Low Temperature-Derived 3D Hexagonal Crystalline Fe3O4

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Low Temperature-Derived 3D Hexagonal Crystalline Fe3O4 Nanoplates for Water Purification Xiaoyi Wang,† Yulong Liao,*,†,‡ Huaiwu Zhang,†,‡ Tianlong Wen,‡ Dainan Zhang,‡ Yuanxun Li,‡ Mingzhen Liu,† Faming Li,† Qiye Wen,‡ Zhiyong Zhong,‡ and Xingtian Yin*,§ Center for Applied Chemistry and ‡State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, Sichuan 610054, China § Electronic Materials Research Laboratory, International Center for Dielectric Research, Key Laboratory of the Ministry of Education, School of Electronic & Information Engineering, Xi’an Jiaotong University, Xi’an, Shanxi 710049, China Downloaded via IOWA STATE UNIV on January 5, 2019 at 03:04:10 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

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ABSTRACT: Fe3O4 nanoplates were fabricated by an anodic oxidation process and a subsequent water assisted crystallization process at low temperature, which was found to be very efficient and environmentally friendly. The as-prepared Fe3O4 nanoplates have hexagonal outlines with a thickness of about 20 nm. Tremendous grooves were distributed on the entire surfaces of the nanoplates, making the two-dimension nanoplates have a unique 3D morphology. Transmission electron microscopy results confirmed that the single-crystalline nature of the nanoplates was well maintained. Owing to the unique structures and porous morphologies, the as-prepared 3D nanoplates show excellent ability for absorbing solar energy and absorbing organic pollutants, which can be utilized for cleaning up water. Moreover, the Fe3O4 nanoplates show good magnetic properties that enable them to be easily collected and recycled. We believe this study will inspire the application of Fe3O4 nanoplates with 3D structures in energy and environmental areas. KEYWORDS: hexagonal Fe3O4, 3D nanoplates, low-temperature, porous, green chemistry, water treatment

1. INTRODUCTION Nanostructured materials have attracted great attention due to the fact that their properties are heavily influenced not only by the chemical stoichiometry, but also by their particular microstructures and morphologies.1−3 As a result, nanoscale magnetite (Fe3O4) was intensively investigated on account of its distinct properties, which could be widely utilized in many fields including targeted drug delivery, water treatment, magnetic resonance imaging, and energy storage.4−7 So far, Fe3O4 with a variety of structures and morphologies have been prepared and studied such as nanowires,8 hollow spheres,9 and nanorings.10 Recently, hexagonal Fe3O4 nanoplates were successfully synthesized by Li and co-workers using the supercritical fluid (SCF) technique, where ferrocene was employed as the Fe source and supercritical carbon dioxide (sc-CO2) acted as both the solvent and reactant.11 Besides the SCF method, other routes were also used to synthesize Fe3O4 nanoplates, which showed excellent performances in energy and environmental areas.12,13 The prepared 2D Fe3O4 nanoplates were found of single-crystalline nature, and they had a regular hexagonal outline and smooth surfaces. The single-crystalline nature of metal oxides is very important for electronic related applications, such as sensors and batteries, because fewer defects and crystal boundaries in a single crystal could lead to long electron diffusion length and lower electron−hole recombination rate.14 Meanwhile, porous morphologies with structural coherence are favorable for some © 2018 American Chemical Society

applications with mass transportation or chemical reactions, such as catalysts and biocarrier, because the porous morphology provides a highly accessible surface area.15 However, it is a challenge to prepare metal oxides materials owning both porous morphology and single-crystalline nature at the same time. In 2013, Edward and co-workers successfully synthesized mesoporous TiO2 single crystals with enhanced mobility and optoelectronic performance,16 and this work has drawn lots of attention. Until now, reports on single-crystalline iron oxides with porous morphologies are still few. Synthesizing Fe3O4 nanoplates that both possess single crystalline feature and porous morphologies is urgent and will provide an opportunity for their applications in energy and environmental areas. To the best of our knowledge, hexagonal Fe3O4 nanoplates with a porous morphology have not yet been reported to date. In this study, we report the preparation of single-crystalline Fe3O4 3D hexagonal nanoplates with porous morphologies, for the first time. The synthesis procedure was very simple and conducted at low temperature under ambient atmosphere. It consisted of two steps: (1) anodization and (2) immersion in H2O for crystallization. The morphological and structural properties of the 3D Fe3O4 hexagonal nanoplates were investigated in detail. The crystallization mechanism of how Received: November 18, 2017 Accepted: January 5, 2018 Published: January 19, 2018 3644

