CN114797783B - Adsorbent for selectively removing Cr (VI) and preparation method and application thereof - Google Patents
Adsorbent for selectively removing Cr (VI) and preparation method and application thereof Download PDFInfo
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Abstract
The invention provides an adsorbent for selectively removing Cr (VI), and a preparation method and application thereof. The preparation method of the invention comprises the following steps: fully and uniformly mixing graphene oxide aqueous dispersion liquid, thiourea and 3-aminopropyl trimethoxy silane, and then carrying out low-temperature reaction; separating solid, washing, freeze drying to obtain adsorbent. According to the invention, thiourea and 3-aminopropyl trimethoxy silane are used as main modifiers, a one-step low-temperature reaction is adopted to realize chemical modification of graphene oxide, reaction conditions are controlled, and an amino functionalized graphene nanocomposite with relatively high specific surface area is synthesized and used as an adsorbent for adsorbing chromium; and by introducing thiourea and silane molecules, self-accumulation of graphene oxide in the low-temperature treatment process is avoided. The preparation process is simple, green and environment-friendly; the adsorbent can selectively remove Cr (VI) in water, has high adsorption capacity for the Cr (VI) and good adsorption effect.
Description
Technical Field
The invention belongs to the technical field of adsorption separation of heavy metals, and particularly relates to an adsorbent for selectively removing Cr (VI), and a preparation method and application thereof.
Background
In the recent development of the human society, especially the continuous promotion of the industrialization process, a great deal of harmful pollutants are discharged into the surrounding environment, such as heavy metal ions, organic wastes, inorganic pollutants, medicinal poisons and the like. Heavy metal ions generally refer to atoms having an atomic mass of 63.5 to 200.6 and a relative density greater than 5.0. These toxic ions are difficult to biodegrade, and can multiply in the human body due to biological enrichment, interfering with normal physiological functions of the human body. Chromium (Cr, atomic number 52), particularly chromium (VI) from electroplating, spinning, leather tanning, pigment manufacturing, mining and smelting, is considered an internationally recognized carcinogen and can cause a serious set of physiological reactions including headache, nausea, diarrhea, vomiting, skin and respiratory damage. Cr (III) is considered as another form of chromium, a trace element that promotes the growth and development of the human body. Thus, there is a need to find a suitable and efficient method for removing Cr (VI) or converting more toxic Cr (VI) into less toxic Cr (III).
To date, open work has reported a variety of purification techniques such as membrane filtration, ion exchange, chemical precipitation, electrochemical processing, and the like. The adsorption method is simple in operation and wide in applicability, and is remarkable in various removing methods. Graphene Oxide (GO) has been studied for the enrichment and separation of toxic Cr (VI) in water as a unique and outstanding adsorbent due to its unique specific surface area advantage, fine two-dimensional structure and abundant surface functional groups. However, the two-dimensional pi conjugated structure and the large number of oxygen-containing groups of graphene oxide lead to self-stacking and excessive electronegativity of graphene oxide, which further limit the practical application of graphene oxide in pollutant treatment. Another considerable problem is that the formation of a hydrated shell of graphene oxide covers the active sites of graphene oxide, which would severely affect the maximum effect of graphene oxide on removal of contaminants from water.
One viable and effective strategy to solve the above problems is to chemically modify graphene oxide, where amino functionalization is the most widely used modification method; the amino-functionalized graphene oxide can enhance the adsorption capacity of Cr (VI) through mechanisms such as electrostatic action, reduction action, hydrogen bonding action and the like. For example, chinese patent document CN108380177a discloses a preparation method of a magnetic modified graphene oxide hydrogel, wherein an oxidant is used to replace the traditional Hummers method to synthesize graphene oxide, thiourea is used to thiolate the graphene oxide to obtain sulfhydryl graphene oxide, L-cysteine is copolymerized with the sulfhydryl graphene oxide, and finally the magnetic modified graphene oxide hydrogel is synthesized by a chemical coprecipitation method. The prepared modified magnetic graphene oxide hydrogel has good separation and regeneration performance and adsorption performance on heavy metal ions, and realizes synchronous adsorption of various heavy metal ions and rapid separation of adsorption materials and wastewater. However, the preparation steps of the invention are complicated, and the obtained hydrogel has poor adsorption performance on Cr (VI); in addition, the invention adopts methylene dichloride as a solvent, and adopts m-chloroperoxybenzoic acid, hydrobromic acid and the like in the preparation process, which is not friendly to the environment.
