Reactivity of Thioglycolic Acid Physically and Chemically Bound to Silica Gel as New Selective Solid Phase Extractors for Removal of Heavy Metal Ions From Natural Water Samples

A method is presented for the immobilization of thioglycolic acid moiety on the surface of active silica gel via a simple and direct synthetic route and based on one step reaction procedure. Two-product solid phase extractors were successfully synthesized according to physical adsorption and chemical immobilization binding techniques, phases (I) and (II), respectively. The mode of interaction between the silanol group and the thioglycolic moiety was also discussed for both phases based on the infrared analysis studies. The thermal stability properties as well as the effect of buffer solutions on the percentage hydrolysis of the two silica gel phases were examined and revealed the high stability and superiority of silica phase (II) in these respects. The evaluation of the selectivity and metal uptake properties incorporated in these two silica gel phases were also studied and discussed for a series of divalent heavy metal ions under different controlling factors. The mmol/g values were found to be higher in case of phase (I). The selective removal and extraction of some heavy metal ions, viz . Cu(II), Zn(II), and Hg(II) from natural seawater samples was successfully accomplished with the percentage recovery values for the three tested metal ions in the range of 96.5-98.4 - 0.2-0.6%. The presence of higher concentrations of Na(I), K(I), Mg(II) and Ca(II) showed insignificant role or no matrix effect on such selective extraction process due to their 0% values of removal by these silica gel phases (I) and (II).     

Hydrogenation of arenes over silica-supported catalysts that combine a grafted rhodium complex and palladium nanoparticles: evidence for substrate activation on Rh(single-site)-Pd(metal) moieties

The complex Rh(cod)(sulfos) (Rh(I); sulfos = (-)O(3)S(C(6)H(4))CH(2)C(CH(2)PPh(2))(3); cod = cycloocta-1,5-diene), either free or supported on silica, does not catalyze the hydrogenation of benzene in either homogeneous or heterogeneous phase. However, when silica contains supported Pd metal nanoparticles (Pd(0)/SiO(2)), a hybrid catalyst (Rh(I)-Pd(0)/SiO(2)) is formed that hydrogenates benzene 4 times faster than does Pd(0)/SiO(2) alone. EXAFS and DRIFT measurements of in situ and ex situ prepared samples, batch catalytic reactions under different conditions, deuterium labeling experiments, and model organometallic studies, taken together, have shown that the rhodium single sites and the palladium nanoparticles cooperate with each other in promoting the hydrogenation of benzene through the formation of a unique entity throughout the catalytic cycle. Besides decreasing the extent of cyclohexa-1,3-diene disproportionation at palladium, the combined action of the two metals activates the arene so as to allow the rhodium sites to enter the catalytic cycle and speed up the overall hydrogenation process by rapidly reducing benzene to cyclohexa-1,3-diene.     

以陶瓷纤维为基材的硅胶吸附材料的制备与性能

以陶瓷纤维纸为基材，经水玻璃浸泡，絮凝剂沉积，盐酸调节pH值得到陶瓷纤维基硅胶吸附材料：探讨水玻璃浓度、絮凝剂浓度，盐酸浓度等条件对硅胶吸附剂吸附性能的影响：采用扫描电镜(SEM)，多孔介质孔隙分析仪揭示吸附材料的表面形貌、比表面积及孔径大小。实验结果显示：当水玻璃浓度为26．67wt%，絮凝剂浓度为15wt％，盐酸浓度为0．5mol／L时，吸附剂具有较好的吸附性能：硅胶能较好分散在纤维表面及其空隙中，BET比表面积为347．4m^2／g，总孔容为0．20295cm^2／g，其中，微孔所占比例为50．54％，平均孔径为，微孔0．4939nm，中孔3．907nm。     

Composite Water Sorbents of the Salt in Silica Gel Pores Type: The Effect of the Interaction between the Salt and the Silica Gel Surface on the Chemical and Phase Compositions and Sorption Properties

The influence of the inorganic salt-silica gel surface interaction on the chemical and phase compositions and sorption properties of composites of the salt in silica gel pores type is studied. Two possible interaction mechanisms are considered: (1) the ion-exchange adsorption of metal cations on the silica gel surface from a solution of a salt (CaCl₂, CuSO₄, MgSO₄, Na₂SO₄, and LiBr) and (2) the solid-phase spreading of a salt (CaCl₂) over the silica gel surface. The adsorption of metal cations on the silica gel surface in the impregnation step affords ≡Si-OM ⁿ⁺¹ surface complexes in the composites. As a result, two salt phases are formed in silica gel pores at the composite drying stage, namely, an amorphous phase on the surface and a crystalline phase in the bulk. The sorption equilibrium between the CaCl₂/SiO₂ system and water vapor depends on the ratio of the crystalline phase to the amorphous phase in the composite.     

