CN113477233B - PEI-nitric acid modified oil tea shell and preparation method and application thereof - Google Patents
PEI-nitric acid modified oil tea shell and preparation method and application thereof 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
- B01J20/22—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising organic material
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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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- C—CHEMISTRY; METALLURGY
- 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
- C02F1/28—Treatment of water, waste water, or sewage by sorption
- C02F1/285—Treatment of water, waste water, or sewage by sorption using synthetic organic sorbents
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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
- C02F1/28—Treatment of water, waste water, or sewage by sorption
- C02F1/286—Treatment of water, waste water, or sewage by sorption using natural organic sorbents or derivatives thereof
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- B01J2220/40—Aspects relating to the composition of sorbent or filter aid materials
- B01J2220/48—Sorbents characterised by the starting material used for their preparation
- B01J2220/4812—Sorbents characterised by the starting material used for their preparation the starting material being of organic character
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/105—Phosphorus compounds
Abstract
The invention provides a PEI-nitric acid modified oil tea shell and a preparation method and application thereof, wherein the method comprises the following steps: placing the camellia oleifera shell in a first container, and adding HNO into the first container3The method comprises the steps of preparing a solution, namely placing a first container in a specific environment, taking the container out after a preset time, washing the camellia oleifera shells in the first container by using deionized water until the washing liquid in the first container is neutral, and obtaining nitric acid modified camellia oleifera shells; and adding the PEI solution and the nitric acid modified oil-tea shell into a second container for mixing, then placing the second container into a constant-temperature water bath oscillation pot for treatment, filtering the solid-liquid mixture to obtain a solid target object, alternately washing the solid target object with absolute ethyl alcohol and deionized water, and drying to obtain the PEI-nitric acid modified oil-tea shell. According to the PEI-nitric acid modified oil tea shell and the preparation method and application thereof, the PEI-nitric acid modified oil tea shell is obtained by utilizing nitric acid modified oil tea shell and loading polyethyleneimine, and the technical problems that the preparation process of the oil tea shell adsorbent is complex and the energy consumption is high in the prior art are solved.
Description
Technical Field
The invention relates to the technical field of water eutrophication, in particular to a PEI-nitric acid modified oil tea shell and a preparation method and application thereof.
Background
With the continuous development of cities and industries and the use of agricultural fertilizers and phosphorus-containing detergents, a large amount of industrial wastewater and domestic sewage are discharged to rivers and lakes to influence the water quality of a water body, so that the death of aquatic organisms is caused, and the balance of an aquatic ecosystem is further damaged.
At present, many kinds of phosphorus removal methods have been developed, mainly including biological phosphorus removal methods, chemical precipitation methods, adsorption methods, and the like. Among them, the adsorption method is simple to operate, has high removal efficiency and is suitable for different wastewater conditions, and is considered as one of the most promising phosphate removal technologies. The camellia oleifera shells, which are byproducts of camellia oleifera products, account for about 60% of the whole camellia oleifera fruits by mass, contain a large amount of hemicellulose, cellulose, lignin, pectin and other components.
In the prior art, the preparation of the adsorbent by using the oil-tea camellia shell has been studied and is used for removing methylene blue, U (VI), Pb (II) and the like; however, the adsorbent is obtained by performing acid-base modification after the camellia oleifera shells are prepared into the activated carbon, and in the method, the preparation process of the adsorbent is complex, the energy consumption is high, and the improvement of the adsorption performance of the phosphate is limited.
Disclosure of Invention
Based on the above, the invention aims to provide a PEI-nitric acid modified camellia oleifera shell and a preparation method and application thereof, which are used for solving the technical problems of complex preparation process and high energy consumption of camellia oleifera shell adsorbent in the prior art.
One aspect of the application provides a preparation method of a PEI-nitric acid modified oil tea shell, which comprises the following steps:
taking a certain amount of pretreated oil-tea camellia shells, placing the oil-tea camellia shells in a first container, and adding 2-5mol/L HNO into the first container3The solution is prepared by placing the first container in a specific environment, taking out the container after a preset time, and washing the camellia oleifera shells in the first container with deionized water until the washing liquid in the first container is neutral to obtain nitric acid modified camellia oleifera shells;
adding the prepared PEI solution and the nitric acid modified oil-tea shell into a second container, mixing to obtain a solid-liquid mixture, arranging the solid-liquid mixture in the second container, placing the second container into a constant-temperature water bath oscillation pot, treating at a specific temperature, filtering the solid-liquid mixture to obtain a solid target, washing the solid target alternately with absolute ethyl alcohol and deionized water for a certain number of times, and drying at a preset temperature to obtain the PEI-nitric acid modified oil-tea shell.
On the other hand, the PEI-nitric acid modified oil tea shell is prepared by adopting the PEI-nitric acid modified oil tea shell preparation method.
According to the PEI-nitric acid modified oil tea shell preparation method and the PEI-nitric acid modified oil tea shell obtained by adopting the PEI-nitric acid modified oil tea shell preparation method, the PEI-nitric acid modified oil tea shell is obtained by utilizing nitric acid modified oil tea shell and loading polyethyleneimine, and the phosphate removing composite adsorbent is obtained.
