Catalytic degradation of Acid Orange 7 by H2O2 as promoted by either bare or V-loaded titania under UV light, in dark conditions, and after incubating the catalysts in ascorbic acid

AbstractPure and V-loaded mesoporous titania (with 2.5 wt-% V) were prepared by template-assisted synthesis and compared to commercial titania (Degussa P25), both as such and after vanadium loading. Mesoporous TiO2 occurred as pure anatase nanoparticles with higher surface area (SSA = 150 m2 g−1) than P25 (SSA = 56 m2 g−1).Degradation of the azo dye Acid Orange 7 by H2O2 was used as a test reaction: under UV light, no difference emerged between mesoporous TiO2 and P25, whereas in dark conditions, higher SSA of the mesoporous sample resulted in higher conversions. Under UV illumination, surface V5+ species inhibited photocatalytic activity, by forming inactive V4+ species. Similarly, in dark conditions, V5+ surface species reacted with H2O2, likely yielding ·O2H radicals and reducing to V4+. On the contrary, V-containing catalysts were very active after pretreatment with ascorbic acid, which reduced V5+ species to V3+species, the latter promoting very lively a Fenton-like reaction

Mesoporous Titania: Synthesis, Properties and Comparison with Non-Porous Titania

Some relevant physico-chemical and photocatalytic properties of ordered mesoporous TiO2 as obtained by template-assisted synthesis methods are reported. After a review of the crucial aspects related to different synthesis procedures reported by the literature, the focus is pointed on the (often) superior physico-chemical properties of ordered mesoporous TiO2 with respect to (commercial) bulk TiO2. Those are essentially higher specific surface area and ordered mesoporosity; possibility to control the formation of different crystalline phases by varying the synthesis conditions and possibility to obtain films, nanoparticles with different morphologies and/or materials with hierarchical porosity. Although mesoporous TiO2 is extensively studied for many applications in the fields of photocatalysis, energy and biomedicine, this chapter focuses on the use of mesoporous TiO2 in environmental photocatalysis, by putting in evidence how the physico-chemical properties of the material may affect its photocatalytic behaviour and how mesoporous TiO2 behaves in comparison with commercial TiO2 samples

A decadal perspective on north water microbial eukaryotes as Arctic Ocean sentinels

The North Water region, between Greenland and Ellesmere Island, with high populations of marine birds and mammals, is an Arctic icon. Due to climate related changes, seasonal patterns in water column primary production are changing but the implications for the planktonic microbial eukaryote communities that support the ecosystem are unknown. Here we report microbial community phenology in samples collected over 12 years (2005–2018) from July to October and analysed using high throughput 18S rRNA V4 amplicon sequencing. Community composition was tied to seasonality with summer communities more variable than distinct October communities. In summer, sentinel pan- Arctic species, including a diatom in the Chaetoceros socialis-gelidus complex and the picochlorophyte Micromonas polaris dominated phytoplankton and were summer specialists. In autumn, uncultured undescribed open water dinoflagellates were favored, and their ubiquity suggests they are sentinels of arctic autumn conditions. Despite the input of nutrients into surface waters, autumn chlorophyll concentrations remained low, refuting projected scenarios that longer ice-free seasons are synonymous with high autumn production and a diatom dominated bloom. Overall, the summer sentinel microbial taxa are persisting, and a subset oceanic dinoflagellate should be monitored for possible ecosystem shifts as later autumn ice formation becomes prevalent elsewhere

Application of reverse micelle sol-gel synthesis for bulk doping and heteroatoms Surface Enrichment in Mo-Doped TiO 2 nanoparticles

TiO 2 nanoparticles containing 0.0, 1.0, 5.0, and 10.0 wt.% Mo were prepared by a reverse micelle template assisted sol-gel method allowing the dispersion of Mo atoms in the TiO 2 matrix. Their textural and surface properties were characterized by means of X-ray powder diffraction, micro-Raman spectroscopy, N 2 adsorption/desorption isotherms at -196 °C, energy dispersive X-ray analysis coupled to field emission scanning electron microscopy, X-ray photoelectron spectroscopy, diffuse reflectance UV-Vis spectroscopy, and ζ-potential measurement. The photocatalytic degradation of Rhodamine B (under visible light and low irradiance) in water was used as a test reaction as well. The ensemble of the obtained experimental results was analyzed in order to discover the actual state of Mo in the final materials, showing the occurrence of both bulk doping and Mo surface species, with progressive segregation of MoO x species occurring only at a higher Mo content

