Preparação de carvão ativado com ZnCL2 assistido por micro-ondas a partir do endocarpo de noz de macadâmia (Macadâmia integrifolia) : otimização das condições de preparo usando a metodologia de superfície de resposta (MSR) e sua aplicação na adsorção de corante

Abstract

The preparation of activated carbons (ACs) from renewable sources such as agro-industrial wastes, and new methods of preparation have attracted great interest from the scientific community due to economic viability. In this work the use of macadamia nutshell (Macadamia integrifolia) as a precursor for the production of AC through chemical activation by microwave radiation was proposed. The ACs were prepared by a two-step methodology, carbonization followed by activation via microwave heating, using ZnCl2 as activating agent. The optimization of factors, impregnation ratio of ZnCl2:char (w:w), activation time (min) and microwave power (W) in the preparation of ACs was performed by applying the response surface methodology (RSM) with the assistance of the central composite rotatable design (CCRD). The results showed that the optimal conditions for production of AC were: impregnation ratio of 3:1 of ZnCl2:char (w:w), activation time of 20 minutes and activation power of 720 W. The AC obtained in optimum conditions (ACop) was characterized by the techniques of FT-IR, SEM, 13C NMR, Boehm method, pHdrift and BET surface area. The surface of ACop was consisted mainly of carboxylic groups (0.657 mmol g-1), presenting pHdrift of 6.0, and surface area of 598 m2 g-1. Adsorption studies with methylene blue dye (MB) were carried out. The kinetic model of pseudo second order and the isotherm model of Redlich-Peterson were best fitted to the experimental data. The ACop showed maximum monolayer adsorption capacity (Qm) of 194.7 mg g-1 for MB dye.