Preferably, the step of taking a certain number of pretreated oil tea shells to place in the first container comprises:
taking waste oil tea shells, crushing the waste oil tea shells to be below 100 meshes, washing with water, and drying to obtain the pretreated oil tea shells.
Preferably, the specific environment is that the first container is placed in a constant-temperature water bath shaking pot for normal-temperature modification, the specific temperature is normal temperature, and the step of filtering after treatment at the specific temperature comprises:
and oscillating the load at the normal temperature at 120r/min for 48h, and filtering after the load is finished.
Preferably, the preset temperature is 60 ℃.
Preferably, the step of washing the camellia oleifera shells in the first container with deionized water until the washing liquid in the first container is neutral to obtain nitric acid modified camellia oleifera shells further comprises:
and drying the nitric acid modified oil tea shells for later use.
Preferably, the step of drying at a preset temperature to obtain the PEI-nitric acid modified camellia oleifera shell comprises the following steps:
and (3) storing the PEI-nitric acid modified oil tea shell in a sealing way.
Preferably, the first container and the second container are both erlenmeyer flasks.
The application also provides an application of the PEI-nitric acid modified oil tea shell, wherein the PEI-nitric acid modified oil tea shell is adopted, and the application is as follows:
mixing a certain amount of prepared PEI-nitric acid modified oil tea shells with phosphate solution with a certain concentration and volume in a conical flask, placing the conical flask filled with the mixture into a water bath oscillation pot at normal temperature, oscillating and adsorbing for a certain time at a certain rotating speed, centrifuging the mixture after adsorption is finished, taking supernatant, and measuring the content of phosphate in the supernatant by adopting an ammonium molybdate spectrophotometry.
Drawings
FIG. 1 is a flow chart of a manufacturing method in a first embodiment of the present invention;
FIG. 2 is a flow chart of a manufacturing method in a second embodiment of the present invention
FIG. 3 is an XRD spectrogram before and after modification of oil tea shells;
FIG. 4 is an infrared spectroscopic analysis chart;
FIG. 5 SEM images of adsorbent material before and after modification;
FIG. 6 is a thermogravimetric analysis curve of a PEI-nitric acid modified oil tea shell;
FIG. 7 shows the comparison of the adsorption performance of nitric acid modified camellia shells before and after loading PEI;
FIG. 8 effect of initial pH of solution on adsorbed phosphate;
FIG. 9 effect of adsorbent dosage on adsorbed phosphate;
FIG. 10 isothermal adsorption curves;
FIG. 11 adsorption kinetics curve (a) and intraparticle diffusion model (b);
FIG. 12 XPS spectra of N1s and P1s before and after adsorption of PEI-nitric acid modified Camellia oleifera shells;
FIG. 13 effect of adsorbent regeneration on adsorption effectiveness;
the following detailed description will further illustrate the invention in conjunction with the above-described figures.
Detailed Description
To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Several embodiments of the invention are presented in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
According to the method, the PEI-nitric acid modified oil-tea shells are prepared by carrying out pre-modification treatment on the oil-tea shells at different concentrations and time by using nitric acid and then loading Polyethyleneimine (PEI). Meanwhile, researches on the adsorption performance and adsorption mechanism of PEI-nitric acid modified oil-tea shells on phosphate in water are investigated, and theoretical references are provided for high-value utilization of the oil-tea shells and effective treatment of the phosphate in wastewater.
The nitric acid modification can effectively remove impurity components such as hemicellulose in the oil-tea camellia shell, and the amino functional groups can be greatly increased by loading polyethyleneimine, so that the phosphorus adsorption capacity of the oil-tea camellia shell can be improved, and the problem of water solubility of the polyethyleneimine can be effectively solved.
In the preparation and verification of the performance of the PEI-nitric acid modified oil tea shell, the required raw materials and reagents are as follows: camellia oleifera shells, commercially available; sodium hydroxide, polyethyleneimine, potassium dihydrogen phosphate, absolute ethyl alcohol, hydrochloric acid, concentrated sulfuric acid, antimony potassium tartrate and ascorbic acid, all of which are analytically pure.
The required test instruments are: ultraviolet visible spectrophotometer, water bath constant temperature oscillator, Fourier infrared spectrometer, X-ray diffractometer, element analyzer, X-ray photoelectron spectrometer, and scanning electron microscope.
Example one
Referring to fig. 1, a method for preparing PEI-nitric acid modified oil tea shells in a first embodiment of the present invention is shown, and the method includes steps S101 to S102:
s101, taking a specific number of pretreated oil-tea shells, placing the oil-tea shells in a first container, and adding 2-5mol/L HNO into the first container3And (3) solution, namely placing the first container in a specific environment, taking the container out after a preset time, and washing the camellia oleifera shells in the first container by using deionized water until the washing liquid in the first container is neutral to obtain the nitric acid modified camellia oleifera shells.
