Chemical Methods for Synthesis of Hybrid Nanoparticles

C H A P T E R

9 Chemical Methods for Synthesis of Hybrid Nanoparticles Balakrishnan Karthikeyan1, R. Govindhan1 and M. Amutheesan2 1

2

Department of Chemistry, Annamalai University, Chidambaram, Tamil Nadu, India Department of Aeronautical Engineering, Hindustan Institute of Technology & Science, Chennai, Tamil Nadu, India

9.1 INTRODUCTION Nanomaterial is described exactly as material that is having one or more dimension(s) in the nanoscale range (,100 nm). Atoms/molecules are combined in a controllable way by bottom-up procedures to prepare (chemical synthesis) nanostructural materials. Larger surface to volume ratio is the master key for nanomaterials which make them work with more reactive surfaces and different functionality than bulk materials. As compared to the single nanoparticles of noble metals or metal oxides, their hybrid nanoparticles may have different optical, magnetic, electronic, and structural properties. The properties of these nanohybrids are based not only on the structural arrangement of each individual nanocomponent, but also on the concentration of the mixed single-component nanoparticles. Bottom-up chemical synthesis is the ideal methodology for the preparation of nanohybrids. It uses a chemical reducing agent that reduces the metal ion and integrates on another metal surface at the nano-level. Bottom-up procedures have been followed by the scientists to combine the atomic molecules in the nano-scale in the controllable way. In this method, the reaction time, heat treatment during the preparation process, and the choice of reducing agent affect the size, morphology, and the structure of the nanocomposite. Purity of the material and the synthetic route affect the nanomaterial preparation in a greater way. But in this method, the desired applications of the nanomaterial are affected

Noble Metal-Metal Oxide Hybrid Nanoparticles DOI: https://doi.org/10.1016/B978-0-12-814134-2.00016-4

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© 2019 Elsevier Inc. All rights reserved.

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9. CHEMICAL METHODS FOR SYNTHESIS OF HYBRID NANOPARTICLES

due to the aggregation of the nanoparticles during sorption processes. Various chemical methods are discussed as follows.

9.2 SEED GROWTH METHOD A novel method of microwave (MW) 2 polyol method used in this study; reported in [1,2]. The synthesis of Au@Ag core
shell nanocrystals was prepared by two steps. The first method is synthesis of Au core, and the next step is the preparation of Ag shell. Initially, 2.4 mM of HAuCl4 4H2O is added into the solution in 20 mL of ethylene glycol solution. After that, 1 M of PVP in terms of monomeric units (molecular weight 40,000) is slowly added to the above solution. The mixture is heated by MW irradiation in a CW mode (Shikoku Keisoku, 400 W) for 2 min. After the solution is heated, it is then cooled to room temperature, and then AgNO3 is added. The [AgNO3]/[HAuCl4] molar ratio is varied in the range of 1:10. The mixture solution is heated again by MW irradiation for 2 min. Au core
Au/Ag alloy shell particles, denoted as Au@Au/Ag, are prepared by the addition of 2.4 mM of HAuCl4 4H2O to Au@Ag nanocrystals obtained at an [AgNO3]/ [HAuCl4] molar ratio of 1:1. Product particles after the first and second MW irradiations were characterized by using TEM (JEOL JEM-2010 and JEM 3000F). The images are shown in Scheme 9.1. It was reported that noble metal (Au, Ag, Pt)
Fe3O4 hybrid nanoparticles could be synthesized by using seeding growth methods [3,4]. In these studies, the seeds were either the preformed Fe3O4 nanoparticles [3] or noble metal nanoparticles (AuNPs [4]).





SCHEME 9.1 Crystal structures and seed growth mechanism of Au@Ag core
shell nanohybrids prepared by the microwave
polyol synthetic routes. Source: Reprinted with permission from M. Tsuji, N. Miyamae, S. Lim, K. Kimura, X. Zhang, S. Hikino, et al., Crystal structures and growth mechanisms of Au@Ag core
shell nanoparticles prepared by the microwave
polyol method, Cryst. Growth Des. 6 (8) (2006) 1801
1807. Copyright 2006 American Chemical Society.

