JP7095858B2 - Filter unit - Google Patents

Description

The present invention mainly relates to a filter unit used for separating a gas phase or a liquid phase.

Distillation is widely used in the gas separation industry to obtain high-purity products, supplying other industries with high-purity N ₂ , O ₂ and noble gases, whereas distillation is said to gasify liquids. Along with the phase change, the energy consumed for this phase change is large.
Therefore, instead of phase change-based molecular separation such as distillation, a new radically alternative separation technique such as membrane-based molecular separation has been sought. Membrane-based separation technology can be realized with a simpler device and has a smaller footprint than conventional technology based on phase change, and energy is reduced by 90% compared to distillation, resulting in significant CO ₂ emissions. Can be reduced.

One of the most promising membranes is a carbon material such as a monolayer graphene membrane with nanoscale sized windows (nanowindows). Since the periphery of the nanowindow is composed of a single layer of carbon atoms, when a substance permeates through the nanowindow, ultrafast permeation is possible without being hindered by the nanowindow.
Due to the thickness of one atom, robustness, chemical stability, and ease of processing into sieves, one of the most important uses of graphene is its use as a separation membrane. Since the graphene synthesis process is continuously improved, mass production of graphene with almost no defects is expected in the near future.

Raw graphene sheets do not allow even the smallest gases such as He to permeate, so nanowindows need to be formed. There are many methods for producing graphene containing nanowindows, such as ion impact, template synthetic mesh, and high temperature oxidation. Since high-temperature oxidation only requires heating up to about 600 K in an oxidizing environment, the size of the nanowindow can be easily expanded and it is inexpensive (Patent Documents 1 and 2).

Carbon materials with nanowindows have the potential to be the most selective and energy efficient membranes for molecular separation.
In addition, since the gaps between carbon nanotubes and the gaps between carbon nanohorns also exhibit the same properties as nanowindows, it is expected that the film will have the same energy efficiency.
Therefore, there has been a demand for a filter unit capable of separating molecules using a carbon material.

Japanese Patent Publication No. 2013-536077 Japanese Unexamined Patent Publication No. 2009-07327

The present invention has been made to solve the above problems, and an object of the present invention is to provide a high-performance filter unit used for separating molecules.

In the present invention, the means for solving the above problems are as follows.
The first invention is one or more conductive carbon filters having through holes, one or more pairs of electrodes that apply a voltage to the carbon filters, and one or more electrodes that prevent current from flowing between the electrodes. It is a filter unit characterized by being equipped with an insulator.

The second invention is a flexible nanowindow in which the transmission hole of the carbon filter can switch the orientation of two or more kinds of functional groups formed on the rim by applying a voltage, and the carbon filter is formed by the electrode. It is characterized in that the molecular selectivity or the molecular permeability of the carbon filter is changed by applying a voltage.

In the third invention, the branch flow path is provided downstream from the main flow path of the fluid, and the main flow path or the branch flow path is provided in conjunction with the change of application to the carbon filter by the electrode. It is characterized by providing a switching valve that selectively opens.

According to the first invention, one or more conductive carbon filters having through holes, one or more pairs of electrodes for applying a voltage to the carbon filters, and preventing current from flowing between the electrodes 1 With one or more insulators, the charge attracts the ions, thus reducing the energy cost of increasing the pressure of the gas or liquid for filter separation.

According to the second invention, the permeation hole of the carbon filter is a flexible nanowindow capable of switching the orientation of two or more kinds of functional groups formed on the rim by applying a voltage, and the carbon by the electrode. By changing the molecular selectivity or molecular permeability of the carbon filter by applying a voltage to the filter, two kinds of molecules having substantially the same van der Waals diameter can be separated.

According to the third invention, a branch flow path that branches from the main flow path of the fluid is provided downstream of the carbon filter, and the main flow path or the branch flow is linked to a change in the application of the electrode to the carbon filter. By providing a switching valve that selectively opens the path, the two separated substances can be automatically divided into a main flow path and a branch flow path and supplied.

