(562bf) Insights into the Properties of AgBiO3 Photocatalyst and Its Application in Immobilized State for E. coli and 4-Nitrophenol Degradation

Numerous efforts have been contributed to developing highly active photocatalyst in visible region for water decontamination. AgBiO₃ (AB) is such a material with a perovskite structure whose properties have not been well explored in the literature. The band gap of AB is a debatable issue. Ma et al. reported the band gap to be 0.8 eV from DFT calculations [1]. Yu et al. reported AB prepared via ion exchange method between AgNO₃ and NaBiO₃ to have a band gap of 2.5 eV [2]. Therefore, this study critically evaluates the optical properties of the material. In the current work AB nanoparticles were prepared via hydrothermal route. Optimizing the temperature and time of hydrothermal reaction was very crucial to obtain highly active crystalline AgBiO₃ nanoparticles as determined by XRD. The unique properties of a photocatalyst such as band gap, conduction band, valence band edge, work function, fermi level of AB nanoparticles was investigated by UV-Vis DRS, UPS and Mott Schottky analysis. These nanoparticles were successfully immobilized on cellulose acetate by phase inversion technique. Finally, the possible mechanism involved in the 4-Nitrophenol (4-NP) and Escherichia coli (E. coli) inactivation was proposed based on scavenger experiments and band structure analysis.

For catalyst preparation, temperature and time of hydrothermal reaction was optimized to 150°C and 24 h to obtain photoactive nanoparticles. From XRD pattern, AB was found to have rhombohedral structure. XPS confirms Ag and Bi to be in +1 and +5 oxidation states respectively. DRS reveals the material to absorb in the entire visible range with an indirect band gap (E_g) of 0.75 eV. Mott Schottky and UPS analysis show the material to be an n-type semiconductor with valence band edge (E_vb) at +0.35 V vs NHE. The conduction band edge (E_cb) was at -0.4 V signifying the energy level to be sufficient enough to generate superoxide radicals (O₂^.-) at -0.33 V vs NHE. AB nanoparticles immobilized on cellulose acetate could successfully degrade 4-NP and E. coli with rate constants of 0.313 h^-1 and 0.175 min^-1 as compared to rate constants of 0.018 h^-1 and 0.024 min^-1 respectively for photolysis without catalyst. To elucidate the mechanism of E. coli and 4-NP degradation reactions, scavenger studies were performed. O₂^.-was identified as the main reactive oxygen species responsible for the degradation of these pollutants.

Thus, AgBiO₃ can be used as a potential photocatalyst to decontaminate water and the properties investigated can be exploited to form hybrid photocatalysts for better activity.

References:

1. Ma, K. Wu, B. Sun, C. He, Band engineering of AgSb_{1− x}Bi_xO₃ for photocatalytic water oxidation under visible light, Journal of Materials Chemistry A, 3 (2015) 8466-8474.
2. Yu, J. Zhou, Z. Wang, W. Cai, Preparation of visible light-responsive AgBiO₃ bactericide and its control effect on the Microcystis aeruginosa, Journal of Photochemistry and Photobiology B: Biology, 101 (2010) 265-270.