Academic literature on the topic 'Silver-titanium nanoparticles'

Titanium dioxide nanoparticles combined with silver and hydroxyapatite (TiO₂-Ag-Hap) form a photocatalytic composite capable of oxidizing and mineralizing a wide spectrum of microbiological and chemical contaminants in water, while silver nanoparticles have long been employed for their antimicrobial properties. These materials were evaluated through an iterative series of experiments that evaluated microbial reduction, material formulation, method of application, surface-interface interactions, and reusability. The TiO₂ formulation was assessed as an antimicrobial film coated onto fabric and ceramic beads in three experimental designs: a gravity filtration column, a portable treatment capsule, and a static chamber. Colloidal floating Ag nanoparticles in solution were also assessed. Reduction of Escherichia coli, Klebsiella terrigena, MS2 bacteriophage, and Rotavirus was evaluated though standard culture-based methods. Significant microbial reduction was only observed in the static open pan design for the TiO₂-Ag-HAp materials. Colloidal silver was more effective and caused a 5 log reduction of K. terrigena, within 60 minutes, and a 5 and 4 log reduction of MS2 within 120 and 90 minutes respectively in initial trials. The anti-microbial properties of both materials were apparent, but further investigations are necessary to assess the potential of the materials for integration and development in water treatment technologies.

>Magister Scientiae - MSc<br>The global lack of clean water for human sanitation and other purposes has become an emerging dilemma for human beings. The presence of organic pollutants in wastewater produced by textile industries, leather manufacturing and chemical industries is an alarming matter for a safe environment and human health. For the last decades, conventional methods have been applied for the purification of water but due to industrialization these methods fall short. Advanced oxidation processes and their reliable application in degradation of many contaminants have been reported as a potential method to reduce and/or alleviate this problem. Lately, it has been assumed that incorporation of some metal nanoparticles such as magnetite nanoparticles as photocatalyst for Fenton reaction could improve the degradation efficiency of contaminants. Core/shell nanoparticles, are extensively studied because of their wide applications in the biomedical, drug delivery, electronics fields and water treatment. The current study is centred on the synthesis of silver-doped Fe₃O₄/SiO₂/TiO₂ photocatalyst. Magnetically separable Fe₃O₄/SiO₂/TiO₂ composite with core–shell structure were synthesized by the deposition of uniform anatase TiO₂ NPs on Fe₃O₄/SiO₂ by using titanium butoxide (TBOT) as titanium source. Then, the silver is doped on TiO₂ layer by hydrothermal method. Integration of magnetic nanoparticles was suggested to avoid the post separation difficulties associated with the powder form of the TiO₂ catalyst, increase of the surface area and adsorption properties. Lastly and most importantly magnetic nanoparticles upsurge the production of hydroxyl groups or reduced charge recombination. The a synthesized catalysts were characterized using Transmission Electron Microscopy, X-ray Diffraction; Infra-red Spectroscopy, Scanning Electron Microscope and Energy Dispersive Spectroscopy. Other characterization techniques includeVibrating Sample Magnetometry, Brunauer Emmett Teller analysis and Thermogravimetric analysis. The average size of the particles size is 72 nm. Furthermore the photocatalytic performances of the magnetic catalysts were assessed in comparison with that commercial titanium dioxide for the degradation of methylene blue using photochemical reactor under ultra violet light. The results showed that the photocatalytic activity was enhanced using Fe₃O₄/SiO₂/TiO₂ and Ag-Fe₃O₄/SiO₂/TiO₂ compared with that for Fe₃O₄, commercial titanium dioxide powder.