It is a figure which shows the arrangement of each component of the filter unit which concerns on this invention, (a) (b) (c) (d) show an example which the positional relationship of a filter body, a working electrode and an insulator is different, respectively, and (e). (F) shows an example in which the positional relationship between the filter body, the counter electrode, and the insulator is different. (A) is an explanatory diagram showing a first embodiment of the filter unit, and (b) is an explanatory diagram showing a second embodiment of the filter unit. It is explanatory drawing which shows the example which provided the three-way valve in the filter unit of this invention. It is a model of multiple nanowindows of different sizes and the distribution of functional groups, and the van der Waals diameter of each nanowindow (hereinafter sometimes expressed as NW-x) is 2.57 Å for (a) and 2.73 for (b). Å, (c) is 2.97 Å, (d) is 3.30 Å, (e) is 3.70 Å, (f) is 3.78 Å, and (g) is a graph showing the transmittance of molecules in each model. It is a diagram showing respiration-like expansion and contraction in a nanowindow of NW-3.30 Å, (a) shows a 2D histogram contour of the distance between two pairs of oxygen atoms at the opposite poles of the rim during MD simulation, (b). Shows two pairs of oxygen atoms (O1 and O2 pairs, O3 and O4 pairs) used in the length calculation in (a). It is an explanatory diagram of the effect of the rotation of the functional group of the nanowindow of NW-3.30 Å on the transmission rate of N ₂ , and (a) to (d) are the results of MD simulation of N ₂ permeability at 77 K. , (A) show a flexible nanowindow structure, (b) shows a high-speed rigid nanowindow structure, (c) shows a medium-speed rigid nanowindow structure, and (d) shows a low-speed rigid nanowindow structure. , (E) show some typical orientations of the functional groups in (b), (f) show some typical orientations of the functional groups in (c), and (g) shows (d). Shows some typical orientations of the functional groups in. It is an explanatory diagram of the effect of opening and closing of functional groups on the permeation rate of O ₂ at 90K in a nanowindow of NW-2.73Å, (a) shows two examples of open permeation, and (b) is closed. Two examples of non-transmissive (atomic gate) states are shown.

Hereinafter, the filter unit according to the embodiment of the present invention will be described.
The filter unit consists of a filter body, an insulator, and an electrode, and is used for applications such as separation of gas phase and liquid phase, or removal of foreign matter.

The filter body needs to be a conductive filter.
A carbon filter can be mentioned as a typical filter body, but a filter made of other materials can also be used.
As the material of the carbon filter, nanocarbons such as graphene, carbon nanotubes, carbon nanoribbons, carbon nanohorns, graphene oxide, and diamond-like carbon can be used. Further, a thin film of a carbon precursor such as an acrylic resin may be carbonized and used. Electrically conductive carbon particles such as acetylene black and conductive carbon black represented by Cabot's Vulcan XC72 can also be used if they can form transmission holes of uniform size.

When forming the film of the carbon filter, the nanotube ink or slurry may be mixed with a dispersant, a binder, conductive particles (such as Nafion or an ionic liquid), a thickener and the like, if necessary.
The carbon filter is provided with fine transmission holes. The through hole refers to a hole having a diameter of about 10 μm or less. Molecules that can pass through these through holes and molecules that cannot pass through can be separated by a filter unit.
As the permeation pores, nanowindows may be perforated in a film such as graphene by high temperature oxidation or other chemical methods, or carbon nanotubes or carbon nanohorns may be formed in a film formed by aggregating carbon nanotubes or carbon nanohorns. The gap may be used.

As the filter other than the carbon filter, a metal film such as ITO having a porous structure or a platinum thin film having nanothrough holes can be used.

A pair of electrodes consisting of a working electrode and a counter electrode (counter electrode) has a role of applying a voltage to the filter body.
The performance required for the electrode is to have high conductivity and corrosion resistance when used in a liquid.
As the material of the electrode, platinum may be used, or a surface such as copper plated with platinum may be used.

Further, the highly conductive carbon filter itself can be used as a working electrode.
Alternatively, a liquid phase electrode such as a salt bridge can be used. Liquid phase electrodes are inefficient, but have the advantage that standard electrodes can be used.

The insulator has a role of insulating the working electrode and the counter electrode.
Power consumption can be suppressed by applying a voltage to the filter body by the working electrode and preventing the current from flowing in the circuit by the insulator.

