Pathways to relativistic curved momentum spaces: de Sitter case study

© 2016 World Scientific Publishing Company Several arguments suggest that the Planck scale could be the characteristic scale of curvature of momentum space. As other recent studies, we assume that the metric of momentum space determines the condition of on-shellness while the momentum space affine connection governs the form of the law of composition of momenta. We show that the possible choices of laws of composition of momenta are more numerous than the possible choices of affine connection on a momentum space. This motivates us to propose a new prescription for associating an affine connection to momentum composition, which we compare to the one most used in the recent literature. We find that the two prescriptions lead to the same picture of the so-called (Formula presented.)-momentum space, with de Sitter (dS) metric and (Formula presented.)-Poincaré connection. We then show that in the case of “proper dS momentum space”, with the dS metric and its Levi–Civita connection, the two prescriptions are inequivalent. Our novel prescription leads to a picture of proper dS momentum space which is DSR-relativistic and is characterized by a commutative law of composition of momenta, a possibility for which no explicit curved momentum space picture had been previously found. This momentum space can serve as laboratory for the exploration of the properties of DSR-relativistic theories which are not connected to group-manifold momentum spaces and Hopf algebras, and is a natural test case for the study of momentum spaces with commutative, and yet deformed, laws of composition of momenta

Green synthesis of vanillin: Pervaporation and dialysis for process intensification in a membrane reactor

In the present work, two different membrane processes (pervaporation and dialysis) are compared in view of their utilization in a membrane reactor, where vanillin, which is probably the most important aroma of the food industry, is synthesized in a green and sustainable way. The utilized precursor (ferulic acid, which is possibly a natural product from agricultural wastes) is partially oxidized (photocatalytically or biologically) and the product is continuously recovered from the reacting solution by the membrane process to avoid its degradation. It is observed that pervaporation is much more selective towards vanillin than dialysis, but the permeate flux of dialysis is much higher. Furthermore, dialysis can work also at lower temperatures and can be used to continuously restore the consumed substrate into the reacting mixture. A mathematical model of the integrated process (reaction combined with membrane separation) reproduces quite satisfactorily the experimental results and can be used for the analysis and the design of the process

Overview on oxidation mechanisms of organic compounds by TiO2 in heterogeneous photocatalysis

This review provides the reader with a general overview on heterogeneous photocatalytic oxidation mechanisms in the presence of TiO2, with a special address to conversion of aliphatic and aromatic organic species. The aim was to clarify the steps of the photo-oxidation of the various classes of compounds and to relate them with the properties of the catalysts and the experimental conditions used. Reactions carried out to perform complete degradation and photocatalytic partial oxidations have been deeply discussed. Recent isotopic studies highlighted new reaction pathways concerning partial oxidation of alcohols to aldehyde and oxidation of benzene while EPR investigations confirmed that not only the photogenerated hole but also the OH radicals are involved in the oxidation of the substrates

Visible Light Induced Oxidation of Trans-ferulic Acid by TiO2 Photocatalysis

The oxidation of trans-ferulic acid (C 10H 10O 4) in aqueous TiO 2 dispersion occurs via the formation of a charge-transfer complex on the TiO 2 surface that is able to absorb visible light (\u3bb 65 400 nm). The main product is CO 2, whereas secondary oxidation products are organic species such as vanillin, caffeic acid, homovanillic acid, and vanillylmandelic acid. Oxidation through the formation of a charge-transfer complex occurs only in the presence of specific TiO 2 samples. Experiments in the absence of oxygen, in the presence of bromate ions and by using a phosphate-modified TiO 2, have been carried out for investigating the reaction mechanism. In order to study the interaction between trans-ferulic acid and TiO 2 surface and to characterize the charge-transfer complex, UV-Vis diffuse reflectance and FT-IR spectroscopies have been used. FT-IR characterization of TiO 2 samples in contact with the aqueous trans-ferulic acid solution indicates that the charge-transfer complex formation occurs via adsorption of bidentate ferulate species

Sequential biological and photocatalysis based treatments for shipboard slop purification: A pilot plant investigation

This study investigated the treatment of a shipboard slop containing commercial gasoline in a pilot plant scale consisting of a membrane biological reactor (MBR) and photocatalytic reactor (PCR) acting in series. The MBR contributed for approximately 70% to the overall slop purification. More precisely, the biological process was able to remove approximately 40%, on average, of the organic pollution in the slop. Nevertheless, the membrane was capable to retain a large amount of organic molecules within the system, amounting for a further 30% of the influent total organic content removal. However, this affected the membrane fouling, thus resulting in the increase of the pore blocking mechanism that accounted for approximately 20% to the total resistance to filtration (2.85∙10 13 m −1 ), even if a significant restoration of the original membrane permeability was obtained after chemical cleanings. On the other hand, the biological treatment produced a clear solution for the photocatalytic system, thereby optimizing the light penetration and generation of highly oxidizing active oxygen species that enabled the degradation of bio-recalcitrant compounds. Indeed, low total organic carbon (TOC) values (<10 mg L −1 ) were achieved in the output of the photocatalytic reactor by means of only 60 Einstein (E) of cumulative impinging energy after the addition of K 2 S 2 O 8 . Overall, coupling the two processes enabled very high TOC removal (ca. 95%)