S102, adding the prepared PEI solution and the nitric acid modified oil-tea shell into a second container, mixing to obtain a solid-liquid mixture, arranging the solid-liquid mixture in the second container, placing the second container into a constant-temperature water bath oscillation pot, filtering the solid-liquid mixture after treatment at a specific temperature to obtain a solid target, washing the solid target alternately with absolute ethyl alcohol and deionized water for a certain number of times, and drying at a preset temperature to obtain the PEI-nitric acid modified oil-tea shell.
As a specific example, the specific environment is that the container is placed in a constant temperature water bath shaking pot, and the first container is taken out after modification at normal temperature for a certain time. Specifically, the first container and the second container may be any of instruments such as a conical flask and a flask, and preferably, a conical flask is used. Further, the specific temperature in the present application is normal temperature.
In summary, according to the preparation method of the PEI-nitric acid modified oil tea shell, the PEI-nitric acid modified oil tea shell is obtained by utilizing the nitric acid modified oil tea shell and loading polyethyleneimine, so that the phosphate removing composite adsorbent is obtained.
Example two
Referring to fig. 2, a method for preparing PEI-nitric acid modified oil tea shells according to a second embodiment of the present invention is shown, and the method includes steps S201 to S203:
s201, taking the waste oil tea shells, crushing the waste oil tea shells to be below 100 meshes, washing with water, and drying to obtain the pretreated oil tea shells.
S202, taking a certain amount of pretreated oil-tea camellia shells, placing the oil-tea camellia shells into a conical flask, and adding 2-5mol/L HNO into the conical flask3And (3) putting the conical flask into a constant-temperature water bath oscillation pot, modifying for a certain time at normal temperature, taking out the conical flask, and washing the camellia oleifera shells in the conical flask with deionized water until the washing liquid in the conical flask is neutral to obtain the nitric acid modified camellia oleifera shells.
In this example, the oil-tea camellia shell is added into the conical flask, and HNO with the concentration of 2, 3, 4, 5 and 6mol/L is added3And (3) oscillating the solution in a water bath kettle at normal temperature for modification, setting the rotating speed to be 120r/min, setting the modification time to be 4h, 6h, 8h, 10h and 12h respectively, taking out the conical flask after modification, and washing the camellia oleifera shells in the conical flask with deionized water until the washing liquid in the conical flask is neutral to obtain the nitric acid modified camellia oleifera shells.
Specifically, after drying at a preset temperature to obtain the nitric acid modified oil tea shells, in order to ensure the usability of the nitric acid modified oil tea shells, the nitric acid modified oil tea shells need to be dried for later use.
S203, adding the prepared PEI solution and the nitric acid modified oil tea shell into a conical flask for mixing to obtain a solid-liquid mixture, then putting the conical flask containing the solid-liquid mixture into a constant-temperature water bath oscillation pot, oscillating and loading at the normal temperature for 48 hours at 120r/min, filtering the solid-liquid mixture after loading is finished to obtain a solid target, washing the solid target with absolute ethyl alcohol and deionized water alternately for 3 times, and drying at the temperature of 60 ℃ to obtain the PEI-nitric acid modified oil tea shell.
As a specific example, a PEI solution is a polyethyleneimine solution, a 50g/L polyethyleneimine solution is prepared by deionized water, 40ml of the prepared polyethyleneimine solution is mixed with 0.5g of nitric acid modified camellia oleifera shells, the mixed mixture is placed in a constant temperature water bath shaking pot, shaking and loading are carried out at 120r/min for 48h at normal temperature, after that, filtration is carried out, solid targets are alternately washed by absolute ethyl alcohol and deionized water for 3 times, and then drying is carried out at 60 ℃ to obtain PEI-nitric acid modified camellia oleifera shells.
Further, after the PEI-nitric acid modified oil tea shell is obtained by drying at 60 ℃, the PEI-nitric acid modified oil tea shell needs to be stored in a sealed manner.
In summary, according to the preparation method of the PEI-nitric acid modified oil tea shell, the PEI-nitric acid modified oil tea shell is obtained by utilizing the nitric acid modified oil tea shell and loading polyethyleneimine, so that the phosphate removing composite adsorbent is obtained.
EXAMPLE III
On the other hand, the PEI-nitric acid modified oil tea shell is prepared by adopting the preparation method of the PEI-nitric acid modified oil tea shell of any embodiment.
The application also provides an application of the PEI-nitric acid modified oil tea shell, wherein the PEI-nitric acid modified oil tea shell is applied as follows:
mixing a certain amount of prepared PEI-nitric acid modified oil tea shells with phosphate solution with a certain concentration and volume in a conical flask, placing the conical flask filled with the mixture into a water bath oscillation pot at normal temperature, oscillating and adsorbing for a certain time at a certain rotating speed, centrifuging the mixture after adsorption is finished, taking supernatant, and measuring the content of phosphate in the supernatant by adopting an ammonium molybdate spectrophotometry.
