Proton control of oxidation and spin state in a series of iron tripodal imidazole complexes

Reaction of iron salts with three tripodal imidazole ligands, H(3)(1), H(3)(2), H(3)(3), formed from the condensation of tris(2-aminoethyl)amine (tren) with 3 equiv of an imidazole carboxaldehyde yielded eight new cationic iron(III) and iron(II), [FeH(3)L](3+or2+), and neutral iron(III), FeL, complexes. All complexes were characterized by EA(CHN), IR, UV, M?ssbauer, mass spectral techniques and cyclic voltammetry. Structures of three of the complexes, Fe(2).3H(2)O (C(18)H(27)FeN(10)O(3), a = b = c = 20.2707(5), cubic, I3d, Z = 16), Fe(3).4.5H(2)O (C(18)H(30)FeN(10)O(4.5), a = 20.9986(10), b = 11.7098(5), c = 19.9405(9), beta = 109.141(1), monoclinic, P2(1)/c), Z = 8), and [FeH(3)(3)](ClO(4))(2).H(2)O (C(18)H(26)Cl(2)FeN(10)O(9), a = 9.4848(4), b = 23.2354(9), c = 12.2048(5), beta = 111.147(1) degrees, monoclinic, P2(1)/n, Z = 4) were determined at 100 K. The structures are similar to one another and feature an octahedral iron with facial coordination of imidazoles and imine nitrogen atoms. The iron(III) complexes of the deprotonated ligands, Fe(1), Fe(2), and Fe(3), are low-spin while the protonated iron(III) cationic complexes, [FeH(3)(1)](ClO(4))(3) and [FeH(3)(2)](ClO(4))(3), are high-spin and spin-crossover, respectively. The iron(II) cationic complexes, [FeH(3)(1)]S(4)O(6), [FeH(3)(2)](ClO(4))(2), [FeH(3)(3)](ClO(4))(2), and [FeH(3)(3)][B(C(6)H(5))(4)](2) exhibit spin-crossover behavior. Cyclic voltammetric measurements on the series of complexes show that complete deprotonation of the ligands produces a negative shift in the Fe(III)/Fe(II) reduction potential of 981 mV on average. Deprotonation in air of either cationic iron(II) or iron(III) complexes, [FeH(3)L](3+or2+), yields the neutral iron(III) complex, FeL. The process is reversible for Fe(3), where protonation of Fe(3) yields [FeH(3)(3)](2+).     

Sorption of Cs(I) on Magnetite in the Presence of Silicates

The sorption of H(4)SiO(4) on magnetite has been qualified and quantified using three different surface complexation models, CCM, DLM, and NEM. The three tested models can account for the sorption of silicates using the same stoichiometry, one neutral species binding on a neutral surface, and the same constant, error aside. Experiments have also been performed to demonstrate that the sorption of dissolved silicates has a nonnegligible effect on the behavior of the surface of magnetite. Then, the sorption of cesium is insignificant on the neat surface of magnetite and is increased up to 10-20% when silicates are present in solution. A theoretical model, where the rule of electrostatics is pointed out, has been developed to account for the experimental observations. This model allows the reproduction of the sorption of cesium in the presence of dissolved silicates for the following four cases: -concentration of silicates under solubility limit -concentration of silicates over solubility limit -binary mixtures of silica and magnetite -natural magnetite with silica as impurity. The reaction given in the model to account for the experimental observations proposes that silicates may act as a "bridge" between the surface of magnetite and cesium. Copyright 2000 Academic Press.     

