Performance evaluation of direct Z-scheme based modified titania composite for photocatalytic degradation of organic pollutants

Abstract

Ceramic materials are widely used as a photocatalyst due to their low cost synthesis, photostability, suitable bandgap and excellent photodegradation properties. One such material is TiO2 however, it shows very low efficiency because it is only active in UV region (4 % of solar spectrum), have high holes-electrons recombination and low adsorption capacity. To address these limitations, highly active modified TiO2 based ceramic materials like Er2O3/TiO2, Molybdenum loaded TiO2 and TiO2/Er2O3 photocatalysts were synthesized by Sol-gel method. These synthesized photocatalysts were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, photoluminescence (PL) emission spectroscopy, UV–vis spectra, and Brunauer–Emmett–Teller (BET). The incorporation of Er2O3 into TiO2 and metal loading of molybdenum reduced the bandgap of TiO2 from 3.3 eV to 3.25 eV, 3.1 eV, and 3.09 eV for TiO2–Er2O3, Mo loaded TiO2 and Mo loaded TiO2–Er2O3, respectively. BET analysis revealed the enhancement of surface area by adding Er2O3 and Mo (from SBET = 39.9 m2/g to SBET = 67 m2/g) which is one of the crucial factors to increase the photocatalytic activity. The loading of molybdenum enhanced the immobilization of carriers that facilitated the photo-oxidation process and suppressed the electron-holes recombination (from 800 counts to 200 counts) as confirmed by the PL spectroscopy. The photocatalytic activity of these catalysts were evaluated by studying the photodegradation of Methylene blue (MB) under sunlight in standard conditions (1 sun, 1 atm). The synergistic effect of inclusion of Erbium Oxide and loading of molybdenum in titania-Erbium Oxide composite enhanced the photodegration efficiency from 13.2% to 75 %. The photocatalytic activities were in order of Mo@TiO2–Er2O3 > Mo@TiO2 > TiO2–Er2O3 > TiO2. These modifications also improved the conductivity of titania (σ = 4.43 × 10−4 Sm−1 to σ = 5.31 × 10−4 Sm−1) that was confirmed by Hall effect. These results supported the effectiveness of titania-modified composite for the degradation of industrial textile dye wastewater under sunlight and can be used for an optoelectronics applications.