CN112723325A - Phosphorus-doped graphite-phase carbon nitride nanosheet and preparation method and application thereof - Google Patents
Phosphorus-doped graphite-phase carbon nitride nanosheet and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to the technical field of fluorescence detection, and provides a phosphorus-doped graphite-phase carbon nitride nanosheet and a preparation method and application thereof. The method comprises the steps of firstly preparing graphite-phase carbon nitride solid powder by adopting a thermal decomposition method, ultrasonically dispersing the graphite-phase carbon nitride solid powder in water, and then obtaining the phosphorus-doped graphite-phase carbon nitride nanosheet through centrifugal separation and filtration. According to the invention, the phosphorus-doped graphite-phase carbon nitride in the bulk phase is prepared into the nanosheets with large specific surface areas and holes by using element doping and ultrasonic stripping methods, and the obtained phosphorus-doped graphite-phase carbon nitride nanosheets have good fluorescence properties and good stability, have selective response to iron ions, and are suitable for analyzing and detecting trace iron ions. The results of the examples show that when the phosphorus-doped graphite-phase carbon nitride is applied to the detection of iron ions, the detection limit can reach 1.63 mu mol/L.
Description
Technical Field
The invention relates to the technical field of fluorescence detection, in particular to a phosphorus-doped graphite-phase carbon nitride nanosheet and a preparation method and application thereof.
Background
Heretofore, there have been many methods for detecting metal ions, such as fluorescence, spectrophotometry, electrochemistry, chromatography, and the like. Among them, the fluorescence method is characterized in that the concentration of an analyte can be indirectly calculated by measuring the decrease in fluorescence intensity after introduction of the analyte. Compared with other methods, the fluorescence method has no damage to the sample and even can be used reversibly, the operation is simple and convenient, trace detection can be realized, and the instrument and equipment are simple.
Graphite phase carbon nitride (g-C)3N4) As an organic nonmetal semiconductor material capable of being responded by visible light, compared with the traditional semiconductor, the organic nonmetal semiconductor material has a unique material structure and an electronic structure, and has superiority in performance, such as good wear resistance, high thermal stability, high chemical stability, good fluorescence performance and the like, because a C-N heterocyclic ring is combined by covalent bonds. With the continuous and intensive research, g-C is found3N4Has good application prospect in the aspects of sensing, medicine, catalysis, luminescence regulation and control and the like.
Iron ion (Fe)3+) Is one of the important nutrients in human health and water environment, but excessive intake and accumulation of iron can lead to side effects and irreversible damage. At present, g-C has not been utilized3N4And (3) related reports of fluorescence detection of iron ions.
Disclosure of Invention
In view of the above, the present invention provides a phosphorus-doped graphite-phase carbon nitride (P-g-C)3N4) Nanosheet and preparation method and application thereof. The phosphorus-doped graphite phase carbon nitrideThe rice flake has good fluorescence property and stability, has selective response to iron ions, and is suitable for analyzing and detecting trace iron ions.
In order to achieve the above object, the present invention provides the following technical solutions:
a preparation method of a phosphorus-doped graphite-phase carbon nitride nanosheet comprises the following steps:
(1) mixing nitrogen-containing organic matters and ammonium phosphate, and then carrying out thermal decomposition to obtain phosphorus-doped graphite-phase carbon nitride solid powder;
(2) mixing the phosphorus-doped graphite-phase carbon nitride solid powder with water, and then carrying out ultrasonic dispersion to obtain a phosphorus-doped graphite-phase carbon nitride suspension;
(3) and carrying out centrifugal separation on the phosphorus-doped graphite-phase carbon nitride suspension, and filtering the obtained supernatant to obtain a colloidal solution of the phosphorus-doped graphite-phase carbon nitride nanosheets.
Preferably, the nitrogen-containing organic matter comprises melamine and/or urea; the ammonium phosphate comprises one or more of ammonium phosphate, ammonium dihydrogen phosphate and diammonium hydrogen phosphate; the molar ratio of the nitrogen-containing organic matter to the ammonium phosphate is 0.024: 0.0004-0.0075.
