Osvaldo A. Serra

Biomimetical catalytic activity of iron(III) porphyrins encapsulated in the zeolite X

The approach adopted for the obtention of zeolite-encapsulated FeP led to clean syntheses of biomimetical catalyst. The catalysts were obtained through the zeolite synthesis method, where NaX zeolite was synthesised around one of the cationic FePs: iron(III) 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin (FeP1) or iron(III) 5-mono(2,6-dichloro-phenyl)10,15,20-tris(4-N-methylpyridyl)porphyrin (FeP2). The syntheses yielded pure FeP1NaX and FeP2NaX catalysts without any by-products blocking the zeolite nanopores. FeP1NaX and FeP2NaX efficiently catalysed the epoxidation of (Z)-cyclooctene by iodosylbenzene (PhIO) in DCE, giving rise to cis-epoxycyclooctane yields of 85% and 95%, respectively. Hydroxylation of adamantane shows a preferable alkane oxidation at the tertiary CH bond, indicating a hydrogen abstraction through the FeIV(O)P·+species in the initial step. The total adamantanol yields were 52% and 45% for FeP1NaX and FeP2NaX, respectively. Concerning selectivity, FeP1NaX and FeP2NaX gave an 1-adamantanol (Ad-1-ol)/2-adamantanol (Ad-2-ol) ratio of 20:1 and 11:1, respectively (after statistical correction). Therefore, these results indicate a free radical activation of the CH bonds of adamantane as expected for P-450 models. In the cyclohexane oxidation catalysed by FeP1NaX in DCE, a cyclohexanol (C6-ol) yield of 50% and an alcohol/ketone ratio of 10 was obtained. The hydroxylation occurs according to the so-called oxygen rebound mechanism, as expected for a P-450 model system. FeP2NaX is less selective (C6-ol yield=25% and alcohol/ketone=1.2). One possible explanation is that a Russell-type mechanism involving O2 imprisoned within the zeolite cages may be operating parallelly, generating both C6-ol and cyclohexanone.

A new procedure to obtain Eu3+ doped oxide and oxosalt phosphors

A different route to the synthesis of Eu3+ phosphors in matrices such as Y2O3, YVO4, La(BO3)3 or YNbO4, and the characterization and luminescent properties of these compounds, were studied. The new route (Pechini method) consists of the formation of a polymeric resin obtained by polyesterification between metal chelate complexes (formed by metallic ions and α-hydroxycarboxylic acids) and a polyfunctional alcohol. Ignition of this resin at low temperature renders the selected composition of Eu3+ doped oxides or oxosalts. Luminescent and X-ray spectroscopy and thermogravimetric analysis were used to characterize the materials.

Low-temperature upconversion spectroscopy of nanosized Y2O3:Er,Yb phosphor

This work reports on the structural characterization and on the low-temperature upconversion spectroscopy of the Y2O3:2%Er,1%Yb nanophosphor prepared by thermal decomposition of a polymeric resin (Pechini’s method [U.S. Patent No. 3,330,697 (July 11 1967)]). The average particle size evaluated from transmission electron microscopy lies in the range of 05–25nm. The high-resolution upconversion luminescence spectrum at 10K in the ultraviolet to near infrared (UV-NIR) spectral regions shows narrow lines, characteristic of Er3+ transitions occupying both Y3+ sites with point symmetries C2 and C3i in the oxide cubic system. The excitation spectrum at 10K in the IR region was used to monitor the green upconversion and IR luminescences and it displayed Er and Yb lines. Power dependence measurements at 298 and 10K indicate that the main upconversion mechanism is a two-photon excitation process. The temperature dependence of the upconversion luminescence shows a decrease in the emission intensity with increasing t...

The blue phosphor Sr2CeO4 synthesized by Pechini's method

Abstract Blue emitters are very attractive research subjects because of their possible industrial applications as phosphors for field emission displays. Recently, a blue phosphor, Sr 2 CeO 4 , was identified by a combinatorial materials synthesis technique. This material was further synthesized using the chemical coprecipitation method and the decomposition of acetates, carbonates and oxalates in a tedious procedure. In this work, we present the use of Pechini’s method as an alternative for the synthesis of this promising material. When the precursor, (Sr/Ce) polymer citrate–ethylene glycol, was fired at 850°C for 2 h, a mixture of Sr 2 CeO 4 and SrCeO 3 (inactive) was obtained, whereas the amount of Sr 2 CeO 4 was increased by further heating at 1100°C for 2 h in an oxygen atmosphere, as shown by the diffraction pattern. The excitation spectra present two broad bands with maxima at 294 and 344 nm and the emission spectrum has a broad band (half width ∼80 nm) centered at ∼475 nm. The unusually long lifetime of the compound fired at 1100°C of ∼0.04 ms is in good agreement with literature data. In conclusion, the blue phosphor material Sr 2 CeO 4 synthesized at 1100°C in an oxygen flux has comparable or even better emitter properties than that prepared over several days and/or at higher temperatures. The method is very attractive for industrial purposes.

Chlorin photosensitizers sterically designed to prevent self-aggregation.

