Synthesis of hexagonal Zn3(OH)2V2O7·2H2O nanoplates by a hydrothermal approach: Magnetic and photocatalytic properties

M A TE RI A L S C HA RACT ER I ZA TI O N 86 ( 20 1 3 ) 1 3 9–1 4 5

Available online at www.sciencedirect.com

ScienceDirect www.elsevier.com/locate/matchar

Synthesis of hexagonal Zn3(OH)2V2O7·2H2O nanoplates by a hydrothermal approach: Magnetic and photocatalytic properties Fangfang Wanga , Wenbin Wua , Xiujuan Suna , Shuyan Songb , Yan Xinga,⁎, Jiawei Wanga , Donghui Yua , Zhongmin Sua,⁎ a

College of Chemistry, Northeast Normal University, Changchun 130024, PR China State Key Laboratory of Rare Earth Resource Utilizations, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, PR China

b

AR TIC LE D ATA

ABSTR ACT

Article history:

Hexagonal Zn3(OH)2V2O7·2H2O nanoplates have been successfully synthesized via a facile

Received 15 May 2012

and template-free hydrothermal method. The nanocrystals have a hexagonal shape with

Received in revised form

650–750 nm in diameter and 120–140 nm in thickness. The possible mechanism of forming

27 August 2013

such hexagonal Zn3(OH)2V2O7·2H2O nanoplates may be due to its inherent anisotropic

Accepted 6 October 2013

crystal structure. Magnetic hysteresis measurement indicates that the as-synthesized hexagonal Zn3(OH)2V2O7·2H2O nanoplates have weak ferromagnetic property at room temperature. Compared to the floriated-like nanostructured Zn3V2O7(OH)2(H2O)2 synthesized

Keywords:

by a hydrothermal route, the as-prepared hexagonal Zn3(OH)2V2O7·2H2O nanoplates exhibited

Hexagonal nanoplates

a significant increase in the methylene blue (MB) photodegradation rate under UV irradiation.

Hydrothermal approach

© 2013 Elsevier Inc. All rights reserved.

Magnetic properties Photocatalytic properties

1.

Introduction

Over the past decade, the shape control of anisotropic nanoand microcrystals has attracted extensive attention because the morphology, dimensionality, and size of materials have great effects on their physical and chemical properties, as well as on their applications in various fields [1,2]. Among a variety of morphologies, two-dimensional (2D) nano- and microstructures, including sheet, plate, or disk-shaped morphologies have drawn much attention due to their potential applications in information storage, transducer, catalyst and sensor [3–5]. Moreover, 2D nanoplates are superior over spherical nanocrystals as building blocks for constructing nanodevices with crystal orientation controlled by a bottom-up method owing to their anisotropic structures [6].

Metal vanadates, as one of the most important family of functional materials, have numerous applications in the fields of catalysts [7], optical devices [8], magnetic materials [9] as well as battery materials [10–12]. Stimulated by both the promising applications and the interesting properties, much attention has been directed to the controlled synthesis of metal vanadates micro/nanomaterials such as FeVO4 [13,14], Cu3V2O7(OH)2·2H2O [15–18], LiV3O8 [19], BiVO4 [7,20–22] and Ag2V4O11 [23]. Zn3(OH)2V2O7·2H2O has an interesting framework assembled from layers of Zn octahedra connected by pyrovanadate groups. With such a structure, this material is a potential candidate for many applications in different areas [24]. It would be of promising application as anode material for lithium ion battery owing to the channel structure in V–O layers [25,26]. In addition, Zn3V2O7(OH)2(H2O)2 also exhibits

⁎ Corresponding authors. Tel.: +86 431 8 09 9657; fax: + 86 431 8 509 9108. E-mail address: [email protected] (Y. Xing). 1044-5803/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.matchar.2013.10.006

