CN109967024B - Method for synthesizing nano zero-valent iron by using vitamin C and green tea and in-situ remediation method - Google Patents

Method for synthesizing nano zero-valent iron by using vitamin C and green tea and in-situ remediation method Download PDF

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CN109967024B
CN109967024B CN201910286805.XA CN201910286805A CN109967024B CN 109967024 B CN109967024 B CN 109967024B CN 201910286805 A CN201910286805 A CN 201910286805A CN 109967024 B CN109967024 B CN 109967024B
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nano zero
green tea
valent iron
vitamin
solution
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CN109967024A (en
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徐楠
李铎
张刚
皇甫新星
叶志
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Suzhou University of Science and Technology
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
    • B09C—RECLAMATION OF CONTAMINATED SOIL
    • B09C1/00—Reclamation of contaminated soil
    • B09C1/002—Reclamation of contaminated soil involving in-situ ground water treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
    • B09C—RECLAMATION OF CONTAMINATED SOIL
    • B09C1/00—Reclamation of contaminated soil
    • B09C1/08—Reclamation of contaminated soil chemically
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B22F1/054—Nanosized particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/14—Treatment of metallic powder
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/14—Treatment of metallic powder
    • B22F1/145—Chemical treatment, e.g. passivation or decarburisation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • 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
    • C02F1/281—Treatment of water, waste water, or sewage by sorption using inorganic sorbents
    • 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
    • C02F1/70—Treatment of water, waste water, or sewage by reduction
    • C02F1/705—Reduction by metals
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C02F2101/20—Heavy metals or heavy metal compounds
    • C02F2101/22—Chromium or chromium compounds, e.g. chromates

Abstract

The invention relates to a method for synthesizing nano zero-valent iron by using vitamin C and green tea and an in-situ restoration method. The method mainly comprises the following steps: preparing a green tea extracting solution, preparing an iron salt solution, adding vitamin C into the green tea extracting solution at room temperature in a nitrogen atmosphere to obtain a vitamin C-green tea mixed solution, mixing the vitamin C-green tea mixed solution with the iron salt solution, stirring the solution to obtain a nano zero-valent iron suspension, performing centrifugal separation on the nano zero-valent iron suspension to obtain a nano zero-valent iron solid, cleaning the nano zero-valent iron solid, performing vacuum drying, grinding and sieving to obtain nano zero-valent iron particles. The nano zero-valent iron prepared by the method has good suspension stability, excellent mobility and high heavy metal removal capacity, and particularly has high-efficiency removal effect on hexavalent chromium in water.

Description

Method for synthesizing nano zero-valent iron by using vitamin C and green tea and in-situ remediation method
Technical Field
The invention relates to the technical field of inorganic nano material preparation and water purification environment, in particular to a method for synthesizing nano zero-valent iron by using vitamin C and green tea and an in-situ restoration method.
Background
The nano zero-valent iron (nZVI) has large specific surface area, high reaction activity, strong adsorption capacity and high reaction rate, and can be directly injected into polluted soil and water, so that the nano zero-valent iron has incomparable advantages in the aspects of soil remediation and water purification. Particularly, when pollutants with lower concentration ratio are treated, the removal rate of the nano zero-valent iron to the pollutants is higher, and the removal effect is more obvious. The nanometer zero-valent iron particles have small particle size, van der Waals force exists among the particles, the surfaces of the particles have magnetism, the particles are particularly easy to agglomerate, the specific surface area of the particles is reduced after agglomeration, and then the reaction activity of the particles is far lower than that of the nanometer particles before agglomeration. Meanwhile, the nano zero-valent iron particles are increased in mass due to agglomeration, are easier to settle, are difficult to realize remote migration in a targeted pollution area, and reduce the degradation range of the nano zero-valent iron particles; the nano zero-valent iron is exposed in the air, has extremely poor stability and can be oxidized quickly, so that the reaction activity is reduced; when the nano zero-valent iron reacts with degraded substances, precipitates such as Fe (OH)3 and the like are generally generated and cover the surfaces of the nano zero-valent iron, so that the inside zero-valent iron cannot contact with pollutants and cannot react with the pollutants, and the degradation efficiency of the nano zero-valent iron is reduced. Therefore, inhibiting the agglomeration of nano zero-valent iron particles and improving the reaction activity are the main problems to be faced.
