Nickel-Decorated Fe3O4 Nanoparticles as Recyclable Magnetic Self

Jan 6, 2017 - On the basis of the charming magnetic feathers of Fe3O4 and the fine catalysis activity of Ni, the Fe3O4@PZS-Ni nanoparticles could not ...
0 downloads 0 Views 3MB Size
Download PDF
Research Article pubs.acs.org/journal/ascecg

Nickel-Decorated Fe3O4 Nanoparticles as Recyclable Magnetic SelfStirring Nanocatalysts for Microreactions Lin Miao,† Yi-Zhou Zhu,‡ and He-Fang Wang*,† †

Research Center for Analytical Sciences, College of Chemistry, Key Laboratory of Biosensing and Molecular Recognition, State Key Laboratory of Medicinal Chemical Biology and ‡State Key Laboratory of Elemento-Organic Chemistry Institute, Nankai University, Tianjin 300071, China

Downloaded via UNIV OF TOLEDO on June 29, 2018 at 20:25:17 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: We presented the first exploration of the easily prepared nickel-decorated magnetic Fe3O4 nanoparticles as recyclable nanosized magnetic self-stirring catalysts for microdroplet reactions. The cross-linked polymer poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) was used as the intermediary to link Fe3O4 and anchored nickel nanodots. On the basis of the charming magnetic feathers of Fe3O4 and the fine catalysis activity of Ni, the Fe3O4@PZS-Ni nanoparticles could not only self-stir or make the reactants move along the tiny channels with the help of the external rotating magnetic field but also exhibit high catalysis activity and convenient recyclability. The Fe3O4@PZS-Ni nanoparticles have the merits of small size, good suspension, easy fabrication, and most importantly, superior flexibility and adaptability to any shape of the microreactors or nanoreactors; thus, they may bring new inspiration for self-stirring catalytic reactions in micro/nanochips or micro/nanobiological tubules or tissues. KEYWORDS: Nickel, Fe3O4, Magnetic self-stirring, Catalysts, Microreactions

■

INTRODUCTION The rapid and effective mixing of substances in tiny channels or droplets is essential for microreactions in sensing, liquid transport, microfluidics, and other applications.1−4 To that end, rigid magnetic Fe3O4 nanochains5 and spindle-shaped yolk/shell Pd−Fe@m-SiO2 magnetic bars6 have been reported as nanoscale magnetic self-stirring bars to fasten the mass transport in microreactors.7 Very recently, the magnetic selfstirring mode by the Co@g-C3N4-rGO composite has also displayed higher catalytic activity than the magneton stirring mode in batch reactors.8 Though great progress has been made, the existing nanoscaled self-stirring bars suffer from the complex fabrication process. Inspired by the self-stirring capability of Fe3O4 nanochains5 and self-assembled behavior of magnetic Fe3O4 nanoparticles into magnetic photonic crystals,9,10 we deduce that Fe3O4 nanoparticles themselves could be in situ self-assembled and could self-stir under the rotating magnetic field for churning whole solutions in nanoreactors. Compared with the cobaltbased composite,8 Fe3O4 nanoparticles displayed higher saturation magnetization and better superparamagnetism (lower coercivity and remanence), which was beneficial for the rapid harvest and redispersion of magnetic nanoparticles into reactant solutions. Compared with Fe3O4 nanochains or yolk/shell Pd−Fe@m-SiO2 self-stirring bars, nanostirring bars composed of Fe3O4 magnetic nanoparticles have merits of much smaller size, much better suspension, much easier fabrication, and most importantly, much better flexibility and adaptability to any shape of microreactors or nanoreactors. © 2017 American Chemical Society

Herein, we presented the use of nickel-decorated Fe3O4 nanoparticles as recyclable magnetic self-stirring catalysts for microdroplet reactions. Fe3O411−13 was involved as the internal core responsible for the magnetic self-stirring and convenient separation of the reactants/products and catalysts and thereby improved recyclability and efficiency.14−16 The cross-linked polymer poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS)17−19 was used as the intermediary to link Fe3O4 and the anchored nickel nanodots (Scheme 1). Nickel instead of palladium was chosen here, as nickel catalysis is currently experiencing intensified interests, not only because of its low cost but also because of its catalyst capability for intriguing, valuable, and difficult transformations.20,21 This work reports the detailed synthesis and characterization of Fe3O4@PZS-Ni nanoparticles and, most importantly, highlights the promising prospect of the application of Fe3O4@PZS-Ni nanoparticles as recyclable nanosized magnetic self-stirring catalysts for microreactions. To demonstrate the functions of self-stirring bars and the recyclable catalyst of Fe3O4@PZS-Ni, the common reactions, namely, the reduction of 4-nitrophenol22−25 and methylene blue,5,26 were involved as models. To the best of our knowledge, this is the first exploration of functionalized Fe3O4 nanoparticles as both nanosized self-stirring bars and recyclable catalysts. Received: October 26, 2016 Revised: December 8, 2016 Published: January 6, 2017 1864