Synthesis, characterization, and sorption properties of amorphous titanium phosphate and silica-modified titanium phosphates

Amorphous titanium hydroxyphosphate with formula Ti(OH)(1.36)(HPO(4))(1.32).2.3H(2)O and a new silica-modified titanium hydroxyphosphate with a general formula Ti(OH)(2x)(HPO(4))(2-x).ySiO(2).nH(2)O are synthesized and characterized using IR, TG, XRD, SEM, solid-state NMR, and BET techniques. It is concluded that SiO(2) is evenly distributed within the titanium phosphate (TiP) agglomerates and that neither the separate silica phase nor the titanium silicates are formed during the synthesis of silica-modified titanium hydroxyphosphate. Correlations between the texture, ion-exchange properties of the amorphous titanium hydroxyphosphate, and the amount of SiO(2) present within the TiP matrix are established. Sorption properties of silica-modified titanium hydroxyphosphate toward Cs(+) and Sr(2+) are studied in a series of samples with an increasing amount of silica, at different pH, and in NaCl solutions with a varying ionic strength. It is found that sorption of Cs(+) does not depend practically on the amount of SiO(2) present, whereas the Sr(2+) uptake drastically decreases with an increase of silica amount. The effects of pH and of the electrolyte concentration on the sorption behavior of titanium phosphate are discussed in terms of ionic hydration shell and titanium phosphate structural specificity. The kinetics of sorption processes is also investigated, and the diffusion coefficients for cesium and strontium are obtained.     

Bis(diisopropylphosphino)pyridine iron dicarbonyl, dihydride, and silyl hydride complexes

Treatment of the bis(diisopropylphosphino)pyridine iron dichloride, ((iPr)PNP)FeCl2 ((iPr)PNP = 2,6-(iPr2PCH2)2(C5H3N)), with 2 equiv of NaBEt3H under an atmosphere of dinitrogen furnished the diamagnetic iron(II) dihydride dinitrogen complex, ((iPr)PNP)FeH2(N2). Addition of 1 equiv of PhSiH3 to ((iPr)PNP)FeH2(N2) resulted in exclusive substitution of the hydride trans to the pyridine to yield the silyl hydride dinitrogen compound, ((iPr)PNP)FeH(SiH2Ph)N2, which has been characterized by X-ray diffraction. The solid-state structure established a distorted octahedral geometry where the hydride ligand distorts toward the iron silyl. Both ((iPr)PNP)FeH2(N2) and ((iPr)PNP)FeH(SiH2Ph)N2 form eta2-dihydrogen complexes upon exposure to H2. The iron hydrides and the eta2-H2 ligands are in rapid exchange in solution, consistent with the previously reported "cis" effect, arising from a dipole/induced dipole interaction between the two ligands. Taken together, the spectroscopic, structural, and reactivity studies highlight the relative electron-donating ability of this pincer ligand as compared to the redox-active aryl-substituted bis(imino)pyridines.     

Preparation of silica-magnetite nanoparticle mixed hemimicelle sorbents for extraction of several typical phenolic compounds from environmental water samples

A novel type of superparamagnetic silica-coated (Fe3O4/SiO2 core/shell) magnetite nanoparticle modified by surfactants has been successfully synthesized and was applied as an effective sorbent material for the pre-concentration of several typical phenolic compounds (bisphenol A (BPA), 4-tert-octylphenol (4-OP) and 4-n-nonylphenol (4-NP)) from environmental water samples. Compared with pure magnetic particles, a thin and dense silica layer would protect the iron oxide core from leaching out in acidic conditions. In order to enhance their adsorptive tendency towards organic compounds, cetylpyridinium chloride (CPC) or cetyltrimethylammonium bromide (CTAB) were added, which adsorbed on the surface of the Fe3O4/SiO2 nanoparticles (Fe3O4/SiO2 NPs) and formed mixed hemimicelles. Main factors affecting the adsolubilization of analytes were optimized and comparative study on the use of CPC and CTAB-coated Fe3O4/SiO2 NPs mixed hemimicelles-based SPE was also carried out. CPC-coated Fe3O4/SiO2 NPs system was selected due to lower elution volume required and more effective adsorption of the target compounds. Under selected conditions, concentration factor of 1600 was achieved by using this method to extract 800 mL of different environmental water samples. The detection limits obtained for BPA, 4-OP and 4-NP with HPLC-FLD were 7, 14, and 20 ng/L, respectively.     

