Single and competitive dye adsorption onto chitosan-based hybrid hydrogels using artificial neural network modeling.

Chitosan-based hybrid hydrogels such as chitosan hydrogel (CH), chitosan hydrogel with activated carbon (CH-AC), scaffold-chitosan hydrogel (SCH), scaffold-chitosan hydrogel with activated carbon (SCH-AC) and scaffold-chitosan hydrogel with carbon nanotubes (SCH-CN) were synthesized, characterized and applied to adsorb Acid Blue 9 (AB) and Allura Red AC (AR) from single and simultaneous binary liquid systems. Experimental results revealed competitive adsorption as the adsorption capacity was reduced in binary system for each dye. In addition, SCH-CN presented the highest adsorption capacity for both dyes, indicating that the modification increased the number of active sites and the functionalization with OH groups favored the interactions with sulfonated groups of the dyes. A predictive artificial neural network (ANN) was implemented to forecast the adsorption capacity for AB and AR dyes as a function of initial molar concentration of each dye, adsorption time, porosity and mass percentage of carbonaceous material on each hydrogel. The network was trained with the Levenberg-Marquardt back-propagation optimization, and according to the high correlation coefficient (R = 0.9987) and low values of root mean square error (RMSE = 0.0119), sum of the absolute error (SAE = 0.7541) and sum of squares error (SSE = 0.0132), the best topology was found to be 5-10-10-10-2. The ANN proved to be effective in predicting dye adsorption capacity of each hydrogel, even for the competitive adsorption, as the R values were close to unity for all simulation systems.

Removal of Al (III) and Fe (III) from binary system and industrial effluent using chitosan films.

Adsorption of Al (III) and Fe (III) onto chitosan films from individual and binary systems were investigated. The matrix effect was evaluated using an industrial effluent of the scrubber of gases from the production process of Al2(SO4)3. The adsorption study was carried out by response surface methodology to optimize the adsorption operation as a function of pH (3, 4.5 and 6) and film dosage (FD) (100, 200 and 300 mg L-1).The possible interactions film-ions were investigated by thermal analysis, X-ray diffraction, scanning electron microscopy and dispersive energy X-ray spectroscopy. The more suitable conditions for all experimental designs were the FD values in 100 mg L-1and pH 4.5.The adsorption capacity of Fe (III) in the individual and binary systems were 140.2 mg g-1 and 132.3 mg g-1 respectively; however, in the experiment conducted on the real effluent, the adsorption capacity was reduced to 66.30 mg g-1.Already to Al (III), the adsorption capacities in the individual and binary systems were 665.5 mg g-1 to 621.2 mg g-1 respectively, and when the operation was performed using real effluent the adsorption capacity was reduced to 275.7 mg g-1.

Preparation of nanoemulsions containing unsaturated fatty acid concentrate-chitosan capsules.

HYPOTHESIS: Fish oil is rich in unsaturated fatty acids (ω-3), which are highly susceptible to oxidative degradation. The use of encapsulation process to retard the fatty acid oxidation is an interesting alternative. In this work, nanoemulsions containing capsules of unsaturated fatty acids concentrate (UFAC) using chitosan as wall material were prepared and characterized. EXPERIMENTS: The UFAC were obtained from carp viscera and chitosan was obtained from shrimp wastes. The nanocapsules were prepared by the emulsion method. Four formulations were tested, using different combinations of chitosan concentration and homogenization times. In the more suitable conditions, the emulsion was freeze-dried to obtain a microstructure with capacity to increase the capsules stability. FINDINGS: The results showed that the nanocapsules presented a spherical shape. The use of low wall material concentration and high homogenization time provided nanocapsules with smallest size (332 nm) and lowest polydispersity index (0.214). The microstructure obtained by freeze drying was irregular and porous. The peroxide values demonstrated that the microstructure was able to protect the UFAC regarding to primary oxidation. The encapsulation efficiency was 74.1%, showing that chitosan has potential to be used as encapsulating agent for unsaturated fatty acid concentrate (UFAC).

New physicochemical interpretations for the adsorption of food dyes on chitosan films using statistical physics treatment.

