ZSM-5 type molecular sieve as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of molecular sieve synthesis, and discloses a ZSM-5 type molecular sieve as well as a preparation method and application thereof. The preparation method comprises the following steps: firstly, carrying out calcination treatment and low-temperature plasma treatment on rectorite to obtain modified rectorite; then adding the modified rectorite and a supplementary silicon source into water, sequentially adding butane-1, 4-bis (dodecyl dimethyl ammonium bromide) and hexadecyl trimethyl ammonium bromide, raising the temperature, adding a template agent, adjusting the pH value of the system, and quickly aging by microwave treatment to obtain a precursor; and finally, heating the precursor, carrying out hydrothermal crystallization reaction, washing, drying and grinding a product, and calcining to obtain the ZSM-5 type molecular sieve. The rectorite is used as all aluminum sources and part of silicon sources for molecular sieve synthesis, the aluminum activity and nucleation sites of the rectorite are improved through modification, then two surfactants are introduced, and microwave treatment is combined, so that silicon and aluminum species in a system are rapidly nucleated, and the efficient, economical and higher-performance ZSM-5 type molecular sieve is prepared.

Description

Technical Field

[0001] The present invention belongs to the technical field of molecular sieve synthesis, and particularly relates to a ZSM-5 type molecular sieve, a preparation method thereof, and an application thereof. Background Art

[0002] With the continuous development of the national industrial production capacity, more and more heavy metal pollutants are discharged into the environment, posing a great threat to the ecological environment. The "National Soil Pollution Survey Bulletin" jointly released by the Ministry of Environmental Protection and the Ministry of Land and Resources of the country shows that among many heavy metal pollutions, cadmium pollution is the most serious, with a site exceeding standard rate of 7%, posing a great threat to human health. The treatment of cadmium pollution is extremely urgent, and it is of practical significance to develop more economical and efficient cadmium pollution treatment materials. As an efficient adsorption material, ZSM-5 molecular sieve is widely used in the treatment of heavy metal pollution. Its unique pore structure and good adsorption performance enable it to effectively adsorb and solidify heavy metal ions in wastewater, thereby reducing its harm to the environment and providing new ideas and methods for solving the heavy metal pollution problem.

[0003] ZSM-5 molecular sieve is usually synthesized by using inorganic chemical silicon-aluminum salts such as water glass and aluminum sulfate as precursors in an alkaline environment by the classical hydrothermal crystallization method. These inorganic chemical silicon-aluminum salts used in the synthesis of ZSM-5 molecular sieve are mainly prepared from natural minerals through complicated reaction and separation processes, which are typical processes with high energy consumption, high material consumption, and high pollution emissions, and thus are high-cost and non-green processes. In recent years, technologies for preparing ZSM-5 molecular sieve by using natural minerals as aluminum source and / or silicon source have emerged. However, due to the high impurity content and complex composition of natural minerals, the silicon-aluminum reaction activity therein is low, resulting in low synthesis efficiency, and problems such as insufficient crystallinity and irregular crystal grain morphology in the synthesized molecular sieve. At the same time, the long-time heating in the water bath aging step in the existing hydrothermal crystallization method is also accompanied by problems of high energy consumption and long time consumption, which greatly reduces the production efficiency and affects the large-scale production and application of molecular sieve. Summary of the Invention[[ID=I4]]

[0004] The technical problem to be solved by the present invention is to provide a ZSM-5 type molecular sieve, a preparation method thereof, and an application thereof in view of the deficiencies existing in the prior art. Using rectorite as all the aluminum source and part of the silicon source for the synthesis of molecular sieve, the aluminum activity and nucleation sites of rectorite are improved by modification, and then two surfactants are introduced and combined with microwave treatment to enable the rapid nucleation of silicon-aluminum species in the system, achieving a uniform and regular crystal grain morphology, mesoporous structure, and higher crystallinity, and realizing the preparation of a highly efficient, economical, and higher-performance ZSM-5 type molecular sieve.

[0005] To solve the technical problems proposed by the present invention, the present invention provides a preparation method of a ZSM-5 type molecular sieve, comprising the following steps:

[0006] 1) First, calcine the rectorite, and then perform low-temperature plasma treatment to obtain modified rectorite, which serves as all the aluminum source and part of the silicon source for zeolite synthesis.

