Microporous Titanosilicate ETS-10 Research Articles

Removal of rare-earth elements from aqueous solutions by microporous titanosilicate ETS-4

The mining of Rare-Earth Elements (REE) is an unsustainable practice that raises environmental, economic, and societal concerns. As a result, there is a need to develop suitable technologies for the removal of these elements from contaminated waters. Sorption is a clean and efficient method for decontaminating water, and microporous titanosilicates have shown promise for REE removal. However, the influence of solution parameters on this process remains poorly understood. In this study, the effect of pH (4–8), concentration (1–5 μM), and sorbent amount (20–180 mg L−1) on the removal of a mixture of REE3+ (Y, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy) from water by the microporous titanosilicate ETS-4 (Na9Ti5Si12O38(OH)·12H2O) was assessed. A Box-Behnken design was used to investigate the experimental conditions, and the results were presented as three-dimensional response surfaces. The removal mechanism involves the ion exchange of Na+ by REE3+, with pH being the main variable in the process due to competition with H+. Increasing pH resulted in higher removal, with 100% removal achieved at ETS-4 amounts of 180 mg L−1 and REE concentrations of 1 μM. Most REE3+ removal occurs within the first 15 min, with little difference between metals (except for Y, which exhibits lower removal). At ETS-4 amounts of 20 mg L−1, REE are highly concentrated in the sorbent, reaching 145 mg g−1 (15% of the sorbent's mass, post-sorption). These results demonstrate that even low amounts of ETS-4 have the potential to remove high concentrations of REE3+ from aqueous solutions with pH levels similar to those found in natural systems.

Improved therapeutic nitric oxide delivery by microporous Cu-bearing titanosilicate

Copper was incorporated into microporous titanosilicate ETS-4 framework via the in situ hydrothermal synthesis to achieve a more controlled and extended nitric oxide (NO) release profile. Exogeneous delivery of this gasotransmitter may be effective in the therapeutic setting and titanosilicates, in particular ETS-4, has already evidenced its potential as a NO carrier. Copper ions have high affinity for NO coordination and their substitution within the ETS-4 framework was confirmed by energy dispersive X-ray spectrometry (EDS). Samples were also characterized by PXRD, SEM microscopy, UV–Vis and Raman spectroscopy, TG and DSC. ETS-4Cu presents higher NO adsorption capacity (up to 4.5 mmol g−1 solid) comparing with the parent material, excellent stability in biological media and exhibits high compatibility in different cell lines, including primary keratinocytes (HEKn). Its NO release profile in biological conditions demonstrated a controlled release over at least 4 h, never achieved by any other porous materials so far. This may be reflected by its peculiar NO adsorption mechanism through the formation of stable nitro species on the framework.

Ionic conductivity of microporous titanosilicate ETS-10 and ion-exchanged Mn+-ETS-10 (where, Mn+ = Li+, Na+, Mg2+, Zn2+, Ca2+) thin films prepared by secondary growth method

