Preparation method and application of hexavalent chromium treating agent based on nanoscale zero-valent iron

Abstract

The invention discloses a preparation method and application of a hexavalent chromium treating agent based on nanoscale zero-valent iron, and relates to the technical field of hexavalent chromium treating agents. The key points of the technical scheme are as follows: nanoscale zero-valent iron (mFe0) prepared by using a macro preparation technology is firstly subjected to weak acid etching modification treatment; the preparation method comprises the following steps: preparing a kaolin-loaded nano zero-valent iron-copper (Ko-cFe0 / cCu0) material from nano zero-valent iron (cFe0), carrying out modification treatment on the nano zero-valent iron-copper (cFe0) loaded by a chemical reduction method to prepare a nano zero-valent iron-copper (mFe0 / cCu0) material, and finally carrying out modification treatment on nano zero-valent iron (cFe0) loaded kaolin (Kaco-cFe0 / cCu0) prepared by a chemical reduction method, which is almost equivalent and has a better loading effect, to prepare the kaolin-loaded nano zero-valent iron-copper (Kaco-cFe0 / cCu0) material, and preparing the kaolin-loaded nano zero-valent iron-copper (Kaco-cFe0 / cCu0) material. A material for removing Cr (VI) in water is successfully developed, and the problems that nano zero-valent iron is low in degradation efficiency, poor in stability, serious in agglomeration phenomenon and the like are gradually solved.

Description

Technical Field

[0001] The present invention relates to the technical field of hexavalent chromium treatment agents, and more particularly to a preparation method and application of a hexavalent chromium treatment agent based on nanometer zero-valent iron. Background Art

[0002] With the rapid development of industrialization, heavy metal pollution has become a global environmental problem, posing a serious threat to ecosystems and human health. Hexavalent chromium (Cr(VI)) has attracted considerable attention due to its high toxicity, easy migration, and carcinogenicity. Chromium and its compounds are widely used in industries such as electroplating, leather making, and printing and dyeing. Wastewater discharged from these industries is the primary source of Cr(VI) in the environment. While traditional Cr(VI) treatment methods, such as chemical reduction precipitation, adsorption, and ion exchange, have achieved some success, they still suffer from low treatment efficiency and a high risk of secondary pollution.

[0003] In recent years, nano-zero-valent iron, as a new type of environmental remediation material, has shown great application potential in the field of heavy metal pollution control due to its advantages such as large specific surface area, high reactivity, strong reducing ability and low environmental impact. Nano-zero-valent iron can reduce highly toxic and highly mobile Cr(VI) to low-toxic and poorly mobile trivalent chromium (Cr(III)), and fix it through co-precipitation, thereby achieving efficient degradation and removal of Cr(VI). However, nano-zero-valent iron still faces prominent problems such as easy agglomeration and easy oxidation deactivation in practical applications, which limits its large-scale application. In addition, although existing modification technologies (such as surface modification, loading materials, bimetallic doping, etc.) can improve the performance of nano-zero-valent iron, their process complexity and cost issues limit its application in actual production. Finally, the behavior of nano-zero-valent iron in the environment and its potential ecotoxicity have not been fully clarified, which also poses an obstacle to its large-scale application.

[0004] Therefore, developing low-cost and efficient nano-zero-valent iron preparation and modification technologies to solve its mass production problems has important scientific significance and practical application value. Summary of the Invention

[0005] The present invention aims to provide a method for preparing a hexavalent chromium treatment agent based on nano-zero-valent iron and its application. Through green synthesis, low-cost modification techniques, or the development of novel composite materials, the present invention aims to overcome key bottlenecks in the mass production of nano-zero-valent iron and provide technical support for its large-scale application in Cr(VI) pollution remediation. This invention helps reduce the production cost of nano-zero-valent iron, improve its stability and environmental safety, and promote its widespread application in industrial wastewater treatment, groundwater remediation, and other fields.

[0006] The above technical purpose of the present invention is achieved through the following technical solutions: a hexavalent chromium treatment agent based on nano zero-valent iron, wherein the hexavalent chromium treatment agent is Kao-cFe 0 / cCu 0 .

[0007] The present invention further provides a method for preparing a hexavalent chromium treatment agent:

[0008] mFe 0 Modification treatment: 0.5g mFe 0 The powder and 50 mL of 1.5% acetic acid solution were added to a conical flask. The constant temperature water bath was set to 25°C and the stirring frequency of the mechanical stirrer was 500 r / min. After reacting for 15 minutes, the suspension in the conical flask was poured into a suction filtration device and filtered through a water filter membrane. After the solution was filtered, it was washed three times with anhydrous ethanol and stirred appropriately in the device to remove residual acetic acid. After the filtration and washing, the powder on the filter membrane was placed in a petri dish and left to dry at room temperature for 5-10 minutes to remove residual anhydrous ethanol.

[0009] Material mFe 0 / cCu 0 Preparation: At room temperature, 0.268g CuCl2·H2O was prepared into 160mL of aqueous solution and 0.5g mFe 0 The powders are added to a three-necked flask, and about 0.38g of NaBH4 is configured into a 100mL NaBH4 aqueous solution and added to a constant pressure separatory funnel; after the powders and the solution are added, the reaction device is assembled, N2 is passed into the three-necked flask at a flow rate of 50mg / min, the rotation rate of the mechanical stirring paddle is 800r / min, and the NaBH4 solution is controlled to drip at a rate of 1-2 drops per second until it is completely dripped and then the device is stopped 5 minutes after it is completely dripped to ensure complete reaction; the solution in the three-necked flask is then poured into a suction filtration device, and filtered with the help of a water filter membrane. After the solution is filtered, it is washed three times with anhydrous ethanol and stirred appropriately to remove residual solutes; after the filtration and cleaning are completed, it is placed in a vacuum drying oven and dried and stored under low vacuum and 60°C for 10h, and finally a mass ratio of mFe is formed. 0 :cCu 0 =5:1mFe 0 / cCu 0 Material;

