Inorganic nanoarchitectonics : from design and fabrication to sustainable solutions

Resume : To extend the UV response of TiO2 photocatalyst towards Vis, several paths are already established including anion (and possible cation) doping, metal NP association, etc. The paper discusses another route that exploits the advantages of n-p junctions, developed between TiO2 photocatalyst coupled with p-type CuxS. Bi-layered thin films of n-p photocatalysts and multi-layered structures are further analysed, detailing the main design principles based on energy bands alignment. Further on, the importance of the working conditions is outlined, allowing the selection of the favorable pH window that supports: (1) to get enhanced electrostatic attraction substrate ? pollutant, and (2) the choice of the electrochemical potential of the oxidant species, according to the substrate?s band energy system. This design concept is discussed for the TiO2/CuxS and the TiO2/CuxS, CuO/SnO2 tandem structures, which were further obtained by sequential spray pyrolysis deposition. The experimental results prove the importance of the crystallinity and morpohology control of each layer and of the entire assembly, to reach an optimal charge carriers flow and to limit recombinations. The concept is validated based on the results obtained in investigating the tandems as photocatalysts under simulated solar radiation (85% Vis 15%UV) for the methylene blue decomposition. The results show that bleaching efficiency is very good and mineralization reaches (in optimized conditions) over 70% after 360 h.

Resume : Photo-electrochemical (PEC) water splitting is one of the most emerging fields for green energy generation and storage. For efficient PEC devices two efficient and stable photoelectrodes are needed. n-type Si can be used as photoanode but it suffers of surface oxidation and has an unfavorable band edge position for oxygen evolution; p-type Si can be instead used as photocathode, it has a favorable band edge position for hydrogen evolution. Although the p-type Si is considerably more stable against photo oxidation than the n-type, it has a low quantum yield (QY). Also its high reflectance is typically an issue. The QY of p-type Si can be increased by surface modification, e.g. using a catalyst. Reflectance can be reduced by surface structuring. In the present work we show a study of microstructured Si covered by a TiO2 layer and nano-islands. The microstructures are prepared by Galvanostatic selective etching of Si in HF medium. The TiO2 layer was deposited by atomic layer deposition (ALD) to protect the microstructured photocathode against corrosion. The microstructured TiO2/Si were decorated with TiO2 nano islands using a modified ALD technique to enhance the absorption of light in the photocathode. The obtained microstructured photocathode showed a shift in onset potential of 300mV towards anodic direction as compared to bare Si.

Resume : In general, white LEDs are fabricated by combination of a yellow phosphor and a blue LED based on GaN. In order to improve the efficiency of phosphor-converted LED (pc-LED), to use the appropriate phosphors is important. At fabricating a pc-LED, the mixture of phosphors and encapsulant is coated on the LED chip. Small particle size, narrow size distribution and spherical shape of the phosphor particles can provide better mixing with encapsulant in the fabrication of pc-LED. Ce3+-activated yttrium aluminum garnet Y3Al5O12:Ce3+ (YAG:Ce3+) has been known to be efficient for converting the blue emission by LED into yellow light. In this work, one-pot solution process using the hydrolysis reaction of urea with a dispersant was designed to synthesize YAG:Ce nanospheres. In the reaction, the used solvent was a mixed solution of alcohol and water. As a precipitant for co-precipitation of Y3+, Al3+ and Ce3+ metal ion components, excess urea was used. The volume ratio of alcohol to water and the concentration of metal ions, dispersant (Hydoroxy propyl cellulose) and urea were optimized based on the morphology and the emission intensity of the nanospheres. Several tens to 500 nm of YAG nanospheres were prepared with the changes of synthetic conditions. The optimum ratio of the alcohol/water mixture was around 5. The XRD study indicated that the single phase of yttrium aluminum garnet is formed with firing at 900℃ without the formation of intermediate phases such as YAlO3 (YAP) and Y4A

Resume : Silver nanoparticles (AgNPs) decorated on TiO2 photoelectro-catalytic thin films were prepared by immersion of AgNO3 under UV irradiation. Prior to the immersion, the TiO2 films were prepared by dip-coating, spray-coating and screen-printing techniques. Using Focus Ion Beam (FIB) and Field Emission Scanning Electron Microscope (FE-SEM), AgNPs were found to evenly distribute in the TiO2 films with narrow size distribution of around 20 nm. Photoelectro-catalytic activities of all the TiO2 films decorated with the AgNPs were tested with methylene blue and textile wastewater effluents and compared.

