CN110180510B

CN110180510B - Nano thin film and device for slowing down reservoir overturning phenomenon

Info

Publication number: CN110180510B
Application number: CN201910474916.3A
Authority: CN
Inventors: 李轶; 陆宇苗; 张文龙; 张弛; 吴海楠
Original assignee: Hohai University HHU
Current assignee: Hohai University HHU
Priority date: 2019-06-03
Filing date: 2019-06-03
Publication date: 2021-05-11
Anticipated expiration: 2039-06-03
Also published as: CN110180510A

Abstract

The invention relates to a nano film for slowing down reservoir overturning phenomenon of a reservoir, which comprises a three-layer structure, wherein the first layer is a graphene oxide/water-soluble Arabic gum/polyvinyl alcohol nanofiber film, the second layer is a biological carbon adsorption layer, and the third layer is a polyacrylonitrile-biological carbon nanofiber film. The invention achieves the purpose of slowing down the deterioration of water quality caused by the reservoir overturning phenomenon through the special design of the nano film layer.

Description

Nano thin film and device for slowing down reservoir overturning phenomenon

Technical Field

The invention relates to a nano film, in particular to a nano film for slowing down the reservoir overturning phenomenon of a reservoir.

Background

One of the purposes of reservoir construction is its interest, runoff regulation, flood storage and depletion compensation, so that natural incoming water can better meet the requirements of people in time and space, and drinking water and irrigation water can be provided for nearby areas. One of the specific reasons for the reservoir "turnover" (reservoir "turnover") phenomenon is that the sludge at the reservoir bottom is in an anaerobic state due to long-term overstocking and has a large amount of anaerobic bacteria, and as the temperature rises and the dissolved oxygen is insufficient, the sludge is rapidly fermented to generate anaerobic gas such as methane and the like and continuously rises, so that the water body is blackened, and pollutants in the sludge can be brought into the overlying water body. The reservoir turning phenomenon of the reservoir can affect the water quality of the water body.

The nanofiber membrane is mainly prepared from high molecular polymers, and the electrostatic spinning technology is more concerned in the current preparation technology. The prepared nanofiber membrane has the advantages of large specific surface area of fibers, small aperture, good bonding property among pores, easy loading of a catalyst, wide applicability and the like, so that the nanofiber membrane has good application prospects in the fields of water treatment, medicines, tissue engineering and the like. The nanofiber has a thinned diameter, so that the probability of exposing a fiber molecule chain segment or a functional group on the surface of the nanofiber is improved, the possibility of loading a catalyst on the surface of the nanofiber is also improved, the functionalization efficiency of the nanofiber membrane is improved, and the application of the nanofiber membrane in the aspects of environmental management and restoration is met.

The biochar is a solid product rich in aromatic carbon and minerals, which is obtained by heating and decomposing a biomass material under the conditions of limited oxygen and low temperature (<800 ℃). Due to the special porous structure and the high specific surface area, the biochar is not only used as a soil restoration agent to improve the fertility of soil, but also can capture carbon elements from the atmosphere to the soil so as to slow down the climate change, and is used as an adsorbent to effectively adsorb pollutants in water and soil and reduce the availability and toxicity of the pollutants to organisms. Biochar consists of different organic and inorganic components and can react with pollutants by different mechanisms, such as coordination, adsorption, aromatic ring-pi bond and cation-pi bond reactions, and electrostatic attraction. The ability of biochar to remove pollutants in water makes it one of the suitable adsorbents in water treatment, especially in complex sewage containing multiple pollutants, and due to its economical and efficient characteristics, it is widely concerned by people in the aspects of pollutant treatment and drinking water body remediation.

In the prior patent of biochar used for water treatment, soil remediation and the like, the preparation and application of the biochar have the following problems:

(1) biochar prepared from different biomasses has different characteristics, and has larger difference in stability of application effect in the face of different environments and pollution conditions.

(2) In the preparation process of the biochar, the pyrolysis temperature has great influence on the specific surface area and the porosity of the biochar and influences the adsorption effect of the biochar applied to pollutants.