Alkali metals plus silica gel: powerful reducing agents and convenient hydrogen sources

Alkali metals absorbed into silica gel yield three stages of unique loose black powders (M-SG) that are strong reducing agents. All react nearly quantitatively with water to form hydrogen. Liquid Na-K alloys form air-sensitive powders at room temperature that can be converted at 150 degrees C to a form that is sensitive to moisture but not to dry air. Slowly heating sodium and silica gel to 400 degrees C yields a third type that can be handled in ambient air with only slow degradation by atmospheric moisture. These materials eliminate many hazards associated with pure alkali metals and provide easily handled reducing agents and hydrogen sources. They could be used in continuous-flow reactors to reduce and protonate aromatics, dechlorinate alkyl and aryl halides, and desulfurize various compounds.     

甲烷氧化偶联Na-W-Mn/SiO2催化剂的喇曼光谱

By calcinating commercial silica gel at 1500℃or adding Na2C2O4 and then calcinating at 850℃,α-cristobalite was formed. On the basis of the vibration spectroscopy of silica support, Na-W-Mn/SiO2 catalyst was characterized by Raman spectroscopy. The results show that the structure of support and the interaction among metal components have significant effect on the dispersion and the structure of metal sites, and the tetrahedrally coordinated [WO4] formed on α-cristobalite surface is the most possible site of methane activation with high C2 selectivity.     

Characterization of silicate monomer with sodium,calcium and strontium but not with lithium and magnesium ions by fast atom bombardment mass spectrometry

Fast atom bombardment mass spectrometry (FABMS) was applied to the direct detection of silica species dissolved in LiCl, NaCl, MgCl(2), CaCl(2) and SrCl(2) solutions in order to investigate its dissolution process in solution. Several species of dissolved silicate complexes in the solution were directly detected by FABMS. The peak intensities of [SiO(2)(OH)(2)Na](-), [SiO(3)(OH)Ca](-) and [SiO(3)(OH)Sr](-) increased with increasing concentrations of NaCl, CaCl(2) and SrCl(2), whereas the peak intensities of [SiO(2)(OH)(2)Li](-) and [SiO(3)(OH)Mg](-) did not increase with increasing concentrations of LiCl and MgCl(2). These results indicte that silicate and cation bind in the solution not after but before ionization. The isotope pattern of Sr(2+) confirmed the existence of the silicate-Sr complex not only with increase of the concentration of silica but also the mass numbers of Sr. The silicate complexes formed with Na(+), Ca(2+) and Sr(2+) showed high stability in chloride solution. This is in good accordance with the fact that Na(+), Ca(2+) and Sr(2+) accelerate the dissolution of silica to form complexes during solution equilibrium. Considering that the stability constant was examined and reported in other papers, this new findings that Mg(2+) does not form a complex with silicic acid (Si(OH)(4)) is very important.     

Metal-modified silica adsorbents for removal of humic substances in water

As novel adsorbents for humic substances, Fe-, Mg-, and Ca-modified silica gels SiO(2)Fe, SiO(2)Mg, and SiO(2)Ca were prepared, and their adsorbabilities to humic and fulvic acids were evaluated in water at 25 degrees C for 20 h. Among these adsorbents, SiO(2)Fe indicated the highest adsorbability, in which removing humic substances in water was accomplished to 80-97%. By calcination at 600 degrees C and washing with water, adsorbabilities of the silica adsorbents deteriorated except for the case of calcination of SiO(2)Ca. This is due to changing metal modification structures and losing chlorine, judging from elemental analysis, TG-DTA, and XPS. Especially, the modifier Fe was tightly fixed on the silica surface of SiO(2)Fe, since the metal content was almost constant even after the calcination and water washing unlike the other adsorbents. Therefore, we found that SiO(2)Fe is the most useful adsorbent among the silica adsorbents and that its modification structure is composed of SiOFe, FeCl, and FeOH. In addition, the adsorption mechanism is explained by an interaction between Fe and humic substance molecule having carboxylate and phenolate groups, accompanied with anion exchange of chloride ion Cl(-) for the humic substance molecule via the silica pores. SiO(2)Fe may be applied to an adsorbent alternative for charcoal in water purification plants, and the used SiO(2)Fe may be further reused as a fertilizer since humic substances have plant-glowing ability and silica strengthens plant parts.     

