Interaction of thin films of hydroxo-oxobis(8-quinolyloxo) vanadium (V) with ammonia vapour

Hydroxo-oxobis(8-quinolyloxo) vanadium (V) organometallic complex has been prepared as thin films from dichloromethane solution by spin coating and the kinetics of its interaction with ammonia vapour is investigated using Surface plasmon resonance (SPR) technique. Thin film parameters are deduced from SPR measurements as well as spectroscopic ellipsometry and UV-vis spectral absorption measurements. Initial exposure to ammonia vapour has resulted in a permanent change to the baseline of the measured kinetic response, which is explained by the formation of the ammonium salt of the complex. Further exposures to ammonia vapour after 24 h and beyond, are shown to be highly reversible, which can be ascribed to formation of hydrogen bonding of second ammonia molecule with the highly negatively charged ammonium salt of the vanadium complex. Exposures to other organic vapours such as ethanol, chloroform and benzene are also studied in order to examine the selectivity of this material to ammonia vapour. (C) 2008 Elsevier B.V. All rights reserved

Effect of 1,4-Napthaquinone (NQ) and benzophenone (BPH)on the photodegradation and biodegradation of methyl cellulose film

The induced photodegradation of methyl cellulose (MC) films in air was investigated in the absence and presence of aromatic carbonyl compounds(photosenssitizers): 1,4-naphthaquinone (NQ) and benzophenone (BPH) by accelerated weathering tester. The addition of (0.01 wt %) of low molecular weight aromatic carbonyl compounds to cellulose derivatives films(25µm in thickness) enhanced the photodegradation of the polymer films.The photodegradation rate was measured by the increase in carbonyl absorbance. Decreases in solution viscosity and reduction of molecular weight were also observed in the irradiated samples. Changes in the number-average chain scission, the degree of deterioration and in the quantum yield of chain scission values are also observed, and it was concluded that branching or cross-linking has occurred for cellulose derivative with NQ and BPH. Findings from all analytical techniques indicated that the 1,4-naphthaquinone (NQ) photosensitizer enhance the photodegradation of methyl cellulose more than benzophenone (BPH). The effect of the photosensitizer concentration, (ranging from 0.01 to 0.1 %), on the rate of photodegradation was also monitored for MC films. The rates are increased with increasing the photosensitizer concentration. The effect of film thickness is also studied at fixed sensitizer concentration (0.05%), and results show that the rate of cellulose derivative photodegradation decreases with increasing film thickness. The rate constants of the photodegradation of the photosensitizers deduced in cellulose derivatives films, [at concentration of (0.1%)by weight and thickness (25µm)]. Biodegradation of irradiated cellulose derivatives films was conclusively established with bacteria type Pseudomonas aeuroginosa Rb-19 isolated from crude oil. The amount of bacteria growth on MC after 30 days was lower, while there was no growth observed in MC with BP

Light-Driven Heterogeneous Reduction of Carbon Dioxide: Photocatalysts and Photoelectrodes

Although modern photoelectrochemistry is often traced back to 1972 and the report by Honda and Fujishima 1 that a TiO2 photoanode in an electrochemical cell caused the splitting of water into O2 and H2 when illuminated, the first report of this type of phenomenon dates back to Becquerel’s studies, published in 1839. 2 This makes photoelectrochemistry one of the oldest investigated techniques for the conversion of sunlight into usable energy. Over this time frame, two general types of photoelectrochemical cells have been developed. The first, typified by Honda’s electrochemistry, is focused primarily on the storage of light energy as high energy chemical products. Initially, this was termed “artificial photosynthesis,” and was focused for the most part on splitting water to generate H2 as an environmentally benign fuel. The second type of photoelectrochemical cell utilizes a chemically reversible redox couple that undergoes a redox change of state at the photoelectrode, followed by conversion of the product species back to the reactant at the counter electrode. The net effect of this reaction is a chemically invariant system that generates electricity from light. The initial implementation of the Grätzel cell, which used a 3 reversible I 2/I 3- couple and a dye-sensitized TiO2 photoanode, is an example of this type of system.3 The work under consideration in this paper focuses on the photosynthetic cells and related systems. However, an analysis of these systems, as is more obviously critical to electricity-generating systems, must take into account whether the system is merely catalytic for the reaction of interest or is a system that actually converts light energy into stored chemical energy. Thus, how one parameterizes and evaluates a heterogeneous photoinduced charge transfer process becomes a critical issue that is therefore reviewed in this work