Catalytic reduction of organic dyes at gold nanoparticles impregnated silica materials: influence of functional groups and surfactants

Gold nanoparticles (Au NPs) in three different silica based sol–gel matrixes with and without surfactants are prepared. They are characterized by UV–vis absorbance and transmission electron microscopic (TEM) studies. The size and shape of Au NPs varied with the organo-functional group present in the sol–gel matrix. In the presence of mercaptopropyl functionalized organo-silica, large sized (200–280 nm) spherical Au NPs are formed whereas in the presence of aminopropyl functionalized organo-silica small sized (5–15 nm) Au NPs are formed inside the tube like organo-silica. Further, it is found that Au NPs act as efficient catalyst for the reduction of organic dyes. The catalytic rate constant is evaluated from the decrease in absorbance of the dye molecules. Presence of cationic or anionic surfactants greatly influences the catalytic reaction. The other factors like hydrophobicity of the organic dyes, complex formation of the dyes with anionic surfactants, repulsion between dyes and cationic surfactant, adsorption of dyes on the Au NPs also play important role on the reaction rate.     

Investigation on F–B–S tri-doped nano-TiO<Subscript>2</Subscript> films for the photocatalytic degradation of organic dyes

F–B–S tri-doped titanium dioxide thin films on common glass were prepared by a modified sol–gel method, in which tetrabutyl titanate (Ti(OC₄H₉)₄) was chosen as the precursor and boric acid (H₃BO₃), sodium fluoride (NaF), and thiourea (N₂H₄CS) were employed as boron, fluorine, and sulfur sources, respectively. The microstructure and optical property were characterized by X-ray diffraction, high-resolution field emission scanning electron microscopy, N₂ adsorption–desorption isotherms, photoluminescence spectrum, and UV–Vis diffraction reflectance spectroscopy. The photocatalytic performances were evaluated by decomposition of organic dyes in solution. The experimental results revealed that the F–B–S tri-doped TiO₂ thin film was composed of uniform round-like nano-particles with the size range of 5–8 nm. F–B–S tri-doping not only significantly promoted the UV-induced photodecomposition activities of TiO₂ films but also extended the optical response of TiO₂ red shift to visible light region, herein improving the visible light-induced degradation of organic dyes. The improvement mechanism by F–B–S tri-doping was also discussed.     

Titanium oxide xerogel films in porous aluminum oxide for photocatalytic application

We have used the sol–gel method to synthesize titanium dioxide in the pores of an anodic aluminum oxide membrane. The samples were used for the test reaction of degradation of the organic dye rhodamine B. The concentration of the dye rhodamine B was monitored from the change in the absorption spectra in the 554 nm region, for an aqueous solution containing the dye and exposed to the emission from a mercury lamp. The synthesized samples of titanium oxide xerogel in the porous anodic aluminum oxide membrane are efficient photocatalysts for decomposition of organic dyes in an aqueous medium.     

Characterization of a green and environmentally friendly sensitizer for a low cost dye-sensitized solar cell

Clean and cheap device, namely dye-sensitized solar cells (DSSCs) were fabricated using a natural dye extracted from Sambucus ebulus. We prepared five sample solutions with various pH in the extraction process to improve power conversion efficiency. The UV–visible absorption investigation of sample solutions and on photoanode show the dyes from J-type aggregation on a photoanode substrate. Redox properties of all sample solutions certify thermodynamically a charge transfer from excited state to conduction band TiO₂. The optical properties of various dye solutions were investigated and results showed darkness and bluish tint effect of dye solutions extracted in basic environment rather than those extracted in acidic condition. Moreover, in comparison to the basic condition, the dye solutions extracted in acidic environment were more saturated and colorimetrically less different from that one which extracted in neutral condition. Photophysical and photoelectrochemical performance of natural extraction dyes have been studied in dye-sensitized solar cell devices. The results show the rather high conversion efficiency of 0.57%, 1.15%, 1.02%, 0.35% and 0.15% of each individual dye extraction, respectively.     

Entrapment of dye molecules within submicron silver particles

We describe a method for the preparation of metal–organic composites submicron particles. Specifically, the preparation of silver particle-clusters 150–200 nm in size, doped with an organic dye Congo-red, is reported. The use of sodium citrate coupled with sodium hypophosphite facilitated the formation of these particle-clusters, which were fully characterized by TEM analysis, Zeta potential and size measurements, scanning electron microscopy, UV–Vis measurements, and thermogravimetric analysis. The latter reveals a catalytic action of the metal on the thermal oxidative decomposition of the entrapped dye. The use of these particles to obtain dense thin metallic films was demonstrated by the coating of ITO glass.     

