TiO2-Bi2O3/(BiO)2CO3-reduced graphene oxide composite as an effective visible light photocatalyst for degradation of aqueous bisphenol A solutions

Article abstract of DOI:10.1016/j.cattod.2018.02.039

TiO₂ nanorods (T) were combined with a narrow band gap semiconductor β-Bi₂O₃ (B) to form a heterojunction, which makes it possible for TiO₂ to become active as a photocatalyst also under visible light illumination. To further increase the photocatalytic activity of TiO₂ + Bi₂O₃/(BiO)₂CO₃ (TB) composite, we used a hydrothermal procedure to link it with reduced graphene oxide (rGO). Structural, surface and electronic properties of the obtained catalysts were analyzed and correlated to their performance in photocatalytic oxidation of aqueous bisphenol A (BPA) solution conducted in a batch reactor under visible light illumination. XRD, FTIR, UV–vis DR spectroscopy and photocurrent measurements of visible light illuminated TB composite catalyst clearly showed that (i) β-Bi₂O₃ acts as a photosensitizer for TiO₂ and (BiO)₂CO₃ present in the TB composite, (ii) holes (h⁺) are photo-generated in valence band (VB) of β-Bi₂O₃ and due to the β-Bi₂O₃/TiO₂ heterojunction transferred into VB of TiO₂, (iii) p-n junction between β-Bi₂O₃ and TiO₂ allows the photo-generated electrons (e^?) in the conduction band (CB) of β-Bi₂O₃ to transfer to TiO₂, and (iv) p-n junction between β-Bi₂O₃ and (BiO)₂CO₃ allows the photo-generated electrons in the conduction band of β-Bi₂O₃ to transfer to (BiO)₂CO₃. This means that more charge carriers are available to participate in the catalytic visible-light triggered oxidation process for the degradation of organic pollutants dissolved in water. The highest photocurrent density was measured for multi-phase TBR (TB + rGO) composite, which indicates that visible-light generated charge carriers in TB composite are injected into the reduced graphene oxide. The latter acts as a web for charge carrier percolation and suppresses the recombination of electron-hole pairs, thus resulting in improved catalytic activity of TBR. The results of UV–vis DR spectroscopy and photocurrent density measurements were entirely in line with the results of photocatalytic oxidation of water dissolved bisphenol A (BPA) in batch reactor under visible light illumination.