DOI: 10.1021/acsami.7b17582 ACS Appl. Mater. Interfaces 2018, 10, 3644−3651

Research Article

ACS Applied Materials & Interfaces

the reagents were analytical grade and used as received without further purification. 2.4. Characterizations. The crystal phases were analyzed by X-ray diffraction (XRD, D/max 2400, Rigaku, Japan) and the radiation source was Cu Kα. The morphologies and microstructures were investigated by scanning electron microscopy (SEM, JSM7600F, Japan) and transmission electron microscopy (TEM, JEOL2100F, Japan). X-ray photoelectron spectroscopy was employed to identify the Fe3O4 phase, and the radiation source was Al Kα (XPS, Escalab 250Xi, America). Surface properties of the as-synthesized 3D Fe3O4 nanoplates were investigated by Brunauer−Emmett−Teller (BET) method via nitrogen adsorption and desorption measurements (BELSORP-MAX, Japan). Magnetic property of the as-synthesized Fe3O4 was investigated by employing a vibrating sample magnetometer (SQUID-VSM, Quantum Design) with an applied field range of −20000−20000 Oe at room temperature. The ferromagnetic resonance (FMR) response was measured by using a broadband VNA-FMR (vetor-network-analyzer ferromagnetic resonance) spectrometer with an in-plane configuration, and the frequency was fixed at 8 G Hz and changing the magnetic field to observe the absorption signals. The photothermal activities were investigated by an infrared camera (Flir C2, America), and the light source was a lamp (OSRAM, ultra vitalux E27, 300W). Specifically, we weighed the two samples (one beaker only contained water; the other one contained the same weight of water and a piece of synthesized Fe3O4 foil) first before the irradiation. Then the lamp was placed directly above the two beakers at a distance of 30 cm, with an infrared camera recording the temperature changes. After that, the two samples were weighed again, and the mass changes of them were obtained. The concentration of the aqueous methyl orange solution was measured by ultraviolet and visible spectrophotometer (UV−vis, UV-762, China).

the amorphous iron oxides transformed into Fe3O4 and further transformed into hexagonal nanoplates from small particles were discussed. In addition, the intrinsic magnetic property makes it a promising candidate in many fields. The assynthesized 3D Fe3O4 nanoplates were tested for steam generation using solar irradiation and cleaning up organic pollutants.

2. EXPERIMENTAL SECTION 2.1. Preparation of Amorphous Iron Oxides. In a typical procedure, an electrochemical anodization method was used to prepare amorphous iron oxides, as shown in Figure 1a. Prior to

3. RESULTS AND DISCUSSION Digital photos of the samples at different experimental stages are shown in Figure 1c and d. The raw Fe foils have a metallic luster and color, and after anodization, the reaction region turned into reddish brown, see Figure 1c. The as-anodized sample was then immersed in water at 95 °C, and the sample was crystallized very swiftly within 5 min. Figure 1d shows the reddish brown film changed into black color. XRD patterns of the as-anodized sample are shown in Figure 2a. No obvious peak could be observed except for the characteristic peaks of raw iron substrate at 44.7 and 65.2°, indicating the amorphous nature of the product after anodization step. SEM results reveal that the amorphous iron oxides are composed of nanoparticles, see Figure 2b. Interestingly, after the immersion step at 95 °C for 5 min, the products show totally different XRD patterns compared with the as-anodized sample. In addition to the substrate signals, the diffraction peaks attributed to the (220), (311), (400), (422), (511), and (440) planes of face-centered cubic Fe3O4 (JCPDS no. 19−0629) were obviously observed, see Figure 2c. The calculated lattice constant from the XRD results is a = 8.398 Å, which is in good agreement with the reported literature of magnetite,11,17 indicating that the amorphous iron oxides had been successfully transformed into Fe3O4. Meanwhile, TEM results indicate the morphologies of the samples also dramatically changed from nanoparticles into hexagonal nanoplates, see Figure 2d. Because of the fact that the XRD patterns of Fe3O4 are quite similar to that of γFe2O3, XPS was employed to identify the phase of the product. It is acknowledged that C 1s peaks are usually used for the calibration of XPS data; Figure S2 (Supporting Information) presents the C 1s peaks with a binding energy at 284.8 eV, fitting well with the standard C−C peak.18 Figure 2e and f show XPS patterns of the as-synthesized sample and a high resolution XPS spectrum of Fe 2p ranging from 700−740 eV. Two peaks

Figure 1. (a, b) Schematic process of the synthesis. (c, d) Digital photos of the samples in different stages showing the color change.

