CN111957347A

CN111957347A - Preparation method of nano PS-CHO/RGO composite microspheres and method for degrading methylene blue by using same

Info

Publication number: CN111957347A
Application number: CN202010841911.2A
Authority: CN
Inventors: 严长浩; 倪镜博; 邹雯婷; 刘如一; 张明
Original assignee: Yangzhou University
Current assignee: Yangzhou University
Priority date: 2020-08-20
Filing date: 2020-08-20
Publication date: 2020-11-20
Anticipated expiration: 2040-08-20
Also published as: CN111957347B

Abstract

The invention relates to a preparation method of a nano PS-CHO/RGO composite microsphere and a method for degrading methylene blue, belonging to the field of preparation and application of graphene-based composite functional materials. Mixing the PS-CHO/RGO composite microspheres and ethanol according to the concentration of 2.3-2.7 g/L, and then adding the mixture into printing and dyeing wastewater containing methylene blue for mixing, so that the mass ratio of the PS-CHO/RGO composite microspheres to the methylene blue in the mixed solution is 1-3: 1, stirring and mixing for 10-15min, adding a potassium hydrogen persulfate aqueous solution into the mixed solution to ensure that the mass concentration of the potassium hydrogen persulfate in the mixed solution is 0.48-0.52 g/L, and continuously stirring to ensure that the color of the mixed solution gradually becomes lighter from blue to colorless to complete the degradation of methylene blue.

Description

Preparation method of nano PS-CHO/RGO composite microspheres and method for degrading methylene blue by using same

Technical Field

The invention relates to the technical field of preparation of graphene-based composite functional materials, in particular to a preparation method of a nano PS-CHO/RGO composite microsphere and a method for degrading methylene blue by using the same.

Background

Graphene (GE) is sp of carbon atoms²The thickness of the honeycomb two-dimensional crystal structure formed by hybridization is the thickness of a monoatomic layer, and the honeycomb two-dimensional crystal structure is the basis for preparing other graphene-based composite materials. Because of its high thermal conductivity, superior mechanical strength, flexibility and large specific surface area, it is widely used in the fields of ultra-high speed transistors, biosensors, energy storage devices, transparent electrodes and electromechanical systems. Graphene Oxide (GO) is a graphene derivative of a single-layer nanosheet layer formed by taking Graphite Powder (GP) as a raw material, destroying the crystal structure of the graphite powder by strong acid, introducing oxygen-containing groups, and finally carrying out ultrasonic stripping. According to a chemical model, GO is composed of flat aromatic graphene fragments and oxygen-containing groups such as epoxy groups, shuttle groups and the like carried by the edges of the flat aromatic graphene fragments. Unique structural features impart special surface chemistry properties such as amphiphilicity, negative charge, and various oxygen-containing groups. Chemically Reduced Graphene (RGO) is formed from GO reduced by a strong reducing agent, and RGO exhibits a very strong electron mobility compared to GO. However, in the reduction process due to sp²The recovery of the carbon atom network introduces strong pi-pi interaction again to destroy the original microstructure, thereby bringing adverse effects on the aspects of adsorption, ion migration, catalysis and the like. The problem of stacking between sheets must be solved.

Due to sp²The electrons hybridized with carbon atoms are easy to delocalize and form interaction with other materials providing conjugated pi electrons, and meanwhile, oxygen-containing groups on the sheet layer are easy to functionalize, so that the graphene material is easy to react with other materials including high polymers, DNA and goldThe metal oxide and the inorganic nano particles form a composite material. The introduced substance acts as a barrier between the sheets, increasing the interlayer spacing and weakening the interlayer interaction force, and the method has the advantage of ensuring that the original microstructure is not damaged by the barrier during the reduction process as the barrier successfully prevents the re-stacking effect between the sheets. Therefore, graphene-based composite materials are an important research direction in the field of graphene application.

In a recent study, sulfate radicals (SO)₄ ^•—) Exhibits specific hydroxyl radical (OH) due to higher oxidation potential (2.5-3.1 eV)^•—2.7 eV), has strong environmental adaptability, and can be applied to the condition of a large range of pH values without any coagulation. Homogeneous Co (II)/Peroxymonosulfate (PMS) has been shown to have a good degradation effect on a variety of organic contaminants. However, the disadvantage of this system is that divalent cobalt ions Co (II) are required to excite Peroxosulfate (PMS) before reaction, and Co (II) almost inevitably leaches out, causing new pollution to water and environment. In view of the new requirements of green color and sustainable development, an environmentally friendly metal-free catalyst was developed.

