Method for preparing chromium-containing nano colloid from humic acid

Abstract

The invention provides a method for preparing chromium-containing nano colloid by using humic acid, and relates to the technical field of heavy metal pollution research. According to the method, humic acid is used as a representative organic matter in a water body environment, a continuous stirring reaction is carried out under the condition of simulating natural light or natural light, then ultrafiltration membrane filtration and dialysis are further carried out to extract a nano colloidal substance, and the colloidal substance is characterized after freeze drying. The chromium-containing nano colloid provided by the invention is simple in preparation and extraction processes, and can dynamically monitor the adsorption and conversion effects of humic acid on hexavalent chromium, thereby realizing nanoscale analysis and tracking of heavy metals in a water environment. By simulating natural illumination in a water body, the photosensitization mechanism of humic acid and the effect of humic acid in the photochemical reaction process of environmental pollutants can be studied.

Description

Technical Field

[0001] The invention relates to the technical field of heavy metal pollution research, and in particular to a method for preparing chromium-containing nano-colloid by utilizing humic acid. Background Art

[0002] Chromium in the natural environment mainly exists in trivalent and hexavalent forms. In recent years, the rapid development of industries such as electroplating, leather manufacturing, metal processing, automobile manufacturing and mining has caused serious pollution of chromium in the environment, including soil, groundwater, surface water and atmosphere. Hexavalent chromium is one of the most common heavy metal ions in polluted water environments, and its toxicity is much stronger than trivalent chromium. Hexavalent chromium can be transmitted through the food chain, causing direct or indirect harm to human life and health. Hexavalent chromium and its compounds are mainly absorbed by the human body through the skin, digestive tract and respiratory mucosa, which can induce diseases such as skin ulcers, lung cancer and decreased reproductive system function. Hexavalent chromium pollution in the ecological environment can also cause toxic effects on plants and affect their normal growth and development. High concentrations of cadmium pollution can inhibit the growth of aquatic crops such as rice, causing a reduction in rice production. Therefore, the toxicity of hexavalent chromium to the ecological environment and human health has received widespread attention in recent years.

[0003] Humic acid is a natural organic matter widely distributed in the natural environment. Due to its special composition and structure, it can affect the migration, geochemical behavior and ecological effects of pollutants in different environments. Humic acid is composed of complex organic substances. It contains a variety of functional groups that can react chemically with heavy metal ions and play an adsorption role. The basic units involved in the reaction mainly include quinones, phenols and flavonoids. These groups can act as reducing agents and stabilizers in the reaction between humic acid and metal ions. Humic acid in natural water bodies can produce active oxygen species under natural light or simulated light conditions, participate in the chemical reaction between humic acid and metal ions, and thus affect the migration and transformation of heavy metal pollutants in the environment.

[0004] Humic acid plays an important role in the morphological transformation of hexavalent chromium in aquatic environments, thereby affecting its migration, bioavailability and toxicity in the environment. However, research in recent years has focused on the effects of the properties of humus on its interaction with heavy metals, and relatively little research has been done on the transformation and fate of heavy metals in aquatic environments. Nanocolloids can be produced by chemical reactions and adsorption between metal ions and organic matter in the environment, and can exist stably in environments such as soil and water, becoming important carriers of pollutants such as heavy metals, thereby changing the harm caused by heavy metals to the ecological environment and human health. Organic matter in aquatic environments, represented by humic acid, can combine with inorganic matter to form nanocolloids. However, there is currently a lack of research on nanocolloids formed by the interaction of polluting heavy metals with humic acid. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a method for preparing chromium-containing nanocolloids using humic acid. The present invention prepares colloidal substances produced by the reaction of hexavalent chromium with humic acid in an aquatic environment, which is conducive to subsequent research and has important significance for revealing the migration, transformation and toxicity of hexavalent chromium in the environment.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing chromium-containing nano-colloid by using humic acid, comprising the following steps:

[0008] Dissolving humic acid and hexavalent chromium salt in water, adjusting the pH value, and obtaining a reaction solution;

[0009] The reaction solution is continuously stirred under simulated natural light or natural light conditions to make the humic acid react with hexavalent chromium to form a colloid, and then filtered through an ultrafiltration membrane, dialyzed and freeze-dried to obtain a chromium-containing nano-colloid.

[0010] Preferably, the simulated natural light is a xenon lamp solar simulator that simulates natural light with an irradiance of 500 W / m 2 .

[0011] Preferably, the ultrafiltration membrane filtration comprises: filtering the feed liquid obtained after continuous stirring through a tangential flow ultrafiltration system composed of an ultrafiltration membrane package and a peristaltic pump.

[0012] Preferably, the hexavalent chromium salt is potassium dichromate.

[0013] Preferably, the concentration of hexavalent chromium in the reaction solution is 80 μmol / L.

