Uso do Basalto como catalisador heterogêneo natural na degradação da Atrazina por Foto-Fenton

Abstract

The use of heterogeneous catalysts from natural sources has recently been approached as an alternative to traditional Fenton and photo-Fenton processes, due to the potential for reuse, low cost and sustainability. In view of Brazil is a country with high geological potential, which it has a diversified wealth in rocks rich in minerals such as basalt, in this present study, for the first time, the applicability of basalt powder as a new natural catalyst was evaluated in the photo-Fenton process under different sources of irradiation (UV-C and visible) to remove the herbicide atrazine (ATZ) in aqueous matrix. Basalt was characterized by X-ray fluorescence (XRF), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD) and infrared spectroscopy by Fourier transform with attenuated total reflection (IR/FR-ATR). Adsorption desorption isotherms and specific surface area were determined from the linear Brunauer– Emmett–Teller (BET) release form, and the total volume and average pore size by the Barrett-Joyner-Halenda method. (BJH), beyond the zeta potential. The basalt samples showed a heterogeneous structure and low porosity with a content of 13.5% (m/m) of Fe2O3 highly dispersed on the surface of the particles. A photo-oxidation study was carried out, applying the processes of photolysis, photocatalysis, photo-peroxidation, and photo-Fenton under UV-C and visible light. It was possible to evaluate the mechanisms and reactions that contribute to the photo-Fenton heterogeneous process with basalt as the catalyst. The effects of operating parameters such as pH (2–7), catalyst dosage (0.25–1.00 g L−1), and H2O2 concentration (0.8–6.4 mM) were optimized. High performance liquid chromatography (HPLC) and UV-vis spectral scanning techniques were used to identify ATZ and its metabolites of desethylatrazine (DEA), deisopropylatrazine (DIA) and hydroxyatrazine (HA). The material after thermal treatment at 600 °C showed excellent catalytic efficiency, removing 96.0% and 56% of atrazine in 180 min in heterogeneous photo-Fenton processes under UV-C and visible irradiation, respectively, following operating conditions: catalyst dosage of 0.50 g L-1 (UV-C) and 0.75 g L-1 (vis), initial concentration of H2O2 of 1.6 mM and pH at 6. It was proposed that the adsorption mechanism on the catalyst surface started the action of basalt as a photo-Fenton catalyst and dealkylation was the main pathway of atrazine degradation. After treatments, the effluents showed lower acute toxicity (phytotoxicity and antibacterial activity) than the initial atrazine solution at 5 mg L-1 . Under optimal conditions, the inhibition of ATZ removal efficiency was evaluated with the addition of isopropanol and chloroform as radical scavengers, emphasizing the significant role of hydroxyl radicals on superoxide in ATZ oxidation by photo-Fenton type process. The sintered catalyst has high stability and efficiency in the photo-Fenton process under UV-C after three successive cycles of reuse, with removal greater than 91%, and it was possible to adjust its removal kinetics to the first-order model, with k equal to 0.0169 min-1 . Atrazine removal by photo-Fenton solar was also evaluated reaching 31.4% of ATZ in approximately 60 min. The kinetic behavior was like the process under visible light irradiation. In addition, the persulfate oxidant potential was also evaluated, promoting removals of 91%, 62% and 76% of ATZ, in photo-Fenton processes under UV-C, vis and solar, respectively. The results showed that basalt powder can be successfully used as a natural catalyst in the heterogeneous photo-Fenton process for the degradation of the herbicide atrazine.