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 lm, porosity of 92.2 ± 1.2% and specific surface area of 1135 ± 2 m2 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).

Use of Spirulina platensis micro and nanoparticles for the removal synthetic dyes from aqueous solutions by biosorption

In this research, micro and nanoparticles of Spirulina platensis dead biomass were obtained, characterized and employed to removal FD&C red no. 40 and acid blue 9 synthetic dyes from aqueous solutions. The effects of particle size (micro and nano) and biosorbent dosage (from 50 to 750 mg) were studied. Pseudofirst order, pseudo-second order and Elovich models were used to evaluate the biosorption kinetics. The biosorption nature was verified using energy dispersive X-ray spectroscopy (EDS). The best results for both dyes were found using 250 mg of nanoparticles, in these conditions, the biosorption capacities were 295 mg g−1 and 1450 mg g−1, and the percentages of dye removal were 15.0 and 72.5% for the FD&C red no. 40 and acid blue 9, respectively. Pseudo-first order model was the more adequate to represent the biosorption of both dyes onto microparticles, and Elovich model was more appropriate to the biosorption onto nanoparticles. The EDS results suggested that the dyes biosorption onto microparticles occurred mainly by physical interactions, and for the nanoparticles, chemisorption was dominant.

Preparation of bionanoparticles derived from Spirulina platensis and its application for Cr (VI) removal from aqueous solutions

Spirulina platensis nanoparticles were prepared by mechanical agitation and were applied to removal Cr (VI) from aqueous solutions. Nanoparticles preparation was function of stirring rate and contact time. In the optimal conditions, Cr (VI) removal by nanoparticles as a function of pH and initial ion concentration was carried out. The optimal conditions for preparation were 10,000 rpm and 20 min, and the nanoparticles presented mean diameter of 215.6 nm and polydispersity index of 0.151. The best conditions for Cr (VI) removal were at pH 4 and ion concentration of 250 mg L 1, and the Cr (VI) removal percentage was 99.1%.