CN115400699B - Preparation method and application of reduced graphene oxide/phosphate polyvinyl alcohol composite aerogel - Google Patents
Preparation method and application of reduced graphene oxide/phosphate polyvinyl alcohol composite aerogel Download PDFInfo
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- CN115400699B CN115400699B CN202211071700.0A CN202211071700A CN115400699B CN 115400699 B CN115400699 B CN 115400699B CN 202211071700 A CN202211071700 A CN 202211071700A CN 115400699 B CN115400699 B CN 115400699B
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- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
- C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
- C02F1/14—Treatment of water, waste water, or sewage by heating by distillation or evaporation using solar energy
Abstract
The invention provides a preparation method of reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel, which is characterized in that the composite aerogel is prepared by utilizing polycondensation reaction between phosphated polyvinyl alcohol and graphene oxide, and the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel with strong mechanical property, super hydrophilicity, low thermal conductivity and high photo-thermal conversion efficiency can be prepared by fully utilizing the super hydrophilicity of phosphated polyvinyl alcohol and the excellent optical property and higher specific surface area of graphene oxide. The reduced graphene oxide/phosphate polyvinyl alcohol composite aerogel prepared by the method provided by the invention can be applied to evaporation of water molecules in brine, actual seawater, black and odorous water or heavy metal dye wastewater.
Description
Technical Field
The invention relates to the technical field of photo-thermal water evaporation materials, in particular to a preparation method and application of reduced graphene oxide/phosphate polyvinyl alcohol composite aerogel.
Background
With the development of human socioeconomic performance, the problems of energy shortage and water pollution are increasingly highlighted. In order to reduce the pollution to the environment, the utilization of clean energy is a necessary way for human development. Traditional water purification technologies, such as reverse osmosis technology, membrane distillation technology and the like, have the characteristics of high energy consumption, centralized infrastructure and large scale, and under the inspired of natural evaporation, solar driven interfacial evaporation technology is provided. Solar energy is used as a clean sustainable energy source, and can convert absorbed light energy into heat for heating water molecules at a water/air interface. Thus, solar-driven interfacial evaporation technology is considered one of the promising alternatives to freshwater resource mitigation and carbon footprint reduction.
In the solar-driven interfacial evaporation technology, a photo-thermal absorption material is an important point, wherein Graphene Oxide (GO) provides a great opportunity for reasonable design and utilization of a solar evaporator due to excellent sunlight absorptivity, high chemical stability and lighter density, and is widely applied to interfacial evaporation. In the prior art, the application number is 202210251817.0, the publication date is 2022, 4 and 29, and the name is a photo-thermal interface water evaporation material of cellulose nanofiber aerogel and a preparation method thereof. Although the nanofiber aerogel can be prepared in the technical scheme, the preparation process is complex, the preparation flow is long, the cost is high, and the method is not friendly to the environment; in addition, in the technical scheme, through introducing cellulose nanofiber and a crosslinking agent to crosslink polyvinyl alcohol and graphene oxide, the internal structure of the aerogel is difficult to regulate and control, the water transmission rate is low, and the evaporation efficiency of the composite aerogel in interface evaporation application is affected.
In view of the above, there is a need to design an improved method for preparing three-dimensional reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel with high super-water absorption and high performance and application thereof, so as to solve the above problems.
Disclosure of Invention
The invention aims to provide a preparation method and application of reduced graphene oxide/phosphate polyvinyl alcohol composite aerogel.
In order to achieve the aim of the invention, the invention provides a preparation method of reduced graphene oxide/phosphate polyvinyl alcohol composite aerogel, which comprises the following steps:
s1, adding preset amounts of polyvinyl alcohol, N-dimethylformamide and phosphorus pentoxide into a reaction container, uniformly mixing, and reacting the reaction container in an oil bath; after the reaction is finished, washing and drying the product to obtain the phosphated polyvinyl alcohol;
s2, preparing graphene oxide by adopting an improved Hummers method;
s3, dispersing the graphene oxide prepared in the step S2 in deionized water, adding a predetermined amount of urea, and uniformly mixing to obtain a graphene oxide solution; adding the phosphated polyvinyl alcohol prepared in the step S1 into the graphene oxide solution, uniformly mixing, and transferring the mixed solution into a high-pressure reaction kettle for hydrothermal reaction to form cylindrical three-dimensional composite hydrogel; and finally, taking out the cylindrical three-dimensional composite hydrogel, and washing and freeze-drying to obtain the reduced graphene oxide/phosphate polyvinyl alcohol composite aerogel.
