Composite adsorption material filled adsorption column for purifying PFASs in drinking water as well as preparation method and application of composite adsorption material filled adsorption column

Abstract

The invention discloses a composite adsorption material filled adsorption column for purifying PFASs in drinking water as well as a preparation method and application of the composite adsorption material filled adsorption column. The composite adsorption material filled in the adsorption column takes granular active carbon as a carrier, and multi-walled carbon nanotubes modified by layered double hydroxides are loaded on the surface and in pores of the granular active carbon to form micron-sized composite particles. A multi-layer stacked unitized filling structure is adopted in the adsorption column, each unit is composed of a supporting layer and an adsorbent layer borne by the supporting layer, water flow is forced to evenly pass through, channeling and adsorbent compaction are effectively avoided, and stable hydraulic conditions and pressure drop are ensured. The adsorption column is compact in structure, and the joint is detachable and convenient to maintain. During application, drinking water containing PFASs passes through the column body, and the composite adsorption material shows high adsorption capacity and rapid adsorption kinetics on various PFASs such as PFOS, PFOA and the like by virtue of the synergistic effect of the components, can stably run for a long time, is large in penetration capacity and is suitable for deep purification of the drinking water.

Description

Technical Field

[0001] This invention relates to the field of water purification technology using adsorption materials, specifically to a composite adsorption material-filled adsorption column for purifying PFASs in drinking water, its preparation method, and its application. Background Technology

[0002] Among existing water treatment technologies, adsorption is considered one of the most promising deep purification methods due to its relatively simple operation, low energy consumption, and significant removal effect on low-concentration pollutants. The core of this method lies in utilizing porous adsorption materials to capture and fix PFAS molecules in water onto the material surface or within the pores through mechanisms such as physical adsorption, chemical bonding, or ion exchange. Traditional adsorption materials such as granular activated carbon (GAC) and ion exchange resins have been used in some engineering projects, but they have limited adsorption capacity and low selectivity for some short-chain or emerging PFASs, and suffer from problems such as difficult regeneration and susceptibility to interference from coexisting substances in the water. To improve adsorption performance, researchers have turned their attention to nanomaterials. Among them, layered bimetallic hydroxides (LDHs) exhibit unique electrostatic attraction and ion exchange capabilities for anionic PFASs due to the positively charged layers and the exchangeable anions between the layers; multi-walled carbon nanotubes (MWCNTs) possess a huge specific surface area and abundant surface functional groups, providing a large number of adsorption sites. The LDHs-MWCNTs nanocomposite material, prepared by combining the two, exhibited adsorption capacity and rate far exceeding those of traditional materials in laboratory static adsorption studies. However, when transferring this high-performance nanocomposite material from laboratory beakers to actual continuous flow treatment devices, it encountered severe engineering bottlenecks. While its extremely high specific surface area due to its nanoscale particle size brings excellent adsorption performance, it also presents insurmountable solid-liquid separation challenges. During the operation of the dynamic adsorption column, ultrafine nanoparticles are easily penetrated and lost with the water flow, causing not only material loss and turbid effluent but also potential secondary pollution. Simultaneously, nanoparticles can easily cause pore blockage when filling the column, leading to a sharp increase in bed pressure drop, increased energy consumption, and difficulty in controlling the water flow path, forming channeling or dead zones. This prevents a large amount of adsorbent from effectively contacting pollutants, severely weakening the overall treatment efficiency. Furthermore, the mechanical strength of nanomaterials is generally weak, and they may pulverize under long-term water flow shearing, further exacerbating the aforementioned problems. Therefore, although LDHs-MWCNTs composite materials have significant advantages in adsorption performance, their inherent morphological defects make them difficult to directly apply in practical water treatment processes requiring long-term stable operation. How to endow them with a suitable macroscopic structure, mechanical strength, and hydraulic properties for fixed-bed operation without sacrificing their high adsorption activity has become a key technical challenge that urgently needs to be solved in this field. In view of this, this invention aims to overcome the structural limitations of nano-adsorbent materials in practical applications. Through innovative material composites and column design, it develops an adsorption column device that can maintain the high adsorption performance of nanomaterials while meeting the requirements for long-term stable operation in continuous flow processes, providing a practical solution for the efficient and deep purification of PFASs in drinking water. Summary of the Invention

