KR102235307B1 - Chitosan-carbon nanotube core-shell nanohybrid based humidity sensor - Google Patents

Abstract

The present invention provides a method of manufacturing a humidity sensor in which a chitosan-multi-walled carbon nanotube solution prepared by homogenizing a multi-walled carbon nanotube in a chitosan solution is fixed to an electrode.
The humidity sensor according to the present invention is economical because it can send sufficient current even with a very small voltage due to low resistance, that is, high conductivity compared to existing humidity sensors, and high sensitivity, stability and constant stability even at different voltages, frequencies, and temperatures It has an excellent advantage in that it has reproducibility.
In addition, it can be used in a wide range of 30%RH to 100%RH, and while the reaction rate according to each humidity is very fast, it has high reproducibility with little errors. The measured value is very stable over time and can be used for a long period of time.

Description

Chitosan-CARBON NANOTUBE CORE-SHELL NANOHYBRID BASED HUMIDITY SENSOR}

The present invention relates to a method of manufacturing a chitosan-multi-walled carbon nanotube humidity sensor, a chitosan-a nanohybrid including a multi-walled carbon nanotube, and a humidity sensor including the same.

In general, a sensor refers to an element with a function of detecting/detecting or measuring various types of physical quantities such as temperature, pressure, sound, and light, and transmitting them as signals, or a measuring instrument using such elements, especially water vapor in the air. A sensor that detects / detects is called a humidity sensor. These humidity sensors are manufactured in a variety of structures, and a structure that uses a thin film that detects moisture and changes electrical conductivity when the thin film is exposed to moisture is mainly used. In this case, a polymer thin film such as polyimide may be used as a moisture-sensitive film, which is recently used as a material to replace the existing thin film. However, since it is difficult to obtain electrical properties of a polymer thin film by itself, a polymer thin film is formed on another thin film and the electrical properties are changed by deformation of the polymer thin film.

Humidity sensors work on two main principles of operation: capacitive and resistive sensing methods. Capacitive sensors generally require very high resistance and high electrical energy, which makes it difficult to mass-produce. However, since the electrical resistance sensor has a small error, it is easy to produce and has the advantage of being able to make accurate measurements.

In general, a resistive humidity sensor is a device that measures relative humidity by converting humidity into an electric quantity, and a resistive humidity sensor is a device that measures the relative humidity by placing it in the gas to be measured, and depending on the relative humidity of the place, water vapor absorbs and desorbs from the film surface and the resistance value changes. To measure. Resistance sensing type humidity sensors require special electrodes with thermal and chemical safety.

Carbon nanotube (CNT) is a type of carbon allotrope in which carbons are bonded in a hexagonal shape to form a cylindrical tube structure, and is referred to as a nanotube because it has a tube shape as small as several nm in diameter. These carbon nanotubes are light because they are hollow, and are attracting attention as a new material due to their tensile strength up to 100 times higher than that of steel of the same thickness, and their physical properties that bend up to 90° without damage. In addition, it has high thermal conductivity and electrical conductivity, and shows the characteristics of conductors and semiconductors depending on the angle at which the carbon layer is wound. In addition, carbon nanotubes are also classified into single walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) according to the number of walls. Recently, carbon nanotubes (hereinafter, also abbreviated as CNTs) are a powerful material for nanotechnology, and the possibility of application in a wide range of fields is being investigated.

The humidity sensor based on this multi-walled carbon nanotube (MWCNT) shows advantages of low cost, simple structure, small size, and high electrical conductivity compared to other types of humidity sensors. However, according to the high change in relative humidity, the surface hydrophilicity was low and the resistance change was small, resulting in inefficient sensitivity. Therefore, it is required to develop a desirable humidity sensor with good sensitivity and acceptable response time.

Chitosan is a biocompatible, biodegradable, non-toxic, natural biopolymer. It is obtained from chitin, the second most abundant natural polymer on Earth, and is a linear, partially acetylated (1-4)-2-amino-2-deoxy-β-D-glucan polymer. There have been studies for use in various fields such as separation membranes, artificial skin, bone substitutes, and water treatment. Chitosan has excellent film forming ability, high water permeability, excellent adhesion and sensitivity to chemical modification, and provides a convenient polymeric scaffold for enzyme fixation. Chitosan is successfully used as an immobilization matrix for biosensors and biocatalysts (Huang, H. et al., 2002. Anal. Biochem. 308, 141-151; Guerente, LC et al., 2005. Electrochem. Acta 50, and 2865-2877). However, because chitosan has low conductivity, there are many difficulties in manufacturing an electrochemical biosensor.

