CN113390748A - Humidity sensor based on quartz crystal microbalance and preparation method - Google Patents
Humidity sensor based on quartz crystal microbalance and preparation method Download PDFInfo
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- 238000003380 quartz crystal microbalance Methods 0.000 title claims abstract description 80
- 238000002360 preparation method Methods 0.000 title claims abstract description 15
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- 239000000463 material Substances 0.000 claims abstract description 16
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- 229910052939 potassium sulfate Inorganic materials 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N5/00—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid
- G01N5/02—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid by absorbing or adsorbing components of a material and determining change of weight of the adsorbent, e.g. determining moisture content
- G01N5/025—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid by absorbing or adsorbing components of a material and determining change of weight of the adsorbent, e.g. determining moisture content for determining moisture content
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
- B05D3/002—Pretreatement
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D5/00—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
- B05D7/24—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials for applying particular liquids or other fluent materials
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/02—Analysing fluids
- G01N29/022—Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D2518/00—Other type of polymers
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Abstract
The invention discloses a humidity sensor based on a quartz crystal microbalance and a preparation method thereof. The preparation method comprises the specific steps of cleaning a QCM transducer, mixing an ethanol/water mixed solvent, 1.5 wt% of concentrated sulfuric acid and rice straw powder in a reaction kettle, stirring for 3 hours at 180 ℃, and then washing and drying to obtain lignin; then uniformly dispersing lignin in ethanol with the help of ultrasound to obtain uniform sensitive material dispersion liquid; and then coating the surface of an electrode of a quartz crystal microbalance, and drying for 6-8 hours to prepare the humidity sensor coated with the lignin. The humidity sensor based on the quartz crystal microbalance not only has the advantages of high sensitivity, quick response/recovery time, good repeatability, low wet retardation and the like, but also has the advantages of simple manufacturing method, low cost, degradable sensitive materials and the like.
Description
Technical Field
The invention belongs to the technical field of humidity sensors, and particularly relates to a Quartz Crystal Microbalance (QCM) humidity sensor and a preparation method thereof.
Background
Effective monitoring and control of humidity levels is a prerequisite for normal production in aerospace, power generation and power conversion, warehouse storage, industrial and agricultural production, and other fields. Therefore, higher demands are made on the humidity sensor. Therefore, the humidity sensor becomes a research hotspot at present, countries around the world participate in the research of the humidity sensor at a time, and the main research direction is to develop a novel humidity sensitive element.
Quartz Crystal Microbalance (QCM) is a novel quality type transducer, has the advantages of simple operation, high sensitivity, low cost, detection precision reaching nanogram magnitude and the like, and is becoming a research hotspot of gas-humidity sensitive sensors.
When the QCM is used as a gas humidity sensor, the mass change caused by the adsorption of gas molecules by a humidity sensitive film on the surface of an electrode of the QCM is mainly utilized and then converted into the resonance frequency change of the QCM for humidity measurement. The resonant frequency change can be calculated using the following equation:
wherein Δ m, Δ f represent mass change (ng) and frequency change (Hz), respectively; f. of0And A represents the fundamental frequency (Hz) and the effective area (cm) of the QCM2)；ρqAnd muqRespectively represent the density (. rho.) of the quartz crystalq＝2.648g.cm-3) And modulus of elasticity (. mu.)q＝2.947*1011g.cm-1.s-2)。
Humidity-sensitive materials currently used as QCM humidity sensors include various metal oxides such as ZnO, TiO2, etc., carbon materials such as graphene oxide, carbon nanotubes, fullerenes, etc., polymers such as polyvinyl alcohol, polyvinyl amide, cellulose, etc., and ordered silicon-based mesoporous materials SBA-15, metal organic frameworks, etc. However, the moisture-sensitive materials are high in price, large in environmental pollution or harmful to human bodies, and have the problems of low sensitivity, large moisture stagnation, slow response time and the like.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a humidity sensor based on a quartz crystal microbalance and a preparation method thereof, so that the humidity sensitive material has the characteristics of low price, greenness, no pollution, reproducibility, degradability and no harm to a human body, and has the advantages of simple preparation method, high sensitivity, quick response time, good repeatability and stability and the like.
