Influence of plasma treatment on the physical and chemical properties of sisal fibers and environmental application in adsorption of methylene blue

The sisal fiber (agave sisalana) is a natural material that presents interesting physical and chemical properties, such as, good adsorption capacity, biodegradability and possibility to be used in composites. Improving these properties is of great importance since sisal fiber may be used in various technological applications. The aim of this work was to study the influence of surface treatment on sisal fibers properties and its effect over methylene blue (MB) adsorption using kinetics models and isotherms studies. The treatment herein used was reactive microwave-assisted cold plasma using mixtures of Ar and CO2, which appears as an alternative to traditional chemical treatments. The adsorption kinetics studies were conducted in order to elucidate the behavior between adsorbent and adsorbate. For this purpose, two isotherm models were used, (i) Redlich-Peterson and (ii) Langmuir. The results show that the plasma treatment promoted an increase in fiber surface roughness, a slight and insignificant decrease in the fiber crystallinity index as well as the breaking and removal of hydroxyl groups with consequent modification of the lignocellulosic material's original structure. The surface modification of sisal fibers by using cold plasma method promoted greater removal of the MB molecules reaching a 96 %. Kinetic and isotherm studies indicated that the adsorption mechanisms were favorable for both fibers and probably occurred in heterogeneous sites for both pristine and plasma-treated fibers. It was observed that the plasma treatment did not cause the loss of the original properties of the fibers and plays a fundamental role in increasing the adsorption, being indicated for wastewater pollutant removal processes at a low production cost as an alternative to the chemical process currently used.