Preferably, the thermal decomposition temperature is 500-650 ℃, the time is 3.5-6 h, and the heating rate of heating to the thermal decomposition temperature is 3-6 ℃/min.
Preferably, the mass ratio of the phosphorus-doped graphite-phase carbon nitride solid powder to water is 1: 300-500.
Preferably, the ultrasonic dispersion time is 10-13 h, and the power is 50-70 Hz.
Preferably, the centrifugal separation comprises a first centrifugal separation and a second centrifugal separation which are sequentially carried out, the rotating speed of the first centrifugal separation is 7000-9000 r/min, and the time is 6-9 min; the rotating speed of the second centrifugal separation is 10000-12000 r/min, and the time is 15-20 min.
Preferably, the filtration membrane is an aqueous phase microporous membrane.
The invention provides the phosphorus-doped graphite-phase carbon nitride nanosheet prepared by the preparation method in the scheme, and the size of the phosphorus-doped graphite-phase carbon nitride nanosheet is 50-100 nm.
The invention provides application of the phosphorus-doped graphite-phase carbon nitride nanosheet in the scheme in fluorescent sensing detection of iron ions.
The invention provides a preparation method of phosphorus-doped graphite-phase carbon nitride nanosheets, which comprises the steps of firstly preparing graphite-phase carbon nitride solid powder by a thermal decomposition method, ultrasonically dispersing the graphite-phase carbon nitride solid powder in water, and then obtaining a colloidal solution of the phosphorus-doped graphite-phase carbon nitride nanosheets by centrifugal separation and filtration. The invention utilizes the element doping and ultrasonic stripping methods to prepare the massive phosphorus-doped graphite-phase carbon nitride into the nanosheets with large specific surface area and holes, and the obtained phosphorus-doped graphite-phase carbon nitride nanosheets are uniformly and stably dispersed in the colloidal solution, are not easy to agglomerate, have good fluorescence performance, show obvious Tyndall phenomenon and blue fluorescence characteristic, have selective response to iron ions, and are suitable for analyzing and detecting trace iron ions in complex samples such as organisms, foods, environments and the like. The example result shows that when the phosphorus-doped graphite-phase carbon nitride nanosheet is applied to detection of iron ions, the detection limit can reach 1.63 mu mol/L.
Drawings
FIG. 1 is a diagram of the preparation of P-g-C in an example of the present invention3N4A process schematic of the nanoplatelets;
FIG. 2 shows P-g-C in example 13N4Solid powder and P-g-C3N4A microtopography of the nanoplatelets, wherein (a) is P-g-C3N4SEM image of solid powder, (b) is P-g-C3N4TEM image of nano-sheet, (b) inserting image at upper right corner is P-g-C3N4A fluorescence effect graph of the nanosheet colloidal solution under laser irradiation;
FIG. 3 shows P-g-C in example 13N4Solid powder and P-g-C3N4XRD pattern of nanosheet;
FIG. 4 shows P-g-C in example 13N4Solid powder and P-g-C3N4FT-IR plot of nanoplatelets;
FIG. 5 shows P-g-C in example 13N4Solid powder and P-g-C3N4Ultraviolet spectrum of the nanosheets;
FIG. 6 shows P-g-C in example 13N4Solid powder and P-g-C3N4The fluorescence spectrum of the nano-sheet, the picture inserted at the upper right corner is P-g-C3N4A fluorescence effect diagram of the nano-sheet colloidal solution under ultraviolet irradiation;
FIG. 7 shows P-g-C in example 23N4A test result graph of the selectivity of the nanosheets to iron ions, wherein (a) is P-g-C3N4Adding Fe into the nanosheet colloidal solution3+,Cu2+,Al3+,Zn2+,Sr2+,Mg2+,Cr2+,Bb2+The fluorescence intensity change pattern after (b) is a pattern of conversion to Cu2+,Al3+,Zn2+,Sr2+,Mg2+,Cr2+,Bb2+P-g-C of3N4Adding Fe into the nanosheet colloidal solution3+The subsequent fluorescence intensity change map;
FIG. 8 shows P-g-C in example 33N4Adding Fe into nanosheet colloidal solution3+Front and back fluorescence lifetime curves;
FIG. 9 shows P-g-C3N4Adding Fe with different concentrations into the nano colloidal solution3+The result of the fluorescence intensity test is shown in the upper right-hand corner of the graph as a linear fitting curve.
