Greatly enhanced photocatalytic activity and mechanism of H 3 PW 12 O 40 /polymethylmethacrylate/polycaprolactam sandwic
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Ce Liu College of Chemical Engineering, North China University of Science and Technology, Tangshan 063009, China
Libao An College of Mechanical Engineering, North China University of Science and Technology, Tangshan 063009, China
Yuqing Li, Weiwei Zhang, Lu Liu, and Zhiming Zhangb) College of Material Science and Engineering, Hebei Provincial Key Laboratory of Inorganic Nonmetallic Materials, North China University of Science and Technology, Tangshan 063009, China (Received 29 May 2016; accepted 8 August 2016)
H3PW12O40/polymethylmethacrylate (PMMA)/polycaprolactam (PA6) nanofibrous membrane with a sandwich structure was prepared by electrospinning. Characterization with Fourier transformation infrared spectroscopy (FT-IR), energy-dispersive x-ray spectroscopy (EDX), and x-ray photoelectron spectroscopy (XPS) indicated that H3PW12O40 has been successfully loaded into the upper and bottom layers of the sandwich membrane and its Keggin structure was not destroyed. The photocatalytic efficiency of the sandwich membranes were much higher ($87.2%) than that of H3PW12O40 only (15.6%) and H3PW12O40/PMMA composite nanofibrous membrane (11.6%) in the degradation of methyl orange (MO) under ultraviolet irradiation. It may be caused by two factors: one was the photoreduction mechanism induced by the electron donating from PA6 to H3PW12O40, the other was the double contact area between H3PW12O40 and MO due to the sandwich structure of the laminated membrane. What is noteworthy is that the sandwich membranes were stable in water, so that they could be easily separated from the aqueous MO solution and reused without appreciable losses in photocatalytic activity after three photocatalytic cycles. In view of this, H3PW12O40/PMMA/PA6 sandwich nanofibrous membrane is promising as a photocatalyst to remove organic pollutants from practical wastewater.
I. INTRODUCTION
Contamination of water by organic dyes has become an increasing concern to the environment.1 Many methods have been used to solve this problem, including physical absorption, oxidation–reduction reaction in chemistry, biological process, and so on. In recent times, the application of heterogeneous solid acid catalysts have attracted extensive interest owing to their easy separation, excellent reusability, environmental benignity, and operational simplicity.2 Compared with transition metal building blocks, polyoxometalates (POMs) took on much superiority for their characteristics of oxygen rich surface, high charge density, and controllable size.3 POMs can function as photocatalysts through the photoexcitation of the Contributing Editor: Akira Nakajima Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2016.313
oxygen-to-metal charge transfer bands to separate the electron–hole pair used for reductive and oxidative reactions with surrounding molecules.4 Due to a number of featured advantages, POMs attracted considerable attentions as photocatalysts for degrading organic dyes.5 The photooxidat
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