The extensive use of nanoparticles (NPs) has started receiving increased attention because of the knowledge gaps regarding their fate in the environment and the possible impact on the environment and human health. The production of silver nanoparticles (AgNPs) and titanium dioxide nanoparticles (TiO2-NPs) is increasing and it is expected that, due to their great number of applications, their concentration in waste streams will increase in the future. The presence of NPs in waste streams may affect the treatment process (e.g., composting) and, if they are not successfully removed from the waste streams, their presence in the treated waste (e.g., compost) may present an environmental risk. Composting of the biodegradable fractions of municipal solid waste (MSW) is a widely used waste management practice, mainly because it is a cost-effective treatment technology and the final product (i.e., compost) presents several benefits to the environment, particularly as a soil conditioner. The overall aim of this thesis is to assess the effect of Ag-TiO2NPs and AgNPs that may be present in the biodegradable fractions of municipal solid waste on composting and subsequent soil application of compost. For that purpose in-vessel composting of artificial municipal solid waste contaminated with commercial nanoparticles was investigated at laboratory scale, simulating a range of relevant concentration levels. Subsequently, the fate of NPs present in mature compost use as a top-layer soil conditioner was investigated using a column approach at laboratory scale. The toxicity effect of NPs present mature compost on plant growth was further investigated. The impact of NPs during composting was assessed by monitoring the temporal dynamics of organic matter (OM) using Excitation Emission Matrix (EEM) fluorescence spectroscopy. The fate of NPs following application of contaminated mature compost as a top-soil conditioner and potential release to groundwater was investigated using a column leaching experiment while the phytotoxicity of mature compost contaminated with NPs was assessed using a seed germination bioassay. Finally, to investigate further possible environmental impacts due to the application of mature compost contaminated with NPs to soils, a Life Cycle Assessment (LCA) was conducted. The impact of commercial Ag-TiO2 NPs and AgNPs on the in-vessel composting of biodegradable municipal solid waste was investigated over 21 days, using initial concentrations of 0, 5, 10, 20 and 50 mg Ag / kg of OM. Microbial activity was inhibited in the biodegradable waste reactors using 2% NaN3 to evaluate abiotic losses. Physicochemical parameters such as pH, ash content, weight loss, and the formation of humic substances (HS) were determined after 0, 4, 7, 14 and 21 days of composting and after a maturation phase. The results indicated that the presence of 2% NaN3 in biodegradable MSW inhibited effectively the microbial activity during the first week of composting. The microbial population was activated during the second week of composting but the decomposition rate was so low that did not result in the formation of humic substances (HS) following 21 days of composting when 2% NaN3 was used. Both treatments, using Ag-TiO2-NPs and AgNPs, did not show any inhibition of the decomposition process for all the tested concentrations and EEM peaks shifted towards the HS region during in-vessel composting. Higher inorganic carbon removal resulted from NP-contaminated compost with higher NP concentrations. This may indicate that the formation of humins was higher for non-contaminated compost and decreased as the NP concentration in waste increased. The shift of the peaks towards the HS region during composting for all the treatments suggested that NPs did not have an effect on humification and therefore on compost stability. The leaching properties of the NP-contaminated compost were investigated using a column leaching test. Five samples of leachate, of 50 mL each, were collected. The highest concentrations of HS were observed in the first two leaching samples. The leaching results suggested that only a low percentage of the total NPs (in weight) in compost, up to ca. 5% for Ag and up to ca. 15% for Ti, leached out from the columns, which was assumed the amount that potentially could leach to the environment. These results suggested that NPs will mainly accumulate in soils’ top layers following application of compost contaminated with NP. The phytotoxicity of NP-contaminated compost was assessed using a seed germination bioassay and the germination index was then calculated. The results indicated that the NP-contaminated compost did not present any toxic effects to cress germination. The possible environmental impacts due to the NP-contaminated compost application to soils were investigated by conducting a comparative LCA study. The LCA study indicated that the effects of NP-contaminated compost to human health and ecosystems endpoint categories increased due to the presence of NPs. The risks are associated with terrestrial ecotoxicity and human toxicity midpoint categories and are mainly attributed to the accumulation of Ag to soils.