I. FUNDAMENTALS

9.4 SONOCHEMICAL SYNTHESIS

181

9.3 COPRECIPITATION METHOD ZnO
MgO nanocomposites are prepared by coprecipitation method by dissolving 0.58 g of ZnSO4 7H2O, 0.49 g of MgSO4 7H2O, and 0.75 g of NaOH in DI water (60 mL) under constant blending in a 100 mL glass beaker. Final solution is refluxed for 24 h in a 100 mL glass conical flask at 90 C. The precipitate mixture is centrifuged at 8000 rpm at room temperature, continuously and repeatedly washed with DI water. The obtained colorless semisolid samples are allowed to dry for 12 h at 80 C. Likewise, ZnO and MgO nanoparticles are prepared by using the homogeneous precipitation method [5], where 0.58 g of ZnSO4 7H2O (or 0.49 g of ZnSO4 7H2O) and 0.75 g of NaOH are homogeneously added in 60 mL of DI water. Colorless powder nanoparticles are formed in the final condition. Pure ZnO and MgO nanoparticles are formed via reaction (9.1) and (9.2), and (9.3) and (9.4), respectively. ZnO
MgO nanocomposites are formed via reaction (9.5) and (9.6).











ZnSO4 7H2 O 1 NaOH-ZnðOHÞ2 1 NaSO4 1 6H2 O

(9.1)

ZnðOHÞ2 -ZnO 1 6H2 O

(9.2)

MgSO4 7H2 O 1 NaOH-MgðOHÞ2 1 NaSO4 1 6H2 O

(9.3)

MgðOHÞ2 -MgO 1 6H2 O

(9.4)









ZnSO4 7H2 O 1 MgSO4 7H2 O 1 NaOH-ZnðOHÞ2 MgðOHÞ2 1 NaSO4 1 6H2 O



ZnðOHÞ2 MgðOHÞ-ZnO 2 MgO 1 2H2 O

(9.5) (9.6)

Au
metal oxide hybrids, such as Au
Fe2O3, Au
NiO and Au
Co3O4, are prepared by coprecipitation method [6] using the sodium carbonate, HAuCl4, and metal nitrate. Similarity, Au
ZnO hybrid nanoparticles have been synthesized by using Na2CO3, HAuCl4, and Zn(NO3)2 [7,8]. Ag
Fe3O4 core
shell nanowires have been also successfully synthesized by coprecipitation method using FeCl3, FeCl2, and polyvinylpyrrolidone (PVP) [9].

9.4 SONOCHEMICAL SYNTHESIS 9.4.1 Synthesis of (Pd, Co)@Pt Nanohybrids Ultraviolet photoelectron (UPS) reactions are used to prepare Pd, Co@Pt nanohybrid materials, through Pd(acac)2, Pt(acac)2, Co(acac)2, and the carbon support. These are added to a three-necked flask containing ethylene glycol (30 mL), through which pure argon gas was bubbled for 45 min before the addition. Three reactions with different mM ratios of (Pd:Co:Pt as 0.05:0.025:0.05, 0.025:0.025:0.05, and 0.0125:0.025:0.05 mM) and weighed amounts of carbon (about 30 mg) were added. Amplitude of 30% ultrasound from a 500 kW ultrasound generator (Sonic and Materials, VC-500, 20 kHz with a 13 mm solid probe) was applied for 3 h under Ar gas at room temperature. The final solution of blackish slurry is filtered, washed with ethanol, and then dried under vacuum for 12 h at room temperature. In the end, all samples are heated at 350 C under the flow of mixed gas (4% H2 and 94% N2) for 4 h to remove the residual organics [10]. I. FUNDAMENTALS