The existing preparation method of the amino functionalized graphene is mostly multi-step reaction, and the preparation steps are complicated; the raw materials used relate to toxic reagents such as organic solvents and the like, which are not beneficial to environmental protection; the graphene in the obtained material has a self-stacking phenomenon; and the adsorption performance of a plurality of modified graphene oxide materials on Cr (VI) is poor, and effective separation of Cr (VI) is difficult to realize under the condition that a plurality of metal ions coexist.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides an adsorbent for selectively removing Cr (VI), and a preparation method and application thereof. According to the invention, thiourea and 3-aminopropyl trimethoxy silane are used as main modifiers, a one-step low-temperature reaction is adopted to realize chemical modification of graphene oxide, reaction conditions are controlled, and an amino functionalized graphene nanocomposite with relatively high specific surface area is synthesized and used as an adsorbent for adsorbing chromium; and by introducing thiourea and silane molecules, self-accumulation of graphene oxide in the low-temperature treatment process is avoided. The preparation process is simple, green and environment-friendly; the adsorbent can selectively remove Cr (VI) in water, has high adsorption capacity for the Cr (VI) and good adsorption effect.
The technical scheme of the invention is as follows:
an adsorbent for selectively removing Cr (VI), wherein the adsorbent is an amino-functionalized graphene nanocomposite; the amino-functionalized graphene nanocomposite is synthesized by taking thiourea and 3-aminopropyl trimethoxy silane as modifiers through one-step low-temperature reaction.
According to the invention, preferably, the amino-functionalized graphene nanocomposite has a microscopic morphology of: has a three-dimensional porous structure composed of nano sheets rich in wrinkles.
According to the invention, preferably, the BET specific surface area of the amino-functionalized graphene nanocomposite is 100-200m 2 /g。
The preparation method of the adsorbent for selectively removing Cr (VI) comprises the following steps:
fully and uniformly mixing graphene oxide aqueous dispersion liquid, thiourea and 3-aminopropyl trimethoxy silane, and then carrying out low-temperature reaction; separating solid, washing, freeze drying to obtain adsorbent.
According to the invention, the concentration of the graphene oxide aqueous dispersion is preferably 1-5mg/mL, preferably 2mg/mL. The graphene oxide aqueous dispersion is prepared according to the prior method, preferably by adopting the prior improved Hummers method and diluting.
According to the invention, preferably, the mass ratio of thiourea to graphene oxide is 4-6:1, preferably 5:1; the mass ratio of the volume of the 3-aminopropyl trimethoxysilane to the graphene oxide is 1-4 mu L/mg, preferably 2.5 mu L/mg.
According to the invention, the low temperature reaction temperature is preferably 80-100 ℃, preferably 90 ℃.
According to the invention, the low-temperature reaction time is preferably from 4 to 8 hours, preferably 6 hours.
According to the present invention, preferably, the washing is an alternating washing using cold and hot deionized water.
The application of the adsorbent for selectively removing Cr (VI) is applied to adsorbing heavy metal Cr (VI).
According to the present invention, preferably, the adsorbent is applied to a method for adsorbing heavy metal Cr (VI), comprising the steps of:
(1) Adjusting the pH value of the Cr (VI) -containing solution;
(2) Dispersing the adsorbent in the Cr (VI) containing solution in the step (1), fully mixing and contacting, and adsorbing Cr (VI) in the Cr (VI) containing solution by the adsorbent so as to remove the Cr (VI) in the Cr (VI) containing solution.
