Mo doping-enhanced dye absorption of Bi2Se3 nanoflowers
© Zhong et al.; licensee Springer. 2013
Received: 14 July 2013
Accepted: 10 September 2013
Published: 30 October 2013
A simple solvothermal approach is explored to prepare Bi2−xMo x Se3 nanostructures by employing N,N-dimethylformamide (DMF) as the solvent. Mo plays an important role in the assembly of the Bi2−xMo x Se3 nanostructures from nanoplates to nanoflowers. Structural and morphological studies indicate that the resulting products are large specific surface area single-crystalline Bi2−xMo x Se3 nanoflowers self-assembled from thin nanoplates during the reaction process. The absorption properties of the as-prepared samples are investigated with Rhodamine B (RhB) as dye, and it is found that the Bi1.85Mo0.15Se3 nanoflowers show an optimal adsorption capacity, implying that Mo doping not only changes the morphologies of the nanostructures but also enhances their absorption behaviors.
Water pollution has now become an urgent problem owing to the rapidly growing global industrial process [1, 2]. Public health and social economies are threatened by various organic dye pollutants from textile industries . A variety of methods have been introduced to remove dyes from wastewaters, such as membrane filtration , flotation [5, 6], solvent extraction , chemical oxidation [8, 9], adsorption [10, 11], and photocatalytic degradation [12, 13]. Among these methods, adsorption has been proved to be an effective way for wastewater treatment in terms of simplicity of design, user-friendly control, and insensitivity to toxic substances. Dye removal from industrial wastewaters by adsorption techniques has been widely concerned and researched in recent years [10–15]. Activated carbon is considered one of the best adsorbents for the removal of organic contaminants, but activated carbon is too expensive to use widely in practical applications . Therefore, the development of low-cost, high-efficiency, renewable, and eco-friendly materials as absorbent for the removal of dyes has attracted more and more interests. Recently, many kinds of materials such as SnS2 nanosheets , WO3 nanorods , Cu2O nanocrystals [18, 19], and other highly adsorbent materials have been investigated.
Bismuth selenide (Bi2Se3) nanostructures have been extensively studied due to their unique properties and promising applications in the fields of optical recording systems, laser materials, optical filters, sensors, solar cells, strain gauges, electromechanical and thermoelectric devices, and topological insulators [20–23]. During the past few years, the preparation and application of doped Bi2Se3 have been extensively investigated [24–27]. In addition, due to the high surface state and unique optical or electrical properties , Bi2Se3 can also be applied in the fields of visible-light photocatalytic degradation [27, 29]. For example, Bi2Se3-TiO2 complex nanobelts  and S-doped BiSe  show excellent visible-light photocatalytic degradation performance. However, to our knowledge, there is no report on the absorption properties of Bi2Se3 nanostructures, especially the systematic study of the Mo doping-enhanced absorption behavior of Bi2Se3 nanostructures.
In this work, we synthesized self-assembled Mo-doped Bi2Se3 nanoflowers by a simple solvothermal route. We find that the absorption behavior of Bi2−xMo x Se3 on Rhodamine B (RhB) varies as a function of Mo content and reaches its highest absorption capacity with 15% Mo doping.
Preparation of Bi2−xMo x Se3
All of the chemical reagents used in this experiment are of analytical grade and used without further purification. Bi2−xMo x Se3 (x = 0, 0.01, 0.03, 0.05, 0.10, and 0.15) is obtained by a simple solvothermal method. In a typical Bi2−xMo x Se3 (x = 0.15) synthesis, 0.85 mmol of Bi(NO3)3·5H2O and 0.15 mmol of (NH4)6Mo7O24·4H2O are added to 18 ml of N,N-dimethylformamide under vigorous stirring to form a homogeneous solution. Then additional ammonia is added to the above solution to adjust the pH value to 9 to 10 under continuous stirring. After that, Se powder and Na2SO3 are added to the above solution under magnetic stirring. The final solution is transferred into a Teflon-lined autoclave (25-ml capacity), kept at 160°C for 20 h, and cooled to room temperature under ambient conditions. The products are finally washed several times with ethanol and distilled water, followed by drying at 80°C for 12 h under vacuum. For comparison, we also synthesized Bi2−xMo x Se3 samples with different Mo contents (x = 0, 0.01, 0.03, 0.05, 0.10, and 0.15), which are labeled as samples A, B, C, D, E, and F, respectively.
Dye adsorption experiments
The adsorption activities of the as-prepared products are investigated using RhB as dyes. In each experiment, 0.08 g of adsorbent was added to 50 ml of a 10-mg/l RhB solution. Under constant stirring in the dark, about 6 ml of the mixture solution is taken out at intervals and centrifuged to separate solid particles for analysis. After centrifugation, the adsorption behavior is investigated.
The phase composition and crystallographic structure of the as-prepared samples are examined by X-ray diffraction (XRD) technique with Cu Kα irradiation. The sizes and morphologies of the products are investigated using a field emission scanning electron microscope (FESEM; S-4800, Hitachi, Minato-ku, Tokyo, Japan). The dye adsorption behavior is measured with a UV-visible (UV–vis) spectrum (Lambda 900, PerkinElmer Instruments, Branford, CT, USA).
Results and discussion
Structure and morphology
The chemical composition of Bi2−xMo x Se3 was determined by energy-dispersive X-ray analysis (EDXA) attached to the FESEM. In Figure 3b, the EDXA spectrum of the Bi1.85Mo0.15Se3 nanosheets shows that the nanosheets contain only Mo, Bi, and Se without any trace of by-products.
Adsorption ability of Bi2−xMo x Se3
In summary, Bi2−xMo x Se3 nanomaterials were prepared by a solvothermal approach, and different morphologies of Bi2−xMo x Se3 have been obtained. The doping concentration of Mo plays an important role in controlling both the morphologies of Bi2−xMo x Se3 nanostructures and their absorption behavior. The sample with the best absorption behavior is that with 15% Mo concentration. We believe that the study of dye absorption behavior brings a new application realm for Bi2Se3 nanostructures.
This work is supported by the National Natural Science Foundation of China (grant nos. 11104250 and 61274099), the Science Technology Department of Zhejiang Province (grant no. 2012C21007), and the Zhejiang innovative team (2011R50012).
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