Cláudia G. Silva

Influence of Excitation Wavelength (UV or Visible Light) on the Photocatalytic Activity of Titania Containing Gold Nanoparticles for the Generation of Hydrogen or Oxygen from Water

Gold nanoparticles supported on P25 titania (Au/TiO(2)) exhibit photocatalytic activity for UV and visible light (532 nm laser or polychromatic light λ > 400 nm) water splitting. The efficiency and operating mechanism are different depending on whether excitation occurs on the titania semiconductor (gold acting as electron buffer and site for gas generation) or on the surface plasmon band of gold (photoinjection of electrons from gold onto the titania conduction band and less oxidizing electron hole potential of about -1.14 V). For the novel visible light photoactivity of Au/TiO(2), it has been determined that gold loading, particle size and calcination temperature play a role in the photocatalytic activity, the most active material (Φ(H2) = 7.5% and Φ(O2) = 5.0% at 560 nm) being the catalyst containing 0.2 wt % gold with 1.87 nm average particle size and calcined at 200 °C.

Water Stable Zr-Benzenedicarboxylate Metal-Organic Frameworks as Photocatalysts for Hydrogen Generation

The Zr-containing metal-organic frameworks (MOFs) formed by terephthalate (UiO-66) and 2-aminoterephthalate ligands [UiO-66(NH(2))] are two notably water-resistant MOFs that exhibit photocatalytic activity for hydrogen generation in methanol or water/methanol upon irradiation at wavelength longer than 300 nm. The apparent quantum yield for H(2) generation using monochromatic light at 370 nm in water/methanol 3:1 was of 3.5% for UiO-66(NH(2)). Laser-flash photolysis has allowed detecting for UiO-66 and UiO-66(NH(2)) the photochemical generation of a long lived charge separated state whose decay is not complete 300 μs after the laser flash. Our finding and particularly the influence of the amino group producing a bathochromic shift in the optical spectrum without altering the photochemistry shows promises for the development of more efficient MOFs for water splitting.

Layered Double Hydroxides as Highly Efficient Photocatalysts for Visible Light Oxygen Generation from Water

Oxygen generation through photocatalytic water splitting under visible light irradiation is a challenging process. In this work we have synthesized a series of Zn/Ti, Zn/Ce, and Zn/Cr layered double hydroxides (LDH) at different Zn/metal atomic ratio (from 4:2 to 4:0.25) and tested them for the visible light photocatalytic oxygen generation. The most active material was found to be (Zn/Cr)LDH with an atomic ratio of 4:2 that exhibits two absorption bands in the visible region at lambda(max) of 410 and 570 nm. It was found that the efficiency of these chromium layered double oxides for oxygen generation increases asymptotically with the Cr content. Using iron oxalate as chemical actinometer we have determined that the apparent quantum yields for oxygen generation (Phi apparent = 4 x mol oxygen/mol incident photons) are of 60.9% and 12.2% at 410 and 570 nm, respectively. These quantum yields are among the highest values ever determined with visible light for solid materials in the absence of light harvesting dye. The overall efficiency of (Zn/Cr)LDH for visible light oxygen generation was found to be 1.6 times higher than that of WO(3) under the same conditions.

Metal–organic frameworks as semiconductors

The aim of the present feature article is to present the current evidence in support of considering some MOFs as semiconductors. While MOFs and zeolites share common structural properties derived from the microporous crystal structure, zeolites are insulating materials and most of the attempts to exploit them in optoelectronics have met with failure. In contrast, some MOFs may have interesting photochemical properties that derive from the fundamental event of charge separation in electrons and holes upon light absorption. Photoinduced charge separation is the hallmark of a semiconductor that can behave simultaneously as an oxidizing or reducing agent. Considering the novelty of this field, most of the available data about MOFs as semiconductor have been obtained from MOF-5, a case that is complicated due to its low structural stability. Therefore, we point out that further studies showing the semiconducting properties of other MOFs are still welcome. The purpose of this feature article is to trigger intense research in this area including the synthesis of semiconducting MOFs by design and development of applications.

Bone mineral density and depression: a community study in women.

In a community sample of 102 Portuguese white women we evaluated the relationship between osteoporosis and indexes of psychopathology and well-being. Depressive symptoms were assessed by the Beck Depression Inventory (BDI), psychopathology by the Hopkins Symptom Checklist-90 Revised (SCL-90-R), and quality of life using the Psychological General Well-Being Index. A questionnaire comprising social, demographic, clinical, and behavioral characteristics was also used. The sample prevalence of osteoporosis was 47.1%. Women with osteoporosis presented significantly higher scores on the total BDI (16+/-9 vs. 13+/-10, p=0.045) and lower scores in the hostility (0.8+/-0.6 vs. 1.2+/-0.7, p=0.012) and phobic anxiety (1.1+/-0.8 vs. 1.5+/-0.9, p=0.041) subscales of the SCL-90-R. No differences were found regarding mean general well-being scores (62+/-17 vs. 64+/-19, p=0.665). This study showed that women with osteoporosis have significantly higher levels of depressive symptoms and a corresponding higher prevalence of depression, independent of other factors strongly associated with osteoporosis, such as age or body mass index.

Laccase immobilization over multi-walled carbon nanotubes: Kinetic, thermodynamic and stability studies.