Impedance spectroscopy was used to investigate the long-range ionic conductivity of the microporous, titanosilicate (Na,K)-ETS-10 and ion-exchanged Mn+-ETS-10 (where, Mn+ = Li+, Na+, Mg2+, Zn2+, Ca2+) thin films prepared by secondary growth method. To figure out the effect of grain boundary on ionic conduction, as-synthesized (Na,K)-ETS-10 films possessing different thicknesses of columnar grain structure (i.e., films prepared via 4h-, 6h-, 8h-, and 10h-growth) were tested. The conductivities of the films with different thicknesses at 723 K were in the range of ∼10−3 Ω−1cm−1. However, activation energies of the films decreased from 52.8 to 47.3 kJ mol−1 (i.e., 0.6 to 0.5 eV) for 4h-(Na,K)-ETS-10 to 10h-(Na,K)-ETS-10 films, respectively. The as-synthesized (Na,K)-ETS-10 film prepared via 6h-growth (denoted as (Na,K)-6h-ETS-10) and monovalent cation-exchanged samples Li- and Na-6h-ETS-10 films exhibit conductivities of 2.1 × 10−3, 2.4 × 10−4, and 2.7 × 10−4 Ω−1cm−1, respectively, at 723 K and activation energies of 50.1, 55.5, and 55.4 kJ mol−1, respectively, in the temperature range 573–773 K. Divalent cation-exchanged samples Mg-, Zn- and Ca-6h-ETS-10 films exhibit conductivities of 2.3 × 10−4, 2.9 × 10−4, and 8.8 × 10−5 Ω−1cm−1, respectively, at 723 K and activation energies of 62.5, 57.9, and 65.2 kJ mol−1, respectively, in the temperature range 573–773 K. The data shown here indicate that ionic conductivity of intergrown (Na,K)-ETS-10 films prepared by secondary growth method were significantly enhanced with respect to pressed pellets of powder zeolite and zeo-type materials which imply the importance of engineering the microstructure of the zeolite film to improve the conductivity of zeolites and zeo-type materials.

Structure Determination and Time-Resolved Raman Spectroscopy of Yttrium Ion Exchange into Microporous Titanosilicate ETS-4.

The ion exchange of yttrium, one of the five most critical rare-earth elements as outlined by the U.S. Department of Energy, into ETS-4 is a dynamic, multistep ion exchange process. The ion exchange process was followed using in situ time-resolved Raman spectroscopy, and the crystal structures of the pre-exchange and post-exchange forms were determined by single-crystal X-ray diffraction. In situ Raman spectroscopy is an ideal tool for this type of study, as it measures the spectral changes that are a result of molecular geometry changes at fast time intervals, even where symmetry and unit volume changes are minimally detected by X-ray diffraction. By tracking the stepwise changes in the peak positions and intensities in the spectra, where we focused primarily on the strong spectral features corresponding to titania quantum wires and three-membered-ring bending and breathing modes, we constructed molecular models to explain the changes in the Raman spectrum during ion exchange. The multistep ion exchange process started with rapid absorption of Y into the Na2 site, causing titania quantum wires to kink. After this initial uptake, the exchange process slowed, likely caused by hydration coordination changes within the channels. Next, Y exchange accelerated again, during which time the Y site moved closer to the framework O2-. Crystal structures of the maximal Y exchanged ETS-4 material were determined and confirmed the splitting of the Y site. Inductively coupled plasma optical emission spectroscopy was also used to quantify the extent of Y exchange and to measure if there were indications of titania leaching from the framework.

Pt-CoOx nanoparticles supported on ETS-10 for preferential oxidation of CO reaction

In this paper we prepare bimetallic Pt-CoOx nanoparticles which are further supported in microporous titanosilicate ETS-10. This support has been previously demonstrated as a good candidate for this reaction in the presence of CO2 and H2O. The bimetallic nanoparticles and the supported catalysts containing different loadings of nanoparticles have been extensively characterized and tested in the PROX reaction. The characterization of the nanoparticles discarded the formation of a metallic alloy, although Co and Pt are intimately in contact in the nanoparticle as the HAADF-STEM images revealed. XPS confirmed that the calcined nanoparticles would consist of metallic platinum and cobalt and Pt oxides. The catalyst containing 1.4wt.% of PtCo nanoparticles can achieve complete CO conversion in the temperature range 120–150°C working at WHSV=30Lh−1g−1.

