Sandwich structure formaldehyde degradation functional cementitious building material and preparation method thereof

Abstract

The application aims to provide a sandwich structure formaldehyde degradation functional alkali-activated cementitious material, which is composed of an intermediate layer and surface layers covering the upper and lower surfaces of the intermediate layer, and the intermediate layer and the surface layers comprise the following raw materials: 40-60 parts by mass of blast furnace slag, 10-20 parts by mass of low-calcium fly ash, 10-20 parts by mass of alkaline magnesium slag, and 10-15 parts by mass of alkali-activator; the surface layers further comprise 2-7 parts by mass of functional catalyst; the functional catalyst is gel-like micro-nano TiO2 particles. The sandwich structure formaldehyde degradation functional cementitious building material has an alkali-activated cementitious material intermediate composed of C-A-S-H gel and three-dimensional network zeolite-like structure, and a hydrophobic gel-like TiO2 photocatalyst layer-like outer layer. The indoor living environment is improved, the application field of the photocatalyst is widened, and high-value-added application of solid waste-based alkali-activated cementitious material is realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of functional utilization of solid waste, and particularly relates to a sandwich structure formaldehyde degradation functional cementitious building material and a preparation method thereof. BACKGROUND

[0002] With the acceleration of industrialization and the improvement of social productivity, the over-exploitation of energy not only leads to the outbreak of energy crisis, but also causes great damage to the environment. Among them, the current traditional building materials play an important role in social production and life and in national economic activities in the form of important role, in recent years, the rapid increase in demand not only consumes a large amount of non-renewable resources, but also releases a large amount of CO2 in the production process of traditional building materials, causing a series of environmental problems such as greenhouse effect. The large accumulation of fly ash (FA), magnesium slag (MS) and blast furnace slag (BFS) not only causes serious pollution to the ecological environment, but also is a kind of idle resources.

[0003] Compared with traditional cement, alkali activated cementitious material (AACM) is a potential green material to replace Portland cement, which has the advantages of low energy consumption, green environmental protection and sustainable development. It not only has the advantage of utilizing industrial by-products, but also has excellent mechanical properties while reducing energy consumption. Due to its similar zeolite ring molecular chain structure, it can be used as an adsorbent to remove indoor formaldehyde. In addition, in the field of heavy metal ion solidification, AACM shows better performance than Portland cement due to its zeolite-like structure composed of ring molecular chains.

[0004] In addition, at present, residents spend a large amount of time indoors every day, so it is necessary to keep the indoor environment healthy. Formaldehyde, as a typical indoor pollutant, can cause a series of problems in human respiratory system, immune system and skin. Photocatalytic oxidation technology is a very promising indoor air purification technology developed in recent years. Its conversion is a process of converting pollutants into harmless substances by using nano photocatalyst under light conditions. Nano TiO2 can excite electrons and holes under light conditions, and is considered to be the most commonly used photocatalyst. The negative valence electron and the positive valence hole will have an oxidation-reduction reaction with the substances adsorbed on the surface of the catalyst. The oxidation groups generated by nano TiO2 oxidize and decompose organic matter, and finally generate water and carbon dioxide. Photocatalytic technology can effectively control pollutants without generating secondary pollutants, and shows great potential in maintaining the indoor environment towards being beneficial to human health. With people's pursuit of high-quality life and the longing for a good living environment, photocatalysts are embedded in building materials to give them the functions of antibacterial, self-cleaning, purification and decomposition of harmful gases, and degradation of formaldehyde under light conditions. However, the photocatalyst TiO2 with the function of degrading formaldehyde is directly attached to AACM, and the band gap of nano titanium dioxide and the rapid recombination of photo-generated electrons and holes restrict its catalytic degradation efficiency. Therefore, the preparation of functional green building materials with the ability to degrade pollutants in industrial solid waste to some extent represents the development trend of future building materials. The present application uses fly ash, slag, magnesium slag and nano TiO2 as main raw materials to prepare alkaline-activated functional cementitious materials with certain adsorption and degradation capacity for formaldehyde. SUMMARY

