Synthetic Approaches to the Incorporation of Gallium and Germanium into Inorganic Polymer Structures

<p>New sol-gel and solid-state synthesis methods and combinations of these were developed for the preparation of several new inorganic polymers related to aluminosilicate inorganic polymers, attempting to substitute gallium and germanium for aluminium and silicon. Gallium could successfully substitute for aluminium, but germanium could not be substituted for silicon by these methods. Gallium silicate and gallium aluminosilicate inorganic polymers were synthesised from mixtures of KGaO2, KAlO2, KOH solutions with finely divided SiO2 (silica fume) using a combination of sol-gel and solid-state techniques. The products of these reactions were studied by X-ray powder diffraction (XRD), solid-state 27Al, 29Si, 71Ga and 39K nuclear magnetic resonance with magic-angle spinning (MAS NMR) and scanning electron microscopy (SEM). For the synthesis of these mixed gallium-aluminium silicate inorganic polymers, the optimal SiO2:(Ga2O3+Al2O3) ratio was found to be 7 and the Ga:Al ratio could range from 100% Ga to 100% Al, with all intermediate ratios yielding inorganic polymers. The products showed all the characteristics of a true inorganic polymer, being X-ray amorphous and containing gallium and/or aluminium in tetrahedral coordination states. 29Si MAS NMR showed the occurrence of Si(3Ga) and Si(2Ga) sites when gallium was present, and Si(3Al) and Si(2Al) sites when aluminium was present. Unreacted silica was also detected in these compounds by 29Si NMR and spherical silica particles were observed by SEM. Heat treatment of gallium silicate, gallium aluminosilicate and aluminosilicate inorganic polymers synthesised by variations of the sol-gel method was monitored by thermal analysis methods (DSC-TGA) which revealed a water loss at 75 [degrees]C and 160 [degrees]C followed by a phase transition at 950 [degrees]C. At this temperature the inorganic polymers crystallised to KGaSi2O6 and KAlSi2O6. The thermal behaviour of these samples was found to be different at 1200 [degrees]C; the high-temperature products derived from the gallium silicate inorganic polymers remained as crystalline KGaSi2O6 and retained their shape, while gallium aluminosilicate and aluminosilicate inorganic polymers melted and slumped, losing their shape and becoming X-ray amorphous. Attempts to substitute germanium for silicon in the inorganic polymer structure were unsuccessful. A sol-gel approach using GeO2 produced crystalline K6Ga6(GeO4)6(H2O)7. In an alternative solid-state approach, potassium germanate was synthesised and subsequently reacted with KGaO2 in a solidstate reaction to form partially amorphous hydraulic precursors; however, these did not set on the addition of water. A solid-state reaction of potassium germanate with KGa5O8 formed a partially amorphous precursor powder that set with the addition of water. However, the cured product was not amorphous, but proved to be crystalline K6Ga6(GeO4)6(H2O)7. In another approach, a sol-gel reaction of NaAlO2 solution and GeO2 with KOH solution set to an X-ray amorphous but brittle product. 27Al MAS NMR showed this to contain aluminium in both tetrahedral and octahedral coordination states. When KAlO2 was used instead of NaAlO2, the products were crystalline. The study of the structure of these germanium compounds is hindered by the inaccessibility of the germanium nuclide to MAS NMR. Nevertheless, the ability to synthesise a new category of materials by these new methods opens up the possibility of their potential applications as fluorescent materials and as components of optoelectronic devices.</p>

Synthetic Approaches to the Incorporation of Gallium and Germanium into Inorganic Polymer Structures

