Investigação estrutural, fotoluminescente e propriedades antibacterianas da argila palygorskita purificada e superfície impregnada com microcristais de α-Ag2WO4

Abstract

The presence of organic contaminants in aquatic environments, such as antibiotics, induces the proliferation of resistant pathogens, giving rise to the need to develop new materials with antimicrobial action. Therefore, in this work, we report new results for purifying Palygorskite clay (Pal) with a surface impregnated with alpha-silver tungstate (α-Ag2WO4) microcrystals abbreviated as AWO, and its structural, photoluminescence (PL) and antibacterial investigation. The p-Pal clay was obtained by purifying natural Pal. At the same time, the sonochemical method synthesized AWO microcrystals, followed by impregnation of the p-Pal clay surface. X-ray diffraction (XRD) patterns, Rietveld refinement, and Fourier transform infrared spectroscopy (FT-IR) were used to identify and quantify the crystalline phases. Field emission scanning electron microscopy (FE-SEM) was used to observe the morphological characteristics. Ultraviolet-visible spectroscopy (UV-Vis) in diffuse reflectance mode and PL measurements were used to analyze the optical properties of p-Pal clay, AWO microcrystals, and p-Pal/x% AWO microcrystals. Moreover, we investigated the inactivation of gram-negative (Escherichia coli) and gram-positive (Staphylococcus aureus) bacterial strains at concentrations of p-Pal/x% AWO from x = 4 to 32%. XRD patterns and Rietveld refinement data confirmed that the p-Pal clay is composed of two crystal phases (Mg2.074Al1.026)(Si4O10.48)2(OH)2(H2O)10.68 with an orthorhombic structure and α-SiO2 with a rhombohedral structure; the AWO microcrystals are singlephase with an orthorhombic structure. In contrast, the p-Pal clay/x% AWO decrease the intensity of the p-Pal clay XRD peaks as the x% mass of the AWO microcrystals increases. The FT-IR spectra revealed the three structures' main optically active vibrational modes. The UV-Vis spectra show an increase in the Egap of the mixed system compared to the isolated materials, indicating a synergistic interaction between the energy levels of both materials. The FE-SEM images display the presence of several elongated fibers and hexagonal crystals in the p-Pal clay and rod-like AWO microcrystals. In contrast, p-Pal clay/AWO microcrystals exhibit the presence of all three types of structures. The PL spectra show a high emission for the p-Pal/4% AWO clay, indicating a better synergistic effect for charge transfer between the distorted clusters from p-Pal clay to AWO crystals. At the same time, AWO crystals have a low PL intensity due to the lower recombination rate of electron/hole pairs. Finally, the microbiological tests show that as the proportion of AWO crystals on the p-Pal clay surface increases, there is an improvement in antibacterial activity.