Kinetics and mechanism for transparent polyethylene-TiO2 films mediated self-cleaning leading to MB dye discoloration under sunlight irradiation

• Methylene blue (MB) undergoes discoloration on innovative. TiO2-PE films.
• MB discoloration is induced by solar simulated light on TiO2-PE thin film.
• The mechanism, energetics and de-excitation of MB* are reported.
• MB discolors with a concomitant increase in the MB fluidity followed by ATR-IR spectroscopy.

Polyethylene-TiO2 (from now on PE-TiO2) transparent, non-scattering sputtered films have been found effective in the discoloration of methylene blue (MB) under low intensity solar simulated light. By Fourier transform attenuated infrared spectroscopy (ATR-FTIR), the systematic shift and decrease in the νs(CH2) and νs(CC) vibration-rotational bands was observed preceding MB discoloration. RF-pretreatment allowed a significant increase in the TiO2 loading on PE compared to non-pretreated PE as shown by X-ray fluorescence (XRF). The PE-TiO2 photo-switching from a hydrophobic to a hydrophilic surface was observed within 60 min under light while the reverse process was complete within 24 h in the dark. The position of the MB* and MB*/MB+ levels allowing electron injecting into the TiO2cb is discussed. The probability for the MBT deactivation and of MB* reacting with O2 leading to the short lived MB+ cation is estimated. A mechanism for MB discoloration on PE-TiO2 is suggested.

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