[C60]Fullerene Nanowhisker-Silver Nanoparticle Composites

Catalytic Activity for Reduction of 4-Nitrophenol with [C60]Fullerene Nanowhisker-Silver Nanoparticle Composites

Jeong Won Ko1 and Weon Bae Ko1,2,*

1Department of Convergence Science, Graduate School, Sahmyook University, Seoul 139–742, South Korea 2Department of Chemistry, Sahmyook University, Seoul 139–742, South Korea

Silver nanoparticle solution was prepared by the addition of silver nitrate (AgNO3), trisodium citrate dihydrate (C6H5Na3O7·2H2O), sodium borohydride (NaBH4), cetyltrimethyl ammonium bromide ((C16H33)N(CH3)3Br), and ascorbic acid (C6H8O6), which was subsequently added to distilled water. The resulting solution was subjected to ultrasonic irradiation for 3 h. [C60]fullerene nanowhisker-silver nanoparticle composites were prepared using C60-saturated toluene, silver nanoparticle solution, and isopropyl alcohol by the liquid-liquid interfacial precipitation (LLIP) method. The product of [C60]fullerene nanowhisker-silver nanoparticle composites was con rmed by x-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. The activity of [C60]fullerene nanowhisker-silver nanoparticle composites as a catalyst was characterized by the reduction of 4-nitrophenol by UV-vis spectroscopy. [doi:10.2320/matertrans.M2016214]

(Received June 10, 2016; Accepted September 26, 2016; Published November 25, 2016)

Keywords: [C60]fullerene nanowhisker-silver nanoparticle composites, catalyst, 4-nitrophenol, reduction