(3) The subsequent recovery treatment problem exists after the biochar adsorbs pollutants.

Disclosure of Invention

The invention provides a nano film for slowing down reservoir overturning, aiming at solving the problem that the reservoir overturning phenomenon affects the water quality of a reservoir, and the aim of slowing down the water quality deterioration caused by the reservoir overturning phenomenon is achieved through the special design of the nano film layer.

The technical scheme adopted by the invention is as follows: a nano-film for slowing down reservoir overturning phenomenon comprises a three-layer structure, wherein the first layer is a graphene oxide/water-soluble Arabic gum/polyvinyl alcohol nanofiber film (GO/GA/PVA), namely the first layer of the nanofiber film comprises GO, GA and PVA, the second layer is a biochar adsorption layer, and the third layer is a Polyacrylonitrile (PAN) -biochar nanofiber film.

Further, the preparation method of the polyacrylonitrile-biochar nanofiber membrane comprises the following steps:

s1, adding the biochar prepared from the taxus chinensis into an alkali solution, fully stirring and mixing, and performing high-temperature activation, cleaning and drying on a sample to obtain activated biochar;

s2 polyacrylonitrile is dissolved in a mixed solution of N, N-dimethylformamide and dimethyl sulfoxide (DMF/DMSO), activated charcoal is added to obtain a mixture, the mixture is prepared into a PAN-charcoal nanofiber membrane through an electrostatic spinning technology, and the PAN-charcoal nanofiber membrane is cleaned and dried.

Further, the preparation method of the biochar adsorption layer comprises the following steps: putting the dried leaves into an atmosphere furnace, heating to 800-1000 ℃ at the heating rate of 5-10 ℃/min under the argon atmosphere, preserving the heat for 1-2h, soaking the carbonized leaves into a hydrochloric acid solution after the reaction is finished, and then drying to obtain the product.

Further, the preparation method of the graphene oxide/water-soluble gum arabic/polyvinyl alcohol nanofiber film comprises the following steps:

s1, mixing sulfuric acid and graphite powder, stirring in an ice bath to obtain a homogeneous solution, adding potassium permanganate and sodium nitrate into the homogeneous solution, stirring, adding deionized water to carry out water bath heating to continue reaction after reaction for a period of time, cooling to room temperature after reaction is finished, adding hydrogen peroxide, stirring, centrifuging to obtain a supernatant, adding deionized water and hydrochloric acid into the supernatant, stirring, centrifuging, and drying to obtain graphene oxide; the sulfuric acid is strong protonic acid and can enter between graphite layers, the sulfuric acid is added to provide an acid environment, and the oxidizing property of the potassium permanganate is enhanced under the acid condition. Hydrogen peroxide was added to remove excess potassium permanganate. The ice bath is used to prepare the homogeneous solution because the concentrated sulfuric acid reaction is exothermic and the ice bath reduces the ambient temperature so that the reaction is not too severe.

S2, respectively dissolving water-soluble Arabic gum and polyvinyl alcohol in deionized water to obtain a water-soluble Arabic gum solution and a polyvinyl alcohol solution, adding graphene oxide into the water-soluble Arabic gum to obtain a mixed solution, stirring, adding the polyvinyl alcohol solution, and preparing the GO/GA/PVA nanofiber film by using an electrostatic spinning technology.

Further, the preparation method of the biochar comprises the steps of pyrolyzing the taxus chinensis at the temperature of 520-530 ℃, wherein the pyrolysis time is 2-4 min; the alkali solution is NaOH solution, and the concentration of the NaOH solution is 150-250 g/L; the activation condition of the high-temperature activation is that the temperature is increased to 800 ℃ at the temperature increase rate of 5-10 ℃/min and is kept at 800 ℃ for 2 hours, and nitrogen with the flow rate of 200mL/min flows in the activation period; the drying condition is 18-24h at 50-60 ℃.

Further, the volume ratio of the N, N-dimethylformamide to the dimethyl sulfoxide is 8:1-10: 1; the purity of the N, N-dimethylformamide and the dimethyl sulfoxide is 99.99 percent, and the mass ratio of the activated biochar to the mixture of the PAN and the DMF/DMSO is 1.5-2 percent; the drying condition is drying for 8-12h at 50-60 ℃.

