Title : Mechanistic insights into charge carrier dynamics in TiO₂-SWCNT nanocomposites for enhanced photocatalysis
Abstract:
The development of high-performance photocatalysts requires a detailed mechanistic understanding of photoinduced charge carriers that extend beyond conventional metrics. In this context, mixed-phase TiO2 (anatase + rutile) and its composites with single-walled carbon nanotubes (SWCNT) are investigated as a model system to understand the photo-physical processes governing charge generation, separation, and recombination.
Photoluminescence (PL) and photoluminescence excitation (PLE) studies under successive light irradiation are utilized to elucidate the quenching behaviour of spectra attributed to a dead-layer model driven by surface-adsorbed oxygen species. A synergistic dual role for TiO2 polymorphs has been identified: rutile supports electron–hole generation due to its strong light absorption, while anatase is responsible for a long-lived charge carriers via defect-related states. Additionally, a striking contrast in behaviour was observed when PLE analysis is conducted for the pristine anatase and pristine rutile samples following irradiation. The increase in the PLE band intensity for rutile was attributed to the downward barrier of a space-charge separation region because of hydroxyl group’s aggregation. Conversely, the decline in the PLE band intensity within anatase structure was attributed to the accumulation of superoxide species leading in an upward depletion region.
The incorporation of SWNT in the TiO2 (anatase + rutile) matrix has not a passive role but acts as electron acceptor centre that promotes electron delocalization and enhances charge separation efficiency. In this context, detailed spectroscopic insights given by Raman and FTIR are essential to confirm the formation of TiO2-SWCNT interfacial coupling that governs the space-charge separation region.
The present study establishes a mechanistic framework in which the generation of charge (governed by rutile), the stabilization of charge (established by anatase), and the extraction of charge (facilitated by SWNTs) operate simultaneously, providing a robust strategy for engineering next generation photocatalysts. Furthermore, these findings demonstrate that subtle photo-physical processes such as band bending and defect states are of critical importance to photocatalytic performance. Consequently, their in-depth understanding is imperative for the rational design of advanced photocatalytic systems.