[0007] 2) Add the modified rectorite and supplementary silicon source to water, then successively add butane-1,4-bis(dodecyldimethylammonium bromide) (gBDDA) and cetyltrimethylammonium bromide (CTAB) and mix evenly. Then, under stirring conditions, raise the temperature, add the template agent and adjust the pH of the system to 9 - 11, and use microwave treatment for rapid aging to obtain a precursor.

[0008] 3) Raise the temperature of the precursor for hydrothermal crystallization reaction. After the product is washed, dried and ground, calcine it to remove the template agent to obtain ZSM-5 type zeolite.

[0009] In the above scheme, the particle size of the rectorite is ≤100 mesh, the Al2O3 content is ≥33.5%, and the SiO2 content is ≥46.5%.

[0010] In the above scheme, in step 1), the calcination temperature is 600 - 700 °C, and the calcination time is 1 - 2 h.

[0011] In the above scheme, the power of the low-temperature plasma treatment is 50 - 200 W, the atmosphere is a mixed gas of Ar, O2 and CF4, the gas flow rate is 10 - 30 sccm, the pressure is 50 - 200 Pa, the treatment temperature is 20 - 80 °C, and the treatment time is 5 - 10 min.

[0012] Furthermore, the atmosphere is a mixed gas composed of Ar, O2, and CF4 with volume fractions of 40 - 60%, 20 - 40%, and 10 - 30% respectively.

[0013] In the above scheme, the supplementary silicon source is one or more of sodium silicate nonahydrate, tetraethoxysilane (TEOS), and silica sol.

[0014] In the above scheme, the template agent is one or two of tetrapropylammonium bromide (TPABr) and tetrapropylammonium hydroxide (TPAOH).

[0015] In the above scheme, in step 2), control the molar ratio of Si to Al in the system to be (8 - 10):1.

[0016] In the above scheme, in step 2), the molar ratio of the template agent to Si in the system is (0.7 - 1.2):10.

[0017] In the above scheme, in step 2), the molar ratio of water to Si in the system is (900 - 1100):10.

[0018] In the above solution, the molar ratio of butane-1,4-bis(dodecyldimethylammonium bromide), cetyltrimethylammonium bromide and the template is (1-2):(1-2):10.

[0019] In the above solution, the specific addition process of butane-1,4-bis(dodecyldimethylammonium bromide) and cetyltrimethylammonium bromide is as follows: first, add butane-1,4-bis(dodecyldimethylammonium bromide) under stirring conditions, and then perform microwave treatment; then add cetyltrimethylammonium bromide under stirring conditions, and then perform microwave treatment.

[0020] In the above solution, in step 2), the stirring rate under the stirring conditions is 100-200 rpm, including the stirring during heating and the stirring when adding butane-1,4-bis(dodecyldimethylammonium bromide) and cetyltrimethylammonium bromide.

[0021] In the above solution, in step 2), the heating temperature for heating is 65-75 °C.

[0022] In the above solution, in step 2), the pH of the system is adjusted with sulfuric acid, and the sulfuric acid concentration is 1-3 mol / L.

[0023] In the above solution, in step 2), the frequency of the microwave treatment is 2400-2500 MHz, and the power is 200-800 W, including the microwave treatment during rapid aging and the microwave treatment when adding butane-1,4-bis(dodecyldimethylammonium bromide) and cetyltrimethylammonium bromide.

[0024] In the above solution, the microwave treatment time after adding butane-1,4-bis(dodecyldimethylammonium bromide) is 30-60 s, and the microwave treatment time after adding cetyltrimethylammonium bromide is 30-60 s.

[0025] In the above solution, in step 2), the microwave treatment time during rapid aging is 10-20 min.

[0026] In the above solution, the reaction temperature of the hydrothermal crystallization reaction is 140-160 °C, and the reaction time is 48-72 h.

[0027] In the above solution, the drying temperature for drying is 100-120 °C, and the drying time is 2-4 h.

[0028] In the above solution, in step 3), the calcination temperature is 500-600 °C, and the calcination time is 3-5 h.