Preferably, in step (1), the pH of the Cr (VI) containing solution is adjusted to a pH of 1 to 10, preferably to a pH of 2.
Preferably, in the step (1), the reagent used for adjusting the pH value is hydrochloric acid or sodium hydroxide.
Preferably, in the step (2), the volume ratio of the mass of the adsorbent to the Cr (VI) containing solution is 0.3-2.0: 1g/L.
Preferably, in step (2), the adsorption temperature is 25-55deg.C, and the adsorption time is 120-200min, preferably 180min.
Preferably, in step (2), the adsorption is carried out under shaking conditions at a rate of 200-250rpm/min, preferably 220rpm/min.
Preferably, in the step (2), after the adsorption of the adsorbent is completed, the method further comprises a step of separating the adsorbent from the solution.
The invention has the technical characteristics and beneficial effects that:
1. according to the invention, thiourea and 3-aminopropyl trimethoxy silane are used as main modifiers to obtain the amino functionalized graphene nanocomposite adsorbent. According to the invention, the specific modifier thiourea can react with the epoxy bond ring opening of the graphene oxide, and the specific silane can realize effective grafting with the graphene oxide. The method has the advantages of simple synthesis steps, low-cost and easily-obtained raw materials, and environment friendliness.
2. The adsorbent provided by the invention has the advantages that in the Cr (VI) containing solution, the amino groups on the adsorbent are positively charged after protonation, and can effectively generate electrostatic attraction with Cr anions, so that the adsorption and removal of Cr (VI) are realized, the good adsorption performance is shown, and certain anti-interference capability is realized on other anions; at the same time, the protonated amino group can be mutually repelled with other positively charged metal ions under the acidic condition, thereby showing good adsorption selectivity.
3. The amino-functionalized graphene oxide nanocomposite is prepared by adopting a one-step low-temperature reaction, and the material has a three-dimensional porous structure with rich folds; by introducing thiourea and silane molecules, self-accumulation of graphene oxide in the low-temperature treatment process is avoided. The adsorbent has good adsorption performance, adsorption selectivity and anti-interference performance on heavy metal Cr (VI), the removal rate of the heavy metal Cr (VI) reaches 99.5%, and the adsorption capacity reaches 193.8mg/g; when a plurality of metal ions coexist and the concentration of other metal cations is 5 times of that of Cr (VI), the removal rate of the adsorbent provided by the invention to heavy metal Cr (VI) can still reach 63.9%, and the adsorbent has good adsorption selectivity to other metals which are not more than 5%. By optimizing the adsorption conditions, efficient adsorption of heavy metal Cr (VI) can be realized.
Drawings
FIG. 1 is a scanning electron micrograph of the adsorbent of example 1.
FIG. 2 is an infrared spectrum of the adsorbent in example 1.
FIG. 3 is a graph showing the adsorption and desorption curves of nitrogen from the adsorbent of example 1.
FIG. 4 is an adsorption isotherm plot of the adsorbent of example 2 for Cr (VI).
FIG. 5 is a graph showing the removal rate of 10 different coexisting metal ions by the adsorbent in example 7.
Detailed Description
The invention will now be further illustrated by, but is not limited to, the following specific examples in connection with the accompanying drawings.
The experimental methods described in the examples, unless otherwise specified, are all conventional; the reagents and materials employed, unless otherwise indicated, are all those commercially available.
In the following examples, after the completion of the adsorption separation process, the concentration of metal ions in the solution after centrifugation was measured by ICP-OES (inductively coupled plasma emission spectroscopy), and the calculation formula of the metal ion removal rate used was as follows:
wherein C is 0 And C e (mg/L) represents the concentration of the metal ion in the solution before and after adsorption, respectively.
