CN113045722A - Imino covalent organic framework polymer, preparation method and application thereof, ammonia gas sensor and preparation method thereof, and ammonia gas sensing detection method - Google Patents
Imino covalent organic framework polymer, preparation method and application thereof, ammonia gas sensor and preparation method thereof, and ammonia gas sensing detection method Download PDFInfo
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Abstract
The invention provides an imino covalent organic framework polymer-based chemiresistive ammonia gas sensor and a preparation method thereof, belonging to the technical field of gas sensors. The imino covalent organic framework polymer provided by the invention has a structure shown in a formula I. The imino covalent organic framework polymer provided by the invention has a pi electron conjugated system formed by imino bridged chain aromatic rings, and has high conjugation degree and small resistance value. Can react with NH under room temperature3The method has the advantages of obvious sensing response signal generation, high sensing response value to ammonia gas, short response time, high selectivity and stability, and great application potential in the field of high-sensitivity monitoring of ammonia gas in the environment.
Description
Technical Field
The invention relates to the technical field of gas sensors, in particular to an imino covalent organic framework polymer, a preparation method and application thereof, an ammonia gas sensor, a preparation method thereof and an ammonia gas sensing detection method.
Background
With the rapid development of modern industries, petrochemical industries and other industries, a large amount of ammonia gas is continuously discharged into the air, so that the human respiratory tract is strongly stimulated, and great harm is caused to the environment and the life safety of human beings. The chemical resistance type ammonia gas sensor is used for effectively monitoring the emission concentration of ammonia gas, and becomes a hotspot in the fields of gas sensing foundation and application research.
Gas sensors generally use certain chemical and physical signal changes of sensing materials caused by interaction between gas to be measured and sensing layer materials to monitor the concentration of the gas to be measured. For example, chinese patent CN201910842895.6 discloses a gas sensor of covalent organic framework material with a supported thin film structure, which can adsorb gas molecules to be detected into a pore channel, and change the refractive index of the covalent organic framework material, thereby generating rapid and significant color change, and realizing detection of various gases including ammonia gas.
Disclosure of Invention
In view of the above, the invention aims to provide an imino covalent organic framework polymer, a preparation method and an application thereof, an ammonia gas sensor, a preparation method thereof and an ammonia gas sensing detection method.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides an imino covalent organic framework polymer, which has a structure shown in a formula I:
in the formula I, R1Is composed of
Wherein denotes a grafting site;
R2is composed of
Wherein denotes the grafting site.
The invention provides a preparation method of the imino covalent organic framework polymer, which comprises the following steps:
mixing aromatic polyamine, aromatic polyaldehyde, scandium trifluoromethanesulfonate and a mixed organic solvent, and carrying out polymerization reaction to obtain an imino covalent organic framework polymer;
the aromatic polyamine comprises aromatic diamine or aromatic triamine; the aromatic diamine comprises p-phenylenediamine or biphenyldiamine; the aromatic triamines comprise 1,3, 5-tri (4-aminophenyl) benzene or 1,3, 5-tri (4-aminophenyl) -2,4, 6-triazine;
the aromatic polyaldehyde preferably comprises an aromatic dialdehyde or an aromatic trialdehyde; the aromatic dialdehyde comprises terephthalaldehyde, terephthaldehyde or terterphthalaldehyde; the aromatic ternary aldehyde comprises trimesic aldehyde, 1,3, 5-tri (4-aldehyde phenyl) benzene or 1,3, 5-tri (4-aldehyde phenyl) -2,4, 6-triazine.
Preferably, the molar ratio of the amino group in the aromatic polyamine to the aldehyde group in the aromatic polyaldehyde is 1: 1.
Preferably, the molar ratio of the amino group in the aromatic polyamine to scandium trifluoromethanesulfonate is 1: (0.005-0.20).
Preferably, the temperature of the polymerization reaction is room temperature, and the time is 0.5-72 h.
The invention provides an application of the imino covalent organic framework polymer in the technical scheme or the imino covalent organic framework polymer obtained by the preparation method in the technical scheme in a chemical resistance type ammonia gas sensor.
The invention provides a chemical resistance type ammonia gas sensor, which comprises a ceramic substrate metal interdigital electrode and a sensing layer attached to the surface of the ceramic substrate metal interdigital electrode;
the sensing layer is the imino covalent organic framework polymer in the technical scheme or the imino covalent organic framework polymer obtained by the preparation method in the technical scheme.
Preferably, the thickness of the imino covalent organic framework polymer sensing layer film is 20-2000 nm.
The invention provides a preparation method of the chemiresistor ammonia sensor in the technical scheme, which comprises the following steps:
placing the imino covalent organic framework polymer in a low-boiling-point solvent to perform ultrasonic dispersion treatment and centrifugal separation in sequence to obtain supernatant;
and dripping the supernatant on the surface of the ceramic substrate metal interdigital electrode and drying to obtain the chemical resistance type ammonia gas sensor.
The invention also provides an ammonia gas sensing detection method, wherein two poles of the ceramic substrate metal interdigital electrode of the chemical resistance type ammonia gas sensor or the preparation method of the technical scheme are respectively and electrically connected with two wiring terminals of an electrochemical workstation, voltage is applied to the electrochemical workstation, and after gas to be detected is introduced, current of a loop consisting of the chemical resistance type ammonia gas sensor, a lead and the electrochemical workstation is collected and converted to obtain a resistance-time curve;
calculating a sensing response value according to the change of the resistance value of the sensor before and after ammonia gas exposure on the resistance-time curve;
and calculating the concentration of ammonia in the gas to be detected according to the sensing response value.
