An economical preparation strategy of magnetic biochar with high specific surface area for efficient removal of methyl orange.

Magnetic biochar (MBC) was obtained from pepper straw by impregnation-microwave pyrolysis method. The pyrolysis temperature and FeCl impregnation concentration were investigated on the structural properties of MBC and the adsorption of methyl orange (MO) in water. Characterization results showed that pyrolysis temperature and iron species significantly increased the specific surface area of MBC, which could reach the maximum of 2038.61 m/g, and also provided more active adsorption sites by promoting the generation of graphitized structures and surface polar functional groups. MBC-900 was selected as the adsorbent for MO with the maximum adsorption capacity reached 437.18 mg·g, 3.4 times higher than the virgin biochar. The adsorption process was dominated by chemisorption as well as spontaneous and exothermic. The adsorption mechanisms included pore-filling interaction, π-π EDA interaction, electrostatic interaction, hydrogen bonding, and Lewis acid-base electron interaction. In addition, MBC also exhibited excellent separability and reusability as a low-cost adsorbent. This study provided some theoretical foundation and technological support for producing high-performance biochar and developing pollutant removal technology in wastewater.