The beneficial role of nano-sized Fe3O4 entrapped in ultra-stable Y zeolite for the complete mineralization of phenol by heterogeneous photo-Fenton under solar light.

Highly efficient, separable, and stable magnetic iron-based-photocatalysts produced from ultra-stable Y (USY) zeolite were applied, for the first time, to the photo-Fenton removal of phenol under solar light. USY Zeolite with a Si/Al molar ratio of 385 was impregnated under vacuum with an aqueous solution of Fe2+ ions and thermally treated (500-750 °C) in a reducing atmosphere. Three catalysts, Fe-USY500°C-2h, Fe-USY600°C-2h and Fe-USY750°C-2h, containing different amounts of reduced iron species entrapped in the zeolitic matrix, were obtained. The catalysts were thoroughly characterized by absorption spectrometry, X-ray powder diffraction with synchrotron source, followed by Rietveld analysis, X-ray photoelectron spectroscopy, N2 adsorption/desorption at -196 °C, high-resolution transmission electron microscopy and magnetic measurements at room temperature. The catalytic activity was evaluated in a recirculating batch photoreactor irradiated by solar light with online analysis of evolved CO2. Photo-Fenton results showed that the catalyst obtained by thermal treatment at 500 °C for 2 h under a reducing atmosphere (FeUSY-500°C-2h) was able to completely mineralize phenol in 120 min of irradiation time at pH = 4 owing to the presence of a higher content of entrapped nano-sized magnetite particles. The latter promotes the generation of hydroxyl radicals in a more efficient way than the Fe-USY catalysts prepared at 600 and 750 °C because of the higher Fe3O4 content in ultra-stable Y zeolite treated at 500 °C. The FeUSY-500°C-2h catalyst was recovered from the treated water through magnetic separation and reused five times without any significant worsening of phenol mineralization performances. The characterization of the FeUSY-500°C-2h after the photo-Fenton process demonstrated that it was perfectly stable during the reaction. The optimized catalyst was also effective in the mineralization of phenol in tap water. Finally, a possible photo-Fenton mechanism for phenol mineralization was assessed based on experimental tests carried out in the presence of scavenger molecules, demonstrating that hydroxyl radicals play a major role.

Use of Zeolites in the Capture and Storage of Thermal Energy by Water Desorption-Adsorption Cycles.

In this work, four zeolite-bearing materials (three naturally occurring and one of synthetic origin) were considered for thermal energy capture and storage. Such materials can store thermal energy as heat of desorption of the water present therein, heat that is given back when water vapor is allowed to be re-adsorbed by zeolites. This study was carried out by determining the loss of water after different activation thermal treatments, the water adsorption kinetics and isotherm after an activation step of the zeolites, the intergranular and intragranular porosity, and the thermal conductivity of the zeolite-bearing materials. Moreover, the thermal stability of the framework of the zeolites of the four materials tested was investigated over a large number of thermal cycles. The results indicate that zeolite 13X was the most suitable material for thermal energy storage and suggest its use in the capture and storage of thermal energy that derives from thermal energy waste.

Removal of sulfanilamide by tailor-made magnetic metal-ceramic nanocomposite adsorbents.

Three tailor-made magnetic metal-ceramic nanocomposites, obtained from zeolite A (ZA1 and ZA2) and a natural clinoptilolite (LB1), have been used as adsorbents to remove sulfanilamide (SA), a sulfonamide antibiotic of common use, from water. A patented process for the synthesis of nanocomposites has been suitably modified to maximize the efficiency of the SA removal, as well as to extend the applicability of the materials. The role played by the main process parameters (kinetic, pH, initial concentration of SA) has been characterized. The significant effect of the pH on the SA removal has been explained identifying two possibly coexisting mechanisms of SA adsorption, based on polar and hydrophobic interactions, respectively. The adsorption kinetics have been in all cases described by the pseudo second-order model. The adsorption isotherms obtained with ZA1 have been satisfactorily described by the Langmuir model, suggesting a monolayer adsorption of SA on the magnetic nanocomposites resulting from a uniform surface energy. The isotherms obtained with LB1 could be described by a more complex approach, deriving by the additive superposition of Langmuir and Sips models. In order to ensure an effective removal of the antibiotic and a proper recycle of the magnetic adsorbents, a sustainable regeneration procedure of the exhausted adsorbent has been developed, based on the treatment with a dilute solution of NaOH.

