Excitonic and vibronic spectra of Frenkel excitons in a two-dimensional simple latice

Excitonic and vibronic spectra of Frenkel excitons (FEs) in a two-dimensional (2D) lattice with one molecule per unit cell have been studied and their manifestation in the linear absorption is simulated. We use the Green function formalism, the vibronic approach (see Lalov and Zhelyazkov [Phys. Rev. B \textbf{75}, 245435 (2007)]), and the nearest-neighbor approximation to find expressions of the linear absorption lineshape in closed form (in terms of the elliptic integrals) for the following 2D models: (a) vibronic spectra of polyacenes (naphthalene, anthracene, tetracene); (b) vibronic spectra of a simple hexagonal lattice. The two 2D models include both linear and quadratic FE--phonon coupling. Our simulations concern the excitonic density of state (DOS), and also the position and lineshape of vibronic spectra (FE plus one phonon, FE plus two phonons). The positions of many-particle (MP-unbound) FE--phonon states, as well as the impact of the Van Hove singularities on the linear absorption have been established by using typical values of the excitonic and vibrational parameters. In the case of a simple hexagonal lattice the following types of FEs have been considered: (i) non-degenerate FEs whose transition dipole moment is perpendicular to the plane of the lattice, and (ii) degenerate FEs with transition dipole moments parallel to the layer. We found a cumulative impact of the linear and quadratic FE--phonon coupling on the positions of vibronic maxima in the case (ii), and a compensating impact in the case (i).Comment: 13 pages, 12 figure

Iwasawa Effects in Multi-layer Optics

There are many two-by-two matrices in layer optics. It is shown that they can be formulated in terms of a three-parameter group whose algebraic property is the same as the group of Lorentz transformations in a space with two space-like and one time-like dimensions, or the $Sp(2)$ group which is a standard theoretical tool in optics. Among the interesting mathematical properties of this group, the Iwasawa decomposition drastically simplifies the matrix algebra under certain conditions, and leads to a concise expression for the S-matrix for transmitted and reflected rays. It is shown that the Iwasawa effect can be observed in multi-layer optics, and a sample calculation of the S-matrix is given.Comment: RevTex 10 pages including 1 psfi

111 oriented gold nanoplatelets on multilayer graphene as visible light photocatalyst for overall water splitting

[EN] Development of renewable fuels from solar light appears as one of the main current challenges in energy science. A plethora of photocatalysts have been investigated to obtain hydrogen and oxygen from water and solar light in the last decades. However, the photon-to-hydrogen molecule conversion is still far from allowing real implementation of solar fuels. Here we show that 111 facet-oriented gold nanoplatelets on multilayer graphene films deposited on quartz is a highly active photocatalyst for simulated sunlight overall water splitting into hydrogen and oxygen in the absence of sacrificial electron donors, achieving hydrogen production rate of 1.2 molH2 per gcomposite per h. This photocatalytic activity arises from the gold preferential orientation and the strong gold–graphene interaction occurring in the composite system.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa and CTQ2012-32315) and Generalitat Valenciana (Prometeo 2013-019) is gratefully acknowledged. D.M. and I.E.-A. thank to Spanish Ministry of Science for PhD scholarships.Mateo Mateo, D.; Esteve Adell, I.; Albero Sancho, J.; Sánchez Royo, JF.; Primo Arnau, AM.; García Gómez, H. (2016). 111 oriented gold nanoplatelets on multilayer graphene as visible light photocatalyst for overall water splitting. Nature Communications. 2016(7):1-8. https://doi.org/10.1038/ncomms11819S1820167Lv, X. J., Zhou, S., Huang, X., Wang, C. & Fu, W. F. Photocatalytic overall water splitting promoted by SnOx-NiGa2O4 photocatalysts. Appl. Cat. B: Environ. 182, 220–228 (2016).Xu, J., Wang, L. & Cao, X. 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Acceleration and increase of hydrogen production by simultaneous fermentation of Clostridium butyricum and Rhodobacter sphaeroides on wine-vinasse substrate

A fermentation process for hydrogen production as a result of the simultaneous effect of Rhodobacter sphaeroides and Clostridium butyricum on a wine-vinasse substrate was realized in a single illuminated bioreactor. The kinetics of the cooperative process indicates rapid and enhanced production of hydrogen showing yield of 65.41 mmol/l vinasse with a mixed culture as compared to processes using the two bacteria separately that have yields of 27.41 and 25.49 mmol/l vinasse for Rhodobacter and Clostridium, respectively. The experiment with a mixture of the two bacteria revealed co-operative assimilation of almost all components studied in the following sequence: malic acid > lactic acid > residual sugars> tartaric acid > citric acid. The use of vinasse substrate for hydrogen production would be a significant ecological energy resource for enterprises producing wine brandies together with waste utilization

Biometanation of Distillery Wastewater in an Anaerobic Baffled Reactor System

Anaerobic digestion is an established technology for distillery effluent treatment witch seems to be a promising alternative for Bulgarian industry. In this study the methanogenic activity of two different naturally formed microbial consortiums was compared. The better one was used to start continuous anaerobic digestion of high-strength distillery wastewater (COD 85 520 mgO2 . l-1) in laboratory scale anaerobic baffled reactor system. The average applied organic loading rate and hydraulic retention time were 4.28 kg COD m-3 . d-1 and 20 d respectively. A COD reduction of about 98 % and specific methane production of 0.39 m3 . kg-1 CODremoved were reached. Effects of different inhibitory factors such as low pH and presence of oxygen were investigated. In spite of unfavorable factors were applied simultaneously after an adaptation period the reactor showed stable response. The results obtained show the feasibility of this anaerobic process for distillery effluent treatment, representing a valid option to up-grade the existing wastewater treatment processes