anodization, pure iron foils with 0.2 mm thickness (purity: 99.9%, size: 5 × 1.5 cm2) were washed by detergent to remove the superficial stains away, then the foils were sonicated in ethyl alcohol, followed by drying in oven at 80 °C for 1 h. This process was carried out by using a twoelectrode system with one piece of iron foils as anode, and the distance between the anode and cathode was 1.5 cm. The electrolyte (ethylene glycol solution containing 3.0 vol % deionized water and 0.3 wt % NH4F) was freshly prepared, and the potential across two electrodes was set to 60 V by using a DC power source. In addition, a lowtemperature thermostat bath was employed to make sure the temperature of the electrolyte and the surrounding water maintained at 10 °C (optimization process of the anodization temperature is presented in Figure S1 (Supporting Information)), and the anodization time was 1 h, along with magnetic stirring. Afterward, washing the sheet thoroughly with ethyl alcohol and putting it into oven (80 °C) for 8 h, then the amorphous iron oxides with a reddish brown color were obtained on iron substrate. 2.2. Preparation of Fe3O4 Hexagonal Nanoplates. A sample bottle containing 10 mL of deionized (DI) water was placed in the oven (set up at 95 °C) for 4 h, making sure the DI water was totally heated up to 95 °C (optimization process of the immersion temperature is presented in Figure S1 (Supporting Information)). Then the as-synthesized reddish brown foil was immersed in bottle and put in the oven, maintained for 5 min. Subsequently, the foil was taken out and distinct transition could be observed from reddish brown to black, followed by immersing in ethyl alcohol for 10 min. Then the black sheet was taken out and dried in ambient air, and Fe3O4 hexagonal nanoplates were finally obtained, as shown in Figure 1d. 2.3. Preparation of High Temperature Control Sample. After the anodization step, the reddish brown sample was sintered at 400 °C for 3 h with a heating up rate of 2 °C/min, and then the sintered sample was cooled to room temperature and taken out for study. All 3645

DOI: 10.1021/acsami.7b17582 ACS Appl. Mater. Interfaces 2018, 10, 3644−3651

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ACS Applied Materials & Interfaces

Figure 3. (a, b) SEM images of the Fe3O4 products when the immersion time is 3 min; (c, d) SEM images of the Fe3O4 products when the immersion time is 5 min.

sample. Figure 3c shows the Fe3O4 nanoplates have a clear hexagonal shapes. Meanwhile, 3D morphologies of the Fe3O4 nanoplates are still well maintained, and the grooves are densely and uniformly distributed forming a sulcus-like morphology (see yellow square in Figure 3d). Furthermore, the samples immersed for a longer time are also studied (10 and 30 min) as shown in Figure S5. As for the 10 min sample, most of the nanoplates were broken. When the immersion time was prolonged to 30 min, it is noteworthy that some Fe3O4 had already fallen off the iron substrate. The Fe3O4 sample with 5 min immersion duration was further investigated by TEM. As shown in Figure 4a, hexagonal nanoplates can be clearly seen along with some fragments and nanoparticles. A well-defined hexagonal nanoplate is presented in Figure 4b, with an internal angle of 120° and side lengths of

Figure 2. (a, b) XRD patterns and SEM image of the as-anodized sample; (c, d) XRD patterns and TEM image of the after-immersion product (immersion temperature is 95 °C, immersion duration time is 5 min); (e) XPS spectra of the synthesized Fe3O4 product; (f) magnification spectra of Fe 2p ranging from 700−740 eV.

locating at 711.2 and 724.8 eV were observed, corresponding to Fe 2p3/2 and Fe 2p1/2, respectively, which is in accordance with the literature.19,20 These results prove that the as-anodized samples were crystallized and transformed from amorphous iron oxides nanoparticles into Fe3O4 hexagonal nanoplates after simply immersing them into H2O only for 5 min. Figure 3 shows the SEM images of Fe3O4 nanoplates with different immersion times. As shown in Figure 3a, when immersing the as-anodized sample into DI for 3 min, the asprepared Fe3O4 nanoplates are found close to each other and form a honeycomb texture. Figure 3b presents a corresponding magnifying image, and it can be seen that the nanoplates are about 20 nm in thickness. More interesting is that surfaces of the plates are full of distributed grooves (see blue square in Figure 3b), which makes the obtained Fe3O4 products have a 3D morphology other than normal 2D Fe3O4 nanoplates. A corresponding high resolution SEM image is also displayed in Figure S3 (Supporting Information) to study the groove structure more clearly. In addition, the nitrogen adsorption− desorption isotherms of the obtained Fe3O4 nanoplates immersed for 3 min are shown in Figure S4 (Supporting Information). The corresponding surface area calculated by Brunauer−Emmett−Teller (BET) method was 78.2 m2/g, which is higher than that of the reported Fe3O4 nanospheres20 and Fe3O4 hollow submicrospheres,9 and calculated mean pore size was about 17 nm. When the immersion time was prolonged to 5 min, the outlines of the obtained Fe3O4 nanoplates become more regular than that of the 3 min

