CN114272904B - Preparation method of magnetic super-hydrophobic starch-based aerogel for oil-water separation - Google Patents
Preparation method of magnetic super-hydrophobic starch-based aerogel for oil-water separation Download PDFInfo
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- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
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- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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- Y02A20/20—Controlling water pollution; Waste water treatment
- Y02A20/204—Keeping clear the surface of open water from oil spills
Abstract
The invention discloses a preparation method of magnetic super-hydrophobic starch-based aerogel for oil-water separation, and belongs to the field of oil-water separation. The invention carries out hexadecyl trimethoxy silane modification on nano starch prepared by an enzymolysis regeneration method, takes the modified nano starch as a super-hydrophobic coating, and then carries out quick coprecipitation on Fe prepared by a quick coprecipitation method 3 O 4 The surface of the magnetic nano particle is modified by tetraethoxysilane and KH560 silane coupling agent, the modified magnetic nano particle with shell-core structure is compounded with starch to prepare magnetic starch-based aerogel, and finally the super-hydrophobic coating suspension is sprayed on the surface of the aerogel to prepare the magnetic super-hydrophobic starch-based aerogel. The magnetic super-hydrophobic starch-based aerogel disclosed by the invention shows excellent water-oil selective absorptivity, namely an oil-water separation characteristic, can be used for remotely controlling floating oil absorption under the guidance of a magnetic field, can be absorbed and recovered by a magnet after oil absorption is finished, and shows great potential in application to ocean oil leakage cleaning.
Description
Technical Field
The invention relates to a preparation method of magnetic super-hydrophobic starch-based aerogel for oil-water separation, and belongs to the field of oil-water separation.
Background
Petroleum is essential energy oil for daily life and production, but frequent marine oil spill accidents in recent years also attract attention. The leaked petroleum contains toxic compounds such as benzene, toluene and the like, and the toxic compounds can be rapidly diffused in an ocean system under the action of ocean currents and ocean waves, so that serious toxicity is caused to lower algae to higher mammals, and huge economic and energy losses are brought to human society. In many conventional oil-water separation methods for cleaning oil spills, physical adsorbents have been widely used with relatively low cost and convenient operability. However, the traditional physical adsorbent has low hydrophobic property, low water-oil separation efficiency, and difficult convenient operation and recycling at sea. Therefore, the development of smart adsorbents with high water-oil selectivity is urgently needed.
Porous materials with low density and high specific area are commonly used as oil absorbents, and starch molecules can form a network-like gel structure in an environment without a cross-linking agent, and the gel can be converted into various porous starch-based adsorbing materials through different drying methods, and the materials are generally called starch-based aerogels. The prior research reports the application of starch-based aerogel in oil absorption (carbohydrate. Polymer.2011, 86, 1181-1186), but the common starch-based aerogel has no selective absorption on oil and water, which is not beneficial to the realization of oil-water separation.
In recent years, the inspired on a leaf-type bionic structure of a load bearing type endows the adsorbent with super-hydrophobic property from two aspects of reducing surface energy and constructing a multi-level micro-nano rough structure, and further realizes efficient oil removal in water. However, no reports on the development and research of the super-hydrophobic starch-based aerogel related technology are found at present. In addition, magnetic adsorbents that respond to external magnetic fields have received much attention because they can be remotely controlled and recovered. For example, chinese patent No. CN 111589186A reports a magnetic super-hydrophobic polyurethane sponge compounded with nano Fe3O4, which not only realizes oil-water separation, but also improves the recoverability of the polyurethane sponge.
Therefore, the magnetic super-hydrophobic starch-based aerogel developed to realize the oil-water separation and convenient recovery of remote control has very important application value.
Disclosure of Invention
[ problem ] to
Research reports that starch-based aerogel has good oil absorption performance, but the starch-based aerogel does not have water-oil selective absorption capacity and cannot realize efficient oil-water separation. In addition, the problems of remote control and recoverability of the adsorbent can be generally solved by the composite nano magnetic particles, but the magnetic particles tend to self-aggregate, and the dispersibility in the starch solution is poor. These deficiencies limit the development of magnetic starch-based aerogels and their application in marine oil spill clean-up.