Brookite, a sometimes under evaluated TiO2polymorph

Some of the advancements concerning the study of phase-pure brookite and, especially, brookite-containing TiO2 mixed phases are reviewed. Relevance is given to their prospective photocatalytic applications, where the (positive) effect of the presence of brookite has been demonstrated, especially when solar light is concerned. From the literature, it emerges that, besides the band gap determination, which still requires more detailed studies (band gap values in a wide range are reported), the roles of brookite-containing heterojunctions, of the surface properties (i.e. acidity, redox behaviour, and the presence of coordinatively unsaturated sites), of the particular crystalline structure and of brookite influence on the anatase to rutile transition are crucial for its applications in the field of (solar) photocatalysis and electrocatalysis, but also electrochemical applications (i.e. Li batteries). The need emerges for a deeper understanding of the physico-chemical phenomena underlying their (recently demonstrated) capacity of stabilizing photogenerated electron/hole pairs. In perspective, the development of green synthesis methods to tailor the surface and structural properties of phase-pure brookite and brookite-containing mixed phases could extend their photo- and electrochemical applications

Photocatalysts for organics degradation

Organics degradation is one of the challenges of Advanced Oxidation Processes (AOPs), which are mainly employed for the removal of water and air pollutants [...

Undoped and Fe-Doped Anatase/Brookite TiO2 Mixed Phases, Obtained by a Simple Template-Free Synthesis Method: Physico-Chemical Characterization and Photocatalytic Activity towards Simazine Degradation

For the first time, Fe-doping (0.05, 1.0, and 2.5 wt.% Fe) was performed on a high-surface-area anatase/brookite TiO2 by adopting a simple template-free sol-gel synthesis followed by calcination at a mild temperature. The powders’ textural and surface properties were characterized by following a multi-technique approach. XRD analysis showed that the anatase/brookite ratio slightly varied in the Fe-doped TiO2 (from 76.9/23.1 to 79.3/22.7); Fe doping noticeably affected the cell volume of the brookite phase, which decreased, likely due to Fe3+ ions occupying interstitial positions, and retarded the crystallite growth. N2 sorption at −196 °C showed the occurrence of samples with disordered interparticle mesopores, with an increase in the specific surface area from 236 m2 g−1 (undoped TiO2) to 263 m2 g−1 (2.5 wt.% Fe). Diffuse Reflectance UV-Vis spectroscopy showed a progressive decrease in the bandgap energy from 3.10 eV (undoped TiO2) to 2.85 eV (2.5 wt.% Fe). XPS analysis showed the presence of some surface Fe species only at 2.5 wt.% Fe, and accordingly, the ζ-potential measurements showed small changes in the pH at the isoelectric point. The photocatalytic degradation of simazine (a persistent water contaminant) both under UV and simulated solar light was performed as a probe reaction. Under UV light, Fe-doping improved simazine degradation in the sample at 0.05 wt.% Fe, capable of degrading ca. 77% simazine. Interestingly, the undoped TiO2 was also active both under UV and 1 SUN. This is likely due to the occurrence of anatase/brookite heterojunctions, which help stabilize the photogenerated electrons/holes

Aperçus taxonomiques et génomiques des communautés microbiennes face à un environnement fluctuant dans la Polynie des Eaux du Nord (Canada-Groenland)

