Visible light enhanced degradation of sulfamethoxazole by beta zeolite/TiO 2 photocatalyst

Abstract

A visible light photoactive layered beta zeolite supported titanium dioxide (TiO2) was successfully fabricated, whereby N,Ndimethylacetamide was used for the first time as a stacking agent, and tetramethylammonium hydroxide pentahydrate (TMAOH) as a template for beta structure via sol–gel assisted hydrothermal method. High-resolution transmission electron microscopy (HRTEM) results confirmed homogenous dispersion of spherical TiO2 nanoparticles onto the zeolite. The ultraviolet– visible (UV–vis) diffuse reflectance spectroscopy (UV–vis DRS), and Raman spectral shifts proved that nanocomposite had a visible light redshift bandgap of 2.88 eV for zeolite/TiO2 (3.18 eV, TiO2). Fourier-transform infrared (FTIR) and energy-dispersive X-ray spectroscopy (EDS) analysis of zeolite/TiO2 revealed the presence of a nitrogen atom from NH4OH, causing a redshift of the photocatalysts by substituting oxygen (O) atom from O─Ti─O to form O─Ti─N bond. This photocatalytic removal efficiency for sulfamethoxazole was 82% after 120 min of visible light irradiation at pH 5.5. This photocatalyst has superior visible light activity with k = 0.018 min−1 and 82% performance for SMX degradation compared to some recent zeolite/TiO2 nanocomposite with UV light limitation. The recyclability and stability tests revealed efficient reuse for five cycles without major decline. A Type-II heterojunction system observed suggest a cyclic charge pair transfer whereby an electron moves from a high CB of zeolite into low CB of TiO2, whereas holes (h+) move from a lower VB of TiO2 into higher VB of zeolite.