Figure 4. (a−d) TEM, HRTEM, and SAED images of the typical hexagonal Fe3O4 nanoplates (immersion time of 5 min). 3646

DOI: 10.1021/acsami.7b17582 ACS Appl. Mater. Interfaces 2018, 10, 3644−3651

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Figure 5. (a) Schematic diagram of the crystallization process from the amorphous iron oxides to the crystallized Fe3O4 products. (b) Schematic diagram of the oriented attachment process from the nanoparticles to the nanoplates.

increased treatment duration, dehydration process occurs that the water molecules escape away carrying the oxygen atoms from octahedra, resulting in the linkage of two octahedra by sharing their edges. Then the third tetrahedra also proceed in this hydration-dehydration process with the assistance of water, leading to the linkage of octahedra and tetrahedra that share common vertexes. Finally, the octahedra−tetrahedra assembly will connect with other assemblies and form a unit cell of Fe3O4. Actually, this is a process that the disordered molecules in the as-anodized products become long-range ordered with the help of water, this kind of amorphous-to-crystalline transformation is analogous to that of other metal oxides and the deeper insight is under research.22 Additionally, if we take a close look, there are many Fe3O4 nanoplates fragments that could be observed in Figure 2d, Figure 3c, and Figure 4a. TEM images of those Fe3O4 nanoplates fragments are shown in Figure S9 (Supporting Information). These fragments help us build a full picture of how the regular hexagonal Fe3O4 nanoplates formed. The transition of nanoparticles to hexagonal nanoplates could be attributed to the oriented attachment mechanism, which begins with an entropy-driven process, and the final crystals are composed by the coalescence of nanoparticles,23−26 see Figure 5b. Specifically speaking, when the as-anodized products are immersed in water, the nanoparticles (see Figure 2b) start to aggregate and crystallize at the initial stage. Then some nanoplates with polygon shapes formed at the cost of nanoparticles, in which process the adjacent nanoparticles self-assemble through rotation by sharing an identical crystallographic orientation and then grow into a whole (see dashed square). It is well-known that the driving force of the oriented attachment process mainly from the decrease of surface free energy by eliminating the interfaces of nearby nanoparticles.23,27,28 However, the consumption of nanoparticles is not complete in this stage, just like the SEM images of the products with 3 min immersion time (Figure 2a,b). With increased crystallization time, the polygon nanoplates and remaining nanoparticles continue growing and the hexagon Fe3O4 nanoplates are finally obtained. Since ethylene glycol and ethyl alcohol are verified that they have no influence on the

120 or 150 nm. It is noteworthy that a light and shade interlaced feature is observed on surfaces of the nanoplates, which could be attributed to the distributed grooves. The highresolution transmission electron microscopy (HRTEM) image shows that the lattice spacing is 0.25 nm (see Figure 4c), which could be assigned to the (311) plane of face-centered cubic Fe3O4.21 In spite of the randomly distributed grooves in the nanoplates, clear hexagonal diffraction spots was observed from the selected area electron diffraction (SAED) image (see Figure 4d), indicating the single-crystalline nature of the 3D Fe3O4 hexagonal nanoplates. It is well-known that the single-crystal structure could result in fewer defects, lower electron−hole recombination rate, and longer carrier diffusion length, making it promising in many fields. On the basis of the above results, it can be concluded that the 3D Fe3O4 hexagonal nanoplates were successfully obtained by a water immersion treatment at a low temperature of 95 °C. To better understand the mechanism that how the amorphous iron oxides transformed into Fe3O4 in water, we did two controlled trials by putting the as-anodized samples into ethylene glycol and ethyl alcohol, respectively. No obvious changes could be observed from the digital photos even for a quite long immersion time (24 h) at room temperature, see Figure S6 (Supporting Information). XRD patterns and SEM images of the trial samples immersed in ethylene glycol or ethyl alcohol are also displayed (Figure S7, Supporting Information), from which we can find that all of them are almost the same as that of the as-anodized sample. Therefore, we can conclude that whether the ethylene glycol in electrolyte or ethyl alcohol in washing procedure contributes no influence in this amorphousto-Fe3O4 phase transition. In addition, high temperature condition was also studied and the solution was composed of DI water and ethylene glycol or DI water and ethyl alcohol with different ratios as shown in Figure S8 (Supporting Information). We can conclude that H2O molecules play an essential role in the transformation, and the crystallization process from the amorphous iron oxides to the crystallized Fe3O4 products is schematically shown in Figure 5a. First, when the amorphous iron oxides immersed in DI water, a hydration process occurs owing to the surface hydroxyl groups of octahedra. With the 3647

