Journal of Alloys and Compounds 647 (2015) 392e396
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Nanoparticles green synthesis by Hibiscus Sabdariffa flower extract: Main physical properties N. Thovhogi a, b, A. Diallo a, b, A. Gurib-Fakim a, b, M. Maaza a, b, * a
UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk Ridge, PO BOX 392, Pretoria, South Africa b Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure Road, Somerset West 7129, PO BOX 722, Western Cape, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 May 2015 Accepted 9 June 2015 Available online 24 June 2015
This contribution reports on the synthesis and the main physical properties of CeO2 nanoparticles (which can be as small as 〈fCeO2〉 ~ 3.9 nm in diameter) engineered for the first time by a completely green process using Hibiscus Sabdariffa natural extract as an effective chelating agent. Their morphological, structural and optical properties were investigated using various complementary surface/interface characterization techniques. © 2015 Elsevier B.V. All rights reserved.
Keywords: Green synthesis Nanomaterials Ceria Nanoparticles Hibiscus Sabdariffa Natural extract
1. Introduction Cerium oxide or Ceria “CeO2” is a semiconductor oxide with a wide band gap ranging between 3.0 and 3.2 eV and a UV cut-off wavelength at around 370 nm. In its bulk form, it is a singular rare earth oxide as it does not show any known crystallographic change from room temperature up to its melting point of 2700 C [1e4]. It is used in a wide range of applications such as, catalyst, sensor, solid oxide fuel cells, sun-screen cosmetics, O2 storage capacity, and CO2 solar conversion applications due to their unique ability to switch oxidation states [5e8]. Likewise, Ceria nanoparticles (NPs) have emerged as a promising system in biomedical and cosmetics [9e11]. In these later fields specifically, Das et al. reported on the use of nano-scaled CeO2 as antioxidants in biological systems [12], while Estevez et al. reported on the potential use of CeO2 NPs for neurodegenerative disease therapy [13]. Likewise, Pesic et al. reported on anti-cancer effects of CeO2 NPs on specific human cancer cells and their intracellular redox activity [14e16]. Up to now, several
* Corresponding author. Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure Road, Somerset West 7129, PO BOX 722, Western Cape, South Africa. E-mail addresses:
[email protected],
[email protected] (M. Maaza). http://dx.doi.org/10.1016/j.jallcom.2015.06.076 0925-8388/© 2015 Elsevier B.V. All rights reserved.
physical and chemical methodologies were used for the synthesis of CeO2 NPs with various shape and size distributions. However, most of these techniques are complex, and/or require either vacuum conditions or generate harmful waste based precursors [7e10]. Within the rising green synthesis trends, methodologies for synthesis of biocompatible and harmless CeO2 NPs using natural extracts are being explored [6]. This approach has the merit of a minimum of waste if not zero-waste byproduct, no usage of harmful reduction/oxidizing agents, neither standard acid/base compounds nor elevated temperatures [17e23]. For the best of our knowledge, Arumugam, et al. are the only ones who reported on green synthesis of CeO2 NPs using Gloriosa superba L. leaf extract [10]. This contribution reports on the synthesis and the main physical properties of nano-scaled pure CeO2 particles engineered for the 1st time by an entirely green chemistry process using Hibiscus Sabdariffa's flower extract as an effective chelating agent without addition of any acid or base standard components. 2. Experiments & results 2.1. Biosynthesis process via Hibiscus Sabdariffa's flower aqueous extract Hibiscus Sabdariffa (H Sabdariffa) is a shrub belonging to the family Malvaceae with red flowers in a form of calyces. Although
