39,677 research outputs found

    Detoxification of water by semiconductor photocatalysis

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    An overview of the use of semiconductor photocatalysis for water purification is given. The basic principles of semiconductor photocatalysis are described along with the current understanding of the underlying reaction mechanism(s) and how it fits in with the major features of the observed Langmuir-Hinshelwood-type kinetics of pollutant destruction. These features are illustrated based on literature on the destruction of aqueous solutions of 4-chlorophenol as a pollutant, using titanium dioxide as the photocatalyst. The range of organic and inorganic pollutants that can be destroyed by semiconductor photocatalysis are reported and discussed. The basic considerations that need to be made when designing a reactor for semiconductor photocatalysis are considered. These include: the nature of the reactor glass, the type of illumination source, and the nature and type of semiconductor photocatalyst. The key basic photoreactor designs are reported and discussed, including external illumination, annular, and circular photoreactors. Actual designs that have been used for fixed and thin falling film semiconductor photocatalyst reactors are illustrated and their different features discussed. Basic non-concentrating and concentrating solar photoreactors for semiconductor photocatalysis are also reported. The design features of the major commercial photocatalytic reactor systems for water purification are reported and illustrated. Several case studies involving commercial photocatalytic reactors for water purification are reported. An attempt is made briefly to compare the efficacy of semiconductor photocatalysis for water purification with that of other, more popular and prevalent water purification processes. The future of semiconductor photocatalysis as a method of purifying water is considered

    Synthesis of titanate nanofibers co-sensitized with ZnS and Bi2S3 nanocrystallites and their application on pollutants removal

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    The synthesis of nanocomposite materials combining titanate nanofibers (TNF) with nanocrystalline ZnS and Bi2S3 semiconductors is described in this work. The TNF were produced via hydrothermal synthesis and sensitized with the semiconductor nanoparticles, through a single-source precursor decomposition method. ZnS and Bi2S3 nanoparticles were successfully grown onto the TNF's surface and Bi2S3-ZnS/TNF nanocomposite materials with different layouts were obtained using either a layer-by-layer or a co-sensitization approach. The samples' photocatalytic performance was first evaluated through the production of the hydroxyl radical using terephthalic acid as probe molecule. All the tested samples show photocatalytic ability for the production of this oxidizing species. Afterwards, the samples were investigated for the removal of methylene blue. The nanocomposite materials with best adsorption ability for the organic dye were the ZnS/TNF and Bi2S3ZnS/TNF. The removal of the methylene blue was systematically studied, and the most promising results were obtained considering a sequential combination of an adsorption-photocatalytic degradation process using the Bi2S3ZnS/TNF powder as a highly adsorbent and photocatalyst material.Comment: 26 pages, 10 figure

    Evaluation of the Relationship between Bulk Organic Precursors and Disinfection Byproduct Formation for Advanced Oxidation Processes

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    Advanced oxidation processes (AOPs) are gaining traction as they offer mineralization potential rather than transferring contaminants between media. However, AOPs operated with limited energy and/or chemical inputs can exacerbate disinfection byproduct (DBP) formation, even as precursors such as dissolved organic carbon, UV254, and specific UV absorbance (SUVA) decrease. This study examined the relationship between DBP precursors and formation using TiO2 photocatalysis experiments, external AOP and non-AOP data, and predictive DBP models. The top-performing indicator, SUVA, generally correlated positively with trihalomethanes and haloacetic acids, but limited-energy photocatalysis yielded contrasting negative correlations. The accuracy of predicted DBP values from models based on bulk parameters was generally poor, regardless of use and extent of AOP treatment and type of source water. Though performance improved for scenarios bounded by conditions used in model development, only 0.5% of the model/dataset pairings satisfied all measured parameter boundary conditions, thereby introducing skepticism toward model usefulness. Study findings suggest that caution should be employed when using bulk indicators and/or models as a metric for AOP mitigation of DBP formation potential, particularly for limited-energy/chemical inputs

    The Impact of Capsid Proteins on Virus Removal and Inactivation During Water Treatment Processes

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    This study examined the effect of the amino acid composition of protein capsids on virus inactivation using ultraviolet (UV) irradiation and titanium dioxide photocatalysis, and physical removal via enhanced coagulation using ferric chloride. Although genomic damage is likely more extensive than protein damage for viruses treated using UV, proteins are still substantially degraded. All amino acids demonstrated significant correlations with UV susceptibility. The hydroxyl radicals produced during photocatalysis are considered nonspecific, but they likely cause greater overall damage to virus capsid proteins relative to the genome. Oxidizing chemicals, including hydroxyl radicals, preferentially degrade amino acids over nucleotides, and the amino acid tyrosine appears to strongly influence virus inactivation. Capsid composition did not correlate strongly to virus removal during physicochemical treatment, nor did virus size. Isoelectric point may play a role in virus removal, but additional factors are likely to contribute

    Comparison of the effectiveness of chlorine, ozone, and photocatalytic disinfection in reducing the risk of antibiotic resistance pollution

