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Occlusion of magnetic nanoparticles within calcium carbonate single crystals under external magnetic field

  • Lifu Zhang , Ruoyu Huang , Peng Tao , Chengyi Song , Jianbo Wu , Tao Deng EMAIL logo and Wen Shang EMAIL logo
Published/Copyright: June 13, 2017
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Pure and Applied Chemistry
From the journal Pure and Applied Chemistry Volume 89 Issue 12

Abstract

This work studied the growth of calcium carbonate single crystals on top of the monolayer of Fe3O4@SiO2 nanoparticles (NPs) with added external magnetic field. It showed that the occlusion process of the NPs into calcium carbonate single crystals varies as the force balance on the NPs shifts. Under no or weak magnetic field, the NPs are relatively mobile, the separation force from the substrate on NPs due to the growing calcium carbonate crystals is larger than the attraction force to the substrate by the magnetic field. The complete occlusion of the NPs into the single crystals is therefore observed. As the magnetic field strength increases, the balance shifts toward the attraction force. The mobility of NPs decreases and partial occlusion of the NPs into the single crystals is gradually observed. The findings in this study offer further insight into the occlusion process experienced by the NPs and also potential approach in engineering the force balance for the design and generation of composite materials that occlude foreign materials into their matrix.

Keywords: biomimetic synthesis; crystal growth; magnetic field; nanoparticles; NICE-2016

Introduction

In nature, many living organisms have the ability to produce inorganic minerals with remarkable morphologies and properties through the process of bio-mineralization. With the incorporation of guest materials such as bio-micromolecules [1], [2], cellular tissue networks [3], and organic molecules into the inorganic matrix [4], [5], [6], [7], the biominerals generated often show enhanced mechanical and optical properties. Examples include sea urchin skeletons, mollusk shells, teeth, and bones, etc. More strikingly, while many biologic inorganic/organic composite materials are often in the form of amorphous or polycrystalline aggregates, some biominerals can retain single crystal morphology even with the inclusion of foreign components [2], [5], [8], [9].

Inspired by the biologically controlled mineral growth and the unique properties of the biominerals, significant efforts have been focused on the synthesis of artificial materials with controlled architectures and superior functionalities similar to or even outperforming those biominerals produced in nature [5], [9], [10], [11]. As one of the most abundant biominerals, calcium carbonate has been studied extensively due to its unique morphologies [12], [13], hierarchical organization [14], [15], and importance in biological systems [16]. The occlusion of different guest materials, such as polymers, gels, metal oxide, and nanoparticles, into the single crystals of calcium carbonate has been successfully demonstrated using various approaches. For example, Kim et al. included metal oxide within the host of calcite single crystal with the aid of gel [17]. Using ordered latex particle structure as the template, Lu et al. prepared porous calcium carbonate crystals [18]. Hetherington et al. studied the growth of calcite around a layer of silica spheres and found that silica spheres can be incorporated into the growing crystal [19]. With the ability of incorporating foreign components into the single crystal structure of calcium carbonate, new properties such as coloring and paramagnetism, etc. were also achieved for the synthetic calcium carbonate [20], [21].

Besides the synthesis of calcium carbonate composite crystals with desired morphologies and properties, many efforts also focused on the fundamental understanding on the mechanism of incorporating the guest materials into the crystalline phase of the calcium carbonate [22], [23], [24], [25], [26], [27]. Depending on different situations, the incorporation mechanisms are also different. When the incorporated foreign materials are particles, the occlusion of the particles into the crystals is favorable if the mutual wetting interaction between the particle surface and the growth front of the crystal is favorable. Fast crystal growth rate can also promote the incorporation of the particles into the calcium carbonate crystals [28], [29]. On the other hand, the incorporation of polymer networks into the calcium carbonate single crystals follows different mechanisms from the incorporation of particles. Li et al. studied the occlusion of 3D agarose hydrogel into the single crystals of calcium carbonate and found that besides the gel concentration and the rate of the crystal growth, the strength of hydrogel was also an important factor for either complete incorporation of gel network into the crystal lattice or total exclusion of the gel material from the crystal structure [30]. Using annular dark-field scanning TEM, they were able to visualize the 3D structure of hydrogel networks inside the single crystals. They concluded that the incorporation of the uncharged agarose hydrogel networks into the calcium carbonate single crystal structure was a simple physical entrapment process rather than a chemical process, due to the lack of specific crystal face of calcium carbonate that was associated with chemical process [7]. Recently De Yoreo et al. used in-situ liquid-phase transmission electron microscopy (TEM) technique to study the nucleation of calcium carbonate in the matrix of polystyrene sulphonate and revealed that such process is driven by specific ion-binding and is independent of any other factors that contributed to the free-energy barriers [23]. Using atomic force microscopy (AFM), they further discovered a different mechanism for the nanoscale occlusion of micelles and demonstrated that the specific binding of micelle particles to steps enabled the entrapment of the micelles into the crystal phase [22].

