Adsorption of Cu2+ Ions from Aqueous Solutions on Nano-Titanate Engelhard Titanosilicate-2 (ETS-2).

Adsorption of Cu2+ ions from aqueous solutions is an increasingly important problem. Nano-titanate ETS-2 (Engelhard Titanosilicate-2) was studied for Cu2+ removal from aqueous solutions through the batch technique at room temperature. Structural and chemical properties of both ETS-2 sorbent and aqueous solution were studied by different characterization tests such as Thermogravimetric Analysis, Energy Dispersive X-ray spectroscopy, X-ray Photoelectron Spectroscopy and Inductively Coupled Plasma measuremen. Copper adsorption capacity was found to increase upon raising the contact time or the pH of the solution. The maximum uptake of Cu2+ (99.9%) by ETS-2 occurred at pH of 6.7 and 30 min of contact time. The Cu2+ removal capacity of ETS-2 was found to be 53.58 mg/g at pH = 5.16, which improved to 54.02 mg/g, when rising the contact time to 90 min. Chemical properties of ETS-2 indicated that ETS-2 surface possessed sodium exchange sites making it a favourable sorbent for metal exchange.

Cu-Cr-O Functionalized ETS-2 Nanoparticles for Hot Gas Desulfurization.

Engelhard Titanium Silicate-2 (ETS-2), a sodium nanotitanate, was surface functionalized by ion exchanging the solid with copper and chromium ions. The ability of this bi-metallic adsorbent to remove H2S at elevated temperatures was assessed using a dynamic breakthrough system and contrasted against an analogous mixed metal oxide, Cu-Cr-O. Unlike Cu-Cr-O, the H2S capacity for Cu-Cr-ETS-2 remains unchanged from 350 °C up to 950 °C. Using ETS-2 as a support for the metals increased the adsorbents surface area and improved its sulfur capacity from 35 mg H2S/g for Cu-Cr-O to 61 mg H2S/g adsorbent for CuCr-ETS-2. The consistent presence of Cu9S5 on the sulfided adsorbents suggests that chromium effectively stabilizes the copper against reduction to metallic copper up to temperatures as high as 950 °C.

A clinoptilolite-PDMS mixed-matrix membrane for high temperature water softening.

A mixed-matrix membrane composed of polydimethylsiloxane (PDMS) as the continuous phase and clinoptilolite, a naturally occurring zeolite, as the active phase has been used to decrease the conductivity of water by more than 80% across the membrane. Testing was carried out using a cross-flow configuration at temperatures as high as 160 °C using a constant transmembrane pressure of 8 bar. The simple fabrication method for the membrane, the durability of the system under the test conditions, and a suitable flux rate make such membranes promising candidates for industrial wastewater treatment.

Monoethanolamine Impregnation of Titanosilicate Zeolite ETS-10.

ETS-10, a mixed octahedral/tetrahedral titanosilicate molecular sieve, has a unique architecture where its 0.8 nm pores are lined exclusively with silicon which imparts a high degree of chemical stability, yet the anionic framework can be modified by cation exchange. In this work, the hydrogen-exchanged form of ETS-10 was impregnated with monoethanolamine and the thermal stability and CO2 adsorption characteristics were analyzed. The surface area of the material was characterized by N2 physisorption, the thermal stability of the material assessed through TG-MS experiments, the CO2 capacity was measured via static volumetric adsorption experiments, and the influence of moisture as a carbamate promoter was investigated through a series of gravimetric CO2 adsorption/desorption cycling experiments. Several measurements converge on ~7 wt% monoethanolamine loading which occupies about half of the available pore volume of the sieve. The results suggest that the monoethanolamine is so effectively retained by the molecular sieve that, while the amine is effectively immobilized, under both humid and dry process streams the monoethanolamine is either chemically or sterically hindered and is unable to react measurable quantities of CO2.

Natural clinoptilolite composite membranes on tubular stainless steel supports for water softening.

Disk membranes generated from high-purity natural clinoptilolite mineral rock have shown promising water desalination and de-oiling performance. In order to scale up production of these types of membranes for industrial wastewater treatment applications, a coating strategy was devised. A composite mixture of natural clinoptilolite from St. Cloud (Winston, NM, USA) and aluminum phosphate was deposited on the inner surface of porous stainless steel tubes by the slip casting technique. The commercial porous stainless steel tubes were pre-coated with a TiO2 layer of about 10 µm. Phase composition and morphology of the coating materials were investigated using X-ray diffraction and scanning electron microscopy. Water softening performance of the fabricated membranes was evaluated using Edmonton (Alberta, Canada) municipal tap water as feed source. Preliminary experimental results show a high water flux of 7.7 kg/(m(2) h) and 75% reduction of hardness and conductivity in a once-through membrane process at 95 °C and feed pressure of 780 kPa. These results show that natural zeolite coated, stainless steel tubular membranes have high potential for large-scale purification of oil sands steam-assisted gravity drainage water at high temperature and pressure requirements.

A study of silver species on silver-exchanged ETS-10 and mordenite by XRD, SEM and solid-state 109Ag, 29Si and 27AI NMR spectroscopy.

Silver zeolites, especially Ag-ETS-10 and Ag-mordenite, actively bind xenon and iodine, two prime contaminants common to nuclear accidents. The evolution of silver species on silver exchanged ETS-10 (Ag/ETS-10) and mordenite (Ag/Mor) has been investigated by exposing the materials to a series of activation conditions in Ar, air and H2. The samples were characterized by XRD, SEM and solid-state 109Ag, 29Si and 27AI MAS NMR. The silver reduction and structural evolution have been illustrated by those techniques. The effectiveness of one sample of each type of sieve was tested for its ability to trap mercury from a gas stream. However, the results from this study demonstrate that the adsorption characteristics of silver-loaded sieves cannot necessarily be predicted using a full complement of structural characterization techniques, which highlights the importance of understanding the formation and nature of silver species on molecular sieves.