[0005] The content of the present application is to provide a method for preparing cementitious materials by using fly ash from coal-fired power plants, which can utilize fly ash, blast furnace slag and magnesium slag, reduce the landfill accumulation of solid waste, and provide corresponding technical support for the functional application of green building materials. At the same time, it broadens the application field of photocatalyst, promotes the large-scale application of photocatalyst, and realizes the high value-added application of solid waste-based alkaline-activated cementitious materials. The photocatalyst is attached to AACM by blending method, so that the material has the functions of self-cleaning, decomposition of harmful gases and degradation of formaldehyde under light conditions. Not only does it solve the stability problem of photocatalyst attached to the base material, but also makes the composite material not only have the advantages of AACM such as low energy consumption and high strength, but also can be used as a green self-cleaning material in people's daily life, thereby saving energy and protecting the environment.

[0006] The present application achieves the above-mentioned purposes by the following technical solutions:

[0007] A sandwich structure formaldehyde degradation functional alkali-activated cementitious material, which is composed of an intermediate layer and surface layers covering the upper and lower surfaces of the intermediate layer, and the intermediate layer and the surface layers comprise the following raw materials: 40-60 parts by mass of blast furnace slag, 10-20 parts by mass of low-calcium fly ash, 10-20 parts by mass of alkaline magnesium slag, and 10-15 parts by mass of alkali-activator; the surface layer further comprises 2-7 parts by mass of functional catalyst; the functional catalyst is gel-like micro-nano TiO2 particles; preferably, the surface layer further comprises 3-5 parts by mass of functional catalyst.

[0008] Further, the gel-like micro-nano TiO2 particles are prepared by a sol-gel method under acidic conditions in the presence of alcohol and water; preferably, the alkyl titanate is at least one of n-butyl titanate and tetrabutyl titanate; the alcohol is at least one of methanol and ethanol; and the acid is at least one of hydrochloric acid, hydrobromic acid, and hydroiodic acid.

[0009] Preferably, the thickness of the intermediate layer is 30-50 mm, and the thickness of the surface layer is 5-10 mm.

[0010] Preferably, the blast furnace slag has a specific surface area of 400-650 m 2 / kg; more preferably, the blast furnace slag comprises the following components by mass percentage: 27-33 wt% of SiO2, 17-20 wt% of Al2O3, 0.4-0.6 wt% of Na2O, 35-40 wt% of CaO, and 6-8 wt% of MgO.

[0011] Preferably, the low-calcium fly ash is obtained from the fine ash collected from flue gas of a coal-fired power plant. More preferably, the fly ash comprises the following components by mass percentage: 45-55 wt% of SiO2, 32-37 wt% of Al2O3, 0.8-1.1 wt% of Na2O, 3.5-5 wt% of CaO, and 0.6-0.9 wt% of MgO.

[0012] Preferably, the magnesium slag is a residue from the slag of the Pidgeon process for magnesium production. More preferably, the magnesium slag comprises the following components by mass percentage: 30-40 wt% of SiO2, 0.5-3 wt% of Al2O3, 40-50 wt% of CaO, 8-13 wt% of MgO, and 3-9 wt% of Fe2O3.

[0013] Preferably, the alkali-activator is a mixed aqueous solution of water glass (Na2O·nSiO2) and NaOH configured in a mass ratio of 3-6:1, and the modulus n of the alkali-activator is 1.0-3.0. More preferably, the mass ratio of water glass to NaOH is 4-5:1.