Some examples of the arrangement of each component of such a filter unit are shown. For convenience, the working electrode shall be located to the left of the counter electrode.
In FIG. 1A, one surface of the membrane of the filter body 1 is in contact with the flat surface of the disk-shaped working electrode 2, and the opposite surface of the filter body 1 is in contact with the flat surface of the disk-shaped insulator 4.
Further, in FIG. 1B, the filter main body 1 is in contact with one flat surface of the disk-shaped working electrode 2, and the flat surface of the disk-shaped insulator 4 is in contact with the opposite surface of the working electrode 2.
When arranging the filter unit in the liquid, the working electrode 2 may be arranged apart from the filter main body 1 as shown in FIG. 1 (c), and the liquid may be dissolved and electrically contacted. .. The insulator 4 is in contact with the opposite surface of the filter body 1.
Further, as shown in FIG. 1 (d), the end portion of the rod-shaped working electrode 2 may be brought into contact with one surface of the film of the filter main body 1. The insulator 4 is in contact with the opposite surface of the filter body 1.
Since it is preferable that a sufficient voltage can be applied to the filter main body 1 without bias, FIGS. 1 (a) and 1 (b) are preferable.

On the other hand, as shown in FIG. 1 (e), the disk-shaped counter electrode 3 is arranged so as to be in contact with the opposite side of the working electrode 2 when viewed from the disk-shaped insulator 4. Further, another object or a second filter body may be sandwiched between the counter electrode 3 and the insulator 4.
Further, when the filter unit is arranged in the liquid, the counter electrode 3 may be arranged apart from the working electrode 2 when viewed from the insulator 4, as shown in FIG. 1 (f).

Further, the filter main body 1 may have one or more, the electrodes 2 and 3 may have two or more pairs, and the insulator 4 may have two or more.

The first embodiment of the specific filter unit will be described below.
As shown in FIG. 2 (a), as the filter bodies 1a and 1b, a single-walled carbon nanotube (EC2.0 manufactured by Meijo Nanocarbon Co., Ltd.) dispersion liquid generated by the DIPS method is applied to a polycarbonate membrane filter 5 (Merck Co., Ltd.). Isopore) is spray-coated and dried at 100 ° C, then a single-walled carbon nanotube dispersion is also spray-coated on the back surface and dried at 100 ° C, and then baked at 200 ° C for 5 minutes to form two circles. A plate-shaped carbon filter was obtained.
In this carbon filter, the gap between the carbon nanotubes functions as a transmission hole.
Further, the membrane filter 5 functions as an insulator.
From the outside of each of the filter bodies 1a and 1b, platinum was sandwiched between the disc-shaped electrodes 2 and 3 knitted into a mesh and brought into contact with each other, and set in the filter holder 6 to form a filter unit. The working electrode 2 was arranged upstream of the filter bodies 1a and 1b, and the counter electrode 3 was arranged downstream.

The second embodiment of the filter unit will be described below.
As shown in FIG. 2B, as the filter bodies 1a and 1b, a slurry of single-walled carbon nanotubes was bar-coded on both sides of a polycarbonate membrane filter 5 and dried to obtain two disc-shaped carbon filters. ..
In this carbon filter, the gap between the carbon nanotubes functions as a transmission hole.
Also in the second embodiment, the membrane filter 5 functions as an insulator.
The filter bodies 1a and 1b and the membrane filter 5 were set in the filter holder 6. A disk-shaped working electrode 2 made of platinum woven into a mesh was brought into contact with the filter body 1a on the upstream side from the upstream side, and a counter electrode 3 made of carbon paper was brought into contact with the filter body 1b on the downstream side to form a filter unit.

Further, as shown in FIG. 3, in the first embodiment or the second embodiment, a branch flow path 8 branching from the main flow path 7 is provided downstream of the filter main bodies 1a and 1b, and the main flow path 7 or the branch flow path 7 or the branch flow path 8 is provided in this branching portion. A three-way valve 9 or other switching valve that selectively opens the branch flow path 8 may be provided.
The switching of the flow path by the three-way valve 9 is controlled so as to be interlocked with the change of the voltage applied to the filter main bodies 1a and 1b. It is not necessary to operate the power supply device 10 (change the voltage) for applying a voltage to the filter bodies 1a and 1b and to switch the three-way valve 9 at exactly the same time, and leave a predetermined time difference from the operation of the power supply device 10. The three-way valve 9 may be switched.