[0029] The present invention also provides a ZSM-5 type molecular sieve, which is prepared by the above method.

[0030] In the above scheme, the particle size of the ZSM-5 molecular sieve is 240-260 nm, and the specific surface area is 300-320 m 2 / g, it has both micropores and mesopores, the micropore diameter is less than 2nm, the mesopore diameter is 2-5nm, and the total pore volume is 0.16-0.18m 2 / g.

[0031] In the above solution, the ZSM-5 molecular sieve has a cuboid-like crystal morphology, and the crystal size is 15 to 25 μm.

[0032] In the above solution, the ZSM-5 molecular sieve has a relative crystallinity of ≥107% compared with commercial ZSM-5 molecular sieve.

[0033] The present invention also provides the use of the ZSM-5 molecular sieve in repairing Cd-contaminated water phase and repairing Cd-contaminated soil.

[0034] In the above scheme, the method for applying the ZSM-5 molecular sieve in repairing the Cd-contaminated water phase is: adding the ZSM-5 molecular sieve to the Cd-contaminated water phase to adsorb the Cd in the water phase.

[0035] Furthermore, the Cd concentration of the Cd-contaminated water phase is 5 to 10 mg / L.

[0036] Furthermore, the amount of the ZSM-5 molecular sieve added to the Cd-contaminated aqueous phase is 0.003 to 0.005 g / mL.

[0037] Furthermore, the adsorption temperature is 20-25° C., and the adsorption time is 2-6 hours.

[0038] Furthermore, the ZSM-5 molecular sieve has a removal rate of Cd in the aqueous phase of ≥90%.

[0039] In the above scheme, the method for applying the ZSM-5 molecular sieve in remediating Cd-contaminated water phase is: adding the ZSM-5 molecular sieve to Cd-contaminated soil to solidify the Cd in the soil.

[0040] Furthermore, the exchangeable Cd content of the Cd-contaminated soil is 30-35 mg / kg.

[0041] Furthermore, the amount of the ZSM-5 molecular sieve added to the Cd-contaminated soil is 0.12 to 0.15 g / g.

[0042] Furthermore, the curing temperature is 20-25° C., and the curing time is 4-12 hours.

[0043] Furthermore, during solidification, the soil solid content is controlled to be 15-20% by adding water.

[0044] Furthermore, the solidification rate of the ZSM-5 type molecular sieve for exchangeable Cd in soil is ≥ 80%.

[0045] The technical concept and principle of the present invention are as follows:

[0046] The present invention aims to use the aluminum in rectorite as the only aluminum source, make full use of its silicon and aluminum elements, and prepare ZSM-5 type molecular sieve by hydrothermal crystallization method. However, its composition is complex, and the reaction activity of silicon and aluminum in it is low, resulting in low synthesis efficiency. The synthesized molecular sieve has problems such as insufficient crystallinity and irregular crystal grain morphology. Therefore, the present invention solves the above problems through the following technical measures:

[0047] 1) Modify rectorite; first, through pre-calcination, the original structure of rectorite is destroyed, and the internal silicate structure undergoes a certain degree of rearrangement and decomposition, thus being more conducive to the new structure of ZSM-5 crystallization; then, the surface of pre-calcined rectorite is treated by low-temperature plasma, so that the molecules on the surface of rectorite are excited, dissociated and ionized, and thus some active atoms, free radicals and unsaturated bonds are formed on the surface. These active sites can serve as the starting points for molecular sieve nucleation, contribute to the formation and growth of molecular sieve. At the same time, plasma treatment can etch the surface of rectorite to promote the dissociation of aluminum from the lattice of rectorite and enter the solution. This dissociation process increases the solubility of aluminum, making it easier to react with other substances, thereby improving the utilization rate of aluminum; the low-temperature plasma treatment uses a mixed gas of Ar, O2 and CF4 as the atmosphere. As an inert gas, Ar can provide a stable discharge environment to avoid the decomposition or excessive reaction of other active gases. O2 can introduce oxygen-containing groups such as hydroxyl (-OH) and carbonyl (-CO), enhance the hydrophilicity and chemical reactivity of the rectorite surface, and thus improve its activity as an aluminum source. The fluorine atoms generated by the decomposition of CF4 in the plasma can remove the organic impurities on the surface of rectorite or adjust the surface chemical composition through chemical etching, further optimizing its performance as an aluminum source; in addition, by pre-calcining to destroy the internal structure of rectorite and then treating it by low-temperature plasma to form a uniform negatively charged surface and make the structure looser, the specific surface area can be increased, and the active sites can be further increased;

