Preparation and optimization method of Ce-based adsorbent for efficient removal of Cr(VI)

Abstract

The present application relates to a kind of preparation and optimization of Ce-based adsorbent of high-efficiency Cr (VI) removal, which is prepared by calcination treatment with metal organic framework as precursor, the obtained Ce-based adsorbent has higher specific surface area, and a large number of hydroxyl functional groups are introduced on the surface;After optimization, the content of Ce (III) and oxygen vacancy of adsorbent increases, further improves the adsorption capacity and reduction capacity of Cr (VI). The Ce-based adsorbent prepared in the present application belongs to environmentally friendly material, which has the advantages of simple production process, good adsorption performance, wide working pH range, strong stability, multiple recycling and the like. At the same time, the obtained adsorbent in the present application is applied to Cr (VI) containing wastewater treatment, can realize high-efficiency adsorption of Cr (VI) and reduce high-toxicity Cr (VI) to low-toxicity Cr (III), can effectively solve the problem of chromium pollution in water, has great application potential.

Description

TECHNICAL FIELD

[0001] The application relates to preparation and optimization of a Ce-based adsorbent, in particular to preparation and optimization of a Ce-based adsorbent for efficient removal of Cr(VI), and belongs to the technical field of environmental protection and materials. BACKGROUND

[0002] Chromium (Cr) is a toxic heavy metal derived from nature and human activities, which is released into water bodies with its extensive use in industry and other fields, causing serious heavy metal pollution in water bodies. There are mainly two stable forms of chromium in water: trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)), among which the toxicity and persistence of Cr(VI) are obviously higher than those of Cr(III), and Cr(VI) is easily transported, absorbed and accumulated in organisms, so the related environmental pollution of chromium is mainly caused by Cr(VI). Cr(VI) has strong carcinogenic, teratogenic and mutagenic effects, and can further pose a huge threat to ecology and life through the accumulation and amplification effects of the food chain. Therefore, it is urgent to develop efficient Cr(VI) removal technology.

[0003] At present, there are many treatment technologies for removing Cr(VI), such as adsorption, coagulation, ion exchange, electro-catalysis, photo-catalysis and biological methods. Among these technologies, adsorption has the advantages of low cost, high efficiency, simple implementation and high efficiency, and is considered to be one of the most promising strategies. In the aspect of chromium removal by adsorption, magnetic carbon, biological waste, activated carbon, metal oxide modified materials and other adsorbents have been used, and the effect is good, but there are still disadvantages such as high preparation cost, narrow applicable pH range and poor reusability.

[0004] In recent years, cerium oxide nanoparticles have been gradually used for wastewater treatment. Cerium is the most abundant rare earth element and is widely used as a catalyst, adsorbent, magnetic material and alloy. Cerium-based adsorbents have specific physical and chemical properties, such as particle size and the ability to change oxidation state, oxygen vacancies and low toxicity, and are suitable for a wide range of pH, so they have important advantages in the application of removing Cr(VI). Among the materials found: Chinese patent document CN115353187B discloses a Ce-doped pyrite FeS2 environmental purification material for treating vanadium (V) and Cr(VI) pollution: using ferrous sulfate, cerium nitrate, thiourea and sulfur powder as raw materials, a Ce-doped pyrite is obtained under the hydrothermal conditions of 160-℃20 water, and the material can simultaneously remove mixed heavy metal pollution of vanadium (V) and Cr(VI), and the maximum adsorption capacity of the material for Cr(VI) is about 20mg / g. However, a certain amount of H2S gas will be produced in the preparation process, which will cause further environmental pollution. At the same time, the specific surface area of traditional cerium-based metal adsorbents is small, and the adsorption capacity of the adsorbents for pollutants is limited.

