Vapor Phase Infiltration of Titanium Oxide into P3HT to Create Organic-Inorganic Hybrid Photocatalysts

Herein, we report for the first time the use of vapor phase infiltration (VPI) to infuse conducting polymers with inorganic metal oxide clusters that together form a photocatalytic material. While vapor infiltration has previously been used to electrically dope conjugated polymers, this is the first time, to our knowledge, that the resultant hybrid material has been demonstrated to have photocatalytic properties. The system studied is poly(3-hexylthiophene-2,5-diyl) (P3HT) vapor infiltrated with TiCl₄ and H₂O to create P3HT-TiO_x organic-inorganic hybrid photocatalytic materials. X-ray photoelectron spectroscopy analysis shows that P3HT-TiO_x VPI films consist of a partially oxidized P3HT matrix, and the infiltrated titanium inorganic is in a 4+ oxidation state with mostly oxide coordination. Upon visible light illumination, these P3HT-TiO_x hybrids degrade methylene blue dye molecules. The P3HT-TiO_x hybrids are 4.6× more photocatalytically active than either the P3HT or TiO₂ individually or when sequentially deposited (e.g., P3HT on TiO₂). On a per surface area basis, these hybrid photocatalysts are comparable or better than other best in class polymer semiconductor photocatalysts. VPI of TiCl₄ + H₂O into P3HT makes a unique hybrid structure and idealized photocatalyst architecture by creating nanoscale TiO_x clusters concentrated toward the surface achieving extremely high catalytic rates. The mechanism for this enhanced photocatalytic rate is understood using photoluminescence spectroscopy, which shows significant quenching of excitons in P3HT-TiO_x as compared to neat P3HT, indicating that P3HT acts as a photosensitizer for the TiO_x catalyst sites in the hybrid material. This work introduces a new approach to designing and synthesizing organic-inorganic hybrid photocatalytic materials, with expansive opportunities for further exploration and optimization.