- Email: [email protected]
Structural regulation of NiFe2O4 colloidal nanocrystal assembly and their magnetic and electrocatalytic properties
Colloids and Surfaces A 570 (2019) 218–223
Contents lists available at ScienceDirect
Colloids and Surfaces A journal homepage: www.elsevier.com/locate/colsurfa
Structural regulation of NiFe2O4 colloidal nanocrystal assembly and their magnetic and electrocatalytic properties
T
Shuqing Wang, Rongyue Wang, Yuanzhe Cheng, Baoyan Wang, Qianbin Wang, Shuping Yuan, ⁎ Hongliang Li, Peizhi Guo Institute of Materials for Energy and Environment, State Key Laboratory of Bio-fibers and Eco-textiles, School of Materials Science and Engineering, Qingdao University, Qingdao, 266071, PR China
GRAPHICAL ABSTRACT
ARTICLE INFO
ABSTRACT
Keywords: NiFe2O4 Colloidal nanocrystal assembly Magnetism Electrocatalysis
In-situ assembly of colloidal nanocrystals provides us an effective way to synthesize unique functional assemblies. Submicrometric spheres with tunable structures, which are assembled by nickel ferrite colloidal nanocrystals, were synthesized through solvothermal synthesis. The morphologies and structures of NiFe2O4 colloidal nanocrystal assemblies (CNAs) were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. One of the NiFe2O4 CNAs adopt an inverse spinel structure with a size of around 300 nm from the sodium acetate-contained synthesis system, in which the crystallite size of NiFe2O4 nanocrystals is about 11 nm. However, provided that the urea were added into the synthesis system, the as-prepared NiFe2O4 CNAs has a normal spinel structure, which these clusters assembled by 31 nm nanocrystals are 600 nm in size. The magnetometric measurement results showed that the small NiFe2O4 CNAs displayed nearly superparamagnetic behavior at room temperature while the large NiFe2O4 CNAs performed ferromagnetic behavior mainly owing to the effect of crystallite size. In particular, electrochemical sensing measurements showed that the size of the NiFe2O4 nanocrystals played an important role in the electrochemical reduction of H2O2. Based on the experimental results, the formation mechanisms of both NiFe2O4 CNAs as well as the relationship between their structures and properties were analyzed and discussed in this paper.
1. Introduction Self-assembly of nanomaterials enable the whole assembly to have ⁎
special properties and sometimes those properties of small nanocrystal units or bulk materials are highly different [1–6]. Although the selfassembly of organic molecules has been studied for more than half a
Corresponding author. E-mail addresses: [email protected], [email protected] (P. Guo).
https://doi.org/10.1016/j.colsurfa.2019.03.003 Received 15 January 2019; Received in revised form 2 March 2019; Accepted 2 March 2019 Available online 02 March 2019 0927-7757/ © 2019 Elsevier B.V. All rights reserved.
Colloids and Surfaces A 570 (2019) 218–223
S. Wang, et al.
centrary [7–12], self-assembly of inorganic nanocrystals merely has been received attention until the last two decades [1]. To a large extent, this change is because of the successful synthesis of nanomaterials and the development of synthesis methodology [13–20]. Assembly of inorganic nanocrystals usually can be divided into two groups, namely insitu assembly and ex-situ assembly. In-situ assembly refers to the assembly of intermediate nanocrystals formed during the synthesis process [21–23], and then leading to the direct synthesis of the targeted assemblies. On the contrary, ex-situ assembly means the assembly of the as-prepared nanocrystals [24], during the preparation process which either single or multi-component nanocrystals can be involved. Recently, many type of superstructures via ex-situ assembly have been obtained [13,25,26]. For example, surface caped CdSe-Cds nanorods can form colloidal superparticles in ethylene glycol with spherical or needle-like shapes [25]. In-situ assembly provides us with another method to synthesize the functional assemblies with a submicrometric scale [27–29]. During the last decade, several types of colloidal nanocrystal assemblies (CNAs) via in-situ assembly have been realized, including magnetic CNAs [30], noble metal CNAs [2,31–35] and weak magnetic CNAs [36]. A large part of inorganic CNAs are magnetic CNAs. For example, CNAs of Fe3O4 and ferrites were synthesized by solution-based strategy [21,30]. Until very recently, the structure of Mn1-xNixFe2O4 CNAs were adjusted through simply changing the microenvironment of the synthesis systems [37]. Generally, these CNAs can show nearly superparamagnetic performance due to the assembly effect of small magnetic nanocrystals. Assemblies composed of large nanocrystals usually are apt to display magnetic behavior, which is similar to large nanocrystals [38–40]. However, the assembly of nanocrystals, rather than single crystalline structures with a size similar to the assembly, has abundant spatial space [41–45]. This can be helpful for classifying the relationship between the structures and properties of CNAs [37,46–48]. In our work, NiFe2O4 CNAs have been synthesized via solvethermal method. The structure of NiFe2O4 CNAs can be regulated by simply adjusting the synthesis system. Experimental data showed that small NiFe2O4 CNAs assembled by 11 nm nanocrystals displayed a normal spinel structure with a high saturation magnetization value, which is similar to large inverse spinel NiFe2O4 CNAs composed of 31 nm nanocrystals. Small NiFe2O4 CNAs exhibit an electroreduction peak at a further negative voltage than large NiFe2O4 CNAs during the electrocatalysis of hydrogen peroxide.
2.3. Characterization The XRD patterns of NiFe-Ac and NiFe-Ur were conducted on an Xray diffractometer (Bruker D8) equipped with Cu-Kα radiation (λ = 0.15418 nm). The morphologies of both NiFe2O4 CNAs were measured with a JSM-6390LV scanning electron microscopy (SEM) operated at 20 kV. Transmission electron microscopy (TEM) and high resolution TEM (HRTEM) images were recorded on a JEM-2100 F transmission electron microscope. Magnetic measurements were obtained by using a vibrating sample magnetometer (VSM, LDJ9500) at room temperature. 2.4. Electrochemical sensing measurements The electrochemical measurements of NiFe-Ac and NiFe-Ur were performed on an electrochemical workstation (CHI760E) with a threeelectrode cell at room temperature. A saturated calomel electrode was used as the reference electrode and a platinum foil electrode as the counter electrode. The buffer solution was aqueous phosphate PBS (0.1 M, pH 7.4). The working electrode was a bare glass carbon electrode (GCE) with a diameter of 3 mm and NiFe2O4-modified GCEs. The NiFe2O4 suspension (1 mg mL−1) was ultra-sonicated for 30 min, and then 10 mL of suspension was uniformly dropped on the surface of the GCE. Before being used, the modified electrode obtained above was dried under temperate conditions. In the experiments, H2O2 solutions (30%) were injected into the PBS solution to adjust the targeted concentration of H2O2. 3. Results and discussion 3.1. Morphology and structure The morphologies of both NiFe2O4 CNAs were shown in the SEM images (Fig. 1). As depicted in Fig. 1A and B, NiFe-Ac has a spherical shape and the size of those microspheres was distributed narrowly with a dimension of 300 ± 50 nm. Obviously, spherical NiFe-Ur CNAs have a larger size of around 600 ± 60 nm with a very little part of the small nanoparticles (Fig. 1C and D). The morphologies of NiFe2O4 CNAs were similar to those other ferrite systems probably ascribed to the smallest surface energy of the spherical structures [9]. As evidenced by the XRD measurements (Fig. S1), both NiFe-Ac and NiFe-Ur belong to a spinel structure (JCPDS NO.54-0964). Based on the measurements of the (311) plane in the XRD patterns, the average crystallite sizes in NiFe-Ac and NiFe-Ur calculated from the Scherrer equation were about 11 and 31 nm, respectively. These data indicated that both NiFe-Ur and NiFeAc are composed of small NiFe2O4 nanocrystals, that is to say the formation of submicrometric NiFe2O4 CNAs is due to the in-situ assembly of nanocrystals initiated from the synthesis system [21,30]. The microstructures of NiFe-Ac and NiFe-Ur were investigated by TEM and HRTEM characterizations (Fig. 2). As depicted in Fig. 2A, NiFe-Ac CNAs are well separated and each NiFe-Ac assembly has a smooth surface ascribed to the nature of the small crystallite sizes of NiFe2O4 nanocrystals. The size of NiFe-Ac CNAs is about 300 nm, which is similar to the SEM observation. Compared with NiFe-Ur, two obvious differences can be observed. Those differences are given below, one is the size of NiFe-Ur is about 600 nm, which is larger than that of NiFeAc. The other is that the surface of NiFe-Ur CNAs is much rough and it can be attributed to the large crystallite size of nanocrystals in NiFe-Ur. The crystalline nature of the CNAs can be distinguished from the selected area electron diffraction (SAED) pattern of a single assembly (insets in Fig. 2A and C). The appearance of the diffraction arcs recorded on an isolated circle in Fig. 2A are contributed to the high orientations to assemble primary NiFe2O4 nanocrystals owing to the slight misalignments [49], indicating that the spherical structures of NiFe-Ac are assembled efficiently by NiFe2O4 nanocrystals [21]. Circular shape composed of bright spots are observed from the SAED pattern of single
2. Experimental 2.1. Materials and reagents The chemicals including NiCl2•6H2O, FeCl3•6H2O, CH3COONa, CO (NH2)2, ethylene glycol, and hydrogen peroxide (30%) used in this article were of analytical grade (Purchased from Sinopharm Chemical Reagent Company) and used as received. Double distilled water was used in the experiments except ultrapure water (18.2 MΩ cm) for electrochemical measurements. 2.2. Synthetic process In a typical run, a certain proportion of FeCl3•6H2O (2 mmol) and NiCl2•6H2O (1 mmol) were dissolved in 30 ml ethylene glycol solution with continuous magnetic stirring at room temperature. Then an amount of CH3COONa (9 mmol) or CO(NH2)2 (9 mmol) was added into the above mixture. The homogeneous mixture was transferred into a 40 mL Teflon-lined autoclave before it was tightly sealed and heated at 200 °C for 12 h in an oven. After heating, the autoclave was cooled to room temperature naturally. Finally, the products were collected by centrifugation, washed separately with distilled water and ethanol for several times, and dried in an oven at 60 °C for 12 h. The final products from the systems containing CH3COONa or CO(NH2)2 were named as NiFe-Ac and NiFe-Ur, respectively. 219