[0005] On this basis, in order to obtain more efficient metal-based adsorbent, researchers have developed a new generation of metal organic framework (MOFs) based adsorbent, which is derived from metal oxide with layered micro-nano structure, has high specific surface area and pore volume, good thermal stability, adjustable pore structure, easy functionalization, and can provide more active sites for chromium adsorption. Among the materials found: such as Chinese patent document: CN116178741A discloses an organic ligand DKTA generated by reacting 3-aminopyrazine-2-carboxylic acid with dibenzoylmethane (DBM), and a zirconium-based MOF adsorbent is prepared by combining the organic ligand DKTA with ZrCl4, which can be used for targeted removal of copper ions in solution, and the adsorption rate of the zirconium-based MOF adsorbent to copper ions can reach 99.84%, and after 5 times of repetition, the adsorption rate of copper ions can also reach 91.65%. Such as Chinese patent document: CN115814765A discloses a MOF composite adsorbent loaded with MnO2 and a preparation method and application thereof. The composite adsorbent comprises a carrier and an active component loaded on the carrier; wherein the carrier comprises a metal-organic framework material, and the active component comprises MnO2, and the specific surface area of the prepared MnO2@Al-adsorbent OF can reach 2102.3-2732.6m 2 / g, and when the limit concentration is 1200-1500mg / L, the saturated adsorption capacity of thorium ions can reach 1500-2100mg / g. These MOFs materials have a larger specific surface area and stronger adsorption capacity for contaminated ions, but still have problems such as high cost, narrow applicable pH range, and secondary pollution.

[0006] Therefore, based on the above findings, Ce can be combined with MOFs materials to obtain a more simple and efficient Ce-based adsorbent by controlling the preparation conditions, which not only retains the properties of the original materials Ce and MOFs, but also can increase the specific surface area and pore volume, increase the active sites and functional groups, make the obtained adsorbent have a wider applicable pH range, higher adsorption capacity and stronger regeneration capacity. SUMMARY

[0007] In order to overcome the shortcomings of the prior art such as narrow applicable pH range, low adsorption capacity and poor regeneration, the present application provides a preparation and optimization method of Ce-based adsorbent for efficient adsorption of Cr(VI), which controls the proportion of Ce, calcination temperature and other conditions to prepare adsorbents with different Ce content and form, and applies them to the treatment of Cr(VI) containing wastewater. The preparation method is simple in steps and convenient to operate, the obtained adsorbent has strong adsorption capacity, strong stability and good regeneration effect.

[0008] The technical scheme of the present application is as follows:

[0009] A method for preparing and optimizing a Ce-based adsorbent with high efficiency in removing Cr(VI) includes the following steps:

[0010] (1) Preparation step: dissolve cerium salt and organic ligand in a beaker according to a certain molar ratio, centrifuge after sufficient stirring, wash 3 times, and dry at 60°C to obtain an organic metal framework Ce x -MOF. The Ce x -MOF is evenly laid in a magnetic boat, the magnetic boat is transferred to a high-temperature tube furnace, calcination treatment is performed under different atmospheres, the temperature is raised to a certain temperature at a rate of 5°C / min, and then the temperature is kept for 2 hours, and the adsorbent is obtained after cooling to room temperature.

[0011] (2) Optimization step: a certain amount of the above adsorbent is taken in a beaker, deionized water is added, magnetic stirring is performed to make it uniformly diffuse, then different amounts of ascorbic acid powder are added, and stirring reaction is performed under water bath heating conditions for 30-150 min, and after the reaction is completed, filtration separation is performed, and deionized water and anhydrous ethanol are sequentially used for washing, and drying is performed to obtain the optimized cerium-based adsorbent.

[0012] According to the application, preferably, in step (1), the cerium salt is cerium nitrate hexahydrate and cerium chloride heptahydrate, and the organic ligand is trimesic acid and terephthalic acid.

[0013] According to the application, preferably, in step (1), the molar ratio of cerium nitrate hexahydrate to trimesic acid is 1:1-1:4, the atmosphere is air, nitrogen or argon, and the calcination treatment temperature is 400-600°C.