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the composition of this plant has been thoroughly studied [24], one notable but underreported group of compounds present in this plant is phenolic compounds. The phenolic compounds found in this plant include organic and phenolic acids, such as citric acid, hydroxycitric acid and hibiscus acid. Flavonoids such as quercetin, luteolin or gossipetin, and their respective glycosides are also present. Anthocyanins, detected in high amounts in the calyces, are responsible for their bright red color. The most frequent anthocyanins of Hibiscus Sabdariffa flower are cyanidin-3-glucoside, delphinidin-3-glucoside, cyanidin-3-sambubioside, and delphinidin3-sambubioside [25e30]. Its major bioactive components are indicated in Fig. 1. Fresh flowers of H Sabdariffa flowers were air dried under shade at room temperature. The identity of the plant was confirmed by the taxonomy expert in the Herbarium of the Department of Life Science at the University of the Western Cape, South Africa. The dried red flowers were then washed thoroughly to remove dust. For the extraction of the natural dye, all used chemical reagents were purchased either from SigmaeAldrich or Merck. They were of analytical grade, hence used without further purification. In a typical procedure, 10.0 g of clean H Sabdariffa flowers were weighed in a beaker and added to 400 ml of distilled water. The solution was kept at room temperature for ~2 h. The obtained red solution was filtered twice using Whatman filters to eliminate any residual solids. 2.0 g of Ce(NO3)3 6H2O was added in 100 ml of the red H
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Sabdariffa flower water extract solution. The solution was mixed homogeneously and heated for ~2 h. A solid precipitate was observed upon cooling to room temperature. This precipitate is presumably CeOX and Ce(OH)X mixture. The solid deposit was purified by repeated centrifugation at ~10000 rpm for 10 min. It was then dried in oven set at ~100 C and thereafter annealed at ~500 C for 2 h using a high temperature tubular furnace. The samples were then characterized using High Resolution Electron Microscopy (HRTEM), Scanning Electron Microscopy (SEM), Electron Dispersive X-rays Spectroscopy (EDS), X-Rays Diffraction (XRD), Infrared (ATRFTIR), Raman, and X-Rays Photoelectron Spectroscopy (XPS). 2.2. Surface morphology & elemental analysis Fig. 2 reports a characteristic HRTEM micrograph obtained on the centrifuged filtered CeOx powder and dried in a standard oven at ~100 C. The HRTEM was carried using a FEI Tecnai G2 Field Emission Gun HRTEM operating at 200 kV. From this, it can be established that the particles are nano-scaled with a mixed population of amorphous and crystalline particles yet with a nonnegligible degree of polydispersity in size. The particle size distribution analysis carried out using Image J software while approximating the NPs as spheres showed an average particle size of 〈f〉 ~3.9 nm (Fig. 2a). The zoom of Fig. 2b shows a typical ordered atomic reticular planes in a typical crystalline NP. The atomic
Fig. 1. Structure of the major bioactive molecular compounds within the Aspalathus Linearis natural extract.
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Advanced D8 diffractometer with monochromated Cu Ka radiation of wavelength 1.5406 Å operating at a current of 40 mA and a voltage of 40 kV in the Bragg-Brentano geometry. Fig. 4 shows the typical XRD profile obtained on the centrifuged filtered CeOx powder and dried in a standard oven at ~100 C in the 2Q angular range of 20e70 Deg. The presence of several broad Bragg peaks centered at 28.55, 47.47, 56.33, 69.40, 79.07 Deg corresponds to the (111), (200), (220), (311), (222), (400), (331) and (420) reticular orientations (Table 1). More precisely, all Bragg peaks are assigned to the face centered cubic phase of CeO2 (JCPDS 34e0394) with a lattice constant 〈aCeO2〉 ¼ 5.412 Å. This later crystallographic phase consists of a cubic fluorite-type oxide in which each Cerium site is surrounded by 8 Oxygen sites in an fcc arrangement while each Oxygen site has a tetrahedron Cerium site. From the broadening of the Bragg peaks and using the Debye-Scherrer approximation, the average size of the NPs 〈fNPs〉 ranges within 2.21 and 4.68 nm (Table 1) in agreement with the previous HRTEM observations of Section 2.2. In addition, and based on Table 1, the value of Ddexp/dbulk ¼ (dbulk e dexp)/dbulk fluctuates between 1.09 and þ0.73% which indicates that the CeO2 NPs are subjected to compressive or elongation strain/stress depending on the crystallographic directions. Fig. 2. HRTEM of the Cerium oxide NPs (Dried in a standard oven at ~100 C).