DOI: 10.1021/acssuschemeng.6b02581 ACS Sustainable Chem. Eng. 2017, 5, 1864−1870

Research Article

ACS Sustainable Chemistry & Engineering Scheme 1. Schematic Diagram of Synthesis of Fe3O4@PZS-Ni Nanoparticles

■

the Fe3O4@PZS-Ni were harvested with a magnet and dried in vacuum overnight. The Ni catalyst was prepared for comparison. To a 100 mL threenecked flask under an argon atmosphere, 30 mL of water was added, and 5 mL of aqueous solution of nickel acetate (15.5 mg) was slowly added under magnetic agitation using a commercial magnetic stir bar. Then, the flask was soaked in an ice bath, and 8 mL of aqueous solution of KBH4 (10 mg) was injected dropwise. The mixture was magnetically stirred for 30 min. The final product was washed with water and ethanol three times, respectively, centrifuged, and dried in vacuum. Reduction of Methylene Blue. Onto a Teflon platform placed on a turn-on magnetic stirrer, 28 μL of methylene blue aqueous solution (9 × 10−5 mol L−1) was dropped. Then, 25 μL of KBH4 solution (90 mmol L−1) without any catalyst or with Fe3O4@PZS-Ni catalyst (nickel concentration of 0.34 mmol L−1) was injected into the droplets. The tiny Fe3O4@PZS-Ni nanocatalysts were churning in the droplet, and the blue color faded subsequently, whereas the droplet without any catalyst stayed blue all the time (Video 1, Supporting Information). The methylene blue was also reduced in a glass capillary. Two microliters of Fe3O4@PZS-Ni solution (nickel concentration 3.0 mmol L−1) and 2 μL of methylene blue solution (1.8 × 10−4 mol L−1) were dropped onto the Teflon platform, respectively. One end of the glass capillary was first drawn into the Fe3O4@PZS-Ni droplet and then into the methylene blue droplet. In this way, two segments (the blue methylene blue solution and the gray Fe3O4@PZS-Ni solution) were found within the capillary. The capillary was put on the upside of the magnetic stirrer, with the gray end far away from the magnetic center. The gray fluid was stirred immediately upon turning on the magnetic stirrer, moving forward toward the magnetic center, and the blue liquid faded gradually (Video 2, Supporting Information). Reduction of 4-Nitrophenol. For the reaction in droplets, 2 mL of aqueous solution of 4-nitrophenol (4 × 10−4 mol L−1) was pipetted into a tube, followed by the addition of 22 mg of KBH4. The color of light yellow was deepened upon the addition of KBH4. Onto the Teflon platform put on a turn-on magnetic stirrer, 8 μL of the above mixed solution was transferred to form a droplet, and 2 μL of Fe3O4@ PZS-Ni solution (nickel content of 0.90 mmol L−1) was dripped into that droplet. The tiny Fe3O4@PZS-Ni nanocatalysts were rotating rapidly upon addition of the droplets, and the yellow droplets turned colorless gradually (Video 3, Supporting Information). To further quantify the catalytic activity, the reduction of 4nitrophenol was monitored by UV−vis spectrometry. Three mL of aqueous solution of 4-nitrophenol (1 × 10−4 mol L−1) was added into a cuvette, followed by addition of KBH4 (14 mg) and 0−120 μL of Fe3O4@PZS-Ni solution (with nickel content of 0.90 mmol L−1). The spectra were scanned every 2 min in the range of 250−550 nm. The activity of the catalyst (reaction rate constant) was evaluated in the kinetic mode, where the absorbance at 400 nm was recorded at 0.5 s intervals.