Further, the mass ratio of the sulfuric acid to the graphite powder is 26:1-28:1, potassium permanganate and sodium nitrate are added and stirred, and the stirring condition is that the stirring is carried out for 20-30min at the temperature of 35-45 ℃; adding deionized water into a mixture of sulfuric acid, graphite powder, potassium permanganate and sodium nitrate, and reacting for 30-40min under the condition of 75-85 ℃ water bath.

Further, the mass ratio of the needed water-soluble Arabic gum to the needed polyvinyl alcohol is 1:20:20-1:25: 25.

Further, electrostatic spinning parameters in the electrostatic spinning technology are electric field intensity: 1.0-1.2KV/cm, flow rate: 1.2-1.4mL/h, fiber collection device speed: 300-400 rpm.

Furthermore, a hollow tube is fixed on the periphery of the nano film, the side wall of the hollow tube is provided with a plurality of small holes, the small holes are communicated to the outside of the hollow tube from the cavity of the hollow tube, and the small holes are arranged at the joint of the nano film and the hollow tube.

Further, the hollow pipe is a PVC hose.

The beneficial effects produced by the invention comprise: the invention relates to a nano film for slowing down reservoir overturning phenomenon of a reservoir, which mainly plays a role of a plurality of layers of nano films. The upper layer is a GO/GA/PVA nanofiber membrane, the middle layer is a biochar adsorption layer, and the lower layer is a PAN-biochar nanofiber membrane. When the sludge at the bottom of the reservoir is subjected to anaerobic gas generation and is turned over, the sludge contacts the PAN-biochar nanofiber film at the lower layer, certain separation and adsorption effects are achieved on the sludge and part of pollutants, and due to the high specific surface area of the biochar at the middle layer of the film, the pollutants entering the middle layer of the film have good buffering and adsorption effects on the pollutants, so that the pollutants are prevented from being diffused to the upper layer. The upper layer is a GO/GA/PVA nanofiber film, has certain hydrophobicity, is in contact with an overlying water body, and reduces infiltration of the overlying water body.

Based on the above, the present invention has the following advantages:

(1) according to the invention, the biological carbon and the graphene oxide are adopted to prepare the nanofiber membrane, the specific surface area is high, the material basal plane is rich in functional groups, the large area can be tightly combined with pollutants, and the effect of quickly and efficiently removing the pollutants is achieved.

(2) The invention has the advantages of environment-friendly material, optimized design of the preparation process of the nanofiber membrane, and adoption of a novel electrostatic spinning manufacturing technology, so that the nanofiber membrane has the characteristics of higher porosity, uniform diameter distribution and the like.

(3) The structural design adopted by the invention fully considers the conditions of reservoir overturning and the like, and the PVC hose is provided with the holes, so that the film can not burst due to accumulation of excessive gas while blocking pollutants.

(4) The invention has the characteristics of simple structure, flexible arrangement, easy recycling, no secondary pollution to water environment, cleanness, high efficiency and environmental protection.

Drawings

FIG. 1 is a schematic cross-sectional view of a structure according to an embodiment of the present invention;

FIG. 2 is a SEM image of a PAN-biochar nanofiber membrane;

FIG. 3 is a graph showing the change of phosphorus element with time in example 2.

In fig. 1, a multi-layer nanofiber membrane 1, a PVC hose 2, and a membrane holder 3.

Detailed Description

The present invention is explained in further detail below with reference to the drawings and the detailed description, but it should be understood that the scope of the present invention is not limited by the detailed description.

Example 1:

as shown in figure 1, the invention aims to adsorb and remove pollutants brought by reservoir overturning by utilizing a nano film, a main structure 1 of the invention is a multi-layer nano fiber film which is used as a main part for treating the pollutants, an upper layer is a GO/GA/PVA nano fiber film, a middle layer is a biochar adsorption layer, and a lower layer is a PAN-biochar nano fiber film. 2 is a PVC hose, and the joint of the PVC hose and the film is provided with a small hole.