En raison de la fonte pluriannuelle des glaces dans l'Océan Arctique et de la fonte de la calotte glaciaire du Groenland, les communautés microbiennes sont exposées à de plus grandes fluctuations de salinité au cours de la saison de croissance et dans de vastes zones géographiques. Les Eaux du Nord très productives ont subi des changements marqués dans les tendances saisonnières de la chlorophylle de surface observées grâce à la télédétection et les données in situ, mais l'interprétation de ces données en termes d'espèces reste difficile puisque la phénologie de la communauté et la variabilité spatio-temporelle sont encore inconnues. Il est essentiel de bien comprendre la dynamique des assemblages de phytoplancton et d'autres espèces microbiennes pour comprendre les réponses des écosystèmes face au changement global. De plus, les grandes fluctuations de salinité ou stress salin et le choc osmotique sont parmi les principaux facteurs environnementaux limitant la croissance et la productivité des plantes et des microorganismes. Pour combler ce manque de connaissance, nous avons premièrement appliqué le séquençage d'amplicon à haut débit pour étudier les communautés microbiennes d'eucaryotes arctiques d'été et d'automne des deux côtés du nord de la baie de Baffin sur plus de 12 ans (2005 à 2018). Ces communautés sont soumises à des régimes de stratification et de courants opposés. Deuxièmement, nous avons étudié la réponse transcriptionnelle d'une microalgue associée à la glace exposée à des salinités progressivement décroissantes afin de mieux comprendre la capacité génétique de cette algue à tolérer les fluctuations de salinité, ainsi que d'identifier les gènes de stress clés. Enfin, nous avons combiné une approche métagénomique comparative avec le séquençage des amplicons d'ARNr 18S pour étudier les capacités fonctionnelles, la diversité et la dynamique des microorganismes dans la colonne d'eau supérieure du nord de la baie de Baffin pendant deux étés consécutifs (2017-2018). Nous avons constaté que la saisonnalité était un facteur majeur déterminant les assemblages de communauté des eaux de surface estivales avec le complexe d'espèces Chaetoceros socialis-gelidus et Micromonas polaris dominant le phytoplancton, et les Alpha et Gammaproteobactéries dominant la communauté bactérienne. En automne, les dinoflagellés d'eau libre non-cultivés et non-décrits étaient favorisés. Nos résultats suggèrent que la production automnale de l'Arctique, due à des conditions d'eau libre plus longue, pourrait ne pas refléter une floraison printanière dominée par les diatomées, comme le prévoient certains scénarios des saisons sans glace plus longues. Par ailleurs, une réponse progressive et une adaptation spécifique aux conditions arctiques froides et salines ont été observées avec l'expression différentielle de plusieurs protéines antigel, comme la protéine de liaison à la glace et une acyl-estérase toutes deux impliquées dans l'adaptation au froid. Nos résultats suggèrent que la protéine de liaison à la glace peut également jouer un rôle crucial dans l'adaptation à un changement rapide de salinité et à la survie cellulaire. Par ailleurs, grâce à l'annotation fonctionnelle, nous avons examiné les gènes impliqués dans la protection des photosystèmes, la régulation osmotique et les protéines antigel, cruciales pour l'acclimatation à un environnement froid. L'utilisation de la génomique comparative permettrait de révéler les évolutions des familles de gènes conférant l'adaptation des microorganismes aux transitions entre eau salée et eau douce. Ce travail de thèse aura des implications non seulement pour l'Arctique où les communautés de surface sont soumises à de grandes fluctuations de salinité, de température et de lumière, mais il contribuera également aux connaissances fondamentales dans les domaines de la production de biocarburants et de la prévision des efflorescences algales potentiellement nuisibles.As the Arctic Ocean freshens due to multiyear ice and Greenland Ice Sheet melt, the microbial communities are being exposed to greater salinity fluctuations over the growth season and across wide geographic areas. Although remote sensing and limited in situ data have shown that the highly productive North Water has undergone marked changes in the seasonal patterns of surface chlorophyll. Interpreting this data in terms assemblages of species is difficult since the community phenology and spatiotemporal variability is unknown. Understanding the dynamics of phytoplankton and other microbial species assemblages is critical to understand ecosystem responses to global change. Moreover, greater salinity fluctuations or salt stress and osmotic shock are among the main environmental factors limiting the growth and productivity of plants and microorganisms. To address this knowledge gap, firstly, high throughput amplicon sequencing was applied to investigate summer-fall Arctic microbial communities from two sides of Northern Baffin Bay over 12 years (2005 to 2018), that are subjected to very different stratification and major current regimes. Secondly, we investigated the transcriptional response of an ice-associated microalga exposed to progressively decreasing salinities to gain a deeper understanding of the genetic capacity of this alga to tolerate salinity fluctuations, as well as to identify key stress genes. And lastly, we combined comparative metagenomic approach with 18S rRNA amplicon sequencing to investigate the functional capacities, diversity and dynamics of the microorganisms in upper water column of the Northern Baffin Bay during two consecutive summers (2017-2018). We found that seasonality was a major factor determining communities with summer species complex Chaetoceros socialis-gelidus and Micromonaspolaris dominating phytoplankton and Alpha and Gammaproteobacteria dominating bacterial community. In autumn uncultured undescribed open water dinoflagellates were favored. Our results suggest that Arctic autumn production due to longer open water conditions may not mirror a diatom dominated spring bloom as projected in some scenarios of longer ice-free seasons. Furthermore, a gradual response and specific adaptation to cold saline Arctic conditions were seen with differential expression of several antifreeze proteins, an ice-binding protein and acyl-esterase involved in cold adaptation. Our results suggest that ice-binding protein may also have a crucial role for the adaptation of a rapid change of salinity, by providing survival advantage to the cells. Moreover, through functional annotation, we examined potential genes involved in photosystem protection, osmotic regulation and antifreeze proteins, to be crucial for acclimatization to cold environment. The use of comparative genomics would reveal evolutions of gene families conferring adaptation of microorganisms to transitions between salt and fresh water. The combination of these several methodologies provides invaluable insights into the composition, the metabolic repertoire and putative functional profile of a microbial assemblage. This thesis work will have implications not only for the Arctic where surface communities are subject to large fluctuations in salinity and light but will also contribute to fundamental knowledge in the fields of biofuel production and harmful algal bloom prediction

