JP7489701B2 - Fullerene nanocube, its manufacturing method and quartz crystal resonator gas sensor using the same - Google Patents

Description

Article 30, Paragraph 2 of the Patent Act applies (1) Published on December 3, 2019, Royal Society of Chemistry, Materials Horizons, 2020, vol. 7,787-795 DOI:10.1039/c9mh01866b (2)Published on March 2, 2020 The 13th MANA International Symposium 2020 jointly with ICYS Proceedings P. 9

The present invention relates to fullerene nanocubes, their manufacturing method, and quartz crystal resonator gas sensors using them.

In recent years, fullerene nanocubes have been reported by the liquid-liquid interface precipitation method (LLIP method) (see, for example, Non-Patent Document 1). According to Non-Patent Document 1, fullerene nanocubes made of _C70 are reported to be produced at the interface between mesitylene and isopropanol. It is expected that such fullerene nanocubes will be further improved and used for new applications.

Chibeom Park et al., Angew. Chem. Int. Ed., 2010, 49, 9670-9675

Based on the above, the objective of the present invention is to provide a functional fullerene nanocube, a manufacturing method thereof, and a quartz crystal resonator gas sensor using the same.

The fullerene nanocube of the present invention is composed mainly of fullerene, is porous, and contains nitrogen atoms, thereby solving the above-mentioned problems.
The fullerene may be at least one selected from the group consisting of _C60 fullerene, _C70 fullerene, _C76 fullerene, _C78 fullerene, _C82 fullerene, _C84 fullerene, _C90 fullerene, _C94 fullerene, and derivatives thereof.
The fullerene may be a _C70 fullerene and/or a derivative thereof.
It may have a simple cubic lattice structure (sc) and a hexagonal close packed structure (hcp).
It may be hydrophilic.
It may be a square prism with one side having a length in the range of 1 μm to 4 μm.
The FTIR spectrum measured by a Fourier transform infrared spectrophotometer may have a peak due to N--H stretching vibration in the range of 3000 cm ^-1 to 3450 cm ^-1 .
The compound may have a nitrogen N1s peak in a binding energy range of 398.5 eV or more and 400.5 eV or less in an XPS spectrum measured by X-ray photoelectron spectroscopy.
The nitrogen atoms may be contained in an amount ranging from 3 atomic % to 10 atomic %.
The nitrogen atom may be oxidized.
The surface of the fullerene nanocube may be aminated.
The method for producing fullerene nanocubes according to the present invention comprises mixing a fullerene dispersion in which fullerenes are dispersed in mesitylene with a lower alcohol having 5 or less carbon atoms, forming fullerene nanocubes by liquid-liquid interface precipitation, adding ethylenediamine in a range of 2 wt % to 10 wt % based on the total of the mesitylene and the lower alcohol to obtain a mixed solution, and incubating the mixed solution for 5 minutes to 30 minutes, thereby solving the above-mentioned problem.
Following said incubation, the method may further comprise washing the product with said mixture of mesitylene, a lower alcohol and ethylenediamine.
The lower alcohol may be at least one selected from the group consisting of methanol, ethanol, propanol, and isopropanol.
The forming of the fullerene nanocubes may be performed while performing an ultrasonic treatment.
The obtaining of the mixture may be performed while subjecting the mixture to ultrasonic treatment.
The fullerene may be a _C70 fullerene and/or a derivative thereof.
The quartz crystal resonator gas sensor provided with the gas sensor film according to the present invention solves the above-mentioned problems by containing the above-mentioned fullerene nanocubes.
An acid gas selected from the group consisting of formic acid, acetic acid and propionic acid may be detected.

The fullerene nanocubes of the present invention contain nitrogen and therefore have hydrophilicity. This allows the fullerene nanocubes of the present invention to have excellent dispersibility in water, making them applicable to bio-related applications. The fullerene nanocubes of the present invention are porous, and are therefore expected to be applicable to bio-related applications such as encapsulation, transportation, and release of nanometer-sized or submicron-sized objects using the pores. In addition, the fullerene nanocubes of the present invention show excellent selectivity for volatile acidic gases. Therefore, the fullerene nanocubes of the present invention can be used in quartz crystal resonator gas sensors.