Detailed Description
The invention provides a preparation method of a phosphorus-doped graphite-phase carbon nitride nanosheet, which comprises the following steps:
(1) mixing nitrogen-containing organic matters and ammonium phosphate, and then carrying out thermal decomposition to obtain phosphorus-doped graphite-phase carbon nitride solid powder;
(2) mixing the phosphorus-doped graphite-phase carbon nitride solid powder with water, and then carrying out ultrasonic dispersion to obtain a phosphorus-doped graphite-phase carbon nitride suspension;
(3) and carrying out centrifugal separation on the phosphorus-doped graphite-phase carbon nitride suspension, and filtering the obtained supernatant to obtain the phosphorus-doped graphite-phase carbon nitride nanosheet.
The invention mixes nitrogen-containing organic matter and ammonium phosphate salt and then carries out thermal decomposition to obtain phosphorus-doped graphite phase carbon nitride (P-g-C)3N4) And (3) solid powder. In the present invention, the nitrogen-containing organic substance preferably comprises melamine and/or urea, more preferably melamine; the ammonium phosphate salt preferably comprises one or more of ammonium phosphate, ammonium dihydrogen phosphate and diammonium hydrogen phosphate, and more preferably diammonium hydrogen phosphate; according to the invention, ammonium phosphate is used as a phosphorus source, so that the introduction of impurities can be avoided; the molar ratio of the nitrogen-containing organic substance to the ammonium phosphate salt is preferably 0.024: 0.0004-0.0075, and more preferably 0.024: 0.001-0.005.
In the present invention, the method for mixing the nitrogen-containing organic substance and the ammonium phosphate salt is preferably: mixing nitrogen-containing organic matters and ammonium phosphate, grinding, and stirring and mixing the mixed solid powder and water to obtain mixed feed liquid; and drying the mixed material liquid and then grinding again to obtain the mixture of the nitrogen-containing organic matter and the ammonium phosphate. In the invention, the dosage ratio of the mixed solid powder and water is preferably 3.2g:50mL, the stirring and mixing time is preferably 1h, the drying temperature is preferably 60 ℃, and the drying time is preferably 12 h; the grinding conditions are not particularly required in the invention, and the solid powder which is uniformly mixed can be obtained by adopting the conditions which are well known by the technical personnel in the field.
In the invention, the thermal decomposition temperature is preferably 500-650 ℃, more preferably 550-600 ℃, the thermal decomposition time is preferably 3.5-6 h, more preferably 4h, and the heating rate of heating to the thermal decomposition temperature is preferably 3-6 ℃/min; the thermal decomposition is preferably carried out in a shaft furnace. In the thermal decomposition process, the melamine is pyrolyzed to generate graphite-phase carbon nitride, meanwhile, the phosphate ammonium salt is pyrolyzed, and the generated phosphorus atoms are doped in the graphite-phase carbon nitride to obtain the phosphorus-doped graphite-phase carbon nitride. The invention dopes phosphorus in the graphite phase carbon nitride, which can cause the fluorescence peak of the graphite phase carbon nitride to have red shift and wide side, but can not change the wavelength range of light absorption of the pure graphite phase carbon nitride.
After thermal decomposition is finished, the polymerization product is preferably naturally cooled to room temperature and then ground to obtain phosphorus-doped graphite-phase carbon nitride solid powder; the phosphorus-doped graphite-phase carbon nitride solid powder obtained by the invention is a block phase.