29Si chemical shift anisotropies in calcium silicates from high-field 29Si MAS NMR spectroscopy

29Si chemical shift anisotropy (CSA) data have been determined from (29)Si MAS NMR spectra recorded at 14.1 T for a number of synthetic calcium silicates and calcium silicate hydrates. These are beta- and gamma-Ca(2)SiO(4), Ca(3)SiO(4)Cl(2), alpha-dicalcium silicate hydrate (alpha-Ca(2)(SiO(3)OH)OH), rankinite (Ca(3)Si(2)O(7)), cuspidine (Ca(4)Si(2)O(7)F(2)), wollastonite (beta-Ca(3)Si(3)O(9)), pseudowollastonite (alpha-Ca(3)Si(3)O(9)), scawtite (Ca(7)(Si(6)O(18))CO(3).2H(2)O), hillebrandite (Ca(2)SiO(3)(OH)(2)), and xonotlite (Ca(6)Si(6)O(17)(OH)(2)). The (29)Si MAS NMR spectra of rankinite and wollastonite clearly resolve manifolds of spinning sidebands from two and three Si sites, respectively, allowing the CSA parameters to be obtained with high precision for each site. For the (29)Si Q(1) sites in rankinite and cuspidine, the CSA asymmetry parameters (eta(sigma) approximately 0.6) contrast the general expectation that sorosilicates should possess small eta(sigma) values as a result of the nearly axially symmetric environments of the SiO(4) tetrahedra. The (29)Si CSA parameters provide an improved insight into the electronic and geometric environments for the SiO(4) tetrahedra as compared to the values solely for the isotropic chemical shift. It is shown that the shift anisotropy (delta(sigma)) and the CSA asymmetry parameter (eta(sigma)) allow a clear distinction of the different types of condensation of SiO(4) tetrahedra in calcium silicates. This relationship may in general be valid for neso-, soro-, and inosilicates. The CSA data determined in this work may form a valuable basis for (29)Si MAS NMR studies of the structures for tobermorites and calcium silicate hydrate phases resulting from hydration of Portland cements.     

Synthesis and characterization of manganese(II) and iron(III) d5 tripodal imidazole complexes. Effect of oxidation state, protonation state and ligand conformation on coordination number and spin state

The 1 : 3 Schiff base condensates of tris(2-aminoethyl)amine (tren) or tris(3-aminopropyl)amine (trpn) with 4-methyl-5-imidazolecarboxaldehyde, H3L1 and H3L2, respectively, were generated in situ and used to prepare complexes with manganese(II) and iron(III). The resultant complexes, [MnH3L1](ClO4)2, [MnH3L1](ClO4)2.EtOH.H2O, [MnH3L2](ClO4)2, [FeH3L1](ClO4)3.1.5(EtOH) and [FeHL1](I3) (0.525)(I)(0.475).2.625H2O, have been characterized by EA, IR, ES MS, variable temperature magnetic susceptibility, X-ray crystallography, and M?ssbauer spectroscopy for the iron complexes. The three manganese(II) complexes are high spin with [MnH3L2](ClO4)2 exhibiting coordination number seven while the others are six coordinate. [FeH3L1](ClO4)3.1.5(EtOH) has two iron sites, a seven coordinate and a pseudo seven coordinate site. The complex is high spin at room temperature but exhibits a magnetic moment that decreases with temperature corresponding to conversion of one of the sites to low spin. [FeHL1](I3) (0.525)(I)(0.475).2.625H2O is low spin even at room temperature. In the present complexes the apical nitrogen atom, N(ap), of the tripodal ligand is pyramidal and directed toward the metal atom. The data show that the M-N(ap) distance decreases as the oxidation state of the metal increases, as the number of bound imidazole protons on the ligand increases, and as the number of carbon atoms in the backbone of the ligand (tren vs. trpn) increases. In a limiting sense, short M-N(ap) distances result in high spin seven coordinate mono capped octahedral complexes and long M-N(ap) distances result in low spin six coordinate octahedral complexes.     