<p>New sol-gel and solid-state synthesis methods and combinations of these were developed for the preparation of several new inorganic polymers related to aluminosilicate inorganic polymers, attempting to substitute gallium and germanium for aluminium and silicon. Gallium could successfully substitute for aluminium, but germanium could not be substituted for silicon by these methods. Gallium silicate and gallium aluminosilicate inorganic polymers were synthesised from mixtures of KGaO2, KAlO2, KOH solutions with finely divided SiO2 (silica fume) using a combination of sol-gel and solid-state techniques. The products of these reactions were studied by X-ray powder diffraction (XRD), solid-state 27Al, 29Si, 71Ga and 39K nuclear magnetic resonance with magic-angle spinning (MAS NMR) and scanning electron microscopy (SEM). For the synthesis of these mixed gallium-aluminium silicate inorganic polymers, the optimal SiO2:(Ga2O3+Al2O3) ratio was found to be 7 and the Ga:Al ratio could range from 100% Ga to 100% Al, with all intermediate ratios yielding inorganic polymers. The products showed all the characteristics of a true inorganic polymer, being X-ray amorphous and containing gallium and/or aluminium in tetrahedral coordination states. 29Si MAS NMR showed the occurrence of Si(3Ga) and Si(2Ga) sites when gallium was present, and Si(3Al) and Si(2Al) sites when aluminium was present. Unreacted silica was also detected in these compounds by 29Si NMR and spherical silica particles were observed by SEM. Heat treatment of gallium silicate, gallium aluminosilicate and aluminosilicate inorganic polymers synthesised by variations of the sol-gel method was monitored by thermal analysis methods (DSC-TGA) which revealed a water loss at 75 [degrees]C and 160 [degrees]C followed by a phase transition at 950 [degrees]C. At this temperature the inorganic polymers crystallised to KGaSi2O6 and KAlSi2O6. The thermal behaviour of these samples was found to be different at 1200 [degrees]C; the high-temperature products derived from the gallium silicate inorganic polymers remained as crystalline KGaSi2O6 and retained their shape, while gallium aluminosilicate and aluminosilicate inorganic polymers melted and slumped, losing their shape and becoming X-ray amorphous. Attempts to substitute germanium for silicon in the inorganic polymer structure were unsuccessful. A sol-gel approach using GeO2 produced crystalline K6Ga6(GeO4)6(H2O)7. In an alternative solid-state approach, potassium germanate was synthesised and subsequently reacted with KGaO2 in a solidstate reaction to form partially amorphous hydraulic precursors; however, these did not set on the addition of water. A solid-state reaction of potassium germanate with KGa5O8 formed a partially amorphous precursor powder that set with the addition of water. However, the cured product was not amorphous, but proved to be crystalline K6Ga6(GeO4)6(H2O)7. In another approach, a sol-gel reaction of NaAlO2 solution and GeO2 with KOH solution set to an X-ray amorphous but brittle product. 27Al MAS NMR showed this to contain aluminium in both tetrahedral and octahedral coordination states. When KAlO2 was used instead of NaAlO2, the products were crystalline. The study of the structure of these germanium compounds is hindered by the inaccessibility of the germanium nuclide to MAS NMR. Nevertheless, the ability to synthesise a new category of materials by these new methods opens up the possibility of their potential applications as fluorescent materials and as components of optoelectronic devices.</p>

Relationship between Acidity and Activity on Propane Conversion over Metal-Modified HZSM-5 Catalysts

A systematic study of the comparative performances of different metal-impregnated HZSM-5 catalysts (Zn, Ga, Mo, Co, and Zr) for propane conversion is presented. The physicochemical properties of catalysts were characterized by means of XRD, BET, SEM, TEM, FTIR, XPS, 27Al MAS NMR, NH3-TPD and Py-FTIR. It was found that the acidities of the catalysts were significantly influenced by loading metal. More specifically, Mo-, Co- or Zr-modified catalysts showed a large metal size and low acidic density, resulting high olefin selectivity, while Zn- or Ga-modified catalysts maintained their small metal size and acidic density, and mainly reduced B/L due to the Lewis acid sites created by Zn or Ga species, resulting in high aromatics selectivity. Experimental results also showed that there is a balance between metals size and medium and strong acidity on propane conversion. Moreover, based on the different acidity of metal-modified HZSM-5 catalysts, the mechanism of propane conversion was also discussed.

