CN111389458B - Carboxyl-containing perylene bisimide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst and preparation method and application thereof - Google Patents

Carboxyl-containing perylene bisimide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst and preparation method and application thereof Download PDF

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CN111389458B
CN111389458B CN202010046812.5A CN202010046812A CN111389458B CN 111389458 B CN111389458 B CN 111389458B CN 202010046812 A CN202010046812 A CN 202010046812A CN 111389458 B CN111389458 B CN 111389458B
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oxygen
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pdi
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徐婧
王周平
高遒竹
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Jiangnan University
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Abstract

The invention discloses a carboxyl-containing perylene bisimide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst and a preparation method and application thereof, wherein the photocatalyst is formed by compounding carboxyl-containing perylene bisimide and oxygen-doped carbon nitride nanosheets through electrostatic interaction and pi-pi interaction, wherein the mass ratio of the oxygen-doped carbon nitride nanosheets to the carboxyl-containing perylene bisimide is 1: 0.001-0.8; the carboxyl perylene bisimide is modified on the oxygen-doped carbon nitride nanosheet through an in-situ method. Compared with the prior art, the invention has the following advantages: (1) compared with O-CN and PDI in the prior art, the photocatalyst has more excellent performances of photocatalytic degradation of pollutants, killing of pathogenic bacteria and photolysis of water to generate oxygen; (2) the method has the advantages of low raw material cost and simple process, effectively reduces the product cost, is suitable for industrial mass production, and has very high application prospect and practical value.

Description

Carboxyl-containing perylene bisimide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst and preparation method and application thereof
Technical Field
The invention belongs to the technical field of photocatalytic materials, and relates to a heterojunction photocatalyst, in particular to a carboxyl-containing perylene bisimide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst, and a preparation method and application thereof.
Background
The carbon nitride is a nonmetal n-type organic semiconductor visible light photocatalyst, has the advantages of simple preparation, low cost, good stability, no toxicity, easy regulation and control and the like, and is widely applied to the aspects of pollutant degradation, antibiosis and the like. However, carbon nitride prepared by the traditional polycondensation method has large particle size, low visible light utilization rate and low quantum efficiency, so that the photocatalytic activity of the carbon nitride is not ideal enough. Therefore, it is important to develop a carbon nitride-based photocatalyst with a nano-structure morphology, a wide visible spectrum response range and a rapid photon-generated carrier separation and migration capability.
Perylene bisimide (PDI) is a novel n-type organic semiconductor photocatalyst, PDI supermolecule nanofiber with a continuous energy level structure is prepared by a self-assembly method, and the advantages of wide spectral response range, strong photooxidation capability and the like are shown, so that the perylene bisimide (PDI) is widely applied to the aspects of pollutant degradation, water photolysis oxygen generation, tumor resistance and the like. However, the PDI of the end-position unmodified hydrophilic group has poor dispersibility in water, the catalytic activity is easily influenced by pH, the recombination probability of a photo-generated electron-hole pair is high, and the photoreduction capability is weak, so that the application prospect of the PDI in the field of photocatalysis is influenced.
Disclosure of Invention
The technical problem to be solved is as follows: in order to overcome the defects of the prior art and obtain a photocatalyst with a nano-structure shape, a wide visible spectrum response range and rapid photo-generated carrier separation and migration capacity, the invention provides a carboxyl-containing perylene bisimide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst and a preparation method and application thereof.
The technical scheme is as follows: the carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst is formed by compounding carboxyl-containing perylene imide and oxygen-doped carbon nitride nanosheets through electrostatic interaction and pi-pi interaction, wherein the mass ratio of the oxygen-doped carbon nitride nanosheets to the carboxyl-containing perylene imide is 1: 0.001-0.8; the carboxyl perylene bisimide is modified on the oxygen-doped carbon nitride nanosheet through an in-situ method.
The preparation method of the carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst comprises the steps of taking 3-amino-1, 2, 4-triazole as a raw material, preparing the oxygen-doped carbon nitride nanosheet through a thermal etching-hydrothermal combination method, preparing carboxyl-containing perylene imide supramolecular nanofibers through a self-assembly method, and finally modifying the carboxyl perylene imide onto the oxygen-doped carbon nitride nanosheet through an in-situ method.
Preferably, the method comprises the following specific steps:
(1) calcining 3-amino-1, 2, 4-triazole serving as a raw material in an air atmosphere to prepare blocky carbon nitride, grinding the blocky carbon nitride, then calcining for the second time in the air atmosphere to prepare carbon nitride nanosheets, ultrasonically dispersing the carbon nitride nanosheets in aqueous hydrogen peroxide, carrying out hydrothermal reaction, cooling after the reaction is finished, carrying out solid-liquid separation, collecting precipitates, drying and grinding the precipitates into powder to prepare oxygen-doped carbon nitride nanosheets;
(2) mixing 3,4,9, 10-tetracarboxylic dianhydride, imidazole and beta-aminopropionic acid, heating for reflux reaction, cooling to room temperature, adding ethanol and hydrochloric acid, stirring for reaction, performing solid-liquid separation to collect precipitate, filtering and washing the precipitate to be neutral, drying and grinding to obtain a carboxyl-containing perylene imide crude product, dispersing the crude product in water, adding triethylamine, and stirring to completely dissolve the carboxyl-containing perylene imide to form a carboxyl-containing perylene imide solution;
(3) ultrasonically dispersing the oxygen-doped carbon nitride nanosheet obtained in the step (1) in water, adding the carboxyl-containing perylene imide solution obtained in the step (2), stirring and ultrasonically mixing, adding nitric acid, heating and stirring, carrying out solid-liquid separation after the reaction is finished, collecting precipitate, washing, drying and grinding the precipitate to obtain the carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst.
Preferably, the calcination in the step (1) comprises a heating-up stage and a constant-temperature stage which are sequentially carried out; the heating rate of the heating stage is 1-12 ℃/min; the temperature of the constant temperature stage is 450-600 ℃, and the constant temperature time is 1-8 h; the ultrasonic power is 200-800W, the ultrasonic frequency is 10-50 kHz, and the ultrasonic time is 5-60 min.
Preferably, the concentration of the aqueous hydrogen peroxide solution in the step (1) is 0.1-40 vol%, and the mass-to-volume ratio g/mL of the carbon nitride to the aqueous hydrogen peroxide solution is 1: 30-150; the hydrothermal reaction temperature is 80-150 ℃, and the reaction time is 2-10 h.