[0048] 2) Optimize the hydrothermal crystallization synthesis step; introduce the gemini ionic surfactant butane-1,4-bis(dodecyldimethylammonium bromide) (gBDDA) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) successively in two steps; when using a single type of surfactant to synthesize hierarchical pore ZSM-5 zeolite, the two steps of silicate condensation to form the zeolite framework and self-assembly under the action of the surfactant to form the mesoporous structure are incompatible, and there is a large strain in the mesoporous formation, which will destroy the long-range order of the zeolite framework; when gBDDA and CTAB are used in combination, gBDDA, as a bifunctional multi-quaternary ammonium salt surfactant with two quaternary ammonium groups, can simultaneously direct the formation of micropores and mesopores, while CTAB has the ability to induce the MFI structure, which can stabilize micelles and inhibit the abnormal growth of zeolites. The two work together to improve the crystallinity and structural order of the zeolite; during this period, microwave treatment is used to assist the two added surfactants to achieve efficient distribution, reduce the competition between the two surfactants, direct the formation of the inorganic framework, optimize the mesopore aperture of the zeolite, and make the product crystal grains uniform in size and regular in morphology; and microwave treatment is used to quickly age and nucleate, enabling the silicon-aluminum species to reach the nucleation and growth conditions faster, thereby shortening the synthesis cycle and improving production efficiency.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0050] The present invention uses rectorite as all the aluminum source and part of the silicon source for zeolite synthesis. By pre-calcining and low-temperature plasma treatment of rectorite, the aluminum activity and nucleation sites in rectorite are improved. Then, during the synthesis process, two surfactants, butane-1,4-bis(dodecyldimethylammonium bromide) and cetyltrimethylammonium bromide, are introduced, combined with microwave treatment, to enable the silicon-aluminum species in the system to nucleate quickly and achieve a uniform and regular crystal grain morphology, mesoporous structure, and higher crystallinity, realizing the preparation of high-efficiency, economical, and higher-performance ZSM-5 zeolite. Description of the Drawings

[0051] Figure 1 XRD patterns of the ZSM-5 zeolites synthesized in Example 1 and Example 2.

[0052] Figure 2 SEM image of the ZSM-5 zeolite synthesized in Example 1. Detailed Embodiments

[0053] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments, but the content of the present invention is not limited to the following embodiments.

[0054] In the following embodiments, the rectorite used comes from Zhongxiang, Hubei. After flotation and purification treatment, its particle size ≤ 100 mesh, Al2O3 content is 33.6%, and SiO2 content is 46.5%.

[0055] Example 1

[0056] A preparation method of ZSM-5 type molecular sieve, comprising the following steps:

[0057] 1) First, place rectorite in a muffle furnace and calcine it at 650 °C for 2 h, then perform low-temperature plasma treatment in a plasma cleaner. The power is 150 W, and the atmosphere is a mixed gas composed of Ar, O2, and CF4 with volume fractions of 50%, 30%, and 20% respectively. The gas flow rate is 20 sccm, the pressure is 100 Pa, the temperature is 50 °C, and the treatment time is 10 min to obtain modified rectorite, which serves as all the aluminum source and part of the silicon source for molecular sieve synthesis;

[0058] 2) Add the modified rectorite and supplementary silicon source (sodium silicate nonahydrate) to deionized water. Then, first add gBDDA under stirring at 150 r / min, turn off the stirring and perform microwave treatment for 30 s. Then, add CTAB under stirring at 150 r / min, turn off the stirring and perform microwave treatment for 30 s. Then, raise the temperature to 70 °C in a water bath under stirring at 150 r / min. At the same time, add TPABr and adjust the pH of the system to 10 ± 0.1 with 2 mol / L sulfuric acid. Finally, perform microwave water bath aging for 15 min at this temperature to obtain a precursor; in this step of the system, the Si / Al molar ratio is 9:1, the TPABr / Si molar ratio is 1:10, the deionized water / Si molar ratio is 1000:10, and the gBDDA / CTAB / TPABr molar ratio is 1.2:1.2:10; the microwave treatment uses a microwave digestion instrument with a frequency of 2450 MHz and a power of 400 W;

