Bromate removal from water by polypyrrole tailored activated carbon

Bromate adsorption behavior and mechanism were examined on a novel adsorbent devised via depositing polypyrrole (Ppy) into the pores of nut shell-based activated carbon (NAC). This Ppy-tailored activated carbon (Ppy-NAC) hosted positively charged polypyrrole functionality that offered considerable sorption capacity for bromate. Specifically, the Ppy-NAC achieved a bromate loading of 62.5 mg/g in the adsorption isotherm, 8.3 times higher than the pristine NAC. The adsorption isotherm data were fitted well by the Langmuir model, and the adsorption kinetics were described well by the pseudo-second-order equation. The occurrence of chloride ions in solution showed that Cl− exchanged with BrO3− during the adsorption process. The X-ray photoelectron spectroscopy (XPS) analysis and the detection of bromide in solution indicated that some of BrO3− were reduced to Br−, and the produced bromide ions were released to the solution and adsorbed on the Ppy-NAC. The increase of oxygen-containing functional groups on Ppy-NAC after adsorption verified that the redox reaction occurred during the adsorption process. The mechanisms of bromate removal by the Ppy-NAC included ion exchange and reduction reaction of bromate on the Ppy-NAC surfaces.