Sorption behaviour of nanocrystalline MOR type zeolite for Th(IV) and Eu(III) removal from aqueous waste by batch treatment

The nanocrystalline mordenite (MOR) type zeolite materials with initial chemical composition Na(2)O:Al(2)O(3):10SiO(2):48H(2)O have been synthesized under hydrothermal conditions. MOR1 and MOR2 are spherically shaped nanocrystals, whereas MOR3 and MOR4 have rod-like morphology. This paper reports the sorption characteristics of MOR analogues for Th(IV) and Eu(III) removal from aqueous nuclear waste. Sorption of Th(IV) and Eu(III) on MOR1, MOR2, MOR3 and MOR4 in a single component system with varying initial metal ion concentration, solution pH, contact times, sorbent dose and temperatures has also been investigated. Further, the Langmuir and Freundlich sorption models have been applied to describe equilibrium isotherms at different temperatures. The adsorption capacity increases largely with increasing solution pH and temperature of the system. Specific surface area and pore volume have been investigated by Brunauer-Emmett-Teller (BET) method. The N(2) adsorption isotherm presents a type IV isotherm with narrow hysteresis loop which indicates the presence of mesopores related to inter-particle voids. Thermodynamic results indicate that the sorption follows an endothermic physisorption process. It has been found that these exchangers have good sorption capacity and out of which MOR4 has highest sorption capacity. Thus, nanocrystalline MOR4 is proved to be good sorbent for both Th(IV) and Eu(III).     

表面酸性对Ni/SiO_2-Al_2O_3催化剂催化1,4-丁炔二醇高压加氢性能的影响

通过浸渍法分别在Al(OH)_3和Al_2O_3中引入SiO_2,经焙烧后制备具有不同表面酸性质的SiO_2-Al_2O_3载体,以上述SiO_2-Al_2O_3及Al_2O_3为载体,采用等体积浸渍法制备Ni负载量为15%的Ni/SiO_2-Al_2O_3催化剂(分别为Ni/SA-1和Ni/SA-2)与Ni/Al_2O_3.采用N2物理吸附、Py-FTIR、NH3-TPD、XRD、H2-TPR和H2-TPD手段对催化剂进行表征,考察了表面酸性质对催化剂催化1,4-丁炔二醇高压加氢性能的影响.结果表明,SiO_2引入方式会影响Ni/Al_2O_3催化剂表面酸性质及活性组分Ni在载体表面的分散行为.在Al(OH)3中引入SiO_2时,Ni/SA-1催化剂不仅活性组分具有高分散度,而且表面具有丰富的L酸位点,L酸位点与Ni活性中心协同作用有效提高了催化剂的高压加氢性能.而在Al_2O_3中直接引入SiO_2时,SiO_2覆盖了Al_2O_3表面的L酸位点,催化剂活性组分分散度较低,表现出低的加氢活性.     

Synthesis and characterization of homo- and heterodinuclear M(II)-M'(III) (M(II) = Mn or Fe, M'(III) = Fe or Co) mixed-valence supramolecular pseudo-dimers. The effect of hydrogen bonding on spin state selection of M(II)