[0059] 3) Transfer the precursor to a hydrothermal reaction kettle, seal the reaction kettle and place it in an oven, perform hydrothermal crystallization reaction at 150 °C for 48 h. After the reaction is completed, take out the product, wash it with ultrapure water and centrifuge it 3 times repeatedly, then transfer it to an evaporating dish, perform drying treatment in a drying oven at 120 °C for 2 h, and then grind it using a mortar and pestle. Place the ground powder in a muffle furnace and calcine it at a high temperature of 550 °C for 4 h to remove the template agent TPABr, thereby obtaining the final product ZSM-5 type molecular sieve.

[0060] After detection, the particle size of the obtained ZSM-5 type molecular sieve is 250.5 nm, and the specific surface area is 302.6 m 2 / g. It has both micropores and mesopores at the same time. The micropore diameter is <2 nm, the mesopore diameter is 2 - 5 nm, and the total pore volume is 0.16 cm 3 / g. Figure 1XRD patterns of the ZSM-5 zeolites synthesized in Example 1 and Example 2, which also involve a commercial ZSM-5 zeolite. The commercial zeolite is the XFF04-3 type ZSM-5 zeolite produced by Jiangsu Xianfeng Nano XFNANO Co., Ltd., with a particle size of 381.3 nm, a specific surface area of 253 m 2 / g, a pore diameter of 0.58 nm, and a pore volume of 0.13 cm 3 / g. Figure 1 It shows that the zeolite synthesized by the method of the present invention has obvious five-finger type spectral peaks identical to those of the commercial zeolite. Its characteristic waveform appears mainly between 2θ of "7-9°" and "22-25°", and it is a typical crystalline material. Combining the analysis with Jade software, it is obtained that the relative crystallinities of the ZSM-5 zeolites synthesized in Example 1 and Example 2 compared with the commercial zeolite are 107.5% and 108.9% respectively, which have higher crystallinity, and have a more developed pore structure and a larger specific surface area, thus providing more adsorption sites for molecules, enabling the zeolite to adsorb more target molecules and bringing better adsorption performance. Its pore structure is regular and uniform, and the pore diameter size has good consistency, which means it can selectively adsorb more precisely according to the characteristics such as the size and shape of molecules.

[0061] Figure 2 SEM image of the ZSM-5 zeolite synthesized in Example 1, Figure 2 showing that the zeolite synthesized by the method of the present invention has a cuboid-like particle morphology. The morphology and size of each crystal grain are highly uniform, the crystal grain size is 15-25 μm, the dispersibility and homogeneity are good, the crystallization condition is good, the crystal morphology is complete, and the surface of the crystal grain is more regular than that of the traditional method.

[0062] Example 2

[0063] Preparation method of REC-ZSM-5 zeolite, comprising the following steps:

[0064] 1) First, place rectorite in a muffle furnace and calcine it at 680 °C for 1.5 h, then carry out low-temperature plasma treatment in a plasma cleaner. The power is 150 W, the atmosphere is a mixed gas composed of Ar, O2, and CF4 with volume fractions of 60%, 20%, and 20% respectively, the gas flow rate is 25 sccm, the pressure is 150 Pa, the temperature is 60 °C, and the treatment time is 10 min to obtain modified rectorite, which is used as all the aluminum source and part of the silicon source for zeolite synthesis;

