Photocatalytic Activity in CH

Some TiO2 powders, prepared from titanium(IV)tetraisopropoxide by the sol-gel method and thermally treated between 100 and 1000∘C, have been characterized by X-ray powder diffraction and by nitrogen adsorption and desorption at 77 K to calculate the BET-specific surface area, from which the micropore volume and the external surface area can be derived. The photocatalytic activity (ka) of the above powders has been evaluated considering the TiO2-sensitized photo-oxidation of 4-methoxybenzyl alcohol in CH3CN as the test reaction. The decrease of ka have been related to the decrease of the BET surface area, the micropore volume, and the external surface area of the TiO2 powders, but a satisfactory linear correlation is observed only for the last superficial parameter

Role of Surface Defects on Photoinduced Reactivity in SiO₂ Nanoparticles

Silica nanostructured materials find application in different fields, since they are cheap, versatile, and easy to functionalize as materials. However, silica reactivity has not been deeply investigated yet, mainly due to a poor understanding of how it is affected by superficial defects. In the present study, the electronic and optical properties of nanoparticles have been investigated using bare silica nanoparticles (SNP) and amino- or phosphonate-functionalized silica nanoparticles (SNP–APTES and SNP-phosphonate), prepared by a sol-gel procedure, and their morphology has been investigated using transmission electron microscopy (TEM) analysis. The prepared silica nanomaterials were characterized by means of reflectance and emission spectroscopies to determine the types of defects that can be found on silica nanoparticles’ surface. In order to understand the effect of surface defects on the reactivity of silica, the nanoparticles were employed for the photocatalytic degradation of Rhodamine 6G (R6G), upon selective irradiation at 320 nm, where only silica colloids absorb. The photoreaction was carried out in ethanol and in water and was monitored following the fluorescence signal of the dye. The evaluation of the fluorescent intensities allowed for the determination of the degradation efficiencies

Methods of preparation of novel composites of poly(epsilon-caprolactone) and a modified Mg/Al hydrotalcite

12-Hydroxydodecanoate (HD) anions were intercalated, via an ionexchange procedure, onto a Mg/Al hydrotalcite-like compound. The obtained intercalate, characterized by chemical and thermal analyses, X-ray powder diffraction, and Fourier transform infrared spectroscopy, with interlayer distance of 2.27 nm. Structural considerations indicated that the charge balancing anions were accommodated in the interlayer region as a monofilm of partially interdigitated alkyl chains in a trans planar conformation and bearing the alcoholic group. The organically modified hydrotalcite was used to prepare novel composites based on poly(e-caprolactone) (PCL) with different procedures: (1) solvent casting, (2) ring-opening polymerization of e-caprolactone, and (3) blending of precursors consisting of a PCL intercalated oligomer with a high-molecular-weight PCL. Microcomposites were obtained by the solvent casting of a mixture of a high-molecular-weight PCL and the modified hydrotalcite. The ring-opening polymerization of e-caprolactone initiated by the hydroxyl groups of the alkyl chains intercalated in the hydrotalcite led to hybrid materials in which a low-molecular-weight PCL was in part intercalated into the modified hydrotalcite. Nanocomposites containing exfoliated hydrotalcite were obtained through the mixing, in different weight ratios, of hybrids consisting of PCL oligomers and modified hydrotalcite with a commercial high-molecular-weight PCL

Extensive Screening of Green Solvents for Safe and Sustainable UiO-66 Synthesis

Zirconium based Metal-Organic Framework UiO-66 is to date considered one of the benchmark compound among stable MOFs and it has attracted a huge attention for its employment in many strategic applications. Large scale production of UiO-66 for industrial purposes requires the use of safe and green solvents, fulfilling the green chemistry principles and able to replace the use of N,N-Dimethyl-Formamide (DMF), which, despite its toxicity, is still considered the most efficient solvent for obtaining UiO-66 of high quality. Herein we report on a survey of about 40 different solvents with different polarity, boiling point and acidity, used for the laboratory scale synthesis of high quality UiO-66 crystals. The solvents were chosen according the European REACH Regulation 1907/2006 among those having low cost, low toxicity and fully biodegradable. Concerning MOF synthesis, the relevant parameters chosen for establishing the quality of the results obtained are the degree are the crystallinity, microporosity and specific surface area, yield and solvent recyclability. Taking into account also the chemical physical properties of all the solvents, a color code was assigned in order to give a final green assessment for the UiO-66 synthesis. Defectivity of the obtained products, the use of acidic modulators and the use of alternative Zr-salts have been also taken into consideration. Preliminary results lead to conclude that GVL (γ-valerolactone) is among the most promising solvents for replacing DMF in UiO-66 MOF synthesis. </p

Adsorptive removal of H2S in biogas conditions for high temperature fuel cell systems

