Zeolite–titanium dioxide nanocomposites: Preparation, characterization, and adsorption properties

Synthesis conditions are optimized to obtain η-phase/zeolite and Hombifine N/zeolite nanocomposites by the modified cold-impregnation method (method 1), which consists of the codispersion of the samples containing the η-phase or Hombifine N with nano-anatase in a dilute KOH solution, and Beta(25) and ZSM-5 zeolites with different modulus, MOR and Y, for the first time, as well as by the TiO₂/zeolite in situ method (method 2), which consists of the addition of zeolites into the reaction mixture during the synthesis of titanium dioxide. The starting components and nanocomposites are characterized by different methods, such as wide- and small-angle Х-ray scattering, scanning electron microscopy, and low-temperature nitrogen adsorption (the Brunauer–Emmet–Teller method). The interaction between nanosized titanium dioxide (NTD) and zeolites (except Y) during the formation of the NTD/zeolite nanocomposite (method 2) and the η-phase/MOR nanocomposite (method 1) is revealed, and the presence of NTD in the nanocomposites in nanocrystalline (Hombifine N/zeolite) or amorphous (η-phase/Beta(25) and η-phase/ZSM-5(300)) states is established. It is found that the use of microwave and ultrasonic treatment upon the synthesis of the nanocomposite gives rise to the uniform distribution of spherical particles in the samples; furthermore, they are the same size (η-phase/ZSM-5(12), η-phase/ZSM-5(300), and η-phase/Y) or smaller (η-phase/MOR, η-phase/Beta(25), and η-phase/ZSM-5(40)) when compared to the original η-phase. The size of spherical particles in the η-phase/ZSM-5(40) nanocomposite is comparable with the starting ZSM-5(40) zeolite. It is found that the preparation of nanocomposites by method 2 leads to an increase in the specific surface for the NTD/ZSM-5(12) and NTD/Y nanocomposites and to a decrease in the specific surface for the remaining nanocomposites (most significantly for NTD/MOR) when compared to the zeolite matrix, and promotes the high adsorption capacity of the NTD/zeolite nanocomposites with regard to the extraction of the P(V) ions from the model aqueous system with the maximum value (99.48%) for the NTD/MOR nanocomposite.