Storage and delivery of nitric oxide by microporous titanosilicate ETS-10 and Al and Ga substituted analogues

Exogenous administration of nitric oxide may be a therapy for several pathologies because this molecule regulates many biological systems. Here, the storage and release of NO by microporous titanosilicate ETS-10 and samples where the silicon was substituted by aluminium (ETAS-10) or gallium (ETGS-10) are studied. The Al- and Ga-doped materials exhibit an increase in the storage capacity of 95% and 55%, respectively, the highest values observed, so far, for microporous titanosilicates. ETAS-10 releases more NO and ETGS-10 almost the same amount as ETS-10. In ETAS-10 and ETGS-10, the irreversibly adsorbed NO amount increases relatively to ETS-10. Tests of NO release in haemoglobin solutions indicate that biologically relevant amounts are release and that ETS-10 and ETGS-10 display a release slower than ETAS-10, more adequate for a sustained delivery. Cytotoxicity studies show that the samples have very low toxicity (cell viability above 87%, after 72 h) at high concentration (0.45 mg cm−3). Tests at variable ETS-10 concentration further confirm the low cytotoxicity of this material, even at high concentrations (up to 1.8 mg cm−3).

Synthesis of nanoporous materials to dispense pheromone for trapping agricultural pests

In this study, to develop an effective pheromone dispenser, zeolite A was modified with cetyltrimethylammonium ion as a cationic surfactant. Its capacity for aggregation of the pheromone components was confirmed by total organic carbon analysis before and after field testing. Furthermore, weekly examinations of soybean fields (Daewonkong variety) and plum orchards were undertaken from April to August in 2014 to determine the number of Riptortus pedestris trapped by the aggregation pheromone dispersed from the pheromone loaded surfactant-modified zeolite A (SMZ-A) in a netted cylindrical trap. The powder-type SMZ-A exhibited superior performance when compared to other dispensers in a comparative study of attractiveness using cylinder- and powder-type surfactant-modified zeolite A (CSMZ-A and PSMZ-A), microporous titanosilicate ETS-10, and a commercial product (CP). The performance followed the trend PSMZ-A > > CSMZ-A > ETS-10 > CP, suggesting that the SMZ-A material has potential as a slow-releasing pheromone dispenser.

Synergistic Effect of Combining Titanosilicate and 1-Ethyl-3-Methylimidazolium Acetate in Mixed Matrix Membranes for Efficient C02 Separation

The separation and capture of CO 2 from these sources is becoming important for greenhouse emission. The membrane-based separation process use to remove CO 2 takes advantages in energy efficient and environmentally friendly aspects and has been recognized as an important technology for CO 2 capture and gas separation. The novel mixed matrix membranes (MMMs) were fabricated by incorporating microporous titanosilicate ETS-10 and a highly CO 2 absorbent ionic liquid , [EMIM][Ac] into a Chitosan (CS) matrix to improve CO 2 separation performance, and were prepared, characterized and tested for CO 2 and N 2 . The solubility values show that the CO 2 solubility increases upon addition of ETS-10 particles. The N 2 solubility in the ETS-10/[EMIM][Ac]/CS was reduced, while CO 2 solubility remained constant. FT-IR spectra revealed a good interaction between the components in the MMMs. Subtle differences in the intensity and position of all individual bands, were observed in the region between 3600 and 2700 cm -1 and 1700 and 900 cm -1 . These indicated bonding of the components in the film, confirming the good interaction existing among the components, and that may account for the higher flexibility of the hybrid membrane materials imparted to both CS and ETS-10/CS MMMs, , due to the singular interaction between CS and [EMIM][Ac]. Keywords: CO 2 solubility, CO 2 separation, microporous titanosilicate ETS-10, Chitosan, mixed matrix membranes (MMMs).

Catalytic isomerisation of α-pinene oxide in the presence of ETS-10 supported ferrocenium ions

