Colloid Polym Sci DOI 10.1007/s00396-015-3727-0
ORIGINAL CONTRIBUTION
Synthesis and stabilization of Pt nanoparticles in core cross-linked micelles prepared from an amphiphilic diblock copolymer Gökhan Kocak 1 & Vural Bütün 1
Received: 14 April 2015 / Revised: 25 July 2015 / Accepted: 27 July 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract In this study, an amphiphilic poly(ethylene glycol)methyl ether-block-poly(glycidyl methacrylate) diblock copolymer (MPEG-b-PGMA) was synthesized via atom transfer radical polymerization (ATRP), and its micellar solution was prepared in acetone/water mixture. Core crosslinked (CCL) micelles were synthesized by cross-linking the epoxy functional group of poly(glycidyl methacrylate) block with ethylenediamine. These CCL micelles were used in the synthesis and stabilization of platinum nanoparticles (PtNPs) in aqueous media. Transmission electron microscopy (TEM) images showed that well-dispersed PtNPs with a diameter of around 5 nm were formed within the MPEG-b-PGMA spherical CCL micelles having 22.0±3.0 nm diameters. The mean TEM diameter of the PtNPs is of the order of several nanometers, which is consistent with the plasmon absorption peaks observed at around 205 and 261 nm. The catalytic activity of CCL micelle-PtNP dispersion was also investigated in the reduction of p-nitrophenol to p-aminophenol in the presence of NaBH4. The results showed that the PtNPs exhibit a good catalytic activity toward reduction of p-nitrophenol. CCL micelle-stabilized PtNP dispersions were stable for long periods of time without changing properties at room
Electronic supplementary material The online version of this article (doi:10.1007/s00396-015-3727-0) contains supplementary material, which is available to authorized users. * Vural Bütün
[email protected] Gökhan Kocak
[email protected] 1
Polymer Research Group, Department of Chemistry, Faculty of Arts and Science, Eskisehir Osmangazi University, Eskisehir 26480, Turkey
temperature. CCL micelles found to be good hostage or stabilizer for the NPs in aqueous media. Keywords Core cross-linked micelle . Diblock copolymer . Catalytic activity . Platinum nanoparticle . Glycidyl methacrylate . Nanoreactors
Introduction Nanometals have attracted much attention in the fields of physics, chemistry, and biotechnology owing to their potential technological uses in opticals, medicine, catalysts, and electronics [1–6]. Their potential technological usages are strongly dependent on the sizes, compositions, and shapes of metal nanomaterials [7–10]. Additionally, stabilization of metal nanoparticles is one of the most important problems in the modern colloid chemistry and technology known in nowadays as nanoscience and nanotechnology. Synthesis of metal nanoparticles using polymers as a stabilizing agent is very common. Hydrogels [11], microspheres [12, 13], (co)polymers [14–19], and dendrimers [20] are widely used polymeric systems. Among the nanoparticle syntheses that have emerged, one promising method involves nanoparticle formation within the core of amphiphilic block and doublehydrophilic copolymer micelles as nanoreactors [8, 21]. However, the practical applications of micelles are limited due to their structural instability since the micellar structure can hardly keep stable upon dilution or changes of external conditions such as changes in pH, ionic strength, type of solvent, and temperature [22]. In order to enhance the stability, core cross-linked (CCL) [23, 24], shell crosslinked (SCL) [22–24], and intermediary layer cross-linked (ILCL) [25, 23] micelles were then developed (Fig. S1).