The biocatalytic performance of immobilized enzyme systems depends mostly on the intrinsic properties of both biomolecule and support, immobilization technique and immobilization conditions. Multi-walled carbon nanotubes (MWCNTs) possess unique features for enzyme immobilization by adsorption. Enhanced catalytic activity and stability can be achieved by optimization of the immobilization conditions and by investigating the effect of operational parameters. Laccase was immobilized over MWCNTs by adsorption. The hybrid material was characterized by Fourier transformed infrared (FTIR) spectroscopy, scanning and transmission electron microscopy (SEM and TEM, respectively). The effect of different operational conditions (contact time, enzyme concentration and pH) on laccase immobilization was investigated. Optimized conditions were used for thermal stability, kinetic, and storage and operational stability studies. The optimal immobilization conditions for a laccase concentration of 3.75μL/mL were a pH of 9.0 and a contact time of 30min (522 Ulac/gcarrier). A decrease in the thermal stability of laccase was observed after immobilization. Changes in ΔS and ΔH of deactivation were found for the immobilized enzyme. The Michaelis-Menten kinetic constant was higher for laccase/MWCNT system than for free laccase. Immobilized laccase maintained (or even increased) its catalytic performance up to nine cycles of utilization and revealed long-term storage stability.

Photocatalytic Oxidation of Phenolic Compounds by Using a Carbon Nanotube‐Titanium Dioxide Composite Catalyst

A nanostructured multiwalled carbon nanotube (CNT) and titanium dioxide composite catalyst is prepared by a modified acid-catalyzed sol-gel method. Pure anatase TiO(2) and the CNT-TiO(2) composite are tested in the photocatalytic degradation of four para-substituted phenols: 4-chlorophenol, 4-aminophenol, 4-hydroxybenzoic acid and 4-nitrophenol. The effect of several operational parameters on the photoefficiency of the composite catalyst is studied by using 4-chlorophenol as model compound, namely catalyst loading, pH of the medium, hydrogen peroxide concentration, substrate concentration. A relationship between the Hammett constant of each para-substituted phenolic compound and its degradability by the photocatalysts is found. The effect of the carbon phase in the catalyst is ascribed to its photosensitizer action. A clear beneficial effect is observed for the degradation of 4-aminophenol and 4-chlorophenol. For the molecules with stronger electron-withdrawing (deactivating) groups, such as 4-hydroxybenzoic acid and 4-nitrophenol, no synergy effect is observed.

Expression of TGF-alpha and EGFR in Breast Cancer and its Relation to Angiogenesis.

Abstract: Immunohistochemical analysis of the expression of transforming growth factor α (TGF‐α) and its receptor, epidermal growth factor receptor (EGFR), was performed in a series of 86 invasive carcinomas of the breast. TGF‐α immunostaining was observed in the majority of the cases (72.1%), both in epithelial cells and in adjacent stromal cells. EGFR was also present in tumors (34.2%) and in the endothelial cells (46.1% of the cases) near the tumors. A significant association was observed between TGF‐α expression and angiogenesis evaluated by immunohistochemistry using an antibody against factor VIII‐related antigen. No association was observed between TGF‐α expression and other clinicopathologic features. In contrast, EGFR expression in the tumor was associated with features of poor prognosis, such as tumor size, histologic grade, lymph node status, estrogen receptor content, p53 expression, sialyl‐Tn expression, and age. The presence of EGFR in endothelial cells was correlated to young patient age. We also observed an association of EGFR in endothelial cells and angiogenesis in tumors with a size of less than 2 cm. Inversely, in larger tumors, angiogenesis was only associated with tumor TGF‐α expression. These results indicate that endothelial EGFR may play a role in the early steps of breast cancer angiogenesis.

Nanodiamond–TiO2 composites for photocatalytic degradation of microcystin-LA in aqueous solutions under simulated solar light

Titanium dioxide (TiO2) has been under intensive investigation for photocatalytic degradation of cyanobacterial toxins. In order to develop more efficient photocatalysts, TiO2 and oxidized nanodiamonds (NDox) were combined as a composite catalyst (NDox–TiO2), which was tested in the photocatalytic oxidation of microcystin-LA (MC-LA), a cyanotoxin frequently found in freshwater. NDox–TiO2 and neat TiO2 photocatalysts were prepared by a liquid phase deposition method. A wide variety of analytical techniques, including physical adsorption of nitrogen, X-ray diffraction (XRD), UV-Vis and IR diffuse reflectance spectroscopies (DRUV-Vis and DRIFT), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), were used to characterize the materials. The performance of the photocatalysts was studied under both simulated solar and visible light. The kinetic results show remarkable efficiency for the NDox–TiO2 composite under simulated solar light irradiation with a synergistic factor of more than 15 relative to neat TiO2, while negligible photocatalytic activity was observed for the degradation of MC-LA when NDox–TiO2 was used under visible light illumination due to the wide band gap of the composite material. The photocatalytic efficiency of NDox–TiO2 was ascribed to the good dispersion of both phases in the composite material, facilitating the possible electronic interaction at the heterojunction interface between NDox and TiO2.

Nanocrystalline CNT-TiO2 Composites Produced by an Acid Catalyzed Sol-Gel Method

Carbon nanotube-TiO2 composites and pure TiO2 are prepared by a modified sol-gel method. The nanoscaled materials obtained are extensively characterized by spectroscopic, microscopic and calorimetric techniques. Their photoactivity is tested in the degradation of phenol under visible illumination. A correlation between the CNT content and the changes in the UV–vis absorption properties was found. The effect induced by CNT on the composite catalysts is explained in terms of an interphase interaction between CNT and TiO2 in the composite catalysts.