Influência dos íons Ce4+, Sm3+ e Gd3+ nas propriedades fotoluminescentes e fotocatalíticas do óxido de zinco

Abstract

Nanoestructures of ZnO pure and doped with rare earth ions (TR: Ce4+, Sm3+ and Gd3+), prepared by the microwave hydrothermal (MH) method, with photoluminescent and photocatalytic properties were obtained in the present work. The materials were synthesized under low temperature at 90 °C and in short reaction times of 2 and 16 minutes. The formation of the wurtzite hexagonal phase was observed for samples of pure ZnO and doped with the Ce4+, Sm3+ and Gd3+ ions. The Rietveld refinement results exhibited reliability coefficients for good refinement. Raman spectra revealed the presence of the E2H mode at 438 cm-1 confirming the formation of the ZnO wurtzite hexagonal structure for all samples obtained and the local distortions generated by the addition of the rare earth ions causing a short-range disorder in the ZnO structure. MEV-FEG images showed the importance of the time of synthesis in the formation of pure and doped ZnO nanostructures. The samples synthesized in 2 minutes are irregularly shaped particles, while after 16 minutes of synthesis, a directional growth of the particles was observed with the formation of homogeneous plates with a mean thickness of 45 nm. The EDX spectra confirmed the presence of the cerium, samarium and gadolinium elements in the doped samples and their purity. All samples presented photoluminescent properties with broad band in the visible region of the spectrum, with maximum emission in the green-orange region. The incorporation of doping ions led to an increase in the percentage of emission area in the green region, associated to the presence of oxygen vacancies. The morphology and size of the formed particles, which had a special influence on doping and hydrothermal reaction time, played a fundamental role in the photocatalytic activity of the synthesized materials. All the materials obtained showed photocatalytic activity, and the catalysts that presented the best performance against the degradation of the methylene blue dye were: ZnO doped with 2 mol% Gd3+ at 2 minutes, 1 mol% Gd3+ at 16 minutes and 2 mol% Sm3+ at 16 minutes, with 65%, 73% and 100% efficiency, respectively.