Quantum-chemical study of effect of conjugation on structure and spectral properties of C105 sensitizing dye

The structure and spectral properties of two organic ruthenium complexes used as sensitizing dyes for solar batteries (well-known N3 dye and its selenophene-conjugated analogue C105 ([Ru(bpy)(bpysef)(COOH)₂(NCS)₂] (bpy = 2,2′-bipyridine, bpysef = 4,4′-bis(5-hexylselenophene-2-yl)2,2′-bipyridine)) are comparatively studied within the density functional method. It is shown that the conjugation of the bipyridine ligand with selenophene affects the electronic structure of the C105 dye. A multilevel model for interpreting the electronic spectra of dyes is proposed based on the analysis of the shapes of molecular orbitals. The nature of the absorption bands of these ruthenium complexes in the region of 300–800 nm is explained. It is found that, in the polar acetonitrile solvent, these dyes are negatively solvatochromic, which agrees with the current classical views on the effect of the solvent on the shape of electronic absorption spectra of related compounds.     

Evaluation of Raman and SERS analytical protocols in the analysis of Cape Jasmine dye (Gardenia augusta L.)

The identification of organic colorants in works of art (such as dyes on textiles or organic pigments) by Raman spectroscopy is generally limited by the presence of a strong fluorescence background. In this paper, the effectiveness of minimizing fluorescence in the analysis of Cape Jasmine (Gardenia augusta L.) by dispersive Raman spectroscopy at three different excitation wavelengths (633, 785 and 1064 nm) and by surface‐enhanced Raman spectroscopy (SERS) with and without acid hydrolysis is evaluated and compared. It is shown that these vibrational techniques offer an alternative analytical approach, when, as is particularly the case of Cape Jasmine, sample preparation procedures that are routinely applied for natural organic dyes and pigments cause alterations that lead to low sensitivity in the more classical high‐performance liquid chromatography‐photodiode array (HPLC‐PDA) analytical protocols. Samples of the yellow dye G. augusta L. in the following forms were analyzed: dyed on alum mordanted wool, dyed on nonmordanted and alum mordanted silk, pigment precipitated on hydrated aluminum oxide, extract mixed with a protein binder and painted on glass, and as a water‐based glaze applied on a mock‐up of a typical Chinese wall‐painting. Raman bands at 1537, 1209 and 1165 cm⁻¹ are identified as discriminating markers for the carotenoid colorant components crocetin and crocin. Copyright © 2009 John Wiley & Sons, Ltd.     

Bleaching of red lake paints in encaustic mummy portraits

The present paper reports on the study of the development of whitish opacity in pink paints in encaustic mummy portraits. Non-invasive measurements carried out on two encaustic portraits belonging to the Ny Carlsberg Glyptotek, Copenhagen, by reflectance FTIR and UV–vis fluorescence have shown that the areas prone to the bleaching phenomenon had been painted with melted beeswax and an anthraquinone vegetal lake mixed with calcium sulphate hemihydrate and dihydrate. The hypothesis that the bleaching disease was neither related to a degradation of the dyes nor to an alteration of the wax but rather to a dehydration–hydration reaction of the CaSO₄–H₂O system, has been corroborated by the analyses of two microsamples from the bleached areas and ascertained by accelerated ageing experiments on encaustic models.     

Modeling the binding of peptides on carbon nanotubes and their use as protein and DNA carriers

An in-depth study of a novel functionalization of carbon nanotubes for their application as protein and DNA carriers is presented. First, the optimum conditions for the dispersion of single-walled carbon nanotubes (SWCNTs) with amphiphilic polypeptides were obtained, and the SWCNT–polypeptide complexes were characterized by different techniques (UV–Vis-NIR, CD, and AFM). Based on the properties of the SWCNT–polypeptide complexes, a model that characterizes the adsorption of natural proteins onto SWCNT was described for the first time. This model predicts the adsorption of natural proteins on SWCNTs based on the protein structure and composition, and therefore, allows the design of methods for the preparation of SWCNT–protein complexes. Besides, the use of cationic-designed amphiphilic polypeptides to disperse SWCNTs is applied for subsequent and efficient binding of DNA to carbon nanotubes by a bilayer approach. Therefore, in this article, we develop procedures for the use of SWCNTs as protein and DNA carriers. The systems were delivered into cells showing that the efficiency of delivery is affected by the charge of the complexes, which has important implications in the use of SWCNT as platforms for protein and DNA binding and subsequent use as delivery systems.     

