27 research outputs found
Micro-sized TiO2 photocatalyst for the purification of air from acetone and acethaldeide
No full textIn the last years increasingly restrictive regulations about the concentration limit of
pollutants in air enhanced the development of more efficient treatment processes. In
particular, advanced oxidation processes (AOPs) are chemical oxidation technologies
that rely on the formation of the hydroxyl radical (OH ̇) to further oxide organic
contaminants which are completely mineralized or converted to less harmful products.
AOPs based on UV radiation involve photocatalysts, such as titanium dioxide (TiO2)
mostly in nanometric size. However, nanoparticles give rise to many problems such as
the catalyst-recovering, hindering their commercial application, other than possible
damages on both human safety and environment. The present paper reports a
comparative study on the application of nano (P25 by Evonik) and micro-sized (1077 by
Kronos) TiO2 samples as photocatalyst on degradation of acetone (AC) and
acetaldehyde (AD). Photocatalytic degradations of
both pollutants were performed in a Pyrex glass
cylindrical reactor of 5 L with 0.05 g of photocatalyst.
The gaseous mixture in the reactor was obtained by
mixing hot chromatographic air, humidified at 4, 40
and 75%, and an initial concentration of pollutant of
400 ppmV verified by an online micro-GC. The irradiation is carried out by an iron
halogenide lamp (Jelosil, model HG 500) emitting in the 315-400 nm wavelength range
(UV-A) with power of 30 W/m2. As shown in Fig. 1 the activity of the micro-TiO2 is
comparable with that of the nano-sized one even if it is a little bit slower. In both cases,
micro-GC analyses detected the formation of CO2 after the degradation: experimental
results indicate the formation of CO2 at 100%, confirming a full degradation of the
starting molecule (acetone).Considering these outcomes, the employment of microsized
TiO2 as a photocatalyst turns out to be a valid alternative to the nano-sized
catalysts. Moreover, in order to complete this study, TiO2 samples have been also doped
with F to verify the influence of such a dopant on the material photoefficiency
On the Role of Morphology of CoFeO4 Spinel in Methanol Anaerobic Oxidation
No full textA CoFe2O4 inverse spinel calcined at two
different temperatures (450 and 750 °C), in order to modulate
the growth of the crystallites, has been employed in methanol
anaerobic oxidation. A correlation between physicochemical
properties and catalytic performances of the material has been
pursued. The study of both surface and bulk properties has
been carried out by means of different experimental
techniques, among which are X-ray diffraction (XRD),
transmission electron microscopy (TEM), and in situ FTIR
spectroscopy. The FTIR study of both bulk and surface
spectral features reveals that the calcination step is responsible
for the different type of exposed surface sites and as a
consequence for the different catalytic behavior. As the use of
the spinel as the catalyst for methanol transformation into H2 necessarily implies a regeneration step with steam, in order to
recover the oxidative capacity of the solid, both surface and bulk features of the reoxidized solids have been also studied. All
results reveal that the two samples, originally morphologically quite different from one another, become very similar after just one
redox cycle. Still, it has been also demonstrated that both used materials irreversibly modify their surface properties after the reduction/oxidation process
Synthesis and structural characterisation of CuII-based MOFs constructed by combining functionalised 1,4-bis(1H-imidazol-1-Yl)benzene ligands with copper sulfate
No full textAnion-pillared metal-organic frameworks (APMOFs) are a class of coordination polymers in which divalent anions connect two adjacent layers of a 2D network generated by neutral ligands and cationic metal centres. This class of MOFs is commonly composed by materials built using pyridine-based ligands and octahedral fluorinated anions as linear pillars. Only recently, the use of nitrogen based five-membered ring ligands and/or tetrahedral anions, such as sulfate, has been reported. The combination of 1,1′-(2-(trifluoromethyl)-1,4-phenylene)bis(1H-imidazole) (bibCF3) ligand with copper(ii) sulfate generates a 2D MOF (UdP-20) of minimal formula [CuSO4(bibCF3)1.5]·3H2O. UdP-20 possesses a square lattice (sql) topology in which the copper sulfate dimer molecular building block acts as 4-connected nodes and exhibits flexibility, transitioning to a closed pore phase (UdP-20-cp) upon heating. The use of different functionalised bib ligands allowed us to obtain three new examples of APMOFs: UdP-21 with 1,1′-(2-chloro-1,4-phenylene)bis(1H-imidazole) (bibCl), UdP-22 with 1,1′-(2-methyl-1,4-phenylene)bis(1H-imidazole) (bibMe) and UdP-23 with 1,1′-(2-methoxy-1,4-phenylene)bis(1H-imidazole) bibOMe. All these materials possess 2D layers connected to each other by bridging sulfate anions leading to an overall 3D anion pillared framework. All the herein reported materials were characterised by elemental analysis, thermogravimetric analysis, and powder and single crystal X-ray diffraction. Moreover, their CO2 adsorption behaviour was investigated, revealing results in alignment with what is already reported in the literature for similar materials in the case of UdP-20, while UdP-21, UdP-22 and UdP-23 exhibited moderate CO2 adsorption, due to transition to denser phases upon activation
Spettroscopia IR di specie adsorbite: monitoraggi dell'acidità/basicità di superficie di sistemi ZrO2 puri e drogati per mezzo dell'adsorbimento di (CH3)2CO
No full textEffect of textural properties on the drug delivery behaviour of nanoporous TiO2 matrices