The adsorption capacity used was calculated as follows:
wherein C is 0 And C e (mg/L) represents the concentration of metal ions in the solution before and after adsorption, respectively; v is the volume of the solution (mL), m is the mass of adsorbent added (mg).
Example 1
1. Synthesis of amino-functionalized graphene nanocomposite adsorbent
The 325 mesh graphite powder was subjected to deep oxidation using a modified Hummers method (W.S.Hummers, R.E.Offeman, preparation of Graphitic Oxide, J Am Chem Soc 80 (6) (1958) 1339-1339) to give an aqueous dispersion of Graphene Oxide (GO) at a concentration of 8.2 mg/mL.
The amino-functionalized graphene nanocomposite (TAGN) is prepared by adopting a one-step low-temperature reaction. In a typical process, the initial 8.2mg/mL graphene oxide dispersion is diluted to 2mg/mL, where 50mL of ultrasound dispersion forms a uniform suspension. Subsequently, 0.5g of thiourea was added to the above-mentioned homogeneous mixture and stirred for 30 minutes, after which 250. Mu.L of APTMS (3-aminopropyl trimethoxysilane) was injected with a constant volume pipette and stirred for 30 minutes. The resulting solution was transferred to a glass bottle, sealed and then treated in an electric oven at 90℃for 6 hours. Filtering the obtained reaction liquid to separate solid, alternately washing the obtained solid with cold water and hot water, and freeze-drying at-50 ℃ for 48 hours to obtain the amino-functionalized graphene nanocomposite adsorbent (TAGN).
The synthesized material is characterized, and the scanning electron microscope image of the adsorbent in fig. 1 shows that the microstructure of the material presents a three-dimensional porous structure with rich folds, and the three-dimensional porous structure is composed of nano sheets with rich folds. The successful synthesis of the amino-functionalized graphene nanocomposite is demonstrated by the characteristic peaks in the infrared spectrogram of fig. 2. FIG. 3 shows that the BET specific surface area of the amino-functionalized graphene nanocomposite is 139.19m based on a nitrogen adsorption and desorption curve 2 /g。
Adsorption process of Cr (VI)
Preparing a Cr (VI) -containing solution: 0.2829g of potassium dichromate dried at 110 ℃ for 2 hours is weighed, dissolved in water, transferred to a 100mL volumetric flask, diluted to 1000mg/L of Cr (VI) containing solution with deionized water, and added with concentrated hydrochloric acid to adjust the pH to 2.
Taking 3.2mL 1000mg/L Cr (VI) containing solution, diluting to 10mL 320mg/L Cr (VI) containing solution in a centrifuge tube, adding 10mg of the adsorbent prepared in the embodiment, adsorbing for 3 hours under mechanical oscillation at 25 ℃ and 220rpm, ensuring that the adsorbent is fully contacted with the water phase, centrifuging after the adsorption is finished, testing the residual concentration of Cr (VI) in the water phase, and calculating the adsorption capacity.
In the adsorption separation process, the adsorption capacity of the amino-functionalized graphene nanocomposite (TAGN) prepared in the embodiment reaches 193.8mg/g.
Example 2
1. Synthesis of amino-functionalized graphene nanocomposite adsorbent
The method for synthesizing the adsorbent in this example is the same as in example 1.
Adsorption process of Cr (VI)
Preparing a Cr (VI) -containing solution: 0.2829g of potassium dichromate dried at 110℃for 2 hours was weighed, dissolved in water, transferred to a 100mL volumetric flask, and diluted with deionized water to 1000mg/L of a Cr (VI) -containing solution. The Cr (VI) containing solutions were diluted with deionized water to 40mg/L, 80mg/L, 120mg/L, 160mg/L, 200mg/L, 240mg/L, 280mg/L, 320mg/L, respectively, and concentrated hydrochloric acid was added to adjust the pH to 2.