[0010] Kao-cFe 0 / cCu 0Preparation: At room temperature, 0.484g FeCl3·6H2O and 0.054g CuCl2·H2O are prepared into 160mL of aqueous solution, and added into a three-necked flask together with 0.5g Kao powder, and about 0.306g NaBH4 is prepared into 100mL of aqueous solution and added into a constant pressure separatory funnel; after the powder and solution are added, the reaction device is assembled, the flow rate of N2 is 50mg / min, the rotation rate of the mechanical stirring paddle is 800r / min, and the NaBH4 solution is dripped at a rate of 1-2 drops per second until it is completely dripped and then the reaction device is stopped 5 minutes after it is completely dripped to ensure complete reaction; then the solution in the three-necked flask is poured into a suction filtration device for suction filtration, and after the solution is filtered, it is washed three times with anhydrous ethanol and stirred appropriately to remove residual solutes. After the suction filtration and cleaning are completed, it is placed in a vacuum drying oven, vacuumed, dried and stored at 60°C for 10 hours to obtain Kao-cFe 0 / cCu 0 .

[0011] The present invention further provides application of a hexavalent chromium treatment agent in treating Cr(VI) in wastewater.

[0012] In summary, the present invention has the following beneficial effects:

[0013] mFe after weak acid etching 0 Significantly improved the degradation effect of Cr(VI), and the adsorption amount was increased from directly using mFe 0 0.399mg / g increased to 6.334mg / g; mFe 0 / cCu 0 Composite materials with cCu 0 The electron transfer path is changed, the potential barrier is lowered, the degradation efficiency is further improved, and the oxidation resistance of the material is significantly improved. 0 component, the adsorption capacity reaches 40.00 mg / g; Kao-cFe 0 / cCu 0 The composite material successfully solved the cFe 0 Agglomeration problem, significantly improved the utilization rate and degradation effect of materials, for cFe 0 The adsorption capacity was further increased to 117.81 mg / g. Adsorption isotherms, adsorption kinetics, and thermodynamic analysis determined the material's adsorption behavior and mechanism, demonstrating that the adsorption process conforms to the Langmuir and pseudo-second-order kinetic models and is primarily controlled by chemical adsorption. X-ray photoelectron spectroscopy was also used to analyze the surface changes before and after the reaction. This research provides new ideas, theoretical foundations, and technical support for the industrial mass production and large-scale application of nano-zero-valent iron in the remediation of Cr(VI) pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The mFe 0 Etching operation process;

[0015] Figure 2 The material mFe in the present invention 0 / cCu 0 Preparation flow chart of

[0016] Figure 3 The material Kao-cFe in the present invention 0 / cCu 0 Preparation flow chart of

[0017] Figure 4 (a) is the SEM image of Kao; (b) is the SEM image of Kao-cFe 0 20 / cCu 0 SEM image of 4;

[0018] Figure 5 (a)(b)(c)Kao-cFe 0 20 / cCu 0 TEM image of 4; (d) Energy spectrum of Cu; (e) Energy spectrum of Fe; (f) Energy spectrum of Al; (g) Energy spectrum of O; (h) Energy spectrum of Si;

[0019] Figure 6 (a) Kao-mFe 0 / cCu 0 TEM image; (b) Energy spectrum of Fe; (c) Energy spectrum of Cu; (d) Energy spectrum of O; (e) Energy spectrum of Si; (f) Energy spectrum of Al;

[0020] Figure 7 (a) Adsorption-desorption curve of Kao; (b) Kao-cFe 0 20 / cCu 0 Adsorption-desorption curve of 4;

[0021] Figure 8 The cFe in the present invention 0 XRD data diagram of

[0022] Figure 9 Kao-cFe in the present invention 0 20 / cCu 0 XRD data of 4;

[0023] Figure 10 Kao-cFe in the present invention 0 20 / cCu 0 4 hysteresis loop data diagram;

[0024] Figure 11 Kao-cFe in the present invention 0 20 / cCu 0 4 Schematic diagram of morphology;

[0025] Figure 12 This is a comparison chart of the effects of different materials in the present invention on removing Cr(VI);

[0026] Figure 13 The different Kao-cFe in the present invention 0 20 / cCu 0 4. The effect of dosage on removal effect;

[0027] Figure 14 (a) Effect of different initial Cr(VI) concentrations on Kao-cFe 0 20 / cCu 0 4. The influence of the removal effect; (b) Normalized image;

[0028] Figure 15 (a) Effect of different dispersion levels on Kao-cFe 0 20 / cCu 0 4. The influence of the removal effect; (b) Normalized image;

[0029] Figure 16 The different pH values ​​of the solution in the present invention affect the Kao-cFe 0 20 / cCu 0 4. The impact of removal effect;

[0030] Figure 17 The different reaction temperatures in the present invention have an effect on the Kao-cFe 0 20 / cCu 0 4. The impact of removal effect;

[0031] Figure 18 The different Kao-cFe in the present invention 0 20 / cCu 0 4. The effect of oxidation time on removal effect;

[0032] Figure 19 (a) Different Kao-cFe 0 High School Entrance Examination and CEIBS 0 Scale diagram; (b) different Kao-cFe 0 Removal effect diagram;

[0033] Figure 20 (a) Different Kao-cFe 0 / cCu 0 High School Entrance Examination, CE 0 and cCu 0Scale diagram; (b) different Kao-cFe 0 / cCu 0 Removal effect diagram. DETAILED DESCRIPTION

[0034] The following is combined with Figure 1-20 The present invention is described in further detail.