Colloids and Surfaces A 570 (2019) 218–223
S. Wang, et al.
Fig. 1. SEM images of NiFe2O4 samples: NiFe-Ac (A and B), NiFe-Ur (C and D).
Fig. 2. TEM images of NiFe-Ac (A), NiFe-Ur (B), HRTEM images of NiFe-Ac (C) and NiFe-Ur (D). The insets in A and C are the SAED patterns.
NiFe-Ur entry, as shown in the inset in Fig. 2C. This may be caused by the assembly nature of the large nanocrystals in NiFe-Ur CNAs, to put it another way, large nanocrystal cannot assemble extraordinary orderly and the properties of the assembly of large nanocrystals would be apt to
represent the nanocrystals themselves [47]. The HRTEM images of an edge of an isolated assembly are shown in Fig. 2B and D. The atomic lattice fringes can be clearly observed, and the lattice spacings are calculated to be 2.95 and 2.51 Å for NiFe-Ac, attributing to the (220) 220
Colloids and Surfaces A 570 (2019) 218–223
S. Wang, et al.
Fig. 5. CV curves of the GCE, NiFe-Ac/GCE and NiFe-Ur/GCE in the electrolytes at H2O2 concentrations of 1.96 mM in 0.1 M PBS (pH 7.4) solutions.
Fig. 3. Raman spectra of NiFe-Ac (a) and NiFe-Ur (b).
and (311) crystal planes of spinel NiFe2O4, respectively, while the lattice spacings are about 4.88 and 2.50 Å for NiFe-Ur corresponding to the (111) and (311) plane reflections of spinel NiFe2O4, respectively. Fig. S2 shows the energy dispersive X-ray spectroscopy (EDS) results of both NiFe2O4 CNAs. According to EDS data, the Ni/Fe/O atomic ratio is 1/2/4 for NiFe-Ac and NiFe-Ur, which is corresponding to the XRD results and the molecular formula of NiFe2O4. The differences in the structures of NiFe-Ac and NiFe-Ur are ascribed to the diverse synthesis systems. In the system of NiFe-Ac, the intermediate products collected after 2 h reaction gradually form the crystalline structure. Clearly, a majoring of α-Fe2O3 was formed after 4 h reaction. Along with the reaction up to 6 h, pure NiFe2O4 sample is obtained. However, for the synthesis system containing urea, the intermediate collected after 1 h and 2 h showed the formation of α-Fe2O3 phase. If the reaction was 4 h, pure NiFe2O4 phase is obtained for the products. These results indicated the nature of sodium acetate and urea would lead to the change of reaction during the synthesis of NiFe2O4 CNAs. Thus, NiFe-Ac and NiFe-Ur formed by in-situ assembly of small and large NiFe2O4 nanocrystals, respectively, which is similar to other ferrite CNAs [30–38]. The structural natures of NiFe-Ac and NiFe-Ur were further explored by Raman spectroscopy measurements, aiming to disclose the coordination characteristics of octahedral and tetrahedral sites in NiFe2O4. As we can see, normal spinel NiFe2O4 has all the Fe3+ positioned in octahedral sites and Ni2+ ions positioned in tetrahedral sites, respectively. However, Ni2+ ions occupied the octahedral places in inverse spinel NiFe2O4 with about half of the Fe3+ and the left Fe3+ ions in tetrahedral positions. This difference between NiFe-Ac and NiFeUr can be observed from the Raman spectra shown in Fig. 3. Compared with our recent reports [37], we can conclude that NiFe-Ac can display
an inverse spinel structure possibly is due to the low concentration of sodium acetate in the beginning system, which may alter the coordination microenvironment of two types of metal ions that thereby influence the spinel structure. 3.2. Magnetic characterization The magnetic properties of NiFe2O4 CNAs were measured at room temperature and the magnetic field was assigned as H = 1.4 × 104 Oe. Fig. 4A shows the magnetization curves of NiFe-Ac and NiFe-Ur at the full scale and whether the hysteresis loop is existed cannot be found easily under this condition. In fact, NiFe-Ac exhibited nearly superparamagnetic behaviour. The saturation magnetization (Ms) value of NiFe-Ac was 44.94 emu g−1, slightly lower than the value of NiFe-Ur (45.74 emu g−1). This Ms value of inverse spinel NiFe-Ac is much smaller than that of our recent reported NiFe2O4 CNAs and it possibly due to the smaller crystallite size of primary nanocrystals in NiFe-Ac [50]. Specific area enlarged view is depicted in Fig. 4B, and NiFe-Ac and NiFe-Ur showed obviously small hysteresis loops, indicating that NiFe-Ur displayed a weak ferromagnetic behavior. It is suggested that the assembly of small nanocrystals in NiFe-Ac not only contributed to a high saturation magnetization compared with NiFe-Ur, but also led to the transformation from the ferromagnetic to superparamagnetic behaviour. The results were consistent with those reported in literatures [51,52]. Usually, the increase of the ratio of surface atoms to the whole atoms of materials can slightly attribute to the surface effect for the large particles. However, when the size of NiFe2O4 nanocrystals in CNAs is down to a small value, the change of particles size would greatly influence the physicochemical properties of CNAs. The remnant
Fig. 4. Magnetization hysteresis (A) of NiFe-Ac (a) and NiFe-Ur (b) and (B) the partially magnified graph of A. 221
Colloids and Surfaces A 570 (2019) 218–223
S. Wang, et al.
Fig. 6. CV curves of the NiFe-Ac/GCE (A) and NiFe-Ur/GCE (B) in the electrolytes at different H2O2 concentrations from (a) to (e): 0, 0.49, 0.98, 1.47, 1.96 mM in 0.1 M PBS (pH 7.4) solutions.
saturation magnetization (Ms) and coercivity (Hc) values of NiFe-Ac were 0.12 emu g−1 and 1.3 Oe, respectively, which is much smaller than those values of NiFe-Ur (1.3 emu g−1 and 23.5 Oe), indicating that NiFe-Ac exhibited a more superparamagnetic behavior than NiFe-Ur. These results demonstrated that the crystallite size and assembly of nanocrystals in CANs affected the superparamagnetic-ferromagnetic transformation and the CNAs performed a corresponding growth in coercivity as the crystallines grow larger [53].
electrocatalytic performances [59–61]. 4. Conclusions Colloidal nanocrystal assemblies of NiFe2O4 were synthesized with controlled structure by solvothermal method. The experimental data show that the NiFe2O4 assemblies are formed by in-situ assembly of small nanocrystals during the synthesis process. As the crystallite size of nanocrystals increased, the saturation magnetization, coercivity, and remnant magnetization values of the assemblies increase obviously. And the assemblies composed of smaller nanocrystalls showed almost superparamagnetic behavior with the saturation magnetization value of 44.94 emu g−1 which is similar to the assembly formed by larger nanocrystals of 45.74 emu g−1. The crystallite size and assembly of the nanocrystals in the assemblies play key roles in determining the sensing properties toward the electrochemical catalysis of H2O2 in a physiological system. These results presented in this work are helpful for the controlled synthesis of targeted magnetic ferrite materials by rational design.