Reaction of H(3)L(1), the Schiff base condensate of tris(2-aminoethyl)amine with three equivalents of 5-methyl-1H-pyrazole-3-carboxaldehyde, with manganese(II)perchlorate or iron(II)tetrafluoroborate results in the isolation of [MH(3)L(1)]X(2) (M = Mn and X = ClO(4) and M = Fe and X = BF(4)). These complexes are high spin d(5) and d(6), respectively, as inferred from the long M-N bond distances obtained by single crystal X-ray diffraction for both and variable temperature magnetic susceptibility and M?ssbauer spectroscopy for the iron complex. Aerobic treatment of a solution of [CoH(3)L(1)](2+) with three equivalents of potassium hydroxide produced [CoL(1)]. Homonuclear pseudo-dimers were prepared by the aerobic reaction of [FeH(3)L(1)](BF(4))(2) with 1.5 equivalents of potassium hydroxide to give {[FeH(1.5)L(1)](BF(4))}(2) or by the metathesis reaction of [FeH(2)L(1)][FeHL(1)](ClO(4))(2) with sodium hexafluorophosphate to give [FeH(3)L(1)][FeL(1)](PF(6))(2). The complexes were characterized by EA, IR, ESI-MS, variable temperature single crystal x-ray diffraction and M?ssbauer spectroscopy. The iron(III) atom is low spin while the iron(II) atom is spin crossover. Heteronuclear pseudo-dimers were prepared by the 1:1 reaction of [FeH(3)L(1)](BF(4))(2) or [MnH(3)L(1)](ClO(4))(2) with [CoL(1)]. [MH(3)L(1)][CoL(1)](X)(2) (M = Fe and X = BF(4) or M = Mn and X = ClO(4)), were characterized by IR, EA, variable temperature single crystal X-ray diffraction and M?ssbauer spectroscopy in the iron case. The data support a spin crossover and high spin assignment for the iron(II) and manganese(II), respectively. DFT calculations demonstrate that the spin state of the iron(II) atom in {[FeH(3)L(1)][FeL(1)]}(2+) changes from high spin to low spin as the iron(II)-iron(III) distance decreases. This is supported by experimental results and is a result of hydrogen bonding interactions which cause a significant compression of the M(II)-N(pyrazole) bond distances.     

Sol-Gel Coatings on 316L Steel for Clinical Applications

SiO2 and SiO2-CaO-P2O5 coatings have been prepared by dipping electropolished stainless steel 316L samples and microscope glass slides in three different sol-gel solutions. Multilayered dense SiO2 coatings, and thick silica films obtained from equimolar contents of TEOS and MTES were used. The latter were able to strongly reduce both the corrosion attack on the steel and the iron diffusion to the sample surface. SiO2-CaO-P2O5 coatings were also obtained and applied onto the silica films, in order to provide a bioactive external surface for contact with living tissue. In-vitro evaluation of these coatings and films is discussed.     

Sorption of selenium(IV) onto magnetite in the presence of silicic acid

Sorption of selenium(IV) and silicic acid onto magnetite (Fe(3)O(4)) was investigated in binary systems, with concentrations of silicic acid under the solubility limit of amorphous silica. Using the double diffuse layer model (DDLM), surface complexation constants of selenium(IV) and H(4)SiO(4) onto magnetite were extracted using Fiteql 4.0. Then, prediction curves of the sorption of selenium(IV) in the presence of silicic acid onto magnetite were obtained, using the calculated surface complexation constants. Finally, laboratory experiments were performed and showed a competition between selenium(IV) and silicic acid for the surface sites of magnetite. Experimental results matched the model predictions, confirming its ability to model qualitatively and quantitatively the ternary system.     

Modeling and electrokinetic evidences on the processes of the Al(III) sorption continuum in SiO2(s) suspension

