Síntese verde de nanopartículas de MnO2 utilizando extrato de folha da acerola e aplicação em fotocatálise para remoção do corante azul de metileno

Abstract

Liquid effluents containing organic dyes are pollutants that pose a high environmental risk. Photocatalysis has been reported as an effective method for the degradation of these contaminants. In this work, green synthesis of MnO2 nanoparticles was carried out using an aqueous extract of acerola leaves. The effect of pH and plant extract concentration on the material properties was investigated, and its efficiency in removing methylene blue dye was evaluated. The doping of nanoparticles with praseodymium was also studied. Structural, compositional, and morphological characterizations were conducted using various techniques. The discoloration experiments were performed under UV light radiation. The results showed that for 30 g·L-1 of extract, an increase in pH decreased the particle diameter, while with 60 g.L -1, the opposite effect was observed. The crystalline phase was identified as α-MnO2 with a mesoporous structure. Doping with 1% Pr3+ increased the Mn3+/Mn4+ ratio, promoting the generation of surface defects that induced morphological changes, leading to the growth of nanoneedles in the structure and increasing the available surface area (180.8 m2 .g-1). These factors improved the separation of photogenerated charges, reduced the bandgap, and optimized the photocatalytic activity of the nanoparticles, which removed about 85.3% of the dye (50 mg.L-1) after 60 minutes of contact, showing superior performance compared to undoped samples. The green-synthesized MnO2 demonstrates excellent potential for technological applications in the remediation of organic pollutants, such as dyes, in aqueous solutions.