.6 Å for naproxen, depending on the specific synthesis route followed. Experimental data suggest the anion molecules form a tilted bilayer, with the carboxylate groups pointing towards the brucite-like layers. The solids are stable up to 230 °C and their evolution from 350 °C upwards is very similar to that observed for a carbonate-containing hydrotalcite, forming mostly amorphous solids with a large specific surface area.