Insights into the performance and mechanism of Cr(VI) and U(VI) removal in water using innovative cross-linked chitosan adsorbent

Abstract

The primary aim of this work is to test a novel adsorbent prepared by cross-linking of tetrafluoroterephthalonitrile with chitosan (CS-TFT) for the removal of Cr(VI) and U(VI). The CS-TFT is stable until 250 °C and possesses amino functional groups due to the presence of CS that remain intact even after the cross-linking reaction, thus being a benefit for adsorption properties; while the TFT brought roughness to CS-TFT that keeps its high porosity. The adsorption efficiency of CS-TFT is evaluated in the batch experiment of Cr(VI) and U(VI) adsorption along with the effect of different experimental parameters (pH, time, temperature, initial concentrations, and co-existing inorganic cations). The maximum adsorption capacity of CS-TFT for adsorption of Cr(VI) and U(VI) was 265.96 mg·g-1 at pH = 3 and 346.06 mg·g-1 at pH = 5, respectively, at 298 K and the corresponding partition coefficients were 12,454 and 6181 mg g-1 mM-1, respectively. The kinetics of the adsorption process is identified as a pseudo-second-order model and the Langmuir isotherm model is considered. The CS-TFT shows satisfactory reusability since it can be used after 6 cycles of regeneration with a removal efficiency of Cr(VI) and U(VI) higher than 90 %. The adsorption mechanism is also proposed based on investigation of CS-TFT by FTIR, XPS and SEM-EDS before and after adsorption. The results show that hydroxy (–OH) and amino (–NH2) groups play a key role in the chemical adsorption. All these findings suggest that CS-TFT could be a promising adsorbent for wastewaters treatment.