Colloid Polym Sci
SCL micelles are generally prepared at high dilution in order to avoid undesirable intermicellar cross-linking, and thus, the efficiency is quite low. Probably, the more suitable method is to carry out CCL or ILCL instead of SCL micelles [22, 25]. Nanometal stabilization using cross-linked micelles are limited in the literature [26–31]. The size, size distribution, and shape of nanoparticles were found to be determined by the rates of nucleation and growth of nanoparticles which, in turn, are controlled by the type of reducing agent, synthetic pathway, stabilizer/metal ratio, and characteristics of stabilizer [32–43]. The changes in the size, size distribution, and shape of nanoparticles are the most important factors in the method of synthesis and the type of reducing agent. A number of methods such as sonochemical, chemical, physical, biological, photochemical, and electrochemical have been developed for the synthesis of metal nanoparticles [44]. Various reduction agents, such as sodium citrate, sodium borohydride (NaBH4), hydrazines, glucose, chitosan, KBH4, alcohols, H2, and UV light, were used for the production of different nanometals (Ag, Au, Pt, etc.). However, NaBH4 is the most commonly used reducing agent which allows the synthesis of smaller metal nanoparticles (increased surface). There are many works for the preparation of CCL, SCL, and ILCL micelles. In the literature, various crosslinking chemistries have been reported for cross-linking the micelles. Armes group and van Nostrum reported in detail how the cross-linked micelles can be prepared [23, 22]. Chemicals such as 1,2-bis(2-iodoethoxy)-ethane, divinyl sulfone, diamines, bifunctional azides (click chemistry), reversible photo cross-linked (coumarin ring), and gluteraldehyde have been widely used to prepare cross-linked micelles. When the micelles form block copolymer containing reactive functional groups in ether core or corona, the micelles can be crosslinked by the addition of a bifunctional reagent [23]. Herein, we report the synthesis of CCL micelles via cross-linking reaction between the epoxy functional groups of poly(glycidyl methacrylate) block and ethylenediamine which are very cheap and commercially available. Zhu et al. have produced hollow micelles with similar diblock copolymer and prepared cross-linked hollow micelles using hexamethylenediamine (HDA) and dodecylamine (DA) (0.5–1.0 μm) [45]. It is worth to mention that Zhu’s group reported spherical cross-linked hollow micelles in their study. In our study, we report spherical CCL micelles with a diameter of 22.0± 3.0 nm by using similar cross-linking chemistry. After cross-linking of poly(glycidyl methacrylate) (PGMA) core of micelles with access amount of ethylenediamine, the core became functional group-rich due to formation of primary amine, secondary amine, and hydroxyl groups. These groups can
get complexation with palatinate-type anions in the core of CCL micelle and provide us to prepare single metal nanoparticle (NP) in the core of each CCL micelle.
Experimental section Materials Glycidyl methacrylate (Aldrich, 98 %) was passed through a basic alumina column to remove the radical inhibitor before use. Poly(ethylene glycol) (Fluka, MPEG-OH, M n 2000 g mol−1), Cu(I)Br (98 %, Aldrich), dialysis tubing (Sigma, 14,000 g mol−1 cutoff), 2,2′-bipyridyl (Bpy, Fluka, ≥98 %), 2-bromoisobutyryl bromide (BIBB, Aldrich, 98 %), toluene (Sigma-Aldrich, 99.8 %), H2PtCl6·6H2O (Merck, ∼40 % Pt), NaBH4 (Across, 98 %), p-nitrophenol (p-NP, ABCR, 99 %), tetrahydrofuran (THF) (Sigma-Aldrich, ≥99.9 %), n-hexane (Sigma-Aldrich, 95 %), and diethyl ether (Sigma-Aldrich, ≥99.9 %) were all used as received.
Instrumentation Molecular weight (Mn) and molecular weight distribution (Mw/Mn) of diblock copolymer were determined by using gel permeation chromatography (GPC). The GPC consisted of an Agilent Iso Pump, a refractive index detector, combination of Mixed BD^ and Mixed BE^ columns (ex. Polymer Labs), and calibration was carried out using PMMA standards (ex. Polymer Labs), with Mn ranging from 1100 to 218,000 g mol−1. The GPC eluent was HPLC-grade THF stabilized with BHT, at a flow rate of 1.0 mL min−1. The compositions of all precursor block copolymers and the degree of betainization were determined from proton NMR spectra by using a Bruker 500 MHz Avance II spectrometer (solvent CDCl3). To determine hydrodynamic diameter and relative variance (μ 2 /Γ 2 ) values of micelles, dynamic light scattering (DLS) studies were carried out by using an ALV/CGS3 compact goniometer system (Malvern Instruments, Inc., UK). The ALV/CGS-3 system was equipped with a 22 mW He–Ne laser operating at λo 632.8 nm, an avalanche photodiode detector with high quantum efficiency, and an ALV/LSE-5003 multiple tau digital correlator electronics system. The particle sizes were also determined by transmission electron microscopy (TEM) using a Jeol JEM-1220 electron microscope. The TEM samples were prepared on carbon-coated copper TEM grids. Bandelin Sonorex ultrasonic bath with a frequency of 35 KHz and a nominal power 350 W was used for the synthesis of PtNPs.