Preferably, the mass ratio of the 3,4,9, 10-tetracarboxylic dianhydride to the beta-aminopropionic acid in the step (2) is 1: 1-5, the mass ratio of the 3,4,9, 10-tetracarboxylic dianhydride to the imidazole is 1: 1-20, the temperature of the heating reflux reaction is 88-150 ℃, and the reaction time is 0.5-10 hours; the concentration of the hydrochloric acid is 0.1-10 mol/L; the mass-volume ratio g/mL of the 3,4,9, 10-tetracarboxylic dianhydride to the ethanol is 1: 10-150, and the mass-volume ratio g/mL of the 3,4,9, 10-tetracarboxylic dianhydride to the hydrochloric acid is 1: 10-500; the reaction time of stirring is 5-30 h.
Preferably, the mass volume ratio mg/mL of the carboxyl-containing perylene imide crude product to water in the step (2) is 1: 0.1-10, and the mass volume ratio mg/microliter of the carboxyl-containing perylene imide crude product to triethylamine is 1: 0.1-10; the reaction time of stirring is 0.1-5 h.
Preferably, the mass-to-volume ratio mg/mL of the oxygen-doped carbon nitride nanosheet to water in the step (3) is 1: 0.1-10; the ultrasonic power is 200-800W, the ultrasonic frequency is 10-50 kHz, and the ultrasonic treatment time is 0.1-5 h; the mass ratio of the oxygen-doped carbon nitride nanosheet to the carboxyl-containing perylene imide is 1: 0.001-0.8, and the stirring reaction time is 0.5-5 h; the concentration of the nitric acid is 0.1-10 mol/L, and the mass-volume ratio of the carboxyl-containing perylene imide to the nitric acid is 1mg: 0.01-1 mL; the heating reaction temperature is 30-100 ℃, and the stirring reaction time is 0.5-10 h.
The carboxyl-containing perylene bisimide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst is applied to preparation of pollutant degradation compounds.
The carboxyl-containing perylene bisimide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst is applied to preparation of an antibacterial agent.
The principles of the carboxyl-containing perylene bisimide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst and the preparation method thereof are as follows: on one hand, the blocky carbon nitride obtained by taking 3-amino-1, 2, 4-triazole as a precursor has narrower band gap and wider spectral response compared with the blocky carbon nitride prepared by calcining the precursor of cyanamide/dicyandiamide/melamine; the blocky carbon nitride can be further thermally etched into carbon nitride nanosheets by secondary calcination, so that the mobility of photo-generated carriers is improved; meanwhile, the hydrothermal treatment can dope oxygen element into the carbon nitride nanosheet structure, enhance the light absorption of the carbon nitride nanosheet structure, adjust the energy band structure of the carbon nitride nanosheet structure, and enable the O-CN surface to be positively charged. On the other hand, the water solubility of PDI is improved by connecting short alkane side chains of carboxylic acid groups into two amide positions of PDI, so that the PDI can be dissolved in water under alkaline conditions, and self-assembly is carried out under acidic conditions through pi-pi action between PDI molecules and hydrogen bonding action between the carboxylic acid groups to form supermolecule nanofibers with negative charges on the surfaces. And O-CN is added in the process of PDI self-assembly, and the PDI nano-fiber and the O-CN can be combined through electrostatic interaction and pi-pi interaction to form a PDI/O-CN heterojunction photocatalyst in situ.
According to the invention, the space and electronic structure of the carbon nitride for photocatalysis are optimized through precursor optimization, morphology regulation and element doping, and then the carbon nitride is compounded with PDI supermolecule nano-fiber to realize the rapid transfer of the carbon nitride photogenerated charges and the expansion of the spectrum absorption range, so that the PDI/O-CN heterojunction photocatalyst with excellent pollutant degradation, antibacterial property and oxygen generation performance is prepared.
The method adopts an in-situ method, and the PDI/O-CN heterojunction photocatalyst is prepared by carrying out in-situ combination with O-CN through electrostatic interaction and pi-pi interaction in the PDI self-assembly process; in a PDI/O-CN system, the energy band positions of O-CN and PDI are arranged in a crossed manner, which is beneficial to the formation of n-n type heterojunction and the construction of a built-in electric field, thereby promoting the separation and transfer of photo-generated electron-hole pairs at a heterointerface; meanwhile, pi-pi interaction between PDI and O-CN can cause electron delocalization effect and promote migration of photo-generated electrons. Compared with O-CN, the PDI/O-CN heterojunction has wider photoresponse range, faster separation efficiency of photo-generated electron-hole pairs and stronger photooxidation capacity, and has important significance for improving the application prospect and the practical value of the photocatalyst; in addition, the in-situ method has the characteristics of high efficiency, greenness and mildness.
Has the advantages that: (1) compared with O-CN and PDI in the prior art, the photocatalyst has more excellent performances of photocatalytic degradation of pollutants, killing of pathogenic bacteria and photolysis of water to generate oxygen; (2) the method has the advantages of low raw material cost and simple process, effectively reduces the product cost, is suitable for industrial mass production, and has very high application prospect and practical value.