In the application, 0.01g of prepared PEI-nitric acid modified oil tea shell is taken and mixed with phosphate (such as KH) with the concentration of 100mg/L and the volume of 40mL2PO4) And (3) mixing the solution in a conical flask, placing the mixed solution into a water-bath oscillation pot at normal temperature, oscillating and adsorbing for 8 hours at 120r/min, centrifuging to obtain supernatant after adsorption, and measuring the content of phosphate in the supernatant by adopting an ammonium molybdate spectrophotometry, so that the content of phosphate in liquid after adsorption can be measured, and obtaining the adsorption effect of the PEI-nitric acid modified oil-tea shell on the phosphate according to the content.
According to the application of the PEI-nitric acid modified oil tea shell, the PEI-nitric acid modified oil tea shell is obtained by utilizing nitric acid modified oil tea shell and loading polyethyleneimine, and the phosphate removing composite adsorbent is obtained.
In order to better investigate the adsorption performance and adsorption mechanism of the PEI-nitric acid modified oil tea shell on phosphate in water, the application also provides an adsorption test, which specifically comprises the following steps:
putting 0.025g of PEI-modified oil tea shell material into a conical flask, adding 25mL of phosphate solution with the concentration of 100mg/L, adjusting the initial pH value to (2-7) by hydrochloric acid at the temperature of 25 ℃ for 8h, centrifuging, taking supernatant, and determining the phosphate concentration.
Putting 0.01g of PEI-nitric acid modified oil tea shell into a conical flask, adding 40mL of phosphate solution with the concentration of 100mg/L, oscillating and adsorbing for 8h at the initial pH value (3.0 +/-0.1) and the temperature of 15 ℃, centrifuging, taking supernatant, and determining the concentration of phosphate.
Putting 0.01g of PEI-nitric acid modified oil tea shell into a conical flask, adding 40mL of phosphate solution with the concentration of (1-200) mg/L, carrying out water bath constant temperature oscillation adsorption for 8h at the initial pH value (3.0 +/-0.1) and the temperature of 15 ℃, 25 ℃ and 35 ℃ respectively, centrifuging, taking supernatant, and determining the concentration of phosphate.
Putting 0.01g of PEI-nitric acid modified oil tea shell into a conical flask, adding 40mL of phosphate solution with the concentration of 50mg/L and 100mg/L, carrying out water bath constant temperature oscillation adsorption for 8h at the initial pH value (3.0 +/-0.1) and the temperature of 15 ℃, centrifuging, taking supernatant, and determining the phosphate concentration.
After the adsorption experiment, standing the solution to obtain a supernatant, and measuring the phosphate concentration by using an ultraviolet-visible spectrophotometer, wherein the calculation formula is as follows:
in the formula: q. q.seTo balance the adsorption capacity; v is the volume of the solution, L; m is the mass of the adsorbing material, g; c0Is the initial mass concentration of the monopotassium phosphate, mg/L; ceIs the equilibrium mass concentration of the potassium dihydrogen phosphate, mg/L.
The above experiments were demonstrated as follows:
【1】 Crystal form structure analysis of PEI-nitric acid modified oil tea shell
As can be seen from fig. 3, the peak shapes of characteristic absorption peaks are similar in the camellia oleifera shells, the nitric acid-modified camellia oleifera shells, and the PEI-nitric acid-modified camellia oleifera shells. It can be seen from the figure that: two different diffraction peaks are at 16.4 degrees and 21.8 degrees of 2 theta, are the same as most natural celluloses and are consistent with the crystal form I of the celluloses, and respectively correspond to the diffraction peaks of a (101) crystal face and a (002) crystal face. One of the main peak values is a (002) crystal face peak which is mainly related to an aromatic ring structure in the oil-tea camellia shell cellulose. Under the nitric acid modification, the peak is widened and heightened, which indicates that the crystal area of the camellia oleifera shell is partially damaged, but the structure is not changed essentially; after the PEI loads the modified oil tea shell, the peak shape is obviously improved.
【2】 Elemental analysis of PEI-nitric acid modified Camellia oleifera Shell
The contents of C, H, O, N elements in the oil-tea camellia shell, the nitric acid-modified oil-tea camellia shell and the PEI-nitric acid-modified oil-tea camellia shell were measured by an element analyzer, and the results are shown in table 1. After nitric acid modification, the content of C and H elements in the oil-tea camellia shell is reduced, and the content of O and N elements is increased. The nitric acid oxidizes the cellulose of the camellia oleifera shells, removes part of impurity cellulose, reduces elements C and H, and increases the content of element O; by impregnation with nitric acid, part of the NO3 -1The N element is left in the oil-tea camellia shell, so that the content of the N element is possibly increased; after the polyethyleneimine is loaded and modified, a large number of amino functional groups are introduced onto the camellia oleifera shells, so that the content of the N element is further obviously increased.
TABLE 1 elemental analysis Table
【3】 Microstructure analysis of PEI-nitric acid modified oil-tea shell
The infrared spectrogram of the oil-tea camellia shell, the nitric acid modified oil-tea camellia shell and the PEI-nitric acid modified oil-tea camellia shell is shown in FIG. 4. According to spectrogram analysis, in the infrared spectrum of the oil-tea camellia shell and the nitric acid modified oil-tea camellia shell, 3410cm-1Is the stretching vibration peak of the O-H group; 1740cm-1Is a non-conjugated carbonyl group C ═ C group stretching vibration peak; 1620cm-1Is C ═ C double bond stretching vibration peak; 1020cm-1Is a C-O group stretching vibration peak.