The method for producing fullerene nanocubes of the present invention advantageously simplifies the production process by producing fullerene nanocubes that have the above-mentioned hydrophilic properties and are highly functional without the need for additional hydrophilic treatment.

Schematic diagram showing fullerene nanocubes of the present invention. Schematic diagram showing exemplary fullerenes constituting the fullerene nanocubes of the present invention. A flow chart showing the steps for producing fullerene nanocubes of the present invention. Front view of a quartz crystal gas sensor using fullerene nanocubes of the present invention. Side view of a quartz crystal gas sensor using fullerene nanocubes of the present invention. FIG. 3 shows an SEM image of fullerene nanocubes obtained in step S210 of FIG. Diagram showing the side length distribution of fullerene nanocubes Figure showing an STEM image of a fullerene nanocube FIG. 1 shows an SEM image of a sample of Example 1. FIG. 1 shows an STEM image of a sample of Example 1. FIG. 1 shows the side length distribution of the sample in Example 1 TEM and HRTEM images of the sample of Example 1. FIG. 1 shows an XRD pattern of a sample of Example 1. FIG. 1 shows the Raman spectrum of the sample of Example 1. FIG. 1 shows the FTIR spectrum of the sample in Example 1 on the high frequency side. FIG. 1 shows the FTIR spectrum of the sample in Example 1 on the low frequency side. FIG. 1 shows the UV-vis spectrum of the sample of Example 1. FIG. 1 shows the XPS spectrum of the sample of Example 1. FIG. 1 shows an XPS spectrum of the N1s core level of the sample of Example 1. FIG. 1 shows the QCM frequency shift for various volatile organic compounds using the QCM sensor of Example 1.

The following describes an embodiment of the present invention with reference to the drawings. Note that similar elements are given similar reference numerals and their description will be omitted.

(Embodiment 1)
In the first embodiment, the fullerene nanocube and the method for producing the same of the present invention will be described in detail.
FIG. 1A is a schematic diagram showing a fullerene nanocube of the present invention.
FIG. 1B is a schematic diagram showing exemplary fullerenes that make up the fullerene nanocubes of the present invention.

As shown in FIG. 1A, the fullerene nanocube 100 of the present invention has a columnar structure and is porous with mesopores 110. The columnar structure may be a cube.

The fullerene nanocube 100 of the present invention is mainly composed of fullerene. In the present specification, the fullerene is not particularly limited as long as it is a spherical molecule containing carbon atoms with and/or without a substituent, but is illustratively selected from the group consisting of _C60 fullerene, _C70 fullerene, _C76 fullerene, _C78 fullerene, _C82 fullerene, _C84 fullerene, _C90 fullerene, _C94 fullerene, and derivatives thereof. Note that the fullerene derivative means a compound in which at least a part of the fullerene is modified.

Among them, the fullerene is more preferably _C70 fullerene and/or its derivatives. This allows nanocubes to be produced with good yield by the method described below. When the fullerene is _C70 , the fullerene nanocubes of the present invention preferably have a simple cubic lattice structure (sc) and a hexagonal close-packed structure (hcp).

In this specification, the term "mainly composed of fullerene" means that there are no clear diffraction peaks other than those of fullerene in the X-ray diffraction pattern, but for example, the fullerene nanocube contains 90% by mass or more, preferably 95% by mass or more of fullerene.

In the fullerene nanocube 100 of the present invention, the fullerene contains a nitrogen atom. The nitrogen atom may be substituted for a carbon atom constituting the fullerene, or may be contained in a substituent that modifies the fullerene. The nitrogen atom gives the fullerene nanocube 100 hydrophilicity.

The nitrogen atoms are preferably contained in a range of 3 atomic % or more and 10 atomic % or less. This results in high hydrophilicity. The nitrogen atoms are more preferably contained in a range of 4 atomic % or more and 6 atomic % or less. This results in even higher hydrophilicity. The nitrogen atom content is measured by X-ray photoelectron spectroscopy (XPS).