Fourier‐transform surface‐enhanced Raman spectroscopy (FT‐SERS) applied to the identification of natural dyes in textile fibers: an extractionless approach to the analysis

In the present study, an application of a silver colloid substrate in order to obtain Fourier‐transform surface‐enhanced Raman (FT‐SER) spectra of natural historical dyes is presented. In detail, we collected a spectral database from solutions of pure dyes and then we carried out extractionless both hydrolysis and non‐hydrolysis FT‐SERS analyses on wool fibers previously dyed in our laboratory and on ancient textiles. The term ‘extractionless’ refers to a method of SERS analysis applied directly on the fiber, thus avoiding the extraction of dyes from textile samples. The combination of a low‐energy source of radiation, as in the FT‐Raman technique, with SER spectroscopy can bring the important advantage of reducing the fluorescence typical of ancient samples and organic dyes. In some historical textile samples, for which SER spectra by use of visible excitation could not be obtained, the FT‐SER spectrum of an iron‐gall dye was recorded without hydrolysis, while, with an HF hydrolysis pre‐treatment on ancient fibers, madder, lac dye and brazilwood were clearly recognized. Copyright © 2014 John Wiley & Sons, Ltd.     

Highly stable Ag nanoparticles in agar-agar matrix as inorganic–organic hybrid

A novel synthesis of inorganic–organic hybrid films containing well dispersed and almost uniform size Ag nanoparticles in agar-agar matrix has been reported. The films are found to be highly stable for more than a year. The colloidal particles of Ag can be obtained in large quantities in the form of a film or in the gel form when dispersed in agar-agar or by dissolving in a suitable solvent as solution. Characterization has been done by UV–visible spectroscopy and TEM. The hybrid may be of interest to study third-order non-linear susceptibility.     

Dual-band lasing of benzopyran dyes in the red region of the spectrum

We have studied the spectral and energy characteristics of lasing for two benzopyran dyes in a dispersive cavity with a diffraction grating when the dyes are excited at several different wavelengths using an additional flashlamp-pumped dye laser. These dyes have high fluorescence quantum yield and lase efficiently in the red region of the spectrum. The tuning range of their lasing spectrum is greater than 100 nm. We discuss the characteristic features of conversion of the selective excitation energy by these dye molecules. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 401–404, May–June, 2006.     

Janus nanoparticles: reaction dynamics and NOESY characterization

Janus nanoparticles were prepared by taking advantage of interfacial ligand exchange reactions of hydrophobic hexanethiolate-protected gold nanoparticles with hydrophilic 2-(2-mercaptoethoxy)ethanol (MEA). A monolayer of the particles was first formed at the air–water interface by the Langmuir technique and then deposited onto a substrate surface by the Langmuir–Blodgett method. The particle monolayer was then immersed into an aqueous solution of MEA for different periods of time. It was found that the exchange reactions occurred but were limited only to the top face of the nanoparticles and the reaction reached equilibrium in about 8 h. The resulting particles exhibited amphiphilic characters as confirmed by contact angle and UV–visible, FTIR and NMR spectroscopic measurements. Of these, the structural discrepancy between the Janus nanoparticles and bulk-exchanged particles was clearly manifested, in particular, by NOESY NMR measurements.     

Novel technique for transient absorption probing

An original absorption probe technique using a laser plume as a probe source of UV–visible continuum radiation is proposed and tested. To our knowledge, this is the first time that laser plume emission is used as a UV–VIS (190–510 nm) probe beam in transient absorption spectroscopy. The technique allows virtually single-shot recording of continuous fluorescence and absorption spectra and proved its applicability even when used at a high-voltage high-current e-beam gun facility with a high level of electromagnetic interference. The developed technique is applied to record the transient absorption spectra of e-beam-excited Ne, Ar, and Kr gases.     

Pre-columbian nanotechnology: reconciling the mysteries of the maya blue pigment

The ancient Maya combined skills in organic chemistry and mineralogy to create an important technology – the first permanent organic pigment. The unique color and stability of Maya Blue can be explained by a new model where indigo dye fills the grooves present at the surface of palygorskite clay, forming a hydrogen bonded organic/inorganic complex. Existing theory assumes the dye is dispersed inside the channels of an opaque mineral. Based on data from thermal analysis, synchrotron and neutron diffraction, ESEM and chemical modelling calculations, our new concept of Maya Blue structure resolves this contradiction and suggests some novel possibilities for more durable, environmentally benign pigments. PACS 61.66-f; 62.23.St; 61.66.Fn; 61.66.Hq     

Sensitization of fluorescence of dye molecules in nanoparticles of metal complexes

