(668a) Balancing Charge Carrier Kinetics and Photo-Absorption Capacity through Strain Engineering to Maximize Photocatalysis Under Visible-Light.

Addition of noble metal halides certainly transform TiO₂ into a visible-light photocatalyst, but whether this transformation is due to a reduction in it's bandgap or a synergy of enhanced photoelectrical properties of TiO₂ and noble metal halides, is a subject of debate. Furthermore, the optimized loading of noble metal halides at which best photocatalytic activity occurs has neither been correlated with a single material property in the literature consistently nor linked to the photogenerated charge carrier dynamics. In this study, we investigate the change in intrinsic lattice strain of TiO₂ by loading different concentrations of AgBr; a popular photoactive plasmonic semiconductor which narrows the bandgap of TiO₂ and makes the resulting nanocomposite, a visible-light active photocatalyst. XRD analysis revealed that beyond a maximum strain developed at an optimum AgBr loading level of 25wt.%, the grain boundary interface of TiO₂ and AgBr nanoislands could no longer withstand the increased strain in their Ti—Ti, and Ti—O bonds. A chain of thermodynamically governed crystalline phase transformation then begins within TiO₂ which creates defect states in the band tails of anatase TiO₂ thus lowering it's bandgap. Faster dye degradation kinetics corroborate the hypothesis that catalyst possessing maximum lattice strain show superior photocatalytic properties. Photoelectrochemical studies was used to quantify the rate of charge transfer (k_ct) and rate of recombination (k_r) of photogenerated electrons and holes. These studies revealed that high lattice strain reduced the recombination of charge carriers by trapping e^- within the transient interband tails of TiO_2. At AgBr concentrations higher than 25wt.%, the k_ct was increased due to plasmonic resonance but ultimately k_r overtook the net charge carrier flux decreasing the photocatalytic efficiency of TiO₂. This work establishes the role of lattice strain in constructing high-performance plasmonic photocatalysts suitable for visible light application by balancing their optical and electrical properties.