double periodicity within the scale shown in yellow in Fig. 2b is of the order of ~10.86 Å corresponding to a lattice periodicity of 〈dhkl〉 ~5.42 Å quasi-similar (within the bar error) to the value of the crystal lattice parameters of the face centered cubic CeO2: 〈abulk〉 ¼ 5.41134 Å. Fig. 3 reports a typical EDS elemental analysis using an Oxford instruments X-Max solid state Silicon drift detector (20 keV). As one can notice, excluding the carbon from the Carbon coated grid, Gold and Palladium which were coated on the samples for conductivity and charge effects minimization, they are no other elements observed except Cerium (Several peaks in relation to the f-electrons nature of Ce) and Oxygen in addition to Potassium and Calcium. These later ones, i.e. K and Ca can originate only from the natural extract's organic compounds. Following an optimization phase, it was found that an additional annealing at ~500 C for 2 h decomposes any Ca or K based compounds.
2.4. Chemical bonding & vibration spectroscopy To validate once more the nature of the synthesized CeO2 NPs, Attenuated Total Reflection-Flourier Transform InfRared Spectroscopy (ATR-FTIR) studies were performed. As the ATR-FTIR spectra of the centrifuged filtered CeO2 nano-powder dried in a standard oven at ~100 C exhibited a low CeeO signature within the range of 300e800 cm1, it was annealed at ~500 C for 2 h using a high temperature tubular furnace. Fig. 5 reports a corresponding ATRFTIR spectrum of the pressed powder in the wavenumber range of 300e4000 cm1. Two strong intense absorption bands at 3415 and 483.8 cm1 were observed. The band at 3415 cm1 corresponds to the standard OH modes of (H- bonded) water molecules. The characteristic band corresponding to the CeeO stretching mode is observed at 483.8 cm1. More precisely, this mode observed by Chadar et al. and Darroudi et al. [6,7], corresponds to the specific so called n CeeO mode [6,7]. In view of the relative intensity of the
2.3. Crystallographic structure To identify the crystallographic phase of the likely CeO2 NPs, room temperature XRD analysis was carried out using a Bruker
Fig. 3. Typical EDS spectrum of the Cerium oxide NPs (Dried in a standard oven at ~100 C).
Fig. 4. Typical room temperature X-rays diffraction of the Cerium oxide NPs (Dried in a standard oven at ~100 C).
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Table 1 Main characteristics of the XRD Bragg peaks of the CeO2 dried powder in a standard oven at ~100 C in air. Miller indexation (hkl)
q bulk (rad)
dbulk (Å)
dexp (Å)
Ddexp/dbulk (%)
FWHM (rad)
〈fParticles〉 (Å)
〈aexp〉 (Å)
(111) (200) (220) (311) (400) (331)
0.250 0.286 0.414 0.489 0.606 0.672
3.123 2.705 1.913 1.631 1.353 1.250
3.102 2.725 1.911 1.637 1.351 1.236
0.67 þ0.73 0.08 þ0.36 0.13 1.09
0.029 0.047 0.045 0.048 0.048 0.080
46.8 30.2 33.2 32.1 34.9 22.1
5.37 5.45 5.41 5.42 5.41 5.39
Fig. 5. Attenuated Total Reflection FTIR spectrum of the Cerium oxide NPs (Dried in a standard oven at ~100 C and annealed at 500 C in air for 2 h).
CeeO modes to the adsorbed OH compounds, one can pre-conclude on the high crystallinity and purity of the synthesized CeO2 NPs. To sustain the nature as well as the purity of the synthesized CeO2 NPs, room temperature Raman spectroscopy investigations were performed using the 532 nm Raman excitation line of an Ar laser source in the spectral range of 200e800 cm1. Fig. 6 reports a representative Raman spectrum of the CeO2 NPs which exhibits 1 strong peak with a shoulder centered at 460.1 and 379.6 cm1 as well as a low intensity mode at 581.1 cm1. The strong intense band at 460 cm 1 fits with the F2g Raman active-mode of fluorite type cubic structure [31,32]. Considering the results of Wang et al. [33], the relatively broad weak band at 581.1 cm1 is attributed to a symmetrical stretching mode of the CeeO vibrational unit & nanocrystalline nature of CeO2 [32,33]. Likewise, the shoulder mode at 379.6 cm1 which has not been observed in single crystal or poly-crystalline CeO2 is considered as it arises from size effects [33].
