CuO nanoparticles in mesoporous material by solid state reaction

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 114 (2013) 298–302

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Synthesis of Cu/CuO nanoparticles in mesoporous material by solid state reaction Sh. Sohrabnezhad a,⇑, A. Valipour b a b

Department of Chemistry, Faculty of Science, University of Guilan, P.O. Box 1914, Rasht, Iran Department of Chemistry, Faculty of Science, Payam_Noor University, Ardabil, Iran

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 Incorporation of CuO in MCM-41

material by solid state reaction.  Cu/CuO nanoparticles produced when

Cu2+/MCM-41 calcined at 500 °C.

MCM-41

 Presence of Cu nanoparticles depends

to amount of Cu2+ and calcined temperature.

Cu

CuO

a r t i c l e

i n f o

Article history: Received 30 December 2012 Received in revised form 15 May 2013 Accepted 24 May 2013 Available online 3 June 2013 Keywords: Plasmon resonance Copper clusters Diffuse reflectance spectroscopy Solid state reaction Cu/MCM-41

a b s t r a c t The Mobil Composition of Matter No. 41 (MCM-41) containing 1.0 and 5.0 wt.% of Cu was synthesized under solid state reaction. The calcinations of samples were done at two different temperatures, 500 and 300 °C. X-ray diffraction (XRD), UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM) were used for samples characterization. Powder X-ray diffraction showed that when Cu(CH3COO)2 content is about 1.0 wt.% in Cu/MCM-41, the guest CuO-NPs and copper ions is formed on the silica channel wall, and more exists in the crystalline state. When Cu(CH3COO)2 content exceeds this value (5.0 wt.%), CuO nanoparticles and Cu2+ ions can be observed in low crystalline state. From the diffuse reflectance spectra it was confirmed that 5 wt.% Cu/MCM-41 sample calcined at 500 °C show plasmon resonance band due to Cu nanoparticles in the range between 500 and 600 nm and small copper clusters Cun in 450 nm. It also shows that some of the Cu2+ ions are present octahedrally in extraframework position in all samples. Both fourier transform infrared and diffuse reflectance spectra indicate that some of Cu2+ ions are tetrahedrally within the framework position in 1 wt.% Cu/MCM-41 samples. TEM images indicated that nanoparticles size of CuO is in range of 30–40 nm. Ó 2013 Elsevier B.V. All rights reserved.

Introduction Metal and semiconductor nanoparticles with explicit sizedependence of their physical properties offer great opportunities in the development of new-generation electronic devices.

⇑ Corresponding author. Tel.: +98 131 3233262. E-mail address: [email protected] (Sh. Sohrabnezhad). 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.05.083

Electro- and photostimulated charge-transfer processes in materials with nanoparticles are challenging for the design of ultrafast switching elements based both on effects of electronic excitation in quantum dots and the one-electronics concept in quantum-size areas. The main tasks in the fabrication of devices with nanoparticles are the proper control of size, shape, and position of nanoparticles providing desirable physical properties [1–3]. The main drawbacks are the need for complex filtration procedures and the high turbidity that decreases the radiation flux. Such

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Intensity

Table 1 Effects of Cu content on physicochemical properties of samples. Samples

Cu (wt.%)

Crystalline size (nm)

SBET (m2/g)

MCM-41 1Cu/MCM-41-500 5Cu/MCM-41-500 1Cu/MCM-41-300 5Cu/MCM-41-300

– 1 5 1 5

90 30.9 29.2 32.3 29.4

927 859 870 844 862

(CuO) (CuO) (CuO) (CuO)

88.8 89.5 90.8 91.3

(matrix) (matrix) (matrix) (matrix)

a

2

3

4

6 2θ

5

7

8

9

10

Fig. 1. The XRD pattern of MCM-41.

CuO

Intensity

5Cu/MCM -41300

b

5Cu/MCM -41500

Fig. 3. TEM image of (a) MCM-41 and (b)1Cu/MCM-41-500 samples.

1Cu/MCM -41300

1Cu/MCM -41500

10

16

22

28

34

40

46

2θ θ

52

58

64

70

76 79

Fig. 2. XRD patterns of copper containing MCM-41.

problems have motivated the development of supported photocatalysts in which semiconductors is immobilized on different adsorbent materials. In this contest, molecular sieves have attracted greater attention due to their adsorption capacity that helps in pooling the pollutants to the vicinity of the semiconductors surface [4–6]. Molecular sieves offer excellent control of size distribution and morphology through the main pulsation of the wet chemical processing parameters. Microporous molecular sieves have been widely used for hosting nanoparticles, but they are limited to pore opening of less than 1 nm [7]. The recent discovery of mesoporous