Hereinafter, separation using a filter unit will be described.
<Ion separation in liquid phase>
Next, ion separation using a filter unit will be described.
By bringing the cathode (working electrode 2) into contact with the upstream side of the filter body 1 and applying a voltage of 0.1 V to 10 V, the transmission hole of the filter body 1 functions as a hole having an electrostatic attractive force and a repulsive force. .. When the ion solution is supplied, the metal cation is attracted to the cathode and the filter body 1 to make it difficult to pass through the filter body 1, and the anion repels the filter body 1 to make it difficult to pass through the filter body 1.
As a result, the ionic solution is separated into a high-concentration cationic solution on the upstream side of the filter body 1 and a low-concentration cationic solution on the downstream side.

Therefore, by installing the filter unit of the present invention in a water pipe or the like, unnecessary ions and the like can be separated and removed from the water.
For example, when a cathode is brought into contact with the upstream side of the filter body 1 and a voltage is applied, alkali metal ions (calcium ions and magnesium ions) in water are attracted to the cathode and it becomes difficult to pass through the filter body 1, so that the filter body 1 Soft water that has permeated through can be used.

When the three-way valve 9 is provided as shown in FIG. 3, the main flow path 7 is opened when a voltage is applied to the filter main body 1 (1a), and soft water can be supplied to the downstream side. When the voltage is turned off, the branch flow path 8 is opened, and water having a high alkali metal ion concentration can be discarded from the branch flow path 8.

When the ion to be removed is an anion, a cathode (working electrode 2) is brought into contact with the cathode (working electrode 2) from the downstream side of the filter body 1 to apply a voltage, and an anode (counter electrode 3) is arranged on the upstream side with the insulator 4 interposed therebetween.
When a voltage is applied to the filter main body 1, anions (silica ions or the like) in the water are attracted to the anode and are difficult to permeate through the filter main body 1, so that water having a low anion concentration can be obtained.

As described above, by using the filter unit of the present invention, since ions are attracted by electric charges, it is possible to reduce the energy cost of increasing the pressure of gas or liquid for separation by the filter.
Further, when the voltage application is turned off, the object separated on the upstream side of the filter main body 1 also flows on the downstream side. Therefore, unlike the conventional filtration, the object is less likely to be accumulated on the upstream side, and the frequency of maintenance such as filter replacement can be reduced.
In addition, since it functions as a filter with electrostatic attraction and repulsion, it is possible to realize high-performance separation at a lower energy cost than a conventional membrane.

Further, a branch flow path 8 that branches from the main flow path 7 downstream of the filter main body 1 is provided, and a three-way valve 9 that selectively opens the main flow path or the branch flow path in conjunction with the application of a voltage to the filter main body 1 is provided. By providing the two separated substances, the two separated substances can be automatically divided into the main flow path 7 and the branch flow path 8 and supplied.

<Carbon filter with flexible nanowindow>
In order to perform more effective separation in the filter unit of the present invention, it is preferable to use a carbon filter (filter body) having a flexible nanowindow.
The flexible nanowindow means a nanowindow capable of transmitting a molecule larger than its own van der Waals diameter by adding a functional group or a heteroatom described later to a carbon atom constituting a peripheral edge (rim).
Hereinafter, the case where graphene having a flexible nanowindow is adopted as a carbon filter will be mainly described.

Heteroatoms mean atoms other than hydrogen and carbon, such as oxygen (O), nitrogen (N), sulfur (S), phosphorus (P), chlorine (Cl), iodine (I), bromine (Br), and boron. (B) and the like can be exemplified.
The functional group means a general functional group that imparts chemical properties, in particular, one that is added to an atom constituting the rim. In particular, a functional group containing a hetero atom is preferable, and a hydroxyl group, a carboxyl group, a carbonyl group and the like can be exemplified.