Although the studies on the occlusion of the guest materials into the host calcium carbonate have been increasingly reported, there is still lack of clear understanding on such process, as well as the factors that might affect the outcome of the occlusion. In this work, we intended to investigate the effect of particle mobility on the occlusion of NPs into the host calcium carbonate crystals. Specifically, a monolayer of magnetic Fe3O4@SiO2 core/shell nanoparticles (NPs) on glass surface was used as the guest materials, and the occlusion process of these particles into the calcium carbonate single crystals with an added external magnetic field was investigated. Depending on the strength of the external magnetic field, the mobility of NPs changed and different occlusion results were observed. Without the magnetic field or when the applied magnetic field was weak, the interaction between the growing crystals and the particles was strong enough to “lift” the particles from the substrate and enabled the full inclusion of the particles inside the calcium carbonate crystals. With the increase of the magnetic field strength, and thus the magnetic force on the particles, the particles mobility on surface decreased, and it became difficult to “lift” the particles from the substrate surfaces, which eventually resulted in the uncompleted inclusion of the particles at the surface of the calcium carbonate crystal. With the observed occlusion behaviors, this work not only provides additional insights into the encapsulation of foreign objects into the single crystals of biological systems but also helps to design new composite materials with desired functionalities. Extension of this approach beyond calcium carbonate will also lead to novel approaches for the construction of synthetic materials with unique new properties.

Results and discussion

Scheme 1 presents the experimental design for this work. A glass slide covered with monolayer of Fe3O4@SiO2 NPs was placed upside down at the air-water interface of the supersaturated solution of calcium carbonate. During the growth of the calcium carbonate crystals, an external magnetic field was applied on the glass slide. The magnetic field strength varied from 0 to 21.0 T/m for different groups of samples. The effect of the magnetic force on the occlusion of magnetic NPs into the calcium carbonate crystals was investigated in this study.

Scheme 1: Schematic of crystallization of calcium carbonate on top of the magnetic NP surface under external magnetic field. The magnetic blocks were placed above the cover glass substrate, which floated at the top surface of the supersaturated solution of calcium carbonate.
Scheme 1:

Schematic of crystallization of calcium carbonate on top of the magnetic NP surface under external magnetic field. The magnetic blocks were placed above the cover glass substrate, which floated at the top surface of the supersaturated solution of calcium carbonate.

Occlusion of Fe3O4@SiO2 NPs into calcium carbonate crystals without external magnetic field

We chose silica coated magnetic particles (Fe3O4@SiO2 NPs) as the guest material in this study due to the easy embedment of silica particles into the calcium carbonate crystal without surface modification [19]. Figure 1 shows the TEM and SEM characterization of the Fe3O4@SiO2 NPs. The particles have a core-shell structure with Fe3O4 as the core material and a thin layer of SiO2 as the shell material (Fig. 1a, b). The average diameter of the NPs is ~630 nm based on the dynamic light scattering (DLS) study (Fig. S1).

