Cooperative self-construction and enhanced optical absorption of nanoplates-assembled hierarchical Bi2WO6 flowers

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Abstract

Bi2WO6 hierarchical multilayered flower-like assemblies are fabricated on a large scale by a simple hydrothermal method in the presence of polymeric poly(sodium 4-styrenesulfonate). Such 3D Bi2WO6 assemblies are constructed from orderly arranged 2D layers, which are further composed of a large number of interconnected nanoplates with a mean side length of ca. 50 nm. The bimodal mesopores associated with such hierarchical assembly exhibit peak mesopore size of ca. 4 nm for the voids within a layer, and peak mesopore size of ca. 40 nm corresponding to the interspaces between stacked layers, respectively. The formation process is discussed on the basis of the results of time-dependent experiments, which support a novel ‘coupled cooperative assembly and localized ripening’ formation mechanism. More interestingly, we have noticed that the collective effect related to such hierarchical assembly induces a significantly enhanced optical absorbance in the UV–visible region. This work may shed some light on the design of complex architectures and exploitation of their potential applications.

Graphical abstract

Bi2WO6 hierarchical multilayered flower-like assemblies are fabricated on a large scale by a simple hydrothermal method in the presence of polymeric poly(sodium 4-styrenesulfonate).

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Introduction

A variety of biological minerals with fascinating shapes and microstructures was created in nature. Such natural materials are usually composed of only ordinary composition but exhibit fascinating properties due to their unique structure [1]. With expectation of achieving novel or enhanced properties, great efforts have been focused on the controlled synthesis of inorganic or inorganic/organic hybrid materials with specific shape or highly ordered construction [2], [3], [4]. Especially, the hierarchical assembly of 1D or 2D nanoscale building blocks into 3D arrayed superstructures or complex architectures attracts intensive attention, which would offer opportunities to explore their novel collective optical, magnetic, and electronic properties [5], [6].

Bi2WO6 is one promising visible-light responsive photocatalyst [7], [8], [9], [10], [11], [12]. The morphology and texture microstructures are usually important factors in modifying the photophysical and photocatalytic properties. Many preparative routes (such as solid-state, hydrothermal, sonochemical, etc.) and preparative conditions have been studied for the synthesis of Bi2WO6 with tunable morphology, such as nanoparticles, nanoplates, etc. [9], [10], [11]. In particular, hierarchical microspheres have been synthesized with or without polymer [13], [14], [15], [16]. However, their formation mechanism is quite divergent.

Herein, we show that novel Bi2WO6 hierarchical multilayered flower-like assemblies can be easily fabricated by a hydrothermal process in the presence of poly(sodium4-styrenesulfonate), and a novel ‘coupled cooperative assembly and localized ripening’ formation mechanism is proposed. In addition, a significant enhancement of the optical absorbance in the UV–visible region associated with such hierarchical assembly has been observed, which may provide another new approach for increasing their photoactivity.

Section snippets

Synthesis

All chemicals are of analytical grade, and used as received without further purification. Ordered assemblies of Bi2WO6 nanoplates were prepared by a simple polymer-mediated hydrothermal process. In a typical synthesis, 0.002 mol Bi(NO3)3·5H2O and 0.001 mol Na2WO4 were added into 80 mL 1 g/L aqueous solution of poly(sodium4-styrenesulfonate) (PSS) (Aldrich, Mw ca. 1 000 000) under vigorous stirring. After stirring for another 15 min, the slurry solution was transferred into a 100 mL autoclave with a

Hierarchical assemblies of Bi2WO6 nanoplates

Fig. 1 shows XRD patterns of as-prepared products obtained with and without PSS. The results demonstrate that well-crystallized Bi2WO6 crystals can be easily prepared whether the organic additive is added or not. All the diffraction peaks can be readily indexed as a pure orthorhombic structure with cell parameters a=5.46 Å, b=5.44 Å and c=16.44 Å, which is in good agreement with the literature values (JCPDS No. 73-1126) [11], [13]. The presence of polymer in the synthetic system slightly inhibit

Conclusions

Bi2WO6 hierarchical multilayered flower-like assemblies, constructed from primary nanoplates, are fabricated on a large scale by a simple polymeric PSS-mediated hydrothermal method. Such Bi2WO6 flowers exhibit bimodal mesopores due to hierarchical assembly. The peak mesopore size for the voids within a layer is ca. 4 nm, while the peak mesopore size corresponding to the interspaces between stacked layers is ca. 40 nm. The formation mechanism is proposed as ‘coupled cooperative assembly and

Acknowledgments

This work was partially supported by the National Natural Science Foundation of China (20473059, 50625208 and 20773097). This work was also financially supported by the Key Research Project of Chinese Ministry of Education (No. 106114) and National Basic Research Program of China (2007CB613302).

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