Luis Filipe Vieira Ferreira

Use of Titanium Dioxide Photocatalysis on the Remediation of Model Textile Wastewaters Containing Azo Dyes

The photocatalytic degradation of two commercial textile azo dyes, namely C.I Reactive Black 5 and C.I Reactive Red 239, has been studied. TiO2 P25 Degussa was used as catalyst and photodegradation was carried out in aqueous solution under artificial irradiation with a 125 W mercury vapor lamp. The effects of the amount of TiO2 used, UV-light irradiation time, pH of the solution under treatment, initial concentration of the azo dye and addition of different concentrations of hydrogen peroxide were investigated. The effect of the simultaneous photodegradation of the two azo dyes was also investigated and we observed that the degradation rates achieved in mono and bi-component systems were identical. The repeatability of photocatalytic activity of the photocatalyst was also tested. After five cycles of TiO2 reuse the rate of colour lost was still 77% of the initial rate. The degradation was followed monitoring the change of azo dye concentration by UV-Vis spectroscopy. Results show that the use of an efficient photocatalyst and the adequate selection of optimal operational parameters may easily lead to a complete decolorization of the aqueous solutions of both azo dyes.

Surface Photochemistry: Organic Molecules within Nanocavities of Calixarenes

: In order to gain more information regarding photochemical processes in heterogeneous environments (opaque or powdered samples) laser induced time resolved luminescence and diffuse reflectance transient absorption spectroscopies were used for the study of benzophenone (and other neutral organic molecules) as guests and p-tert-butylcalix[n]arenes with n = 4, 6 and 8 (H(n)CLX[n]) and partially or totally O-propylated p-tert-butylcalix[4]arenes (H(n)Pr(m)CLX[4], n = 2, 1 and 0; m = 2, 3 and 4, respectively) were used as hosts. One of the main conclusions was that the solid support can deeply affect or even control the photochemistry of an adsorbed probe. A simple new methodology for lifetime distribution analysis of the decay of the probes included into calixarenes and other nanocavities was applied with success for decay data obtained with the use of intensified charge couple devices, i.e. intensified charge couple devices, ICCDs. Diffuse reflectance laser flash photolysis and gas chromatography - mass spectrometry techniques also provided complementary information, the former about transient species and the latter regarding the final products formed after light absorption.

Photochemistry on surfaces: solvent–matrix effect on the swelling of cellulose. An emission and absorption study of adsorbed auramine O

Auramine O exhibits a significant fluorescence emission at room temperature when adsorbed on microcrystalline cellulose. This emission is about two to four orders of magnitude higher than the previously reported emission in different solvents, also at room temperature. The fluorescence quantum yield, ϕF, varies with the residual degree of humidity of the sample, as alterations in the rigidity of the environment greatly affect the non-radiative de-excitation of auramine O. A limiting upper value of ϕF≈ 0.35 was obtained after prolonged evacuation of the samples.A matrix-isolation mechanism was evaluated by using room-temperature fluorescence measurements of powdered samples of auramine O adsorbed on microcrystalline cellulose. Using polar protic and aprotic solvents, different degrees of swelling of the microcrystalline cellulose were obtained, resulting in changes of the ground-state reflectance spectra of auramine O trapped in the natural polymer chains, as shown by remission function data. The amount of dye adsorbed or entrapped is reflected in both the fluorescence quantum yields and lifetimes.When auramine O was adsorbed on porous silica, the fluorescence quantum yield was much lower, indicating a higher mobility of dye molecules on the silica surface. Oxygen does not affect the room-temperature fluorescence emission of auramine O in silica or in cellulose.

Chapter 7 – PHOTONIC AND ELECTRONIC SPECTROSCOPIES FOR THE CHARACTERIZATION OF ORGANIC SURFACES AND ORGANIC MOLECULES ADSORBED ON SURFACES