[0014] Further preferably, the organic ligand is trimesic acid, the cerium salt is cerium nitrate hexahydrate, the molar ratio of cerium nitrate hexahydrate to trimesic acid is 1:2, the washing is performed using 50% ethanol aqueous solution, the heat treatment atmosphere is nitrogen, and the calcination temperature is 500°C.

[0015] According to the application, preferably, in step (2), the amount of ascorbic acid powder added per 1g of the original adsorbent is 0.002mol-0.1mol.

[0016] Further preferably, the amount of ascorbic acid powder required per 1g of the original adsorbent is 0.002-0.02mol, the stirring reaction temperature is 20-30°C, and the reaction time is 90-120 min.

[0017] The Ce-based adsorbent obtained by the application is used for adsorbing and removing Cr(VI) in wastewater.

[0018] Preferably, according to the application, the specific adsorption removal method is as follows: under the conditions of a temperature of 25-45 DEG C and a pH of 2.0-12.0, a Ce-based adsorbent is added into a Cr(VI)-containing solution, the addition amount is 0.1-1 g of the Ce-based adsorbent per liter of the wastewater, and the water bath oscillation reaction is performed for 0-6 h at an oscillation speed of 160 r / min.

[0019] The efficient Ce-based adsorbent of the application can effectively remove Cr(VI) under the pH conditions of 2.0-12.0, i.e. the obtained Ce-based adsorbent can be applied under the natural conditions of the pH of the water body. According to experimental determination, the efficient Ce-based adsorbent obtained by the preparation method of the application is in the form of dark brown powder, and the zeta potential is located between 20.39 mV and -24.17 mV.

[0020] The Ce-based adsorbent prepared by the application can be used as a new efficient water treatment agent and is widely applied in the field of Cr(VI)-containing water treatment, and has the following advantages compared with the existing adsorbents.

[0021] 1. The preparation method of the application uses trimesic acid and cerium nitrate hexahydrate to synthesize an organic metal framework as a precursor, and the Ce-based adsorbent is obtained through high-temperature carbonization. The reagents used have low cost, the preparation process is simple to operate, and there is no secondary pollution, so the synthesis process is green and environmentally friendly. At the same time, the preparation method of the application can almost ignore the influence of the performance of the precursor, and the organic ligand and the cerium salt can be used as raw materials after simple stirring and drying, so the method has many advantages for industrial production.

[0022] 2. The preparation method of the application uses trimesic acid and cerium nitrate hexahydrate to synthesize an organic metal framework as a precursor, and the Ce-based adsorbent is obtained through high-temperature carbonization. The surface of the Ce-based adsorbent contains a large number of hydroxyl functional groups, contains a high proportion of Ce(III) and oxygen vacancies, is a high-efficiency Cr(VI) adsorbent with a negative surface, can undergo complexation and redox reactions with Cr(VI), has strong adsorption capacity for Cr(VI), high removal efficiency, and large adsorption capacity, and can realize the conversion of highly toxic Cr(VI) into low-toxicity Ce(III), thereby realizing the efficient and low-toxicity removal of Cr(VI).

[0023] 3. The preparation method of the application uses trimesic acid and cerium nitrate hexahydrate to synthesize an organic metal framework as a precursor, and the Ce-based adsorbent is obtained through high-temperature carbonization. The Ce-based adsorbent has a wide pH range, mild reaction conditions, a simple regeneration method, strong regeneration capacity, good stability, and can realize the repeated use of the cerium-based adsorbent, thereby saving the cost.