DOI: 10.1021/acsami.7b17582 ACS Appl. Mater. Interfaces 2018, 10, 3644−3651

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Figure 6. (a) Room temperature magnetic hysteresis curves of the as-synthesized Fe3O4 nanoplates; the inset is enlarged partial curves. (b) XRD patterns and SEM image of the high temperature annealing products. (c, d) Digital photo of the magnet tests.

Figure 7. (a) Infrared (IR) images presenting the temperatures of the water-only sample (left beaker) and the water-with-Fe3O4 sample (right beaker) as a function of time; (b) plot of the temperature change of the water-only sample and the water-with-Fe3O4 sample; (c) plot of the mass change through water evaporation for the water-only sample and the water-with-Fe3O4 sample.

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DOI: 10.1021/acsami.7b17582 ACS Appl. Mater. Interfaces 2018, 10, 3644−3651

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interface to investigate the evaporation ability. As shown in Figure 7a, the temperature of the sample that contained Fe3O4 increased from 20 °C to about 44 °C when exposed to the irradiation for 600 s, while the water only increased 10 °C under the same condition, indicating that the as-synthesized Fe3O4 products played a vital role in absorbing solar light. This could be attributed to the distinct porous structures that enable the lights stay more time. Figure 7b and c show the temperature and mass changes as a function of the illumination time, respectively. It can be seen that with the increase of illumination time, the temperature of the system with Fe3O4 nanoplates increased much faster than that of water, under the same light illumination condition. As for the mass change, the sample that only contained water is about 0.7 kg/m2 when irradiated for 600 s, but the sample that contained Fe3O4 products is as high as 3.4 kg/m2, which is comparable to that of the Singamaneni’s work.34 Although the mass change of the sample that contained an as-anodized foil is 1.2 kg/m2 (maintaining other conditions same, see Figure S13 (Supporting Information)), it is still not comparable to that of the crystalline Fe3O4 sample. The Fe3O4 nanoplates stacked up with each other, leading to a considerable inner space and the porous morphology significantly increased the surface area, which are very conductive to the light absorption. The above results indicate that the prepared 3D Fe3O4 nanoplates are excellent at absorbing lights and can be a promising candidate for purifying water. Further, the aqueous methyl orange solution was utilized to investigate the water purification performance of the 3D Fe3O4 nanoplates. As shown in Figure S14 (Supporting Information), when the as-prepared products were put into the solution for just 1 h, the concentration of methyl orange decreased promptly. With time increased to 5 h, almost all the methyl orange was disappeared from water (see the digital photos in the inset of Figure S14, Supporting Information). The excellent absorption properties of the 3D Fe3O4 nanoplates for methyl orange can be attributed to the porous morphologies, which provide a considerable surface area. Because of their magnetic properties as shown in Figure 6, the Fe3O4 products can be easily collected by magnets after the degradation process, which will significantly lower the cost.