[ solution ]
In order to solve the defects, the nano-starch prepared by modifying enzyme regeneration by hexadecyl trimethoxy silane is used as a coating to endow the starch-based aerogel with super-hydrophobicity. In addition, the invention adopts tetraethoxysilane and KH560 silane coupling agent to couple Fe 3 O 4 The nano particles are subjected to surface modification in sequence, so that the nano particles can be uniformly dispersed in a starch solution, and the starch-based aerogel is further endowed with magnetism. The magnetic super-hydrophobic starch-based aerogel prepared by the method can solve the problems of oil leakage cleaning on the water surface, water quality purification and the like.
The first object of the present invention is to provide a method for preparing magnetic super-hydrophobic starch-based aerogel, comprising the following steps:
(1) Preparation of hydrophobic suspension:
adding nano starch into an ethanol solution containing hexadecyl trimethoxy silane and ammonia water, and uniformly mixing to obtain a hydrophobic suspension;
(2) Preparation of magnetic starch-based aerogel:
modifying starch-containing KH560 silane coupling agent modified shell-core structure SiO 2 -Fe 3 O 4 Heating and pasting the aqueous solution of the magnetic particles, refrigerating, freezing and drying to obtain magnetic starch-based aerogel;
(3) Preparing magnetic super-hydrophobic starch-based aerogel:
and (3) spraying the hydrophobic suspension obtained in the step (1) on the surface of the magnetic starch-based aerogel obtained in the step (2), and drying to obtain the magnetic super-hydrophobic starch-based aerogel.
In one embodiment of the present invention, the concentration of hexadecyltrimethoxysilane by mass relative to the mass of ethanol in the step (1) is 0.1 to 2.5wt%, and the concentration of ammonia by mass relative to the mass of ethanol is 8 to 12wt%.
In one embodiment of the present invention, the nano starch in the step (1) is added in an amount of 0.1 to 2.5wt% based on the mass of ethanol.
In one embodiment of the present invention, the preparation method of the nano starch in step (1) comprises the following steps:
dispersing starch in buffer solution, heating for gelatinization, and cooling; adding pullulanase for incubation; heating the incubated solution to inactivate enzyme, centrifuging, taking supernatant, recrystallizing, washing and drying to obtain the nano starch.
In one embodiment of the present invention, the starch in the preparation method of nano starch in step (1) is waxy corn starch; the concentration of the starch in the buffer solution is 8-12 wt%; the pH value of the buffer solution is 4.5-5.5; the heating gelatinization is carried out for 30-45 min at 70-100 ℃; the temperature after cooling is 50-60 ℃; the pullulanase is added with the enzyme activity of 25-35 ASPU per gram dry starch; the incubation temperature and time are respectively 50-60 ℃ and 6-10 hours; the enzyme is deactivated by heating in boiling water; the recrystallization temperature and time are 3-5 ℃ and 6-10 hours respectively.
In one embodiment of the present invention, the mixing in step (1) is performed by stirring at 200 to 500rpm for 0 to 8 hours.
In one embodiment of the present invention, the starch in step (2) includes one or more of tapioca starch, common corn starch, waxy corn starch, rice starch, wheat starch, and potato starch.
In one embodiment of the invention, the starch-containing and KH560 silane coupling agent modified shell-core structure SiO in the step (2) 2 -Fe 3 O 4 The concentration of starch in the aqueous solution of the magnetic particles relative to water is 4.0-10.0 wt%; the concentration of the KH560 silane coupling agent modified shell-core structure magnetic particles relative to water is 0.2-0.4 wt%.
In one embodiment of the invention, the heating gelatinization in the step (2) is carried out for 30-45 min at 70-100 ℃; the refrigeration temperature and time are respectively 3-5 ℃ and 20-30 hours; the freezing temperature and the freezing time are respectively-20 to-30 ℃ and 20 to 30 hours; the drying method is freeze drying.
