Preparation method of carbon nitride-attached cement-based material induced by magnesium salt and coupled with carbonization curing

Abstract

The present invention discloses a method for preparing a carbon nitride-attached cementitious material that is cured by magnesium salt-induced coupled carbonization. The method involves first colloidizing the carbon nitride to obtain a uniformly dispersed, negatively charged colloidal carbon nitride. This colloidal carbon nitride is then compounded with a soluble magnesium salt to obtain a dispersion containing the magnesium salt and colloidal carbon nitride. The dispersion is then sprayed onto the surface of the hardened cementitious material for carbonization curing. The carbonization product (magnesium carbonate) bridges the adjacent carbon nitride and cement matrix, resulting in a photocatalytic cementitious material with stably attached carbon nitride. Unlike conventional photocatalytic layers prepared using binders, the present invention utilizes in situ formed magnesium carbonate for bridging. This not only overcomes the drawback of carbon nitride active sites being encapsulated by the binder, but also exhibits excellent aging and wear resistance, effectively ensuring the long-term purification efficacy of the photocatalytic cementitious material.

Description

Technical Field

[0001] The present invention belongs to the field of environmental materials, and in particular relates to a method for preparing a carbon nitride-attached cement-based material induced by magnesium salt and coupled with carbonization curing. Background Art

[0002] With the impact of global warming and the acceleration of urbanization, the area of ​​hard road pavement and building density in cities are increasing, causing an increase in ground rainwater runoff. The pollution caused by heavy metal ions, suspended solids, organic matter and other pollutants in rainwater is becoming increasingly serious. In particular, heavy metal ions and organic pollutants in the accumulated water remain on the ground, which will increase the concentration of road pollutants. The odor and volatile organic compounds emitted by rainwater will also pollute the air. In addition, the exhaust gas emitted by cars on the road contains nitrogen oxides (NO x ) will lead to a sharp deterioration in air quality. Therefore, the purification of rainwater runoff pollution and NO x The prevention and control of pollution is urgent. Combining green and sustainable photocatalytic environmental remediation technology with cement-based pavement materials to develop new cement-based pavement materials with rainwater and exhaust gas purification functions is considered one of the most promising green methods for purifying rainwater runoff pollution and exhaust gas.

[0003] Current research on photocatalytic cement-based materials focuses on constructing photocatalytic coatings on their surfaces. For example, patent CN115180976A discloses a method for preparing a photocatalytic cement-based material; patent CN116920831A discloses a VOCs decomposition photocatalyst coating, its preparation method, and application; patent CN116673074A discloses a titanium dioxide photocatalytic coating, its preparation method, and product; and patent CN114308123A discloses a photocatalytic coating material and its preparation method. To ensure stable adhesion of the photocatalyst to the cement substrate, existing research often employs a uniform mixing of a binder and the photocatalyst to prepare the photocatalytic coating. However, this results in the photocatalyst being encapsulated by the binder, preventing it from fully contacting the target pollutants and light, resulting in significantly limited purification efficiency. Furthermore, organic binders suffer from poor aging resistance and weak mechanical properties, making them incapable of maintaining effective long-term purification performance. Therefore, exploring strategies for stable, binder-free photocatalyst attachment is crucial for maximizing the purification efficiency and long-term performance of photocatalytic cement-based materials. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing a carbon nitride-attached cement-based material induced by magnesium salt and coupled with carbonization curing. The method uses positively charged magnesium ions to compound negatively charged colloidal carbon nitride, and sprays it on the surface of the cement-based material. The magnesium ions are converted into magnesium carbonate through carbonization curing, so that the magnesium carbonate is used to bridge the adjacent carbon nitride and cement matrix to form a stable three-dimensional bridging structure. The method not only overcomes the problem of photocatalyst shielding caused by traditional adhesive mixing, but also greatly improves the aging resistance and wear resistance of the photocatalytic layer and reduces material costs.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A magnesium salt-induced coupled carbonization-cured carbon nitride-attached cement-based material, the preparation method of which comprises the following steps:

[0007] (1) Dispersing carbon nitride powder in a sodium hydroxide solution at 80±2°C, stirring magnetically and centrifuging, dispersing the precipitate in deionized water to obtain a colloidal carbon nitride dispersion;

[0008] (2) Under a protective atmosphere, dissolving a soluble magnesium salt in the colloidal carbon nitride dispersion obtained in step 1) by magnetic stirring to obtain a dispersion containing magnesium salt and colloidal carbon nitride;

[0009] (3) After removing the calcium carbonate layer from the surface of the hardened cement-based material, the dispersion containing magnesium salt and colloidal carbon nitride obtained in step (2) is sprayed on the surface of the hardened cement-based material, and then carbonization curing is performed to obtain a cement-based material with stably attached carbon nitride.