[0035] The main experimental materials and reagents used in the examples of the present invention are as follows:

[0036]

[0037] The main experimental instruments and devices used in the embodiments of the present invention are as follows:

[0038]

[0039] Example 1: Preparation method of hexavalent chromium treatment agent based on nano-zero-valent iron

[0040] mFe 0 Modification treatment: 0.5g mFe 0 Add the powder and 50 mL of 1.5% acetic acid solution to a conical flask. Set the constant temperature water bath to 25°C and the mechanical stirrer to 500 rpm. After 15 minutes of reaction, pour the suspension in the conical flask into a suction filtration device and filter it through a water-based filter membrane. After the solution is filtered, add anhydrous ethanol and rinse three times with appropriate stirring in the device to remove residual acetic acid. After the filtration and cleaning is completed, place the powder on the filter membrane in a petri dish and let it dry at room temperature for 5-10 minutes to remove residual anhydrous ethanol.

[0041] Through the mFe 0 Weak acid etching is performed and used to degrade Cr(VI) in aqueous solution. 0 SEM, TEM, XRD, BET, VSM and XPS characterization tests and analyses were carried out to explore the effects of different factors on the degradation of Cr(VI) by the material. At the same time, the adsorption isotherm, adsorption kinetics and adsorption thermodynamics of the degradation process were explored to determine the mFe 0 The adsorption behavior and adsorption mechanism of . The following conclusions can be drawn:

[0042] (1)mFe 0 It is a spherical particle with uniform particle size, good crystallinity, and a core-shell structure. The outer shell is ferroferric oxide, which can protect the Fe 0 However, it also makes the degradation effect extremely poor, and it is a soft magnetic material, so the agglomeration phenomenon is serious.

[0043] (2) 0.5g mFe 0The best etching time is 15 min in 1.5% weak acid solution. The stability after etching is poor and it is easy to oxidize. Low pH value and high temperature make degradation reaction easy to proceed. Under the conditions of initial pH=7 and reaction temperature of 25℃, mFe 0 The adsorption capacity of Cr(VI) increased from 0.399 mg / g to 6.334 mg / g when used directly.

[0044] (3) mFe after etching 0 The degradation process of Cr(VI) conforms to the Langmuir model and the pseudo-second-order kinetic model, is an endothermic process, and is spontaneous, mainly based on chemical adsorption; mFe 0 Fe 0 Cr(VI) is reduced to Cr(III) and precipitated, and then dried to form oxides. 0 Mainly oxidized to Fe3+.

[0045] Material mFe 0 / cCu 0 Preparation: At room temperature, 0.268g CuCl2·H2O was prepared into 160mL of aqueous solution and 0.5g mFe 0 Add the powder into the three-necked flask, and add about 0.38g NaBH4 into 100mL NaBH4 aqueous solution into the constant pressure separatory funnel; after the powder and solution are added, assemble as shown Figure 2 In the reaction apparatus of step 2, N2 was passed into the three-necked flask at a flow rate of 50 mg / min, the rotation rate of the mechanical stirring paddle was 800 r / min, and the NaBH4 solution was controlled to drip at a rate of 1-2 drops per second. The apparatus was stopped 5 minutes after the solution was completely dripped to ensure complete reaction.

[0046] Then pour the solution in the three-necked flask into the filtration device and filter it with the help of a water filter membrane. After the solution is filtered, add anhydrous ethanol to wash it three times and stir it properly to remove the residual solute. After the filtration and cleaning is completed, put it into a vacuum drying oven and dry it at 60℃ for 10 hours. The final mass ratio of mFe 0 :cCu 0 =5:1mFe 0 / cCu 0 Material.

[0047] mFe was chemically reduced using NaBH4 0 Load cCu 0 particles, and finally prepared to form mFe 0 / cCu 0 , and used to degrade Cr(VI) in aqueous solution. 0SEM, TEM, XRD, BET, VSM and XPS characterization and analysis were carried out to explore the influence of different factors on the degradation of Cr(VI) by the material. By exploring the adsorption isotherm, adsorption kinetics and adsorption thermodynamics of the degradation process, the mFe 0 / cCu 0 The adsorption behavior and adsorption mechanism of . The following conclusions can be drawn:

[0048] (1) Material mFe 0 / cCu 0 , is in mFe 0 Surface loading of some cCu 0 particles, and evenly distributed, cCu 0 There is only a slight Cu2O oxide layer on the particle surface. 0 The soft magnetic properties of the material are still serious.

[0049] (2)mFe 0 Formation of mFe on the load 0 / cCu 0 After that, the antioxidant capacity is greatly enhanced, and the degradation reaction is easy to proceed at low pH and high temperature; under the conditions of initial pH=7 and reaction temperature of 25℃, by loading cCu 0 Form a bimetallic system to modify mFe 0 The adsorption capacity of Cr(VI) increased from 6.334 mg / g after acid etching to 40.00 mg / g.

[0050] (3)mFe 0 / cCu 0 The degradation process of Cr(VI) conforms to the Langmuir model and the pseudo-second-order kinetic model, is an endothermic process, and is spontaneous, mainly based on chemical adsorption; mFe 0 / cCu 0 Mainly through cCu 0 Fe 0 The electron transfer between the reaction with Cr(VI) greatly improves the degradation efficiency.

[0051] Kao-cFe 0 / cCu 0 Preparation: In the subsequent characterization analysis and analysis of most degradation influencing factors, Kao-cFe 0 20 / cCu 0 4 as an example for analysis, the meaning of the numbers in the material name is based on Kao as a reference, the cFe contained in the composite material 0 The mass is 20% of Kao, containing cCu 0 The mass of Kao is 4% of Kao. Kao-cFe 020 / cCu 0 The preparation process of 4 is as follows.