The traditional preparation method of the nano zero-valent iron mainly comprises a physical gas phase condensation method, a ball milling method, a liquid phase reduction method, a thermal decomposition method and the like. The traditional preparation methods have limitations, high cost and complex process, some methods can also generate toxicity and corrosivity, and the green synthesized nano zero-valent iron has the characteristics of low cost and environmental protection, and is receiving more and more attention of researchers. The green synthesized nano zero-valent iron is firstly manufactured and applied by VeruTEK and the United states environmental protection agency. The method comprises preparing a polyphenol solution by heating plant extracts (coffee, green tea, black tea, lemon, balsam, sorghum, etc.) in water to a temperature close to the boiling point. The extract prepared by the method is separated from the plant residue and then mixed with the iron ion solution to obtain the nano zero-valent iron. Compared with the nano zero-valent iron synthesized by a physical and chemical method, the nano zero-valent iron synthesized by using the green tea extract has the characteristics of better adsorption and reduction capability and long-term activity maintenance, and is more suitable for environmental restoration to a certain extent than the nano material synthesized by the physical and chemical method. However, the removal capability of the heavy metals of the nano zero-valent iron synthesized by the synthesis method is still low.
Disclosure of Invention
Therefore, it is necessary to provide a method for synthesizing nanoscale zero-valent iron by using vitamin C and green tea, aiming at the problem that nanoscale zero-valent iron synthesized by the conventional synthesis method has low heavy metal removal capability.
A method for synthesizing nano zero-valent iron by using vitamin C and green tea comprises the following steps:
s100, preparing a green tea extracting solution: adding tea leaves of green tea into deoxidized deionized water, carrying out water bath under a sealed condition, standing after the water bath is finished, and carrying out vacuum filtration after the liquid temperature is cooled to room temperature to obtain a green tea extracting solution for later use;
s200, preparing an iron salt solution: dissolving ferric salt in deoxidized deionized water to obtain ferric salt solution for later use, wherein the ferric salt is soluble ferric salt or soluble ferrous salt;
s300, preparing nano zero-valent iron: adding vitamin C into the green tea extract at room temperature to obtain vitamin C-green tea mixture; mixing the vitamin C-green tea mixed solution with an iron salt solution in a nitrogen atmosphere, and stirring the solution to obtain a nano zero-valent iron suspension for later use;
s400, obtaining nano zero-valent iron particles: and (3) carrying out centrifugal separation on the nano zero-valent iron suspension to obtain a nano zero-valent iron solid, cleaning the nano zero-valent iron solid, then carrying out vacuum drying, grinding and sieving to obtain the nano zero-valent iron particles.
The nano zero-valent iron prepared by the method has good suspension stability, excellent mobility and high heavy metal removal capacity, and particularly has high-efficiency removal effect on hexavalent chromium in water.
In one embodiment, in step S100, the deoxidized deionized water is prepared by introducing nitrogen into deionized water for 30min, and the water bath is performed under a sealed condition, wherein the water bath temperature is 80 ℃ and the water bath time is 30-60 min.
In one embodiment, in step S100, the tea leaves of green tea are added to the deoxidized deionized water according to the following ratio: the amount of tea leaves added per 1L of deoxidized and deionized water is 10-100g, and the green tea extract serves as a reducing agent in the reaction.
In one embodiment, in step S200, the soluble ferric salt is ferric sulfate or ferric chloride, the iron-containing ion concentration of the soluble ferric salt is 0.04-0.1mol/L, the soluble ferrous salt is ferrous sulfate, and the iron-containing ion concentration of the soluble ferrous salt is 0.04-0.1 mol/L.
