Browsing by Author "Granbohm, Henrika"
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Item Control of the size of silver nanoparticles and release of silver in heat treated SiO2-Ag composite powders(2018-01-05) Granbohm, Henrika; Larismaa, Juha; Ali, Saima; Johansson, Leena Sisko; Hannula, Simo Pekka; Department of Chemistry and Materials Science; Department of Bioproducts and Biosystems; Aalto Nanofab; Advanced and functional Materials; Bio-based Colloids and MaterialsThe growth of silver nanoparticles, the activation energy for silver particle growth, and the release of silver species in heat treated SiO2-Ag composite powders are investigated. The silver particle growth is controlled by heat treatment for 75 min of the as-synthesized SiO2-Ag composite powder at 300-800 °C. During heat treatment the mean size of the Ag particles increases from 10 nm up to 61 nm with increasing temperature, however, the particle size distribution widens and the mean size increases with increasing heat treatment temperature. Based on X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) studies, silver particles are crystalline and in a metallic state after annealing in all SiO2-Ag composite powders. The growth of Ag particles is suggested to take place via diffusion and Ostwald ripening. The activation energy for particle growth was determined as 0.14 eV. The dissolution of silver in aqueous solutions from the SiO2-Ag composites heat treated, at 300 °C, 600 °C, and 700 °C, was investigated by varying pH and temperature. The dissolution was reduced in all conditions with increasing silver particle size, i.e., when the total surface area of Ag particles is reduced. It is suggested that the dissolution of silver from the composite powders can conveniently be adjusted by controlling the Ag particle size by the heat treatment of the composite powder.Item Effect of ethanol on Ag@Mesoporous silica formation by in situ modified stöber method(2018-06-01) Chen, Qian; Ge, Yanling; Granbohm, Henrika; Hannula, Simo Pekka; Department of Chemistry and Materials Science; Advanced and functional MaterialsTunable core-shell Ag@Mesoporous SiO2 spheres were synthesized via an in situ modified Stöber approach by varying the amount of ethanol (EtOH) expanding their potentials in many applications. Mesoporous silica was generated by adding tetraethyl orthosilicate (TEOS) to the mixture of colloidal Ag particles prepared by reducing silver nitrate (AgNO3) with L-ascorbic acid and using hexadecyltrimethylammonium bromide (CTAB) as a template at the presence of ethanol and sodium hydroxide (NaOH) at pH 10 as a catalyst. The average sizes of the Ag cores at the three increasing volumes of ethanol were ~47 ± 6, 36 ± 4, and 11 ± 5 nm, while the silica particle size and the thickness of the silica shells increased, resulting in a blueshift of localized surface plasmon resonances (LSPR) of the Ag NPs. The corresponding specific surface areas of silica particles were 356 ± 10, 419 ± 20 and 490 ± 25 m2 g−1, and average pore diameters varied from 5.7, 5.0 to 3.3 nm according to BET and BJH analyses. TEM studies confirmed the core-shell structure, pore sizes and shapes of mesoporous shells. The dissolution tests demonstrated that the release of Ag from the powder samples is pH-sensitive and time-dependent.Item Fotokatalys: teori, material och användningsområden(2015-04-27) Ruismäki, Ronja; Granbohm, Henrika; Kemiantekniikan korkeakoulu; Forsén, OlofItem Nanosilver–silica composite: Prolonged antibacterial effects and bacterial interaction mechanisms for wound dressings(2017-09-06) Mosselhy, Dina A.; Granbohm, Henrika; Hynönen, Ulla; Ge, Yanling; Palva, Airi; Nordström, Katrina; Hannula, Simo Pekka; Department of Materials Science and Engineering; Department of Bioproducts and Biosystems; Department of Chemistry and Materials Science; Biomolecular Materials; Advanced and functional Materials; University of HelsinkiInfected superficial wounds were traditionally controlled by topical antibiotics until the emergence of antibiotic-resistant bacteria. Silver (Ag) is a kernel for alternative antibacterial agents to fight this resistance quandary. The present study demonstrates a method for immobilizing small-sized (~5 nm) silver nanoparticles on silica matrix to form a nanosilver–silica (Ag–SiO2) composite and shows the prolonged antibacterial effects of the composite in vitro. The composite exhibited a rapid initial Ag release after 24 h and a slower leaching after 48 and 72 h and was effective against both methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli). Ultraviolet (UV)-irradiation was superior to filter-sterilization in retaining the antibacterial effects of the composite, through the higher remaining Ag concentration. A gauze, impregnated with the Ag–SiO2 composite, showed higher antibacterial effects against MRSA and E. coli than a commercial Ag-containing dressing, indicating a potential for the management and infection control of superficial wounds. Transmission and scanning transmission electron microscope analyses of the composite-treated MRSA revealed an interaction of the released silver ions with the bacterial cytoplasmic constituents, causing ultimately the loss of bacterial membranes. The present results indicate that the Ag–SiO2 composite, with prolonged antibacterial effects, is a promising candidate for wound dressing applications.Item Titania and silica based nanomaterials for decontamination and antibacterial applications(Aalto University, 2018) Granbohm, Henrika; Hannula, Simo-Pekka, Prof., Aalto University, Department of Chemistry and Materials Science, Finland; Kemian ja materiaalitieteen laitos; Department of Chemistry and Materials Science; Advanced and functional materials; Kemian tekniikan korkeakoulu; School of Chemical Technology; Hannula, Simo-Pekka, Prof., Aalto