Korean Patent Registration Publication 10-0987375 Korean Patent Registration Publication 10-1242391

Under this background, the present inventors have high sensitivity and stability, including chitosan (CS) coated MWCNT (CS-MWCNT) nanohybrid fiber having a high electrical conductivity and hydrophilic surface as an electrical resistance sensor material for humidity detection. The humidity sensor of was completed.

An object of the present invention is to provide a method of manufacturing a humidity sensor in which a chitosan-multi-walled carbon nanotube nanohybrid is fixed to an electrode.

An object of the present invention is to provide a humidity sensor according to the manufacturing method.

An object of the present invention is a multi-walled carbon nanotube having a diameter of 20 to 30 nm and a length of 10 to 30 μm; And a chitosan-multi-walled carbon nanotube-fixed electrode comprising chitosan having a deacetylation degree of 75 to 85% and a molecular weight of 50,000 to 190,000 Daltons.

The present invention comprises the steps of (a) dissolving chitosan in an acidic solution to prepare a chitosan solution;

(b) homogenizing the multi-walled carbon nanotubes in the chitosan solution;

(c) neutralizing the acidic chitosan-multi-walled carbon nanotube solution prepared in (b) and dialysis to prepare a chitosan-multi-walled carbon nanotube solution; And

(d) adding the chitosan-multi-walled carbon nanotube solution prepared in (c) dropwise to the electrode and drying to fix the chitosan-multi-walled carbon nanotube nanohybrid to the electrode;

It provides a humidity sensor manufacturing method comprising a.

The humidity sensor according to the present invention is economical because it can send sufficient current even with a very small voltage due to low resistance, that is, high conductivity compared to existing humidity sensors, and has high sensitivity, stability and constant stability even at different voltages, frequencies, and temperatures. It has an excellent advantage in that it has reproducibility.

In addition, it can be used in a wide range of 30% RH to 100% RH, and while the reaction rate according to each humidity is very fast, it has high reproducibility with little error. The measured value is very stable over time and can be used for a long period of time.

The method for manufacturing a humidity sensor according to the present invention includes the step of (a) dissolving chitosan in an acidic solvent to prepare a chitosan solution.

In the present invention, the term chitosan (CS) refers to a polymer compound obtained by deacetylating chitin. Preferably, chitosan according to the present invention has a degree of deacetylation of 75 to 85%, and a molecular weight of 50,000 to 190,000 Daltons, but is not limited thereto as long as it is within a range capable of achieving the object of the present invention. Such chitosan may be purchased and used commercially, or may be prepared and used directly.

In the present invention, the acidic solution may be at least one selected from the group consisting of an aqueous acetic acid solution, an aqueous formic acid solution, trifluoracetic acid (TFA), hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid. Preferably, it is an aqueous acetic acid solution. In the present invention, a chitosan solution is provided by dissolving chitosan in an acidic solution.

The method of manufacturing a humidity sensor according to the present invention includes the step of (b) homogenizing the multi-walled carbon nanotubes in the chitosan solution.

In the present invention, the term carbon nanotube is a carbon allotrope, which is a substance in which one carbon is bonded to another carbon atom in a hexagonal honeycomb pattern to form a tube, and refers to a carbon allotrope having a very small area at the level of nanometers in diameter of the tube. .

In addition, in the present invention, the term multi-walled carbon nanotube (MWCNT) refers to a carbon allotrope in which a tube constituting the carbon nanotube is composed of two or more walls. Preferably, the multi-walled carbon nanotubes according to the present invention have a diameter of 20 to 30 nm and a length of 10 to 30 μm.

In the present invention, the chitosan-multi-walled carbon nanotube nanohybrid preferably contains 25 to 90% by weight of carbon nanotubes based on the total weight. If the carbon nanotube content is less than this, the electrical conductivity of the nanohybrid is low, and thus it is not suitable for use in a humidity sensor, and if it is more than this, the mechanical strength of the nanohybrid may be weakened. The chitosan-multi-walled carbon nanotube according to the present invention may be formed in a form in which chitosan surrounds the multi-walled carbon nanotube, that is, the multi-walled carbon nanotube is a core and the chitosan surrounds it.

In the present invention, homogenizing the multi-walled carbon nanotubes in a chitosan solution is to perform mechanical stirring or ultrasonic treatment, and this may be performed according to a conventional method using an apparatus known in the art. It is preferably homogenized using a homogenizer. In the present invention, a chitosan-multi-walled carbon nanotube solution is provided by homogenizing the multi-walled carbon nanotubes in a chitosan solution.