Drawings
FIG. 1 is a graph showing the degradation performance of physically mixed carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheets prepared in example 1, the oxygen-doped carbon nitride nanosheets prepared in comparative example 1, the non-self-assembled carboxyl-containing perylene imide and self-assembled carboxyl-containing perylene imide prepared in comparative example 2, and the physically mixed carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheets prepared in comparative example 3 in phenol under visible light; wherein, (a) a graph comparing the change of phenol concentration with time; (b) apparent rate constant (k) comparison of degrading phenol;
in the figure: the carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheet prepared in example 1 is abbreviated as PDI/O-CN, the samples with the mass ratios of PDI to O-CN of 10%, 20%, 40%, 50% and 60% are respectively marked as PDI/O-CN-10%, PDI/O-CN-20%, PDI/O-CN-40%, PDI/O-CN-50% and PDI/O-CN-60% by taking the amount of PDI added as a standard name, the oxygen-doped carbon nitride nanosheet prepared in the comparative example 1 is abbreviated as O-CN, the non-self-assembled carboxyl-containing perylene imide and the self-assembled carboxyl-containing perylene imide prepared in the comparative example 2 are abbreviated as non-self-assembled PDI and self-assembled PDI respectively, the physically mixed carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheet prepared in comparative example 3 is referred to as PDI/O-CN-40% (physically mixed);
FIG. 2 is a graph comparing the antibacterial performance under visible light of PDI/O-CN-40% prepared in example 1 and O-CN prepared in comparative example 1;
FIG. 3 is a graph comparing the oxygen evolution performance under visible light of PDI/O-CN-40% prepared in example 1 with that of O-CN prepared in comparative example 1 and that of self-assembled PDI prepared in comparative example 2;
FIG. 4 is a Zeta potential diagram in aqueous solution of the PDI/O-CN-40% prepared in example 1 and the O-CN prepared in comparative example 1, the self-assembled PDI prepared in comparative example 2;
FIG. 5 is a TEM comparison of the PDI/O-CN-40% in example 1 with the O-CN prepared in comparative example 1, the self-assembled PDI prepared in comparative example 2; TEM images in which (a) O-CN, (b) self-assembled PDI, and (c) PDI/O-CN-40%;
FIG. 6 is an SEM comparison of PDI/O-CN-40% in example 1 with O-CN prepared in comparative example 1, and the self-assembled PDI prepared in comparative example 2; SEM images of (a) O-CN, (b) self-assembled PDI and (c) PDI/O-CN-40%;
FIG. 7 is a XRD comparison of PDI/O-CN prepared in example 1 with O-CN prepared in comparative example 1 and self-assembled PDI prepared in comparative example 2;
FIG. 8 is a FTIR comparison plot of PDI/O-CN prepared in example 1 versus O-CN prepared in comparative example 1, and self-assembled PDI prepared in comparative example 2;
FIG. 9 is a DRS plot of PDI/O-CN-40% prepared in example 1 compared to O-CN prepared in comparative example 1, and the self-assembled PDI prepared in comparative example 2;
FIG. 10 is a graph comparing the photoelectric properties of the PDI/O-CN-40% prepared in example 1 with the O-CN prepared in comparative example 1 and the self-assembled PDI prepared in comparative example 2; wherein, (a) photocurrent response diagrams of O-CN, self-assembled PDI and PDI/O-CN-40% under light and dark alternation; (b) an Nyquist plot of the electrochemical impedance of O-CN, self-assembled PDI and PDI/O-CN-40% under visible light;
FIG. 11 is a PL comparison plot of PDI/O-CN prepared in example 1 versus O-CN prepared in comparative example 1;
FIG. 12 is a comparison of the band structures of the O-CN prepared in comparative example 1 and the self-assembled PDI prepared in comparative example 2, wherein (a) the bands of the O-CN, the self-assembled PDI and the PDI/O-CN-40% are calculated; (b) Mott-Schottky curves for O-CN, self-assembled PDI, and PDI/O-CN-40%.
Detailed Description
The following examples further illustrate the present invention but are not to be construed as limiting the invention. Modifications and substitutions to methods, procedures, or conditions of the invention may be made without departing from the spirit and substance of the invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art.
Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.
In the following examples, a Transmission Electron Microscope (TEM) image was taken using a JEOL JEM-2100 type transmission electron microscope with an electron beam acceleration voltage of 200 kV; taking a Scanning Electron Microscope (SEM) image by using an FEI aspect F50 type scanning electron microscope; the X-ray diffraction spectrum (XRD) of the sample was studied using a Bruker D2-phaseX-ray diffractometer (CuK α, 30kV, 10 mA); obtaining infrared spectroscopy (FTIR) of the sample using a Nicolet iS10 spectrometer; the Zeta potential of the sample is measured by adopting a Zetasizer nano ZS analyzer; measuring the photoluminescence spectrum (PL) of the sample with a Hitachi F-7000 fluorescence spectrometer at an excitation wavelength λ 370 nm; the Diffuse Reflectance Spectrum (DRS) of the sample was recorded using a Shimadzu UV-3600Plus UV-vis spectrophotometer.
Example 1
A carboxyl-containing perylene bisimide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst is prepared by the following steps:
firstly, 3-amino-1, 2, 4-triazole is placed in a crucible, placed in a muffle furnace, heated to 550 ℃ at the speed of 2 ℃/min and calcined for 4h, and the product is ground to obtain brick red blocky carbon nitride; grinding the blocky carbon nitride, placing the grinded blocky carbon nitride in a crucible, placing the crucible in a muffle furnace, heating to 500 ℃ at the speed of 5 ℃/min, carrying out secondary calcination for 2h, and grinding the product to obtain carbon nitride nanosheets; 0.9g of carbon nitride nanosheets dispersed in 100mL of 30 vol% H2O2And (3) performing ultrasonic treatment on the water solution for 30min (560W, 40kHz), transferring the dispersion liquid into a hydrothermal kettle, heating the hydrothermal kettle at 120 ℃ for 6h, centrifuging, collecting precipitates, washing the precipitates for several times by using water, drying and grinding the precipitates into powder to obtain a bright yellow powder product, namely the oxygen-doped carbon nitride nanosheet (O-CN). Secondly, mixing 1.373g of 3,4,9, 10-tetracarboxylic dianhydride, 18g of imidazole and 2.495g of beta-aminopropionic acid, stirring and reacting for 4 hours at 100 ℃ under an argon atmosphere, naturally cooling a reaction product to room temperature, adding 100mL of ethanol and 300mL of 2.0mol/L hydrochloric acid, and stirring for 15 hours; filtering with 0.45 μm water-based filter membrane, collecting precipitate, washing the precipitate with water for several times to neutrality, drying, and grinding into powder to obtain dark red powder product, i.e. carboxyl-containing perylene imide (PDI) crude product; ultrasonically dispersing a crude product of 330mg PDI in 123mL of water, adding 515 mu L of triethylamine, and stirring for 2h to completely dissolve carboxyl-containing perylene bisimide to form dark perylene bisimideRed PDI solution. And finally, weighing 100mg of O-CN, dispersing in 30mL of deionized water, performing ultrasonic treatment (560W, 40kHz) for 2h, adding a certain volume of PDI solution, wherein the mass fraction of PDI relative to the O-CN is respectively 10%, 20%, 40%, 50% and 60%, stirring for 60min, performing ultrasonic treatment (560W, 40kHz) for 15min, then adding a certain volume of 4mol/L nitric acid (the mass-volume ratio of carboxyl-containing perylene imide to nitric acid is 1mg:0.0511mL), heating and stirring for 1.5 h in a water bath at 60 ℃, centrifuging, collecting precipitates, washing the precipitates for several times by water, drying and grinding into powder to obtain the product, namely the carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheet (PDI/O-CN) heterojunction photocatalyst.