Modified by nitric acid oxidation to 3410cm-1The stretching vibration peak of the O-H group becomes broad and the vibration intensity becomes weak because the O-H group is oxidized; 1670cm-1Is a C ═ O group stretching vibration peak in the carbonyl group; 1620cm-1The tensile vibration peak intensity of C ═ C double bond becomes weaker; 1020cm-1The C-O group has a broadened vibration peak and a weakened vibration strength because the C-O group is oxidized by nitric acid.
3410cm in infrared spectrum of PEI-nitric acid modified oil tea shell-1The absorption peak becomes strong because the peak portions of the stretching vibration of the O-H group and the N-H group overlap; 1640cm-1Is a C-N bond flexural vibration peak of an amide group; 1540cm-1Is the N-H bending vibration peak in the amide group; 1450cm-1The C-N bond stretching vibration peak in the secondary amine and tertiary amine groups also indicates that PEI modification is connected to the camellia oleifera shell through an amide bond. After the PEI-nitric acid modified oil tea shell adsorbs phosphate, 3410cm-1The absorption peak is reduced and broadened due to the protonation of the amino function and the reaction with phosphate; 1540cm-1The peak of vibration was also weakened due to the protonation of amino groups in combination with phosphate, which also demonstrated the adsorption of phosphate on the PEI-nitric acid-modified camellia shells.
【4】 Microscopic morphology analysis of PEI-nitric acid modified oil-tea shell
The surface appearance of the camellia oleifera shells and the surface appearance of the camellia oleifera shells before and after modification are observed by a scanning electron microscope. As can be seen from fig. 5(a), the surface of the camellia oleifera shell which is only pretreated is smooth, compact and regular; however, as can be seen from fig. 5(b), after the nitric acid modification, the surface of the camellia oleifera shell is etched, becomes rough and uneven, and forms an irregular layered structure; as can be seen from fig. 5(c), the surface of the camellia oleifera shell contains a large number of spherical PEI particles, which demonstrates the successful loading of PEI to the surface of the camellia oleifera shell.
【5】 Thermogravimetric analysis of PEI-nitric acid modified oil tea shell
Thermogravimetric analysis (TGA) and thermogravimetric Differential (DTG) curves of the PEI-nitric acid modified oil tea shell are shown in FIG. 6, and it can be seen that the thermogravimetric analysis curve of the PEI-oil tea shell material can be divided into the following four stages. The first stage is as follows: the mass loss rate of the PEI-oil tea shell composite material is about 4.98% from the normal temperature of-184.6 ℃, and the mass loss is mainly caused by the evaporation of water in the material; and a second stage: the mass loss rate of the PEI-oil tea shell material is about 10.05% from 184.6-264.6 ℃, and mainly caused by the fact that polyethyleneimine starts to decompose along with the rise of temperature; and a third stage: the mass loss rate of the PEI-nitric acid modified oil-tea camellia shell is about 49.41% from 264.6-464.5 ℃, the mass loss is mainly caused by carbonization of cellulose, hemicellulose and lignin in the oil-tea camellia shell, and the maximum loss temperature is 304.6 ℃; a fourth stage: after 564.6 ℃, the mass is essentially unchanged, which is the carbonized product after burning.
【6】 Effect of nitric acid modification conditions and PEI Loading on phosphate adsorption
Pretreating the camellia oleifera shells, taking the adsorption amount of phosphate as an evaluation index, and investigating the influence of factors such as nitric acid modification concentration, modification time and the like on the adsorption amount of phosphate. The reaction conditions of the pretreated oil-tea camellia shell loaded with polyethyleneimine are as follows: mixing the oil tea fruit shell with a water solution of polyethyleneimine, and oscillating and loading for 48 hours; the adsorption experiment conditions are as follows: the dosage of the adsorbent is 0.01g, the initial concentration of the potassium dihydrogen phosphate solution is 100mg/L, the pH value is (3.0 +/-0.1), the reaction temperature is 15 ℃, and the oscillation adsorption time is 8 h.
The effect of the nitric acid concentration on the pretreatment effect was examined, and the results are shown in FIG. 7, in which the optimum modification time of nitric acid was 8 hours and the optimum modification concentration of nitric acid was 5mol/L, as can be seen from the curve (a). Taking the modification time of 8h and the modification concentration of 5mol/L as an example: the concentration of the nitric acid is 2-5mol/L, the adsorption amount of the nitric acid to phosphorus is obviously increased, which shows that the nitric acid modification can promote the adsorption effect of the nitric acid; as the nitric acid concentration is increased from 5mol/L to 6mol/L, the adsorption amount of phosphate is remarkably reduced. The reason is that the increase of the concentration of the nitric acid can destroy hemicellulose in the oil tea fruit shell, so that the hemicellulose is broken and dissolved, the fiber structure is loosened, and the reaction accessibility of the cellulose is increased; when the concentration of nitric acid is too high, hemicellulose is removed and the lignin content is increased, resulting in a decrease in the accessibility of cellulose. On the other hand, by comparing the PEI-loaded and the PEI-unloaded materials, it can be seen that the PEI-loaded oil tea shell with the nitric acid modification time of 8h and the concentration of 5mol/L has a better adsorption effect.
