A colorimetric sensor based on an electronic storage mechanism, its preparation method and application

Abstract

The present invention discloses a colorimetric sensor based on an electronic storage mechanism, its preparation method and applications. The preparation includes the preparation of functionalized carbon nitride: bulk carbon nitride is obtained by calcining a carbon nitride precursor, and then it is ground thoroughly with a potassium salt or a sodium salt respectively. The ground mixture is calcined in an inert gas to obtain alkali metal-doped carbon nitride; the product is centrifuged and washed, and after vacuum drying, functionalized carbon nitride is obtained; the preparation of the colorimetric oxygen sensor: the obtained functionalized carbon nitride is dispersed in an electron sacrificial agent, oxygen in the suspension is removed, and it is stored in a sealed manner. The sensor prepared by the present invention is a colorimetric oxygen sensor with reusable and highly reversible color conversion and multiple color changes, which effectively solves the problems of low reversibility in colorimetric sensing in the prior art, irreversible changes in molecular structure accompanying color conversion, and single color regulation, etc.

Description

Technical Field

[0001] The present invention belongs to the field of colorimetric sensing, and particularly relates to a colorimetric sensor based on an electron storage mechanism, a preparation method thereof, and an application thereof. Background Art

[0002] In recent decades, colorimetric sensors have been widely used in the fields of biology, chemistry, and environment due to their convenient and fast operation, high sensitivity and selectivity, and visible color changes. Compared with relatively primitive colorimetric sensors such as pH test papers, more complex catalytic oxidation systems, with 3,3',5,5'-tetramethylbenzidine (TMB) as a chromogenic substrate, have been applied to enzyme-linked immunosorbent assays (ELISAs). However, these color changes are usually accompanied by irreversible molecular structure transformations or require additional chemical substances to recover, which brings difficulties to multiple detections. The decomposition and assembly of gold nanoparticles, generating the localized surface plasmon resonance (LSPR) phenomenon, provides a new idea for solving the problem of multiple detections as a unique color reversible switch. However, the high cost of noble metal materials and their special particle size requirements hinder the large-scale synthesis and utilization of the materials.

[0003] In recent years, the electron storage phenomenon found in metal oxides such as TiO2, WO3, ZnO, and functionalized carbon nitride has received increasing attention. This phenomenon is similar to photosynthesis, where the material accumulates electrons in the form of long-lived photoreduced states under light excitation and visually appears as a unique blue color. The metastable charge and discharge of these electrons do not cause permanent molecular structure changes.

[0004] Oxygen is involved in almost all living organisms and is also an important detection standard in the fields of food packaging, environmental pollution, and industrial safety. Current oxygen sensing mechanisms mainly include electrochemistry, fluorescence quenching effect, solid polymer electrochemistry, phosphorescence, fluorescence, and ultraviolet-visible light absorption. However, most oxygen sensing generally requires electricity and has poor selectivity and recyclability, which is extremely disadvantageous for use in underdeveloped areas. Compared with existing commercial sensors, it has comparable sensitivity and detection range and excellent selectivity, which is not reflected in commercial sensors. Summary of the Invention

[0005] Object of the Invention: Aiming at the problems existing in current colorimetric sensing technologies, the present invention provides a preparation method of a colorimetric sensor based on an electron storage mechanism. The sensor prepared by this method is a colorimetric oxygen sensor with reusable, highly reversible color conversion, and multiple color changes, which effectively solves the problems of low reversibility, irreversible molecular structure changes accompanied by color conversion, and single color regulation in the prior art.

[0006] The present invention also provides the colorimetric sensor based on an electronic storage mechanism and its application as described above.

[0007] Technical solution: To achieve the above object, a preparation method of a colorimetric sensor based on an electronic storage mechanism according to the present invention includes the following steps:

[0008] (1) Preparation of functionalized carbon nitride: Bulk carbon nitride is obtained by calcining a carbon nitride precursor, and then it is sufficiently ground with a potassium salt or a sodium salt respectively. The ground mixture is calcined in an inert gas to obtain alkali metal-doped carbon nitride; the product is centrifuged and washed, and after vacuum drying, functionalized carbon nitride CN-K or CN-Na is obtained;

[0009] (2) Preparation of the colorimetric sensor: The obtained functionalized carbon nitride CN-K or CN-Na is dispersed in a mixed solution of an electron sacrificial agent and water, oxygen in the suspension is removed, and it is sealed and stored to obtain suspensions of two kinds of colorimetric sensors of CN-K or CN-Na.