Ferrocenium ions, [Fc]+, have been immobilised in the microporous titanosilicate ETS-10 by ion exchange of Na+/K+ ions under hydrothermal conditions. The resultant hybrid inorganic-organometallic (ETS-10/[Fc]+) material was characterised by elemental analysis, diffuse reflectance UV–Vis spectroscopy, FT-IR spectroscopy, powder X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The ETS-10/[Fc]+ sample was tested as a catalyst for the isomerisation of α-pinene oxide (PinOx) at 35 °C. With α,α,α-trifluorotoluene (TFT) as solvent, campholenic aldehyde (CPA) was the main product formed in 38% yield at 100% conversion and 30 min reaction. Other reaction products included trans-carveol, iso-pinocamphone and trans-pinocarveol. The same PinOx conversion and CPA yield could be reached within 1 min reaction time by increasing the reaction temperature (to 55 °C) and the Fe:PinOx molar ratio. Other solvents (hexane, CH3CN, toluene) led to poorer results than TFT. Characterisation of the used catalyst, together with an analysis of the catalytic activity of the liquid phase obtained after contact of ETS-10/[Fc]+ with TFT, indicated that the ETS-10/[Fc]+ sample was resistant toward leaching of iron-containing active species. When the recovered solid was reused in a second batch run, catalytic activity was lower than in the first run, while selectivity to CPA was higher.

Synthesis and Characterization of ETS-10/Chitosan Nanocomposite Membranes for Pervaporation

Chitosan (CS) and microporous titanosilicate ETS-10/CS mixed matrix membranes (MMMs) were prepared. The pervaporation performance was tested on the water-ethanol mixtures in the range 85–96 wt.% ethanol. The permeate flux increased from 0.45 to 0.55 kg m−2 h−1 at 50°C for the ETS-10/CS MMM with respect to the pure CS membranes. Characterization by SEM and TEM, XRD, DSC, and TGA allowed inferring an intimate contact between the dispersed ETS-10 and the continuous chitosan phase. The 5 wt.% loading of titanosilicate scarcely decreased the hydrophilic character of the mixed matrix membrane but increased the molecular sieving effect on the transport and separation properties, thus affecting the membrane behavior on pervaporation.

Microporous titanosilicates Cu2+- and Co2+-ETS-4 for storage and slow release of therapeutic nitric oxide.

Although nitric oxide (NO) is very toxic in low concentrations it plays a key role in the regulation of several biological systems of the human body. The potential of copper and cobalt ion-exchanged microporous titanosilicate ETS-4 for therapeutic storage and release of nitric oxide was assessed. Materials were characterized by powder X-ray diffraction, nitrogen adsorption at -196 °C and chemical analysis. Cation-exchanged materials showed an increased surface area and minor structural changes, relative to the parent Na-ETS-4. The NO storage and release kinetics was studied in the gas and liquid phases. NO loaded materials were also studied by diffuse reflectance infrared Fourier transform spectroscopy. The NO amounts released in the liquid phase were within the physiological range (nanomolar), while the release kinetics was slow (0.023 min-1 for 85% release). The NO loading and release from ETS-4 were affected by the presence of Cu2+ and Co2+ cations. Assays with HeLa cells indicated that the materials have low cytotoxicity, which depends on the ion-exchanged cation. The performance of ETS-4 improved when the extra-framework Na+ cations were exchanged by Cu2+ and Co2+.

Modelling ion exchange kinetics in zeolyte-type materials using Maxwell-Stefan approach

AbstractIn this essay, the Maxwell-Stefan (MS) formalism was adopted to model the removal of cadmium(II) and mercury(II) ions from aqueous solutions using microporous titanosilicate ETS-4. The embodied transport mechanism is surface diffusion, since the small pore diameters of such zeolite-type materials imply that counter ions never escape from the force field of the matrix co-ions, mainly owing to the strong and long range electrostatic interactions. The parameters of the global model are the MS diffusivities of ion–ion and ion–solid pairs, and a convective mass transfer coefficient. The average absolute relative deviations (AARD) achieved for Cd2+/Na+/ETS-4 and Hg2+/Na+/ETS-4 systems were only 3.47 and 7.34%, respectively. The model calculates concentration profiles and their evolution along time under transient regime, being able to represent the initial steep branches of removal curves and subsequent transition to equilibrium, where kinetic curves are frequently very difficult to fit. The well-known ...

