(1)H relaxivity of water in aqueous suspensions of Gd(3+)-loaded NaY nanozeolites and AlTUD-1 mesoporous material: the influence of Si/Al ratio and pore size

The results of a (1)H nuclear magnetic relaxation dispersion (NMRD) and EPR study on aqueous suspensions of Gd(3+)-loaded NaY nanozeolites and AlTUD-1 mesoporous material are described. Upon increase of the Si/Al ratio from 1.7 to 4.0 in the Gd(3+)-loaded zeolites, the relaxation rate per mM Gd(3+) (r1) at 40 MHz and 25 degrees C increases from 14 to 27 s(-)1 mM(-1). The NMRD and EPR data were fitted with a previously developed two-step model that considers the system as a concentrated aqueous solution of Gd(3+) in the interior of the zeolite that is in exchange with the bulk water outside the zeolite. The results show that the observed increase in relaxivity can mainly be attributed to the residence lifetime of the water protons in the interior of the material, which decreased from 0.3 to 0.2 micros, upon the increase of the Si/Al ratio. This can be explained by the decreased interaction of water with the zeolite walls as a result of the increased hydrophobicity. The importance of the exchange rate of water between the inside and the outside of the material was further demonstrated by the relatively high relaxivity (33 s(-1) mM(-1) at 40 MHz, 25 degrees C) observed for a suspension of the Gd(3+)-loaded mesoporous material AlTUD-1. Unfortunately, Gd(3+) leaches rather easily from that material, but not from the Gd(3+)-loaded NaY zeolites, which may have potential as contrast agents for magnetic resonance imaging.     

Zeolite GdNaY nanoparticles with very high relaxivity for application as contrast agents in magnetic resonance imaging

In this paper we explore Gd(3+)-doped zeolite NaY nanoparticles for their potential application as a contrast agent in magnetic resonance imaging (MRI). The nanoparticles have an average size of 80-100 nm, as determined by TEM and XRD. A powdered sample loaded with La3+ was characterised by means of multinuclear solid-state NMR spectroscopy. The NMR dispersion (NMRD) profiles obtained from aqueous suspensions of samples with Gd3+ doping ratios of 1.3-5.4 wt% were obtaining at different temperatures. The relaxivity increases drastically as the Gd3+ loading decreases, with values ranging between 11.4 and 37.7 s-1 mM-1 at 60 MHz and 37 degrees C. EPR spectra of aqueous suspensions of the samples suggest that an interaction between neighbouring Gd3+ ions within the same particle produces a significant increase in the transversal electronic relaxation rates in samples with a high Gd3+ content. The experimental NMRD and EPR data are explained with the use of a model that considers the system as a concentrated aqueous solution of Gd3+ in the interior of the zeolite that is in exchange with the bulk water outside the zeolite. The results obtained indicate that the Gd3+ ion is immobilised in the interior of the zeolite and that the relaxivity is mainly limited by the relatively slow diffusion of water protons from the pores of the zeolite channels into the bulk water.     

碱处理脱硅与提高Y型分子筛硅铝比——矛盾的对立与统一

考察了 "水热处理"以及"碱处理+水热处理"两种方法所制得的超稳 Y 分子筛的骨架硅铝比、孔结构特征以及酸量, 并探讨了"碱处理+水热处理"方法对起始 NaY 分子筛的适应性. 结果表明, 在水热处理前, 对 NaY 分子筛进行碱处理脱硅可在不改变最终样品的骨架超稳化水平和酸量的同时, 样品的介孔体积显著增加. 直接水热处理 NaY 分子筛所得样品介孔体积不超过 0.14 cm3/g, 而先碱处理后水热处理, 所得样品介孔体积可达 0.22 cm3/g. 该法适用于制备骨架硅铝比高的 NaY 分子筛. 起始原料的骨架硅铝比较低时, 所得样品的介孔体积增幅小, 而且微孔受损严重.     