[0010] Among them, the carbon nitride precursor in step (1) is an organic compound containing carbon and nitrogen elements; preferably, the carbon nitride precursor is urea, dicyandiamide, melamine, monocyanamide or thiourea.

[0011] Among them, the potassium salt in step (1) is KSCN, KCl or KI; the sodium salt is NaCl or NaI.

[0012] Among them, the calcination condition of the bulk carbon nitride in step (1) is to raise the temperature to 500-600 °C at a rate of 10-12 °C / min and keep it warm for 3-5 h; the calcination of the ground mixture is to raise the temperature to 500-600 °C at a rate of 2-2.5 °C / min and keep it warm for 4-6 h.

[0013] Preferably, the calcination condition of the bulk carbon nitride in step (1) is to raise the temperature to 500-600 °C at a rate of 10-12 °C / min and keep it warm for 4 h; the calcination of the ground mixture is to raise the temperature to 550 °C at a rate of 2.5 °C / min and keep it warm for 6 h.

[0014] Among them, the mass ratio of the bulk carbon nitride to the potassium salt or the sodium salt in step (1) is 1 / 6 - 1 / 30.

[0015] Preferably, the mass ratio of the bulk carbon nitride to the potassium salt or the sodium salt is 1 / 6.

[0016] Among them, the electron sacrificial agent in step (2) is triethanolamine (TEOA), methanol, isopropanol or 4-methylbenzyl alcohol (4-MBA).

[0017] Among them, the ratio of the volume of the electron sacrificial agent described in step (2) to the total volume of the mixed solution is 1 / 2 - 1 / 50. In step (2), the functionalized carbon nitride is dispersed in a mixed solution of an electron sacrificial agent and water, and the concentration is 0.5 - 2 mg / mL.

[0018] Preferably, the ratio of the volume of the electron sacrificial agent to the total volume is 1 / 8. Preferably, the functionalized carbon nitride is dispersed in a mixed solution of an electron sacrificial agent and water, and the concentration is 1 mg / mL.

[0019] Preferably, in step (2), the concentration of the functionalized carbon nitride in the electron sacrificial agent / water is 1 mg / mL, and the volume is 2 mL; the time for purging oxygen with Ar is 5 min.

[0020] The colorimetric sensor based on the electron storage mechanism prepared by the preparation method of the present invention.

[0021] The application of the colorimetric sensor based on the electron storage mechanism of the present invention in detecting oxygen.

[0022] Among them, after the suspension of the colorimetric oxygen sensor based on the electron storage mechanism is deoxygenated and irradiated with light, the color of the suspension after irradiation becomes blue or brown; then oxygen is injected, and after the suspension contacts oxygen, the color changes from blue or brown to the original yellow. The light irradiation time of the colorimetric oxygen sensor using potassium salt is 3 - 10 min, and the light irradiation time of the colorimetric oxygen sensor using sodium salt is 10 - 20 min.

[0023] Preferably, the light irradiation time of the CN-K colorimetric oxygen sensor formed by using potassium salt in step (2) is 5 min, and the light irradiation time of the CN-Na colorimetric oxygen sensor formed by using potassium salt is 15 min.

[0024] The present invention places the suspension of the doped carbon nitride colorimetric oxygen sensor in a quartz cuvette, and then connects it to a 120 mL device built with an empty flask. The entire device is continuously purged with argon to remove oxygen; after deoxygenation, the cuvette is irradiated with light under a xenon lamp. After irradiation, the color of the suspension becomes blue (CN-K colorimetric oxygen sensor) or brown (CN-Na colorimetric oxygen sensor), indicating that electrons are stored; then oxygen is injected into the empty flask with a micro syringe. After the suspension contacts oxygen, the color changes from blue or brown to the original yellow, indicating that the stored electrons are consumed.