The invention provides an imino covalent organic framework polymer, which has a structure shown in a formula I. The imino covalent organic framework polymer provided by the invention has a pi electron conjugated system formed by imino bridged chain aromatic rings, has high conjugation degree and small resistance value, and can react with NH under room temperature3And a remarkable sensing response signal is generated, and the resistance value of the sensing layer material is changed due to the hydrogen bond interaction between the imine bond in the imine covalent organic framework material and ammonia gas, so that the high-selectivity sensing detection of the ammonia gas is realized. The sensor has the advantages of large sensing response value, short response time, high stability and sensitivity, and great application potential in the field of high-sensitivity monitoring of ammonia in the environment.
The invention provides a preparation method of the imino covalent organic framework polymer in the technical scheme. The imino covalent organic framework polymer prepared by the invention has a pi electron conjugated system formed by imino bridge chain aromatic rings, has high conjugation degree and good conductivity, and has significantly improved sensing response value and sensing selectivity to ammonia gas under the same conditions compared with the covalent organic framework polymer prepared by taking a monomer without a conjugated structure as a raw material or taking weak acid as a catalyst, and has huge application potential in the field of high-sensitivity monitoring of ammonia gas in the environment; moreover, the preparation method is simple to operate and suitable for industrial production.
The invention provides the imino covalent organic framework polymer in the technical scheme or the imino covalent organic framework polymer obtained by the preparation method in the technical scheme, and the imino covalent organic framework polymer has certain conductive capability. The imine bridge chain aromatic ring in the imine covalent organic framework polymer provided by the invention forms a pi electron conjugated system, and the imine bridge chain aromatic ring has high conjugation degree and has conductivity. Can react with NH under room temperature3Generates obvious sensing response signals and can be used for preparing a chemi-resistance type ammonia gas sensor.
The invention provides a chemical resistance type ammonia gas sensor, which comprises a ceramic substrate metal interdigital electrode and a sensing layer material attached to the surface of the ceramic substrate metal interdigital electrode; the sensing layer material is the imino covalent organic framework polymer in the technical scheme or the imino covalent organic framework polymer obtained by the preparation method in the technical scheme; the imino covalent organic framework polymer is the imino covalent organic framework polymer in the technical scheme or the imino covalent organic framework polymer obtained by the preparation method in the technical scheme. The chemi-resistance ammonia gas sensor provided by the invention takes the imino covalent organic framework polymer with high conjugation degree as a gas-sensitive substance, realizes high-selectivity and high-sensitivity sensing detection on ammonia gas molecules at room temperature, has positive correlation between a sensing response value and concentration, and can be used for other gas molecules such as SO2、NO、NO2、CO、CO2、H2VOCs (toluene, CH)3OH) and the like do not show obvious sensing signals and have high selectivity to ammonia.
The invention provides a preparation method of the chemical resistance type ammonia gas sensor in the technical scheme. According to the preparation method provided by the invention, the supernatant obtained after ultrasonic dispersion treatment and centrifugal separation of the imino covalent organic framework polymer and the low-boiling point solvent is used as an active layer, so that the reaction is sensitive and the response time is short; moreover, the preparation method is simple to operate and suitable for industrial production.
The invention also provides an ammonia gas detection method. The ammonia gas detection method provided by the invention is simple to operate, low in detection limit and high in detection sensitivity.
Drawings
FIG. 1 is a sensor response versus ammonia concentration standard curve;
FIG. 2 is an infrared spectrum of an imino-covalent organic framework polymer prepared in examples 1-4;
FIG. 3 is a powder XRD spectrum of an imino-covalent organic framework polymer prepared in example 1;
FIG. 4 is a nitrogen sorption/desorption isotherm plot of the imino-covalent organic framework polymer prepared in example 1;
FIG. 5 is a room temperature sensing characteristic curve of the chemiresistor-type ammonia gas sensor prepared in example 1, wherein (a) is a resistance-time curve and (b) is a sensing response value-time curve;
FIG. 6 is a room temperature sensing characteristic curve of the chemiresistor-type ammonia gas sensor prepared in comparative example 1, in which (a) is a resistance-time curve and (b) is a sensing response value-time curve;
FIG. 7 is a room temperature sensing characteristic curve of the chemiresistor-type ammonia gas sensor prepared in example 2, wherein (a) is a resistance-time curve and (b) is a sensing response value-time curve;
FIG. 8 is a room temperature sensing characteristic curve of the chemiresistor-type ammonia gas sensor prepared in comparative example 2, in which (a) is a resistance-time curve and (b) is a sensing response value-time curve;
FIG. 9 is a room temperature sensing characteristic curve of the chemiresistor-type ammonia gas sensor prepared in example 3, wherein (a) is a resistance-time curve and (b) is a sensing response value-time curve;
FIG. 10 is a room temperature sensing characteristic curve of the chemiresistor-type ammonia gas sensor prepared in comparative example 3, in which (a) is a resistance-time curve and (b) is a sensing response value-time curve;
FIG. 11 is a room temperature sensing characteristic curve of the chemiresistor-type ammonia gas sensor prepared in example 4, wherein (a) is a resistance-time curve and (b) is a sensing response value-time curve;
FIG. 12 is a room temperature sensing characteristic curve of the chemiresistor-type ammonia gas sensor prepared in comparative example 4;
FIG. 13 is a graph showing the results of selectivity of the sensing performance of the chemiresistor-type ammonia gas sensor prepared in example 4 for various kinds of toxic contaminant gases;
fig. 14 shows the results of the repeated ammonia sensing performance test of the chemiresistor ammonia sensor prepared in example 4.
Detailed Description
The invention provides an imino covalent organic framework polymer, which has a structure shown in a formula I:
in the formula I, R1Is composed of
Wherein denotes a grafting site;
R2is composed of
Wherein denotes the grafting site.
In the present invention, the imino-covalent organic framework polymer has a specific structural formula, and preferably:
when in use
When is in use, the
When in use
When is in use, the
When in use
When is in use, the
When is in use, the
When is in use, the
In the present invention, the constitutional unit of the imino-covalent organic framework polymer preferably has any one of the structures represented by the formulae I-1 to I-5, wherein in the formulae I-1 to I-5, the wavy line represents a graft site:
the invention provides a preparation method of the imino covalent organic framework polymer, which comprises the following steps:
mixing aromatic polyamine, aromatic polyaldehyde, scandium trifluoromethanesulfonate and a mixed organic solvent, and carrying out polymerization reaction to obtain the imino covalent organic framework polymer with the structure shown in the formula I.