>Magister Scientiae - MSc<br>Despite the wide success of antimicrobial agents against waterborne pathogens, waterborne disease continues to pose a threat to both mankind and animals. A major concern is that certain bacteria have developed resistance to antimicrobial agents, as a result of their overuse. Silver (Ag) nanoparticles are widely used for antibacterial purposes such as medical dressings. However, they are highly toxic to human cells. Hence, there is a great interest in developing next generation antibacterial nanoparticles that are as effective as Ag nanoparticles for antibacterial functions, while having less toxicity to human cells. Several methods can be used to generate these antimicrobial nanoparticles, one of which is green nanotechnology. Green nanotechnology uses natural plants such as tea to synthesise nanoparticles rather than chemicals, thus reduce human and animal harm and improve sustainability of antibacterial agents. Silver-titanium nano-composites (Ag-TiO2 NCs) were synthesised with the hydrothermal method using a tea extract from Aspalathus linearis (Rooibos, RB), and distilled water in the presence of nitrogen. The resulting structures were characterised with high resolution transmission electron microscopy (HRTEM), energy-dispersive spectroscopy (EDS) analysis X-Ray Diffraction (XRD) and Thermogravimetric Analysis (TGA). The antibacterial characteristics of these new NCs were evaluated against 3 bacteria: Bacillus cereus, Cupriavidus metallidurans, and Escherichia coli. The optimum processing conditions to produce 6-nm spherical NPs included maintaining the temperature at 90 °C, the pH at 4.35, and using RB extract at a concentration of 2 mg/mL. The size of silver NPs was reduced in acidic conditions, agglomerated in neutral conditions, and highly reduced in alkaline conditions. Increasing the pH decreased the particle size and narrowed the particle size distribution. Gram-positive B. cereus showed slight resistance or tolerance to the Ag-TiO2 nanocomposite compared to the gram-negative bacteria E. coli and C. metallidurans. The treatment concentration required for total inhibition of E. coli and C. metallidurans growth was 100 mg/mL. Supported silver nanoparticles has shown to be a suitable way to obtain highly dispersed silver over higher surface area. This approach allowed Ag-TiO2 nanocomposite to be an efficient bactericide, with less silver amount employed.

Microbial resistance to the current available antibiotics is considered a global health problem, especially for the Multi-Drug Resistant pathogens (MDR) including methicillin resistant Staphylococcus aureus. Recently nanoparticles (NPs) have been involved in variety of antimicrobial applications due to their unique properties of antibacterial effects. However, the molecular mechanisms behind their antibacterial activity are still not fully understood. In this study, we produced silver Ag NPs (average size 27 nm) and silver-Titanium Ag-TiO2 NPs (average size 47 nm) using picosecond laser ablation. Our results showed that both laser NPs had obvious size-dependent antibacterial activity. The laser Ag NPs with a size of 19 nm and Ag-TiO2 NPs with a size 20 nm presented the highest bactericidal effect. The laser generated Ag and Ag-TiO2 NPs with concentrations 20, 30, 40, and 50 Î1⁄4g/ml showed strong antibacterial effect against three bacterial strains: E. coli, P. aeruginosa, and S. aureus, and induced the generation of reactive oxygen species (ROS), lead to cell membrane interruption, lipid peroxidation, DNA damages, glutathione depletion and the eventual cell death. Both types of laser NPs at two concentrations (2.5 and 20 Î1⁄4g/ml) showed low cytotoxicity to the in vitro cultured five types of human cells originated from the lung (A549), kidney (HEK293), Liver (HepG2), skin (HDFc) and blood vessel cells (hCAECs). The antibacterial activity of the laser generated Ag and Ag-TiO2 NPs had lasted for over one year depending on the degree of air exposure and storage conditions. Frequent air exposure increased particle oxidation and reduced the antibacterial durability of the laser generated Ag NPs. The laser generated Ag NPs had lower antibacterial activity when stored in cold compared to that stored at room temperature. The antibacterial activity of laser generated Ag and Ag-TiO2 NPs were also compared with four types of commercial based-silver wound dressings (Acticoat TM, Aquacel® Ag, Contreet ®Foam, and Urgotul® SSD) against E. coli to inform future application in this area. In conclusion, laser generated Ag and Ag-TiO2 NPs have strong bactericidal effect and low toxicity to human cells which could be a type of promising antibacterial agents for future hygiene and medical applications.

