Open Access

Mo doping-enhanced dye absorption of Bi2Se3 nanoflowers

Nanoscale Research Letters20138:451

DOI: 10.1186/1556-276X-8-451

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.


Solvothermal Bi2−xMo x Se3 Nanoflowers Nanoplates Higher adsorption capacity


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 [3]. A variety of methods have been introduced to remove dyes from wastewaters, such as membrane filtration [4], flotation [5, 6], solvent extraction [7], 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 [1015]. 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 [16]. 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 [15], WO3 nanorods [17], 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 [2023]. During the past few years, the preparation and application of doped Bi2Se3 have been extensively investigated [2427]. In addition, due to the high surface state and unique optical or electrical properties [28], Bi2Se3 can also be applied in the fields of visible-light photocatalytic degradation [27, 29]. For example, Bi2Se3-TiO2 complex nanobelts [30] and S-doped BiSe [31] 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.

Sample characterization

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 as-prepared samples are examined by XRD techniques, and the XRD patterns of samples A to F are shown in Figure 1. All the peaks in the patterns can be indexed according to the power diffraction card of hexagonal Bi2Se3 (no. 33-0214), and no impurity phase related to the Mo complex could be found. The diffraction peaks shift to higher angles with the increase of Mo6+ content from samples A to F, indicating that Mo6+ has been incorporated in the Bi2Se3 lattice, and the lattice parameter gets smaller with the increase of Mo6+. This is understandable considering the fact that the ionic radius of Mo6+ (0.065 nm) [24] is smaller than that of Bi3+ (0.103 nm) [25].
Figure 1

XRD patterns of samples (a) A, (b) B, (c) C, (d) D, (e) E, and (f) F.

The morphology and size of the as-synthesized products are characterized by FESEM observations (Figure 2). The low-magnification FESEM image in Figure 2a shows that a large number of platelike nanostructures are randomly dispersed on the surface of the substrate. Comparatively, a perfect hexagonal morphology for Bi2Se3 is observed from the image. A magnified FESEM image (Figure 2b) shows that the width of the nanosheets is in the range of 100 to 400 nm with a thickness of about 10 to 30 nm. The doping of Mo changes the morphologies of the nanosheets greatly. The low-magnified FESEM image (Figure 2c) demonstrates that the typical product of Bi1.85Mo0.15Se3 consists of a large quantity of uniform flowerlike nanospheres. The average diameter of flowerlike nanospheres is about 100 to 200 nm, and they are made up of curved nanoplates with an average thickness of 5 to 10 nm as shown in the high-magnification FESEM image (Figure 2d).
Figure 2

Low-resolution FESEM images of samples (a) A and (c) F and their respective high-resolution SEM images (b, d).

To confirm the structure, crystallinity, and details of the flowerlike nanospheres, high-resolution transmission electron microscopy (HRTEM) techniques are employed. A representative HRTEM image taken from the edge of a Bi1.85Mo0.15Se3 nanoflower is shown in Figure 3a, which clearly indicates that nanoflowers contain a perfectly periodic arrangement with an interplanar distance of a = 0.356 nm, which is smaller than that of bulk anatase (a = 0.413 nm) crystal.
Figure 3

A HRTEM image of sample F (a) and the EDXA spectrum of sample F (b).

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.

From the FESEM observations, we can conclude that the Mo concentration influences the morphologies of the nanoplates greatly. In order to understand the role of Mo in the evolution process of Bi2−xMo x Se3 from nanoplates to nanoflowers, Bi2−xMo x Se3 samples with varied x values are synthesized and studied. With the increase of the x value (Mo concentration), the nanostructures gradually change from hexagonal nanosheets to smaller-sized hexagonal nanosheets and finally to flowerlike spheres, combined with a size change. For example, when no Mo is contained, the sizes of the nanosheet are about 100 to 500 nm in width and 20 to 30 nm in thickness, as shown in Figure 4 (a-1 and a-2). With increasing amounts of Mo, morphologies of the as-synthesized Bi2−xMo x Se3 products change from nanosheets to nanoflowers (Figure 4 (a-1 to f-2). From Figure 4 (b-1 to d-2), we can see that the products are still composed of nanosheets, but the sizes of Bi2Se3 have become smaller. When the Mo concentration increased up to 15% (Figure 4 (f-1 and f-2), regular flowerlike spheres consisting of thin nanoplates were formed. The average diameter of nanoflowers is about 100 to 200 nm, and they are made up of curved nanoplates with an average thickness of 5 to 10 nm as shown in the magnified image. With the increase of Mo contents in Bi2−xMo x Se3, the diameter of the products was found to be lower than that of pure Bi2Se3. So we believe that Mo is the main driving force for the formation of a flowerlike structure.
Figure 4