In the present invention, all the raw material components are commercially available products well known to those skilled in the art unless otherwise specified.
In the invention, the aromatic polyamine comprises aromatic diamine or aromatic triamine, and the structural formula is shown as formula 1-4; the aromatic diamine preferably comprises p-phenylenediamine (the structure is shown as formula 1) or biphenyldiamine (the structure is shown as formula 2); the aromatic triamine preferably comprises 1,3, 5-tri (4-aminophenyl) benzene (the structure is shown as the formula 3) or 1,3, 5-tri (4-aminophenyl) -2,4, 6-triazine (the structure is shown as the formula 4).
Aromatic polyamine:
in the invention, the aromatic polyaldehyde preferably comprises aromatic dialdehyde or aromatic trialdehyde, and the structural formula is shown as formula 5-10; the aromatic dialdehyde preferably comprises terephthalaldehyde (with a structure shown in formula 5), terephthalaldehyde (with a structure shown in formula 7) or terterphthalaldehyde (with a structure shown in formula 8); the aromatic ternary aldehyde preferably comprises trimesic aldehyde (the structure is shown as a formula 6), 1,3, 5-tri (4-aldehyde phenyl) benzene (the structure is shown as a formula 9) or 1,3, 5-tri (4-aldehyde phenyl) -2,4, 6-triazine (the structure is shown as a formula 10).
Aromatic polyaldehyde:
in the present invention, when the aromatic polyamine is an aromatic diamine, the aromatic polyaldehyde is preferably an aromatic trialdehyde; when the aromatic polyamine is an aromatic triamine, the aromatic polyaldehyde is preferably an aromatic dialdehyde. In the present invention, the molar ratio of the amino group in the aromatic polyamine to the aldehyde group in the aromatic polyaldehyde is preferably 1: 1. The invention controls the ratio of amino and aldehyde groups to be 1:1 for polymerization reaction, has less unreacted residue and good ammonia sensing performance.
In the present invention, the molar ratio of the amino group in the aromatic polyamine to scandium trifluoromethanesulfonate is preferably 1: (0.005-0.20), preferably 1: (0.01 to 0.15), more preferably 1: (0.05-0.10). According to the invention, by controlling the dosage of the catalyst scandium trifluoromethanesulfonate, the adjustment of the imino covalent organic framework polymer structure is realized, the resistance of the corresponding sensor device is influenced, and the accurate regulation and control of the ammonia gas sensing performance are further realized.
In the present invention, the mixed organic solvent preferably includes 1, 4-dioxane and mesitylene; the volume ratio of the 1, 4-dioxane to the mesitylene is preferably (2-5): 1, more preferably (3-4): 1. in the present invention, the ratio of the amount of the amino group in the aromatic triamine to the volume of the mixed organic solvent is preferably 1 mmol: (40-1) mL, more preferably 1 mmol: (15-10) mL.
In the present invention, the order of mixing the aromatic polyamine, the aromatic polyaldehyde, scandium trifluoromethanesulfonate and the mixed organic solvent is preferably such that the aromatic polyamine, the aromatic polyaldehyde and the mixed organic solvent are first mixed, and scandium trifluoromethanesulfonate is added to the resulting mixed solution to perform second mixing. In the present invention, the first mixing is preferably ultrasonic mixing, and the power of the ultrasonic mixing is not particularly limited, and the aromatic polyamine and the aromatic polyaldehyde may be dissolved in the mixed organic solvent; the ultrasonic mixing time is preferably 3-20 min, more preferably 5-15 min, and most preferably 10 min. The second mixing method is not particularly limited, and the second mixing method known to those skilled in the art may be adopted, specifically, stirring and mixing; in the present invention, the conditions for the second mixing are not particularly limited, and the raw materials may be mixed uniformly.
In the present invention, the polymerization reaction temperature is preferably room temperature; the time of the polymerization reaction is preferably 0.5 to 72 hours, more preferably 5 to 50 hours, and most preferably 10 to 36 hours. In the present invention, the polymerization reaction is preferably carried out under a static condition. The invention carries out polymerization reaction, and in the polymerization reaction process, the amino in the aromatic polyamine and the aldehyde group in the aromatic aldehyde are subjected to imidization reaction. The invention has the advantages of polymerization reaction at room temperature, mild reaction conditions, economy and environmental protection.
After the polymerization reaction, the invention preferably further comprises the steps of carrying out centrifugal separation on the system of the polymerization reaction, adding a low-boiling-point solvent into the obtained solid component for washing, and drying the obtained solid product to obtain the imino covalent organic framework polymer with the structure shown in the formula I. In the invention, the rotation speed of centrifugal separation is preferably 5000-12000 rpm, and more preferably 8000-10000 rpm; the time of the centrifugal separation is preferably 3-30 min, more preferably 5-25 min, and most preferably 10-20 min. In the present invention, the boiling point of the low boiling point solvent is preferably < 100 ℃, and the low boiling point solvent preferably includes methanol, acetone, ethanol or n-hexane; the ratio of the amount of the substance of amino groups in the aromatic polyamine to the volume of the low-boiling solvent is preferably 0.6 mmol: 20-50 mL, more preferably 0.6 mmol: 30-40 mL. In the invention, the washing time is preferably 0.1-72 h, more preferably 0.5-24 h, and most preferably 5-10 h; the purpose of the washing is to remove unreacted starting materials as well as the resulting oligomer impurities.
