دانلود رایگان مقاله لاتین فتوکاتالیست کامپوزیت از سایت الزویر
عنوان فارسی مقاله:
ساخت عمودی طرح-Z نوع WO3 فتوکاتالیست کامپوزیت Ag3PO4 با اجرای فوتوکاتالیستی نور مرئی افزایش یافته
عنوان انگلیسی مقاله:
Fabrication of a direct Z-scheme type WO3/Ag3PO4 composite photocatalyst with enhanced visible-light photocatalytic performances
سال انتشار : 2017
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مقدمه انگلیسی مقاله:
1. Introduction
As a promising technology, photocatalysis has been widely studied in various fields such as environmental purification, solar energy conversion, and water splitting, etc [1–3]. However, there are still several problems in photocatalysis, such as poor utilization of solar light, low photo-to-current efficiency, and weak stability [4,5]. To utilize sunlight efficiently, a great deal of visible light responsive photocatalysts were developed over the past decades, including binary semiconductors WO3, CdS, MoS2, g-C3N4, ternary compounds CuFe2O4, ZnIn2S4, BiOX(X = Cl, Br, I), etc [6–13]. In recent, as a new-type photocatalyst, Ag-based photocatalysts have attracted considerable attention for organic pollutants removal. Particularly, Ag3PO4 is considered as a promising visible light responsive photocatalyst due to its narrow indirect and direct band gap of 2.36 eV and 2.43 eV, respectively [14–17]. Yi et al. reportedthat Ag3PO4 exhibits extremely high capability in the O2 evolution from photooxidation of water and decomposition of organic dye under visible light, and the quantum efficiencies achieved up to 90% at wavelengths greater than 420 nm, which prominent photocatalytic performancesmay be ascribed to the inductive effect of PO4 3− and the dispersive conduction band [18]. Zhu et al. revealed that the relatively low valence band level is favorable of its oxidizing ability, meanwhile, the * orbit in the conduction band improves the electrons migration rate and separation efficiency of photo-generated charge carriers [19]. To further improving Ag3PO4 photoelectric and photocatalytic activity, some efforts have been devoted to modulate its shape, morphology, and crystal facet[20–23], and others are interested in developing novel Ag3PO4-based bi/multi- component photocatalysts [16,24,25]. In recent years, Z-scheme photocatalysis process inspired by natural photosynthesis in green plants is considered as an efficient system for water splitting, in which two different photocatalysts with proper band energies are combined via a suitable shuttle redox mediator [26–28]. Comparing with conventional single component water splitting systems, each photocatalyst in the Z-schemesystem is only responsible for one half-reaction (H2 evolution reaction or O2 evolution reaction), and visible light could be utilized more efficiently in Z-scheme system because the energy required to drive each photocatalyst is reduced. Similar to the heterojunction-type photocatalyst composites, the Z-scheme system also features the spatial isolation of photogenerated carriers, which reduces the probability of bulk electron-hole recombination. Moreover, the shuttle redox mediator participates and optimizes the process of electron transfer in the complex redox reactions. Generally, some soluble redox ion pairs, including Fe3+/Fe2+, IO3 −/I−,[Co(bpy)3]3+/2+/[Co(phen)3] 3+/2+ etc. were selected as suitable redox mediators and greatly enhance the activity for overall water splitting in the liquid-state Z-scheme systems [29–31]. In 2006, Tada et al. firstly prepared all-solid-state Z-scheme photocatalyst of CdS/Au/TiO2, where anchored solid Au nanoparticles between CdS and TiO2 acted as electron transfer mediator [32]. This three-component system exhibits excellent activity, far exceeding those ofthe single/two component systems, because the photogenerated electrons in the conduction band of TiO2 could be transferred through the Au medium and recombine with the photogenerated holes left in valance band of CdS. Thus, the photogenerated electrons and holes are accumulated in the conduction band of CdS and the valance band of TiO2, respectively. Besides the noble metals, some nonmetals also were used for transferring Z-scheme electron. Amal et al. found that the reduced graphene oxide could serve as electron transfer when it was embedded between BiVO4 and Ru/SrTiO3:Rh [33]. It is clear that either liquid-state or solid-state redox mediators play important roles in shuttling the photogenerated carriers in Z-scheme systems [34–36]. However, the presence of a shuttle redox mediator would also cause some drawbacks, such as light-shielding effect, competitive oxidation of redox couples, and high cost of noble metal etc. So it is an advisable choice to construct mediator-free direct Z-scheme systems only consisting of two components, which would drew more and more attention. More recently, it was demonstrated that many Ag3PO4 based photocatalytic systems, such as g-C3N4-Ag3PO4, grapheneAg3PO4 hybrid photocatalysts show a direct Z-scheme mechanism without an electron mediator [37,38]. These composite can not only effectively avoid the Ag3PO4 dissolution, but also improve their photocatalytic activity due to the quick separation of photogenerated charge carriers. Thus, it is a promising alternative to fabricate a novel direct Z-scheme Ag3PO4 based photocatalyst for promoting its overall catalytic performance. In this work, tungsten oxide (WO3), an environment-friendly semiconductor material with narrow band gap (2.4–2.8 eV) and good stability in aqueous media was employed to combine with the Ag3PO4 to obtain WO3/Ag3PO4 hybrid photocatalyst [39,40]. Firstly, a facile double-step hydrothermal method was applied to prepare WO3/Ag3PO4, following by SEM, XRD, UV–vis DRS, IR, PL, andXPS characterizations. Secondly,the photocatalytic activities of the WO3/Ag3PO4 composite were evaluated by the degradation of methylene blue (MB) and methyl orange (MO) under visible light. Finally, the relevant photocatalytic mechanism was investigated and the stability of the WO3/Ag3PO4 composite was also examined.
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کلمات کلیدی:
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