Adsorption, excitation analysis, and the mechanism of tetracycline photodegradation by Ca₁₂O₁₂-PEDOT, Mg₁₂O₁₂-PEDOT, and Zn₁₂O₁₂-PEDOT hybrid materials: Perspective from first-principles study

Tetracycline (TC) residues threaten aquatic ecosystems by infiltrating water bodies and disrupting aquatic life, potentially affecting the food chain. In our quest to address this ecological concern, we embarked on a fascinating investigation exploring the photodegradation of tetracycline using nanocomposite materials: Ca₁₂O₁₂-PEDOT, Mg₁₂O₁₂-PEDOT, and Zn₁₂O₁₂-PEDOT within the framework of density functional theory (DFT) at the ωB97XD/def2svp method. The results obtained showed that tc@Ca₁₂O₁₂-PEDOT composite exhibited unparalleled stability with an adsorption distance of 1.922 Å, surpassing its counterparts tc@Mg₁₂O₁₂-PEDOT and tc@Zn₁₂O₁₂-PEDOT. The tc@Ca₁₂O₁₂_PEDOT system displayed a compact energy gap, suggesting its superior photon absorption capability from the valence band compared to the others. The sequential order of stabilization energies was observed as follows: Zn₁₂O₁₂-PEDOT > Mg₁₂O₁₂-PEDOT > Ca₁₂O₁₂-PEDOT, with values of 73.26 kcal/mol, 49.35 kcal/mol, and 10.66 kcal/mol, respectively. The analysis of charge transfer showed that tc@Mg₁₂O₁₂_PEDOT had the highest magnitude of charge transfer, followed by tc@Zn₁₂O₁₂_PEDOT and tc@Ca₁₂O₁₂_PEDOT. The characterization of the hole and electron separation through the computed back donation revealed a distinct pattern: tc@Zn₁₂O₁₂_PEDOT > tc@Mg₁₂O₁₂_PEDOT > tc@Ca₁₂O₁₂_PEDOT. The presence of t-index >0 indicated substantial hole and electron separation due to charge transfer. The investigation into hole and electron distribution exhibited a small Hole Distribution Index (HDI), signifying a narrow spatial extent of this charge separation. The order of spatial extent was found to be tc@Zn₁₂O₁₂_PEDOT > tc@Ca₁₂O₁₂_PEDOT > tc@Mg₁₂O₁₂_PEDOT. Similar conclusions can be drawn for the Electron Distribution Index (EDI). When comparing tc@Mg₁₂O₁₂_PEDOT with tc@Ca₁₂O₁₂_PEDOT, we observed a fascinating redshift in the first excited state (41.83 nm), second excited state (27.01 nm), and third excited state (7.59 nm).