Desulfurization represents a crucial step in fuel processing for high temperature fuel cells, because of catalysts stringent requirements. Moreover, when fuel cell stacks are used in micro-CHP applications, it is necessary to build an efficient and compact system. The use of biogas from anaerobic digestion could have a significant impact in terms of fossil fuels saving and environmental conservation. Biogas contains different impurities, among which H2S represents one of the most harmful components. Adsorption tests for H2S removal were carried out in biogas conditions, using commercial adsorbents, defining the materials characterized by the best performance and resulting in a predominance of impregnated activated carbons. The influence on adsorption capacity of operating parameters, such as gas hourly space velocity, gas matrix composition (N2, CH4 and CO2), humidity, temperature (30\u2013150 \ub0C), H2S concentration (50\u20131000 ppmv) and filter geometry, was investigated. The aim of the study was the functional parameters optimization to obtain a compact filter with high removal activity

Incorporation of Mg-Al hydrotalcite into a biodegradable poly (epsilon, caprolactone) by high energy ball milling

The technique of high energy ball milling (HEBM) was used to prepare nanocomposites of poly(epsilon-caprolactone) (PCL) and an organically modified Mg–Al layered double hydroxide. The amount of inorganic material was varied from 0 to 6 wt%, and the samples were melted and quenched in ice–water after milling. The molecular weight of PCL decreased and its distribution increased as a consequence of milling. The structural analysis of the milled samples, conducted by X-ray diffraction and infrared absorption techniques, showed that the 12-hydroxydodecanoates organic modifier was still attached to the inorganic lamellae even if a partial delamination of the layered compounds occurred. The mechanical parameters (modulus, stress at yield point, strain at break point and stress at break values) derived from the stress– strain curves, improved in the composite samples containing up to 2.8 wt% of inorganic filler, with respect to the pure polymer, in spite of the molecular weight decrease. The thermodynamic diffusion coefficient of water vapor in composite samples was lower than in pure PCL, indicating an improvement of the barrier effec

Solvent dependent synthesis of micro- and nano- crystalline phosphinate based 1D tubular MOF: structure and CO2 adsorption selectivity

International audienceA novel porous tubular 1D-MOF, built from Cu(II), 1,2-bis(4-pyridyl) ethane and P, P'-diphenyl-diphosphinate, has been prepared by an easy and direct self-assembly process in either needle microcrystal or nanorod form depending on the synthesis conditions. The CO2 absorption kinetics drastically increased from the micrometric crystals to the nanorods. The selectivity towards other gases and polar solvents was also investigated

On the evolution of proton conductivity of Aquivion membranes loaded with CeO2 based nanofillers: effect of temperature and relative humidity

Surface modified CeO2 nanoparticles were prepared by reacting nanometric CeO2 with a fluoroalkyl (C8F17-C2H4-PO(OH)2) or a fluorobenzyl phosphonic acid (C6F5-CH2-PO(OH)2). Both non-modified and fluorophosphonic acid modified CeO2 were used as fillers of composite Aquivion membranes, with loadings up to 5 wt%. Ex situ accelerated ageing using the Fenton reaction shows that non-modified CeO2 is a more efficient radical scavenger than the two fluorophosphonic acid modified fillers. Fluoride emission rate data for pristine Aquivion and for the composite membranes are consistent with the corresponding changes in the values of ion exchange capacity (IEC) and elastic modulus. The conductivity of membranes containing non-modified CeO2, measured as a function of relative humidity at 80 and 110 °C, decreases with increasing filler loading. For loadings > 2 wt%, an increase in temperature from 80 to 110 °C results in further conductivity drop and in the concomitant IEC decrease, due to partial filler solubilisation, thus indicating that the composite membranes are unstable at temperature > 80 °C. However such conductivity drops are strongly reduced, especially at 80 °C, for composites with fluorophosphonic acid modified CeO2

A Solvent Free Synthetic Route for Cerium(IV) Metal-Organic Frame-works with UiO-66 Architecture and Their Photocatalytic Application

A novel solvent-free synthesis for Ce-UiO-66 metal-organic frameworks (MOFs) is presented. The MOFs are obtained by simply grinding the reagents, cerium ammonium nitrate (CAN) and the carboxylic linkers, in a mortar for few minutes with the addition of a small amount of acetic acid (AcOH) as modulator (1.75 eq, o.1 ml). The slurry is then transferred into a 1 ml vial and heated at 120°C for 1 day. The MOFs have been characterized for their composition, crystallinity and porosity and employed as heterogenous catalysts for the photo-oxidation reaction of substituted benzylic alcohols to benzaldaldehydes under near ultraviolet light irradiation. The catalytic performances, such as yield, conversion and kinetics, exceed those of similar systems studied by chemical oxidation and using Ce-MOF as catalyst. Moreover, the MOFs were found to be reusable up to three cycles without loss of activity. Density functional theory (DFT) calculations gave an estimation of the band-gap shift due to the different nature of the linkers used and provide useful information on the catalytic activity experimentally observed. </div