Preparation method of effective microporous modified activated carbon for adsorbing radon gas

Abstract

The invention discloses a preparation method of effective microporous modified activated carbon for adsorbing radon gas, and relates to the technical field of preparation of effective microporous modified activated carbon, and the preparation method comprises the following steps: adsorbing nano SiO2 into a pore channel by using an activated carbon base material, and drying to obtain an activated carbon / SiO2 compound; the doping amount of the nano SiO2 is 10 to 30 weight percent; mixing the activated carbon / SiO2 compound with polytetrafluoroethylene, and drying to obtain a mixture; the mass ratio of the activated carbon / SiO2 compound to the polytetrafluoroethylene is less than or equal to 1: 3; and calcining the mixed product to obtain the modified activated carbon with the target effective micropore aperture. Effective micropores matched with radon adsorption can be accurately regulated, the number of the effective micropores is remarkably increased, and the problem that in the prior art, the accurate directional regulation degree of effective micropores matched with radon is low is solved. The adsorption coefficient of the modified activated carbon to radon is larger than 10 L / g, the size of a radon adsorption device and the replacement frequency of an invalid carbon bed can be effectively reduced, and the purposes of efficient adsorption and energy conservation can be achieved.

Description

Technical Field

[0001] This invention relates to the field of effective microporous modified activated carbon preparation technology, and in particular to a method for preparing effective microporous modified activated carbon for adsorbing radon gas. Background Technology

[0002] Radon (including 222 Rn and thorium gas 220 Radon (Rn) is a naturally occurring radioactive gas and has become one of the most significant indoor air pollutants, easily accumulating in poorly ventilated environments. The World Health Organization (WHO) has clearly identified radon as the second leading cause of lung cancer and recommends that indoor radon levels should be below 300 Bq / m³. 3 Investigations show that the average radon concentration in many underground projects is as high as 2702 Bq / m³. 3 The highest value reached 5000 Bq / m 3 The levels exceeded the national standard limit by more than 12.5 times. Due to the special limitations of underground engineering structures and concealment, effective ventilation for radon reduction is inefficient and energy-intensive. In such cases, mobile adsorption devices filled with activated carbon have become a key technology for radon removal in local spaces due to their advantages of low cost, low energy consumption, and ease of use.

[0003] Surveys show that there are currently no activated carbon products specifically designed for radon removal on the market. High-quality coconut shell activated carbon exhibits the best radon adsorption performance, but its adsorption coefficient is still below 5 L / g, leading to frequent regeneration and replacement, which fails to meet the demands for efficient radon removal. Numerous studies have focused on improving the radon adsorption performance of activated carbon. Research indicates that radon adsorption on activated carbon is primarily physical, with the microporous structure, especially the pore size matching the atomic size of radon, playing a dominant role. However, effective micropore control methods for radon adsorption are still lacking.

[0004] Activated carbon exhibits high adsorption selectivity for radon in pores with a diameter of 0.42–0.60 nm, with the highest selectivity observed around 0.55 nm. However, activated carbon typically contains macropores, mesopores, and micropores, with a wide pore size distribution. Even coconut shell activated carbon, which is predominantly microporous, has a pore size distribution concentrated in micropores > 0.7 nm. The number of effective micropores suitable for radon adsorption is small, and this pore size mismatch leads to low radon adsorption capacity. To regulate the effective micropores suitable for radon adsorption, Chinese patent CN111389366 B discloses a method for modifying activated carbon with liquid nitrogen to control its pore structure. This method increases the number of effective micropores for radon adsorption in activated carbon to a certain extent. The modified activated carbon achieves a radon adsorption coefficient of 6.67 L / g, a 35% improvement compared to the initial activated carbon. Chinese patent CN 109351327 B discloses a method for graphene-modified activated carbon and an activated carbon-graphene composite material, optimizing the hierarchical pore structure in the activated carbon, achieving a radon adsorption coefficient of 6.1 L / g. Furthermore, Chinese patent CN118663216 B discloses a method for fluorination-modified activated carbon to improve radon adsorption capacity. This method uses fluorine gas to regulate the micropores of activated carbon and introduces fluorine atoms to enhance radon adsorption, achieving a radon adsorption coefficient of 8.2 L / g for the fluorinated activated carbon. While these methods optimize and regulate the micropores of activated carbon to some extent, micropore regulation is somewhat random, and the degree of precise controllability in achieving effective micropores that match radon adsorption is limited. Moreover, the radon adsorption coefficient of the activated carbon modified by these methods is still less than 10 L / g, falling short of the requirements for highly efficient radon adsorption, resulting in poor performance in large-scale radon adsorption devices in practical applications. Therefore, accurately controlling the effective micropore size that matches radon adsorption is crucial for achieving efficient radon adsorption with activated carbon. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing an effective microporous modified activated carbon for adsorbing radon gas, thereby overcoming the defect of low adsorption coefficient for radon in the above-mentioned activated carbon.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing effective microporous modified activated carbon for adsorbing radon gas, comprising the following steps: Nano-SiO2 is adsorbed into the pores of an activated carbon substrate and dried to obtain an activated carbon / SiO2 composite; the amount of nano-SiO2 incorporated is 10~30 wt%. The activated carbon / SiO2 composite was mixed with polytetrafluoroethylene and then dried to obtain a mixture; the mass ratio of the activated carbon / SiO2 composite to the polytetrafluoroethylene was ≤ 1:3. The mixed product is calcined to obtain modified activated carbon with the target effective micropore size.

[0007] Further, in the step of adsorbing nano-SiO2 into the pores using an activated carbon substrate, the nano-SiO2 is first dispersed in deionized water, and then the activated carbon substrate is added; the nano-SiO2 is dispersed in the deionized water by ultrasonic dispersion and / or high-speed shear dispersion; the ultrasonic dispersion is performed at a power of 600~1200W, a frequency of 20~25kHz, and a time of 10~15min; the high-speed shear dispersion is performed at a shearing speed of 10000~15000 rpm and a shear rate of 10. 5 ~10 6 s -1 Cutting time: 10~15min.