Low- and high-magnification FESEM images of the samples. Low-magnification (a1, b1, c1, d1, e1, and f1) and high-magnification (a2, b2, c2, d2, e2, and f2) FESEM images of samples A (a1, a2), B (b1, b2), C (c1, c2), D (d1, d2), E (e1, e2), and F (f1, f2).

A diagram of the formation mechanism of nanoplates and nanoflowers of Bi2−xMo x Se3 is presented in Figure 5. When no Mo is contained, tiny clusters of Bi2Se3 nanosheets are first generated upon heating and then enriched to assemble into bigger nanosheets. However, with the increase of Mo concentration in Bi2−xMo x Se3, nanosheets assemble into nanoflowers.
Figure 5

Schematic diagram showing the growth mechanism of nanosheets and nanoflowers of Bi 2− x Mo x Se 3 .

Adsorption ability of Bi2−xMo x Se3

To investigate the potential application of the as-synthesized Bi2−xMo x Se3 nanocrystals and their relationship with the amount of Mo in Bi2−xMo x Se3, we study the adsorption ability of Bi2−xMo x Se3 using RhB as dyes. The experiments are carried out with Bi2−xMo x Se3 dispersed in the solution of RhB in the dark several times with constant stirring. After centrifugation, the UV–vis absorption of the supernatant was measured and the characteristic absorption of RhB at about 553 nm was selected to estimate the adsorption process. Figure 6 shows the UV–vis adsorption spectra of RhB as a function of time using the as-prepared Bi1.99Mo0.01Se3 as adsorbent. From Figure 6, we can see that the intensity of the absorption spectra gradually decreases and nearly disappears within 60 min; at the same time, the solution becomes colorless when observed with the naked eye.
Figure 6

Time-dependent absorption of 2.0 × 10 −4 M 50-ml aqueous solutions of RhB in the presence of 50-mg as-prepared Bi 1.99 Mo 0.01 Se 3 .

Figure 7 shows the variation in RhB concentration with the adsorption time over different adsorbents. When there is no adsorbent, the concentration of the RhB solution remains the same with its original state for up to 60 min, which demonstrates that RhB is stable under the experimental conditions. Pure Bi2Se3 shows a weak adsorption activity. After 60 min of absorption, only 20% of RhB is removed from the pure Bi2Se3 sample. The adsorption activities are strengthened with the increase of Mo contents in Bi2Se3. Bi1.85Mo0.15Se3 has a maximum adsorption behavior, and nearly 100% of the RhB dyes are removed in 20 min. All of this clearly shows that the doping of Mo in Bi2Se3 is an efficient way to enhance its adsorption activity. The results indicate that the as-synthesized Bi2−xMo x Se3 might possess a profound application in the fields of treatment of dye-polluted wastewater.
Figure 7

A plot showing the extent of RhB degradation as a function of adsorption time for different catalysts. RhB degradation is monitored at 554 nm. Lines a, b, c, d, e, f, and g represent, respectively, samples blank, A, B, C, D, E, and F.


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).