用CO_2吸附法分析分子筛的孔结构

以NaA,NaY和NaZSM-5分子筛为研究对象,以CO2为吸附质,通过吸附数据测定,研究分子筛材料微孔结构的吸附表征方法.计算了NaA、NaY和NaZSM-5分子筛的微孔孔容,其中基于D-A方程的微孔孔容值与文献值一致.根据CO2吸附数据分析了3种分子筛的孔径分布.发现对于含有球形孔结构的NaA,NaY分子筛和NaA+NaY混合物,HK(Horvath-Kawazoe)球形模型(HKsphere)能够很好地描述其孔径分布,而HK柱状模型(HKcylinder)能够很好地表征具有柱状孔道结构的NaZSM-5分子筛.单一的HK方法不能表征同时含有柱状孔和球形孔的NaA+NaZSM-5混合物,使用HKcylinder只能得到混合物材料中柱状孔的分布情况,而使用HKsphere只能得到球形孔的分布情况.     

Platinum species in the pores of NaX, NaY and NaA zeolites studied using EPR, XAS and FTIR spectroscopies

The results of X-band EPR, X-ray absorption and Fourier transform infrared spectroscopy on Pt(NH(3))(4)(2+) exchanged NaX, NaY and NaA zeolites reveal after oxygen calcination at 573 K that diamagnetic Pt(2+) is not the only product. Calcination provides Pt(3+) cations, but depending on the heating rate, the decomposition of amino groups during calcination also produces hydrogen that reduces Pt(3+) to Pt(2+) and Pt(+). NaX (Si/Al = 1.23) has a more negative framework charge than NaY (Si/Al = 2.31), so Pt(3+) can be stabilized only in NaX, whereas lower oxidation states of Pt such as Pt(+) can be stabilized in both, NaX and NaY, and neither of the paramagnetic Pt cations are stabilized in NaUSY (Si/Al = 3). The autoreduction process allows controlling the number of Pt(3+) and Pt(+) in the NaX zeolite by changing the calcination heating rate: a heating rate of 1.25 K min(-1) gives only Pt(+), but 0.5 K min(-1) gives a Pt(3+)/Pt(+) ratio close to 1. The structure of the support is also important for the synthesis of Pt species. While isolated paramagnetic Pt ions were stabilized in faujasite zeolites (NaX and NaY), a paramagnetic Pt dimer was obtained in a Linde type A zeolite (LTA, Si/Al = 1) by applying the same preparation methods. The fraction of paramagnetic Pt species which were characterized by X-band EPR spectroscopy amounts to 2-18% of the total Pt in the zeolites, the remaining Pt must be diamagnetic.     

不同方法制备的脱铝Y沸石的孔结构

Y沸石脱铝有多种方法。由于在脱铝过程中发生水解、聚合、重排等反应,分子筛的孔结构将发生很大的变化,如形成空穴,甚至可导致骨架结构单元的崩塌,形成二次孔。由于不同的脱铝方法的脱铝机理不同,即使它们的脱铝程度一致,产生的孔结构也将不同,这必将导致它们的酸性质和催化性能的差异。目前关于Y沸石孔结构的研究报导还很少,尤其对SSY,US-SSY沸石孔结构的报导更为鲜见。本文用低温N_2吸附-脱附等温线和层厚t等方法,对四种不同方法制备的脱铝Y沸石(USY,DAY,SSY和US-SSY)的微孔、二次孔及其孔径分布(2.0～60.0nm)进行了初步研究,得到了一些有用的信息,为进一步研究其酸性质和催化性能打下了基础。     

Synthesis, characterization and examination of Gd[DO3A-hexylamine]-functionalized silica nanoparticles as contrast agent for MRI-applications

Spherical, nonporous and monodisperse silica nanoparticles (NPs) with a diameter of about 100 nm were synthesized and covalently functionalized with lanthanoid(III) (Ln=Gd or Y) chelate complexes, which serve as contrast agents (CAs) for magnetic resonance imaging (MRI). The materials were fully characterized after each synthetic step by different analytical methods, such as dynamic light scattering, scanning electron microscopy, DRIFT and NMR spectroscopy, thermogravimetry and elemental analysis, as well as zetapotential measurements. High surface concentrations of Gd(III) complexes (up to 50 μmol g(-1)) were determined by ICP-AES and T(1)-measurements, respectively. MRI experiments show the typical concentration-dependent increase of the longitudinal relaxation rate. T(1)-weighted images of samples with more than 25 μg NPs per 100 μL agar display a clear contrast enhancement in the agar layer. The transverse relaxivities r(2) of the materials are significantly higher than r(2) of the corresponding free Gd(III) complexes in water and medium, whereas the longitudinal relaxivities r(1) are slightly increased. Due to the high loading of Gd(III) complexes, the relaxivities per particle are remarkably high (up to 2.78×10(5) mM(-1) s(-1) for r(1)). Thus, new hybrid materials, based on nonporous silica NPs with high local relaxivity values were synthesized, which can serve as very effective CAs for MRI.     