[0025] The sensitivity of the CN-K colorimetric oxygen sensor suspension is relatively high, but the detection range is narrow; while the sensitivity of the CN-Na colorimetric oxygen sensor suspension is high and the detection range is wide; for comparison, a CN-K / Na sensor (K / Na mass ratio is 1 / 1) was obtained, and the sensitivity and linear detection range of the suspension are both in the middle of CN-K and CN-Na. Among them, as a comparison sample, carbon nitride without doping alkali metal salts was prepared under the same conditions as a blank sample; carbon nitride doped with potassium salt and sodium salt at the same time was also prepared, and the mass ratios of potassium salt and sodium salt are 3 / 1, 2 / 1, 1 / 1, 1 / 2 and 1 / 3 respectively.

[0026] By doping different alkali metal salts, the obtained doped carbon nitride is modified with different functional groups. Through characterization, it is found that CN-K is modified with cyano groups, while CN-Na is modified with cyano groups and carbonyl groups; K + and Na + can both be located in the channels of carbon nitride. In addition to having the function of transporting electrons, they can also stabilize the electrons stored in the carbon nitride skeleton of the material; at the same time, the CN-K colorimetric oxygen sensor suspension shows blue, the surface charging state, while the CN-Na colorimetric oxygen sensor shows brown. In addition to charging, there is also a reduction reaction; when oxygen contacts the suspension, electrons are consumed and the color of the suspension changes back to the initial yellow. Therefore, the charge-discharge process of the electronic metastable state does not change the molecular structure and can keep the material with good repeatability. We use the optical fiber of Ocean Optics to immediately detect the change of the reflectivity of the suspension to determine the oxygen content.

[0027] To sum up, the sensor prepared by the present invention utilizes the electron storage mechanism of functional group-modified carbon nitride to quantitatively detect oxygen through the color change during the charge-discharge process; among them, cyano groups and carbonyl groups are beneficial to the electron storage of carbon nitride, while K + and Na + are beneficial to stabilizing the stored electrons. Under closed conditions, the electrons can be stored stably for a long time.

[0028] The present invention first proposes a new colorimetric oxygen sensing mechanism based on electron storage; different functional groups are modified with CN to regulate different color changes of the sensing system and the sensitivity and range of oxygen detection; the sensor has good selectivity and cyclicity. The sensor prepared by the present invention adopts a new colorimetric sensing mechanism. The existing colorimetric sensing includes indicators, surface plasmon resonance (LSPR) and photonic crystals; however, the color change of the indicator is accompanied by a change in structure and is not recoverable, while LSPR has high requirements for the size of metal nanoparticles and is expensive, which is not conducive to large-scale use. The sensor of the present invention has rich material resources, low price and good detection cyclicity for the detection method.

[0029] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0030] 1. The synthesis method of the colorimetric sensing material prepared by the present invention is simple, with high yield and low cost, and can be mass-produced.

[0031] 2. By regulating different functional groups modified on carbon nitride, different colorimetric sensors can be obtained in the present invention, and different sensitivities and linear ranges to oxygen can be exhibited.

[0032] 3. The sensor prepared by the present invention will not cause the change of its own structure during the charge and discharge process of electrons, and can keep good repeatability of oxygen sensing; and the sensor shows good selectivity to oxygen, with good cyclicity and selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is the structural characterization diagrams of CN-K and CN-Na in Example 1, including (a) X-ray diffraction pattern XRD, (b) Fourier transform infrared spectrum FT-IR, (c) C1s of X-ray photoelectron spectroscopy XPS diagram, (d) O1s of XPS diagram;

[0034] Figure 2 It is the transmission electron microscope images (TEM) of CN (a), CN-K (b), and CN-Na (c) in Example 1;

[0035] Figure 3 (a) is the color evolution process of the suspension of CN, CN-K, and CN-Na colorimetric oxygen sensors after deoxygenation and illumination and the color change after contact with oxygen; (b) is the color change process of the suspension of samples with different doping ratios of K / Na; (c) is the reversible cycle diagram of the color change of CN-K before and after illumination;

[0036] Figure 4 It is (a) the electron spin resonance (ESR) spectra of the suspension of CN, CN-K, and CN-Na colorimetric oxygen sensors before and after illumination, (b) the open circuit potential (OCP) of CN-K and CN-Na, (c) the oxygen consumption of CN-K, CN-Na, and CN-1 / 1;

[0037] Figure 5 (a) is the device diagram for oxygen detection, (b) the calibration curves of the reflectance of CN-K, CN-Na, and CN-K / Na before and after detecting oxygen, (c) the selectivity of the oxygen sensor;

[0038] In the figure, ESR represents electron spin resonance, OCP represents open circuit potential, and vol represents volume ratio. DETAILED DESCRIPTION OF THE INVENTION

[0039] The present invention will be further described below in conjunction with specific examples and drawings.