Authors’ Affiliations

Research Center for Light Emitting Diodes (LED), Zhejiang Normal University


  1. Schwarzenbach RP, Egli T, Hofstetter TB, von Gunten U, Wehrli B: Global water pollution and human health. Annu Rev Environ Resour 2010, 35: 109–136. 10.1146/annurev-environ-100809-125342View ArticleGoogle Scholar
  2. Hanley N, Shogren J, White B: Introduction to Environmental Economics. Oxford: Oxford University Press; 2013:1–20.Google Scholar
  3. Laing IG: The impact of effluent regulations on the dyeing industry. Rev Prog Color Relat Top 1991, 21(1):56–71.View ArticleGoogle Scholar
  4. Ersahin ME, Ozgun H, Dereli RK, Ozturk I, Roest K, van Lier JB: A review on dynamic membrane filtration: materials, applications and future perspectives. Bioresour Technol 2012, 122: 196–206.View ArticleGoogle Scholar
  5. Zodi S, Merzouk B, Potier O, Lapicque F, Leclerc JP: Direct red 81 dye removal by a continuous flow electrocoagulation/flotation reactor. Sep Purif Technol 2013, 108: 215–222.View ArticleGoogle Scholar
  6. Zheng YM, Yunus RF, Nanayakkara KGN, Chen JP: Electrochemical decoloration of synthetic wastewater containing rhodamine 6G: behaviors and mechanism. Ind Eng Chem Res 2012, 51(17):5953–5960. 10.1021/ie2019273View ArticleGoogle Scholar
  7. Hu HS, Yang MD, Dang J: Treatment of strong acid dye wastewater by solvent extraction. Separation and Purification Technology 2005, 42(2):129–136. 10.1016/j.seppur.2004.07.002View ArticleGoogle Scholar
  8. Malik PK, Saha SK: Oxidation of direct dyes with hydrogen peroxide using ferrous ion as catalyst. Sep Purif Technol 2003, 31(3):241–250. 10.1016/S1383-5866(02)00200-9View ArticleGoogle Scholar
  9. Chen X, Xue Z, Yao Y, Wang W, Zhu F, Hong C: Oxidation degradation of rhodamine B in aqueous by treatment system. Int J Photoenergy 2012, 2012: 1–5.Google Scholar
  10. Mittal A, Thakur V, Gajbe V: Adsorptive removal of toxic azo dye Amido Black 10B by hen feather. Environ Sci Pollut Res 2013, 20(1):260–269. 10.1007/s11356-012-0843-yView ArticleGoogle Scholar
  11. Khan TA, Dahiya S, Ali I: Use of kaolinite as adsorbent: equilibrium, dynamics and thermodynamic studies on the adsorption of rhodamine B from aqueous solution. Appl Clay Sci 2012, 69: 58–66.View ArticleGoogle Scholar
  12. Turchi CS, Ollis DF: Photocatalytic degradation of organic water contaminants: mechanisms involving hydroxyl radical attack. Journal of Catalysis 1990, 122(1):178–192. 10.1016/0021-9517(90)90269-PView ArticleGoogle Scholar
  13. Le HA, Linh LT, Chin S, Jurng J: Photocatalytic degradation of methylene blue by a combination of TiO2-anatase and coconut shell activated carbon. Powder Technol 2012, 225: 167–175.View ArticleGoogle Scholar
  14. Zhang W, Shi L, Tang K, Liu Z: Synthesis, surface group modification of 3D MnV2O6 nanostructures and adsorption effect on Rhodamine B. Mater Res Bull 2012, 47(7):1725–1733. 10.1016/j.materresbull.2012.03.038View ArticleGoogle Scholar
  15. Li X, Zhu J, Lv FJ, Wang JG, Xie ZL, Hoang M, Li HX: An efficient removal of rhodamine B in water by targeted adsorption on SnS2 nanosheets. Adv Mater Res 2012, 356: 1708–1711.Google Scholar
  16. Mezohegyi G, van der Zee FP, Font J, Fortuny A, Fabregat A: Towards advanced aqueous dye removal processes: a short review on the versatile role of activated carbon. J Environ Manage 2012, 102: 148–164.View ArticleGoogle Scholar