Reactions of Al(III) at the interface between SiO2(s) and aqueous solution were characteristically and quantitatively studied using electrophoretic methods and applying a surface complexation/precipitation model (SCM/SPM). The surface and bulk properties of Al(III)/SiO2 suspensions were determined as functions of pH and initial Al(III) concentration. Simulated modeling results indicate that the SCM, accounting for the adsorption mechanism, predicts sorption data for low surface coverage only reasonably well. Al(III) hydrolysis and surface hydroxide precipitation must be invoked as the Al(III) concentration and/or pH progressively increase. Accordingly, the three processes in the Al(III) sorption continuum, from adsorption through hydrolysis to surface precipitation, could be identified by the divergence between the SCM/SPM predictions and the experimental data. SiO2(s) suspensions with low Al(III) concentrations (1 x 10(-4) and 1 x 10(-5) M) exhibit electrophoretic behavior similar to that of a pure SiO2(s) system. In Al(III)/SiO2 systems with high Al concentrations of 1 x 10(-3), 5 x 10(-3) and 1 x 10(-2) M, three charge reversals (CR) are observed, separately representing, in order of increasing pH, the point of zero charge (PZC) on the SiO2 substrate (CR1), the onset of the surface precipitation of Al hydroxide (CR2), and at a high pH, the PZC of the Al(OH)3 coating (CR3). Furthermore, in the 1 x 10(-3) M Al(III)/SiO2(s) system, CR2 is consistent with the modeling results of SCM/SPM and provides evidence that Al(III) forms a surface precipitate on SiO2(s) at pH above 4. SiO2(s) dissolution was slightly inhibited when Al(III) was adsorbed onto the surface of SiO2(s), as compared to the dissolution that occurs in a pure SiO2(s) suspension system. Al hydroxide surface precipitation dramatically reduced the dissolution of SiO2(s) because the Al hydroxide passive film inhibited the corrosion of the SiO2(s) surface by OH- ions.     

Sorption of the antibiotic ofloxacin to mesoporous and nonporous alumina and silica

Mesoporous and nonporous SiO(2) and Al(2)O(3) adsorbents were reacted with the fluoroquinolone carboxylic acid ofloxacin over a range of pH values (2-10) and initial concentrations (0.03-8 mM) to investigate the effects of adsorbent type and intraparticle mesopores on adsorption/desorption. Maximum ofloxacin adsorption to SiO(2) surfaces occurs slightly below the pK(a2) (pH 8.28) of the antibiotic and sorption diminishes rapidly at pH>pK(a2). For Al(2)O(3), maximum sorption is observed at pH values slightly higher than the adsorbent's point of zero net charge (p.z.n.c.) and less than midway between the pK(a) values of ofloxacin. The effects of pH on adsorption and ATR-FTIR spectra suggest that the zwitterionic compound adsorbs to SiO(2) solids through the protonated N(4) in the piperazinyl group and, possibly, a cation bridge; whereas the antibiotic sorbs to Al(2)O(3) solids through the ketone and carboxylate functional groups via a ligand exchange mechanism. Sorption edge and isotherm experiments show that ofloxacin exhibits a higher affinity for mesoporous SiO(2) and nonporous Al(2)O(3), relative to their counterparts. It is hypothesized that decreased ofloxacin sorption to mesoporous Al(2)O(3) occurs due to electrostatic repulsion within pore confines. In contrast, it appears that the environment within SiO(2) mesopores promotes sorption by inducing formation of ofloxacin-Ca complexes, thus increasing electrostatic attraction to SiO(2) surfaces.     

