Vapor-phase synthesis of mesoporous SiO2-P2O5 thin films

Mesoporous SiO2-P2O5 films were synthesized from the vapor phase onto a silicon substrate. First, a precursor solution of cetyltrimethylammonium bromide (C16TAB), H3PO4, ethanol, and water was deposited on a silicon substrate by a spin-coating method. Then, the C16TAB-H3PO4 composite film was treated with tetraethoxysilane (TEOS) vapor at 90-180 degrees C for 2.5 h. The H3PO4-C16TAB composite formed a hexagonal structure on the silicon substrate before vapor treatment. The TEOS molecules penetrated into the film without a phase transition. The periodic mesostructure of the SiO2-P2O5 films was retained after calcination. The calcined films showed a high proton conductivity of about 0.55 S/cm at room temperature. The molar ratio of P/Si in the SiO2-P2O5 film was as high as 0.43, a level that was not attained by a premixing sol-gel method. The high phosphate group content and the ordered periodic mesostructure contributed to the high proton conductivity.     

Synthesis of aluminium borate-boron oxide and binary titanium-boron and zirconium-boron oxides from metal alkoxides and (MeO)3B3O3 in non-aqueous solvents

The reaction of metal alkoxides M(OR)4 (M = Ti, Zr; R = organyl) with (MeO)3B3O3 (1 : 0.67) in dry propan-2-one at room temperature led to gels which when dried and calcined in air for 24 h at 500-1000 degrees C afforded bi-phased mixed-oxide materials formulated as 4TiO2 x 3B2O3 and ZrO2 x B2O3 in high ceramic yields and purity; the B2O3 phases of these materials were amorphous. The materials remained amorphous upon calcination at lower temperatures. The TiO2 phase of the 4TiO2 x 3B2O3 was crystalline when calcined at higher temperatures with either anatase (600 degrees C) or rutile (>800 degrees C) being obtained. The ZrO2 phase of the ZrO2 x B2O3 was crystalline when calcined at higher temperatures and was obtained as a metastable tetragonal phase (<700 degrees C) or baddeleylite (>800 degrees C). In a similar reaction, Al(O(i)Pr)3 (2 : 1) gave a bi-phased aluminium borate-boron oxide (Al18B4O(33).7B2O3) after calcination at >700 degrees C. The dried gels and oxide materials were all characterized by elemental analysis, TGA-DSC, and powder XRD.     

Development of new glass composite membranes and their properties for low temperature H2/O2 fuel cells.

A new glass electrolyte formed by constant amounts of titanium oxide (TiO2) and various amount of phosphotungstic acid (PWA) doped P2O5-SiO2 is prepared using the sol-gel process. The structural formation is confirmed by Fourier infrared spectroscopy (FTIR) and from thermogravimetric and differential thermal analysis (TG/DTA) measurements, the glasses display good thermal stability. Further characterisation is undertaken by N2 adsorption/desorption measurements, proton conductivity and hydrogen permeability analyses and a H2/O2 fuel cell test is also performed. The glass materials with large pores and specific surface area are suitable for use as the electrolyte in H2/O2 fuel cells. The effect of TiO2 processing with constant amount of PWA in phosphosilicate glasses, is investigated and discussed. The hydrogen permeability is 1.57x10(-11) mol cm(-1) s(-1) Pa(-1) at 110 degrees C for 0.8 mm thick glass; a power density of 46.3 mW cm(-2) at 125 mA cm(-2) and a current density of 175 mA cm(-2) is obtained (T=28 degrees C, relative humidity).     