Fig. 1: Crystallization of calcium carbonate on top of the NP monolayer surface with no external magnetic force. (a) TEM image of the Fe3O4@SiO2 NPs and (b) SEM image of the Fe3O4@SiO2 NPs: the average size of the particles is ~630 nm; (c) The top surface of calcium carbonate crystals after growth for 24 h; (d) Calcium carbonate crystals after 12 h growth, observation from the bottom side; (e) Calcium carbonate crystals after 18 h growth, observation from the bottom side; (f) Calcium carbonate crystals after 24 h growth, observation from the bottom side, showing that the NPs were fully embedded.
Fig. 1:

Crystallization of calcium carbonate on top of the NP monolayer surface with no external magnetic force. (a) TEM image of the Fe3O4@SiO2 NPs and (b) SEM image of the Fe3O4@SiO2 NPs: the average size of the particles is ~630 nm; (c) The top surface of calcium carbonate crystals after growth for 24 h; (d) Calcium carbonate crystals after 12 h growth, observation from the bottom side; (e) Calcium carbonate crystals after 18 h growth, observation from the bottom side; (f) Calcium carbonate crystals after 24 h growth, observation from the bottom side, showing that the NPs were fully embedded.

Figures 1c–f show the growth of calcium carbonate crystals on glass substrate that covered with monolayer of Fe3O4@SiO2 NPs after different growth time, without the external magnetic field. The monolayer of Fe3O4@SiO2 NPs on glass was formed using evaporation-assisted self-assembly approach [31], [32]. Most crystals grew on NP monolayer surface were single calcite crystals with typical rhombohedra morphology and an average size of ca. 10 μm. The top surfaces of the crystals not in contact with the NPs were smooth in general with almost no defects (Fig. 1c), while the bottom sides of the calcite crystals were relatively rough, due to the existence of the NPs (Fig. 1d–1f). After 12 h, only a small portion of the Fe3O4@SiO2 monolayer was embedded into the calcium carbonate single crystal (Fig. 1d). With the elongation of growth time, the NPs were gradually incorporated into the calcium carbonate crystals and eventually were fully embedded inside the crystals after 24 h. According to previous studies on the occlusion of NPs attached to a surface into the single crystal of calcium carbonate [19], the calcium carbonate crystal initially grew with a planar face in contact with the particle surface. The growth of crystals then continued across the NP layer and eventually encapsulated the particles into the crystal lattice of the calcium carbonate. Our observation is consistent with such growth model. With the full encapsulation of NPs into the crystals after 24 h, the bottom surfaces of the calcium carbonate that were in contacted with the NPs became flat with only few cavities left on the surface. These cavities could be due to the limitation of ion diffusion at the bottom of the crystals during the crystal growth.

Occlusion of Fe3O4@SiO2 NPs into calcium carbonate crystals with added external magnetic field

With the addition of the external magnetic field onto the Fe3O4@SiO2 NPs, after the same duration time of crystal growth, however, the degree of NP embedding into the calcium carbonate single crystals shows magnetic strength dependence (Fig. 2). When a relative weak external magnetic field was applied on the NPs, the interaction between NPs and the glass surface was also relative weak. The growth of the calcite crystal and the inclusion of NPs into the calcite crystal are similar to the situation without the magnetic field. Most of the NPs could be fully embedded into the crystals after 24 h (Fig. 2a–c). There were a few cavities on the bottom surfaces of the crystals that showed NPs were included inside. With the increasing of external magnetic strength to 153.5 mT, most of the NPs could still be fully embedded but with more defects appeared on the crystal surface (Fig. 2d). With the magnetic strength increased to 176.0 mT and then 197.7 mT, NPs started to show partial encapsulation into the crystals (Fig. 2e, 2f) with many defects formed on the bottom surfaces of the calcite crystals. The magnetic induction intensity distribution of magnets was measured with a magnetometer. (MZ-520A, Beijing Boland Magnetoelectricity Technology Co., LTD). The corresponding magnetic field gradients were calculated and the results are shown in Fig. 3a. Based on the obtained gradient of magnetic field, the approximate magnetic force Fm that was applied onto each NP can be obtained using the following equation [33]:

Fig. 2: Occlusion of magnetic Fe3O4@SiO2 NPs into the calcite crystals under external magnetic field with different magnetic strength. (a) Group 1, 70.1 mT; (b) Group 2, 89.3 mT; (c) Group 3, 117.5 mT; (d) Group 4, 153.5 mT; (e) Group 5, 176.0 mT; (f) Group 6, 197.7 mT; all observations in (a)–(f) were imaged from the bottom side of the crystals after 24 h growth.
Fig. 2:

Occlusion of magnetic Fe3O4@SiO2 NPs into the calcite crystals under external magnetic field with different magnetic strength. (a) Group 1, 70.1 mT; (b) Group 2, 89.3 mT; (c) Group 3, 117.5 mT; (d) Group 4, 153.5 mT; (e) Group 5, 176.0 mT; (f) Group 6, 197.7 mT; all observations in (a)–(f) were imaged from the bottom side of the crystals after 24 h growth.