甲烷氧化偶联:Mn2O3-Na2WO4/SiO2催化剂的金属氧化物MOx(M=Ti,Mg,Ga,Zr)改性及掺杂效应研究

甲烷 (页岩气、天然气、可燃冰和煤层气的主要成分) 是地球上储量巨大的优质能源和高品味的碳氢资源, 我国也拥有储量居全球前列的页岩气、可燃冰和煤层气. 虽然甲烷经由合成气可以间接转化为乙烯等产品, 但工艺流程长以及合成气造气高温、高能耗和高物耗也是不争的事实, 这在一定程度上降低了间接合成路线的竞争优势. 特别是, 甲烷的间接转化需要将本应部分保留于产品的 C-H 键全部打断生成合成气, 然后再在催化剂作用下重组得到烃类产品, 故而并不完美.因此, 甲烷的直接转化一直是科学家孜孜以求的理想路径, 甲烷氧化偶联制乙烯 (OCM 反应) 也再一次引起关注.目前, Mn2O3-Na2WO4/SiO2是最富有应用前景的催化剂, 但其适宜反应温度仍高达 800 ℃ 以上, 极大地制约了其工业化应用. 为提高其低温催化性能, 本文采用金属氧化物 MOx(TiO2, MgO, Ga2O3或 ZrO2) 对 Mn2O3-Na2WO4/SiO2催化剂进行了掺杂改性, 利用扫描电子显微镜、N2吸附-脱附等温曲线、X 射线衍射、拉曼光谱、电感耦合等离子体原子发射光谱等手段对改性后的催化剂进行了系统表征. 结果表明, TiO2掺杂的 Mn2O3-Na2WO4/SiO2催化剂在 700 ℃(催化剂床层温度)下, CH4转化率可达 23%, 同时 C2-C3烃类选择性约为 73%, 且能够稳定运行 300 h 无失活迹象; MnTiO3的形成对提高OCM 反应的低温活性和选择性至关重要, 本质在于低温 (≤ 700 ℃) 化学循环"MnTiO3?Mn2O3"的形成替代了未改性催化剂的高温 (＞ 800 ℃) 化学循环"MnWO4?Mn2O3". 对于 MgO 改性的 Mn2O3-Na2WO4/SiO2催化剂, 其催化性能与未改性催化剂相当, 反应过程中 Mn2O3与 MgO 生成了新物相 Mg2MnO4; 虽然也形成了新的 MnWO4?Mg2MnO4氧化还原循环, 但是该循环与 MnWO4?Mn2O3循环类似, 需在高温下才可高效进行. 对于 Ga2O3或 ZrO2改性的催化剂, 其催化性能低于未改性催化剂, 原因在于反应过程中 Ga2O3或 ZrO2的引入促进了 MnWO4物相的生成并对其有稳定作用, 反应后的催化剂无论是体相还是表面都只能检测到 MnWO4, 推测认为α-方石英、Na2WO4和 Mn2O3的缺失是导致 Ga2O3或 ZrO2改性催化剂性能下降的主要原因.     

Sorption and desorption of phenanthrene onto iron, copper, and silicon dioxide nanoparticles

The sorption and desorption of phenanthrene by three engineered nanoparticles including nanosize zerovalent iron (NZVI), copper (NZVC), and silicon dioxide (NSiO2) were investigated. The sorption of phenanthrene onto NSiO2 was linear and reversible due to the hydrophilic properties of NSiO2. In comparison, sorption of phenanthrene onto NZVI and NZVC was nonlinear and irreversible, which was potentially due to the existence of significantly heterogeneous surface energy distribution patterns detected by a standard molecular probe technique. Naphthalene exerted significant competitive sorption with phenanthrene for NZVI and NZVC, and the isotherm of phenanthrene changed from being significantly nonlinear to nearly linear when naphthalene was simultaneously absorbed. A surface adsorption mechanism was proposed to explain the observed sorption and competition of phenanthrene on both NZVI and NZVC. In contrast, no competition was observed for sorption onto NSiO2. The sorption of phenanthrene on all three nanoparticles significantly decreased with increasing pH. The sorption irreversibility of phenanthrene on NZVI and NZVC were significantly enhanced with decreasing pH. A pH-dependent hydrophobic effect and dipole interactions between the charged surface (electron acceptors) and phenanthrene with electron-rich pi systems (electron donors) were proposed to explain the observed pH-dependent sorption.     