The synthesis and photophysical evaluation of new chlorin derivatives are described. The Diels-Alder reaction between protoporphyrin IX dimethyl ester and substituted maleimides furnishes endo-adducts that completely prevent the self-aggregation of the chlorins. Fluorescence, resonant light scattering (RLS) and (1)H NMR experiments, as well as X-ray crystallographic have demonstrated that the configurational arrangement of the synthesized chlorins prevent π-stacking interactions between macrocycles, thus indicating that it is a nonaggregating photosensitizer with high singlet oxygen (Φ(Δ)) and fluorescence (Φ(f)) quantum yields. Our results show that this type of synthetic strategy may provide the lead to a new generation of PDT photosensitizers.

Hexagonal mesoporous silica modified with copper phthalocyanine as a photocatalyst for pesticide 2,4-dichlorophenoxiacetic acid degradation

A new mesoporous catalyst was prepared by the reaction between 3-aminopropyltrimethoxisylane and Cu(II)-hexadecafluorophthalocyanine, followed by co-condensation of tetraethylorthosilicate around a micelle formed by n-dodecylamine. The surfactant was removed from the pores by continuous extraction with ethanol, giving the Si-CuF16Pc catalyst. This catalyst was characterized by SEM, FTIR, TGA, 29Si NMR, N2 adsorption and X-ray diffraction. SEM images confirmed that the catalyst material is formed by nanoaggregates with a diameter of 100 nm. N2 adsorption isotherms showed that Si-CuF16Pc has a surface area of approximately 200 m2 g(-1) and a porous diameter of 7.7 nm, characterizing the mesoporosity of this product. This novel material shows an excellent photocatalytic activity, degrading almost 90% of 2,4-dichlorophenoxyacetic acid (2,4-D) up to 30 min, while only approximately 40% of photodegradation was obtained in its absence.

Organic complexes of Eu3+ supported in functionalized silica gel: highly luminescent material

Abstract Eu III ion and its chelates of 1,10-phenantroline (phen), 2,2-bipyridine (bpy), benzoyltrifluoroacetone (bfa) and acetylacetone (acac) were supported on silica gel (SG) and silica gel functionalyzed with propyl imidazole (IPG). The luminescence studies of Eu III showed an increase in the intensity and lifetime of the Eu IIII 5 D 0 a 7 F 2 transition in the presense of IPG, when compared with SG. The energy transfer from bfa and phen to the Eu III ion was also detected. In these cases, an increase in the intensity and lifetime of Eu III related to the direct excitation at the metallic ion was observed.

Luminescence study of the [Eu(bpy)2]3+ supported on Y zeolite

Abstract The photophysical properties of Eu3+ and its complex with 2,2′-bipyridine (bpy), [Eu(bpy)2]3+, supported on Y zeolite are reported. The ability of the bpy sensitizing Eu3+ ions into the Y zeolite cages is proved by the strong excitation at 319 nm via the ligand. The different 5 D 0 → 7 F 1 5 D 0 → 7 F 2 ratio for the sample indicates structural changes in the Eu3+ surrounding. The Eu3+ lifetimes for Eu(bpy)2Y (τ1 = 0.17 ms, τ2 = 0.43 ms) and [Eu(bpy)2]3+ in methanol (τ = 0.32 ms) is in agreement with these data. These results show that the zeolites are a very efficient host lattice for the luminescence of the rare earth ions bounded to an appropriate ligand as antenna.

Studies on the coordinate bond. VII. Complexes of diimines with iron, synthesis and spectral properties.

Abstract In order to investigate the spectral properties of iron diimine complexes a new series of complexes was synthesized and characterized. Their electronic spectra were studied including solid state liquid nitrogen temperature (LNT) measurements. This study showed that in the case of the ferrous complexes three metal to ligand electron transfer (MLET) bands can be observed, in the visible region, although many authors have assigned them to vibrational structure of the main band. The d-d bands in the spectra of the ferrous complexes are discussed. Very intense internal ligand electron transfer (lLET) bands are observed in the UV region and discussed. In the case of the ferric complexes we observed two ligand to metal electron transfer (LMET) bands in the visible region and lLET bands in the UV region. A correlation between the energy of these transitions in the ferrous and ferric complexes is discussed.

A phthalocyanine covalently bonded to a silica network by a sol–gel process

Abstract The preparation and properties of a phthalocyaninosilica, where the phthalocyanine is covalently bonded to an inorganic network, are described. The synthesis consists of the reaction between tetrachlorosulfonylphthalocyanine (PcSO2Cl) and 3-aminopropyltriethoxysilane (APTES) under reflux in dry dichloroethane. After that, ethanol, tetraethoxysilane, water and 1 M HCl or 1 M NH4OH were added to the reaction mixture. The properties of this new material were determined by thermal analysis (TGA/DTA), absorption, luminescence and infrared spectroscopy. The absorption spectra confirmed the presence of the phthalocyanine in the material. The emission spectra of the phthalocyanine and phthalocyaninosilica were measured to verify the structure of the phthalocyanine after its incorporation into the silica. The thermal analysis shows the presence and the retention of the thermal stability of phthalocyanine in the matrix. The resulting materials are presented as blue films and monoliths with optical quality.