Resume : The low wetting by aluminum melt of solid nonmetallic phases is a significant problem at reception of composite materials on the basis of a Al–matrix reinforced by oxide, basalt, carbon and other fibres, by a free spontaneous impregnation method, and at the soldering of nonmetallic materials by aluminum solders. The dense Al2O3–film on a surface of metal is the reason of bad wetting. Special methods of capillary purification of the surface of aluminum alloy, the substantial increase of temperature of the soldering or impregnation (the last is possibly only in some cases), and also drawing of metal coatings are giving the limited effect (exception a Ni–film). The wetting (sessile drop method) of many nonmetallic materials (Al2O3, SiO2, SiC, CaF2, basalt, graphite and others), on surfaces of which the nickel coating (thickness of 150–400 nm) is put, is investigated. The high degree of wetting (the contact angle makes 20–50°) at temperature 700 °C is observed. It is explained that similar is wetted similar, and also in system Al/Ni the exothermic reaction with intermetalles formation takes place. Reaction is accompanied by rise in temperature (strong, local, small time of action), by dispersion, and evaporation and, it is possible, is by result of formation of pure contact between a solid phase and liquid aluminum. This effect for receipt oxide ceramics soldering joining and manufacturing of composite material Al/basalt fibres is used.

Resume : 2D layered materials such as MoS₂ and WS₂ have received much attention as alternatives to Pt for hydrogen evolution reaction (HER) catalysts. Here, we synthesized several types of MoS₂/rGO hybrid catalysts with tunable size and morphology by controlling amount of graphene oxide during solvothermal synthesis of MoS₂. Catalytic performance of MoS₂/rGO for HER depended on surface area of catalytically active edge site of MoS₂. Also, we studied correlation of catalytic performance and crystallinity of MoS₂ after annealing of each MoS₂/rGO catalyst.

Resume : TiO2 nanoparticles are widely used as powder, thin films or dispersions, in a broad field of photocatalysis applications like wastewater treatment, self-cleaning,etc. In special applications (chemical weapon decontamination) the development of TiO2 photocatalytic inks represents an alternative, if certain stability of the nano-particles disperse system is reached. In a continuous medium the nanoparticles naturally tend to agglomerate and deposit driven by the van der Waals and electrostatic forces. The stability remains a key problem in designing proper dispersions for specific applications. In this study, TiO2 Degussa P25 dispersions were obtained in aqueous, alcoholic or water:alcohol solvent. The influence of the suspension’s concentration, the solvent, pH and the surfactant (STA)/polymer addition on the dispersion stability was studied. Based on the double layer and DLVO theories, a stabilization mechanism is proposed, considering the steric effect of STA/polyvinylpyrrolidone adsorbed at the particles/liquid interface with formation of stabilized architectural structures and the double layer formation/modification and charge in the presence of alcohol. The dispersions photocatalytic activity was tested on methylorange, after the deposition on glass/textile substrates via spraying at room temperature. Correlations on the film stability-morphology–photocatalytic activity were discussed considering the interactions between the dispersions components and dispersion–substrate.

Resume : Ag:AlN nanocomposites have been shown to exhibit plasmonic behavior making them suitable for a range of applications. We explored structurally the photo-modulation of the nanoarchitecture of multilayered nanocomposites. Stratified composites of Ag nanoparticles (NPs) were deposited on Si substrates by magnetron sputtering. Both amorphous AlN (a-AlN) and wurtzite AlN (w-AlN) matrices were employed. The multilayers were then processed by laser annealing (LA) in order to promote ripening of embedded NPs. The effect of LA was assessed through structural characterization performed by TEM/HRTEM and XRD. It was found that LA led to a grading of NP size through partial dissolution of NP layers. w-AlN appears to constrain the phenomenon compared to a-AlN. De-stratification was promoted by LA under pressure. The NPs retained their average spherical shape and became better separated through ripening. HRTEM showed a local crystallization of a-AlN by LA. Optical reflectivity measurements confirmed the improved optical response due to enhanced localized surface plasmon resonance after LA. Structural features were quantified by peak profile analysis, which identified the variation of Ag NP size vs LA conditions. Acknowledgement: Research funded from the EU (ESF) and Greek national funds through the Research Funding Program: Heracleitus II (A. Siozios) and from the People Programme (MC Actions) LASER-PLASMON (FP7/2007-2013) under REA grant agreement PIEF-GA-2012-330444 (N. Kalfagiannis).

