Controlled Synthesis of Gold-based Magnetic Nanocomposites and Their Catalytic Performance

doi:10.15541/jim20170394

Abstract

Abstract:

With the rapid development of nanocatalysts, gold-based nanocomposites have attracted more and more attention due to their excellent catalytic capability. In this study, a novel kind of gold-based magnetic nanocomposite with uniform size, high dispersity, magnetic separability, highly catalytic efficiency, and stability was facilely fabricated via a controllable in-situ reducing approach. Firstly, magnetic nanocomposites were synthesized through coating 100 nm-sized hydrophobic Fe₃O₄ nanoparticles with organosilica shell formed by the hydrolysis of mercaptopropyltriethoxysilane (MPTES). Then, size-controllable gold nanoparticles (2 nm or 6 nm) formed via in situ reduction was anchored onto the organosilica shell via Au-S covalent bonding, so that gold-based magnetic nanocomposites consisted of Fe₃O₄ nanoparticles as core and gold nanoparticles decorated organosilica as shell were obtained. Various techniques, such as Transmission Electron Microscope (TEM), Dynamic Light Scattering (DLS) and Vibrating Sample Magnetometer (VSM) were employed to characterize the as-synthesized samples. It is demonstrated that the as-prepared nanocomposite is highly-dispersed, core-shell structured and superparamagnetic with diameter of ~150 nm. The saturation magnetization was measured to be 32.1 Am²/kg. Furthermore, the turnover frequency (TOF) of MCN-Au (2 nm) is calculated to be 70 s^-1 towards the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). More importantly, the conversion rate maintains 98% after 5 cycling usage, verifying its highly catalytic capability and reusability.

Key words: in situ reduction, gold-based nanocomposite, superparamagnetic, highly catalytic capability, reusability

CLC Number:

TQ174

LI Yong-Sheng, CHEN Ling. Controlled Synthesis of Gold-based Magnetic Nanocomposites and Their Catalytic Performance[J]. Journal of Inorganic Materials, 2018, 33(2): 221-228.

Figures/Tables 10

Fig. 1 Schematic illustration for preparation of the MCN-Au

Fig. 2 TEM images of (a) Fe3O4 particles, (b) MCN nanospheres, (c-e) MCN-Au (2 nm); (f) Size distribution of Au NPs on MCN-Au (2 nm)

Fig. 3 TEM images of (a-c) MCN-Au (6 nm); (d) Diameter distribution of Au NPs on MCN-Au (6 nm)

Fig. 4 SEM images of (a) Fe3O4 nanoparticles, (b) MCN, (c) MCN-Au (2 nm), (d) MCN-Au (6 nm); (e) Diameter distribution curves of different particles

Fig. 5 STEM image of MCN-Au (2 nm) nanocomposites (a); scanning mapping of Au elements (b1), Fe elements (b2) and S elements (b3). Scale bar is 100 nm; (c) EDS pattern of MCN- Au (2 nm)

Fig. 6 Wide-angle XRD patterns of (a) Fe3O4 nanoparticles, (b) MCN, (c) MCN-Au (2 nm) and (d) MCN-Au (6 nm)

Fig. 7 UV-Vis spectra of (a) MCN-Au (2 nm) (black curve) and (b) MCN-Au (6 nm) (red curve) The insets are the digital photos of MCN-Au (2 nm) and MCN-Au (6 nm)

Fig. 8 Room-temperature magnetization hysteresis loops of the Fe3O4 nanoparticles, MCN, MCN-Au (2 nm), and MCN-Au (6 nm) The inset is a photograph of the MCN-Au (2 nm) under an external magnetic field

Fig. 9 UV-Vis spectra of the reduction of 4-NP in aqueous solution recorded every 20 s using MCN-Au (2 nm) as a catalyst

Fig. 10 Curves of (a) Ct/C0 and (b) ln(Ct/C0) versus the reaction time for the reduction of 4-NP over MCN-Au; the reusability of the (c) MCN-Au (2 nm) and (d) MCN-Au (6 nm)

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