University, Department of Chemistry and Materials Science, FinlandThe nanomaterials in this thesis are developed to counteract harmful organic pollutants and bacteria in our environment. Titania-based nanomaterials are prepared and the properties are examined for photocatalytic purposes to decontaminate waters with organic pollutants. Silica-silver nanomaterials are developed for antibacterial purposes. Titania-based nanotubes and composites were developed for organic contaminants removal via photocatalysis. The nanotubes were prepared by chemical solution processing and rapid breakdown anodization (RBA) methods and further subjected to heat treatment. The chemical solution processing method yielded titanate-anatase mixed crystal structures, and anatase, rutile or brookite structures when using RBA. The heat treatment caused the tubular structure to collapse into rods and further into particles in both cases. The thermal stability of the tubular structure was higher for the titanate nanotubes compared to the nanotubes prepared by RBA. The surface area and amount of hydroxide functional groups reduced upon increasing heat treatment temperatures. The titania based composite consisted of four components, i.e., titania, graphene oxide, silver, and silver chloride. The photocatalytic efficiency was investigated using methylene blue (MB), methyl orange (MO) and rhodamine B (RhB) under UV and/ or sunlight irradiation. The photocatalytic decolorization of MB under UV light was reduced upon increased heat treatment temperatures for the titanate nanotubes, due to the reduced hydroxyl groups and surface area. Almost complete photocatalytic decolorization of MO and RhB was achieved using titania nanotubes under sunlight irradiation. The graphene oxide/titania/silver/silver chloride composites showed a high adsorptive capability of MB, due to the abundance of hydroxyl functional groups. The photocatalytic decolorization reached 55 % under UV-light irradiation and increased by ca 80 % with the addition of graphene oxide to the titania/silver/silver chloride composites. The silica-silver composites were prepared by a modified Stöber method. The silica-silver composite powders were subjected to heat treatment to study the silver nanoparticle growth and to determine the activation energy for silver particle growth. The mean size of the silver particles grew with increasing heat treatment temperature. The activation energy for silver particle growth was determined as 0.14 eV, and the growth took place via diffusion and Ostwald ripening. The feasibility of a prolonged silver release from the composites was investigated via dissolution tests, which showed a prolonged release for at least 7 days' time. One silica-silver composite was chosen for antibacterial tests for wound dressing applications. The silica-silver composite hindered the growth of both methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli. The composite was also impregnated in a gauze to simulate a wound dressing and hindered the bacterial growth more efficiently than a commercial silver containing gauze. The antibacterial mechanism was elucidated for MRSA, where the silver ions eventually caused the loss of bacterial membranes.Item Titania nanotubes prepared by rapid breakdown anodization for photocatalytic decolorization of organic dyes under UV and natural solar light(2018-06-14) Ali, Saima; Granbohm, Henrika; Lahtinen, Jouko; Hannula, Simo-Pekka; Department of Chemistry and Materials Science; Surface Science; Advanced and functional Materials; Department of Applied PhysicsTitania nanotube (TNT) powder was prepared by rapid breakdown anodization (RBA) in a perchloric acid electrolyte. The photocatalytic efficiency of the as-prepared and powders annealed at temperatures between 250 and 550 °C was tested under UV and natural sunlight irradiation by decolorization of both anionic and cationic organic dyes, i.e., methyl orange (MO) and rhodamine B (RhB), as model pollutants. The tubular structure of the nanotubes was retained up to 250 °C, while at 350 °C and above, the nanotubes transformed into nanorods and nanoparticles. Depending on the annealing temperature, the TNTs consist of anatase, mixed anatase/brookite, or anatase/rutile phases. The bandgap of the as-prepared nanotubes is 3.04 eV, and it shifts towards the visible light region upon annealing. The X-ray photoelectron spectroscopy (XPS) results show the presence of titania and impurities including chlorine on the surface of the TNTs. The atomic ratio of Ti/O remains unchanged for the annealed TNTs, but the concentration of chlorine decreases with temperature. The photoluminescence (PL) indicate high electron-hole recombination for the as-prepared TNTs, probably due to the residual impurities, low crystallinity, and vacancies in the structure, while the highest photocurrent was observed for the TNT sample annealed at 450 °C. The TNTs induce a small degradation of the dyes under UV light; however, contrary to previous reports, complete decolorization of dyes is observed under sunlight. All TNT samples showed higher decolorization rates under sunlight irradiation than under UV light. The highest reaction rate for the TNT samples was obtained for the as-prepared TNT powder sample under sunlight using RhB (κ1 = 1.29 h−1). This is attributed to the bandgap, specific surface area and the crystal structure of the nanotubes. The as-prepared TNTs performed most efficiently for decolorization of RhB and outperformed the reference anatase powder under sunlight irradiation. This could be attributed to the abundance of reactive sites, higher specific surface area, and degradation mechanism of RhB. These RBA TNT photocatalyst powders demonstrate a more efficient use of the sunlight spectrum, making them viable for environmental remediation.