[0052] At room temperature, 0.484g FeCl3·6H2O and 0.054g CuCl2·H2O were prepared into 160mL of aqueous solution, and added together with 0.5g Kao powder into a three-necked flask. About 0.306g NaBH4 was prepared into 100mL of aqueous solution and added into a constant pressure separatory funnel. After the powder and solution were added, assemble as shown in the following figure. Figure 3 In the reaction apparatus of step 2, the flow rate of N2 is 50 mg / min, the rotation rate of the mechanical stirring paddle is 800 r / min, and the NaBH4 solution is dripped at a rate of 1-2 drops per second. The reaction apparatus is stopped 5 minutes after the solution is completely dripped to ensure complete reaction.

[0053] The solution in the three-necked flask was then poured into a suction filtration device for filtration. After the solution was filtered, it was washed three times with anhydrous ethanol and stirred appropriately to remove residual solutes. After filtration and washing, it was placed in a vacuum drying oven, vacuumed, and dried at 60°C for 10 hours.

[0054] Example 2: Structural Characterization of Hexavalent Chromium Treatment Agent

[0055] Figure 4 The SEM image of Kao shows that it has a lamellar structure with a large surface area and can be used for Fe 0 The particles provide numerous attachment sites. Figure 4 It is Kao-cFe 0 20 / cCu 0 From the SEM image of Figure 4, we can see that there are roughly two types of particles. One type has a larger particle size of about 100nm, and the other has a very small particle size. The two types of particles are well attached and dispersed, and almost all of them are attached to the surface of Kao, and the agglomeration problem is effectively solved. At the same time, we can also see that both particles are spherical.

[0056] Figure 5 It is Kao-cFe 0 / cCu 0 TEM image and energy spectrum. It can be seen from the energy spectrum that the large particles correspond to the area where the Fe element is distributed, namely cFe 0 , small particles correspond to the area where Cu element is distributed, namely cCu 0 ;from Figure 5 cFe 0 Particles and mFe 0 The particles also have obvious core-shell structure. From the energy spectrum, we can see that in addition to Fe and Cu elements, Kao-cFe 0 / cCu 0It also contains Al, Si, and O elements. Al and Si elements come from Kao (the main chemical composition is Al2[(OH)4 / Si2O5]). In addition to being distributed in the locations where Al, Si, and Fe elements exist, O element is also distributed in the locations far away from cFe. 0 The location of Cu element in the particles is also distributed, which shows that cFe 0 Particles and cCu 0 The particle loading is good, on the other hand, it shows that cFe 0 There is an oxide layer on the surface, and at the same time, there is no oxide layer attached to the cFe 0 cCu on the surface 0 Significant oxidation of the particles also occurs.

[0057] Figure 6 It’s Kao-mFe 0 / cCu 0 TEM image, we can see mFe 0 Particles and cCu 0 The particles can achieve loading to a certain extent, but the overall loading effect is not good, the loading efficiency is low, only part of the material can achieve loading, a large number of Kao and mFe 0 / cCu 0 Independent existence, so the research object was changed to Kao-cFe 0 / cCu 0 , and explore the corresponding 0 / cCu 0 Based on this, load it onto the material effect on Kao.

[0058] According to BET analysis, the specific surface area of ​​Kao is 18.4137m 2 / g, Kao-cFe 0 20 / cCu 0 The specific surface area of ​​4 is 24.6585m 2 / g, if mFe 0 / cCu 0 With cFe 0 / cCu 0 The specific surface area of ​​mFe 0 / cCu 0 The specific surface area is 30.0111m 2 / g, so it can well explain Kao-cFe 0 20 / cCu 0 The specific surface area of ​​4 is between Kao and mFe 0 / cCu 0 At the same time, it also indirectly shows that the material loading effect is good.

[0059] Figure 7 where a and b are Kao and Kao-cFe respectively 0 20 / cCu 0 The adsorption-desorption curves of 4 are not typical isotherms and hysteresis loops. They can be roughly regarded as type IV isotherms and H3 hysteresis loops, but are close to non-porous type II isotherms. Kao is mainly due to the accumulation of particles in the lamellar structure of Kao, which will produce slit-shaped mesopores. Kao-cFe 0 20 / cCu 0 4 Mainly due to Kao, cFe 0 、cCu 0 The mesopores of various shapes are formed by the mutual extrusion of the three, and of course there are also Kao surface defects and cFe 0 Surface oxide layer defects, even isolated cCu 0 The defects of the surface oxide layer lead to capillary condensation, which eventually produces a weak hysteresis loop. This indirectly shows that the Kao surface can provide many attachment points and Kao-cFe 0 20 / cCu 0 4 Well loaded - particles are embedded between the lamellar structure of Kao.

[0060] From Kao-cFe 0 20 / cCu 0 4 XRD Figure 9 It can be seen that the peaks at 12.362° and 24.872° correspond to the (001) and (002) directions of Kao, respectively, and the peaks at 43.341° and 36.520° correspond to the (111) direction of copper and the (111) direction of Cu2O, respectively. Although the mass ratio of copper added during preparation is very low, the Cu2O peak is very obvious. 0 The proportion of direct loading on the Kao surface or independent existence is not low, resulting in obvious oxidation products. In the XRD pattern, the peak corresponding to iron is almost invisible, so the Fe 0 The XRD test analysis of the particles, the test results are as follows Figure 8 .

