Molecular dynamic simulations for interactions of oxytetracycline with copper(II)-exchanged NaY zeolite

This study was devoted to examine the effect of the surface structure of Cu²⁺-Y against pure NaY on the photodegradation of oxytetracycline (OTC). The lattice strain examined by Rietveld analysis of XRD data showed strain induced peak broadening at 0.124 for NaY, which diminished to 0.119 for Cu²⁺-Y, prompted by the exchange of Cu²⁺ onto the NaY zeolite. Scanning electron microscope (SEM) statistical analysis of Cu²⁺-Y revealed better crystallinity with larger cube width, >2 µm, compared with NaY, 1.7 µm. The vibrational modes and optical properties of Cu²⁺-Y and NaY were compared using Fourier transform infrared (FTIR) spectra, Raman spectroscopy, and ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS). An IR band at 665 cm⁻¹ associated with ν_s(Si-O-Cu) was evident for Cu²⁺-Y, which was absent from the spectrum of pure NaY. The Raman bending vibration at 490 cm⁻¹ due to 4-membered ring I in the Cu²⁺-Y displayed a blue shift and a lower value of the full width at half maximum (FWHM) by about 3.02 nm and 0.74 cm⁻¹, respectively, compared with that of NaY. It was proposed that Cu²⁺ ions are attached to shared oxygen of double 4-rings in Y-zeolite. The electronic analysis of Cu²⁺-Y revealed an indirect energy bandgap of 3.17 eV together with an excitonic absorption band at ∼2 eV. The computational molecular adsorption calculations demonstrated the potential effect of Cu²⁺-Y to accommodate five molecules of OTC per unit cell. Molecular dynamics (MD) simulations were committed to support the response behind the higher efficiency and stability of Cu²⁺-Y towards adsorption of the OTC under the force of interaction. OTC molecules brought into being travel toward positions of copper in the optimized OTC@Cu²⁺-Y. In contrast, Na⁺ ions in OTC@NaY held moving towards the edges of the zeolite unit cell and no evidence of the presence of OTC molecules inside the confines of the zeolite cavities. H-bond distribution indicate a close connection and a more stable configuration of OTC inside the Cu²⁺-Y. Thus, MD simulations can safely predict the potential of Cu²⁺ to attract the OTC molecules to form OTC@Cu²⁺-Y complexes.