CuOx/TiO2光催化水蒸气还原CO2

以商品TiO2-P25为原料,通过浸渍法负载一定量过渡金属Cu,得到一系列不同含量的CuOx/TiO2光催化剂。利用X射线衍射（XRD）,X－射线光电子能谱（XPS）,BET,高分辨率透射镜（HRTEM）,X射线荧光光谱（XRF）和光致发光光谱（PL）等方法对催化剂进行了详细表征,在自建的光催化反应器中评价了气态水光催化还原CO2反应的活性和CH4收率。结果表明负载CuOx后的TiO2纳米材料光催化性能显著提高,其中1%CuOx/TiO2样品紫外光照72 h后,CH4生成量达到了24.86 µmol•gTi-1。同时,CuOx负载量、反应温度、反应时间等因素对CH4收率均有显著影响。     

X-ray absorption spectroscopy of Mn/Co/TiO2 Fischer-Tropsch catalysts: relationships between preparation method, molecular structure, and catalyst performance

The effects of the addition of manganese to a series of TiO(2)-supported cobalt Fischer-Tropsch (FT) catalysts prepared by different methods were studied by a combination of X-ray diffraction (XRD), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), and in situ X-ray absorption fine structure (XAFS) spectroscopy at the Co and Mn K-edges. After calcination, the catalysts were generally composed of large Co(3)O(4) clusters in the range 15-35 nm and a MnO(2)-type phase, which existed either dispersed on the TiO(2) surface or covering the Co(3)O(4) particles. Manganese was also found to coexist with the Co(3)O(4) in the form of Co(3-x)Mn(x)O(4) solutions, as revealed by XRD and XAFS. Characterization of the catalysts after H(2) reduction at 350 degrees C by XAFS and TEM showed mostly the formation of very small Co(0) particles (around 2-6 nm), indicating that the cobalt phase tends to redisperse during the reduction process from Co(3)O(4) to Co(0). The presence of manganese was found to hamper the cobalt reducibility, with this effect being more severe when Co(3-x)Mn(x)O(4) solutions were initially present in the catalyst precursors. Moreover, the presence of manganese generally led to the formation of larger cobalt agglomerates ( approximately 8-15 nm) upon reduction, probably as a consequence of the decrease in cobalt reducibility. The XAFS results revealed that all reduced catalysts contained manganese entirely in a Mn(2+) state, and two well-distinguished compounds could be identified: (1) a highly dispersed Ti(2)MnO(4)-type phase located at the TiO(2) surface and (2) a less dispersed MnO phase being in the proximity of the cobalt particles. Furthermore, the MnO was also found to exist partially mixed with a CoO phase in the form of rock-salt Mn(1-x)Co(x)O-type solid solutions. The existence of the later solutions was further confirmed by scanning transmission electron microscopy with electron energy loss spectroscopy (STEM-EELS) for a Mn-rich sample. Finally, the cobalt active site composition in the catalysts after reduction at 300 and 350 degrees C was linked to the catalytic performances obtained under reaction conditions of 220 degrees C, 1 bar, and H(2)/CO = 2. The catalysts with larger Co(0) particles ( approximately >5 nm) and lower Co reduction extents displayed a higher intrinsic hydrogenation activity and a longer catalyst lifetime. Interestingly, the MnO and Mn(1-x)Co(x)O species effectively promoted these larger Co(0) particles by increasing the C(5+) selectivity and decreasing the CH(4) production, while they did not significantly influence the selectivity of the catalysts containing very small Co(0) particles.     

A dimeric titanium-containing polyoxometalate. Synthesis, characterization, and catalysis of H2O2-based thioether oxidation

