Isomorphous Zn-Substitution on Y Zeolite Structure by the Hydrothermal Method As a Novel Strategy: Evaluation by Methyl Orange Photodegradation

Isomorphous substitution of Zn-Y zeolite (Zn-DYZ) was successfully conducted with different Zn/Al ratios of 0.5:9.5, 1:9, 1.5:8.5, and 2:8 mol ratios (hereafter designed as Zn-DZY-1, Zn-DZY-2, Zn-DZY-3, and Zn-DZY-4, respectively) by the hydrothermal synthesis method. Spectroscopic studies indicate that Zn is decorated into the zeolite framework. The insertion of Zn instead of Al in the zeolite framework in small amounts (0.5:9.5, 1:9 mol ratios of Zn/Al) does not affect the zeolite framework. However, at high Zn loading (mainly Zn-DZY-4, 2:8 mol ratio), the zeolite structure collapse due to the imbalance in electrical charge, as confirmed by XRD analysis. In addition, by increasing the loading of Zn, the deviation of d-spacing and shift in the peak position of the XRD pattern occurs, which is related to the radius of zinc ion compared to aluminum, thus causing the lattice expansion. A significant increase in BET surface area and pore volume was observed in Zn-DZY toward NaY (870 toward 906.5 and 0.37 cm3 g−1 towards 0.392 cm3 g−1, respectively), which may be related to the expansion of the zeolite framework because of the replacement of Zn instead to that of Al. These results confirm by XPS data. The XPS results show two different chemical environments are related to Al-O-Zn and Si–O-Zn with bit shifts. In addition, the peak position is higher than toward ZnO which is a significant reason for the formation of ZnO42− in the zeolite framework. The photocatalytic activity of the related catalysts is investigated in the removal of methyl orange. The effect of several parameters including catalyst loading, pH, dye contamination, and zinc loading was studied in the photodegradation process. The best results were obtained in the presence of 32 ppm methyl orange, 70 mg catalyst, pH = 7, and 1:9 Zn/Al ratio under UV irradiation. It was found that the photodegradation kinetics follows pseudo-first-order kinetics. COD experiment was used to measure the mineralization of methyl orange (69