140

M A TE RI A L S CH A RACT ER IZ A TI O N 86 (2 0 1 3 ) 1 3 9–1 4 5

efficient UV-light-driven photocatalytic activity for the degradation of organic pollutants [27,28]. However, studies of nano- and micro-scale Zn3(OH)2V2O7·2H2O have been limited. Very recently, Wang et al. reported the synthesis of 3D hierarchical Zn3(OH)2V2O7·2H2O microspheres by a glycineassisted hydrothermal route [29]. Chen et al. have fabricated Zn3(OH)2V2O7·2H2O nanodisks via a CTAB-assisted hydrothermal method [30]. Well-crystallized zinc vanadium oxide hydroxide hydrate Zn3(OH)2V2O7·nH2O nanobelts were successfully synthesized by He and his coworkers [31]. They have also prepared Zn3(OH)2V2O7·nH2O nanosheets and demonstrated their application in lithium ion batteries [25]. However, these reported methods usually require organic additives or surfactants. Recently, Zhu et al. prepared floriated like and nanobelt nanostructures of Zn3(OH)2V2O7(H2O)2 through a template-free hydrothermal route and investigated the photocatalytic activity of flowerlike Zn3(OH)2V2O7(H2O)2 under UV light irradiation [27]. To date, there is no report concerning the Zn3(OH)2V2O7·2H2O nanocrystals with regular hexagon-shaped platelike morphology via a direct facile synthesis route without any templates and surfactants. Accordingly, in this paper, we report for the first time the successful synthesis of well-defined Zn3(OH)2V2O7·2H2O hexagonal nanoplates by an easy and straightforward hydrothermal route in a large scale. The morphology evolution and the growth mechanism were investigated in detail, based on the electron microscopy observation. The photodegradation of methylene blue (MB) was employed to evaluate the photocatalytic activity of the hexagonal Zn3(OH)2V2O7·2H2O nanoplates under UV light irradiation. Moreover, the magnetic property of hexagonal Zn3(OH)2V2O7·2H2O nanoplates has also been investigated.

2.

Experimental Section

2.1.

Synthesis

atmosphere was N2, and the heating rate was 5 °C min−1. The magnetic properties of the samples were measured by using Quantum Design SQUID MPMS XL-7 instruments. UV–vis diffuse reflectance spectra (DRS) of the samples were obtained by using a Hitachi U-3010 UV–vis spectrophotometer.

2.3.

Photocatalytic Tests

The photocatalytic activity of the hexagonal Zn3(OH)2V2O7·2H2O nanoplates was evaluated by degradation of methylene blue (MB) under a 11 W bactericidal lamp with a 254 nm cutoff filter. The average light intensity was about 0.8 mW cm− 2. The reaction cell was placed in a sealed black box of which the top was opened under UV light irradiation. The photocatalyst (50 mg) was added to 100 mL of the MB solution (1.0 × 10− 5 mol L− 1). Before the light was turned on, the solution was stirred continuously for 30 min in the dark to establish an adsorption– desorption equilibrium. The concentration of the MB solution during the degradation was monitored colorimetrically by using a UV/vis spectrometer.

3.

Results and Discussion

3.1. Characterization of Hexagonal Zn3(OH)2V2O7·2H2O Nanoplates The XRD pattern of the as-prepared Zn3(OH)2V2O7·2H2O product is shown in Fig. 1. All the diffraction peaks can be indexed to pure hexagonal phase Zn3(OH)2V2O7·2H2O with lattice constants a = 0.6049 nm and c = 0.7196 nm (JCPDS card No. 50-0570). No other impurities are detected, which shows the high purity of the product. The morphology of the products synthesized by hydrothermal treatment at 160 °C for 24 h was examined by field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). From Fig. 2a, a large number of plate-like Zn3(OH)2V2O7·2H2O nanostructures can

All chemical reagents were of analytical grade and used as received without further purification. In a typical process, 0.6 mmol of Na3VO4·12H2O was dissolved in 30 mL distilled water, then 0.9 mmol of Zn(NO3)2·6H2O was added into the solution. After stirring for 20 min, the pH value of the obtained homogeneous white suspension is about 8.8. Then the suspension was transferred into a Teflon-lined stainless steel autoclave with a capacity volume of 50 mL. After heating at 160 °C for 24 h, the autoclave was cooled down to room temperature naturally. The resulting sample was collected and washed with deionized water and dried at 60 °C in air.

2.2.