Atomic Resolution Analysis of Microporous Titanosilicate ETS‐10 through Aberration Corrected STEM Imaging

It′s all your fault! Microporous titanosilicate ETS-10 crystals have been analyzed by advanced electron microscopy techniques. With the last generation of spherical aberration corrected electron microscopes, truly atomic resolution images have been recorded. Owing to the extremely high-resolution images that have been obtained, the multiple defects (stacking faults, lack of porosity and “double-pores”) present in this type of material can be analyzed in great detail.

Impact of photogenerated charge behaviors on luminescence of Eu3+-incorporated microporous titanosilicate ETS-10

A series of Eu3+-incorporated ETS-10 samples were successfully prepared based on the traditional ion exchange method. The relationship between photogenerated charge behaviors and luminescent properties has been investigated in detail. It has been demonstrated that as a result of the charge transfer from the titanate quantum wires to Eu3+ crystal field states, the host matrix ETS-10 functions as the sensitizer of Eu3+ to enhance the red luminescence, while Eu3+ cations contribute to the recombination of photogenerated charges. The behavior of photogenerated charges has significant impact on the luminescent properties of Eu3+-incorporated ETS-10 materials.

“Extracting” the Key Fragment in ETS-10 Crystallization and Its Application in AM-6 Assembly

The mechanism of crystallization of microporous titanosilicate ETS-10 was investigated by Raman spectroscopy combined with (29)Si magic-angle spinning (MAS) NMR spectroscopy, DFT calculations, and SEM imaging. The formation of three-membered ring species is shown to be the key step in the hydrothermal synthesis of ETS-10. They are formed by means of a complex process that involves the interaction of silicate species in the reaction mixture, which promotes the dissolution of TiO(2) particles. These insights into the mechanism of ETS-10 growth led to the successful development of a new synthesis route to the vanadosilicate AM-6 that involves the use of intermediates that contain three-membered ring species as an initiator.

Structure and Basicity of Microporous Titanosilicate ETS-10 and Vanadium-Containing ETS-10

ETS-10 has attracted considerable attention as a base catalyst. It is desirable to confirm the location of basic sites. Vanadium-substituted ETS-10 also attracts much attention for the interesting feature that the Ti can be fully replaced by V without changing its topology. It is important to characterize the local environment upon V substitution for understanding the property and reactivity of ETVS-10. The structural and acid–base properties of pure titanosilicate ETS-10 and a series of vanadium-substituted ETVS-10 with different framework V content were studied by a combination of Raman spectroscopy and FTIR of absorbed acetylene and carbon monoxide as molecular probes. The substitution of up to 70% of Ti atoms with V in the structure of ETS-10 results in ETVS-10 materials with a homogeneous distribution of Ti and V species. At higher V concentrations, a distinct phase separation between the vanadium-rich domains is observed. The intrinsic basicity of ETVS-10 as revealed by FTIR spectroscopy of adsorbed...

Preparation and Photocatalytic Activity of Lanthanide Loaded Microporous Titanosilicate ETS-10 Catalysts