1. Introduction sized silver metal, which can be attributed to their large ratio of surface to volume.17) 4-nitrophenol reduction to 4-amino- Among the fullerene family, [C60]fullerene has been found phenol in the presence of NaBH4 with silver nanoparticles is to be remarkably stable and consists of 12 pentagons and 20 an important intermediate for the preparation of antipyretic hexagons with the symmetry of a soccer ball.1) Fine solid nee- and analgesic drugs.18–21) dle-like bres of [C60]fullerene have been identi ed as sin- Some instances of the use of 4-nitrophenol reduction in gle-crystal [C60]fullerene nano bers called [C60]fullerene previous classical reaction tests to evaluate catalytic proper- 2) nanowhiskers. [C60]fullerene nanowhiskers have been ties of many nanosized metals, and similar kinetic studies shown to be one-dimensional single-crystal nanorods consist- with silver nanoparticles dispersed in other conducting matri- 22–24) ing of [C60]fullerene, and possess unique physical and chem- ces, are given in the following literature. The dispersion ical properties due to the presence of novel conjugated pi-sys- of silver nanoparticles on nanosized [C60]fullerene nanowhis- tems.3) The liquid-liquid interfacial precipitation (LLIP) kers is attractive for catalytic applications.5,25) Therefore, method developed by Miyazawa and co-workers is a versatile here, we prepared hybrid nanocomposites with [C60]fullerene method for the fabrication of one-dimensional crystals of nanowhiskers and silver nanoparticles using the liquid-liquid 4) [C60]fullerene nanowhiskers. [C60]fullerene nanowhiskers interfacial precipitation (LLIP) method, and investigated the are prepared using the liquid-liquid interfacial precipitation characterization of [C60]fullerene nanowhisker-silver (LLIP) method, which depends on the diffusion of a poor nanoparticle composites and their catalytic activity for reduc- [C60]fullerene solvent, such as isopropyl alcohol, into a tion of 4-nitrophenol in the presence of sodium borohydride. 4,5) [C60]fullerene-saturated toluene solution. The growth of [C60]fullerene nanowhiskers is affected by light, temperature, 2. Experimental Procedure and concentration of water ratio of the poor solvent to the 5–10) good solvent for [C60]fullerene during the LLIP method. 2.1 Reagents and instruments The polymerization of [C60]fullerene molecules by weak Silver nitrate (AgNO3) was supplied by Sigma-Aldrich. van der Waals interactions has attracted attention due to its Trisodium citrate dihydrate (C6H5Na3O7·2H2O), cetyl- 11,12) promising properties as a carbon nanomaterial. trimethyl ammonium bromide ((C16H33)N(CH3)3Br), ascor- [C60]fullerene nanowhiskers polymerize under laser-beam ir- bic acid (C6H8O6), and toluene were obtained from Samchun 11,12) radiation conditions. The peak, Ag(2) pentagonal pinch Chemicals. [C60]fullerene was supplied by Tokyo Chemical mode of [C60]fullerene, was a good indicator of [C60]fuller- Industry Co., Ltd, and sodium borohydride (NaBH4) was pur- ene nanowhisker polymerization, with the shift of the Ag(2) chased from Kanto Chemical Co., Inc. peak taking place from 1469 cm−1 to 1457 cm−1 in the Ra- X-ray diffraction (XRD; Bruker, D8 Advance) analysis 5,12,13) man spectra upon polymerization. [C60]fullerene was used to examine the structure of the nanocomposites at nanowhiskers are used in a wide range of applications in var- 40 kV and 40 mA. Imaging of the sample surface was per- ious elds including catalysts, electronic devices, fuel cells, formed by scanning electron microscopy (SEM; JEOL Ltd., chemical sensors, solar cells, eld-effect transistors, and su- JSM-6510) at an accelerating voltage of 0.5 to 30 kV. The per conductors.5,14–16) particle size and morphology of the sample were identi ed by Silver nanoparticles are used for many chemical reactions transmission electron microscopy (TEM; AP Tech, Tecnai G2 due to their higher catalytic ef ciency compared with macro- F30 S-Twin) at an acceleration voltage of 200 kV. Raman spectroscopy (Thermo Fisher Scienti c, DXR Raman Micro- * Corresponding author, E-mail: [email protected] scope) was used to observe polymerization of the composites, Catalytic Activity for Reduction of 4-Nitrophenol with [C60]Fullerene Nanowhisker-Silver Nanoparticle Composites 2123 and UV-vis spectrophotometry (Shimazu UV-1691 PC) was 17.63°, 20.67°, 28.01°, 30.91°, and 32.62° correspond to used to characterize their catalytic activity. (111), (220), (222), (420), (422), and (333) planes, due to the [C60]fullerene nanowhiskers. The peaks of 37.90°, 44.37°, 2.2 Synthesis of [C60]fullerene nanowhisker-silver 64.54°, 77.47°, and 81.97°correspond to (111), (200), (220), nanoparticle composites (311), and (322) planes, due to the silver nanoparticles. The 2.2.1 Synthesis of silver nanoparticles corresponding d-spacing values of the silver nanoparticles are A silver-nanoparticle seed solution was prepared by dis- 2.37 Å, 2.04 Å, 1.44 Å, 1.23 Å and 1.17 Å, respectively. −2 −2 solving 2.5 × 10 M silver nitrate (AgNO3), 2.5 × 10 M Scherrer’s equation was used to calculate the crystallite size trisodium citrate dihydrate (C6H5Na3O7·2H2O), and 2.64 ml of the silver nanoparticles: 1 M sodium borohydride (NaBH ) in 11 ml distilled water. A 4 λκ silver nanoparticle growth solution was prepared with 2.5 × D = −2 −1 cos θ β 10 M AgNO3 and 1.25 × 10 M cetyltrimethyl ammonium · bromide ((C16H33)N(CH3)3Br) in 44 ml distilled water. Silver where λ is the wavelength of powder X-ray diffraction with nanoparticles were prepared by mixing 11 ml seeding solu- CuKα radiation (λ = 0.154178 nm), κ is a shape factor taken tion with 33 ml growth solution, and subsequently adding as 0.89, 2θ is the angle between the incident and scattered 0.52 ml 0.2 M ascorbic acid (C6H8O6) and ultrasonicating the x-rays, and β is the full width at half maximum (FWHM). The solution for 3 h. crystallite size and d-spacing value of the silver nanoparticles 2.2.2 Synthesis of [C60]fullerene nanowhisker-silver are shown in Table 1. The average crystallite size of the silver nanoparticle composites nanoparticles was 30.67 nm. The SEM image of the 50 mg [C60]fullerene and 50 ml toluene were added to a [C60]fullerene nanowhisker-silver nanoparticle composites is 100-ml Erlenmeyer ask, stirred for 15 min, and then ultra- shown in Fig. 2. The silver nanoparticles were clustered and sonicated for 45 min. The [C60]fullerene solution was dis- placed on the [C60]fullerene nanowhiskers, which are rod-like solved in toluene and then solution ltered through lter pa- bres. per. The resulting [C60]fullerene solution and isopropyl alco- The amount of silver nanoparticles that collected by them- hol were placed in the refrigerator for 20 min. selves and attached to the [C60]fullerene nanowhiskers was 5 ml [C60]fullerene solution, 2.5 ml silver nanoparticle 25 mM. Raman spectra of the nanocomposites are shown in solution, and 37.5 ml isopropyl alcohol were placed in a 50- ml vial. The resulting solution was ultrasonicated for 10 min, and then refrigerated for 16 h. The cold solution was ltered through lter paper, and dried to the solid state in an oven at 100°C for 1 h. The amount of silver nanoparticles loaded on the [C60]fullerene nanowhiskers was 0.25 mM. 2.2.3 Characterization of [C60]fullerene nanowhisker- silver nanoparticle composites The XRD pattern of the [C60]fullerene nanowhisker-silver nanoparticle composites was obtained from powder x-ray diffraction with Cu Kα radiation (λ = 0.154178 nm). The mor- phological shape of the nanocomposites was observed by SEM, and TEM was used to observe the specimen size. The hybrid nanocomposites were characterized using Raman spectroscopy. 2.2.4 Evaluation of catalytic activity through 4-nitrophenol reduction The absorbance peak in the UV-vis spectrum of 1.5 mg (1.1 mM) 4-nitrophenol at 400 nm was monitored, as it appeared in the presence of 5 mg (13.2 mM) NaBH4 dissolved in 10 ml distilled water. 1 mg [C60]fullerene nanowhisker-silver nanoparticle composites was used as the catalyst for the Fig. 1 XRD pattern of [C60]fullerene nanowhisker-silver nanoparticle com- 4-nitrophenol reduction. The absorbance was monitored at posites. 5 min intervals to con rm 4-nitrophenol reduction.