[0014] The functional photocatalyst is obtained by a preparation method comprising the following steps:

[0015] (T1), 70-100 parts of ethanol, 5-10 parts of water, 3-5 parts of hydrochloric acid are configured into solution A according to mass fraction;

[0016] (T2), 40-50 parts of alkyl titanate, 60-70 parts of ethanol are configured into solution B according to mass fraction;

[0017] (T3), solution A is slowly added to solution B, when the solution presents a gel, an ethanol solution containing 5-10 parts of hydroiodic acid is added, stirring for 15 min, 15-20 parts of low-calcium fly ash is added to the sol, ultrasonic dispersion for 30 min at constant temperature 25℃. 3-5 parts of deionized water is added at a rate of 0.5 mL / min until gel-like micro-nano TiO2 particles are obtained.

[0018] The functional catalyst-nano TiO2 hydrophobic gel is prepared by sol-gel method. The n-butyl titanate is dissolved in ethanol solvent, then mixed with deionized water to carry out hydrolysis and condensation reaction, which can effectively avoid the initial titanium dioxide particles from agglomerating into large particles. Then through the physical compression effect of centrifugation and solvent evaporation, the colloidal particles are forced to approach each other, overcome the repulsion, and realize gelation. The photocatalyst can be well attached to the three-dimensional network zeolite-like structure of the base material, thereby forming single-particle TiO2, which can be uniformly distributed on the base material without damaging the basic structure of the base material; the gel-like micro-nano TiO2 particles also effectively avoid the separation from the three-dimensional network of the base material, prolong the service life of the composite material, and ensure the stability of the photocatalytic composite material; at the same time, the zeolite-like structure of the base material enhances the adsorption capacity of formaldehyde gas, thereby increasing the contact efficiency of the photocatalyst and the target degradation pollutant formaldehyde, and improving the degradation efficiency.

[0019] The application also provides a preparation method of the sandwich structure formaldehyde degradation functional alkali-activated cementitious material, which comprises the following steps:

[0020] (S1) according to mass fraction, slag, fly ash, magnesium slag, alkali activator are added into a stirring tank to obtain mortar I; according to mass fraction, slag, fly ash, magnesium slag, alkali activator, functional catalyst are added into a stirring tank to obtain mortar II;

[0021] (S2) the mortar I is prepared into an intermediate layer by 3D printing method or template method, and the surface layer is prepared on the upper and lower surfaces of the intermediate layer by using the mortar II; the alkali-activated cementitious material is obtained by curing at room temperature.

[0022] The process for preparing the three-layer sandwich structure gel material by the 3D printing method or template method is well known in the art.

[0023] For the template method, the slurry I is poured into a mold in which the acrylic plate is placed, leaving a gap to continue pouring the slurry II, then the mold is turned over, the acrylic plate is removed, the slurry II is poured, forming a sandwich structure, the slurry I as the intermediate layer material, and the slurry II as the surface layer material on the upper and lower surfaces of the intermediate layer. The amount of slurry I and slurry II is controlled to make the thickness of the intermediate layer 30-50mm and the thickness of the surface layer 5-10mm.

[0024] For the 3D printing method, the slurry I is poured on the experimental table through the 3D printing nozzle, and when it forms a thickness of 5-10mm, the slurry II is poured as the intermediate layer on the slurry I through the 3D printing nozzle, making it form a thickness of 30-50mm, and finally the remaining slurry I is poured in the same way through the 3D printing nozzle to form a sandwich structure.

[0025] The application also provides the application of the sandwich structure formaldehyde degradation functional alkali-activated cementitious material as a building material.

[0026] The beneficial effects of the present application relative to the prior art are:

[0027] (1) The present application uses fly ash, magnesium slag and slag and other solid waste to prepare green building materials with photocatalytic degradation of formaldehyde capacity. Compared with traditional matrix materials, the alkali-activated cementitious material of the present application has the advantage of using industrial by-products, and has excellent mechanical properties while reducing energy consumption, and the irregular three-dimensional network structure of the alkali-activated cementitious material formed by the corner of silicon-oxygen tetrahedron and aluminum-oxygen tetrahedron provides a large number of sites for the loading of photocatalysts.