Characterization

X-ray powder diffraction (XRD) analysis was performed on a Siemens D5005 Diffractometer with CuKα radiation (λ = 1.5418 Å). Field-emission scanning electron microscopy (FESEM) images were obtained by using a Hitachi S-4800 microscope. Transmission electron microscopy (TEM) images, high-resolution transmission electron microscopy (HRTEM) images were obtained on a JEM-2100F microscope with an accelerating voltage of 200 kV. Thermogravimetric analysis (TGA) was performed on a DuPont 1090 thermal analyzer, the

Fig. 1 – XRD pattern of hexagonal Zn3(OH)2V2O7·2H2O nanoplates obtained after 24 h at 160 °C (inset shows the diffraction peaks except the (001) signal in higher magnification).

M A TE RI A L S C HA RACT ER I ZA TI O N 86 ( 20 1 3 ) 1 3 9–1 4 5

141

Fig. 2 – SEM images (a, b), TEM image (c) and HRTEM image (d) of the as-prepared hexagonal Zn3(OH)2V2O7·2H2O nanoplates.

be observed. The nanoplates are 650–750 nm in diameter (side-to-side length) and 120–140 nm in thickness (Fig. 2b). Transmission electron microscopy image (Fig. 2c) further shows that the product consists of well-defined plate-

shaped structures having a hexagonal outline. Fig. 2d shows a representative high-resolution transmission electron microscopy (HRTEM) image of a nanoplate. Lattice fringes with a spacing of 0.209 nm are clearly visible, which agrees well with the lattice

Fig. 3 – SEM images of samples obtained by hydrothermal treatment at 160 °C for different time intervals: (a) 0, (b) 3, (c) 6, and (d) 16 h.

142

M A TE RI A L S CH A RACT ER IZ A TI O N 86 (2 0 1 3 ) 1 3 9–1 4 5

spacing of (022). The thermal behavior of the hexagonal Zn3(OH)2V2O7·2H2O nanoplates was investigated by means of thermogravimetric (TG) and different scanning calorimetry (DSC) measurement in N2 atmosphere at a heating rate of 5 °C min− 1 (see Supporting information, Fig. S1a). The TG curve shows the weight loss between 50 and 700 °C, which are related to the elimination of water molecules and the phase transformations. The total mass loss is 12.1 wt.% and can be divided into two processes. The weight loss region from 50 to 203 °C is caused by the loss of adsorbed water and crystal water. The mass loss of 7.7 wt.% is in agreement with the theoretical value of 7.5% according to Eq. (1). The second mass loss (4.4 wt.%) is consistent with the theoretical value of 4.0% according to Eq. (2) Zn3 ðOHÞ2 V2 O7 d2H2 O →Zn3 ðOHÞ2 V2 O7 þ 2H2 O

ð1Þ

Zn3 ðOHÞ2 V2 O7 →Zn3 ðVO4 Þ2 þ H2 O:

ð2Þ

On the DSC curve two endothermic and two exothermic peaks are observed. The endothermic peak at 179 °C is mainly attributed to the loss of the crystal water. The exothermic peak at 203 °C is produced by the formation of Zn3(VO4)2 oxide. Hence, the small peak at 229 °C results from the crystallization of Zn3(VO4)2. Finally, the peak at 640 °C is produced by the phase transition of Zn3(VO4)2. The above results suggest that Zn3(VO4)2 can be formed in the temperature range 230–600 °C by calcining the corresponding Zn3(OH)2V2O7·2H2O precursors, which is in agreement with the XRD results (Fig. S1b).

(Fig. S3c). These observations suggest that the reaction temperature has an important effect on the morphology of the obtained products. To reveal the morphology evolution of hexagon-shaped structure of Zn3(OH)2V2O7·2H2O, time-dependent shape evolution experiments were performed by intercepting intermediate products at different reaction stages under 160 °C. When the Na3VO4·12H2O and Zn(NO3)2·6H2O were stirred in a solution for 20 min at room temperature, the solution became turbid and a homogeneous white suspension was formed. Fig. 3a shows the SEM image of this initial formed precursor before thermal treatment, a large number of irregular nanoplates was obtained. Increasing the reaction time to 3 h, many irregular nanoplates together with a small proportion of thin hexagonal nanoplates were observed (Fig. 3b). As the reaction was extended to 6 h, many irregular nanoplates have developed into hexagon-shaped nanoplates (Fig. 3c). With further prolonging the reaction time to 16 h, most of the products show the characteristics of hexagonal nanoplates (Fig. 3d). When the reaction proceeded 24 h, hexagonal nanoplates were the exclusive product morphology formed and the nanoplates became more thicker and more regular in shape (Fig. 2b).