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    Effectiveness of conventional chlorine and ozone disinfection on reduction of antibiotic resistance was compared with less commonly applied heterogeneous photocatalytic process. For this purpose plasmid DNA isolated from a multi-resistant Escherichia coli (E. coli) HB101 was treated in two different concentrations with the three oxidation processes. Oxidative damage on the plasmid DNA was analyzed with gel electrophoresis by comparing the extent of conformational changes in the DNA structure. The effectiveness of the applied oxidant in reducing the risk of resistance transfer was also evaluated by comparing the ability of treated plasmid DNA to transform competent cells. Chlorine did not affect plasmid DNA structure at the studied doses, while ozone and photocatalytic treatment resulted in conformational changes and the damage increased with increasing oxidant doses. Transformation experiments confirmed a similar trend. Chlorine did not affect the transformability and the cell counts of competent cells transformed with chlorine treated plasmid DNA were similar to those transformed by non-treated plasmid DNA in the control experiments

    Self-cleaning Properties of Thin Printed Layers of Titanium Dioxide

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    Tenk├ę vrstvy oxidu titani─Źit├ęho byly imobilizov├íny na sodnov├ípenat├í skla a skeln├Ż uhl├şk pou┼żit├şm jak techniky materi├ílov├ęho tisku tak metodou chemick├ęho napa┼Öov├ín├ş. Pro p┼Ö├şpravu titani─Źit├Żch sol┼» byly pou┼żity metody sol-gelu a nebo hydroterm├íln├ş synt├ęzy. Struktura p┼Öipraven├Żch vrstev byla zkoum├ína rastrovac├ş elektronovou mikroskopi├ş a mikroskopi├ş atom├írn├şch sil. Krystalick├í struktura p┼Öipraven├Żch TiO2 byla analyzov├íny pomoc├ş XRD metody. Fotoindukov├ín├í superhidrofility pripraven├Żch vzork┼» byla charakterizov├ína m─Ť┼Öen├şm kontaktn├şch ├║hl┼». Fotokatalytick├í aktivity p┼Öipraven├Żch vzork┼» byla testov├ína na fotokatalytick├ę oxidaci 2,6-dichlorindofenolu a kyseliny mraven─Ź├ş. V p┼Ö├şpad─Ť sol-gel vrstev byl zkoum├ín vliv mno┼żstv├ş nanesen├ęho TiO2 a mno┼żstv├ş PEG, kter├Ż byl do solu p┼Öid├ín jako praskliny potla─Źuj├şc├ş ─Źinidlo. V p┼Ö├şpad─Ť hydroterm├íln├şch vrstev byl zkoum├ín vliv ─Źasu a teploty synt├ęzy a mno┼żstv├ş vrstev na v├Żslednou ├║─Źinnost vzorku. U chemicky napa┼Öen├Żch vzork┼» byl zji┼í┼ąov├ín vliv intenzity z├í┼Öen├ş. Byla porovn├ína fotokatalitick├í aktivita vrstev p┼Öipraven├Żch materi├ílov├Żm tiskem a chemick├Żm napa┼Öov├ín├şm a byl vyhodnocen nejaktivn─Ťj┼í├ş vzorek.Titanium dioxide was immobilized on soda-lime glass substrates and glassy carbon substrates by two techniques: material printing and chemical vapour deposition. Two methods of sol preparation were used; sol-gel and hydrothermal synthesis. Morphology of all prepared titania layers were studied by scanning electron microscopy and atomic force microscopy analysis. Crystallite phase of prepared TiO2 was determined using XRD analysis. Photoinduced superhydrophilicity was examined using the sessile drop method. Photocatalytic activity was investigated as a degradation rate of 2,6-dichloroindophenol or formic acid. We studied the influence of sol-loading and amount of PEG on final activity in case of sol-gel process. PEG was added as an anticracking agent. The influence of time and temperature of hydrothermal synthesis or amount of layers on final efficiency was examined for hydrothermally synthesized samples. The influence of different intensities of irradiation was investigated for the layers deposited by CVD process. The activity of titania thin films prepared by material printing and CVD process was compared and the best sample was evaluated.

    Chemical vapor deposition of TiO2 for photocatalytic applications and biocidal surfaces

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    Through a few examples, we present a short review on properties and applications of TiO2 films deposited by various CVD processes. The constraints due to the growth process make difficult optimization of properties that were correlated with microstructures. We focus on the photocatalytic activity in the visible range and on the antibacterial behavior of these functional thin layers

    Photocatalytic Decomposition of Phenol under Visible and UV Light Utilizing Titanium Dioxide Based Catalysts

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    Pollution in wastewater effluvia from phenol and phenolic compounds is a common occurrence in many industrial manufacturing plants. Phenol is toxic to human beings as well as a contaminant to the environment, meanwhile, it is difficult to remove from wastewater due to its non-biodegradable nature. To boost the rate of decomposition, various catalytic approaches have been developed. With the interest of decreasing operation cost, titanium dioxide (TiO2) based catalysts have emerged as good candidates for the photocatalytic process. In this honors project, a series of TiO2 based catalysts, including TiO2, N-TiO2, Cu-TiO2, and Cu-N-TiO2, were utilized to study the decomposition of phenol. Each catalyst was studied under the visible light (589nm) and UV light (385nm) conditions. The UV-Vis spectrophotometer was used to evaluate the catalytic performance. The results revealed that the addition of nitrogen improved the decomposition rate of phenol compared with that of TiO2 itself. Copper did not show improved photocatalysis and requires further investigation
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