Efficient removal of selenate in water by cationic poly(allyltrimethylammonium) grafted chitosan and biochar composite

Abstract

The discovery of cheap and eco-friendly functional materials for the removal of anionic heavy metal ions is still challenging in the treatment of heavy metal-contaminated water. Herein, a new poly(allyltrimethylammonium) grafted chitosan and biochar composite (PATMAC-CTS-BC) was introduced for the removal of selenate (SeO42−) in water. Results suggest that the PATMAC-CTS-BC showed a rapid removal of SeO42− with efficiency of >97% within 10 min and it followed a pseudo-second-order model. High capacity of SeO42− adsorption by the composite was achieved, with maximum value of 98.99 mg g−1 based on Langmuir model, considerably higher than most of reported adsorbents. The thermodynamic results reflected the spontaneous and exothermic nature of SeO42− adsorption onto the composite. The composite could be applied at a wide initial pH range (2–10) with high removal efficiency of SeO42− because of permanent positive charges of quaternary ammonium groups (=N+–). The removal mechanisms of SeO42− were mainly attributed to electrostatic interactions with =N+– and protonated –NH3+ groups, and redox-complexation interactions with –NH2, –NH–, and –OH groups. Besides SeO42−, the hexavalent chromium (Cr2O72−) was considered as example to further demonstrate the anion removal capability of cationic hydrogel-BC composite. The study outcomes open up new opportunities to efficiently remove anionic heavy metal ions (e.g., SeO42− and Cr2O72−) in water using these materials.