[0008] The particle size of the nano-SiO2 is 7~100 nm.

[0009] Furthermore, the polytetrafluoroethylene is in the physical state of powder or emulsion; the mass ratio of SiO2 to polytetrafluoroethylene is 0.07~0.2.

[0010] Furthermore, during the calcination of the mixed product, a protective gas is introduced; the protective gas includes at least one of nitrogen and argon.

[0011] Furthermore, when calcining the mixed product, the temperature is first raised to 800-1100 ℃ at a rate of 5-10 ℃ / min, then held at that temperature for 1-4 h, and then naturally cooled to room temperature.

[0012] Furthermore, the activated carbon substrate includes at least one of coconut shell activated carbon, coal-based activated carbon, resin-based activated carbon, and wood-based activated carbon.

[0013] Furthermore, the drying process involves drying at 80~105 ℃ for 8~12 h.

[0014] Furthermore, the exhaust gas generated during the calcination of the mixed product is treated by absorption with an alkaline solution; the alkaline solution includes a 1 mol / L sodium hydroxide solution, a 1 mol / L sodium carbonate solution, or a 0.02 mol / L calcium hydroxide solution.

[0015] Secondly, the present invention provides an effective microporous modified activated carbon for adsorbing radon gas, wherein the effective microporous modified activated carbon is prepared by the method described above.

[0016] Thirdly, the present invention provides the application of the effective microporous modified activated carbon prepared by the above preparation method in the efficient adsorption of radon gas.

[0017] As can be seen from the above technical solution, the technical effects achieved by the present invention are as follows: This invention first pre-adsorbs nano-SiO2 into the internal pores of activated carbon, then regulates the micropores of the activated carbon by reacting polytetrafluoroethylene (PTFE) with SiO2 to generate gaseous SiF4 (the activated carbon / SiO2 composite is mixed with PTFE to obtain a mixture product; during calcination, the difluorocarbon free radicals formed by the decomposition of PTFE react with the nano-SiO2 in the pores to generate gaseous SiF4, which etches the activated carbon and escapes from the inside to open pores). Utilizing the similarity between the SiF4 molecular size (0.488 nm) and the radon atomic size (0.417 nm), the effective micropore size matching radon adsorption is precisely controlled. The modified activated carbon exhibits a fully microporous characteristic, with micropore volume accounting for more than 95% of the total pore volume. Among them, the effective micropore volume of 0.5~0.7 nm, matching radon, accounts for more than 65% of the total micropore volume, a significant increase compared to the initial activated carbon's effective micropore volume (accounting for 53.03% of the total micropore volume). By enhancing the radon adsorption capacity through pore matching, the modified activated carbon achieved a radon adsorption coefficient of up to 13.75 L / g (adsorption environment at 25℃), which is 247.22% higher than the initial activated carbon's 3.96 L / g.

[0018] Compared with existing technologies, this invention can precisely control the effective micropores that match radon adsorption, significantly increasing the number of effective micropores and overcoming the problem of low precision and directional control of effective micropores for radon matching in existing technologies. The modified activated carbon exhibits a radon adsorption coefficient greater than 10 L / g, effectively reducing the volume of the radon adsorption device and the frequency of replacing the depleted carbon bed, thus facilitating efficient adsorption and energy saving.

[0019] Furthermore, this invention primarily adsorbs radon through the physical adsorption of effective micropores, and desorption can be achieved through heating or negative pressure, making the material easily regenerable. The modification method is simple and low-cost, and the modified material can be recycled and reused, laying the foundation for subsequent industrial applications. Attached Figure Description

[0020] The accompanying drawings, which are provided to further illustrate the invention and constitute a part of this invention, are illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention.

[0021] In the attached diagram: Appendix Figure 1 This is a flowchart illustrating the preparation process of the modified activated carbon prepared according to the present invention.

[0022] Appendix Figure 2 The N2 adsorption-desorption curves of the activated carbon prepared in this invention before and after modification.

[0023] Appendix Figure 3 The diagram shows the pore size distribution of the activated carbon prepared in this invention before and after modification.

[0024] Appendix Figure 4 The images show the activated carbon prepared in this invention before and after modification using scanning electron microscopy.

[0025] Appendix Figure 5 The diagram shows the dynamic adsorption performance of the modified activated carbon prepared in this invention for radon under different operating conditions.

[0026] Appendix Figure 6 The diagram shows the regeneration and recycling performance of the modified activated carbon prepared in this invention.

[0027] Appendix Figure 7 This is a pore size distribution diagram of the modified activated carbon prepared in this invention after regeneration. Detailed Implementation

[0028] To facilitate a clear description of the technical solutions in the embodiments of the present invention, the terms "first" and "second" are used to distinguish identical or similar items with essentially the same function and effect. For example, the first threshold and the second threshold are merely used to distinguish different thresholds and do not limit their order. Those skilled in the art will understand that the terms "first" and "second" do not limit the quantity or execution order, and that the terms "first" and "second" are not necessarily different.

[0029] It should be noted that in this invention, the terms "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in this invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of terms such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0030] In this invention, "at least one" means one or more, and "more than one" means two or more. "And / or" describes the relationship between the associated objects, indicating that three relationships can exist.

[0031] The experimental materials, chemical reagents, and testing instruments used in the following examples are from the following sources: The activated carbon raw materials used in this invention are not particularly limited and are all commercially available activated carbon. The materials can be coconut shell activated carbon, coal-based activated carbon, resin-based activated carbon, and wood-based activated carbon.

[0032] In this embodiment, the surface area and pore size distribution tester is a CANTA NOVA 3200e from the United States.

