Photocatalytic\nEstrogen Degradation by the Composite\nof Tin Oxide Fine Particles and Graphene-like Carbon Nitride

This study investigates whether 17β-estradiol (E2),\na natural\nestrogen and one of the endocrine-disrupting chemicals responsible\nfor water pollution, can be oxidatively decomposed under simulated\nsolar light using a composite of tin oxide nanoparticles and graphene-like\ncarbon nitride (g-CN) as a photocatalyst. The composite photocatalyst\nwas prepared by heating a mixture of urea and tin acetate. FT-IR measurements\nrevealed that g-CN possesses structural units similar to g-C<sub>3</sub>N<sub>4</sub>, a well-studied graphite-like carbon nitride. However,\nunlike g-C<sub>3</sub>N<sub>4</sub>, sharp diffraction lines were\nnot observed in the XRD diffraction pattern of g-CN, indicating lower\ncrystallinity. Elemental analysis showed that g-CN is slightly nitrogen-rich\ncompared to g-C<sub>3</sub>N<sub>4</sub>, and UV–vis measurements\nindicated that the band gap of g-CN is slightly smaller than that\nof g-C<sub>3</sub>N<sub>4</sub>. The presence of tin in the composite\nof tin oxide and g-CN was clearly confirmed by XPS, although no sharp\ndiffraction peaks were observed in the XRD patterns, suggesting the\npresence of microcrystals. Furthermore, FE-SEM observations did not\nreveal large tin oxide crystals, although EDS mapping indicated the\npresence of tin oxide. It was found that the prepared tin oxide and\ng-CN composites function effectively as photocatalysts for degrading\nE2 under simulated solar light. The degradation rate constant was\nevaluated to be <i>k</i> = 3.34 (0.14) × 10<sup>–2</sup> min<sup>–1</sup>. Peroxide ion radicals were detected in\nESR measurements from the irradiated solution, suggesting that peroxide\nion radicals are generated through oxygen photoreduction as the counter-reaction\nof the oxidative decomposition of E2.