[0028] (2) The photocatalyst of the present application has been specially treated to make it more effective in degrading formaldehyde gas under natural light conditions; the specially treated photocatalyst can be well attached to the three-dimensional network zeolite-like structure of the matrix material, ensuring the stability of the photocatalytic composite material; at the same time, the zeolite-like structure of the matrix material enhances the adsorption capacity of formaldehyde gas, thereby increasing the contact efficiency of the photocatalyst and the target degradation pollutant formaldehyde and improving the degradation efficiency.

[0029] (3) The application provides a catalyst for degrading formaldehyde prepared from solid waste, which can not only efficiently degrade formaldehyde gas, but also solves the problem of the lack of mechanical strength of traditional photocatalysts and the inability of the photocatalysts to be practically applied, and realizes the resource utilization of the solid waste, thereby reducing the load on the environment caused by the negative accumulation. Through the above implementation mode, the indoor living environment is improved, the indoor airflow quality is positively circulated, the application field of the photocatalyst is widened, the large-scale application of the photocatalyst is promoted, the high-value-added application of the solid waste-based alkali-activated cementitious material is realized, the purpose of green development is achieved, and the application has high practical value. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a TEM photo of the gel-like micro-nano TiO2 particles prepared in Preparation Example 1;

[0031] Figure 2 is a TEM image of the functional alkali-activated cementitious material obtained in Example 1;

[0032] Figure 3 is a macroscopic photo of the sandwich structure formaldehyde degradation functional alkali-activated material of Examples 1-5 and without adding a functional catalyst;

[0033] Figure 4 is a TEM image of the functional alkali-activated cementitious material obtained in Comparative Example 1. DETAILED DESCRIPTION

[0034] In order to make the objects, technical solutions and advantages of the application clearer, the technical solutions of the application will be described in detail below. The following examples facilitate better understanding of the application, but do not limit the application. In the following examples, the experimental methods are conventional methods, unless otherwise specified.

[0035] The reagents and raw materials used in the application are all commercially available, the blast furnace slag (BFS) is purchased from Tang Steel Company, the fly ash (FA) is purchased from Henan Hengyuan New Material Co., Ltd., and the magnesium slag (MS) is from Shaanxi Dongfeng Magnesium Co., Ltd. and Xilong Science and Technology Co., Ltd. The blast furnace slag, fly ash and magnesium slag are analyzed by XRF-1800 continuous X-ray fluorescence spectrometer, and the results are shown in Table 1 below:

[0036] Table 1

[0037] Raw materials SiO2(wt%) Al2O3 (wt%) Na2O (wt%) CaO (wt%) MgO (wt%) F2O3 (wt%) BFS 31.59 18.79 0.45 37.59 7.32 0.319 FA 50.28 35.56 0.964 4.06 0.715 6.39 MS 38.43 0.95 / 43.79 9.65 4.51

[0038] Preparation Example 1

[0039] (T1), 100 parts of ethanol, 10 parts of water and 3 parts of hydrochloric acid are configured into solution A according to the mass fraction.

[0040] (T2), 50 parts of n-butyl titanate and 70 parts of ethanol were configured into solution B according to mass fraction.

[0041] (T3), solution A was slowly added to solution B, when the solution showed gel-like, 10 parts of hydroiodic acid in ethanol solution was added, stirred for 15 min, 20 parts of low calcium fly ash was added, ultrasonic dispersion was carried out for 30 min at constant temperature 25℃, 5 parts of deionized water was added at a rate of 0.5 mL / min until gel-like micro-nano TiO2 particles were obtained as functional catalyst.

[0042] Figure 1 It is a TEM picture of the gel-like micro-nano TiO2 particles prepared in Preparation Example 1, it can be seen that the TiO2 hydrophobic gel does not agglomerate with each other, but shows uniform dispersion.

[0043] Preparation Example 2

[0044] (T1), 70 parts of ethanol, 5 parts of water and 5 parts of hydrochloric acid were configured into solution A according to mass fraction.