Fig. 6. Raman spectrum of the Cerium oxide NPs (Dried in a standard oven at ~100 C and annealed at 500 C in air for 2 h).
2.5. Chemical valence states & XPS To complement the HRTEM, EDS, XRD, ATR-FTIR and Raman results, X-rays Photoemission spectroscopy (XPS) studies were carried out to investigate the oxidation state of Ce and O as well as the composition of the surface functionalization of the CeO2 NPs if any. The XPS studies were acquired using a constant 50 eV pass energy mode, in 0.1 eV increments at 50 ms dwell time with the signal averaged for at several regular scans. The XPS system was equipped with a dual Mg Ka-Al Ka anode for photoexcitation. Fig. 7 shows the typical XPS spectrum of the annealed CeO2 NPs. In view of the f-electron nature of Ce, the binding energy of CeO2 NPs exhibits several bands with the mains ones centered at about 882.2, 888.5, 897.7 and 916.3 eV corresponding to the Ce4þ 3d3/2 and Ce4þ 3d5/2 are shown at binding energy. This is consistent with the
Fig. 7. Co2p X-rays photoemission spectroscopy spectrum of the Cerium oxide NPs (Dried in a standard oven at ~100 C and annealed at 500 C in air for 2 h).
reported values in the literature [10]. Yet there is slight potentially discernable peak at about 886.2 eV which could be assigned to Ce3þ, and in view of the O1s peak at 531 eV, it can be concluded that the bulk of Ce is in 4þ valence state. 3. Conclusions The synthesis of high purity and crystalline CeO2 NPs by green novel and environmental friendly procedd using the natural extract
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of H Sabdariffa as an effective chelating chemical agent was demonstrated. A thermal annealing at 500 C during 2 h under normal air conditions allows the obtention of highly crystallized single phase CeO2 NPs as substantiated by HRTEM, EDS, XRD, ATRFTIR, Raman and XPS investigations. The follow up study will consist of identifying the mechanism and the dynamic of formation of the CeO2 NPs during the interaction of the Cerium salt precursor and the H Sabdariffa extracts compounds. More specifically, the bioactive compounds would be identified. In addition, the synthesis of less stable oxides such as semi-metallic and metallic CeO2 NPs is being investigated. Acknowledgments The research programme was generously supported by grants from the National Research Foundation of South Africa (NRF) (NRF Scienti2015 MM), the French Center National pour la Recherche fique (SA-CNRS 2014 MM 4200220), iThemba LABS, The UNESCOUNISA African Chair in Nanoscience and Nanotechnology (U2ACN2 2015-52259064), the Organization of Women in Science for the Developing World (OWSDW) (OWSDW 2015 MM) and the Abdus Salam ICTP via the Nanoscience African network (NANOAFNET) (ICTP AFNT 2014-63) as well as the African Laser Center (ALC) to whom we are grateful. References [1] H.N. Chandrakala, B. Ramaraj, Shivakumaraiah, Siddaramaiah, Optical properties and structural characteristics of zinc oxide-cerium oxide doped polyvinyl alcohol films, J. Alloys Compd. 586 (2014) 333e342. [2] J. Chen, W. Chen, Y. Tien, C. Shih, Effect of calcination temperature on the crystallite growth of cerium oxide nano-powders prepared by the coprecipitation process, J. Alloys Compd. 