UNDOPED TETRAGONAL ZrO2 APPLIED ASADSORBENT FOR ENVIRONMENTAL REMEDIATION

The ecological equilibrium has been impaired due to contamination of aquatic media by industrial effluents such as methylene blue (MB).[1] In order to minimize environment impacts of that practice, this research aimed at performing decolorization of solutions containing MB using zirconium dioxide (ZrO2). The material was synthesized by the modified Pechini method using Zirconium Butoxide as precursor.[2] Zirconia was obtained as final product of the synthesis, as indicated by the X-ray diffraction pattern (Figure 1a), which presents intense peaks assigned to the tetragonal phase and low-intensity peaks assigned to the monoclinic phase. The presence of tetragonal structure occurs in spite of being a high temperature phase, probably due to the small particle size, as previously reported.[2] The zeta potential of the material was analyzed and a negative surface was identified whatever the pH of the suspension and a greater negative electrical density was observed for higher pH values. ZrO2 was added into a quartz reactor containing 100 mL of MB solution at 10 ppm and subjected to irradiation with three UVC lamps under constant stirring for 24 h. The pH of the MB solution was adjusted to 2, 5, 7 or 10 using buffer solutions.[3] After irradiation, ZrO2 was separated from suspension by centrifugation and all solutions were analyzed by UV-Visible spectroscopy, in the wavelength range from 400 to 700 nm, obtaing the MB spectrophotometric profile (Figure 1b). The average concentrations of the dye solutions were quantified by an analytical curve (Figure 1c) previously produced according to the intensities of the UV-Vis spectra at 663 nm at concentrations of 1, 2, 4, 6, 8 and 10 ppm. It was observed that different decolorization values were obtained depending on the pH of the suspension, as indicated in Figure 1d. The biggest decolorization was attained at pH 2 with 94,4%, due to the positive charge of the MB dye, which favored the adsorption process. At pH 10 a high decolorization of 82,5% was also attained, probably due to the highly negative surface of ZrO2. Moreover, the appearance of a light blue color in the zirconia powder after irradiation proved that MB dye adsorbed on its surface, without degradation by photocatalytic processes in spite of the long exposition time. Finally, it is concluded that zirconia favored the decolorization of Methylene Blue solutions by adsorption, as ZrO2 is an insulating material with large band gap, being the pH 2 suspension most efficient to minimizing the ecological impacts.

Figure 1: (a) XRD pattern (ZrO2), (b) UV-Vis spectra of the MB, (c) zeta potential and (d) graphic of decolorization vs solution pH.

References: [1] DILEEPKUMAR et al. NaFeS2 as a new photocatalytic material for the degradation of industrial dyes. Journal of Environmental Chemical Engineering. 2020; [2] NERIS et al. Undoped tetragonal ZrO2 obtained by Pechini method: termal evaluation of tetragonal-monoclinic phase and application as catalyst for biodiesel synthesis. Journal of Thermal Analysis and Calorimetry. 2020. [3] LIOYD, D.; Preparation of pH buffer solutions. Available in <<http://delloyd.50megs.com>>.