crystallization process, water is considered to be the key factor that affects the surface growth and finally leads to this kind of hexagonal shape. Figure 6a presents the hysteresis loop of the Fe3 O4 nanoplates (immersion time of 5 min) measured at room temperature. It can be seen that the magnetization saturation value (Ms) of the Fe3O4 nanosheets is about 75 emu/g, which is close to that of the bulk sample of Fe3O4 (92 emu/g);29 in addition, the remanent magnetization value (Mr) of the product is 3 emu/g, and the coercivity value (Hc) is 20 Oe (the inset of Figure 6a). It is well-known that the magnetic properties are strongly related to the sizes and morphologies of materials, the relatively high Ms and low Mr compared with other Fe3O4 nanomaterials could be attributed to this unique structure of 3D nanoplates. In general, thermal annealing at high-temperature is widely adopted to crystallize amorphous metal oxides. As shown in Figure 6b, when the as-anodized foil was annealed at 400 °C for 3 h, only characteristic peaks of Fe2O3 instead of Fe3O4 phase could be observed, along with some diffraction peaks from the iron substrate and some impurities. SEM observation reveals that only nanoparticles instead of nanoplates were formed for the traditional high-temperature annealing products, see the inset of Figure 6b. The differences of magnetic properties of the low-temperature DI-immersion products and high-temperature annealing products are studied by ferromagnetic resonance measurement as shown in Figure S10 (Supporting Information). It can be seen that the high temperature annealed products show a straight line, indicating no FMR response. In the contrast, the FMR absorption signals of the water-assisted crystallized products showed a resonance characteristic with a ferromagnetic resonance width value of 420 Oe, indicating the as-synthesized 3D Fe3O4 nanoplates are ferromagnetic, in accordance with the hysteresis loop results. Furthermore, a magnet was also used to identify the different magnetic features of these two kinds of products. In a typical procedure, the high-temperature and low-temperature products were scraped from the substrates, and then a permanent magnet was employed to approach the powers, respectively (see Figure S11 (Supporting Information)). For the hightemperature annealing powders, no obvious response was observed even at a very close distance. However, the powders treated by the water-immersion process were attracted to the magnet immediately at a relatively long distance (Figure 6c,d). This test indicates that the 3D Fe3O4 nanoplates with strong magnetism were successfully prepared through a low temperature crystallization process at 95 °C in water, which cannot be achieved by the traditional thermal annealing method at high temperatures. It is well-known that water scarcity is becoming a serious challenge due to the increasing industrial pollution and land desertification. Solar thermal evaporation has been proved to be a promising technique for generating clear water because of the abundant and renewable energy source of solar irradiation.30−34 Owing to the porous morphologies and magnetic performances of the 3D Fe3O4 nanoplates, it is no doubt that they possess high surface areas and could be collected easily, which are promising in water purification fields. In this research, the potential of the as-synthesized Fe3O4 hexagonal nanoplates used for water evaporation is further explored. When the 3D Fe3O4 nanoplates were exposed to the illumination in the air, the surface temperature rapidly increased to about 100 °C within 400 s (see Figure S12 (Supporting Information)). Then the foil with 3D Fe3O4 nanoplates was placed at the water/air

4. CONCLUSION In summary, we have successfully synthesized single-crystalline Fe3O4 nanoplates for the first time, through an original and facile process without ferric salts as precursors or surfactants. The as-synthesized Fe3O4 nanoplates have a regular hexagonal outline, with about 20 nm in thickness. The surfaces of the single-crystalline Fe3O4 nanoplates are full of grooves, and porous morphologies are observed with the grooves distributed densely and uniformly. This new strategy provides an environmentally friendly approach to synthesize 3D Fe3O4 nanoplates at a low-temperature of 95 °C, while former reported methods usually required high temperature and pressure. In addition, magnetic properties and water purification abilities of the 3D Fe 3 O 4 nanoplates are investigated and they are found very promising for applications in a variety of fields.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b17582. 3649

DOI: 10.1021/acsami.7b17582 ACS Appl. Mater. Interfaces 2018, 10, 3644−3651

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ACS Applied Materials & Interfaces