The fullerene nanocube 100 of the present invention preferably has a peak due to N-H stretching vibration in the range of 3000 cm ^-1 to 3450 cm ^-1 in the FTIR spectrum measured by a Fourier transform infrared spectrophotometer. By having this peak due to N-H stretching vibration, it can exhibit hydrophilicity.

More preferably, the fullerene nanocube 100 of the present invention has a peak due to N-H stretching vibration in the range of 3300 cm ^-1 to 3350 cm ^-1 in the FTIR spectrum measured by a Fourier transform infrared spectrophotometer, which allows it to exhibit high hydrophilicity.

The fullerene nanocube 100 of the present invention preferably has a nitrogen N1s peak in the binding energy range of 398.5 eV to 400.5 eV in the XPS spectrum measured by X-ray photoelectron spectroscopy. This allows for high hydrophilicity. More preferably, the nitrogen atoms contained in the fullerene nanocube 100 of the present invention are preferably oxidized. This makes the nitrogen atoms stable. The presence of such oxidized nitrogen atoms can be determined by unfolding the N1s core level peak in the XPS spectrum.

The surface of the fullerene nanocube 100 of the present invention is preferably aminated as shown in FIG. 1B. In FIG. 1B, _C70 is shown as an example of fullerene, but the fullerene is not limited to this. In the manufacturing method described below, the surface is aminated by reaction of ethylenediamine, which is used as a raw material, with fullerene, and therefore the fullerene can exhibit high hydrophilicity. The amination of the surface can be identified by mass spectrometry.

Of course, the fullerene nanocubes 100 of the present invention may contain oxidized nitrogen, may have aminated surfaces, or may have both.

The fullerene nanocube 100 of the present invention is preferably a square prism having a side length in the range of 1 μm to 4 μm. The fullerene nanocube 100 of the present invention is more preferably a square prism having a side length in the range of 1 μm to 2 μm. The square prism may preferably be a cube. By having such a size, it shows high selectivity to acid.

Next, a method for producing fullerene nanocubes according to the present invention will be described.
FIG. 2 is a flow chart showing the steps of producing fullerene nanocubes of the present invention.

The fullerene nanocubes of the present invention are produced by the following steps S210 to S230.
Step S210: A fullerene dispersion in which fullerenes are dispersed in mesitylene is mixed with a lower alcohol having 5 or less carbon atoms, and fullerene nanocubes are formed by liquid-liquid interface precipitation.
Step S220: Ethylenediamine is added in an amount of 2 wt % to 10 wt % based on the total weight of mesitylene and the lower alcohol to obtain a mixed solution.
Step S230: The mixture is incubated for a period of time ranging from 5 minutes to 30 minutes.

Each step will be described in detail.
In step S210, the fullerene is the same as the fullerene described above, and therefore the description will be omitted. The resulting fullerene nanocubes are not porous, and are, for example, square pillars each having a side length of 1 μm to 4 μm.

In step S210, mesitylene is a good solvent for fullerenes, so fullerenes can be dispersed well.

In step S210, the lower alcohol is a poor solvent for fullerene and can form a liquid-liquid interface with mesitylene. There are no particular limitations as long as the above-mentioned number of carbon atoms is satisfied, but preferably at least one is selected from the group consisting of methanol, ethanol, propanol, and isopropanol. These can form a liquid-liquid interface with mesitylene, and fullerene nanocubes can be obtained in good yield.

In step S210, a lower alcohol is preferably added to the fullerene dispersion. This promotes the formation of a liquid-liquid interface. Furthermore, the lower alcohol is preferably added while the fullerene dispersion is ultrasonically treated. This promotes the formation of a good quality liquid-liquid interface and the formation of fullerene nanocubes.

In step S210, the lower alcohol is preferably added in an amount of 1.5 to 3 times the volume of the aromatic hydrocarbon. This forms a liquid-liquid interface, accelerating the formation of fullerene nanocubes.

