Efficient recovery of nanocatalysts, especially the graphene supported noble metal catalysts, is a challenge. In this study, we report a simple one-step route to prepare the graphene supported Pt/Ni nanocatalysts with ideal superparamagnetic properties. We demonstrated that they had excellent catalytic activities in the catalytic reduction of aromatic nitro compounds and could be easily separated from the reaction mixtures by applying an external magnetic field.
Graphene [
Here, we report a one-step route to prepare the graphene supported Pt/Ni hybrids (Pt/Ni-G) (Scheme
Illustration of preparing Pt/Ni-G hybrids.
Graphite oxide was prepared by the modified Hummers method [
To investigate the catalytic activity of the as-prepared hybrids, the reduction of p-nitrophenol (4-NP) was tested in a quartz cuvette. In brief, 20
The as-prepared Pt/Ni-graphene hybrids were characterized by high-resolution transmission electron microscopy (HRTEM) (Philips Tecnai G2 F20), scanning electron microscopy (SEM) (Hitachi S-4800), energy dispersive X-ray spectroscopy (EDX) (Philips Tecnai G2 F20 & Hitachi S-4800), and X-ray photoelectron spectroscopy (XPS) (PerkinElmer, PHI 1600 spectrometer). The X-ray diffraction (XRD) was conducted on a Bruker-Nonius D8 FOCUS diffractometer. The catalytic activity of Pt/Ni-G hybrids was measured by UV absorption spectra on a UV-2802H system with a temperature controller.
The XRD diffraction pattern of the Pt/Ni-graphene hybrids was recorded to identify the product (Figure
XRD pattern of the as-prepared Pt/Ni-G hybrids.
Further evidence for the chemical state and composition of the hybrids was obtained by X-ray photoelectron spectra (XPS). Compared with GO (Figure
Survey XPS spectra of GO (a) and Pt/Ni-G (b). C1s XPS spectra of GO (c) and Pt/Ni-G (d). Pt 4f spectra (e) and Ni 2p3 spectra (f) of Pt/Ni-G.
The surface morphological study was carried out by using TEM. As shown in Figure
TEM image and size distribution (total no.: 101, mean diameter: 15.4 nm) (a) and HRTEM image (b) of Pt/Ni-G bimetallic nanoparticles homogeneously decorated on the surface of graphene. Line scanning analysis (c) and corresponding EDX results (d).
Interestingly, it is easy to find that the graphene supported nanoparticles show a dark core and a comparatively pale shell under the HRTEM image of Pt/Ni-G (Figure
These results are further supported by line scanning analysis. As shown in Figure
Interestingly, quantitative analysis by EDX (Figure
SEM image of Pt/Ni-G (a) and corresponding quantitative EDS element mapping of O (b), Ni (c), and Pt (d).
Figure
Hysteresis loop of Pt/Ni-G hybrids measured by SQUID magnetometer at 300 K (a). Successive UV-Vis spectra showing the reduction of 4-NP catalyzed by 4.0
To probe the catalytic performances of the obtained hybrids, reduction of p-nitrophenol (4-NP) to its corresponding amino derivative was used as the model reaction. In brief, the catalytic reduction of 4-NP by excessive NaBH4 was carried out at room temperature under solvent free condition by using as-synthesized Pt/Ni-G hybrids catalysts. The reaction process was monitored by the UV-Vis spectrophotometry and conducted in the absence of catalysts first. It was observed that the yellow color of the solution deepened after the addition of NaBH4, and a red shift of the peak from 317 to 400 nm occurred. This phenomenon was caused by the formation of p-nitrophenolate ions in alkaline condition [
The excellent catalytic activity of the Pt/Ni-G hybrids can be attributed to the alloy nature of the supported Pt/Ni nanoparticles, which usually show superior catalytic performance than their monometallic counterparts [
In summary, we developed a simple one-step route to prepare the graphene supported Pt/Ni nanoparticles (Pt/Ni-G). The supported Pt/Ni nanoparticles had a mean diameter of 15 nm and showed superparamagnetic behavior. Catalytic investigation revealed the excellent catalytic activity of the obtained hybrids in the catalytic reduction of aromatic nitro compounds. Notably, the Pt/Ni-G hybrids could be easily separated from the reaction mixtures by applying an external magnetic field. Given their excellent catalytic performances, as well as their magnetically separable nature, these Pt/Ni-G hybrids are ideal recoverable nanocatalysts and may find potential applications in a variety of reactions.
This study was supported by the National Natural Science Funds for Excellent Young Scholars (no. 21222608), Research Fund of the National Natural Science Foundation of China (no. 21106099), Foundation for the Author of National Excellent Doctoral Dissertation of China (no. 201251), the Tianjin Natural Science Foundation (no. 11JCYBJC01700), and the Programme of Introducing Talents of Discipline to Universities (no. B06006).