[0010] Furthermore, the carbon nitride powder in step (1) is specifically graphite phase carbon nitride powder, which has a two-dimensional layered morphology, a thickness of 20-50 nm, a particle size of 0.3-0.5 μm, and a surface Zeta potential of -15--25 mV.

[0011] Furthermore, the mass concentration of the sodium hydroxide solution in step (1) is 0.5-0.7%.

[0012] Furthermore, in step (1), the amount of carbon nitride powder added to the sodium hydroxide solution is 1-12 g / L.

[0013] Furthermore, the magnetic stirring in step (1) is carried out at a speed of 600 rpm for 12 hours.

[0014] Furthermore, the centrifugal speed in step (1) is 4000 rpm and the time is 5 minutes.

[0015] Furthermore, the concentration of the dispersion of colloidal carbon nitride obtained in step (1) is 0.1-3 g / L; specifically, the obtained colloidal carbon nitride is a carbon nitride sol; wherein the carbon nitride is fibrous, has a particle size of 50-80 nm, is surface-modified with hydroxyl functional groups, and has a Zeta potential of -35-40 mV.

[0016] Furthermore, the protective atmosphere in step (2) is nitrogen with a flow rate of 100 ml / min.

[0017] Furthermore, the soluble magnesium salt in step (2) is magnesium nitrate or magnesium sulfate.

[0018] Furthermore, in step (2), the amount of soluble magnesium salt added to the colloidal carbon nitride dispersion is 7-15 g / L.

[0019] Furthermore, the hardened cement-based material in step (3) is cement paste, cement mortar or concrete with a standard curing period of 28 to 180 days.

[0020] Furthermore, the spraying amount of the dispersion containing magnesium salt and colloidal carbon nitride in step (3) is 0.1~1 L / m 2 .

[0021] Furthermore, the carbonization curing conditions in step (3) are: relative humidity 50-95%, carbon dioxide concentration 0.04-20%, and curing time 48 hours.

[0022] The colloidal carbon nitride in the present invention has a large electronegativity and can be evenly dispersed in an aqueous solution. The bridging nitrogen atoms in its molecular structure have lone pairs of electrons that can chelate with positively charged magnesium ions in the aqueous solution. These magnesium ions can react with carbon dioxide in a carbonized environment to form magnesium carbonate. The in-situ formed magnesium carbonate can bridge the adjacent carbon nitride and the hydrated calcium silicate on the surface of the cement matrix, and form a three-dimensional spatial structure (such as Figure 1 ), thereby consolidating the carbon nitride on the surface of the cement matrix.

[0023] The present invention has the following advantages:

[0024] Compared with the traditional photocatalytic layer prepared with a binder, the present invention uses positively charged magnesium ions to combine with colloidal carbon nitride through electrostatic action and the magnesium carbonate generated in situ through carbonization curing not only does not wrap the active sites on the edge of the carbon nitride, but the three-dimensional bridging structure composed of magnesium carbonate can effectively increase the exposure of the carbon nitride active sites. In addition, the in-situ generated magnesium carbonate not only has better compatibility with the cement matrix, but also can improve the aging resistance and wear resistance of cement-based materials, greatly improving the stability of its long-term photocatalytic purification effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the SEM image of the composite spatial structure of carbon nitride and magnesium carbonate.

[0026] Figure 2 NO x Schematic diagram of the photocatalytic performance test system, including: ① high-purity air; ② pressure reducing valve; ③ flow stabilizing valve; ④ NO cylinder gas; ⑤ gas washing bottle; ⑥ flow rate controller; ⑦ temperature and humidity sensor; ⑧ reactor; ⑨ NO x Analyzer;⑩Tail gas absorption bottle.

[0027] Figure 3 Comparison of carbon nitride-attached cementitious materials prepared in Example (left) and Comparative Example 1 (right) after ultrasonic cleaning. As can be seen, in Comparative Example 1, where no magnesium salt was added, the carbon nitride-attached cementitious material exhibits almost complete loss of carbon nitride after ultrasonic cleaning, revealing the off-white cementitious matrix. DETAILED DESCRIPTION

[0028] The preparation of a magnesium salt-induced coupled carbonization-cured carbon nitride-attached cement-based material comprises the following steps:

[0029] (1) Disperse carbon nitride powder in an amount of 1-12 g / L in a sodium hydroxide solution at 80 ± 2 ° C and a mass concentration of 0.5-0.7%, stir magnetically at 600 rpm for 12 hours, centrifuge at 4000 rpm for 5 minutes, and disperse the precipitate in deionized water by magnetic stirring to obtain a colloidal carbon nitride dispersion with a concentration of 0.1-3 g / L.