Disclosure of Invention

Aiming at the problem that the adsorption, ion migration and catalytic performance of materials are influenced by the stacking effect of redox graphene composite material sheets in the prior art, the invention provides a preparation method of a nano PS-CHO/RGO composite microsphere so as to prepare a reduced graphene oxide composite material with good dispersibility and high electron transmission efficiency.

The invention aims to realize the purpose, and the preparation method of the nano PS-CHO/RGO composite microsphere is characterized by comprising the following steps: firstly, preparing monodisperse polystyrene aldehyde microspheres and graphene oxide respectively, then taking the polystyrene aldehyde microspheres as a carrier and sodium borohydride as a reducing agent, and coating the reduced graphene oxide on the surfaces of the microspheres by an in-situ polymerization method to prepare the nano PS-CHO/RGO composite microsphere material.

According to the preparation method of the nano PS-CHO/RGO composite microsphere, the polystyrene aldehyde group microsphere is used as a barrier to be filled between sheets of the reduced graphene oxide, so that stacking between the sheets is well prevented, the dispersity of the reduced graphene oxide is improved, and in the polymerization process, aldehyde groups provide active sites and are reduced with sodium borohydride in a coordinated manner, so that the graphene oxide is reduced in situ and finally wrapped on the surface of the microsphere, and the original microstructure of the composite material is not damaged; in addition, the RGO composite material has stable structure, can be separated from the system in a high-speed centrifugation mode after the reaction is finished, and can be recycled after being washed by water.

Further, the in-situ polymerization method comprises the following specific processes: uniformly mixing the dried graphene oxide powder with an ammonia water solution with the molar concentration of 1mol/L according to the proportion of 0.00048-0.00052 g/mL to obtain a mixed solution A; uniformly mixing monodisperse polystyrene aldehyde microspheres and ethanol according to the proportion of 0.0023-0.0027 g/mL to obtain a mixed solution B, mixing the mixed solution A and the mixed solution B in an equal volume, continuously adding a sodium borohydride aqueous solution with the concentration of 0.0025-0.0028 g/mL, wherein the adding volume of the sodium borohydride aqueous solution is the sum of the volumes of the mixed solution AB, and reacting the mixed solution in a constant-temperature water bath at 80 ℃ for 2-3h in a dropwise adding process to obtain the PS-CHO/RGO composite microspheres. In the in-situ polymerization process, aldehyde groups on the surfaces of the microspheres provide binding sites, so that part of original layered reduced graphene oxide is coated on the surfaces of the microspheres; due to the influence of interfacial tension, the edge defects and curvature of the reduced graphene oxide can generate a non-six-membered carbon ring, so that the C-C sigma bond is broken to generate a zigzag edge, and pi electrons are not limited by the edge carbon any more due to the unstable state at the edge, so that the composite material has higher chemical activity. Compared with the traditional single reduced graphene oxide with stacked sheets, the edges of the reduced graphene oxide are changed into non-six-membered carbon rings by introducing the PS-CHO (polystyrene aldehyde group microsphere) microspheres, and pi electrons are not limited by the edge carbon any more by breaking the C-C sigma bond, so that the reduced graphene oxide has higher electron transmission efficiency.

Further, when the mixed solution A and the mixed solution B are mixed, a small amount of sodium hydroxide is added to enable the pH value of the mixed solution to be 7.5-8.5, so that the solubility of the graphene oxide is improved.

In order to promote graphene to be uniformly dispersed, when preparing the mixed solution A, the ammonia water is continuously dripped into the graphene oxide powder when the graphene oxide is mixed with the ammonia water, and the mixture is heated to 40 ℃, mechanically stirred for 4 hours and then ultrasonically dispersed for 1 hour, so that the graphene is completely dispersed.

As the optimization of the invention, the method for preparing the monodisperse polystyrene aldehyde-based microspheres comprises the following steps: taking azodiisobutyronitrile as an initiator, polyvinylpyrrolidone as a dispersant and mixed solution of isopropanol and water as a solvent, and taking styrene and acrolein as monomers to perform copolymerization reaction to obtain the monodisperse polystyrene aldehyde group microsphere floating solution.