The previously unknown titanium(IV)-containing mu-hydroxo dimeric heteropolytungstate (Bu4N)7[(PTiW11O39)2-OH] (TBA salt of H1) has been synthesized, starting from H5PTiW11O40, and characterized by elemental analysis, multinuclear (31P, 17O, 183W) NMR, IR, FAB-MS, cyclic voltammetry, and potentiometric titration. 31P NMR reveals that H1 (delta -12.76) readily forms in MeCN from the Keggin monomer (POM), PTiW11O40(5-) (2, delta -13.34), upon the addition of 1.5 equiv of H+, via the protonated species, P(TiOH)W11O39(4-) (H2, delta -13.44). The ratio of H1, 2, and H2, which are present in equilibrium in MeCN solution at 25 degrees C, depends on the concentration of both H+ and H2O. The Ti-O-Ti linkage readily reacts with nucleophilic reagents, such as H2O and ROH, to yield monomeric Keggin derivatives. mu-Hydroxo dimer H1 shows higher catalytic activity than 2 for thioether oxidation by hydrogen peroxide in acetonitrile. The reaction proceeds readily at room temperature and affords the corresponding sulfoxide and sulfone in ca. quantitative yield. The addition of H2O2 to H1 or H2 results in the formation of a peroxo complex, most likely the hydroperoxo complex P(TiOOH)W11O39(4-) (I), which has 31P NMR resonance at -12.43 ppm. The rate of the formation of I is higher from H2 than from H1. When H1 is used as a catalyst precursor, the rates of the thioether oxidation and peroxo complex formation increase with increasing H2O concentration, which favors the cleavage of H1 to H2. H2O2 in MeCN slowly converts 2 to another peroxotitanium complex, P(TiO2)W11O39(5-) (II), which has 31P NMR resonance at -12.98 ppm. Peroxo complexes I and II differ in their protonation state and interconvert fast on the 31P NMR time scale. Addition of 1 equiv of H+ completely converts II to I, while 1 equiv of OH- completely converts I to II. 31P NMR confirms that I is stable under turnover conditions (thioether, H2O2, MeCN). Contrary to two-phase systems such as dichloroethane/aqueous H2O2, no products resulting from the destruction of the Keggin POM were detected in MeCN in the presence of H2O2 (a 500-fold molar excess). The reactivity of I, generated in situ from II by adding 1 equiv of H+, toward organic sulfides under stoichiometric conditions was confirmed using both 31P NMR and UV-vis spectroscopy. This is a rare demonstration of the direct stoichiometric oxidation of an organic substrate by a titanium peroxo complex.     

The reaction of [FeII(tpa)] with H2O2 in acetonitrile and acetone--distinct intermediates and yet similar catalysis

The reaction of [FeII(tpa)(OTf)2] (tpa=tris(2-pyridylmethyl)amine) and its related 5-Me3-tpa complex with hydrogen peroxide affords spectroscopically distinct iron(III)-peroxo intermediates in CH3CN and acetone. The reaction in acetonitrile at -40 degrees C results in the formation of the previously reported Fe(III)-OOH intermediate, the end-on hydroperoxo coordination mode of which is established in this paper by detailed resonance Raman isotope-labeling experiments. On the other hand, the reaction in acetone below -40 degrees C leads to the observation of a different peroxo intermediate identified by resonance Raman spectroscopy to be an FeIII-OOC (CH3)2OH species; this represents the first example of an intermediate derived from the adduct of H2O2 and acetone. The peroxoacetone intermediate decays more rapidly than the corresponding FeIII-OOH species and converts to an FeIV=O species by O-O bond homolysis. This decay process is analogous to that observed for [FeIII(tpa)(OOtBu)]2+ and in fact exhibits a comparable enthalpy of activation of 54(3) kJ mol(-1). Thus, with respect to their physical properties at low temperature, the peroxoacetone intermediate resembles [FeIII(tpa)(OOtBu)]2+ more than the corresponding FeIII-OOH species. At room temperature, however, the behavior of the Fe(tpa)/H2O2 combination in acetone in catalytic hydrocarbon oxidations differs significantly from that of the Fe(tpa)/tBuOOH combination and more closely matches that of the Fe(tpa)/H2O2 combination in CH3CN. Like the latter, the Fe(tpa)/H2O2 combination in acetone catalyzes the hydroxylation of cis-1,2-dimethylcyclohexane to its tertiary alcohol with high stereoselectivity and carries out the epoxidation and cis-dihydroxylation of olefins. These results demonstrate the subtle complexity of the Fe(tpa)/H2O2 reaction surface.     