Solid-state NMR and TGA studies of silver reduction in chabazite.

Silver-exchanged molecular sieves have shown great promise in applications ranging from antimicrobial materials to the adsorption of xenon and iodide, two key contaminants emitted from nuclear reactors. In this work, solid-state 27Al and 29Si MAS NMR and TGA were used to study silver reduction in silver-exchanged chabazite under various thermal conditions. The solid-state NMR results for both 27Al and 29Si show that there are no major changes in the chabazite during silver reduction in an argon stream; however a progressive structural change does take place in the hydrogen stream. The structural change likely involves breaking the silicon oxygen bond of the Si-O-AI fragment of chabazite, leading to the formation of extra-framework aluminum oxide. The TGA results at temperatures up to 600 degrees C indicate that silver reduction is less complete in an argon stream than in a hydrogen stream. In this paper we propose that silver reduction occurs via the following reactions: 2(Ag + ZO-)+H2O --> 1/2O2+2Ag0 + 2ZOH and nAg + mAg = Ag(m+n)n+ (in an argon stream); and Ag(+) + ZO(-) + 1/2H2 = Ag0 + ZOH and 2ZOH = ZO(-) + Z(+) + H2O (in a hydrogen stream).

Palladium nanoparticles formed on titanium silicate ETS-10.

We report that surface templated and supported palladium nanoparticles self assemble on ETS-10 type molecular sieve surfaces by simple exchange and activation procedures in the absence of a reductant. This procedure is similar to the one previously reported for silver nanoparticle self assembly on ETS-10. We observed a bimodal distribution with particle sizes ranging from 2-5 and 15-30 nm. This simple, economical method generates high concentrations (approximately 12 wt% of total composite) of uniform, metallic palladium nanoparticles that are multiply twinned and thermally stable making them potentially unique for advanced catalytic and electronic applications.

Nanosilver particle formation on a high surface area titanate.

Titanium based molecular sieves, such as ETS-10, have the ability to exchange silver ions and subsequently support self assembly of stable silver nanoparticles when heated. We report that a high surface area sodium titanate (resembling ETS-2) displays a similar ability to self template silver nanoparticles on its surface. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show high concentrations of silver nanoparticles on the surface of this sodium titanate, formed by thermal reduction of exchanged silver cations. The nanoparticles range in size from 4 to 12 nm, centered at around 6 nm. In addition to SEM and TEM, XRD and surface area analysis were used to characterize the material. The results indicate that this sodium titanate has a high surface area (>263 m2/g), and high ion exchange capacity for silver (30+ wt%) making it an excellent substrate for the exchange and generation of uniform, high-density silver nanoparticles.

Mercury removal from flue gases by novel regenerable magnetic nanocomposite sorbents.

Magnetic zeolite composites with supported silver nanoparicles are a new class of multifunctional materials with potential applications as recyclable catalysts, disinfectants, and sorbents. This study evaluated the suitability of the magnetic composites as sorbents for the removal of elemental mercury vapor from flue gases of coal-fired power plants. The sorbents were found to completely capture mercury at temperatures up to 200 degrees C, and the mercury capacity of the sorbents was found to be affected by the state, content, and size of the silver particles in the composite. Cumulative or extended thermal treatments at 400 degrees C were found to improve the mercury capture capacity, allowing the sorbent to be regenerated and recycled multiple times without performance degradation. The magnetic sorbent was readily separated from fly ash by magnetic separation, leaving the fly ash essentially free of sorbent contamination. In initial in-plant tests, the sorbents were able to capture mercury from the flue gases of an operational, full-scale, coal-fired power plant The combination of mercury capacity, ease of separation and regeneration, and recyclability makes these multifunctional magnetic composites excellent candidate sorbentsforthe control of mercury emissions from coal-fired power plants.

A novel method to control the size of silver nanoparticles formed on chabazite.

High density, uniform, surface-supported nanosilver particles can be generated on mineral chabazite by thermal reduction of exchanged silver cations. These nanoparticles have properties unique from those of bulk silver, including antimicrobial activity, which are a function of particle size. In this study, the activation environment is manipulated in order to alter the average size of the silver particles. Nanoparticles with mean diameters of 4.2, 6.1 and 35.0 nm are formed in air, Ar and H2 at 400 degrees C, respectively. Interaction with the surface of highly polarizing chabazite stabilizes the nanoparticles, and unreduced silver ions on the nanosilver surfaces may play a critical role in determining particle size.

Anion-controlled pore size of titanium silicate molecular sieves.

Titanium silicate molecular sieves contain structural units that are fundamentally different from classical aluminosilicates. In addition to ordered octahedral titanium chains, members of the zorite family contain pentagonal titanium units which project into the main adsorption channels of the framework. We report that the effective pore size of these materials can be controlled by substituting halogens at the O7 sites that cap the pentagonal pyramids projecting into the channel. The quantity and type of halogen used determines the adsorptive properties of the molecular sieve. Barium exchange stabilizes these materials over a wide temperature range (nominally 200-400 degrees C). The barium-exchanged materials do not contract appreciably with calcination, as is observed in related Molecular Gate materials, and thus halogen content can control the pore size of the materials. This new approach to pore size control may have important implications for the purification of multiple classes of compounds, including light hydrocarbons and permanent gases.