Publisher Summary This chapter describes the synergetic effect obtained on putting together the larger number of available techniques to the service of characterizing surfaces. It describes optical spectroscopies in the ultraviolet visible infrared (UV–Vis–IR) range used in diffuse reflectance arrangement in combination with electronic spectroscopies, specifically X-ray photoelectron spectroscopy (XPS) and high-resolution electron energy spectroscopy. XPS and UV/Vis absorption and luminescence studies have proved to be complementary techniques in the study of dyes in several environments: when adsorbed onto or bound to a natural polymer, microcrystalline cellulose, when forming inclusion complexes with cyclodextrins, and also when interacting with silicas with different pore sizes. UV/Vis ground-state diffuse-reflectance absorption and luminescence studies showed in most cases a huge increase of fluorescence emission quantum yield when compared to solution studies for several dyes, when they are entrapped into microcrystalline cellulose, because of the reduction of mobility and formation of planar and emissive conformers and of the amount and type of aggregates, which are formed. A complementary view is given by X-ray photoelectron studies that provide evidence for hydrogen bond formation as well as preferential attachment by one or two nitrogen atoms per cyanine molecule to the hydroxyl groups in the substrates.

Novel laser-induced luminescence resulting from benzophenone/O-propylated p-tert-butylcalix[4]arene complexes. A diffuse reflectance study

Laser-induced room temperature luminescence of air-equilibrated benzophenone/O-propylated p-tert-butylcalix[4]arene solid powdered samples revealed the existence of a novel emission, in contrast with benzophenone/p-tert-butylcalix[4]arene complexes, where only benzophenone emits. This novel emission was identified as phosphorescence of 1-phenyl-1,2-propanedione, which is formed as the result of an hydrogen atom abstraction reaction of the triplet excited benzophenone from the propoxy substituents of the calixarene. Room temperature phosphorescence was obtained in air-equilibrated samples in all propylated hosts. The decay times of the benzophenone emission vary greatly with the degree of propylation, the shortest lifetimes being obtained in the tri- and tetrapropylated calixarenes. Triplet-triplet absorption of benzophenone was detected in all cases, and is the predominant absorption in the p-tert-butylcalix[4]arene case. where an endo-calix complex is formed. Benzophenone ketyl radical formation occurs with the O-propylated p-tert-butylcalix[4]arenes hosts, suggesting a different type of host/guest molecular arrangement. Diffuse reflectance laser flash photolysis and gas chromatography-mass spectrometry techniques provided complementary information, the former about transient species and the latter regarding the final products formed after light absorption. Product analysis and identification clearly show that the two main degradation photoproducts following laser excitation in the propylated substrates are 1-phenyl-1,2-propanedione and 2-hydroxybenzophenone, although several other minor photodegradation products were identified. A detailed mechanistic analysis is proposed. While the solution photochemistry of benzophenone is dominated by the hydrogen abstraction reaction from suitable hydrogen donors, in these solid powdered samples, the alpha-cleavage reaction also plays an important role. This finding occurs even with one single laser pulse which lasts only a few nanoseconds, and is apparently related to the fact that scattered radiation exists, due to multiple internal reflections possibly trapping light within non-absorbing microcrystals in the sample, and is detected until at least 20 micros after the laser pulse. This could explain how photoproducts thus formed could also be excited with only one laser pulse.

Spectroscopy and photophysics of flavin-related compounds: 3-benzyl-lumiflavin.

Molecular structure, spectroscopic and photophysical data for the singlet state of 3-benzyl-lumiflavin in different solvents are presented. Theoretical studies concerning singlet–singlet and triplet–triplet excitation energies were carried out using time-dependent density functional theory (TD-DFT) calculations. These predictions are in good agreement with the experimental results, which reflect the solvent interactions. All the observable singlet–singlet transitions have π–π* character. The title compound appears to be an efficient sensitizer of the production of singlet oxygen (ϕΔ = 0.53). The crystal structure of 3-benzyl-lumiflavin is also presented, along with its solid-state photophysical data.

Photochemistry and Cytotoxicity Evaluation of Heptamethinecyanine Near Infrared (NIR) Dyes.

The present study investigates the photochemical properties of potential photosensitizers for photodynamic therapy, namely four commercial heptamethinecyanine dyes (IR125, IR780, IR813, IR820). Spectroscopic studies were made by means of laser induced fluorescence and laser flash photolysis in order to obtain fluorescence quantum yields and transient absorption spectra. Fluorescence lifetimes were also determined. The differences encountered were essentially related with the interaction of the sulfonate groups with the solvent, and also regarding the rigidification of the central bridge connecting the two nitrogen-containing heterocyclic groups. Transient absorption studies were performed both in aerated and oxygen free samples, to conclude about the formation of photoisomers and triplet state. For the four dyes under study, a cytotoxic evaluation in the dark and after irradiation was performed using HeLa cells as the model cell line, which revealed significant changes after irradiation mainly in IR125 and IR813 dyes. Confocal microscopy analysis showed that these dyes tend to enter to the intracellular space.