EXPERIMENTAL SECTION

Reagents and Materials. FeCl3·6H2O, CH3COONa, polyethylene glycol (PEG, MW 2000), and KBH4 were bought from Guangfu Fine Chemical Research Institute (Tianjin, China). Ethylene glycol (EG, 99%) and triethylamine (TEA, 99.5%) were from Aladdin (Shanghai, China). Hexachlorocyclophosphazene (HCCP) and 4,4′sulfonyldiphenol (BPS) were from Alfa-Aesar (Shanghai, China). Ethanol and tetrahydrofuran (THF) were from Concord Fine Chemical Research Institute (Tianjin, China). Ni(CH3COO)2·4H2O and methylene blue (MB) were from Tianjin Chemical Reagent Company (Tianjin, China) and Beijing Chemical Reagent Company (Beijing, Chian). 4-Nitrophenol was purchased from J&K Scientific Co., Ltd. (Beijing, China). All chemicals were used directly. Apparatus. The morphology of the materials was observed by a JEOL 100 CXII transmission electron microscope (TEM), being exerted at 200 kV accelerating voltage (JEOL, Tokyo, Japan). The samples were made on a 200-mesh Cu grid coated with a lacey carbon (Zhongjingkeyi Technology, Beijing, China). The X-ray diffraction (XRD) tests were operated on the Rigaku D/max-2500 X-ray diffractometer (Rigaku, Japan) using Cu Kα radiation (λ = 1.5418 Å). Thermogravimetric analysis (TGA) was operated on Rigaku Thermo plus EVO2 TG8121 at the temperature range of 25−700 °C in air with the rate of 15 °C/min. The Fourier transform infrared (FTIR) spectrum (4000−400 cm−1) was recorded with a Nicolet MAGNA-560 FTIR spectrometer (Nicolet, Madison, WI). The absorbance of the catalytic reaction was scanned by a UV−visible spectrophotometer (Shimadzu UV-3600) to monitor the process. The magnetism property of the material was tested by a Squid vibration sample magnetometer (VSM, made by Quantum Design, U.S.A.). Xray photoelectron spectroscopy (XPS) was operated by a PHI 5000 Versa probe, and auger electron spectroscopy results were obtained on a PHI 670 xi scanning auger nanoprobe. Nickel contents were determined by a 725-ES inductively coupled plasma atomic emission spectrometer (ICP-AES, Varian, U.S.A.). Energy dispersive spectroscopy (EDS) and elemental mapping were measured by EDAX TEAM (EDAX, Inc., NJ, U.S.A.). Synthesis of Fe3O4, Fe3O4@PZS, Fe3O4@PZS-Ni, and Ni Catalyst. Fe3O4 nanoparticles were synthesized via a modified hydrothermal reaction.27 To synthesize Fe3O4@PZS, HCCP/BPS at weights of 4/9, 8/18, 12/27, and 20/45 (mg/mg) were dissolved in a mixed solvent of 7.5 mL ethanol and 7.5 mL THF. Then, 1.5 mL of TEA and 50 mg of Fe3O4 nanoparticles were added in sequence. After sonication for 5 min, the dark uniform solution was poured into a glass culture dish (1 cm of height), where the solution was self-stirred under an upside-down magnetic stirrer for 8 h. The final product was washed with ethanol and THF three times, harvested by a magnet, and dried in vacuum overnight. The Fe3O4@PZS-Ni was synthesized by a chemical reduction reaction on the basis of Fe3O4@PZS. First, into a 100 mL threenecked flask under an argon atmosphere, Fe3O4@PZS was dispersed in 30 mL of water, and then, 5 mL aqueous solution of nickel acetate was slowly added under vigorous magnetic self-stirring for 0.5 h. The feeding amounts of nickel acetate/Fe3O4@PZS were 1, 2, 2.5, and 3 mmol g−1. Afterward, the three-necked flask was put into an ice bath, and then the aqueous solution (8 mL) of KBH4 (10 mg) was injected dropwise. The resultant mixture was magnetically self-stirred for 0.5 h. After being washed with water and ethanol three times, respectively,

■

RESULTS AND DISCUSSION Fabrication and Characterization of Fe3O4@PZS and Fe3O4@PZS-Ni. Fe3O4@PZS and Fe3O4@PZS-Ni were synthesized as stated in Scheme 1 and the Experimental Section. To synthesize Fe3O4@PZS, the mixed solution of 1865

DOI: 10.1021/acssuschemeng.6b02581 ACS Sustainable Chem. Eng. 2017, 5, 1864−1870

Research Article

ACS Sustainable Chemistry & Engineering

Figure 1. HRTEM images of (a) Fe3O4@PZS and (b, c) Fe3O4@PZS-Ni synthesized at the mass ratio of 50/12/27 (Fe3O4/HCCP/BPS) and 2 mmol g−1 (nickel acetate/Fe3O4@PZS).