After the phosphorus-doped graphite-phase carbon nitride solid powder is obtained, the phosphorus-doped graphite-phase carbon nitride solid powder is mixed with water and then subjected to ultrasonic dispersion to obtain the phosphorus-doped graphite-phase carbon nitride suspension. In the invention, the mass ratio of the phosphorus-doped graphite-phase carbon nitride solid powder to water is preferably 1: 300-500, and more preferably 1: 350-450; the time of ultrasonic dispersion is preferably 10-13 h, more preferably 11-12 h, and the power is preferably 50-70 Hz, more preferably 55-65 Hz. The invention strips the phosphorus-doped graphite-phase carbon nitride solid powder of the block phase by ultrasonic dispersion, and the obtained phosphorus-doped graphite-phase carbon nitride suspension is a mixture of the block-phase phosphorus-doped graphite-phase carbon nitride and the nano flaky phosphorus-doped graphite-phase carbon nitride.
After the phosphorus-doped graphite-phase carbon nitride suspension is obtained, the phosphorus-doped graphite-phase carbon nitride suspension is centrifugally separated, and the obtained supernatant is filtered to obtain phosphorus-doped graphite-phase carbon nitride nanosheets (P-g-C)3N4Nanoplatelets). In the invention, the centrifugal separation preferably comprises a first centrifugal separation and a second centrifugal separation which are sequentially carried out, the rotating speed of the first centrifugal separation is preferably 7000-9000 r/min, more preferably 8000r/min, and the time is preferably 7-9 min, more preferably 8 min; the rotation speed of the second centrifugal separation is preferably 10000-12000 r/min, more preferably 10000-11000 r/min, and the time is preferably 15-20 min, more preferably 15-18 min. In the present invention, specifically, the supernatant obtained after the first centrifugation is subjected to the second centrifugation. The invention separates and removes undissolved sediment and large-size phosphorus-doped graphite-phase carbon nitride through first centrifugal separation and second centrifugal separation.
In the present invention, the filtration membrane is preferably an aqueous phase microfiltration membrane. The filtrate obtained after filtration is the phosphorus-doped graphite-phase carbon nitride nanosheet colloidal solution, the phosphorus-doped graphite-phase carbon nitride nanosheets finally obtained by the method exist in the form of colloidal solution, and the phosphorus-doped graphite-phase carbon nitride nanosheets are highly uniformly dispersed in the colloidal solution, so that the stability is good. In the present invention, the concentration of the obtained phosphorus-doped graphite-phase carbon nitride nanosheet colloidal solution is preferably 0.06 mg/mL.
The invention also provides the phosphorus-doped graphite-phase carbon nitride nanosheet prepared by the preparation method in the scheme, wherein the size of the phosphorus-doped graphite-phase carbon nitride nanosheet is 50-100 nm, and preferably 60-80 nm. The phosphorus-doped graphite-phase carbon nitride nanosheet provided by the invention exists in the form of a colloidal solution, and the nanosheet is highly and uniformly dispersed in the colloidal solution, is not easy to agglomerate, has good fluorescent property, and has selective response to iron ions.
The invention also provides application of the phosphorus-doped graphite-phase carbon nitride nanosheet in the scheme in fluorescent sensing detection of iron ions. In the present invention, the iron ion is particularly preferably an iron ion in a living being, a food or an environment, such as an iron ion in a complex water body. The invention has no special requirements on the specific detection method of the fluorescence detection, and the method which is well known by the technicians in the field can be adopted; in the specific embodiment of the invention, preferably, the solution to be detected is added into the phosphorus-doped graphite-phase carbon nitride nanosheet colloidal solution prepared by the above scheme, the fluorescence intensity change before and after the addition is tested, and the iron ion content in the solution to be detected is obtained by calculation according to the fluorescence quenching efficiency and the standard curve; the standard curve is a relation curve of fluorescence quenching efficiency and iron ion concentration, and the method for obtaining the standard curve has no special requirement and can be realized by adopting a method well known by the technical personnel in the field.