[0045] (T2), 30 parts of n-butyl titanate and 60 parts of ethanol were configured into solution B according to mass fraction.

[0046] (T3), solution A was slowly added to solution B, when the solution showed gel-like, 10 parts of hydroiodic acid in ethanol solution was added, stirred for 15 min, 20 parts of low calcium fly ash was added, ultrasonic dispersion was carried out for 30 min at constant temperature 25℃, 5 parts of deionized water was added at a rate of 0.5 mL / min until gel-like micro-nano TiO2 particles were obtained as functional catalyst.

[0047] Example 1

[0048] A preparation method of a sandwich structure formaldehyde degradation functional alkali-activated material, comprising the following steps:

[0049] S1: collecting blast furnace slag discharged from an iron smelting plant; grinding the blast furnace slag in a planetary ball mill; adding 53 parts of slag, 17 parts of fly ash, 13 parts of magnesium slag and 13 parts of alkali-activator (which is composed of 4 parts of water glass, 1 part of NaOH and 8 parts of water, and the modulus n is 1.5) into a stirring tank to obtain slurry I; adding 53 parts of slag, 17 parts of fly ash, 13 parts of magnesium slag, 13 parts of alkali-activator and 2 parts of functional catalyst prepared in Preparation Example 1 into the stirring tank to obtain slurry II;

[0050] (S2) Pouring slurry I into a 40 mm x 40 mm x 40 mm mold, placing a 5 mm acrylic plate at the bottom of the mold, controlling the amount of slurry I added to make the middle layer 30 mm thick, leaving a 5 mm gap at the top of the mold, pouring slurry II to obtain a 5 mm surface layer, then turning over the mold, removing the acrylic plate, pouring slurry II, and thus forming a surface layer with a thickness of 5 mm on the upper and lower surfaces of the middle layer. After curing at room temperature for 7 days, a sandwich-structured formaldehyde-degradation functional alkali-activated cementitious material with a middle layer thickness of 30 mm and a surface layer thickness of 5 mm is obtained.

[0051] Figure 2 is a TEM image of the functional alkali-activated cementitious material obtained in Example 1, from which it can be seen that TiO2 hydrophobic gel is uniformly dispersed in the matrix material.

[0052] Example 2

[0053] The other operations and conditions are the same as in Example 1, except that the amount of functional catalyst added in slurry II is 3 parts by mass.

[0054] Example 3

[0055] The other operations and conditions are the same as in Example 1, except that the amount of functional catalyst added in slurry II is 5 parts by mass.

[0056] Example 4

[0057] The other operations and conditions are the same as in Example 1, except that the amount of functional catalyst added in slurry II is 6 parts by mass.

[0058] Example 5

[0059] The other operations and conditions are the same as in Example 1, except that the amount of functional catalyst added in slurry II is 7 parts by mass.

[0060] Figure 3 is a macroscopic photograph of the sandwich-structured formaldehyde-degradation functional alkali-activated material of Examples 1-5, and a material without the addition of a functional catalyst, (a) is a material without the addition of a functional catalyst, and (b) to (f) are materials prepared in Examples 1-5, respectively. It can be seen that the addition or non-addition of a functional catalyst, and the amount of addition, have no significant effect on the macroscopic structure of the material.

[0061] Example 6

[0062] The other operations and conditions are the same as in Example 3, except that the functional catalyst is prepared in Preparation Example 2.

[0063] Example 7

[0064] Other operations and conditions are the same as Example 3, except that the raw materials of Mortar I are 40 parts by mass of slag, 10 parts by mass of fly ash, 10 parts by mass of magnesium slag, and 10 parts by mass of alkali activator; and the raw materials of Mortar II are 40 parts by mass of slag, 10 parts by mass of fly ash, 10 parts by mass of magnesium slag, 10 parts by mass of alkali activator, and 5 parts by mass of the functional catalyst prepared in Preparation Example 1.