In this work, statistical physics treatment was employed to study the adsorption of food dyes onto chitosan films, in order to obtain new physicochemical interpretations at molecular level. Experimental equilibrium curves were obtained for the adsorption of four dyes (FD&C red 2, FD&C yellow 5, FD&C blue 2, Acid Red 51) at different temperatures (298, 313 and 328 K). A statistical physics formula was used to interpret these curves, and the parameters such as, number of adsorbed dye molecules per site (n), anchorage number (n'), receptor sites density (NM), adsorbed quantity at saturation (N asat), steric hindrance (τ), concentration at half saturation (c1/2) and molar adsorption energy (ΔE(a)) were estimated. The relation of the above mentioned parameters with the chemical structure of the dyes and temperature was evaluated and interpreted.

Chitosan scaffold as an alternative adsorbent for the removal of hazardous food dyes from aqueous solutions.

HYPOTHESIS: The dye adsorption with chitosan is considered an eco-friendly alternative technology in relation to the existing water treatment technologies. However, the application of chitosan for dyes removal is limited, due to its low surface area and porosity. Then we prepared a chitosan scaffold with a megaporous structure as an alternative adsorbent to remove food dyes from solutions. EXPERIMENTS: The chitosan scaffold was characterized by infrared spectroscopy, scanning electron microscopy and structural characteristics. The potential of chitosan scaffold to remove five food dyes from solutions was investigated by equilibrium isotherms and thermodynamic study. The scaffold-dyes interactions were elucidated, and desorption studies were carried out. FINDINGS: The chitosan scaffold presented pore sizes from 50 to 200 µm, porosity of 92.2±1.2% and specific surface area of 1135±2 m(2) g(-1). The two-step Langmuir model was suitable to represent the equilibrium data. The adsorption was spontaneous, favorable, exothermic and enthalpy-controlled process. Electrostatic interactions occurred between chitosan scaffold and dyes. Desorption was possible with NaOH solution (0.10 mol L(-1)). The chitosan megaporous scaffold showed good structural characteristics and high adsorption capacities (788-3316 mg g(-1)).

Statistical optimization, interaction analysis and desorption studies for the azo dyes adsorption onto chitosan films.

Chitosan films (CF) were applied to remove azo dyes (tartrazine and amaranth) from aqueous solutions by adsorption. CF were prepared by casting technique and characterized. Response surface methodology was employed to optimize the adsorption process as a function of pH (2, 3 and 4) and CF concentration (100, 150 and 200 mg L(-1)). The possible interactions CF-dyes were investigated by Fourier transform infrared spectroscopy, dispersive energy X-ray spectroscopy, thermogravimetric analysis and color parameters. Adsorption-desorption cycles were also performed. The more appropriate conditions for the adsorption of both dyes were pH of 2 and CF concentration of 100 mg L(-1). Under these conditions, the tartrazine and amaranth adsorption capacities were 413.8 and 278.3 mg g(-1), respectively. The interactions between the CF protonated amino groups and anionic form of the dyes at pH 2 were confirmed. Desorption experiments showed that the CF can keep its adsorption capacity maximum for two cycles.

Biosorption of phenol onto bionanoparticles from Spirulina sp. LEB 18.

The biosorption of phenol onto bionanoparticles from Spirulina sp. LEB 18 was studied. Firstly, the bionanoparticles were prepared from Spirulina sp. strain LEB 18 and characterized. After, response surface methodology was employed to optimize the biosorption process as a function of pH (3.2-8.8) and bionanoparticles dosage (0.15-1.85 g L(-1)). Finally, equilibrium and thermodynamic studies were performed at different temperatures (298-328 K). The bionanoparticles presented hydrodynamic diameter of 232±3 nm and polydispersity index of 0.150. It was found that the more adequate condition for the phenol biosorption was pH of 6.0 and bionanoparticles dosage of 1.85 g L(-1). The Langmuir model presented satisfactory fit with the equilibrium experimental data. The maximum biosorption capacity was 159.33 mg g(-1), obtained at 298 K. The thermodynamic parameters showed that the biosorption was a spontaneous, favorable and exothermic process. Based on these results, it can be affirmed that the bionanoparticles are an alternative, renewable and eco-friendly biosorbent to removal phenol from aqueous solutions.

