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The biopolymers chitin (CTN) and chitosan (CTS) were functionalized with APTES (3-aminopropyltriethoxysilane) in order to enhance its adsorption potential for sunset yellow dye (SYD). The functionalization was proved by several techniques like FTIR (Fourier transform infrared spectroscopy), XRD (X-ray diffraction), N2 adsorption/desorption isotherms, SEM (scanning electron microscopy) and EDS (energy dispersive spectroscopy). The insertion of APTES in the biopolymers has improved the adsorption properties of both, CTN and CTS. The best performance was obtained using CTS functionalized with APTES (CTS-AP), at pH of 4.0, where, more than 99% of the SYD was removed from the solution. Adsorption of SYD on CTS-AP and CTS followed the n-order kinetic model, being that, the use of CTS-AP provided a much faster rate. Freundlich model has better described the isotherms of SYD adsorption on CTS-AP and CTS. An endothermic and physical adsorption was verified. The maximum adsorption capacities were 85 and 95 mg g-1 for CTS and CTS-AP, respectively. The functionalization of CTS with APTES was able to improve the adsorption capacity. However, the main roles of the functionalization was provides a faster adsorption rate, decreasing in 50% the equilibrium time, and, a great recyclability for the adsorbent.

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Pará chestnut husk (Bertholletia excelsa) (PCH), an agro-industrial waste largely generated in Brazil, was employed as a low-cost and efficient biosorbent to remove the cationic dyes Crystal Violet (CV) and Methylene Blue (MB) from aqueous media. PCH presented an amorphous structure containing carboxylic acids, esters, ketones and aldehydes on the surface. Non-porous and irregular particles were also observed. For both dyes, the biosorption capacity was favored under acid conditions. Equilibrium was attained within 40 min at 25 °C with a PCH dosage of 0.5 g L. The biosorption kinetic curves were satisfactory explained by the pseudo-first-order model. The Freundlich model was best for representing the equilibrium curves. The maximum biosorption capacities were 83.6 and 83.8 mg g for CV and MB, respectively. PCH was efficient for treating a simulated textile effluent containing several dyes and chemicals, achieving a color removal of 90%. In this way, PCH can be considered as an option for treating colored effluents containing textile dyes.

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