3.2. Investigation of Influencing Factors and Possible Growth Mechanism In order to reveal the factors influencing the formation of hexagonal Zn3(OH)2V2O7·2H2O nanoplates, controlled experiments have been carefully performed by changing one reaction parameter (pH value, reaction temperature and reaction time) while the other reaction conditions were kept constant. The pH value of the solution plays an important role in the formation of regular hexagonal Zn3(OH)2V2O7·2H2O nanoplates. Most of the Zn3(OH)2V2O7·2H2O crystals prepared at pH 7.0 still kept the hexagonal plate-like morphology (Fig. S2a). Products prepared at pH 11.0 were composed of thinner nanoplates with irregular shapes (Fig. S2b). When the pH was increased to 12.0, more regular thin nanoplates with a broad size distribution were obtained (Fig. S2c). The obvious differences in the Zn3(OH)2V2O7·2H2O nanoplate morphologies can be ascribed to the different nucleation rates of Zn3(OH)2V2O7·2H2O induced by different pH values. It was also found that the variation of reaction temperature greatly changes the product morphology. When the reaction was carried out at 80 °C for 24 h, keeping other experimental parameters constant, irregular plate-like nanostructures were produced (Fig. S3a). When the temperature was increased to 120 °C, the size and shape of nanoplates became more uniform (Fig. S3b). When the temperature was controlled at 180 °C, keeping other reaction conditions constant, the product was comprised of irregular nanoparticles and large microrods

Fig. 4 – (a) Room temperature hysteresis loop of hexagonal Zn3(OH)2V2O7·2H2O nanoplates; (b) the enlarged magnetization curve between − 800 and 800 Oe.

M A TE RI A L S C HA RACT ER I ZA TI O N 86 ( 20 1 3 ) 1 3 9–1 4 5

In many solution-phase processes without any organic additives or templates, the morphology of the final product is largely determined by the anisotropic nature of the building blocks [32,33]. Therefore studying the natural chemical character of Zn3(OH)2V2O7·2H2O can help to understand the growth mechanism of these zinc vanadate hexagonal nanoplates. Zn3(OH)2V2O7·2H2O has a layered anisotropic lattice structure composed of zinc oxide/hydroxide octahedra layers and V–O layers [24]. This intrinsic crystal property may dominate the shape of the primary Zn3(OH)2V2O7·2H2O particles (i.e., platelet seed), resulting in the formation of hexagonal plate-like crystals, as reported previously for the formation of hexagonal LaF3 nanoplates [34] and β-NaLuF4 hexagonal microplates [35]. Therefore, it is reasonable to conclude that the formation of platelet-like morphology of Zn3(OH)2V2O7·2H2O should be related to their inherently anisotropic crystal structure, resulting in much faster growth along the top–bottom crystalline planes than along the c-axis.

3.3.

Magnetic Property

The magnetic property has been quantified by using a superconducting quantum interference device magnetometer

143

(SQIDM) at room temperature. Fig. 4 shows a typical hysteresis loop (M–H curve) of hexagonal Zn3(OH)2V2O7·2H2O nanoplates synthesized at 160 °C. There exists a small hysteresis loop at lower field, which indicates the existence of a weak ferromagnetic component at room temperature. This is quaint considering the fact that quinquevalent vanadium compounds were merely reported to be paramagnetic or antiferromagnetic at room temperature [23,36,37]. The magnetic hysteresis loop shows the coercive force (Hc) value and the saturated magnetic (Ms) moment are 28.2 Oe and 0.02722 emu/g, respectively. It is proposed that the room temperature ferromagnetic property of Zn3(OH)2V2O7·2H2O comes from oxygen vacancy [31].

3.4.

Photocatalytic Activity

The photophysical property of the hexagonal Zn3(OH)2V2O7·2H2O nanoplates was investigated by UV/vis diffuse reflectance spectroscopy (Fig. 5a). The sample shows the absorption onset in the UV light region. The band gap was estimated to be 3.27 eV from the onset of the absorption edge. Accordingly, the photocatalytic activity of Zn3(OH)2V2O7·2H2O was evaluated by degradation of methylene blue (MB) under UV light irradiation, a hazardous solution pollutant as well as a

Fig. 5 – (a) Diffuse reflection spectrum of hexagonal Zn3(OH)2V2O7·2H2O nanoplates. (b) The UV/vis spectroscopic changes of the MB aqueous solution in the presence of hexagonal Zn3(OH)2V2O7·2H2O nanoplates. (c) Concentration changes of MB at 662 nm as a function of light irradiation time in the presence of hexagonal Zn3(OH)2V2O7·2H2O nanoplates. (d) Kinetics of MB decolorization in solutions.