A first-principles study on quasi-1D alkali metal chains within zeolite channels

We report first-principles studies on systems formed by alkali metal (Na, K, or Rb) added to zeolite ITQ-4. Geometric and electronic structures of the quasi-1D chains of intercalated alkali metal atoms at experimental loading (4 metal atoms per 32 Si) are studied. Clear differences between different kinds of alkali metal are found, with a general trend of decreased ionization and less metallic character for the lighter alkali metals. Within the zeolite channels, it is possible to form insulated and metallic alkali metal chains by doping Na or Rb. Agreeing with experiments, only Rb here is found to be a good candidate to generate inorganic electride. We also predict that a large quantity of Na can be doped into the zeolite channel, while no more than 4 Rb per 16 Si can be doped.     

甲烷氧化偶联Mn_2O_3-Na_2WO_4/SiO_2催化剂——Ⅰ.表面分散状态和氧化物/担体相互作用

担载型Mn_2O_3-Na_2WO_4/SiO_2催化剂具有优异的甲烷氧化偶联制乙烯催化活性。在最佳反应条件下,甲烷转化率和C_2烃收率分别达到37.1％和23.9％;在1000 h连续操作后性能基本维持不变;并且由于它适于流化床操作,对这类强放热反应的工业化较为有利,本文报导用XRD、XPS和PASCA(化学分析正电子湮没谱)方法研究该催化剂活性组分Na_2WO_4和Mn_2O_3在SiO_2载体上的分散状态和氧化物/担体相互作用的结果。 催化剂由混浆法和浸渍法制备,并经750—850℃焙烧。系列配比的催化剂均经AAS分析证实体相组成。催化剂比表面积用Sorptmaeic—1822型比表面积测定仪测定(N_2吸附,     

多孔活性硅胶的制备及吸附性能的研究

以硅酸钠和氯化铵为原料,通过添加表面活性剂制备高吸附活性的多孔硅胶.采用SEM,IR和XRI)等手段对硅胶样品的结构和形貌进行表征,并利用紫外分光光度法研究硅胶样品对垃圾渗滤液中有机污染物的吸附性能.结果表明,合成的硅胶样品是由纳米量级的无定形二氧化硅颗粒组成的多孔性、疏松状物质,对垃圾渗滤液中的有机物分子具有较强的吸...     

Effect of embedded metal compound on porosity of silica colloids prepared by spray reaction of silicon tetrachloride

Attempts to prepare macroporous silica particles and metal-compound-nanoparticle-embedded silica microspheres were carried out using reactions between silicon tetrachloride and ultrasonic generating microdroplets including metal (Na, K, Al, Ni, Ti, Pt) compounds. Samples were collected by dry and wet processes. In the case of using nickel and aluminum compounds, acid-treated samples were also prepared. The obtained samples were characterized by scanning electron microscopy, X-ray fluorescence spectroscopy, powder X-ray diffractometry, mercury porosimetry, and the nitrogen adsorption method. The macroporous silica particles were prepared by removing the salt crystals, such as NaCl and KCl, formed in the silica frame. For acid-resistant metals, platinum- and titanium-compound nanoparticles are easily embedded in silica microspheres using these metal-compound solutions. For acid-soluble metals, aluminum- and nickel-compound-nanoparticle-embedded silicas were prepared by applying neutralization of the collection water. Micropores and mesopores were produced in wet-process samples. Acid treatment induced the increase of micropore volumes.     