MCM-41 offers a possibility for synthesizing 3D heterostructures in a previously inaccessible size range, by inclusion chemistry [8]. In the present study, the solid state approaches for synthesis of copper nanoparticles are considered and are in progress for ultrafine semiconductors in MCM-41 mesoporous material in different concentration of copper. Because of their high surface areas, regular pore channels, and large pore diameters (2–20 nm), ordered MCM-41 mesoporous material has been used as suitable scaffolds for the dispersion of small metal and semiconductor nanoparticles [9]. Nanoparticles in high concentrations of copper are incorporated in the crystalline MCM-41 mesopore matrices stabilizing both the few-atomic clusters (Cun) and Cu/CuO nanoparticles in the range 30–40 nm. Nanoparticles provide an optical response of the material due to the plasmon resonance band with variable spectral position and shape [10,11]. Chemical routes of nanoparticle synthesis admit easy control of their size and consequently their optical properties. The nanoparticles in mesoporous matrix can be transformed into semiconductors without destruction of the mesoporous material, or semiconductor nanoparticles can be directly synthesized in matrices [12,13]. Experimental Synthesis of MCM-41 material The MCM-41 material was synthesized by a room temperature method with some modification in the described procedure in

300

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the literature [14]. We used tetraethylorthosilicate (TEOS: Merck,800658) as a source of silicon and hexadecyltrimethylammonium bromide (HDTMABr;BOH,103912) as a surfactant template for preparation of the mesoporous material. The molar composition of the reactant mixture is as follows:

SiO2 : 1:6EA : 0:215HDTMABr : 325H2 O where the EA stands for ethylamine. The MCM-41 prepared was calcined at 550 °C for 5 h to decompose the surfactant to obtained white powder. MCM-41 surfactant-free was used for loading the nanoparticles. Preparation of Cu/MCM-41 The copper-containing catalysts (1.0 and 5.0 wt.% copper loading) were prepared by solid state reaction of 1 g of MCM-41 with amount 0.038 and 0.0228 g of Cu(CH3COO)2. After mixing, the solid phase samples were calcined in airflow at 300 and 500 °C for 5 h. The prepared samples are termed as xCu//MCM-41-t(x is 1.0 and 5.0 wt.% and t is 300 and 500 °C).

Powder X-ray diffraction patterns of the samples were recorded using an X-ray diffractometer (Bruker D8 Advance) with Co Ka radiation (k = 1.789 A°) under the conditions of 40 kV and 30 mA, at a step size of 2h = 0.02°. The UV–Vis diffused reflectance spectra (UV–Vis DRS) obtained from UV–Vis Scinco 4100 spectrometer with an integrating sphere reflectance accessory. BaSO4 was used as reference material UV–Vis absorption spectra were recorded using a Shimadzu 1600 PC in the spectral range of 190–900 nm. The infrared spectra on KBr pellet were measured on a Bruek spectrophotometer. The transmission electron micrographys (TEM) were recorded with a Philips CM10 microscope, working at a 100 kV accelerating voltage. Samples for TEM were prepared by dispersing the powdered sample in acetone by sonication and then drip drying on a copper grid coated with carbon film.

Results and discussion Phase structures and morphology The low angle X-ray powder diffraction patterns of the prepared matrix are presented in Fig. 1. The XRD pattern of MCM-41 shows typical characteristic three-peak pattern with a very strong one at a low 2h and two peaks at higher 2h values [15,16]. No peak is observed between 2h = 10° and 80° for matrix (not shown) [15]. Fig. 2 shows the XRD results obtained in wide-angle region for xCu/MCM-41 samples calcined at 300 and 500 °C (x is 1.0 and 5.0 wt.%). In Fig. 2, a broad peak and a sharp diffraction line

5Cu/MCM -41 300

Absorbance (Au)

5Cu/MCM -41 500

Absorbance (AU)

Characterization

1Cu/MCM -41 300

5Cu/MCM-41 500

500

600

700

800

Wavelenght (nm)

Absorbance (Au)

1Cu/MCM -41 500

MCM -41

300

400

500

600

700

800

Wavelength (nm) Fig. 4. The UV–Vis diffuse reflectance spectra of MCM-41 matrix and xCu/MCM41-t samples.

5Cu/MCM-41 300

500

600

700

800

Wavelenght (nm) Fig. 5. The UV–Vis diffuse reflectance spectra of xCu/MCM-41-t samples in range of 450–800 nm.