496 (2010) 364e369. [3] B. Lee, T. Nakayama, Y. Tokoi, T. Suzuki, K. Niihara, Synthesis of CeO2/TiO2 NPs by laser ablation of Ti target in cerium (III) nitrate hexahydrate (Ce(NO3) 3$6H2O) aqueous solution, J. Alloys Compd. 509 (2011) 1231e1235. [4] S. Gangopadhyay, D.D. Frolov, A.E. Masunov, S. Seal, Structure and properties of cerium oxides in bulk and nanoparticulate forms, J. Alloys Compd. 584 (2014) 199e208. [5] C. Hu, Z. Zhang, H. Liu, P. Gao, Z.L. Wang, Direct synthesis and structure characterization of ultrafine CeO2 NPs, Nanotechnology 17 (2006) 5983e5987. [6] N.K. Chadar, R. Jayavel, Synthesis and characterization of C14TAB passivated cerium oxide NPs prepared by co-precipitation route, Phys. E 58 (2014) 48e51. [7] M. Darroudi, S.J. Hoseini, R.K. Oskuee, H.A. Hosseini, L. Gholami, S. Gerayli, Food-directed synthesis of cerium oxide NPs and their neurotoxicity effects, Ceram. Int. 40 (2014) 7425e7430. [8] G. Renu, V.V. Divya Rani, S.V. Nair, K.R.V. Subramanian, V. Lakshmanan, Development of cerium oxide NPs and its cytotoxicity in prostate cancer cells, Adv. Sci. Lett. 5 (2012) 1e9. [9] J.J. Ketzial, A.S. Nesaraj, Synthesis of CeO2 NPs by chemical precipitation and the effects of a surfactant on the distribution of particles sizes, J. Ceram. Process. Res. 12 (1) (2011) 74e79. [10] A. Arumugam, C. Karthikeyan, A.S.H. Hameed, K. Gopinath, S. Gowri, V. Karthika, Synthesis of cerium oxide NPs using Gloriosa superba L. leaf extract and their structural, optical and antibacterial properties, Mater. Sci. Eng. C 49 (2015) 408e415. [11] M.S. Wason, J. Zhao, Cerium oxide NPs: potential applications for cancer and other diseases, Am. J. Transl. Res. 5 (2) (2013) 126e131. [12] S. Das, J.M. Dowding, K.E. Klump, J.F. McGinnis, W. Self, S. Seal, Cerium oxide
[13] [14]
[15]
[16]
[17] [18]
[19]
[20]
[21]
[22]
[23]
[24] [25]
[26]
[27]
[28] [29] [30]
[31]
[32]
[33]
NPs: applications and prospects in nanomedicine, Nanomedicine 8 (9) (2013) 1483e1508. A.Y. Estevez, J.S. Erlichman, The potential of cerium oxide NPs (nanoceria) for neurodegenerative disease therapy, Nanomedicine 9 (10) (2014) 1437e1440. M. Pesi c, A. Podolski-Reni c, S. Stojkovi c, B. Matovic, D. Zmejkoski, V. Koji c, G. Bogdanovi c, A. Pavi cevi c, M. Mojovi c, A. Savi c, I. Milenkovi c, A. Kalauzi, K. Radotic, Anti-cancer effects of cerium oxide NPs and its intracellular redox activity, Chemico-Biological Interact. 232 (2015) 85e93. A. García, R. Espinosa, L. Delgado, E. Casals, E. Gonz alez, V. Puntes, C. Barata, nchez, Acute toxicity of cerium oxide, titanium oxide and iron X. Font, A. Sa oxide NPs using standardized tests, Desalination 269 (2011) 136e141. S.R.S. Ting, J.M. Whitelock, R. Tomic, C. Gunawan, W.Y. Teoh, R. Amal, M.S. Lord, Cellular uptake and activity of heparin functionalized cerium oxide NPs in monocytes, Biomaterials 34 (2013), 4377e4386. C. Dong, X. Zhang, H. Cai, Green synthesis of monodisperse silver NPs using hydroxy propyl methyl cellulose, J. Alloys Compd. 