Fig. 3: External-magnetic-field dependent embedment of magnetic NPs into calcite single crystals. (a) Measured magnetic induction intensity and the corresponding magnetic field gradient; (b) Applied external-magnetic-force on different groups of samples and the corresponding outcomes of embedment.
Fig. 3:

External-magnetic-field dependent embedment of magnetic NPs into calcite single crystals. (a) Measured magnetic induction intensity and the corresponding magnetic field gradient; (b) Applied external-magnetic-force on different groups of samples and the corresponding outcomes of embedment.

(1) F m = ∇ ( μ ⋅ B)

where μ is the saturation magnetic moment of each Fe3O4@SiO2 NP and B is the relevant magnetic induction intensity. The value of μ can be obtained using equation 2:

(2) μ ≈ 50 emu/g ∗ m

here m is the mass of each Fe3O4@SiO2 NP with a value of ca. 4.6×10−13 g based on the average size of NP and the core-shell components of the NPs. μ is therefore calculated to be 2.3×10−11 emu. The approximate magnetic force Fm that was applied onto each NP for different groups of NPs was then obtained and shown in Fig. 3b. The statistic results on the external-magnetic-field dependent occlusion of magnetic NPs into the calcite single crystals are also summarized in Fig. 3b. Under the condition used in this study, we found that weak magnetic force had little impact on the occlusion process and the particles could be fully included into the single crystals of calcite under the weak external magnetic field. When the external magnetic field became stronger and magnetic force on the NPs is increased to the order of larger than 3.4×10−13 N, partial embedding of the NPs into the crystal lattice was observed.

Analysis

The influence of magnetic field on the crystal growth of calcium carbonate has been known for a long time and the anti-scale magnetic treatment of hard water has been employed in many industrial applications that involve boilers, heat exchangers, and pipelines. The mechanisms, however, are not fully understood, and controversial results had been reported in the literatures [34], [35], [36]. Tai et al. observed the lower growth rate of calcite in the presence of magnetic field under low pH and supersaturation conditions while the growth rate seemed to increase at high pH condition [34]. Saksono et al. conducted the magnetic treatment during the calcium carbonate precipitation process and found the number of calcite crystals increased but with decreased crystal size [35]. Earlier, the study by Evangelos Dalas et al. [36] showed that the growth rate of calcite decreased only under a relatively strong magnetic field (>5 T).

In the study reported in this work, although the external magnetic force may have some effect on the growth of calcium carbonate crystals, such effect should be small due to the relative weak magnetic field (<0.2 T) used in the experiments. The impact of magnetic field on the occlusion process of magnetic NPs into the calcite crystal phase, however, is more pronounced. Under the condition with relative strong magnetic field, elongation of crystal growth time only resulted in the crystals with larger sizes, with the NPs were still partially embedded (Fig. 4). Such phenomenon further indicates that the partial embedment of the magnetic NPs was not due to the slow growth of the calcite, and rather it was due to the low mobility of the NPs on the surface with stronger external magnetic force.

Fig. 4: Partial embedment of magnetic NPs into calcite single crystals under strong external magnetic field (197.7 mT, 21.0 T/m), elongation of growth time yielded similar result, with only the size of crystal increased. (a) Calcite crystal with 24 h growth; (b) Calcite crystal with 48 h growth; (c) Calcite crystal with 72 h growth.
Fig. 4:

Partial embedment of magnetic NPs into calcite single crystals under strong external magnetic field (197.7 mT, 21.0 T/m), elongation of growth time yielded similar result, with only the size of crystal increased. (a) Calcite crystal with 24 h growth; (b) Calcite crystal with 48 h growth; (c) Calcite crystal with 72 h growth.