Fig. 2 is an SEM image of the middle layer PAN-biochar nanofiber membrane. From SEM image, it can be clearly and intuitively seen that the filamentous fibers of the nanofiber membrane are tightly combined, and certain porosity is ensured. The components of the PAN-biochar have good adsorption and combination effects on pollutants, and meanwhile, water molecules can smoothly pass through the film.

The preparation process of the PAN-biochar nanofiber membrane in this example is as follows:

s1, sawing the Chinese yew into small blocks with the same size, and placing the small blocks in an atmosphere furnace at 520 ℃ for 3min to obtain the charcoal. Weighing 25g of NaOH and dissolving in 100mL of deionized water, adding 10g of the biochar to obtain a mixture, wherein the added biochar is ground biochar powder, and the NaOH is an active agent. The mixture was magnetically stirred at 150rpm for 2h at room temperature and then oven dried at 80 ℃ for 24 h. And putting the dried sample into an atmosphere furnace, introducing nitrogen as a protective gas at the flow rate of 200mL/min, heating to 800 ℃ at the heating rate of 10 ℃/min, keeping the temperature at 800 ℃ for 2h, and cooling to room temperature. After the sample is washed to be neutral by deionized water and 0.1mol/L HCl, the salt solution is washed by the deionized water and is dried in an oven at 55 ℃ for 24 hours to obtain activated charcoal.

S2, 2g of Polyacrylonitrile (PAN) is dissolved in a mixed solution of N, N-dimethylformamide/dimethyl sulfoxide (DMF/DMSO, volume ratio 10:1), and magnetic stirring is carried out until a clear solution is obtained. Activated biochar was added to the solution at a rate of 2% by mass compared to polyacrylonitrile and magnetically stirred for 56 h. Under the condition of room temperature (the temperature is 25 ℃, the humidity is 35%), a PAN-biochar nanofiber film is prepared by an electrostatic spinning technology through a fiber collecting device (the length is 25cm, and the diameter is 10 cm). The film was washed with methanol for 120min to remove excess solvent, washed with deionized water and dried at 60 ℃ for 8 h.

The preparation process of the biochar adsorption layer in the embodiment is as follows: and (3) putting the dried leaves into an atmosphere furnace, heating to 800 ℃ at a heating rate of 5 ℃/min under an argon atmosphere, and keeping for 2 h. After the reaction is finished, the carbonized leaves are soaked in 2mol/L HCl for 12 hours to remove inorganic ions, and then are placed into an oven for drying for 12 hours at the temperature of 60 ℃.

The preparation process of the GO/GA/PVA nanofiber membrane in the embodiment is as follows:

s1, 50mL of sulfuric acid (96wt%) and 3g of graphite powder were added to a 500mL Erlenmeyer flask and stirred in an ice bath to obtain a homogeneous solution. Slowly add 7g of potassium permanganate and add 1g of sodium nitrate with constant stirring. After stirring at 40 ℃ for 30min at the rotating speed of 300r/min, 80mL of deionized water is added and the mixture is transferred to 80 ℃ water bath for reaction for 40 min. The potassium permanganate is added at the beginning, the reaction is more violent, so the reaction can be carried out at a lower temperature, the reaction temperature needs to be increased after the reaction is carried out to a certain degree to ensure the full reaction, so the 80 ℃ water bath reaction is selected, partial deionized water is evaporated by the temperature rise, the ion concentration is further influenced, and the deionized water bath heating is needed. After the reaction was completed, the mixed solution was cooled to room temperature, and 100mL of hydrogen peroxide (30wt%) was added to remove excess potassium permanganate, and vigorous stirring was required to terminate the reaction because the reaction between the peroxide and potassium permanganate was vigorous. After centrifugation at 7500r/min for 5min, the supernatant (i.e., graphene oxide) was redispersed in deionized water. 40mL of hydrochloric acid (20wt%) was added, stirred and centrifuged, and this step was repeated three times to purify the product. And dispersing the product in deionized water, centrifuging twice to obtain a solution with the pH value of 7, and freeze-drying the solution to obtain Graphene Oxide (GO) powder which is stored in a dryer for later use.