【7】 Effect of initial pH on phosphate adsorption
The effect of the initial pH of the solution on phosphate removal is shown in figure 8. The results show that at a pH of 2, the PEI-nitric acid modified oil tea shell has a very low phosphate adsorption because the protonation of the amino functional groups is too strong in a strongly acidic solution and the phosphate exists mainly in the form of molecules. At pH 3, the phosphate is predominantly H2PO4 -The compound exists in a form of (1), has strong protonation effect and is beneficial to the adsorption of phosphate. At pH (4-7), the amount of phosphorus adsorbed decreases with increasing pH, because protonation of the amino functional group decreases with increasing pH, and phosphate is HPO4 2-Exist in the form of (1). The electrostatic adsorption theory shows that under the acidic condition, the protonation of amino functional groups has positive charges and has stronger affinity to phosphate radicals with negative charges; meanwhile, as the pH value is increased, the protonation of amino functional groups is weakened, and solution OH < - > is increased to compete with phosphate ions for adsorption sites, so that the adsorption quantity of phosphate is reduced.
【8】 Influence of dosage of PEI-nitric acid modified oil tea shell on phosphate adsorption
The effect of sorbent dosing on phosphate adsorption is shown in figure 9. As a result, the amount of the adsorbent charged was increased, and the amount of the phosphate adsorbed was decreased from 105.4mgP/g (mg of phosphorus per gram) to 41.0 mgP/g. The reason is that for adsorbate with a certain concentration, the adsorbent is excessively put, binding sites on the surface of the adsorbent are excessive, the adsorption cannot reach a saturated state, and the unit adsorption capacity is low; when the adsorbent is less in dosage, the surface binding sites of the adsorbent are completely reacted, and the unit adsorption capacity is higher. The results showed that the unit adsorption was the highest at an adsorbent loading of 0.01 g.
【9】 Isothermal adsorption Curve analysis
The adsorption process of the PEI-nitric acid modified oil tea shell adsorbent can be described by adopting Langmuir and Freundlich isothermal adsorption models, which are as follows:
Qe＝KfCe 1/n (3)
in the formula, Qe(mg·g-1) Is the adsorption capacity in adsorption equilibrium, Qm(mg·g-1) Is the maximum adsorption capacity of the adsorbent to the adsorbent, Ce(mg/L) is the mass concentration of adsorbate in solution at adsorption equilibrium, K (L/mg) is the Langmuir equilibrium constant, KfIs the Freund's constant associated with adsorption capacity; n is the Freund's constant related to the adsorption strength.
Fig. 10 is an isothermal adsorption curve of PEI-nitric acid modified camellia shells to phosphate, and table 2 is nonlinear fitting data. From table 2 it can be derived: r of Langmuir model2Larger than Freundlich model, and the maximum adsorption quantity Q calculated by Langmuir modelmThe data values are in substantial agreement with the experimental data and these results indicate that the Langmuir model is more suitable than the Freundlich model for describing the adsorption of phosphate. The fundamental characteristics of the Langmuir model can be measured by the infinitesimal dispersion constant [ R ]L＝1/(1+K*C0)]Described according to RLThe value judges the credibility of the Langmuir equation when 0<RL<1, the obtained data basically conform to a Langmuir model, and the obtained Langmuir equation is credible; when R isL(ii) 0 or RL>1, the Langmuir equation is not reliable. In this experiment, C0For example a phosphate concentration of 100mg/L,r at 15 DEG CLValue 0.841, R at the remaining temperatureLThe values are all between 0 and 1, so the data obtained by the experiment basically conform to a Langmuir model, and the obtained Langmuir equation is credible. Based on the assumption of the Langmuir model, the adsorption of phosphate by the PEI-camellia oleifera shell material belongs to single-layer adsorption.
TABLE 2 PEI-nitric acid modified oil tea Shell isothermal adsorption model parameters
【10】 Thermodynamic analysis of adsorption
The adsorption thermodynamics mainly refers to the research on an adsorption action mode and a balanced adsorption mathematical model, and distribution coefficients at different temperatures can be obtained according to a balanced test. PEI-nitric acid modified oil-tea shell adsorption water phosphate Gibbs free energy change (delta G)0) Enthalpy change (Δ H)0) And entropy change (Δ S)0) The iso-thermodynamic parameters are calculated by the following formula:
ΔG0＝－RT lnKd (4)
ΔG0＝ΔH0－TΔS0 (5)
in the formula: k isdIs the adsorption equilibrium coefficient, mL/g; c0Is the initial solution concentration; v is the volume of the solution; m is the mass of the adsorbent; t is the reaction temperature, K; r is an ideal gas constant, 8.314 (J. mol)－1·K－1)。
From table 3 it can be derived: in the range of 288K-308K, the delta H is a negative value, which indicates that the adsorption process of the PEI-nitric acid modified oil-tea shell to phosphate is a heat release process, and the temperature rise is not beneficial to adsorption; the delta S is a negative value, which indicates that the phosphate is randomly increased in the adsorption process and is beneficial to removal, namely the disorder degree of the system is reduced; Δ G is negative, indicating that the adsorption process of phosphate can proceed spontaneously.
