Degradação do herbicida metribuzin a partir da catálise heterogênea em hidrocarvão ativado com ferro na presença de peroxidissulfato

Abstract

The advancement of modern agriculture is closely tied to the use of inputs and technologies that enhance productivity, with agricultural pesticides playing a crucial role in helping to ensure higher yields. However, the improper use of these compounds can cause severe environmental impacts, potentially leading to the pollution of surface and groundwater, compromising water quality, and posing risks to public health and the balance of ecosystems. Among agrochemicals, the herbicide Metribuzin stands out, widely used for controlling invasive plants. In this context, the study proposes the development of a catalyst that offers greater economic and sustainable viability for mitigating pollution caused by Metribuzin contamination. The objective of this work was to synthesize and characterize hydrochar and subsequently apply it in heterogeneous catalysis. The catalyst was synthesized from rice husk residues, an agricultural byproduct with no added value. Through the hydrothermal carbonization (HTC) process, these residues are converted into functional carbonaceous materials. The HTC process was conducted at 180 °C for 6 hours, with a biomass-to-water ratio of 1 g:5mL, followed by hydrochar activation with iron salts (ferric nitrate and ferrous sulfate) in an alkaline medium. The advanced oxidation process (AOP) used to promote Metribuzin degradation employed peroxydisulfate (PDS) as the oxidizing agent. The hydrochar yields showed high conversion values of up to 70.48%, indicating that the established reaction parameters were effective. Material characterization was performed using Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), and X-ray Diffraction (XRD). The data indicate that iron-activated hydrochar (Fe-HC) exhibits superior adsorptive properties compared to conventional hydrochar, featuring a heterogeneous and porous surface, a composition predominantly of carbon, oxygen, and iron, a partially amorphous structure containing iron oxide phases, and the presence of oxygenated functional groups. The presence of microcracks on the surface suggests that iron activation contributed to bond breaking, increasing the material’s surface area. The PDS-activated removal results demonstrated that at lower concentrations (5 mmol.L-1), the system achieved high herbicide removal efficiency, reaching 84.98% in 120 minutes at pH 3.5 and 85.10% in 360 minutes at pH 7.5, respectively. These results indicate that time and pH did not have a determining influence on process performance, allowing its application across a wide operational range. This behavior corroborates the findings of the statistical analysis conducted using the Central Composite Rotational Design (CCRD), which showed that the interactions among the evaluated factors were not statistically significant at a 95% confidence level. Although no significant statistical correlations were observed, the factors of time, pH, and notably PDS contribute to the overall response of the heterogeneous catalytic system.