Example 2
A carboxyl-containing perylene bisimide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst is prepared by the following steps:
firstly, 3-amino-1, 2, 4-triazole is placed in a crucible, placed in a muffle furnace, heated to 450 ℃ at the speed of 1 ℃/min and calcined for 1h, and the product is ground to obtain brick red blocky carbon nitride; grinding the blocky carbon nitride, placing the grinded blocky carbon nitride in a crucible, placing the crucible in a muffle furnace, heating to 450 ℃ at the speed of 1 ℃/min, carrying out secondary calcination for 1h, and grinding the product to obtain carbon nitride nanosheets; dispersing 1g of carbon nitride nanosheets in 30mL of 0.1 vol% H2O2And (2) performing ultrasonic treatment (200W, 10kHz) for 5min in the aqueous solution, transferring the dispersion liquid into a hydrothermal kettle, heating for 2h at 80 ℃, centrifuging, collecting precipitate, washing the precipitate for several times by using water, drying, and grinding into powder to obtain a bright yellow powder product, namely the oxygen-doped carbon nitride nanosheet (O-CN). Secondly, mixing 1g of 3,4,9, 10-tetracarboxylic dianhydride, 1g of imidazole and 1g of beta-aminopropionic acid, stirring and reacting for 0.5h at 88 ℃ under an argon atmosphere, naturally cooling a product after reaction to room temperature, adding 10mL of ethanol and 10mL of 0.1mol/L hydrochloric acid, and stirring for 5 h; filtering with 0.45 μm water-based filter membrane, collecting precipitate, washing the precipitate with water for several times to neutrality, drying, and grinding into powder to obtain dark red powder product, i.e. carboxyl-containing perylene imide (PDI) crude product; ultrasonically dispersing 100mg of PDI crude product in 10mL of water, adding 10 mu L of triethylamine, and stirring to completely dissolve carboxyl-containing perylene imide to form dark red PDI solution. And finally, weighing 100mg of O-CN, dispersing in 10mL of deionized water, performing ultrasonic treatment (200W, 10kHz) for 0.1h, adding a PDI solution with a certain volume, wherein the mass fraction of PDI relative to the O-CN is 0.1%, stirring for 0.5h, performing ultrasonic treatment (200W, 10kHz) for 0.1h, then adding 0.1mol/L nitric acid (the mass-volume ratio of carboxyl-containing perylene imide to nitric acid is 1mg:0.01 mL) with a certain volume, heating and stirring for 0.5h in a water bath at 30 ℃, centrifuging, collecting precipitates, washing the precipitates for several times with water, drying, and grinding into powder to obtain the product, namely the carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheet (PDI/O-CN) heterojunction photocatalyst.
Example 3
A carboxyl-containing perylene bisimide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst is prepared by the following steps:
firstly, 3-amino-1, 2, 4-triazole is placed in a crucible, placed in a muffle furnace, heated to 600 ℃ at the speed of 12 ℃/min and calcined for 8 hours, and the product is ground to obtain brick red blocky carbon nitride; grinding the blocky carbon nitride, placing the grinded blocky carbon nitride in a crucible, placing the crucible in a muffle furnace, heating to 600 ℃ at the speed of 12 ℃/min, carrying out secondary calcination for 8 hours, and grinding the product to obtain carbon nitride nanosheets; dispersing 1g of carbon nitride nanosheets in 150mL of 40 vol% H2O2And (2) performing ultrasonic treatment (800W and 50kHz) for 60min in the aqueous solution, transferring the dispersion liquid into a hydrothermal kettle, heating for 10h at 150 ℃, centrifuging, collecting precipitate, washing the precipitate for several times by using water, drying, and grinding into powder to obtain a bright yellow powder product, namely the oxygen-doped carbon nitride nanosheet (O-CN). Secondly, mixing 1g of 3,4,9, 10-tetracarboxylic dianhydride, 20g of imidazole and 5g of beta-aminopropionic acid, stirring and reacting for 10 hours at 150 ℃ under an argon atmosphere, naturally cooling a product after reaction to room temperature, adding 150mL of ethanol and 500mL of 10.0mol/L hydrochloric acid, and stirring for 30 hours; filtering with 0.45 μm water-based filter membrane, collecting precipitate, washing the precipitate with water for several times to neutrality, drying, and grinding into powder to obtain dark red powder product, i.e. carboxyl-containing perylene imide (PDI) crude product; and ultrasonically dispersing 100mg of a PDI crude product in 1000mL of water, adding 1mL of triethylamine, and stirring for 5h to completely dissolve carboxyl-containing perylene imide to form a dark red PDI solution. Finally, 100mg of O-CN is weighed and dispersed in 100Adding 0mL of deionized water, performing ultrasonic treatment (800W and 50kHz) for 5 hours, adding a certain volume of PDI solution, wherein the mass fraction of PDI relative to O-CN is 80%, stirring for 5 hours, performing ultrasonic treatment (800W and 50kHz) for 5 hours, then adding a certain volume of 10mol/L nitric acid (the mass-to-volume ratio of carboxyl-containing perylene imide to nitric acid is 1mg:1mL), heating and stirring for 10 hours in a water bath at 100 ℃, centrifuging, collecting precipitate, washing the precipitate for several times with water, drying, and grinding into powder to obtain the product, namely the carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheet (PDI/O-CN) heterojunction photocatalyst.
Comparative example 1
Preparing an oxygen-doped carbon nitride nanosheet by a thermal etching-hydrothermal method: placing 3-amino-1, 2, 4-triazole in a crucible, placing the crucible in a muffle furnace, heating to 550 ℃ at the speed of 2 ℃/min, calcining for 4h, and grinding the product to obtain brick red blocky carbon nitride; grinding the blocky carbon nitride, placing the grinded blocky carbon nitride in a crucible, placing the crucible in a muffle furnace, heating to 500 ℃ at the speed of 5 ℃/min, carrying out secondary calcination for 2h, and grinding the product to obtain carbon nitride nanosheets; 0.9g of carbon nitride nanosheets dispersed in 100mL of 30 vol% H2O2And (3) performing ultrasonic treatment on the water solution for 30min (560W, 40kHz), transferring the dispersion liquid into a hydrothermal kettle, heating the hydrothermal kettle at 120 ℃ for 6h, centrifuging, collecting precipitates, washing the precipitates for several times by using water, drying and grinding the precipitates into powder to obtain a bright yellow powder product, namely the oxygen-doped carbon nitride nanosheet (O-CN).
