Characterization and photoactivity of coupled ZnO–ZnWO4 catalysts prepared by a sol–gel method

Abstract

a b s t r a c tZnO-ZnWO 4 nanocomposites were synthesized by a novel sol-gel method and characterized through X-ray diffraction, BET specific surface area analysis, UV-Vis diffuse reflectance spectroscopy, scanning electron microscopy and transmission electron microscopy. The photocatalytic activity of the samples was evaluated using the degradation of 4-nitrophenol under UV light as probe reaction. The ZnO/ZnWO 4 molar ratio was varied in order to study its influence on the photoefficiency of the mixed samples. The ZnO-ZnWO 4 nanocomposites showed higher photoactivity than ZnO and ZnWO 4 . The high efficiency of the mixed samples was explained by the coupling and the intimate contact of two different semiconductors having suitable energy levels of their conduction and valence bands that allow an improved charge separation of the photogenerated electron-hole pairs.

Eu2+ and Eu3+ Doubly Doped ZnWO4 Nanoplates with Superior Photocatalytic Performance for Dye Degradation

“…When compared with the Er 3+ doped ZnWO 4 single crystals [4], our ZnWO 4 nanoplates are nanomaterials with large specific surface area. When compared with ZnWO 4 nanoparticles and nanorods synthesized via the sol-gel, sonochemical, and hydrothermal methods [3,11,15,21,22], our Eu-doped ZnWO 4 nanoplates are unique in their highly exposed facets. As documented in the literature, the exposed crystal facets directly determine their physicochemical properties [31,32,33,34].…”

“…Among these applications, the photocatalytic properties of ZnWO 4 nanostructures have been intensively investigated in order to solve one of the most serious environmental problems in our modern society via semiconductor-based photocatalytic degradation of organic contaminants in water under sunlight [6,7,8,9,10,11]. Up to date, a diverse range of strategies has been developed to enhance the photocatalytic activity of ZnWO 4 nanostructures, which can be classified into three categories: (i) synthesis of ZnWO 4 nanorods and nanosheets with large specific surface area [19]; (ii) coupling ZnWO 4 with other semiconductors and metals such as In 2 S 3 [20], Ag [21], ZnO [22], and Cu 2 O [23]; and (iii) defect engineering ZnWO 4 via doping with non-metal ions (B, C, N, F) [24,25,26], transition metal ions (Sn 2+ , Cr 3+ , Mn 2+ , Cu 2+ ) [27,28], and lanthanide ions (Dy 3+ , Er 3+ ) [29,30]. Interestingly, the defect engineering is found to be able to significantly enhance the photocatalytic performances of ZnWO 4 nanostructures.…”

Photocatalytic Semiconductors

“…The high efficiency of the mixed samples was likely due to an improved charge separation as consequence of the relative values of their conduction and valence bands, as shown in Fig. 2.9 (Hamrouni et al 2014). The coupling of graphene with BiFeO 3 also displays photocatalytic enhanced properties under visible-light illumination.…”

Strong Photo-Oxidative Capability of ZnWO4 Nanoplates with Highly Exposed {0 1 1} Facets

“…Zinc tungstate (ZnWO 4 ) is known for its use as an efficient scintillator [1], phosphor [2], photocatalyst [3], and photoelectrocatalyst [4,5]. In order to solve the serious environmental problem of organic contaminants in waste water by harnessing the solar power of sunlight, a variety of ZnWO 4 nanostructures were intensively investigated as photocatalysts [6][7][8][9][10][11][12]. With the aim of significantly improving the photocatalytic activity of ZnWO 4 photocatalysts, previous research activities can be divided into three classes: (i) morphology engineering by varying the morphology of ZnWO 4 from nanoparticles [3,7,11], to nanorods [3,6,10,12,13], nanowires [9], and nanosheets [14]; (ii) defect engineering by doping ZnWO 4 with non-metal ions (i.e., B, C, N, F [15][16][17]), transition metal ions (i.e., Sn 2+ , Cr 3+ , Mn 2+ , Cu 2+ , Bi 3+ , Dy 3+ [18][19][20]); and (iii) coupling ZnWO 4 with other semiconductors (i.e., In 2 S 3 [21], ZnO [7], Cu 2 O [22]) or metals (Ag) [6].…”