In the invention, the drying mode is preferably vacuum drying, and the temperature of the vacuum drying is preferably 50-100 ℃, more preferably 60-90 ℃, and most preferably 70-80 ℃; the vacuum drying time is preferably 12-36 h, more preferably 15-30 h, and most preferably 20-25 h. The invention is dried under the conditions, can dry the residual low-boiling-point solvent and does not destroy the chemical structure of the imino covalent organic framework polymer.
The invention provides an application of the imino covalent organic framework polymer in the technical scheme or the imino covalent organic framework polymer obtained by the preparation method in the technical scheme in a chemical resistance type ammonia gas sensor. In the chemical resistance type ammonia gas sensor, the imino covalent organic framework polymer is used as a gas sensitive material of the sensor and can react with NH under the room temperature condition3The method has the advantages of generating obvious sensing response signals, having high sensing response value, selectivity and sensitivity to ammonia gas, and having great application potential in the field of ammonia gas high-sensitivity monitoring in the environment.
The invention provides a chemical resistance type ammonia gas sensor, which comprises a ceramic substrate metal interdigital electrode and a sensing layer attached to the surface of the ceramic substrate metal interdigital electrode; the sensing layer is the imino covalent organic framework polymer in the technical scheme or the imino covalent organic framework polymer obtained by the preparation method in the technical scheme.
In the present invention, the ceramic substrate metal interdigital electrode is preferably a ceramic substrate noble metal interdigital electrode, and more preferably a ceramic substrate gold interdigital electrode, a ceramic substrate palladium interdigital electrode, or a ceramic substrate platinum interdigital electrode. The ceramic substrate metal interdigital electrode adopted by the invention preferably comprises a ceramic substrate gold interdigital electrode, a ceramic substrate palladium interdigital electrode or a ceramic substrate platinum interdigital electrode. In the present invention, the ceramic substrate metal interdigital electrode is preferably purchased from Guangzhou Yu core sensing technology, Inc.
In the present invention, the thickness of the sensing layer is preferably 20nm to 2000nm, more preferably 50nm to 1000nm, and most preferably 100nm to 400 nm.
The invention provides a preparation method of the chemiresistor ammonia sensor in the technical scheme, which comprises the following steps:
placing the imino covalent organic framework polymer in a low-boiling-point solvent to perform ultrasonic dispersion treatment and centrifugal separation in sequence to obtain supernatant;
and dripping the supernatant on the surface of the ceramic substrate metal interdigital electrode and drying to obtain the chemical resistance type ammonia gas sensor.
The imino covalent organic framework polymer is placed in a low-boiling-point solvent to be sequentially subjected to ultrasonic dispersion treatment and centrifugal separation, and supernatant is obtained.
In the invention, the ceramic substrate metal interdigital electrode is preferably dried after being washed by an organic solvent before being used. In the present invention, the organic solvent preferably includes N, N-Dimethylformamide (DMF), acetone, or absolute ethanol. In the present invention, the drying mode is preferably air drying, the drying temperature is preferably room temperature, the drying time is not particularly limited, and the organic solvent remaining on the surface of the ceramic substrate metal interdigital electrode can be completely volatilized.
In the present invention, the low boiling point solvent preferably includes acetone, n-hexane, anhydrous ethanol or acetonitrile. In the present invention, the mass ratio of the imino-covalent organic framework polymer to the low-boiling point solvent is preferably 1: (30-100), more preferably 1: (50-80), most preferably 1: (60-70) mL.
In the invention, the time of ultrasonic dispersion treatment is preferably 3-30 min, more preferably 5-25 min, and most preferably 10-20 min; the power of the ultrasonic dispersion treatment is 200W.
In the invention, the rotation speed of the centrifugal separation is preferably 3000-6000 rpm, more preferably 3500-5500 rpm, and most preferably 4000-5000 rpm; the time of the centrifugal separation is preferably 1-30 min, more preferably 2-20 min, and most preferably 5-10 min.
After the supernatant is obtained, the supernatant is dripped on the surface of the ceramic substrate metal interdigital electrode and then dried, and the chemical resistance type ammonia gas sensor is obtained. In the invention, the dropping coating mode is preferably dropping coating; the drop coating is preferably carried out using a 10. mu.L pipette. In the present invention, the drying mode is preferably airing, and the airing temperature is preferably room temperature; the air-drying time is not particularly limited, and the low-boiling-point solvent in the supernatant can be volatilized. In the invention, the dripping and the drying are repeated, and drying is carried out after each dripping, and then the next dripping is carried out. In the invention, the repetition frequency is preferably 5-50 times, more preferably 10-40 times, and most preferably 20-30 times; the volume of the supernatant liquid of single dripping is preferably 0.5-10 mu L, more preferably 2-8 mu L, and most preferably 5-6 mu L. The invention can form a layer of continuous imino covalent organic framework film on the surface of the ceramic substrate metal interdigital electrode by repeating the operations of dripping and drying, and the film has sensing detection capability on ammonia as a sensing layer.
The invention provides an ammonia gas detection method, which is characterized in that two poles of a ceramic substrate metal interdigital electrode of the chemical resistance type ammonia gas sensor or the preparation method of the technical scheme are respectively and electrically connected with two wiring terminals of an electrochemical workstation, voltage is applied to the electrochemical workstation, after gas to be detected is introduced, current of a loop consisting of the chemical resistance type ammonia gas sensor, a lead and the electrochemical workstation is collected and converted to obtain a resistance-time curve;
calculating a sensing response value of the chemical resistance type ammonia gas sensor according to the resistance-time curve;
and calculating the concentration of ammonia in the gas to be detected according to the sensing response value.
The invention respectively electrically connects two poles of the ceramic substrate metal interdigital electrode of the chemical resistance type ammonia gas sensor or the preparation method of the technical scheme with two connecting terminals of an electrochemical workstation, applies voltage to the electrochemical workstation, collects the current of a loop consisting of the chemical resistance type ammonia gas sensor, a lead and the electrochemical workstation after the gas to be detected is introduced, and converts the current into a resistance-time curve. In the present invention, the electrical connection is preferably by a wire, which is preferably a copper wire. In the present invention, the voltage is 1V.