We propose the following occlusion mechanism for the incorporation of magnetic NPs into the calcite single crystals in the presence of external magnetic field, as shown in Scheme 2. Initially the nucleation and growth of the calcite single crystals for all the samples should be similar, since the growth condition, such as temperature, concentrations of the ions, surface chemistry, are all the same for different samples. Meanwhile the surfaces of the silica coated magnetic particles are usually negatively charged, which should promote the adsorption of the calcium ions and subsequent calcium carbonate nucleation on the particle surface [23]. If the NPs are in the free form in solution, with the growth of the crystals, the NPs may be excluded away from the crystals if the crystal growth rate is slow, due to the crystallization pressure [37], or may be included into the crystals if the crystal growth rate is fast. For the crystal growth condition used in this study, the particles were attached to the glass surface and the occlusion of the NPs into the crystal phase of the calcite should occur as previously reported in the literature [19]. After the nucleation on the particle surface, the crystal can continue to grow toward both the glass surface or toward the opposite direction. Due to the diffusion limitation, the crystals growth is slower in the direction toward the glass and faster in the opposite direction. Therefore initially the calcite crystals form without occlusion of the NPs, and with a planar face in contact with the particle monolayer [19]. As the crystals continue to grow in the direction toward the glass substrate, they can gradually extend over the surface of the particles and form steps due to the breakage of the crystal lattice. When there is no or relative weak magnetic field, the mobility of the particles is relatively high, and particles can be lifted off from the surface and included into the calcite crystal under the crystal lattice strain. The steps could eventually close together and result in the fully embedding of the NPs. When a strong magnetic field is applied, the magnetic particles experience strong magnetic forces and are fixed tightly on the glass substrate. The particles could not move around even under the crystal strain, and thus are partially embedded into the single crystals of the calcium carbonate.

Scheme 2: Encapsulation of Fe3O4@SiO2 NPs into the single crystals of calcium carbonate under the external magnetic field. Each NP experienced the attraction force (Fs, Fm, and Fb) towards the glass substrates and the separation force (Fg and Fc) from the glass substrates. Depending on the external magnetic force, the balance between attraction force and separation force shifts. Weak magnetic force would result in the full embedment of magnetic NPs into the single crystal of calcium carbonate, while strong magnetic force results in the partial embedment of magnetic NPs. Here Fs is the surface force between the NPs and the glass substrate, Fm is the magnetic force, Fb is the buoyancy force, Fg is the gravity force, and Fc represents the interfacial interaction between the NPs and the calcite crystal.
Scheme 2:

Encapsulation of Fe3O4@SiO2 NPs into the single crystals of calcium carbonate under the external magnetic field. Each NP experienced the attraction force (Fs, Fm, and Fb) towards the glass substrates and the separation force (Fg and Fc) from the glass substrates. Depending on the external magnetic force, the balance between attraction force and separation force shifts. Weak magnetic force would result in the full embedment of magnetic NPs into the single crystal of calcium carbonate, while strong magnetic force results in the partial embedment of magnetic NPs. Here Fs is the surface force between the NPs and the glass substrate, Fm is the magnetic force, Fb is the buoyancy force, Fg is the gravity force, and Fc represents the interfacial interaction between the NPs and the calcite crystal.

To gain further understanding of the effect from magnetic field on the occlusion process of NP into crystal lattice of calcium carbonate, especially to probe crystallization pressure and interfacial crystal lattice strain effect on such process, we constructed a simplified physical model to analyse forces that were placed on individual NP. As indicated in Scheme 2, the forces experienced by each NP include gravity (Fg), buoyancy (Fb), surface force (Fs) that represents the interaction between the magnetic particles and the surface of the substrates, and also the magnetic force (Fm) that is induced by the applied magnetic field. The surface force Fs mostly is van der Waals force in nature, but could also include some contributions from electrostatic and dipole interactions [38]. During the occlusion process, as the calcite crystals grow, the NPs should also experience an interfacial force between the NPs and the calcite crystal, which is represented as Fc. Fc is related to crystallization pressure and the crystal lattice strain during the encapsulation process of the particles. Here Fs, Fb, and Fm are the forces that help fix the NPs on the glass substrate, while Fg and Fc are the forces that help separate NPs from the substrate. For the situation studied in this work, Fb (~12.8×10−16 N) and Fg (~4.1×10−15 N) are relatively small and can be neglected. Fc thus is in competition with Fs and Fm. When there is no magnetic force Fm, Fc is larger than Fs, and the particles would be separated from the substrate and fully incorporated into the calcite crystals. When a small external magnetic field (Hc) is applied, the particles would still be separated from the surface and fully incorporation of the particles since Fm is small. As Hc increases more, Fm also becomes larger. At a critical magnetic field (Hc), the attraction force (Fs and Fm) to the substrate on the NPs overcomes the interfacial force Fc and NPs stay attached on the glass substrate throughout the crystal growth process, which leads to the incomplete incorporation of the particles into the calcite crystals.