3.3. Electrochemical sensing performance The as-formed NiFe2O4 entries are explored to detect hydrogen peroxide in a physiological system. Fig. 5 shows the cyclic voltammograms of a bare glass carbon electrode (GCE) and the modified GCEs by NiFe-Ac and NiFe-Ur abbreviated as NiFe-Ac/GCE and NiFe-Ur/GCE, respectively, in PBS solutions in the presence of H2O2 of 1.96 mM. The modified GCEs exhibit a good electrochemical response related to the reduction of H2O2. For NiFe-Ac/GCE, a peak at -0.57 V is observed with the catalytic current of about 75 μA, of which the onset potential is about 0.08 V for the reduction of H2O2 while there is no obvious response at a bare GCE. The reduction peak of NiFe-Ur/GCE for H2O2 is positioned at -0.65 V, which is higher than NiFe-Ac/GCE. Obviously, the onset potential for NiFe-Ur is shifted to a lower value about 0.01 V. This indicated that NiFe-Ac/GCE showed a better electrocatalytic activity than NiFe-Ur/GCE. It is suggested that NiFe-Ac CNAs are composed of smaller nanocrystals than NiFe-Ur, which lead to the existence of a large accessible catalytic active sites for NiFe-Ac toward electroreduction of H2O2 [54,55]. As observed, experimental data showed that samples NiFe-Ac and NiFe-Ur showed electrocatalytic activities lower than α-Fe2O3 [54,56] and NiOx [57] nanostructures, but higher than ZnFe2O4 [30] colloidal nanocrystal assemblies. These indicated that the nature of the oxides should play an important role in the electrocatalysis of H2O2. Fig. 6 displays the cyclic voltammograms of the as-modified electrodes at different H2O2 concentrations of H2O2 in PBS solutions. With the concentration of H2O2 increasing, the peak currents increase subsequently for both samples. The result is similar to the previous reported α-Fe2O3 nanorings prepared by a microwave-assisted hydrothermal process [52]. It was clear that the reduction peaks of NiFe-Ac is obviously higher than NiFe-Ur at varied concentrations of H2O2. As depicted in the insets of Fig. 6, the calibration curve shows the amperometric response of the modified GCEs to various concentrations of H2O2 in PBS solutions. The as-fabricated biosensor presents a linear response to H2O2 concentration in the experimental range, with correlation coefficient of r = 0.9408 and 0.9346 for NiFe-Ac and NiFe-Ur, respectively. Moreover, the peak potentials of the spinel samples were higher than these of hematite samples [58], indicating that the NiFe2O4 modified GCEs for electrochemical sensor shows superior
Acknowledgements This work was financially supported by the National Natural Science Foundation of China (No. 21773133), the Double First Class University Construction of Shandong Province and the Taishan Scholars Advantageous and Distinctive cipline rogram for supporting the research team of energy storage materials of Shandong Province. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.colsurfa.2019.03.003. References [1] M.A. Boles, M. Engel, D.V. Talapin, Self-assembly of colloidal nanocrystals: from intricate structures to functional materials, Chem. Rev. 116 (2016) 11220–11289. [2] P. Yang, X. Yuan, H. Hu, Y. Liu, H. Zheng, D. Yang, L. Chen, M. Cao, Y. Xu, Y. Min, Y. Li, Q. Zhang, Solvothermal synthesis of alloyed PtNi colloidal nanocrystal clusters (CNCs) with enhanced catalytic activity for methanol oxidation, Adv. Funct. Mater. 28 (2018) 1704774–1704781. [3] C. Waltmann, N. Horst, A. Travesset, Capping ligand vortices as "Atomic orbitals" in nanocrystal self-assembly, ACS Nano 11 (2017) 11273–11282. [4] D. Caruntu, T. Rostamzadeh, T. Costanzo, S.S. Parizi, G. Caruntu, Solvothermal synthesis and controlled self-assembly of monodisperse titanium-based perovskite colloidal nanocrystals, Nanoscale 7 (2015) 12955–12969. [5] P. Guo, Z. Li, S. Liu, J. Xue, G. Wu, H. Li, X.S. Zhao, Electrochemical properties of colloidal nanocrystal assemblies of manganese ferrite as the electrode materials for supercapacitors, J. Mater. Sci. 52 (2017) 5359–5365. [6] F. Zhan, R. Wang, J. Yin, Z. Han, L. Zhang, T. Jiao, J. Zhou, L. Zhang, Q. Peng, Facile solvothermal preparation of Fe3O4-Ag nanocomposite with excellent catalytic Performance, RSC Adv. 9 (2019) 878–883.
222
Colloids and Surfaces A 570 (2019) 218–223
S. Wang, et al. [7] S.I. Stupp, L.C. Palmer, Supramolecular chemistry and self-assembly in organic materials design, Chem. Mater. 26 (2014) 507–518. [8] M. Liu, L. Zhang, T. Wang, Supramolecular chirality in self-assembled systems, Chem. Rev. 115 (2015) 7304–7397. [9] R. Guo, T. Jiao, R. Li, Y. Chen, W. Guo, L. Zhang, J. Zhou, Q. Zhang, Q. Peng, Sandwiched Fe3O4/carboxylate graphene oxide nanostructures constructed by layer-by-layer assembly for highly efficient and magnetically recyclable dye removal, ACS Sustain. Chem. Eng. 6 (2017) 1279–1288. [10] S. Sun, C. Wang, S. Han, T. Jiao, R. Wang, J. Yin, Q. Li, Y. Wang, L. Geng, X. Yu, Q. Peng, Interfacial nanostructures and acidichromism behaviors in self-assembled terpyridine derivatives Langmuir-Blodgett films, Colloids Surf. A 564 (2019) 1–9. [11] R. Guo, R. Wang, J. Yin, T. Jiao, H. Huang, X. Zhao, L. Zhang, Q. Li, J. Zhou, Q. Peng, Fabrication and highly efficient dye removal characterization of beta-cyclodextrin-Based composite polymer fibers by electrospinning, Nanomaterials 9 (2019) 127. [12] K. Liu, R. Xing, Y. Li, Q. Zou, H. Mçhwald, X. Yan, Mimicking primitive photobacteria: sustainable hydrogen evolution based on peptide-porphyrin Co-assemblies with a self-mineralized reaction center, Angew. Chem. Int. Ed. 55 (2016) 12503–12507. [13] B. Yan, H. Xu, K. Zhang, S. Li, J. Wang, Y. Shi, Y. Du, Cu assisted synthesis of selfsupported PdCu alloy nanowires with enhanced performances toward ethylene glycol electrooxidation, Appl. Surf. Sci. 434 (2018) 701–710. [14] S. Zhang, M.D. Regulacio, M. Han, Self-assembly of colloidal one-dimensional nanocrystals, Chem. Soc. Rev. 43 (2014) 2301–2323. [15] G. Caputo, N. Pinna, Nanoparticle self-assembly using p-p interactions, J. Mater. Chem. A 1 (2013) 2370–2378. [16] L. Jiang, C. Zou, Z. Zhang, Y. Sun, Y. Jiang, W. Leow, B. Liedberg, S. Li, X. Chen, Synergistic modulation of surface interaction to assemble metal nanoparticles into two-dimensional arrays with tunable plasmonic properties, Small 10 (2014) 609–616. [17] Y. Li, W. Wang, W.R. Leow, B. Zhu, F. Meng, L. Zheng, J. Zhu, X. Chen, Optoelectronics of organic nanofibers formed by co-assembly of porphyrin and perylenediimide, Small 10 (2014) 2776–2781. [18] E. Traversa, H. Idriss, Materials for Renewable and Sustainable Energy provides the connection between materials, energy, and sustainability, Mater. Renew. Sustain. Energy 1 (2012) 2. [19] Y. Xu, B. Ren, R. Wang, L. Zhang, T. Jiao, Z. Liu, Facile preparation of rod-like MnO nanomixtures via hydrothermal approach and highly efficient removal of methylene blue for wastewater treatment, Nanomaterials 9 (2019) 10–25. [20] E. Goikolea, B. Daffos, P.L. Taberna, P. Simon, Synthesis of nanosized MnO2 prepared by the polyol method and its application in high power supercapacitors, Mater. Renew. Sustain. Energy 2 (2013) 16. [21] J. Ge, Y. Hu, M. Biasini, W.P. Beyermann, Y. Yin, Superparamagnetic magnetite colloidal nanocrystal clusters, Angew. Chem. Int. Ed. 46 (2007) 4342–4345. [22] Z. Li, W. Wang, Y. Chen, C. Xiong, G. He, Y. Cao, H. Wu, M.D. Guiver, Z. Jiang, Constructing efficient ion nanochannels in alkaline anion exchange membranes by in-situ assembly of poly (ionic liquid) in metal-organic frameworks, J. Mater. Chem. A 4 (2016) 2340–2348. [23] A. Uysal, B. Stripe, B. Lin, M. Meron, P. Dutta, Assembly of amorphous clusters under floating monolayers: a comparison of in situ and ex situ techniques, Langmuir 29 (2013) 14361–14368. [24] M. Zheng, Y. Cui, X. Li, S. Liu, Z. Tang, Photoelectrochemical sensing of glucose based on quantum dot and enzyme nanocomposites, J. Electroanal. Chem. 656 (2011) 167–173. [25] T. Wang, J. Zhuang, J. Lynch, O. Chen, Z. Wang, X. Wang, D.L. Montagne, H. Wu, Z. Wang, Y. Cao, Self-assembled colloidal superparticles from nanorods, Science 338 (2012) 358–363. [26] K. Li, G. Zou, T. Jiao, R. Xing, L. Zhang, J. Zhou, Q. Zhang, Q. Peng, Self-assembled MXene-based nanocomposites via layer-by-layer strategy for elevated adsorption capacities, Colloids Surf. A: Physicochem. Eng. Asp. 553 (2018) 105–113. [27] Z. Lu, Y. Yin, Colloidal nanoparticle clusters: functional materials by design, Cheminform 41 (2012) 6874–6887. [28] X. Liang, L.F. Nazar, In situ reactive assembly of scalable core-shell Sulfur-MnO2 composite cathodes, ACS Nano 10 (2016) 4192–4198. [29] W. Chen, S. Li, C. Chen, L. Yan, Self-assembly and embedding of nanoparticles by in situ reduced graphene for preparation of a 3D graphene/nanoparticle aerogel, Adv. Mater. 