Sustainable Synthesis of Pure Silica Zeolites from a Combined Strategy of Zeolite Seeding and Alcohol Filling

Currently, the synthesis of pure silica zeolites always requires the presence of organic structure‐directing agents (OSDAs), which direct the assembly pathway and ultimately fill the pore space. A sustainable route is now reported for synthesizing pure silica zeolites in the absence of OSDAs from a combined strategy of zeolite seeding and alcohol filling, where the zeolite seeds direct crystallization of zeolite crystals from amorphous silica, while the alcohol is served as pore filling in the zeolites. Very importantly, the alcohol could be fully washed out from zeolite pores by water at room temperature, which completely avoids calcination at high temperature for removal of OSDAs in the synthesis of pure silica zeolites.     

液固相同晶取代法制备Sn-NaY催化环己酮Baeyer-Villiger氧化

以微孔分子筛NaY为载体,SnCl_4·5H_2O为锡源,通过液固相同晶取代法制备催化材料Sn-NaY,研究了脱铝预处理和焙烧两个因素对制备Sn-NaY的影响.采用FT-IR、UV-Vis、XRD、N_2物理吸附、ICP、NH_3-TPD、吡啶红外、激光拉曼等手段对催化材料进行了表征.结果表明:对载体进行脱铝预处理有利于分子筛在催化剂制备过程中保持良好的骨架结构,焙烧有利于进入分子筛骨架中的Sn(Ⅳ)与硅羟基成键,从而形成有催化活性的四配位的Sn(Ⅳ),而空气氛围下焙烧容易产生骨架外SnO_2物种.Sn-NaY催化环己酮Baeyer-Villiger氧化结果表明,在环己酮0.03 mol,n(H_2O_2)∶n(酮)=1.5∶1,0.35 g催化剂,15 mL乙腈,70℃反应24 h的工艺条件下,N_2氛围焙烧的同晶取代脱铝催化剂性能最好,环己酮的转化率可达44%,己内酯的选择性为62%.     

Highly soluble tris-hydroxypyridonate Gd(III) complexes with increased hydration number, fast water exchange, slow electronic relaxation, and high relaxivity

The design, synthesis, and relaxivity properties of highly soluble TACN-capped trishydroxypyridonate-Gd(III) complexes are presented. Molecular mechanics modeling was used to help design a complex capable of possessing three water molecules in the inner metal coordination sphere, an attractive property for high-relaxivity MRI contrast agents. The measured relaxivities of 13.1 and 12.5 mM-1 s-1 (20 MHz, 298 K) for two TACN-capped complexes are among the highest known relaxivities of low-molecular weight Gd complexes and are consistent with three coordinated waters, an extremely fast water exchange rate, and long electronic relaxation time. Luminescence measurements to confirm the number of coordinated water molecules for the first time in the HOPO series are also discussed.     

改性Y沸石的孔结构与催化性能

测定了不同方法改性的Y沸石样品的N_2吸附和脱附等温线, 并计算了样品的微孔、大孔和二次孔的孔容和表面积, 以及样品的二次孔分布, 证实改性方法对样品的孔结构有显著的影响。同时, 还考察了不同尺码探针分子在改性Y沸石样品上的酸催化反应活性, 将所得数据与样品的酸量、酸强度和二次孔容相关联, 取得了满意的结果。说明对大尺码反应分子, 改性过程中生成的大孔径二次孔, 对提高沸石催化剂的反应活性是有利的。     