[0065] Example 8

[0066] Other operations and conditions are the same as Example 3, except that the raw materials of Mortar I are 60 parts by mass of slag, 20 parts by mass of fly ash, 20 parts by mass of magnesium slag, and 15 parts by mass of alkali activator; and the raw materials of Mortar II are 60 parts by mass of slag, 20 parts by mass of fly ash, 20 parts by mass of magnesium slag, 15 parts by mass of alkali activator, and 5 parts by mass of the functional catalyst prepared in Preparation Example 1.

[0067] Comparative Example 1

[0068] Other operations and conditions are the same as Example 3, except that the functional catalyst is anatase nano-titanium dioxide, and the amount of the functional catalyst added is such that the content of TiO2 in the surface layer is the same as in Example 3.

[0069] Figure 4 is a TEM image of the functional alkali-activated cementitious material obtained in Comparative Example 1, from which it can be seen that the unmodified nano-TiO2 particles are agglomerated on the matrix material.

[0070] Performance test

[0071] Using the samples provided in the examples and comparative examples, the compressive strength of the samples aged for 3d and 7d was tested according to GB / T 17671-1999 using a microcomputer-controlled electronic universal testing machine (CMT4304) with a loading area of 40mm x 40mm and a loading rate of 5mm / min. The formaldehyde degradation experiment was performed using the gel materials cured for 7d under simulated solar light irradiation at an input power of 500W, with an initial formaldehyde concentration of 50ppm, according to the test method of GB / T18883-2002 "Indoor air quality standard", by heating the formaldehyde gas output in a water bath at 80℃, feeding it into the reactor through a gas supply system, and using a suction pump type formaldehyde detector to test the formaldehyde concentration and calculate the formaldehyde degradation efficiency. The light irradiation time was maintained for 10d, and the change in formaldehyde degradation efficiency was monitored, with the results shown in Table 2:

[0072] Table 2 Performance indicators of catalyst-cementitious materials

[0073]

[0074] As can be seen from Table 2, the addition amount of the functionalization agent is increased, the formaldehyde degradation rate is improved; at the same time, due to the functional catalyst nanoparticles filled into the material, the porosity of the material is reduced, thereby improving the microstructure thereof; however, with the further increase of the content of the functional catalyst nanoparticles, the agglomeration phenomenon of the nanoparticles in the cementitious material is prone to occur, resulting in the destruction of the structure of the matrix material, thereby causing the compressive strength of the material to decrease. To some extent, the addition of the functional catalyst also improves the mechanical strength of the material, but when the addition amount is further increased, the mechanical strength of the material decreases, and when the raw material ratio of Example 3 is adopted, the compressive strength is the maximum of 44.63 MPa. At the same time, the degradation efficiency of formaldehyde is also satisfactory, and the formaldehyde degradation rate is 46.0% after 2h of illumination. Moreover, the photocatalyst provided by the present application has stable performance and long service life, and the formaldehyde degradation rate is basically not reduced under the condition of 10d of continuous illumination. However, if the nano-TiO2 is directly added into the slurry as a photocatalyst, the prepared gel material has a higher initial formaldehyde degradation rate, but the photocatalyst activity is obviously reduced after 10d of illumination. The possible reason is that the nano-TiO2 is agglomerated after being recycled, thereby reducing the contact area of the photocatalyst with the target pollutants; and with the extension of the use time, the photocatalyst is further wrapped by the gel material, which also reduces the degradation efficiency thereof.

[0075] In conclusion, the present application utilizes fly ash, magnesium slag and slag and other bulk solid waste to prepare green building materials with certain photocatalytic degradation capacity of formaldehyde, which not only can efficiently degrade formaldehyde gas, but also solves the shortcomings of traditional photocatalysts, i.e. lack of mechanical strength and inability to be practically applied, and at the same time, the solid waste is resourcefully utilized, thereby reducing the negative load on the environment caused by passive accumulation. Thus, the high-value application of solid waste-based alkali-activated cementitious materials is realized, the indoor formaldehyde residue is reduced, and the human living environment is improved.

