Remoção dos herbicidas 2,4-D e picloram utilizando catalisadores a base de biocarvão e dióxido de titânio

Abstract

Herbicides are widely used for controlling invasive plants, but their residues and degradation products can contaminate the environment, affecting non-target organisms and biodiversity. Among these compounds, 2,4-D and picloram stand out due to their toxicity, persistence in soil, and high mobility, making the development of efficient methods for their removal from soil, water, and sediments essential. TiO₂ photocatalysts, for example, provide rapid and efficient decontamination of matrices contaminated with pesticides. However, they face challenges related to recovery and significant catalytic efficiency only under ultraviolet irradiation. In this context, carbon-based materials, such as biochars, have gained special attention in the development of catalysts combined with photocatalysts like TiO₂, improving contaminant removal performance and facilitating material reuse. This study evaluates the use of biochars derived from sugarcane bagasse obtained at different pyrolysis temperatures as support materials for TiO₂ in the removal of 2,4-D and picloram herbicides from aqueous media. The catalyst with the best herbicide removal performance (BDT900) was prepared using the biochar BC900, obtained at 900 °C. For this catalyst, scanning electron microscopy revealed the impregnation of TiO₂ into the cavities on the biochar surface. Fourier-transform infrared spectroscopy indicated the formation of C=C bonds associated with aromatic rings in the biochar, resulting from graphitic structures generated during the high-temperature pyrolysis process. The use of ultrasonic treatment during catalyst preparation effectively increased the biochar's adsorption capacity by clearing pores and cavities in the carbonaceous structure. This enhancement contributed to adsorption dominating over photocatalytic removal processes during the first hour of catalyst application under UV-C irradiation. Kinetic studies on picloram and 2,4-D degradation using the BDT900 catalyst demonstrated a removal efficiency exceeding 89% within 6 hours under UV-C light. The mixture of BC900 precursors (after sonication) + TiO₂ showed a global herbicide removal capacity similar to that of the BDT900 catalyst, suggesting limited synergy in the catalyst formation regarding the photodegradation process. However, the extent of adsorptive and photocatalytic processes was altered due to changes in the number of adsorption sites and the effective light absorption by the photocatalyst. On the other hand, the reuse of the catalyst was more favorable than the mixture, given the ease of material decantation. These findings highlight the potential of BDT900 as an excellent adsorbent and photocatalyst for remediating water contaminated with 2,4-D and picloram.