The partial charge of the heteroatom applied to the rim induces a strong electrostatic field of GV / m inside the nanowindow. The interaction of this electric field with a molecule with a polarized charge center, such as N ₂ , facilitates the process of permeation of the nanowindow by the molecule. In addition, the coordinated movement of surface functional groups in the rim of the nanowindow can accelerate the permeation of molecules with polarized charged centers.

The difference in electronegativity between carbon atoms and heteroatoms such as H and O atoms bonded to C in the rim atoms of different nanowindows, along with the addition of defects in the graphene network, is the electron of the atoms that make up the rim of the nanowire. Induces density heterogeneity. These partial charges along the rim induce an electrostatic field around a nanowindow as large as GV / m. It has an attractive interaction with molecules that have permanent multipoles, such as the O ₂ and N ₂ quadrupole moments. Examples of heteroatoms to be introduced are nitrogen, oxygen, sulfur, phosphorus, chlorine, iodine, bromine and boron, with oxygen and boron acting particularly effectively. Due to the difference in electronegativity, the oxygen atom acts as a donor and the boron atom acts as an acceptor to the carbon atom of the nanowindow rim, giving the nanowindow rim an inhomogeneous electron distribution. Similar effects can be obtained with the addition of donor substances such as tetrathiafulvalene (TTF) and acceptor substances such as tetracyanoquinodimethane (TCNQ), but the direct introduction of heteroatoms into the nanowindow rim is more direct. The effect is great. In addition, the formation of nanowindows and the treatment for introducing heteroatoms may cause defects (defects) of carbon atoms in the nanowindow rim, which has the same effect on the nanowindow rim as the introduction of heteroatoms. ..

Also, the rim of the flexible nanowindow can vibrate and relax during molecular permeation. Although the relaxation of such cyclic polyaromatic molecular nanowindows varies depending on the type of permeate molecule, the permeation energy barrier has been reduced by 2 to 5 times.
If the nanowindow is regarded as having a structure equivalent to that of an aperiodic polycyclic polyaromatic molecule, it is expected that the mitigation effect will be very large. This is because the structure of such aperiodic polycyclic polyaromatic molecules is much stronger than the periodic structure and causes phonon oscillations. The introduction of flexibility through rim relaxation into the nanowindow is important because it occurs in parallel with molecular permeation.

The mechanism by which molecules larger than nanowindows permeate the nanowindow is that the electron distribution of the nanowindow rims and functional groups changes (coordinates) due to the interaction between the electrons of the nanowindow rims and functional groups and the electrons of the permeating molecules. As a result, a Coulomb-like attractive force is generated (relaxed) with the permeating molecule, and the kinetic energy of the permeating molecule can sufficiently break through the steric obstacle of the nanowindow rim itself.
The dynamic motion of the rim and the partial charge distribution produced by the heteroatoms distinguish molecules such as gases and cause selective permeation.
The smallest two-dimensional shapes of O ₂ , N ₂ , and Ar are 2.99 Å, 3.05 Å, and 3.63 Å, respectively.
O ₂ has weak coordination with nanowindow rims and functional groups, and relaxation also occurs, but the relaxation effect is small due to the weak coordination (it can pass through nanowindows smaller than its own size).
N ₂ has a large relaxation effect (it is easier to pass through nanowindows smaller than its own size than oxygen) because strong coordination occurs with nanowindow rims and functional groups and strong relaxation occurs.
Ar has no mitigation effect because it does not cooperate with nanowindow rims or functional groups.

In addition, functional groups such as hydroxyl, carboxyl and carbonyl have several orientations with respect to the nanowindow. Their dynamic orientation changes the shape of the nanowindow and strongly influences the transmission mechanism and its selectivity.

Also, the nanowindow rim is not static, but breathing vibrates, acting as if breathing and relaxing. Similar to the charge distribution, this vibration also causes relaxation by coordinating nanowindow rims and functional groups with transmitted molecules.
Graphene has phonon motion and a natural vibration mode, which causes coordinated vibration in the rim of the nanowindow. These vibrations change the effective size and / or shape of the nanowindow and determine its transmission properties.
From the shape of the distance histogram in FIG. 5 (a), it is clear that the cooperative operation of the breathing vibration of the rim is not symmetrical. In fact, the Pearson correlation coefficient between the O1-O2 distance and the O3-O4 distance shown in FIG. 5 (b) is -0.38, which is perpendicular to this while one direction of the nanowindow rim length contracts. It means that one direction extends. The vibration of the nanowindow rim coordinated with this permeate molecule is very similar to that observed in the skeletal dynamics of small pore zeolites called the "window breathing" mode. Molecule permeation is effective when the shorter OO distance (ie, O1-O2) exceeds its average.