In order to achieve the above object, the humidity sensor based on a quartz crystal microbalance of the present invention comprises a QCM transducer, and is characterized in that:
the electrode surface of the QCM transducer is coated with a moisture-sensitive film of lignin.
The invention also provides a preparation method of the humidity sensor based on the quartz crystal microbalance, which is characterized by comprising the following steps of:
(1) QCM energy converter is washd
Sequentially putting the QCM transducer into deionized water and absolute ethyl alcohol, ultrasonically cleaning for 1 minute, then putting the QCM transducer into a drying oven at 40-60 ℃ for drying for 2 hours, and then putting the QCM transducer into a clean container for later use;
(2) and preparing lignin
Mixing an ethanol/water mixed solvent, 1.5 wt% concentrated sulfuric acid and rice straw powder in a reaction kettle, stirring for 3 hours at 180 ℃, and then washing, filtering and drying to obtain lignin;
(3) preparing sensitive material dispersion liquid
Weighing quantitative lignin, adding into quantitative solvent, and performing ultrasonic treatment for 3-5 hr to obtain lignin with concentration of 1-4 mg/ml;
(4) coated moisture-sensitive film
And (3) horizontally placing the QCM transducer obtained in the step (1), coating the sensitive material dispersion liquid prepared in the step (3) on the surface of an electrode of the QCM transducer, drying to obtain a humidity sensitive film, preparing a humidity sensor coated with lignin, and finishing the preparation of the humidity sensor based on the quartz crystal microbalance.
The object of the invention is thus achieved.
The invention relates to a humidity sensor based on a quartz crystal microbalance and a preparation method thereof, wherein the electrode surface of a QCM transducer is coated with a humidity sensitive film of lignin. Lignin contains a large number of hydroxyl groups, and thus, in different humidity environments, lignin spontaneously adsorbs or desorbs water molecules, which causes mass change. The QCM sensor is a mass response type sensor with detection precision reaching nanogram magnitude, and can convert mass change of lignin into frequency change to be reflected, so that the invention can detect humidity. In the invention, the lignin is adopted as the moisture-sensitive material, and has the characteristics of low price, greenness, no pollution, reproducibility, degradability and no harm to human bodies. Meanwhile, the preparation method has the advantage of simplicity. According to tests, lignin is adopted as a humidity-sensitive material and coated on the surface of an electrode of the QCM transducer to form a humidity-sensitive film, and the prepared humidity sensor based on the quartz crystal microbalance has the advantages of high sensitivity, short response time, good repeatability and stability and the like.
Drawings
FIG. 1 is a flow chart of one embodiment of a method for manufacturing a humidity sensor based on a quartz crystal microbalance of the present invention;
FIG. 2 is a micro-topography of lignin;
FIG. 3 is a schematic diagram of a built-up test system for a humidity sensor based on a quartz crystal microbalance;
FIG. 4 is a graph of the dynamic response of the quartz crystal microbalance-based humidity sensor of the present invention between 11.3% RH and 97.3% RH;
FIG. 5 is a sensitivity curve of a humidity sensor of the present invention based on a quartz crystal microbalance between 11.3% RH and 97.3% RH;
FIG. 6 is a logarithmic fit curve between 11.3% RH and 97.3% RH for the quartz crystal microbalance-based humidity sensor of the present invention;
FIG. 7 is a hysteresis curve of a quartz crystal microbalance-based humidity sensor of the present invention between 11.3% RH and 97.3% RH;
FIG. 8 is a response/recovery curve of a quartz crystal microbalance-based humidity sensor of the present invention between 11.3% RH and 84.3% RH;
FIG. 9 is a graph showing the repeatability of the humidity sensor of the present invention based on a quartz crystal microbalance between 11.3% RH and 84.3% RH.
FIG. 10 is a graph of the long term stability of a humidity sensor based on a quartz crystal microbalance of the present invention.
Detailed Description
The following description of the embodiments of the present invention is provided in order to better understand the present invention for those skilled in the art with reference to the accompanying drawings. It is to be expressly noted that in the following description, a detailed description of known functions and designs will be omitted when it may obscure the subject matter of the present invention.