S2, respectively dissolving water-soluble Arabic Gum (GA) and polyvinyl alcohol (PVA) in deionized water, and magnetically stirring at 300rpm at 80 ℃ for 5h to obtain a GA (10wt%) aqueous solution and a PVA (10wt%) aqueous solution. Adding 0.5wt% of GO into a 10wt% GA solution, magnetically stirring at 90 ℃ for 30min to prepare a uniform dispersion solution, adding an equal volume of 10wt% PVA aqueous solution, and preparing the GO/GA/PVA nanofiber membrane by using an electrostatic spinning technology.

Example 2

The preparation is carried out after the preparation conditions of the film are adjusted in consideration of the stability of the nanofiber film prepared under different preparation conditions. Some parameters in the preparation conditions of the PAN-biochar nanofiber membrane are changed as follows: the volume ratio of the N, N-dimethylformamide to the dimethyl sulfoxide is changed to 8:1, the drying condition is changed to 60 ℃ for drying for 8 hours, the pyrolysis temperature of the taxus chinensis is less than 530 ℃, the pyrolysis time is 2min, the concentration of the NaoH solution is 250g/L, and the drying condition is 18 hours at 60 ℃. Some preparation parameters of the biochar adsorption layer are changed as follows: heating to 800 ℃ at the speed of 5 ℃/min and preserving heat for 2 h. Some preparation parameters of the GO/GA/PVA nanofiber film are changed into: the ratio of sulfuric acid to graphite powder is 28:1, and the mass ratio of graphene oxide, water-based Arabic gum to polyvinyl alcohol is 1:20: 20. The other preparation parameters were the same as in example 1.

Example 3:

the preparation is carried out after the preparation conditions of the film are adjusted in consideration of the stability of the nanofiber film prepared under different preparation conditions. Some parameters in the preparation conditions of the PAN-biochar nanofiber membrane are changed as follows: the volume ratio of N, N-dimethylformamide to dimethyl sulfoxide is changed to 9:1, the drying condition is changed to 55 ℃ for drying for 10h, the pyrolysis temperature of the redwood is less than 530 ℃, the pyrolysis time is 2min, the concentration of Na OH solution is 250g/L, and the drying condition is 18h at 60 ℃. Some preparation parameters of the biochar adsorption layer are changed as follows: heating to 900 ℃ at the speed of 5 ℃/min and preserving heat for 2 h. Some preparation parameters of the GO/GA/PVA nanofiber film are changed into: the ratio of sulfuric acid to graphite powder is 26:1, and the mass ratio of graphene oxide, water-based Arabic gum to polyvinyl alcohol is 1:23: 23. The other preparation parameters were the same as in example 1.

Example 4:

in order to study the effect of the nanofiber membrane in adsorbing pollutants, the adsorption of the membrane prepared in example 1 on phosphorus was used as a model. 50mg of biochar and 25mL of 10mg/L KH were added to a 50mL glass tube₂PO₄The solution was adjusted to pH 5 with NaOH and HCl. Placing the mixture into a constant temperature oscillator to oscillate at the rotating speed of 200r/min under the condition of room temperature. Collecting reaction liquid during adsorption for 1, 3 and 7 days, centrifuging at 3000r/min for 15min, filtering with 0.45 μm filter membrane, and measuring the content of residual phosphorus in the solution.

FIG. 3 is a graph showing the change of phosphorus element with time in example 4. It can be seen that, in the experimental period 7d, the content of phosphorus element in the solution added with the biochar is obviously reduced compared with that of the blank control group without the biochar, which indicates that the biochar prepared by the method has good adsorption and fixation effects on pollutants.

The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.

The above description is only a preferred embodiment of the present invention, and the present invention is not limited to the content of the embodiment. It will be apparent to those skilled in the art that various changes and modifications can be made within the technical scope of the present invention, and any changes and modifications made are within the protective scope of the present invention.

