Effects of Iron Species of the Iron-Based Corn Stalk Biochar on the Adsorption of Salicylic Acid from Aqueous Solutions

In order to extend the insight into the mechanism about different kinds of iron-based biochar in the treatment of organic pollutants, three types of biochar including FeOOH, Fe3O4, and nZVI loaded biochars were prepared, and the characterization, performance, and mechanism for the adsorption of salicylic acid, which was extensively used in medicine and cosmetics industry, were explored. The results showed that the adsorption capacity followed the order nZVI-BC > Fe3O4-BC > FeOOH-BC, the rate-limiting steps were surface adsorption, intra-particle diffusion, and channel diffusion for FeOOH-BC, while film diffusion and chemical reaction for Fe3O4-BC and nZVI-BC. π-π interaction and -OH, H-bonding, and O–C groups and the oxidation of ZVI mainly contributed to the removal of SA by FeOOH-BC, Fe3O4-BC, and nZVI-BC, respectively, according to the structure morphology and surface properties. Additionally, the adsorption capacity was significantly affected when pH was at a high level. PO43- in water would precipitate with the materials to inhibit the adsorption. This study demonstrated the efficiency of the iron-based biochars and the significance of iron species in removing salicylic acid