Colloid Polym Sci
Synthesis and characterization of polymer and nanometal dispersions First, PEG-based ATRP macroinitiator was synthesized and followed by the synthesis of MPEG-b-PGMA diblock copolymer via ATRP method [46] over PEG-Br macroinitiator. Synthesis of PEG-based macroinitiator (MPEG45-Br) Into a dry 250-mL round-bottom flask, MPEG 45-OH (Mw/Mn 1.02, 10.0 g, 5.0 mmol) and 100 mL dry toluene were added. Triethylamine (1 mL, 7 mmol) was added to the reaction mixture under continuous stirring just before addition of 2-bromoisobutyryl bromide (0.8 mL, 6.5 mmol). The final mixture was stirred at room temperature for 24 h. After the reaction was completed, it was filtered to remove the triethylamine hydrobromide salt. The solution was concentrated by using rot evaporator just before precipitation of macroinitiator in diethyl ether. This dissolution and precipitation cycle was repeated for three times before drying in a vacuum oven overnight at room temperature. MPEG 45 -Br macroinitiator was obtained as a white powder. The related reaction scheme was given in Fig. 1. Synthesis of MPEG45-b-PGMA63 diblock copolymer Both MPEG45-Br (2.0 g, 1 mmol) and GMA monomer (6.4 mL, 50.0 mmol) were first dissolved in THF (25.0 mL). After purging with nitrogen for 15 min, Cu(I)Br (143 mg, 1 mmol) and Bpy (360 mg, 2.3 mmol) were added under N2 atmosphere. The reaction mixture became dark brown, and the reaction mixture was stirred for 72 h at 50 °C. After completion of the reaction and exposure to air, the solution turned into green indicating aerial oxidation of the Cu(I) catalyst. The
resulting copolymer was diluted with methanol and passed through a silica column to remove the ATRP catalyst. Any unreacted MPEG-Br macroinitiator and MPEG45-b-PGMAn diblock copolymer impurities were removed by precipitation of the diblock copolymer into excess n-hexane (three times). The final MPEG 45-bPGMAn triblock copolymer was dried under vacuum overnight to obtain a white product before structural characterization with GPC and proton NMR spectroscopy. The conversion of monomer was more than 95 %. The theoretical degree of polymerization (DP) was calculated by the mole ratio of monomer to macroinitiator. Preparation of micelles from MPEG45-b-PGMA63 diblock copolymer A clear polymer solution was prepared as unimers by dissolving 0.05 g of MPEG45-b-PGMA63 in 1 mL of acetone. After stirring 10 min, polymeric micelles were obtained by adding water drop by drop (2 mL min−1) at a stirring rate of 1000 rpm. The solution became slightly turbid after the addition of distilled water (9.0 mL), which indicated the formation of aggregates or micelles. The schematic representation of the preparation of 0.5 wt% micellar solution was given in Fig. 2. The related solutions were investigated with DLS studies in order to explain micellar structure and diameters. Preparation of core cross-linked micelles Ethylenediamine (15.2 mg) was added to the 0.5 wt% micellar solution (10 mL) and stirred at 25 °C to prepare CCL micelles via cross-linking reaction between the epoxy functional group of poly(glycidyl methacrylate) block and ethylenediamine. Excess ethylenediamine (1.5-fold) was added based on the mole of epoxy residues in the micelle core as a cross-linking agent. It was
Fig. 1 Synthetic route for the synthesis of MPEG45-Br macroinitator (a) and MPEG45-b-PGMAn (b)
Colloid Polym Sci Fig. 2 The schematic representation of CCL micelle formation from MPEG45-bPGMA63 diblock copolymer at 25 °C
aimed to convert all epoxy groups of PGMA block in the micelle core and to get some unreacted amine end groups of cross-linker to enhance complexation capacity of CCL micelle core with metal cations and/or metal containing complex anions. Excess ethylenediamine was easily removed by dialysis (14,000 g mol−1 cutoff). The cross-linking was also accomplished by dispersing the related micelles in different organic solvents (methanol, ethanol, acetone, and THF). For this step, CCL micelle solution was first transferred into dialysis tubing and dialyzed in related solvents before DLS studies. Synthesis of Pt nanoparticles (PtNPs) with sonochemical method The CCL micellar solution was diluted with 0.50 to 0.25 wt% water. CCL micelle-[PtCl6]2− solutions were prepared by the addition of H 2 PtCl 6 (epoxy groupplatinate molar ratio of 4:1 and 8:1) to the CCL micellar solution at pH 2.6. The solution was stirred at room temperature for 12 h. Then, the aqueous solution of NaBH4 was added to the medium as reducing agents to form PtNPs by stirring the reaction medium for further 3 h in an ultrasonic bath at room temperature. After all additions, the final volume was adjusted to 5.0 mL in each case. The resulting nanoparticle dispersion was dialyzed with a dialyzing tubing (14,000 g mol−1 cutoff) to remove unreacted/small impurities. Experimental conditions in the synthesis of PtNPs were summarized in Table 2.