Preferably, in step S1, the mass ratio of the polyvinyl alcohol, the N, N-dimethylformamide and the phosphorus pentoxide is (1 to 3): (10-100): (1-3).
Preferably, in step S1, the reaction temperature of the reaction is 100 to 200 ℃ and the reaction time is 1 to 5 hours.
Preferably, in step S3, the mass ratio of the graphene oxide, the urea, and the phosphated polyvinyl alcohol is (1 to 3): (10-100): (1-3).
Preferably, in the step S3, the reaction temperature of the hydrothermal reaction is 100-200 ℃ and the reaction time is 1-5 h; preferably, the height of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel is 0.5-3 cm.
Preferably, in step S2, the specific preparation process of the graphene oxide is as follows: under the magnetic stirring condition, graphite powder and sulfuric acid are mixed, sodium nitrate and potassium permanganate are sequentially added, a container for containing the mixture is transferred into an oil bath for oil bath reaction, deionized water is added in the reaction process for heating reaction, deionized water and hydrogen peroxide are added for reaction, and after the reaction is finished, the product is washed and dried, so that the graphene oxide can be prepared.
Preferably, the mass ratio of the graphite powder to the sulfuric acid to the sodium nitrate to the potassium permanganate to the hydrogen peroxide is (1-3): (10-50): (1-3): (1-10): (10-50).
Preferably, the reaction temperature of the oil bath reaction is 10-100 ℃ and the reaction time is 100-200 min; the washing process is carried out by hydrochloric acid and deionized water, and the washing times are 3-5 times.
In particular, the invention also provides application of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel, which is carried out in the following manner: placing the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel in a water body to be treated, enabling the temperature and the humidity of the environment to be constant under simulated sunlight, and calculating the photo-thermal evaporation rate driven by sunlight through the change of the sum of the mass of the water body and the mass of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel, which is monitored by an electronic analytical balance.
Preferably, the water body is brine, actual seawater, black and odorous water body or heavy metal dye wastewater.
The beneficial effects of the invention are as follows:
1. according to the preparation method of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel, the super-hydrophilic phosphated polyvinyl alcohol is prepared firstly, and then is compounded with graphene oxide, so that the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel with strong mechanical property, super-hydrophilicity, low thermal conductivity and high photo-thermal conversion efficiency is finally prepared. By the method, the problems of complex preparation process, long preparation flow, high cost and the like in the process of preparing the photo-thermal interface water evaporation material by utilizing the nanofibers in the prior art are effectively solved, and the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel capable of being widely applied to evaporation of water molecules in brine, actual seawater, black and odorous water or heavy metal dye wastewater is prepared.
2. According to the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel prepared by the invention, by introducing the super-hydrophilic phosphated polyvinyl alcohol, the super-hydrophilicity of the composite aerogel can be endowed, so that when the composite aerogel is used for water evaporation, the composite aerogel can more rapidly convey the water to an evaporation interface, and the efficient evaporation of the water can be ensured under concentrated light intensity; the interaction between water and a network structure formed between the phosphated polyvinyl alcohol and the graphene oxide can be utilized to activate water molecules, so that the energy required by water evaporation is reduced, and the water evaporation rate is improved; the low thermal conductivity of the composite aerogel can concentrate heat in the photo-thermal conversion process at an evaporation interface, so that heat exchange with the environment is reduced, and the evaporation process is facilitated; because of the three-dimensional structure of the composite aerogel, the evaporation refrigeration effect of the composite aerogel in the evaporation process enables the temperature of the side edge of the composite aerogel to be lower than the ambient temperature, so that additional energy can be extracted from the environment for evaporating water molecules in the water body; in addition, the super-hydrophilicity and the rapid water transmission of the composite aerogel can construct the dynamic balance between salt crystallization and salt release, so that the phenomenon that salt blocks the internal pore canal of the aerogel in the process of evaporating seawater is avoided, and the continuous proceeding of the evaporating process is ensured.