Laser desorption/ionization mass spectrometry on porous silica and alumina for peptide mass fingerprinting

We investigated a variant of desorption/ionization on porous silicon (DIOS) mass spectrometry utilizing an aqueous suspension of either porous silica gel or porous alumina (pore size of 60 and 90 A, respectively). Laser desorption/ionization (LDI) from samples directly deposited on a stainless steel surface without any inorganic substrates was also achieved. Synthetic peptides designed to cover large sequence diversity constituted our model compounds. Sample preparation, including material conditioning, peptide solubilization, and deposition protocol onto standard matrix-assisted laser desorption/ionization (MALDI) probe, as well as ionization source tuning were optimized to perform sensitive reproducible LDI analyses. The addition of either a cationizing agent or an alkali metal scavenger to the sample suspension allowed modification of the ionization output. Comparing hydrophilic silica gel to hydrophobic reversed-phase silica gel as well as increasing material pore size provided further insights into desorption/ionization processes. Furthermore, mixtures of peptides were analyzed to probe the spectral suppression phenomenon when no interfering organic matrix was present. The results gathered from synthetic peptide cocktails indicated that LDI mass spectrometry on silica gel or alumina constitutes a promising complementary method to MALDI in proteomics for peptide mass fingerprinting.     

The unique liquid chromatographic properties of Group 11 transition metals for the separation of unsaturated organic compounds

Silver(I) and copper(I) are known to form reversible complexes with π bonds, which have been exploited in LC for separating unsaturated organic compounds. Prominent examples include the use of AgNO₃‐impregnated silica gel in LC, and the use of copper(I) salts for selective extraction of alkenes from hydrocarbon mixtures. The Dewar–Chatt–Duncanson model is often invoked to explain the interaction between Ag(I) and Cu(I) and π bonds. However, it is unclear if such a reversible interaction is directly related to their d¹⁰ outer electronic configurations. Particularly, Au(I) has not been reported to separate olefins with different numbers of double bonds in LC. Also, there has not been a systematic comparison of the liquid chromatographic properties of other d¹⁰ transition metal salts (e.g., Zn(II), Cd(II)), making it difficult to fully understand the observed reversible interactions of Ag(I) and Cu(I) with π bonds. We demonstrate for the first time that silica gel impregnated with all three Group 11 transition metals with 1+ oxidation state strongly and similarly retain olefin compounds in LC, while transition metals from Groups 10 and 12 do not. We also tested a range of functionalized silica gels to improve the stability of Cu(I) and Au(I) ions on the surface of the silica.     

Removal of Cd Ions by Sol-Gel Silica Doped with 1-(2-Pyridylazo)-2-Naphthol

1-(2-Pyridylazo)-2-Naphthol (PAN) doped sol-gel silica has been investigated for removal of metal ions from aqueous media. In the doped sol-gel silica, the large reagent molecules are entrapped inside the pores while small metal ions can diffuse into the pores where they are complexed by the reagent and retained inside the pores. This new solid sorbent was applied for removal of Cd(II) from aqueous solutions. The kinetics, adsorption isotherm, equilibration time and pH effect on the removal were studied to optimize the conditions to be utilized on a large scale. It was observed that a sol gel loaded with 0.09 mmol PAN/g, had a capacity of 0.044 mmol Cd/g. The desorption of metal ions was carried by 1 M HCl and the sol-gel silica sorbent could be regenerated and reused repeatedly.     

Selective retention of basic compounds by metal aquo‐ion affinity chromatography

A novel metal aquo‐ion affinity chromatography has been developed for the analysis of basic compounds using heat‐treated silica gel containing hydrated metal cations (metal aquo‐ions) as the packing material. The packing materials of the metal aquo‐ion affinity chromatography were prepared by the immobilization of a single metal component such as Fe(III), Al(III), Ag(I), and Ni(II) on silica gel followed by extensive heat treatment. The immobilized metals form aquo‐ions to present cation‐exchange ability for basic analytes and the cation‐exchange ability for basic analytes depends on pK_a of the immobilized metal species. In the present study, to evaluate the retention characteristics of metal aquo‐ion affinity chromatography, the on‐line solid‐phase extraction of drugs was investigated. Obtained data clearly evidence the selective retention capability of metal aquo‐ion affinity chromatography for basic analytes with sufficient capacity.     