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centered at about 23° and 29° originates from the diffraction of the amorphous framework of MCM-41 [17] and amorphous silica [18], respectively. There is characteristic diffraction peaks of CuO and Cu2+-ion exchange MCM-41 mesopore in all samples. But, strong diffraction peak of CuO and Cu2+ ions is observed for 1Cu/MCM-41500 sample with respect to other copper samples [19–21]. In fact, intensity in 1Cu/MCM-41 samples is higher than 5Cu/MCM-41 samples (not show). Probably, in high content of copper, Cu is present in nanocomposite in the forms of CuO and Cu nanoparticles. The average crystallite sizes of matrix and CuO calculates by scherrer’s equation are listed in Table 1. All the Cu/MCM-41 samples have almost the same crystallite sizes (ca. 30 nm for CuO and 90 nm for MCM-41 matrix), implying that the deposition of CuO clusters on the MCM-41 surface has no obvious influence on the crystallite size. TEM was further used to study the morphology and microstructures of the Cu/MCM-41 samples. Fig. 3 shows a typical TEM image (1Cu/MCM-41-500). As can be seen from this image Cu/MCM-41 consists of a large number of crystalline nanoparticles of about 25–85 nm in size. The large crystallites belong to MCM-41 matrix and small crystallites correspond to CuO nanoparticles according to the XRD data shows in Fig. 2. UV–Vis diffuse reflectance spectra The UV–Vis diffuse reflectance spectra of MCM-41 matrix and xCu/MCM-41-t samples are shown in Fig. 4. Synthesized MCM-41 shows an intense peak located at 320 and 380 nm. These bands are attributed to a charge transfer transition of framework tetrahedral atoms [15]. The Cu2+ ions have a 3d9 electronic structure. In the presence of a crystal field generated by ligands or oxygen ions, d–d transitions appear in the visible or near-IR range. The band at

301

380 nm is due to O2 ! Cu2þ ligand to metal charge transfer transition where the copper ions occupy isolated sites over the support. [17]. In Fig. 4, intensity of peaks decreases in Cu-containing MCM41 samples at 320 and 380 nm. This decrease is attributed to presences of copper in mesoporous matter and O2 ! Cu2þ ligand to metal charge transfer transition. The 5Cu/MCM-41-500 sample shows three broad bands at about 450–500, 500–600 and 600–720 nm (Fig. 5). These bands are due to atomic copper cluster, Plasmon resonance band and octahedral Cu2+ ions in MCM-41 matrix, respectively [22,23]. At 5Cu/MCM-41-300 sample that temperature is low, peaks due to atomic copper cluster and Plasmon resonance disappeared. This fact confirms that when amount of copper species in matrix is low, probably they are present in MCM-41 material in form of CuO. FT-IR spectra The FT-IR spectra nanoparticles of MCM-41 and Cu/MCM-41 samples are shown in Fig. 6. The 1Cu/MCM-41500 shows a band at 956 cm1 which attributed to Cu2+ ions incorporated into framework of MCM-41 material. This band is mainly assigned to the Si-OH vibrations, but when metals are incorporated, the intensity of the band increases. This is generally considered to be a proof of the incorporation of heteroatom into the framework. Parida and Rath have reported similar results [15] using other metal ion-impregnated MCM-41. Because of the copper ions in MCM-41 matrix undergoes oxidation at elevated temperature and copper oxide is generated. The presence of a specific bands at 2929, 2860 and 1423 cm1, suggests the existence of CuO nanoparticles in the MCM-41 structure [20]. The spectra show a broad band around 3410–3450 cm1, which is due to adsorbed water molecules by samples. Conclusions

462.88

804.26

%T

1423.37 1369.37

3446.56

2929.67 2860.24

1703.03 1641.31

75

5Cu/MCM-41 500 1085

0 3760

2250

cm-1

1500

750

541.96 466.74

802.33

1369.37

1Cu/MCM-41 500 1087

0

956.63

3444.63

%T

1699.17 1635.52

2929.67 2860.24

75

750

543.89

References

453.24

1512.09

1500

808.12

3417.63

75 MCM-41

1074

%T

cm-1

1704.96 1645.17

2250

1369.37

3760

0 3760

2250

1500

In this work, XRD studies reveal that the modified samples retain the mesoporosity. Also, XRD results support the presence of crystalline CuO at low copper loadings (1 wt.%). There is no appreciable change in pore diameter and unit cell parameter in Cu/MCM-41. CoS and NiS nanoparticles are prepared in AlMCM-41 by ion exchange method. Neutron radiation interacts with target nuclei without any restriction. Neutron radiation directly interacts with nuclei and releases free-radicals. Released radical’s causes to accomplish chemical bindings between particles and so, increases and decreases aggregation in remainder CoS and NiS nanoparticles, respectively. In facts, irradiation with neutron at room temperature formed simple RDs in nanocomposite semiconductors incorporated in AlMCM-41. Change in optical properties cannot be related to degradation of host material based on spectra images and hosting material has important role in causing simple radiation defect by semiconductor neutron interaction.

750

cm-1 Fig. 6. The FT-IR spectra nanoparticles of MCM-41 and Cu/MCM-41 samples.

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