As another preferred aspect of the present invention, the step of preparing the monodisperse polystyrene aldehyde-based microspheres comprises:

1.1) mixing isopropanol and a polyvinylpyrrolidone dispersing agent, placing the mixture in a constant-temperature water bath at 70 ℃ after ultrasonic-assisted dissolution, and mechanically stirring the mixture to prepare 12-15 g/100mL of polyvinylpyrrolidone isopropanol dispersion liquid;

1.2) dissolving an azodiisobutyronitrile initiator in styrene to prepare an azodiisobutyronitrile/styrene initiator solution B with the concentration of 1.6-2.0g/100 mL;

1.3) mixing the dispersion from step 1.1) with 1.2) of initiator in a ratio of 3: 1, adding acrolein with the volume of 1/2 of the initiator after uniformly stirring, reacting for 8-12 h at the constant temperature of 70 ℃, then washing for 2-3 times by using deionized water ultrasonic centrifugation, and drying to obtain the monodisperse polystyrene aldehyde group microsphere.

The invention also provides a method for degrading methylene blue by adopting the nano PS-CHO/RGO composite microspheres prepared by the method, which is used for degrading methylene blue in printing and dyeing wastewater.

The method for degrading methylene blue comprises the following steps: mixing PS-CHO/RGO composite microspheres and ethanol according to the concentration of 2.3-2.7 g/L, and then adding the mixture into printing and dyeing wastewater containing methylene blue for mixing, so that the mass ratio of the PS-CHO/RGO composite microspheres to the methylene blue in the mixed solution is 1-3: 1, stirring and mixing for 10-15min, adding a potassium hydrogen persulfate aqueous solution into the mixed solution to ensure that the mass concentration of the potassium hydrogen persulfate in the mixed solution is 0.48-0.52 g/L, and continuously stirring to ensure that the color of the mixed solution gradually becomes lighter from blue to colorless to complete the degradation of methylene blue.

In the method for degrading methylene blue, PS-CHO/RGO composite microspheres are used as a catalyst, reduced graphene oxide on the surface of the composite material provides electrons and holes, and potassium hydrogen persulfate is catalyzed to generate sulfate radicals (SO) with strong oxidizing property₄ ^•—) Thereby realizing the oxidative degradation of the methylene blue dye wastewater; compared with the traditional Co (II)/Peroxymonosulfate (PMS) system, the invention has the advantages of cheap and easily obtained raw materials, simple synthesis process and stable material performance; the degradation process is rapid and efficient, and no secondary pollution is caused.

Further, the temperature of the reaction system is 45-55 ℃.

Further, the pH value of the mixed solution is adjusted to 6.5-6.8 by ammonia water.

Furthermore, the PS-CHO/RGO composite microspheres in the mixed solution after the methylene blue degradation are separated by filtration and washed by centrifugation, and can be recycled for multiple times.

Drawings

FIG. 1 is a representation of the infrared spectra of the materials of the present invention.

Fig. 2 is a raman spectrum characterization chart of each material of the present invention.

FIG. 3a is a transmission electron micrograph of the PS-CHO microspheres of the present invention.

FIG. 3b is a transmission electron micrograph of the PS-CHO/RGO composite microsphere of the present invention.

Fig. 4a is a scanning electron micrograph of graphite powder.

Fig. 4b is a scanning electron micrograph of the graphene oxide of the present invention.

FIG. 4c is a scanning electron micrograph of the PS-CHO/RGO composite microspheres of the present invention.

FIG. 5 XRD spectra of materials of the present invention.

FIG. 6a is a UV spectrum of methylene blue solutions of different concentrations.

FIG. 6b is a standard curve of absorbance versus concentration of methylene blue solution.

FIG. 7a is a UV spectrum of the natural degradation of methylene blue solution without catalyst.

FIG. 7b is a UV spectrum of methylene blue degraded using PS-CHO/RGO composite microspheres and oxone.

FIG. 8a is a UV spectrum of a methylene blue solution degraded using only PS-CHO/RGO composite microspheres.

FIG. 8b is a UV spectrum of a solution of methylene blue degraded with oxone alone.

FIG. 9 is a graph showing the degradation cycle of PS-CHO/RGO composite microspheres.

