N. P. Smirnova

Growth and fragmentation of silver nanoparticles in their synthesis with a fs laser and CW light by photo-sensitization with benzophenone

The photo-sensitization synthetic technique of making silver nanoparticles using benzophenone is studied using both a laser and a mercury lamp as light sources. The power and irradiation time dependence of the synthesized nanoparticle absorption spectra and their size distribution [as determined by transmission electron microscopy (TEM)] are studied in each method and compared. In the laser synthesis, as either the laser power or the irradiation time increases, the intensity of the surface plasmon resonance absorption at 400 nm is found to increase linearly first, followed by a reduction of the red edge of the plasmon resonance absorption band. The TEM results showed that in the laser synthesis low powers and short irradiation times produce nanoparticles around 20 nm in diameter. Increasing the power or irradiation time produces a second population of nanoparticles with average size of 5 nm in diameter. These small particles are believed to be formed from the surface ablation of the large particles. The surface plasmon absorption band is found to be narrower when the nanoparticles are produced with laser irradiation. Throughout the exposure time with the CW lamp, the plasmon resonance absorption band of the particles formed first grows in intensity, then blue shifts and narrows, and finally red shifts while decreasing in intensity. The TEM results for lamp samples showed particle formation and growth, followed by small nanoparticle formation. The above results are discussed in terms of a mechanism in which, the excited benzophenone forms the ketal radical, which reduces Ag+ in solution and on the Ag nanoparticle surface. As the time of irradiation or the light energy increases the benzophenone is consumed, which is found to be the limiting reagent. This stops the formation of the normal large nanoparticles while their photo-ablation continues to make the small particles.

Synthesis and characterization of photocatalytic porous Fe3+/TiO2 layers on glass

Wet chemical synthesis and preliminary photocatalytical characteristics of titania and Fe(III)-containing TiO2 layers are presented. A highly stable coating colloids could be prepared under base- as well as acid-catalyzed condensation conditions. Structural properties of the as-prepared wet gels and sintered films were investigated using SEM, TEM, XRD as well as optical absorption spectroscopy, DTA-TG analysis and photomineralisation studies. X-ray amorphous wet titania gel layers start to crystallize at 500°C forming the characteristic anatase phase. In the presence of iron ions (Fe/Ti = 1), nanocrystalline FeTiO3 ilmenite phase forms. Both TiO2 and Fe-containing TiO2 films demonstrate a photocatalytic activity in the process of the photomineralization of dichloroacetic acid.

Photoelectrochemical characterization and photocatalytic properties of mesoporous TiO2/ZrO2 films

Optically transparent, crack-free mesoporous titania and zirconia-doped titania thin film photocatalysts were fabricated by sol-gel technique, using nonionic amphiphilic block copolymer Pluronic P123 as template. The structural and optical properties of these films were characterized using SEM, low-angle XRD, and UV/Vis spectroscopy, hexane adsorption investigation. Band gap energy and the position of flatband potentials were estimated by photoelectrochemical measurements. Enhancing of photocatalytic activity of zirconia-doped films relative to pure TiO2 originates from an anodic shift of the valence band edge potential. Catalytic activity of mesoporous TiO2 and TiO2/ZrO2 (5–50% of ZrO2) films in the processes of CrVI to CrIII photoreduction and 2,4-dinitroaniline photooxidation correlates with crystalline size and growth with increasing of specific surface area of the samples.

Effect of conditions of silica film preparation on the spectral behaviour of a fluorescent probe

Abstract Using the sol-gel technique for the hydrolysis of tetraethoxysilane (TEOS), the synthesis of porous silicate films was carried out in the presence of additives comprising the non-ionic surfactant Triton X-100 (type I films), or the polymer poly(ethylene oxide) (PEO) (type II films) with molecules of the fluorophore pyrene (Py) and with Cu 2+ ions as luminescence quenchers, incorporated at the gelation stage. The reaction between photoexcited molecules of Py and Cu 2+ ions was used to characterize the adsorption and the structural features of the compounds formed. In both types of film, the fluorophore was firmly held in a silica gel matrix. A photoreaction involving electron transfer from Py to Cu 2+ ions does not occur in type I films and the efficiency of Py fluorescence remains high irrespective of the quencher concentration. In type II films, the quenching of the Py fluorescence is effected by Cu 2+ ions. A conclusion was reached about the solubilization of Py inside micelles of Triton X-100 and encapsulation in a type I silica matrix during its maturation. Rate constants of quenching calculated according to the Stern-Volmer equation for variations of intensity and lifetimes of Py ∗ in type II films indicate a mixed reaction mechanism involving electron phototransfer which includes dynamic and static components.

