Síntese e otimização de carbonos mesoporosos pelo método de hard templating para adsorção do corante violeta cristal

Abstract

In the present work, the potential of Aerosil®380 was investigated as a "hard template" in the production of mesoporous carbon materials, using sucrose as a carbon precursor aiming at its application as an adsorbent material for the removal of crystal violet (CV) dye. Initial tests showed that carbon with template and leaching substantially improved the adsorption capacity. To optimize this process, the response surface methodology was used. The results showed that carbonization reached its maximum performance, in terms of CV dye removal, under the conditions of T = 800 °C, R = 18.36 °C/min and t = 60 min, reaching a CV adsorption capacity of 155.45 mg Sequentially, evaluating the carbon-template concentrations, the optimal condition was reached with Cs = 23% and CT = 17.07%, resulting in 223 .54 mg g". The characterization indicated that the mesoporous carbon (CM) had particles with an avenge size of 1.045 mm, as well as a pHpez value close to neutrality (6.66). Speciation of the CV dye indicated the presence of cationic species, with a favorable adsorption range between pH 6.66 and 9.5 due to electrostatic attraction between CV+ICM-'.The low solubility of CV at alkaline pHs was also observed, with the possibility of precipitation at pH > 10. XRD analyses confirmed the formation of amorphous graphite, while TGA-DTG indicated the degradation of the precursor organic structure at approximately 350 °C, marking the beginning of the formation of the carbon structure. SEM highlighted greater roughness on the surface of mesoporous carbon after leaching. EDS and LIBS analyses confirmed the effectiveness of the leaching agent NaOH in removing template, revealing residual amounts of silicon of 0.1 and 0.323(% m/m), respectively. This resulted in the creation of a porous structure, facilitating the interaction with the adsorbate and increasing the surface area and porosity of carbon, as confirmed by the physisorption analysis of N2, in which a micro-mesoporous material with remarkable area values were obtained (Antal = 607.828 m2/g and Amic,„ = 165.165 m2/g), and an average pore diameter of 9.6 nm, textural properties that are favorable for the internal diffusion of CV molecules. FTIR indicated the presence of oxygenated groups, which can act as active sites for the adsorbate. In the analysis of the adsorption behavior, a high affinity for the CV dye was observed under alkaline conditions. The BET model adequately fitted the equilibrium behavior, indicating that concentrations below 60 mg L" exhibited a monolayer behavior, while higher concentrations exhibited a multilayer behavior. Adsorption kinetics also showed different behavior for low and high concentrations, with an equilibrium time of 10 hours for lower concentrations (Co < 60 mg/L) and approximately 36 hours for higher concentrations (C0 > 80 mg /L) and monolayer-multilayer adsorption model adequately described this behavior. In general, it was possible to optimize the production of mesoporous carbon with desirable textural and chemical properties for removing pollutants such as the CV dye, indicating a high potential for other applications of this type of material.