No full textIn this work several nanoporous titania powders have been considered as potential carriers for the sustained release of ibuprofen, used as model drug. The textural features and the physico-chemical nature of the surface carriers have been investigated by means of N2 physisorption measurements and FT-IR analyses. The delivery profiles have been collected in vitro in physiological solution at pH 7.4, maintaining the temperature at 37°C. It has been possible to observe a close correlation between the drug release kinetic and the textural properties of the carriers, in particular for what concerns their pores dimension. The choice of the proper synthetic approach allows a high control of the properties of the final material and of its behaviour in the drug delivery process that can be controlled to a very high extent
Characterization and Modeling of Reversible CO2 Capture from Wet Streams by a MgO/Zeolite Y Nanocomposite
No full textThe synthesis of CO2 sorbents capable of working on combustion flue gases is a challenging topic in the field of carbon capture and sequestration. Indeed, the presence of moisture in combustion exhausts makes most of the materials capturing CO2 through physisorption ineffective, their affinity being larger for H2O than for CO2. In this work, we investigate a novel nanocomposite sorbent based on a Mg overexchanged zeolite Y (MgOHY), showing single Mg2+ ions and nanoconfined (MgO)(n) clusters. The interaction of CO2 with the material is studied thoroughly by combining IR spectroscopy and simulation, comparing dry and wet conditions. IR spectroscopy shows that while in dry conditions the adsorption is mainly driven by the Mg2+ ions, in wet ones, the (MgO) clusters react with carbon dioxide by forming (bi)carbonate-like species. These easily decompose at mild temperatures (25-200 degrees C). Density functional theory simulations are used to investigate the origin of the CO2 interaction with representative (MgO) clusters in the periodic zeolite structure and their enthalpy of formation as a function of the water coverage. The calculations disclose a synergic effect between CO2 and H2O that, while favoring the CO2 fixation, results in the formation of (bi)carbonate-like species less stable than those formed in the absence of water
Aerogel and xerogel WO3/ZrO2 samplesfor fine chemicals production
No full textWO3/ZrO2 systems were prepared by sol-gel technique using different procedures for the solvent extraction: evaporation in vacuum at RT (xerogel) and extraction in supercritical conditions (aerogel). Two reactions of industrial interest were investigated under mild conditions: (i) acylation of veratrole with acetic anhydride; (ii) acylation of anisole with benzoic anhydride. Several techniques were employed in order to study the influence of the synthetic parameters on texture and catalytic activity: N2 physisorption, FT-IR spectroscopy, XPS, TPR and TPO analyses. The solvent extraction strongly influences metal reducibility, surface area, pores organisation, W/Zr surface density and metal interaction. The aerogel sample shows the best catalytic results for both conversion and yield. The supercritical extraction plays a central role especially in the recycling: by proper air activation, the aerogel sample attains the complete restoration of the catalytic activity even after three runs
A Systematic Study of Isomorphically Substituted H-MAlPO-5 Materials for the Methanol-to-Hydrocarbons Reaction
No full textSubstituting metals for either aluminum or phosphorus in crystalline, microporous aluminophosphates creates Brønsted acid sites, which are well known to catalyze several key reactions, including the methanol to hydrocarbons (MTH) reaction. In this work, we synthesized a series of metal-substituted aluminophosphates with AFI topology that differed primarily in their acid strength and that spanned a predicted range from high Brønsted acidity (H-MgAlPO-5, H-CoAlPO-5, and H-ZnAlPO-5) to medium acidity (H-SAPO-5) and low acidity (H-TiAlPO-5 and H-ZrAlPO-5). The synthesis was aimed to produce materials with homogenous properties (e.g. morphology, crystallite size, acid-site density, and surface area) to isolate the influence of metal substitution. This was verified by extensive characterization. The materials were tested in the MTH reaction at 450 °C by using dimethyl ether (DME) as feed. A clear activity difference was found, for which the predicted stronger acids converted DME significantly faster than the medium and weak Brønsted acidic materials. Furthermore, the stronger Brønsted acids (Mg, Co and Zn) produced more light alkenes than the weaker acids. The weaker acids, especially H-SAPO-5, produced more aromatics and alkanes, which indicates that the relative rates of competing reactions change upon decreasing the acid strength
Tuning the negative thermal expansion behavior of the metal− Organic framework Cu3BTC2 by retrofitting
No full textRationalization of TS-1 synthesis through the design of experiments
No full textTitanium Silicalite-1 (TS-1) is a zeolite used as a catalyst in partial oxidation reactions, whose synthesis is often performed under hydrothermal conditions by exploiting alkoxides as Ti and Si precursors. A rational study of the synthesis procedure of TS-1 using the experimental design approach was performed. Seven variables (i.e. times and temperatures of the various synthesis steps) were explored, by fixing the reagents ratio to establish which of them could affect the Ti incorporation and speciation. The syntheses were chosen following a D-optimal experimental design strategy, and each variable was explored at two levels and one center point. The responses monitored were: the yield of the synthesis; the total Ti content of the catalyst; the wavelength for the onset of the Ligand-to-Metal Charge Transfer (LMCT) transition involving Ti; and the vibrational fingerprint of tetrahedral Ti (centred at 960 cm−1 in the IR spectra). It was found that a few variables affect the Ti content and speciation (time and temperature of the hydrothermal treatment and the time of hydrolysis of the Ti precursor), whereas the yield is determined by the time of crystallization