In one embodiment, in step S300, the concentration of vitamin C in the mixed solution of vitamin C and green tea is 15-20 g/L.
In one embodiment, in the step S300, the stirring time is 30min, and the stirring speed is 200 r/min.
In one embodiment, in step S100, the tea leaves of green tea are added to the deoxidized deionized water according to the following ratio: the amount of tea leaves added to each 1L of the deoxidized deionized water is 60g, in the step S200, the soluble ferric salt is ferric sulfate, the concentration of iron-containing ions of the soluble ferric salt is 0.04mol/L, in the step S300, the concentration of vitamin C in the vitamin C-green tea mixed solution is 20g/L, and the volume ratio of the ferric salt solution to the vitamin C-green tea mixed solution is 1: 1.
in one embodiment, in the step S400, the drying time of the vacuum drying is 12 hours, the drying temperature is 50 ℃, the cleaning is 3 times by using absolute ethyl alcohol, the grinding and sieving is to grind and pass through a 100-mesh sieve, the centrifugal speed is 4000r/min, and the centrifugal time is 7 min.
In one embodiment, in step S300, mixing the vitamin C-green tea mixed solution with an iron salt solution, and stirring the solution to obtain a nano zero-valent iron suspension includes: firstly, stirring and adding an iron salt solution into a reaction vessel, keeping a stirring state after the iron salt solution is completely added, adding a vitamin C-green tea mixed solution into the reaction vessel, and continuously stirring for 30min after the vitamin C-green tea mixed solution is completely added to obtain a nano zero-valent iron suspension, wherein the feeding speed is 25 mL/s.
An in-situ remediation method, wherein nano zero-valent iron particles are prepared according to the method, and the nano zero-valent iron particles are used for in-situ remediation of heavy metal contaminated soil or underground water.
Drawings
Fig. 1 is an XRD characterization pattern of nano zero-valent iron synthesized by the method of the embodiment of the present invention.
FIG. 2 is a scanning electron microscope image of nano zero valent iron synthesized by the method of the embodiment of the invention.
Fig. 3 shows the adsorption reduction of hexavalent chromium (pH 6.0) by nano zero-valent iron synthesized using green tea.
Fig. 4 shows the hexavalent chromium adsorption-reduction process (pH 6.0) using nano zero-valent iron synthesized by the method of the embodiment of the present invention.
Fig. 5 is an absorption reduction image of hexavalent chromium by nano zero-valent iron synthesized by the method of the embodiment of the present invention under the condition of initial pH (pH 4.0).
Fig. 6 is a sedimentation diagram of nano zero-valent iron synthesized by the method of the embodiment of the invention in an electrolyte solution.
FIG. 7 is a graph showing the penetration of nanoscale zero-valent iron in saturated porous media, wherein the background solutions are 0.1mM NaCl,1mM NaCl and 10mM NaCl, respectively, according to the method of the embodiment of the present invention.
FIG. 8 is a graph showing the penetration curves of the nano zero-valent iron in the saturated porous medium, wherein the background solutions are 0.01mM NaCl,0.1mM NaCl and 1mM CaCl, respectively, according to the method of the embodiment of the present invention2。
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.
It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present.
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.