[0033] The static adsorption method used in the examples was used to test the radon adsorption coefficient of activated carbon before and after modification. Specifically, the test can be performed according to the test method in the literature (Xie Lifei, Qiu Shoukang, Tang Quan, et al. Study on static adsorption coefficient measurement of radon by activated carbon adsorption, Nuclear Electronics and Detection Technology [J]. 2019, 39(03): 255-259.).

[0034] The specific method is as follows: Activated carbon is placed in a 1 L sealed adsorption container, followed by the injection of radon with an activity of 56.4 ± 2.3 Bq. The adsorption container is then placed in a constant temperature and humidity chamber (25 ℃ / 50 %RH) for continuous adsorption for 15 h. After adsorption is complete, a ST-203 scintillation chamber detector (0.51 L volume, calibrated using the standard radon chamber calibration coefficient of our laboratory) is used to sample the remaining radon gas in the adsorption container. After standing for 3 h to allow radon and its short-lived progeny to reach decay equilibrium, the radon activity is measured using an FD-125 radon-thorium analyzer. The static adsorption coefficient is calculated using the following formula:

[0035] Among them, K s N is the static adsorption coefficient of activated carbon for radon (L / g); M is the mass of activated carbon (g), N is the static adsorption coefficient of activated carbon for radon (L / g). t N g N0 and N0 represent the total count rate, the measured count rate, and the background count rate of the scintillation chamber, respectively (s). －1 ); λ is 222 Rn decay constant (7.56 × 10⁻⁶) -3 / h); t is the time (h) for activated carbon to adsorb radon.

[0036] The dynamic adsorption method used in this invention is used to test the radon adsorption coefficient of modified activated carbon. Specifically, the test can be performed according to the test method in the literature (Wang X, MaFY, LiuST, et al. Thermodynamics-Kinetics-Balanced Metal-OrganicFramework for In-Depth Radon Removal under Ambient Conditions[J]. Journal of the American Chemical Society, 2022, 144(30): 13634-13642.).

[0037] The specific method is as follows: Radon in the standard radon chamber is passed through a blank gas path at a rate of 1 L / min for 2 hours to test the initial radon concentration. After the radon concentration stabilizes, the gas path is switched, and radon gas at a stable concentration is passed through an adsorption column filled with adsorbent material (the column size and the mass of adsorbent material are determined based on the space velocity during adsorption). The radon concentration at the adsorption column outlet is measured in real time using a RAD7 radon meter (5 min / cycle). When the outlet radon concentration reaches the initial concentration again and remains there for more than 30 min, the adsorption column is considered to have been completely penetrated. Because the penetration time measured by the RAD7 radon meter has a certain delay, the error between the dynamic and static adsorption tests caused by this delay effect is less than 10%. The dynamic adsorption coefficient is calculated using the following formula:

[0038]

[0039] Where Q is the adsorption capacity (Bq / g); K d denoted as , where is the dynamic adsorption coefficient of activated carbon for radon (L / g); F is the test flow rate (L / min); M is the mass of activated carbon (g); t is the adsorption time (min); C0 and C t Radon concentration (Bq / m³) measured at the initial time and time t, respectively. 3 ).

[0040] The adsorption coefficient is the ratio of the concentration of the adsorbed component (radon) in the solid phase adsorbent (activated carbon) to its concentration in the gas phase, and it reflects the strength of the adsorption performance of the adsorbent.

[0041] The nano-SiO2 loading (wt%), SiO2 to polytetrafluoroethylene mass ratio, etching temperature (°C), and etching time (h) in Examples 1 to 12 are shown in Table 1 below.

[0042] Table 1. Preparation parameters for activated carbon modification

[0043] Based on the parameters in Table 1 above, the following Examples 1 to 12 are set up as follows: Example 1 A method for preparing effective microporous modified activated carbon for radon adsorption includes the following steps: First, nano-SiO2 was ultrasonically dispersed in deionized water at a power of 600W and a frequency of 20kHz for 15 min, with a mass-to-volume ratio of SiO2 to deionized water of 0.05 g / mL. Then, coconut shell activated carbon substrate was added to adsorb the nano-SiO2 into the pores. After drying at 105℃ for 12 h, activated carbon / SiO2 composite was obtained. The amount of nano-SiO2 incorporated was 10 wt%, and the particle size of SiO2 was 7~100 nm. The activated carbon / SiO2 composite was mixed with polytetrafluoroethylene powder and dried at 105℃ for 12 h to obtain a mixture; the mass ratio of activated carbon / SiO2 composite to polytetrafluoroethylene powder was 1:1; the mass ratio of SiO2 to polytetrafluoroethylene powder was 0.09. Under a nitrogen atmosphere, the mixed product was calcined by first heating it to 900℃ at a rate of 7℃ / min, then holding it at that temperature for 3 hours, and then naturally cooling it to room temperature to obtain modified activated carbon with the target effective micropore size. The tail gas generated during calcination was treated with a 1 mol / L sodium hydroxide solution.

[0044] Example 2 A method for preparing effective microporous modified activated carbon for radon adsorption includes the following steps: First, nano-SiO2 was ultrasonically dispersed in deionized water at a power of 1200W and a frequency of 25kHz for 10 min, with a mass-to-volume ratio of SiO2 to deionized water of 0.05 g / mL. Then, coconut shell activated carbon substrate was added to adsorb the nano-SiO2 into the pores. After drying at 80℃ for 8 h, an activated carbon / SiO2 composite was obtained. The amount of nano-SiO2 incorporated was 20 wt%, and the particle size of SiO2 was 7~100 nm. The activated carbon / SiO2 composite was mixed with polytetrafluoroethylene powder and dried at 80℃ for 8 h to obtain a mixture; the mass ratio of activated carbon / SiO2 composite to polytetrafluoroethylene powder was 1:1.8; the mass ratio of SiO2 to polytetrafluoroethylene powder was 0.09. Under a nitrogen atmosphere, the mixed product was calcined by first heating it to 900℃ at a rate of 8℃ / min, then holding it at that temperature for 3 hours, and finally allowing it to cool naturally to room temperature to obtain modified activated carbon with the target effective micropore size. The exhaust gas generated during calcination was treated with a 1 mol / L sodium carbonate solution.

