Modification of porphyrin/dipyridine metal complexes on the surface of TiO 2 nanotubes with enhanced photocatalytic acti
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ARTICLE Modification of porphyrin/dipyridine metal complexes on the surface of TiO2 nanotubes with enhanced photocatalytic activity for photoreduction of CO2 into methanol Yiming Song School of Chemical Engineering, Northwest University, Xi’an, Shaanxi 710069, China
Jun Li Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, College of Chemistry & Materials Science, Northwest University, Xi’an, Shaanxi 710069, China
Chen Wanga) School of Chemical Engineering, Northwest University, Xi’an, Shaanxi 710069, China (Received 15 June 2018; accepted 26 July 2018)
Three photosensitizers containing zinc(II) porphyrin, ruthenium(II) dipyridine, and their combined porphyrin–polypyridyl metal complexes were used to modify TiO2 nanotubes that were obtained through the hydrothermal method to get inorganic–organic nanocomposite photocatalysts. The photosensitizer with distinctive structure can expand the photoresponse range of TiO2 toward the range of visible light, and the complexes with large conjugated p-electron systems are beneficial for improving the separation of photoelectrons from vacancies, effectively extending the life of excited electrons and thus enhancing the photocatalytic efficiency, thus establishing a favorable foundation for an efficient photocatalysis reaction. The photocatalytic reduction of CO2 aqueous solution into methanol was used to evaluate the photocatalytic effect of sensitized samples. All the photosensitized catalysts exhibited superior selectivity in liquid products during this process and methanol was the only liquid product in the system. The ZnPyP–RuBiPy sensitized TiO2 nanotubes showed the best photocatalytic effect. A possible mechanism for the photoreduction was also proposed in this paper.
I. INTRODUCTION
Along with the development of global economy, the CO2 concentration has been increasing rapidly in the atmosphere. The environmental hazards caused by CO2 have urged people to eliminate carbon footprint in some effective ways.1–4 How to convert CO2 into organic fuel has become the focus of many researchers.5–8 In 1979, Inoue et al. first used a series of semiconductors as photocatalysts to reduce CO2 to organic compounds such as methanol, methane, formaldehyde, etc.9 It is significant that solar energy was used as the energy source and semiconductor materials acted as the photocatalysts in the photoreduction process. It is worth noting that solar energy is a renewable and clean energy, which can regulate the global energy structure. TiO2 as an n-type semiconductor has attracted much attention due to its nontoxic nature and cheap prices. The large specific surface area and the superior photocatalytic activity of TiO2 have made it extremely useful and have been used in various fields such as photocatalysis, a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2018.294 J. Mater. Res., 2018
photovoltaic cells, environmental protection, selfpurification building materials, paints, and so forth.10,11 Therefore, photoca
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