Enhanced activation of persulfate by carbohydrate-derived carbon cryogels for effective removal of organic pollutants

Nanocarbons are promising alternatives to metal-based catalysts in advanced oxidation processes for wastewater treatment. Herein, carbon cryogels were prepared through the hydrothermal carbonization (HTC) of glucose directed by polyaniline (PANI) and their catalytic performances towards persulfate (PS) activation for the degradation of organic pollutants were investigated. When the polymerization temperature of PANI was increased from 0 to 80 °C, carbon cryogels exhibited increased total pore volume (0.23-0.33 cm3 g−1) and decreased average particle diameter (132-63 nm), which further enhanced their adsorption and catalytic activity for PS activation. The excellent catalytic activity of carbon cryogels for PS activation was universal in the degradation of different organic pollutants, comparable to various metal catalysts and reported metal-free catalyst, applied to a wide pH range (pH 3-9), and easily regenerated through calcination, proving that it had potential practical application for organic wastewater treatment. Radical quenching and electron paramagnetic resonance (EPR) experiments demonstrated the nonradical pathway in catalytic oxidation of orange acid 7 (AO7) on carbon cryogels. It was found that the reaction rate of catalytic oxidation of AO7 was positively correlated with the meso-/macropore volume and negatively with particle diameter of carbon cryogels. Finally, the catalytic process for organic pollutants on carbon cryogels was suggested.