Enhanced photocatalytic activity in porphyrin-sensitized TiO 2 nanorods
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Chen Wangb) School of Chemical Engineering, Northwest University, Xi’an, Shaanxi 710069, People’s Republic of China
Xiao Liu and Jun Lia) Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of Education, School of Chemistry & Materials Science, Northwest University, Xi’an, Shaanxi 710069, China (Received 3 April 2017; accepted 23 May 2017)
Two novel porphyrins (5,10,15,20-tetra(3-(carboethoxymethyleneoxy)phenyl)porphyrin, H2TEPp and 5,10,15,20-tetra(3-(carboxymethyleneoxy)phenyl)porphyrin, H2TCPp) and their copper(II) porphyrins (CuTEPp, CuTCPp) were synthesized. With these porphyrins, four new porphyrinsensitized TiO2 nanorod composites (H2TEPp/TiO2, H2TCPp/TiO2, CuTEPp/TiO2, and CuTCPp/ TiO2) were prepared and characterized by methods of XRD, SEM, TEM, FT-IR, UV-vis DRS, nitrogen adsorption–desorption and fluorescence spectra. Besides, the photocatalytic activity and stability of the composites were assessed in the degradation of 4-nitrophenol (4-NP). The results indicate that the morphologies and structures of these composites are less influenced by the loaded porphyrins or copper porphyrins compared with the nanorods TiO2 (anatase). The porphyrin or copper porphyrin molecules are confirmed to bond on the surface of TiO2 through carboxyl group, which is beneficial to the electron transfer between porphyrin and TiO2. All composites exhibit enhanced photoactivities compared with the bare TiO2 nanorods. The possible reason is that the recombination of photoproduced electron–hole has been controlled effectively in these composites, which can be seen from their decreased fluorescence emission. The stability results of composites show that they still hold considerable photocatalytic activities after six cycling experiments.
I. INTRODUCTION
The photocatalysis based on semiconductor materials have aroused extensive concern on account that they can utilize the solar energy directly.1–4 Among various photocatalysts, titanium dioxide (TiO2) is considered as the most promising material in fields of photocatalytic water purification, photocatalytic water splitting into H2, CO2 photoreduction and so on due to its low-cost, chemical stability, and nontoxicity.5–7 However, practical applications of TiO2 are severely hampered by its large band gap (3.2 eV of anatase), which can only be activated under UV irradiation. Meanwhile, TiO2 semiconductor also suffers from an easy electron–hole recombination.8 In the past decades, much effort has been devoted to improving visible light absorption and decreasing the recombination of photogenerated electron–hole of TiO2 by diversified strategies, such as doping,9,10 exposure of reactive facets Contributing Editor: Xiaobo Chen Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2017.230
of TiO211,12 and dye sensitization.13,14 Anatase-type TiO2 has been investigated intensively for photocatalytic applications owing to its high photoreactivity. Recently, it has been found that low-dimensional TiO2