[0065] 2) Add the modified rectorite and supplementary silicon source (sodium silicate nonahydrate) to deionized water. Then, first add gBDDA under the stirring condition of 180 r / min, turn off the stirring and perform microwave treatment for 40 s. Next, add CTAB under the stirring condition of 180 r / min, turn off the stirring and perform microwave treatment for 40 s. Then, raise the temperature to 75 °C in a water bath under the stirring condition of 180 r / min, add TPABr at the same time and adjust the pH of the system to 10 ± 0.1 with 2 mol / L sulfuric acid. Finally, carry out microwave water bath aging for 20 min at this temperature to obtain the precursor; in this step of the system, the Si / Al molar ratio is 10:1, the TPABr / Si molar ratio is 0.7:10, the deionized water / Si molar ratio is 1100:10, and the gBDDA / CTAB / TPABr molar ratio is 1.5:1.5:10; the microwave treatment is carried out using a microwave digestion instrument with a frequency of 2500 MHz and a power of 600 W;

[0066] 3) Transfer the precursor to a hydrothermal reaction kettle, seal the reaction kettle and place it in an oven, carry out hydrothermal crystallization reaction at 150 °C for 72 h. After the reaction is completed, take out the product, wash it with ultrapure water and centrifuge it 3 times repeatedly, then transfer it to an evaporating dish, carry out drying treatment in a drying oven at 120 °C for 2 h, and then grind it using a mortar and pestle. Place the ground powder in a muffle furnace and calcine it at a high temperature of 550 °C for 4 h to remove the template agent TPABr, thereby obtaining the final product, ZSM-5 type molecular sieve.

[0067] Example 3

[0068] Preparation method of REC-ZSM-5 type molecular sieve, comprising the following steps:

[0069] 1) First, calcine the rectorite at 660 °C for 2 h, and then carry out low-temperature plasma treatment in a plasma cleaner with a power of 150 W, an atmosphere of a mixed gas composed of Ar, O2, and CF4 with volume fractions of 40%, 30%, and 30% respectively, a gas flow rate of 15 sccm, a pressure of 75 Pa, a temperature of 60 °C, and a treatment time of 10 min to obtain the modified rectorite, which is used as all the aluminum source and part of the silicon source for molecular sieve synthesis;

[0070] 2) Add the modified rectorite and supplementary silicon source (silica sol) into deionized water. Then, add gBDDA under the stirring condition of 140 r / min first, turn off the stirring and perform microwave treatment for 25 s. Next, add CTAB under the stirring condition of 140 r / min, turn off the stirring and perform microwave treatment for 25 s. Then, raise the temperature of the water bath to 65 °C under the stirring condition of 140 r / min, add TPAOH at the same time and adjust the pH of the system to 10 ± 0.1 with 2 mol / L sulfuric acid. Finally, carry out microwave water bath aging for 15 min at this temperature to obtain the precursor. In this step of the system, the Si / Al molar ratio is 8:1, the TPABr / Si molar ratio is 1.2:10, the deionized water / Si molar ratio is 900:10, and the gBDDA / CTAB / TPAOH molar ratio is 1:1:10. The microwave treatment is carried out with a microwave digestion instrument, with a frequency of 2450 MHz and a power of 400 W;

[0071] 3) Transfer the precursor to a hydrothermal reaction kettle, seal the reaction kettle and place it in an oven, carry out hydrothermal crystallization reaction at 150 °C for 48 h. After the reaction is completed, take out the product, wash it with ultrapure water and centrifuge it 3 times repeatedly, then transfer it to an evaporating dish, carry out drying treatment in a drying oven at 120 °C for 2 h, and then grind it with a mortar and pestle. Place the ground powder in a muffle furnace and calcine it at a high temperature of 550 °C for 4 h to remove the template agent TPABr, so as to obtain the final product ZSM-5 molecular sieve.

[0072] Comparative Example 1

[0073] The difference between Comparative Example 1 and Example 1 is only that: pre-calcination is not carried out in step 1). Compared with the commercial ZSM-5 molecular sieve, the relative crystallinity of the obtained molecular sieve is lower than 100%.

[0074] Comparative Example 2

[0075] The difference between Comparative Example 2 and Example 1 is only that: low-temperature plasma treatment is not carried out in step 1). The particle size of the obtained molecular sieve is 255.2 nm, and the specific surface area is 290.4 m 2 / g. Compared with the commercial ZSM-5 molecular sieve, the relative crystallinity is 104.6%. This shows that the combined treatment of calcination and low-temperature plasma treatment can significantly improve the specific surface area of the product and make the combination of each item in the system more sufficient, resulting in a higher crystallization effect.