Detailed Description

Example 1

Firstly, preparing polystyrene aldehyde group microspheres:

(1) mixing 18 mL of isopropanol and 2.5 g of polyvinylpyrrolidone (PVP) dispersing agent, adding the mixture into a three-neck flask with a condensing tube after ultrasonic-assisted dissolution, placing the three-neck flask into a constant-temperature water bath kettle at 70 ℃, and mechanically stirring and keeping the rotating speed at 315 r/min;

(2) dissolving 0.1 g of Azobisisobutyronitrile (AIBN) initiator in 6 mL of styrene to prepare a styrene solution in which the initiator is dissolved;

(3) the styrene solution (2) containing the initiator dissolved therein was added to the system obtained in (1), and after stirring and thoroughly mixing for 30 minutes, 3 mL of acrolein (C) was added₃H₄O), reacting for 8 hours at a constant temperature of 70 ℃, after the reaction is stopped, ultrasonically centrifuging and washing for three times by using deionized water to prepare polystyrene aldehyde based sphere emulsion, and drying to obtain the monodisperse polystyrene aldehyde based PS-CHO microspheres.

The second step is that: preparation of graphene oxide according to the modified Hummers method:

mixing Graphite Powder (GP) with sodium nitrate (NaNO)₃) According to the mass ratio of 1: 1.25 mixing in an ice-water bath, 10mL of concentrated sulfuric acid (H) was slowly dropped thereinto₂SO₄) (ii) a Then adding a potassium permanganate/water solution with the concentration of 0.066 g/mL, maintaining the system to react for 6h at the constant temperature of 4 ℃, then continuously dropwise adding 50 mL of deionized water, and heating to 40 ℃ after dropwise adding is finished to react for 1.5 h; rapidly adding 70mL of deionized water again, reacting for 15min, and slowly dropwise adding 5 mL of 30% hydrogen peroxide (H)₂O₂) Cooling to room temperature and then coolingAnd (3) performing centrifugal separation, washing the precipitate with dilute hydrochloric acid (HCl) with the molar concentration of 0.1mol/L, washing the precipitate with deionized water to be neutral, and finally performing vacuum drying at 40 ℃ to obtain dry Graphene Oxide (GO) powder.

Finally, the monodisperse polystyrene aldehyde (PS-CHO) microspheres are used as a matrix to prepare PS-CHO/RGO composite microspheres: mixing the dried Graphene Oxide (GO) powder with an ammonia water solution with a molar concentration of 1mol/L according to a proportion of 0.0005 g/mL, vigorously stirring at 40 ℃ for 4h and performing ultrasonic dispersion for 1h to obtain a mixed solution A for later use; and then mixing the monodisperse polystyrene aldehyde microspheres with ethanol according to the proportion of 0.0025 g/mL, ultrasonically dispersing for 2 hours to obtain a mixed solution B, mixing the mixed solution A with the mixed solution B under the condition of a constant-temperature water bath at 70 ℃, adding a small amount of sodium hydroxide solution to adjust the pH value of the mixed solution to 8, dropwise and continuously dropwise adding 0.0026 g/mL sodium borohydride/water solution, heating to 80 ℃ and reacting for 2 hours to obtain the PS-CHO/RGO composite microspheres of the embodiment.

To verify the components of the above-described preparation process, the following analysis and verification were performed on the components of the materials in this example:

firstly, the Graphene Oxide (GO), polystyrene aldehyde group microspheres (PS-CHO) and PS-CHO/RGO composite microspheres prepared in the embodiment are respectively mixed with potassium bromide according to the proportion of 1:100, and the mixture is dried under an ultraviolet lamp. Grinding into fine powder in mortar, tabletting under 5MPa, and characterizing by Fourier infrared spectrometer as shown in FIG. 1, GO is at 1043, 1228, 1577, 1726, 1734cm^-1Absorption peaks are found, and they are respectively assigned to C-O-C stretching vibration, C-OH stretching vibration, O-H deformation vibration, C-C stretching vibration and C-O stretching vibration. After reduction, the peak strength of the oxygen-containing functional group of the PS-CHO/RGO composite microsphere is weakened, which indicates that the original oxygen-containing functional group is effectively reduced. PS-CHO microspheres at 3100 ℃ and 2800cm^-1Four peaks at are all from sp of benzene ring²C-H stretching vibration; at 1499cm^-1And 1455cm^-1The peak of (A) belongs to sp of a benzene ring skeleton (-C = C-)²C-H stretching vibration; the C-H deformation vibration peak of the monosubstituted benzene is 1029cm^-1And 753cm^-1At least one of (1) and (b); 1724cm^-1C = O absorption peak and 2706cm of aldehyde group at (2)^-1C-H absorption peak of aldehyde group shows that styrene and acrolein have copolymerization reaction, and the aldehyde group is fixed on the surface of the microsphere.