Resume : This work deals with the design of a low energetic demanded and simple synthesis route for producing SiO2-crystalline-TiO2 nanocomposites at ambient temperature. The as-prepared nanocomposites are designed to provide self-cleaning activities, along with the ability to strengthen and protect the building substrates. The SiO2-crystalline-TiO2 self-cleaning nanocomposites are obtained by mixing titanium and silicon alkoxides in the presence of oxalic acid. An organosilane was also added in order to provide hydrophobic properties through the reduction of the surface energy. The designed nanocomposites differed in the concentration of the oxalic acid. In the proposed synthesis route, the oxalic acid acts as: (a) a hole-scavenger during the photocatalytic process; (b) a sol-gel catalyst; (c) a chelating agent of the titanium precursor; (d) an increasing agent of the gel time of the nanomaterial and finally, (e) it contributes to the formation of anatase crystals at ambient temperature through a peptization process. The nanostructure and the chemical bonds formed proved that the formation of the independent domains of anatase crystals inside the silica matrix was essential for improving the photocatalytic properties of the nanocomposites. The nanocomposites were assessed on marbles and limestones as protective and strengthening agents; they exhibit self-cleaning and hydrophobic properties and are able to reinforce the microstructure of the examined lithic substrates.

Resume : Because of their direct contact with the external and internal environment, one of the main risk occurred in patients with feeding tubes is the high rate of infection. As device associated infections are difficult to treat health threatening conditions, novel approaches for reducing the incidence of infections in prosthetised patients are needed. The purpose of this study was to prepare and assess the biological effect of silver/sodium oleate nanostructures deposited as thin films through matrix assisted pulsed laser evaporation (MAPLE) on the surface of gastrastomy (G) tubes in order to increase their resistance to microbial contamination. Silver nanoparticles coated with sodium oleate (NanoSilver) were prepared by a simple wet chemical route and characterized by FT-IR, DTA-TG, TEM, SAED and EDS. After the primary characterization, the prepared nanopowder was used to create a thin uniform surface by advanced laser processing in order to obtain G tubes with high resistance to microbial colonization and biofilm development. The prepared surfaces were characterized by SEM, TEM, IR Microscopy, XRD, in vitro and in vivo biological activity was assessed. In vitro results demonstrate that the prepared nano-silver coatings have improved resistance to both Gram-positive and Gram-negative bacteria colonization and interfere with biofilms formation. On the other hand, these coatings have no citotoxic effect on human cultured cells, allowing their normal growth and development. In vivo experiments demonstrated that the nanoparticle solution used for the preparation of coated G tubes have no pathologic impact on treated mice. These nanoparticles are completely eliminated from the body in few days, after 2 weeks the only anatomical place that was positive for their presence being the spleen. According to our results, the NanoSilver coatings have a remarkable potential to be used in creating customized surfaces for different catheters and medical tubes with a low risk of infection.

Resume : In this study, we report the synthesis and characterization of newly prepared thin magnetic coatings deposited by Matrix Assisted Pulsed Laser Evaporation (MAPLE) to be used as antimicrobial surfaces for medical purpose. The magnetite nanoparticles were prepared by co-precipitation method. Silica was generated from TEOS and CTAB as a coating agent on the surface of magnetite. Prepared magnetite@silica was calcinated for 24 h at 650 oC in order to eliminate the CTAB template and to create a new nanoarhitectonics. Tetracycline was entrapped into 10 nm iron oxide@silica structure and further used for preparation of thin coatings. The obtained surfaces were characterized by SEM, TEM, IR and XRD. In order to establish the biologic effect of the obtained material we realized we in vitro tests on eukaryotic and prokaryotic cells and in vivo assays using a mice model treated for up to 14 days with the prepared nanostructures. The anti-microbial adherence properties were tested for up to 3 days and the results recommend this newly prepared coating to prevent Gram-positive and Gram-negative attachment and biofilm development on different medical surfaces. The biodistribution of these nanoarhitectonics revealed that they are well tolerated and eliminated by the host organisms, after 14 days the structures being presented only in spleen of tested mice. The results proved that the prepared surface based on iron oxide, silica network and tetracycline deposited by advanced laser technique can be used without any impediments to improve the resistance to colonization of medical devices.