And after a resistance-time curve is obtained, calculating a sensing response value of the chemical resistance type ammonia gas sensor according to the resistance-time curve. In the invention, the calculation formula of the resistance is as follows: resistance is given in Ω, voltage is given in V, and current is given in a. In the present invention, the sensing response value is a relative deviation of a response-state resistance value (i.e., a resistance value of the chemi-resistive ammonia gas sensor after adsorbing the gas to be detected) with respect to a blank-state resistance value (i.e., a resistance value of the chemi-resistive ammonia gas sensor when no gas to be detected is adsorbed).
And after the sensing response value is obtained, calculating the concentration of the ammonia in the gas to be detected according to the sensing response value.
In the present invention, it is preferable that the sensing response value-ammonia concentration standard curve is obtained by measuring the sensing response value at each ammonia concentration. In the present invention, the calculation formula of the sensing response value is represented by formula (1):
sensing response value ═ RAmmonia gas-RAir (a))÷RAir (a)X 100% (formula 1), wherein the unit of the sensory response value is%.
In the embodiment of the present invention, the ammonia gas concentration is preferably 5ppm, 10ppm, 25ppm, 50ppm, 75ppm and 100ppm respectively, the sensing response value-ammonia gas concentration standard curve is shown in fig. 1, and the linear relation between the sensing response value and the ammonia gas concentration is shown in formula (2):
y is (0.09297 ± 0.0057) x + (14.68 ± 0.3234) formula (2), wherein x is the ammonia gas concentration (ppm) and y is the sensing response value (%).
And then calculating the concentration of the ammonia gas according to the sensing response value-ammonia gas concentration standard curve. In the present invention, the ammonia gas concentration is represented by the following formula (3):
ammonia concentration ═ (sensor response-14.68%)/+ 0.0009297 formula (3),
wherein the ammonia concentration unit is ppm, and the sensing response value unit is%.
In the invention, the detection of the ammonia gas is preferably performed in a gas-sensitive testing device, and the chemical resistance type ammonia gas sensor is preferably arranged on a sample rack of the gas-sensitive testing device. In the present invention, the gas to be tested is preferably introduced by injecting into the cavity of the gas sensitive testing apparatus.
The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
(1) Imino-covalent organic framework polymers
Adding 0.3mmol of terephthalaldehyde and 0.2mmol of 1,3, 5-tri (4-aminophenyl) benzene into a mixed solvent of 4.8mL of 1, 4-dioxane and 1.2mL of mesitylene, ultrasonically mixing for 10min, adding 0.003mmol of scandium trifluoromethanesulfonate into the obtained mixed solution, uniformly mixing, then carrying out polymerization reaction for 72h at room temperature and under a standing condition, then centrifuging for 10min at 5000rpm, washing the obtained solid product for 24h with 20mL of methanol, and drying the obtained solid phase for 12h under vacuum at 50 ℃ to obtain the imido covalent organic framework polymer with the structure shown in the formula I-1.
(2) Chemical resistance type ammonia gas sensor
The gold interdigital electrode (purchased from Guangzhou Yu core sensing technology Co., Ltd.) of the ceramic substrate was cleaned with DMF and then dried. Placing 3mg of the imino covalent organic framework polymer obtained in the step (1) in 300mg of ethanol for ultrasonic dispersion treatment for 10min, placing in a centrifuge tube, centrifuging at the speed of 3000rpm for 10min, then using a pipette to transfer 0.5uL of supernatant liquid, dropwise adding the supernatant liquid on the surface of the ceramic-based gold interdigital electrode, and airing at room temperature to volatilize ethanol; and repeating the operations of dropwise coating and airing for 20 times to obtain the chemi-resistance ammonia gas sensor, wherein the thickness of the sensing layer is 80 nm.
Example 2
(1) Imino-covalent organic framework polymers
Adding 0.3mmol of p-phenylenediamine and 0.2mmol of trimesic aldehyde into a mixed solvent of 4mL of 1, 4-dioxane and 2mL of mesitylene, ultrasonically mixing for 3min, adding 0.012mmol of scandium trifluoromethanesulfonate into the obtained mixed solution, uniformly mixing, then carrying out polymerization reaction for 24h under the conditions of room temperature and standing, then centrifuging for 3min under the condition of 12000rpm, washing the obtained solid product for 36h with 40mL of acetone, and carrying out vacuum drying on the obtained solid phase for 18h under the condition of 70 ℃ to obtain the imino covalent organic framework polymer with the structure shown in the formula I-2.
(2) Chemical resistance type ammonia gas sensor
The palladium interdigital electrode (purchased from Guangzhou Yu core sensing technology Co., Ltd.) on the ceramic substrate was cleaned with acetone and then dried. Placing 5mg of imino-imino covalent organic framework polymer obtained in the step (1) in 400mg of n-hexane for ultrasonic dispersion treatment for 3min, placing the imino-imino covalent organic framework polymer in a centrifuge tube, centrifuging the imino-imino covalent organic framework polymer for 8min at the speed of 4000rpm, then using a liquid-transferring gun to transfer 3uL of supernatant liquid, dropwise adding the supernatant liquid on the surface of the ceramic-based palladium interdigital electrode, and airing the mixture at room temperature to volatilize the n-hexane; and repeating the operations of dropwise coating and airing for 30 times to obtain the chemi-resistance ammonia gas sensor, wherein the thickness of the sensing layer is 150 nm.
Example 3
(1) Imino-covalent organic framework polymers
Adding 0.3mmol of biphenyl dialdehyde and 0.2mmol of 1,3, 5-tris (4-aminophenyl) -2,4, 6-triazine into a mixed solvent of 4.5mL of 1, 4-dioxane and 1.5mL of mesitylene, ultrasonically mixing for 15min, adding 0.06mmol of scandium trifluoromethanesulfonate into the obtained mixed solution, uniformly mixing, then carrying out polymerization reaction for 12h at room temperature and under a standing condition, centrifuging for 15min at 7000rpm, washing the obtained solid product for 72h with 50mL of absolute ethyl alcohol, and drying the obtained solid phase for 24h under vacuum at 90 ℃ to obtain the imido covalent organic framework polymer with the structure shown in the formula I-3.