[0061] from Figure 8 It can be seen that cFe prepared by chemical reduction using NaBH4 0 The crystallinity is very poor, and only a very short and wide peak of 44.662° can be seen, which corresponds to the (001) crystal orientation of iron and is similar to that of mFe 0 The peaks in the XRD patterns of cFe 0 The iron in the particles is amorphous. Therefore, cFe is loaded on Kao 0After the particles are formed, the base of the XRD image increases, and the proportion of iron in the overall material is small, and the characteristic peak height is very low, so it is impossible to Figure 9 Find the characteristic peaks corresponding to elemental iron and possible iron oxides.

[0062] from Figure 10 Kao-cFe can be obtained 0 20 / cCu 0 The coercivity H of 4 C =168.044Oe, residual magnetization M r =3.012emu / g, saturation magnetization M s =22.883emu / g, and mFe 0 and mFe 0 / cCu 0 Compared with the two materials, under the dilution of Kao, the material is much less affected by the magnetic field, and cFe 0 It relies on chemical bonds to tightly adhere to the Kao surface, which significantly reduces the agglomeration phenomenon.

[0063] Example 3: Comparison of Cr(VI) removal effects of different materials

[0064] Through Kao, cFe 0 、cCu 0 、Kao-cFe 0 20. cFe 0 / cCu 0 20 (20 represents cCu 0 Mass is cFe 0 20%), Kao-cFe 0 20 / cCu 0 4 Comparative study of the removal effect of Cr(VI) by six materials to determine the source and reason for the improvement of material removal effect. 0 or cCu 0 The materials were prepared using the same preparation device and method as above, with only the dosage of the reaction solutes FeCl3·6H2O, CuCl2·2H2O and the reducing agent NaBH4 being changed. The dosages of 1g / L Kao, 0.2g / L cFe 0 、0.04g / L cCu 0 、1.2g / LKao-cFe 0 20, 0.24g / L cFe 0 / cCu 0 20, 1.24g / L Kao-cFe 0 20 / cCu 04. Degrade 20mg / LCr(VI) solution at 25℃ and pH=7 to ensure that the basic components Kao and cFe in various materials with different addition amounts are 0 、cCu 0 The usage is consistent, and the degradation is as follows Figure 12 .

[0065] As can be seen from the figure, a simple Kao or cCu 0 The degradation rates of Kao were 12.84% and 9.89% respectively. The low degradation rate of Kao is mainly due to its physical adsorption of Cr(VI). Although Cr(VI) can be adsorbed on the surface of Kao in solution, during the process of sampling and placing it into the colorimetric tube, it will be filtered through a syringe with a filter head, and most of the Cr(VI) attached to the surface will be detached from the surface. 0 The low degradation rate is because it will be quickly oxidized to produce an oxide shell after preparation, isolating the internal Cu 0 atoms react with Cr(VI). But cFe 0 The removal effect is more obvious, which is 41.65%.

[0066] At the same time, cFe 0 Load Kao or cFe 0 Load cCu 0 Compared with simple cFe 0 Compared with the previous ones, the effects are obviously improved. The material Kao-cFe 0 and cFe 0 / cCu 0 The degradation rates of Kao and cCu were 61.66% and 58.22% respectively. 0 Both cFe 0 The removal effect of cFe is improved. 0 Disperse, solve the agglomeration problem to a large extent, and expose the surface active sites that can participate in the degradation reaction as much as possible; for pure cFe 0 Compared with most Fe 0 The atomic electrons overcome the potential barrier of the oxide layer and transfer to Cr(VI). 0 It can serve as an intermediate bridge between the two reactions, providing a path with lower barriers, faster and more efficient.

[0067] In Kao and cCu 0 Both with cFe 0 After loading together, the material formed is the best, that is, cFe 0The degradation effect and utilization rate of the Cr(VI) were maximized, with a degradation rate of 96.07%. The final material has both of the above advantages and has the best degradation effect on Cr(VI).

[0068] Example 4: Effect of different parameters on Kao-cFe 0 / cCu 0 Effect of Cr(VI) removal

[0069] 1. The influence of different material dosage

[0070] Through a large number of repeated experiments with controlled variables, Kao-cFe 0 / cCu 0 Effect of different dosage on the degradation of Cr(VI). 0 20 / cCu 0 4. The dosages were 0.4 g / L, 1 g / L, 2 g / L, 3 g / L, and 8 g / L, respectively. The initial solution concentration of Cr(VI) was 20 mg / L, pH = 7, the temperature was 25 °C, and the rotation speed of the mechanical stirring paddle was 500 r / min.

[0071] from Figure 13 It can be seen that with the increase of Kao-cFe 0 20 / cCu 0 4. With the increase of dosage, the degradation rate of Cr(VI) gradually increased, and the initial degradation rate gradually increased. When the dosage was ≥1g / L, Cr(VI) was completely degraded, and Kao-cFe 0 20 / cCu 0 4. Excessive dosage. This is because as the dosage increases, Cr(VI) and Kao-cFe 0 20 / cCu 0 4 increases the contact area and the number of active sites that can participate in the reaction. From the perspective of initial reaction rate, the larger the dosage, the better. However, from the perspective of 2h degradation rate and Kao-cFe 0 20 / cCu 0 4. Taking into account the full utilization of the angle, for 20mg / L Cr(VI) solution, the present invention selects 1g / L as the best dosage, the degradation rate is 95.01%, relative to the whole material, the adsorption capacity is 19.00mg / g, but relative to the real removal effect of mFe 0 For example, the adsorption capacity is 117.81 mg / g.

[0072] 2. Effect of different initial solution concentrations

[0073] The effects of different initial concentrations of Cr(VI) on the degradation effect were studied by repeated experiments with controlled variables. 0 20 / cCu 0 4. The dosage is 1 g / L, the initial solution concentrations of Cr(VI) are 5 mg / L, 10 mg / L, 15 mg / L, 20 mg / L, and 25 mg / L, respectively; the pH is 7; the temperature is 25°C; and the rotation speed of the mechanical stirring paddle is 500 r / min.