The method for manufacturing a humidity sensor according to the present invention comprises the steps of (c) neutralizing the acidic chitosan-multi-walled carbon nanotube solution prepared in (b) and dialysis to prepare a chitosan-multi-walled carbon nanotube solution.

In the present invention, the neutralization in step (c) may be neutralization by treating one or more solutions selected from the group consisting of a basic solution, preferably, ammonia solution, sodium hydroxide solution, potassium hydroxide and calcium hydroxide. More preferably, it may be neutralized by treating an ammonia solution.

Dialysis in the present invention may be performed on the basis of a molecular weight of 10,000 to 15,000 Da, preferably a molecular weight of 12,000 to 14,000 Da.

In the present invention, an acidic chitosan-multi-walled carbon nanotube solution is neutralized and neutralized by dialysis, and a solution containing chitosan-multi-walled carbon nanotubes within a certain molecular weight range is provided.

The method of manufacturing a humidity sensor according to the present invention comprises the steps of (d) adding the chitosan-multi-walled carbon nanotube solution prepared in (c) dropwise to the electrode and drying the chitosan-multi-walled carbon nanotube nanohybrid to the electrode. Includes.

In the present invention, the electrode includes all electrodes to which the chitosan-multi-walled carbon nanotube nanohybrid can be coated. The electrode is preferably selected from the group consisting of iron, gold, silver, copper, platinum, titanium, aluminum and palladium, and particularly preferably gold.

The concentration of the chitosan-multi-walled carbon nanotube solution in step (d) is 1 mg/ml to 10 mg/ml, preferably 5 to 7 mg/ml, such as about 6 mg/ml. In addition, in the step of dropwise adding the solution to the electrode, 1 μl to 20 μl amount per time, preferably 5 to 15 μl, such as about 10 μl of chitosan-multi-walled carbon nanotube solution is added dropwise on the electrode to 1 to 6 times. , Preferably, it can be coated about 3 times. Preferably, a chitosan-multi-walled carbon nanotube solution in an amount of 10 μl per time may be added dropwise onto the electrode, and coating may be performed three times.

In the present invention, prior to the step (d), the electrode is _{immersed in an HCl/H 2} O ₂ mixture for 5 to 60 seconds and dried at 40 to 80° C. may be further included. Preferably, it may be soaked for 10 seconds and dried at 60°C. Gold particles used as electrodes may be cleaned through such a process.

The dropwise addition in step (d) is according to a method of immobilizing the metal particles of a conventional chitosan-multi-walled carbon nanotube solution, and the metal particles may be coated by dropwise addition and drying.

In addition, a chitosan-multi-walled carbon nanotube solution may be added dropwise to the electrode and dried to form a chitosan-multi-walled carbon nanotube membrane on the electrode.

The present invention provides a humidity sensor manufactured by the above method.

In the present invention, the humidity sensor may be a capacitive humidity sensor or an electrical resistive humidity sensor. Preferably, the humidity sensor according to the present invention is an electrical resistance humidity sensor.

The electrical resistance humidity sensor according to the present invention is easy to use as a humidity sensor in a wide range of conditions due to excellent stability while exhibiting excellent detection capability.

The present invention is a multi-walled carbon nanotubes having a diameter of 20 to 30 nm and a length of 10 to 30 μm; And

It provides a humidity sensor including a chitosan-multi-walled carbon nanotube-fixed electrode comprising chitosan having a deacetylation degree of 75 to 85% and a molecular weight of 50,000 to 190,000 Daltons.

The humidity sensor according to the present invention may be one using chitosan-multi-walled carbon nanotubes manufactured through the above manufacturing method including the above configuration. As previously mentioned, the chitosan-multi-walled carbon nanotube may be formed in a form in which chitosan surrounds the multi-walled carbon nanotube, that is, the multi-walled carbon nanotube is a core and the chitosan surrounds it.

In the present invention, the chitosan-multi-walled carbon nanotube of the humidity sensor may have a molecular weight of 10,000 to 15,000 Da. Chitosan-multi-walled carbon nanotubes have two stages corresponding to the first stage of loss of CS surrounding the surface of MWCNTs at about 200 to 350°C, and the second stage of decomposition of MWCNTs at 350 to 600°C. It can have a pattern with weight loss. In addition, according to the analysis of the FT-IR spectrum, chitosan and multi-walled carbon nanotubes have characteristics that include all of the characteristics of the FT-IR spectrum.

