Three-dimensionally ordered macroporous WO3 supported Ag3PO4 with enhanced photocatalytic activity and durability
Graphical abstract
Introduction
The visible light photocatalysis is considered as the most promising technology to solve the environmental pollution and energy shortage, which could completely decompose environmental pollutions and split water to yield hydrogen fuel by utilizing solar energy. Many attempts have been made to design and fabricate advanced visible light photocatalysts, such as energy band engineering, morphology control, nano-assembly and theoretical studies [1], [2].
In the last decade, the three-dimensionally ordered macroporous (3DOM) materials, also named as inverse opals, have received much attention due to their special periodic structure coming from the template of cubic-close-packed array of colloidal spheres [3], [4], [5], [6], [7], [8]. These 3DOM materials have an open, inter-connected macropore structure and nanosized wall components, which could facilitate the mass transfer. Moreover, the periodic structure of 3DOM materials exhibited significant slow photon effect [9], [10], which could forbid the propagation of light with certain wavelengths through the material and resulted in a stop-band reflection. The slow photon effect could increase the photon-matter interaction length and enhance the light energy conversion efficiency.
The enhancement of light harvesting efficiency by inverse opals was demonstrated by Mallouk and co-workers [11], [12] in a dye-sensitized solar cell through coupling a TiO2 photonic crystal layer to a conventional TiO2 film. After that, a series of 3DOM semiconductor materials were prepared and used as photocatalysts, including TiO2 [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], Bi2WO6 [25], InVO4 [26], [27], [28], WO3 [29], [30], BiVO4 [31], [32] and SnO2 [33], [34]. Su and co-workers [13], [14], [15] prepared 3DOM TiO2 with different pore diameters and studied the influence of the photonic structure on the activity of TiO2 for the photodegradation of Rhodamine B (RhB). Qi et al. [16] reported Ti3+ doped TiO2 inverse opals and these photocatalysts showed notably enhanced visible light harvesting ability. Dai and co-workers [26], [27], [28] reported 3DOM InVO4 and noble metal loaded 3DOM InVO4–BiVO4 catalysts, which performed excellently for MB and RhB degradation under visible light irradiation. These reported 3DOM semiconductor materials show an attractive prospect in the photocatalysis field, however, the related studies are still extremely lack. Particularly, the composite photocatalysts based on 3DOM materials were seldom reported till now [28], [32], [33], [34].
Silver orthophosphate (Ag3PO4), as a very efficient visible-light-driven catalyst [35], [36], [37], [38], [39], [40], [41], can oxidize water to release oxygen as well as degrade organic contaminants under visible light irradiation, however, it always suffered from stability issue [42], [43], [44], [45]. In this work, a series of 3DOM-WO3 materials with different pore sizes were synthesized through a PMMA colloidal crystal template method, and the Ag3PO4 nanoparticles were firstly deposited in the macropores of 3DOM-WO3. These novel Ag3PO4/3DOM-WO3 composites were evaluated in the visible light degradation of organic contaminants and water oxidation. An amazing increase in photocatalytic efficiency was expected over these Ag3PO4/3DOM-WO3 composites due to the effective separation of electron–hole pairs, facile mass transfer and slow photon effect derived from inverse opals. Moreover, the advantages of these photocatalysts were also reflected in the notably enhanced stability attributed to the effective transfer of electrons and holes.
Section snippets
Materials
Methyl methacrylate (MMA) stabilized with 30 ppm MEHQ, silver nitrate (AgNO3) and quartz sand were purchased from Aladdin. Potassium persulfate (K2S2O8), cetyltrimethylammonium bromide (CTAB), methanol and disodium hydrogen phosphate (Na2HPO4) were obtained from Sinopharm Chemical Reagent Co., Ltd. 2,2-Azobis(2-methylpropionamidine) dihydrochloride (AIBA) and ammonium metatungstate hydrate ((NH4)6H2W12O40·xH2O) were purchased from Energy Chemical and Beijing HWRK Chem Co., Ltd., respectively.
Characterization of the 3DOM-WO3 materials
The as-synthesized 3DOM-WO3, rodlike WO3 and platelike WO3 were characterized by XRD and SEM. As shown in Fig. 1, the characteristic diffraction peaks of (0 0 1), (0 2 0), (2 0 0), (1 2 0), (1 1 1), (2 0 1), (2 2 0), (1 2 1), (2 2 1), (0 0 2), (0 4 0), (1 4 0) and (4 2 0) can be perfectly indexed as the orthorhombic phase WO3 (JCPDS no. 20-1324). The SEM images of 3DOM-WO3, rodlike WO3 and platelike WO3 are shown in Fig. 2. It could be seen from Fig. 2(a–c) that a well-ordered inverse opal structure was appeared in
Conclusions
In this work, novel Ag3PO4/3DOM-WO3 photocatalysts were synthesized and employed in the visible light degradation of organic contaminants (including phenol, BPA, RhB, MB and MG) and water splitting for oxygen evolution. Compared with Ag3PO4, 3DOM-WO3, Ag3PO4/Rod-WO3 and Ag3PO4/Plate-WO3, Ag3PO4/3DOM-WO3 exhibited notably enhanced photocatalytic efficiency. This was mainly attributed to the synergic effect of Ag3PO4 and 3DOM-WO3 as well as the periodic macroporous structure of 3DOM-WO3, which
Acknowledgements
This work was supported by the National High Technology Research and Development Program of China(Grant no. 2012AA063008), the National Natural Science Foundation of China (Grant no. 21203102), the Tianjin Municipal Natural Science Foundation (Grant nos. 14JCQNJC06000 and 14JCZDJC32000) and MOE (IRT13R30).
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