[0045] Example 3 A method for preparing effective microporous modified activated carbon for radon adsorption includes the following steps: First, nano-SiO2 was ultrasonically dispersed in deionized water at a power of 800W and a frequency of 22kHz for 12 min, with a mass-to-volume ratio of SiO2 to deionized water of 0.05 g / mL. Then, coconut shell activated carbon substrate was added to adsorb the nano-SiO2 into the pores. After drying at 90℃ for 10 h, activated carbon / SiO2 composite was obtained. The amount of nano-SiO2 incorporated was 30 wt%, and the particle size of SiO2 was 7~100 nm. The activated carbon / SiO2 composite was mixed with polytetrafluoroethylene powder and dried at 90℃ for 10 h to obtain a mixture; the mass ratio of activated carbon / SiO2 composite to polytetrafluoroethylene powder was 1:2.5; the mass ratio of SiO2 to polytetrafluoroethylene powder was 0.09. Under a nitrogen atmosphere, the mixed product was calcined by first heating it to 900℃ at a rate of 10℃ / min, then holding it at that temperature for 3 hours, and finally allowing it to cool naturally to room temperature to obtain modified activated carbon with the target effective micropore size. The exhaust gas generated during calcination was treated with a 0.02 mol / L calcium hydroxide solution.

[0046] Example 4 A method for preparing effective microporous modified activated carbon for radon adsorption includes the following steps: First, nano-SiO2 is subjected to a rotation speed of 10000 rpm and a shear rate of 10. 5 s -1 The SiO2 nanoparticles were dispersed in deionized water under high-speed shearing for 10 min, with a mass-to-volume ratio of 0.05 g / mL. Coconut shell activated carbon substrate was then added to adsorb the nano-SiO2 into the pores. After drying at 105℃ for 12 h, an activated carbon / SiO2 composite was obtained. The amount of nano-SiO2 incorporated was 20 wt%, and the SiO2 particle size was 7–100 nm. The activated carbon / SiO2 composite was mixed with polytetrafluoroethylene powder and dried at 105℃ for 12 h to obtain a mixture; the mass ratio of activated carbon / SiO2 composite to polytetrafluoroethylene powder was 1:0.8; the mass ratio of SiO2 to polytetrafluoroethylene powder was 0.2. Under a nitrogen atmosphere, the mixed product was calcined by first heating it to 900℃ at a rate of 5℃ / min, then holding it at that temperature for 3 hours, and finally allowing it to cool naturally to room temperature to obtain modified activated carbon with the target effective micropore size. The exhaust gas generated during calcination was treated with a 1 mol / L sodium hydroxide solution.

[0047] Example 5 A method for preparing effective microporous modified activated carbon for radon adsorption includes the following steps: First, nano-SiO2 is subjected to a rotation speed of 15000 rpm and a shear rate of 10. 6 s -1 The SiO2 particles were dispersed in deionized water under high-speed shearing for 15 min, with a mass-to-volume ratio of 0.05 g / mL to deionized water. Then, coconut shell activated carbon substrate was added to adsorb the nano-SiO2 into the pores. After drying at 105℃ for 12 h, an activated carbon / SiO2 composite was obtained. The amount of nano-SiO2 incorporated was 20 wt%, and the particle size of SiO2 was 7~100 nm. The activated carbon / SiO2 composite was mixed with polytetrafluoroethylene powder and dried at 105℃ for 12 h to obtain a mixture; the mass ratio of activated carbon / SiO2 composite to polytetrafluoroethylene powder was 1:1.5; the mass ratio of SiO2 to polytetrafluoroethylene powder was 0.11. Under a nitrogen atmosphere, the mixed product was calcined by first heating it to 900℃ at a rate of 6℃ / min, then holding it at that temperature for 3 hours, and finally allowing it to cool naturally to room temperature to obtain modified activated carbon with the target effective micropore size. The exhaust gas generated during calcination was treated with a 1 mol / L sodium hydroxide solution.

[0048] Example 6 A method for preparing effective microporous modified activated carbon for radon adsorption includes the following steps: First, nano-SiO2 is subjected to a rotation speed of 12000 rpm and a shear rate of 10. 6 s -1 The SiO2 nanoparticles were dispersed in deionized water under high-speed shearing for 12 min, with a mass-to-volume ratio of 0.05 g / mL. Coconut shell activated carbon substrate was then added to adsorb the nano-SiO2 into the pores. After drying at 105 °C for 12 h, an activated carbon / SiO2 composite was obtained. The amount of nano-SiO2 incorporated was 20 wt%, and the SiO2 particle size was 7–100 nm. The activated carbon / SiO2 composite was mixed with polytetrafluoroethylene powder and dried at 105℃ for 12 h to obtain a mixture; the mass ratio of activated carbon / SiO2 composite to polytetrafluoroethylene powder was 1:2.3; the mass ratio of SiO2 to polytetrafluoroethylene powder was 0.07. Under a nitrogen atmosphere, the mixed product was calcined by first heating it to 900℃ at a rate of 7℃ / min, then holding it at that temperature for 3 hours, and finally allowing it to cool naturally to room temperature to obtain modified activated carbon with the target effective micropore size. The exhaust gas generated during calcination was treated with a 1 mol / L sodium hydroxide solution.