The humidity sensor may measure a change in electrical conductivity by depositing an electrode on an upper surface of a substrate to form a pattern in the shape of an electrode, and generating an electron transfer reaction according to an amount of humidity (moisture). Preferably, it may have a structure of a conventional commercial humidity sensor as shown in (b) of FIG. 1.

The substrate may be made of a conventional substrate layer such as silicon or aluminum, and an electrode is positioned on the substrate layer. These electrodes are fixed by coating chitosan-multi-walled carbon nanotubes.

That is, the humidity sensor according to the present invention comprises a substrate;

An electrode part positioned on an upper end of the substrate part;

It is located on the electrode portion and provides a humidity sensor including a membrane made of chitosan-multi-walled carbon nanotubes.

The humidity sensor includes a substrate portion positioned at the bottom, an electrode portion positioned on an upper surface of the substrate portion and having two electrodes facing each other, and a membrane positioned above the electrode portion, and made of chitosan-multi-walled carbon nanotubes. Characterized in that.

The electrode unit 100 is composed of two electrodes 100 facing each other, the electrodes being made of an electrode having a plurality of branches, and the branches of the two electrodes are alternately spaced apart from each other.

To explain this in detail, it is as shown in FIG. 8.

The humidity sensor 10 of FIG. 8 includes an electrode portion 100, a membrane 101, and a substrate portion 102.

The substrate portion 102 is positioned at the bottom of the humidity sensor and may be made of silicon, aluminum, or the like. The electrode part 100 is provided on the upper surface of the substrate part 102.

The membrane 101 is for measuring humidity, and includes chitosan-multi-walled carbon nanotubes. The bottom surface of the membrane 101 is made to be coupled to the electrode. The bottom surface of the membrane 101 is in contact with the electrode part 100.

The electrode unit 100 is positioned between the upper end of the substrate unit 102 and the bottom surface of the membrane 101. The electrode unit 100 further includes a sheet (bond pad) 104 for connecting to the impedance analyzer 103 from both sides of the bottom surface of the membrane 101. The electrode of the electrode unit 100 may be at least one selected from the group consisting of iron, gold, silver, copper, platinum, titanium, aluminum, and palladium. In some cases, a portion of the electrode portion 100 on the bottom surface of the membrane 101 may be formed of an electrode array.

The humidity sensor according to the present invention is economical because it can send sufficient current even with a very small voltage due to low resistance, that is, high conductivity compared to existing humidity sensors, and has high sensitivity, stability and constant stability even at different voltages, frequencies, and temperatures. It has an excellent advantage in that it has reproducibility.

In addition, it can be used in a wide range of 30%RH to 100%RH, and while the reaction rate according to each humidity is very fast, it has high reproducibility with little errors. The measured value is very stable over time and can be used for a long period of time.

1 is a SEM and TEM image of the nanohybrid prepared in Example 1 of the present invention, (A) is a schematic diagram of a CS-shell/MWCNT-core nanohybrid structure, SEM and TEM images, (B) is a commercial alumina A photograph of the base humidity sensor electrode, (C) shows a photograph of a humidity sensor electrode coated by a CS-MWCNT nanohybrid and an SEM image of an electrode interconnected by a CS-MWCNT nanohybrid.
2 is a thermogravimetric analysis diagram, FT-IR spectrum of the nanohybrid prepared in Example 1 of the present invention. Specifically, (A) is a TGA thermogravimetric analysis diagram of CS, MWCNT, and CS-MWCNT, and (B) is an FT-IT spectrum of CS, MWCNT, and CS-MWCNT50.
3 is a graph showing the relative humidity versus resistance curves of nanohybrids having different MWCNT contents prepared in Example 1 of the present invention. Specifically, (A) is the relative humidity versus resistance curve when the MWCNT content is 0, 25, 50, 75, 90%, respectively, and (B) is the number of coatings (3 to 10 times) of the CS-MWCNT25-coated sensor. Is the relative humidity versus resistance curve.
Figure 4 shows the FE-SEM image and EDS spectrum of the gold electrode of the humidity sensor prepared in Example 1 of the present invention. (A) is the gold electrode before the CS-MWCNT nanohybrid is fixed, and (B) is the gold electrode to which the CS-MWCNT nanohybrid is fixed.
5 shows (A) different voltages of 0.1 V, 0.5 V, 1.0 V, 1.25 V, (B) different frequencies of 0.1 to 100 kHZ, (C) CS- at different temperatures of 10° C., 25° C., 40° C. It shows the relative humidity versus resistance curve of the MWCNT25 sensor.
6 shows the (A) humidity hysteresis curve and (B) dynamic transient response of the CS-MWCNT25 sensor when the humidity changes from 30% to 100%RH at 25°C.
7 shows the long-term stability at 25° C., 50%, 70%, and 90% RH of the CS-MWCNT25 humidity sensor.
8 is a diagram for explaining a humidity sensor according to the present invention.

