Cellulose-embedded polyacrylonitrile/amidoxime for the removal of cadmium (II) from wastewater: Adsorption performance and proposed mechanism

Abstract

The adsorption of metals using unmodified cellulose is often unsatisfactory owing to insufficient active functional groups on its surface. The objective of this work is to modify cellulose to enhance its adsorption capacity for cadmium (II). In this work, a chelating polyacrylonitrile/amidoxime-functionalized cellulose (Cel/PAN/AO) composite was successfully synthesized as modified cellulose and applied as a novel adsorbent to efficiently remove Cd2+ from aqueous solution. Cel/PAN/AO composite was synthesized by Michael's addition between cellulose and acrylonitrile, followed by amidoximation. Tools including SEM, EDS, FTIR, XRD, TGA, XPS, BET, and zeta potential were exploited to give insights about the Cel/PAN/AO adsorbent nature as well as the adsorption mechanism. The numerous available adsorption active sites embedded into modified cellulose contribute to enhancing the adsorption capacity of Cel/PAN/AO (in comparison to unmodified cellulose) toward Cd2+. Using the produced composite, cadmium was removed from the water at 50 mg/L Cd2+ by reacting 0.1 g Cel/PAN/AO with Cd2+ at pH 5 for 90 min at 298 K. The maximum adsorption capacity of Cel/PAN/AO toward Cd2+ was 123.23 mg/g. Cel/PAN/AO adsorbent exhibits competitive adsorption capacity as compared with other reported adsorbents. Pseudo-first-order and Langmuir's isotherm fit the sorption mechanism quite well. Cd2+ sorption onto the Cel/PAN/AO composite was found to be an exothermic, random, and spontaneous process in the thermodynamic analyses. Moreover, Cd2+ adsorption was also confirmed through SEM, EDS, FTIR, and XPS analysis of Cd2+-loaded adsorbent. Using 0.9 M KCl and 1:70 S:L ratio for 90 min, Cd2+ was also desorbed from Cd-loaded Cel/PAN/AO. In addition, after six cycles of Cd2+ adsorption-elution, the Cel/PAN/AO sorbent was regenerated and showed excellent reusability. It appears from the adsorption performance results of this work that the Cel/PAN/AO formulation has promise as an adsorbent for extracting Cd2+ from wastewater.