[0049] Example 7 A method for preparing effective microporous modified activated carbon for radon adsorption includes the following steps: First, nano-SiO2 was ultrasonically dispersed in deionized water at a power of 800W and a frequency of 22kHz for 12 min, with a mass-to-volume ratio of SiO2 to deionized water of 0.05 g / mL. Then, coconut shell activated carbon substrate was added to adsorb the nano-SiO2 into the pores. After drying at 105℃ for 12 h, activated carbon / SiO2 composite was obtained. The amount of nano-SiO2 incorporated was 20 wt%, and the particle size of SiO2 was 7~100 nm. The activated carbon / SiO2 composite was mixed with polytetrafluoroethylene powder and dried at 105℃ for 12 h to obtain a mixture; the mass ratio of activated carbon / SiO2 composite to polytetrafluoroethylene powder was 1:1.8; the mass ratio of SiO2 to polytetrafluoroethylene powder was 0.09. Under a nitrogen atmosphere, the mixed product was calcined by first heating it to 800℃ at a rate of 7℃ / min, then holding it at that temperature for 3 hours, and finally allowing it to cool naturally to room temperature to obtain modified activated carbon with the target effective micropore size. The exhaust gas generated during calcination was treated with a 1 mol / L sodium hydroxide solution.

[0050] Example 8 A method for preparing effective microporous modified activated carbon for radon adsorption includes the following steps: First, nano-SiO2 was ultrasonically dispersed in deionized water at a power of 800W and a frequency of 22kHz for 12 min, with a mass-to-volume ratio of SiO2 to deionized water of 0.05 g / mL. Then, coconut shell activated carbon substrate was added to adsorb the nano-SiO2 into the pores. After drying at 105℃ for 12 h, activated carbon / SiO2 composite was obtained. The amount of nano-SiO2 incorporated was 20 wt%, and the particle size of SiO2 was 7~100 nm. The activated carbon / SiO2 composite was mixed with polytetrafluoroethylene powder and dried at 105℃ for 12 h to obtain a mixture; the mass ratio of activated carbon / SiO2 composite to polytetrafluoroethylene powder was 1:1.8; the mass ratio of SiO2 to polytetrafluoroethylene powder was 0.09. Under a nitrogen atmosphere, the mixed product was calcined by first heating it to 1000℃ at a rate of 6℃ / min, then holding it at that temperature for 3 hours, and finally allowing it to cool naturally to room temperature to obtain modified activated carbon with the target effective micropore size. The exhaust gas generated during calcination was treated with a 1 mol / L sodium hydroxide solution.

[0051] Example 9 A method for preparing effective microporous modified activated carbon for radon adsorption includes the following steps: First, nano-SiO2 was ultrasonically dispersed in deionized water at a power of 800W and a frequency of 22kHz for 12 min, with a mass-to-volume ratio of SiO2 to deionized water of 0.05 g / mL. Then, coconut shell activated carbon substrate was added to adsorb the nano-SiO2 into the pores. After drying at 105℃ for 12 h, activated carbon / SiO2 composite was obtained. The amount of nano-SiO2 incorporated was 20 wt%, and the particle size of SiO2 was 7~100 nm. The activated carbon / SiO2 composite was mixed with polytetrafluoroethylene powder and dried at 105℃ for 12 h to obtain a mixture; the mass ratio of activated carbon / SiO2 composite to polytetrafluoroethylene powder was 1:1.8; the mass ratio of SiO2 to polytetrafluoroethylene powder was 0.09. Under a nitrogen atmosphere, the mixed product was calcined by first heating it to 1100℃ at a rate of 9℃ / min, then holding it at that temperature for 3 hours, and finally allowing it to cool naturally to room temperature to obtain modified activated carbon with the target effective micropore size. The exhaust gas generated during calcination was treated with a 1 mol / L sodium hydroxide solution.

[0052] Example 10 A method for preparing effective microporous modified activated carbon for radon adsorption includes the following steps: First, nano-SiO2 was ultrasonically dispersed in deionized water at a power of 800W and a frequency of 22kHz for 12 min, with a mass-to-volume ratio of SiO2 to deionized water of 0.05 g / mL. Then, coconut shell activated carbon substrate was added to adsorb the nano-SiO2 into the pores. After drying at 105℃ for 12 h, activated carbon / SiO2 composite was obtained. The amount of nano-SiO2 incorporated was 20 wt%, and the particle size of SiO2 was 7~100 nm. The activated carbon / SiO2 composite was mixed with polytetrafluoroethylene powder and dried at 105℃ for 12 h to obtain a mixture; the mass ratio of activated carbon / SiO2 composite to polytetrafluoroethylene powder was 1:1.8; the mass ratio of SiO2 to polytetrafluoroethylene powder was 0.09. Under a nitrogen atmosphere, the mixed product was calcined by first heating it to 900℃ at a rate of 7℃ / min, then holding it at that temperature for 1 hour, and then naturally cooling it to room temperature to obtain modified activated carbon with the target effective micropore size. The exhaust gas generated during calcination was treated with a 1 mol / L sodium hydroxide solution.

[0053] Example 11 A method for preparing effective microporous modified activated carbon for radon adsorption includes the following steps: First, nano-SiO2 was ultrasonically dispersed in deionized water at a power of 800W and a frequency of 22kHz for 12 min, with a mass-to-volume ratio of SiO2 to deionized water of 0.05 g / mL. Then, coconut shell activated carbon substrate was added to adsorb the nano-SiO2 into the pores. After drying at 105℃ for 12 h, activated carbon / SiO2 composite was obtained. The amount of nano-SiO2 incorporated was 20 wt%, and the particle size of SiO2 was 7~100 nm. The activated carbon / SiO2 composite was mixed with polytetrafluoroethylene powder and dried at 105℃ for 12 h to obtain a mixture; the mass ratio of activated carbon / SiO2 composite to polytetrafluoroethylene powder was 1:1.8; the mass ratio of SiO2 to polytetrafluoroethylene powder was 0.09. Under a nitrogen atmosphere, the mixed product was calcined by first heating it to 900℃ at a rate of 7℃ / min, then holding it at that temperature for 2 hours, and finally allowing it to cool naturally to room temperature to obtain modified activated carbon with the target effective micropore size. The exhaust gas generated during calcination was treated with a 1 mol / L sodium hydroxide solution.