Hydrochloric Acid Modification and Lead Removal Studies on Naturally Occurring Zeolites from Nevada, New Mexico, and Arizona

Four naturally occurring zeolites were examined to verify their assignments as chabazites AZLB-Ca and AZLB-Na (Bowie, Arizona) and clinoptilolites NM-Ca (Winston, New Mexico) and NV-Na (Ash Meadows, Nevada). Based on powder X-ray diffraction, NM-Ca was discovered to be mostly quartz with some clinoptilolite residues. Treatment with concentrated HCl (12.1 M) acid resulted in AZLB-Ca and AZLB-Na, the chabazite-like species, becoming amorphous, as confirmed by powder X-ray diffraction. In contrast, NM-Ca and NV-Na, which are clinoptilolite-like species, withstood boiling in concentrated HCl acid. This treatment removes calcium, magnesium, sodium, potassium, aluminum, and iron atoms or ions from the framework while leaving the silicon framework intact as confirmed via X-ray fluorescence and diffraction. SEM images on calcined and HCl treated NV-Na were obtained. BET surface area analysis confirmed an increase in surface area for the two zeolites after treatment, NM-Ca 20.0(1) to 111(4) m2/g and NV-Na 19.0(4) to 158(7) m2/g. 29Si and 27Al MAS NMR were performed on the natural and treated NV-Na zeolite, and the data for the natural NV-Na zeolite suggested a Si:Al ratio of 4.33 similar to that determined by X-Ray fluorescence of 4.55. Removal of lead ions from solution decreased from the native NM-Ca, 0.27(14), NV-Na, 1.50(17) meq/g compared to the modified zeolites, 30 min HCl treated NM-Ca 0.06(9) and NV-Na, 0.41(23) meq/g, and also decreased upon K+ ion pretreatment in the HCl modified zeolites.

Hydrochloric Acid Modification and Lead Removal Studies on Naturally Occurring Zeolites from Nevada, New Mexico, and Arizona.

Four naturally occurring zeolites AZLB-Ca and AZLB-Na (Bowie, Arizona), NM-Ca (Winston, New Mexico), and NV-Na (Ash Meadows, Nevada) were studied to evaluate structural modifications after treatment with HCl acid. AZLB-Ca and AZLB-Na are chabazite-like species and become amorphous when boiled in concentrated HCl acid as confirmed by powder X-ray diffraction. In contrast, NM-Ca and NV-Na which are clinoptilolite-like species withstood boiling in concentrated HCl acid. This treatment removes calcium, magnesium, sodium, potassium, aluminum, and iron atoms or ions from the framework while leaving the silicon framework intact as confirmed via X-ray fluorescence and diffraction. SEM images on calcined and HCl treated NV-Na were obtained. BET surface area analysis confirmed an increase in surface area for the two zeolites after treatment, NM-Ca (20.0(1) to 111(4) m2/g) and NV-Na (19.0(4) to 158(7) m2/g). 29Si and 27Al MAS NMR were performed on the natural and treated NV-Na zeolite and the data for the natural NV-Na zeolite suggested a Si:Al ratio of 4.33 similar to that determined by X-Ray fluorescence of 4.55. Removal of lead ions from solution decreased from the native (NM-Ca, 0.27(14), NV-Na, 1.50(17) meq/g) compared to the modified zeolites (30 min HCl treated NM-Ca 0.06(9) and NV-Na, 0.41(23) meq/g) and also decreased upon K+ ion pretreatment in the HCl modified zeolites.

Synthesis of Layered Octadecyltrimethylammonium-Templated Aluminosilicate and its Use as a Thickening Agentfor Lubricating Grease

We describe herein the use of octadecyltrimethylammonium-templated aluminosilicate (designated as LS) as a thickener to induce gelation. LS samples with different aluminum/silicon molar ratios (Al/Si = 0, 0.05, 0.10, 0.15, 0.20) were synthesized hydrothermally and characterized by X-ray diffraction analysis, 27Al MAS NMR spectra, elemental analysis, and scanning electron microscopy. The aluminum/silicon molar ratio was shown to be an important factor affecting the rheological properties of LS gels. With increasing Al/Si molar ratio, the viscoelasticity and structural strength of LS gel were enhanced, the dropping point increased, and the amount of oil separation decreased. LS(0.20) gel exhibited superior relative elastic character. The strength of the LS(0.20) gel was also enhanced with increasing LS(0.20) content. In SRV tests, LS(0.20) gel with different contents showed good performance in terms of load-bearing ability and anti-wear property, indicating that LS was strongly adhered on the friction surface, and thereby promoted lubrication. Owing to simple preparation, the promising rheological and tribological properties, LS gel hold great potential application in lubricating grease.