<Opening and closing by rotation of functional group>
The free rotation of the functional groups of the nanowindow and the vibration of the rim can create a kind of gate for the transmitted molecule.
By mimicking the nanochannels of proteins, nanowindows with negatively charged carboxylic acid groups have been demonstrated to exhibit an asymmetric energy profile of ion permeation on both sides of the graphene wall. This was due to different methods of creating different environments on either side of the graphene wall so that the carboxylic acid groups face the graphene surface. For this reason, MD simulations need to sample all energy-efficient nanowindow configurations, taking into account the flexible skeleton.

Out-of-plane graphene functional groups can also dynamically switch their orientation. The change in transmittance due to the orientation of functional groups (eg, hydroxyl groups containing O1, O2, O3 and O4 in FIG. 5 (b)) in the nanowindow rim was simulated by MD. The MD simulation set of N ₂ transmission through the flexible NW-3.30 nanowindow (see Figure 6 (a)) has a transmission rate (10 ± 5 μs ^-1 ) even with simulation times up to 20 nanoseconds. Shows very large fluctuations.
The H atom (electrostatically interacting with the N ₂ molecule) attached to O in the hydroxyl group has a degree of freedom of movement in response to the rotation of the HOCC dihedral angle, but has a minimum local energy configuration (specific). When the nanowindow skeleton is quenched at this time), H is temporarily locked.

This made it possible to identify three different velocity regimes of transmission. When the pair of H-O1 and H-O2 atoms are oriented toward the opposite side of the graphene surface and away from each other, a fast transmission regime (k = 28 ± 11 μs ^-1 , Fig. 6 (b)) is generated. It occurs (see FIG. 6 (e); the notation of each O atom also sees FIG. 5 (b)), allowing the larger nanowindow space to be open for transparent N ₂ . In all of these cases, H-O2 turned towards FIG. 6 to create a favorable environment for permeation. At moderate transmission velocities (k = 3.3 ± 0.5 μs ^-1 in FIG. 6 (c)), the atomic pairs of H-O1 and H-O2 point in opposite directions and converge to each other outside the graphene plane. Or, they face the same direction outside the graphene plane but away from each other (see FIG. 6 (f)). Finally, in the slow velocity transmission regime (k = 0.1 ± 0.2 μs ^-1 , FIG. 6 (d)), both atomic pairs point in the same out-of-graphene direction and in the direction of convergence (FIG. 6 (g)). By doing so, it behaves like an atomic gate that clogs the nanowindow.

In the slow-velocity transmission regime, the twisting of the functional groups H-O1 and H-O2 makes the nanowindow a purely electrostatic gate for N ₂ transmission (H is modeled as a charging point lacking dispersion interaction). For). Since the O1-O2 distance is at the shortest open distance at this time, not only the O1-O2 distance plays a major role in transmission, but also as an atomic gate for molecules with which the positions of H atoms interact electrostatically. You can also see that it behaves. This indicates that this effect is likely to be utilized by including other electrostatic functional groups within the rim of the nanowindow.

Since O ₂ is smaller than N ₂ , gate opening and closing occurs in nanowindows smaller than N W-2.73 than in N ₂ (NW-x is shown as the van der Waals diameter φ of the nanowindow. (Å)).
In the first case, a slow system (see FIG. 7 (a), rate constant 1.8 μs ^-1 ) occurs in which O ₂ permeates when each hydrogen opens in the opposite direction to the graphene surface. In the second case, when both hydrogens bend in the same direction with respect to the graphene plane, thus closing the nanowindow and acting like an atomic gate (see Figure 7 (b), rate constant <0.001 ^{μs- 1} ) occurs.
The open position of the nanowindow is slightly thermodynamically advantageous compared to the closed nanowindow (ΔE = -1.3kJ / mol).