10mL of Cr (VI) containing solutions with different concentrations are respectively taken into a centrifuge tube, 10mg of the adsorbent prepared in the embodiment is added, the adsorbent is adsorbed for 3 hours under mechanical oscillation at 25 ℃ and 220rpm, the sufficient contact between the adsorbent and the water phase is ensured, centrifugal separation is carried out after the adsorption is finished, the residual concentration of Cr (VI) in the water phase is tested, and the adsorption capacity is calculated. And obtaining the corresponding relation between the equilibrium concentration and the adsorption capacity. The adsorption capacities obtained at various concentrations of Cr (VI) -containing solutions were plotted against the equilibrium concentrations (FIG. 4), R being obtained by Freundlich adsorption isotherm fitting 2 0.9843, the adsorption process is further described as a multi-layer adsorption process occurring on heterogeneous surfaces (R.Chakraborty, R.Verma, A.Asthana, S.S.Vidya, A.K.Singh, adsorption of hazardous chromium (VI) ions from aqueous solutions using modified sawdust: kinetic, isotherm and thermodynamic modelling, int J Environ an Ch 101 (7) (2021) 911-928).
Example 3
1. Synthesis of amino-functionalized graphene nanocomposite adsorbent
The method for synthesizing the adsorbent in this example is the same as in example 1.
Adsorption process of Cr (VI)
Preparing a Cr (VI) -containing solution: 0.2829g of potassium dichromate dried at 110℃for 2 hours was weighed, dissolved in water, transferred to a 100mL volumetric flask, and diluted with deionized water to 1000mg/L of a Cr (VI) -containing solution. Then dilute to 80mg/L of Cr (VI) containing solution with deionized water. Adding concentrated hydrochloric acid or sodium hydroxide aqueous solution into the Cr (VI) containing solution to adjust the pH to be 1-10 respectively.
The main existence form of Cr (VI) in aqueous solutions with different pH values is as follows: cr (VI) is treated with HCrO at pH 7 or less 4 - 、Cr 2 O 7 2- Exists as HCrO 4 - Mainly comprises; cr (VI) is CrO when the pH is more than or equal to 7 4 2- 、HCrO 4 - Exists as CrO 4 2- Mainly.
10mL of Cr (VI) containing solutions with different pH values are respectively taken into a centrifuge tube, 10mg of the prepared adsorbent is added, the adsorbent is adsorbed for 3 hours under the mechanical oscillation of 220rpm at 25 ℃, the sufficient contact between the adsorbent and the water phase is ensured, centrifugal separation is carried out after the adsorption is finished, the residual concentration of Cr (VI) in the water phase is tested, and the adsorption capacity under different initial pH values is calculated.
TABLE 1 pH adsorption capacities of different adsorbents for Cr (VI)
| pH | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| Adsorption capacity (mg/g) | 72.9 | 75.1 | 56.8 | 38.2 | 37.8 | 33.4 | 25.1 | 20.0 | 18.0 | 15.5 |
In the adsorption separation process, the adsorption capacity of Cr (VI) is shown in Table 1 under different pH conditions, and the adsorption capacity of the adsorbent for Cr (VI) is increased and then decreased with the increase of the pH, and the adsorbent has the optimal adsorption capacity when the pH is equal to 2.
Example 4
1. Synthesis of amino-functionalized graphene nanocomposite adsorbent
The method for synthesizing the adsorbent in this example is the same as in example 1.
Adsorption process of Cr (VI)
Preparing a Cr (VI) -containing solution: 0.2829g of potassium dichromate dried at 110℃for 2 hours was weighed, dissolved in water, transferred to a 100mL volumetric flask, and diluted with deionized water to 1000mg/L of a Cr (VI) -containing solution. Then dilute the solution to 80mg/L with deionized water, and add concentrated hydrochloric acid to adjust the pH to 2.
