Petruta Oancea

Kinetics of tartrazine photodegradation by UV/H2O2 in aqueous solution

In the present work, kinetics of tartrazine decay by UV irradiation and H2O2 photolysis, and the removal of total organic carbon (TOC) under specific experimental conditions was explored. Irradiation experiments were carried out using a photoreactor of original design with a low-pressure Hg vapour lamp. The photodegradation rate of tartrazine was optimised with respect to the H2O2 concentration and temperature for the constant dye concentration of 1.035 × 10−5 M. Tartrazine degradation and the removal of TOC followed the pseudo-first-order kinetics. The much higher kobs value for tartrazine degradation (7.91 × 10−4 s−1) as compared with the TOC removal (2.3 × 10−4 s−1) confirmed the presence of reaction intermediates in the solution.

Halophilic bacteria are able to decontaminate dichlorvos, a pesticide, from saline environments

Dichlorvos (DDVP) is an organophosphorous pesticide with a high degree of dangerous effect towards the environment. We have investigated the growth and susceptibility to DDVP of halophilic bacteria isolated from Romanian salt lakes. The growth of four strains was affected by DDVP, which may be correlated with the rate constant values of DDVP disappearance from the saline solutions. This is due not to a chemical degradation in solution but to the diffusion process and namely DDVP penetration into the cell cytoplasm by an “organic-osmolyte” mechanism. The permeability coefficient P was calculated.

Solid-state study of Captopril and Metoprolol Tartrate binary system

The structural and thermal characterization of Captopril (CA) and Metoprolol Tartrate (MT) pure compounds and binary system have been obtained. Solid–liquid equilibrium for binary mixture CA–MT was investigated using differential scanning calorimetry. Simple eutectic behavior for this system was observed. The experimental solid–liquid phase temperatures were compared with predictions obtained from available eutectic equilibrium models. The results indicate non-ideality in this mixture. The negative value of the mixing enthalpy indicates the presence of clusters with hydrogen bonds formation in the melt, as confirmed by FT-IR measurements. The preparation of ground mixtures demonstrated that the application of mechanical energy can result in the partial melting of the sample because of the eutectic behavior. Trans–cis iso-merization of CA was observed for the samples annealed at high temperature, anticipated due to the presence of MT in the system.

Chlorobenzene Degradation Assisted by TiO2 under UV Irradiation in Aqueous Solutions

Abstract We report the photocatalytic degradation of chlorobenzene (CB) in suspended TiO2 aqueous solution at pH7 under UV irradiation. We measured the kinetics of CB degradation and Cl- release and calculated a pseudo-first-order rate constant in both cases. We found a higher value of the rate constant kCB than of kCl-one, which show that the dechlorination does not take place concomitantly with the •OH attack on CB. This oxidation reaction obeyed Langmuir-Hinshelwood equation. The half life time value resulted from this equation was lower than that of the pseudo-first order rate constant at any CB initial concentration. This showed us the existence of competition between the byproducts and the pollutant for •OH radical consumption. Also, we demonstrate the positive effect of doped S-TiO2on CB photocatalytic degradation (powder or film) due to its enhanced absorption in UV and in addition to a new absorption band in visible.

Photosensitized Chlorobenzene Degradation by UV/H2O2 Oxidation

Abstract The degradation of chlorobenzene (CB) in UV/H2O2 system in aqueous solution, at pH 7, was studied. CB degradation was monitored by gas chromatography, Cl- liberation was monitored by ion chromatography at various irradiation times and a pseudo-first order kinetic in respect to both components was found. The rate constant kCl- was lower than kCB, which suggests that chlorinated intermediates are firstly formed by the attack of •OH radicals on CB, followed by chlorine liberation. When the CB concentration was kept constant we found a linear increase in the rate constants with H2O2 concentration, followed by a short interval with unmodified kI values and a decrease at higher H2O2 concentration. The variation of CB concentration at constant ratio [H2O2]/ [CB] led to the decrease in the degradation efficiency due to the competition with the intermediates, for •OH radicals consumption. Our kinetic results agreed with the literature information on the CB degradation mechanism.