[0074] from Figure 14 As can be seen from Figure b, with the increase of the initial solution concentration of Cr(VI), the degradation rate of Cr(VI) gradually decreases, and the initial relative degradation rate gradually decreases. When the initial concentration of Cr(VI) solution is ≤20 mg / L, Cr(VI) is completely degraded, and Kao-cFe 0 20 / cCu 0 The dosage of 4 is excessive. This is because as the initial solution concentration of Cr(VI) increases, the amount of Cr(VI) per unit volume increases, but at the same time, Kao-cFe 0 20 / cCu 0 The dosage of 4 remains unchanged, and the active sites that can participate in the reaction are constant, so Kao-cFe 0 20 / cCu 0 The absolute degradation rate and adsorption amount of 4 are constant, and the relative degradation rate and degradation rate of Cr(VI) per unit volume decrease. From the perspective of initial reaction rate, the lower the initial solution concentration of Cr(VI), the better. However, from the perspective of 2h degradation rate and adsorption of Kao-cFe 0 / cCu 0 Taking into comprehensive consideration the full utilization of the Cr(VI) solution, for a dosage of 1 g / L, the present invention selects an initial Cr(VI) solution concentration of 20 mg / L as the best.

[0075] 3. Impact of different degrees of dispersion

[0076] Through a large number of repeated experiments with controlled variables, the effects of different dispersion levels of solutes in the reaction solution on the degradation effect were studied. 0 20 / cCu 0 4. The dosages are 0.25g / L, 0.5g / L, 0.75g / L, 1g / L, 1.25g / L, and the corresponding initial solution concentrations of Cr(VI) are 5mg / L, 10mg / L, 15mg / L, 20mg / L, 25mg / L, maintaining the unit volume of Kao-cFe 0 20 / cCu 0The ratio of the amount of 4 and Cr(VI) remained unchanged, the pH was 7, the temperature was 25°C, and the rotation speed of the mechanical stirring blade was 500 r / min.

[0077] from Figure 15 As can be seen from Figure b, as the dispersion of the reaction solution gradually increases (in the figure, the initial solution concentration of Cr(VI) decreases), the degradation rate of Cr(VI) gradually decreases, and the initial relative degradation rate gradually decreases. When the dosage is ≥20 mg / L, Cr(VI) is completely degraded, and Kao-cFe 0 20 / cCu 0 4. Excessive dosage. This is because the solute Cr(VI) and Kao-cFe in the reaction solution 0 20 / cCu 0 4. The dispersion of Cr(VI) ions and Kao-cFe 0 20 / cCu 0 4. The number of particles decreases. Under the condition of stirring reaction, the probability of the two encountering, adsorbing and reacting is reduced, and the absolute degradation rate of the system slows down. Finally, in the same time, for the same amount of substance, the degradation rate of Cr(VI) and Kao-cFe 0 20 / cCu 0 4, the dispersion becomes larger, that is, the volume of the reaction solution becomes larger, mFe 0 The relative degradation rate and degradation rate of Cr(VI) are reduced. In summary, for the degradation system, within a certain range, the dispersion degree should be reduced as much as possible.

[0078] 4. Effect of different pH values ​​of the solution

[0079] The effects of different initial pH values ​​of the reaction solution on the degradation effect were studied by repeated experiments with controlled variables. 0 20 / cCu 0 4. The dosage was 1 g / L, the corresponding initial solution concentration of Cr(VI) was 20 mg / L, the pH of the reaction solution was adjusted to 3, 5, 7, 9, and 11 with sulfuric acid solution and sodium hydroxide solution, the temperature was 25°C, and the rotation speed of the mechanical stirring paddle was 500 r / min.

[0080] from Figure 16 It can be seen that as the initial pH value of the reaction solution decreases, the degradation rate of Cr(VI) gradually increases, and the initial degradation rate gradually increases. When the pH is ≤ 5, Cr(VI) is completely degraded, and Kao-cFe 0 20 / cCu 0 4. Excessive dosage. Since Cr(VI) exists in two forms: CrO4 2– and Cr2O72– , under acidic conditions, a large amount of CrO4 2– Converted to Cr2O7 2– , and CrO4 2– Relatively stable, Cr2O7 2– It has strong oxidizing properties and is also related to Kao-cFe 0 20 / cCu 0 4 The main form of the reaction. At the same time, H + It can also effectively inhibit the Fe generated after surface reaction 2+ or Fe 3+ The formation of precipitates or oxides hinders the further progress of the reaction. Therefore, as the initial pH value of the reaction solution decreases, H + The concentration of CrO4 increases exponentially. 2– A large amount of conversion is easily converted into Kao-cFe 0 20 / cCu 0 4 Reduced Cr2O7 2– , so the degradation rate and degradation rate are significantly increased. From the perspective of initial degradation rate and degradation rate, the smaller the initial pH value of the reaction solution, the better.

[0081] 5. Effect of different reaction temperatures

[0082] The effects of different reaction temperatures on the degradation effect were studied by repeated experiments with controlled variables. 0 20 / cCu 0 4. The dosage was 1 g / L, the corresponding initial solution concentration of Cr(VI) was 20 mg / L, pH = 7, the temperatures in the constant temperature culture oscillator were set to 15°C, 25°C, 35°C, 45°C, and 55°C, and the oscillation frequency was set to 200 r / min.