[0030] (2) dissolving a soluble magnesium salt in an amount of 7 to 15 g / L in the colloidal carbon nitride dispersion obtained in step 1) by magnetic stirring under nitrogen at a flow rate of 100 ml / min to obtain a dispersion containing the magnesium salt and the colloidal carbon nitride;

[0031] (3) After removing the surface calcium carbonate layer of the hardened cement-based material with a grinding and polishing machine, press 0.1~1 L / m 2 The dispersion containing magnesium salt and colloidal carbon nitride obtained in step (2) is sprayed in an amount of , and then moved into a carbonization box and cured for 48 hours under the conditions of relative humidity of 50-95% and carbon dioxide concentration of 0.04-20% to obtain a cement-based material with stably attached carbon nitride.

[0032] The carbon nitride powder in step (1) is specifically graphite phase carbon nitride powder, which has a two-dimensional layered morphology, a thickness of 20 to 50 nm, a particle size of 0.3 to 0.5 μm, and a surface Zeta potential of -15 to -25 mV.

[0033] The soluble magnesium salt in step (2) is magnesium nitrate or magnesium sulfate.

[0034] The hardened cement-based material in step (3) is cement paste, cement mortar or concrete with a standard curing period of 28 to 180 days.

[0035] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0036] The carbon nitride powder used in the examples is specifically graphite phase carbon nitride powder, which has a two-dimensional layered morphology, a thickness of 20 to 50 nm, a particle size of 0.3 to 0.5 μm, and a surface Zeta potential of -15 to -25 mV. Example

[0037] This embodiment adopts magnesium salt induced coupled carbonization curing to prepare the colloidal carbon nitride-attached cement-based material, and its specific preparation steps are as follows:

[0038] Take 0.5g of carbon nitride powder and disperse it in 200mL of sodium hydroxide solution (80℃, mass fraction of sodium hydroxide is 0.5 wt%) by magnetic stirring (600 rpm), keep stirring for 12 hours and then centrifuge for 5 minutes (4000 rpm), take the precipitate and disperse it in 300mL of deionized water to obtain a dispersion of colloidal carbon nitride with a concentration of 0.5g / L. Take 3.5g of magnesium nitrate and dissolve it in the above-mentioned dispersion of colloidal carbon nitride by magnetic stirring, and introduce nitrogen at a flow rate of 100 ml / min to obtain a dispersion containing magnesium salt and colloidal carbon nitride. Take the cement slurry that has been cured for 28 days by standard, remove the surface carbonized layer with a grinder, and then spray the dispersion containing magnesium salt and colloidal carbon nitride on its surface, and control the spraying amount to 0.5 L / m 2 , and then moved into the carbonization box, the carbonization conditions were controlled to be 70% relative humidity and 15% carbon dioxide concentration, and after curing for 48 hours, a photocatalytic cement-based material with stably attached colloidal carbon nitride was obtained.

[0039] In order to simulate the scenarios of rain erosion, mechanical wear and UV aging that may be encountered in actual applications, ultrasonic cleaning experiments, wear experiments and accelerated aging experiments were set up respectively. Specifically, the obtained photocatalytic cement-based material specimens (1) were ultrasonically cleaned in a CNC ultrasonic cleaner at a power of 40 watts for 1 minute to simulate the effect of rain erosion; (2) the obtained photocatalytic cement-based material specimens were polished in a grinder at a power of 500 watts for 2 minutes with a grinding wheel of 36 meshes to simulate the effect of mechanical wear; (3) the obtained photocatalytic cement-based material specimens were placed in an aging box and irradiated under a xenon lamp light source with an intensity of 1200W / m 2, accelerated aging for 15 days in an environment with a blackboard temperature of 60°C and a humidity of 60% to simulate UV aging.

[0040] After the above test blocks were cleaned and dried naturally, the photocatalytic gas purification experiment was carried out. Figure 2 The NO shown x The photocatalytic performance test system was carried out as follows: the entire test system was a closed space, with nitric oxide as the simulated air pollutant. The target gas concentration was controlled to be 1 ppm NO through a gas mixing device, the gas flow rate was 1 L / min, the humidity was 50±2%, and the temperature was 25±2°C. A concrete sample (Φ30 mm×15 mm) was filled in the reactor, and a fluorescent lamp (wavelength>420 nm) was installed 10 mm above the reactor. The gas passing through the reactor directly entered the NO x The analyzer collects NO in the gas in real time x The photocatalytic efficiency of photocatalytic steel slag exposed concrete is calculated according to the following formula:

[0041] ,

[0042] Where ƞ is the photocatalytic efficiency (%), C off is the NO concentration when the light is not on, C on is the NO concentration when the light is on.