Fig. 2 is a raman spectrum characterization chart of each material prepared in this example. 1340cm⁻¹Is located at 1580 cm of peak D⁻¹The peaks marked with G represent the disordered and ordered states of the material and the stacking mode of carbon atoms respectively. GO and PS-CHO/RGO have both an outstanding G-band and an obvious D-band due to structural defects and E_2gFirst order scattering of vibrational modes. Intensity ratio of D-band to G-band (I)_D /I_G) Can be used to measure the degree of disorder of the graphite crystals. As can be seen from FIG. 2, the size of D-band and G-band in the spectrum of GO is substantially the same, and I_D/I_G= 087, this is because the oxygen-containing functional groups inserted in the GO lamellae greatly increase their disordered state, the regularity of the material decreases, and defects increase. I of PS-CHO/RGO compared to GO_D/I_GIncreased to 1.07. This is due to the formation of non-covalent pi-pi stacking between the benzene ring of the PS chain and the RGO basal plane. After grafting of PS chains onto RGO backbones, the moiety sp²Conversion of carbon atoms to sp³Carbon atom, resulting in a band intensity ratio I_D /I_GAnd is increased. Shows that the GO is sp in the process of being reduced²The average size of the regions decreases, the number of polyaromatic domains increases and the highly defective carbon lattice.

As shown in FIG. 3, FIG. 3a is a transmission electron micrograph of a polystyrene aldehyde based microsphere (PS-CHO) of the present invention.

As can be seen from FIG. 3a, the PS-CHO microspheres have uniform particle size and good dispersibility, and the diameter of the microspheres is about 200 nm. FIG. 3b demonstrates the success of PS-CHO/RGO core-shell structure microspheres, where RGO can be seen to adhere to the microsphere surface, and the characteristic fold structure of RGO can also be seen between the microspheres.

As shown in fig. 4, fig. 4a is a scanning electron micrograph of graphite powder.

Fig. 4b is a scanning electron microscope image of Graphene Oxide (GO) in the present embodiment.

FIG. 4c is a scanning electron micrograph of the PS-CHO/RGO composite microspheres of this example.

In each scanning electron micrograph, as can be seen from fig. 4a, the graphite powder has a loose structure and a smooth surface; as can be seen from fig. 4b, the dried Graphene Oxide (GO) is formed by stacking dense and fine nano-sheets, and the sheet gap is large; as can be seen from fig. 4c, the reduced graphene oxide is coated on the surface of the microsphere; no free agglomerated RGO was seen around, all adhered to the PS-CHO microspheres, indicating that the structure was stable. The PS-CHO/RGO composite functional material has an oriented structure and a continuous network, and the generated network establishes a conductive path in the whole system and accelerates the conduction of electrons.

FIG. 5 is an XRD spectrum of each material in the present invention.

The graphite powder has a sharp characteristic peak at 2 theta =26.38 degrees, and the GO band has a remarkable characteristic peak at 2 theta =11.15 degrees, which is represented by the Bragg formula:

wherein d is interplanar spacing in nm; n is any positive integer, also called diffraction order, in this embodiment 1; λ is the wavelength of the X-rays, which is 0.154 nm in this example; theta is the complement of the angle of incidence. Calculated to know that d_GP=0.152nm，d_GO=0.303 nm. The fact that a large number of oxygen-containing functional groups are inserted between the layers of the graphite in the oxidation process is shown, and the interlayer spacing of the product GO is enlarged. The amorphous peak appearing in the XRD pattern of PS-CHO around 2 θ =19 ° is a characteristic peak of polystyrene. The XRD pattern of PS-CHO/RGO has a weak diffraction peak at 2 θ =18.05 ° due to the removal of oxygen-containing groups from the GO surface during the reduction process.

Example 2

This example was verified by degradation of methylene blue solutions of varying concentrations using the PS-CHO/RGO composite microspheres prepared in example 1.

First, to facilitate verification and monitoringFirstly, according to the ultraviolet spectra of methylene blue solutions with different concentrations, as shown in fig. 6a, linear fitting is carried out on the absorbance corresponding to different concentrations, and a standard curve chart is obtained, as shown in fig. 6 b. As can be seen from the standard curve, the absorbance increases linearly with increasing concentration. The fitted linear equation is y =0.1894x-0.3318, R²= 0.9817. A better linear relationship is exhibited.