HCCP, BPS, and Fe3O4 was self-stirred in a glass culture dish placed under an upside-down magnetic stirrer. In that way, the magnetic attraction was in the opposite direction of gravity, and the suspension of the Fe3O4 was much better. The thickness of the PZS coatings (the gray layers in the TEM images) on the Fe3O4 (dark black images, Figure S1a) was controllable by adjusting the feeding amount ratio of Fe3O4 to HCCP and BPS (Figure S1b−e, the mass ratio of HCCP/BPS was set as 4/9). To prepare Fe3O4@PZS-Ni, Fe3O4@PZS and nickel acetate were stirred first to obtain a sufficient interaction of Ni(II) with N = P of PZS, and then, KBH4 was added to reduce Ni(II) to Ni nanodots. The density and size of the Ni nanodots were dependent on the relative feeding amount of Fe3O4@PZS and nickel acetate (Figure S 1f−h). An increase in the feeding amount of nickle acetate resulted in higher density and a larger size of the Ni nanodots. However, the catalytic activity of Fe3O4@PZS-Ni was not linearly related to the feeding amount of Ni (II). Too little feeding amount of Ni (II) would have less catalytic active sites, whereas too much feeding amount of Ni (II) would result in a larger size but lower specific surface area and less surficial active sites of Ni nanodots and finally worse catalytic activity. Fe3O4@PZS-Ni synthesized at the mass ratio of 50/12/27 (Fe3O4/HCCP/BPS) and 2 mmol g−1 (nickel acetate/Fe3O4@PZS) exhibited the best catalyst activity as revealed by the highest reaction rate constant for the reduction of 4-nitrophenol (Figure S2); thus, it was typically used for the following characterization and evaluation of the self-stirring catalyst. The high resolution TEM images (Figure 1), EDS (Figure 2), and elemental mapping (Figure 3) verified the layered structure and the elemental distribution of Fe3O4@PZS-Ni. Compared with the smooth surface of Fe3O4@PZS (Figure 1a), the surface of Fe3O4@PZS-Ni was obviously spiky, decorated with some nanodots at about 5 nm of diameter (Figure 1b and c). EDS demonstrated that Fe3O4@PZS-Ni contained Fe, Ni, P, N, and S elements (Figure 2), and the elemental mappings (Figure 3) displayed the distributions of those elements. Fe was located in the middle of the nanoparticles, while P, N, and S ascribed to PZS were situated around Fe, and Ni was epitaxially grown outside. In addition, the uniform distribution of those elements on the Fe3O4@PZS-Ni nanoparticles revealed the homogeneity of the prepared Fe3O4@PZS-Ni. XRD patterns (Figure S3) further supported the existence of Fe3O4 in the prepared Fe3O4@PZS-Ni; however, no peaks corresponding to Ni were observed, which was ascribed to the amorphous nickel nanodots generated from the reduction of Ni (II) by KBH4.28−30 The superior magnetic characteristics of Fe3O4@PZS-Ni were reflected by the hysteresis loops (Figure S4a). Fe3O4@ PZS-Ni and Fe3O4@PZS had high saturation magnetization

Figure 2. EDS of Fe3O4@PZS-Ni synthesized at the mass ratio of 50/ 12/27 (Fe3O4/HCCP/BPS) and 2 mmol g−1 (nickel acetate/Fe3O4@ PZS).

(63.50 and 70.79 emu g−1), low coercivity (31.16 and 33.31 Oe), and negligible remanence (1.986 and 2.328 emu g−1), respectively (measured at 25 °C). The decreased coercivity and remanence of Fe3O4@PZS-Ni against Fe3O4@PZS suggested that incorporation of Ni onto Fe3O4@PZS led to better superparamagnetism of Fe3O4@PZS-Ni. These magnetic features of Fe3O4@PZS-Ni were superior over the Co@gC3N4-rGO composite8 and enabled its fast harvest by magnet, easy redispersion, and thus good recyclability and self-stirring capability in the solution of reactants. Due to the protection of Ni at the outside layer, the loss of PZS in Fe3O4@PZS-Ni happened at higher temperature compared with that in Fe3O4@PZS (TGA curves, Figure S4b). In addition, the incorporation of Ni onto Fe3O4@PZS resulted in less weight loss of Fe3O4@PZS-Ni against Fe3O4@ PZS (roughly 5%), which was ascribed to the relatively lower PZS content in Fe3O4@PZS-Ni caused by the noncombustible Ni and oxidation of Ni during the TGA test under an air atmosphere. This good thermostability of Fe3O4@PZS-Ni was beneficial for its use as a self-stirring catalyst in the reactions of high temperature. The accurate content of Ni in Fe3O4@PZSNi determined by ICP-AES was 7.1 ± 0.25%, while that in Ni catalyst was 94.7 ± 4.4%. To further examine the surface chemistry of Fe3O4@PZS-Ni, the XPS spectra of Fe3O4@PZS-Ni, Fe3O4@PZS, and Ni nanoparticles were recorded. The full spectra (Figure 4a) revealed that the surface of Fe3O4@PZS-Ni contained Ni, P, S, and N, which was in accordance with the elemental mapping in Figure 3. Nearly the same binding energy of Ni 2p3 in Fe3O4@ 1866

DOI: 10.1021/acssuschemeng.6b02581 ACS Sustainable Chem. Eng. 2017, 5, 1864−1870

Research Article

ACS Sustainable Chemistry & Engineering

Figure 3. Elemental mapping of Fe3O4@PZS-Ni synthesized at the mass ratio of 50/12/27 (Fe3O4/HCCP/BPS) and 2 mmol g−1 (nickel acetate/ Fe3O4@PZS) acquired by EDAX TEAM (SEM).

