Robust sensitizer-assisted platinized titanium dioxide in photocatalytic removal of 4-chlorophenol in water: Light tunable sensitizer

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Vol. 358; pp. 100 - 110
• Main Authors: Wang, Kuo-Ting, Lu, Norman, Chu, Chun-Wei, Feng, Tsung-Yao, Kung, Chih-Chieh, Tu, Wen-Han, Yeh, Yun-Peng, Francisco, Joseph S.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01.05.2018; Elsevier BV
• Subjects: 4-Chlorophenol; Absorption spectra; Bubbling; Charge transfer; Chlorophenol; Dyes; Efficiency; Fluorescence; Irradiation; Ligands; Light irradiation; Open circuit voltage; Phenols; Photocatalysis; Photocatalytic; Photodegradation; Platinized TiO2; Pollutants; Robustness; Sensitized; Titanium; Titanium dioxide; Tunable; Visible light irradiation; Water treatment; Wavelength; 44Pt(bdt); Photocatalytic; Visible light irradiation; 33PtCl2; 44PtCl2; 4-Chlorophenol; Tunable; Sensitized; Platinized TiO2; 33Pt(bdt)
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2018.02.031

[Note: (dye drawing) O: red; N: blue; S; golden color; Pt: dark grey; C: grey.] [Display omitted] •By using blue or yellow light instead of UV, one can eliminate the production of ozone during the irradiation process.•33Pt(bdt) dye on 1 wt.% Pt coated TiO2 under 420 nm visible light speeds up the degradation efficiency.•Oxidized 33PtCl2 could also be reduced to its original form by the sacrificial donor, 4-CP.•Using yellow light, OH radicals can be slowly generated so that both dyes are not heavily attacked by radicals.•TEM studies and fluorescence quenching experiments help to unravel morphology and charge separation process of dye systems. The photodegradation of 4-chlorophenol (4-CP) by using 3,3′-Pt(dcbpy)(bdt), 33Pt(bdt), sensitized platinized titanium dioxide, Pt-TiO2, under 420 nm light irradiation while bubbling O2 has been studied in this research. The 84% degradation efficiency was reached in 3 h, and this efficiency was much better than that assisted by 4,4′-Pt(dcbpy)(bdt), 44Pt(bdt), under the same conditions using 420 nm light. The possible reason is due to the difference in UV–vis absorption spectra of these two dyes around 420 nm. The 33Pt(bdt) dye which has been first synthesized in this study and has the twisted geometry shows larger open circuit voltage, higher molar extinction coefficient of π–π* transition around 420 nm and much better in 4-CP photodegradation than its 4,4′-analogue under blue light. Under 580 nm light irradiation for 6 h, both 33Pt(bdt) and 44Pt(bdt) sensitized Pt-TiO2-catalyzed 4-CP degradation with O2 bubbling could reach 94% photodegradation efficiency based on metal ligand charge transfer, MLCT, mechanism. Fluorescence quenching experiments have been carried out to affirm the enhanced photo-induced charge separation and transmission during 33Pt(bdt)-assisted reaction. To our knowledge, this is the first time to show that under blue or yellow light irradiation dye-sensitized Pt-TiO2-catalyzed 4-CP degradations have different mechanisms and are tunable by light wavelength. Dye 33Pt(bdt) is more robust and better sensitizer in 4-CP degradation than 44Pt(bdt) under blue light. Thus, by the careful selection of light wavelength and using the robust dye, one can tune the system to efficiently harvest specific visible light for the photodegradation of small organic pollutants.