Comparative example 2
Preparing self-assembled carboxyl-containing perylene bisimide by a self-assembling method: mixing 1.373g of 3,4,9, 10-tetracarboxylic dianhydride, 18g of imidazole and 2.495g of beta-aminopropionic acid, stirring and reacting for 4 hours at 100 ℃ under an argon atmosphere, naturally cooling a reaction product to room temperature, adding 100mL of ethanol and 300mL of 2.0mol/L hydrochloric acid, and stirring for 15 hours; filtering with 0.45 μm water-based filter membrane, collecting precipitate, washing the precipitate with water for several times to neutrality, drying, and grinding into powder to obtain dark red powder product, i.e. non-self-assembled carboxyl-containing perylene imide (non-self-assembled PDI); ultrasonically dispersing 100mg of non-self-assembled PDI in 37.3mL of water, adding 156 muL of triethylamine, stirring for 2h to completely dissolve carboxyl-containing perylene imide to form a dark red PDI solution, then adding 5.11mL of 4mol/L of nitric acid, stirring for 30min, centrifugally collecting precipitates, washing the precipitates for several times with water to be neutral, drying and grinding into powder to obtain a dark red powder product, namely the self-assembled carboxyl-containing perylene imide (self-assembled PDI).
Comparative example 3:
preparing physically mixed carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheets by a grinding method: 100mg of O-CN and 40 mg of self-assembled PDI are weighed, mixed and ground for 30min, and the obtained product is physically mixed carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheet (PDI/O-CN-40% (physical mixing)).
The tests were carried out on the products obtained in examples 1 to 3 and comparative examples 1 to 2, the results and analyses being as follows:
1. photocatalytic pollutant degradation performance test
Phenol is used as a target degradation product, the degradation activity of the PDI/O-CN heterojunction photocatalyst is inspected under visible light, a 500W xenon lamp is used as a light source and a 420nm filter is added to the visible light, and the average light intensity is 30mW/cm2(ii) a Taking 50mL of 5ppm phenol solution, adding 25.0mg of photocatalyst, firstly ultrasonically dispersing the dispersion liquid for 15min, and then stirring for 1h in a dark environment to ensure that the photocatalyst and the target pollutant reach adsorption balance; starting a xenon lamp light source to start a photocatalytic reaction, taking 2mL of reaction solution every 1h, centrifuging (the rotating speed is 11000rpm/min) to remove the photocatalyst in the solution, and filtering supernate by using a 0.22-micron water system filter membrane; the concentration of phenol in the supernatant was determined by High Performance Liquid Chromatography (HPLC) at 270nm (Waters-C18, methanol/water volume ratio 60:40, flow rate 1 mL/min).
FIG. 1 is a graph comparing the degradation performance of PDI/O-CN prepared in example 1 with that of O-CN prepared in comparative example 1, that of non-self-assembled PDI and self-assembled PDI prepared in comparative example 2, and that of PDI/O-CN-40% (physical mixing) prepared in comparative example 3 on phenol under visible light. As can be seen from fig. 1(a), under visible light, the photocatalytic activity of PDI/O-CN heterojunction material is enhanced compared to O-CN, self-assembled PDI and non-self-assembled PDI, and as the loading of self-assembled PDI increases, the photodegradation rate of PDI/O-CN gradually increases and then gradually decreases; wherein the photocatalytic activity of the heterojunction material is optimal when the self-assembled PDI loading is 40%, and the self-assembled PDI and the O-CN are carried out in the same proportionThe photocatalytic activity of the PDI/O-CN-40% (physically mixed) sample obtained by physical mixing is hardly improved, which indicates that the self-assembled PDI and O-CN can be successfully compounded by an in-situ method. The apparent rate constant k of photocatalytic degradation is calculated by fitting a quasi-first order kinetic equation (FIG. 1(b)), and the comparison shows that PDI/O-CN-40% has the highest photocatalytic activity, and the apparent rate constant k is 0.164h-1About O-CN (0.045 h)-1) 3.6 times of that of the gene, is self-assembled PDI (0.130 h)-1) The result is 1.3 times that of the material, and the self-assembled PDI and the O-CN are compounded into the heterojunction material which can actually play a role in improving the photocatalytic degradation activity of the O-CN. Compared with oxygen-doped carbon nitride nanosheets and self-assembled carboxyl-containing perylene bisimides, the carboxyl-containing perylene bisimides/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst has more excellent photocatalytic pollutant degradation performance.
2. Photocatalytic antibacterial property test
Gram-positive bacteria staphylococcus aureus (S.aureus) is used as an object, and the photocatalytic antibacterial performance of the prepared material is tested. Culturing S.aureus in Luria Bertani (LB) liquid medium at 37 deg.C for 5h under shaking, centrifuging (4000rpm, 5min) to collect bacterial cells, washing with sterile 0.9% NaCl solution for several times, and then resuspending the bacterial cells in physiological saline solution; the concentration of S.aureus in the antibacterial test is1 × 107cfu·mL-1The concentration of the photocatalyst is 0.2 g.L-1The light source used in the photocatalytic antibacterial process is a 500W xenon lamp (lambda)>420 nm); taking equivalent bacterial liquid at regular intervals, diluting with sterile normal saline, taking 0.1mL of diluent, coating the diluent on an LB solid culture medium, culturing at 37 ℃ for 12h, and counting the number of floras in the bacterial liquid after different illumination times by using a flat plate bacterial colony counting method; the light control group is not added with photocatalyst, the control group is not illuminated, and each group of experiments are carried out in triplicate; the experimental set-up and the physiological saline solution used were sterilized at 121 ℃ under high pressure for 20 min.
FIG. 2 is a graph comparing the antibacterial properties under visible light of PDI/O-CN-40% prepared in example 1 and O-CN prepared in comparative example 1. As can be seen from fig. 2, almost no s.aureus was killed in the light control group (without photocatalyst but with visible light (λ >420nm) illumination). Under dark conditions, the sterilization effect of PDI/O-CN-40% on s.aureus was negligible, indicating that the material itself is not toxic to s.aureus cells. Under visible light, compared with O-CN, the PDI/O-CN-40% heterojunction material has obviously enhanced sterilization efficiency, almost all S.aureus is killed after 3 hours of illumination, and the sterilization rate of O-CN is only 62.2%, which is consistent with the result of photocatalytic degradation of phenol. Compared with the oxygen-doped carbon nitride nanosheet, the carboxyl-containing perylene bisimide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst has more excellent photocatalytic antibacterial performance.