In one embodiment of the present invention, the KH560 silane coupling agent modified shell-core structure SiO in step (2) 2 -Fe 3 O 4 The preparation method of the magnetic particles comprises the following steps:
will contain Fe 3+ And Fe 2+ The aqueous solution of (A) is mixed with an ammonia solution, and the mixture reacts for 25 to 35 minutes at a temperature of between 65 and 75 ℃ and at a speed of between 500 and 700rpm under the protection of inert gas; after the reaction is finished, washing to obtain a product; adding ethanol, water, ethyl orthosilicate and ammonia water into the product, and reacting for 5-7 hours at the temperature of 20-30 ℃ and the rpm of 200-400; then adding KH560 silane coupling agent, reacting for 1.5-2.5 hours at 45-55 ℃ and 200-400 rpm to obtain the shell-core structure magnetic particles modified by the KH560 silane coupling agent.
In one embodiment of the present invention, the inert gas is one or two of argon and nitrogen.
In one embodiment of the present invention, the method for preparing the magnetic particles having a shell-core structure modified with the KH560 silane coupling agent in step (2) comprises Fe 3+ And Fe 2+ The volume ratio of the aqueous solution to the aqueous ammonia solution of (1): 9. The following examples E-mail protocol11, wherein the concentration of ammonia water is 0.30-0.40 mol/L, fe 2+ With Fe 3+ The mass ratio of (1): 1.5 to 2.5; the addition amounts of ethanol, water, ethyl orthosilicate, ammonia water and KH560 are respectively 100, 20-30, 0.2-0.3, 4-6 and 0.1-0.3 g/g product.
In one embodiment of the present invention, the spraying amount of the hydrophobic suspension in the step (3) is 0.0005 to 0.0015g/cm 2 。
The second purpose of the invention is the magnetic super-hydrophobic starch-based aerogel prepared by the method.
The third purpose of the invention is to apply the magnetic super-hydrophobic starch-based aerogel in the field of oil-water separation.
In one embodiment of the invention, the application comprises cleaning of oil spills at sea.
[ advantageous effects ]
(1) In the preparation method of the magnetic super-hydrophobic starch-based aerogel for oil-water separation, the used base and coating raw materials are low-cost degradable starch, toxic hydrophobic modification reagents containing fluorine, chlorine and the like are not involved in the preparation and modification processes, and secondary pollution is not easily generated in practical application.
(2) The invention adopts hexadecyl trimethoxy modified nano starch suspension as a surface coating raw material, and endows the starch-based aerogel with super-hydrophobic characteristics (the contact angle is more than 151.5 degrees and more than 150.0 degrees, and the sliding angle is less than 8.0 degrees and less than 10.0 degrees).
(3) The invention adopts a rapid coprecipitation method to prepare Fe 3 O 4 Nano particles are sequentially modified by tetraethoxysilane and KH560 silane coupling agent to make Fe 3 O 4 SiO is covered on the surfaces of the nano particles 2 A shell layer which provides more hydroxyl groups for the KH560 silane coupling agent to graft, and improves Fe 3 O 4 The surface potential of the nano particles improves the dispersibility of the nano particles in aqueous solution.
(4) The invention relates to Fe modified by tetraethoxysilane and KH560 silane coupling agent 3 O 4 The nanometer particles are compounded with starch to prepare the magnetic materialStarch-based aerogels, fe 3 O 4 The nanoparticles were uniformly dispersed in the aerogel and fixed therein via an ether bond, giving a saturation magnetization of 5.04emu/g to the starch-based aerogel.
(5) The magnetic super-hydrophobic starch-based aerogel provided by the invention shows excellent water-oil selective absorptivity, namely an oil-water separation characteristic, can be subjected to remote control floating oil absorption under the guidance of a magnetic field, can be recovered by magnet adsorption after oil absorption is finished, and shows great potential for being applied to ocean oil leakage cleaning.
Drawings
FIG. 1 is an X-ray diffraction pattern of the magnetic super-hydrophobic starch-based aerogel prepared in example 1.
FIG. 2 is a scanning electron microscope image of the magnetic super-hydrophobic starch-based aerogel prepared in example 1.
Fig. 3 is a hysteresis regression curve of the magnetic superhydrophobic starch-based aerogel prepared in example 1.
FIG. 4 is a graph of water contact angles of magnetic superhydrophobic starch-based aerogels prepared in example 2 and comparative example 1 after treatment with coating suspensions having different contents of hexadecyltrimethoxysilane.
Fig. 5 is a water contact angle of the magnetic super-hydrophobic starch-based aerogels prepared in example 3 and comparative example 2 after being treated with coating suspensions with different nano-starch contents.