3. According to the preparation method of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel, the polycondensation reaction between the phosphated polyvinyl alcohol and the graphene oxide is utilized, the excellent optical performance and the three-dimensional environment enhancement effect of the graphene oxide can be fully utilized to combine with the super hydrophilicity and low evaporation enthalpy of the phosphated polyvinyl alcohol, the composite aerogel is endowed with high evaporation rate and energy utilization efficiency, and meanwhile, the reaction between the phosphated polyvinyl alcohol and the graphene oxide effectively enhances the mechanical strength of the composite aerogel, and the practical application performance of the composite aerogel in water purification technology is improved.
Drawings
FIG. 1 is a schematic diagram of a method for preparing a reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel according to the present invention;
FIG. 2 is an SEM image of a reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel prepared in example 1 of the present invention;
FIG. 3 is an XRD pattern of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel prepared in example 1 of the present invention;
FIG. 4 is a FTIR chart of a reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel prepared in example 1 of the present invention;
FIG. 5 is an XPS diagram of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel prepared in example 1 of the present invention;
FIG. 6 is a graph showing the absorbance intensity of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel prepared in example 1 of the present invention;
FIG. 7 is a Raman spectrum of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel prepared in example 1 of the present invention;
FIG. 8 is a DSC chart of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel prepared in example 1 of the present invention;
FIG. 9 is a graph showing the comparison of evaporation rates of pure water of reduced graphene oxide/phosphated polyvinyl alcohol composite aerogels prepared according to the present invention, having different thicknesses.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in detail with reference to the accompanying drawings and specific embodiments.
It should be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and/or processing steps closely related to aspects of the present invention are shown in the drawings, and other details not greatly related to the present invention are omitted.
In addition, it should be further noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
Referring to fig. 1, the preparation method of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel provided by the invention comprises the following steps:
s1, preparing phosphated polyvinyl alcohol: adding a preset amount of polyvinyl alcohol, N-dimethylformamide and phosphorus pentoxide into a reaction container, uniformly mixing, and transferring the reaction container into an oil bath environment for reaction; washing the product with deionized water after the reaction is finished, and drying to obtain the phosphated polyvinyl alcohol;
s2, preparing graphene oxide: the graphene oxide is prepared by adopting the improved Hummers method, and the specific preparation process is as follows: under the magnetic stirring condition, mixing graphite powder with sulfuric acid, sequentially adding sodium nitrate and potassium permanganate, transferring a container for containing the mixture into an oil bath for oil bath reaction, adding deionized water for heating reaction in the reaction process, adding deionized water and hydrogen peroxide for reaction, washing the solution with hydrochloric acid and deionized water for 3-5 times after the reaction is finished, and drying to obtain graphene oxide;
s3, preparing reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel;
adding the graphene oxide obtained in the step S2 into deionized water, uniformly mixing, adding a predetermined amount of urea, and uniformly mixing to obtain a graphene oxide solution; adding the phosphated polyvinyl alcohol prepared in the step S1 into graphene oxide solution, uniformly mixing, transferring the mixed solution into a high-pressure reaction kettle for hydrothermal reaction, and reacting for 1-5 h at 100-200 ℃, wherein the phosphated polyvinyl alcohol and the graphene oxide undergo polycondensation reaction in the process to form cylindrical three-dimensional composite hydrogel; and finally, washing the composite hydrogel with deionized water for 3-5 times, and performing freeze drying treatment to obtain the reduced graphene oxide/phosphate polyvinyl alcohol composite aerogel.
Preferably, in step S1, the mass ratio of the polyvinyl alcohol, the N, N-dimethylformamide and the phosphorus pentoxide is (1 to 3): (10-100): (1-3).
Preferably, in step S1, the reaction temperature is 100 to 200 ℃ and the reaction time is 1 to 5 hours.
Preferably, in step S2, the mass ratio of graphite powder, sulfuric acid, potassium permanganate, sodium nitrate and hydrogen peroxide is (1-3): (10-50): (1-3): (1-10): (10-50).
Preferably, in the step S2, the reaction temperature of the oil bath reaction is 10-100 ℃, and the reaction time is 100-200 min.
Preferably, in step S3, the mass ratio of graphene oxide, urea and phosphated polyvinyl alcohol is (1 to 3): (10-100): (1-3).
Preferably, in step S3, the reaction temperature is 100 to 200 ℃ and the reaction time is 1 to 5 hours.