Hydrolytic stability of organic monolayers supported on TiO2 and ZrO2

The hydrolytic stability of C18 monolayers supported on TiO2 and ZrO2 was studied. Three types of monolayers were prepared from the following octadecyl modifiers: (1) octadecyldimethylchlorosilane (C18H37Si(CH3)2Cl); (2) octadecylsilane (C18H37SiH3); and (3) octadecylphosphonic acid (C18H37P(O)(OH)2). The hydrolysis of the surfaces prepared was studied under static conditions at 25 and 65 degrees C at pH 1-10. On the basis of the loss of grafted material, the stability of the monolayers fall in the following range: C18H37P(O)(OH)2 > or = C18H37SiH3 > C18H37Si(CH3)2Cl. At 25 degrees C, monolayers from C18H37P(O)(OH)2 showed only approximately 2-5% loss in grafting density after one week at pH 1-10. The high stability of these monolayers was explained because of the strong interactions of the phosphonic acids with the substrates. Monolayers from C18H37Si(CH3)2Cl showed poor hydrolytic stability at any pH, which was explained because of the low stability of Ti-O-Si and Zr-O-Si bonds. Unlike monofunctional silanes, trifunctional silane (C18H37SiH3) yielded surfaces that showed good hydrolytic stability. This suggests that the stability of the monolayers from trifunctional silanes is primarily due to "horizontal" bonding (Si-O-Si or Si-OH...HO-Si) rather than due to bondingwith the matrix (M-O-Si). At 65 degrees C, all C18 surfaces become more susceptible to hydrolysis; however, the trend observed for 25 degrees C remained unchanged. Low-temperature nitrogen adsorption was used to study the adsorption properties of the monolayers as a function of their grafting density. The energy of adsorption interactions showed a significant increase as the grafting density of the monolayers decreased. The order of the alkyl groups in the monolayers, as assessed from CH2 stretching, decreased as the grafting density of the monolayers decreased.     

Mesoporous TiO2 nanostructures: a route to minimize Pt loading on titania photocatalysts for hydrogen production

Mesostructured TiO(2) nanocrystals have been prepared using Pluronic F127 as the structure-directing agent. Platinum nanoparticles at different contents (0.1-1.0 wt%) have been photochemically deposited onto the mesoporous TiO(2). TEM investigation of 0.2 wt% Pt/TiO(2) calcined at 450 °C reveals that the TiO(2) particles are quite uniform in size and shape with the particle sizes of TiO(2) and Pt being 10 and 3 nm, respectively. The photocatalytic activities of the Pt loaded TiO(2) have been assessed and compared with those of nonporous commercial Pt/TiO(2)-P25 by determining the rates and the photonic efficiencies of molecular hydrogen production from aqueous methanol solutions. The results show that the amount of hydrogen evolved on Pt/TiO(2)-450 at low Pt loading (0.2 wt%) is three times higher than that evolved on Pt/TiO(2)-P25 and twelve times higher than that evolved on Pt/TiO(2)-350. Despite the BET surface area of the TiO(2)-450 photocatalyst being 3.5 times higher than that of TiO(2)-P25, a 60% smaller amount of the Pt co-catalyst is required to obtain the optimum photocatalytic hydrogen production activity. The reduced Pt loading on the mesoporous TiO(2) will be important both from a commercial and an ecological point of view.     

On the morphology and stability of Au nanoparticles on TiO2(110) prepared from micelle-stabilized precursors

The morphology and stability of well-ordered, nanostructured Au/TiO2(110) surfaces, prepared by deposition of Au loaded micelles on TiO2(110) substrates and subsequent oxidative removal of the polymer shell in an oxygen plasma, was investigated by noncontact AFM, SEM and XPS. The resulting arrays of Au nanoparticles (particle sizes 1-5 nm) form a nearly hexagonal pattern with well-defined interparticle distances and a narrow particle size distribution. Particle size and particle separation can be controlled independently by varying the Au loading and the block-copolymers in the micelle shell. The oxygen plasma treatment does not affect the size and distance of the Au nanoparticles; the latter are fully metallic after subsequent UHV annealing (400 degrees C). The particles are stable under typical CO oxidation reaction conditions, up to at least 200 degrees C, making these surfaces ideally suited as defined model systems for catalytic studies. Significant changes in the height distributions of the Au nanoparticles are found upon 400 degrees C annealing in O2. For adlayers with small interparticle distances, this leads to a bimodal particle size distribution, which together with the preservation of the lateral order points to Ostwald ripening.     

