Nanopartículas de Zn(1-x)AgxO para tratamento de efluentes da indústria petroquímica

Abstract

Nanoparticles (NPs) of oxides are used as photocatalysts in the degradation of pollutants in industrial effluents due to their band gap (3.37 eV). To improve the photocatalytic and optical properties of ZnO, a noble metal dopant is added. In this work, pure and Ag-doped ZnO NPs (0.5%, 1.0%, 2.0%, 3.0%, 4.0% and 5.0%) were synthesized and characterized. These NPs were used as photocatalysts in the degradation of terephthalic acid (PTA). The synthesis method used was microwave-assisted hydrothermal at 120°C for 32 min. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and spectroscopy analysis in the UV-Vis region. XRD identified the hexagonal phase of the wurtzite structure (COD 96-900-4179) for ZnO. It was verified that from 2.0% of Ag in the samples, there was the formation of Ag2O and Ag0 indexed to the letters COD 96-101-0487 and COD 96-901-2962, respectively. From 3.0% Ag, characteristic peaks of Na2O were identified (COD 01-077-0208). The average crystallite size of the synthesized NPs increased with Ag doping, from 34 nm to 38 nm (for 3.0% and 5.0% Ag). Deformations were observed in the lattice parameters in samples doped with Ag, suggesting the incorporation of Ag+ in the ZnO lattice. By SEM it was observed that the synthesized materials showed morphology of nanoplates with lengths between 394 and 309 nm and thickness between 55 and 31 nm. For ZnO doped with Ag, a reduction in the band gap to 3.29 eV was observed. Photocatalysts were used in the degradation of PTA under exposure to UVA (Ultraviolet A), UVC (Ultraviolet C) and solar radiation. Under solar radiation, the system was more efficient, reaching values greater than 90% of PTA degradation in 30 min. Under UVA and UVC radiation, the percentage of degradation was around 90%, but with 60 min of exposure. Samples with higher concentrations of Ag (3.0%, 4.0% and 5.0%) showed the best percentages for PTA degradation (>77% in 5 min). In the kinetic studies, all systems satisfactorily obeyed the Chan and Chu and Pseudo-First Order models with R2average around 97 to 98%, for all systems studied.