Figure 4. XPS (a) full spectra of Fe3O4@PZS-Ni, Fe3O4@PZS, and Ni. (b) Ni 2p3 peaks in Fe3O4@PZS-Ni and Ni. (c) N 1s peaks and (d) P 2p peaks in Fe3O4@PZS-Ni and Fe3O4@PZS. Fe3O4@PZS was synthesized at the mass ratio of 50/12/27 (Fe3O4/HCCP/BPS), and Fe3O4@PZS-Ni was synthesized at 2 mmol g−1 (nickel acetate/Fe3O4@PZS).

comparing the performance of Fe3O4@PZS-Ni with other catalysts. The naked-eye visible self-stirring and catalytic effect of Fe3O4@PZS-Ni were first studied. The presence of Fe3O4@ PZS-Ni in the droplets of either 4-nitrophenol (with KBH4) or methylene blue displayed fine catalytic activity (Figure S5) and excellent magnetic self-stirring (Videos 3 and 1 in the Supporting Information). With fine catalytic activity and good magnetic self-stirring, the yellow droplet of 4-nitrophenol (with addition of KBH4) quickly faded within 6 min, and the blue droplet of methylene blue turned colorless within 60 s. In contrast, the blue (for MB) and yellow (for 4-nitrophenol with addition of KBH4) droplets without the addition of Fe3O4@

PZS-Ni and the Ni catalyst (Figure 4b) indicated the reduced metal Ni. However, the binding energies of N 1s and P 2p in Fe3O4@PZS-Ni were decreased a little bit compared to those in Fe3O4@PZS, inferring that Ni atoms were anchored onto PZS through the N and P atoms (Figure 4c and d). Self-Stirring, Catalytic Activity, and Recyclable Usage of Fe3O4@PZS-Ni. To evaluate the self-stirring and catalytic performance of Fe3O4@PZS-Ni, the reductions of 4-nitrophenol31 and methylene blue were chosen as the model reactions due to the visible color changes in the proceedings of those reactions. Besides, those two reactions were widely used as models in much literature,32,33 which was beneficial for 1867

DOI: 10.1021/acssuschemeng.6b02581 ACS Sustainable Chem. Eng. 2017, 5, 1864−1870

Research Article

ACS Sustainable Chemistry & Engineering

Figure 5. Time-dependent UV−vis spectra of the aqueous solution of 4-nitrophenol (1 × 10−4 mol L−1) upon the addition of KBH4 in the case of (a) without any catalyst, (b) with Fe3O4@PZS-Ni (with nickel content of 3.6 × 10−5 mol L−1), and (c) with Ni (with nickel content of 5.6 × 10−5 mol L−1). (d) Plots of A/A0 against reaction time corresponding to (a)−(c).

PZS-Ni stayed the same all the time (Figure S5). The reduction of MB in a capillary (Video 2) further revealed the self-stirring and catalyst effect of Fe3O4@PZS-Ni. Besides, with the help of external magnetic field, Fe3O4@PZS-Ni could make the reactants move along the narrow channels and mix throughout (Video 2). To further quantitatively describe the catalytic activity of the self-stirring Fe3O4@PZS-Ni catalyst, a UV−vis spectrometer was used to monitor the reduction of 4-nitrophenol (Figure 5). The absorbance of 4-nitrophenol was at 317 nm in acidic or neutral conditions, but it red-shifted to 400 nm upon the addition of KBH4 due to the formation of 4-nitrobenzenolate. The 400 nm absorbance was almost the same without any catalyst (Figure 5a) and gradually decreased with the addition of Ni catalyst (Figure 5c, with nickel content of 5.6 × 10−5 mol L−1) but rapidly decreased upon the addition of Fe3O4@PZSNi (Figure 5b, with nickel content of 3.6 × 10−5 mol L−1). The new absorbance at 295 nm in Figure 5b and c revealed the conversion from 4-nitrophenol to 4-aminophenol, whereas there was no 295 nm absorbance in Figure 5a even during 30 min. The plots of A/A0 (A and A0 were the absorbance at 400 nm at any time and at the very beginning, respectively) against the reaction time (Figure 5d) further proved the superior catalytic activity of Fe3O4@PZS-Ni over Ni. Fe3O4 and Fe3O4@ PZS were only the catalyst carriers, as no catalytic effect was observed (Figure S6). These results demonstrated that the catalysts with nickel were required for the transformation of 4nitrophenol to 4-aminophenol, and Fe3O4@PZS-Ni displayed much higher catalytic activity than Ni. Certainly, the amount of Fe3O4@PZS-Ni catalyst significantly influenced the proceeding of the reduction of 4nitrophenol (Figure S7). The reaction was greatly accelerated with the increasing amount of Fe3O4@PZS-Ni; however, it was not improved further as the amount of Fe3O4@PZS-Ni reached 3.6 × 10−5 mol L−1 (calculated as Ni, in 3 mL of aqueous solution). To further quantitatively determine the rate constant, the reaction was monitored by a UV−vis spectrometer in the kinetic mode (Figure 6). From the linear relationship of ln(A/

Figure 6. Estimation of the rate constant (k) by UV−vis spectrometer in kinetic mode. Here, A and A0 were the absorbance at 400 nm at any time and at the very beginning, respectively; A was measured at 0.5 s intervals.