  17. Zhu J, Wang S, Xie S, Li H: Hexagonal single crystal growth of WO3 nanorods along a [110] axis with enhanced adsorption capacity. Chem Commun 2011, 47(15):4403–4405. 10.1039/c1cc00064kView ArticleGoogle Scholar
  18. Li B, Cao H, Yin G, Lu Y, Yin J: Cu2O@ reduced graphene oxide composite for removal of contaminants from water and supercapacitors. J Mater Chem 2011, 21(29):10645–10648. 10.1039/c1jm12135aView ArticleGoogle Scholar
  19. Shang Y, Zhang D, Guo L: CuCl-intermediated construction of short-range-ordered Cu2O mesoporous spheres with excellent adsorption performance. J Mater Chem 2012, 22(3):856–861. 10.1039/c1jm14258eView ArticleGoogle Scholar
  20. Batabyal SK, Basu C, Das AR, Sanyal GS: Solvothermal synthesis of bismuth selenide nanotubes. Mater Lett 2006, 60(21):2582–2585.View ArticleGoogle Scholar
  21. Cho S, Butch NP, Paglione J, Fuhrer MS: Insulating behavior in ultrathin bismuth selenide field effect transistors. Nano Letters 2011, 11(5):1925–1927. 10.1021/nl200017fView ArticleGoogle Scholar
  22. Wu S, Liu G, Li P, Liu H, Xu H: A high-sensitive and fast-fabricated glucose biosensor based on Prussian blue/topological insulator Bi2Se3 hybrid film. Biosens Bioelectron 2012, 38(1):289–294. 10.1016/j.bios.2012.06.001View ArticleGoogle Scholar
  23. Mellnik A, Grab J, Mintun P, Lee JS, Richardella A, Samarth N, Ralph D: Efficient generation of spin current and spin transfer torque by the topological insulator bismuth selenide. Bull Am Phys Soc 2013, 58: 00011.Google Scholar
  24. Hong SS, Cha JJ, Kong D, Cui Y: Ultra-low carrier concentration and surface-dominant transport in antimony-doped Bi2Se3 topological insulator nanoribbons. Nat Commun 2012, 3: 757.View ArticleGoogle Scholar
  25. Choi YH, Jo NH, Lee KJ, Yoon JB, You CY, Jung MH: Transport and magnetic properties of Cr, Fe, Cu-doped topological insulators. J Appl Phys 2011, 109: 07E312.Google Scholar
  26. Alemi A, Hanifehpour Y, Joo SW, Min BK, Oh TH: Structural studies and optical and electrical properties of novel Gd3+-doped Sb2Se3 nanorods. J Nanomater 2012, 2012: 70.View ArticleGoogle Scholar
  27. Song L, Zhang S, Chen C, Hu X, Wei Q: Synthesis of sulphur doped bismuth selenide photocatalysts by the solvothermal method and their photocatalytic activities under visible-light irradiation. Chem Eng J 2011, 171(3):1454–1457. 10.1016/j.cej.2011.05.048View ArticleGoogle Scholar
  28. Kandala A, Richardella A, Zhang D, Flanagan TC, Samarth N: Surface-sensitive two-dimensional magneto-fingerprint in mesoscopic Bi2Se3 channels. Nano Letters 2013, 13(6):2471–2476. 10.1021/nl4012358View ArticleGoogle Scholar
  29. Lei J, Qie N, Zhou J, Hua Y, Ji T: Preparation and characterization of TiO2 nanobelts deposited with Bi2Se3 nanoplates. Mater Lett 2012, 83: 108–111.View ArticleGoogle Scholar
  30. Yu CL, Yang K, Shu Q, Yu JC, Cao FF, Li X, Zhou XC: Preparation, characterization and photocatalytic performance of Mo-doped ZnO photocatalysts. Sci China Chem 2012, 55(9):1802–1810. 10.1007/s11426-012-4721-8View ArticleGoogle Scholar
  31. Wang X, Bai H, Meng Y, Zhao Y, Tang C, Gao Y: Synthesis and optical properties of Bi3+ doped NaTaO3 nano-size photocatalysts. J Nanosci Nanotechnol 2010, 10(3):1788–1793. 10.1166/jnn.2010.2122View ArticleGoogle Scholar


© Zhong et al.; licensee Springer. 2013

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