FIG. 6 shows the water contact angles of the magnetic super-hydrophobic starch-based aerogel prepared in example 4 after being treated with coating suspensions for different stirring times.
FIG. 7 is a bar graph of the absorption capacity of the magnetic super-hydrophobic starch-based aerogel for oil-water separation prepared in example 1 for various organic liquids.
FIG. 8 shows the oil absorption condition at the water bottom of the magnetic super-hydrophobic starch-based aerogel for oil-water separation prepared in example 1.
Fig. 9 is a water contact angle of the magnetic starch-based aerogel prepared in comparative example 1 without the super-hydrophobic nano-starch coating treatment.
FIG. 10 shows the water bottom oil absorption of the magnetic starch-based aerogel prepared by the treatment of the non-excess water nano-starch coating prepared in comparative example 1.
FIG. 11 is a scanning electron microscope image of the distribution state of the magnetic particles without modification by tetraethoxysilane and KH560 silane coupling agent in the super-hydrophobic starch-based aerogel prepared in comparative example 5.
Fig. 12 is a surface potential histogram of the shell-core structure magnetic particles prepared in example 1 and comparative examples 5, 6, and 7.
Detailed Description
The following description of the preferred embodiments of the present invention is provided for the purpose of better illustrating the invention and is not intended to limit the invention thereto.
The reagents or instruments used in the examples are not indicated by the manufacturer, and are regarded as conventional products commercially available.
The test method comprises the following steps:
1. measurement of Water contact Angle and sliding Angle
Contact angle and sliding angle of 5. Mu.L and 10. Mu.L water droplets on the sample surface were measured using KRUSS DSA100 contact angle measuring instrument, respectively.
2. Magnetic correlation characterization test
Measuring an X-ray diffraction spectrum of the magnetic particles by using a D2 PHASER 154X-ray diffractometer; observing the dispersion state of the magnetic particles by adopting an S-4800 field emission scanning electron microscope; measuring the magnetism of the sample in a magnetic field of 20kOe by using a PPMS Dynacool vibration sample magnetometer; the particle surface potential of the magnetic particles was measured using a zetasizerano zs90 nm particle size potential analyzer.
3. Measurement of oil absorption Capacity
Weighing the prepared magnetic super-hydrophobic starch-based aerogel for oil-water separation, and marking the weight as m 1 Putting the mixture into a beaker filled with 30g of organic liquid, wherein the mass of the organic liquid is recorded as m 2 (i.e., m) 2 Equal to 30 g), take out the aerogel after 45 minutes of absorption, weigh the mass m of the organic liquid remaining in the beaker 3 The formula is calculated according to the oil absorption capacity:
oil absorption capacity = (m) 2 -m 3 )/m 1
Example 1
A method for preparing magnetic superhydrophobic starch-based aerogel comprising the steps of:
(1) Preparing nano starch:
dispersing waxy corn starch in a buffer solution with the pH value of 5.0, and heating and gelatinizing the waxy corn starch at the temperature of 95 ℃ for 45min, wherein the concentration of the waxy corn starch in the buffer solution is 10.0wt%; cooling to 55 deg.C, adding pullulanase into the above solution with enzyme activity of 30ASPU per gram dry starch, incubating at 55 deg.C for 8 hr, heating in boiling water to inactivate enzyme, and centrifuging to obtain supernatant; and then recrystallizing the supernatant for 8 hours at 4 ℃, washing the obtained precipitate to be neutral, and drying to obtain the nano starch.