TABLE 3 adsorption thermodynamic parameters of PEI-nitric acid modified Camellia oleifera shells
【11】 Adsorption kinetics Curve analysis
The kinetic process of adsorbing phosphate by PEI-nitric acid modified oil tea shell is shown in figure 11. The result shows that the adsorption amount of the PEI-nitric acid modified oil-tea shell to the phosphate is increased along with the increase of the initial concentration of the phosphate. In general, a quasi-first-order, quasi-second-order kinetic model and an intraparticle diffusion model can be used to study adsorption kinetics, and the three models of the quasi-first-order, quasi-second-order kinetic model and the intraparticle diffusion model are expressed by equation (7), equation (8) and equation (9), respectively:
in the formula, Qe(mg·g-1) For the adsorption amount in adsorption equilibrium, Qt(mg·g-1) The adsorption amount at t (min), K1(min-1) Is a quasi first order adsorption rate constant, K2(g·(mg·min)-1) Quasi-second order adsorption rate constant, K (mg. g.min.)1/2)-1) Is an intra-particle diffusion model constant, C (Mg. g)-1) Is a constant of the boundary layer thickness.
From table 4, it can be seen that: quasi second orderCoefficient of kinetic correlation R2The correlation coefficient is larger than that of quasi-first-order kinetics, which shows that the fitting effect of the quasi-second-order kinetic equation on the adsorption process of the PEI-nitric acid modified oil-tea shell on the phosphate is better, and the theoretical adsorption capacity QeAnd the experimental value QtAnd closer. To further study the adsorption mechanism of PEI-nitric acid modified camellia oleifera shells on phosphate, as shown in fig. 11(a), a kinetic fitting graph of an intra-particle diffusion model of two different concentrations of adsorbates is shown. As can be seen from fig. 11 (b): there are two or more adsorption steps, the first linear portion comprising an adsorption period of (0-10) min, mainly external diffusion and binding of phosphate, which means that the initial stage of adsorption is mainly concentrated on the surface active centers of the adsorbent. The second linear portion, which includes the adsorption period of (20-90) min, takes a long time to complete, indicating that phosphate is diffused in and bound to active sites distributed on the inner surface. In addition, as can be seen from Table 5, the slope K1>K2This can also be explained by the fact that phosphate binds to the active sites on the surface of the adsorbent from the beginning, so the initial adsorption rate is high; when the surface active sites reach saturation, phosphate begins to diffuse inward, resulting in a decrease in adsorption rate due to resistance in pore diffusion.
TABLE 4 adsorption kinetics parameters of PEI-nitric acid modified Camellia oleifera shells
TABLE 5 intraparticle diffusion model parameters of PEI-nitric acid modified Camellia oleifera shells
【12】 Valence state analysis of PEI-nitric acid modified oil-tea shell
In order to better study the adsorption mechanism of PEI-nitric acid modified oil tea shell on phosphate, X-ray photoelectron spectroscopy analysis was performed on the adsorbent before and after phosphate adsorption, and the results are shown in FIG. 12. The results show that: XPS spectrum of P1s showed H at 134.3eV and 133.2eV after adsorption of phosphate3PO4And H2PO4-The two characteristic peaks prove that the phosphate is successfully adsorbed on the PEI-nitric acid modified oil-tea shell. The interaction mechanism between the PEI-nitric acid modified oil tea shell and phosphate was analyzed by XPS spectrum of N1 s. The XPS spectrum of N1s prior to adsorption was divided into three peaks at 398.1eV, 398.9eV and 399.6eV, which were attributed to-N ═ NH-and-NH-respectively2The result is the same as the infrared spectrum analysis result, and the successful connection of the polyethyleneimine on the camellia oleifera shells is proved. After adsorption of phosphate, -N ═ NH-and-NH2The characteristic peaks of the spectra of (1) are shifted forward to positions of 398.8ev, 399.8ev and 401.1ev, respectively, because the binding energy becomes large after the reaction of the adsorbent with phosphate to cause the characteristic peaks to shift forward. After the simultaneous adsorption, a new N1s characteristic peak 401.7ev appears, which is-NH formed by protonation under acidic condition3+Further proves that the PEI-nitric acid modified oil tea shell and the phosphate have electrostatic adsorption effect. In addition, in-NH-and-NH2Reduction of characteristic peak area at-NH3+The position area of the characteristic peak of (2) is increased.
【13】 Desorption and regeneration of PEI-nitric acid modified oil-tea shell
Regeneration and reuse performance is an important indicator for evaluating economic performance of an adsorbent. Fig. 13 is a result of the cyclic use performance of PEI-nitric acid-modified camellia oleifera shells on phosphate adsorption.