23 (2011) 5679–5683. [30] P. Guo, L. Cui, Y. Wang, M. Lv, B. Wang, X.S. Zhao, Facile synthesis of ZnFe2O4 nanoparticles with tunable magnetic and sensing properties, Langmuir 29 (2013) 8997–9003. [31] R. Ding, X. Wu, G. Han, Q. Wang, H. Lu, H. Li, A. Fu, P. Guo, Synthesis of palladium colloidal nanocrystal clusters and their enhanced electrocatalytic properties, ChemElectrochem 2 (2015) 427–433. [32] H. Xu, P. Song, J. Wang, F. Gao, Y. Zhang, J. Guo, Y. Du, J. Di, Visible‐light‐Improved catalytic performance for methanol oxidation based on plasmonic PtAu dendrites, ChemElectroChem 5 (2018) 1191–1196. [33] Y.V.M. Reddy, B. Sravani, H. Maseed, T. Łuczak, M. Osinska, L. SubramanyamSarma, V.V.S.S. Srikanth, G. Madhavi, Ultrafine Pt-Ni bimetallic nanoparticles anchored on reduced graphene oxide nanocomposites for boosting electrochemical detection of dopamine in biological samples, New J. Chem. 42 (2018) 16891–16901. [34] C. Wang, S. Sun, L. Zhang, J. Yin, T. Jiao, L. Zhang, Y. Xu, J. Zhou, Q. Peng, Facile
[35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53]
[54] [55] [56] [57] [58] [59] [60]
[61]
223
preparation and catalytic performance characterization of AuNPs-loaded hierarchical electrospun composite fibers by solvent vapor annealing Treatment, Colloids Surf. A 561 (2019) 283–291. C. Alegre, S. Siracusano, E. Modica, A.S. Aricò, V. Baglio, Titanium-tantalum oxide as a support for Pd nanoparticles for the oxygen reduction reaction in alkaline electrolytes, Mater. Renew. Sustain. Energy 7 (2018) 8–17. P. Guo, R. Wang, J. Xue, B. Xu, Y. Sang, H. Li, X.S. Zhao, Assembly of colloidal cuprous oxide nanocrystals and study of its magnetic and electrocatalytic properties, Colloids Surf. A: Physicochem. Eng. Asp. 522 (2017) 295–303. Q. Wang, L. Bi, W. Ye, H. Cao, X. Wang, X. Wang, M. He, G. Wang, S. Liu, Y. Long, H. Li, P. Guo, Regulation of structure and ionic intercalation of colloidal nanocrystal assembly, Colloids Surf. A: Physicochem. Eng. Asp. 538 (2018) 229–237. Z. Li, K. Gao, G. Han, R. Wang, H. Li, X.S. Zhao, P. Guo, Solvothermal synthesis of MnFe2O4 colloidal nanocrystal assemblies and their magnetic and electrocatalytic properties, New J. Chem. 39 (2015) 361–368. J. Song, K. Ma, T. Jiao, R. Xing, L. Zhang, J. Zhou, Q. Peng, Preparation and selfassembly of graphene oxide-dye composite Langmuir films: nanostructures and aggregations, Colloids Surf. A: Physicochem. Eng. Asp. 529 (2017) 793–800. R. Liu, M. Lv, Q. Wang, H. Li, P. Guo, X.S. Zhao, Solvothermal synthesis of sizetunable ZnFe2O4 colloidal nanocrystal assemblies and their electrocatalytic activity towards hydrogen peroxide, J. Magn. Magn. Mater. 424 (2017) 155–160. J. Yang, M.K. Choi, D.H. Kim, T. Hyeon, Designed assembly and integration of colloidal nanocrystals for device applications, Adv. Mater. 28 (2015) 1176–1207. X. Mou, X. Wei, Y. Li, W. Shen, Tuning crystal-phase and shape of Fe2O3 nanoparticles for catalytic applications, CrystEngComm 14 (2012) 5107–5120. M.V. Kovalenko, M. Scheele, D.V. Talapin, Colloidal nanocrystal with molecular metal chalcogenide surface ligands, Science 324 (2009) 1417–1420. X. Fan, R.R. Gaddam, N. Ashok Kumar, X.S. Zhao, A hybrid Mg2+ /Li+ battery based on interlayer-expanded MoS2/graphene cathode, Adv. Energy Mater. 7 (2017) 1700317. R.R. Gaddam, D. Yang, R. Narayan, K. Raju, N. Ashok Kumar, X.S. Zhao, Biomass derived carbon nanoparticle as anodes for high performance sodium and lithium ion batteries, Nano Energy 26 (2016) 346–352. Y. Cui, M.T. Bjork, J.A. Liddle, C. Sonnichsen, B. Boussert, A.A. Alivisatos, Integration of colloidal nanocrystals into lithographically patterned devices, Nano Lett. 4 (2004) 1093–1098. J. Henzie, V. Etacheri, M. Jahan, H. Rong, C.N. Hong, V.G. Pol, Biomineralizationinspired crystallization of monodisperse α-Mn2O3 octahedra and assembly of highcapacity lithium-ion battery anodes, J. Mater. Chem. A 5 (2017) 6079–6089. K. Liu, C. Yuan, Q. Zou, Z. Xie, X. Yan, Self-assembled zinc/cystine-based chloroplast mimics capable of photoenzymatic reactions for sustainable fuel synthesis, Angew. Chem. Int. Ed. 56 (2017) 7876–7880. U. Lüders, M. Bibes, J.F. Bobo, J. Fontcuberta, Tuning the growth orientation of NiFe2O4 films by appropriate underlayer selection, Appl. Phys. A 80 (2005) 427–431. J. Ku, D.M. Aruguete, A.P. Alivisatos, P.L. Geissler, Self-assembly of magnetic nanoparticles in evaporating solution, J. Am. Chem. Soc. 133 (2011) 838–848. J. Tan, W. Zhang, A. Xia, Facile synthesis of inverse spinel NiFe2O4 nanocrystals and their superparamagnetic properties, Mater. Res. 16 (2013) 237–241. O.V. Yelenich, S.O. Solopan, T.V. Kolodiazhnyi, V.V. Dzyublyuk, A.I. Tovstolytkin, A.G. Belous, Superparamagnetic behavior and AC-losses in NiFe2O4 nanoparticles, Solid State Sci. 20 (2013) 115–119. X. Li, G. Tan, W. Chen, B. Zhou, D. Xue, Y. Peng, F. Li, N. Mellors, Nanostructural and magnetic studies of virtually monodispersed NiFe2O4 nanocrystals synthesized by a liquid-solid-solution assisted hydrothermal route, J. Nanopart. Res. 14 (2012) 1–9. X. Hu, J. Yu, J. Gong, Q. Li, G. Li, α-Fe2O3 nanorings prepared by a microwaveassisted hydrothermal process and their sensing properties, Adv. Mater. 19 (2007) 2324–2329. Q. Wang, S. Liu, L. Fu, Z. Cao, W. Ye, H. Li, P. Guo, X.S. Zhao, Electrospun γ-Fe2O3 nanofibers as bioelectrochemical sensors for simultaneous determination of small biomolecules, Anal. Chim. Acta 1026 (2018) 125–132. P. Guo, Z. Wei, B. Wang, Y. Ding, H. Li, G. Zhang, X.S. Zhao, Controlled synthesis, magnetic and sensing properties of hematite nanorods and Microcapsules, Colloids Surf. A: Physicochem. Eng. Asp. 380 (2011) 234–240. L. Long, X. Liu, L. Chen, D. Li, J. Jia, A hollow CuOx/NiOy nanocomposite for amperometric and non-enzymatic sensing of glucose and hydrogen peroxide, Microchim. Acta 186 (2019) 74. H. Bayrakdar, O. Yalcin, U. Cengiz, S. Ozum, E. Anigi, O. Topel, Comparison effects and electron spin resonance studies of α-Fe2O4 spinel type ferrite nanoparticles, Acta Part A 132 (2014) 160–164. L. Xu, L. Ma, Y. Ling, X. Zhou, X. Xuyao, MoSe2/phosphorus-doped graphene nanocomposite: synthesis and its electrochemical sodium-storage and catalytic performance, Colloids Surf. A 551 (2018) 87–94. Y.V.M. Reddy, B. Sravani, S. Agarwal, V.K. Gupta, G. Madhavi, Electrochemical sensor for detection of uric acid in the presence of ascorbic acid and dopamine using the poly(DPA)/SiO2@Fe3O4 modified carbon paste Electrode, J. Electroanal. Chem. 820 (2018) 168–175. Y. Yin, N. Ma, J. Xue, G. Wang, S. Liu, H. Li, P. Guo, Insights into the role of polyvinylpyrrolidone on the synthesis of palladium nanoparticles and their electrocatalytic properties, Langmuir 35 (2019) 787–795.