(2) Preparation of hydrophobic suspension:
preparing an absolute ethyl alcohol solution with 1.5wt% of hexadecyl trimethoxy silane and 10.0wt% of ammonia water, immediately adding 1.5wt% of the nano starch in the step (1) relative to the amount of the absolute ethyl alcohol into the solution, and stirring at 300rpm for 5 hours to obtain a hydrophobic suspension;
(3) Preparation of magnetic particles of shell-core structure
Under the protection of argon, feCl is contained 3 And FeCl 2 With 0.38mol/L aqueous ammonia in a ratio of 1:10v/v mixing and stirring the reaction at 600rpm at 70 ℃ for 30 minutes; after the reaction is finished, washing to obtain a product; wherein Fe 2+ With Fe 3+ The mass ratio of (a) to (b) is 1:2;
adding ethanol, water, ethyl orthosilicate and ammonia water into the product at the ratio of 100 g/g, 25 g/g, 0.25 g/g and 5g/g (relative to the product), stirring at 25 ℃ and 300rpm for 6 hours, adding 0.2g/g (relative to the product) of KH560 silane coupling agent into the product, and continuously stirring at 50 ℃ and 300rpm for 2 hours to prepare the magnetic particles with the shell-core structure;
(4) Preparing magnetic starch-based aerogel:
heating and gelatinizing an aqueous solution containing potato starch and the shell-core structure magnetic particles in the step (3) at 95 ℃ for 45min, and then sequentially refrigerating at 4 ℃ for 24 hours, freezing at-30 ℃ for 24 hours and freeze-drying to obtain the magnetic starch-based aerogel; wherein the concentration of potato starch relative to water is 8.0wt%; the concentration of the shell-core structure magnetic particles with respect to water was 0.3wt%;
(5) Preparing magnetic super-hydrophobic starch-based aerogel:
spraying the hydrophobic suspension obtained in the step (2) onto the surface of the magnetic starch-based aerogel obtained in the step (4), and drying to obtain the magnetic super-hydrophobic starch-based aerogel, wherein the spraying amount of the hydrophobic suspension is 0.001g/cm 2 。
The obtained magnetic super-hydrophobic starch-based aerogel is tested, and the test results are as follows:
FIG. 1 is an X-ray diffraction pattern of a magnetic super-hydrophobic starch-based aerogel; as can be seen from fig. 1: fe appears in an X-ray diffraction pattern of the magnetic super-hydrophobic starch-based aerogel 3 O 4 All characteristic peaks of the nanoparticles.
FIG. 2 is a scanning electron microscope image of magnetic super-hydrophobic starch-based aerogel. As can be seen from fig. 2: fe 3 O 4 The nanoparticles are uniformly dispersed and complexed therein.
Fig. 3 is a hysteresis regression curve of magnetic superhydrophobic starch-based aerogels. As can be seen from fig. 3: the hysteresis regression line shows that it is given a saturation magnetization of 5.04 emu/g.
Example 2 optimization of hexadecyltrimethoxysilane
The procedure (2) in the adjustment example 1 was:
preparing an absolute ethanol solution with the concentration of hexadecyl trimethoxy silane of 0.5, 1.0, 1.5, 2.0 and 2.5wt percent and the concentration of ammonia water of 10.0wt percent, immediately adding the nano starch in the step (1) of the amount of 1.5wt percent relative to the amount of the absolute ethanol into the solution, and stirring at 300rpm for 5 hours to obtain a hydrophobic suspension;
the rest is kept the same as example 1, and the magnetic super-hydrophobic starch-based aerogel is obtained.
The obtained magnetic super-hydrophobic starch-based aerogel is tested, and the test result is shown in fig. 4:
as can be seen from fig. 4: the water contact angles of the surfaces of the magnetic starch-based aerogels prepared with the concentrations of hexadecyltrimethoxysilane of 0.5, 1.0, 1.5, 2.0 and 2.5wt are 104.4 °, 138.6 °, 151.5 °, 151.1 ° and 150.6 °, respectively, and the surfaces of the magnetic starch-based aerogels spray-treated with a coating suspension containing more than 1.5wt% of hexadecyltrimethoxysilane can achieve a superhydrophobic degree.
Example 3 optimization of Nano-starch
The procedure (2) in example 1 was adjusted to:
preparing an absolute ethanol solution with 1.5wt% of hexadecyl trimethoxy silane and 10.0wt% of ammonia water, immediately adding 0.5, 1.0, 1.5, 2.0 and 2.5wt% of the nano starch in the step (1) relative to the amount of the absolute ethanol into the solution, and stirring at 300rpm for 5 hours to obtain a hydrophobic suspension;
the rest is kept the same as example 1, and the magnetic super-hydrophobic starch-based aerogel is obtained.