583 (2014) 267e271. R. Mata, J.R. Nakkala, S.R. Sadras, Catalytic and biological activities of green silver NPs synthesized from Plumeria alba (frangipani) flower extract, Mater. Sci. Eng. C 51 (2015) 216e225. B. Mohapatra, S. Kuriakose, S. Mohapatra, Rapid green synthesis of silver NPs and nanorods using Piper nigrum extract, J. Alloys Compd. 637 (2015) 119e126. P.C. Nethravathi, G.S. Shruthi, D. Suresh, Udayabhanu, H. Nagabhushana, S.C. Sharma, Garcinia xanthochymus mediated green synthesis of ZnO NPs: photoluminescence, photocatalytic and antioxidant activity studies, Ceram. Int. (2015), http://dx.doi.org/10.1016/j.ceramint.2015.03.084. J.K. Sharma, M. Akhtar, S. Ameen, P. Srivastava, G. Singh, Green synthesis of CuO NPs with leaf extract of Calotropis gigantea and its dye-sensitized solar cells applications, J. Alloys Compd. 632 (2015) 321e325. N. Bala, S. Saha, M. Chakraborty, M. Maiti, S. Das, R. Basu, P. Nandy, Green synthesis of zinc oxide NPs using Hibiscus subdariffa leaf extract: effect of temperature on synthesis, anti-bacterial activity and anti-diabetic activity, RSC Adv. 7 (5) (2014) 4993e5003. A.K. Das, A. Marwal, D. Sain, One step green synthesis and characterization of flower extract-mediated mercuric oxide (HgO) NPs from callistemon viminalis, research and review, J. Pharm. Nanotechnol. 2 (2) (2014), 2347e7849. N.M. Shivali, P. Kamboj, Hibiscuss sabdariffa linn, an overview, Nat. Product. Radiance 8 (1) (2009) 77e83. T.O. Alaga, M.O. Edema, A.O. Atayese, M.O. Bankole, Phytochemica and in vitro antibactetial properties of Hibiscus sabdariffa (Roselle) juice, J. Med. Plant Res. 8 (6) (2014) 339e344. B.H. Ali, N. Al Wabel, G. Blunden, Phytochemical, pharmacological and toxicological aspects of Hibiscus sabdariffa L.: a review, Phytotherapy Res. 19 (5) (2005) 369e375. kou, A.J. Djaman, J.D. N'guessan, M. Kone, A.P. Obouayeba, D.N. Bernard, D. Se T.H. Kouakou, Phytochemical and antioxidant activity of roselle (Hibiscus Sabdariffa L.) petal extracts. Research journal of pharmaceutical, Biological Chem. Sci. (2014), 0975e8585: 1453. S. Guardiola, N. Mach, Therapeutic potential of Hibiscus sabdariffa: a review of the scientific evidence,, Endocrinol. Nutr. 61 (5) (2014) 274e295. S. Patel, Hibiscus sabdariffa: an ideal yet under-exploited candidate for nutraceutical applications, Biomed. Prev. Nutr. 4 (2014) 23e27. ndez-Arroyoa, D. Arr I. Borr as-Linares, S. Ferna aez-Romanam, P.A. Palmerosles, A. Ferna ndez-Gutie rrez, Su arez, R. Del Val-Díaz, I. Andrade-Gonza mez-Leyvac, A. Segura-Carreteroa, Characterization of phenolic comJ.F. Go pounds, anthocyanidin, antioxidant and antimicrobial activity of 25 varieties of Mexican Roselle (Hibiscus sabdariffa), Industrial Crops Prod. 69 (2014) 385e394. D. Girija, H.S.B. Naik, C.N. Sudhamani, B.V. Kumar, Cerium oxide NPs-green, reusable, and highly efficient heterogenous catalyst for the synthesis of polyhydroquinolines under solvent-free conditions, Archives Appl. Sci. Res. 3 (3) (2011) 373e382. S.B. Khan, M. Faisal, M.M. Rahman, K. Akhtar, A.M. Asiri, A. Khan, K.A. Alamry, Effect of particle size on the photocatalytic activity and sensing properties of CeO2 NPs, Int. J. Electrochem. Sci. 8 (2013) 7284e7297. S. Wang, W. Wang, J. Zuo, Y. Qian, Study of the Raman spectrum of CeO2 nanometer thin films, Mater. Chem. 68 (2001) 246e248.