Lignin (Lignin) is an organic substance widely found in various herbs, woody, and vascular plants, and is the world's second largest source of biomass energy second only to cellulose. The lignin has the advantages of being renewable, degradable, free of environmental pollution and the like, and the lignin also contains rich active groups such as aromatic ring structures, aliphatic and aromatic hydroxyl groups, quinone groups and the like, and has excellent hydrophilic performance.
Thus, the invention is based on a humidity sensor for a quartz crystal microbalance in which the electrode surface of the QCM transducer is coated with a humidity sensitive film of lignin.
FIG. 1 is a flow chart of an embodiment of a method for manufacturing a humidity sensor based on a quartz crystal microbalance according to the present invention;
in this embodiment, as shown in fig. 1, the method for manufacturing a humidity sensor based on a quartz crystal microbalance of the present invention comprises the following steps:
step S1: cleaning QCM energy converter
And sequentially putting the QCM transducer into deionized water and absolute ethyl alcohol, ultrasonically cleaning for 1 minute, then putting the QCM transducer into a drying oven at the temperature of 40-60 ℃ for drying for 2 hours, and then putting the QCM transducer into a clean container for later use.
Wherein, the natural frequency of the QCM transducer can be 4MHz-40MHz, and 5MHz, 8MHz, 10MHz and 20MHz are common; metal electrodes for QCM are typically gold, silver and aluminum.
In this example, a blank (uncoated humidity sensitive membrane) QCM transducer, purchased from Zheng State original electronics, Inc., with a quartz wafer diameter of 8.7mm, electrode material of silver, electrode diameter of 5mm, and fundamental frequency of 10 MHz.
Step S2: preparation of Lignin
Mixing an ethanol/water mixed solvent, 1.5 wt% concentrated sulfuric acid and the rice straw powder in a reaction kettle, stirring for 3 hours at 180 ℃, and then washing, filtering and drying to obtain the lignin.
In this example, the mixing ratio of the ethanol/water mixed solvent was 3:1 (ethanol weight: 3, water weight: 1), and the ethanol/water mixed solvent was used for washing at a mixing ratio of 10:1 (ethanol weight: 10, water weight: 1).
Step S3: preparation of sensitive Material Dispersion
Weighing a certain amount of lignin, adding the lignin into a certain amount of solvent, and carrying out ultrasonic treatment for 3-5 hours to prepare sensitive material dispersion liquid with the concentration of 1-4 mg/ml.
In this example, 20mg of the lignin obtained in step S3 was weighed using a balance, and then 20ml of 75% ethanol solution was measured using a measuring cylinder as a solvent, and mixed and sonicated for 4 hours to obtain a sensitive material dispersion having a concentration of 1 mg/ml.
Step S4: coating moisture-sensitive films
And (4) horizontally placing the QCM transducer obtained in the step (S1), coating the sensitive material dispersion liquid prepared in the step (S3) on the surface of an electrode of the QCM transducer, drying to obtain a humidity sensitive film, and preparing the humidity sensor coated with lignin to finish the preparation of the humidity sensor based on the quartz crystal microbalance.
In this example, a micro pipette was used to apply 3 ml of the sensing material dispersion to the center of the electrode surface of the QCM transducer, and the QCM transducer was naturally dried for 10 hours to produce a lignin-coated humidity sensor having a lignin layer with a thickness of about 225.8 nm. The surface micro-topography is shown in figure 2.
Examples of the invention
In this example, as shown in fig. 3, a test system of a humidity sensor based on a quartz crystal microbalance is built, and the test system mainly comprises the humidity sensor based on the quartz crystal microbalance, a start oscillation circuit, a frequency meter, a humidity generation device and a computer.
In this example, as shown in fig. 3, the humidity generating device uses different saturated salt solutions LiCl, MgCl2, NaBr, NaCl, KCl, and K2SO4 to generate fixed relative humidity levels of 11.3% RH, 32.8% RH, 57.6% RH, 75.3% RH, 84.3% RH, and 97.3% RH. The pin of the humidity sensor based on the quartz crystal microbalance is connected into a vibration starting circuit, a frequency meter is used for recording the frequency of the humidity sensor, and a computer is directly connected with the frequency meter.