The obtained magnetic super-hydrophobic starch-based aerogel is tested, and the test results are shown in fig. 5:
as can be seen from fig. 5: when the concentration of the nano starch is 0.5, 1.0, 1.5, 2.0 and 2.5wt, the water contact angles of the surfaces of the prepared magnetic starch-based aerogel are 141.2 degrees, 147.3 degrees, 151.5 degrees, 144.3 degrees and 131.4 degrees respectively, the sliding angles are 25.7 degrees, 13.9 degrees, 8.0 degrees, 8.9 degrees and 9.4 degrees respectively, and the surface of the magnetic starch-based aerogel subjected to spraying treatment by the coating suspension containing 1.5wt% of the nano starch can reach the super-hydrophobic degree.
Example 4
The procedure (2) in example 1 was adjusted to:
preparing an absolute ethyl alcohol solution with 1.5wt% of hexadecyl trimethoxy silane and 10.0wt% of ammonia water, immediately adding 1.5wt% of the nano starch in the step (1) relative to the amount of the absolute ethyl alcohol into the solution, and stirring at 300rpm for 0, 1, 2, 3, 4, 5, 6, 7 and 8 hours to obtain a hydrophobic suspension;
the rest is kept the same as example 1, and the magnetic super-hydrophobic starch-based aerogel is obtained.
The obtained magnetic super-hydrophobic starch-based aerogel is tested, and the test results are shown in fig. 6:
as can be seen from fig. 6: the water contact angles of the surfaces of the magnetic starch-based aerogels treated by the hydrophobic suspensions respectively obtained by stirring for 0, 1, 2, 3, 4, 5, 6, 7 and 8 hours are respectively 34.2 degrees, 66.0 degrees, 126.8 degrees, 132.6 degrees, 145.9 degrees, 151.5 degrees, 151.6 degrees, 151.9 degrees and 151.9 degrees, the sliding angles are respectively more than 90.0 degrees, 42.5 degrees, 23.0 degrees, 14.2 degrees, 8.0 degrees, 8.9 degrees, 8.7 degrees and 8.1 degrees, and the surfaces of the magnetic starch-based aerogels treated by spraying the coating aerogel suspension stirred for more than 5 hours can achieve the super-hydrophobicity.
Example 5 oil-water separation
Selecting the magnetic super-hydrophobic starch-based aerogel prepared in example 1 to perform oil absorption capacity test on organic liquid; the test results are shown in fig. 7 and 8:
as can be seen from fig. 7: the magnetic super-hydrophobic starch-based aerogel for oil-water separation prepared in example 1 has absorption capacities of 3.96, 3.01, 3.95, 4.13, 2.57, 3.40, 6.34, 7.53, 5.25, 4.36, 3.34 and 3.36g/g for olive oil, gasoline, toluene, silicone oil, N-hexane, cyclohexane, dichloromethane, chloroform, dimethyl sulfoxide, N-dimethylformamide, acetone and ethanol, respectively; namely: the magnetic super-hydrophobic starch-based aerogel can effectively adsorb various organic liquids, wherein the chloroform absorption capacity is the best.
As can be seen from fig. 8: the magnetic super-hydrophobic starch-based aerogel for oil-water separation prepared in the embodiment 1 can completely absorb oil drops at the bottom of water, is not wetted by water, has good selective water-oil absorption, and realizes water-oil separation.
Comparative example 1
The steps (1), (2) and (5) of example 1 are omitted, namely the super-hydrophobic suspension spraying treatment is not carried out on the magnetic starch-based aerogel, and the steps are kept consistent with those of example 1 to obtain the magnetic starch-based aerogel.
The resulting magnetic starch-based aerogels were tested and the results are shown in fig. 9 and 10:
as can be seen from fig. 9: the water contact angle of the surface of the obtained magnetic starch-based aerogel is 0 degrees, because the porous aerogel can completely absorb water drops without being covered by the super-hydrophobic silanized nano starch coating, and the water repellency, namely the selective absorbency of anhydrous oil is not shown.
As can be seen from fig. 10: the obtained magnetic starch-based aerogel is completely soaked by water and cannot absorb oil drops at the water bottom, and oil-water separation cannot be realized.
Comparative example 2
The hexadecyl trimethoxy silane in step (2) of example 1 was omitted, and the rest was the same as in example 1, to obtain a magnetic starch-based aerogel.
