Desenvolvimento de adsorvente à base de taninos aplicado na remoção de corantes em sistemas aquosos

Abstract

This study presents an innovative adsorbent material, obtained from the dialysis of an aqueous solution of condensed tannins functionalized with amino groups. After dialysis, freezing the dialysate solution leads to the formation of a waterinsoluble precipitate (TND). The dialyzed material was characterized by spectroscopy in the infrared region with Fourier transform (FT-IR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Zeta potential measurements (PZ) obtaining values positive in the pH 2.0 and 4.0 range, remaining practically constant ([zeta] = 5.0 mV). However, from pH 4.0, the values of [zeta] decrease to negative values, reaching -15,59 mV at pH 6.0, suggesting the applicability in the adsorption of anionic and cationic dyes. The adsorbent was applied in adsorption studies to remove the dyes acid black 172 (AcB) and methylene blue (AM). Kinetic and equilibrium studies were performed, where the pseudo-first order kinetic model showed better fit in the adsorption process of the AcB (R2 = 0.983), while the pseudo-second order kinetic model showed better fit for AM (R2 = 0.986). For both processes, the isothermal model that showed the best fit was the Sips model, in which the maximum amount (qmax) removed from the dyes reached 99.5 mg g–1 for AcB (R2 = 0.993) and 306.7 mg g–1 for the AM (R2 = 0.970). Thermodynamic evaluation revealed that the adsorption process is spontaneous, since they presented negative ΔGo for AcB (–3.33 kJ mol–1) and for AM (–4.16 kJ mol–1), the adsorption process has a physical character and endothermic. TND showed regeneration potential, indicated by three cycles of adsorption/desorption. After adsorption, XPS spectra confirmed the presence of dyes on the surface of the adsorbent material. The tannin-based adsorbent is efficient for removing dyes from aqueous systems.