[0024] 4. The optimization method of the application uses ascorbic acid as a reducing agent to adjust the valence state of Ce in the Ce-based adsorbent by liquid-phase reduction. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Appearance photo of the Ce-based adsorbent for efficient removal of Cr(VI) of the application;

[0026] Figure 2 XRD characterization graph of the Ce-based adsorbent of the application;

[0027] Figure 3 Effect graph of the Ce-based adsorbent of the application for removal of Cr(VI) in multiple adsorption-desorption cycles;

[0028] Figure 4 Ce elution graph of the Ce-based adsorbent of the application in the process of adsorbing Cr(VI) under different pH conditions;

[0029] Figure 5 Ce-based adsorbent of the application in the process of adsorbing Cr(VI) under different pH conditions. DETAILED DESCRIPTION

[0030] In order to more clearly understand the embodiments of the application or the technical solutions in the prior art, the following will be further described in detail with the drawings needed to be used in the description of the embodiments or the prior art. In the drawings, several embodiments of the present disclosure are shown in an exemplary but not limiting manner, wherein:

[0031] Example 1:

[0032] A preparation method of a Ce-based adsorbent for efficient removal of Cr(VI) includes the following steps:

[0033] (1) Dissolve cerium nitrate hexahydrate and trimesic acid in a beaker in a mass ratio of 1:2, mix and stir for 1.5 h, centrifuge, wash with ethanol / water (1:1) for 3 times, dry, and obtain an organic metal framework Ce 0.5 -MOF.

[0034] (2) Place 1.5 g of Ce 0.5 -MOF in a magnetic boat, transfer the magnetic boat to a tube furnace, and perform high-temperature carbonization under a nitrogen atmosphere at a heating rate of 5℃ / min to 500℃, keep the temperature for 2 h, cool to room temperature, grind, obtain a Ce-based adsorbent, and name it as Ce 0.5 @C-500(N). The appearance photo of the prepared Ce-based adsorbent for efficient removal of Cr(VI) is shown in Figure 1 ​

[0035] Example 2

[0036] A preparation method of Ce-based adsorbent for removing Cr(VI) efficiently, which is the same as example 1, except that the high-temperature carbonization temperature in step (2) is 400℃, and the obtained Ce-based adsorbent is represented by Ce 0.5 @C-400(N).

[0037] Example 3

[0038] A preparation method of Ce-based adsorbent for removing Cr(VI) efficiently, which is the same as example 1, except that the high-temperature carbonization temperature in step (2) is 600℃, and the obtained Ce-based adsorbent is represented by Ce 0.5 @C-600(N).

[0039] Example 4

[0040] A preparation method of Ce-based adsorbent for removing Cr(VI) efficiently, which is the same as example 1, except that the molar ratio of cerium nitrate hexahydrate to trimesic acid in step (1) is 1:1, and the obtained Ce-based adsorbent is represented by Ce

[0041] Example 5

[0042] A preparation method of Ce-based adsorbent for removing Cr(VI) efficiently, which is the same as example 1, except that the molar ratio of cerium nitrate hexahydrate to trimesic acid in step (1) is 1:4, and the obtained Ce-based adsorbent is represented by Ce 0.25 @C-500(N).

[0043] Example 6

[0044] A preparation method of Ce-based adsorbent for removing Cr(VI) efficiently, which is the same as example 1, except that the gas atmosphere in step (2) is air, and the obtained Ce-based adsorbent is represented by Ce 0.5 @C-500(A).

[0045] Example 7

[0046] A preparation method of Ce-based adsorbent for removing Cr(VI) efficiently, which is the same as example 1, except that the gas atmosphere in step (2) is air, and the high-temperature carbonization temperature is 400℃, and the obtained Ce-based adsorbent for removing Cr(VI) efficiently is represented by Ce 0.5 @C-400(A).

[0047] An optimization method of Ce-based adsorbent for removing Cr(VI) efficiently, comprising the following steps:

[0048] Example 8:

[0049] Take 0.5g of Ce 0.5 @C-500(N) was placed in a beaker, 100mL of deionized water was added, and magnetic stirring was carried out for 30min to disperse the sample. 0.001mol of ascorbic acid powder was added to the above solution, and stirring was continued for 2h. After the reaction was completed, separation was carried out by suction filtration, and washing was carried out with deionized water and anhydrous ethanol, and drying was carried out to obtain the optimized Ce-based material R1-Ce 0.5 @C-500(N).

