Synthesis and Compactness Dependence on Flower-like Copper Germanate

Flower-like CuGeO3 has been obtained using a simple hydrothermal process by controlling the compactness. Xray diffraction shows that the flower-like CuGeO3 is composed of orthorhombic CuGeO3 phase. Scanning electron microscopy displays that the size of each flower-like CuGeO3 is about 3 μm which consists of the accumulation of dozens of CuGeO3 nanorods with the diameter and length of less than 100 nm and about 1 μm, respectively. Compactness dependence results demonstrate that the compactness is the key factor for the formation of flowerlike CuGeO3. Free-standing CuGeO3 nanowires can be obtained by improving the compactness. Hydrothermal temperature and reaction time have important roles on the size and formation of the flower-like CuGeO3. [DOI: 10.1380/ejssnt.2011.326]

Single crystalline CuGeO 3 nanobelts have been synthesized by a simple hydrothermal route using cetyltrimethylammonium bromide (CTAB) as the surfactant at 180 • C for 24 h [19].The obtained CuGeO 3 nanobelts show distinct susceptibility behaviors in comparison with CuGeO 3 bulk crystals.Interesting magnetic properties of the layered CuGeO 3 nanobelts were also obtained.In our past research, by the combination of hydrothermal method and deposition process, single crystalline CuGeO 3 nanowires have been synthesized using GeO 2 , copper sheets [20] and GeO 2 , CuO, copper sheets [21] as the Ge raw material, Cu raw material and deposition substrate, respectively.The obtained CuGeO 3 nanowires display good optical and electrochemical properties.The CuGeO 3 nanowires can be used as a kind of novel electrochemical modified electrode material which exhibits a novel electrocatalytic effect to the electrochemical reaction of L-cysteine.The intensities of two electrochemical anodic peaks at the modified electrode are proportional to the concentration of cys-teine, which can be used to detect cysteine sensitively [22].
Very recently, single crystalline CuGeO 3 nanowires in bulk have been successfully synthesized via a facile hydrothermal process using GeO 2 and Cu(CH 3 COO) 2 •H 2 O as the raw materials in the absence of any surfactants by us so as to improve the yield of the CuGeO 3 nanowires [23].The yield of the CuGeO 3 nanowires is higher than 80 wt.%.It is noticed that the compactness of the autoclave is a very important factor for the formation of 1D nanostructures with different morphologies [24].The volume ratio of water in the autoclave is called compactness.In the paper, we report the synthesis of flower-like CuGeO 3 by controlling the compactness using GeO 2 and Cu(CH 3 COO) 2 •H 2 O as the raw materials without using any surfactants.The compactness dependence on the formation of the CuGeO 3 nanostructures has been analyzed and the formation process of the flower-like CuGeO 3 is also discussed.The light blue samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) spectrum.XRD pattern was carried out on a Bruker AXS D8 X-ray diffractometer equipped with a graphite monochromatized Cu-Kα radiation (λ = 1.5406Å).The samples were scanned at a scanning rate of 0.05 • /s in the 2θ range of 20-80 • .SEM observation was performed using JEOL JSM-6490LV SEM with a 15-KV accelerating voltage.FTIR spectroscopy (Perkin Elmer PE, WQF-410 spectrometer) was used at room temperature in the range of 4000-450 cm −1 with a resolution of 4 cm −1 .

