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<p>This study investigates the concentration-dependent photokinetics of Rhodamine B (RhB) in the presence of Anatase TiO₂ under natural sunlight and 532&#xa0;nm laser irradiation (2.19 × 10³ and 2.07 × 10⁴ W·m⁻²). At 2.09 × 10⁻⁶ M, high-power laser irradiation yielded the highest apparent rate constant (k = 7.73 × 10⁻³ min⁻¹; t½ = 89.7&#xa0;min), whereas at 2.09 × 10⁻⁷ M, sunlight showed superior performance (k = 3.61 × 10⁻² min⁻¹; t½ = 19.2&#xa0;min), highlighting the role of photon flux and spectral distribution. Spectroscopic analyses (UV–Vis, PL, FTIR, DRS) support a dye-sensitized charge-transfer mechanism, where photoexcited RhB injects electrons into the TiO₂ conduction band. Kinetic modeling (PFO, PSO, Langmuir–Hinshelwood) reveals concentration-dependent apparent behavior, transitioning from surface-reaction-dominated to sensitization-driven pathways. In particular, the degradation rate on high-power laser irradiation (2.09 × 10⁻⁶ M) was almost 2 orders of magnitude greater than it was under low-power irradiation, emphasizing the importance of photon flux. These findings demonstrate that photocatalytic performance is governed by the combined effects of photon flux, spectral distribution, and dye concentration, providing a basis for designing tunable light-driven systems.</p>

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Concentration-dependent photokinetics of rhodamine B/TiO2 systems under sunlight and laser exposure : a route toward ultrafast optical response media

  • 期刊论文

  • 发表日期：

    2026年4月29日

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  • Sabreen J. Jassem,
  • Rawaa A. Faris,
  • Zainab F. Mahdi

摘要

This study investigates the concentration-dependent photokinetics of Rhodamine B (RhB) in the presence of Anatase TiO₂ under natural sunlight and 532 nm laser irradiation (2.19 × 10³ and 2.07 × 10⁴ W·m⁻²). At 2.09 × 10⁻⁶ M, high-power laser irradiation yielded the highest apparent rate constant (k = 7.73 × 10⁻³ min⁻¹; t½ = 89.7 min), whereas at 2.09 × 10⁻⁷ M, sunlight showed superior performance (k = 3.61 × 10⁻² min⁻¹; t½ = 19.2 min), highlighting the role of photon flux and spectral distribution. Spectroscopic analyses (UV–Vis, PL, FTIR, DRS) support a dye-sensitized charge-transfer mechanism, where photoexcited RhB injects electrons into the TiO₂ conduction band. Kinetic modeling (PFO, PSO, Langmuir–Hinshelwood) reveals concentration-dependent apparent behavior, transitioning from surface-reaction-dominated to sensitization-driven pathways. In particular, the degradation rate on high-power laser irradiation (2.09 × 10⁻⁶ M) was almost 2 orders of magnitude greater than it was under low-power irradiation, emphasizing the importance of photon flux. These findings demonstrate that photocatalytic performance is governed by the combined effects of photon flux, spectral distribution, and dye concentration, providing a basis for designing tunable light-driven systems.