Preferably, in step S3, the height of the composite aerogel produced is 0.5-3 cm, the height of the composite aerogel being determined by the volume of solution added during the hydrothermal reaction.
Preferably, in step S3, the time of the freeze-drying treatment is 48 hours.
In particular, the invention also provides an application method of the graphene oxide/phosphate polyvinyl alcohol composite aerogel, which comprises the following steps: placing composite aerogel with the diameter of 2cm and the height of 0.5-3 cm in a water body to be treated, when the temperature and the humidity of the environment are constant, adopting simulated solar light irradiation, and calculating the photo-thermal evaporation rate driven by sunlight through the change of the sum of the mass of the water body and the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel monitored by an electronic analytical balance; the sunlight intensity in the process is 50-300 mW cm -2 The wind speed is 1.5-2.5 m s -1 The water body is brine, actual seawater, black and odorous water body or heavy metal dye wastewater.
The preparation method and application of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel provided by the invention are further described below with reference to specific examples:
example 1
The embodiment prepares the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel, which comprises the following preparation steps:
s1, preparing phosphated polyvinyl alcohol: adding polyvinyl alcohol and N, N-dimethylformamide into a five-neck flask, and adding phosphorus pentoxide into the flask, and uniformly mixing, wherein the mass ratio of the polyvinyl alcohol to the N, N-dimethylformamide to the phosphorus pentoxide is 1.25:50:1; transferring the five-neck flask to an oil bath environment at 130 ℃ for reaction for 4 hours; washing the product with deionized water after the reaction is finished, and drying to obtain the phosphated polyvinyl alcohol;
s2, preparing graphene oxide: the graphene oxide is prepared by adopting the improved Hummers method, and the specific preparation process is as follows: under the magnetic stirring condition, adding graphite powder and sulfuric acid into a five-neck flask, uniformly mixing, sequentially adding sodium nitrate and potassium permanganate, transferring the five-neck flask containing the mixture into an oil bath pot at 35 ℃ for reaction for 2 hours, adding deionized water, then carrying out heating reaction, adding deionized water and hydrogen peroxide for reaction, washing the solution with hydrochloric acid and deionized water for 3-5 times after the reaction is finished, and drying to obtain graphene oxide; wherein the mass ratio of the graphite powder to the sulfuric acid to the sodium nitrate to the potassium permanganate to the hydrogen peroxide is 1:46:1:6:20;
s3, preparing reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel;
adding the graphene oxide obtained in the step S2 into deionized water, uniformly mixing, adding a predetermined amount of urea, and uniformly mixing to obtain a graphene oxide solution; adding the phosphated polyvinyl alcohol prepared in the step S1 into graphene oxide solution, uniformly mixing, transferring the mixed solution into a high-pressure reaction kettle for hydrothermal reaction, and reacting for 3 hours at 160 ℃ to obtain cylindrical three-dimensional reduced graphene oxide/phosphated polyvinyl alcohol composite hydrogel; and washing the composite hydrogel with deionized water for 3 times, and performing freeze drying treatment for 48 hours to obtain the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel, wherein the mass ratio of graphene oxide to urea to phosphated polyvinyl alcohol is 1:30:1.