The embodiment of the invention provides a method for synthesizing nano zero-valent iron by using vitamin C and green tea, which comprises the following steps:
s100, preparing a green tea extracting solution: adding tea leaves of green tea into deoxidized deionized water, carrying out water bath under a sealed condition, standing after the water bath is finished, and carrying out vacuum filtration after the liquid temperature is cooled to room temperature to obtain a green tea extracting solution for later use;
s200, preparing an iron salt solution: dissolving ferric salt in deoxidized deionized water to obtain ferric salt solution for later use, wherein the ferric salt is soluble ferric salt or soluble ferrous salt;
s300, preparing nano zero-valent iron: adding vitamin C into the green tea extract at room temperature to obtain vitamin C-green tea mixture; mixing the vitamin C-green tea mixed solution with an iron salt solution in a nitrogen atmosphere, and stirring the solution to obtain a nano zero-valent iron suspension for later use;
s400, obtaining nano zero-valent iron particles: and (3) carrying out centrifugal separation on the nano zero-valent iron suspension to obtain a nano zero-valent iron solid, cleaning the nano zero-valent iron solid, then carrying out vacuum drying, grinding and sieving to obtain the nano zero-valent iron particles.
The nano zero-valent iron prepared by the method has good suspension stability, excellent mobility and high heavy metal removal capacity, and particularly has high-efficiency removal effect on hexavalent chromium in water.
In one embodiment, in step S100, the deoxidized deionized water is prepared by introducing nitrogen into deionized water for 30min, and the water bath is performed under a sealed condition, wherein the water bath temperature is 80 ℃ and the water bath time is 30-60 min.
In one embodiment, in step S100, the tea leaves of green tea are added to the deoxidized deionized water according to the following ratio: the amount of tea leaves added per 1L of deoxidized and deionized water is 10-100g, and the green tea extract serves as a reducing agent in the reaction.
In one embodiment, in step S200, the soluble ferric salt is ferric sulfate or ferric chloride, the iron-containing ion concentration of the soluble ferric salt is 0.04-0.1mol/L, the soluble ferrous salt is ferrous sulfate, and the iron-containing ion concentration of the soluble ferrous salt is 0.04-0.1 mol/L.
In one embodiment, in step S300, the concentration of vitamin C in the mixed solution of vitamin C and green tea is 15-20 g/L.
In one embodiment, in the step S300, the stirring time is 30min, and the stirring speed is 200 r/min.
In one embodiment, in step S300, the volume ratio of the ferric salt solution to the vitamin C-green tea mixed solution is 1: 1.
in one embodiment, in the step S400, the drying time of the vacuum drying is 12 hours, the drying temperature is 50 ℃, the cleaning is 3 times by using absolute ethyl alcohol, the grinding and sieving is to grind and pass through a 100-mesh sieve, the centrifugal speed is 4000r/min, and the centrifugal time is 7 min.
In one embodiment, in step S300, mixing the vitamin C-green tea mixed solution with an iron salt solution, and stirring the solution to obtain a nano zero-valent iron suspension includes: firstly, stirring and adding an iron salt solution into a reaction vessel, keeping a stirring state after the iron salt solution is completely added, adding a vitamin C-green tea mixed solution into the reaction vessel, and continuously stirring for 30min after the vitamin C-green tea mixed solution is completely added to obtain a nano zero-valent iron suspension, wherein the feeding speed is 25 mL/s. The reason why the above-mentioned flow rate is selected to be 25mL/s is that the flow rate is too slow, the reducing substance in the solution is easily oxidized, the flow rate is too fast, and the reaction of the reducing substance in the solution with iron is incomplete.
The embodiment of the invention also provides an in-situ remediation method, the nano zero-valent iron particles are prepared according to the method, and the nano zero-valent iron particles are used for in-situ remediation of heavy metal contaminated soil or underground water.
When the soil is repaired in situ, the nano zero-valent iron particles prepared by the method can be directly scattered on the polluted soil, and under the scouring action of rainwater and the like, the nano zero-valent iron particles can enter the soil and migrate, so that the polluted soil is repaired. The remediation is mainly to remove heavy metals in the soil through the adsorption and reduction effects of the nano zero-valent iron. Of course, the nano zero-valent iron particles prepared by the method can be prepared into a suspension and then sprinkled on the polluted soil.
When the groundwater is repaired in situ, a drainage channel can be built, the groundwater flows through the drainage channel, and the nano zero-valent iron particles or the suspension prepared by the method are placed in the drainage channel. And (4) taking out heavy metals in the underground water through the adsorption and reduction of the nano zero-valent iron.
