Estudo da adsorção dos corantes sintéticos azul de metileno e vermelho do congo e do antibiótico tetraciclina utilizando o argilomineral haloisita

Abstract

Halloysite (Hal) is a clay mineral with potential applications in various industrial sectors, primarily due to it is tubular morphology. The use of this material as an adsorbent in the removal process of pharmaceuticals like tetracycline, and for eliminating synthetic dyes such as Congo Red (CR) and Methylene Blue (MB) in aqueous solutions, is considered an efficient, non-toxic, and cost-effective method. The utilization of Hal for dye and pharmaceutical removal has proven to be economically and environmentally feasible for industrial applications. In this study, the characterization of this material, in it is natural form (Hal) and after acid treatment (Hal-A), was conducted using techniques such as X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and N2 adsorption/desorption. TEM analysis revealed the formation of nanotubes ranging from 60 to 600 nm in length, and N2 adsorption/desorption indicated that the clay mineral is mesoporous with a surface area of 38.10 m2.g-1 for Hal-A. The determination of adsorbate concentrations was carried out via UV-Visible spectrophotometry. Various kinetic and equilibrium models were applied to elucidate the adsorption mechanism, and the experimental data fitted well with the pseudo-second-order kinetic model (R2 = 0,9999) for all used adsorbates, suggesting that the mechanism for this process relies on chemisorption. The maximum adsorption capacity of tetracycline calculated from the Langmuir equilibrium isotherm (R2 = 0.9909) was 4.08 mg.g-1 for Hal-A, with removal rates of approximately 92% (Hal) and 98% (Hal-A). The adsorbent also exhibited potential in removing the dyes CR (> 98%) and MB (> 85%) with in 180 minutes, using 0.3 g of adsorbent and an initial dye concentration of 250 mg.L-1. The halloysite clay mineral demonstrated high efficiency as an adsorbent material for the removal of both CR and MB dyes as well as the pharmaceutical tetracycline, standing out for its natural origin, low cost, and environmentally friendly nature.