Adsorption of crystal violet on biomasses from pecan nutshell, para chestnut husk, araucaria bark and palm cactus: Experimental study and theoretical modeling via monolayer and double layer statistical physics models

Biomasses from pecan nutshell (PN), para chestnut husk (PCH), araucaria bark (AB) and palm cactus (PC) were employed to study the adsorption mechanism of a relevant textile pollutant namely crystal violet (CV). Experimental isotherm data performed at the best condition of pH showed that the temperature had no effect on the adsorption of CV on PN and PCH, while the CV dye removal with AB and PC was significant affected by this operating parameter. Monolayer and double layer adsorption models were applied to analyze and explain, based on statistical physics, the removal mechanism of CV using these adsorbents. The application of these statistical physics models allowed to deduce theoretically that the active sites of PN and PCH practically attracted the same number (i.e., 1.12 < n(ms) < 1.20) of CV dye molecules at all adsorption temperatures; while a variable number of CV dye molecules (0. 81 < n(ms) < 2.10) could be bonded by the adsorption sites of adsorbents AB and PC. It was also confirmed that the temperature has a negligible effect on the adsorbed quantity of the systems CV-PN and CV-PCH, but it significantly impacted the systems CV-AB and CV-PC generating different magnitudes of the adsorption energies. The adsorption energy was calculated and the adsorption mechanism was analyzed thus suggesting that hydrogen bindings and van der Waals interactions could be possible for the adsorption of this dye on tested biomasses at optimum pH.