144

M A TE RI A L S CH A RACT ER IZ A TI O N 86 (2 0 1 3 ) 1 3 9–1 4 5

common model compound to test the photodegradation capability of photocatalysts. When the suspension was stirred in the dark for 2 h or irradiated with UV light for 2 h in the absence of photocatalyst, there was no apparent change in the concentration of MB. However, in the presence of the hexagonal Zn3(OH)2V2O7·2H2O nanoplates, MB was almost completely degraded after 80 min of UV light irradiation (Fig. 5b). Fig. 5c displays the concentration changes of MB at 662 nm as a function of irradiation time during the degradation process in aqueous solution in the presence of hexagonal Zn3(OH)2V2O7·2H2O nanoplates. To analyze the photocatalysis kinetics of the MB degradation in our experiments, we applied the pseudo-first-order model as expressed by Eq. (3), which is generally used for photocatalytic degradation processes if the initial concentration of pollutant is low [38,39]. ln ðC=C 0 Þ ¼ kt

ð3Þ

where C0 and C are the concentrations of organic dye in solution at time 0 and t, respectively, and k is the pseudofirst-order rate constant. Fig. 5d shows the photocatalytic reaction kinetics of MB degradation in solution on the basis of the data plotted in Fig. 5c. As it can be seen, a rather good correlation to the pseudo-first-order reaction kinetics (R > 0.99) was found. Via the first-order linear fit, the determined reaction rate constant k was 0.03939 min−1, which shows clearly that the reaction constant k of hexagonal Zn3(OH)2V2O7·2H2O nanoplates is twice that of the Zn3V2O7(OH)2(H2O)2 nanostructure previously reported [27]. The higher photocatalytic activity of hexagonal Zn3(OH)2V2O7·2H2O nanoplates might be mainly owing to their special crystal structure, which has an interesting crystalline structure with a porous framework assembled from layers of Zn octahedra connected by pyrovanadate groups.

4.

Conclusions

In summary, hexagonal Zn3(OH)2V2O7·2H2O nanoplates have been successfully prepared via a simple and template-free hydrothermal approach. The formation mechanism studies demonstrate that the anisotropic unit cell structure of the nucleated Zn3(OH)2V2O7·2H2O seeds is an important factor for the shape control. Without any magnetic reaction materials and pollutions, ferromagnetic property of the as-synthesized Zn3(OH)2V2O7·2H2O is observed at room temperature. Moreover, we found that the Zn3(OH)2V2O7·2H2O had photocatalytic activity for MB degradation under UV light irradiation. This simple synthetic route will offer great opportunities for the scale-up preparation of novel-shape transition metal vanadate micro/nanostructures.

Acknowledgments This work was supported by the National Natural Science Foundation of China (Grant No. 21073032) and Opening Fund of State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences.

Appendix A. Supplementary data Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.matchar.2013.10.006.

