Adsorption of Atrazine by Fe-Mn-Modified Biochar: The Dominant Mechanism of π–π Interaction and Pore Structure

It is important to explore efficient materials to alleviate the negative effect of atrazine in soils or water. In this paper, four Fe/Mn-modified biochars were prepared to enhance atrazine removal. The batch adsorption experiment was conducted to explore the adsorption ability of biochar(DBC) and modified biochars (F3M1DBC, F1M3DBC, MnDBC, and FeDBC) on atrazine, and the adsorption mechanism was conducted by XRD, XPS, and FTIR. The modified biochar showed larger specific surface areas and zero-point charge than those of the original biochar. The increased oxygen functional groups (OH, C=C, and C=O) and the formation of Fe3O4, Mn3O4, and FeMnO3 on modified biochar improved atrazine removal. The maximum atrazine adsorption by F3M1DBC was 4.3 times higher than that of DBC. The atrazine adsorption by modified biochar was not pH-dependent, and their removal of atrazine was dominated by adsorption rather than degradation. The desorption rate was 8.61% for F3M1DBC, 15.95% for F1M3DBC, 26.19% for MnDBC, and 29.83% for FeDBC, which were 29.1–79.5% lower than that of DBC, accordingly decreased the environmental risk. XPS and FTIR analysis proved that the adsorption mechanisms of Fe/Mn-modified biochars were mainly attributed to their strong π–π interactions between atrazine and oxygen functional groups, graphitic carbon, and Fe/Mn-oxides on the surface of biochar. In addition, the larger surface area and pore structure of modified biochar contributed to the adsorption and pore filling of atrazine on biochar. In general, the Fe/Mn-modified biochars can be used as effective adsorbents to remove atrazine from soils and waters.