Contents lists available at ScienceDirect
Colloids and Surfaces A journal homepage: www.elsevier.com/locate/colsurfa
Structural regulation of NiFe2O4 colloidal nanocrystal assembly and their magnetic and electrocatalytic properties
T
Shuqing Wang, Rongyue Wang, Yuanzhe Cheng, Baoyan Wang, Qianbin Wang, Shuping Yuan, ⁎ Hongliang Li, Peizhi Guo Institute of Materials for Energy and Environment, State Key Laboratory of Bio-fibers and Eco-textiles, School of Materials Science and Engineering, Qingdao University, Qingdao, 266071, PR China
GRAPHICAL ABSTRACT
ARTICLE INFO
ABSTRACT
Keywords: NiFe2O4 Colloidal nanocrystal assembly Magnetism Electrocatalysis
In-situ assembly of colloidal nanocrystals provides us an effective way to synthesize unique functional assemblies. Submicrometric spheres with tunable structures, which are assembled by nickel ferrite colloidal nanocrystals, were synthesized through solvothermal synthesis. The morphologies and structures of NiFe2O4 colloidal nanocrystal assemblies (CNAs) were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. One of the NiFe2O4 CNAs adopt an inverse spinel structure with a size of around 300 nm from the sodium acetate-contained synthesis system, in which the crystallite size of NiFe2O4 nanocrystals is about 11 nm. However, provided that the urea were added into the synthesis system, the as-prepared NiFe2O4 CNAs has a normal spinel structure, which these clusters assembled by 31 nm nanocrystals are 600 nm in size. The magnetometric measurement results showed that the small NiFe2O4 CNAs displayed nearly superparamagnetic behavior at room temperature while the large NiFe2O4 CNAs performed ferromagnetic behavior mainly owing to the effect of crystallite size. In particular, electrochemical sensing measurements showed that the size of the NiFe2O4 nanocrystals played an important role in the electrochemical reduction of H2O2. Based on the experimental results, the formation mechanisms of both NiFe2O4 CNAs as well as the relationship between their structures and properties were analyzed and discussed in this paper.
1. Introduction Self-assembly of nanomaterials enable the whole assembly to have ⁎
special properties and sometimes those properties of small nanocrystal units or bulk materials are highly different [1–6]. Although the selfassembly of organic molecules has been studied for more than half a
Corresponding author. E-mail addresses: [email protected], [email protected] (P. Guo).
https://doi.org/10.1016/j.colsurfa.2019.03.003 Received 15 January 2019; Received in revised form 2 March 2019; Accepted 2 March 2019 Available online 02 March 2019 0927-7757/ © 2019 Elsevier B.V. All rights reserved.
Colloids and Surfaces A 570 (2019) 218–223
S. Wang, et al.
centrary [7–12], self-assembly of inorganic nanocrystals merely has been received attention until the last two decades [1]. To a large extent, this change is because of the successful synthesis of nanomaterials and the development of synthesis methodology [13–20]. Assembly of inorganic nanocrystals usually can be divided into two groups, namely insitu assembly and ex-situ assembly. In-situ assembly refers to the assembly of intermediate nanocrystals formed during the synthesis process [21–23], and then leading to the direct synthesis of the targeted assemblies. On the contrary, ex-situ assembly means the assembly of the as-prepared nanocrystals [24], during the preparation process which either single or multi-component nanocrystals can be involved. Recently, many type of superstructures via ex-situ assembly have been obtained [13,25,26]. For example, surface caped CdSe-Cds nanorods can form colloidal superparticles in ethylene glycol with spherical or needle-like shapes [25]. In-situ assembly provides us with another method to synthesize the functional assemblies with a submicrometric scale [27–29]. During the last decade, several types of colloidal nanocrystal assemblies (CNAs) via in-situ assembly have been realized, including magnetic CNAs [30], noble metal CNAs [2,31–35] and weak magnetic CNAs [36]. A large part of inorganic CNAs are magnetic CNAs. For example, CNAs of Fe3O4 and ferrites were synthesized by solution-based strategy [21,30]. Until very recently, the structure of Mn1-xNixFe2O4 CNAs were adjusted through simply changing the microenvironment of the synthesis systems [37]. Generally, these CNAs can show nearly superparamagnetic performance due to the assembly effect of small magnetic nanocrystals. Assemblies composed of large nanocrystals usually are apt to display magnetic behavior, which is similar to large nanocrystals [38–40]. However, the assembly of nanocrystals, rather than single crystalline structures with a size similar to the assembly, has abundant spatial space [41–45]. This can be helpful for classifying the relationship between the structures and properties of CNAs [37,46–48]. In our work, NiFe2O4 CNAs have been synthesized via solvethermal method. The structure of NiFe2O4 CNAs can be regulated by simply adjusting the synthesis system. Experimental data showed that small NiFe2O4 CNAs assembled by 11 nm nanocrystals displayed a normal spinel structure with a high saturation magnetization value, which is similar to large inverse spinel NiFe2O4 CNAs composed of 31 nm nanocrystals. Small NiFe2O4 CNAs exhibit an electroreduction peak at a further negative voltage than large NiFe2O4 CNAs during the electrocatalysis of hydrogen peroxide.
2.3. Characterization The XRD patterns of NiFe-Ac and NiFe-Ur were conducted on an Xray diffractometer (Bruker D8) equipped with Cu-Kα radiation (λ = 0.15418 nm). The morphologies of both NiFe2O4 CNAs were measured with a JSM-6390LV scanning electron microscopy (SEM) operated at 20 kV. Transmission electron microscopy (TEM) and high resolution TEM (HRTEM) images were recorded on a JEM-2100 F transmission electron microscope. Magnetic measurements were obtained by using a vibrating sample magnetometer (VSM, LDJ9500) at room temperature. 2.4. Electrochemical sensing measurements The electrochemical measurements of NiFe-Ac and NiFe-Ur were performed on an electrochemical workstation (CHI760E) with a threeelectrode cell at room temperature. A saturated calomel electrode was used as the reference electrode and a platinum foil electrode as the counter electrode. The buffer solution was aqueous phosphate PBS (0.1 M, pH 7.4). The working electrode was a bare glass carbon electrode (GCE) with a diameter of 3 mm and NiFe2O4-modified GCEs. The NiFe2O4 suspension (1 mg mL−1) was ultra-sonicated for 30 min, and then 10 mL of suspension was uniformly dropped on the surface of the GCE. Before being used, the modified electrode obtained above was dried under temperate conditions. In the experiments, H2O2 solutions (30%) were injected into the PBS solution to adjust the targeted concentration of H2O2. 3. Results and discussion 3.1. Morphology and structure The morphologies of both NiFe2O4 CNAs were shown in the SEM images (Fig. 1). As depicted in Fig. 1A and B, NiFe-Ac has a spherical shape and the size of those microspheres was distributed narrowly with a dimension of 300 ± 50 nm. Obviously, spherical NiFe-Ur CNAs have a larger size of around 600 ± 60 nm with a very little part of the small nanoparticles (Fig. 1C and D). The morphologies of NiFe2O4 CNAs were similar to those other ferrite systems probably ascribed to the smallest surface energy of the spherical structures [9]. As evidenced by the XRD measurements (Fig. S1), both NiFe-Ac and NiFe-Ur belong to a spinel structure (JCPDS NO.54-0964). Based on the measurements of the (311) plane in the XRD patterns, the average crystallite sizes in NiFe-Ac and NiFe-Ur calculated from the Scherrer equation were about 11 and 31 nm, respectively. These data indicated that both NiFe-Ur and NiFeAc are composed of small NiFe2O4 nanocrystals, that is to say the formation of submicrometric NiFe2O4 CNAs is due to the in-situ assembly of nanocrystals initiated from the synthesis system [21,30]. The microstructures of NiFe-Ac and NiFe-Ur were investigated by TEM and HRTEM characterizations (Fig. 2). As depicted in Fig. 2A, NiFe-Ac CNAs are well separated and each NiFe-Ac assembly has a smooth surface ascribed to the nature of the small crystallite sizes of NiFe2O4 nanocrystals. The size of NiFe-Ac CNAs is about 300 nm, which is similar to the SEM observation. Compared with NiFe-Ur, two obvious differences can be observed. Those differences are given below, one is the size of NiFe-Ur is about 600 nm, which is larger than that of NiFeAc. The other is that the surface of NiFe-Ur CNAs is much rough and it can be attributed to the large crystallite size of nanocrystals in NiFe-Ur. The crystalline nature of the CNAs can be distinguished from the selected area electron diffraction (SAED) pattern of a single assembly (insets in Fig. 2A and C). The appearance of the diffraction arcs recorded on an isolated circle in Fig. 2A are contributed to the high orientations to assemble primary NiFe2O4 nanocrystals owing to the slight misalignments [49], indicating that the spherical structures of NiFe-Ac are assembled efficiently by NiFe2O4 nanocrystals [21]. Circular shape composed of bright spots are observed from the SAED pattern of single
2. Experimental 2.1. Materials and reagents The chemicals including NiCl2•6H2O, FeCl3•6H2O, CH3COONa, CO (NH2)2, ethylene glycol, and hydrogen peroxide (30%) used in this article were of analytical grade (Purchased from Sinopharm Chemical Reagent Company) and used as received. Double distilled water was used in the experiments except ultrapure water (18.2 MΩ cm) for electrochemical measurements. 2.2. Synthetic process In a typical run, a certain proportion of FeCl3•6H2O (2 mmol) and NiCl2•6H2O (1 mmol) were dissolved in 30 ml ethylene glycol solution with continuous magnetic stirring at room temperature. Then an amount of CH3COONa (9 mmol) or CO(NH2)2 (9 mmol) was added into the above mixture. The homogeneous mixture was transferred into a 40 mL Teflon-lined autoclave before it was tightly sealed and heated at 200 °C for 12 h in an oven. After heating, the autoclave was cooled to room temperature naturally. Finally, the products were collected by centrifugation, washed separately with distilled water and ethanol for several times, and dried in an oven at 60 °C for 12 h. The final products from the systems containing CH3COONa or CO(NH2)2 were named as NiFe-Ac and NiFe-Ur, respectively. 219
Colloids and Surfaces A 570 (2019) 218–223
S. Wang, et al.
Fig. 1. SEM images of NiFe2O4 samples: NiFe-Ac (A and B), NiFe-Ur (C and D).
