Simona Gabriela Muntean

Kinetic and thermodynamic studies on methylene blue biosorption using corn-husk

A low-cost waste biomass derived from corn plant (husk) was tested as an alternative to other expensive treatment options, for the removal of methylene blue (MB), from aqueous solutions. The effects of different experimental parameters, such as biosorbent dosage, dye concentration, contact time, and temperature, on the adsorption process were investigated. An optimum value of discoloration was observed at pH 6.0 and 2 g L−1 biomass dosage. The amount of dye removed per adsorbent unit decreased with increasing adsorbent dosage, temperature, and increased with increasing contact time, and concentration. Experimental data were modeled using first-order, pseudo-second-order, Elovich, and intraparticle diffusion kinetics models. The adsorption kinetics of MB could be described by the pseudo-second order reaction model. The experimental data were fitted to: Langmuir, Freundlich, Temkin, Redlich–Peterson, Toth, and Sips isotherm models and the best fitting was obtained with the Sips model. The thermodynamic parameters (ΔH°, ΔS° and ΔG°) obtained revealed that MB adsorption is a spontaneous, exothermic and physical process. The obtained results indicated that corn husk as a low-cost biomaterial is an attractive candidate for the removal of basic dye MB from aqueous solutions.

Dye adsorbed on copolymer, possible specific sorbent for metal ions removal

The efficiency of styrene-divinylbenzene functionalized with trimethylamonium groups as sorbent for the direct dye removal from aqueous solutions was investigated. The influence of process variables such as initial concentration, temperature and pH was developed. The amount of adsorbed dye was maximized at higher initial dye concentrations, while the removal percentage decreased. The increase of the temperature induced a positive effect on the adsorption indicating that the process is endothermic. The maximum removal percentage was obtained in acidic medium. The adsorption kinetics followed the pseudo-second-order equation, with regards to the intra-particle diffusion rate. The experimental data was well correlated by the Sips adsorption model, and the maximum theoretical adsorption capacity was determined to be 83.75 mg dye g−1 copolymer. The new obtained specific sorbent (dye-attached to copolymer) was investigated in the removal of heavy metals ions (Cu, Zn). Very high adsorption rates were observed at the beginning of the adsorption process and the equilibrium was achieved in about 5 minutes.

Ultrasound effect on dyeing wool fibers with two anthraquinone dyes

Environmental and quality demands generate new approaches for finding better solutions in textile dyeing. A less polluting and more ecological procedure has been investigated, on this purpose. This study reveals the influence of ultrasounds (US) on wool dyeing. It presents comparatively the dyeing results for two frequently used anthraquinone dyes, one reactive (CI Reactive Blue 19) and the other acid (CI Acid Blue 62), applied on wool fibers. The comparison between the classic and the US dyeing procedures was performed in terms of: dye bath exhaustion, wash fastness and the color analysis. The dye aggregation was evidenced through the visible spectra, and the effect of US in this respect, was underlined, especially for the acid dye case. For the reactive dye, the higher bath exhaustion in US dyeing conditions was explained.

Decontamination of colored wastewater using synthetic sorbents

Abstract In the recent years, the adsorption capacities of synthetic polymeric adsorbents have been intensively studied due to their diversity in surface and porosity, physicochemical stability and the regeneration potentiality. In this study four synthetic polymers have been used as alternative adsorbent for the removal of two azo dyes from aqueous solutions. The effects of dye concentration, adsorbent nature, temperature, and pH of the solution onto the kinetics of the adsorption process were in detail investigated. With the increase in the initial concentration from 5.10–5 to 1.10–3 mol/L the amount of dye adsorbed increased, while the removal percentage decreased. The increase of the temperature (298–338 K) induced a positive effect on the adsorption indicating that the process is endothermic, and the increase of pH induced a decrease in removal percentage. The maximum dye removal percentage obtained was found to be up to 99 %. The experimental data were well correlated by the Sips adsorption model, and the results were applied for obtaining the equilibrium parameters.

