Avaliação da influência dos parâmetros de síntese de hidróxidos duplo lamelares ZnAl para aplicação como adsorventes em tratamento de água

Abstract

Studies on the use of various materials as adsorbent agents have been growing more and more, especially about the treatment of effluents. Lamellar Double Hydroxides (HDLs), also known as anionic clays, consist of stacking layers of mixed hydroxides of tri and divalent cations where hydrated anions occupy the spaces between the lamellae. These materials have been highlighted as adsorbent materials due to the multitude of products that can be produced by varying factors such as chemical composition, reaction parameters, reactor layout, among others. In this work, a 2 3 factorial experimental design was carried out with triplicate at the central point, to produce HDLs composed of ZnAl. The reaction factors were evaluated: pH (8, 10 and 12), time (6, 15 and 24 hours) and temperature (20, 40 and 60ºC). A total of 11 materials were produced by the coprecipitation method at increasing pH, with the aim of evaluating the influence of the factors explored in the Malachite Green dye adsorption process, since this poses a health risk and can be widely used, as well as as in the chemical and physical changes of the adsorbents, using the percentage of dye removal, the surface area, the crystallite size and the zero charge potential as planning response. The synthesized materials were characterized by PCZ, DRX, TG/DTG, SEM, FTIR and BET techniques to validate the ZnAl production and provide the main differences in the synthesized products. These HDLs were used in adsorption tests carried out in a finite bath to remove Malachite Green from aqueous solutions. Analysis of the experimental design shows that pH was the most significant factor at its upper level for all responses studied. The time at its lower level was significant for almost all responses, except for surface area, where temperature was more significant at its upper level, with temperature being the least significant parameter for the other responses. The linear model test was sufficient to generate a statistically significant equation, except for the crystallite size, where the quadratic model was also tested and still showed a lack of fit. Among the materials synthesized in the 11 syntheses, the material S6-T60pH12t6 stood out in the adsorption of the Malachite Green dye, presenting a removal capacity greater than 87%. The kinetic study suggests that the system reaches equilibrium in 240 minutes and the experimental data are better fitted by the pseudo-second order model. The isotherms are better represented by the Sips model, showing a value of maximum adsorption capacity at 60°C of 572.84 mg g-1. The positive value of ΔHo suggests that the adsorption is endothermic in nature. The positive value of ΔSo indicates that structural changes may have occurred on the surface of the adsorbent material. Negative ΔGo values for all temperatures studied indicate that the Malachite Green dye adsorption process occurs spontaneously and viable. In short, the synthesized HDLs are more influenced according to the pH of the synthesis reaction, the S6-T60pH12t6 presented itself as an excellent adsorptive material.