In step S210, the concentration (mg/mL) of fullerene in the fullerene dispersion is preferably in the range of 0.05 mg/mL or more and 0.2 mg/mL or less. This range promotes the formation of fullerene nanocubes.

The liquid-liquid interface precipitation method in step S210 may be carried out at a temperature range of 15°C or higher and lower than 200°C. If the temperature exceeds 200°C, the reaction may not proceed. The temperature is preferably 15°C or higher and 100°C or lower, and more preferably 15°C or higher and 50°C or lower.

In step S220, the above-mentioned predetermined amount of ethylenediamine is added to cause amination between the ethylenediamine and the fullerene nanocubes.

In step S220, if the amount of ethylenediamine added is less than 2 wt%, amination may not proceed sufficiently. Even if the amount of ethylenediamine added exceeds 10 wt%, there is no change in the progress of amination, so it is advisable to set the upper limit at 10 wt%. More preferably, the amount of ethylenediamine added is in the range of 2 wt% to 6 wt% of the total of mesitylene and the lower alcohol. Within this range, amination can proceed efficiently.

The inventors of the present application discovered that by performing the incubation process in step S230, the fullerene nanocubes obtained in step S210 are etched to form porous fullerene nanocubes.

In detail, in step S230, a predetermined concentration of ethylenediamine is used and the fullerene nanocube is incubated (held) for 5 to 30 minutes, so that each face of the fullerene nanocube is etched evenly, and the square prism shape is maintained even after etching.

In step S230, the incubation may be performed with ultrasonic treatment, which will accelerate the etching.

Following incubation, the product may be washed one or more times with a mixture of mesitylene, a lower alcohol, and ethylenediamine, which can further enhance etching.

In this way, the fullerene nanocubes of the present invention are obtained, and following step S230, centrifugation may be performed, and the product may be dried and recovered after washing with a lower alcohol.

(Embodiment 2)
In the second embodiment, a quartz crystal resonator gas sensor using the fullerene nanocubes of the present invention described in the first embodiment will be described.
FIG. 3A is a front view of a quartz crystal gas sensor using fullerene nanocubes according to the present invention.
FIG. 3B is a side view of a quartz crystal gas sensor using fullerene nanocubes of the present invention.

The quartz crystal oscillator (QCM) electrode 310 of the QCM gas sensor 300 according to the present invention is provided with a gas sensor film 320 containing fullerene nanocubes as described in the first embodiment.

In detail, the QCM electrode 310 comprises a quartz substrate 330, electrodes 340a, 340b formed on the front and back principal surfaces thereof, and lead wires 350a, 350b connected to the electrodes 340a, 340b, respectively. The quartz substrate 330 is an AT-cut substrate having a substantially circular plate shape. The electrodes 340a, 340b are electrodes made of gold, platinum, chromium, nickel, or the like, formed by physical vapor deposition or the like. The lead wires 350a, 350b are connected to an AC power source or the like, and can be connected to a frequency counter or the like capable of applying a potential to the quartz substrate 330 and measuring changes in frequency. The gas sensor film 320 is provided on at least one of the electrodes 340a, 340b, but may be formed on both the electrodes 340a, 340b.

The gas sensor film 320 may be in the form of a film containing fullerene nanocubes 100. Such a film can be obtained by dispersing fullerene nanocubes 100 in water or an organic solvent and applying this to the quartz substrate 330 on which the electrodes 340a, 340b are formed. The organic solvent is illustratively ethanol, ethylene glycol, or α-terpineol. The application is performed by coating, drop casting, spraying, immersion, spin coating, screen printing, or the like. Preferably, heating is performed to remove the solvent after application. The gas sensor film 320 has a thickness in the range of 50 nm to 500 nm. This enhances the sensor sensitivity. The gas sensor film 320 may be made of fullerene nanocubes 100 alone, or may additionally contain an organic binder resin, an organic solvent, or the like.