The obtained magnetic starch-based aerogel is tested, and the test results are as follows:
the water contact angle of the magnetic starch-based aerogel is 31.3 degrees, because the surface of the aerogel is not modified by hexadecyl trimethoxy silane which can reduce the surface energy, the surface of the aerogel presents stronger hydrophilicity and does not meet the requirement of super hydrophobicity.
Comparative example 3
The step (1) of the example 1 is not carried out, the nano starch in the step (2) of the example 1 is omitted, and the rest is consistent with the step (1) of the example 1, so that the magnetic starch-based aerogel is obtained.
The obtained magnetic starch-based aerogel was tested, and the test results were as follows:
the water contact angle and the sliding angle of the surface of the magnetic starch-based aerogel are respectively 130.2 degrees and 40.0 degrees, because no nano starch capable of constructing a multi-layer micro-nano structure exists, the roughness of the aerogel is not enough to meet the requirement of super hydrophobicity.
Comparative example 4
The step (3) in the example 1 is not carried out, the magnetic particles with the shell-core structure in the step (4) in the example 1 are omitted, and the rest is consistent with the example 1, so that the super-hydrophobic starch-based aerogel is obtained.
The obtained super-hydrophobic starch-based aerogel is tested, and the test results are as follows:
the saturation magnetization of the super-hydrophobic starch-based aerogel is 0.00emu/g, namely, the super-hydrophobic starch-based aerogel is nonmagnetic.
Comparative example 5 No modification
The tetraethoxysilane and KH560 silane coupling agent in the step (3) of the example 1 are omitted, and the rest is consistent with the example 1, so that the magnetic super-hydrophobic starch-based aerogel is obtained.
The obtained super-hydrophobic starch-based aerogel is tested, and the test result is shown in fig. 11:
as can be seen from fig. 11: fe modified by silane coupling agent without tetraethoxysilane and KH560 3 O 4 The nanoparticles are present in the aerogel in an aggregated form, not homogeneously dispersed.
Comparative example 6 Ethyl orthosilicate alone
KH560 silane coupling agent in step (3) of example 1 was omitted, and the others were kept the same as in example 1, to obtain magnetic particles of a shell-core structure.
Comparative example 7 KH560 silane coupling agent alone
Tetraethoxysilane in step (3) of example 1 was omitted, and the same procedure as in example 1 was repeated to obtain magnetic particles having a shell-core structure.
The shell-core structure magnetic particles obtained in example 1 and comparative examples 5, 6 and 7 were tested, and the test results are shown in fig. 12:
as can be seen from fig. 12: tetraethoxysilane alone, KH560 silane coupling agent alone, and Fe without tetraethoxysilane and KH560 silane coupling agent modification 3 O 4 The surface potentials of the nanoparticles are-4.52,6.33 and-5.46 mV respectively, while the surface potential of the magnetic particles with the shell-core structure in example 1 is increased to 10.53mV, which indicates that the surface modification combination of the tetraethoxysilane and the KH560 silane coupling agent enhances the repulsion force between particles (i.e. reduces the mutual attraction force between particles), so that the magnetic particles can be more stably and uniformly dispersed in the starch water solution and the aerogel.
Comparative example 8
The hexadecyl trimethoxy silane in the example 1 is adjusted to be trichlorosilane, and the rest is consistent with the example 1, so that the magnetic super-hydrophobic starch-based aerogel is obtained.
And (3) carrying out performance test on the obtained magnetic super-hydrophobic starch-based aerogel, wherein the test result is as follows:
since the hydrogen chloride (i.e., hydrochloric acid) generated in the modification process can hydrolyze the starch, the starch-based aerogel modified by trichlorosilane is fragile, has high brittleness and extremely poor mechanical properties.
Comparative example 9
The hexadecyl trimethoxy silane in the example 1 is adjusted to be polydimethylsiloxane, and the rest is kept the same as the example 1, so that the magnetic super-hydrophobic starch-based aerogel is obtained.
And (3) carrying out performance test on the obtained magnetic super-hydrophobic starch-based aerogel, wherein the test result is as follows:
because the prepolymer reagent polydimethylsiloxane needs to be cured at a high temperature (80-160 ℃) for a long time, the starch-based aerogel modified by the polydimethylsiloxane can be obviously deformed and cracked in the curing process.