[0040] In the experimental methods described in the examples, unless otherwise specified, they are all conventional methods; the reagents and materials, unless otherwise specified, can all be obtained from commercial sources.

[0041] In the examples, CN represents carbon nitride without doping under the same conditions; CN-K represents carbon nitride doped with potassium salt; CN-Na represents carbon nitride doped with sodium salt; TEOA represents triethanolamine.

[0042] Example 1

[0043] The preparation processes of CN-K and CN-Na are as follows:

[0044] The volume of urea in the crucible is 2 / 3. Cover 2 / 3 of the crucible lid, leaving a certain gap, and then place it in the muffle furnace; heat it to 500 °C at a rate of 12 °C / min, hold for 4 h, and cool naturally to room temperature. Then weigh 0.5 g of the obtained bulk carbon nitride, and then weigh 3 g of KI or NaI. After mixing with the bulk carbon nitride, grind it with an agate mortar to obtain a uniformly mixed sample; then place the mixed sample in the crucible, and leave a certain gap for the crucible lid (cover 2 / 3 of the crucible lid), and place it in the tube furnace; first pass argon for 30 min to ensure that the entire tube furnace is in an argon atmosphere, and then heat it to 550 °C at a rate of 2.5 °C / min, hold for 6 h. The entire calcination process is carried out in an argon atmosphere; after cooling to room temperature, wash the obtained sample with deionized water by centrifugation three times, and then wash it with absolute ethanol by centrifugation three times. Finally, dry the sample in a vacuum at 60 °C for 24 h to obtain a dried sample.

[0045] The preparation of the colorimetric oxygen sensor is as follows:

[0046] Disperse the obtained functionalized carbon nitride CN-K or CN-Na in a mixed solution of electron sacrificial agent / water (TEOA / H2O), and the volume ratio of TEOA / H2O is 1 / 8; the concentration of CN-K or CN-Na in the suspension is 1 mg / mL to obtain suspensions of two CN-K or CN-Na colorimetric oxygen sensors.

[0047] Method for detecting oxygen:

[0048] As Figure 5The experimental setup diagram shown in (a) includes an air inlet, an empty flask, a cuvette, an air outlet, and an Ocean Optics optical fiber, which are connected in sequence. The cuvette is connected to the experimental setup. Take 2 mL (1 mg / mL) of the colorimetric oxygen sensor suspension of CN-K or CN-Na to be measured and place it in the cuvette. First, use the optical fiber to detect the reflectance Ro of the suspension. Then, introduce argon into the entire device for deoxygenation. After deoxygenation, irradiate the suspension under a xenon lamp (300 W) at room temperature for 5 min. At this time, the CN-K suspension changes from yellow to blue, and CN-Na changes from yellow to brown. Then, measure the reflectance R1 of the discolored suspension. At this time, inject a certain amount of oxygen (0 - 300 μL) into the reaction system through a microsyringe. The charged suspension will come into contact with oxygen, and electrons will be gradually consumed, and the color will gradually change from blue to the original yellow. The reflectance during this process will also change with the increase of oxygen. And at this time, both CN-K and CN-Na show different linear detection ranges and sensitivities, as detailed in Figure 5 (b).