The operation of the QCM gas sensor 300 of the present invention will be described. A potential is applied to the quartz substrate 330 via the lead wires 350a, 350b and electrodes 340a, 340b of the QCM gas sensor 300. This causes the quartz substrate 330 to vibrate at a predetermined resonance frequency by thickness-shear vibration. When an acidic gas is passed through the QCM gas sensor 300, the acid in the gas is adsorbed by the fullerene nanocubes in the gas sensor film 320. This causes an energy loss equivalent to the mass of the adsorbed acid, and the predetermined resonance frequency changes. The frequency change is measured by a frequency counter or the like via the lead wires 350a, 350b. In this way, the QCM gas sensor 300 of the present invention can be used to detect the acid in the gas by the frequency change.

In particular, the QCM gas sensor 300 of the present invention preferably detects acidic gases selected from the group consisting of formic acid, acetic acid, and propionic acid with high accuracy.

The fullerene nanocubes of the present invention have been described as being used as QCM sensors due to their high selectivity for acidic gases, but because the fullerene nanocubes of the present invention are hydrophilic, they can also be used in bio-related applications, such as encapsulating nano- or submicron-sized objects and transporting or releasing them.

Next, the present invention will be described in detail using specific examples, but please note that the present invention is not limited to these examples.

[Example 1]
In Example 1, an attempt was made to produce fullerene nanocubes according to the method shown in FIG.

Fullerene _C70 powder (purity 99.5%, manufactured by MTR Ltd.) was dispersed in mesitylene (purity 99.8%, manufactured by Nacalai Tesque, Inc.) and ultrasonicated for 1 hour to prepare a fullerene dispersion. The fullerene concentration in the fullerene dispersion was 0.1 mg/mL. Fullerene nanocubes were formed by liquid-liquid interface precipitation using the fullerene dispersion (step S210 in FIG. 2).

In detail, the fullerene dispersion (1 mL) was placed in a 13.5 mL cleaned glass bottle, which was placed in an ultrasonic bath and sonicated. Isopropanol (2 mL, 99.7% purity, Nacalai Tesque, Inc.) was then added quickly (approximately 2 seconds) to the fullerene dispersion. Sonication was performed for 1 minute, and the glass bottle was removed from the ultrasonic bath and kept at 25°C for 5 minutes.

Some samples were centrifuged, the product was washed with isopropanol, and dried at 80°C for 24 hours. The formation of fullerene nanocubes (hereafter sometimes referred to as FC) was confirmed using a field emission scanning electron microscope (Hitachi High-Technologies Corporation, S-4800), and the distribution of the side length (side length) of the FC was investigated. The results are shown in Figures 4 to 6.

Ethylenediamine (EDA, purity 99.0%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the fullerene dispersion to obtain a mixed liquid (step S220 in FIG. 2). At this time, the concentration of ethylenediamine was 4 wt % relative to the total of mesitylene and isopropanol.

After addition, the mixture was incubated (step S230 in FIG. 2). The incubation was performed at 25°C for 10 minutes with ultrasonic treatment.

The resulting mixture was brown in color. Finally, the mixture was centrifuged, and the product was washed three times with isopropanol and dried at 80°C for 24 hours before being observed and evaluated. The sample used for evaluation is sometimes called FC-EDA.

The samples were observed using a field emission scanning electron microscope and a field emission transmission electron microscope (TEM, JEM-2100F, manufactured by JEOL Ltd.). The samples were evaluated using an X-ray diffraction apparatus (XRD, Rigaku Corporation, RINT-Ultima III). The surface functional groups of the samples were identified using an attenuated total reflection Fourier transform infrared spectrophotometer (ATR-FTIR, Thermo Fisher Scientific Inc., Nexus 670).

The Raman spectrum of the sample was measured using a triple laser Raman spectrometer (T64000, manufactured by Jobin Yvon). A laser with an output of 0.01 mW and a wavelength of 514.5 nm was used for the measurement.