A0) versus time (A and A0 were the absorbance at 400 nm at any time and at the very beginning, respectively), the pseudofirst-order rate constant (k) was calculated as 7.04 × 10−3 s−1, which was comparable to the Rh noble metal nanoparticles23 and other catalysts34−38 (Table S1). Another merit of the Fe3O4@PZS-Ni catalyst is the convenient reusability (Figure 7). Owing to the superior magnetism of Fe3O4@PZS-Ni, the special catalyst could be conveniently harvested and redispersed in the reactant solutions. Besides, Fe3O4@PZS-Ni displayed high catalytic activity for five uses, and the morphology had no obvious changes as revealed by the TEM image after the fifth use (Figure S8). Although the catalytic effect was gradually decreased with the uses, it still remained at a good level (the reaction was completed within 20 min for the fifth use, Figure 7). The gradually decreased catalytic effects in the recyclable uses were observed very often for the solid nanocatalysts,39 which was most probably because of the irreversible adsorption of the reactants or the products on the surface of the catalysts (as proved by the increased UV−vis absorbance in 300−420 1868

DOI: 10.1021/acssuschemeng.6b02581 ACS Sustainable Chem. Eng. 2017, 5, 1864−1870

ACS Sustainable Chemistry & Engineering

■

nm and TGA weight loss of the fifth-recycled Fe3O4@PZS-Ni over the fresh one, Figure S9). In summary, we reported the first exploration of functional magnetic nanoparticles Fe3O4@PZS-Ni as self-stirring catalysts for microreactions. On the basis of the charming magnetic feathers of Fe3O4 and the fine catalysis activity of Ni, the Fe3O4@PZS-Ni nanoparticles could not only self-stir and make the reactants move along the narrow channels with the help of an external rotating magnetic field but also exhibit high catalysis activity and convenient recyclability. The nanostirring bars composed of individual Fe3O4@PZS-Ni magnetic nanoparticles have the merits of small size, good suspension, easy fabrication, and most importantly, superior flexibility and adaptability to any shape of microreactors or nanoreactors, and thus, may bring new inspiration for catalytic reactions in micro/nanochips or micro/nanobiological tubules or tissues.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.6b02581. Additional information as noted in the text. (PDF) Video 1. (sc6b02581_si_002) Video 2. (sc6b02581_si_004) Video 3. (sc6b02581_si_003)