Hereinafter, the present invention will be described in more detail through examples. However, these examples are for illustrative purposes only, and the scope of the present invention is not limited to these examples.

Example 1. Fabrication of core-shell chitosan-multi-walled carbon nanotube humidity sensor

Example 1-1. material

Multi-walled carbon nanotubes (hereinafter referred to as MWCNT,> 95%, 20-30 nm outer diameter, 10-30 μm length) and chitosan (CS) (low molecular weight, degree of deacetylation 75-85%, 50,000-190,000 Da) Was purchased from EM-Power (Changwon, Korea) and Sigma-Aldrich (St. Louis, MA, USA), respectively. Prior to use, for 1 day, pristiine MWCNT was refluxed in 5 N HCl solution and washed with deionized water. _{All chemicals, including glacial acetic acid, NH 4} OH, and organic solvents, purchased from Sigma-Aldrich, were of analytical grade and were used without further purification.

Example 1-2. Fabrication of core-shell structured chitosan-multi-walled carbon nanotube nanohybrids

A chitosan solution was prepared by dissolving 750 (500, 250) mg chitosan in 100 ml of acetic acid (1 v/v%). Then, 250 (500, 750) mg MWCNT was homogenized in chitosan solution using a homogenizer (NanoDeBee 45-3, Bee International, Massachusetts state/South Easton, USA). After dropping 1 N ammonia solution to neutralize the acidic CS-MWCNT solution slowly, a molecular weight of 12,000 to 14,000 Da (Spectrum Laboratories, Savannah, GA, USA) is used with a membrane tube to remove possible small molecules including inorganic by-products. Dialysis was performed for 3 days against deionized water at the cutoff.

Each MWCNT molecule is a core-shell structure wrapped by chitosan molecules (wrapped) CS-MWCNT complex was prepared in the composition ratio as shown in Table 1:

Example 1-3. Fabrication of humidity sensor containing chitosan-multi-walled carbon nanotube nanohybrid

The surface of the gold electrode was first washed with ultrasonic waves for 30 seconds in deionized water. Then, the gold electrode _{was immersed in a mixture of HCl/H 2} O ₂ (v/v = 1/1) for 10 seconds, rinsed with distilled water, and dried at 60°C. 10 μl of the CS-MWCNT solution was added dropwise to the washed gold electrode and dried at 60° C. to fix the CS-MWCNT nanohybrid on the surface of the gold electrode. This process was repeated several times. The resulting CS-MWCNT-coated electrode was rinsed with water and absolute ethanol to remove as small molecules as possible, including inorganic by-products.

Example 1-4. Shape analysis of core-shell chitosan-multi-walled carbon nanotube humidity sensor

Morphological images of CS-MWCNT nanohybrid samples were obtained by high-resolution transmission electron microscopy (HR-TEM; JEOL Ltd, JEM 3010, Japan) and field emission scanning electron microscopy (FE-SEM; TESCAN, MIRA LMH microscopy, Tescan, Czech Republic). ). SEM studies were performed using samples sputter-coated with a 10 nm Pt layer prior to analysis.

The morphological images of chitosan-multi-walled carbon nanotubes prepared according to Examples 1-2 and 1-3 are shown in FIG. 1.

As can be seen in (A) of FIG. 1, the CS-MWCNT nanohybrid used as a resistive humidity sensor has an MWCNT-core/CS-shell structure prepared by pH-control. In the case of CS-MWCNT25, the average thickness of the CS layer wrapped around individual MWCNT molecules was measured as 5.08 ± 0.136 nm in the TEM image. In addition, the thickness of the CS layer wrapped in CS-MWCNT50 and CS-MWCNT75 was 3.22 ± 0.116 and 1.22 ± 0.102 nm, respectively.

Figure 1 (B) shows a commercial humidity sensor based on an alumina substrate patterned by photolithography using a gold clad laminate (10 μm thickness) in which an electrical resistance microchip having a rectangular shape of 10.0 mmХ5.0 mm is used. .

The CS-MWCNT composite moisture-sensitive film was physically adhered to the alumina substrate by hydrogen bonding, as shown in Fig. 1(C). SEM images showed that both the positive and negative electrodes can be successfully fixed by the CS-MWCNT nanohybrid, and it was confirmed that the electrodes were fixed and interconnected.