[0076] Comparative Example 3

[0077] The difference between Comparative Example 3 and Example 1 is only that: in step 2), only CTAB is added without adding gBDDA. The specific surface area of the obtained molecular sieve is reduced to 293.6 m under the same particle size condition as in Example 1 2 / g, and the total pore volume is only 0.12 cm 3 / g. Compared with commercial ZSM-5 molecular sieve, the relative crystallinity is 107.4%, which reflects that although CTAB can stabilize the formation of system micelles and reduce the abnormal growth of molecular sieves, it lacks the ability to guide the formation of both micropores and mesopores simultaneously with gBDDA. Although the molecular sieve reaches a relatively high relative crystallinity, the lack of pore volume indicates that it is difficult to form sufficient pores inside the molecular sieve.

[0078] Comparative Example 4

[0079] The difference between Comparative Example 4 and Example 1 is only that: in step 2), CTAB is not added and only gBDDA is added. The specific surface area of the obtained molecular sieve under the same particle size condition as in Example 1 is reduced to 281.6 m2 / g, and the total pore volume is 0.15 cm 3 / g. Compared with commercial ZSM-5 molecular sieve, the relative crystallinity is 99.6%, which reflects that gBDDA has excellent ability to guide the formation of molecular sieve pores, but using only gBDDA as a template agent may bring the problem of abnormal growth of molecular sieves, resulting in a significant reduction in the relative crystallinity of the molecular sieve.

[0080] Comparative Example 5

[0081] The difference between Comparative Example 5 and Example 1 is only that: in step 2), microwave treatment is not used, and the microwave treatment after adding gBDDA and CTAB is replaced by stirring for the same time, and the microwave water bath aging for 15 min is replaced by stirring water bath aging for 8 h. Compared with commercial ZSM-5 molecular sieve, the relative crystallinity of the obtained molecular sieve is 102.9%, indicating that microwave treatment can not only significantly reduce the aging time, but also synergistically promote the improvement of crystallinity with gBDDA and CTAB.

[0082] Application Example 1

[0083] The ZSM-5 molecular sieves prepared in each example and each comparative example were applied to the repair of Cd-polluted aqueous phase. Using a water body with a Cd(II) concentration of 10 mg / L, the ZSM-5 molecular sieve was added at an addition amount of 0.005 g / mL, and adsorbed at 25 °C for 2 h, and the removal rate of Cd in the aqueous phase was calculated.

[0084] )]]Application Example 2

[0085] The ZSM-5 molecular sieves prepared in each example and each comparative example were applied to the repair of Cd-polluted soil. Using a polluted soil with a Cd(II) content of 50 mg / kg and an exchangeable Cd content of 33.9 mg / kg, the ZSM-5 molecular sieve was added at an addition amount of 0.15 g / g, and water was added to control the soil solid content to 20%, and cured at 25 °C for 6 h, and the solidification rate of exchangeable Cd in the soil was calculated.

[0086] Table 1

[0087]

[0088]

[0089] As can be seen from Table 1, the ZSM-5 type molecular sieve prepared in the embodiment of the present invention has good treatment effects on Cd in both the aqueous phase and soil; in Comparative Example 1, since the rectorite raw material was not pre-calcined, the pore structure of the rectorite was not improved, and it was impossible to form a more uniform pore and microporous structure during the hydrothermal crystallization process, and the crystallinity of the product ZSM in the example could not be achieved, resulting in a significant reduction in the treatment effects on Cd in the aqueous phase and soil; in Comparative Example 2, since the low-temperature plasma treatment was not carried out, the relative crystallinity and specific surface area of the product decreased, and the internal pore structure of the molecular sieve was inferior to that of the example, resulting in a significant reduction in the treatment effects on Cd in the aqueous phase and soil; in Comparative Examples 3 and 4, since only one of gBDDA and CTAB was added, the synergistic effect of gBDDA and CTAB was lacking to guide the formation of micropores during the synthesis process, and the synthesized ZSM molecular sieve could not take into account both the relative crystallinity and the pore volume, resulting in a reduction in the treatment effects on Cd in the aqueous phase and soil; in Comparative Example 5, since the raw material microwave treatment was not carried out, the surface roughness and active sites of the raw materials were insufficient during the synthesis process, and it was difficult to form a ZSM type molecular sieve with high crystallinity compared with the example, and the pore structure was insufficient, resulting in a significant reduction in the treatment effects on Cd in the aqueous phase and soil.