Vis absorption spectra were recorded at certain time interval in a scanning range of 250–550 nm.
Results and discussion MPEG45-b-PGMA63 diblock copolymer was synthesized via ATRP method and characterized by using GPC and proton NMR spectroscopy. The number average molecular weight (Mn) and molecular weight distribution (Mw/ Mn) were determined to be 11,500 g mol−1 and 1.08, respectively (see Fig. S2 for GPC chromatograms). Comonomer composition of the diblock copolymer was determined by 1H NMR spectroscopy (see Fig. S3) and given in Table 1. Comonomer composition and absolute degree of polymerization were determined by comparing well-defined peak integrals assigned to the different comonomers. Good agreement with the expected value was observed. Peaks of Bg,^ Bh,^ and Bf^ belonging to PGMA block were observed in the proton NMR spectrum (Fig. S3 a). The peak integral of the protons of the PGMA residues at δ 4.25 and 3.75 (f peaks), 3.25 (g peak), 2.75, and 2.25 (h peaks) were compared with that of repeating units of PEO at δ 3.6 (Fig. S3 a, b). By using PEO as end group having degree of polymerization of 45 (Fig. S3 a), the absolute value of the degree of polymerization of each PGMA block was
Catalytic activity studies of PtNPs The catalytic activity of CCL micelle-PtNP dispersions was determined in a well-known model reaction which is the reduction of p-nitrophenol (p-NP) to paminophenol (p-AP) in the presence of NaBH4 in aqueous media. p-NP aqueous solution was bright yellow, and the reduction product p-AP was colorless. The reduction was conducted in a standard quartz cell with a path length of 1.0 cm. Freshly prepared NaBH4 (0.1 M, 0.1 mL) was mixed with polymer-metal dispersion (50 μL) in water (2.5 mL). Immediately, p-NP (50 μL, 1.15 mM) was added and stirred. The UV–
Table 1 Copolymer compositions, number average molecular weights (Mn, g mol−1), molecular weight distributions (Mw/Mn), and degrees of polymerizations (DPs) (Co)polymer Mn DP Mna DPb Mnb Mw/ −1 (theory) (theory) (g mol ) (Exp.) (g mol−1) Mna (Exp.) MPEG45-Br MPEG45-b -PGMA63 a b
2150 9250
45 45–50
3150 11,500
45 45–63
2150 11,100
1.02 1.08
As determined by GPC
As determined from 1 H NMR spectrum by comparing relevant signals of each block
Colloid Polym Sci Fig. 3 The reaction products of ethylenediamine with an epoxy ring: a cross-linking via the reaction of two epoxy rings with a primary diamine, b bonding resulting from the reaction of an epoxy rings with a primary diamine, and c cross-linking via the reaction of four epoxy rings with a primary diamine
determined to be 63. Thus, the block copolymer was denoted as MPEG45-b-PGMA63. Glycidyl methacrylate is one of the interesting functional monomers in a wide range of industrial applications. The biggest advantage of the GMA-containing polymer is easily reacted epoxy groups. By reaction of epoxy groups with a variety of nucleophiles allows obtaining several derivative polymers. Reactions of PGMA with primary [47–49] and secondary amines [49–51] have attracted great attention (see Fig. 3). Ethylenediamine is a primary diamine, and each amine group may react with one or two epoxy ring as shown in Fig. 3. However, the secondary amines react with only one epoxy ring. Since the presence of ethylenediamine and epoxy ring in the reaction medium, the reactions may remain incomplete in some cases as seen in Fig. 3b. MPEG45-b-PGMA63 diblock copolymer is an amphiphilic diblock copolymer which has a hydrophobic PGMA block and hydrophilic PEG block. Therefore, MPEG 4 5 -b-PGMA 6 3 diblock copolymer can give PGMA-core micelles in aqueous media. In order to get better micellar size distribution, use of cosolvent is the most commonly preferred way. In our case, micelles in aqueous media were obtained by using acetone as cosolvent. Specific bluish color of the solution indicated
Fig. 4 Digital photographs of each solution in the preparation of PtNPs by CCL micelle process (dispersion is diluted 10-fold)
the formation of related micelles (Fig. 4). PGMA formed the core, and PEG formed the shell of the spherical core–shell micelle. The micellar structure was stabilized, upon dilution or changes of external conditions such as changes in pH, ionic strength, solvent change, and temperature, with ethylenediamine crosslinking agents. Due to easy reaction of epoxy groups with (di)amine, it is possible to cross-link the core of MPEG-b-PGMA micelles in aqueous media.
