Formulation of Bismuth (Bi₂O₃) and Cerium Oxides (CeO₂) Nanosheets for Boosted Visible Light Degradation of Methyl Orange and Methylene Blue Dyes in Water

Annealing of periodic mesoporous organosilica supported with bismuth (Bi@PMOS) and cerium (Ce@PMOS) nanoparticles was carried out to derive bismuth oxide (Bi₂O₃) and cerium oxide (CeO₂) nanosheets. The hydrothermal sol-gel method was used to synthesize hexagonal Bi@PMOS and Ce@PMOS. These PMOS provided an opportunity for bismuth and cerium to retain a hexagonal configuration alongside their traditional crystalline phases (tetragonal and cubic) in Bi₂O₃ and CeO₂ nanosheets. All produced materials were found to be dynamic under sunlight irradiation for the degradation of methylene blue (MB) and methyl orange (MO). However, the Bi₂O₃ and CeO₂ nanosheets showed better potential and photo-catalytic performances than Bi@PMOS and Ce@PMOS due to the presence of the unique blend of crystalline phases. The synthesized Bi@PMOS, Ce@PMOS, Bi₂O₃, and CeO₂ were structurally characterized by FTIR and XRD techniques. These showed characteristic vibrations of successfully loaded bismuth and cerium with hexagonal symmetry. EDX results confirmed the elemental detection of bismuth and cerium, while SEM images revealed the nanosheets in the synthesized materials. The optical response and detection of reactive species were carried out by photoluminescence (PL) and showed emissions at 700 nm. The PL data were also used to calculate band gaps of 3.72, 3.70, 3.35, and 2.88 eV for Ce@PMOS, Bi@PMOS, CeO₂, and Bi₂O₃, respectively. A UV/visible spectrophotometer scanned the photocatalytic competences of the synthesized nanomaterials through the degradation of MB and MO dyes. Then, 10 mg of Bi@PMOS and Ce@PMOS degraded 15 mg and 8.4 mg of MB and 10.8 mg and 8 mg of MO, respectively, in 20 mg/L solutions. However, equivalent quantities of Bi₂O₃ and CeO₂ (10 mg of each) exhibited more efficient photocatalysis of the 20 mg/L solutions of MB and MO, degrading 18.4 mg and 15.4 mg, and 12.4 mg and 17 mg, respectively, in only 1 h. The Bi₂O₃ and CeO₂ photocatalysts were regenerated and their photodegradation results were also recovered. Bi₂O₃ and CeO₂ showed only 10% and 8% (for MB), and 8% and 10% (for MO) decline in catalytic efficiency, respectively, even after four consecutive recycles. These results demonstrate that these materials are dynamic, long-lasting photocatalysts for the rapid degradation of azo dyes in contaminated water.