[0054] Example 12 A method for preparing effective microporous modified activated carbon for radon adsorption includes the following steps: First, nano-SiO2 was ultrasonically dispersed in deionized water at a power of 800W and a frequency of 22kHz for 12 min, with a mass-to-volume ratio of SiO2 to deionized water of 0.05 g / mL. Then, coconut shell activated carbon substrate was added to adsorb the nano-SiO2 into the pores. After drying at 105℃ for 12 h, activated carbon / SiO2 composite was obtained. The amount of nano-SiO2 incorporated was 20 wt%, and the particle size of SiO2 was 7~100 nm. The activated carbon / SiO2 composite was mixed with polytetrafluoroethylene powder and dried at 105℃ for 12 h to obtain a mixture; the mass ratio of activated carbon / SiO2 composite to polytetrafluoroethylene powder was 1:1.8; the mass ratio of SiO2 to polytetrafluoroethylene powder was 0.09. Under a nitrogen atmosphere, the mixed product was calcined by first heating it to 900℃ at a rate of 7℃ / min, then holding it at that temperature for 4 hours, and finally allowing it to cool naturally to room temperature to obtain modified activated carbon with the target effective micropore size. The exhaust gas generated during calcination was treated with a 1 mol / L sodium hydroxide solution.

[0055] Comparative Example 1 An effective microporous modified activated carbon material is provided, which differs from Example 2 in that: the SiO2 is analytically pure, amorphous, and has a particle size greater than 300 nm, while the rest is the same as in Example 2.

[0056] Comparative Example 2 The difference from Example 2 is that: the nano-SiO2 is not loaded in the internal pores of the activated carbon, but the gaseous SiF4 generated by the reaction of nano-SiO2 with polytetrafluoroethylene is introduced into the activated carbon from the outside at a flow rate of 200 mL / min to modify it, thereby obtaining the modified activated carbon material; the other parameters are the same as in Example 2.

[0057] Comparative Example 3 In Comparative Example 3, compared with Example 8, coconut shell activated carbon was directly heated to 900 °C at a rate of 6 °C / min under nitrogen protection and held at that temperature for 3 h. After naturally cooling to room temperature, modified activated carbon material was obtained.

[0058] Comparative Example 4 In Comparative Example 4, the difference from Example 8 is that the activated carbon / SiO2 composite was directly calcined without mixing with polytetrafluoroethylene powder, heated to 900°C at a rate of 6°C / min, then held at that temperature for 3 hours, and naturally cooled to room temperature to obtain modified activated carbon with the target effective micropore size.

[0059] Comparative Example 5 In Comparative Example 5, the difference from Example 8 is that coconut shell activated carbon and polytetrafluoroethylene were mixed at a mass ratio of 0.45, dried at 105°C for 12 h to obtain a mixture of activated carbon and polytetrafluoroethylene, and the mixture was heated to 900°C under nitrogen protection and kept at that temperature for 3 h. After naturally cooling to room temperature, the modified activated carbon material was obtained.

[0060] The pore structure and radon adsorption coefficient of the modified activated carbon prepared in Examples 1-12 and Comparative Examples 1-5 were tested using the specific surface area test and static adsorption method described above, and the results are shown in Table 2.

[0061] Table 2 Comparison of pore structure and radon adsorption coefficient of modified activated carbon prepared with different parameters

[0062] As shown in Table 2, a comparison of the original activated carbon and the modified activated carbon obtained in Examples 1-12 reveals a significant increase in the micropore volume ratio of the modified activated carbon, accounting for over 95% of the total pore volume, exhibiting a pore structure dominated by micropores. Furthermore, the proportion of the 0.5–0.7 nm ultramicropores, which are well-matched for radon adsorption, also increases to varying degrees, thereby enhancing the radon adsorption capacity. The modified activated carbons obtained in Examples 2, 4, 6, 8, and 12 all have radon adsorption coefficients exceeding 10 L / g, representing increases of 177.53%, 162.88%, 165.91%, 247.22%, and 159.34% respectively compared to the original activated carbon (3.96 L / g). Therefore, the fully microporous structure and the 0.5–0.7 nm ultramicropores, well-matched for radon adsorption, play a crucial role in enhancing radon adsorption capacity.

[0063] In Examples 1-3, controlling the SiO2 loading increased both the micropores and ultrapores of the resulting modified activated carbon, leading to varying degrees of improvement in radon adsorption. The modified activated carbon with a 20% wt SiO2 loading showed the highest radon adsorption, indicating that a 20% wt SiO2 loading is suitable for modification. In contrast, the modified activated carbon in Comparative Example 5, without SiO2 loading, relied solely on the decomposition of polytetrafluoroethylene (PTFE) to fail to react with SiO2 to generate gaseous SiF4 for pore control. This resulted in a small effective micropore volume of 0.5–0.7 nm, with a radon adsorption coefficient of only 6.03 L / g.

[0064] In Examples 4-6, with a fixed SiO2 loading of 20%wt, the etching process of gaseous SiF4 was adjusted by controlling the mass ratio of polytetrafluoroethylene (PTFE) to SiO2, thereby optimizing the effective microporous structure. The resulting modified activated carbons all had abundant micropores and ultramicropores, and the radon adsorption coefficient was higher than 10 L / g. This demonstrates the important role of gaseous SiF4 generated by the etching of PTFE and SiO2 in the precise control of the effective micropores of activated carbon.

[0065] In Examples 7-9, activated carbon was modified at different etching temperatures. The radon adsorption coefficient of the resulting materials showed a trend of first increasing and then decreasing with the increase of etching temperature. This indicates that too low a temperature may lead to insufficient etching reaction between polytetrafluoroethylene and SiO2, resulting in a smaller number of effective micropores, while a higher temperature may lead to excessive etching reaction, thereby destroying the effective microporous structure. Among them, the activated carbon prepared by modification at 1000 °C had the highest radon adsorption coefficient of 13.74 L / g.

