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.
Keywords: Adsorption; Biochar; Cationic hydrogel; Mechanisms; Selenium removal.
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