A cellulose/bentonite grafted polyacrylic acid hydrogel for highly-efficient removal of Cd(II)

In order to remove Cd(II) from waste water, a highly-effective hydrogel named microcrystalline cellulose/bentonite grafted polyacrylic acid (MCC/Ben-g-PAA) was synthesized using microcrystalline cellulose (MCC) and bentonite (Ben) as raw materials with ammonium persulfate (APS) as the initiators and N, N′-Methylene bisacrylamide (MBA) acting as the crosslinker. The adsorbent was characterized by SEM, FTIR, XPS, TG and the results showed that the MCC/Ben-g-PAA contains abundant C and O-containing surface groups, which are favorable for the adsorption of Cd(II). Batch experiments showed that the adsorption of Cd(II) could reach a peak of 242.53 mg/g under the optimal conditions, with the dosage of 1 g/L at pH 6 and the Cd(II) initial concentration of 50–800 mg/L. The adsorption kinetics fitted the pseudo-second order dynamics, and the adsorption isotherm followed the Freundlich model, indicating that the Cd(II) adsorption by MCC/Ben-g-PAA was a chemisorption-based multi-layer process, mainly controlled by intraparticle diffusion. Ion-competition experiments showed that the adsorbent was highly selective with removal rates higher than 95 % for Cd(II) in presence of various cations and anions. Regeneration experiment showed that the adsorbent maintained a Cd(II) removal rate of 88.37 % after 10 cycles. Therefore, the MCC/Ben-g-PAA is an easily-prepared, remarkably-effective and highly-reusable adsorbent, which is rather promising for the treatment of heavy metal-containing wastewater.