■

REFERENCES

(1) Song, H.; Chen, D. L.; Ismagilov, R. F. Reactions in Droplets in Microfluidic Channels. Angew. Chem., Int. Ed. 2006, 45 (44), 7336− 7356. (2) Biswal, S. L.; Gast, A. P. Micromixing with Linked Chains of Paramagnetic Particles. Anal. Chem. 2004, 76 (21), 6448−6455. (3) Song, Y.; Hormes, J.; Kumar, C. S. S. R. Microfluidic Synthesis of Nanomaterials. Small 2008, 4 (6), 698−711. (4) Ferraro, D.; Lin, Y.; Teste, B.; Talbot, D.; Malaquin, L.; Descroix, S.; Abou-Hassan, A. Continuous chemical operations and modifications on magnetic gamma-Fe2O3 nanoparticles confined in nanoliter droplets for the assembly of fluorescent and magnetic SiO2@gammaFe2O3. Chem. Commun. 2015, 51 (95), 16904−16907. (5) Yang, S.; Cao, C.; Sun, Y.; Huang, P.; Wei, F.; Song, W. Nanoscale magnetic stirring bars for heterogeneous catalysis in microscopic systems. Angew. Chem., Int. Ed. 2015, 54 (9), 2661−2664. (6) Yang, S. L.; Cao, C. Y.; Peng, L.; Huang, P. P.; Sun, Y. B.; Wei, F.; Song, W. G. Spindle-shaped nanoscale yolk/shell magnetic stirring bars for heterogeneous catalysis in macro- and microscopic systems. Chem. Commun. 2016, 52 (8), 1575−1578. (7) Chong, W. H.; Chin, L. K.; Tan, R. L.; Wang, H.; Liu, A. Q.; Chen, H. Stirring in suspension: nanometer-sized magnetic stir bars. Angew. Chem., Int. Ed. 2013, 52 (33), 8570−8573. (8) Duan, S.; Han, G.; Su, Y.; Zhang, X.; Liu, Y.; Wu, X.; Li, B. Magnetic Co@g-C3N4 Core−Shells on rGO Sheets for Momentum Transfer with Catalytic Activity toward Continuous-Flow Hydrogen Generation. Langmuir 2016, 32 (25), 6272−6281. (9) He, L.; Wang, M. S.; Ge, J. P.; Yin, Y. D. Magnetic Assembly Route to Colloidal Responsive Photonic Nanostructures. Acc. Chem. Res. 2012, 45 (9), 1431−1440. (10) Wang, M. S.; Yin, Y. D. Magnetically Responsive Nanostructures with Tunable Optical Properties. J. Am. Chem. Soc. 2016, 138 (20), 6315−6323. (11) Wang, D.; Astruc, D. Fast-growing field of magnetically recyclable nanocatalysts. Chem. Rev. 2014, 114 (14), 6949−6985. (12) Baig, R. B. N.; Varma, R. S. Magnetically retrievable catalysts for organic synthesis. Chem. Commun. 2013, 49 (8), 752−770. (13) Manaenkov, O. V.; Mann, J. J.; Kislitza, O. V.; Losovyj, Y.; Stein, B. D.; Morgan, D. G.; Pink, M.; Lependina, O. L.; Shifrina, Z. B.; Matveeva, V. G.; Sulman, E. M.; Bronstein, L. M. Ru-Containing Magnetically Recoverable Catalysts: A Sustainable Pathway from Cellulose to Ethylene and Propylene Glycols. ACS Appl. Mater. Interfaces 2016, 8 (33), 21285−21293. (14) Baig, R. B. N.; Verma, S.; Varma, R. S.; Nadagouda, M. N. Magnetic Fe@g-C3N4: A Photoactive Catalyst for the Hydrogenation of Alkenes and Alkynes. ACS Sustainable Chem. Eng. 2016, 4 (3), 1661−1664. (15) Verma, S.; Nasir Baig, R. B.; Han, C.; Nadagouda, M. N.; Varma, R. S. Magnetic graphitic carbon nitride: its application in the C-H activation of amines. Chem. Commun. 2015, 51 (85), 15554−15557. (16) Nasir Baig, R. B.; Verma, S.; Nadagouda, M. N.; Varma, R. S. Advancing Sustainable Catalysis with Magnetite. Surface Modification and Synthetic Applications. Tetrahedron 2016, 49 (2), 35−41. (17) Fu, J.; Xu, Q.; Chen, J.; Chen, Z.; Huang, X.; Tang, X. Controlled fabrication of uniform hollow core porous shell carbon spheres by the pyrolysis of core/shell polystyrene/cross-linked polyphosphazene composites. Chem. Commun. 2010, 46 (35), 6563−6565. (18) Hu, Y.; Meng, L.; Niu, L.; Lu, Q. Highly cross-linked and biocompatible polyphosphazene-coated superparamagnetic Fe3O4 nanoparticles for magnetic resonance imaging. Langmuir 2013, 29 (29), 9156−9163. (19) Zhou, J.; Meng, L.; Feng, X.; Zhang, X.; Lu, Q. One-pot synthesis of highly magnetically sensitive nanochains coated with a highly cross-linked and biocompatible polymer. Angew. Chem., Int. Ed. 2010, 49 (45), 8476−8479. (20) Tasker, S. Z.; Standley, E. A.; Jamison, T. F. Recent advances in homogeneous nickel catalysis. Nature 2014, 509 (7500), 299−309.

Figure 7. Reuse of Fe3O4@PZS-Ni for the reduction of 4-nitrophenol. ΔA = A0 − A; A and A0 were the absorbance at 400 nm at any time and at the very beginning, respectively. Three milliliters of aqueous solution of 4-nitrophenol (1 × 10−4 mol L−1) was catalyzed by 3.6 × 10−5 mol L−1 (calculated as Ni) of Fe3O4@PZS-Ni.

■

Research Article

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

He-Fang Wang: 0000-0003-4127-5038 Author Contributions

The manuscript was written through contributions of all authors. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (No. 21575070 and 21435001). 1869