We studied the dependence of absorption and fluorescence spectra of complexes of Al, In, Sc, Y, and La with dibenzoylmethane and naphthoyltrifluoroacetone, as well as the dependence of sensitized fluorescence of dyes in nanoparticles of these complexes, in relation to the water pH, the ratio between ions and diketones, and the ion selection. We showed that the ability of complexes of ions to form nanoparticles that efficiently sensitize dye molecules incorporated into them is determined by stability constants of these ions with organic ligands and by their ability to compete with the formation of hydroxy complexes of these ions. We found that nanoparticles consist of diketonates of different compositions and that Nile red incorporated into nanoparticles is an indicator of the dependence of the composition of nanoparticles on the selection of the central ion of complexes and conditions of their formation. We revealed that complexes M(diketone)(OH)₂ self-assemble into nanoparticles with an admixture of dye molecules and efficiently sensitize dyes upon excitation into absorption bands of complexes. We showed that, at concentrations of rhodamine 6G in water smaller than 50 nM, the use of a solution that contains 50 μM of Al(III), In(III), or Sc(III) + 50 μM of naphthoyltrifluoroacetone makes it possible to increase the sensitivity of the luminescence analysis by 20-fold for the presence of rhodamine 6G in an aqueous solution.     

Lasing efficiency of dyes incorporated into a nanoporous glass-polymer composite

We have used microsecond coherent pumping to study the lasing efficiency of active elements based on a nanoporous glass-polymer composite activated by organic dyes, as a function of the spectral composition of the pump within the main absorption band of the dye. We have shown that under the indicated excitation conditions, the lasing efficiency can exceed 40% and can be comparable with the lasing of liquid elements. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 708–716, September–October, 2008.     

Pulse properties of a synchronously mode-locked,cavity dumped,picosecond dye laser system

A synchronously mode-locked, cavity-dumped picosecond dye laser is described. The structure and intensity of the picosecond pulses measured under different conditions are reported. It was found that the structure of the pulses from the synchronously pumped dye laser depends critically on the length of the Ar⁺ laser pulses. At the shortest Ar⁺ laser pulses of about 70 ps the dye pulses are as short as 1.1 ps. With Ar⁺ laser pulses of 200 ps the dye laser pulses contains a broad satellite pulse which contains a large fraction of the total intensity. When a cavity dumper is added to the system one gets dye laser pulses 15–20 ps long with a substructure, which indicates incomplete mode-locking. Well mode-locked 1.5–2.0 ps pulses were obtained in the red part of the dye laser action spectrum, i.e. 620–650 nm for R6G, 595–608 nm for R 110 and 657–662 nm for RB, respectively. Addition of mode-locking dyes also improved the pulse quality at some wavelengths.     

Fluorescent properties and spontaneous Raman spectroscopy of new ketocyanine probes in organic solvents

We have used fluorescence spectroscopy and spontaneous Raman spectroscopy to study the characteristics of two ketocyanine dyes: 2,5-di[(E)-1-(4-diethylaminophenyl)methylidene]-1-cyclopentanone (CPET) and 2-[(E)-1-(4-diethylaminophenyl)methylidene]-5-{(E)-1-[4-(4,7,10,13-tetraoxa-1-azacyclopentadecalin) phenyl]methylidene}-1-cyclopentanone (CPMR) in organic solvents. The position of their electronic spectra depends strongly on the polarity of the solvent. We measured the dipole moments of the dyes in the equilibrium ground state and the Franck-Condon excited state. In mixtures of neutral nonpolar toluene with aprotic polar dimethylsulfoxide, we observe inhomogeneous broadening of the electronic spectra for the indicated compounds, due to fluctuations in solution of the intermolecular interaction energy. The time-resolved characteristics of fluorescence obtained suggest formation of an intermolecular hydrogen bond between the dye and the surrounding medium in a toluene-ethanol mixture. We measured the Raman spectra of CPET and CPMR in different organic solvents. The most intense lines in the 1582–1591 cm⁻¹ region can be assigned to stretching of the phenyl rings of the molecules; the lines in the 831–842 cm⁻¹ region can be assigned to a cyclopentanone ring mode; the lines at 1186–1195 cm⁻¹ can be assigned to stretching of the =C-C-bond of the phenyl ring and rocking of the H atoms of the phenyl ring. We have observed that the position and width of the lines for the stretching vibrations of the ketocyanines depend substantially on the polarity of the surrounding medium. The studied dyes can be used as probes for studying different biological systems by site-selective laser spectroscopy and Raman spectroscopy. The fact that these two methods can be used simultaneously for diagnostics of biosystems is an important advantage of ketocyanine dyes compared with other known probes. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 763–769, November–December, 2006.