Separation of Biological Entities From Human Blood by Using Magnetic Nanocomposites Obtained From Zeolite Precursors.

In this work, three novel magnetic metal-ceramic nanocomposites were obtained by thermally treating Fe-exchanged zeolites (either A or X) under reducing atmosphere at relatively mild temperatures (750-800 °C). The so-obtained materials were thoroughly characterized from the point of view of their physico-chemical properties and, then, used as magnetic adsorbents in the separation of the target gene factors V and RNASE and of the Staphylococcus aureus bacteria DNA from human blood. Such results were compared with those obtained by using a top ranking commercial separation system (namely, SiMAG-N-DNA by Chemicell). The results obtained by using the novel magnetic adsorbents were similar to (or even better than) those obtained by using the commercial system, both during manual and automated separations, provided that a proper protocol was adopted. Particularly, the novel magnetic adsorbents showed high sensitivity during tests performed with small volumes of blood. Finally, the feasible production of such magnetic adsorbents by an industrial process was envisaged as well.

Preparation and Characterization of Magnetic and Porous Metal-Ceramic Nanocomposites from a Zeolite Precursor and Their Application for DNA Separation.

In this work, metal-ceramic nanocomposites were obtained through short (up to 2 h) thermal treatments at relatively moderate temperatures (750­800 °C) under a reducing atmosphere, using Fe-exchanged zeolite A as the precursor. The as-obtained materials were characterized by X-ray powder diffraction analysis, N2 adsorption at ­196 °C, and highresolution transmission electron microscopy. The results of these analyses showed that the nanocomposites consisted of a dispersion of metallic Fe nanoparticles within a porous ceramic matrix, mainly based on amorphous silica and alumina. These nanocomposites were magnetically characterized, and their magnetic response was studied. Finally, the obtained metal-ceramic nanocomposite materials were used in the separation of Escherichia coli DNA from a crude cell lysate. The results of the DNA separation experiments showed that the obtained materials could perform this type of separation.

Effect of the mineralizer solution in the hydrothermal synthesis of gadolinium-doped (10% mol Gd) ceria nanopowders.

BACKGROUND: Gadolinium-doped ceria is an attractive electrolyte material for potential application in solid oxide fuel cells (SOFCs) operating at intermediate temperatures typically with 10%-20% substitution of Ce+4 by Gd+3. In particular, 10% gadolinium-doped ceria seems to have the highest values of conductivities among the other dopant compositions. METHODS: Nanosized powders of gadolinium-doped ceria were prepared by hydrothermal treatment using coprecipitate as a precursor and in the presence of 3 different mineralizer solutions. The powders obtained were characterized by X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy and thermal analysis, while the electrical behavior of the corresponding pellets were ascertained by AC impedance spectroscopy. RESULTS: Nanocrystalline gadolinium-doped ceria powders with fluorite cubic crystal structure were obtained by hydrothermal treatment. Independent of the mineralizer used, these powders were able to produce very dense ceramics, especially when selecting an optimized sintering cycle. In contrast, the electrical behavior of the samples was influenced by the mineralizer solution, and the samples synthesized in the neutral and alkaline solutions showed higher values of electrical conductivity, in the range of temperatures of interest. CONCLUSIONS: By the coprecipitation method, it has been possible to synthesize nanosized gadolinium-doped cerium oxide in a fluorite structure, stable in a wide range of temperatures. Hydrothermal treatment directly on the as-synthesized coprecipitates, without any drying step, had a very positive effect on the powders, which can be sintered with a high degree of densification, especially with an optimized sintering cycle. Furthermore, the electrical behavior of these samples was very interesting, especially for the samples synthesized using neutral mineralizer solution and basic mineralizer solution.

Application of highly porous materials for simazine removal from aqueous solutions.