Fig. 2. TEM images of NiFe-Ac (A), NiFe-Ur (B), HRTEM images of NiFe-Ac (C) and NiFe-Ur (D). The insets in A and C are the SAED patterns.
NiFe-Ur entry, as shown in the inset in Fig. 2C. This may be caused by the assembly nature of the large nanocrystals in NiFe-Ur CNAs, to put it another way, large nanocrystal cannot assemble extraordinary orderly and the properties of the assembly of large nanocrystals would be apt to
represent the nanocrystals themselves [47]. The HRTEM images of an edge of an isolated assembly are shown in Fig. 2B and D. The atomic lattice fringes can be clearly observed, and the lattice spacings are calculated to be 2.95 and 2.51 Å for NiFe-Ac, attributing to the (220) 220
Colloids and Surfaces A 570 (2019) 218–223
S. Wang, et al.
Fig. 5. CV curves of the GCE, NiFe-Ac/GCE and NiFe-Ur/GCE in the electrolytes at H2O2 concentrations of 1.96 mM in 0.1 M PBS (pH 7.4) solutions.
Fig. 3. Raman spectra of NiFe-Ac (a) and NiFe-Ur (b).
and (311) crystal planes of spinel NiFe2O4, respectively, while the lattice spacings are about 4.88 and 2.50 Å for NiFe-Ur corresponding to the (111) and (311) plane reflections of spinel NiFe2O4, respectively. Fig. S2 shows the energy dispersive X-ray spectroscopy (EDS) results of both NiFe2O4 CNAs. According to EDS data, the Ni/Fe/O atomic ratio is 1/2/4 for NiFe-Ac and NiFe-Ur, which is corresponding to the XRD results and the molecular formula of NiFe2O4. The differences in the structures of NiFe-Ac and NiFe-Ur are ascribed to the diverse synthesis systems. In the system of NiFe-Ac, the intermediate products collected after 2 h reaction gradually form the crystalline structure. Clearly, a majoring of α-Fe2O3 was formed after 4 h reaction. Along with the reaction up to 6 h, pure NiFe2O4 sample is obtained. However, for the synthesis system containing urea, the intermediate collected after 1 h and 2 h showed the formation of α-Fe2O3 phase. If the reaction was 4 h, pure NiFe2O4 phase is obtained for the products. These results indicated the nature of sodium acetate and urea would lead to the change of reaction during the synthesis of NiFe2O4 CNAs. Thus, NiFe-Ac and NiFe-Ur formed by in-situ assembly of small and large NiFe2O4 nanocrystals, respectively, which is similar to other ferrite CNAs [30–38]. The structural natures of NiFe-Ac and NiFe-Ur were further explored by Raman spectroscopy measurements, aiming to disclose the coordination characteristics of octahedral and tetrahedral sites in NiFe2O4. As we can see, normal spinel NiFe2O4 has all the Fe3+ positioned in octahedral sites and Ni2+ ions positioned in tetrahedral sites, respectively. However, Ni2+ ions occupied the octahedral places in inverse spinel NiFe2O4 with about half of the Fe3+ and the left Fe3+ ions in tetrahedral positions. This difference between NiFe-Ac and NiFeUr can be observed from the Raman spectra shown in Fig. 3. Compared with our recent reports [37], we can conclude that NiFe-Ac can display
an inverse spinel structure possibly is due to the low concentration of sodium acetate in the beginning system, which may alter the coordination microenvironment of two types of metal ions that thereby influence the spinel structure. 3.2. Magnetic characterization The magnetic properties of NiFe2O4 CNAs were measured at room temperature and the magnetic field was assigned as H = 1.4 × 104 Oe. Fig. 4A shows the magnetization curves of NiFe-Ac and NiFe-Ur at the full scale and whether the hysteresis loop is existed cannot be found easily under this condition. In fact, NiFe-Ac exhibited nearly superparamagnetic behaviour. The saturation magnetization (Ms) value of NiFe-Ac was 44.94 emu g−1, slightly lower than the value of NiFe-Ur (45.74 emu g−1). This Ms value of inverse spinel NiFe-Ac is much smaller than that of our recent reported NiFe2O4 CNAs and it possibly due to the smaller crystallite size of primary nanocrystals in NiFe-Ac [50]. Specific area enlarged view is depicted in Fig. 4B, and NiFe-Ac and NiFe-Ur showed obviously small hysteresis loops, indicating that NiFe-Ur displayed a weak ferromagnetic behavior. It is suggested that the assembly of small nanocrystals in NiFe-Ac not only contributed to a high saturation magnetization compared with NiFe-Ur, but also led to the transformation from the ferromagnetic to superparamagnetic behaviour. The results were consistent with those reported in literatures [51,52]. Usually, the increase of the ratio of surface atoms to the whole atoms of materials can slightly attribute to the surface effect for the large particles. However, when the size of NiFe2O4 nanocrystals in CNAs is down to a small value, the change of particles size would greatly influence the physicochemical properties of CNAs. The remnant
Fig. 4. Magnetization hysteresis (A) of NiFe-Ac (a) and NiFe-Ur (b) and (B) the partially magnified graph of A. 221
Colloids and Surfaces A 570 (2019) 218–223
S. Wang, et al.
Fig. 6. CV curves of the NiFe-Ac/GCE (A) and NiFe-Ur/GCE (B) in the electrolytes at different H2O2 concentrations from (a) to (e): 0, 0.49, 0.98, 1.47, 1.96 mM in 0.1 M PBS (pH 7.4) solutions.
saturation magnetization (Ms) and coercivity (Hc) values of NiFe-Ac were 0.12 emu g−1 and 1.3 Oe, respectively, which is much smaller than those values of NiFe-Ur (1.3 emu g−1 and 23.5 Oe), indicating that NiFe-Ac exhibited a more superparamagnetic behavior than NiFe-Ur. These results demonstrated that the crystallite size and assembly of nanocrystals in CANs affected the superparamagnetic-ferromagnetic transformation and the CNAs performed a corresponding growth in coercivity as the crystallines grow larger [53].
electrocatalytic performances [59–61]. 4. Conclusions Colloidal nanocrystal assemblies of NiFe2O4 were synthesized with controlled structure by solvothermal method. The experimental data show that the NiFe2O4 assemblies are formed by in-situ assembly of small nanocrystals during the synthesis process. As the crystallite size of nanocrystals increased, the saturation magnetization, coercivity, and remnant magnetization values of the assemblies increase obviously. And the assemblies composed of smaller nanocrystalls showed almost superparamagnetic behavior with the saturation magnetization value of 44.94 emu g−1 which is similar to the assembly formed by larger nanocrystals of 45.74 emu g−1. The crystallite size and assembly of the nanocrystals in the assemblies play key roles in determining the sensing properties toward the electrochemical catalysis of H2O2 in a physiological system. These results presented in this work are helpful for the controlled synthesis of targeted magnetic ferrite materials by rational design.