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9. CHEMICAL METHODS FOR SYNTHESIS OF HYBRID NANOPARTICLES

9.4.2 Synthesis of Pd
Metal Oxide Hybrid Nanoparticles Pd
CuO nanohybrids have been successfully fabricated by the sonochemical synthesis using copper salt in the presence of palladium and water [11]. The authors reported that in the presence of palladium and water, transition metal salts could be converted into their oxides by aid of ultrasound energy. In their work, the palladium source was either pure metallic palladium Pd(0) or the palladium salts (palladium acetate, palladium nitrate). Ziylan-Yavas et al. [12] have synthesized Pd
TiO2 nanohybrids by using both highfrequency ultrasound (35 KHz) and UV-irradiation (254 nm). In their study, palladium salt (Na2PdCl4 3H2O), commercial TiO2 powder, and polyethylene
glycol monostearate were used.



9.5 SOL
GEL METHOD 9.5.1 Synthesis of Trimetallic Nanoparticles Au/Ag/Pt Based on the known method [13], Au nanoparticles are first prepared by the reducing agent trisodium citrate. 10 mL of aqueous 0.1 % of metal salt (HAuCl4 3H2O) is heated to boiling, and 2 mL of 1 % trisodium citrate is added with continuous stirring. The reaction mixture is allowed to heat for 4 min and cooled to room temperature. The change in color indicates the formation of Au nanoparticles. Then, 10 mL of 0.1% metal salt (H2PtCl6 6H2O) is added to the Au nanoparticles, accompanied by the inclusion of 2 mL of 1% trisodium citrate with constant stirring. Finally 10 mL of 0.1% of metal salt (AgNO3) is added into the Au/Pt nanoparticles. The heating operation is carried out in a (microwave) MW oven for 7 min. The synthesized colloidal sol is sonicated with 30 min with a “fast-clean” ultrasonic cleaner. The preparation method of trimetallic Au/Pt/Ag nanocomposites is shown in Scheme 9.2.





SCHEME 9.2 Modified microwave irradiation method for the synthesis of Au/Pt/Ag trimetallic nanocomposites. Source: Reprinted with permission from S. Sivasankaran, S. Sankaranarayanan, S. Ramakrishnan, A novel sonochemical synthesis of metal oxides based Bhasmas, Mater. Sci. Forum 754 (2013) 89
97. Copyright 2013 Elsevier.

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9.5 SOL
GEL METHOD

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9.5.2 Synthesis of Amine-Functionalized Silica Nanopowder (SiO2 Nanopowder) In order to achieve the faster sol
gel transition, tetraethoxysilane (TEOS) is chosen as a silica source. During the preparation procedure, 3 mL of TEOS and 1 mL of amino propyl tetra ethoxy silane (APTES) are added to 3 mL of distilled ethanol. This final mixture is transferred into a beaker which is carefully shielded to reduce the unwanted evaporation. The mixture is stirred for 30 min at room temperature for the formation of sol
gel product. This product is placed in a hot-air oven for 12 h at 100 C for the total hydrolysis of TEOS/APTES to form SiO2 nanopowder. Scheme 9.3 shows the synthetic route of the SiO2 nanopowder [14].

9.5.3 Synthesis of Trimetallic Au/Pt/Ag Nanocomposites-Doped Amine-Functionalized Silica Nanopowder (Au/Pt/Ag@SiO2) Sol
gel technique is used to prepare Au/Pt/Ag@SiO2 nanopowder. Scheme 9.2C represents the preparation route of the Au/Pt/Ag@SiO2 nanopowder. Briefly, TEOS (3 mL) and APTES (1 mL) are dissolved in distilled ethanol (3 mL) in a beaker and stirred for 30 min at room temperature. In parallel, as-prepared trimetallic Au/Pt/Ag nanocomposites sol (3 mL) is added into the obtained mixture. The final mixture is stirred for another 30 min at room temperature to form Au/Pt/Ag@TEOS/APTES sol
gel mixture [13,14]. This sol
gel mixture is kept in a hot-air oven and dried for 12 h at 100 C for aging, drying, and shrinking. At the end, the sol
gel matrix is well ground to form Au/Pt/Ag@SiO2 nanopowder (Scheme 9.4).