The removal of simazine from both pure water and solute-bearing well water was studied by adsorption on two solids: zeolite H-Y from the commercial Na form and porous silica tailored by the sol-gel technique. The pH dependence of the amount adsorbed in a closed system at constant total simazine content as well as the apparent isotherms of adsorption was measured in all four cases. The low ion content of natural water suffices to alter the adsorption features in the case of silica, but not with zeolite H-Y. Iteration of the adsorption process onto constant amounts of solid allowed bringing the residual simazine concentration below 0.05 mg/L, the value allowed by Italian laws in wastewaters.

The role of outer surface/inner bulk Brønsted acidic sites in the adsorption of a large basic molecule (simazine) on H-Y zeolite.

The simple means adopted for investigating H-Y zeolite acidity in water is the pH-dependence of the amount of a basic molecule adsorbed under isochoric conditions, a technique capable of yielding, under equilibrium conditions, an estimate of the pKa value of the involved acidic centres: the behaviour with temperature of adsorbed amounts yields instead some information on thermodynamics. Simazine (Sim, 2-chloro-4,6-bis(ethylamino)-s-triazine) was chosen as an adsorbate because its transverse dimension (7.5 Å) is close to the opening of the supercage in the faujasite structure of H-Y (7.4 Å). In short term measurements, Sim adsorption at 25 °C occurs only at the outer surface of H-Y particles. Two types of mildly acidic centres are present (with pKaca. 7 and ca. 8, respectively) and no strong one is observed. Previous adsorption of ammonia from the gas phase discriminates between the two. The former survives, and shows features common with the silanols of amorphous silica. The latter is suppressed: because of this and other features distinguishing this site from silanol species (e.g. the formation of dimeric Sim2H(+) species, favoured by coverage and unfavoured by temperatures of adsorption higher than ambient temperature) a candidate is an Al based site. We propose a Lewis centre coordinating a water molecule, exhibiting acidic properties. This acidic water molecule can be replaced by the stronger base ammonia, also depleting inner strong Brønsted sites. A mechanism for the generation of the two sites from surface Brønsted species is proposed. Long term adsorption measurements at 25 °C already show the onset of the interaction with inner strongly acidic Brønsted sites: because of its size, activation is required for Sim to pass the supercage openings and reach inner acidic sites. When adsorption is run at 40-50 °C, uptake is much larger and increases with temperature. Isochoric measurements suggest a pKa value of ca. 3 compatible with its marked acidic nature, although attainment of equilibrium conditions is questionable. Measurements at 60 °C (both isochors and DRIFT) show the onset of changes at the outer surface brought about by the presence of hot water. Control experiments run with USY (Ultra Stabilized zeolite Y), featuring wormholes and cavities rendering accessible internal sites, show the extensive involvement of internal Brønsted sites already at 25 °C.

Adsorption of simazine on zeolite H-Y and sol-gel technique manufactured porous silica: A comparative study in model and natural waters.

In this work, we studied the removal of simazine from both a model and well water by adsorption on two different adsorbents: zeolite H-Y and a porous silica made in the laboratory by using the sol-gel technique. The pH dependence of the adsorption process and the isotherms and pseudo-isotherms of adsorption were studied. Moreover, an iterative process of simazine removal from both the model and well water, which allowed us to bring the residual simazine concentration below the maximum concentration (0.05 mg L(-1)) of agrochemicals in wastewater to be released in surface waters or in sink allowed by Italian laws, was proposed. The results obtained were very interesting and the conclusions drawn from them partly differed from what could reasonably be expected.

Cyclic process of simazine removal from waters by adsorption on zeolite H-Y and its regeneration by thermal treatment.

Removal of the agrochemical simazine from polluted waters through adsorption by zeolite Y in its protonic form was studied. The investigated parameters were: pH, time, initial simazine concentration and solid/liquid ratio. An iterative process of simazine removal from waters is proposed, featuring: (i) final agrochemical concentration well below 0.05 mg/dm(3), the maximum concentration allowed by Italian laws in wastewaters; (ii) regeneration of the adsorbent by a few minutes thermal treatment in air at about 500°C, which results in the combustion of simazine without damage of the adsorbent; (iii) destruction of the agrochemical compound by combustion.