When the verification detection is carried out, four 10mL methylene blue/water solutions with the concentration of 200mg/L are prepared in advance and respectively counted as a solution a, a solution b, a solution c and a solution d, and the methylene blue solution is catalytically degraded by using PS-CHO/RGO composite microspheres as catalysts through the following methods:

wherein, the solution a is mixed with 90mL of deionized water, and then natural degradation reaction is carried out for 60min at the temperature of 50 ℃ under the constant temperature condition of water bath without adding any catalytic liquid and medium; sampling 4 mL every 5-10min for ultraviolet spectrum detection, wherein the detection result is shown in figure 1, and the ultraviolet spectrum shows that the methylene blue structure is stable and hardly degrades at 50 ℃ in a water bath.

When the solution b is degraded, 0.05g of PS-CHO/RGO composite microspheres and 2.5 g/L of ethanol are mixed according to the proportion amount, ultrasonic dispersion is carried out for 2 hours to obtain 20 mL of dispersion liquid, the dispersion liquid is added into the mixed liquid of the solution b and 70mL of deionized water, the mixture is fully stirred for 10min, potassium hydrogen persulfate is added subsequently to ensure that the mass concentration of the potassium hydrogen persulfate in the mixed liquid reaches 0.5g/L, a proper amount of ammonia water is added to ensure that the pH value of the mixed liquid is 6.5, the mixture is reacted for 60min under the constant temperature condition of 50 ℃ water bath, wherein 4 mL of the mixture is sampled every 5-10min, and the ultraviolet spectrum detection is carried out, and the result is shown in figure 7 b. By combining the fitted curve of the concentration and the absorbance in fig. 6b, it can be known that the degradation rate of the methylene blue in the aqueous solution can reach 98.54% after 60min degradation.

When the solution c is degraded, PS-CHO/RGO composite microspheres and ethanol are mixed according to the mass ratio of 2.5 g/L, ultrasonic dispersion is carried out for 2h, 20 mL of dispersion liquid is taken and added into the solution c, 70mL of deionized water is additionally added for mixing, the mixture is fully stirred for 10min, the mixture reacts for 60min at the constant temperature of 50 ℃ in a water bath, 4 mL of dispersion liquid is sampled every 5-10min for ultraviolet spectrum detection, as shown in figure 8a, the PS-CHO/RGO composite microspheres and the ethanol dispersion liquid are combined with the fitted curve of the concentration and the absorbance in figure 6b, and the degradation effect of methylene blue basically does not exist.

When the solution d is degraded, 0.05g of potassium hydrogen persulfate is directly put into the solution d, 90mL of deionized water is additionally added for mixing, the mass concentration of the potassium hydrogen persulfate in the solution is 0.5 mg/mL, the mixture is fully stirred for 10min, the reaction is carried out for 60min at the constant temperature of 50 ℃ water bath, 4 mL is sampled at intervals of 5-10min for ultraviolet spectrum detection, as shown in FIG. 8b, the potassium hydrogen sulfate with the same concentration is used singly by combining the fitted curve of the concentration and the absorbance in FIG. 6, and the degradation effect on methylene blue is far inferior to that of the degradation method of the solution b after the degradation treatment in the same time.

As proved by the degradation verification of the series of methylene blue solutions, the methylene blue has a stable structure and hardly degrades under the water bath temperature of 50 ℃. The PS-CHO/RGO composite microspheres are also very weak in degrading methylene blue. Potassium peroxysulfate has a certain degree of oxidizability and can play a role in degrading methylene blue, but at a slow rate. The PS-CHO/RGO composite material is used as a catalyst, so that the reaction rate of the degradation process can be effectively accelerated, the degradation process is efficient and thorough, and the degradation rate can reach 98.54% in 60 min.

After the degradation, filtering precipitates from the degraded solution, performing high-speed ion centrifugal washing to recover the PS-CHO/RGO composite microspheres, performing degradation verification with the same degradation test parameters as the solution b, and circulating for multiple times to obtain a PS-CHO/RGO composite microsphere circulating degradation diagram shown in FIG. 9.

