Effect of heat treatment on the structure and photocatalytic properties of BiYO3 and BiY0.995Ni0.005O3 ceramic powders

BiYO3 powders were synthesized by the Pechini method under low-temperature conditions. When the heat treatment was performed at T < 600 degrees C, a mixture of tetragonal and cubic phases was obtained, while for T >= 600 degrees C, only the fluorite-like cubic phase was observed. Based on the Rietveld refinement, approximately 2% and 1% of the tetragonal phase remained in samples calcined at 400 degrees C and 500 degrees C for 1 h, respectively. The crystal size calculated for these samples was 4.4-48.1 nm, depending on the calcination temperature. The specific surface area of the samples diminished with heat treatment and reached a minimum at 800 degrees C. The band gap of samples with mixed phases was close to 2.16 eV and was similar to 2 eV for samples with a cubic phase. Photocatalytic tests demonstrate that BiY0.995Ni0.005O3 calcined at 800 degrees C had the best performance: it degraded more than 80% of the antibiotic oxytetracycline when irradiated with visible light. The Ni-doped BiYO3 material could degrade the antibiotic in tap water at an environmentally relevant concentration (mu g L-1 levels) and showed steady activity throughout four reaction cycles.