Biosorption of food dyes onto Spirulina platensis nanoparticles: equilibrium isotherm and thermodynamic analysis.

The biosorption of food dyes FD&C red no. 40 and acid blue 9 onto Spirulina platensis nanoparticles was studied at different conditions of pH and temperature. Four isotherm models were used to evaluate the biosorption equilibrium and the thermodynamic parameters were estimated. Infra red analysis (FT-IR) and energy dispersive X-ray spectroscopy (EDS) were used to verify the biosorption behavior. The maximum biosorption capacities of FD&C red no. 40 and acid blue 9 were found at pH 4 and 298 K, and the values were 468.7 mg g(-1) and 1619.4 mg g(-1), respectively. The Sips model was more adequate to fit the equilibrium experimental data (R2>0.99 and ARE<5%). Thermodynamic study showed that the biosorption was exothermic, spontaneous and favorable. FT-IR and EDS analysis suggested that at pH 4 and 298 K, the biosorption of both dyes onto nanoparticles occurred by chemisorption.

Optimization and kinetic analysis of food dyes biosorption by Spirulina platensis.

The biosorption of food dyes acid blue 9 and FD&C red no. 40 onto Spirulina platensis was studied. A full factorial design was used to analyze the effects of pH (2-4), stirring rate (50-400 rpm) and contact time (20-100 min) on biosorption capacity. In the best conditions, biosorption kinetics was analyzed and the experimental data were fitted with four kinetic models. The best conditions were: pH 2, 400 rpm and 100 min for acid blue 9, and pH 2, 225 rpm and 100 min for FD&C red no. 40. In these conditions, the biosorption capacities were 1653.0 mg g(-1) for acid blue 9 and 400.3 mg g(-1) for FD&C red no. 40. For both dyes, the Avrami kinetic model was the more appropriate to represent the experimental data. These results showed that the S. platensis is a suitable biosorbent for removal of food dyes from aqueous solutions.

Adsorption of food dyes acid blue 9 and food yellow 3 onto chitosan: stirring rate effect in kinetics and mechanism.

Adsorption of food dyes acid blue 9 and food yellow 3 onto chitosan was studied. Stirring rate influence on kinetics and mechanism was verified. Infra-red analysis was carried out before and after adsorption in order to verify the adsorption nature. Adsorption experiments were carried out in batch systems with different stirring rates (15-400 rpm). Kinetic behavior was analyzed through the pseudo-first-order, pseudo-second-order and Elovich models. Adsorption mechanism was verified according to the film diffusion model and HSDM model. Pseudo-second-order and Elovich models were satisfactory in order to represent experimental data in all stirring rates. For both dyes, adsorption occurred by film and intraparticle diffusion, and the stirring rate increase caused a decrease in film diffusion resistance. Therefore, the film diffusivity increased the adsorption capacity and, consequently, intraparticle diffusivity increased. In all stirring rates, the rate-limiting step was film diffusion. Adsorption of acid blue 9 and food yellow 3 onto chitosan occurred by chemiosorption.

Characterization of thin layer drying of Spirulina platensis utilizing perpendicular air flow.

Spirulina is the most extensively used microalgae for animal and human nutrition mostly because of its high protein content, 60-65% on a dry weight basis. The drying is the most expensive operation. The aim of the study was to characterize drying of Spirulina platensis in thin layer. A Statistical model was applied to analyze the effects of independent variables (air temperature and loads of solids in the tray) on the response of solubility in acid medium. The analysis of phycocyanin content was determined at the best drying condition. The Spirulina isotherm data were adjusted through Guggenheim, Anderson and de Boer (GAB) and Brunauer, Emmett and Teller (BET) correlations. The nonlinear regression analysis of isotherms data showed that the GAB equation more effective adjusted the experimental data (R(2)>99% and E%<10%). Drying curves of Spirulina showed only a decreasing rate-drying period. The material load and the interaction between the air temperature and material load were significant effects (P0.05), and the best results of solubility in acid medium ( approximately 79%) occurred at 60 degrees C and 4 kg/m(2). In under these conditions the phycocyanin content was determined to be 12.6% of dried Spirulina.