3. Result and Discussions Table 1 Crystallite size and d-spacing value of silver nanoparticles.

Peak 2θ (degree) FWHM (B) d-spacing h k l Crystallite 3.1 Characterization of [C60]fullerene nanowhisker-sil- value (Å) size (nm) ver nanoparticle composites X-ray diffraction was used to determine the crystal struc- S1 37.90 0.36 2.37 1 1 1 23.06 nm S2 44.37 0.32 2.04 2 0 0 26.50 nm ture and crystallite size of [C60]fullerene nanowhisker-silver S3 64.54 0.36 1.44 2 2 0 27.97 nm nanoparticle composites. The XRD pattern of the [C60]fullerene nanowhisker-silver nanoparticle composites can be seen S4 77.47 0.31 1.23 3 1 1 32.48 nm in Fig. 1, 2θ values range from 10° to 90°. The peaks of 10.97°, S5 81.97 0.24 1.17 2 2 2 43.35 nm 2124 J. W. Ko and W. B. Ko

Fig. 2 SEM image of [C60]fullerene nanowhisker-silver nanoparticle com- Fig. 4 TEM image of [C60]fullerene nanowhisker-silver nanoparticle composites. posites.

nanowhisker-silver nanoparticle composites can be observed in Fig. 4. As can be noted, the silver nanoparticles were found on the surface of the [C60]fullerene nanowhiskers in the composites. The width of the composites was approximately 500 nm, and the size of the silver nanoparticles was 30–40 nm.