SCHEME 9.3 Sol
gel chemical route for the synthesis of amine-functionalized SiO2 nanocomposite. Source: Reprinted with permission from A. Ziylan-Yavas, Y. Mizukoshi, Y. Maeda, N.H. Ince, Supporting of pristine TiO2 with noble metals to enhance the oxidation and mineralization of paracetamol by sonolysis and sonophotolysis, Appl. Catal. B: Environ. 172 (2015) 7
17. Copyright 2015 Springer.

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9. CHEMICAL METHODS FOR SYNTHESIS OF HYBRID NANOPARTICLES

SCHEME 9.4 Sol
gel chemical route for the synthesis of Au/Pt/Ag TNC-doped SiO2 nanocomposite (Au/Pt/ nanocomposite). Ag@SiO2 Source: Reprinted with permission from A. Ziylan-Yavas, Y. Mizukoshi, Y. Maeda, N.H. Ince, Supporting of pristine TiO2 with noble metals to enhance the oxidation and mineralization of paracetamol by sonolysis and sonophotolysis, Appl. Catal. B: Environ. 172 (2015) 7
17. Copyright 2015 Springer.

SCHEME 9.5 Schematic illustrations for the synthesis of Ag/ZnO hybrid nanocomposites via photochemical environments. Source: Reprinted with permission from B. Karthikeyan, B. Loganathan, A close look of Au/Pt/Ag nanocomposites using SERS assisted with optical, electrochemical, spectral and theoretical methods, Phys. E: Low Dimens. Syst. Nanostruct. 49 (2013) 105
110. Copyright 2012 American Chemical Society.

9.6 PHOTOCHEMICAL METHOD Ag/ZnO nanohybrid is prepared using the modified photochemical method [15]. Reactant solution, containing colloidal zinc oxide (5 3 1024 M), silver nitrate (1 3 1024 M), is prepared from stock solutions in 2-propanol. The irradiation of solution is executed using filter-cut 310
390 nm light segment of 1000 W high-pressure mercury lamp or 500 W incandescent lamp in glass 1.0 cm cuvettes. A 5-cm water filter has been placed between the light source and the work cuvette to reduce the heating of reacting mixtures. Before the experiments, oxygen has been removed from the cuvettes via continuous argon atmosphere. Finally, the formation of Ag/ZnO colloidal nanocomposites is obtained (Scheme 9.5).

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185

9.8 HYDROTHERMAL/SOLVOTHERMAL METHOD

9.7 WET-CHEMICAL SYNTHESIS Synthesis of open-ended, cylindrical Au
Ag alloy nanostructures on a Si/SiOx surface is reported [16]. In a typical experiment, a 45-nm-thick Ag film (Scheme 9.1) from the thermally evaporated Ag film with the relatively large Ag grains of size 40
140 nm is achieved. Ag is oxidized by HAuCl4, and the reduced Au is deposited onto the surface of the Ag. Wet-chemical process results in the formation of the open-ended cylindrical structures that are different from what has been observed for the previously studied etched colloidal nanoparticles in three ways: (i) the Ag dots are attached to a substrate surface rather than being dispersed in solution; (ii) the Ag nanodots are anisotropically functionalized with 16-mercaptohexadecanoic acid (MHA) group; and (iii) the Ag dot is in a polycrystalline structure, consisting of multiple grains. These differences are critical and account for the unusual open cylindrical shape of the resulting nanostructures. All data are consistent with the MHA acting as a resist layer forcing the electroless deposition of gold to occur on the sidewalls of the MHA-capped nanostructures (Scheme 9.6). Gold gets initially plated on the outside of the nanostructure and continues to grow vertically as the Ag core is dissolved and supplies electrons for further electroless Au plating. Dramatically, the growth in the vertical direction exceeds in the plane parallel to the substrate. This is a result of the relative surface area of the gold on the sidewalls as compared with that on the top rim. The sidewalls always have significantly greater surface area than the top rim of the open cylinder. Therefore, more gold is required to increase the diameter as compared with the height. This is in contrast to the etching process of spherical nanoparticles or nanocubes, where the particle surfaces are more homogeneously passivated with ligands and isotropic etching is observed, leading to closed hollow structures rather than the open-ended structures.