REFERENCES [1] Ding Y, Wan Y, Min YL, Zhang W, Yu SH. General synthesis and phase control of metal molybdate hydrates MMoO4·nH2O(M = Co, Ni, Mn, n = 0, 3/4, 1) nano/microcrystals by a hydrothermal approach: magnetic, photocatalytic, and electrochemical properties. Inorg Chem 2008;47:7813–23. [2] Song SY, Zhang Y, Xing Y, Wang C, Feng J, Shi WD, et al. Rectangular AgIn(WO4)2 nanotubes: a promising photoelectric material. Adv Funct Mater 2008;18:2328–34. [3] Kim C, Kim YJ, Jang ES, Yi GC, Kim HH. Whispering-gallery-modelike-enhanced emission from ZnO nanodisk. Appl Phys Lett 2006;88:093104. [4] Zhang YW, Sun X, Si R, You LP, Yan CH. Single-crystalline and monodisperse LaF3 triangular nanoplates from a single-source precursor. J Am Chem Soc 2005;127:3260–1. [5] Xu CX, Sun XW, Dong ZL, Cui YP, Wang BP. Nanostructured single-crystalline twin disks of zinc oxide. Cryst Growth Des 2007;7:541–4. [6] Zhang HT, Wu G, Chen XH. Large-scale synthesis and self-assembly of monodisperse hexagon Cu2S nanoplates. Langmuir 2005;21:4281–2. [7] Ren L, Jin L, Wang JB, Yang F, Qiu MQ, Yu Y. Template-free synthesis of BiVO4 nanostructures: I. Nanotubes with hexagonal cross sections by oriented attachment and their photocatalytic property for water splitting under visible light. Nanotechnology 2009;20:115603 (9 pp.). [8] Peng B, Fan ZC, Qiu XM, Jiang L, Tang GH, Ford HD, et al. A novel transparent vanadate glass for use in fiber optics. Adv Mater 2005;17:857–9. [9] Guskos N, Typek J, Zolnierkiewicz G, Szymczak R, Berczynski P, Wardal K, et al. Magnetic properties of a new iron lead vanadate Pb2FeV3O11. J Alloy Compd 2011;509:8153–7. [10] Cheng FY, Chen J. Transition metal vanadium oxides and vanadate materials for lithium batteries. J Mater Chem 2011;21:9841–8. [11] Xiao LF, Zhao YQ, Yin J, Zhang LZ. Clewlike ZnV2O4 hollow spheres: nonaqueous sol–gel synthesis, formation mechanism, and lithium storage properties. Chem Eur J 2009;15:9442–50. [12] Song JM, Lin YZ, Yao HB, Fan FJ, Li XG, Yu SH. Superlong β-AgVO3 nanoribbons: high-yield synthesis by a pyridine-assisted solution approach, their stability, electrical and electrochemical properties. ACS Nano 2009;3:653–60. [13] Ma H, Yang XJ, Tao ZL, Liang J, Chen J. Controllable synthesis and characterization of porous FeVO4 nanorods and nanoparticles. Cryst Eng Commun 2011;13:897–901. [14] Nithya VD, Selvan RK, Sanjeeviraja C, Radheep DM, Arumugam S. Synthesis and characterization of FeVO4 nanoparticles. Mater Res Bull 2011;46:1654–8. [15] Zhang SY, Ci LJ, Liu HR. Synthesis, characterization, and electrochemical properties of Cu3V2O7(OH)2·2H2O nanostructures. J Phys Chem C 2009;113:8624–9. [16] Ni SB, Wang XH, Zhou G, Yang F, Wang JM, He DY. Hydrothermal synthesis and magnetic property of Cu3(OH)2V2O7·nH2O. Mater Lett 2010;64:516–9. [17] Sun XJ, Wang JW, Xing Y, Zhao Y, Liu XC, Liu B, et al. Hydrothermal synthesis of Cu3V2O7(OH)2·2H2O hierarchical

M A TE RI A L S C HA RACT ER I ZA TI O N 86 ( 20 1 3 ) 1 3 9–1 4 5

[18]

[19]

[20]

[21]

[22]

[23]

[24]

[25]

[26]

[27]

[28]

