BACKGROUND: Heterogeneous photocatalysis is influenced by a number of parameters involving synergistic effects; hence, an experimental strategy design that considers interactions between the main variables is needed. The response surface methodology was applied for the investigation of photodegradation of 20 mg L −1 Orange II in aqueous solutions and for optimization of color removal efficiency. Preliminary studies were performed to identify the parameters to be selected for optimization.
The goal of the study was to investigate the sorption behavior of Acid Orange 7 (C.I. 15510) onto soil collected from Iasi area (Romania). The sorption isotherm, kinetic and thermodynamic studies were performed by batch mode. The effects of experimental parameters such as contact time, pH value (2-12) and temperature (20 -40 0 C) have been studied. Also the influence of initial dye concentration (10 -100 mg/L) and sorbent dosage (from 5 g L -1 to 150 g L -1 ) were studied. It was found that equilibrium sorption amount increases with the increase in initial dye concentration, contact time, temperature and solution acidity. The experimental data were analyzed using four isotherm models, Langmuir, Freundlich, Temkin and Dubinin-Radushkevich. Sorption of Acid Orange 7 onto soil followed the Freundlich model. The pseudo first-order, pseudo second-order and intraparticle diffusion equations were selected to analyzed the sorption kinetic. Kinetic parameters, such as rate constants, equilibrium sorption capacities and correlation coefficients were calculated and discussed for each kinetic equation. It was shown that that sorption of Acid Orange 7 onto soil is well described by the pseudo second-order model. The thermodynamic study indicates that the sorption of Acid Orange 7 onto soil is spontaneous and endothermic.
The class of xanthene dyes has a complex chemical structure, which showed to be toxic for mixed culture of microorganisms (i.e. anaerobic granular sludge). Because of the unwanted effects of Erythrosin B (Ery B) on environmental components and some food confirmed previously, the dye was chosen in this study to evaluate its ecotoxicity. Also, the Ery B photocatalytic degradation products were assessed in terms of their ecotoxicity. Three-days of seed germination and root growth tests were conducted using a dicotyledonous plant that is the garden cress (Lepidium sativum L.), in the presence of different dye concentration and its photodegradation products. Dye affected mostly the roots of the plant. According to toxic effects on root growth, toxicity of the dye indicated a 72h exposition average Effective Concentration EC 50 value corresponding to 25 mgL -1 Ery B. The presence of the Ery B photocatalytic degradation products in the aqueous solution leads to a higher efficiency on Lepidium sativum L. germination, favoring the stem length growth.
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