Since the magnetic force experienced by the NPs is directly related to the size of NPs, the diameter of the magnetic NPs (Dm) is thus crucial for the outcome of the occlusion process. We further calculated the magnetic forces on NPs of different sizes under different magnetic field and the results are shown in Fig. S2. With the same particle size, the magnetic forces increase with the increase of the magnetic field. As the particle size increases, the magnetic forces increase under the same magnetic field. Fig. S2 also shows the boundary forces needed to prevent the particles from being lifted from the substrate so they can stay on the substrate and be partially embedded in the crystal. As shown in Fig. S2, the boundary forces also increase with the particle sizes. In general, the magnetic forces are proportional to the volume (∝Dm3) of magnetic NPs while the boundary forces are proportional to the contact areas (∝Dm2) between the crystal and the magnetic NPs. For small particles, the magnetic forces are relative small and a large magnetic field is needed to overcome the boundary force. For example, for particles with diameter of 350 nm, a magnetic field much larger than the maximum magnetic field (21.0 T/m) used in this work is needed to enable the partial embedment. For large particles, the increase of the magnetic forces is much faster than the increase of the boundary forces, so a relatively small magnetic field is needed to overcome the boundary force. For example, for particles with diameter of 850 nm, the boundary force is ~6×10−13 N, and a relatively small magnetic field (12 T/m) can enable the partial embedment.

Conclusions

In summary, we have demonstrated that the external magnetic field affected the occlusion of magnetic NPs, which were attached to a solid surface, into the calcium carbonate crystal lattice. Full encapsulation of magnetic NPs into the crystals can be achieved when the applied magnetic field is small while larger magnetic field would result in the partial inclusion of the NPs. The magnetic force required to prevent the complete encapsulation of single NP is quite strong (in the order of ~10−13 N), which indicates that the interfacial force (Fc) between the NP and the calcite crystal is also relatively strong. Such interfacial effect should be critical for the occlusion process of the foreign materials into the single crystals. This study offers helpful insight in the occlusion process and also possible approach in understanding and engineering the interfacial effect for the design and generation of desired composite materials with the occlusion of different foreign materials.

Experimental

Monolayer coating of Fe3O4@SiO2 NPs on glass surface

The Fe3O4@SiO2 core-shell NPs with average size of ~630 nm were purchased commercially (SUZHOU NANOMICRO TECHNOLOGY CO., LTD., China). The particles are superparamagnetic with a saturation magnetization of 40~60 emu/g. The particles are dispersed in water with a concentration of 1.0 wt%. To prepare monolayer particle coating on cover glass, first the solvent of NPs was exchanged to ethanol through repeated centrifugation/redispersion process. The final concentration of particles in ethanol is ~0.4 wt%. Particle monolayer was formed using an evaporation assisted self-assembly technique. Briefly, a cover glass was first cleaned using ethanol and water. After drying, the glass surface was treated with plasma for 3 min using a plasma cleaner (Harrick, US). The glass was then placed inside a petri-dish with a small tilting angle of ~15 degree. Several drops of the ethanol solution containing Fe3O4@SiO2 NPs were slowly deposited onto the glass surface using a pipette. Monolayer coverage of particles was generated on the cover glass after all the solvent evaporated.