Synthesis, characterization and colour determination using CIELAB colour space of stilbene dyes

The synthesis of six new symmetrical disazo direct dyes containing 4,4′-diaminostilbene-2,2′-disulphonic acid as middle component and N-(2-chlorophenyl)-2-hydroxybenzamide, N-(3-chlorophenyl)-2-hydroxybenzamide, N-(4-chlorophenyl)-2-hydroxybenzamide, N-(2-bromophenyl)-2-hydroxybenzamide, N-(3-bromophenyl)-2-hydroxybenzamide, N-(4-bromophenyl)-2-hydroxybenzamide as coupling components is presented. The synthesized dyes were analyzed by thin layer chromatography, electronic spectra and HPLC technique. Their structures were elucidated by FT/IR and 13C-NMR spectroscopy. The CIELAB (1976) colour space was used in all the colour measurements for the six disazo stilbene dyes under the CIE recommended illuminants: D65 (natural day light), A (tungsten light), F2 (fluorescent light) and the standard 10° observer, respectively. The colour differences: ΔEab* and ΔECMC were calculated against one standard. The results reveal a good colouring power of the new azo-stilbene dyes.

Investigation of aggregation behavior using computational methods and absorption spectra for trisazo direct dyes

Direct dyes are likely to self-associate in aqueous solutions. Here, we present the aggregation characteristics of three trisazo direct dyes investigated using a procedure, which combines computational and experimental approaches. The geometric features of the molecules and their aggregates were elucidated by molecular modeling and optimization. The relative energies specific for the aggregation process yielded the optimum number of molecules forming an aggregate: two for AHDS dye and three for SDH and AIDS dyes. The results were further confirmed by using spectrometric determination and mathematical analysis. Accordingly, molecular aggregation was studied in aqueous solutions as a function of dye concentration (10−6–10−3 mol/l) and solution pH (4–10). As the dye concentration increased, shifts in absorption spectra were observed, suggesting the formation of aggregates. The pH variation produced a change in the spectral maximum, confirming the aggregation. The mathematical processing of the absorption spectrum data confirmed the number of chemical species of each aggregate as resulted from computational calculations.

Adsorption studies on copper, cadmium, and zinc ion removal from aqueous solution using magnetite/carbon nanocomposites

ABSTRACT Magnetite/carbon nanocomposites were tested as adsorbents for removal of metal ions from aqueous solutions. The effect of adsorption parameters such as solutions pH (ranging between 2 and 9), the nature and the quantity of the sorbent (10, 20, 40, and 60 mg), initial concentration of metal ions (10, 30, 50, 100, and 150 mg/L), and temperature (25, 45, and 65°C) was evaluated. The removal efficiency of metal ions depends on solution pH and increases with increasing carbon content, the dose of magnetite/carbon nanocomposites, and the temperature and decrease with initial concentration of the metal ions. The adsorption kinetics was described by pseudo-second-order model, and the equilibrium experimental data were well fitted to the Sips isotherm, yielding a maximum adsorption capacity of 41.11, 76.67, and 48.45 mg/g for copper, cadmium, and zinc, respectively. The thermodynamic parameter Gibbs free energy was determined to be negative, which indicated that the adsorption process is spontaneous. The optimum conditions (1 g/L adsorbent, 25°C, and pH 6) were selected for removal of metal ions from real wastewaters, with good results indicating that investigated nanocomposites could be used for the application in real systems.

Removal of Colored Organic Pollutants from Wastewaters by Magnetite/Carbon Nanocomposites: Single and Binary Systems

This work develops a methodology for selective removal of industrial dyes from wastewaters using adsorption technology based on magnetic adsorbents. The magnetic nanoparticles embedded within a matrix of activated carbon were tested as adsorbents for removal of industrial dyes from aqueous solutions. The effects of four independent variables, solution pH, initial concentration of pollutant, adsorbent dose, contact time, and their interactions on the adsorption capacity of the nanocomposite were investigated in order to optimize the process. The removal efficiency of pollutants depends on solution pH and increases with increasing the carbon content, with initial concentration of the pollutants, the temperature, and the dose of magnetite/carbon nanocomposites. Pseudo-second-order kinetic model was fitted to the kinetic data, and adsorption isotherm analysis and thermodynamics were used to elucidate the adsorption mechanism. The maximum adsorption capacities were 223.82 mg g−1 for Nylosan Blue, 114.68 mg g−1 for Chromazurol S, and 286.91 mg g−1 for Basic Red 2. The regeneration and reuse of the sorbent were evaluated in seven adsorption/desorption cycles. The optimum conditions obtained for individual adsorption were selected as starting conditions for simultaneous adsorption of dyes. In binary systems, in normal conditions, selectivity decreases in the order: Red Basic 2 > Nylosan Blue > Chromazurol S.