3.2 Catalytic and kinetic activity of [C60]fullerene nanowhisker-silver nanoparticle composites for 4-nitrophenol reduction The catalytic activity of the [C60]fullerene nanowhisker-silver nanoparticle composites using NaBH4 for 4-nitrophenol reduction can be seen in Fig. 5(a) and (b). Even though NaBH4 is a strong reducing agent, Fig. 5(a) clearly shows that NaBH4 by itself was unable to reduce the 4-nitrophenolate ion to 4-aminophenol. Therefore, without the [C60]fullerene nanowhisker-silver nanoparticle composites, the peak due to the 4-nitrophenolate ion remained unaltered for 50 min. Fig- ure 5(b) reveals that the [C60]fullerene nanowhisker-silver nanoparticle composites functioned as a catalyst for the reduction of 4-nitrophenol. The UV-vis spectrum reveals di- minished peaks at 400 nm related to the formation of 4-ni- tophenolate ions following the addition of NaBH4. Due to Fig. 3 Raman spectra of [C ]fullerene nanowhisker-silver nanoparticle 60 4-aminophenol production in the presence of NaBH4 with the composites. [C60]fullerene nanowhisker-silver nanoparticle composites, a new peak at 300 nm simultaneously appeared. Because [C60]fullerene nanowhisker is a porous structure material Fig. 3. The Raman shifts of the [C60]fullerene nanowhisker- containing a number of nanosized ne pore, the advantage of silver nanoparticle composites reveal the squashing mode [C60]fullerene nanowhisker structure is to help the diffusion −1 −1 Hg(1) at 269 cm , breathing mode Ag(1) at 492 cm , and of silver nanoparticles into the [C60]fullerene nanowhisker to −1 pentagonal pinch mode Ag(2) at 1459 cm . The Raman make hybrid [C60]fullerene nanowhisker-silver nanoparticle spectroscopy of the [C60]fullerene nanowhisker-silver composites as an effective catalyst in chemical reaction. The nanoparticle composites used a laser density of 10 mW/mm2 distribution of silver nanoparticles on the surface of and a laser wavelength of 532 nm. [C60]fullerene nanowhiskers, and the effective electron trans- From the Raman shift data, which show a blue shift of fer from [C60]fullerene nanowhiskers to silver nanoparticles, −1 Ag(2) to 1459 cm , it can be identi ed that the [C60]fuller- may result in [C60]fullerene nanowhisker-silver nanoparticle ene nanowhiskers polymerized from [C60]fullerene to form composites being an ef cient catalyst for the reduction of longer rod-like crystals. TEM images of the [C60]fullerene 4-nitrophenol. The [C60]fullerene nanowhisker-silver Catalytic Activity for Reduction of 4-Nitrophenol with [C60]Fullerene Nanowhisker-Silver Nanoparticle Composites 2125

Fig. 6 Kinetics of reduction for 4-nitrophenol using [C60]fullerene nanowhisker-silver nanoparticle composites.

acterized by XRD, Raman spectroscopy, SEM, and TEM. The reduction of 4-nitrophenol, when applied with NaBH4, resulted in good catalytic activity of the hybrid nanocomposites using UV-vis spectroscopy. The kinetics of reduction for 4-nitrophenol in the presence of NaBH4 with [C60]fullerene nanowhiskers-silver nanoparticle composites as a catalyst followed a pseudo- rst-order reaction law.

Acknowledgments

This study was supported by research funding from Sah- myook University, South Korea.

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