X-ray photoelectron spectra of the samples were measured using a Theta Probe Spectrometer (Thermo Electron). Al-Kα monochromatic radiation (energy 15 keV) was used for the measurements. Core level XPS C1s (energy peak position of C 1s orbital), O1s (energy peak position of O 1s orbital), and N1s (energy peak position of N 1s orbital) were recorded in 0.05 eV steps. To avoid charge accumulation on the samples, a built-in electroflood gun was used for the measurements. UV-vis spectra of the samples were measured using a spectrophotometer (JASCO Corporation, V-670). Mass spectrometry spectra of the samples were measured using a mass spectrometer (MALDI-TOF-MS, Shimadzu Corporation, H17S00282).

The gas sensor capabilities of the obtained samples were investigated using a quartz crystal microbalance (QCM). Using a resonant frequency of 9 MHz (AT-cut), the frequency change during adsorption/desorption of guest gas was recorded for Au resonators (QCM electrodes) coated with each sample. The QCM electrodes were prepared as follows: the sample (0.5 mg) was dispersed in isopropanol (1 mL) and stirred for 30 s. An aliquot (2 μL) of the resulting suspension was drop-cast onto the QCM electrode and dried in vacuum at 80°C for 12 h.

When the frequency change reached equilibrium, the QCM electrode was exposed to air to desorb the adsorbed gas. To test the reproducibility of the QCM electrode, the time dependence of the frequency shift (Δf) when gas exposure and desorption were repeated was recorded. The results are shown in Figures 7 to 18.

FIG. 4 is a diagram showing an SEM image of the fullerene nanocubes obtained in step S210 of FIG.
FIG. 5 is a diagram showing the side length distribution of fullerene nanocubes.
FIG. 6 is a diagram showing an STEM image of a fullerene nanocube.

Figure 4 shows that the nanocubes are square pillars (fullerene nanocubes) made of uniformly crystalline fullerenes. The nanocubes had smooth surfaces and were cubic. Figure 5 shows a histogram of the side lengths of 100 nanocubes randomly selected from the SEM image. Figure 5 shows that the nanocubes have side lengths in the range of 1 μm to 3 μm. Figure 6 also shows that the fullerene nanocubes are not porous.

FIG. 7 shows an SEM image of the sample of Example 1.
FIG. 8 is a diagram showing an STEM image of the sample of Example 1.
FIG. 9 is a diagram showing the side length distribution of the samples of Example 1.
FIG. 10 shows TEM and HRTEM images of the sample of Example 1.

According to Figures 7 and 8, the sample of Example 1 was porous with many pores and had a square prism shape. The sample of Example 1 had two types of pores: macrochannels and microchannels. Comparing the surface of the sample of Example 1 with that of the fullerene nanocube (Figure 4), the surface of the sample of Example 1 was rougher than that of the fullerene nanocube.

Figure 9 shows a histogram of the side lengths of 100 nanocubes randomly selected from the SEM images. According to Figure 9, the side lengths of the sample in Example 1 were in the range of 1 μm or more and 2 μm or less. This suggests that the sample in Example 1 maintained the size of the fullerene nanocube before etching even after etching in step S230 in Figure 2, and each face of the fullerene nanocube was uniformly etched.

Figure 10 shows a TEM image (A) and an HR-TEM image (B) of the sample of Example 1. According to Figure 10(B), the sample of Example 1 exhibits lattice fringes derived from fullerene _C70 , and it was found to have crystallinity even after etching.

Figure 11 shows the XRD pattern of the sample in Example 1.

In addition to the XRD pattern of the sample (FC-EDA) of Example 1, the XRD pattern of the fullerene nanocubes (FC) before etching is also shown in Figure 11. It was found that _C70 exhibited a hexagonal close-packed structure (hcp) with lattice parameters a = 1.08 nm and c = 1.74 nm, while FC had a simple cubic lattice structure (sc) with lattice parameters a = 1.06 nm and V = 1.194 ^nm3 . Surprisingly, the sample of Example 1 after etching had both a simple cubic lattice structure with lattice parameters a = 1.05 nm and V = 1.142 ^nm3 and a hexagonal close-packed structure with lattice parameters a = 1.08 nm and c = 1.5 nm.

Figure 12 shows the Raman spectrum of the sample in Example 1.