3.3. Electrochemical sensing performance The as-formed NiFe2O4 entries are explored to detect hydrogen peroxide in a physiological system. Fig. 5 shows the cyclic voltammograms of a bare glass carbon electrode (GCE) and the modified GCEs by NiFe-Ac and NiFe-Ur abbreviated as NiFe-Ac/GCE and NiFe-Ur/GCE, respectively, in PBS solutions in the presence of H2O2 of 1.96 mM. The modified GCEs exhibit a good electrochemical response related to the reduction of H2O2. For NiFe-Ac/GCE, a peak at -0.57 V is observed with the catalytic current of about 75 μA, of which the onset potential is about 0.08 V for the reduction of H2O2 while there is no obvious response at a bare GCE. The reduction peak of NiFe-Ur/GCE for H2O2 is positioned at -0.65 V, which is higher than NiFe-Ac/GCE. Obviously, the onset potential for NiFe-Ur is shifted to a lower value about 0.01 V. This indicated that NiFe-Ac/GCE showed a better electrocatalytic activity than NiFe-Ur/GCE. It is suggested that NiFe-Ac CNAs are composed of smaller nanocrystals than NiFe-Ur, which lead to the existence of a large accessible catalytic active sites for NiFe-Ac toward electroreduction of H2O2 [54,55]. As observed, experimental data showed that samples NiFe-Ac and NiFe-Ur showed electrocatalytic activities lower than α-Fe2O3 [54,56] and NiOx [57] nanostructures, but higher than ZnFe2O4 [30] colloidal nanocrystal assemblies. These indicated that the nature of the oxides should play an important role in the electrocatalysis of H2O2. Fig. 6 displays the cyclic voltammograms of the as-modified electrodes at different H2O2 concentrations of H2O2 in PBS solutions. With the concentration of H2O2 increasing, the peak currents increase subsequently for both samples. The result is similar to the previous reported α-Fe2O3 nanorings prepared by a microwave-assisted hydrothermal process [52]. It was clear that the reduction peaks of NiFe-Ac is obviously higher than NiFe-Ur at varied concentrations of H2O2. As depicted in the insets of Fig. 6, the calibration curve shows the amperometric response of the modified GCEs to various concentrations of H2O2 in PBS solutions. The as-fabricated biosensor presents a linear response to H2O2 concentration in the experimental range, with correlation coefficient of r = 0.9408 and 0.9346 for NiFe-Ac and NiFe-Ur, respectively. Moreover, the peak potentials of the spinel samples were higher than these of hematite samples [58], indicating that the NiFe2O4 modified GCEs for electrochemical sensor shows superior
Acknowledgements This work was financially supported by the National Natural Science Foundation of China (No. 21773133), the Double First Class University Construction of Shandong Province and the Taishan Scholars Advantageous and Distinctive cipline rogram for supporting the research team of energy storage materials of Shandong Province. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.colsurfa.2019.03.003. References [1] M.A. Boles, M. Engel, D.V. Talapin, Self-assembly of colloidal nanocrystals: from intricate structures to functional materials, Chem. Rev. 116 (2016) 11220–11289. [2] P. Yang, X. Yuan, H. Hu, Y. Liu, H. Zheng, D. Yang, L. Chen, M. Cao, Y. Xu, Y. Min, Y. Li, Q. Zhang, Solvothermal synthesis of alloyed PtNi colloidal nanocrystal clusters (CNCs) with enhanced catalytic activity for methanol oxidation, Adv. Funct. Mater. 28 (2018) 1704774–1704781. [3] C. Waltmann, N. Horst, A. Travesset, Capping ligand vortices as "Atomic orbitals" in nanocrystal self-assembly, ACS Nano 11 (2017) 11273–11282. [4] D. Caruntu, T. Rostamzadeh, T. Costanzo, S.S. Parizi, G. Caruntu, Solvothermal synthesis and controlled self-assembly of monodisperse titanium-based perovskite colloidal nanocrystals, Nanoscale 7 (2015) 12955–12969. [5] P. Guo, Z. Li, S. Liu, J. Xue, G. Wu, H. Li, X.S. Zhao, Electrochemical properties of colloidal nanocrystal assemblies of manganese ferrite as the electrode materials for supercapacitors, J. Mater. Sci. 52 (2017) 5359–5365. [6] F. Zhan, R. Wang, J. Yin, Z. Han, L. Zhang, T. Jiao, J. Zhou, L. Zhang, Q. Peng, Facile solvothermal preparation of Fe3O4-Ag nanocomposite with excellent catalytic Performance, RSC Adv. 9 (2019) 878–883.
222
Colloids and Surfaces A 570 (2019) 218–223
S. Wang, et al. [7] S.I. Stupp, L.C. Palmer, Supramolecular chemistry and self-assembly in organic materials design, Chem. Mater. 26 (2014) 507–518. [8] M. Liu, L. Zhang, T. Wang, Supramolecular chirality in self-assembled systems, Chem. Rev. 115 (2015) 7304–7397. [9] R. Guo, T. Jiao, R. Li, Y. Chen, W. Guo, L. Zhang, J. Zhou, Q. Zhang, Q. Peng, Sandwiched Fe3O4/carboxylate graphene oxide nanostructures constructed by layer-by-layer assembly for highly efficient and magnetically recyclable dye removal, ACS Sustain. Chem. Eng. 6 (2017) 1279–1288. [10] S. Sun, C. Wang, S. Han, T. Jiao, R. Wang, J. Yin, Q. Li, Y. Wang, L. Geng, X. Yu, Q. Peng, Interfacial nanostructures and acidichromism behaviors in self-assembled terpyridine derivatives Langmuir-Blodgett films, Colloids Surf. A 564 (2019) 1–9. [11] R. Guo, R. Wang, J. Yin, T. Jiao, H. Huang, X. Zhao, L. Zhang, Q. Li, J. Zhou, Q. Peng, Fabrication and highly efficient dye removal characterization of beta-cyclodextrin-Based composite polymer fibers by electrospinning, Nanomaterials 9 (2019) 127. [12] K. Liu, R. Xing, Y. Li, Q. Zou, H. Mçhwald, X. Yan, Mimicking primitive photobacteria: sustainable hydrogen evolution based on peptide-porphyrin Co-assemblies with a self-mineralized reaction center, Angew. Chem. Int. Ed. 55 (2016) 12503–12507. [13] B. Yan, H. Xu, K. Zhang, S. Li, J. Wang, Y. Shi, Y. Du, Cu assisted synthesis of selfsupported PdCu alloy nanowires with enhanced performances toward ethylene glycol electrooxidation, Appl. Surf. Sci. 434 (2018) 701–710. [14] S. Zhang, M.D. Regulacio, M. Han, Self-assembly of colloidal one-dimensional nanocrystals, Chem. Soc. Rev. 43 (2014) 2301–2323. [15] G. Caputo, N. Pinna, Nanoparticle self-assembly using p-p interactions, J. Mater. Chem. A 1 (2013) 2370–2378. [16] L. Jiang, C. Zou, Z. Zhang, Y. Sun, Y. Jiang, W. Leow, B. Liedberg, S. Li, X. Chen, Synergistic modulation of surface interaction to assemble metal nanoparticles into two-dimensional arrays with tunable plasmonic properties, Small 10 (2014) 609–616. [17] Y. Li, W. Wang, W.R. Leow, B. Zhu, F. Meng, L. Zheng, J. Zhu, X. Chen, Optoelectronics of organic nanofibers formed by co-assembly of porphyrin and perylenediimide, Small 10 (2014) 2776–2781. [18] E. Traversa, H. Idriss, Materials for Renewable and Sustainable Energy provides the connection between materials, energy, and sustainability, Mater. Renew. Sustain. Energy 1 (2012) 2. [19] Y. Xu, B. Ren, R. Wang, L. Zhang, T. Jiao, Z. Liu, Facile preparation of rod-like MnO nanomixtures via hydrothermal approach and highly efficient removal of methylene blue for wastewater treatment, Nanomaterials 9 (2019) 10–25. [20] E. Goikolea, B. Daffos, P.L. Taberna, P. Simon, Synthesis of nanosized MnO2 prepared by the polyol method and its application in high power supercapacitors, Mater. Renew. Sustain. Energy 2 (2013) 16. [21] J. Ge, Y. Hu, M. Biasini, W.P. Beyermann, Y. Yin, Superparamagnetic magnetite colloidal nanocrystal clusters, Angew. Chem. Int. Ed. 46 (2007) 4342–4345. [22] Z. Li, W. Wang, Y. Chen, C. Xiong, G. He, Y. Cao, H. Wu, M.D. Guiver, Z. Jiang, Constructing efficient ion nanochannels in alkaline anion exchange membranes by in-situ assembly of poly (ionic liquid) in metal-organic frameworks, J. Mater. Chem. A 4 (2016) 2340–2348. [23] A. Uysal, B. Stripe, B. Lin, M. Meron, P. Dutta, Assembly of amorphous clusters under floating monolayers: a comparison of in situ and ex situ techniques, Langmuir 29 (2013) 14361–14368. [24] M. Zheng, Y. Cui, X. Li, S. Liu, Z. Tang, Photoelectrochemical sensing of glucose based on quantum dot and enzyme nanocomposites, J. Electroanal. Chem. 656 (2011) 167–173. [25] T. Wang, J. Zhuang, J. Lynch, O. Chen, Z. Wang, X. Wang, D.L. Montagne, H. Wu, Z. Wang, Y. Cao, Self-assembled colloidal superparticles from nanorods, Science 338 (2012) 358–363. [26] K. Li, G. Zou, T. Jiao, R. Xing, L. Zhang, J. Zhou, Q. Zhang, Q. Peng, Self-assembled MXene-based nanocomposites via layer-by-layer strategy for elevated adsorption capacities, Colloids Surf. A: Physicochem. Eng. Asp. 553 (2018) 105–113. [27] Z. Lu, Y. Yin, Colloidal nanoparticle clusters: functional materials by design, Cheminform 41 (2012) 6874–6887. [28] X. Liang, L.F. Nazar, In situ reactive assembly of scalable core-shell Sulfur-MnO2 composite cathodes, ACS Nano 10 (2016) 4192–4198. [29] W. Chen, S. Li, C. Chen, L. Yan, Self-assembly and embedding of nanoparticles by in situ reduced graphene for preparation of a 3D graphene/nanoparticle aerogel, Adv. Mater. 