Magnetically Recoverable Hierarchical Pt/Fe2O3

Microflower: Superior Catalytic Activity and

Stability for Reduction of 4-Nitrophenol

Peng Zhang,a Xiaoyan Yang,b Hailong Peng,a Dan Liu,*a Hui Lu,c Junfu Wei,a and Jianzhou Gui*a

a State Key Laboratory of Separation Membranes and Membrane Processes, School of Environmental

and Chemical Engineering, Tianjin Polytechnic University, Tianjin 300387, China

b School of Chemistry and Chemical Engineering, Shangqiu Normal University, Shangqiu 476000,

China

c State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of

Sciences, Dalian 116023, China

*Corresponding Author:

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Prof. Dan Liu: Tel: +86-022-83955668; E-mail: danliu_939@hotmail.com

Prof. Jianzhou Gui: Tel: +86-022-83955668; E-mail: jzgui@hotmail.com

Experimental

Synthesis of Catalysts

The chemical reagents used in this work were all of analytical grade and did not undergo any further

treatment. The low-temperature hydrothermal synthesis was adopted to prepare the γ-Fe2O3

microflower. For a typical procedure, 0.48 g of ferrous chloride and 32 mL of ethylene glycol (EG)

were added into 22 mL of deionized water under magnetic stirring at room temperature, yielding a

yellow solution. After 10 mL of urea aqueous solution (0.5 M) was dropwise added under continuous

stirring, the resulting solution was transferred into a 100 mL Teflon-lined autoclave and then heated

at 180 °C for 15 h. When the reaction finished, the autoclave was naturally cooled to the room

temperature. The product was collected through filtering, throughout rinsed with deionized water and

ethanol, and dried at 80 °C under vacuum for 3 h. Finally, a resulting brown powder of γ-Fe2O3

microflower was obtained, which is hereafter denoted as Fe2O3 MF.

The EG-reduction method was employed to support Pt nanoparticles on the surface of γ-Fe2O3

microflower. Typically, 0.15 g of γ-Fe2O3 microflowers were dispersed in 100 mL of EG under

vigorous stirring to obtain the tested reaction mixture. When heated up to 140 °C, 400 L of H2PtCl6

aqueous solution (10 g/L) were dropwise added into the aforementioned reaction mixture under

continuous stirring, which was afterwards maintained at 140 °C for 30 min. At the end of reaction,

the reaction product undergoes filtering and washing with deionized water and ethanol. After dried at

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80 °C under vacuum for 3 h, the final solid sample was collected and denoted as Pt/Fe2O3 MF in this

work.

For comparison, Fe2O3 particles were adopted as the carrier to prepare Pt-supported Fe2O3 particle

catalysts under identical experimental conditions as the Pt/Fe2O3 MF. Typically, 0.15 g of commercial

Fe2O3 particles were dispersed in 100 mL of EG under vigorous stirring to yield the reaction

mixture. After heated up to 140 °C, 400 L of H2PtCl6 aqueous solution (10 g/L) were dropwise

added into the resultant reaction mixture under continuous stirring, which was maintained at 140 °C

for 30 min. After that, the products collected were used as the comparative sample, and denoted as

Pt/Fe2O3 particle.

Characterization of Catalysts

X-ray diffraction patterns (XRD) were recorded on a Rigaku D/Max-2400X apparatus with Cu Kα

irradiation, operated at 40 kV and 100 mA. Details of the morphology of the solid catalysts were

observed using Scanning Electron Microscopy (SEM, Quanta 450) and Transmission Electron

Microscopy (TEM, JEM-2000EX). The size distribution of supported Pt nanoparticles was based on

150 Pt monomers in the Pt/Fe2O3 microflower sample. The chemical compositional analysis was

carried out by inductively coupled plasma-optical emission spectroscopy (ICP-OES, Optima

200DV), energy-dispersive X-ray spectrometry (EDX, Oxford X-Max), and X-ray photoelectron

spectroscopy (XPS, Thermo Escalab 250). N2 adsorption-desorption isotherms were measured at -

196 °C with a Micromeritics ASAP 2020 instrument. Before analysis, samples were degassed at 250

°C for 5 h.

Catalytic reduction of 4-nitrophenol

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The catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) was studied as described in

previous papers[1, 2] by in-situ monitoring the reactant consumption using UV-vis spectroscopy

(Thermo evolution 300) at room temperature. 25 L of 4-NP aqueous solution (0.01 M) was added

into the quartz cuvette containing 2.5 mL of fresh NaBH4 aqueous solution (0.01 M), yielding a deep

yellow solution. When 5 mg of catalyst was introduced, the reaction mixture was immediately

transferred into the UV-vis spectrometry and the absorbance variation at intervals of 1.25 min was

monitored. After 11.25 min of reaction time, the catalyst was separated from the reaction solution

with a magnet, thoroughly washed with deionized water and absolute ethanol, and then dried at 80

°C overnight. The recovered catalyst was used for the next cycling reaction to investigate its

reusability and stability.

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Figure S1. Powder XRD patterns of the Pt/Fe2O3 MF and Fe2O3 MF catalysts.

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Figure S2. Typical SEM image of the Fe2O3 MF catalyst.

Figure S3. (a) SEM, (b) TEM and (c) magnified TEM images of the Fe2O3 MF catalyst.

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Figure S4. EDX spectrum of the Pt/Fe2O3 MF catalyst.

Figure S5. (a) XPS of the Pt/Fe2O3 MF catalyst and (b) high-resolution XPS of Fe 2p.

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Figure S6. Reduction of 4-NP recorded every 1.25 min over (a) no catalyst and (b) the Fe2O3 MF

catalyst.

Figure S7. Plots of C/C0 versus reaction time for the reduction of 4-NP over the Pt/Fe2O3 MF and

Pt/Fe2O3 particle. Insets are the corresponding plots of ln(C/C0) versus reaction time.

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Scheme S1. Reaction mechanism of the reduction of 4-NP by NaBH4 using the Pt/Fe2O3 MF catalyst.

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Figure S8. Reusability of the Pt/Fe2O3 MF for the reduction of 4-NP. Reaction conditions: 5

mg Pt/Fe2O3 MF, 25 L of 4-NP (0.01 M), 2.5mL of NaBH4 (0.01M), time 12 min. Inset

shows the separation process of the Pt/Fe2O3 MF with a magnet after reaction.

References

[1] Yang Y, Li X, Yang F, Zhang W, Zhang X, Yang R. New route toward integrating large nickel

nanocrystals onto mesoporous carbons. Appl. Catal. B. 2015; 165: 94-102.

[2] Yang Y, Ren Y, Sun C, Hao S. Facile route fabrication of nickel based mesoporous carbons with

high catalytic performance towards 4-nitrophenol reduction. Green Chem. 2014; 16(4): 2273-2280.

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