It can be understood that the nano zero-valent iron prepared by the method can be used for directly treating heavy metal polluted water. For example, the removal of heavy metals in heavy metal contaminated water by adsorption reduction using nano zero-valent iron prepared by the embodiment of the present invention includes:
adding the nano zero-valent iron into heavy metal polluted water at room temperature, adjusting the pH of the polluted water to 2-6, oscillating or rotating the polluted water for more than or equal to 3 hours, and then filtering and separating.
Further, the dosage of the nano zero-valent iron is 0.5 g/L; the heavy metal in the polluted water is hexavalent chromium, and the concentration range of the heavy metal is 10-200 mg/L.
The above method is further described in detail below by specific examples.
Preparing vitamin C and green tea synthesized nano zero-valent iron:
adding green tea into deoxidized deionized water according to the following mixture ratio: adding 60g of tea into per 1L of deoxidized and deionized water, heating in 80 deg.C water bath under sealed condition for 0.5h, cooling to room temperature, vacuum filtering to obtain green tea extractive solution, and keeping. And (3) dissolving solid hydrated ferric sulfate into the deoxidized deionized water to obtain a ferric sulfate solution, wherein the concentration of ferric ions is 0.04mol/L for later use. Pretreatment of vitamin C: grinding the vitamin C tablets at room temperature, sieving the vitamin C tablets by a 100-mesh sieve, and collecting powder below the sieve for later use. Adding vitamin C powder into the green tea extract at room temperature, and mixing and dissolving for later use. The concentration of vitamin C in the mixed solution of vitamin C and green tea is 20 g/L. And (3) taking an electric stirrer, placing a stirring rod in a reaction vessel, starting stirring, adding the ferric sulfate solution into the reaction vessel, keeping a stirring state after the ferric sulfate solution is fed completely, adding the green tea-vitamin C solution into the reaction vessel, continuing stirring for 0.5h after the green tea-vitamin C extracting solution is fed completely, and stopping stirring to obtain a zero-valent iron suspension for later use. The volume ratio of the ferric sulfate solution to the vitamin C-green tea mixed solution is 1: 1. and (3) carrying out centrifugal separation on the nano zero-valent iron suspension, carrying out vacuum drying on the obtained nano zero-valent iron solid for 12 hours at the drying temperature of 50 ℃, grinding and sieving by a 100-mesh sieve after drying. So as to obtain the green synthesized nano zero-valent iron by utilizing the vitamin C and the green tea. Storing under vacuum condition. The following experiment was performed.
Adsorption reduction experiment:
comparison experiment one:
as shown in fig. 3, the adsorption reduction experiment was performed on nano zero-valent iron synthesized only by green tea. Specifically, the adsorption reduction test of chromium was performed by an adsorption test method at room temperature (25 ℃) and at a pH of 6.0 ± 0.02. 40mL of chromium-contaminated solution with different concentration gradients (10-200mg/L) was added to 50mL centrifuge tubes, and 0.02g of nanoscale zero-valent iron synthesized from green tea was added to each centrifuge tube, and the pH was adjusted to 6.0. Rotating the waste water on a rotator at normal temperature for 3 hours at the speed of 30r/min so as to remove the heavy metal chromium in the waste water. And (3) carrying out solid-liquid separation on the solution after adsorption, filtering the supernatant by using a filter membrane of 0.45 mu m, and respectively measuring the residual hexavalent chromium concentration and the total chromium concentration after adsorption of the filtrate by using a diphenylcarbonyldihydrazide spectrophotometry and an atomic flame absorption method. The experimental result is shown in figure 3, and the removal capacity of the nano zero-valent iron synthesized by the green tea on the hexavalent chromium is 95.117mg/g at most.