As can be seen from FIG. 13, the adsorption amount of phosphate was still above 80mgP/g after 5 times of repeated use of PEI-nitric acid modified Camellia oleifera shells. This shows that the NaOH solution can be used for the regeneration of the adsorbent and can effectively remove phosphate; meanwhile, after the PEI-nitric acid modified oil tea shell adsorbent is continuously used for 5 times, the adsorption capacity is still kept at a higher level (85.4mgP/g), and the adsorption quantity of phosphate is not remarkably reduced, so that the PEI-nitric acid modified oil tea shell adsorbent has good stability, reproducibility and reusability.
In conclusion, the PEI-nitric acid modified oil tea shell modified by nitric acid is prepared by utilizing the oil tea shell of agricultural and forestry waste and adopting an impregnation method, and the performance and the mechanism of adsorbing phosphate are discussed. The result shows that the nitric acid modified and polyethyleneimine loaded camellia oleifera shells can obviously improve the adsorption performance; the initial pH value of the solution has an important influence on the removal of the phosphate oil by the PEI-nitric acid modified oil-tea shells. The PEI-nitric acid modified oil-tea shell is subjected to fitting of a kinetic model and a thermodynamic model, and the result shows that the adsorption kinetics of the adsorbent to phosphate meet a quasi-second order kinetic equation and an intra-particle diffusion model; the thermodynamic model is basically consistent with the Langmuir model, and the adsorption is a single-layer adsorption process; the results of adsorption thermodynamics and XPS analysis show that the adsorption is an exothermic and spontaneous process, and the adsorption mechanism is electrostatic adsorption. The PEI-nitric acid modified oil-tea camellia shell is an adsorbent for quickly, non-toxically and efficiently removing phosphate, and an effective way is provided for high-value utilization of the oil-tea camellia shell.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The above examples only show some embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (9)
1. A preparation method of PEI-nitric acid modified oil tea shells is characterized by comprising the following steps:
taking a certain amount of pretreated oil-tea camellia shells, placing the oil-tea camellia shells in a first container, and adding 2-5mol/L HNO into the first container3The solution is prepared by placing the first container in a specific environment, taking out the container after a preset time, and washing the camellia oleifera shells in the first container with deionized water until the washing liquid in the first container is neutral to obtain nitric acid modified camellia oleifera shells;
adding the prepared PEI solution and the nitric acid modified oil-tea shell into a second container, mixing to obtain a solid-liquid mixture, arranging the solid-liquid mixture in the second container, placing the second container into a constant-temperature water bath oscillation pot, treating at a specific temperature, filtering the solid-liquid mixture to obtain a solid target, washing the solid target alternately with absolute ethyl alcohol and deionized water for a certain number of times, and drying at a preset temperature to obtain the PEI-nitric acid modified oil-tea shell.
2. The method for preparing PEI-nitric acid modified oil tea shells according to claim 1, wherein the step of taking a certain amount of pretreated oil tea shells into the first container comprises:
taking waste oil tea shells, crushing the waste oil tea shells to be below 100 meshes, washing with water, and drying to obtain the pretreated oil tea shells.
3. The method for preparing the PEI-nitric acid modified oil tea shell according to claim 1, wherein the specific environment is that the first container is placed in a constant temperature water bath shaking pot for normal temperature modification, the specific temperature is normal temperature, and the step of filtering after treatment at the specific temperature comprises the following steps:
and oscillating the load at the normal temperature at 120r/min for 48h, and filtering after the load is finished.
4. The method for preparing the PEI-nitric acid modified oil tea shell according to claim 1, wherein the preset temperature is 60 ℃.
5. The method for preparing the PEI-nitric acid modified oil tea shell according to claim 1, wherein the step of washing the oil tea shell in the first container with deionized water until the washing liquid in the first container is neutral, and obtaining the nitric acid modified oil tea shell further comprises the following steps:
and drying the nitric acid modified oil tea shells for later use.
6. The method for preparing the PEI-nitric acid modified oil tea shell according to claim 1, wherein the step of drying at a preset temperature to obtain the PEI-nitric acid modified oil tea shell comprises the following steps:
and (3) storing the PEI-nitric acid modified oil tea shell in a sealing way.
7. The method for preparing the PEI-nitric acid modified oil tea shell according to claim 1, wherein the first container and the second container are both erlenmeyer flasks.
8. A PEI-nitric acid modified oil tea shell, which is characterized by being prepared by the method for preparing the PEI-nitric acid modified oil tea shell according to any one of claims 1 to 7.
9. The application of the PEI-nitric acid modified oil tea shell in water purification treatment is characterized in that the PEI-nitric acid modified oil tea shell of claim 8 is adopted, and the application is as follows:
mixing a certain amount of prepared PEI-nitric acid modified oil tea shells with phosphate solution with a certain concentration and volume in a conical flask, placing the conical flask filled with the mixture into a water bath oscillation pot at normal temperature, oscillating and adsorbing for a certain time at a certain rotating speed, centrifuging the mixture after adsorption is finished, taking supernatant, and measuring the content of phosphate in the supernatant by adopting an ammonium molybdate spectrophotometry.
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