Zeolite-Polymer Composite Materials as Water Scavenger

The influence of the charge compensating cation nature (Na⁺, Mg²⁺) on the water adsorption properties of LTA-type zeolites used as filler in composite materials (zeolite/polymers) was investigated. Large scale cation exchanges were performed on zeolite powder at 80 °C for 2 h using 1 M magnesium chloride (MgCl₂) aqueous solutions. XRF, ICP, and EDX analyses indicate a successful cationic exchange process without the modification of the zeolite structure as shown by XRD and solid-state NMR analyses. Composite materials (granulates and molded parts) were manufactured using to extrusion and injection processes. In the case of MgA zeolite, nitrogen adsorption–desorption experiments allowed us to measure a microporous volume, unlike NaA zeolite, which is non-porous to nitrogen probe molecule. SEM and EDX analyses highlighted the homogeneous distribution of zeolite crystals into the polymer matrix. Water adsorption capacities confirmed that the trends observed in the zeolite powder samples are preserved after dragging zeolites into composite formulations. Granulates and molded parts composite samples containing the magnesium exchanged zeolite showed an increase of their water adsorption capacity up to +27% in comparison to composite samples containing the non-exchanged zeolite. The MgA composite is more promising for water decontamination applications due to its higher water adsorption properties than the NaA composite.     

亚硝胺在小微孔沸石上的“嵌入式”吸附探讨

通过结构计算分析了大体积的六亚甲基亚硝胺（NHMI）和N’-亚硝基去甲烟碱（NNN）在小微孔沸石上各种可能的吸附方式,结合实验事实推断出它们以－N－N=O官能团嵌入沸石孔道进行吸附的几率最大.这种“嵌入式”吸附方式是小微孔沸石得以吸附、分离那些体积远远大于其孔径的毒物分子的重要原因,可用以拓宽沸石在生态环境保护中的应用.     

Synthesis and characterization of zeolites NaA and NaY from rice husk ash

In this study, both zeolites NaA and NaY were synthesized from rice husk ash (RHA) by a simple conventional hydrothermal route. Rice husk (RH) was used as a silicate source to produce various zeolites. The hydrothermal route was conducted via a seeding technique involving the preparation of two separate gels, i.e. colloidal seed and feedstock gel. The zeolite was first produced using commercially available chemicals and followed by the replacement of the commercial silicate sources with RHA derived silicate. The RHA silicate was obtained by combusting the RH at different temperatures and durations i.e. 450 °C for both 2 and 6 hours, as well as 750 °C for 6 hours. Zeolite NaY (faujasite) was successfully synthesized with commercial chemical seed and RHA derived feedstock gel. On the other hand, using RHA silicate in both colloidal seed and feedstock gel would give only zeolite NaA. Elemental, structural and morphological analyses of RHA and zeolites were carried out with X-ray fluorescence (XRF) spectrometer, X-ray diffractometer (XRD) and scanning electron microscopy (SEM).     

Gamma‐Ray Irradiation to Accelerate Crystallization of Mesoporous Zeolites

Gamma‐ray (γ‐ray) irradiation was introduced into zeolite synthesis. The crystallization process of zeolite NaA, NaY, Silicalite‐1, and ZSM‐5 were greatly accelerated. The crystallization time of NaA zeolite was significantly decreased to 18 h under γ‐ray irradiation at 20 °C, while more than 102 h was needed for the conventional process. Unexpectedly, more mesopores were created during this process, and thus the adsorption capacity of CO₂ increased by 6‐fold compared to the NaA prepared without γ‐ray irradiation. Solid experimental evidence and density function theory (DFT) calculations demonstrated that hydroxyl free radicals (OH*) generated by γ‐rays accelerated the crystallization of zeolite NaA. Besides NaA, mesoporous ZSM‐5 with MFI topology was also successfully synthesized under γ‐ray irradiation, which possessed excellent catalytic performance for methanol conversion, suggesting the universality of this new synthetic strategy for various zeolites.     

