Adsorption of methylene blue on agroindustrial wastes: Experimental investigation and phenomenological modelling.

In this work, agro-wastes coming from soursop (peel, seeds and pulp fiber) and sugarcane (bagasse) are used as low-cost biosorbents to remove methylene blue (MB) from aqueous media. Batch experiments are performed under different experimental conditions investigating the effects of biosorbent amount, dye concentration and stirring rate. The best results were found using soursop wastes for a MB concentration of 100 mg L-1, using 0.75 g of residue and a stirring rate of 110 rpm, removing a percentage above 90%. Theoretically, adsorption kinetic can be successfully described by the pseudo-second order model. Redlich-Peterson and Sips models are adopted to interpret the equilibrium adsorption of MB on sugarcane bagasse and soursop residue, respectively. Interestingly, the monolayer model with single energy derived by statistical physics theory is also applied for a deeper explanation of the adsorption mechanism of MB on both the adsorbents. The application of this model allows defining the adsorption geometry of the investigated adsorbate and provides important information about the interactions between the adsorbate and sorbents. In particular, the modelling analysis by statistical physics allows defining that the dye molecules are adsorbed in vertical position and the adsorption process is multi-molecular (i.e. n > 1). Finally, the estimation of adsorption energy suggested that MB adsorption on biosorbent is a physisorption process.

Mesoporous Nb2O5/SiO2 material obtained by sol-gel method and applied as adsorbent of crystal violet dye.

In this work, SiO2/Nb2O5 (SiNb) material was prepared using sol-gel method and employed as adsorbent for removal of crystal violet dye (CV). The material was characterized using nitrogen adsorption-desorption isotherms, FTIR spectroscopy, pHpzc, and SEM-EDS. The analysis of N2 isotherms revealed the presence of micro- and mesopores in the SiNb sample with specific surface area as high as 747 m2 g-1. For the CV adsorption process, variations of several parameters such as of pH, temperature, contact time, and concentration of dye of the process were evaluated. The optimum initial pH of the CV dye solution was 7.0. The adsorption kinetic and equilibrium data for CV adsorption were suitably represented by the general-order and Liu models, respectively. The maximum adsorption capacity of the CV dye by SiNb was achieved at 303 K, which attained 116 mg g-1 at this temperaure. Dye effluents were simulated and used to check the applicability of the SiNb material for treatment of effluents - the material showed very good efficiency for decolorization of dye effluents.

Microwave-assisted activated carbon from cocoa shell as adsorbent for removal of sodium diclofenac and nimesulide from aqueous effluents.

Microwave-induced chemical activation process was used to prepare an activated carbon from cocoa shell for efficient removal of two anti-inflammatories, sodium diclofenac (DFC) and nimesulide (NM), from aqueous solutions. A paste was obtained from a mixture of cocoa shell and inorganic components; with a ratio of inorganic: organic of 1 (CSC-1.0). The mixture was pyrolyzed in a microwave oven in less than 10 min. The CSC-1.0 was acidified with a 6 mol L(-1) HCl under reflux to produce MWCS-1.0. The CSC-1.0 and MWCS-1.0 were characterized using FTIR, SEM, N2 adsorption/desorption curves, X-ray diffraction, and point of zero charge (pHpzc). Experimental variables such as initial pH of the adsorbate solutions and contact time were optimized for adsorptive characteristics of MWCS-1.0. The optimum pH for removal of anti-inflammatories ranged between 7.0 and 8.0. The kinetic of adsorption was investigated using general order, pseudo first-order and pseu do-second order kinetic models. The maximum amounts of DCF and NM adsorbed onto MWCS-1.0 at 25 °C are 63.47 and 74.81 mg g(-1), respectively. The adsorbent was tested on two simulated hospital effluents. MWCS-1.0 is capable of efficient removal of DCF and NM from a medium that contains high sugar and salt concentrations.

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.