In addition to the Raman spectrum of the sample (FC-EDA) of Example 1, Figure 12 also shows the Raman spectrum of the fullerene nanocube (FC) before etching. According to Figure 12, the Raman spectrum of the sample of Example 1 was the same as that of FC. C ₇₀ has major peaks at 1563 cm ^-1 and 1228 cm ^-1 , but there was no peak shift before and after etching with ethylenediamine in step S230. This indicates that C ₇₀ is also the main component in the sample of Example 1 after etching.

FIG. 13 is a diagram showing the FTIR spectrum of the sample of Example 1 on the high frequency side.
FIG. 14 is a diagram showing the FTIR spectrum of the sample of Example 1 on the low frequency side.

13 and 14 show the FTIR spectrum of the sample (FC-EDA) of Example 1 as well as the FTIR spectrum of the fullerene nanocube (FC) before etching. Both FTIRF spectra showed peaks characteristic of fullerene _C70 .

In addition, both FTIR spectra showed small peaks at 3018 cm ^-1 to 2900 cm ^-1 . These peaks are due to C-H stretching vibrations corresponding to solvent molecules. However, the FTIR spectrum of the sample of Example 1 showed a broad band at 3315 cm ^-1 due to N-H stretching vibrations, but the FTIR spectrum of the FC sample did not. This indicates the presence of ethylenediamine-related species on the surface of the sample of Example 1.

Figure 15 shows the UV-vis spectrum of the sample in Example 1.

Figure 15 shows the UV-vis spectrum of the sample of Example 1 (FC-EDA) as well as the UV-vis spectrum of the fullerene nanocube (FC) before etching. According to Figure 15, the intensity of the electronic absorption band of the sample of Example 1 was significantly reduced compared to that of FC. This, as the color of the sample solution of Example 1 was yellowish brown, suggests that the sample of Example 1 contains nitrogen atoms that exhibit Herzberg-Teller vibration-electron interaction, and that the electronic transition is attenuated.

Figure 16 shows the XPS spectrum of the sample in Example 1.

In addition to the XPS spectrum of the sample (FC-EDA) of Example 1, FIG. 16 also shows the XPS spectrum of C ₇₀ and fullerene nanocubes (FC) before etching. According to FIG. 16, the XPS spectrum of C ₇₀ and FC used as raw materials showed core level peaks of C1s and O1s. The oxygen was due to air oxidation. On the other hand, the XPS spectrum of the sample of Example 1 showed a core level peak of N1s at 400 eV in addition to the core level peaks of C1s and O1s. From these, it was shown that fullerene nanocubes containing nitrogen atoms can be obtained by carrying out the manufacturing process of FIG. 2.

Furthermore, the nitrogen atom content was calculated from the XPS spectrum of Example 1 and was found to be 5.3 atomic %. It was found that the fullerene nanocubes of the present invention contain nitrogen atoms in the range of 4 atomic % to 6 atomic %.

Figure 17 shows the N1s core level XPS spectrum of the sample in Example 1.

17 shows the deconvoluted N1s peak of Sample 1, which indicates the presence of oxidized nitrogen atoms in the sample of Example 1. Although not shown, the mass spectrum of the sample of Example 1 was measured, and it was found that the sample of Example 1 is mainly composed of fullerene _C70 and has an aminated surface.

From these, it was found that by carrying out the manufacturing process shown in Figure 2, fullerene reacted with ethylenediamine, and the sample of Example 1 had an aminated surface.

The contact angles of the sample of Example 1 (FC-EDA) and the fullerene nanocubes (FC) before etching were examined. As a result, FC showed high water repellency of over 140°, while the sample of Example 1 showed high hydrophilicity of 40°.

As explained above, it has been found that the manufacturing process shown in Figure 2 can produce porous fullerene nanocubes whose main component is fullerenes containing nitrogen atoms.

Next, we will explain the QCM sensor using the sample of Example 1, which is a porous fullerene nanocube that contains nitrogen atoms and has hydrophilic properties. Hereinafter, the QCM sensor using the sample of Example 1 will be referred to as the QCM sensor of Example 1.