3. Photocatalytic oxygen generation performance test
Photocatalytic oxygen generation experiments were performed using a Labsolar-IIIAG system (PerfectLight) with a light source equipped with a cut-off filter (. lamda.)>420nm) 300W xenon lamp; weighing 25mg of sample powder and adding 100mL of AgNO3In an aqueous solution (10mmol/L), performing ultrasonic treatment for 30min to uniformly disperse the aqueous solution; the light source of the xenon lamp was turned on to start the photocatalytic reaction, and the amount of oxygen generated was detected every 0.5h using a gas chromatograph (GC7920, TCD detector, carrier gas Ar).
FIG. 3 is a graph comparing the oxygen evolution performance under visible light of PDI/O-CN-40% prepared in example 1 with that of O-CN prepared in comparative example 1 and that of self-assembled PDI prepared in comparative example 2. As can be seen from FIG. 3, by AgNO3The oxygen production capacity of the PDI/O-CN-40% heterojunction material with the best degradation activity is also obviously improved as an electron acceptor, the oxygen production amount within 2 hours of visible light irradiation is 3.75 mu mol which is about 1.8 times of that of O-CN (2.04 mu mol), and the oxygen production amount of self-assembled PDI under the same condition is achieved. Compared with the oxygen-doped carbon nitride nanosheet, the carboxyl-containing perylene bisimide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst has more excellent photocatalytic oxygen production performance.
FIG. 4 is a Zeta potential diagram in aqueous solution of the PDI/O-CN-40% prepared in example 1 and the O-CN prepared in comparative example 1 and the self-assembled PDI prepared in comparative example 2. As can be seen from FIG. 4, the Zeta potential of O-CN is 3.01mV, i.e. the surface is positively charged; the Zeta potential of the self-assembled PDI is-22.03 mV, namely the surface is negatively charged; thus O — CN and self-assembled PDI can bind through electrostatic interactions. The Zeta potential of PDI/O-CN-40% is-14.90 mV, which shows that the surface charge of O-CN before and after the O-CN is compounded with the self-assembled PDI is greatly changed, and the in-situ method can successfully compound carboxyl-containing perylene imide with oxygen-doped carbon nitride nanosheets through electrostatic interaction.
FIG. 5 is a TEM comparison of the PDI/O-CN-40% in example 1 with the O-CN prepared in comparative example 1, and the self-assembled PDI prepared in comparative example 2. As shown in fig. 5(a), O — CN is a nanosheet structure, approximately several hundred nanometers in size; the self-assembled PDI represents the nanofiber structure (FIG. 5(b)), with a diameter of about 30nm and a length of 200-500 nm; FIG. 5(c) and a TEM image of PDI/O-CN-40%, the nanofiber structure of the self-assembled PDI can be seen at the edge of the O-CN sheet layer, which proves that the carboxyl-containing perylene imide and the oxygen-doped carbon nitride nanosheet can be successfully compounded by the in-situ method.
FIG. 6 is an SEM comparison of PDI/O-CN-40% in example 1 with O-CN prepared in comparative example 1 and the self-assembled PDI prepared in comparative example 2. As shown in fig. 6(a), O-CN exhibits a lamellar structure, self-assembled PDI (fig. 6(b)) shows a clustered nanofiber morphology, and fig. 6(c) is an SEM image of PDI/O-CN-40%, it can be seen that fibrous self-assembled PDI is successfully supported on the lamellar structure of O-CN, demonstrating that the carboxyl-containing perylene imide and oxygen-doped carbon nitride nanosheet can be successfully compounded by the in situ method according to the present invention.
FIG. 7 is an XRD comparison of PDI/O-CN prepared in example 1 with O-CN prepared in comparative example 1 and self-assembled PDI prepared in comparative example 2. As shown in fig. 7, two characteristic peaks (100) and (002) appeared at 13.2 ° and 27.5 ° for O — CN, corresponding to the interplanar packing of the heptazine unit and the conjugated C — N heterocycle repeated in-plane, respectively; for self-assembled PDI, there are multiple diffraction peaks in the 5-28 ° range, usually with the intensity ratio (I) of the P1 peak (at 26.2 °) to the P0 peakP1/IP0) To evaluate the degree of self-assembly of PDI, I can be seenP1/IP0Greater than 1, indicating a highly ordered pi-pi packing; the self-assembled PDI has a pi-pi stacking characteristic peak at 26.2 degrees, and the corresponding interlayer spacing is 0.34nm and is close to the interlayer spacing (0.32nm) of O-CN, so that favorable conditions are provided for the generation of pi-pi interaction between the self-assembled PDI and the O-CN; with the increase of the loading capacity of the self-assembled PDI, the characteristic diffraction peak of the self-assembled PDI in the PDI/O-CN heterojunction material is enhanced; in addition, and fromCompared with the assembled PDI, the Pi-Pi stacking peak of the PDI/O-CN at 26.2 degrees and the peak at 20.0 degrees are shifted to high angles, which shows that the heterojunction material has smaller Pi-Pi stacking interlayer spacing, which means that the electron cloud overlapping density is higher, and the separation and the migration of photon-generated carriers are facilitated. The in-situ method is proved to be capable of successfully compounding carboxyl-containing perylene bisimide and oxygen-doped carbon nitride nanosheets through pi-pi interaction.
FIG. 8 is a FTIR comparison of PDI/O-CN prepared in example 1 to O-CN prepared in comparative example 1 and to the self-assembled PDI prepared in comparative example 2. As shown in FIG. 8, O-CN is at 808cm-1、1240-1650cm-1Characteristic absorption bands exist and respectively correspond to the normal vibration of the heptazine unit and the stretching vibration of the aromatic heterocycle; self-assembled PDI at 1650cm-1And 1690cm-1The peak at (a) was attributed to stretching vibration of C-C, C-O, respectively, indicating the presence of carboxyl and benzene ring structures, 744cm-1The peak at (a) is due to bending vibration of-O ═ C-N-; with the increase of the loading capacity of the self-assembled PDI, 1650cm of the corresponding PDI in the PDI/O-CN heterojunction material-1、1690cm-1The intensity of the characteristic peak is gradually enhanced; compared with O-CN, the PDI/O-CN is 808cm-1The absorption peak at (A) is red-shifted, which is mainly due to the pi-pi interaction between O-CN and self-assembled PDI. The in-situ method is proved to be capable of successfully compounding carboxyl-containing perylene bisimide and oxygen-doped carbon nitride nanosheets through pi-pi interaction.