Claims

1. A preparation method of a nano PS-CHO/RGO composite microsphere is characterized by comprising the following steps: firstly, preparing monodisperse polystyrene aldehyde microspheres and graphene oxide respectively, then taking the polystyrene aldehyde microspheres as a carrier and sodium borohydride as a reducing agent, and coating the reduced graphene oxide on the surfaces of the microspheres by an in-situ polymerization method to prepare the nano PS-CHO/RGO composite microsphere material.

2. The method for preparing a PS-CHO/RGO composite microsphere material as claimed in claim 1, wherein the in situ polymerization method comprises the following specific steps: uniformly mixing the dried graphene oxide powder with an ammonia water solution with the molar concentration of 1mol/L according to the proportion of 0.00048-0.00052 g/mL to obtain a mixed solution A; uniformly mixing monodisperse polystyrene aldehyde microspheres and ethanol according to the proportion of 0.0023-0.0027 g/mL to obtain a mixed solution B, mixing the mixed solution A and the mixed solution B in an equal volume, continuously adding a sodium borohydride aqueous solution with the concentration of 0.0025-0.0028 g/mL, wherein the adding volume of the sodium borohydride aqueous solution is the sum of the volumes of the mixed solution AB, and reacting the mixed solution in a constant-temperature water bath at 80 ℃ for 2-3h in a dropwise adding process to obtain the PS-CHO/RGO composite microspheres.

3. The method for preparing nano PS-CHO/RGO composite microspheres according to claim 2, wherein a small amount of sodium hydroxide is added to adjust the pH value of the mixed solution to 7.5-8.5 during mixing of the mixed solution A and the mixed solution B, so as to improve the dispersibility of the graphene oxide.

4. The method for preparing a nano PS-CHO/RGO composite microsphere according to claim 2, wherein when preparing the mixed solution A, the ammonia water is continuously added dropwise into the graphene oxide powder when mixing the graphene oxide with the ammonia water, and the mixture is heated to 40 ℃, mechanically stirred for 4 hours and then ultrasonically dispersed for 1 hour to completely disperse the graphene.

5. The method for preparing nano PS-CHO/RGO composite microspheres according to claim 1, wherein the method for preparing monodisperse polystyrene aldehyde-based microspheres comprises: taking azodiisobutyronitrile as an initiator, polyvinylpyrrolidone as a dispersant and mixed solution of isopropanol and water as a solvent, and taking styrene and acrolein as monomers to perform copolymerization reaction to obtain the monodisperse polystyrene aldehyde group microsphere floating solution.

6. The method for preparing a nano PS-CHO/RGO composite microsphere according to claim 5, wherein the step of preparing the monodisperse polystyrene aldehyde-based microsphere comprises:

1.2) dissolving an azobisisobutyronitrile initiator in styrene to prepare an azobisisobutyronitrile/styrene initiator solution B with the concentration of 1.6-2.0g/100 mL;

1.3) mixing the dispersion from step 1.1) with 1.2) of initiator in a ratio of 3: 1, adding acrolein with the volume of 1/2 of initiator volume after uniformly stirring, reacting for 8-12 h at a constant temperature of 70 ℃, then washing for 2-3 times by using deionized water ultrasonic centrifugation, and drying to obtain the monodisperse polystyrene aldehyde group microsphere.

7. A method for degrading methylene blue by adopting the nano PS-CHO/RGO composite microspheres as claimed in any one of claims 1 to 6, is characterized in that the PS-CHO/RGO composite microspheres and ethanol are mixed according to the concentration of 2.3-2.7 g/L to prepare the mixture, and then the mixture is put into printing and dyeing wastewater containing methylene blue to be mixed, so that the mass ratio of the PS-CHO/RGO composite microspheres to the methylene blue in the mixed solution is 1-3: 1, stirring and mixing for 10-15min, adding a potassium hydrogen persulfate aqueous solution into the mixed solution to ensure that the mass concentration of the potassium hydrogen persulfate in the mixed solution is 0.48-0.52 g/L, and continuously stirring to ensure that the color of the mixed solution gradually becomes lighter from blue to colorless to complete the degradation of methylene blue.

8. The method for degrading methylene blue according to claim 7, wherein the temperature of the reaction system is 45-55 ℃.

9. The method of claim 7, wherein the pH of the mixture is adjusted to 6.5-6.8 with ammonia water.

10. The method for degrading methylene blue of claim 7, wherein the PS-CHO/RGO composite microspheres in the mixed solution after the completion of the methylene blue degradation can be recycled after being separated by filtration and washed by centrifugation.