[0066] In Examples 10-12, activated carbon was further modified using different etching times. It can be seen that the radon adsorption coefficient increases with the extension of etching time. This is because a longer etching time allows for a sufficient etching reaction, thereby controlling the number of effective micropores. However, the radon adsorption coefficient of samples etched after 3 hours did not show a significant increase, indicating that the etching reaction had ended. Therefore, 3 hours is a more suitable modification time.

[0067] In Comparative Example 1, amorphous SiO2 (analytical grade, particle size greater than 300 nm), which is less expensive, was loaded onto the original activated carbon for modification. Compared with Example 2, the resulting material exhibited a fully microporous structure with abundant 0.5~0.7 nm effective micropores, and the radon adsorption coefficient reached 9.82 L / g. This indicates that amorphous SiO2 (analytical grade) can also effectively control the micropores of activated carbon and is also beneficial to reducing modification costs.

[0068] In Comparative Example 2, nano-SiO2 was not loaded into the internal pores of activated carbon. Instead, gaseous SiF4 generated by the reaction of nano-SiO2 with polytetrafluoroethylene was introduced into the activated carbon from the outside to modify it. The resulting modified activated carbon had a radon adsorption coefficient of only 5.36 L / g, indicating that the non-in-situ generated gaseous SiF4 had a weak regulatory effect on the pore structure of activated carbon.

[0069] Comparisons of Comparative Examples 3, 4, and 2 demonstrate that pyrolysis modification alone, without the generation of gaseous SiF4 through the etching reaction between PTFE and SiO2, cannot achieve effective micropore control. Furthermore, in Comparative Example 4, the loaded SiO2 was not removed by the etching reaction; instead, it clogged the activated carbon pores, thus reducing its radon adsorption capacity. Its radon adsorption coefficient was only 3.62 L / g. This indicates the crucial role of the gaseous SiF4 generated in situ through the etching process between PTFE and SiO2 in effectively and precisely controlling the micropores of the activated carbon, thereby enhancing radon adsorption.

[0070] Performance testing 1. Pore size distribution test The specific surface area was analyzed using a specific surface area analyzer to perform N2 adsorption-desorption and CO2 adsorption-desorption tests on the original coconut shell activated carbon and the modified activated carbon with the highest radon adsorption coefficient in Example 8, obtaining the specific surface area and full pore size distribution. The specific test procedure was as follows: 50 mg of sample was weighed and placed in a test tube, and degassed at 300 °C for 6 h. After degassed, the N2 adsorption-desorption isotherms at 77 K and the CO2 adsorption-desorption isotherms at 273 K were measured. The obtained N2 and CO2 adsorption-desorption isotherms were analyzed using a QSDFT model to obtain the distribution of mesopores, micropores, and ultramicropores.

[0071] Test results are as follows Figure 2 As shown, the modified activated carbon exhibits a typical Type I adsorption isotherm. The nitrogen adsorption capacity in the low-pressure region increases sharply, proving that it has a large number of microporous structures. In contrast, the nitrogen adsorption capacity of the original activated carbon also increases slowly in the medium- and high-pressure regions, indicating the presence of a certain number of mesopores and macropores. Table 2 summarizes the pore structure parameters in detail. Micropores account for 69.9% of the original activated carbon, while micropores account for 95.25% of the modified activated carbon. The abundant microporous structure is suitable for adsorbing gaseous radioactive pollutants such as radon. Figure 3 The distribution of micropores and ultramicropores was further shown. It can be seen that the number of micropores in the modified activated carbon is significantly higher than that in the unmodified activated carbon. In particular, the number of 0.5~0.7 nm ultramicropores that match radon adsorption is significantly increased. These effective micropores can provide more space for radon adsorption and improve the radon adsorption capacity.

[0072] Figure 4The electron microscope scan images of the original activated carbon and the modified activated carbon obtained in Example 8 are also shown. It can be seen that there are many irregular openings on the surface of the original activated carbon, and the pore size is relatively large. In contrast, the surface of the modified activated carbon in Example 8 is etched to reveal many micropores, which verifies the transformation of activated carbon from the original mesopores to micropores.

[0073] 2. Dynamic adsorption performance test of radon under different operating conditions The modified activated carbon with the best radon adsorption performance in Example 8 was subjected to dynamic radon adsorption tests under different operating conditions. The test conditions were: initial radon concentration of 3000-4000 Bq / m³. 3 The flow rate was 1 L / min, and the adsorbent loading was 10 g. The dynamic adsorption performance of modified activated carbon for radon was tested under the following conditions: room temperature and low humidity (24.5℃ / 11.7 %RH), room temperature and high humidity (24.1℃ / 65.6 %RH), high temperature and low humidity (32.5℃ / 9.55%RH), and low temperature and low humidity (18.7 ℃ / 10.6 %RH).

[0074] Test results are as follows Figure 5 As shown, lowering the temperature helps improve the adsorbent's radon adsorption capacity. Under low temperature and low humidity conditions, the modified activated carbon achieves the highest dynamic adsorption coefficient for radon (14.051 L / g). As the temperature increases, the adsorption coefficient decreases. On the other hand, with increasing humidity, the radon adsorption capacity decreases due to the competitive adsorption between water molecules and radon during the adsorption process.

[0075] 3. Radon-absorbing activated carbon desorption and regeneration test The modified activated carbon obtained in Example 8 was saturated with radon adsorption, and then regenerated by negative pressure desorption. The regeneration conditions were: applying a pressure of -98 kPa at 30 °C and continuously desorbing at a carrier gas flow rate of 200 mL / min for 3 hours to achieve regeneration. The regenerated activated carbon was then subjected to radon adsorption tests again, and five cycles of regeneration experiments were conducted using the same testing method.