[0050] Example 9: An optimization method of a Ce-based adsorbent for efficient removal of Cr(VI), the same as Example 8, except that the ascorbic acid powder was 0.005mol, and the optimized Ce-based material R2-Ce was obtained 0.5 @C-500(N).

[0051] Example 10: An optimization method of a Ce-based adsorbent for efficient removal of Cr(VI), the same as Example 8, except that the ascorbic acid powder was 0.01mol, and the optimized Ce-based material R3-Ce was obtained 0.5 @C-500(N).

[0052] Example 11: An optimization method of a Ce-based adsorbent for efficient removal of Cr(VI), the same as Example 8, except that the ascorbic acid powder was 0.02mol, and the optimized Ce-based material R4-Ce was obtained 0.5 @C-500(N).

[0053] Experimental Example:

[0054] The high-efficiency Ce-based adsorbent synthesized as described above was used for the adsorption of Cr(VI), and the specific application method was as follows:

[0055] A 100mg / L potassium dichromate solution was prepared, 25mL was taken and placed in a conical flask, 0.01g of Ce-based adsorbent (as a group of experiments, examples 1-3 in the preparation method, examples 1 and 4-5 as a group of experiments, examples 1-2 and 6-7 as a group of experiments, and 8-11 in the optimization method as a group of experiments) was added, and was placed in a constant temperature water bath shaker, with a shaking speed of 160r / min, a reaction temperature of 25℃, and was shaken for 4h.

[0056] Table 1 Adsorption effect of Ce-based adsorbent with different calcination temperatures on Cr(VI)

[0057]

[0058] Table 2 Adsorption effect of Ce-based adsorbent with different raw material ratios on Cr(VI)

[0059]

[0060] Table 3. Adsorption effect of Ce-based adsorbents on Cr(VI) under different gas atmospheres.

[0061]

[0062] Table 4 shows the adsorption effect of the optimized Ce-based adsorbent on Cr(VI).

[0063]

[0064] Ce 0.5 @C-500(N) adsorbent was used in the regeneration experiment; the regeneration solution was 1M KCl, and Ce was adsorbed to saturation. 0.5 The C-500(N) adsorbent underwent four Cr(VI) adsorption-desorption processes, with the adsorption effect of each process as follows: Figure 2 As shown in the figure. Simultaneously, the concentration of Ce in the solution after Cr(VI) adsorption was measured at different pH values ​​to assess the metal dissolution from the adsorbent. The test results are shown in the figure. Figure 3 As shown.

[0065] like Figure 1 As shown, the high-efficiency Ce-based adsorbent prepared by this invention has a dark brown appearance because Ce(III) is largely retained during nitrogen calcination.

[0066] like Figure 2 The XRD pattern shows that the unpyrolyzed Ce 0.5 The main diffraction peaks of the MOF are located in the range of 10° to 30°. After pyrolysis in N2, the characteristic peaks changed significantly. (The last sentence appears to be incomplete and possibly contains errors. It seems to be related to Ce.) 0.5 Compared to the diffraction peaks of -MOF, Ce 0.5 @C-400(N) and Ce 0.5 The peak positions of @C-500(N) were shifted, mainly located at 2θ = 10.8°, 15.8°, and 24.7°, which are residual Ce(III) nanocomposites after calcination; Ce 0.5 @C-400(N) and Ce 0.5 The new Ce(III) peaks appearing in @C-500(N) at 2θ = 27.5°, 37.2°, 42.1°, 49.4°, and 56.2° are due to the plane diffraction effect of CeO2; Ce 0.5 The characteristic peak of @C-600(N) is only Ce(IV) because the crystal structure contains only CeO2 polycrystalline material, indicating that Ce(III) is completely oxidized to Ce(IV) at 600℃. 0.5Similar diffraction peaks can be observed in @C-500(A) because Ce(III) is more easily oxidized in air.

[0067] like Figure 3 As shown, the regenerated Ce 0.5 After four adsorption-desorption cycles, the adsorption capacity of @C-500(N) decreased by 46%, but its adsorption capacity was still superior to some reported metal adsorbents.