Effect of gold nanoparticles on an aerosil surface on the fluorescence and Raman spectra of adsorbed tryptophan

We discuss the fluorescence and Raman spectra of the amino acid tryptophan (Trp) in the presence of gold nanoparticles in solution and on the surface of highly dispersed silica (aerosil) containing gold nanoparticles (Au-SiO2). The fluorescence of Trp is efficiently quenched in the presence of gold nanoparticles both in solution and on the SiO2 surface. The fluorescence and excitation spectra contain bands for molecular Trp and a charge transfer complex between Trp and the nanoparticles. In the Raman spectra of Trp with gold nanoparticles, considerably enhanced intense vibrations appear for the carboxyl and amino groups and also for the benzene and pyrrole rings. The effect of gold nanoparticles on the Raman spectra of Trp in a heterogeneous system is considerably weakened due to strong light scattering by the dispersed silica.

Laser-Induced Electron-Transfer Processes in a Pyrene–β-Cyclodextrin Complex in Titanosilicate Systems

We have used fluorescent spectroscopy and laser flash photolysis to investigate the photonics of pyrene molecules in a pyrene–β-cyclodextrin inclusion complex in various media. We have observed a protective effect of β-cyclodextrin relative to solubilized pyrene molecules during quenching of fluorescence by Ti ions (or titanium dioxide particles) in mixed colloids. In the presence of a precursor of silica (a TEOS solution), the pyrene molecules react with the colloidal silica particles formed, and the reaction is accompanied by decomposition of the pyrene–β-cyclodextrin inclusion complex and efficient photoionization of pyrene.

Preparation and optical properties of a new nanostructural material: Silver-ion-doped CdS nanoparticles in silicate matrices

Porous silicate glasses containing cadmium sulfide nanoparticles doped with silver ions have been prepared; light absorption and luminescence have been investigated; and a new general route for the cretion of nanostructural materials of this type has been mapped out.

Fluorescent properties of pyrene-β-cyclodextrin inclusion complexes in titanium-silica sols

Fluorescence of pyrene-β-cyclodextrin inclusion complexes in silica and titanium-silica stable sols is studied. It is revealed that high fluorescence ability of pyrene in the aforementioned systems is retained due to the binding with β-cyclodextrin. The study of the influence of N,N-dimethylaniline on the fluorescence of complexes shows that, varying the ratio between cyclodextrin and molecules capable of penetrating into its hydrophobic cavity, one may both efficiently encapsulate these molecules or replace some of them with others in titanium-silica sols.

Photocatalytic application of titanium oxide formed by sol-gel method in porous anodic alumina

The synthesis of titanium dioxide in the pores of porous anodic alumina (PAA) membrane was realized by solgel method. The samples were used for test reaction of degradation of organic dye rhodamine B. The synthesized samples of titanium oxide xerogel in the membrane of porous anodic alumina are considered as effective photocatalyst for decomposition of organic dyes in aqueous medium.

Design of Ag-Modified TiO2-Based Films with Controlled Optical and Photocatalytic Properties

TiO2-based functional coatings doped with Ag nanoparticles were prepared via template assisted sol–gel method with an attempt to enhance the decomposition reaction rate of industrial water pollutants. The films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron (XPS), and UV–vis spectroscopies. Catalytic activity in photooxidative organic dyes decomposition remarkably enhances TiO2/ZnO samples with homogeneously distributed noble metal nanoparticles. Ag nanoparticles in TiO2 matrix improve an efficiency of charge separation and charge-transfer processes, acting as traps for photoinduced electrons.