Facile synthesis of bismuth oxide nanostructures derived from solvent-mediated oxalates and their visible-light-driven photocatalytic removal of organic pollutants

Stacked plate type beta-Bi2O3 microstructures with a substantial specific surface area and excellent visible-light-driven photocatalytic activity were successfully prepared using a simple precipitation-calcination method. By varying ethanol/water ratio, the solvent-mediated competition between oxalate coordination and bismuth ammonium citrate hydrolysis resulted in the formation of mixture of bismuth oxalate and bismuth hydroxide. A series of micro-structured precursors with various sizes and morphologies were synthesized through adjustment of solvents that allowed the formation of tetragonal beta-Bi2O3 upon further calcination. The optimal catalyst [beta-Bi2O3 (S6)] with exceptional photocatalytic activity due to its enhanced specific surface area (62.7 m(2) g(-1)) and narrower bandgap (2.20 eV), was highly dependent on ethanol-to-water ratio during precursor preparation. The as-prepared catalyst (S6) degraded rhodamine B, methyl orange, methylene blue and ciprofloxacin up to 99%, 98.8%, 71% and 70%, respectively in 180 min under visible-light. Moreover, effects of initial catalyst loading, dye concentration, and solution pH on photocatalytic behavior over S6 were studied. The optimized catalyst degraded 69% of the simulated dye-bath solution in 180 min. Photo-generated holes (h(+)) were identified as dominant active species in photodegradation. The increased surface area and stacked structure facilitated separation and transfer of photo-generated charges and favored active site exposure, resulting in improved photocatalytic activity.