(2) Chemical resistance type ammonia gas sensor
The platinum interdigital electrode (purchased from Guangzhou Yu core sensing technology Co., Ltd.) of the ceramic substrate is cleaned by absolute ethyl alcohol and dried. Placing 10mg of imino-imino covalent organic framework polymer obtained in the step (1) in 500mg of acetone for ultrasonic dispersion treatment for 3min, placing the imino-imino covalent organic framework polymer in a centrifuge tube, centrifuging the imino-imino covalent organic framework polymer for 5min at the speed of 5000rpm, then using a liquid transfer gun to transfer 5uL of supernatant liquid, dropwise adding the supernatant liquid on the surface of the ceramic-based platinum interdigital electrode, and airing the mixture at room temperature to volatilize n-hexane; repeating the operations of dropwise coating and airing for 15 times to obtain the chemi-resistance ammonia gas sensor, wherein the thickness of the sensing layer is 230 nm.
Example 4
(1) Imino-covalent organic framework polymers
Adding 0.3mmol of biphenyldiamine and 0.2mmol of trimesic aldehyde into a mixed solvent of 5mL of 1, 4-dioxane and 1mL of mesitylene, ultrasonically mixing for 20min, adding 0.12mmol of scandium trifluoromethanesulfonate into the obtained mixed solution, uniformly mixing, carrying out polymerization reaction for 0.5h under the conditions of room temperature and standing, centrifuging for 30min under the condition of 9000rpm, washing the obtained solid product for 24h with 50mL of n-hexane, and carrying out vacuum drying on the obtained solid phase for 36h under the condition of 100 ℃ to obtain the imino covalent organic framework polymer with the structure shown in the formula I-4.
(2) Chemical resistance type ammonia gas sensor
The gold interdigital electrode (purchased from Guangzhou Yu core sensing technology Co., Ltd.) of the ceramic substrate was cleaned with acetone and then dried. Placing 15mg of imino-imino covalent organic framework polymer obtained in the step (1) in 450mg of acetonitrile for ultrasonic dispersion treatment for 30min, placing the imino-imino covalent organic framework polymer in a centrifuge tube, centrifuging the imino-imino covalent organic framework polymer for 3min at the speed of 6000rpm, then using a liquid transfer gun to transfer 10uL of supernatant liquid, dropwise adding the supernatant liquid on the surface of the ceramic-based gold interdigital electrode, and airing the mixture at room temperature to volatilize n-hexane; and repeating the operations of dropwise coating and airing for 5 times to obtain the chemi-resistance ammonia gas sensor, wherein the thickness of the sensing layer is 500 nm.
Comparative example 1
An imido-covalent organic framework polymer was prepared according to the procedure of step (1) of example 1, except that 0.003mmol of scandium trifluoromethanesulfonate was replaced with 0.2mL of a 3mol/L acetic acid solution, and the polymerization temperature was 120 ℃.
A chemiresistive ammonia gas sensor was prepared in accordance with the procedure of step (2) of example 1.
Comparative example 2
An imino covalent organic framework polymer was prepared according to the method of example 2 step (1);
a chemiresistor type ammonia gas sensor was prepared in the same manner as in step (2) of example 2, except that the operation of centrifuging at 4000rpm for 8min, in which the thickness of the sensing layer was 0.5mm, was omitted.
Comparative example 3
An imino covalent organic framework polymer was prepared according to the method of example 3 step (1);
a chemiresistor type ammonia gas sensor was prepared according to the method of step (2) of example 3, and the difference from step (2) of example 3 was that the supernatant was discarded after centrifugation, and a dispersion liquid was pipetted from the bottom of a centrifuge tube, wherein the thickness of the sensing layer was 2 mm.
Comparative example 4
An imino-covalent organic framework polymer was prepared according to the method of example 3 step (1), differing from example 3 step (2) in that 1,3, 5-tris (4-aminophenyl) -2,4, 6-triazine was replaced with 1,3, 5-tris (4-aminophenoxy) benzene to give the imino-covalent organic framework polymer of the structure shown in formula II:
a chemiresistive ammonia gas sensor was prepared in accordance with the procedure of step (2) of example 3.
The infrared spectrum of the imino-covalent organic framework polymers prepared in examples 1 to 4 is shown in fig. 2, and a characteristic absorption peak of a C ═ N double bond can be clearly seen from fig. 2, which confirms that all the polymers prepared in examples 1 to 4 have imine functional groups generated.
The powder XRD pattern of the imino-covalent organic framework polymer prepared in example 1 is shown in fig. 3, from which fig. 3 the characteristic peaks of the layered structure and the characteristic peaks of the secondary proximity order of the imino-covalent organic framework polymer prepared in example 1 can be seen.
The nitrogen adsorption and desorption isotherm of the imino-covalent organic framework polymer prepared in example 1 is shown in fig. 4, and it can be seen from fig. 4 that the imino-covalent organic framework polymer prepared in example 1 has the characteristic of pore composition of combination of micropores and mesopores.