[0083] from Figure 17 It can be seen that with the increase of reaction temperature, the degradation rate of Cr(VI) gradually increases, and the initial degradation rate gradually increases. When the temperature is ≥45℃, Cr(VI) is completely degraded, and Kao-cFe 0 20 / cCu 0 4. Excessive dosage. According to the Arrhenius equation, when other conditions remain unchanged, the reaction rate constant increases significantly with the increase of temperature. At the same time, when the dosage does not fully exert its effect within a certain period of time, the degradation rate increases. 0 20 / cCu 0 From the utilization point of view of 4, the higher the temperature of the reaction solution, the better.

[0084] 6. Effect of different oxidation times

[0085] Through a large number of repeated experiments with controlled variables, Kao-cFe 0 20 / cCu 0 4. The effect of different oxidation times on the degradation effect under room temperature. 0 20 / cCu 0 4 After vacuum drying and storage in a vacuum drying oven, the samples were placed in a constant temperature incubator at 25°C without shaking for 0 h, 6 h, 12 h, 24 h, and 48 h, and then subjected to degradation reaction. The dosage was 1 g / L, and the corresponding initial solution concentration of Cr(VI) was 20 mg / L, pH = 7, temperature was 25°C, and the rotation speed of the mechanical stirring paddle was 500 r / min.

[0086] from Figure 18 It can be seen that with the increase of Kao-cFe 0 20 / cCu 0 4. The oxidation time in 25℃ environment becomes longer, and the degradation rate and degradation rate of Cr(VI) are almost unchanged. This is because during the low vacuum drying and storage process after the sample preparation, cFe 0 and cCu 0 The oxidation degree has been stabilized, and the oxidation effect of the environment on it during the degradation reaction can be ignored. 0 / cCu 0 After preparation, it has good stability, is almost unaffected by storage time, and can be stored for a long time.

[0087] 7.cFe 0 The impact of different load ratios Kao

[0088] Through a large number of repeated experiments with controlled variables, Kao-cFe 0 In cFe 0 Under the same usage amount, the effect of loading different proportions of Kao on the degradation effect was investigated. 0 and Kao-cFe with different Kao ratios 0 The ratios are 0.33:1, 0.5:1, 1:1, 2:1, 5:1, and 10:1 respectively. To ensure the addition of Kao-cFe 0 cFe 0 The usage amount is 0.2g / L, so the corresponding dosage is 0.266g / L, 0.3g / L, 0.4g / L, 0.6g / L, 1.2g / L, 2.2g / L, cFe 0The dosage is 0.2 g / L, the initial solution concentration of Cr(VI) is 20 mg / L, pH=7, the temperature is 25°C, and the rotation speed of the mechanical stirring paddle is 500 r / min.

[0089] from Figure 19 As can be seen from b, at the beginning, as the Kao ratio increases, the degradation rate and degradation rate increase, but after the ratio exceeds 5:1, the degradation rate and degradation rate decrease. This is because within a certain range, for cFe 0 As the proportion of doped Kao increases, the proportion of particles attached to the surface of Kao increases, thereby gradually reducing the cFe 0 The agglomeration of particles can make the agglomerated cFe 0 The particles expose more active sites and eventually behave as Kao-cFe 0 Within a certain range, as the ratio increases, the degradation effect becomes better.

[0090] But when the proportion of Kao exceeds a certain limit, too much Kao will cover cFe 0 The surface of the particles makes cFe 0 Almost completely surrounded by Kao, it is isolated from the external solution system, which not only reduces the number of exposed active sites, but also cuts off the possibility of some active sites contacting Cr(VI), thus reducing the number of active sites that can participate in the reaction. At the same time, Kao, as an insulator, will hinder the cFe 0 The electron transfer between Cr(VI) and Kao itself has a certain adsorption capacity, which may be related to cFe 0 There is a certain competition between the adsorption of Cr(VI). Therefore, the above reasons lead to the 0 When the ratio exceeds 5:1, the degradation effect is significantly reduced.

[0091] 8. Different cCu 0 Effect of load

[0092] Through a large number of repeated experiments with controlled variables, Kao-cFe 0 / cCu 0 Load different usage of cCu 0 Effect on degradation effect. Kao-cFe was prepared 0 20 and different proportions of cCu 0 Kao-cFe 0 / cCu 0 , Kao is 100 parts, Fe is 20 parts, Cu is 2 parts, 4 parts, 10 parts, 20 parts respectively, in order to ensure the addition of Kao-cFe 0 / cCu 0 Kao and cFe in0 The usage of Kao-cFe is unchanged, and the sum of the two is 1g / L, so the dosage is 1.017g / L, 1.033g / L, 1.083g / L, 1.167g / L respectively. 0 The dosage of 20 was 1 g / L, the corresponding initial solution concentration of Cr(VI) was 20 mg / L, pH was 7, the temperature was 25°C, and the rotation speed of the mechanical stirring blade was 500 r / min.

[0093] from Figure 20 As can be seen from b, for Kao-cFe 0 , although the load cCu 0 The ratio of cCu is different, but the degradation effect is almost the same. 0 When the loading number is 4, the degradation effect will be better.

[0094] Assume cCu 0 The mass of is m, the unit is g, then cFe 0 The masses are m, 2m, 5m, 10m, and 100nm and 18nm respectively as cFe 0 and cCu 0 The total surface area is calculated based on the particle diameter in units of 10-3cm 3 / nm, it was found that compared with 10:1, 2:1, and 1:1, at a ratio of 5:1, cFe 0 The surface area of ​​the particles is similar to that of cCu 0 The surface area of ​​cFe is the closest. 0 and cCu 0 The usage ratio of 5:1 is slightly better than other ratios, which may be because when the surface areas of the two are similar, the reaction sites provided are similar, which is most conducive to the degradation reaction.