[0076] Test results are as follows Figure 6 As shown, since the physical adsorption of radon is mainly due to effective micropores, radon adsorbed in the pores can be desorbed by applying negative pressure. Even after five regeneration cycles, the modified activated carbon still maintains a radon adsorption coefficient of 12.46 ± 0.95 L / g, retaining over 90% of its initial performance. Furthermore, the pore size distribution of the modified activated carbon after five regeneration cycles was further tested, as shown... Figure 7 As shown, the regenerated activated carbon still maintains a good effective micropore distribution of 0.5~0.7 nm, thus providing good radon adsorption capacity. Therefore, these tests demonstrate that the modified activated carbon prepared in this invention has good reusability.

[0077] Raw wood-based activated carbon was selected and modified according to the parameters set in Example 2. The process was the same as in Example 2 to verify the effect of the precise micropore control method of the present invention on the effective micropore control and radon adsorption performance of other types of activated carbon. The results are shown in Table 3.

[0078] Table 3 Comparison of pore structure and radon adsorption coefficient of wood-based activated carbon before and after modification

[0079] As shown in Table 3, the precise micropore control method of this invention, after modifying wood-based activated carbon, resulted in a 58.91% volume ratio of 0.5–0.7 nm ultramicropores that are well-matched for radon adsorption. Due to the increased number of effective micropores, the modified wood-based activated carbon also exhibits enhanced radon adsorption capacity, achieving a radon adsorption coefficient of 12.69 L / g, which is 8.29 times higher than that of the original activated carbon. This demonstrates that the precise micropore control method of this invention also effectively controls micropores and enhances radon adsorption performance for other types of activated carbon, and can be extended to the modification of other materials.

[0080] The above embodiments are representative implementations of the present invention, but the implementation of the present invention is not limited to the above embodiments. Any changes, substitutions, combinations or simplifications made without departing from the principle of the present invention should be considered within the protection scope of the present invention.

[0081] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art will understand and implement other variations of the disclosed embodiments by reviewing the accompanying drawings, the disclosure, and the appended claims in carrying out the claimed invention. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality. A single processor or other unit can implement several functions listed in the claims. While different dependent claims may recite certain measures, this does not mean that these measures cannot be combined to produce good results.

[0082] Although the invention has been described in conjunction with specific features and embodiments, it is obvious that various modifications and combinations can be made therein without departing from the spirit and scope of the invention. Accordingly, this specification and drawings are merely exemplary descriptions of the invention as defined by the appended claims, and are considered to cover any and all modifications, variations, combinations, or equivalents within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if such modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include such modifications and modifications.

Claims

1. A method for preparing effective microporous modified activated carbon for adsorbing radon gas, characterized in that, Includes the following steps: Nano-SiO2 is adsorbed into the pores of an activated carbon substrate and dried to obtain an activated carbon / SiO2 composite; the amount of nano-SiO2 incorporated is 10~30 wt%. The activated carbon / SiO2 composite was mixed with polytetrafluoroethylene and then dried to obtain a mixture; the mass ratio of the activated carbon / SiO2 composite to the polytetrafluoroethylene was ≤ 1:

3. The mixed product is calcined to obtain modified activated carbon with the target effective micropore size.

2. The method for preparing an effective microporous modified activated carbon for radon adsorption according to claim 1, characterized in that, In the step of adsorbing nano-SiO2 into the pores using an activated carbon substrate, the nano-SiO2 is first dispersed in deionized water, and then the activated carbon substrate is added. The nano-SiO2 is dispersed in deionized water by ultrasonic dispersion and / or high-speed shear dispersion. And / or, The ultrasonic dispersion is performed at a power of 600-1200W, a frequency of 20-25kHz, and a time of 10-15min; the high-speed shear dispersion is performed at a shear speed of 10000-15000 rpm and a shear rate of 10. 5 ~10 6 s -1 Shearing time: 10~15 min; and / or, The particle size of the nano-SiO2 is 7~100 nm.

3. The method for preparing an effective microporous modified activated carbon for radon adsorption according to claim 1, characterized in that, The polytetrafluoroethylene is in the physical state of powder or emulsion; and / or, The mass ratio of SiO2 to polytetrafluoroethylene is 0.07~0.

2.

4. The method for preparing an effective microporous modified activated carbon for radon adsorption according to claim 1, characterized in that, During the calcination of the mixed product, a protective gas is introduced; the protective gas includes at least one of nitrogen and argon.

5. The method for preparing an effective microporous modified activated carbon for radon adsorption according to claim 1, characterized in that, When calcining the mixture, the temperature is first raised to 800-1100 ℃ at a rate of 5-10 ℃ / min, then held for 1-4 h, and then naturally cooled to room temperature.

6. A method for preparing an effective microporous modified activated carbon for radon adsorption according to any one of claims 1 to 5, characterized in that, The activated carbon substrate includes at least one of coconut shell activated carbon, coal-based activated carbon, resin-based activated carbon, and wood-based activated carbon.

7. A method for preparing an effective microporous modified activated carbon for radon adsorption according to any one of claims 1 to 5, characterized in that, The drying process involves drying at 80-105℃ for 8-12 hours.

8. A method for preparing an effective microporous modified activated carbon for radon adsorption according to any one of claims 1 to 5, characterized in that, The exhaust gas generated during the calcination of the mixed product is treated by absorption with an alkaline solution. The alkaline solution includes a 1 mol / L sodium hydroxide solution, a 1 mol / L sodium carbonate solution, or a 0.02 mol / L calcium hydroxide solution.

9. An effective microporous modified activated carbon for adsorbing radon gas, characterized in that, The effective microporous modified activated carbon is prepared by the method described in any one of claims 1 to 8.

10. The application of the effective microporous modified activated carbon prepared by the preparation method according to any one of claims 1 to 8 in the efficient adsorption of radon gas.

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