Experiment one:
as shown in fig. 4, the nano zero-valent iron synthesized by vitamin C and green tea in the examples of the present invention was subjected to adsorption reduction experiments. Specifically, the adsorption reduction test of chromium was performed by an adsorption test method at room temperature (25 ℃) and at a pH of 6.0 ± 0.02. 40mL of chromium-contaminated solution with different concentration gradients (10-200mg/L) was added to 50mL of centrifuge tubes, and 0.02g of the nanoscale zero-valent iron prepared by the above method of the present invention was added to each of the centrifuge tubes, and the pH was adjusted to 6.0. Rotating the waste water on a rotator at normal temperature for 3 hours at the speed of 30r/min so as to remove the heavy metal chromium in the waste water. And (3) carrying out solid-liquid separation on the solution after adsorption, filtering the supernatant by using a filter membrane of 0.45 mu m, and respectively measuring the residual hexavalent chromium concentration and the total chromium concentration after adsorption of the filtrate by using a diphenylcarbonyldihydrazide spectrophotometry and an atomic flame absorption method. The experimental result is shown in figure 4, the nano zero-valent iron synthesized by the method has the highest hexavalent chromium removal efficiency, and the highest removal capacity is 135.917 mg/g. This shows that the reduction capacity and the adsorption capacity of the hexavalent chromium are greatly improved under the condition that the pH value is 6.0 by using the vitamin C and the green synthesized nano zero-valent iron of green tea.
Experiment two:
as shown in fig. 5, the nano zero-valent iron synthesized by vitamin C and green tea in the example of the present invention was subjected to an adsorption reduction experiment, except that the experiment was performed under the condition of initial pH (pH 4.0). Specifically, the adsorption reduction test of chromium was carried out at room temperature (25 ℃ C.) by the adsorption test method. 40mL of chromium pollution solution with different concentration gradients (10-200mg/L) is added into 50mL of centrifuge tubes, and 0.02g of nano zero-valent iron prepared by the method is added into each centrifuge tube. Rotating the waste water on a rotator at normal temperature for 3 hours at the speed of 30r/min so as to remove the heavy metal chromium in the waste water. And (3) carrying out solid-liquid separation on the solution after adsorption, filtering the supernatant by using a filter membrane of 0.45 mu m, and respectively measuring the residual hexavalent chromium concentration and the total chromium concentration after adsorption of the filtrate by using a diphenylcarbonyldihydrazide spectrophotometry and an atomic flame absorption method. The results of the experiment are shown in FIG. 5, where the removal capacity was at most 96.717 mg/g. This shows that the nano zero-valent iron synthesized by using vitamin C and green tea has stronger reducing capability and higher adsorption capability to chromium under the condition of initial pH.
Suspension stability experiments:
test one:
the nano zero-valent iron prepared by the method is prepared into a solution with the concentration of 1g/L, the background solution is 0.1mM NaCl, the pH value is adjusted to be 6.0, and after ultrasonic treatment is carried out for 30min, an ultraviolet spectrophotometer is used for carrying out kinetic measurement, and the measurement time is 2 h.
And (2) test II:
the nano zero-valent iron prepared by the method is prepared into a solution with the concentration of 1g/L, the background solution is 0.1mM NaCl, the pH value is adjusted to 4.0, and after ultrasonic treatment is carried out for 30min, an ultraviolet spectrophotometer is used for carrying out kinetic measurement, and the measurement time is 2 h.
Comparison experiment one:
the nano zero-valent iron prepared only from green tea is prepared into a solution with the concentration of 1g/L, the background solution is 0.1mM NaCl, the pH value is adjusted to 6.0, and after 30min of ultrasonic treatment, a UV spectrophotometer is used for kinetic measurement, and the measurement time is 2 h.
Comparative experiment two:
the nano zero-valent iron prepared only from green tea is prepared into a solution with the concentration of 1g/L, the background solution is 0.1mM NaCl, the pH value is adjusted to 4.0, and after 30min of ultrasonic treatment, a UV spectrophotometer is used for kinetic measurement, and the measurement time is 2 h.