10mL of the Cr (VI) solution is taken in a centrifuge tube respectively, 10mg of the prepared adsorbent is added into the centrifuge tube, the adsorbent is adsorbed for 3 hours under the mechanical oscillation of 220rpm at different temperatures of 25 ℃, 35 ℃, 45 ℃, 55 ℃, and 220 ℃, the sufficient contact between the adsorbent and the water phase is ensured, centrifugal separation is carried out after the adsorption is finished, the residual concentration of Cr (VI) in the water phase is tested, and the adsorption capacity at different temperatures is calculated.
In the adsorption separation process, the adsorption capacity of Cr (VI) is shown in Table 2 under different temperature conditions, and the adsorption capacity of the adsorbent for Cr (VI) gradually increases with the increase in temperature.
TABLE 2 adsorption Capacity of adsorbents for Cr (VI) at different temperatures
| Temperature (. Degree. C.) | 25 | 35 | 45 | 55 |
| Adsorption capacity (mg/g) | 76.3 | 76.9 | 78.1 | 78.5 |
Example 5
1. Synthesis of amino-functionalized graphene nanocomposite adsorbent
The method for synthesizing the adsorbent in this example is the same as in example 1.
Adsorption process of Cr (VI)
Preparing a Cr (VI) -containing solution: 0.2829g of potassium dichromate dried at 110℃for 2 hours was weighed, dissolved in water, transferred to a 100mL volumetric flask, and diluted with deionized water to 1000mg/L of a Cr (VI) -containing solution. Then dilute the solution to 30mg/L with deionized water, and add concentrated hydrochloric acid to adjust the pH to 2.
10mL of the Cr (VI) solution is respectively taken in a centrifuge tube, 3mg, 5mg, 8mg, 10mg, 15mg and 20mg of the prepared adsorbent are respectively added into the centrifuge tube, the adsorbent is adsorbed for 3 hours under the mechanical oscillation of 220rpm at 25 ℃, the sufficient contact between the adsorbent and the water phase is ensured, centrifugal separation is carried out after the adsorption is finished, the residual concentration of Cr (VI) in the water phase is tested, and the adsorption capacity and the removal rate under different adsorbent amounts are calculated.
In the adsorption separation process, the removal rate of Cr (VI) by the adsorbent increases with the increase of the dosage under the condition that different amounts of the adsorbent are added. The results are shown in Table 3.
TABLE 3 removal of Cr (VI) by adsorbents of different masses
| Adsorbent amount (mg) | 3 | 5 | 8 | 10 | 15 | 20 |
| Removal rate of | 51.4％ | 78.1％ | 95.0％ | 97.9％ | 99.4％ | 99.5％ |
Example 6
1. Synthesis of amino-functionalized graphene nanocomposite adsorbent
The method for synthesizing the adsorbent in this example is the same as in example 1.
Adsorption process of Cr (VI)
Preparing a Cr (VI) -containing solution: 0.2829g of potassium dichromate dried at 110℃for 2 hours was weighed, dissolved in water, transferred to a 100mL volumetric flask, and diluted with deionized water to 1000mg/L of a Cr (VI) -containing solution. Then diluting the solution containing Cr (VI) with deionized water to 120mg/L, and preparing the solution containing Cr (VI) with concentration of 120mg/L and Cl with 4 different concentrations (0 mM, 5mM, 10mM, 20 mM) respectively - (provided by hydrochloric acid), SO 4 2- (sulfuric acid supply), NO 3 - (nitric acid provided) solutions, all adjusted to pH 2.
10mL of the Cr (VI) solution is taken into a centrifuge tube respectively, 10mg of the prepared adsorbent is added, the adsorbent is adsorbed for 3 hours under mechanical oscillation at 25 ℃ and 220rpm, the sufficient contact between the adsorbent and water phase is ensured, centrifugal separation is carried out after the adsorption is finished, and the residual concentration of Cr (VI) and the concentration of other ions in the water phase are tested.