Example 2. Characterization of core-shell chitosan-multi-walled carbon nanotube humidity sensor

Each sample of chitosan, MWCNT and CS-MWCNT was analyzed using a thermogravimetric analyzer (TGA; SCINCO, TGA N-1500, Korea) and a Fourier transform infrared spectrometer (FTIR Perkin-Elmer, spectrum BXII FT-IR spectrometer, USA). Quantitative analysis and qualitative analysis were performed.

For TGA measurements, samples (5±0.1 mg) were heated at a rate of 10° C./min at a temperature ranging from 25 to 900° C. under air. And at 4cm ^-1 resolution using 16 scans were recorded as KBr pellets FTIR spectrum condition in a spectrum range of 400 to 4000cm ^-1.

The results of TGA are shown in Fig. 2(A), and the results of FT-IR are shown in Fig. 2(B).

Figure 2 (A) shows the thermal decomposition pattern of MWCNT, CS and CS-MWCNT50. The MWCNT samples do not experience significant mass loss before the vicinity of 600° C., but show a typical pyrolysis pattern with rapid weight loss in the temperature range of 600 to 900° C. This typical weight loss pattern is due to the initial decomposition of the disordered or amorphous carbon on the surface of the MWCNT and the secondary combustion of the crystallized carbon body. Pure chitosan proceeded in two stages in which polysaccharide chains were decomposed into glucosamine units in the range of 200 to 300°C, and oxidative decomposition of glucosamine units occurred at 300 to 650°C. The CS-MWCNT nanohybrid sample has a weight of two steps corresponding to the first step caused by the loss of CS surrounding the surface of the MWCNT at about 200 to 350 °C, and the second step in which decomposition of the MWCNT occurs at 350 to 600 °C. Show losses clearly.

2B shows a comparison result of the spectrum of MWCNT and CS used as precursors in the range of 400 to 4000 cm ^{-1 and the FT-IR spectrum of the CS-MWCNT nanohybrid.} MWCNT showed characteristic peaks at ^{1560 and 1478 cm -1} for the aromatic ring of MWCNT. The spectrum of CS has major bands for OH and C=O stretching vibrations at ^{3460 and 1690 cm -1.} These characteristic peaks related to the two components were clearly observed within the CS-MWCNT spectrum, for example about 3456 cm ^{-1 for the OH stretch of the CS portion and about 1658 cm -1} for the C=O stretch, and A peak was observed at ^{about 1575 cm -1} for the aromatic ring of the MWCNT moiety.

Example 3. Linearity analysis of core-shell chitosan-multi-walled carbon nanotube humidity sensor

Relative humidity (RH) was measured at various temperatures using a humidity and temperature controller (Jeio Tech, model TM-NFM-L, Korea). Resistance was measured with an LCR meter (EDC-1635 model) and impedance was measured with an impedance analyzer (HP 4194).

The sensitivity S of the CS-MWCNT sensor film to humidity was calculated from the equation:

S = △R/R ₀ /△(% RH) (1)

In the above equation, ΔR/R ₀ = (R _RH -R ₀ )/R ₀ is the resistance change, R ₀ is the initial resistance value of the device, and R _RH is the steady state when exposed to different RH values. Resistance.

The results are shown in Fig. 3 and Table 2.

3A shows the resistance of sensor materials (CS and CS-MWCNT25 to 90) with different MWCNT concentrations (0 to 90) as a function of humidity. The curve of the pure CS film shows high nonlinearity and negative slope (dR/dRH <0) with increasing RH. The resistance change of the pure CS humidity sensor was very large in the different RH range of 30-100%. For example, there was a sharp decrease from 70 to 30 MΩ. Unlike pure CS, the curve of the CS-MWCNT humidity sensor showed a nonlinear function of RH and a positive slope (dR/dRH> 0) at extremely low resistance values compared to pure CS (about 12 to 18 Ω).

3A and Table 2 clearly show that the CS-MWCNT25 nanohybrid film has the highest sensitivity and linearity among the tested sensor materials.

The resistance value of the CS-MWCNT25 film as a function of RH according to the number of coatings (3 to 10 times) was tested and shown in Fig. 3(B) and Table 2.

As can be seen in (B) and Table 2 of FIG. 3, the smaller the number of coatings, the higher the sensitivity was. While the conventional well-known resistive humidity sensor exhibited very low sensitivity due to its very high resistance, the sensor material CS-MWCNT25 showed very good performance in the entire RH range of 30 to 100%. The improvement of CS-MWCNT25 in moisture-sensing performance may be due to an increase in the surface area and functional groups of water molecules on the MWCNT surface by coating CS molecules on individual MWCNT molecules in the MWCNT core/CS shell structure.