III. RESULTS AND DISCUSSIONS
The XRD pattern of the light blue products obtained from 180 • C for 24 h with the compactness of 20 vol.% is shown in Fig. 1.All indexed peaks in the spectrum are well matched with those of the orthorhombic structure CuGeO 3 (JCPDS Card No. 32-0333) which is same to that of the CuGeO 3 nanowires prepared from GeO 2 , copper sheets [20]   spectrum further confirming that the obtained product is pure CuGeO 3 .
The SEM images of the light blue products with different magnification are shown in Fig. 2. From the SEM images, it can be seen that the products exhibit flowerlike morphology.So the products are defined as flower-like CuGeO 3 .The size of each CuGeO 3 nanoflower is about 3 µm (Fig. 2(a)).The magnified SEM image (Fig. 2(b)) shows that the flower-like structures are composed of the accumulation of dozens of CuGeO 3 nanorods.The diameter of the nanorods in the flower-like CuGeO 3 is less than 100 nm and the length is about 1 µm.It is found that the nanorods originate from a single center arranging them in a spherical sharp exhibiting flower-like morphology.The morphology of the flower-like CuGeO 3 from a large amount of nanorods is similar to those of ZnO [25] and MoO 3 [26] flower-like morphology grown by hydrothermal process.
The FTIR spectrum of the flower-like CuGeO 3 obtained from 180 • C for 24 h with the compactness of 20 vol.% is shown in Fig. 3.The absorption bands at 2800-3800 cm −1 with the absorption peaks at 3407.60 cm −1 and 2933.19 cm −1 are the characteristic stretching vibration of hydroxylate (-OH) originating from water.Peaks at 1633.41 cm −1 , 1398.14 cm −1 and 620.97 cm −1 are assigned to the vibration of carboxylate (O-C=O) which is caused by the residue (CH 3 COO) − in the product [27].
The absorption peaks at 710-861 cm −1 are attributed to the vibration mode B 2u and A g fundamental of the GeO 4 group of CuGeO 3 [28].CuGeO 3 consists of basic building blocks of corner-sharing GeO 4 tetrahedra.Cu atoms are surrounded by six O atoms forming strongly deformed CuO 6 octahedra.Therefore, these absorption peaks at 854.31 cm −1 , 815.74 cm −1 and 719.32 cm −1 are attributed to GeO 4 group of CuGeO 3 .The absorption peak at 528.39 cm −1 corresponds to the Cu-O deformed vibration of CuGeO 3 [29].
The roles of the hydrothermal temperature and reaction time with the compactness of 20 vol.% on the formation of the flower-like CuGeO  According to the SEM results synthesized from different reaction time and hydrothermal temperature with the compactness of 20 vol.%, it is suggested that the reaction time and hydrothermal temperature play important Figure 7 shows the FTIR spectra of the products obtained from 180 • C for 24 h with the compactness of 40 vol.%, 60 vol.% and 80 vol.%.The FTIR spectra of the products obtained from different compactness exhibit absorption peaks at about 3421.81 cm −1 , 1633.84 cm −1 , 856.56 cm −1 , 812.32 cm −1 , 723.84 cm −1 , 617.05 cm −1 and 528.57cm −1 .The absorption peaks are very similar to that of the products obtained from the compactness of 20 vol.%.The results show that the CuGeO 3 can be formed from different compactness.
According to the present experiment results, the flowerlike CuGeO 3 is considered to be formed by an assembled growth process.At the initial reaction stage of GeO 2 and Cu(CH 3 COO) forming CuGeO 3 crystals.The nanorods originating from the CuGeO 3 nuclei grow continuously with the increase of the reaction time and hydrothermal temperature.When the compactness of the autoclave is low, such as 20 vol.%, the CuGeO 3 nanorods mainly exist in the bottom of the autoclave with less water owing to the vaporization of water arranging themselves in a flower-like structure by an assembled process.With the increase of the compactness of the autoclave, the CuGeO 3 nanorods mainly exist in water resulting in the formation of the free-standing CuGeO 3 nanowires.

IV. CONCLUSIONS
In summary, flower-like CuGeO 3 with orthorhombic CuGeO 3 nanorods has been achieved by a hydrothermal route by controlling the compactness of 20 vol.%.No surfactants are necessary for the synthesis of the flower-like CuGeO 3 .The diameter of the total flower-like structure is in the micrometer scale size.The diameter and the length of the nanorods in the flower-like CuGeO 3 are less than 100 nm and about 1 µm, respectively.Compactness dependence results demonstrate that the compactness is the key factor for the formation of the flower-like CuGeO 3 which can be explained by an assembled growth process.
FIG. 2: (a) and (b) SEM images of the flower-like CuGeO3 with different magnifications.

FIG. 3 :
FIG. 3: FTIR spectrum of the flower-like CuGeO3 obtained from 180 • C for 24 h with the compactness of 20 vol.%.
FIG. 4: Time dependence on the formation of the flower-like CuGeO3 obtained from 180 • C for different time.(a) and (b) 12 h, (c) and (d) 6 h, (e) and (f) 0.5 h.

Figure 5
is the SEM images of the products obtained from 120 • C and 80 • C for 24 h, respectively showing the similar flower-like morphology.The diameter and length of the nanorods in the flower-like CuGeO 3 in Figs.5(a) and (b) are similar to those synthesized from 180 • C for 24 h.However, the diameter and length of the nanorods in the flower-like CuGeO 3 decrease to about 70 nm and 500 nm, respectively (Figs. 5(c) and (d)) when the hydrothermal temperature decreases to 80 • C.

FIG. 5 :
FIG. 5: Temperature dependence on the formation of the flower-like CuGeO3 obtained from different temperature for 24 h.(a) and (b) 120 • C, (c) and (d) 80 • C.
and GeO 2 , Cu(CH 3 COO) 2 •H 2 O [23] respectively.No other impurity peaks are detected in the 2 •H 2 O. GeO 2 reacts with H 2 O forming H 2 GeO 3 .The reaction between Cu 2+ and H 2 GeO 3 yield CuGeO 3 cores.Therefore, nucleation process exists at the initial reaction stage of GeO 2 and Cu(CH 3 COO) 2 •H 2 O