[0014] Preferably, the concentration of humic acid in the reaction solution is 20 mg / L.

[0015] Preferably, the pH value is adjusted to 5-7.

[0016] Preferably, the continuous stirring time is 10 hours.

[0017] Preferably, the freeze-drying comprises: pre-freezing at -80°C for 4 hours and then placing at -50°C for vacuum freeze-drying for 8 hours.

[0018] Preferably, the molecular weight cut-off of the dialysis bag used for dialysis is 3500Da.

[0019] The invention provides a method for preparing chromium-containing nano-colloid by using humic acid, comprising the following steps: dissolving humic acid and hexavalent chromium salt into water, adjusting pH value to obtain reaction solution; continuously stirring the reaction solution under simulated natural light or natural light conditions to make humic acid and hexavalent chromium react to form colloid, and obtaining chromium-containing nano-colloid after filtering with an ultrafiltration membrane, dialyzing and freeze-drying.

[0020] The present invention uses humic acid as a representative organic matter in the water environment, performs continuous stirring reaction under simulated natural light or natural light conditions, further performs ultrafiltration membrane filtration and dialysis to extract nano-colloidal substances, and characterizes the colloidal substances after freeze drying. The chromium-containing nano-colloid provided by the present invention has a simple preparation and extraction process, and can dynamically monitor the adsorption and conversion of hexavalent chromium by humic acid, thereby realizing nano-level analysis and tracking of heavy metals in the water environment.

[0021] The present invention uses a xenon lamp as the light source of the natural light simulator, which has the advantages of high matching degree with the natural light spectrum, fast response speed, high luminous efficiency and stable light output. By simulating natural light in water, the photosensitization mechanism of humic acid and its role in the photochemical reaction process of environmental pollutants can be studied.

[0022] The present invention adopts tangential flow ultrafiltration technology to separate colloids, which has the functions of efficiently separating, concentrating and purifying the colloid substances produced by the reaction, and can effectively alleviate the shortcomings of large particles and molecules being accumulated on the filter membrane in traditional filtration methods. In addition, the method is energy-saving, environmentally friendly and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The figure is the reduction rate of hexavalent chromium ions by humic acid in the embodiment;

[0024] Figure 2 A high-resolution transmission electron microscope image of the chromium-containing nanocolloid in the embodiment;

[0025] Figure 3 This is an energy dispersive X-ray spectrometer surface scan chromium element distribution image of the chromium-containing nano-colloid in the embodiment;

[0026] Figure 4 It is the X-ray diffraction image of the chromium-containing nano-colloid in the embodiment. DETAILED DESCRIPTION

[0027] The present invention provides a method for preparing chromium-containing nano-colloid by using humic acid, comprising the following steps:

[0028] Dissolving humic acid and hexavalent chromium salt in water, adjusting the pH value, and obtaining a reaction solution;

[0029] The reaction solution is continuously stirred under simulated natural light or natural light conditions to make the humic acid react with hexavalent chromium to form a colloid, and then filtered through an ultrafiltration membrane, dialyzed and freeze-dried to obtain a chromium-containing nano-colloid.

[0030] In the present invention, unless otherwise specified, the raw materials used are commercially available products well known in the art.

[0031] The invention dissolves humic acid and hexavalent chromium salt into water, adjusts the pH value, and obtains a reaction solution.

[0032] In the present invention, the water is preferably deionized water; the hexavalent chromium salt is preferably potassium dichromate. The present invention has no special requirements for the dissolution process, as long as the humic acid and the hexavalent chromium salt can be completely dissolved.

[0033] In the present invention, the dissolution is preferably carried out under light-proof conditions. In an embodiment of the present invention, humic acid is first dissolved in deionized water, then filtered using a 0.45 μm filter membrane to obtain a humic acid solution, and then potassium dichromate is added to the humic acid solution to dissolve the potassium dichromate.

[0034] The present invention preferably simulates real polluted water to determine the pH value of the reaction solution, the concentration of humic acid and hexavalent chromium in the reaction solution. Generally, the pH value of the real polluted water body is between 5 and 7. In addition, the concentration of humic acid is 20 mg / L and the concentration of hexavalent chromium is 80 μmol / L, which are also in the common concentration range of polluted water bodies. Therefore, the present invention preferably adjusts the pH value to 5 to 7, and controls the concentration of hexavalent chromium in the reaction solution to 80 μmol / L and the concentration of humic acid to 20 mg / L. In an embodiment of the present invention, the pH value is specifically 5 or 7.

[0035] After obtaining the reaction solution, the present invention continuously stirs the reaction solution under simulated natural light or natural light conditions to react humic acid with hexavalent chromium to form a colloid, and obtains chromium-containing nano-colloid after ultrafiltration membrane filtration, dialysis and freeze drying.