FIG. 9 is a DRS plot of PDI/O-CN-40% prepared in example 1 compared to O-CN prepared in comparative example 1 and the self-assembled PDI prepared in comparative example 2. As shown in FIG. 9, O-CN shows two absorption bands at 400nm and 450-800nm, the absorption band at 400nm is attributed to the pi-pi transition in the conjugated heptazine ring, and the absorption band at 450-800nm is attributed to the n-pi transition in the heptazine ring; the self-assembled PDI shows strong absorption in a visible light region, and the absorption edge is about 720 nm; after being compounded with the self-assembled PDI, the absorption wavelength edge of the PDI/O-CN is expanded to about 710nm, and the absorption performance in a visible light region is obviously enhanced compared with that of the O-CN, so that more photogenerated charges can be generated under the excitation of light, and the photocatalytic reaction is promoted to be carried out. The spectral response range of the carboxyl-containing perylene bisimide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst prepared by the in-situ method is remarkably expanded.
4. Photoelectric performance test
Photocurrent measurements were performed on a CHI 660D electrochemical workstation (Chenhua Instrument), a standard three-electrode system comprising a counter electrode, i.e., a platinum wire, a reference electrode, i.e., a saturated calomel electrode, and a working electrode, while 0.1mol/L Na was added2SO4The solution acts as an electrolyte. The preparation method of the working electrode comprises the following steps: 2mg of the sample powder were dispersed in 1mL of absolute ethanol, and the suspension was coated on an Indium Tin Oxide (ITO) glass surface, dried at room temperature and heated at 180 ℃ for 5 h. A300W xenon lamp (CEL-HXF 300, Mitsui gold source) with a 400nm cut-off filter was used as a visible light source. The photocurrent response test was performed at 0.0V; alternating impedance Spectroscopy (EIS) Spectroscopy at an AC Voltage of 5mV and at 0.05Hz to 10 Hz5Recording in the range of Hz; the starting voltage for the Mott-Schottky (MS) curve test was set to-1.0V-1.0V with a step size of 0.05V.
FIG. 10 is a graph comparing the photoelectric properties of the PDI/O-CN-40% prepared in example 1 with the O-CN prepared in comparative example 1 and the self-assembled PDI prepared in comparative example 2. As shown in FIG. 10(a), under visible light, the O-CN photocurrent response is weaker, the self-assembled PDI photocurrent response is slightly higher, and the PDI/O-CN-40% heterojunction material has the maximum photocurrent response which is about 1.7 times that of the O-CN, which indicates that the separation efficiency of the photo-generated electron-hole pair of the PDI/O-CN-40% heterojunction material is obviously improved after the PDI is loaded. In addition, the EIS spectrum (FIG. 10(b)) shows that the radius of the circular arc of the PDI/O-CN-40% heterojunction material is smaller than that of the self-assembled PDI and O-CN under visible light, and the smaller radius of the circular arc represents the lower reaction resistance of the working electrode, indicating that the n-n type heterojunction structure of the PDI/O-CN has a faster charge transfer rate and a lower charge recombination probability. The separation and migration capabilities of photo-generated carriers of the carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst prepared by the in-situ method are remarkably improved, so that the photocatalyst has more excellent visible light catalytic degradation pollutants and antibacterial and oxygen generation performances.
FIG. 11 is a PL comparison plot of PDI/O-CN prepared in example 1 versus O-CN prepared in comparative example 1. As shown in FIG. 11, O-CN showed a strong fluorescence emission spectrum at an excitation wavelength of 370nm with an emission peak position of about 450 nm; the PL peak intensity of the PDI/O-CN heterojunction material is weaker than that of O-CN, and the phenomenon of fluorescence quenching appears, wherein the quenching degree of PDI/O-CN-40% is most obvious, which indicates that the recombination probability of photo-generated electron-hole pairs is obviously reduced. In addition, compared with O-CN, the emission peak of the PDI/O-CN-40% heterojunction material is subjected to blue shift, which indicates that pi-pi interaction exists between the self-assembled PDI and the O-CN, namely a built-in electric field exists between the O-CN and the self-assembled PDI, so that photogenerated charges can be effectively transferred. The carboxyl-containing perylene bisimide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst prepared by the in-situ method is proved to have the advantages that the recombination probability of photo-generated electron-hole pairs is remarkably reduced, the migration capability of photo-generated charges is remarkably improved, and therefore the photocatalyst has more excellent visible light catalytic degradation pollutants and antibacterial and oxygen generation performances.
FIG. 12 is a graph comparing band structures of O-CN prepared in comparative example 1 and self-assembled PDI prepared in comparative example 2. As shown in FIG. 12(a), the band gap widths were calculated from the DRS Plot using the Tauc-Plot equation, and the band gap (Eg) values for O-CN and self-assembled PDI were 2.34eV and 1.66eV, respectively. As shown in fig. 12(b), the MS curve of the sample is measured to obtain specific information of the semiconductor type and flat band of the material, and the MS graph of O-CN and self-assembled PDI shows S-type and the slope is positive, indicating that both O-CN and self-assembled PDI photocatalyst are n-type semiconductor; according to Cs-2Calculating the flat band potential (E) of O-CN and self-assembled PDI by using-0 linear potential curve intersection pointfb) Respectively are-1.1 eV and-0.23 eV; bottom of conduction band (E)CB) Is calculated according to the following formula: eCB(NHE，pH＝7)＝Efb(SCE, pH 7) +0.24-0.2, and EVB＝ECB+EgCalculating to obtain the top potential (E) of valence bandVB) (ii) a Finally, the obtained energy band position calculation result is as follows: e of O-CNCBAnd EVBE of self-assembled PDI of-1.06 eV and 1.28 eV, respectivelyCBAnd EVBAre-0.19 eV and 1.47 eV. Because the conduction band of the O-CN is higher than that of the self-assembled PDI, photogenerated electrons can be transferred from the conduction band of the O-CN to the conduction band of the PDI, so that a built-in electric field is formed between the PDI and the O-CN, the separation efficiency of photogenerated charges is improved, and the photogenerated electrons can be separated from the PDIThe probability of charge recombination in the PDI/O-CN system is reduced. On the other hand, since the valence band of the self-assembled PDI is lower than that of O-CN, photogenerated holes can be transferred from the valence band of the self-assembled PDI to the valence band of O-CN, so that the holes on the valence band of O-CN show strong oxidizing ability. The cross arrangement of the energy band positions of O-CN and PDI in the carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst prepared by the in-situ method is proved to be beneficial to the separation and migration of photo-generated electron-hole pairs at a heterogeneous interface and the remarkable improvement of photo-oxidation capability, so that the photocatalyst has more excellent visible light catalytic pollutant degradation, antibacterial property and oxygen generation performance.