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(11) Li, Z.; Godsell, J. F.; O’Byrne, J. P.; Petkov, N.; Morris, M. A.; Roy, S.; Holmes, J. D. Supercritical fluid synthesis of magnetic hexagonal nanoplatelets of magnetite. J. Am. Chem. Soc. 2010, 132 (36), 12540−12541. (12) Zhou, H.; Yi, R.; Li, J.; Su, Y.; Liu, X. Microwave-assisted synthesis and characterization of hexagonal Fe3O4 nanoplates. Solid State Sci. 2010, 12 (1), 99−104. (13) Wang, H.; Shrestha, T. B.; Basel, M. T.; Pyle, M.; Toledo, Y.; Konecny, A.; Thapa, P.; Ikenberry, M.; Hohn, K. L.; Chikan, V.; et al. Hexagonal magnetite nanoprisms: preparation, characterization and cellular uptake. J. Mater. Chem. B 2015, 3 (23), 4647−4653. (14) Liu, B.; Aydil, E. S. Growth of Oriented Single-Crystalline Rutile TiO2 Nanorods on Transparent Conducting Substrates for DyeSensitized Solar Cells. J. Am. Chem. Soc. 2009, 131 (11), 3985−3990. (15) Zhang, Y.-X.; Yu, X.-Y.; Jin, Z.; Jia, Y.; Xu, W.-H.; Luo, T.; Zhu, B.-J.; Liu, J.-H.; Huang, X.-J. Ultra high adsorption capacity of fried egg jellyfish-like γ-AlOOH (Boehmite)@ SiO2/Fe3O4 porous magnetic microspheres for aqueous Pb (II) removal. J. Mater. Chem. 2011, 21 (41), 16550−16557. (16) Crossland, E. J.; Noel, N.; Sivaram, V.; Leijtens, T.; AlexanderWebber, J. A.; Snaith, H. J. Mesoporous TiO2 single crystals delivering enhanced mobility and optoelectronic device performance. Nature 2013, 495 (7440), 215−219. (17) Xuan, S.; Hao, L.; Jiang, W.; Song, L.; Hu, Y.; Chen, Z.; Fei, L.; Li, T. A FeCO3 precursor-based route to microsized peanutlike Fe3O4. Cryst. Growth Des. 2007, 7 (2), 430−434. (18) Fu, C.; Mahadevegowda, A.; Grant, P. S. Fe3O4/Carbon Nanofibres with Necklace Architecture for Enhanced Electrochemical Energy Storage. J. Mater. Chem. A 2015, 3 (27), 14245−14253. (19) Lu, J.; Jiao, X.; Chen, D.; Li, W. Solvothermal synthesis and characterization of Fe3O4 and γ-Fe2O3 nanoplates. J. Phys. Chem. C 2009, 113 (10), 4012−4017. (20) Zhu, M.; Diao, G. Synthesis of Porous Fe3O4 Nanospheres and Its Application for the Catalytic Degradation of Xylenol Orange. J. Phys. Chem. C 2011, 115 (39), 18923−18934. (21) Lang, L.; Xu, Z. In situ synthesis of porous Fe3O4/C microbelts and their enhanced electrochemical performance for lithium-ion batteries. ACS Appl. Mater. Interfaces 2013, 5 (5), 1698−1703. (22) Wang, D.; Liu, L.; Zhang, F.; Tao, K.; Pippel, E.; Domen, K. Spontaneous Phase and Morphology Transformations of Anodized Titania Nanotubes Induced by Water at Room Temperature. Nano Lett. 2011, 11 (9), 3649−3655. (23) Wang, Z.; Schliehe, C.; Wang, T.; Nagaoka, Y.; Cao, Y. C.; Bassett, W. A.; Wu, H.; Fan, H.; Weller, H. Deviatoric stress driven formation of large single-crystal PbS nanosheet from nanoparticles and in situ monitoring of oriented attachment. J. Am. Chem. Soc. 2011, 133 (37), 14484−14487. (24) Pacholski, C.; Kornowski, A.; Weller, H. Self-assembly of ZnO: from nanodots to nanorods. Angew. Chem., Int. Ed. 2002, 41 (7), 1188−1191. (25) Chen, X.; Qiao, M.; Xie, S.; Fan, K.; Zhou, W.; He, H. Selfconstruction of core-shell and hollow zeolite analcime icositetrahedra: a reversed crystal growth process via oriented aggregation of nanocrystallites and recrystallization from surface to core. J. Am. Chem. Soc. 2007, 129 (43), 13305−13312. (26) Zhang, Z.-p.; Sun, H.-p.; Shao, X.-q.; Li, D.; Yu, H.; Han, M. Three-Dimensionally Oriented Aggregation of a Few Hundred Nanoparticles into Monocrystalline Architectures. Adv. Mater. 2005, 17 (1), 42−47. (27) Zhang, Q.; Liu, S.-J.; Yu, S.-H. Recent advances in oriented attachment growth and synthesis of functional materials: concept, evidence, mechanism, and future. J. Mater. Chem. 2009, 19 (2), 191− 207. (28) Zhang, Z.; Han, M. Template-directed growth from small clusters into uniform silver nanoparticles. Chem. Phys. Lett. 2003, 374 (1), 91−94. (29) Chen, Y. J.; Gao, P.; Wang, R.-X.; Zhu, C.-L.; Wang, L.-J.; Cao, M.-S.; Jin, H.-B. Porous Fe3O4/Carbon Core/Shell Nanorods:

Digital photos, SEM images, and XRD patterns of investigation process; HRSEM image, XPS spectra, ferromagnetic resonance absorption spectra, nitrogen adsorption−desorption isotherms of Fe3O4 nanoplates; TEM, HRTEM, and SAED images of residual nanoparticles; infrared images of foils in air; histogram and digital photos of degrading methyl orange (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Mingzhen Liu: 0000-0001-8017-9706 Xingtian Yin: 0000-0001-9077-5982 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National R&D Program of China under No. 2017YFA0207400, National Key Research and Development Plan under No. 2016YFA0300801, National Natural Science Foundation of China under Nos. 51502033, 61571079, 61131005, and 51572042, and National Basic Research Program of China under Grant No. 2012CB933104, 111 Project No. B13042, International Cooperation Projects under Grant No. 2015DFR50870, and the Science and technology project of Sichuan Province No. 2017JY0002.