[0036] In the present invention, the simulated natural light is preferably a xenon lamp solar simulator simulating natural light with an irradiance of 500 W / m 2 The present invention uses a xenon lamp as the light source of the natural light simulator, which has the advantages of high matching degree with the natural light spectrum, fast response speed, high luminous efficiency and stable light output. By simulating natural light in water, the photosensitization mechanism of humic acid and its role in the photochemical reaction process of environmental pollutants can be studied.

[0037] In the present invention, the continuous stirring time is determined according to actual needs. When the adsorption and conversion of hexavalent chromium by humic acid is to be dynamically monitored, the continuous stirring and sampling can be stopped at any time. The present invention preferably continuously stirs for 10 hours, thereby improving the conversion rate of hexavalent chromium into chromium-containing nanocolloids, increasing the yield of chromium-containing nanocolloids, and facilitating subsequent analysis and research on chromium-containing nanocolloids.

[0038] The present invention does not impose any particular limitation on the time of continuous stirring, as long as it does not cause splashing.

[0039] After the continuous stirring is completed, the present invention performs ultrafiltration membrane filtration, dialysis and freeze drying on the obtained liquid to obtain chromium-containing nano-colloid.

[0040] In the present invention, the ultrafiltration membrane filtration preferably includes: filtering the feed liquid obtained after continuous stirring through a tangential flow ultrafiltration system composed of an ultrafiltration membrane package and a peristaltic pump. In the present invention, the specifications of the ultrafiltration membrane package are preferably 5kDa, VF05H1, Vivaflow 50. The present invention uses tangential flow ultrafiltration technology to separate colloids, has the effects of efficient separation, concentration and purification of the colloid substances produced by the reaction, can effectively alleviate the shortcomings of large particles and molecules accumulating on the filter membrane in traditional filtration methods, and the method is energy-saving, environmentally friendly and easy to operate.

[0041] In the present invention, the molecular weight cutoff of the dialysis bag used for the dialysis is preferably 3500Da. The present invention has no special requirements for the implementation process of the dialysis, and the implementation process well known in the art can be used. In the embodiment of the present invention, the solution filtered by the ultrafiltration membrane is transferred to a dialysis bag (molecular weight cutoff 3500Da), and placed in deionized water, and replaced every 12 hours, for a total of two changes.

[0042] In the present invention, the freeze drying preferably comprises: pre-freezing at -80°C for 4 hours and then placing at -50°C for vacuum freeze drying for 8 hours.

[0043] The method for preparing chromium-containing nano-colloids by using humic acid provided by the present invention is described in detail below in conjunction with the examples, but they should not be construed as limiting the scope of protection of the present invention.

[0044] Example 1

[0045] (1) Weigh 250 mg of humic acid and dissolve it in 500 mL of deionized water. Stir it continuously for 20 h using a magnetic stirrer at 25 °C and in the dark. Filter it using a 0.45 μm filter membrane. Finally, use a total organic carbon analyzer to detect the TOC of the solution.

[0046] (2) diluting the humic acid solution in step (1) to prepare a humic acid solution with a concentration of 20 mg / L, and measuring 40 mL of the humic acid solution with a concentration of 20 mg / L into a 100 mL quartz beaker, adding potassium dichromate, and adjusting the dichromate ion concentration to 40 μmol / L;

[0047] (3) Using nitric acid and sodium hydroxide, the pH of the reaction system was adjusted to 5, and a quartz glass was placed over the beaker;

[0048] (4) Use a xenon lamp solar simulator to simulate natural light and adjust its radiation intensity to 500W / m 2 ;

[0049] (5) The reaction system was placed on a magnetic stirrer and stirred continuously for 10 h, and the reduction rate of hexavalent chromium in the reaction system was detected at 0, 2, 4, 6, 8, and 10 h;

[0050] (6) After the reaction is completed, 200 mL of the reaction solution is placed in a brown glass bottle, and the nanocolloids are separated, concentrated and purified by a tangential flow ultrafiltration system consisting of an ultrafiltration membrane package and a peristaltic pump;

[0051] (7) Transfer the concentrated reaction solution to a dialysis bag and place it in a beaker containing 1500 mL of deionized water. Replace the solution every 12 hours for a total of two times.

[0052] (8) The dialyzed reaction solution was stored at -80°C and pre-frozen for 4 h;

[0053] (9) The sample was then placed in a vacuum freeze dryer and freeze-dried at -50 °C for 8 h, and the solid powder was collected to obtain nanocolloids.

[0054] Example 2

[0055] The difference from Example 1 is that nitric acid and sodium hydroxide are used in step (3) to adjust the pH of the reaction system to 7, and the other preparation processes are consistent with Example 1.

