Accepted Manuscript Original article A green synthesis of copper nanoparticles using native cyclodextrins as stabilizing agents Javier Suárez-Cerda, Heriberto Espinoza-Gómez, Gabriel Alonso-Nú ñez, Ignacio A. Rivero, Yadira Gochi-Ponce, Lucía Z. Flores-López PII: DOI: Reference:
S1319-6103(16)30104-1 http://dx.doi.org/10.1016/j.jscs.2016.10.005 JSCS 842
To appear in:
Journal of Saudi Chemical Society
Received Date: Revised Date: Accepted Date:
5 August 2016 14 October 2016 27 October 2016
Please cite this article as: J. Suárez-Cerda, H. Espinoza-Gómez, G. Alonso-Nú ñez, I.A. Rivero, Y. Gochi-Ponce, L.Z. Flores-López, A green synthesis of copper nanoparticles using native cyclodextrins as stabilizing agents, Journal of Saudi Chemical Society (2016), doi: http://dx.doi.org/10.1016/j.jscs.2016.10.005
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A green synthesis of copper nanoparticles using native cyclodextrins as stabilizing agents
Javier Suárez-Cerdaa, Heriberto Espinoza-Gómezb, Gabriel Alonso-Núñezc, Ignacio A. Riveroa, Yadira Gochi-Poncea, Lucía Z. Flores-Lópeza,⁎
a
Centro de Graduados e Investigación en Química, Instituto Tecnológico de Tijuana, Blvd.
Alberto Limón Padilla S/N, Tijuana, B. C., México. lzflores@hotmail. b
Facultad de Ciencias Químicas e Ingeniería, Universidad Autónoma de Baja California, Calzada
Universidad 14418 Parque Industrial Internacional, C.P. 22390 Tijuana, B.C., Mexico.
[email protected] c
Centro de Nanociencia y Nanotecnología de la Universidad Nacional Autónoma de México, Km.
107 Carretera Tijuana-Ensenada, C.P. 22860 Ensenada, B. C., México
a
Centro de Graduados e Investigación en Química, Instituto Tecnológico de Tijuana, Blvd.
Alberto Limón Padilla S/N, Tijuana, B. C., México. lzflores@hotmail. b
Facultad de Ciencias Químicas e Ingeniería, Universidad Autónoma de Baja California, Calzada
Universidad 14418 Parque Industrial Internacional, C.P. 22390 Tijuana, B.C., Mexico.
[email protected] c
Centro de Nanociencia y Nanotecnología de la Universidad Nacional Autónoma de México, Km.
107 Carretera Tijuana-Ensenada, C.P. 22860 Ensenada, B. C., México
1
Chemical compounds studied on this article Copper (II) Sulfate Pentahydrate (CuSO4.5H2O, PubChem CID: 24463) α-NCD (C36H60O30, PubChem CID: 444913) β-NCD (C42H70O35, PubChem CID: 444041) γ-NCD (C48H80O40, PubChem CID: 86575) Ascorbic Acid (C6H8O6, PubChem CID: 54670067) keywords: Copper-nanoparticles, Green chemistry method, cyclodextrins as stabilizing agents. Abstract In this work, a comparative study of the effect of the NCDs size as a stabilizing agent, on the synthesis of copper nanoparticles (Cu-NPs) by an easy green method were reported. The nanoparticles were synthesized through the chemical reduction of aqueous solutions of copper (II) sulfate with ascorbic acid, using different native cyclodextrins (NCDs) (α-, β-, or γ-NCD) as stabilizing agents. Cu-NPs were characterized by scanning electron microscopy–energy dispersive spectroscopy (SEM–EDX), powder X-Ray diffraction (XRD) and transmission electron microscopy (TEM). The pattern showed in the typical selected area electron diffraction (SAED) and lattice fringes, evidence that the crystalline structure of Cu-NPs is face-centered cubic (FCC) with a (111), (200) and (220) lattice planes of Cu. The analysis of the TEM images show that the size of the Cu-NPs depends on the type of native cyclodextrin (NCD), also it was observed that the nanoparticles are spherical and with a size between ~2 to 33 nm. The smaller Cu-NPs were obtained with α-NCD (mode 4 nm), while the nanoparticles obtained with β-NCD 2
show the narrow size distribution (mode 6.5 nm). The average particle size and particle size distribution of Cu-NPs depends upon the type of CDs.