Figure 18 shows the QCM frequency shifts for various volatile organic compounds using the QCM sensor of Example 1.

According to FIG. 18, the QCM sensor of Example 1 showed a frequency shift response to formic acid, acetic acid, propionic acid, phenol, formaldehyde, water, etc. In particular, the fullerene nanocube of the present invention showed a larger frequency shift in response to the adsorption of acidic gases such as formic acid, acetic acid, and propionic acid. Although not shown, it was confirmed that the QCM sensor of Example 1 has excellent reproducibility.

The fullerene nanocubes of the present invention are hydrophilic and therefore applicable to bio-related applications. The fullerene nanocubes of the present invention are selectively reactive to specific acidic gases and therefore applicable to quartz crystal gas sensors.

REFERENCE SIGNS LIST 100 Fullerene nanocube 110 Mesopore 300 Quartz crystal oscillator (QCM) gas sensor 310 Quartz crystal oscillator (QCM) electrode 320 Gas sensor film 330 Quartz substrate 340a, 340b Electrode 350a, 350b Lead wire

Claims (17)

A fullerene nanocube mainly composed of fullerene,
It is porous,
The fullerene contains a nitrogen atom ,
It has a simple cubic lattice structure (sc) and a hexagonal close packed structure (hcp),
Fullerene nanocubes with aminated surfaces . 2. The fullerene nanocube of claim 1, wherein the fullerene is at least one selected from the group consisting of _C60 fullerene, _C70 fullerene, _C76 fullerene, _C78 fullerene, _C82 fullerene, _C84 fullerene, _C90 fullerene, _C94 fullerene, and derivatives thereof. The fullerene nanocube of claim 2 , wherein the fullerene is _C70 fullerene and/or a derivative thereof. The fullerene nanocube according to any one of claims 1 to 3 , which has hydrophilicity. The fullerene nanocube according to any one of claims 1 to 4 , which is a square prism having one side of 1 μm or more and 4 μm or less. 6. The fullerene nanocube according to claim 1 , which has a peak due to N--H stretching vibration in the range of 3000 cm ^-1 to 3450 cm ^-1 in an FTIR spectrum measured with a Fourier transform infrared spectrophotometer. 7. The fullerene nanocube according to claim 1 , which has a nitrogen N1s peak in the binding energy range of 398.5 eV to 400.5 eV in an XPS spectrum measured by X-ray photoelectron spectroscopy. The fullerene nanocube according to any one of claims 1 to 7 , wherein the nitrogen atoms are contained in an amount ranging from 3 atomic % to 10 atomic %. The fullerene nanocube according to any one of claims 1 to 8, wherein the nitrogen atom is oxidized. mixing a fullerene dispersion in which fullerene is dispersed in mesitylene with a lower alcohol having 5 or less carbon atoms, and forming fullerene nanocubes by a liquid-liquid interface precipitation method;
adding ethylenediamine in an amount of 2 wt % to 10 wt % based on the total amount of the mesitylene and the lower alcohol to obtain a mixed solution;
and incubating the mixture for a period of 5 minutes to 30 minutes. 11. The method of claim 10 , further comprising washing the product with the mixed solution of mesitylene, a lower alcohol and ethylenediamine following said incubating. 12. The method of claim 10 , wherein the lower alcohol is at least one selected from the group consisting of methanol, ethanol, propanol, and isopropanol. The method according to any one of claims 10 to 12, wherein the forming of the fullerene nanocubes is carried out under ultrasonic treatment. The method according to any one of claims 10 to 13, wherein obtaining the mixture is performed under ultrasonic treatment. The method according to any one of claims 10 to 14 , wherein the fullerene is a _C70 fullerene and/or a derivative thereof. A quartz crystal gas sensor having a gas sensor membrane,
A quartz crystal gas sensor, wherein the gas sensor film contains the fullerene nanocubes according to any one of claims 1 to 9 . 17. The quartz crystal gas sensor according to claim 16 , which detects an acid gas selected from the group consisting of formic acid, acetic acid, and propionic acid.