Example 4. Analysis of electrode surface shape of core-shell chitosan-multi-walled carbon nanotube humidity sensor

SEM analysis of the gold electrode surface of the humidity sensor was performed before and after coating the CS-MWCNT nanohybrid. The characteristics of the electrodes with and without CS-MWCNT were confirmed through qualitative analysis using energy dispersive X-ray spectroscopy (EDS: BRUKER, Quantax, USA). EDS analysis was performed under conditions of 125 eV and SDD type resolution.

The results are shown in FIG. 4.

4A shows a blank gold electrode surface showing a smooth shape of gold particles (about 1 to 2 μm) having a very unique specific surface area.

4B shows that after coating the CS-MWCNT nanohybrid, the gold electrode surface was clearly roughened due to the fixation of the CS-MWCNT nanohybrid fibers interconnected at high density. The high-density CS-MWCNT networking and strong adhesion to the gold electrode surface show that electrical information can be effectively transferred to the gold electrode when a small change in electrical resistance occurs in the CS-MWCNT nanohybrid fiber. Moreover, the SEM image of the gold electrode coated with CS-MWCNT showed a three-dimensional shape similar to that before coating, showing that a large specific surface area is still required for moisture adsorption. CS molecules, which not only connect all MWCNTs, but also strongly attach MWCNTs to the gold electrode surface, can accelerate the adsorption process of water molecules due to the hydrophilicity of CS.

The EDS spectrum of the gold electrode without CS-MWCNT mainly shows Au peak, but the spectrum of the gold electrode with CS-MWCNT shows various peaks related to C, O, N and Au due to the additional presence of CS and CNT. The presence of the CS-MWCNT nanohybrid was confirmed.

Example 5. Analysis of resistance change according to low pressure, frequency, and temperature of a core-shell chitosan-multi-walled carbon nanotube humidity sensor

5A shows a graph of the resistance versus RH for the humidity sensor as a function of the voltage difference at 1 kHz, and room temperature (25° C.). In addition, the change in resistance due to humidity (RH) was found to be about 12 to 19 Ω as in the previous results. There was no difference with respect to the resistance of the humidity sensor with different voltages (0.1 V, 0.5 V, 1.0 V and 1.25 V).

Another important factor that determines the response of the polymer humidity sensor is the test frequency. In Fig. 5B, the different test frequencies do not show a difference in the impedance of the CS-MWCNT25 nanohybrid at 1.0 V and all humidity levels at room temperature (25° C.). This means that the nanohybrid is independent of the test voltage and frequency in the range of RH 30% to 100%. This result indicates that the CS-MWCNT humidity sensor is not affected by voltage and frequency. Therefore, this sensor can be used in a wide range regardless of these variable factors.

The detection curves of the CS-MWCNT humidity sensor were investigated at different temperatures (10° C., 25° C., and 40° C.) of 1.0 V and 1 kHz, and the results are shown in FIG. 5(C).

Temperature generally affects the humidity response of polymer-based humidity sensors. The CS-MWCNT nanohybrid showed that the impedance decreased as the temperature increased, which was the same for the CS-based humidity sensor. This characteristic, which has a different resistance depending on temperature, is one of the disadvantages applied to the electric resistance humidity sensor. However, the temperature coefficient of CS-MWCNT25 showed a low temperature dependence of 0.187%RH/℃ as shown in Table 3, and the influence of temperature was negligible within the error range. Therefore, the CS-MWCNT25 nanohybrid-based humidity sensor can be widely used regardless of temperature.

Example 6. Analysis of hysteresis and dynamic transient response of a core-shell chitosan-multi-walled carbon nanotube humidity sensor

It was found that the impedance of the CS-MWCNT25 sensor increases as the relative humidity (RH%) increases. When the humidity sensing material was measured at an increased or decreased RH, a hysteresis effort was observed.

In Figure 6 (A). The humidity sensing measurement was repeated 5 times from 30% to 100% every 10%. The CS-MWCNT humidity sensor showed excellent humidity sensing characteristics such as fast response, high sensitivity and good linearity. The adsorption and desorption process of the CS-MWCNT25 sensor is very close, and as shown in Table 3 above, the maximum humidity hysteresis is less than 0.300 ± 0.001%.

Response and recovery behavior is one of the most important features for evaluating the performance of a humidity sensor. The time it took for the sensor to achieve 90% of the total impedance change was defined as the response and recovery time. 6B shows the response and recovery characteristics of the CS-MWCNT humidity sensor between 30% and 100% RH at 25°C. If the RH is increased from 30% to 100% RH, the response time of the CS-MWCNT25 humidity sensor is less than 30 seconds. When the RH decreases from 100% to 30%, the recovery time is about 40 seconds.