DOI: 10.1021/acssuschemeng.6b02581 ACS Sustainable Chem. Eng. 2017, 5, 1864−1870

Research Article

ACS Sustainable Chemistry & Engineering (21) Weires, N. A.; Baker, E. L.; Garg, N. K. Nickel-catalysed SuzukiMiyaura coupling of amides. Nat. Chem. 2015, 8 (1), 75−79. (22) Zhang, P.; Shao, C.; Zhang, Z.; Zhang, M.; Mu, J.; Guo, Z.; Liu, Y. In situ assembly of well-dispersed Ag nanoparticles (AgNPs) on electrospun carbon nanofibers (CNFs) for catalytic reduction of 4nitrophenol. Nanoscale 2011, 3 (8), 3357−3363. (23) Sun, J. K.; Zhan, W. W.; Akita, T.; Xu, Q. Toward Homogenization of Heterogeneous Metal Nanoparticle Catalysts with Enhanced Catalytic Performance: Soluble Porous Organic Cage as a Stabilizer and Homogenizer. J. Am. Chem. Soc. 2015, 137 (22), 7063−7066. (24) Wu, Y.-g.; Wen, M.; Wu, Q.-s.; Fang, H. Ni/graphene Nanostructure and Its Electron-Enhanced Catalytic Action for Hydrogenation Reaction of Nitrophenol. J. Phys. Chem. C 2014, 118 (12), 6307−6313. (25) Yang, X.; Zhong, H.; Zhu, Y.; Jiang, H.; Shen, J.; Huang, J.; Li, C. Highly efficient reusable catalyst based on silicon nanowire arrays decorated with copper nanoparticles. J. Mater. Chem. A 2014, 2 (24), 9040−9047. (26) Fu, G.; Tao, L.; Zhang, M.; Chen, Y.; Tang, Y.; Lin, J.; Lu, T. One-pot, water-based and high-yield synthesis of tetrahedral palladium nanocrystal decorated graphene. Nanoscale 2013, 5 (17), 8007−8014. (27) Deng, H.; Li, X.; Peng, Q.; Wang, X.; Chen, J.; Li, Y. Monodisperse Magnetic Single-Crystal Ferrite Microspheres. Angew. Chem., Int. Ed. 2005, 44 (18), 2782−2785. (28) Ingersoll, J. C.; Mani, N.; Thenmozhiyal, J. C.; Muthaiah, A. Catalytic hydrolysis of sodium borohydride by a novel nickel−cobalt− boride catalyst. J. Power Sources 2007, 173 (1), 450−457. (29) Wu, Z.; Mao, X.; Zi, Q.; Zhang, R.; Dou, T.; Yip, A. C. K. Mechanism and kinetics of sodium borohydride hydrolysis over crystalline nickel and nickel boride and amorphous nickel−boron nanoparticles. J. Power Sources 2014, 268, 596−603. (30) Zhang, Q.; Li, H.; Gao, P.; Wang, L. PVP-NiB amorphous catalyst for selective hydrogenation of phenol and its derivatives. Chin. J. Catal. 2014, 35 (11), 1793−1799. (31) Moitra, N.; Kanamori, K.; Ikuhara, Y. H.; Gao, X.; Zhu, Y.; Hasegawa, G.; Takeda, K.; Shimada, T.; Nakanishi, K. Reduction on reactive pore surfaces as a versatile approach to synthesize monolithsupported metal alloy nanoparticles and their catalytic applications. J. Mater. Chem. A 2014, 2 (31), 12535−12544. (32) Kong, X.-k.; Sun, Z.-y.; Chen, M.; Chen, C.-l.; Chen, Q.-w. Metal-free catalytic reduction of 4-nitrophenol to 4-aminophenol by N-doped graphene. Energy Environ. Sci. 2013, 6 (11), 3260−3266. (33) Han, Y.; Wu, X.; Zhang, X.; Zhou, Z.; Lu, C. Reductant-Free Synthesis of Silver Nanoparticles-Doped Cellulose Microgels for Catalyzing and Product Separation. ACS Sustainable Chem. Eng. 2016, 4 (12), 6322−6331. (34) Chen, L.; Leong, G. J.; Schulze, M.; Dinh, H. N.; Pivovar, B.; Hu, J.; Qi, Z.; Fang, Y.; Prikhodko, S.; Pozuelo, M.; Kodambaka, S.; Richards, R. M. Controlled Synthesis of Nanoscale Icosahedral Gold Particles at Room Temperature. ChemCatChem 2012, 4 (10), 1662− 1667. (35) He, J.; Ji, W.; Yao, L.; Wang, Y.; Khezri, B.; Webster, R. D.; Chen, H. Strategy for nano-catalysis in a fixed-bed system. Adv. Mater. 2014, 26 (24), 4151−4155. (36) Yao, T.; Cui, T.; Fang, X.; Cui, F.; Wu, J. Preparation of yolkshell Fe(x)O(y)/Pd@mesoporous SiO2 composites with high stability and their application in catalytic reduction of 4-nitrophenol. Nanoscale 2013, 5 (13), 5896−5904. (37) Deraedt, C.; Rapakousiou, A.; Wang, Y.; Salmon, L.; Bousquet, M.; Astruc, D. Multifunctional redox polymers: electrochrome, polyelectrolyte, sensor, electrode modifier, nanoparticle stabilizer, and catalyst template. Angew. Chem., Int. Ed. 2014, 53 (32), 8445− 8449. (38) Xu, D.; Diao, P.; Jin, T.; Wu, Q.; Liu, X.; Guo, X.; Gong, H.; Li, F.; Xiang, M.; Ronghai, Y. Iridium Oxide Nanoparticles and Iridium/ Iridium Oxide Nanocomposites: Photochemical Fabrication and Application in Catalytic Reduction of 4-Nitrophenol. ACS Appl. Mater. Interfaces 2015, 7 (30), 16738−16749.

(39) Singh, I.; Landfester, K.; Chandra, A.; Munoz-Espi, R. A new approach for crystallization of copper(II) oxide hollow nanostructures with superior catalytic and magnetic response. Nanoscale 2015, 7 (45), 19250−19258.

1870

DOI: 10.1021/acssuschemeng.6b02581 ACS Sustainable Chem. Eng. 2017, 5, 1864−1870