Adsorption of atrazine and 2,4-D pesticides on alternative biochars from cedar bark sawdust (Cedrella fissilis)

Bark residues of the forest species Cedrela fissilis were physically and chemically modified with zinc chloride (ZnCl₂) as an activating agent. The two modified materials were analyzed as adsorbents in removing atrazine and 2,4-D herbicides from effluents. Firstly, the precursor material and the modified ones were characterized by different techniques to identify the structural changes that occurred in the surfaces. Through TGA, it was observed that both modified materials have thermal stability close to each other and are highly superior to the precursor. X-ray diffractions proved that the amorphous structure was not altered, the three materials being highly heterogeneous and irregular. The micrographs showed that the treatments brought new spaces and cavities on the surface, especially for the material carbonized with ZnCl₂. The pHPZC of the modified materials was close to 7.5. The physically modified material had a surface area of 47.31 m² g⁻¹ and pore volume of 0.0095 cm³ g⁻¹, whereas the carbonized material had a surface area of 98.12 m² g⁻¹ and pore volume of 0.0099 cm³ g⁻¹. Initial tests indicated that none of the adsorbents were efficient in removing 2,4-D. However, they showed good potential for removing atrazine. The Koble-Corrigan isothermal model best fits the experimental data, with a maximum capacity of 3.44 mg g⁻¹ and 2.70 mg g⁻¹ for physically modified and with ZnCl₂, respectively. The kinetic studies showed that the system tends to enter into equilibrium after 120 min, presenting good statistical indicators to the linear driving force model (LDF). The surface diffusion coefficients were 2.18×10⁻⁹ and 2.37×10⁻⁹ cm² s⁻¹ for atrazine adsorption on the physically and chemically modified materials. These results showed that the application of residues from the processing of cedar bark is promising. However, new future studies must be carried out to improve the porous development of the material and obtain greater adsorption capacities.