The growth of calcium carbonate single crystals

To grow calcium carbonate single crystals on NP coated cover glass, first 2 mM supersaturated aqueous solution of calcium carbonate was prepared by mixing 4 mM aqueous solution of calcium chloride and 4 mM aqueous solution of sodium carbonate (purchased from Sinopharm Chemical Reagent Co., Ltd). Then a glass slide with the NP monolayer was placed at the liquid-air interface of the supersaturated solution of calcium carbonate in a petri-dish with the particle monolayer facing downward and immersed in the solution. The crystallization process was conducted in the ambient environment and lasted for 24 h. The glass substrates were then removed from the solution, washed with ultrapure water, and dried in air. During the crystallization process, an external magnetic force with different strength was applied onto the NPs by placing permanent magnetic blocks on top of the petri-dish. The N35 magnetic blocks (NdFeB-based) with size of 30*20*2 mm were purchased commercially from Gen Chang Magnetics (Shanghai, China).

Structural characterization of magnetic NPs and measurement of magnetic force for different NP samples

The calcium carbonate crystals that grew on the cover glass with NP monolayer were characterized using electron scanning microscope (SEM). To prepare calcite SEM samples, a conductive tape was pressed slightly against the upper surface of the samples, and the crystals were pulled off from the cover glass to expose the undersides that were in contact with the Fe3O4@SiO2 NP monolayer. Samples were then sputter-coated with a thin layer of Au and imaged with a Sirion 200 scanning electron microscope (SEM) operating at 5 kV or a JEOL 6330 field emission SEM operating at 5 kV. TEM characterization of NP samples was conducted using a JEOL JEM-2100F microscope with an accelerating voltage of 200 kV.

The magnetic induction intensity distribution of magnets was measured with a magnetometer (MZ-520A, Beijing Boland Magnetoelectricity technology Co., LTD). For each sample the measurement was done close to the centre at three different positions with perpendicular distances to the magnet block surface of 0.8 mm, 1.25 mm, and 1.7 mm, respectively. The measurement at each position was repeated for 10 times to reduce the error.

Article note

A collection of invited papers based on presentations at the 3rd International Conference on Bioinspired and Biobased Chemistry and Materials: Nature Inspires Creativity Engineers (NICE-2016), Nice, France, 16–19 October 2016.

Corresponding authors: Professor Tao Deng and Professor Wen Shang, State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, P.R. China; and School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, P.R. China

Acknowledgments

This work was supported by the National Key R&D Program of China (Grant no: 2016YFB0402100), National Natural Science Foundation of China (Grant no: 51521004, 51420105009), and the Zhi-Yuan Endowed fund from Shanghai Jiao Tong University. We also thank Mr. Zhongyong Wang for the help with this project and the Instrumental Analysis Center of Shanghai Jiao Tong University for the access to SEM.

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Published Online: 2017-06-13
Published in Print: 2017-11-27

©2017 IUPAC & De Gruyter. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. For more information, please visit: http://creativecommons.org/licenses/by-nc-nd/4.0/

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https://doi.org/10.1515/pac-2017-0407
Keywords for this article
biomimetic synthesis; crystal growth; magnetic field; nanoparticles; NICE-2016

Articles in the same Issue

  1. Frontmatter
  2. In this issue
  3. Editorial
  4. Open Access: Why IUPAC is a Supporter
  5. Preface
  6. Selected Papers from the 3rd International Conference on Bioinspired and Biobased Chemistry & Materials (NICE-2016)
  7. Conference papers
  8. Occlusion of magnetic nanoparticles within calcium carbonate single crystals under external magnetic field
  9. Superhydrophobic and superoleophobic poly(3,4-ethylenedioxypyrrole) polymers synthesized using the Staudinger-Vilarrasa reaction
  10. From vine to wine: photophysics of a pyranoflavylium analog of red wine pyranoanthocyanins
  11. Spider silk foam coating of fabric
  12. Bioinspired approach toward molecular electrets: synthetic proteome for materials
  13. Electrospun fibers in regenerative tissue engineering and drug delivery
  14. Co-assembly of helical β3-peptides: a self-assembled analogue of a statistical copolymer
  15. Water splitting catalyzed by titanium dioxide decorated with plasmonic nanoparticles
  16. Preparation and characterization of collagen/chitosan/hyaluronic acid thin films for application in hair care cosmetics
  17. Potential of polyhydroxyalkanoate (PHA) polymers family as substitutes of petroleum based polymers for packaging applications and solutions brought by their composites to form barrier materials
  18. IUPAC Technical Report
  19. Calibration, standardization, and quantitative analysis of multidimensional fluorescence (MDF) measurements on complex mixtures (IUPAC Technical Report)
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