An O2 smart plastic film for packaging

The preparation and characterisation of a novel, water-proof, irreversible, reusable, UV-activated, O(2) sensitive, smart plastic film is described. A pigment, consisting of a redox dye, methylene blue (MB), and a sacrificial electron donor, DL-threitol, coated onto an inorganic support with semiconductor functionality, TiO(2), has been extruded in low-density polyethylene (LDPE). The blue-coloured indicator is readily photobleached in <90 s using UVA light (4 mW cm(-2)), whereby MB is converted to its colourless, leuco form, leuco-methylene blue (LMB). This form persists in the absence of oxygen, but is re-oxidised to MB in ~2.5 days in air under ambient conditions (～21 °C, ~65% RH) within the O(2) smart plastic film. The rate of recovery is linearly dependent upon the ambient level of O(2). At the lower temperature of 5 °C, the kinetics of the photobleaching activation step is largely unchanged, whereas that of recovery is markedly reduced to t(1/2) = 36 h at 5 °C (cf. 9 h at 21 °C); the activation energy for the recovery step was calculated as 28 kJ mol(-1). The O(2)-sensitive recovery step was found to be moderately dependent upon humidity at 21 °C, but not significantly dependent upon humidity at 5 °C. The possible application of this type of indicator in food packaging is illustrated and discussed briefly.     

Reactions of [(eta(6)-arene)RuCl(2)](2) with Aromatic Phosphines Containing Methoxy Groups in 2,6-Positions

Reactions of [(eta(6)-arene)RuCl(2)](2) 1 (arene = p-cymene (a), 1,2,3,4-Me(4)C(6)H(2) (b), 1,2,3-Me(3)C(6)H(2) (c)) with tris(2,6-dimethoxyphenyl)phosphine (TDMPP) led to loss of two molecules of CH(3)Cl to give (eta(6)-arene)Ru[{2-O-C(6)H(3)-6-OMe}(2){C(6)H(3)(OMe)(2)-2,6}], 2a-c, which contains a trihapto ligand (eta(3)-P,O,O) derived from TDMPP, whereas the 1,3,5-Me(3)C(6)H(3) (1d), 1,2,3,5-Me(4)C(6)H(2) (1e), and C(6)Me(6) (1f) complexes did not react with TDMPP. The structures of 2a and 2b were confirmed by X-ray analyses: for 2a, a = 11.691(2) ?, b = 15.228(2) ?, c = 10.320(1) ?, alpha = 95.93(1) degrees, beta = 113.783(9) degrees, gamma = 83.86(1) degrees, triclinic, P&onemacr;, Z = 2, R = 0.051; for 2b, a = 17.79(2) ?, b = 15.43(1) ?, c = 20.93(1) ?, beta = 91.25(8) degrees, monoclinic, P2(1)/n, Z = 8, R = 0.056. Bis(2,6-dimethoxyphenyl)phenylphosphine (BDMPP) reacted with 1a, 1b, and 1d at room temperature to give (eta(6)-arene)RuCl[PPh(2-O-C(6)H(3)-6-OMe){C(6)H(3)(OMe)(2)-2,6}], 3a,b,d, which contains a dihapto (eta(2)-P,O) ligand derived from BDMPP by an X-ray analysis of 3a: a = 12.33(1) ?, b = 14.246(8) ?, c = 11.236(9) ?, alpha = 91.47(8) degrees, beta = 117.28(6) degrees, gamma = 111.70(6) degrees, triclinic, P&onemacr;, Z = 2, R = 0.040. A similar reaction with 1f recovered the starting materials, but that in refluxing MeCN produced [(eta(6)-C(6)Me(6))Ru[PPh(2-O-C(6)H(3)-6-OMe}(2)], 4f, containing a trihapto (eta(3)-P,O,O) ligand derived from BDMPP. Complex 1d reacted with BDMPP at reflux in MeCN/CH(2)Cl(2) and resulted in a loss of an arene ring to give a five-coordinate complex, Ru[eta(2)-P,O-PPh(2-O-C(6)H(3)-6-OMe){C(6)H(3)(OMe)(2)-2,6}](2)(MeCN), 5. Treatment of (2,6-dimethoxyphenyl)diphenylphosphine (MDMPP) with 1f gave (eta(6)-C(6)Me(6))RuCl[eta(2)-P,O-PPh(2)(2-O-C(6)H(3)-6-OMe)],6f, and that with 1b gave (eta(6)-1,2,3,4-Me(4)C(6)H(2))RuCl[eta(2)-P,O-PPh(2)(2-O-C(6)H(3)-6-OMe}], 6b, and (eta(6)-1,2,3,4-Me(4)C(6)H(2))RuCl(2)[eta(1)-P-PPh(2){C(6)H(3)(OMe)(2)-2,6}],7b. The phosphine ligand of 6b acted as a bidentate ligand derived from MDMPP: a = 8.074(4) ?, b = 16.816(3) ?, c = 18.916(4) ?, beta = 94.05(3) degrees, monoclinic, P2(1)/n, Z = 4, R = 0.051. Transformation of 7b to 6b readily occurred accompanying an elimination of MeCl. Reaction of 1a with MDMPP eliminated an arene ring to give the octahedral compound RuCl(2)[eta(2)-P,OMe-PPh(2){C(6)H(3)(MeO)(2)-2,6}](2), 8. An X-ray analysis of 8 showed that two MDMPP ligands were in a cis-position: a = 10.596(14) ?, b = 27.586(12) ?, c = 13.036(8) ?, beta = 108.17(7) degrees, monoclinic, P2(1)/n, Z = 4, R = 0.035.     