[0049] To explore the differences between CN-K and CN-Na, first determine the structural differences between them. As Figure 1 shown in (a), CN (prepared by the method of Example 1 without adding potassium salt or sodium salt) shows two obvious peaks at about 13.1° and 27.3°, which are the (100) and (002) crystal planes respectively, representing in-plane stacking and stacking between layers; while the XRD pattern of CN-K shows a shift of the peak at 27° to about 28°, and the peak shape becomes sharper, indicating an increase in the crystallinity of CN-K and a decrease in the layer spacing; and the peak at about 13° disappears, and a new peak appears at about 8°, indicating a change in the in-plane structure. For CN-Na, the peak at about 27° becomes broad and low, indicating poor crystallinity and disordered interlayer stacking, probably due to the introduction of more defects. Figure 1 (b) is the FT-IR diagram. It can be seen from the figure that the characteristic peaks of CN, CN-K, and CN-Na observed at 810 and 1000 - 1700 cm -1 are respectively attributed to the in-plane bending of the heptazine unit ring and the stretching and bending modes of the conjugated CN heterocycle, indicating that they all maintain the basic structure of carbon nitride; while the new peaks that appear at 2200 cm -1 for CN-K and CN-Na are the peaks of the cyano group, which corresponds to the results of solid-state NMR; Figure 1 (c) and (d) In the C1s diagram of the XPS spectrum of CN-Na, 287.4 eV and in the O1s spectrum, 534.7 eV also indicate the presence of carbonyl groups. Through Figure 1 structural characterization, it shows that cyano groups are introduced into CN-K and cyano groups and carbonyl groups are introduced into CN-Na through doping.

[0050] To determine whether alkali metal ions have been introduced into carbon nitride, the contents of K and Na in CN-K and CN-Na were detected by ICP-MS. As shown in Table 1, the atomic percentages are 4.31% and 4.33% respectively, indicating that alkali metal ions have been successfully introduced into carbon nitride.

[0051] Table 1 Atomic percentages of each element

[0052]

[0053] As Figure 2 shown, the morphology of CN without doping alkali metals maintained the original morphology of carbon nitride, which was lamellar with a length of about 3 microns; while the crystallinity of CN-K obtained after doping with KI increased, and it was particles with a particle size of about 20 nm. CN-Na doped with NaI also became spherical particles with a particle size of 50 nm. This indicates that after doping with KI or NaI, the original morphology of the material changed, and the periodic arrangement of interlayer stacking or in-plane stacking may have changed.

[0054] As Figure 3 (a) shown, CN-K or CN-Na was dispersed in a mixed solution of triethanolamine and water. Triethanolamine was used as an electron donor. After deoxygenated light irradiation, the color of the CN-K suspension gradually changed from the original yellow to blue. After oxygen backfilling, the blue gradually disappeared and returned to the original yellow; CN-Na also changed from the original yellow to brown after deoxygenated light irradiation, and after oxygen backfilling, the color of the suspension changed back to yellow. To verify the influence of doping K or Na on the color change of the sample suspension, as Figure 3 (b) shown, a series of samples of CN-K / Na with different doping ratios were prepared (where according to the preparation method of Example 1, a mixed salt of KI and NaI was used, and their mass ratios were 3 / 1, 2 / 1, 1 / 1, 1 / 2, 1 / 3). As the content of doped Na gradually increased, under the same conditions, the color of the suspension after light irradiation gradually changed from blue to brown, indicating that different metal ions have different regulations on the structure of carbon nitride, resulting in different charging states and color changes; Figure 3 (c) is the detection chart of the reversible cycle performance of CN-K. It can be seen from the figure that CN-K can switch between the charge-discharge states before and after light irradiation, and the number of cycles reaches more than 100 times, and the reflectivity does not decrease significantly, indicating its excellent cycle performance and good repeatability.

