Effect of Cyclic Use and Assessment of Environmental Safety of Visible‐Light Photocatalysts CsSn _0.25 W _1.75 O ₆

ABSTRACT

The stability of β‐pyrochlore‐based photocatalysts CsSn _0.25 W _1.75 O ₆ and CsMo _0.25 W _1.75 O ₆ were evaluated under cyclic use conditions for the degradation of methylene blue (MB). The CsSn _0.25 W _1.75 O ₆ catalyst demonstrated stable performance over the cycle (MB conversion 80–94%), while the Mo‐containing analogue showed significant deactivation due to structural instability (overall efficiency drop from 35% to 23% after the first cycle). HPLC‐MS analysis revealed the formation of aromatic intermediates. Permanganate oxidizability (PO) measurements showed that CsSn _0.25 W _1.75 O ₆ achieved mineralization (PO 1–2 mg O ₂ /L), whereas CsMo _0.25 W _1.75 O ₆ resulted in incomplete oxidation (PO 7–8 mg O ₂ /L). Phytotoxicity tests on wheat seedlings ( Triticum aestivum L .) demonstrated that water treated with the CsSn _0.25 W _1.75 O ₆ catalyst supported normal plant growth (Vigour Index 92%–98% of control). Chlorophyll fluorescence analysis revealed optimal photosynthetic performance for CsSn _0.25 W _1.75 O ₆ treated plants (F730/F685 1.01–1.19) whereas CsMo _0.25 W _1.75 O ₆ treated plants exhibited severe stress (F730/F685 2.26). Membrane damage assessment confirmed minimal damage for Sn‐catalyst (3.6%) and significant damage for Mo‐catalyst (24.1%). Bacterial toxicity tests using Escherichia coli showed that the water treated with CsSn _0.25 W _1.75 O ₆ showed significantly low toxicity after the first use, while water treated with CsMo _0.25 W _1.75 O ₆ preserved partial antimicrobial activity. A regeneration protocol involving ethanol washing followed by annealing at 450°C fully restored the activity of the CsSn _0.25 W _1.75 O ₆ catalyst.