Interaction of NO2 with TiO2 surface under UV irradiation: products study

The interaction of NO(2) with TiO(2) solid films was studied under UV irradiation using a low pressure flow reactor (1-10 Torr) combined with a modulated molecular beam mass spectrometer for monitoring of the gaseous species involved. HONO, NO, and N(2)O were observed as the products of the reactive uptake of NO(2) to the illuminated TiO(2) surface with the sum of their yields corresponding nearly to 100% of the nitrogen mass balance. The yield of the products was measured as a function of different parameters such as irradiance intensity, relative humidity (RH), temperature, and concentrations of NO(2) and O(2). The yield of N(2)O was found to be 0.15 ± 0.05 independent of the experimental conditions. The distribution of the products between NO and HONO was found to be independent of temperature in the range T = 280-320 K and was governed by relative humidity: increase in RH led to lower NO and higher HONO yield, with a maximum of nearly 65% reached at ~5% RH. Presence of molecular oxygen was shown to shift the HONO/NO distribution to HONO at low RH (<5%) with no effect at higher RH where the HONO yield is maximum. The following values for the yield of the products of NO(2) interaction with pure TiO(2) under real atmospheric conditions can be recommended from this work: 0.65 ± 0.10, 0.05 ± 0.05, and 0.15 ± 0.05 for HONO, NO, and N(2)O, respectively. The mechanism of the photoinitiated heterogeneous reaction and possible atmospheric implications of the obtained results are discussed.     

Atomic layer deposition in nanometer-level replication of cellulosic substances and preparation of photocatalytic TiO2/cellulose composites

TiO2 replicas of filter paper with nanometer-level accuracy were prepared by atomic layer deposition of thin conformal TiO2 coating, followed by a removal of the paper by air-anneal at 450 degrees C. Photocatalytic anatase TiO2/cellulose composites were also made by leaving the paper intact. The TiO2 films were deposited from Ti(OMe)4 and H2O at 150-250 degrees C. The photocatalytic activity of the TiO2/cellulose composite was verified by photocatalytic reduction of Ag(I) from an aqueous solution to Ag nanoparticles on the TiO2 surface. The TiO2/cellulose composites are mechanically more stable than the free-standing TiO2 replicas and are therefore potentially suitable as lightweight, high surface area photocatalysts.     