The prepared composite aerogel is characterized, the obtained characterization map is shown in figures 2 to 8, wherein figure 2 is an SEM (SEM) map of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel, and the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel can be seen from the SEM map to have a self-assembled three-dimensional interconnection structure, wherein the three-dimensional interconnection structure comprises internal gaps and micro channels which are randomly distributed. FIG. 3 is a reduced graphite oxideXRD pattern of the graphene/phosphated polyvinyl alcohol composite aerogel, the reduced graphene oxide aerogel has a characteristic diffraction peak at 25.1 degrees, the phosphated polyvinyl alcohol has a wide characteristic peak near 22.0 degrees, and the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel has a wide peak near 25.0 degrees, which is the superposition of the characteristic peaks of the phosphated polyvinyl alcohol and the reduced graphene oxide. FIG. 4 is a FTIR chart of a reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel, the FTIR spectrum of graphene oxide showing at 3412cm -1 There was a stretching vibration peak of-OH at 1733cm -1 Stretching vibration at 1617cm for C=O -1 And 1050cm -1 C=c bending vibration and c—o stretching vibration, respectively. 1733cm in reduced graphene oxide FTIR spectra -1 The peak at c=o almost disappeared and the peak of-OH still remained but weakened. The phosphated polyvinyl alcohol is at 1210, 1080 and 935cm -1 The peaks at P= O, P-O-C and P-OH, respectively, demonstrate that the polyvinyl alcohol has been phosphorylated. Functional groups such as C= C, P = O, P-O-C, P-OH exist in the FTIR spectrum of the reduced graphene oxide/phosphated polyvinyl alcohol mixed aerogel, and the successful preparation of the material is proved. FIG. 5 is an XPS graph of a reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel, where in XPS spectrum, P exists, indicating that the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel was successfully compounded. FIG. 6 is an absorption spectrum of a reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel with an absorbance of 94% or more. FIG. 7 is a Raman spectrum of a reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel, which can be divided into free water and intermediate water, the intermediate water being more easily evaporated from the polymer network into steam, so the presence of intermediate water can reduce the energy required for evaporation. FIG. 8 is a DSC of a reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel having an evaporation enthalpy of 1512, 1512J g -1 Far lower than the evaporation enthalpy of pure water (2422J g) -1 )。
Particularly, the invention also explores the photo-thermal evaporation performance of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel, and the specific operation steps are as follows:placing composite aerogel with height of 0.5cm, 1cm, 2cm, 3cm and diameter of 2cm in pure water, respectively, and measuring intensity of 100mW cm -2 As shown in FIG. 9, the evaporation rates of pure water were 2.49, 3.27, 4.10 and 4.89kg m, respectively -2 h -1 The results show that the photo-thermal evaporation rate is highest at a height of 3cm.
At the same time, the invention also explores the photo-thermal transformation performance of the composite aerogel with the height of 3cm and the diameter of 2cm under different test conditions, in particular to the photo-thermal transformation performance of the composite aerogel with the strength of 50, 100, 200 and 300mW cm -2 The evaporation rates of pure water were 2.74, 4.89, 7.10, 9.21kg m, respectively -2 h -1 The method comprises the steps of carrying out a first treatment on the surface of the At wind speeds of 1.5,2.0 and 2.5m s -1 The evaporation rates of pure water were 12.84, 15.07, 16.22kg m, respectively -2 h -1 The method comprises the steps of carrying out a first treatment on the surface of the In brine with a concentration of 3.5wt% and 15wt%, the intensity was 100mW cm -2 The evaporation rate in brine was 4.69 and 4.38kg m, respectively, under simulated sunlight -2 h -1 The method comprises the steps of carrying out a first treatment on the surface of the At wind speeds of 1.5,2.0 and 2.5m s -1 The evaporation rates of pure water were 12.84, 15.07, 16.22kg m, respectively -2 h -1 The evaporation rates of brine at 3.5wt% were 12.59, 14.04, 15.41kg m, respectively -2 h -1 。
The result shows that the reduced graphene oxide/phosphate polyvinyl alcohol composite aerogel prepared by the invention has higher evaporation efficiency and good salt resistance when being applied to salt water evaporation; the method is characterized in that the composite aerogel can be endowed with super-hydrophilicity by introducing the phosphated polyvinyl alcohol in the composite aerogel, so that the saline water is conveyed to an evaporation interface, optical performance of the graphene oxide is utilized to convert optical energy into heat energy, water in the saline water is evaporated, and salt crystallization and salt dissolution in the saline water reach dynamic balance in the conveying and evaporating processes, so that the pore channel structure of the aerogel cannot be blocked, the saline water is prevented from being conveyed to the evaporation interface, and meanwhile, interaction between a network structure formed between the phosphated polyvinyl alcohol and the graphene oxide and water can be utilized in the process, so that water molecules are activated, energy required by water evaporation is reduced, and the evaporation rate of the water molecules is improved.
Examples 2 to 3
Examples 2 to 3 differ from example 1 only in that: in step S1, the mass ratio of polyvinyl alcohol, N-dimethylformamide, and phosphorus pentoxide is different, and other steps are substantially the same as in example 1, and will not be described here again. The mass ratio of polyvinyl alcohol, N-dimethylformamide and phosphorus pentoxide in examples 2 to 3 is set as shown in Table 1, and the results show that the evaporation rate of the composite aerogel is influenced by the mass ratio of polyvinyl alcohol, N-dimethylformamide and phosphorus pentoxide in the preparation process of the phosphated polyvinyl alcohol, and the evaporation rate of the composite aerogel is highest when the mass ratio of polyvinyl alcohol, N-dimethylformamide and phosphorus pentoxide is 1.25:50:1.