In the adsorption separation process, cl with different concentrations - ，SO 4 2- ，NO 3 - Has certain influence on the adsorption capacity of the adsorbent, wherein SO 4 2- Maximum effect, NO 3 - Influencing next, cl - The influence of (2) is minimal. The results are shown in Table 4. And (3) adjusting the pH value of the solution by selecting hydrochloric acid in a batch adsorption experiment.
TABLE 4 influence of Co-existing anions at different concentrations on the adsorption capacity of adsorbents
| Concentration/adsorption capacity | Cl - | SO 4 2- | NO 3 - |
| 0mM | 104.0mg/g | 104.0mg/g | 104.0mg/g |
| 5mM | 97.2mg/g | 77.0mg/g | 94.2mg/g |
| 10mM | 96.4mg/g | 70.6mg/g | 90.1mg/g |
| 20mM | 95.5mg/g | 63.6mg/g | 88.6mg/g |
Example 7
1. Synthesis of amino-functionalized graphene nanocomposite adsorbent
The method for synthesizing the adsorbent in this example is the same as in example 1.
Adsorption process of Cr (VI)
Preparing a multi-metal solution: 0.2829g of potassium dichromate dried at 110℃for 2 hours was weighed, dissolved in water, transferred to a 100mL volumetric flask, and diluted with deionized water to 1000mg/L of a Cr (VI) -containing solution. The Cr (VI) containing solution was then diluted to 20mg/L with deionized water. Preparing a multi-metal mixed solution with the concentration of Cr (VI) of 20Mg/L and the concentration of nine metal ions of Fe (III), ni (II), mn (II), cu (II), zn (II), mg (II), K (I), co (II) and Cd (II) of 100Mg/L, and adding concentrated hydrochloric acid to adjust the pH value to 2. The nine metal ions are all added in the form of their chlorides.
Respectively taking 10mL of the multi-metal solution in a centrifuge tube, adding 10Mg of the prepared adsorbent, adsorbing for 3 hours at 25 ℃ under mechanical oscillation of 220rpm, ensuring that the adsorbent is fully contacted with water phase, centrifuging after the adsorption is finished, and testing the residual concentration of Fe (III), ni (II), mn (II), cu (II), zn (II), mg (II), K (I), co (II), cr (VI) and Cd (II) in the water phase.
In the adsorption separation process, the removal rate of each metal is shown in fig. 5, and it can be seen from fig. 5: the removal rate of the adsorbent to Cr (VI) is up to 63.9%, and the removal rates of Fe (III), ni (II), mn (II), cu (II), zn (II), mg (II), co (II), K (I) and Cd (II) are all not more than 5%. Therefore, the adsorbent has good selectivity for adsorbing and removing Cr (VI).
Comparative example 1
1. The adsorbent was synthesized as described in example 1, except that: thiourea and APTMS are not added; the method comprises the following specific steps: the initial 8.2mg/mL graphene oxide dispersion was diluted to 2mg/mL, where 50mL of the dispersion was sonicated to form a uniform suspension. Subsequently, the resulting solution was transferred into a glass bottle, closed, and then treated in an electric oven at 90℃for 6 hours. Separating solid from the obtained reaction solution, alternately washing the obtained solid with cold and hot water, and freeze-drying at-50 ℃ for 48 hours to obtain the adsorbent (GN for short).
The adsorption process of Cr (VI) is as described in example 1.
In the adsorption separation process, the adsorption capacity prepared in this comparative example was 96.1mg/g; it can be seen that the modifier plays an extremely important role in the adsorption capacity.
Comparative example 2
1. The adsorbent was synthesized as described in example 1, except that: thiourea is not added; other steps and conditions were the same as in example 1, and an adsorbent (abbreviated as AGN) was thus obtained.
The adsorption process of Cr (VI) is as described in example 1.
In the adsorption separation process, the adsorption capacity prepared in this comparative example was 160.9mg/g; it can be seen that the modifier plays an extremely important role in the adsorption capacity.