Example 5
(1) The two poles of the ceramic substrate metal interdigital electrode of the chemiresistive ammonia gas sensor prepared in the embodiment 1 are connected with two connecting terminals of an electrochemical workstation through copper wires, 1V voltage is applied to the electrochemical workstation, and the current of a loop formed by the sensor, the wires and the electrochemical workstation is collected; the chemical resistance type ammonia gas sensor is arranged on a sample rack of the gas-sensitive testing device, ammonia gas with different concentrations is injected into a cavity of the gas-sensitive testing device, loop current at different times is collected and converted to obtain a resistance-time curve, a sensing response value of the chemical resistance type ammonia gas sensor is calculated according to the resistance-time curve, the calculation formula of the sensing response value is shown as a formula (1), and a sensing response value-ammonia gas concentration standard curve (shown as a figure 1) is obtained, wherein the ammonia gas concentrations are respectively 5ppm, 10ppm, 25ppm, 50ppm, 75ppm and 100ppm, and the linear relation between the sensing response value and the ammonia gas concentration is shown as a formula (2); and then obtaining a concentration calculation formula of ammonia according to the sensing response value-ammonia concentration curve, wherein the formula is shown as formula (3):
sensing response value ═ RAmmonia gas-RAir (a))÷RAir (a)X 100% formula (1), wherein the unit of the sensing response value is%;
y ═ 0.09297 ± 0.0057) x + (14.68 ± 0.3234) formula (2), where x is ammonia concentration (ppm) and y is the sensing response value (%);
ammonia gas concentration in ppm and sensor response in% 0.0009297 (3) (sensor response-14.68%)/, where the ammonia gas concentration is in ppm and the sensor response is in%.
(2) According to the test method in the step (1), the room temperature sensing performance of the chemiresistive ammonia gas sensors prepared in the examples 1 to 4 and the comparative examples 1 to 4 on ammonia gas was tested, wherein the concentration of ammonia gas was 100ppm, and the room temperature sensing characteristic curve results of the chemiresistive ammonia gas sensors are shown in fig. 5 to 12.
FIG. 5 is a room temperature sensing characteristic curve of the chemiresistor-type ammonia gas sensor prepared in example 1, wherein (a) is a resistance-time curve and (b) is a sensing response value-time curve; fig. 6 is a room temperature sensing characteristic curve of the chemiresistor-type ammonia gas sensor prepared in comparative example 1, in which (a) is a resistance-time curve and (b) is a sensing response value-time curve. As can be seen from fig. 5 to 6, under the same ammonia gas concentration, the sensing signal intensity of the chemical resistance ammonia gas sensor prepared in example 1 to ammonia gas can reach 17%, while the sensing signal intensity of the chemical resistance ammonia gas sensor prepared in comparative example 1 to ammonia gas is only about 5%, because acetic acid catalysis is adopted, the polymerization reaction speed is slow, the obtained imino covalent organic framework polymer has a high structural arrangement order degree, and the ultrasonic dispersion treatment makes the lamellar structure of the imino covalent organic framework polymer disperse to a lower degree, so that the prepared chemical resistance ammonia gas sensor has relatively large resistance and too weak conductivity, and the sensing signal intensity to ammonia gas is low; the scandium trifluoromethanesulfonate is used as the catalyst, the polymerization reaction speed is high, the structural arrangement of the prepared covalent organic framework polymer is disordered, the dispersion degree of the lamellar structure of the polymer is high through ultrasonic dispersion treatment, and the chemical resistance type ammonia gas sensor is relatively small in resistance, strong in conductivity and strong in sensing signal intensity on ammonia gas.
FIG. 7 is a room temperature sensing characteristic curve of the chemiresistor-type ammonia gas sensor prepared in example 2, wherein (a) is a resistance-time curve and (b) is a sensing response value-time curve; fig. 8 is a room temperature sensing characteristic curve of the chemiresistor-type ammonia gas sensor prepared in comparative example 2, in which (a) is a resistance-time curve and (b) is a sensing response value-time curve. As can be seen from fig. 7 to 8, the sensing characteristic curve of the chemiresistive ammonia sensor prepared in example 2 conforms to a typical sensing response curve, after contacting ammonia molecules, the resistance changes rapidly in one direction, a relatively gentle platform appears after reaching an equilibrium state, the effect of the chemiresistive ammonia sensor on ammonia reaches the maximum, and as ammonia is pumped away, a sensing signal rapidly decreases and returns to the vicinity of a baseline before adsorption. In contrast, the chemiresistive ammonia sensor prepared in comparative example 2 has significantly poor sensing performance for ammonia gas of the same concentration, and not only the characteristic curve shape does not conform to the typical sensing response curve, but also the baseline drifts in one direction, which indicates that the chemiresistive ammonia sensor prepared in comparative example 2 has gradually increased resistance, and the continuous increase of the resistance results in large fluctuation of the sensing characteristic curve within the test time. The essence of this phenomenon is that no ultrasonic dispersion treatment is performed, the imino covalent organic framework polymer is not completely dispersed, and a considerable proportion of the imino covalent organic framework polymer is still in an agglomerated state, in which the resistance is too high, resulting in unstable sensing signals.
FIG. 9 is a room temperature sensing characteristic curve of the chemiresistor-type ammonia gas sensor prepared in example 3, wherein (a) is a resistance-time curve and (b) is a sensing response value-time curve; fig. 10 is a room temperature sensing characteristic curve of the chemiresistor-type ammonia gas sensor prepared in comparative example 3, in which (a) is a resistance-time curve and (b) is a sensing response value-time curve. As can be seen from fig. 9 to 10, the change characteristics shown by the room temperature sensing characteristic curve of the chemi-resistive ammonia sensor prepared in comparative example 3 are almost completely consistent with those of comparative example 2, and as the test time is prolonged, the resistance of the chemi-resistive ammonia sensor is continuously increased, which causes fluctuation and drift of the baseline of the characteristic curve of ammonia sensing. In contrast, example 3 shows a very typical sensing characteristic curve. The result shows that after ultrasonic dispersion treatment, the energy of the ultrasonic wave breaks and disperses the parts of the aggregated imino covalent organic framework polymer, and after centrifugal treatment, larger particles with serious aggregation are precipitated at the bottom, while smaller particles are dispersed in the supernatant, and the parts precipitated at the bottom have relatively high contact resistance with the metal interdigital electrodes on the ceramic substrate due to serious aggregation.