[0043] The results show that the photocatalytic gas purification efficiency of the material was 65% and 61% before and after the ultrasonic cleaning experiment, respectively; the photocatalytic gas purification efficiency of the material was 65% and 50% before and after the mechanical friction experiment, respectively; and the photocatalytic gas purification efficiency of the material was 65% and 60% before and after the accelerated aging experiment, respectively.

[0044] Comparative Example 1

[0045] The colloidal carbon nitride-attached cement-based material prepared in this comparative example without adding magnesium salt has the following specific preparation steps:

[0046] Take 0.5g of carbon nitride powder and disperse it in 200mL of sodium hydroxide solution (80℃, mass fraction of sodium hydroxide is 0.5 wt%) by magnetic stirring (600 rpm), keep stirring for 12 hours and centrifuge for 5 minutes (4000 rpm), take the precipitate and disperse it in 300mL of deionized water, and pass nitrogen at a flow rate of 100 ml / min to obtain a dispersion of colloidal carbon nitride with a concentration of 0.5g / L. Take the cement slurry that has been cured for 28 days, remove the surface carbonized layer with a grinder, and spray the dispersion containing colloidal carbon nitride on its surface, and control the spraying amount to 0.5 L / m 2, and then moved into a carbonization box, and the carbonization conditions were controlled to be 70% relative humidity and 15% carbon dioxide concentration. After curing for 48 hours, a photocatalytic cement-based material with colloidal carbon nitride attached was obtained.

[0047] Experiments were conducted according to the methods described in the examples. The results showed that the photocatalytic gas purification efficiency of the material was 65% before and 5% after ultrasonic cleaning, 65% before and 10% before mechanical friction, and 65% before and 20% after accelerated aging.

[0048] Comparing the experimental results of the Examples with those of Comparative Example 1 reveals that the presence of magnesium ions in colloidal carbon nitride is a key factor in its stable adhesion to the cement matrix. In a carbon dioxide environment, the magnesium ions carbonize to form stable magnesium carbonate, which bridges adjacent carbon nitride and cement matrix, forming a stable three-dimensional bridge structure that ensures the stable adhesion of the carbon nitride to the cement matrix surface.

[0049] Comparative Example 2

[0050] In this comparative example, carbonization curing was not used to prepare the cement-based material with colloidal carbon nitride attached, and the specific preparation steps were as follows:

[0051] Take 0.5g of carbon nitride powder and disperse it in 200mL of sodium hydroxide solution (80℃, mass fraction of sodium hydroxide is 0.5 wt%) by magnetic stirring (600 rpm), keep stirring for 12 hours and centrifuge for 5 minutes (4000 rpm), take the precipitate and disperse it in 300mL of deionized water to obtain a dispersion of colloidal carbon nitride with a concentration of 0.5g / L. Take 3.5g of magnesium nitrate and dissolve it in the above-mentioned dispersion of colloidal carbon nitride by magnetic stirring, and introduce nitrogen at a flow rate of 100 ml / min to obtain a dispersion containing magnesium salt and colloidal carbon nitride. Take cement mortar that has been cured for 28 days by standard, remove the surface carbonized layer with a grinder, and then spray the dispersion containing magnesium salt and colloidal carbon nitride on its surface, and control the spraying amount to 0.5 L / m 2 , and then cured for 48 hours at room temperature (50% relative humidity, 25°C) to obtain a photocatalytic cement-based material with colloidal carbon nitride attached.

[0052] Experiments were conducted according to the methods described in the examples. The results showed that the photocatalytic gas purification efficiency of the material was 65% before and 12% after ultrasonic cleaning, 65% before and 13% before mechanical friction, and 65% before and 22% after accelerated aging.

[0053] Comparison of the experimental results in Example 2 and Comparative Example 2 demonstrates that carbonation curing is another key factor in the stable adhesion of magnesium salt-induced carbon nitride to the cement matrix surface. It provides sufficient carbon dioxide for magnesium ions to react and form magnesium carbonate, a key component that not only bridges adjacent carbon nitrides but also serves as a bridge between carbon nitrides and calcium silicate hydrates in the cement matrix. However, in an air environment with low carbon dioxide concentrations, only low-crystallinity magnesium carbonate is formed, which is unable to firmly embed the carbon nitride.