9.8 HYDROTHERMAL/SOLVOTHERMAL METHOD Usually, in the hydrothermal synthesis of nanohybrids, the ligands, stabilizers, or surfactants can be involved or not. SCHEME

9.6 Synthetic procedure for the open-ended cylindrical Au
Ag alloy nanostructures on Si/SiOX surfaces. Source: Reprinted with permission from B. Loganathan, V.L. Chandraboss, M. Murugavelu, S. Senthilvelan, B. Karthikeyan, J. Sol
Gel Sci. Technol. 74 (2015) 1
14. Copyright 2004 American Chemical Society.

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9. CHEMICAL METHODS FOR SYNTHESIS OF HYBRID NANOPARTICLES

In case of nano-TiO2-based hybrids, without ligands or surfactants, Au/TiO2 nanohybrids [17] and Pt/TiO2 core/shell NPs [18] have been synthesized, by using the hydrothermal process with redox procedure. Whereas, with hexamine as the stabilizer, Ag
TiO2 nanohybrids have been fabricated [19]. In case of nano-Fe3O4 based hybrids, under thermal decomposition process, Ag@Fe3O4 core
shell nanoparticles have been synthesized by using the mixture of oleylamine and oleic acid (as surfactants) [20]. Similarly, by using these surfactants, Ag
Fe3O4 dimer nanoparticles were also fabricated [21]. The Pd
Fe3O4 nanohybrids were successfully synthesized by the thermal decomposition of Fe(CO)5 and the reduction of Pd(OAc)2 in oleylamine and 1-octadecene [22]. It was reported that in the presence of diethanolamine, acting as stabilizer and reducing agent, Ag
ZnO nanohybrids could be prepared under the hydrothermal method [23].

9.9 CONCLUDING REMARKS Among these methods discussed, chemical synthesis has some advantages for creating new generation hybrid nanocomposites. In current societal needs, miniaturization of electronic components are determining the generation of the new materials. The advantage and the desired applications among the hybrid nanomaterial are making researchers think more on the novel and simple nanohybrid preparation techniques. Among the various chemical methods of nanohybrid preparation discussed in this chapter, bottom-up approaches like seed growth mechanism, coprecipitation method, ultrasonochemical synthesis, sol
gel approach, hydrothermal routes, and photochemical synthetic procedures are well studied. Sonochemical is the best and the simplest methodology for the preparation of metal oxides-related nanohybrids with controlled size and morphology for special application like photovoltaic cell or photoelectrochemical application. Coprecipitation method provides the advantage of being a low cost, simple, waterbased reaction, with flexibility, mild reaction conditions, and size control. It is highly acceptable for the synthesis of nanohybrids for mechanical applications: tribological, light weight structures, thermal defensive structures, etc., and highly applicable for biomedical treatment due to the heat producing capability of (Fe2O3) IO
Au core
shell nanohybrids during the cancer cell treatments. Seed growth mechanism is the best method for converting the less observed metal oxides to highly visible light observing nanohybrid structures by arranging the shell over the core of the metal oxides for solar cell applications. Sol
gel method is highly captivating for the preparation of nanostructures having more than one component, since a good structural resultant product is formed due to slow reaction kinetics. It is a fine way to prepare superhydrophobic nanomaterial and to coat nanohybrids over metal surfaces for various technological applications, as well as to determine the water contacting angle and the surface modification, self-cleaning activities of the bulk materials. Hydrothermal method is the superior way to make nanohybrids for novel applications like cosmetology, optoelectronic, etc. by the simple and precise preparation technique.

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