Orientador: Wilson de Figueiredo Jardim<br>Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química<br>Made available in DSpace on 2018-08-19T04:25:34Z (GMT). No. of bitstreams: 1 Marcone_GlaucienePauladeSouza_D.pdf: 3873346 bytes, checksum: 7b3d84f078c155427661a732b0d8a73b (MD5) Previous issue date: 2011<br>Resumo: O principal objetivo deste trabalho foi estudar as interações de nanopartículas de Ag ou nanoprata (nAg ou AgNP) e nanopartículas do semicondutor TiO2 (nTiO2) com a matriz aquática, a fim de avaliar a sua toxicidade a representantes da biota aquática. Estes dois tipos de nanomateriais (NM) foram escolhidos, pois atualmente estão sendo comercializados em grande escala por apresentarem ampla aplicação industrial. Este trabalho envolveu as seguintes etapas: a) síntese de TiO2 na forma de pó e de amostras de AgNP por rotas sintéticas estabelecidas pela literatura; b) caracterização dos NM sintetizados quanto ao tamanho e a morfologia, e no caso das suspensões de AgNP foi realizada a especiação da prata a fim de nortear uma avaliação mais criteriosa sobre ecotoxicidade destas suspensões; c) avaliação da atividade bactericida das amostras de AgNP e do TiO2 sintetizados. Para isto, utilizou-se a bactéria E. coli e um sistema FIA/Condutimétrico para medir a inibição bacteriana através da produção de CO2. d) avaliação da ecotoxicidade das suspensões de AgNP e TiO2 no meio aquático. Foram utilizados os organismos aquáticos: V. fischeri (bactéria marinha), D. similis (microscrustáceo de água doce) e P. subcapitata (alga de água doce). Devido à fotoatividade do TiO2, os testes com D. similis foram adaptados, incorporando a radiação UV-A durante o teste. As amostras de AgNP foram tóxicas aos organismos aquáticos testados nas seguintes faixas de concentração: P. subcapitata (IC50 = 1-122 mg L), D. similis (CE50 = 0,5-50 mg L) e V. fischeri (CE50 = 5,2-32,2 mg L). As amostras de TiO2 se mostraram mais tóxicas para a D. similis (CE50 = 8-57 mg L) em relação ao V. fischeri (CE50 > 100 mg L). A caracterização das amostras de TiO2 e AgNP sintetizadas indicou que fatores como fotoatividade do TiO2 e a concentração de íons Ag nas suspensões de AgNP foram determinantes para a ecotoxicidade apresentada por estas amostras<br>Abstract: The objective of this work was to evaluate the toxicity of silver nanoparticles or nanosilver (nAg or AgNP) and TiO2 semiconductor nanoparticles to some biotic representative aquatic organisms. These two nanomaterials (NM) types were chosen because they are currently being market on a large scale due to their wide industrial application. The work was developed in accordance to the following steps: a) Synthesis of TiO2 powder and AgNP samples by current synthetic routes. b) Shape, morphology and optical characterization of TiO2 powder and AgNP synthesized samples. The Ag speciation was performed in the AgNP suspensions to improve the ecotoxicological assessment of this material; c) Bactericidal activity assessment of TiO2 and AgNP samples using E. coli. The inhibition of the bacterial growth was followed by CO2 produced using a FIA/Conductivity system; d) Ecotoxicity assessment of TiO2 and AgNP suspensions to aquatic organisms. The aquatic organisms used were V. fischeri (marine bacterium), D. similis (microcrustace freshwater) and P. subcapitata (algae freshwater). Due to the TiO2 photoactivity, the tests with D. similis were adapted by include to UV-A radiation during the whole test period. The results showed that AgNP samples were toxic to aquatic organisms in the following ranges: P. subcapitata (CI50 = 1-122 mg L), D. similis (EC50 = 0.5-50 mg L) and V. fischeri (EC50 = 5.2-32.2 mg L). The TiO2 samples were more toxic to the D. similis (EC50 = 8-57mg L) compared to V. fischeri (CE50 > 100 mg L). The characterization of TiO2 and AgNP synthesized samples indicated that factors such as TiO2 photoactivity and Ag ions concentration in AgNP suspensions were responsible to the ecotoxicity showed by this samples<br>Doutorado<br>Quimica Analitica<br>Doutor em Ciências