Fabrication of Fe-POMs as Visible-light-active Heterogeneous Photocatalyst
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doi: 10.1007/s40242-020-0320-y
Article
Fabrication of Fe-POMs as Visible-light-active Heterogeneous Photocatalyst CEN Qing1, XIAO Wei1, LIU Yingqi1, WANG Qi1*, NAFADY Ayman3 and MA Shengqian2* 1. School of Environmental Science and Engineering, Zhejiang Gongshang University, Hangzhou 310018, P. R. China; 2. Department of Chemistry, University of North Texas, Denton, TX 76201, USA; 3. Department of Chemistry, College of Science, King Saud University, Riyadh 11451, Saudi Arabia Abstract Visible-light-active Fe-POMs was fabricated via precipitating Fe3+ with Keggin type polyoxometalates (H3PW12O40, H4SiW12O40 or H3PMo12O40) under solvothermal condition. The as-prepared Fe-POMs were denoted as FePW, FeSiW and FePMo, respectively. Among the three kinds of Fe-POMs, FePMo displayed the highest visible light absorption, the largest specific surface area, the most sensitive photocurrent response and the smallest charge transfer resistance, which were all beneficial for heterogeneous photocatalysis. The efficiency for Cr(VI) reduction was ca. 88% by FePMo after 50 min visible light irradiation. The estimated rate constant(0.042 min –1) was ca. 2.5 and 1.8 times that by FePW and FeSiW, respectively. FTIR spectra indicated that the Keggin structure of PMo 12O403– was maintained in FePMo. Mechanism study indicated that the photogenerated electrons in LUMO and the holes in HOMO were thermodynamically feasible for Cr(VI) reduction and H 2O oxidation, respectively. Using FePMo as an optimized photocatalyst, good stability was also observed after 5 cyclic runs in both photocatalytic performance and XRD structure. Keywords Cr(VI) reduction; Photocatalysis; Polyoxometalate; FePMo; Visible light
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Introduction
Heavy metal chromium is widely used as a raw material in tanning, electroplating, printing, dyeing and other industries[1,2], resulting in a large amount of chromium-containing wastewater. If it is discharged into environment without proper treatment, human beings will suffer from huge health risks. Since the main oxidation states of chromium are Cr(VI) and Cr(III), the vital step for chromium remediation is the reduction of carcinogenic Cr(VI) to Cr(III), which can be easily precipitated and removed under alkaline conditions[3]. Compared with traditional methods[4,5], photocatalysis was considered as a green and energy-saving way[6]. Using the star photocatalyst(TiO2) as an example, electron-hole pairs can be generated in the conduction band(CB) and valence band(VB) under UV light, respectively. Cr(VI) can be reduced to Cr(III) by capturing the photogenerated electrons in CB. However, due to the low proportion of ultraviolet light in solar radiation(FeSiW(8.0 m 2 /g)>FePW
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Fig.3
Comparison of BET surface areas of different Fe-POMs
(7.3 m2/g). Since FePMo displayed the highest SBET, it was selected as the optimized sample for following structural analysis. To further investigate the surface structure, the morphology of FePMo was investigated by SEM and the results are illustrated in Fig.4. It can be observed that t
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