[0090] The above embodiments are merely examples clearly described and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to list all the implementation manners here, and the obvious changes or variations thus derived are still within the protection scope of the present invention.

Claims

1. A preparation method of ZSM-5 type molecular sieve, characterized in that, It includes the following steps: 1) First, calcine the rectorite, and then perform low-temperature plasma treatment to obtain modified rectorite, which serves as all the aluminum source and part of the silicon source for zeolite synthesis; 2) Add the modified rectorite and supplementary silicon source to water, then successively add butane-1,4-bis(dodecyldimethylammonium bromide) and cetyltrimethylammonium bromide and mix evenly. Then, under stirring conditions, raise the temperature, add the template agent and adjust the pH of the system to 9-11, and use microwave treatment for rapid aging to obtain a precursor; 3) Raise the temperature of the precursor for hydrothermal crystallization reaction. After the product is washed, dried and ground, calcine it to remove the template agent to obtain ZSM-5 zeolite.

2. The preparation method of the ZSM-5 type molecular sieve according to claim 1, characterized in that, In step 1), the calcination temperature is 600-700 °C, and the calcination time is 1-2 h; the power of the low-temperature plasma treatment is 50-200 W, the atmosphere is a mixed gas of Ar, O2 and CF4, the gas flow rate is 10-30 sccm, the pressure is 50-200 Pa, the treatment temperature is 20-80 °C, and the treatment time is 5-10 min.

3. The preparation method of the ZSM-5 type molecular sieve according to claim 2, wherein, The atmosphere is a mixed gas composed of Ar, O2, and CF4 at volume fractions of 40-60%, 20-40%, and 10-30% respectively; the particle size of the rectorite is ≤100 mesh, the Al2O3 content is ≥33.5%, and the SiO2 content is ≥46.5%.

4. The preparation method of the ZSM-5 type molecular sieve according to claim 1, wherein, In the system of step 2), the molar ratio of Si to Al is (8-10):1, the molar ratio of the template agent to Si is (0.7-1.2):10, the molar ratio of water to Si is (900-1100):10, and the molar ratio of butane-1,4-bis(dodecyldimethylammonium bromide), cetyltrimethylammonium bromide to the template agent is (1-2):(1-2):

10.

5. The preparation method of the ZSM-5 type molecular sieve according to claim 1, wherein The addition process of butane-1,4-bis(dodecyldimethylammonium bromide) and cetyltrimethylammonium bromide is as follows: first add butane-1,4-bis(dodecyldimethylammonium bromide) under stirring conditions, and then perform microwave treatment for 30-60 s; then add cetyltrimethylammonium bromide under stirring conditions, and then perform microwave treatment for 30-60 s.

6. The preparation method of the ZSM-5 type molecular sieve according to claim 1 or 5, characterized in that, The frequency of the microwave treatment is 2400-2500 MHz, the power is 200-800 W, and the microwave treatment time for rapid aging is 10-20 min.

7. The preparation method of the ZSM-5 type molecular sieve according to claim 1, characterized in that, In step 2), the stirring rate under the stirring conditions is 100-200 rpm, and the temperature increase during the temperature increase is 65-75 °C; in step 3), the reaction temperature of the hydrothermal crystallization reaction is 140-160 °C, the reaction time is 48-72 h, the calcination temperature is 500-600 °C, and the calcination time is 3-5 h.

8. The preparation method of the ZSM-5 type molecular sieve according to claim 1, characterized in that, The supplementary silicon source is one or more of sodium silicate nonahydrate, tetraethoxysilane, and silica sol; the template agent is one or two of tetrapropylammonium bromide and tetrapropylammonium hydroxide.

9. A ZSM-5 zeolite prepared by the preparation method described in claim 1.

10. An application of the ZSM-5 zeolite as described in claim 9 in repairing Cd-polluted water phase and Cd-polluted soil.

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