The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention.
FIG. 1 is a diagram of the preparation of P-g-C in an example of the present invention3N4Schematic process of nanosheets, wherein a bulk phase P-g-C is first prepared using thermal decomposition of ammonium dihydrogen phosphate and melamine3N4(i.e., P-g-C)3N4Solid powder) and then dispersed by ultrasound to obtain a suspension (the suspension comprises a bulk phase P-g-C)3N4And P-g-C3N4Nanoplatelets) afterObtaining P-g-C by a first centrifugation and a second centrifugation3N4Nanosheets.
Example 1
(1) Weighing 3g of melamine and 0.2g of diammonium hydrogen phosphate solid powder, fully grinding, adding 50mL of deionized water, stirring for 1h to completely mix, placing the mixed solution in an oven, drying for 12h at 60 ℃, fully grinding, placing in an alumina crucible, placing in a well-type furnace, keeping the temperature at 550 ℃ for 4h at the programmed heating rate of 4 ℃/min, naturally cooling to room temperature, fully grinding to yellow P-g-C3N4Solid powder is ready for use.
(2) Weighing 100mg of P-g-C3N4Adding the solid powder into a beaker filled with 100mL of deionized water, and continuously performing ultrasonic treatment for 10h to obtain P-g-C3N4A suspension; P-g-C3N4Centrifuging the suspension at 8000rpm/min for 8min, taking out supernatant, centrifuging at 10000rpm/min for 15min to obtain stable and uniform P-g-C3N4Nanosheet (designated as P-gcn) colloidal solution.
For P-g-C3N4Solid powder and P-g-C3N4The microscopic morphology of the nanosheets is observed, and the result is shown in FIG. 2, wherein (a) in FIG. 2 is P-g-C3N4SEM image of solid powder, (b) is P-g-C3N4TEM image of nano-sheet, (b) inserting image at upper right corner is P-g-C3N4A fluorescence effect graph of the nanosheet colloidal solution under laser irradiation; as can be seen from FIG. 2, P-g-C3N4SEM of solid powder shows that the powder is piled up in blocks, and P-g-C3N4The TEM of the nano-sheet is nano-sized and has a planar structure, and a light path can be obviously observed by irradiating the colloidal solution with laser, which is the Tyndall effect of the colloid. As can be seen from the above results, P-g-C obtained by the present invention3N4The solution of the nano-sheets is a colloidal solution and has high stability.
FIG. 3 is P-g-C3N4Solid powder and P-g-C3N4XRD pattern of nanosheet, FIG. 4 is P-g-C3N4Solid powder and P-g-C3N4FT-IR plot of nanoplatelets. As can be seen from FIG. 3, P-g-C3N4The characteristic peak intensity of the nanosheets at 27.69 ° is significantly reduced due to the reduced level spacing of the C — N bonds. Meanwhile, the peak of the nanosheet sample at the (002) plane was found to have shifted slightly from 27.52 ° to 27.69 ° relative to the powdered sample, with the corresponding interbed reduction from 0.32390 to 0.32206 nm; it can be seen from FIG. 4 that the FT-IR spectrum of the material before and after exfoliation is substantially unchanged.
FIG. 5 shows P-g-C3N4Solid powder and P-g-C3N4Ultraviolet spectrum of the nanosheet, P-g-C in FIG. 63N4Solid powder and P-g-C3N4Fluorescence spectrum of the nanosheet, and the inset in the upper right corner of FIG. 6 is P-g-C3N4And (3) a fluorescence effect diagram of the nanosheet colloidal solution under ultraviolet light irradiation. As can be seen from FIG. 5, P-g-C3N4The forbidden band width of the nanosheets increased from 2.51eV to 2.62eV as compared to before exfoliation. Excitation study at 370nm found that bulk phase P-g-C3N4(i.e., P-g-C)3N4Solid powder) has the highest emission intensity at 449nm, and P-g-C3N4The nano-sheet has the highest emission intensity at 430nm, the fluorescence peak of the sample after stripping is blue-shifted by 19nm compared with the sample before stripping due to quantum efficiency generated by stripping, and P-g-C3N4The peak width of the nano-sheet is compared with that of bulk phase P-g-C3N4Narrowing the peak width of (c); as can be seen from the inset in FIG. 6, P-g-C is observed under 365nm UV light3N4The nanosheet colloidal solution exhibited a single stable blue fluorescence.