[0095] Fe 3+ and cCu 0 Kao-cFe was prepared by loading particles onto Kao 0 / cCu 0 , and used to degrade Cr(VI) in aqueous solution. 0 / cCu 0 SEM, TEM, XRD, BET, VSM and XPS characterization and analysis were carried out to explore the influence of different factors on the degradation of Cr(VI) by the material. By exploring the adsorption isotherm, adsorption kinetics and adsorption thermodynamics of the degradation process, the Kao-cFe 0 / cCu 0 The adsorption behavior and adsorption mechanism of . The following conclusions can be drawn:

[0096] (1)Kao-cFe 0 / cCu 0 The main body is a lamellar Kao, on the surface of which cFe is evenly attached. 0 Particles and cCu 0 Particles, especially cCu 0 More particles attached to cFe 0 Particle surface, cFe 0 particles and cCu directly attached to the Kao surface 0 The particles have an oxide layer.

[0097] (2)Kao-cFe 0 / cCu 0 The antioxidant capacity is very strong, low pH value, high temperature is easy to degrade; under the conditions of initial pH = 7, reaction temperature 25 ℃, with mFe 0 / cCu 0 mFe 0 In comparison, Kao-cFe 0 / cCu 0 Medium cFe 0 The adsorption capacity of Cr(VI) increased from 40.00 mg / g to 117.81 mg / L.

[0098] (3)Kao-cFe 0 / cCu 0 The degradation process of Cr(VI) conforms to the Langmuir model and the pseudo-second-order kinetic model, is an endothermic process, and is spontaneous, mainly based on chemical adsorption; Kao-cFe 0 / cCu 0 Mainly through the physical adsorption of Kao and cCu 0 Fe 0 The electron transfer between the atoms and the Cr(VI) reaction greatly improves the degradation efficiency.

[0099] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. After reading this specification, those skilled in the art may make non-creative modifications to this embodiment as needed. However, as long as such modifications are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. Hexavalent chromium treatment agent based on nano-zero-valent iron, characterized by: The hexavalent chromium treatment agent is mFe 0 、mFe 0 / cCu 0 or Kao-cFe 0 / cCu 0 ; The mFe 0 It is a spherical particle with uniform particle size, good crystallinity, and a core-shell structure. The outer shell is ferroferric oxide, which can protect the Fe 0 ; The mFe 0 / cCu 0 It is in mFe 0 Surface loading of some cCu 0 particles, and evenly distributed, cCu 0 There is only a slight Cu2O oxide layer on the particle surface. 0 The soft magnetic properties of the material are still serious. Kao-cFe 0 / cCu 0 The main body is a lamellar Kao, on the surface of which cFe is evenly attached. 0 Particles and cCu 0 Particles, especially cCu 0 More particles attached to cFe 0 Particle surface, cFe 0 particles and cCu directly attached to the Kao surface 0 The particles have an oxide layer.

2. The method for preparing a hexavalent chromium treatment agent based on nano-zero-valent iron according to claim 1, wherein: The mFe 0 Modification treatment: 0.5g mFe 0 The powder and 50 mL of 1.5% acetic acid solution were added to a conical flask. The constant temperature water bath was set to 25°C and the stirring frequency of the mechanical stirrer was 500 r / min. After reacting for 15 minutes, the suspension in the conical flask was poured into a suction filtration device and filtered through a water filter membrane. After the solution was filtered, it was washed three times with anhydrous ethanol and stirred appropriately in the device to remove residual acetic acid. After the filtration and washing, the powder on the filter membrane was placed in a petri dish and left to dry at room temperature for 5-10 minutes to remove residual anhydrous ethanol. The mFe 0 / cCu 0 Preparation: At room temperature, 0.268g CuCl2·H2O was prepared into 160mL of aqueous solution and 0.5gmFe 0 The powders were added to a three-necked flask, and about 0.38 g of NaBH4 was prepared into a 100 mL NaBH4 aqueous solution and added to a constant pressure separatory funnel; After the powder and solution are added, the reaction device is assembled, N2 is passed into the three-necked flask at a flow rate of 50 mg / min, the rotation rate of the mechanical stirring paddle is 800 r / min, and the NaBH4 solution is controlled to drip at a rate of 1-2 drops per second. The device is stopped 5 minutes after the dripping is complete to ensure complete reaction; then the solution in the three-necked flask is poured into the filtration device and filtered with the help of a water filter membrane. After the solution is filtered, it is washed three times with anhydrous ethanol and stirred appropriately to remove residual solutes; after the filtration and cleaning is completed, it is placed in a vacuum drying oven and dried and stored under low vacuum and 60°C for 10 hours to form a mass ratio of mFe 0 :cCu 0 =5:1mFe 0 / cCu 0 Material; Kao-cFe 0 / cCu 0 Preparation: At room temperature, 0.484 g FeCl3·6H2O and 0.054 g CuCl2·H2O were prepared into 160 mL of aqueous solution, and added together with 0.5 g Kao powder into a three-necked flask. Approximately 0.306 g NaBH4 was prepared into 100 mL of aqueous solution and added into a constant pressure separatory funnel. After the powder and solution are added, the reaction device is assembled, the flow rate of N2 is 50 mg / min, the rotation rate of the mechanical stirring paddle is 800 r / min, and the NaBH4 solution is dripped at a rate of 1-2 drops per second until it is completely dripped and then the reaction device is stopped 5 minutes after it is completely dripped to ensure complete reaction; then the solution in the three-necked flask is poured into the suction filtration device for suction filtration, and after the solution is filtered, it is washed three times with anhydrous ethanol and stirred appropriately to remove residual solutes. After the suction filtration and cleaning are completed, it is placed in a vacuum drying oven, vacuumed, and dried at 60°C for 10 hours to obtain Kao-cFe 0 / cCu 0 .

3. Use of the hexavalent chromium treatment agent based on nano-zero-valent iron according to claim 1 in treating Cr(VI) in wastewater.

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