Evaluation of the photodiscoloration efficiency of β-Bi2O3 films deposited on different substrates by pneumatic spray pyrolysis

Immobilization of β-Bi2O3 over corning glass and sintered silica discs was performed to evaluate a competing fixed support as an alternative to slurry based photocatalytic systems. Pneumatic spray pyrolysis technique was used to produce coatings of β-Bi2O3 at 450 °C. Coated substrates were characterized using X-ray diffraction (XRD) and UV-Vis diffused reflectance spectroscopy (DRS), field emission scanning electron microscope (FESEM) and energy dispersive X-ray spectrometry (EDS). The XRD analysis showed that the obtained crystalline structure of the films is tetragonal β-Bi2O3 for both glass and silica. DRS showed the broad absorbance spectra of the films, correlated to β-Bi2O3 with an energy band gap of 2.4 eV. FESEM showed that the morphology of the films was different according to the substrate. In the case of corning glass, random non-compact distribution of particles was observed while over silica discs overlapped sheets of β-Bi2O3 were seen. This is probably due to differences in the wetting and evaporation rate of the sprayed droplets. During photodiscoloration of anionic indigo carmine (IC) dye solution, the β-Bi2O3 coated silica was found more effective than the coated glass, response associated to the larger interaction between the dye molecules and catalysts assisted by the roughness and porosity induced by the silica. Furthermore, photocatalytic evaluation of coated silica in discoloration of other two organic dyes: cationic rhodamine B (RhB) and anionic acid blue 113 (AB) revealed that adsorption and interaction of the dye molecules with coated films could vary due to the presence of different functional and branched groups that overall affect the photocatalytic process, the kinetic rate of discoloration and the TOC analysis. Finally, after the assessment of stability of films and suitability of silica, it was confirmed that silica discs are favorable as a photocatalyst support and last long usage for photodiscoloration of organic dyes.