1. Introduction Nanomaterials have unique properties that distinguish them from the corresponding bulk materials. The shape and size of metal nanoparticles influence their optical, catalytic and conductive properties. [1] Copper nanoparticles (Cu-NPs) have special properties, which have made them important for various applications; for example, super strong materials, antibacterial, sensors and catalysts. Furthermore, they can also interact and react with other nanoparticles due to the high surface area-volume ratio. Recently, it has been reported that Cu-NPs possess superior antibacterial activity than Ag-NPs, for E. coli and B. subtilis.[2,3] Cu-NPs can be synthesized by various methods, for example metal vapor synthesis [4], exploding wire method [5,6], vacuum vapor deposition [7], sonochemical reduction [8], thermal reduction [9], chemical reduction [10-13], biosynthesis [14,15], laser irradiation [16], and microemulsion techniques [17,18]. Of all the above mentioned methods, chemical reduction is the most popular for the synthesis of Cu-NPs. The chemical reduction method has some advantages; it is simple, inexpensive and presents an easy control of geometrical nanoparticles characteristics, like size and shape. However, the disadvantage of this method is that it can affect the environment, due to the use and disposal of toxic solvents and hazardous chemical reducing agents. Some examples of these toxic chemical reductants are sodium borohydride [19,20], hydrazinium hydroxide [21], sodium hypophosphite [22], amines [23], diethylenetriamine [24], or polyols (e.g., ethylene glycol)
3
[25,26]; which they can be "caught" on the surface of Cu-NPs increasing nanoparticles toxicity. [27] Therefore, green chemistry synthesis of Cu-NPs is an alternative method for its preparation, due to some advantages that present: it is eco-friendly, environmentally benign and non-toxic solvents are used. [28-30] Native cyclodextrins (NCDs) have a large number of primary and secondary hydroxyl groups, which can be used as coordination sites for metal chelation, forming covalent bonds at basic pH. Due to those groups, NCDs are water-soluble molecules. These cyclic oligosaccharides possess a non-toxic nature, so they have applications in the pharmaceutical, food, and cosmetic industry, as well as in analytical separations. [31-35] The aim of this study is to determine the effect of the NCDs size used as stabilizing agent, in the characteristics of Cu-NPs synthesized (shape and size) by a green chemistry method, in order to determine which one is the best stabilizing agent. This work is part of a responsible green approach for the development of nanotechnology.
2. Methodology 2.1. Materials and methods CuSO4.5H2O and α(C36H60O30, 972.84 g/mol) ≥ 98%, β(C42H70O35, 1,134.98 g/mol) ≥ 97% and γ (C48H80O40, 1297.12 g/mol) ≥ 98% -NCDs were supplied by Sigma Aldrich. The other reagents used in this work are laboratory grade. The solutions were prepared with distilled water. All glassware was thoroughly washed and rinsed with distilled water, then dried in an oven before use and thus avoid potential contamination.
2.2. Preparation of Cu nanoparticles (Cu-NPs) 4
Initially, separately aqueous solutions of CuSO4.5H2O (0.3975 g/25 mL H2O), ascorbic acid (1.09 g/25 mL H2O) and native cyclodextrin (NCD) (0.25 g/25 mL H2O) were prepared; whereas each NCD was handled separately. The copper aqueous solution was poured in a round bottom flask, and heated at 80oC. Later, it was added drop wise the mixture aqueous solutions of ascorbic acid and NCD, to the metallic solution with magnetic vigorous agitation (700 rpm). The color of the solution changed, from blue light to green light, and finally to a dark yellow; after 5 min began the formation of a brown precipitate. The reaction conditions were maintained for 5 hours and then cooled to room temperature. After that, the solution with the brown precipitate was centrifuged for 10 min at 4000 rpm. The precipitate was washed two times with distilled water (5 mL) and once with ethanol anhydrous (5 mL), to remove any unreacted reagent. Finally, the brown powder was dried at room temperature to obtain the Cu-NPs. Cu-NPs are very sensible to oxidation and tend to form copper oxide nanoparticles. However, the formation of the Cu-NPs was achieved due the reducing and stabilizing properties of ascorbic acid and NCDs, respectively. The formations of Cu-NPs were corroborated by ATR-FTIR, SEM-EDX, XRD and TEM analyses.
