A. M. Eremenko

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.

Structure and spectra of photochemically obtained nanosized silver particles in presence of modified porous silica

Mesoporous silica powders and films modified with organic sensitizer benzophenone were used as photocatalysts in the reaction of silver ion reduction by isopropyl alcohol under UV-irradiation with λ= 253.7 nm and 365 nm in presence of colloidal silica as stabilizer. Morphological changes of silver colloids during irradiation were studied using transmission electron microscopy, and correlated to the absorption spectra.

Luminescence of organic dyes in silica matrices

The luminescence spectra of the acridine dyes adsorbed on the dispersed silica surface and introduced into the silica film composition at the sol-to-gel transition stage have been studied. The formation of protonated forms of adsorbed dyes, the appearance of the anomalously long-time recombination afterglow, and the photoradicalization of dye at low temperature have been found. The effect of the transition metal dopant ions of Fe and Mn in a SiO2 matrix on dye luminescence quenching has been investigated. The luminescence quenching due to the transition metal ions is explained on the basis of an exchange-resonant interaction with contribution of the chemical interaction - complex formation.

The pH-Dependent Stucture and Properties of Au and Ag Nanoparticles Produced by Tryptophan Reduction.

In the work, an attempt was made to combine different experimental conditions to obtain stable gold and silver nanoparticles in the presence of amino acid tryptophan. The pH-dependent properties of gold and silver nanoparticles were studied. UV/visible spectroscopy and laser desorption/ionization mass spectrometry data confirm kynurenine pathway for tryptophan conversion in such systems.

Tryptophan-Assisted Synthesis Reduces Bimetallic Gold/Silver Nanoparticle Cytotoxicity and Improves Biological Activity

Aiming to reduce the potential in vivo hepato-and nephrotoxicity of Ag/Au bimetallic nanoparticles (NPs) stabilized by sodium dodecyl sulphate (SDS), an approach involving a simultaneous reduction of silver nitrate and tetrachlorauratic acid using tryptophan (Trp) as a reducing/stabilizing agent was applied during NP synthesis. The obtained Ag/Au/Trp NPs (5–15 nm sized) were able to form stable aggregates with an average size of 370–450 nm and were potentially less toxic than Ag/Au/SDS in relation to a mouse model system based on clinical biochemical parameters and oxidative damage product estimation. Ag/Au/Trp NPs were shown to exhibit anticancer activity in relation to a Lewis lung carcinoma model. The data generated from the present study support the fact that the use of tryptophan in NP synthesis is effective in attenuating the potential hepatotoxicity and nephrotoxicity of NPs during their in vivo application.

Silver and Gold Nanoparticles on Sol-Gel TiO2, ZrO2, SiO2 Surfaces: Optical Spectra, Photocatalytic Activity, Bactericide Properties

Development of new nanomaterials with metal nanoparticles (Ag, Au, Cu, Rh, Pd, etc.) deposited on oxide surfaces, embedded within pores or encapsulated in its matrices have gained much attention in material science because of expanding applications of such composites in optics, medical diagnostics, analytical chemistry, catalysis, photocatalysis etc. The most widely used catalyst is titanium dioxide. Titania effective properties could be improved by mixing with other oxides (ZrO2, SiO2, ZnO) that act as additives to control structure-sorption, optical and electronic properties. Incorporation of metal nanoparticles into a solid matrix of titania enhances their quantum efficiency (Kim et al, 2001; Alberius, 2002). Semiconductor-metal composite nanoparticles have been shown to facilitate charge rectification in the semiconductor nanostructures that is beneficial for maximizing the efficiency of photocatalytic reactions (Kamat, 2003, Subramanian et al, 2001). The metal NPs, being adsorbed or incorporated into titania matrix, modify the interface and/or alter the pathways with which photogenerated charge carriers undergo recombination or surface reactions. Metal nanoparticles embedded in dielectric matrixes are promising composite materials for optical applications as systems with enhanced third-order electronic susceptibility χ(3) [SiO2-ZrO2-Ag]. Aggregation and reshaping of metal nanoparticles and other processes occurring at the nanometal/porous matrix interfaces on preparation or postreaction treatments, as well as mutual influence of their electronic structures, physical or chemical interactions of phases, affect many characteristics of nanocomposites (Chan et al, 2004; Epifani et al, 2000; Gonella et al, 1999; He J. et al, 2002; He C. et al, 2002; Liz-Marzan et al, 1996; Kelly et al, 2003; Kreibig and Vollmer, 1995; Shacham et al, 2004; Shter et al, 2007; Song et al, 2005). There are hundreds publications devoted to the fabrication techniques of nanosized titaniabased photocatalyst and the properties description of obtained materials. The methods of synthesis including sol-gel process with thermoinduced (Antonelli & Ying, 1995), photoor chemical reduction of metal ions deposited on the TiO2 surface (Smirnova et al, 1992), as well as combination of ion-exchange and reduction process (Gnatyuk, 2005) were proposed for preparation of films containing small particles of metals and semiconductor (Kim et al, 2001; Alberius, 2002; Antonelli & Ying, 1995; Smirnova et al, 1992; Gnatyuk et al, 2005).

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.

Antitumor Activity of Alloy and Core-Shell-Type Bimetallic AgAu Nanoparticles

Nanoparticles (NPs) of noble metals, namely gold and silver, remain promising anticancer agents capable of enhancing current surgery- and chemotherapeutic-based approaches in cancer treatment. Bimetallic AgAu composition can be used as a more effective agent due to the synergetic effect. Among the physicochemical parameters affecting gold and silver nanoparticle biological activity, a primary concern relates to their size, shape, composition, charge, etc. However, the impact of metal components/composition as well as metal topological distribution within NPs is incompletely characterized and remains to be further elucidated and clarified. In the present work, we tested a series of colloidal solutions of AgAu NPs of alloy and core-shell type for an antitumor activity depending on metal molar ratios (Ag:Au = 1:1; 1:3; 3:1) and topological distribution of gold and silver within NPs (AucoreAgshell; AgcoreAushell). The efficacy at which an administration of the gold and silver NPs inhibits mouse Lewis lung carcinoma (LLC) growth in vivo was compared. The data suggest that in vivo antitumor activity of the studied NPs strongly depends on gold and silver interaction arising from their ordered topological distribution. NPs with Ag core covered by Au shell were the most effective among the NPs tested towards LLC tumor growth and metastasizing inhibition. Our data show that among the NPs tested in this study, AgcoreAushell NPs may serve as a suitable anticancerous prototype.