As a method for obtaining graphene having functional groups having two or more kinds of orientations as described above, graphene was treated with air at 600 K for 10 minutes to form nanowindows of a desired size. Further, this graphene was immersed in a 1 mol / L nitric acid aqueous solution at 300 K for 1 hour to introduce a heteroatom. After washing with ultrapure water, it was transferred to a polycarbonate membrane filter and set in a membrane filter holder to form a gas molecular film. Some edges of the exposed flexible nanowindow are passivated at the -H, -OH or COC terminations.
The application of electric charge and infrared irradiation are effective for opening and closing the nanowindow using the charge distribution of the functional group and the nanowindow rim. The charge distribution of the nanowindow rim can be easily controlled by applying the charge. For example, when the entire graphene is applied to the electron-rich state, the nanowindow rim is filled with electrons and the nanowindow is closed.
When irradiated with electromagnetic waves such as infrared rays, the functional groups rotate or become active due to thermal motion, and the nanowindow is closed. In addition, the nanowindow rim is closed due to the effect of phonons generated by electromagnetic wave irradiation.
In addition, after weakly irradiating graphene with infrared rays to maintain high molecular permeability, the nanowindows are opened by stopping infrared irradiation and maintaining the arrangement of functional groups in the open state of the nanowindows for cooling. Can be kept in a state.

Flexible nanowindows can permeate molecules larger than their van der Waals diameter. For example, a 3.0 Å O ₂ molecule can easily penetrate a 2.7 Å nanowindow at an ultrafast speed of 600 m ³ · min ^-1 · m ^-2 .
Further, for two types of molecules having almost the same van der Waals diameter, when one of them acts on the flexible nanowindow and the other does not, the two types of molecules can be separated by the flexible nanowindow.

A third embodiment of the filter unit having a flexible nanowindow will be described below.
As shown in FIGS. 1 (a) and 1 (e), a film made of a polyimide resin having a thickness of 10 μm having a through hole having an average opening diameter of 1 μm is formed, and single-layer graphene (manufactured by Graphene) is transferred to the film. Then, it was heated at 250 ° C. in air to form a flexible nanowindow on graphene. The transferred graphene functions as the filter body 1, and the polyimide film has the function of the insulator 4. Some edges of the exposed flexible nanowindow are passivated at the -H, -OH or COC terminations.
Next, a disk-shaped working electrode 2 made by knitting platinum into a mesh is brought into contact with the filter body 1 on the upstream side from the upstream side, and a counter electrode 3 made of carbon paper is brought into contact with the insulator 4 from the downstream side to form a filter unit. I set it in the filter holder.

Hereinafter, separation using a filter unit will be described.
<Separation in gas phase>
The case where the dry air is separated into O ₂ , N ₂ and Ar by using the filter unit of the present invention will be described.
A carbon filter having a flexible nanowindow is used for the filter main body 1.
When dry air is supplied to the filter unit with the charge turned off, O ₂ permeates the filter body 1 and N ₂ and Ar do not permeate, so that a gas with a high O ₂ concentration is obtained downstream of the filter body 1. Be done.
After that, when a voltage of 1 V to 100 V is applied to the filter body 1, the amount of N ₂ permeated increases, but the amount of Ar permeated does not change, and a gas having a high Ar concentration is obtained upstream of the filter body 1 and downstream. A gas with a high N ₂ concentration can be obtained.

As the size of the nanowindow increases, the permeation rate increases and conversely the selectivity decreases. Therefore, NW-3.78 and NW-3.70 have high transmittance and low separation selectivity.
By reducing the size to 3.3 Å (see NW-3.30 in Figure 4 (d)), the Ar permeation rate is reduced by 50 times, the N ₂ / Ar selectivity is increased to 20, and it is effective as a molecular sieve. Is shown.
The most selective for oxygen in the flexible nanowindow is NW-2.97 (see Figure 4 (c)). Its permeation rate constant is 47 μs ^-1 , which corresponds to 600 m ³ STP · min ^-1 · m ^-2 , which is 50 times (O ₂ :) in O ₂ : N ₂ separation as shown in Fig. 4 (g). It has greater selectivity than 1500 times in Ar separation).
Conventional carbon molecular sieves can achieve about 30 times the O ₂ : N ₂ selectivity, but the diffusion limit is large and the permeation rate is limited. Commercially available polymers such as polysulfone, polycarbonate and polyimide were able to reach about 6 times the permeation rate selectivity for O ₂ : N ₂ . However, even the best membranes, including polymer membranes with confusion matrices, rarely exceed 10-fold O ₂ : N ₂ selectivity. Separation with such polymers provides orders of magnitude lower selectivity than flexible nanowindows.
On the other hand, the present invention has made it possible to significantly reduce the energy cost and CO ₂ emissions for separating molecules as described above.