Example 2
Test P-g-C3N4The selectivity of the nanosheets to iron ions comprises the following steps: selection of different metal ions (Fe)3+,Cu2 +,Al3+,Zn2+,Sr2+,Mg2+,Cr2+,Bb2+) Separately added to the P-g-C prepared in example 13N4In the nanosheet colloidal solution (with the concentration of 0.06mg/mL), the addition amount of metal ions is 1 mmol/L; testing after adding each metal ionFluorescence intensity of the solution, and fluorescence quenching efficiency (I/I) was calculated0Wherein I is the fluorescence intensity after adding metal ions, I0Fluorescence intensity without metal ion addition);
to P-g-C prepared in example 13N4Adding Cu into nanosheet colloidal solution2+,Al3+,Zn2+,Sr2+,Mg2+,Cr2+,Bb2+The addition amount is 1mmol/L, the fluorescence intensity is tested, and then Fe is respectively added into the solution3+The amount added was 0.04 mmol/L. Testing addition of Fe3+Fluorescence intensity of the latter solution.
The results are shown in FIG. 7, where P-g-C is shown in FIG. 73N4A test result graph of the selectivity of the nanosheets to iron ions, wherein (a) is P-g-C3N4Adding Fe into the nanosheet colloidal solution3+,Cu2+,Al3+,Zn2+,Sr2+,Mg2+,Cr2+,Bb2+The fluorescence intensity change pattern after (b) is a pattern of conversion to Cu2+,Al3+,Zn2+,Sr2+,Mg2+,Cr2+,Bb2+P-g-C of3N4Adding Fe into the nanosheet colloidal solution3+The fluorescence intensity change after the above was analyzed. As can be seen from (a) in FIG. 7, Fe3+The fluorescence intensity of the added solution is obviously reduced, the fluorescence quenching rate is obviously higher than that of other metal ions, and the P-g-C of the invention is proved3N4The nano-sheet can be used as a fluorescent probe to detect Fe3+. As can be seen from FIG. 7 (b), Fe was added to the solution3+When the concentration is 25 times less than that of other metal ions, the fluorescence intensity of the solution still further quenches, which indicates that other metal ions are used for Fe3+Has little influence, which shows that the P-g-C of the invention3N4Nanosheet pair Fe3+Has high selectivity.
Example 3
P-g-C3N4Nanosheet pair Fe3+Determination of detection Limit of
(1) Quenching type
By measuring P-g-C3N4Adding Fe into nanosheet colloidal solution3+The lifetime curves before and after determining the type of fluorescence quenching process towards P-g-C3N4Adding Fe into nanosheet colloidal solution3+The fluorescence lifetime curves before and after the addition of Fe are shown in FIG. 8, and it can be seen from FIG. 83+Then, P-g-C3N4The fluorescence lifetime of the nanosheet colloidal solution did not change. Indicates P-g-C3N4And Fe3+The fluorescence quenching process in between mainly results from a static quenching process. The static quenching process follows the Stern-Volmer program, as shown in formula I:
in formula I: f0And F represents the absence and presence of the analyte Fe, respectively3+When P-g-C3N4Fluorescence intensity of the nanosheet colloidal solution; q represents the concentration of the detection object; kSVIs the quenching effect coefficient.
