Highly efficient photocatalytic activity and mechanism of novel Er3+ and Tb3+ co-doped BiOBr/g-C3N5 towards sulfamethoxazole degradation

Bismuth oxyhalides (BiOX (X = Cl, Br, I) are considered to be an important p-type semiconductors in the photocatalysis applications. In particular, tetragonal BiOBr is considered as a stable photocatalyst due to its resilient absorption in the visible region with an band gap energy of 2.8 eV. In the meantime, lanthanide ions (with 3+ oxidation state) implies as conversion catalyst gained huge impact and remain a serious topic in materials chemistry. Here we synthesized upconversion photocatalyst mainly consists of BiOBr with the Er 3+ and Tb 3+ ions along with low band gap g-C3N5 for the improved photocatalytic performances. The synthesized Er3+/ Tb3+@BiOBr-g-C3N5 heterojunction was systematically characterized by XRD, and FT-IR for the confirmation of the composite and their morphology were analysed with FESEM and HR-TEM analysis which revealed that the sheets of g-C3N5 were decorated by Er3+/Tb3+ loaded BiOBr microspheres. The XPS analysis confirmed the suitable oxidation state of all the individual elements existing in the composite. As the UV-DRS analysis showed that the band gap of the Er3+/Tb3+ BiOBr-gC3N5 heterojunction was narrowed to 2.64 eV. To evaluate the photocatalytic efficiency of the synthesized g-C3N5, Er3+/Tb3+@BiOBr and Er3+/Tb3+@BiOBr-gC3N5 heterojunction under the simulated visible light irradiation source towards the aqueous sulfamethoxazole degradation. The Er3+/Tb3+@BiOBr-gC3N5 heterojunction shows maximum degradation efficiency of 94.2% after 60 min of visible light irradiation whereas the pure g-C3N5 provided about 43.8% and Er3+/Tb3+@BiOBr implies 55.2% degradation efficiency. The plausible degradation mechanism of pollutant removal was proposed.

Automated summary

A novel upconversion photocatalyst composed of BiOBr, Er3+ and Tb3+ ions, and low-band gap g-C3N5 was synthesized and characterized, showing improved photocatalytic performance in sulfamethoxazole degradation under visible light. The degradation efficiency of the Er3+/Tb3+@BiOBr-gC3N5 heterojunction was significantly higher compared to pure g-C3N5 and Er3+/Tb3+@BiOBr, with a proposed degradation mechanism for pollutant removal.