Claims (8)

1. The carboxyl-containing perylene bisimide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst is characterized in that the photocatalyst is formed by compounding carboxyl-containing perylene bisimide and oxygen-doped carbon nitride nanosheets through electrostatic interaction and pi-pi interaction, wherein the mass ratio of the oxygen-doped carbon nitride nanosheets to the carboxyl-containing perylene bisimide is 1: 0.001-0.8; the carboxyl-containing perylene imide is modified on the oxygen-doped carbon nitride nanosheet through an in-situ method; the photocatalyst is prepared by the following method: the method comprises the steps of taking 3-amino-1, 2, 4-triazole as a raw material, preparing oxygen-doped carbon nitride nanosheets by a thermal etching-hydrothermal combination method, preparing carboxyl-containing perylene imide supermolecule nanofibers by a self-assembly method, and finally modifying carboxyl-containing perylene imide onto the oxygen-doped carbon nitride nanosheets by an in-situ method; the method comprises the following specific steps:
(1) calcining 3-amino-1, 2, 4-triazole serving as a raw material in an air atmosphere to prepare blocky carbon nitride, grinding the blocky carbon nitride, then calcining for the second time in the air atmosphere to prepare carbon nitride nanosheets, ultrasonically dispersing the carbon nitride nanosheets in aqueous hydrogen peroxide, carrying out hydrothermal reaction, cooling after the reaction is finished, carrying out solid-liquid separation, collecting precipitates, drying and grinding the precipitates into powder to prepare oxygen-doped carbon nitride nanosheets;
(2) mixing 3,4,9, 10-tetracarboxylic dianhydride, imidazole and beta-aminopropionic acid, heating for reflux reaction, cooling to room temperature, adding ethanol and hydrochloric acid, stirring for reaction, performing solid-liquid separation to collect precipitate, filtering and washing the precipitate to be neutral, drying and grinding to obtain a carboxyl-containing perylene imide crude product, dispersing the crude product in water, adding triethylamine, and stirring to completely dissolve the carboxyl-containing perylene imide to form a carboxyl-containing perylene imide solution;
(3) ultrasonically dispersing the oxygen-doped carbon nitride nanosheet obtained in the step (1) in water, adding the carboxyl-containing perylene imide solution obtained in the step (2), stirring and ultrasonically mixing, adding nitric acid, heating and stirring, carrying out solid-liquid separation after the reaction is finished, collecting precipitate, washing, drying and grinding the precipitate to obtain the carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst.
2. The carboxyl-containing perylene imide/oxygen-doped carbon nanosheet heterojunction photocatalyst as claimed in claim 1, wherein the calcining in step (1) comprises a heating-up stage and a constant-temperature stage which are sequentially performed; the heating rate of the heating stage is 1-12 ℃/min; the temperature of the constant temperature stage is 450-600 ℃, and the constant temperature time is 1-8 h; the ultrasonic power is 200-800W, the ultrasonic frequency is 10-50 kHz, and the ultrasonic time is 5-60 min.
3. The carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst as claimed in claim 1, wherein the concentration of the aqueous hydrogen peroxide solution in step (1) is 0.1-40 vol%, and the mass-to-volume ratio g/mL of carbon nitride to the aqueous hydrogen peroxide solution is 1: 30-150; the hydrothermal reaction temperature is 80-150 ℃, and the reaction time is 2-10 h.
4. The carboxyl-containing perylene imide/oxygen-doped carbon nanosheet heterojunction photocatalyst as defined in claim 1, wherein in the step (2), the mass ratio of the 3,4,9, 10-tetracarboxylic dianhydride to the beta-aminopropionic acid is 1: 1-5, the mass ratio of the 3,4,9, 10-tetracarboxylic dianhydride to the imidazole is 1: 1-20, the temperature of the heating reflux reaction is 88-150 ℃, and the reaction time is 0.5-10 h; the concentration of the hydrochloric acid is 0.1-10 mol/L; the mass-volume ratio g/mL of the 3,4,9, 10-tetracarboxylic dianhydride to the ethanol is 1: 10-150, and the mass-volume ratio g/mL of the 3,4,9, 10-tetracarboxylic dianhydride to the hydrochloric acid is 1: 10-500; the reaction time of stirring after adding ethanol and hydrochloric acid is 5-30 h.
5. The carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst as claimed in claim 1, wherein in step (2), the mass-to-volume ratio mg/mL of the carboxyl-containing perylene imide crude product to water is 1: 0.1-10, and the mass-to-volume ratio mg/μ L of the carboxyl-containing perylene imide crude product to triethylamine is 1: 0.1-10; and the reaction time of stirring after adding triethylamine is 0.1-5 h.
6. The carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst as claimed in claim 1, wherein the mass-to-volume ratio mg/mL of the oxygen-doped carbon nitride nanosheet to water in step (3) is 1: 0.1-10; the ultrasonic power is 200-800W, the ultrasonic frequency is 10-50 kHz, and the ultrasonic treatment time is 0.1-5 h; the mass ratio of the oxygen-doped carbon nitride nanosheet to the carboxyl-containing perylene imide is 1: 0.001-0.8, and the reaction time of ultrasonic mixing and stirring is 0.5-5 h; the concentration of the nitric acid is 0.1-10 mol/L, and the mass-volume ratio of the carboxyl-containing perylene imide to the nitric acid is 1mg: 0.01-1 mL; the heating reaction temperature is 30-100 ℃, and the reaction time of adding nitric acid and stirring is 0.5-10 h.
7. The carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst as recited in claim 1, and is used for photocatalytic degradation of pollutants or photolysis of water to generate oxygen.
8. The application of the carboxyl-containing perylene imide/oxygen-doped carbon nitride nanosheet heterojunction photocatalyst as defined in claim 1 in killing pathogenic bacteria.
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