The fluorescence quenching efficiency can be fitted linearly by an equation. The invention mixes Fe with different concentrations3+The solutions were added to P-g-C separately3N4In a nano colloidal solution (concentration of 0.06mg/mL), the relative fluorescence intensity, Fe, was measured3+The concentrations of the solutions were 1. mu. mol/L, 2. mu. mol/L, 3. mu. mol/L, 4. mu. mol/L, 5. mu. mol/L, 6. mu. mol/L, 7. mu. mol/L and 8. mu. mol/L, respectively. Obtaining Fe according to the test result of fluorescence intensity3+The results of the fitted curves of concentration and fluorescence quenching efficiency are shown in FIG. 9. From the linearly fitted curve in FIG. 9, P-g-C3N4Fluorescence intensity and Fe of nanosheet colloidal solution3+The linear relationship of the ion concentration between 1 to 8 mu mol/L is F00.0118c +1.23348, and correlation coefficient R of fitting graph2Is 0.966.
(2) Detection limit
Fitting the fluorescence quenching efficiency through the fitting equation in (1), and detecting to find that Fe is present3+Quenching was almost complete 9min after addition, and 9min was used as standard for all subsequent steps. In addition, the limit of detection (LOD) is carried out by the formula IIAnd (3) calculating:
in formula II, K is a numerical factor chosen for confidence level, determined here as 3, δ is the relative standard deviation of the blank sample under parallel measurement conditions (n-7), and S is the sensitivity of the calibration curve.
The calculation is carried out by the formula II, and the result shows that the Fe content is in the range of Fe3+When the signal to noise ratio is 3, the detection limit LOD is about 1.63 mu mol/L.
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 (9)
1. A preparation method of a phosphorus-doped graphite-phase carbon nitride nanosheet is characterized by comprising the following steps:
(1) mixing nitrogen-containing organic matters and ammonium phosphate, and then carrying out thermal decomposition to obtain phosphorus-doped graphite-phase carbon nitride solid powder;
(2) mixing the phosphorus-doped graphite-phase carbon nitride solid powder with water, and then carrying out ultrasonic dispersion to obtain a phosphorus-doped graphite-phase carbon nitride suspension;
(3) and carrying out centrifugal separation on the phosphorus-doped graphite-phase carbon nitride suspension, and filtering the obtained supernatant to obtain a colloidal solution of the phosphorus-doped graphite-phase carbon nitride nanosheets.
2. The method according to claim 1, wherein the nitrogen-containing organic substance comprises melamine and/or urea; the ammonium phosphate comprises one or more of ammonium phosphate, ammonium dihydrogen phosphate and diammonium hydrogen phosphate; the molar ratio of the nitrogen-containing organic matter to the ammonium phosphate is 0.024: 0.0004-0.0075.
3. The method according to claim 1, wherein the thermal decomposition temperature is 500 to 650 ℃ for 3.5 to 6 hours, and the temperature increase rate for increasing the temperature to the thermal decomposition temperature is 3 to 6 ℃/min.
4. The preparation method according to claim 1, wherein the mass ratio of the phosphorus-doped graphite-phase carbon nitride solid powder to water is 1:300 to 500.
5. The preparation method according to claim 1, wherein the ultrasonic dispersion time is 10-13 h, and the power is 50-70 Hz.
6. The preparation method according to claim 1, wherein the centrifugal separation comprises a first centrifugal separation and a second centrifugal separation which are sequentially carried out, wherein the rotation speed of the first centrifugal separation is 7000-9000 r/min, and the time is 6-9 min; the rotating speed of the second centrifugal separation is 10000-12000 r/min, and the time is 15-20 min.
7. The method according to claim 1, wherein the filtration membrane is an aqueous microporous filtration membrane.
8. The phosphorus-doped graphite-phase carbon nitride nanosheet prepared by the preparation method of any one of claims 1 to 7, wherein the phosphorus-doped graphite-phase carbon nitride nanosheet has a size of 50 to 100 nm.
9. Use of the phosphorus-doped graphite-phase carbon nitride nanosheets of claim 8 in the fluorescent sensing detection of ferric ions.
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