Removal of crystal violet from aqueous solutions using functionalized cellulose microfibers: a beneficial use of cellulosic healthcare waste

Abstract

In this research, the preparation of functionalized cellulosic microfibers (FCMFs) was proposed as a beneficial use of cellulosic healthcare waste for the removal of crystal violet from aqueous solutions. The functionalization process was performed using a sulfonation reaction by chlorosulfonic acid. The results of scanning electron microscopy revealed a significant deformation in the fibrous structure of cellulose as a result of the sulfonation process. The functionalization of cellulosic fibers was confirmed by investigation of the FTIR spectra of cotton and FCMFs. The charge density of FCMFs was calculated from their sulfur content which was measured using a CHNS elemental analyzer. The influence of factors affecting the adsorption process such as pH, salt content, contact time, initial dye concentration and temperature were examined. The adsorption capacity was increased by increasing the salt content and temperature. Equilibrium was achieved after 60 min of mixing. The equilibrium adsorption data were well described by Freundlich, Redlich–Peterson isotherms. The maximum adsorption capacity was found to be 872 mg g⁻¹. The adsorption kinetic data were well fitted to pseudo-second-order and Elovich kinetic models. Thermodynamic parameters indicated that the adsorption process was spontaneous and endothermic in nature. The residual root-mean-square error (RMSE), average absolute relative error (AARE), cross-correlation coefficient (CCC, R) and chi-square test (χ²) were used to evaluate the fitting of the adsorption isotherms and kinetic models to the experimental results. The saturated adsorbent was regenerated by acid washing (HCl, 1 mol L⁻¹) and removal efficiency was decreased slightly in each batch adsorption/regeneration cycle.