Effects of the Brookite Phase on the Properties of Different Nanostructured TiO2 Phases Photocatalytically Active Towards the Degradation of N-Phenylurea

Different sol-gel synthesis methods were used to obtain four nanostructured mesoporous TiO2 samples for an efficient photocatalytic degradation of the emerging contaminant N-phenylurea under either simulated solar light (1 Sun) or UV light. Particularly, two TiO2 samples were obtained by means of as many template-assisted syntheses, whereas other two TiO2 samples were obtained by a greener template-free procedure, implying acidic conditions and, then, calcination at either 200 °C or 600 °C. In one case, anatase was obtained, whereas in the other three cases mixed crystalline phases were obtained. The four TiO2 samples were characterized by X-ray powder diffraction (followed by Rietveld analysis); Transmission Electron Microscopy; N2 adsorption/desorption at −196 °C; Diffuse Reflectance UV/Vis spectroscopy and ζ-potential measurements. A commercial TiO2 powder (i. e., Degussa P25) was used for comparison. Differences among the synthesized samples were observed not only in their quantitative phase composition, but also in their nanoparticles morphology (shape and size), specific surface area, pore size distribution and pHIEP (pH at isoelectric point), whereas the samples band-gap did not vary sizably. The samples showed different photocatalytic behavior in terms of N-phenylurea degradation, which are ascribed to their different physico-chemical properties and, especially, to their phase composition, stemming from the different synthesis conditions

Pure and Fe-doped mesoporous titania catalyse the oxidation of acid orange 7 by H2O2 under different illumination conditions: Fe doping improves photocatalytic activity under simulated solar light

A sample of mesoporous TiO2 (MT, specific surface area = 150 m2\uc2\ub7g\ue2\u88\u921) and two samples of MT containing 2.5 wt.% Fe were prepared by either direct synthesis doping (Fe2.5-MTd) or impregnation (Fe2.5-MTi). Commercial TiO2 (Degussa P25, specific surface area = 56 m2\uc2\ub7g\ue2\u88\u921) was used both as a benchmark and as a support for impregnation with either 0.8 or 2.5 wt.% Fe (Fe0.80-IT and Fe2.5-IT). The powders were characterized by X-ray diffraction, N2 isotherms at \ue2\u88\u92196\ue2\u97\ua6C, Energy Dispersive X-ray (EDX) Spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Diffuse Reflectance (DR) ultra-violet (UV)-Vis and M\uc3\ub6ssbauer spectroscopies. Degradation of Acid Orange 7 (AO7) by H2O2 was the test reaction: effects of dark-conditions versus both UV and simulated solar light irradiation were considered. In dark conditions, AO7 conversion was higher with MT than with Degussa P25, whereas Fe-containing samples were active in a (slow) Fenton-like reaction. Under UV light, MT was as active as Degussa P25, and Fe doping enhanced the photocatalytic activity of Fe2.5-MTd; Fe-impregnated samples were also active, likely due to the occurrence of a photo-Fenton process. Interestingly, the Fe2.5-MTd sample showed the best performance under solar light, confirming the positive effect of Fe doping by direct synthesis with respect to impregnation