Fig. 5 DLS particle size distributions of unimer in acetone (a), micelles in acetone/water (1/9 volume ratio) (b), and core cross-linked micelles in water (c)
Colloid Polym Sci Fig. 6 The change in diameter of the CCL micelles in different solvents (methanol, ethanol, acetone, and THF)
This micelle/aggregate formation was determined by DLS studies, and size distributions were given in Fig. 5. DLS results indicated that the diblock copolymer was molecularly soluble in acetone (see Fig. 5a) and formed near monodisperse micelles with a radius of 17.8 nm and a μ2/Γ2 of 0.12 by addition of water. The hydrodynamic radius of the micelles was slightly decreased from 17.8 to 17.5 nm after cross-linking. The crosslinking was accomplished by the presence of micelles by checking in different organic solvents (methanol, ethanol, acetone, and THF) as given in Fig. 6. CCL micelles were in spherical form in given organic solvents, but their diameters were bigger than the diameter in aqueous media (Fig. 6). In addition, DLS results indicated that CCL micellar size in aqueous media did not show significant change with temperature (from 25 to 55 °C) and pH (from pH 2 to 11). After cross-linking, the micelle core became hydrophilic by gaining hydrophilic amine and –OH functional Table 2
Experimental conditions in the synthesis of PtNPs
Sample code
Mole ratio of GMA/[PtCl6]2−
Mole of [PtCl6]2−
Pt1
4/1
Pt2
8/1
Mole of NaBH4−
[PtCl6]2− (mM)
(4/1) 1.77×10−5
1.42×10−4
3.42
−6
7.09×10−5
1.71
(8/1) 8.85×10
Note that after all additions, the final volume was adjusted to 5.0 mL in each case. MPEG45-b-PGMA63 diblock copolymer concentration was 0.25 wt% (5 mL dialyzed solution)
groups. These groups provided CCL micelles the ability to form complex with metal cations or metal containing complex anions. Thus, CCL micelle core should be a very good host for metal cations in neutral and basic conditions and for metal containing anions such as platinate in acidic conditions. Herein, we aimed to get complexation in CCL core between platinate anions and positively charged quaternary amine groups provided by cross-linking, at pH 2.6. After reducing platinum cation with NaBH4, nanoplatinum particles were obtained in CCL micelle with a great stabilization. Both DLS and TEM studies confirmed stable nanoparticle formation in CCL micellar structure (Figs. 5, 6, and 7). The
Fig. 7 TEM image of CCL micelles of MPEG45-b-PGMA63
Colloid Polym Sci
Fig. 8 TEM image of Pt1 dispersion (mole ratio of GMA/[PtCl6]2− =4/1)
Fig. 9 TEM image of Pt2 dispersion (mole ratio of GMA/[PtCl6]2− =8/1)
schematic representation of the preparation of PtNPs by CCL micelle was also shown in Fig. 2. The digital photographs of related steps were also given in Fig. 3. Experimental conditions in the synthesis of PtNPs were summarized in Table 2. TEM images indicate that there is, generally, a few PtNPs in CCL micelles of MPEG45-b-PGMA63 diblock copolymer with uniform structures (see Figs. 8, and 9). TEM images of Pt1 and Pt2 PtNPs indicate spherical form with average size of 5.5 ± 1.7 and 5.1 ± 1.5 nm (Figs. 8 and 9), respectively. TEM images indicate the spherical shape of the micelle (CCL) structure with metal particles in the core as seen in Figs. 8 and 9. The stabilization of PtNPs was provided for a long time with related CCL micelles. Additionally, MPEG blocks should be considered itself as a good stabilizer for metal nanoparticles as well, as reported in the literature [16, 52]. It is also worth to mention that the diameter of the CCL micelles that was determined from TEM images was to be 22.0±3.0 nm (Fig. 7), while average diameter was measured to be 35.0 nm in DLS measurements. The DLS measurements showed near monodisperse particles in aqueous media. The bigger size of micelle with DLS measurement is due to hydration of CCL in aqueous media which causes expansion of the CCL micelle.