Testing of humidity sensitivity performance: the humidity sensor of the quartz crystal microbalance-based of the present invention coated with lignin, which absorbs water molecules, is placed in a responsive humidity level, the resonant circuit and frequency can be used to record its frequency value, and then the collected data is processed and plotted into a relevant humidity-sensitive performance curve using relevant plotting software in a computer.
As shown in fig. 4, the humidity sensor of the quartz crystal microbalance of the present invention responds well to the change of the humidity level between 11.3% RH and 97.3% RH. As shown in fig. 5, the frequency change of the humidity sensor based on the quartz crystal microbalance is about 2200Hz between 11.3% RH and 97.3% RH, and the sensitivity is about 25.8 Hz/% RH. FIG. 6 is a log fit curve between the humidity sensing 11.3% RH to 97.3% RH of the quartz crystal-based microbalance of the invention. Its fitting equation is y 1.56109+0.01793 x, the correlation coefficient is 0.993, showing a good logarithmic relationship. As shown in fig. 7, the humidity sensor based on the quartz crystal microbalance of the invention has a maximum hysteresis of 4.5% RH between 11.3% RH and 97.3% RH. As shown in fig. 8, the response/recovery time of the humidity sensor of the present invention based on a quartz crystal microbalance between 11.3% RH and 84.3% RH is 17/9 seconds. As shown in fig. 9, the humidity sensor based on the quartz crystal microbalance of the present invention has excellent reproducibility between 11.3% RH and 84.3% RH. As shown in fig. 10, the humidity sensor based on the quartz crystal microbalance of the present invention showed no significant fluctuation in frequency change within 25 days, showing excellent long-term stability. Therefore, by integrating the tests, the humidity sensor based on the quartz crystal microbalance can be well applied to humidity measurement, and has the advantages of high sensitivity, quick response time, good repeatability and stability and the like.
The invention adopts the following main ideas: lignin contains a large number of hydroxyl groups, so that in different humidity environments, lignin spontaneously adsorbs or desorbs water molecules, and mass changes occur. The QCM transducer is a mass response type sensor with detection precision reaching nanogram magnitude, and can convert mass change of lignin into frequency change to be reflected. So that the humidity level can be detected. The invention provides a new idea for detecting the humidity level and also expands the application field of lignin.
Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, and various changes may be made apparent to those skilled in the art as long as they are within the spirit and scope of the present invention as defined and defined by the appended claims, and all matters of the invention which utilize the inventive concepts are protected.
Claims (2)
1. A quartz crystal microbalance-based humidity sensor comprising a QCM transducer, characterized in that:
the electrode surface of the QCM transducer is coated with a moisture-sensitive film of lignin.
2. A method for preparing a humidity sensor of a quartz crystal microbalance is characterized by comprising the following steps:
(1) QCM energy converter is washd
Sequentially putting the QCM transducer into deionized water and absolute ethyl alcohol, ultrasonically cleaning for 1 minute, then putting the QCM transducer into a drying oven at 40-60 ℃ for drying for 2 hours, and then putting the QCM transducer into a clean container for later use;
(2) and preparing lignin
Mixing an ethanol/water mixed solvent, 1.5 wt% concentrated sulfuric acid and rice straw powder in a reaction kettle, stirring for 3 hours at 180 ℃, and then washing, filtering and drying to obtain lignin;
(3) preparing sensitive material dispersion liquid
Weighing quantitative lignin, adding into quantitative solvent, and performing ultrasonic treatment for 3-5 hr to obtain 1-4mg/ml sensitive material dispersion;
(4) coated moisture-sensitive film
And (3) horizontally placing the QCM transducer obtained in the step (1), coating the sensitive material dispersion liquid prepared in the step (3) on the surface of an electrode of the QCM transducer, drying to obtain a humidity sensitive film, preparing a humidity sensor coated with lignin, and finishing the preparation of the humidity sensor based on the quartz crystal microbalance.
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| CN114166681A (en) * | 2021-11-12 | 2022-03-11 | 常州大学 | QCM humidity sensor based on high polymer/inorganic composite sensitive material and preparation method thereof |
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