Comprehensive Photochemistry and Photophysics of Land‐ and Marine‐based β‐carbolines Employing Time‐resolved Emission and Flash Transient Spectroscopy

Abstract The photophysical and photochemical behavior of Norharmane (Norh), Harmane (Hara) and Harmine (Hari) and their cations have been examined as a function of the nature of the solvent. Time-resolved emission in nonprotic polar solvents showed fluorescence for all and also phosphorescence for Hari. All emissions were assigned as those of the neutral molecules. Norh and Hari showed fluorescence of both the neutral and the cation in methanol as well as phosphorescence of the neutral while Hari also had fluorescence of the zwitter ion. In ethanol, Norh and Hari displayed fluorescence and phosphorescence of the neutral. The ground-state cations of Norh and Hari exhibited fluorescences of the cation and Hari also had a phosphorescence (cation). The flash transient spectra in nonprotic solvents of all three carbolines had long-lived triplet transients only of the neutral. Triplet and singlet oxygen yields were quite high, 0.31–0.40. Direct excitation of any of the cations gave only the cation triplet. The triplet yields of the cations appear to be low (0.01–0.10 range). Theoretical calculations were done relative to location of triplet states. Some new information will be reported on other naturally occurring differently substituted marine-based β-carbolines. The impact of all of the foregoing observations on the photosensitizing potential of all compounds is discussed.

Microwave Synthesis, Basic Spectral and Biological Evaluation of Some Copper (II) Mesoporphyrinic Complexes

Cu(II) complexes with asymmetrical and symmetrical porphyrinic ligands were synthesized with superior yields using microwave irradiation. The paper presents the synthesis of 5-(3-hydroxyphenyl)-10,15,20-tris-(4-carboxymethylphenyl)-21,23-Cu(II)-porphine in comparison to its symmetrical complex 5,10,15,20-meso-tetrakis-(4-carboxy-methylphenyl)-21,23-Cu(II) porphine. The two compounds were characterized by FT-IR, UV–Vis and EPR spectroscopy, which fully confirmed the structures. The spectral molecular absorption properties of the porphyrinic complexes were studied in organic solvents (methanol, ethanol, iso-propanol, dimethyl sulfoxide, dimethylformamide and methylene chloride), and the influence of the solvent polarity on the absorbance maxima is described. In order to establish their future potential in biomedical applications preliminary toxicological studies consisting of viability and proliferation of standard tumor cell lines (MCF7 and B16) testing was performed. The obtained results indicate a low toxicity for both compounds and further recommends them for testing in light activation protocols.

Color and Luminescence stability of selected dental materials in vitro

PURPOSE To study luminescence, reflectance, and color stability of dental composites and ceramics. MATERIALS AND METHODS IPS e.max, IPS Classic, Gradia, and Sinfony materials were tested, both unpolished (as-cast) and polished specimens. Coffee, tea, red wine, and distilled water (control) were used as staining drinks. Disk-shaped specimens were soaked in the staining drinks for up to 5 days. Color was measured by a colorimeter. Fluorescence was recorded using a spectrofluorometer, in the front-face geometry. Time-resolved fluorescence spectra were recorded using a laser nanosecond spectrofluorometer. RESULTS The exposure of the examined dental materials to staining drinks caused changes in color of the composites and ceramics, with the polished specimens exhibiting significantly lower color changes as compared to unpolished specimens. Composites exhibited lower color stability as compared to ceramic materials. Water also caused perceptible color changes in most materials. The materials tested demonstrated significantly different initial luminescence intensities. Upon exposure to staining drinks, luminescence became weaker by up to 40%, dependent on the drink and the material. Time-resolved luminescence spectra exhibited some red shift of the emission band at longer times, with the lifetimes in the range of tens of nanoseconds. CONCLUSIONS Unpolished specimens with a more developed surface have lower color stability. Specimens stored in water develop some changes in their visual appearance. The presently proposed methods are effective in evaluating the luminescence of dental materials. Luminescence needs to be tested in addition to color, as the two characteristics are uncorrelated. It is important to further improve the color and luminescence stability of dental materials.