[0068] like Figure 4 As shown, under acidic conditions, the highest leaching amount of Ce in the adsorbent was 3.534 mg / L at pH 4. With increasing alkalinity, the leaching amount of Ce almost decreased, indicating that Ce... 0.5 @C-500(N) exhibits strong stability under various acid and alkaline conditions, possibly due to Ce. 0.5 @C-500(N) has a porous structure, and high-temperature pyrolysis improves the cerium dioxide content in Ce. 0.5 Fixation on @C-500(N).

[0069] like Figure 5 As shown, when pH is between 2 and 4, Ce 0.5 The adsorption capacity of @C-500(N) for Cr(VI) decreases with increasing pH, but it still maintains a relatively high adsorption capacity for Cr(VI). As the pH increases to 4, the adsorption capacity for Ce... 0.5 The adsorption capacity of @C-500(N) decreased because the positive charge of Ce(IV) decreased, leading to a lower surface potential of the adsorbent. The pH of the solution remained almost unchanged after adsorption, indicating that the addition of Ce... 0.5 The addition of @C-500(N) has no effect on the acidity or alkalinity of the solution. Within the pH range of 4-6, Ce increases with increasing pH. 0.5 The adsorption capacity of @C-500(N) increases, while the pH of the solution decreases slightly after the reaction. When pH>10, the negatively charged Ce... 0.5 @C-500(N) and CrO4 2- There is a strong electrostatic repulsion between them, which is not conducive to the adsorption of Cr(VI), but Ce 0.5 The adsorption capacity of @C-500(N) still increases with increasing pH.

[0070] From the above data, the high-efficiency Ce-based adsorbent prepared by the application has good adsorption effect on heavy metal Cr(VI). According to the existing literature, the number of reports on the adsorption of Cr(VI) by cerium-based adsorbents is limited, and the adsorption capacity is low and the effect is poor, while the high-efficiency Ce-based adsorbent prepared by the application can effectively remove Cr(VI), has a wide working pH range, and still has good adsorption capacity in multiple continuous adsorption-desorption processes, and has less Ce precipitation, almost no precipitation under alkaline conditions, good regeneration stability, and can be applied to a certain extent to treat chromium pollution in wastewater.

Claims

1. The application of a Ce-based adsorbent in the removal of Cr(VI), wherein the preparation steps of the Ce-based adsorbent are as follows: (1) Preparation steps: Cerium salt and organic ligand are mixed and dissolved in a beaker according to a certain molar ratio, stirred thoroughly and centrifuged, washed 3 times, dried at 60℃ to obtain organometallic framework Cex-MOF, Cex-MOF is spread evenly in a magnetic boat, the magnetic boat is transferred to a high-temperature tube furnace and calcined under nitrogen atmosphere. The temperature is raised to 500 degrees at a rate of 5℃ / min, held for 2 hours, cooled to room temperature and taken out to obtain adsorbent; (2) Optimization steps: Take a certain amount of the above adsorbent into a beaker, add deionized water, and stir magnetically to make it diffuse evenly. Then add different masses of ascorbic acid powder, stir and react for 30~150 min under water bath heating conditions. After the reaction is completed, filter and separate, wash with deionized water and anhydrous ethanol in sequence, and dry to obtain the optimized cerium-based adsorbent.

2. The application according to claim 1, characterized in that, In step (1), the cerium salt is cerium nitrate hexahydrate and the organic ligand is pyromellitic acid.

3. The application according to claim 2, characterized in that, In step (1), the molar ratio of cerium nitrate hexahydrate to trimesolic acid is 1:

2.

4. The application according to claim 1, characterized in that, The washing method described in step (1) is washing with a 50% ethanol aqueous solution.

5. The application according to claim 1, characterized in that, In step (2), the amount of ascorbic acid powder required for each 1g of the adsorbent mentioned in step (1) is 0.002~0.02mol, the stirring reaction temperature is 20~30℃, and the reaction time is 90~120min.

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