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REFERENCES

(1) Park, J. H.; Kim, S.; Bard, A. J. Novel carbon-doped TiO2 nanotube arrays with high aspect ratios for efficient solar water splitting. Nano Lett. 2006, 6 (1), 24−28. (2) Sun, Y.; Xia, Y. Shape-Controlled Synthesis of Gold and Silver Nanoparticles. Science 2002, 298 (5601), 2176−2179. (3) Wang, H.; Wang, G.; Yuan, S.; Ma, D.; Li, Y.; Zhang, Y. Fe3O4nanoparticle-decorated TiO2 nanofiber hierarchical heterostructures with improved lithium-ion battery performance over wide temperature range. Nano Res. 2015, 8 (5), 1659−1668. (4) Frey, N. A.; Peng, S.; Cheng, K.; Sun, S. Magnetic nanoparticles: synthesis, functionalization, and applications in bioimaging and magnetic energy storage. Chem. Soc. Rev. 2009, 38 (9), 2532−2542. (5) Perez, J. M.; Josephson, L.; O’Loughlin, T.; Högemann, D.; Weissleder, R. Magnetic relaxation switches capable of sensing molecular interactions. Nat. Biotechnol. 2002, 20 (8), 816−820. (6) Won, J.; Kim, M.; Yi, Y.-W.; Kim, Y. H.; Jung, N.; Kim, T. K. A magnetic nanoprobe technology for detecting molecular interactions in live cells. Science 2005, 309 (5731), 121−125. (7) Gao, L.; Zhuang, J.; Nie, L.; Zhang, J.; Zhang, Y.; Gu, N.; Wang, T.; Feng, J.; Yang, D.; Perrett, S.; et al. Intrinsic peroxidase-like activity of ferromagnetic nanoparticles. Nat. Nanotechnol. 2007, 2 (9), 577− 583. (8) Chueh, Y. L.; Lai, M. W.; Liang, J. Q.; Chou, L. J.; Wang, Z. L. Systematic Study of the Growth of Aligned Arrays of α-Fe2O3 and Fe3O4 Nanowires by a Vapor-Solid Process. Adv. Funct. Mater. 2006, 16 (17), 2243−2251. (9) Wang, Y.; Zhu, Q.; Tao, L. Fabrication and growth mechanism of hierarchical porous Fe3O4 hollow sub-microspheres and their magnetic properties. CrystEngComm 2011, 13 (14), 4652−4657. (10) Jia, C.-J.; Sun, L.-D.; Luo, F.; Han, X.-D.; Heyderman, L. J.; Yan, Z.-G.; Yan, C.-H.; Zheng, K.; Zhang, Z.; Takano, M.; et al. Large-scale synthesis of single-crystalline iron oxide magnetic nanorings. J. Am. Chem. Soc. 2008, 130 (50), 16968−16977. 3650

DOI: 10.1021/acsami.7b17582 ACS Appl. Mater. Interfaces 2018, 10, 3644−3651

Research Article

ACS Applied Materials & Interfaces Synthesis and Electromagnetic Properties. J. Phys. Chem. C 2009, 113 (23), 10061−10064. (30) Elimelech, M.; Phillip, W. A. The future of seawater desalination: energy, technology, and the environment. Science 2011, 333 (6043), 712−717. (31) Shannon, M. A.; Bohn, P. W.; Elimelech, M.; Georgiadis, J. G.; Marinas, B. J.; Mayes, A. M. Science and technology for water purification in the coming decades. Nature 2008, 452 (7185), 301− 310. (32) Zhu, G.; Xu, J.; Zhao, W.; Huang, F. Constructing Black Titania with Unique Nanocage Structure for Solar Desalination. ACS Appl. Mater. Interfaces 2016, 8 (46), 31716−31721. (33) Lou, J.; Liu, Y.; Wang, Z.; Zhao, D.; Song, C.; Wu, J.; Dasgupta, N.; Zhang, W.; Zhang, D.; Tao, P.; et al. Bioinspired multifunctional paper-based rGO composites for solar-driven clean water generation. ACS Appl. Mater. Interfaces 2016, 8 (23), 14628−14636. (34) Liu, K.-K.; Jiang, Q.; Tadepalli, S.; Raliya, R.; Biswas, P.; Naik, R. R.; Singamaneni, S. Wood−Graphene Oxide Composite for Highly Efficient Solar Steam Generation and Desalination. ACS Appl. Mater. Interfaces 2017, 9 (8), 7675−7681.

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DOI: 10.1021/acsami.7b17582 ACS Appl. Mater. Interfaces 2018, 10, 3644−3651