2.3 Characterization of Cu-NPs The interaction between NCD and synthesized Cu-NPs was studied using a PerkinElmer Spectrum 400 FT-IR/FT-NIR Spectrometer with Universal ATR Sampling Accessory. The presence of elemental copper was determined by using a VEGA 3 Tescan scanning microscope equipped with EDX capability. The structural characterization using XRD of Cu-NPs were studied using a Philips X´pertMPD. The morphology and size of the as-synthesized Cu-NPs were characterized by transmission electron microscopy (TEM, JEM-2100F, JEOL), at an accelerating voltage of 200 kV and fitted with a CCD camera. 5
3. Results and Discussion The methodology for synthesizing Cu-NPs, using NCDs as stabilizing agent in water, is very simple. However, no reports have been found in the literature concerning to the study of the effect of the NCDs size, as a stabilizing agent, on the colloidal synthesis of Cu-NPs at room temperature by a green chemistry method. In Scheme 1 the proposed mechanism of nanoparticles formation is shown, which considers that the characteristics of the stabilizing agent used influence, the size and shape of the nanoparticles. Copper (II) sulphate dissolved in water, dissociates into Cu2+ and SO42-. Cu2+ is reduced to Cu0 by reduction action of ascorbic acid, forming metallic copper nuclei, which initiate the growth stage. Growing nanoparticles are stabilized by several molecules of cyclodextrins distributed around them (Cu-NPs-NCD). These agglomerates grow to a certain size and, due to the difference in water solubility of NCDs, eventually precipitated. Finally, the NCDs present in the precipitate are removed during washings with water, resulting in pure powder Cu-NPs. Development of Cu-NPs synthesis reaction can be seen in Figure 1. It was observed a color change of the solution from blue to brownish yellow, with the formation of a brown powder; showing the formation of Cu-NPs. 3.1 FTIR-ATR Cu-NPs characterization. Typical FT-IR absorption spectra of β-NCD and Cu-NPs are presented in Figs. 2 a-d, respectively. Characteristic absorption bands at 3297, 2926, 1646, 1416, 1152 and 1020 cm-1 (Fig. 2a) are observed in the FT-IR spectra for the β-NCD. The band at 3297 cm-1 is attributed to the O-H stretching vibration, due to the primary and secondary alcohols present in the NCD. The bands at 1152 and 1020 cm-1, can be assigned to the C-O and CH2-O bending or stretching 6
vibrations respectively, due to the ethers groups and alcohols groups present also in the NCD. So the Cu-NPs spectrums does not present that bands, because the nanoparticles are in a pure form, without capping with the NCD. This can also be seen in the TEM images of the Cu-NPs, in which a shell around the Cu-NPs is not presented. 3.2. SEM-EDX studies The presences of Cu-NPs were confirmed by SEM–EDX analyses. The NCD-Cu-NPs obtained, seems to exhibit a cubic and hexagonal agglomerates morphology. The EDX analysis show a signal corresponding to a significant presence of copper (Fig. 3), without oxygen; indicating that metallic Cu-NPs were obtained.
3.3 XRD studies X-ray diffraction (XRD) is one of the most important and easy tools to determine the crystallite characteristics for any compound. XRD analyses of brown powders prepared by using NCDs as stabilizing agent, confirmed that the final product is metallic. Figure 4 (a-c) shows XRD patterns of the Cu-NPs obtained, which are very similar to those reported in JCPDS Copper: 04-0836 (43.6, 50.8, 74.4). Table 1 summarized the XRD analyses results. d-spacing (the interplanar spacing between the atoms) was calculated using the Bragg´s law (Eq. 1), while the DebyeScherrer was used to determine the average crystallite size. (Eq. 2) Eq.1 where λ=0.15418 nm for Cu Ka, d is the interplanar spacing between atoms, and n is an integer (in this particular case n=1). Eq. 2
7
where K is a numerical constant factor (0.89), λ=0.15418 nm for Cu Ka, FWHM is the full width at half maximum,
is the diffraction angle, and D is the mean crystallite size. The lattice
parameter (a, nm) was calculated by (Eq. 3)
Eq. 3 The result of XRD analysis confirms that the structure of the synthesized Cu-NPs is face centered cubic (FCC) with the space group of Fm3m and a = 0.3620 nm. [36,37] 3.4 TEM studies The analyses of the TEM images are a useful tool for measuring the size and shape of the synthesized nanoparticles. Figure 5 shows typical TEM images of Cu-NPs, their appearance is spherical in shape without any shell around them, and also have a broad size distribution. The Cu-NPs size for α-NCD is between 2-27 nm, with a mode on 4 nm (7.34%); whereas β-NCD sizes are obtained between 2-23 nm, with a 6.5 nm (10%) mode. On another hand, Cu-NPs prepared with γ-NCD show sizes between 5-33 nm, with a mode of 18 nm (8.86%). The NCDs prevent the Cu-NPs grow into large aggregates and, at the same time, it can be seen that the NCDs affect the sizes of Cu-NPs. Therefore, the size of the Cu-NPs is directly proportional to the size of the NCDs. After analyzing the TEM histograms, we find that β-NCD is the best stabilizing agent, since the synthesized particles with it, has a narrow size distribution. This is because the β-NCD has a rather rigid structure, due to the intramolecular hydrogen bonds between C2-OH groups and C3OH groups of adjacent glucose units. These hydrogen bonds stabilize the β-NCD, and are probably the reason for its lowest water solubility compared to other NCDs [38,39]. Therefore,
8
the β-NCD rigid structure and its low water solubility causes those Cu-NPs reach a determined size and precipitate easily, to finally regulate the growth of nanoparticles. These results are in agreement with those previously reported, related to the comparative study of the effect of NCDs as stabilizing agents, in the green synthesis of Ag-NPs. [40] Nanoparticles synthesized by this method are small and have a narrow size distribution than in previous reports. [41-43] TEM images in Fig 6a show the discernible (111) planes for FCC crystalline structure of Cu-NPs (with β-NCD); which are consistent with the SAED pattern analysis (Fig 6b), and XRD results previously discussed (Table 1).