Enrichment of iron(III), cobalt(II), nickel(II), and copper(II) by solid-phase extraction with 1,8-dihydroxyanthraquinone anchored to silica gel before their determination by flame atomic absorption spectrometry

A chelating matrix prepared by immobilizing 1,8-dihydroxyanthraquinone on silica gel modified with 3-aminopropyltriethoxysilane has been characterized by use of cross-polarization magic angle spinning (CPMAS) NMR, diffuse reflectance infrared Fourier transformation (DRIFT) spectroscopy, and thermogravimetric analysis and used to preconcentrate Fe(III), Co(II), Ni(II), and Cu(II) before their determination by flame atomic absorption spectrometry. The optimum pH ranges for quantitative sorption are 6.5-8.0, 6.0-7.0, 6.0-8.0, and 7.0-8.5 for Cu, Fe, Co, and Ni, respectively. All the metal ions can be desorbed with 2 mol L(-1) HCl or HNO3. The sorption capacity ( micromol g(-1) matrix) and preconcentration factor were 226.6, 250; 365.6, 300; 101.8, 150; and 109.0, 250 for Cu, Fe, Co, and Ni, respectively. The lowest concentration for quantitative recovery was 4.0, 3.3, 6.6, and 4.0 ng mL(-1), respectively for the four metal ions. The limits up to which electrolytes NaNO3, NaCl, NaBr, Na2SO4, and Na3PO4 and cations Ca(II) and Mg(II) can coexist with the four metal ions during their sorption without adverse effect are reported. The simultaneous enrichment and determination of all the four metals is possible if the total load of metal ions is less than the sorption capacity. Flame AAS was used to determine the metal ions in underground, tap, and river water samples (RSD相似文献   

Na-W-Mn/SiO2催化剂中的金属-载体作用

研究了Na-W-Mn/SiO₂催化剂中不同活性组份对载体结构的影响.结果表明,Na的诱导作用使无定型氧化硅在焙烧过程中相变为α-方石英结构,同时伴有比表面积的大幅度下降;单独担载Na时,硅小球经焙烧后基本无微孔存在,担载W则能使硅小球焙烧后形成较为均一的微米孔道.SiO₂载体在Na和W作用下发生的结构变化对催化剂的选择性起重要作用.     

Role of framework sodium versus local framework structure in determining the hydrothermal stability of MCM-41 mesostructures.

Two mesostructured MCM-41 silicas that differ dramatically in hydrothermal stability have been examined by (29)Si MAS NMR spectroscopy and pair distribution function (PDF) analysis of synchrotron X-ray scattering data. The less stable mesostructure assembled from sodium silicate and the substantially more stable derivative made from fumed silica possess equivalent local framework wall structures, as judged by NMR and PDF methods. Approximately 80% of the SiO(4) tetrahedra are fully cross-linked as Q(4) (Si(OSi)(4)) units in both calcined samples. Additionally, the structural correlation distances for the two materials are nearly identical, having values of 1.62(1), approximately 2.60, and 3.09(1) A for the Si-O, O-O, and nearest neighbor Si-Si distances in the framework. Sodium ions in the framework play a crucial role in limiting the hydrothermal stability of the mesostructure. Residual sodium ( approximately 0.05-0.10% Na(2)O) is retained in the MCM-41 made from sodium silicate, even after two ion exchange reactions with ammonium ions in more than 300 - fold excess. The entrapped framework sodium ions catalyze the collapse of the mesopores upon exposure to 20% steam at 800 degrees C for 5 h. The sodium - free mesostructure assembled from fumed silica retains an open framework under the same hydrothermal conditions. The stability of the fumed silica derivative, however, is greatly compromised when doped with as little as 0.10% Na(2)O, thus confirming the deleterious effect of sodium on hydrothermal stability.     

Diantipyrilmethane as complex-forming reagents in the thin-layer chromatographic determination of metals

Summary The efficiency of diantipyrilmethane used as a reagent for the chromatographic separation of metals, including titanium, zirconium and hafnium, rare earth elements, transition and platinum metals is shown. The peculiarities of the chromatographic behaviour of metal diantipyrilmethanates and the mechanism of their retention in TLC are discussed. Methods were developed for the determination of metals based on complex formation directly in the sorbent layer or by liquid extraction. The chromatographic separation takes place in silica gel thin layers with elution by organic solvent-mineral acid mixtures. The metals are determined by densitometric or spectrophotometric methods. After the complexes are isolated from the layer. The procedures are characterized by simplicity, efficiency, and a rather high selectivity. They were used to analyze steels, alloys, industrial solutions and other samples.