Claims (8)
1. A method for preparing magnetic super-hydrophobic starch-based aerogel is characterized by comprising the following steps:
(1) Preparation of hydrophobic suspension:
adding nano starch into an ethanol solution containing hexadecyl trimethoxy silane and ammonia water, and uniformly mixing to obtain a hydrophobic suspension;
the preparation method of the nano starch comprises the following steps:
dispersing starch in buffer solution, heating for gelatinization, and cooling; adding pullulanase for incubation; heating the incubated solution to inactivate enzyme, centrifuging, taking supernatant, recrystallizing, washing and drying to obtain nano starch;
the mass concentration of the hexadecyl trimethoxy silane relative to the ethanol is 1.5 to 2.5 wt%;
(2) Preparation of magnetic starch-based aerogel:
modifying starch-containing KH560 silane coupling agent modified shell-core structure SiO 2 - Fe 3 O 4 Heating and pasting the aqueous solution of the magnetic particles, refrigerating, freezing and drying to obtain the magnetic starch-based aerogel;
(3) Preparing magnetic super-hydrophobic starch-based aerogel:
and (3) spraying the hydrophobic suspension obtained in the step (1) on the surface of the magnetic starch-based aerogel obtained in the step (2), and drying to obtain the magnetic super-hydrophobic starch-based aerogel.
2. The method according to claim 1, wherein the nano starch in the step (1) is added in an amount of 0.1 to 2.5wt% based on the mass of the ethanol.
3. The method according to claim 1, wherein the starch-containing KH560 silane coupling agent-modified SiO with shell-core structure in step (2) 2 - Fe 3 O 4 The concentration of starch in the aqueous solution of the magnetic particles relative to water is 4.0 to 10.0wt%; the concentration of the KH560 silane coupling agent modified shell-core structure magnetic particles relative to water is 0.2 to 0.4wt%.
4. The method according to claim 1, wherein KH560 silane coupling agent modified shell-core structure SiO 2 - Fe 3 O 4 The preparation method of the magnetic particles comprises the following steps:
will contain Fe 3+ And Fe 2+ Mixing the aqueous solution with an ammonia solution, and reacting for 25 to 35 minutes at the temperature of between 65 and 75 ℃ and at the speed of between 500 and 700rpm under the protection of inert gas; after the reaction is finished, washing to obtain a product; adding ethanol, water, tetraethoxysilane and ammonia water into the product, and reacting for 5~7 hours at the temperature of 20 to 30 ℃ and the rpm of 200 to 400rpm; and then adding a KH560 silane coupling agent, and continuously reacting for 1.5 to 2.5 hours at the temperature of 45 to 55 ℃ and at the speed of 200 to 400rpm to obtain the magnetic particles with the shell-core structure modified by the KH560 silane coupling agent.
5. The method according to claim 4, wherein KH560 silane coupling agent-modified shell-core structure magnetic particles are prepared by the method comprising Fe 3+ And Fe 2+ The volume ratio of the aqueous solution to the aqueous ammonia solution of (1): 9 to 11, wherein the concentration of ammonia water is 0.30 to 0.40mol/L, and Fe 2+ With Fe 3+ The mass ratio of (1): 1.5 to 2.5; the addition amounts of ethanol, water, ethyl orthosilicate, ammonia water and KH560 are respectively 100, 20 to 30, 0.2 to 0.3, 4~6 and 0.1 to 0.3g/g of product.
6. The method of claim 1, wherein the starch in the process for preparing nano-starch is waxy corn starch; the concentration of the starch in the buffer solution is 8 to 12wt%; the pH value of the buffer solution is 4.5 to 5.5; heating and pasting, namely heating and pasting for 30 to 45min at the temperature of 70 to 100 ℃; the temperature after cooling is 50 to 60 ℃; the pullulanase is added with the enzyme activity of 25 to 35ASPU per gram of dry starch; the incubation temperature and time are respectively 50 to 60 ℃ and 6 to 10 hours; the enzyme is deactivated by heating in boiling water; the recrystallization temperature and time were 3~5 ℃ and 6 to 10 hours, respectively.
7. The magnetic superhydrophobic starch-based aerogel prepared by the method of any of claims 1~6.
8. Use of the magnetic superhydrophobic starch-based aerogel of claim 7 in the field of oil-water separation.
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