Claims

1. A sandwich-structured formaldehyde-degrading functional alkali-activated cementitious material, characterized in that, It consists of an intermediate layer and a surface layer covering the upper and lower surfaces of the intermediate layer. The intermediate layer and the surface layer include the following materials: The composition includes 53 parts by weight of blast furnace slag, 17 parts by weight of low-calcium fly ash, 13 parts by weight of alkaline magnesium slag, and 13 parts by weight of alkaline activator. The alkaline activator is composed of 4 parts by weight of water glass, 1 part by weight of NaOH, and 8 parts by weight of water. The water glass is Na2O·nSiO2 with a modulus n of 1.

5. The surface layer also includes 5-6 parts by weight of functional catalyst, which is gel-like micro / nano TiO2 particles. The functional catalyst is obtained by a preparation method including the following steps: (T1) Prepare solution A by mixing 70-100 parts of ethanol, 5-10 parts of water, and 3-5 parts of hydrochloric acid according to the mass fraction. (T2) Solution B is prepared by mass fractions including 40-50 parts of alkyl titanate and 60-70 parts of ethanol; (T3) Slowly add solution A to solution B. When the solution becomes gel-like, add an ethanol solution containing 5-10 parts of hydroiodic acid and stir for 15 min. Add 15-20 parts of low-calcium fly ash to the sol and sonicate at a constant temperature of 25℃ for 30 min. Add 3-5 parts of deionized water at a rate of 0.5 mL / min until gel-like micro-nano TiO2 particles are obtained.

2. The sandwich-structured formaldehyde-degrading functional alkali-activated cementitious material according to claim 1, characterized in that, The alkyl titanate is tetrabutyl titanate.

3. The sandwich-structured formaldehyde-degrading functional alkali-activated cementitious material according to claim 1, characterized in that, The thickness of the intermediate layer is 30-50 mm, and the thickness of the surface layer is 5-10 mm.

4. The sandwich-structured formaldehyde-degrading functional alkali-activated cementitious material according to claim 1, characterized in that, The blast furnace slag has a specific surface area of ​​400~650 m². 2 / kg.

5. The sandwich-structured formaldehyde-degrading functional alkali-activated gelling material according to claim 4, characterized in that, Blast furnace slag comprises the following components by mass percentage: 27-33 wt% SiO2, 17-20 wt% Al2O3, 0.4-0.6 wt% Na2O, 35-40 wt% CaO, and 6-8 wt% MgO.

6. The sandwich-structured formaldehyde-degrading functional alkali-activated cementitious material according to claim 1, characterized in that, The low-calcium fly ash comprises the following components by mass percentage: 45-55 wt% SiO2, 32-37 wt% Al2O3, 0.8-1.1 wt% Na2O, 3.5-5 wt% CaO, and 0.6-0.9 wt% MgO.

7. The sandwich-structured formaldehyde-degrading functional alkali-activated cementitious material according to claim 1, characterized in that, The alkaline magnesium slag comprises the following components by mass percentage: 30-40 wt% SiO2, 0.5-3 wt% Al2O3, 40-50 wt% CaO, 8-13 wt% MgO, and 3-9 wt% Fe2O3.

8. The preparation method of the sandwich-structured formaldehyde-degrading functional alkali-activated gelling material according to any one of claims 1-7, characterized in that, Includes the following steps: (S1) According to the mass fractions, blast furnace slag, low-calcium fly ash, alkaline magnesium slag, and alkali activator are added to a mixing tank to obtain mortar I; according to the mass fractions, blast furnace slag, low-calcium fly ash, alkaline magnesium slag, alkali activator, and functional catalyst are added to a mixing tank to obtain mortar II. (S2) Mortar I is prepared into an intermediate layer by 3D printing or template method, and mortar II is used to prepare a surface layer on the upper and lower surfaces of the intermediate layer; the alkali-activated cementitious material is obtained by curing at room temperature.

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