As described above, by using a carbon filter having a flexible nanowindow, it is possible to separate two types of molecules having substantially the same van der Waals diameter.
In addition, high-performance separation can be realized at a lower energy cost than conventional membranes.

<Explanation of drawings>
In each model of FIG. 4, light gray atoms represent carbon (C), dark gray atoms represent oxygen (O), and white atoms represent hydrogen (H). Shown as NW-x is the van der Waals diameter φ (Å) of the nanowindow. The transmittance (unit: μs ^-1 ) shown in FIG. 4 (g) is measured for each molecule by adapting the average of the results of many MD simulations to the primary model. As a result of the simulation, the region where the transmittance was <0.004 μs ^-1 was interpreted as the part where the molecule could not penetrate.
FIG. 5 shows the breathing vibration of the nanowindow (vibration that expands and contracts concentrically as if breathing). The color gradient of the rectangle in (a) corresponds to the distance when the N ₂ molecule penetrates the nanowindow, and the darker mark corresponds to the N ₂ center closer to the graphene plane. Therefore, the relationship between the distance of N ₂ to graphene and the breathing oscillation is shown. The shade of the background shows the distribution of the distance between O1 and O2 and the distance between O3 and O4, and the darker the color, the higher the frequency of being at that distance. Therefore, it is shown that the nanowindow in FIG. 5 oscillates with an amplitude of about 3.5 Å around 6.16 and 6.54 Å, respectively, between O1 and O2 and O3 and O4, respectively.
In FIGS. 6 (a) to 6 (d), the light line shows the result of each execution, the black line shows the average value of all the executions, and the shaded area is the standard deviation of each execution. The inserted subgraph is a linearization of all data, including a linear approximation to the mean. Further, in FIGS. 6 (e) to 6 (g), the arrow indicates the orientation of the O (1-2) -H functional group, the black arrow indicates that it is in the graphene plane, and the white arrow indicates the direction toward the back. The dashed arrow indicates the orientation toward you.
In the permeation state of FIG. 7A, the pair of hydrogen atoms at the opposite poles are oriented in opposite directions with respect to the graphene plane. In the non-permeable (atomic gate) state of FIG. 7 (b), a pair of hydrogen atoms at the opposite poles are oriented in the same direction with respect to the graphene plane. Further, in each figure, the energy difference ΔE at the lower left is based on the example on the left side of FIG. 7 (a) (0). Light gray indicates carbon (C), dark gray indicates oxygen (O), and white indicates hydrogen (H).

1,1a, 1b Filter body 2 (Working) Electrode 3 (Counter) Electrode 4 Insulator 5 Membrane filter 6 Filter holder 7 Main flow path 8 Branch flow path 9 Three-way valve 10 Power supply

Claims (2)

With one or more conductive carbon filters with permeation holes,
One or more pairs of electrodes that apply voltage to the carbon filter,
With one or more insulators that prevent current from flowing between the electrodes,
Equipped with
A branch flow path that branches from the main flow path of the fluid is provided downstream of the carbon filter, and the main flow path or the branch flow path is selectively opened in conjunction with a change in the application of the electrode to the carbon filter. Provide a valve ,
The transmission hole of the carbon filter is a flexible nanowindow capable of switching the orientation of two or more kinds of functional groups formed on the rim by applying a voltage, and by applying a voltage to the carbon filter by the electrode. By changing the molecular selectivity or molecular permeability of the above carbon filter,
The above fluid is water
A filter unit characterized in that the carbon filter, the electrode, and the insulator are arranged in a water pipe . The filter unit according to claim 1 , wherein the switching valve is a three-way valve.

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