Rb3In(H2O)Si5O13: a novel indium silicate with a CdSO4-topological-type structure

A novel indium silicate, Rb3In(H2O)Si5O13, has been synthesized using a high-temperature, high-pressure hydrothermal method and characterized by single-crystal X-ray diffraction. The structure consists of five-membered rings of corner-sharing SiO4 tetrahedra connected via corner sharing to four adjacent five-membered rings to form a 3D silicate framework that belongs to the CdSO4 topological type. The InO6 octahedron shares five of its corners with five different SiO4 tetrahedra to form a 3D frame-work that delimits two types of channels to accommodate the rubidium cations. The sixth corner of InO6 is coordinated H2O. The structure is related to that of the titanium silicate ETS-10, and these are the only two metal silicates that have the CdSO4-topological-type structure. In addition, the crystal of Rb3In(H2O)Si5O13 shows an intense second harmonic generation signal. Crystal data: H2Rb3InSi5O14, monoclinic, space group Cc (No. 9), a = 9.0697(5) A, b = 11.5456(6) A, c = 13.9266(8) A, beta = 102.300(1) degrees, V = 1424.8(1) A3, and Z = 4.     

硅对铁基费-托合成催化剂的影响

用共沉淀法制备了一系列不同硅含量的铁基催化剂,采用N2吸附和原位X射线衍射对催化剂进行了表征,在固定床反应器中考察了催化剂的费-托合成反应活性、选择性和稳定性.结果表明,含硅的催化剂具有较大的比表面积和较小的平均孔径,在CO还原及费-托合成反应中生成的碳化铁物种的稳定性比不含硅的催化剂高.在费-托合成反应中,不含硅的催化剂具有较高的初始活性,但易失活;含硅的催化剂具有较低的初始活性,但稳定性较高.Fe7C3是活性最高的碳化铁物种.随着硅含量的增加,催化剂的费-托合成反应更易生成低碳数产物.     

Sorption of uranyl ions on titanium oxide studied by ATR-IR spectroscopy

ATR-IR spectroscopy was used to study the sorption of uranyl ions (10(-4) M) onto titanium oxide (mixture of rutile and anatase). A circulation setup, filled with a solution in D(2)O, allowed recording of the evolution of the antisymmetric O=U=O stretching of uranyl species onto titanium oxide particles deposited on the ATR crystal. The band centered at 915 cm(-1) has been decomposed in two Gaussian peaks at 920 and 905 cm(-1). From these values, and the observation that the ratio of the areas of the two peaks vs pH was constant, we have proposed that uranyl sorption on titanium oxide in the pH range 4-7 leads to the formation of one surface complex where uranium atoms have two different chemical environments. A trimer surface complex linked by two uranium atoms to the titanium oxide surface would be consistent with this interpretation.     

Atomic layer deposition of TiO2 from TiI4 and H2O onto SiO2 surfaces: ab initio calculations of the initial reaction mechanisms

The initial surface reactions involved in the atomic layer deposition (ALD) of TiO2 from TiI4 and H2O onto a SiO2 substrate have been investigated using electronic structure calculations based on cluster models. The detailed atomic growth mechanisms on different types of functionalities on the SiO2 substrate have been proposed. The effects of quantum tunneling and hindered rotations of adsorbates on the rate of surface reactions have been investigated. The effects of tunneling were found to be negligible for all reactions, because typical ALD temperatures range from 150 to 450 degrees C. However, the rotational contributions to the rate constants must be taken into account in certain cases. All of the three surface functionalities investigated exhibit high chemical reactivity toward TiI4 precursors at typical ALD temperatures. The rate constants of the second half-reactions between Ti intermediates and H2O are 5-8 orders of magnitude smaller than the first half-reactions between TiI4 and the surface functionalities. Although the iodine release reaction has been used to explain previous experimental measurements, it is predicted to be unfavorable (kinetically and thermodynamically) and is unlikely to occur at typical ALD temperatures. Substitution of TiI4 with TiCl4 as the metal precursor can increase the binding energies of the absorbates onto the surface due to the high electronegativity of the Cl ligands. However, the activation barriers are not significantly different between these two metal precursors. More importantly, our calculations predict that TiI4 precursors tend to produce TiO2 films with fewer impurities than the TiCl4 precursors.