Enhancing the adsorption capability of areca leaf biochar for methylene blue by K2FeO4-catalyzed oxidative pyrolysis at low temperature

Catalytic oxidative pyrolysis is a promising method for the preparation of highly adsorptive biochar by introducing oxygen-containing groups. Here, a K2FeO4-catalyzed oxidative pyrolysis was described for enhancing the adsorption capability of areca leaf biochar toward methylene blue at low temperature. It was shown that the maximum adsorption capacity of the biochar pyrolyzed at 200 °C was greatly improved from 122.67 to 251.95 mg g−1 with the catalysis of K2FeO4 due to the introduction of surface oxygen-containing groups. In addition, a high adsorption capability was observed over a wide pH range for the K2FeO4-modified biochar and nearly neutral pH was obtained after adsorption, further demonstrating the great advantages of K2FeO4-catalyzed oxidative pyrolysis. Mechanistic studies revealed that the adsorption of the pristine biochar was mainly determined by hydrogen bonding and electrostatic interaction. Whereas, the adsorption of the K2FeO4-modified biochar was attributed to cation exchange besides hydrogen bonding and electrostatic interactions.