[0054] Comparative Example 3

[0055] In this comparative example, magnesium salt and carbon nitride powder are directly mixed (ground) to prepare a dispersion, and then carbonized and cured to prepare a cement-based material with carbon nitride attached. The specific preparation steps are as follows:

[0056] 0.5g of carbon nitride powder was ground and mixed with 3.5g of magnesium nitrate, and then dispersed in 300mL of deionized water by magnetic stirring (600 rpm), and nitrogen was introduced at a flow rate of 100 ml / min to obtain a dispersion containing magnesium salt and carbon nitride. After the cement mortar with standard curing for 28 days was removed by a grinding and polishing machine, the dispersion containing magnesium salt and carbon nitride was sprayed on its surface, and the spraying amount was controlled to 0.5 L / m 2 , and then moved into a carbonization box, and the carbonization conditions were controlled to be 70% relative humidity and 15% carbon dioxide concentration. After curing for 48 hours, a photocatalytic cement-based material with attached carbon nitride was obtained.

[0057] Experiments were conducted according to the methods described in the examples. The results showed that the photocatalytic gas purification efficiency of the material was 35% and 8% before and after ultrasonic cleaning, 35% and 9% before and after mechanical friction, and 35% and 15% before and after accelerated aging, respectively.

[0058] Comparison of the experimental results of Example 3 with Comparative Example 3 shows that the ability of carbon nitride to uniformly bond with magnesium ions is also a key factor in the stable adhesion of carbon nitride to the cement matrix surface. Due to its large surface energy and low Zeta potential, conventional carbon nitride powder easily aggregates into clusters in aqueous solution, making it difficult to fully expose its surface chelating sites for magnesium ions and forming a uniform and stable carbon nitride dispersion. Therefore, although it can form magnesium carbonate during carbonization curing, it cannot effectively bridge adjacent carbon nitride and cement matrices. Furthermore, the agglomerated carbon nitride particles greatly reduce the exposure rate of their active sites, thereby reducing the photocatalytic purification efficiency.

[0059] The applicant declares that the present invention uses the above-described embodiments to illustrate the detailed compositions and methods of the present invention. However, the present invention is not limited to the above-described detailed compositions and methods, and does not necessarily rely on the above-described detailed compositions and methods for implementation. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the raw materials of the present invention, addition of auxiliary ingredients, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a carbon nitride-attached cement-based material induced by magnesium salt and carbonization curing, characterized in that: The steps include: (1) Dispersing carbon nitride powder in a sodium hydroxide solution at 80±2°C, stirring magnetically and centrifuging, dispersing the precipitate in deionized water to obtain a colloidal carbon nitride dispersion; (2) Under a protective atmosphere, dissolving a soluble magnesium salt in the colloidal carbon nitride dispersion obtained in step (1) by magnetic stirring to obtain a dispersion containing magnesium salt and colloidal carbon nitride; (3) After removing the calcium carbonate layer from the surface of the hardened cement-based material, the dispersion containing magnesium salt and colloidal carbon nitride obtained in step (2) is sprayed on the surface of the hardened cement-based material, and then carbonization curing is performed to obtain a cement-based material with stably attached carbon nitride.

2. The preparation method according to claim 1, characterized in that The carbon nitride powder in step (1) is specifically graphite phase carbon nitride powder; the mass concentration of the sodium hydroxide solution is 0.5-0.7%; and the amount of carbon nitride powder added to the sodium hydroxide solution is 1-12 g / L.

3. The preparation method according to claim 1, characterized in that The magnetic stirring speed in step (1) is 600 rpm and the time is 12 hours; the centrifugal speed is 4000 rpm and the time is 5 minutes.

4. The preparation method according to claim 1, characterized in that The concentration of the colloidal carbon nitride dispersion obtained in step (1) is 0.1-3 g / L.

5. The preparation method according to claim 1, characterized in that The protective atmosphere in step (2) is nitrogen gas with a flow rate of 100 ml / min.

6. The preparation method according to claim 1, characterized in that The soluble magnesium salt in step (2) is magnesium nitrate or magnesium sulfate; the amount thereof added to the colloidal carbon nitride dispersion is 7-15 g / L.

7. The preparation method according to claim 1, characterized in that The hardened cement-based material in step (3) is cement paste, cement mortar or concrete with a standard curing period of 28 to 180 days.

8. The preparation method according to claim 1, characterized in that The spraying amount of the dispersion containing magnesium salt and colloidal carbon nitride in step (3) is 0.1~1 L / m 2 .

9. The preparation method according to claim 1, characterized in that The carbonization curing conditions in step (3) are: relative humidity 50-95%, carbon dioxide concentration 0.04-20%, and curing time 48 hours.

10. A cement-based material with stably attached carbon nitride on the surface prepared by the method according to any one of claims 1 to 9.

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