[0056] Structure and performance characterization

[0057] The conversion rates of hexavalent chromium in the process of preparing nanocolloids under pH=5 in Example 1 and under pH=7 in Example 2 were compared and analyzed. Figure 1 As shown, Figure 1 In the figure, a is the conversion rate of hexavalent chromium under the condition of pH = 5; b is the conversion rate of hexavalent chromium under the condition of pH = 7.

[0058] In Example 1 and Example 2, the solution was sampled at 0 h, 2 h, 4 h, 6 h, 8 h and 10 h, respectively, to detect the conversion rate of humic acid to hexavalent chromium.

[0059] Figure 1 Figure a shows that under the condition of pH = 5, the conversion rates of hexavalent chromium at 0h, 2h, 4h, 6h, 8h and 10h are 1.48%, 11.72%, 23.85%, 29.97% and 32.91% respectively;

[0060] Figure 1 Figure b shows that under the condition of pH = 7, the conversion rates of hexavalent chromium at 0h, 2h, 4h, 6h, 8h and 10h are 2.90%, 12.96%, 18.98%, 23.95% and 26.79% respectively. The results show that after 10h of reaction under simulated light conditions, the conversion rate of hexavalent chromium by humic acid under pH = 5 is higher than that under pH = 7.

[0061] The chromium-containing nano-colloid prepared under the conditions of pH=5 and reaction for 10 h in Example 1 and the chromium-containing nano-colloid prepared under the conditions of pH=7 and reaction for 10 h in Example 2 were analyzed using a high-resolution transmission electron microscope. Figure 2 As shown, Figure 2 In the figure, a is the morphology of the nanocolloid prepared under pH = 5; b is the morphology of the nanocolloid prepared under pH = 7. The results show that the nanocolloids generated under pH = 5 and pH = 7 are both nanosheet morphologies. The diameter of the nanocolloid prepared under pH = 5 is about 10-50nm, and the height is about 20-50nm; the diameter of the nanocolloid prepared under pH = 7 is about 100-200nm, and the height is about 150-300nm.

[0062] Energy dispersive X-ray spectrometer was used to in situ identify the chromium distribution of the nano-colloid prepared under the conditions of pH = 5 and reaction for 10 h in Example 1 and the nano-colloid prepared under the conditions of pH = 7 and reaction for 10 h in Example 2. The results are as follows: Figure 3 As shown, the results indicate that the chromium element is evenly distributed in the nano-colloid.

[0063] The composition of the nano-colloid prepared under the conditions of pH=5 and reaction for 10 h in Example 1 and the nano-colloid prepared under the conditions of pH=7 and reaction for 10 h in Example 2 was analyzed by X-ray diffraction technology. The results are as follows: Figure 4 As shown, there is no significant difference in the chromium-containing components of the nanocolloids prepared under pH = 5 and pH = 7, and they mainly include Cr2O3, Na2Cr2O7·2H2O and Na2Cr2O7.

[0064] It can be seen from the above examples that the present invention prepares the colloidal substance produced by the reaction of hexavalent chromium with humic acid in an aquatic environment, which is conducive to subsequent research and is of great significance for revealing the migration, transformation and toxicity of hexavalent chromium in the environment.

[0065] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing chromium-containing nano-colloids using humic acid, characterized in that: The following steps are involved: Dissolving humic acid and hexavalent chromium salt in water, adjusting the pH value, and obtaining a reaction solution; The reaction solution is continuously stirred under simulated natural light or natural light conditions to make the humic acid react with hexavalent chromium to form a colloid, and then filtered through an ultrafiltration membrane, dialyzed and freeze-dried to obtain a chromium-containing nano-colloid.

2. The method according to claim 1, characterized in that The simulated natural light is a xenon lamp solar simulator that simulates natural light with an irradiance of 500 W / m 2 .

3. The method according to claim 1, characterized in that The ultrafiltration membrane filtration comprises: filtering the feed liquid obtained after continuous stirring through a tangential flow ultrafiltration system composed of an ultrafiltration membrane package and a peristaltic pump.

4. The method according to claim 1, characterized in that: The hexavalent chromium salt is potassium dichromate.

5. The method according to claim 1 or 4, characterized in that: The concentration of hexavalent chromium in the reaction solution is 80 μmol / L.

6. The method according to claim 1, characterized in that The concentration of humic acid in the reaction solution is 20 mg / L.

7. The method according to claim 1, characterized in that The pH value is adjusted to 5-7.

8. The method according to claim 1, 2 or 6, characterized in that: The continuous stirring time is 10 hours.

9. The method according to claim 1, characterized in that: The freeze drying comprises: pre-freezing at -80°C for 4 hours and then placing at -50°C for vacuum freeze drying for 8 hours.

10. The method according to claim 1, characterized in that The molecular weight cut-off of the dialysis bag used for the dialysis is 3500Da.

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