[0055] Because the suspensions of CN-K and CN-Na colorimetric oxygen sensors showed different color changes, in order to explore the existence form of electrons in them, as Figure 4(a) As shown by the comparison of the ESR spectra of the suspension before and after light irradiation, there are obvious peaks near g = 2.003 in the suspensions of the CN-K and CN-Na colorimetric oxygen sensors after light irradiation. This is mainly due to the unpaired electrons of the sp2 hybridized carbon in carbon nitride. To explore the electron storage capacity and stability of the CN-K and CN-Na colorimetric oxygen sensors, OCP detection was used. The specific experimental process is as follows: A three-electrode system was adopted. The suspension of the CN-K or CN-Na colorimetric oxygen sensor was deposited on FTO to form a thin film (1 cm * 1 cm) as the working electrode, Ag / AgCl (saturated potassium chloride) as the reference electrode, and a platinum wire as the counter electrode. The electrolyte solution was a mixed solution of triethanolamine (TEOA) and KCl, where the concentration of KCl was 0.1 M and the volume ratio of TEOA / H2O was 1 / 8. The test was carried out in a quartz reaction cell with a screw cap. A hole was drilled in the cap to fix the electrodes and ensure the airtightness of the quartz cell. Before the test, argon was purged for 30 min, and then argon was maintained above the liquid level to keep the entire argon atmosphere, avoiding causing the liquid level to shake. The test instrument was Gamry 600. During the test, the three electrodes were connected, the FTO thin film was facing the xenon light source, and the time interval of the xenon lamp switch shutter was set to ensure that the switch could be automatically turned on or off. The electrochemical workstation was not required during the test. The thin film was excited by the light source to generate electrons, and then the OCP signal was generated. According to the electron storage capacity of the thin film, the OCP cyclic test was carried out (one cycle was the on and off of the light source). As Figure 4 (b) As shown in the OCP diagram, their cyclicity is up to more than 100 cycles, indicating that the stored electrons can exist stably. However, the OCP value of CN-K is about 0.8 V, and the OCP value of the CN-Na colorimetric oxygen sensor is about 0.4 V. The CN-K colorimetric oxygen sensor has a stronger electron storage capacity. However, under the same conditions, as Figure 4 (c) After the suspension of the CN-Na colorimetric oxygen sensor was deoxygenated and changed color under light irradiation, a larger oxygen consumption was required to return to the original state, indicating that in addition to storing electrons in the form of a capacitor, there may be other redox forms in the electron storage of CN-Na, such as a secondary battery.

[0056] The above proves that the newly synthesized CN-K and CN-Na colorimetric oxygen sensors both have the ability to store electrons. Moreover, the electron storage of CN-K is similar to that of a capacitor, and the electron storage of CN-Na is similar to the combination of a capacitor and a secondary battery. The stored electrons have high reducibility and high color reversibility and can be used to detect highly oxidizing oxygen.

[0057] Figure 5As shown in (b), CN-K, CN-Na, and CN-K / Na all exhibited different sensitivities and detection ranges during oxygen detection. CN-K had the highest sensitivity of 2 ppm, while CN-Na had the widest linear detection range of 0.16 - 9.16%. CN-K / Na was in between CN-K and CN-Na sensors. According to the preparation method of Example 1, a mixed salt of KI and NaI was used, and their mass ratios were 3 / 1, 2 / 1, 1 / 1, 1 / 2, and 1 / 3. In summary, a colorimetric sensor with different responses to oxygen can be obtained by regulating the structure of carbon nitride.

[0058] According to Figure 5 b, the sensitivities of the CN-K and CN-Na, as well as the CN-K / Na colorimetric oxygen sensors prepared in Example 1 of the present invention, were obtained. The detection ranges were 0.002 vol%, 0.051 vol% and 0.027 vol%, 0.008 - 0.25 vol%, 0.165 - 9.166 vol% and 0.083 - 4.166 vol% respectively.

[0059] Figure 5 Figure c is the proof of the selectivity of CN-K. By detecting the interference of several different gas molecules on CN-K, the concentration of the gas molecules was 0.258 vol%. After the CN-K suspension was deoxygenated and irradiated with light, it turned blue. It was contacted with different gas molecules respectively, and the change in reflectivity before and after contact was tested; the CN-K suspension contacted with different gases was the test substance with the same concentration, the same volume, and the same deoxygenation and light irradiation time. The study found that after CN-K turned blue, there was no obvious change in reflectivity, that is, no obvious color recovery after contacting with different gas molecules; only acetone and air had a slight color recovery, which was related to the oxygen contained in acetone and air, indicating that the CN-K sensor has good selectivity for oxygen.

[0060] Therefore, the sensor prepared by the present invention has low sensitivity, wide detection range, and good selectivity.

[0061] Example 2

[0062] The preparation processes of CN-K and CN-Na are as follows:

[0063] The volume of melamine in the crucible is 2 / 3. Cover 2 / 3 of the crucible lid, leaving a certain gap, and then place it in a muffle furnace; heat it to 600 °C at a rate of 10 °C / min, hold for 3 h, and after natural cooling to room temperature, weigh 0.5 g of the obtained bulk carbon nitride, then weigh 3 g of KI or NaI, mix it with the bulk carbon nitride, and grind it with an agate mortar to obtain a uniformly mixed sample; then place the mixed sample in the crucible, and leave a certain gap for the crucible lid (the crucible lid covers 2 / 3), and place it in a tube furnace; first pass argon for 30 min to ensure that the entire tube furnace is in an argon atmosphere, then heat it to 600 °C at a rate of 2.5 °C / min, hold for 4 h, and the entire calcination process is carried out in an argon atmosphere; after cooling to room temperature, wash the obtained sample with deionized water by centrifugation three times, then wash it with absolute ethanol by centrifugation three times, and finally dry the sample in vacuum at 60 °C for 24 h to obtain a dried sample CN-K or CN-Na.