4. Conclusions The effect of NCDs type on the green synthesis of Cu-NPs, are reported on this paper; through a simple, safe, and green chemical reduction method. The nanoparticles synthesized by this method, proved to be stable for several months without physical or chemical changes. SEM-EDX and XRD analysis demonstrates the presence of a significant copper content without oxygen, indicating that the synthesized nanoparticles were metallic copper, without trace of copper oxide nanoparticles. The crystallographic structure of the synthesized Cu-NPs was confirmed by XRD, TEM and SAED pattern, proving to be FCC. TEM analyses show that the Cu-NPs obtained are between 2 nm and 33 nm (-NCD 2-23 nm; βNCD 2-23 nm; -NCD 5-33 nm) in size. The sizes of the nanoparticles were as follows: Cu-NPs (-NCD) < Cu-NPs (β-NCD) < Cu-NPs (-NCD), the smaller Cu-NPs were obtained with -
9
NCD. Therefore, we conclude that the Cu-NPs size is directly proportional to the size of the NCDs. On the other hand, the β-NCD is the best stabilizing agent, because the particles synthesized with it, have a smallest size distribution. This is due to the rigid structure and low water solubility of β-NCD, causing their complex precipitate easily; thereby regulating the growth of nanoparticles. In conclusion, the nanoparticle size and size distribution depends on the NCD used as stabilizing agent.
Acknowledgments
We gratefully acknowledge to F. Ruiz for his technical assistance, also we thank to Emigdio Z. Flores López by improvement of the English grammar. This study was funded in part by Dirección General de Educación Superior Tecnológica (DGEST, Grant 5872.16-P) and Consejo Nacional de Ciencia y Tecnología (CONACYT, Grant 174689, CEMIE-Sol-P28 and PAPIIT IN104714). Acknowledgement to CONACyT (259931) and DGAPA-UNAM by sabbatical support (Gabriel Alonso Nuñez).
Conflict of interest: The authors declare no conflict of interest.
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14
CD type
-NCD
β-NCD
-NCD
peak
2
FWHM
hkl
d-spacing
D
a
(degrees)
(planes)
(nm)
(nm)
(nm)
P1
43.09
0.2363
111
0.2099
35.77
0.3636
P2
50.23
0.2849
200
0.1816
30.28
0.3632
P3
73.93
0.3894
220
0.1282
25.27
0.3626
P1
43.32
0.1919
111
0.2089
44.09
0.3619
P2
50.44
0.2484
200
0.1809
34.98
0.3618
P3
74.12
0.2229
220
0.1279
44.2
0.3618
P1
43.28
0.2024
111
0.2090
41.78
0.3620
P2
50.42
0.2782
200
0.1810
31.24
0.3620
P3
74.06
0.3385
220
0.1280
29.09
0.3620
Table 1. XRD analyses of the obtained Cu-NPs.
15
Scheme. 1
16
Captions Scheme Scheme. 1 General reaction for the synthesis and stabilization of Cu-NPs with NCDs.
17
Figure 1
18
Figure 2.
19
Figure 3
20
3500
(a)
3500
111
(b)
3000
3000
(c)
3500
3000
111
111
2500
2500
2500
2000
2000
2000
1500
1500
200
1500
200
200 220
1000
1000
1000
220
220 500
500
500
0
0 30
40
50
60
2 theta
70
80
0 30
40
50
60
2 theta
Figure 43 Figure
21
70
80
30
40
50
60
2 theta
70
80
Figure 5 22
0.21 nm (111)
2
n
m 5
1
/
n
m
Figure 6
23
List of figure captions
Fig. 1. Color development of the synthesis reaction of Cu-NPs formation
Fig. 2. ATR-FTIR spectra of (a) β-NCD, and Cu-NPs synthesized with (b) α-NCD, (c) β-NCD, and (d) γ-NCD.
Fig 3. SEM-EDX analysis of synthesized Cu-NPs. (a) -NCD-Cu-NPs, (b) -NCD-Cu-NPs, (c) -NCD-Cu-NPs agglomerates.
Fig. 4. XRD of Cu-NPs synthesized with (a) -NCD, (b) β-NCD, (c) -NCD.
Fig. 5. Histograms and TEM images of Cu-NPs with different NCDs.
Fig. 6. Crystal analysis of Cu-NPs (a) crystal lattice fringes, (b) SAED pattern
24