Gamma-Ray Irradiation to Accelerate Crystallization of Mesoporous Zeolites

Gamma-ray (γ-ray) irradiation was introduced into zeolite synthesis. The crystallization process of zeolite NaA, NaY, Silicalite-1, and ZSM-5 were greatly accelerated. The crystallization time of NaA zeolite was significantly decreased to 18 h under γ-ray irradiation at 20 °C, while more than 102 h was needed for the conventional process. Unexpectedly, more mesopores were created during this process, and thus the adsorption capacity of CO₂ increased by 6-fold compared to the NaA prepared without γ-ray irradiation. Solid experimental evidence and density function theory (DFT) calculations demonstrated that hydroxyl free radicals (OH*) generated by γ-rays accelerated the crystallization of zeolite NaA. Besides NaA, mesoporous ZSM-5 with MFI topology was also successfully synthesized under γ-ray irradiation, which possessed excellent catalytic performance for methanol conversion, suggesting the universality of this new synthetic strategy for various zeolites.     

Highly active and reusable heterogeneous catalysts for acylation of anisole

In the present study, non-conventional solid acid catalysts such as NaY, metal ion exchanged zeolite NaY (Zn²⁺, Fe³⁺, Ce³⁺, La³⁺ and Nd³⁺), H-mordenite, H-β and HZSM-5 were used in order to overcome the disadvantages of conventional Friedel-Crafts catalysts for the acylation of anisole with acetic anhydride. Among the various zeolites studied, the HY zeolite shows an intermediate activity. Zeolite containing transition metal ions (Zn²⁺ and Fe³⁺) are less active and zeolite NaY is nearly inactive. The catalysts exhibit the activity in the order H-β>transition metal ions (Zn²⁺ and Fe³⁺)>HY>NaY zeolite. The highest catalytic activity of H-β could be due to its larger pore size. The type of acidity and the acid strength in zeolite Y were determined by FTIR and differential scanning calorimetric (DSC) studies on the pyridine adsorbed catalysts. The correlation of catalytic activity with acidity reveals that Brönsted acid sites in zeolite promote the acylation of anisole.     

亚硝胺在沸石催化剂上的程序升温表面反应

 采用程序升温表面反应技术研究了二甲基亚硝胺,吡咯烷亚硝胺和环六亚甲基亚硝胺在NaY,NaZSM－5和HZSM－5等沸石及MCM－41中孔分子筛上的脱附及分解．结果表明,沸石对亚硝胺有独特的吸附和催化分解作用．同时,研究了沸石孔结构及表面酸性对亚硝胺分解反应的影响．     

Intramolecular Hydrogen Bonding Restricts Gd–Aqua-Ligand Dynamics

Aqua ligands can undergo rapid internal rotation about the M−O bond. For magnetic resonance contrast agents, this rotation results in diminished relaxivity. Herein, we show that an intramolecular hydrogen bond to the aqua ligand can reduce this internal rotation and increase relaxivity. Molecular modeling was used to design a series of four Gd complexes capable of forming an intramolecular H-bond to the coordinated water ligand, and these complexes had anomalously high relaxivities compared to similar complexes lacking a H-bond acceptor. Molecular dynamics simulations supported the formation of a stable intramolecular H-bond, while alternative hypotheses that could explain the higher relaxivity were systematically ruled out. Intramolecular H-bonding represents a useful strategy to limit internal water rotational motion and increase relaxivity of Gd complexes.     

Effect of zeolite properties on ground-state and triplet-triplet absorption, prompt and oxygen induced delayed fluorescence of tetraphenylporphyrin at gas/solid interface

The ground-state and transient absorption, prompt and delayed fluorescence of tetraphenylporphyrin (TPP) adsorbed onto the external surface of different zeolites was monitored using diffuse-reflectance steady-state and laser flash photolysis. The delayed fluorescence (DF) of TPP detected in the presence of O2 is attributed to the energy transfer from 3TPP to 3O2 to form 1O2 and subsequent energy transfer from 1O2 to some other 3TPP within the organised molecular ensembles on the zeolite surface. The spectroscopic and kinetic parameters, namely the yield of DF (2-20% relative to prompt fluorescence), depend on the zeolite properties: the observed differences were correlated with the acid-base properties of the two zeolite series studied in this work (KA, NaA, CaA) and (NaA, NaX, NaY).