Claims

1. A nanometer film for slowing down reservoir overturning phenomenon is characterized in that: the nano film comprises a three-layer structure, wherein the first layer is a graphene oxide/water-soluble Arabic gum/polyvinyl alcohol nanofiber film, the second layer is a biological carbon adsorption layer, and the third layer is a polyacrylonitrile-biological carbon nanofiber film;

the preparation method of the biochar adsorption layer comprises the following steps: putting the dried leaves into an atmosphere furnace, heating to 800-1000 ℃ at the heating rate of 5-10 ℃/min under the argon atmosphere, preserving the heat for 1-2h for carbonization, soaking the carbonized leaves into a hydrochloric acid solution after the carbonization is finished, and then drying to obtain the product;

the preparation method of the polyacrylonitrile-biochar nanofiber film comprises the following steps:

s1, adding the biochar prepared from the taxus chinensis into an alkali solution, fully stirring and mixing, and performing high-temperature activation and drying on a sample to obtain activated biochar; wherein the preparation method of the biochar adopts the steps that the taxus chinensis is pyrolyzed at the temperature of 520-530 ℃, and the pyrolysis time is 2-4 min;

s2, dissolving polyacrylonitrile in a mixed solution of N, N-dimethylformamide and dimethyl sulfoxide, adding activated biochar to obtain a mixture, preparing the mixture into a polyacrylonitrile-biochar nanofiber membrane by an electrostatic spinning technology, and drying.

2. The nano-film for slowing reservoir overturning of claim 1, wherein: the alkali solution is NaOH solution, and the concentration of the NaOH solution is 150-250 g/L;

the activation condition of the high-temperature activation is that the temperature is increased to a set temperature at a temperature increase rate of 5-10 ℃/min; the drying condition is drying at 50-60 deg.C for 18-24 h.

3. The nano-film for slowing reservoir overturning of claim 1, wherein: the volume ratio of the N, N-dimethylformamide to the dimethyl sulfoxide is 8:1-10: 1; the mass ratio of the activated charcoal to the mixture of PAN, DMF and DMSO is 1.5-2%; the drying condition is drying for 8-12h at 50-60 ℃.

4. The nano-film for slowing reservoir overturning of claim 1, wherein: the preparation method of the graphene oxide/water-soluble Arabic gum/polyvinyl alcohol nanofiber film comprises the following steps:

s1, mixing sulfuric acid and graphite powder, stirring in an ice bath to obtain a homogeneous solution, adding potassium permanganate and sodium nitrate into the homogeneous solution, stirring for preliminary reaction, adding deionized water, heating in a water bath, continuing reaction, cooling to room temperature after the reaction is finished, adding hydrogen peroxide, stirring, centrifuging to obtain a supernatant, adding deionized water and hydrochloric acid into the supernatant, stirring, centrifuging, and drying to obtain graphene oxide;

s2, respectively dissolving water-soluble Arabic gum and polyvinyl alcohol in deionized water to obtain a water-soluble Arabic gum solution and a polyvinyl alcohol solution, adding graphene oxide into the water-soluble Arabic gum to obtain a mixed solution, stirring, adding the polyvinyl alcohol solution, and preparing the graphene oxide/water-soluble Arabic gum/polyvinyl alcohol nanofiber film by using an electrostatic spinning technology.

5. The nano-film for slowing reservoir overturning of claim 4, wherein: the mass ratio of the sulfuric acid to the graphite powder is 26:1-28: 1.

6. The nano-film for slowing reservoir overturning of claim 4, wherein: the mass ratio of the required graphene oxide to the water-soluble Arabic gum to the polyvinyl alcohol is 1:20:20-1:25: 25.

7. The nano-film for slowing reservoir overturning of claim 4, wherein: the electrostatic spinning parameters in the electrostatic spinning technology are electric field intensity: 1.0-1.2KV/cm, flow rate: 1.2-1.4mL/h, fiber collection device speed: 300-400 rpm.

8. A device for slowing down reservoir overturning phenomenon prepared by the nano film of claim 1, which is characterized in that: the periphery of the nano film is fixedly provided with a hollow tube, the side wall of the hollow tube is provided with a plurality of small holes, and the small holes are communicated to the joint of the hollow tube and the nano film through the hollow tube cavity.