The three dimensional microporous titanosilicate, ETS-10, was synthesized by a hydrothermal synthesis route using TiCl 4 and a sodium silicate aqueous solution as starting materials. Lanthanide (La, Ce, Pr, Nd) loaded ETS-10 catalysts were prepared by the impregnation method. The catalysts were characterized by X-ray diffraction, 29 Si magic angle spinning NMR, UV-Vis diffuse reflectance spectroscopy, N 2 adsorption-desorption measurement, and X-Ray fluorescence spectroscopy. The degradation of methyl orange under near-UV light was used to investigate the photocatalytic activity of the catalysts in aqueous suspensions. The lanthanide loaded ETS-10 catalysts exhibit higher activity than the unmodified ETS-10. The combination of loading lanthanide and increasing the surface defects of ETS-10 by a HF treatment gave an enhancement of the photocatalytic activity, which became comparable with that of anatase TiO 2 . 以水玻璃和四氯化钛为原料, 在不使用有机模板剂、氟离子和晶种的条件下, 用水热法合成了钛-硅沸石 ETS-10, 将 La、Ce、Pr 和 Nd 四种稀土元素负载到合成的 ETS-10 上. 通过 X 射线粉末衍射、N 2 吸附-脱附、 29 Si 魔角旋转核磁共振、紫外漫反射光谱、X 射线荧光光谱等表征手段对负载前后的 ETS-10 进行了表征. 以有机染料甲基橙为底物, 考察了负载各种稀土及氢氟酸腐蚀对 ETS-10 的光催化活性的影响. 结果表明, 四种稀土元素的引入均可有效提高 ETS-10 的光催化活性. 反应活性提高的程度与稀土元素负载量有关. 对 ETS-10 同时进行氢氟酸腐蚀和稀土元素的负载, 可以将 ETS-10 的光催化活性提高近一倍, 与锐钛矿相 TiO 2 相当, 但前者更易分离. Microporous titanosilicate, ETS-10, was prepared and further modified by loading lanthanide or a HF treatment. The resulting catalysts showed a high photocatalytic activity comparable with that of anatase TiO 2 .

Fixed-bed removal of Hg 2+ from contaminated water by microporous titanosilicate ETS-4: Experimental and theoretical breakthrough curves

The present study reports the assembly and operation of a fixed bed using the microporous titanosilicate ETS-4 as sorbent. Sorption–desorption cycles were carried out on an ETS-4 fixed-bed, for the removal of Hg 2+ from contaminated water. The sorption capacity of the ETS-4 in the column in two consecutive cycles remained constant (33.6 and 33.3 mg g −1, respectively); however due to certain difficulties encountered during ETS-4 packaging and operation mode, breakthrough curves corresponding to these cycles showed dissimilar patterns. A concentration gradient of an EDTA-Na 2 solution (0.05–0.25 M) was efficient for bed regeneration, achieving an elution efficiency of 98%. The elution curve had an asymmetrical shape, the concentration peak was attained in less than 5 min, and the concentration factor was 920. Four kinetic models, namely Thomas, Bohart–Adams, Clark and Yoon–Nelson, were applied to predict the breakthrough curves and to estimate the characteristic parameters of the column, which are the basis for the process design at a real scale. The operation of an ETS-4 fixed-bed for the treatment of Hg 2+ contaminated waters was shown to be feasible, despite some limitations mainly related with its loose packing.

Slow Release of NO by Microporous Titanosilicate ETS-4

A novel approach to designing nitric oxide (NO) storage and releasing microporous agents based on very stable, zeolite-type silicates possessing framework unsaturated transition-metal centers has been proposed. This idea has been illustrated with ETS-4 [Na(9)Si(12)Ti(5)O(38)(OH)·xH(2)O], a titanosilicate that displays excellent NO adsorption capacity and a slow releasing kinetics. The performance of these materials has been compared to the performance of titanosilicate ETS-10, [(Na,K)(2)Si(5)TiO(13)·xH(2)O], of benchmark zeolites mordenite and CaA, and of natural and pillared clays. DFT periodic calculations have shown that the presence of water in the pores of ETS-4 promotes the NO adsorption at the unsaturated (pentacoordinated) Ti(4+) framework ions.

Temperature- and Vacuum-Induced Framework Contraction of Na-ETS-4

For the first time, reduced pressure to induce a framework contraction of the microporous titanosilicate ETS-4 is used. A vacuum of 10(-2) Torr decreases the temperature of structural contraction from 200 degrees C to near room temperature and presents a potential alternative to the temperature-induced and anion-controlled molecular gate effect. The dimensions and the reversibility of the temperature- and vacuum-induced framework contractions are evaluated by in situ X-ray diffraction experiments. On the basis of these studies, it is revealed that Na-ETS-4 possesses a more rigid framework than Sr-ETS-4, which discloses a way to control the framework flexibility of ETS-4.