Electron-beam-induced topographical, chemical, and structural patterning of amorphous titanium oxide films

Electrolytically deposited amorphous TiO2 films on steel are remarkably sensitive to electron beam (e-beam) irradiation at moderate energies at 20 keV, resulting in controlled local oxide reduction and crystallization, opening the possibility for local topographical, chemical, and structural modifications within a biocompatible, amorphous, and semiconducting matrix. The sensitivity is shown to vary significantly with the annealing temperature of as-deposited films. Well-defined irradiation conditions in terms of probe current IP (5 microA) and beam size were achieved with an electron probe microanalyzer. As shown by atomic force and optical microscopy, micro-Raman spectroscopy, wavelength-dispersive X-ray (WDX), and Auger analyses, e-beam exposure below 1 Acm-2 immediately leads to electron-stimulated oxygen desorption, resulting in a well-defined volume loss primarily limited to the irradiated zone under the electron probe and in a blue color shift in this zone because of the presence of Ti2O3. Irradiation at 5 Acm(-2) (IP = 5 microA) results in local crystallization into anatase phase within 1 s of exposure and in reduction to TiO after an extended exposure of 60 s. Further reduction to the metallic state could be observed after 60 s of exposure at approximately 160 Acm(-2). The local reduction could be qualitatively sensed with WDX analysis and Auger line scans. An estimation of the film temperature in the beam center indicates that crystallization occurs at less than 150 degrees C, well below the atmospheric crystallization temperature of the present films. The high e-beam sensitivity in combination with the well-defined volume loss from oxygen desorption allows for precise electron lithographic topographical patterning of the present oxides. Irradiation effects leading to the observed reduction and crystallization phenomena under moderate electron energies are discussed.     

Room-temperature hydrogen uptake by TiO(2) nanotubes

TiO(2) nanotubes can reproducibly store up to approximately 2 wt % H(2) at room temperature and 6 MPa. However, only about 75% of this stored hydrogen can be released when the hydrogen pressure is lowered to ambient conditions, suggesting that both physisorption and chemisorption are responsible for the hydrogen uptake. FTIR spectroscopy, temperature-programmed desorption (TPD), and pressure-composition (P-C) isotherms suggest that 75% of the H(2) is physisorbed and can be reversibly released upon pressure reduction. Approximately 13% is weakly chemisorbed and can be released at 70 degrees C as H(2), and approximately 12% is bonded to oxide ions and released only at temperatures above 120 degrees C as H(2)O.     

Metal-catalyzed anaerobic disproportionation of hydroxylamine. Role of diazene and nitroxyl intermediates in the formation of N2, N2O, NO+, and NH3

The catalytic disproportionation of NH(2)OH has been studied in anaerobic aqueous solution, pH 6-9.3, at 25.0 degrees C, with Na(3)[Fe(CN)(5)NH(3)].3H(2)O as a precursor of the catalyst, [Fe(II)(CN)(5)H(2)O](3)(-). The oxidation products are N(2), N(2)O, and NO(+) (bound in the nitroprusside ion, NP), and NH(3) is the reduction product. The yields of N(2)/N(2)O increase with pH and with the concentration of NH(2)OH. Fast regime conditions involve a chain process initiated by the NH(2) radical, generated upon coordination of NH(2)OH to [Fe(II)(CN)(5)H(2)O](3)(-). NH(3) and nitroxyl, HNO, are formed in this fast process, and HNO leads to the production of N(2), N(2)O, and NP. An intermediate absorbing at 440 nm is always observed, whose formation and decay depend on the medium conditions. It was identified by UV-vis, RR, and (15)NMR spectroscopies as the diazene-bound [Fe(II)(CN)(5)N(2)H(2)](3)(-) ion and is formed in a competitive process with the radical path, still under the fast regime. At high pH's or NH(2)OH concentrations, an inhibited regime is reached, with slow production of only N(2) and NH(3). The stable red diazene-bridged [(NC)(5)FeHN=NHFe(CN)(5)](6)(-) ion is formed at an advanced degree of NH(2)OH consumption.     