Facile Method by Bentonite Treated with Heat and Acid to Enhance Pesticide Adsorption

In this work, simple conditions were applied to modify bentonite for the removal of pesticides from aqueous solution. Bentonite was modified in a single step as BA0.5 (with HCl 0.5 M) and BC500 (calcined at 500 °C) and combined steps with different sequences (BA0.5C500 and BC500A0.5). These adsorbents were characterised by XRD, XRF, FT-IR, 27Al MAS NMR, BET, NH3-TPD, TGA, HPLC, particle size analysis and zeta potential. Single-component adsorption with atrazine, diuron, 2,4-D and paraquat was used in aqueous solution at various pesticide concentrations, contact times and pH levels. It was found that the sequence of the treatment significantly affected atrazine adsorption. BC500A0.5 exhibited the highest efficiency for atrazine adsorption in a broad pH range of 3.0–9.0. Its adsorption at pH 6.0 was about 12 times greater than that of other adsorbents with an initial atrazine concentration of 50 mg L−1, which indicates BC500A0.5 specifically for the adsorption of atrazine. In addition, for the simultaneous adsorption of all four pesticides, BC500A0.5 was found to remove the maximum total amount of the pesticides, indicating that it could be used as a good multifunctional adsorbent. All modified bentonites showed similar diuron adsorption better than that of unmodified bentonite. The greatest adsorption of 2,4-D prefers BA0.5C500, occurring at pH 2–4. In the case of paraquat adsorption, all adsorbents are good at absorbing paraquat, but bentonite had the highest rate of paraquat removal, whereas BA0.5C500 was found to have the lowest, and the adsorption increased with increasing pH. Furthermore, the adsorption process on the adsorbents fits well with the Langmuir isotherm and pseudo-second-order kinetics models, as the thermodynamic parameters showed a spontaneous and endothermic process.

Spectroscopic glimpses of the transition state of ATP hydrolysis trapped in a bacterial DnaB helicase

The ATP hydrolysis transition state of motor proteins is a weakly populated protein state that can be stabilized and investigated by replacing ATP with chemical mimics. We present atomic-level structural and dynamic insights on a state created by ADP aluminum fluoride binding to the bacterial DnaB helicase from Helicobacter pylori. We determined the positioning of the metal ion cofactor within the active site using electron paramagnetic resonance, and identified the protein protons coordinating to the phosphate groups of ADP and DNA using proton-detected 31P,1H solid-state nuclear magnetic resonance spectroscopy at fast magic-angle spinning > 100 kHz, as well as temperature-dependent proton chemical-shift values to prove their engagements in hydrogen bonds. 19F and 27Al MAS NMR spectra reveal a highly mobile, fast-rotating aluminum fluoride unit pointing to the capture of a late ATP hydrolysis translation state in which the phosphoryl unit is already detached from the arginine and lysine fingers.

Composite Nanostructure of Manganese Cluster and CHA-Type Silicoaluminaphosphates: Enhanced Catalytic Performance in Dimethylether to Light Olefins Conversion

Light olefins, especially ethylene and propylene, are important chemicals in petrochemical industries with an increasing demand and play an essential role in the global consumption. In this regard, there have been extensive studies to design efficient catalysts for the light olefins productions. In this study, we report a new protocol to induce Mn nanoclusters (MnNC) into the mesopore of a CHA-type silicoaluminaphosphates via a one-pot synthesis of MnNC@SAPO-34 catalysts. The catalysts are characterized by a series of technology, such as TEM, XRD, NH3-TPD, 27Al MAS NMR, ICP-MS, XPS, and as well as N2-physical adsorption methods. The Mn nanoclusters of Mn2O3 and MnO2 species are well dispersed in the framework of the SAPO-34 silicoaluminaphosphates, modifying the porosity and acidic property of the SAPO-34: Giving rise to more mesoporous and improving the acid density. The MnNC@SAPO-34 catalysts exhibit decent 100% conversion and 92.2% olefins selectivity in the dimethyl ether to olefins (DTO) reactions, which is considerably higher than that for SAPO-34 silicoaluminaphosphates (79.6% olefins selectivity). The higher olefins selectivity over the MnNC@SAPO-34 is deemed to associate with the strong acid density and intensity of the silicoaluminaphosphates. Further, the Mn particles largely improve silicoaluminaphosphates’s durability.