Table 1 setting of mass ratio of polyvinyl alcohol, N-dimethylformamide, phosphorus pentoxide in preparation of phosphated polyvinyl alcohol in examples 1 to 3, evaporation rate of the composite aerogel obtained
Examples 4 to 5
Examples 4 to 5 differ from example 1 only in that: in step S1, the reaction temperature is different, and other steps are substantially the same as those in example 1, and will not be described herein. The reaction temperatures in examples 4 to 5 are set as shown in Table 2, and the results show that the evaporation rate of the produced composite aerogel is reduced at the reaction temperatures of 100℃and 200 ℃.
Table 2 setting of reaction temperature in preparation of phosphated polyvinyl alcohol in example 1 and examples 4 to 5 and evaporation rate of the obtained composite aerogel
| Project | Reaction temperature | Evaporation rate (kgm) -2 h -1 ) |
| Example 1 | 130 | 4.89 |
| Example 4 | 100 | 2.24 |
| Example 5 | 200 | 3.11 |
Examples 6 to 7
Examples 6 to 7 differ from example 1 only in that: in step S1, the reaction time is different, and other steps are substantially the same as those in example 1, and are not described herein. The reaction times set in examples 6 to 7 are shown in Table 3, and the results show that the performance of the composite aerogel is affected by the reaction time when the phosphated polyvinyl alcohol is prepared, and that the evaporation rate of the prepared composite aerogel is highest at a certain reaction time.
Table 3 setting of reaction time in preparation of phosphated polyvinyl alcohol in example 1 and examples 6 to 7 and evaporation rate of the obtained composite aerogel
| Project | Reaction time | Evaporation rate (kgm) -2 h -1 ) |
| Example 1 | 4 | 4.89 |
| Example 6 | 1 | 1.56 |
| Example 7 | 5 | 3.67 |
Comparative example 1
Comparative example 1 differs from example 1 only in that: in the process of preparing the composite aerogel, the composite aerogel is prepared by directly using polyvinyl alcohol instead of the phosphated polyvinyl alcohol in the example 1, the comparative example 1 is frozen in a mould, and the example is self-polycondensation reaction in a high-temperature reaction kettle. In order to compare the photo-thermal conversion efficiency of the polyvinyl alcohol/graphene oxide aerogel prepared in comparative example 1 with that of the composite aerogel prepared in example 1, photo-thermal water evaporation test was performed under the same conditions, and the results show that: the evaporation rate of the polyvinyl alcohol/graphene oxide aerogel is lower than that of the composite aerogel because the moisture in the polyvinyl alcohol/graphene oxide aerogel is transported slower and the energy required for evaporation of the water molecules in the aerogel network is higher than that of the composite aerogel.
Comparative example 2
Comparative example 2 differs from comparative example 1 in that: in the step S3, after the polyvinyl alcohol is added into the graphene oxide solution, nanofiber dispersion liquid, butane tetracarboxylic acid and sodium hypophosphite are further added, wherein the mass ratio of the polyvinyl alcohol to the nanofibers in the nanofiber dispersion liquid is 3:10, and the mass of the butane tetracarboxylic acid and the sodium hypophosphite is the same as that of the polyvinyl alcohol; the subsequent steps are the same as those of comparative example 1, and will not be described again.
The composite aerogel prepared in comparative example 2 and the composite aerogel prepared in example 1 were subjected to water evaporation under the same conditions, and the evaporation rate of the composite aerogel prepared in this comparative example was 2.28kg m -2 h -1 This value is significantly lower than the evaporation rate of example 1, 4.89kg m -2 h -1 The result shows that the composite aerogel prepared by the method provided by the invention can realize effective combination of excellent light absorption, super hydrophilicity, low evaporation enthalpy and environmental enhancement, and shows more excellent photo-thermal conversion performance.