23 (2011) 5679–5683. [30] P. Guo, L. Cui, Y. Wang, M. Lv, B. Wang, X.S. Zhao, Facile synthesis of ZnFe2O4 nanoparticles with tunable magnetic and sensing properties, Langmuir 29 (2013) 8997–9003. [31] R. Ding, X. Wu, G. Han, Q. Wang, H. Lu, H. Li, A. Fu, P. Guo, Synthesis of palladium colloidal nanocrystal clusters and their enhanced electrocatalytic properties, ChemElectrochem 2 (2015) 427–433. [32] H. Xu, P. Song, J. Wang, F. Gao, Y. Zhang, J. Guo, Y. Du, J. Di, Visible‐light‐Improved catalytic performance for methanol oxidation based on plasmonic PtAu dendrites, ChemElectroChem 5 (2018) 1191–1196. [33] Y.V.M. Reddy, B. Sravani, H. Maseed, T. Łuczak, M. Osinska, L. SubramanyamSarma, V.V.S.S. Srikanth, G. Madhavi, Ultrafine Pt-Ni bimetallic nanoparticles anchored on reduced graphene oxide nanocomposites for boosting electrochemical detection of dopamine in biological samples, New J. Chem. 42 (2018) 16891–16901. [34] C. Wang, S. Sun, L. Zhang, J. Yin, T. Jiao, L. Zhang, Y. Xu, J. Zhou, Q. Peng, Facile
[35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53]
[54] [55] [56] [57] [58] [59] [60]
[61]
223
preparation and catalytic performance characterization of AuNPs-loaded hierarchical electrospun composite fibers by solvent vapor annealing Treatment, Colloids Surf. A 561 (2019) 283–291. C. Alegre, S. Siracusano, E. Modica, A.S. Aricò, V. Baglio, Titanium-tantalum oxide as a support for Pd nanoparticles for the oxygen reduction reaction in alkaline electrolytes, Mater. Renew. Sustain. Energy 7 (2018) 8–17. P. Guo, R. Wang, J. Xue, B. Xu, Y. Sang, H. Li, X.S. Zhao, Assembly of colloidal cuprous oxide nanocrystals and study of its magnetic and electrocatalytic properties, Colloids Surf. A: Physicochem. Eng. Asp. 522 (2017) 295–303. Q. Wang, L. Bi, W. Ye, H. Cao, X. Wang, X. Wang, M. He, G. Wang, S. Liu, Y. Long, H. Li, P. Guo, Regulation of structure and ionic intercalation of colloidal nanocrystal assembly, Colloids Surf. A: Physicochem. Eng. Asp. 538 (2018) 229–237. Z. Li, K. Gao, G. Han, R. Wang, H. Li, X.S. Zhao, P. Guo, Solvothermal synthesis of MnFe2O4 colloidal nanocrystal assemblies and their magnetic and electrocatalytic properties, New J. Chem. 39 (2015) 361–368. J. Song, K. Ma, T. Jiao, R. Xing, L. Zhang, J. Zhou, Q. Peng, Preparation and selfassembly of graphene oxide-dye composite Langmuir films: nanostructures and aggregations, Colloids Surf. A: Physicochem. Eng. Asp. 529 (2017) 793–800. R. Liu, M. Lv, Q. Wang, H. Li, P. Guo, X.S. Zhao, Solvothermal synthesis of sizetunable ZnFe2O4 colloidal nanocrystal assemblies and their electrocatalytic activity towards hydrogen peroxide, J. Magn. Magn. Mater. 424 (2017) 155–160. J. Yang, M.K. Choi, D.H. Kim, T. Hyeon, Designed assembly and integration of colloidal nanocrystals for device applications, Adv. Mater. 28 (2015) 1176–1207. X. Mou, X. Wei, Y. Li, W. Shen, Tuning crystal-phase and shape of Fe2O3 nanoparticles for catalytic applications, CrystEngComm 14 (2012) 5107–5120. M.V. Kovalenko, M. Scheele, D.V. Talapin, Colloidal nanocrystal with molecular metal chalcogenide surface ligands, Science 324 (2009) 1417–1420. X. Fan, R.R. Gaddam, N. Ashok Kumar, X.S. Zhao, A hybrid Mg2+ /Li+ battery based on interlayer-expanded MoS2/graphene cathode, Adv. Energy Mater. 7 (2017) 1700317. R.R. Gaddam, D. Yang, R. Narayan, K. Raju, N. Ashok Kumar, X.S. Zhao, Biomass derived carbon nanoparticle as anodes for high performance sodium and lithium ion batteries, Nano Energy 26 (2016) 346–352. Y. Cui, M.T. Bjork, J.A. Liddle, C. Sonnichsen, B. Boussert, A.A. Alivisatos, Integration of colloidal nanocrystals into lithographically patterned devices, Nano Lett. 4 (2004) 1093–1098. J. Henzie, V. Etacheri, M. Jahan, H. Rong, C.N. Hong, V.G. Pol, Biomineralizationinspired crystallization of monodisperse α-Mn2O3 octahedra and assembly of highcapacity lithium-ion battery anodes, J. Mater. Chem. A 5 (2017) 6079–6089. K. Liu, C. Yuan, Q. Zou, Z. Xie, X. Yan, Self-assembled zinc/cystine-based chloroplast mimics capable of photoenzymatic reactions for sustainable fuel synthesis, Angew. Chem. Int. Ed. 56 (2017) 7876–7880. U. Lüders, M. Bibes, J.F. Bobo, J. Fontcuberta, Tuning the growth orientation of NiFe2O4 films by appropriate underlayer selection, Appl. Phys. A 80 (2005) 427–431. J. Ku, D.M. Aruguete, A.P. Alivisatos, P.L. Geissler, Self-assembly of magnetic nanoparticles in evaporating solution, J. Am. Chem. Soc. 133 (2011) 838–848. J. Tan, W. Zhang, A. Xia, Facile synthesis of inverse spinel NiFe2O4 nanocrystals and their superparamagnetic properties, Mater. Res. 16 (2013) 237–241. O.V. Yelenich, S.O. Solopan, T.V. Kolodiazhnyi, V.V. Dzyublyuk, A.I. Tovstolytkin, A.G. Belous, Superparamagnetic behavior and AC-losses in NiFe2O4 nanoparticles, Solid State Sci. 20 (2013) 115–119. X. Li, G. Tan, W. Chen, B. Zhou, D. Xue, Y. Peng, F. Li, N. Mellors, Nanostructural and magnetic studies of virtually monodispersed NiFe2O4 nanocrystals synthesized by a liquid-solid-solution assisted hydrothermal route, J. Nanopart. Res. 14 (2012) 1–9. X. Hu, J. Yu, J. Gong, Q. Li, G. Li, α-Fe2O3 nanorings prepared by a microwaveassisted hydrothermal process and their sensing properties, Adv. Mater. 19 (2007) 2324–2329. Q. Wang, S. Liu, L. Fu, Z. Cao, W. Ye, H. Li, P. Guo, X.S. Zhao, Electrospun γ-Fe2O3 nanofibers as bioelectrochemical sensors for simultaneous determination of small biomolecules, Anal. Chim. Acta 1026 (2018) 125–132. P. Guo, Z. Wei, B. Wang, Y. Ding, H. Li, G. Zhang, X.S. Zhao, Controlled synthesis, magnetic and sensing properties of hematite nanorods and Microcapsules, Colloids Surf. A: Physicochem. Eng. Asp. 380 (2011) 234–240. L. Long, X. Liu, L. Chen, D. Li, J. Jia, A hollow CuOx/NiOy nanocomposite for amperometric and non-enzymatic sensing of glucose and hydrogen peroxide, Microchim. Acta 186 (2019) 74. H. Bayrakdar, O. Yalcin, U. Cengiz, S. Ozum, E. Anigi, O. Topel, Comparison effects and electron spin resonance studies of α-Fe2O4 spinel type ferrite nanoparticles, Acta Part A 132 (2014) 160–164. L. Xu, L. Ma, Y. Ling, X. Zhou, X. Xuyao, MoSe2/phosphorus-doped graphene nanocomposite: synthesis and its electrochemical sodium-storage and catalytic performance, Colloids Surf. A 551 (2018) 87–94. Y.V.M. Reddy, B. Sravani, S. Agarwal, V.K. Gupta, G. Madhavi, Electrochemical sensor for detection of uric acid in the presence of ascorbic acid and dopamine using the poly(DPA)/SiO2@Fe3O4 modified carbon paste Electrode, J. Electroanal. Chem. 820 (2018) 168–175. Y. Yin, N. Ma, J. Xue, G. Wang, S. Liu, H. Li, P. Guo, Insights into the role of polyvinylpyrrolidone on the synthesis of palladium nanoparticles and their electrocatalytic properties, Langmuir 35 (2019) 787–795.