[0064] The preparation of the colorimetric oxygen sensor is as follows:

[0065] Disperse the obtained functionalized carbon nitride CN-K or CN-Na in a mixture of electron sacrificial agent / water (TEOA / H2O) with a volume ratio of TEOA / H2O of 1 / 16; the concentration of CN-K or CN-Na in the suspension is 1 mg / mL to obtain suspensions of two CN-K or CN-Na colorimetric oxygen sensors.

[0066] Example 3

[0067] The preparation process of CN-K and CN-Na is as follows:

[0068] The volume of dicyandiamide in the crucible is 2 / 3. Cover 2 / 3 of the crucible lid, leaving a certain gap, and then place it in a muffle furnace; heat it to 550 °C at a rate of 12 °C / min, hold for 4 h, and after natural cooling to room temperature, weigh 0.3 g of the obtained bulk carbon nitride, then weigh 3 g of KCl or NaCl, mix it with the bulk carbon nitride, and grind it with an agate mortar to obtain a uniformly mixed sample; then place the mixed sample in the crucible, and leave a certain gap for the crucible lid (the crucible lid covers 2 / 3), and place it in a tube furnace; first pass argon for 30 min to ensure that the entire tube furnace is in an argon atmosphere, then heat it to 550 °C at a rate of 2.5 °C / min, hold for 6 h, and the entire calcination process is carried out in an argon atmosphere; after cooling to room temperature, wash the obtained sample with deionized water by centrifugation three times, then wash it with absolute ethanol by centrifugation three times, and finally dry the sample in vacuum at 60 °C for 24 h to obtain a dried sample CN-K or CN-Na.

[0069] The preparation of the colorimetric oxygen sensor is as follows:

[0070] Disperse the obtained functionalized carbon nitride CN-K or CN-Na in a mixed solution of electron sacrificial agent / water (TEOA / H2O), and the volume ratio of TEOA / H2O is 1 / 2; the concentration of CN-K or CN-Na in the suspension is 1 mg / mL to obtain suspensions of two CN-K or CN-Na colorimetric oxygen sensors.

[0071] Example 4

[0072] The preparation processes of CN-K and CN-Na are as follows:

[0073] The volume of thiourea in the crucible is 2 / 3. Cover 2 / 3 of the crucible lid, leaving a certain gap, and then place it in a muffle furnace; heat it to 500 °C at a rate of 12 °C / min, keep it warm for 4 h, and after natural cooling to room temperature, weigh 0.2 g of the obtained bulk carbon nitride, then weigh 3 g of KSCN or NaSCN, mix it with the bulk carbon nitride, and grind it with an agate mortar to obtain a uniformly mixed sample; then place the mixed sample in the crucible, and leave a certain gap for the crucible lid (cover 2 / 3 of the crucible lid), and place it in a tube furnace; first pass argon for 30 min to ensure that the entire tube furnace is in an argon atmosphere, then heat it to 600 °C at a rate of 2 °C / min, and keep it warm for 6 h. The entire calcination process is carried out in an argon atmosphere; after cooling to room temperature, wash the obtained sample with deionized water by centrifugation three times, then wash it with anhydrous ethanol by centrifugation three times, and finally dry the sample in a vacuum at 60 °C for 24 h to obtain the dried sample CN-K or CN-Na.

[0074] The preparation of the colorimetric oxygen sensor is as follows:

[0075] Disperse the obtained functionalized carbon nitride CN-K or CN-Na in a mixed solution of electron sacrificial agent / water (isopropanol / H2O), and the volume ratio of isopropanol / H2O is 1 / 20; the concentration of CN-K or CN-Na in the suspension is 0.5 mg / mL to obtain suspensions of two CN-K or CN-Na colorimetric oxygen sensors.

