Mesoporous TiO₂ coated ZnFe₂O₄ nanocomposite loading on activated fly ash cenosphere for visible light photocatalysis

Several activated fly ash cenosphere (AFAC) supporting TiO₂ coated ZnFe₂O₄ (TiO₂/ZnFe₂O₄/AFAC) photocatalysts were prepared by sol-gel and hydrothermal methods. These photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), UV-vis diffuse reflectance spectroscopy (UV-DRS) and nitrogen adsorption analyses for Brunauer-Emmett-Teller (BET) specific surface area measurements. We found that the main components of spherical AFAC were mullite (Al₆Si₂O₁₃) and SiO₂; the crystallite size of the TiO₂/ZnFe₂O₄ nanocomposite was less than 10 nm and its specific surface area was 162.18 m² g^-1. The TiO₂/ZnFe₂O₄ nanocomposite had a band-gap of 2.56 eV, which would photodegrade 95% of rhodamine B (RhB) under visible light within 75 min. When hybridized with 0.02 g AFAC, the TiO₂/ZnFe₂O₄/0.02 g AFAC photocatalyst with a band-gap of 2.50 eV could remove 97.1% of RhB and be reused three consecutive times with minor decrease in photocatalytic performance. However, the photocatalytic performance decreased to 91.0% on increasing the dosage of AFAC to 0.30 g. The mesoporous structure of all the photocatalysts and the strong adsorption ability of AFAC accounted for the notable performance.