FTIR study of adsorption and surface reactions of N(CH3)3 on TiO2

Fourier transform infrared spectroscopy has been employed to investigate the N(CH3)3 adsorption, thermal stability, and photochemical reactions on powdered TiO2. N(CH3)3 molecules are adsorbed on TiO2 without dissociation at 35 degrees C and are completely desorbed from the surface at 300 degrees C in a vacuum. The CH3 rocking frequencies of N(CH3)3 on TiO2 are affected via the interaction between N(CH3)3 and TiO2 surface OH groups. In the presence of O2, adsorbed N(CH3)3 decomposes thermally at 230 degrees C and photochemically under UV irradiation. In the latter case with comparative (16)O2 and (18)O2 studies, CO2(g), NCO(a), HCOO(a), and surface species containing C=N or NH(x) functional groups are identified to be the photoreaction products or intermediates. In the presence of (18)O2, the main formate species formed is HC(16)O(18)O(a). As H2O is added to the photoreaction system, a larger percentage of adsorbed N(CH3)3 is consumed. However, in the presence of (18)O2 and H2O, the amount of HC(16)O(18)O(a) becomes relatively small, compared to HC(16)O(16)O(a). A mechanism is invoked to explain these results. Furthermore, based on the comparison of isotopic oxygens in the formate products obtained from CH3O(a) photooxidation in (16)O2 and (18)O2, it is concluded that the N(CH3)3 photooxidation does not generate CH3O(a) in which the oxygen belongs to TiO2.     

CuOx/TiO2光催化水蒸气还原CO2反应研究

以商品TiO2-P25为原料,通过浸渍法负载一定量过渡金属Cu,得到一系列不同含量的CuOx/TiO2光催化剂.利用X射线衍射(XRD),X-射线光电子能谱(XPS),BET,高分辨率透射镜(HRTEM),X射线荧光光谱(XRF)和光致发光光谱(PL)等方法对催化剂进行了详细表征,在自建的光催化反应器中评价了气态水光催化还原CO2反应的活性和CH4收率.结果表明负载CuOx后的TiO2纳米材料光催化性能显著提高,其中1%CuOx/TiO2样品紫外光照72 h后,CH4生成量达到了24.86μmol.gTi-1.同时,CuOx负载量、反应温度、反应时间等因素对CH4收率均有显著影响.     

Characterization of Zr-doped TiO2 nanocrystals prepared by a nonhydrolytic sol-gel method at high temperatures

Highly crystalline and surface-modified Zr-doped TiO(2) nanorods were successfully prepared using a nonhydrolytic sol-gel method that involves the condensation of metal halides with alkoxides in anhydrous trioctylphosphine oxide (TOPO) at either 320 or 400 degrees C. In addition, the interaction of the cross-condensation between the Ti and Zr species was studied by characterizing the morphologies, crystalline structures, chemical compositions, surface properties, and band gaps of the nanocrystals obtained at different reaction temperatures and Zr-to-Ti stoichiometric ratios. Increases in the concentration of Zr(4+) and in the reaction temperature led to large nanorods and regular shapes, respectively. In addition, only the anatase form was observed in the Zr-doped TiO(2) nanorods. The Zr-to-Ti ratios obtained ranged from 0.01 to 2.05, all of which were far below the stoichiometric ratios used during the preparation of the samples (0.25-4). Moreover, the Zr(4+) units accumulated mainly at the surface of the TiO(2) nanocrystals. The band gaps of the Zr-doped TiO(2) nanorods ranged from 2.8 to 3.8 eV, which are smaller than those of pure TiO(2) (3.7 eV) or ZrO(2) (5.2 eV). The Zr-doped anatase TiO(2) nanorods prepared at 400 degrees C at an initial stoichiometric Zr-to-Ti ratio of 2:3 exhibited the highest photoactivities for the decomposition of rhodamine B because of the presence of trace amounts of Zr(4+) (Zr/Ti = 0.03) in the TiO(2) and the regular shapes of these particles. DSC analysis indicated that the temperatures for forming nanocrystalline TiO(2) and ZrO(2) were 207 and 340 degrees C, respectively. Moreover, the reactivities of condensation between the Ti species were reduced when Zr species were involved in the NHSG reactions. The results obtained in this study clearly demonstrate that the faster kinetics for the generation of TiO(2) controls the material properties as well as the photoactivities of the nonhydrolytic sol-gel-derived nanocrystals.