As shown in fig. 6, the suspension stability of the same material at pH 6.0 was slightly lower than that of the initial pH 4.0. The suspension stability of the nano zero-valent iron prepared by the above method of the present invention is slightly superior to that of the nano zero-valent iron prepared only with green tea under the conditions of pH 6.0 and initial pH 4.0. On the whole, the nano zero-valent iron prepared by the method has good suspension stability.
Migration experiments in saturated porous media:
the method specifically comprises the following steps:
step 1, pretreatment of quartz sand: 1.25kg of quartz sand is put in a 1L beaker, 10mM NaOH solution is poured into the beaker to immerse the quartz sand for 24 hours, then the quartz sand is cleaned by deionized water, then the quartz sand is soaked by 10mM HCl for 24 hours, and then the quartz sand is cleaned by deionized water again, so that the influence of metal oxides and other impurities on the surface of the quartz sand on the experiment is prevented. Drying in 105 deg.C electric heating constant temperature drying oven, cooling, sieving quartz sand with 600 μm standard sample sieve, collecting the sieved uniform particles, and packaging in sealed bag.
Step 2, filling of the quartz sand column: nylon membranes with the pore size of 150 μm are respectively arranged at two ends of the chromatographic column to prevent the effluent from being blocked, and quartz sand is filled in the chromatographic column in the following way: weighing about 35.0g of quartz sand from the prepared quartz sand by using a balance, slowly pouring the quartz sand into a filling column, compacting the quartz sand by using a wood rod, repeating the operation until the chromatography column is just filled, recording the mass of the quartz sand weighed each time and calculating the total mass of the filled quartz sand. When packing the chromatographic column, care should be taken to control the porosity between 0.47 and 0.49.
And 3, saturating the quartz sand column: and after the chromatographic column is filled, injecting deionized water into the chromatographic column by using a peristaltic constant flow pump for saturation, wherein the saturation time is at least 24 h.
Step 4, migration experiment: respectively taking the background solution and the nano zero-valent iron prepared by the method of the invention to prepare 1g/L nano zero-valent iron suspension, adjusting the pH value to be 6.0, and carrying out ultrasonic treatment for 30 min. After the column was saturated with deionized water, 5PV of background solution was pumped in. Pumping 200mL of nano zero-valent iron suspension in the first stage of the migration experiment, and collecting effluent liquid at the moment; 200mL of background solution was pumped in the second stage. The collected effluent was subjected to determination of iron concentration using an ultraviolet-visible spectrophotometer.
Six experiments were performed according to the above procedure. Specifically, the background solution selected in the first experiment is: 0.1mM NaCl. The background solutions selected for experiment two were: 1mM NaCl. Experiment three selected background solutions were: 10mM NaCl. Experiment four background solutions selected were: 0.01mM CaCl2. Experiment five background solutions selected were: 0.1mM CaCl2. The background solutions selected for experiment six were: 1mM CaCl2。
The results of the experiment are shown in fig. 7 and 8. The nanometer zero-valent iron synthesized by using vitamin C and green tea has good migration performance in a saturated porous medium, and the outflow ratio C/C0 is as high as 0.8 in Na + electrolyte; ca2+ electrolyte, the outflow ratio C/C0 is as high as 0.7. This overcomes the disadvantage of poor migration ability of nano zero-valent iron synthesized only by green tea in saturated porous media.
The invention has the beneficial effects that:
1. the green tea and the vitamin C used in the invention are cheap and easily available, and the reducing substances (polyphenol and vitamin C) contained in the green tea and the vitamin C can reduce iron salt to prepare the high-reaction-activity nano zero-valent iron, thereby having good social and economic benefits.
2. The problems of the reactivity, the suspension stability and the like of the material are studied and analyzed in detail, and a good foundation is laid for the treatment and restoration technology of the heavy metal-rich polluted water.