[0076] Example 5

[0077] The preparation processes of CN-K and CN-Na are as follows:

[0078] The volume of urea in the crucible is 2 / 3. Cover 2 / 3 of the crucible lid, leaving a certain gap, and then place it in the muffle furnace; heat it at 10 °C / min to 500 °C, hold for 5 h, and after natural cooling to room temperature, weigh 0.1 g of the obtained bulk carbon nitride, then weigh 3 g of KI or NaI, mix it with the bulk carbon nitride, and grind it with an agate mortar to obtain a uniformly mixed sample; then place the mixed sample in the crucible, and leave a certain gap in the crucible lid (cover 2 / 3 of the crucible lid), and place it in the tube furnace; first pass argon for 30 min to ensure that the entire tube furnace is in an argon atmosphere, then heat it at 2.5 °C / min to 600 °C, hold for 6 h, and the entire calcination process is carried out in an argon atmosphere; after cooling to room temperature, wash the obtained sample with deionized water by centrifugation three times, then wash it with absolute ethanol by centrifugation three times, and finally dry the sample in vacuum at 60 °C for 24 h to obtain the dried sample CN-K or CN-Na.

[0079] The preparation of the colorimetric oxygen sensor is as follows:

[0080] Disperse the obtained functionalized carbon nitride CN-K or CN-Na in a mixed solution of electron sacrificial agent / water (4-MBA / H2O), and the volume ratio of 4-MBA / H2O is 1 / 30; the concentration of CN-K or CN-Na in the suspension is 2 mg / mL to obtain suspensions of two CN-K or CN-Na colorimetric oxygen sensors.

Claims

1. A preparation method of a colorimetric sensor based on an electronic storage mechanism, characterized in that, It includes the following steps: (1) Preparation of functionalized carbon nitride: The carbon nitride precursor is calcined to obtain bulk carbon nitride, which is then thoroughly ground with potassium salt or sodium salt respectively. The ground mixture is calcined in an inert gas to obtain alkali metal-doped carbon nitride; The product is centrifuged and washed, and after vacuum drying, functionalized carbon nitride CN-K or CN-Na is obtained; (2) Construction of the colorimetric sensor: The obtained functionalized carbon nitride CN-K or CN-Na is dispersed in a mixed solution of an electron sacrificial agent and water, the oxygen in the suspension is removed, and it is sealed and stored; the electron sacrificial agent is triethanolamine, methanol, isopropanol or 4-methylbenzyl alcohol.

2. The preparation method according to claim 1, characterized in that, The carbon nitride precursor described in step (1) is an organic compound containing carbon and nitrogen elements; the carbon nitride precursor is urea, dicyandiamide, melamine, monocyanamide or thiourea.

3. The preparation method according to claim 1, characterized in that The potassium salt described in step (1) is KSCN, KCl or KI; the sodium salt is NaCl or NaI.

4. The preparation method according to claim 1, characterized in that, The calcination conditions of the bulk carbon nitride in step (1) are heating to 500-600 °C at a rate of 10-12 °C / min and holding for 3-5 h; the calcination of the ground mixture is heating to 500-600 °C at a rate of 2-2.5 °C / min and holding for 4-6 h.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the bulk carbon nitride to the potassium salt or sodium salt in step (1) is 1 / 6 - 1 / 30.

6. The preparation method according to claim 1, characterized in that, The ratio of the volume of the electron sacrificial agent to the total volume of the mixed solution in step (2) is 1 / 2 - 1 / 50; in step (2), the functionalized carbon nitride is dispersed in a mixed solution of an electron sacrificial agent and water, and the concentration is 0.5-2 mg / mL.

7. A colorimetric sensor based on the electron storage mechanism prepared by the preparation method described in claim 1.

8. Application of the colorimetric sensor based on the electron storage mechanism described in claim 7 in detecting oxygen.

9. The application according to claim 8, characterized in that, After the suspension of the carbon nitride-based colorimetric sensor is deoxygenated and irradiated with light, the color of the suspension after irradiation becomes blue or brown; then oxygen is injected into the detection device. After the suspension contacts oxygen, the color changes from blue or brown to the original yellow. The irradiation time of the colorimetric oxygen sensor using potassium salt is 3-10 min, and the irradiation time of the carbon nitride-based colorimetric sensor using sodium salt is 10-20 min.

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