Comparative example 3
1. The adsorbent was synthesized as described in example 1, except that: APTMS is not added; other steps and conditions were the same as in example 1, thus obtaining an adsorbent (abbreviated as TGN).
The adsorption process of Cr (VI) is as described in example 1.
In the adsorption separation process, the adsorption capacity prepared in this comparative example was 136.7mg/g; it can be seen that the modifier plays an extremely important role in the adsorption capacity.
The present invention is not limited to the above-mentioned embodiments, and any equivalent embodiments which can be changed or modified by the technical content disclosed above can be applied to other fields, but any simple modification, equivalent changes and modification made to the above-mentioned embodiments according to the technical substance of the present invention without departing from the technical content of the present invention still belong to the protection scope of the technical solution of the present invention.
Claims (7)
1. An adsorbent for selectively removing Cr (VI), which is characterized in that the adsorbent is an amino-functionalized graphene nanocomposite; the amino-functionalized graphene nanocomposite has a microscopic morphology of: the three-dimensional porous structure consists of nano sheets rich in wrinkles; the BET specific surface area of the amino-functionalized graphene nanocomposite is 100-200m 2 /g；
The preparation method of the adsorbent for selectively removing Cr (VI) comprises the following steps:
fully and uniformly mixing graphene oxide aqueous dispersion liquid, thiourea and 3-aminopropyl trimethoxy silane, and then carrying out low-temperature reaction; separating solid, washing, freeze drying to obtain adsorbent;
the mass ratio of thiourea to graphene oxide is 4-6:1; the mass ratio of the volume of the 3-aminopropyl trimethoxysilane to the graphene oxide is 1-4 mu L/mg; the low-temperature reaction temperature is 80-100 ℃; the low temperature reaction time is 4-8 hours.
2. The adsorbent for selectively removing Cr (VI) according to claim 1, wherein the concentration of the graphene oxide aqueous dispersion is 1-5mg/mL.
3. The adsorbent for selectively removing Cr (VI) according to claim 1, wherein the mass ratio of thiourea to graphene oxide is 5:1; the mass ratio of the volume of the 3-aminopropyl trimethoxysilane to the graphene oxide is 2.5 mu L/mg.
4. The selective Cr (VI) removal sorbent according to claim 1, wherein the low temperature reaction temperature is 90 ℃; the low temperature reaction time was 6 hours.
5. Use of an adsorbent for the selective removal of Cr (VI) according to any one of claims 1 to 4 for the adsorption of heavy metal Cr (VI).
6. Use of an adsorbent for the selective removal of Cr (VI) according to claim 5, characterized in that the adsorbent is applied in a method for the adsorption of heavy metal Cr (VI), comprising the steps of:
(1) Adjusting the pH value of the Cr (VI) -containing solution;
(2) Dispersing the adsorbent in the Cr (VI) containing solution in the step (1), fully mixing and contacting, and adsorbing Cr (VI) in the Cr (VI) containing solution by the adsorbent so as to remove the Cr (VI) in the Cr (VI) containing solution.
7. Use of an adsorbent for the selective removal of Cr (VI) according to claim 6, comprising one or more of the following conditions:
i. in the step (1), the pH of the Cr (VI) containing solution is regulated to be 1 to 10;
ii. In the step (1), the reagent used for regulating the pH value is hydrochloric acid or sodium hydroxide;
iii, in the step (2), the volume ratio of the mass of the adsorbent to the Cr (VI) containing solution is 0.3-2.0: 1g/L;
iv, in the step (2), the adsorption temperature is 25-55 ℃ and the adsorption time is 120-200min;
v, in the step (2), adsorption is carried out under the condition of oscillation, and the oscillation speed is 200-250rpm; vi, in the step (2), after the adsorption of the adsorbent is completed, the method further comprises a step of separating the adsorbent from the solution.
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