As shown in FIG. 6, the CS-MWCNT25 humidity sensor exhibits very good sensing characteristics such as ultra-fast response time, good stability and good linearity.

Example 7. Long-term stability analysis of core-shell chitosan-multi-walled carbon nanotube humidity sensor

When the humidity sensor has been used for a long time, the sensing characteristics of the humidity sensor are markedly deteriorated. Stability is an important parameter of humidity sensing properties. To test the stability, the sensor was held at 50%, 70%, 90% RH and 25° C. for at least 2 months, and then the resistance shift was measured at various RH levels.

The results are shown in FIG. 7.

As can be seen in Fig. 7, the resistance change versus time curve flattened across all RH ranges. No significant fluctuations were observed and the data showed good consistency, directly confirming the good stability of the CS-MWCNT25 humidity sensor.

Based on the above results, the humidity sensor according to the present invention can be used in a wide range of conditions by showing high sensitivity and stability even at different voltages, frequencies, and temperatures.

The performance of the humidity sensor according to the present invention can be summarized as follows.

From the above description, those skilled in the art to which the present invention pertains will understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential features thereof. In this regard, it should be understood that the embodiments described above are illustrative in all respects and not limiting. The scope of the present invention should be construed that all changes or modifications derived from the meaning and scope of the claims to be described later rather than the above detailed description and equivalent concepts are included in the scope of the present invention.

Claims (11)

(a) dissolving chitosan in an acidic solution to prepare a chitosan solution;
(b) homogenizing the multi-walled carbon nanotubes in the chitosan solution;
(c) neutralizing the acidic chitosan-multi-walled carbon nanotube solution prepared in (b) and dialysis to prepare a chitosan-multi-walled carbon nanotube solution; And
(d) adding the chitosan-multi-walled carbon nanotube solution prepared in (c) dropwise to the electrode and drying to fix the chitosan-multi-walled carbon nanotube nanohybrid to the electrode; Including,
The chitosan-multi-walled carbon nanotube nanohybrid of step (d) is that the carbon nanotube core has a core-shell structure surrounded by a chitosan shell. The method of claim 1,
In the step (b), the weight ratio of chitosan and multi-walled carbon nanotubes is 10:90 to 75:25, a method for manufacturing a humidity sensor. The method of claim 1,
The multi-walled carbon nanotube has a diameter of 20 to 30 nm, a length of 10 to 30 μm,
The chitosan has a degree of deacetylation of 75 to 85%, and a molecular weight of 50,000 to 190,000 Daltons, a humidity sensor manufacturing method. The method of claim 1,
In the step (a), the acidic solution is any one or more solvents selected from the group consisting of an aqueous acetic acid solution, an aqueous formic acid solution, trifluoracetic acid (TFA), hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid. The method of claim 1,
The neutralization in step (c),
To neutralize by treating any one or more solutions selected from the group consisting of ammonia solution, sodium hydroxide solution, potassium hydroxide and calcium hydroxide. The method of claim 1,
The electrode is an electrode consisting of at least one selected from the group consisting of iron, gold, silver, copper, platinum, titanium, aluminum and palladium, a method for manufacturing a humidity sensor. The method of claim 1,
Before the step (d), the electrode is _{immersed in an HCl/H 2} O ₂ mixture for 5 to 60 seconds and dried at 40 to 80°C. A humidity sensor manufactured according to any one of claims 1 to 7. The method of claim 8,
The humidity sensor is an electrical resistance sensor, a humidity sensor. A substrate portion;
An electrode part positioned on an upper end of the substrate part;
A membrane made of chitosan-multi-walled carbon nanotube nanohybrids positioned on the electrode part and fixed to the surface of the electrode part by chemical bonding; As a humidity sensor comprising a,
The chitosan-multi-walled carbon nanotube nanohybrid has a core-shell type in which a multi-walled carbon nanotube core is surrounded by a chitosan shell,
The chitosan is bonded to the surface of the electrode part to fix the chitosan-multi-walled carbon nanotube nanohybrid. The method of claim 10,
Chitosan-multi-walled carbon nanotube nanohybrids are multi-walled carbon nanotubes having a diameter of 20 to 30 nm and a length of 10 to 30 μm; And chitosan having a deacetylation degree of 75 to 85% and a molecular weight of 50,000 to 190,000 Daltons.

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