Estruturas a Base de Carbono como Adsorventes para Remoção de Contaminantes de Preocupação Emergente

Abstract

This work aimed to study the adsorption process of two pharmaceutical compounds, frequently found in solutions, on different carbon structures. For this purpose, single (SWCNT) and multi walled (MWCNT) carbon nanotubes (CNT), and magnetic composites (MC) were used. SWCNT and MWCNT were applied in the removal of the diclofenac potassium (DP) anti inflammatory, a medicine widely used worldwide, and frequently detected in wastewater. And the MC (prepared with proportions of 1:0.5:0.5 and 1:1:1 of acacia biomass, zinc chloride, and nickel chloride, i.e., MC-0,5 e MC-1) in the removal of the metoprolol (MTP) β-blocker, which is widely used, but little studied in the field of adsorption. Both adsorbents were characterized by scanning electron microscopy and had their textural properties determined by N2 adsorption/desorption isotherms. In studies involving CNT, spectroscopy techniques in the infrared region with Fourier transform (FTIR) and Raman were used for adsorbents characterization, as well as to elucidate the interaction process between the adsorbent adsorbate. The MC had their magnetic properties evaluated in a vibrating sample magnetometer, and their structural characteristics via X-ray diffraction. From these analyzes, it was possible to verify that the nickel particles present in the magnetic composites are nanostructured (MC-0.5 and MC-1 have an average crystallite size of 26.26 and 29.62 nm, respectively) and ferromagnetic behavior. In batch adsorption studies, the effects of solution pH, contact time, and temperature on the adsorption capacity of adsorbents were evaluated. The equilibrium time was set at 2h for the studies involving the DP and at 6h for the MTP case study, the experiments were conducted at 25°C. In the isothermal study, the best experimental data fit was obtained by for the Liu isotherm model for both evaluated systems, with a maximum adsorption capacity (Qmax) of 150.3 mg g-1 for NTCPS and 241.3 mg g-1 for MC-0.5. The thermodynamic parameters of the evaluated systems showed that the processes were favorable and spontaneous at all evaluated temperatures, presenting characteristic magnitudes of physical interactions. Based on spectroscopic studies, adsorption tests, and thermodynamic parameters, it was possible to propose an interaction mechanism between CNT and DP. This study is expected to promote the use of spectroscopic techniques as the main tools in the study of the interaction between nanoadsorbents and contaminants of emerging concern (CEC). Furthermore, a new adsorbent produced from black wattle biomass in a single-step microwave assisted route, with magnetic properties and favorable characteristics for application in the removal of CEC is presented.