Investigating the activity of modified TiO2 photocatalysts used for the photoreforming of biomass derivatives

Different TiO2 modified (with Pt, Cu2O, Nb) photocatalysts have been compared for the photo-reforming of glucose and fructose at ambient conditions with the aim of linking the photoactivity to some structural and surface characteristics. A different degree of conversion, distribution of intermediates and H2 production were observed with the various photocatalysts. Moreover, the results obtained with the same catalysts were slightly different with the two substrates, highlighting the importance of the interaction between the catalyst surface and the organic compound. Bare TiO2 was inactive towards H2 production, Cu2O was effective in replacing Pt for hydrogen generation, and the presence of Pt/Nb was beneficial for both H2 production and selective oxidation. Moreover, Pt not only works as a sink for the photoproduced electrons, as it is well known in the literature, but also modifies the surface acid-base properties of catalysts as revealed by DRIFT and TPD measurements

Halloysite Nanotube with Fluorinated Lumen: Non-Foaming Nanocontainer for Storage and Controlled Release of Oxygen in Aqueous Media

Halloysite clay nanotubes were selectivity modified by adsorbing perfluoroalkylated anionic surfactants at the inner surface. The modified nanotubes formed kinetically stable dispersions due to the enhanced electrostatic repulsions exercised between the particles. We proved that the modified nanotubes can be used as non-foaming oxygen nanocontainers in aqueous media. The gas release from supersaturated dispersions can be controlled by external stimuli and system composition. In conclusion, we managed to put forward an easy strategy to develop smart materials from natural nanoclays, which can endow important applications like the storage and delivery of gas

Pt-Nb2O5-TiO2 based semiconductors for photo-reforming of glucose and fructose aqueous solutions

The conversion of biomass derivatives into fuels and valuable compounds under green conditions is increasingly attracting the attention of the scientific community. In this study, the photo-reforming of aqueous glucose and fructose solutions in the presence of 0.5 wt% Pt-loaded homemade bare and Nb2O5-TiO2 catalysts was investigated to maximize the activity of titania for both hydrogen production and valuable chemical production. The most efficient sample was the home-prepared Pt-4 %Nb2O5-HP, for both glucose and fructose conversion, with the highest H2 productivity and the highest selectivity towards partially oxidized compounds. The behaviour of the Pt-4 %Nb2O5-HP derives from a favourable compromise of some surface and intrinsic electronic properties as, for instance, photoluminescence, zeta potential and surface acidity. The presence of Nb2O5 decreased the recombination rate of photoproduced charges. Photo-deposition of Pt was essential for H2 production and, surprisingly, also increased the basicity of the TiO2 surface; an increase in surface acidity was measured when only niobium oxide was added, whereas stronger basic sites were observed in the simultaneous presence of Pt and niobium oxide

Highly stable defective TiO2-x with tuned exposed facets induced by fluorine: Impact of surface and bulk properties on selective UV/visible alcohol photo-oxidation

Titanium dioxide samples were prepared in the presence of different amounts of fluorine via hydrothermal method. It has been found that the presence of fluoride influenced the physico-chemical properties of TiO2 in various ways as polymorphic form stability, surface hydroxylation, generation of hydroxyl radicals under irradiation and formation of Ti3+ centers and oxygen vacancies. The generation rate of [rad]OH radicals was investigated by the photoluminescence technique in the presence of terephthalic acid. X-ray diffractometry indicated that fluorine stabilized the anatase TiO2. X-Ray photoelectron spectroscopy (XPS) revealed the presence of fluorine on the surface and the shift of the valence band edge towards less negative potentials, electron paramagnetic resonance (EPR) confirmed the formation of Ti3+ in the bulk of the photocatalysts, UV–vis spectra showed the extension of the TiO2 photo-response in the visible light region. 2-Propanol degradation and 4-methoxybenzyl alcohol partial oxidation were studied as probe reactions by using the home prepared powders as photocatalysts. Surprisingly, the photocatalytic activity resulted to be mainly affected by [rad]OH radicals formation ability under irradiation, rather than by the presence of {0 0 1} facets, although it cannot be excluded that the latter could influence the ability to form radicals under irradiation