3. The nano zero-valent iron prepared by the method has good reducing capability and adsorption capability on heavy metal chromium with high concentration in water, and has the characteristics of short process, convenient operation, low energy consumption and the like.
4. The nano zero-valent iron prepared by the method has better suspension stability and mobility in aqueous solution, and can be fully migrated in soil groundwater, so that the action range of the nano zero-valent iron for soil groundwater pollution remediation is expanded.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the 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 (6)

1. A method for synthesizing nano zero-valent iron by using vitamin C and green tea is characterized in that: the method comprises the following steps:
s100, preparing a green tea extracting solution: adding tea leaves of green tea into deoxidized deionized water, carrying out water bath under a sealed condition, standing after the water bath is finished, and carrying out vacuum filtration after the liquid temperature is cooled to room temperature to obtain a green tea extracting solution for later use;
s200, preparing an iron salt solution: dissolving ferric salt in deoxidized deionized water to obtain ferric salt solution for later use, wherein the ferric salt is soluble ferric salt or soluble ferrous salt;
s300, preparing nano zero-valent iron: adding vitamin C into the green tea extract at room temperature to obtain vitamin C-green tea mixture; mixing the vitamin C-green tea mixed solution with an iron salt solution in a nitrogen atmosphere, and stirring the solution to obtain a nano zero-valent iron suspension for later use;
s400, obtaining nano zero-valent iron particles: carrying out centrifugal separation on the nano zero-valent iron suspension to obtain a nano zero-valent iron solid, cleaning the nano zero-valent iron solid, then carrying out vacuum drying, and grinding and sieving to obtain nano zero-valent iron particles;
in the step S100, the green tea leaves are added into the deoxidized deionized water according to the following ratio: the amount of tea leaves added to each 1L of the deoxidized deionized water is 60g, in the step S200, the soluble ferric salt is ferric sulfate, the concentration of iron-containing ions of the soluble ferric salt is 0.04mol/L, in the step S300, the concentration of vitamin C in the vitamin C-green tea mixed solution is 20g/L, and the volume ratio of the ferric salt solution to the vitamin C-green tea mixed solution is 1: 1.
2. the method for synthesizing nano zero-valent iron using vitamin C and green tea according to claim 1, wherein: in the step S100, the deoxidized deionized water is prepared by introducing nitrogen into deionized water for 30min, and the deoxidized deionized water is subjected to water bath under a sealing condition, wherein the water bath temperature is 80 ℃ and the water bath time is 30-60 min.
3. The method for synthesizing nano zero-valent iron using vitamin C and green tea according to claim 1, wherein: in the step S300, the stirring time is 30min, and the stirring speed is 200 r/min.
4. The method for synthesizing nano zero-valent iron using vitamin C and green tea according to claim 1, wherein: in the step S400, the drying time of the vacuum drying is 12 hours, the drying temperature is 50 ℃, the cleaning is carried out for 3 times by using absolute ethyl alcohol, the grinding and sieving is carried out by grinding and sieving by using a 100-mesh sieve, the centrifugal speed is 4000r/min, and the centrifugal time is 7 min.
5. The method for synthesizing nano zero-valent iron using vitamin C and green tea according to claim 1, wherein: in the step S300, the mixing the vitamin C-green tea mixed solution with the iron salt solution, and stirring the solution to obtain the nano zero-valent iron suspension includes: firstly, stirring and adding an iron salt solution into a reaction vessel, keeping a stirring state after the iron salt solution is completely added, adding a vitamin C-green tea mixed solution into the reaction vessel, and continuously stirring for 30min after the vitamin C-green tea mixed solution is completely added to obtain a nano zero-valent iron suspension, wherein the feeding speed is 25 mL/s.
6. An in-situ remediation method, comprising: the method of any one of claims 1 to 5, wherein the nano zero-valent iron particles are used for in-situ remediation of heavy metal contaminated soil or groundwater.
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