MESOCARPO DO COCO VERDE (Cocos nucífera) COMO ADSORVENTE PARA OS CORANTES: TURQUESA REMAZOL E AZUL REMAZOL

Abstract

In this work the green coconut mesocarp was used as adsorbent towards two textile dyes: Turquoise Remazol and Blue Remazol. The adsorbent was triturated, washed several times with water for extraction of soluble matter, dried in oven and sieved to obtain particle size between 0.088 and 0.177 mm. Determinations of C/H/N content were performed and the obtained results were: 45.20, 6.24 and 0.74%, respectively. The study of the thermal stability showed that adsorbent is mainly affected up to 200 °C. The infrared and 13C RMN spectra allowed assigning unambiguously vibrational bands the chemical shift characteristics of lignocellulosic materials. According to X-ray and micrographies techniques the adsorbent has an amorphous and irregular structure. The most of the pores diameter values are around 10 to 20 μm, meaning that it can be classified as a macroporous material. The pHzpc of the mesocarp was estimated in 4.1, and the best removal efficiency and uptake were reached at pH 2.0 for both dyes. The kinetic studies were performed at different temperatures (10, 20, 30, 40, 50 oC) , and the best observed uptake results were 91.95%, at 50 ºC, for the Turquoise Remazol, and 97.12%, at 10 ºC, for the Blue Remazol. The best kinetic model that fit well with all the experimental results was the pseudo-second order model (R2 > 0.999), and the observed average contact time for the systems reach the equilibrium was 90 min. The graphic model of adsorption intraparticular presented three lineal segments, indicating that in the adsorption of these dyes three processes are involved: external diffusion or superficial interaction adsorbent/adsorbate, diffusion of the adsorbate into the pores of the adsorbent and interaction of the adsorvate with the active sites inside the pores. The adsorption isotherms followed the Langmuir´s model, and the maximum adsorption values varied between 49.27 to 60.25 mg/g (Turquoise Remazol) and 84.75 to 80.64 mg/g (Blue Remazol) at the temperature interval from 10 to 50 ºC. The thermodynamic parameters confirmed the spontaneity for the two processes of adsorption being endothermic with entropy increase for the Turquoise Remazol and exothermic with entropy increase for the Blue Remazol. The dessorption of the dyes were accomplished in alkaline medium (pH 8,0), and the recovered amounts dyes were of 41.5% (turquoise remazol) and 52.5%, for an equilibrium time of 90 minutes.