microspheres and their electrochemical properties. Mater Lett 2010;64:2019–21. Sun XJ, Wang JW, Xing Y, Zhao Y, Liu XC, Liu B, et al. Surfactant-assisted hydrothermal synthesis and electrochemical properties of nanoplate-assembled 3D flower-like Cu3V2O7(OH)2·2H2O microstructures. Cryst Eng Commun 2011;13:367–70. Pan AQ, Zhang JG, Cao GZ, Liang SQ, Liu J, et al. Nanosheet-structured LiV3O8 with high capacity and excellent stability for high energy lithium batteries. J Mater Chem 2011;21:10077–84. Shen Y, Huang ML, Huang Y, Lin JM, Wu JH. The synthesis of bismuth vanadate powders and their photocatalytic properties under visible light irradiation. J Alloy Compd 2010;496:287–92. Xi GC, Ye JH. Synthesis of bismuth vanadate nanoplates with exposed 001 facets and enhanced visible-light photocatalytic properties. Chem Commun 2010;46:1893–5. Chung CY, Lu CH. Reverse-microemulsion preparation of visible-light-driven nano-sized BiVO4. J Alloy Compd 2010;502:L1–5. Mao CJ, Wu XC, Pan HC, Zhu JJ, Chen HY. Single-crystalline Ag2V4O11 nanobelts: hydrothermal synthesis, field emission, and magnetic properties. Nanotechnology 2005;16:2892–6. Melghit K, Al-Belushi AK, Al-Amri I. Short reaction time preparation of zinc pyrovanadate at normal pressure. Ceram Int 2007;33:285–8. Ni SB, Zhou G, Lin SM, Wang XH, Pan QT, Yang F, et al. Hydrothermal synthesis of Zn3(OH)2V2O7·nH2O nanosheets and its application in lithium ion battery. Mater Lett 2009;63:2459–61. Zhang SY, Xiao X, Lu M, Li ZQ. Zn3V2O7(OH)2·2H2O and Zn3(VO4)2 3D microspheres as anode materials for lithium-ion batteries. J Mater Sci 2013;48:3679–85. Shi R, Wang YJ, Zhou F, Zhu YF. Zn3V2O7(OH)2(H2O) and Zn3V2O8 nanostructures: controlled fabrication and photocatalytic performance. J Mater Chem 2011;21:6313–20. Mondal C, Ganguly M, Sinha AK, Pal J, Sahoo R, Pal T. Robust cubooctahedron Zn3V2O8 in gram quantity: a material for

[29]

[30]

[31]

[32]

[33]

[34]

[35]

[36]

[37]

[38]

[39]

145

photocatalytic dye degradation in water. Crys Eng Commun 2013;15:6745–51. Wang M, Shi YJ, Jiang GQ. 3D hierarchical Zn3(OH)2V2O7·2H2O and Zn3(VO4)2 microspheres: synthesis, characterization and photoluminescence. Mater Res Bull 2012;47:18–23. Cao XF, Zhang L, Ma YL, Chen XT. Hydrothermal preparation of Zn3(OH)2V2O7·2H2O nanodisks. Chin J Inorg Chem 2010;26:787–92. Ni SB, Lin SM, Pan QT, Huang K, Yang F, He DY. Crystallized Zn3(OH)2V2O7·nH2O: hydrothermal synthesis and magnetic property. J Alloys Compd 2009;477:L1–3. Shi WD, Zhou L, Song SY, Yang JH, Zhang HJ. Hydrothermal synthesis and thermoelectric transport properties of impurity-free antimony telluride hexagonal nanoplates. Adv Mater 2008;20:1892–7. Han JT, Huang YH, Huang W, Goodenough JB. Selective synthesis of TbMn2O5 nanorods and TbMnO3 micron crystals. J Am Chem Soc 2006;128:14454–5. Qin RF, Song HW, Pan GH, Bai X, Dong B, Xie SH, et al. Polyol-mediated synthesis of hexagonal LaF3 nanoplates using NaNO3 as a mineralizer. Cryst Growth Des 2009;9:1750–6. Li CX, Yang J, Yang PP, Zhang XM, Lian HZ, Lin J. Two-dimensional β-NaLuF4 hexagonal microplates. Cryst Growth Des 2008;8:923–9. Cui YJ, Meng H, Liu L, Li GH, Chen C, Yi Z, et al. Weakly coordinative interaction between [Cu(4,4′-bipy)]2n+ 2n and [(VO)(HPO4)(H2PO4)]2n− 2n chains forming a new 2-D layer bimetallic phosphate: [Cu(4,4′-bipy)(VO)(HPO4)(H2PO4)]2(4,4′-bipy = 4, 4′-bipyridine). Solid State Sci 2006;8:1108–14. Awaka J, Ito M, Suzuki T, Nagata S. Antiferromagnetic phase transition in garnet-type AgCa2Co2V3O12 and AgCa2Ni2V3O12. J Phys Chem Solids 2005;60:851–60. Chen RG, Bi JH, Wu L, Li ZH, Fu XZ. Orthorhombic Bi2GeO5 nanobelts: synthesis, characterization, and photocatalytic properties. Cryst Growth Des 2009;9:1775–9. Zhang L, Cao XF, Ma YL, Chen XT, Xue ZL. Microwave-assisted preparation and photocatalytic properties of Zn2GeO4 nanorod bundles. Cryst Eng Commun 2010;12:3201–6.