Esther Fanelli

Remediation of Waters Contaminated with MCPA by the Yeasts Lipomyces starkeyi Entrapped in a Sol-Gel Zirconia Matrix

A single-stage sol-gel route was set to entrap yeast cells of Lipomyces starkeyi in a zirconia (ZrO(2)) matrix, and the remediation ability of the resulting catalyst toward a phenoxy acid herbicide, 4-chloro-2-methylphenoxyacetic acid (MCPA), was studied. It was found that the experimental procedure allowed a high dispersion of the microorganisms into the zirconia gel matrix; the ZrO(2) matrix exhibited a significant sorption capacity of the herbicide, and the entrapped cells showed a degradative activity toward MCPA. The combination of these effects leads to a nearly total removal efficiency (>97%) of the herbicide at 30 °C within 1 h incubation time from a solution containing a very high concentration of MCPA (200 mg L(-1)). On the basis of the experimental evidence, a removal mechanism was proposed involving in the first step the sorption of the herbicide molecules on the ZrO(2) matrix, followed by the microbial degradation operated by the entrapped yeasts, the metabolic activity of which appear enhanced under the microenvironmental conditions established within the zirconia matrix. Repeated batch tests of sorption/degradation of entrapped Lipomyces showed that the removal efficiency retained almost the same value of 97.3% after 3 batch tests, with only a subsequent slight decrease, probably due to the progressive saturation of the zirconia matrix.

Use of a New Hybrid Sol−Gel Zirconia Matrix in the Removal of the Herbicide MCPA: A Sorption/Degradation Process

A class II hybrid sol-gel material was prepared starting from zirconium(IV) propoxide and 2,4-pentanedione and its catalytic activity in the removal of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) was revealed. The thermal and structural characterization, performed by thermogravimetry, differential thermal analysis, and diffuse reflectance Fourier transform infrared spectroscopy, demonstrated the hybrid nature of the material. The structure of the material can be described as a polymeric network of zirconium oxo clusters, on the surface of which large part of Zr(4+) ions are involved in strong complexation equilibria with acetylacetonate (acac) ligands. The incubation of MCPA in the presence of this material yielded an herbicide removal fraction up to 98%. A two-step mechanism was proposed for the MCPA removal, in which a reversible first-order adsorption of the herbicide is followed by its catalytic degradation. The nature of the products of the MCPA catalytic degradation as well as the reaction conditions adopted do not support typical oxidation pathways involving radicals, suggesting the existence of a different mechanism in which the Zr(4+):acac enol-type complex can act as Lewis acid catalyst.

On the nature of the second-order optical nonlinearity of nanoinhomogeneous glasses in the Li2O-Nb2O5-SiO2 system

The submicroscopic structure of lithium niobium silicate glasses of the compositions 2xLiNbO3 · (1 − x)(Li2O · 2SiO2) (x = 0.40, 0.45, 0.50) and 30Li2O · 25Nb2O5 · 45SiO2 in the initial state and after heat treatment for different times at temperatures in the vicinity of the glass transition point Tg are investigated using X-ray powder diffraction, small-angle neutron scattering (SANS), synchrotron small-angle X-ray scattering (SAXS), and electron microscopy. A nanostructure with inhomogeneities ∼40 Å in size is formed in glasses at the initial stages of phase separation at temperatures in the range 600–670°C. This structure is responsible for the appearance of the second-order optical nonlinearity. The SANS, SAXS, and electron microscopic data on the inhomogeneity size are in good agreement with each other. According to the X-ray diffraction, SANS, and SAXS data, the ordering of the glass structure and the difference between the density of inhomogeneities and the density of the matrix increase in the course of heat treatment. At the initial stage of amorphous phase separation, the glass decomposes into regions enriched in SiO2 and regions with an increased content of lithium and niobium. An increase in the temperature or time of heat treatment results in the precipitation of LiNbO3 ferroelectric crystals. The results obtained allow us, for the first time, to make the inference that nanoscale changes in the glass structure lead to considerable changes (by one order of magnitude and more) in the quadratic optical nonlinearity, which can be controlled by heat treatment. The origin of the second-order optical nonlinearity is associated with both the nanosized modulations of the polarizability due to the inhomogeneous glass structure and the polarity of structural nanoinhomogeneities from which the LiNbO3 phase precipitates at the later stages of phase separation.

Nanostructuring in potassium titanium phosphate glasses containing SiO2

Abstract Glasses from which the ferroelectrics phase KTiOPO 4 can crystallise have been prepared and studied. Namely, two glasses having the 92(K 2 O·2TiO 2 ·P 2 O 5 )·8SiO 2 (KTP-8Si) and the 88(K 2 O·2TiO 2 ·P 2 O 5 )·12SiO 2 (KTP-12Si) molar compositions have been synthesised by the melt quenching technique. They were examined by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The KTP-8Si glass devitrifies in a single step forming KTiOPO 4 phase, whereas the KTP-12Si glass firstly crystallises in an unknown phase and then, at higher temperatures, KTiOPO 4 crystallites grow. Proper heat treatments performed on the KTP-8Si glass at temperatures just below the glass transition range produce transparent samples the glassy matrix of which contains crystalline nanostructure of the KTP phase.

Nano-Phased Crystallisation of Ferroelectrics from Glasses in the K2O-TiO2-P2O5 and K2O-Nb2O5-SiO2 Systems

Crystallisation behaviour of glasses in the K2O-TiO2-P2O5 (KTP) has been studied by DTA, XRD, EM and SHG techniques to isolate composition ranges where bulk precipitation of ferroelectric phase KTiOPO4 occurs. It was found that bulk crystallisation of KTiOPO4 at temperatures slightly exceeding Tg is initiated by addition of SiO2. Controlled heat treatment leads to formation of optically non-linear KTiOPO4 nano-particles in KTP glasses (like amorphous nanostructuring in KNS glasses) in initial stages of phase separation and produces nanoscaled modulation of polarisability and SHG effect. The results are compared to the xK2O xNb2O5(1-2x)SiO2 (KNS) systems.

Rapid-flux-solvent-atmosphere method for tailoring the morphology of titania substrates over a large area via direct self-assembly of block copolymers

A fast method to direct the self-assembly of block copolymers loaded with metal oxide precursors in specific domains is demonstrated. It consists of performing spin-coating in a controlled atmosphere under a flux of solvent vapors (rapid-flux-vapor-atmosphere). Nanostructured thin films of hybrid composites and regular titania substrates, well oriented over a large area, are rapidly obtained.