Thus, it is concluded that TEM and DLS results support each other. The determination of catalytic efficiency of CCL micelle-PtNP dispersions was also studied in a wellknown model reaction which is the reduction of p-NP to p-AP in aqueous media. p-NP aqueous solution is bright yellow, and the reduction product p-AP is colorless (Fig. 10). The rate of the reduction was assumed to be independent from the concentration of NaBH 4 . Because, this reagent was adjusted to largely exceed concentration of p-NP and supposed to be essentially constant during the reaction. The UV–Vis spectrum exhibits a characteristic plasmon band at 205 nm and 261 (Fig. 11). These values indicate the small diameter up to 5.0 nm PtNPs [53]. As seen in Fig. 12a, b, the decrease in intensity of UV absorption at 400 nm in very short timescale was the indication of its good catalytic activity in the reduction of p-NP (or the increase in absorption intensity at around 300 nm corresponding to p-AP). The rate constant of the reaction was determined from the plot of ln(A/Ao) vs time [54, 55]. Full conversion times of p-NP to p-AP and rate constants were given in Table 3. It is clear that these reactions are very fast and follows pseudo-first order kinetics. The reaction time decreases with an increase in the amount of catalyst (Fig. 12a, b).
Fig. 10 Reduction of pnitrophenol to p-aminophenol in the presence of NaBH4
Colloid Polym Sci Table 3 Full conversion time and rate constants of the reduction of pnitrophenol to p-aminophenol (p-nitrophenol 50 μL, 1.15 mM, NaBH4 0.1 M, 0.1 mL, dispersion 50 μL, water 2.5 mL, temp. 25 °C) Sample code
Mole ratio GMA/[PtCl6]2−
H2PtCl6a (mM)
Time (min)
Degradation rate (s−1)
Pt1 Pt2
4/1 8/1
3.54 1.77
42 20
2.3×10−3 1.3×10−3
a
Concentration before reduction of H2PtCl6·6H2O
dependent on reaction conditions. Our obtained rate constants have the values that can be considered to be good and close to the values given in the literature [56–58]. Fig. 11 Absorption bands of the surface plasmon resonance of Pt1 and Pt2 dispersions
Conclusions We can also see from Fig. 12c, d that the rate constant increases with an increase in the concentration of the catalyst. These results showed that particle size of PtNPs had an important effect on catalytic activity. The pseudo-first-order rate constant at 25 °C was calculated from the slope to be 1.3× 10−3 and 2.3×10−3 s−1 in the case of PtNPs. Values of the rate constants in the literature are between 2.5×10−4 and 1.9×10−1 [56–58]. It should be noted that catalytic activity of PtNPs depends on amount and size of NPs and temperature. Therefore, rate constants should be considered to be
Fig. 12 UV–Vis absorption spectra for the reduction of pnitrophenol by NaBH4 in the presence of CCL micelle-PtNP dispersions: a) reaction time conversion of Pt1 dispersion, b) reaction time-conversion of Pt2 dispersion, c) Pt1 and rate constant determination and plots of ln(A/Ao) vs. time dispersion, and d) Pt2 dispersion (p-NP 50 μL, 1.15 mM, NaBH4 0.1 M, 0.1 mL, dispersion 50 μL, water 2.5 mL, temp. 27 oC)
Core cross-linked (CCL) micelles were synthesized from PGMA-core micelles via cross-linking reaction between the epoxy functional group of PGMA block and ethylenediamine. This process is relatively low-cost and easy. CCL micelles were successfully used in the synthesis and stabilization of PtNPs. TEM and DLS results indicated that the PtNPs are embedded in the CCL micelles. TEM image indicates CCL micelles with 22.0±3.0 nm in diameter in which the smaller black dots of PtNPs with an average diameter 5.5±1.7 (Pt1) and 5.1 ± 1.5 (Pt2) nm were present. CCL micelle-PtNP
Colloid Polym Sci
dispersions were stable for more than 6 months without any change on particle sizes and any flocculation at room temperature. The CCL micelle-PtNP dispersions showed good catalytic activity in the reduction of p-NP in the presence of sodium borohydride. In the near future, we aim to obtain higher micelle concentrations and better cross-linking kinetics with a cross-linker having longer chain length. Synthesis and stabilization of different nanometal dispersions will be studied by improving novel CCL system.
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19. Acknowledgments We are grateful for the financial support of Eskisehir Osmangazi University (ESOGU). This work was supported by the Commission of Scientific Research Projects of ESOGU (Grant Numbers 201119006 and 201319C103). V.B. expresses his gratitude to the Turkish Academy of Sciences (TUBA) as an Associate Member for financial support.
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