Fig. 11 is a room temperature sensing characteristic curve of the chemiresistor-type ammonia gas sensor prepared in example 4, in which (a) is a resistance-time curve and (b) is a sensing response value-time curve. As can be seen from FIG. 11, the sensing response signal of the chemiresistor type ammonia gas sensor is large, and the response value to 100ppm ammonia gas can reach 23%. The imino covalent organic framework polymer has excellent room temperature sensing capability on ammonia gas. And the sensing response time is short, the resistance of the sensor is reduced to the minimum within about 10s of ammonia exposure. The imino covalent organic framework polymer is very sensitive to ammonia gas, has high ammonia gas adsorption speed and response, and is a very sensitive ammonia gas sensor material.
Fig. 12 is a room temperature sensing characteristic curve (resistance-time curve) of the chemiresistive ammonia gas sensor prepared in comparative example 4. As can be seen from fig. 12, the triamine used in comparative example 4 is a non-conjugated monomer, and the imine-based covalent organic framework polymer obtained by polymerization has too large resistance to show a significant sensing signal for ammonia in the test range because it is not a conjugated system. This shows that not all imino covalent organic framework polymers have sensing properties for ammonia gas, and that it is one of the prerequisites of chemiresistive gas sensor materials that they can form a conjugated structure to a large extent to have a certain conductivity.
The procedure of example 5 was followed to testChemi-resistive ammonia sensor pair NH prepared in example 43、SO2、NO、NO2、CO、CO2、H2And room temperature sensing performance of VOCs, the results are shown in fig. 13. As can be seen from fig. 13, the chemiresistor ammonia sensor prepared in example 4 has a significant room temperature sensing performance for ammonia molecules, and has a significant room temperature sensing performance for other gas molecules such as SO2、NO、NO2、CO、CO2、H2VOCs do not show obvious sensing signals, and the chemiresistor ammonia sensor prepared by the method has high sensing selectivity and sensing response value for ammonia.
The chemi-resistive ammonia gas sensor prepared in example 4 was tested for its repeated sensing performance on ammonia gas according to the method of example 5, and the sensing results during 8 repeated tests are shown in fig. 14. As can be seen from fig. 14, in the 8-time repeated test process, the sensing response signal of the chemical resistance type ammonia gas sensor is not significantly reduced, which indicates that the chemical resistance type ammonia gas sensor prepared by the present invention has good room temperature sensing stability for ammonia gas.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. An imino-covalent organic framework polymer having the structure of formula I:
in the formula I, R1Is composed of
Wherein denotes a grafting site;
R2is composed of
Wherein denotes the grafting site.
2. The method of preparing the imino-covalent organic framework polymer of claim 1, comprising the steps of:
mixing aromatic polyamine, aromatic polyaldehyde, scandium trifluoromethanesulfonate and a mixed organic solvent, and carrying out polymerization reaction to obtain an imino covalent organic framework polymer;
the aromatic polyamine comprises aromatic diamine or aromatic triamine; the aromatic diamine comprises p-phenylenediamine or biphenyldiamine; the aromatic triamines comprise 1,3, 5-tri (4-aminophenyl) benzene or 1,3, 5-tri (4-aminophenyl) -2,4, 6-triazine;
the aromatic polyaldehyde preferably comprises an aromatic dialdehyde or an aromatic trialdehyde; the aromatic dialdehyde comprises terephthalaldehyde, terephthaldehyde or terterphthalaldehyde; the aromatic ternary aldehyde comprises trimesic aldehyde, 1,3, 5-tri (4-aldehyde phenyl) benzene or 1,3, 5-tri (4-aldehyde phenyl) -2,4, 6-triazine.
3. The method according to claim 2, wherein the molar ratio of the amino group in the aromatic polyamine to the aldehyde group in the aromatic polyaldehyde is 1: 1.
4. The method according to claim 2, wherein the molar ratio of the amino group in the aromatic polyamine to scandium trifluoromethanesulfonate is 1: (0.005-0.20).
5. The method according to claim 2 or 3, wherein the polymerization reaction is carried out at room temperature for 0.5-72 h.
6. The use of the imino covalent organic framework polymer of claim 1 or of the imino covalent organic framework polymer obtained by the preparation method of any one of claims 2 to 5 in a chemiresistive ammonia gas sensor.
7. A chemical resistance type ammonia gas sensor is characterized by comprising a ceramic substrate metal interdigital electrode and a sensing layer attached to the surface of the ceramic substrate metal interdigital electrode;
the sensing layer is the imino covalent organic framework polymer as described in claim 1 or the imino covalent organic framework polymer obtained by the preparation method as described in any one of claims 2 to 5.
8. The ammonia gas sensor of claim 7, wherein the imino-covalent organic framework polymer sensing layer has a thickness of 20-2000 nm.
9. The method of manufacturing a chemiresistor-type ammonia gas sensor according to claim 7 or 8, comprising the steps of:
placing the imino covalent organic framework polymer in a low-boiling-point solvent to perform ultrasonic dispersion treatment and centrifugal separation in sequence to obtain supernatant;
and dripping the supernatant on the surface of the ceramic substrate metal interdigital electrode and drying to obtain the chemical resistance type ammonia gas sensor.
10. An ammonia gas sensing detection method, which is characterized in that two poles of a ceramic substrate metal interdigital electrode of the chemiresistive ammonia gas sensor according to any one of claims 7 to 8 or the chemiresistive ammonia gas sensor obtained by the preparation method according to claim 9 are respectively and electrically connected with two wiring terminals of an electrochemical workstation, voltage is applied to the electrochemical workstation, after gas to be detected is introduced, current of a loop consisting of the chemiresistive ammonia gas sensor, a lead and the electrochemical workstation is collected and converted to obtain a resistance-time curve;
calculating a sensing response value according to the change of the resistance value of the sensor before and after ammonia gas exposure on the resistance-time curve;
and calculating the concentration of ammonia in the gas to be detected according to the sensing response value.
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