Resume : The aim of this study was to prepare a novel bioactive medical surface in order to prevent microbial contamination and biofilm formation. For this purpose, Cobalt ferrite was prepared by co-precipitation in basic aqueous solution. Silica was applied as a shell from TEOS and CTAB in order to create a nanoarchitectonics. Prepared nanostructure was calcinated for 24 h at 650 oC to remove the template and create a well-ordered nanostructure. Cobalt ferrite@silica/streptomycin was used to prepare a novel surface by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique. Prepared thin coatings were characterized by Scanning Electron Microscopy, Infrared Microscopy and Transmission Electron Microscopy. Time lap in vitro drug release and different biological assays were also performed. The results demonstrated that the obtained thin coated surfaces ensures the controlled release of the active antimicrobial agent and inhibits bacterial colonization and development. Furthermore, experiments performed on human cultured endothelial cells demonstrated that eukaryote cells have a normal morphology and growth rate when cultivated on these surfaces and they do not interfere with any cellular process. In vivo results performed in mouse models also revealed that these nanoparticles tend to agglomerate in intensively blood irrigated organs and cause a low immune response, which is normal for any situation when a foreign material is introduced in the body. After less than two weeks, all organs ale cleared from the tested nanoparticles, they being still persistent in low amounts in spleen only. . Our results have demonstrated that the cobalt ferrite@silica/streptomycin bioactive coatings have significantly inhibited the microbial development on the coated surfaces, and manifested a great in vitro and in vivo biocompatibility.

Resume : With the increased rates of antimicrobial resistant bacterial infections, researchers strive to find alternative methods to limit their spread. In the hospital environment are found the highest multiresistance rates, which result in severe infections affecting mainly intensive care patients and individuals with implanted medical devices. The purpose of this study was to optimize the surface of wide use medical devices with antimicrobial ZnO@silica/erytromycin nanoparticles prepared by matrix assisted pulsed laser evaporation (MAPLE) in order to improve the resistance of medical surfaces to microbial colonization and biofilm formation. The nanoarchitectonics was prepared by Sol-gel method and further subjected to calcination. The functionalized surfaces, ZnO@silica/erytromycin, were characterized by Infrared microscopy, Scanning electron microscopy and High-Resolution Transmision Electron Microscopy, and in vitro / in vivo tests were also performed to establish their biological activity. Their anti-infectious potential was established by evatuating microbial adherence and biofilm formation on the modified surfaces. The microbiological assays proved that MAPLE deposed ZnO@silica/erytrhomycin inhibited the adherence capacity and biofilm development of all tested Gram-positive and Gram-negative bacterial strains, by ensuring a perfect controlled release of the active drug, erytrhomycin. Furthermore, qualitative and quantitative analyses demonstrated that the prepared nanoarchitectonics have a good biocompatibility, allowing the normal growth and metabolism progression on cultured human endothelial cells. In vivo assay, using a balbC mouse model demonstrated that immediately after the injection of the nanoparticles suspension prepared for the MAPLE deposition, a normal inflammatory infiltrate can be observed and the injected nanoparticles tend to aggregate within the well blood irrigated organs (liver, spleen and lungs). However, after 7 days post-treatment all organs are cleared from nanoparticles, excepting the spleen, where small amounts of nanoparticles are still present.

Resume : Hollow and concave nanocrystals find applications in many fields and their fabrication can follow different possible mechanisms. We report a new route to these nanostructures exploiting the oxidation of Cu2-xSe/Cu2-xS core/shell nanocrystals with various etchants. Even though the Cu2-xSe core is encased in a thick Cu2-xS shell, the initial effect of oxidation is the creation of a void in the core. This is rationalized in terms of diffusion of Cu+ ions and electrons from the core to the shell (and from there to the solution). Differently from the classical Kirkendall effect, which entails an unbalance between in-diffusion and out-diffusion of two different species across an interface, the present mechanism can be considered as limit case of such effect and is triggered by the stronger tendency of Cu2-xSe over Cu2-xS to oxidation and by fast Cu+ diffusion in copper chalcogenides. As the oxidation progresses, expansion of the inner void erodes the entire Cu2-xSe core, accompanied by etching and partial collapse of the shell, yielding Cu2-xSySe1-y concave particles. KEYWORDS: hollow nanoparticles, cation exchange, plasmonic materials, copper chalcogenides