In summary, according to the preparation method of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel, the composite aerogel is prepared by utilizing the polycondensation reaction between the phosphated polyvinyl alcohol and the graphene oxide, and the super-hydrophilicity of the phosphated polyvinyl alcohol and the excellent optical performance and the higher specific surface area of the graphene oxide can be fully utilized to prepare the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel with strong mechanical performance, super-hydrophilicity, low thermal conductivity and high photo-thermal conversion efficiency; the introduction of the phosphated polyvinyl alcohol can endow the composite aerogel with super-hydrophilicity, so that the composite aerogel is easier to convey water to an evaporation interface when being used for water evaporation, and can activate water molecules by utilizing the interaction between a network structure formed between the phosphated polyvinyl alcohol and the graphene oxide and water, so that the energy required by water evaporation is reduced, and simultaneously, the photo-thermal conversion performance of the graphene oxide is combined, so that the water evaporation rate is effectively improved. The reduced graphene oxide/phosphate polyvinyl alcohol composite aerogel prepared by the method provided by the invention can be applied to evaporation of water molecules in brine, actual seawater, black and odorous water or heavy metal dye wastewater and can obtain clean water resources.
The above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the technical solution of the present invention.
Claims (9)
1. The preparation method of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel is characterized by comprising the following steps of:
s1, adding preset amounts of polyvinyl alcohol, N-dimethylformamide and phosphorus pentoxide into a reaction container, uniformly mixing, and reacting the reaction container in an oil bath; after the reaction is finished, washing and drying the product to obtain the phosphated polyvinyl alcohol;
s2, preparing graphene oxide by adopting an improved Hummers method;
s3, dispersing the graphene oxide prepared in the step S2 in deionized water, adding a predetermined amount of urea, and uniformly mixing to obtain a graphene oxide solution; and adding the phosphated polyvinyl alcohol prepared in the step S1 into the graphene oxide solution, uniformly mixing, transferring the mixed solution into a high-pressure reaction kettle for hydrothermal reaction, wherein the mass ratio of the graphene oxide to the urea to the phosphated polyvinyl alcohol in the mixed solution is (1-3): (10-100): (1-3), wherein the reaction temperature of the hydrothermal reaction is 100-200 ℃ and the reaction time is 1-5 h, so as to form cylindrical three-dimensional composite hydrogel; and finally, taking out the cylindrical three-dimensional composite hydrogel, and washing and freeze-drying to obtain the reduced graphene oxide/phosphate polyvinyl alcohol composite aerogel.
2. The method for preparing a reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel according to claim 1, wherein in step S1, the mass ratio of the polyvinyl alcohol, the N, N-dimethylformamide and the phosphorus pentoxide is (1-3): (10-100): (1-3).
3. The method for preparing the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel according to claim 1, wherein in the step S1, the reaction temperature is 100-200 ℃, and the reaction time is 1-5 h.
4. The method for preparing a reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel according to claim 1, wherein in step S3, the height of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel is 0.5-3 cm.
5. The method for preparing a reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel according to claim 1, wherein in step S2, the specific preparation process of the graphene oxide is as follows: under the magnetic stirring condition, graphite powder and sulfuric acid are mixed, sodium nitrate and potassium permanganate are sequentially added, a container for containing the mixture is transferred into an oil bath for oil bath reaction, deionized water is added in the reaction process for heating reaction, deionized water and hydrogen peroxide are added for reaction, and after the reaction is finished, the product is washed and dried, so that the graphene oxide can be prepared.
6. The method for preparing a reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel according to claim 5, wherein the mass ratio of the graphite powder to the sulfuric acid to the sodium nitrate to the potassium permanganate to the hydrogen peroxide is (1-3): (10-50): (1-3): (1-10): (10-50).
7. The method for preparing the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel according to claim 6, wherein the reaction temperature of the oil bath reaction is 10-100 ℃ and the reaction time is 100-200 min; the washing process is carried out by hydrochloric acid and deionized water, and the washing times are 3-5.
8. The application of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel prepared by any one of claims 1 to 7 is characterized by adopting the following modes: placing the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel in a water body to be treated, enabling the temperature and the humidity of the environment to be constant under simulated sunlight, and calculating the photo-thermal evaporation rate driven by sunlight through the change of the sum of the mass of the water body and the mass of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel, which is monitored by an electronic analytical balance.
9. The use of the reduced graphene oxide/phosphated polyvinyl alcohol composite aerogel according to claim 8, wherein the water body is brine, actual seawater, black and odorous water body or heavy metal dye wastewater.
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