[0003] Technical Problem Solved: This invention provides a composite adsorption material-filled adsorption column for purifying PFASs in drinking water, its preparation method, and its application. This invention transforms layered bimetallic hydroxide-modified multi-walled carbon nanotube nanomaterials, which exhibit high adsorption performance in the laboratory, into a stable form suitable for continuous flow dynamic adsorption processes, thereby fundamentally avoiding loss and separation difficulties during operation. Simultaneously, it solves the problems of uncontrolled hydraulic residence time and excessive bed pressure drop caused by compaction or channeling within the packed column, ensuring uniform water flow distribution for full and stable utilization of the adsorption capacity. Ultimately, this invention aims to solve the aforementioned engineering challenges while maintaining or even enhancing the broad-spectrum adsorption capacity and rapid adsorption kinetics of the composite material for various typical PFASs pollutants in drinking water, thus providing a long-term stable, easy-to-operate, and highly efficient deep purification device and material for drinking water.

[0004] Technical solution: A composite adsorption material-filled adsorption column for purifying PFASs in drinking water, comprising a column body, an inlet end disposed on the column body, and an outlet end disposed on the column body. The column body is filled with a composite adsorption material, which is granular activated carbon supported on layered bimetallic hydroxide modified multi-walled carbon nanotubes. The filling structure inside the column body consists of at least two structural units that are repeatedly stacked along the axial direction. Each structural unit includes a support layer and an adsorbent layer directly supported thereon. The adsorbent layer is composed of the composite adsorption material.

[0005] Preferably, the average particle size of the granular activated carbon is 10 to 100 mesh.

[0006] Preferably, in the raw materials constituting the composite adsorbent material, the mass percentage of granular activated carbon is 1% to 10%.

[0007] Preferably, the number of the above structural units is 7 to 15.

[0008] Preferably, the mass of the adsorbent layer in each of the above structural units is 0.1 to 0.5 g.

[0009] Preferably, the support layer is a precision filter layer, selected from at least one of PP cotton sheet, non-woven fabric, stainless steel filter screen, hollow fiber filter membrane or ceramic membrane; each support layer is composed of 1 to 10 precision filter layers stacked together.

[0010] Preferably, a primary protection component is provided on the inner side of both the water inlet and the water outlet. The primary protection component includes a stainless steel filter screen and a perforated plate with through holes arranged sequentially from the outside to the inside.

[0011] The preparation method of the composite adsorption material in the above-mentioned adsorption column includes the following steps: mixing granular activated carbon, multi-walled carbon nanotubes, magnesium nitrate, aluminum nitrate and water to obtain a mixture, then adding ammonia water to the mixture to carry out a co-precipitation-in-situ growth reaction to obtain the granular activated carbon-supported layered bimetallic hydroxide modified multi-walled carbon nanotubes; wherein, the average particle size of the granular activated carbon is 10-100 mesh, and in the total mass of raw materials, the granular activated carbon, multi-walled carbon nanotubes, magnesium nitrate and aluminum nitrate are 5-30 parts by mass, 3-4 parts by mass, 45-60 parts by mass and 20-30 parts by mass, respectively.

[0012] The above-mentioned adsorption column is used in the purification of drinking water by passing drinking water containing PFASs through the adsorption column with an empty bed contact time of 0.1 to 1 min.

[0013] The PFASs in the aforementioned drinking water include at least one of perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), and perfluorooctanesulfonyl compounds (PFOS).

[0014] Beneficial effects: First, this invention successfully and stably supports highly active nanoscale adsorption components on micron-scale granular activated carbon carriers, fundamentally solving the inherent problems of easy loss and difficult recovery of nanomaterials in dynamic water flow from a physical perspective. Granular activated carbon itself possesses excellent mechanical strength and hydraulic properties, providing a stable framework for nano-active materials. This allows the resulting composite material to be directly filled into a fixed bed like conventional filter media, realizing the engineering application of the adsorption performance of nanomaterials. Second, the three components are not simply physically mixed, but form a functionally complementary composite structure. Multi-walled carbon nanotubes are uniformly attached to the surface and pores of activated carbon, greatly increasing the specific surface area and interfacial complexity of the material. They not only provide adsorption sites but, more importantly, act as a nanoscaffold, effectively preventing the tight packing of layered bimetallic hydroxide sheets, allowing the positively charged active plates to be fully exposed. The layered bimetallic hydroxide, with its strong electrostatic interaction and anion exchange capacity, becomes a highly efficient site for specifically capturing PFAS anions. In this system, granular activated carbon, besides serving as a macroscopic carrier, also contributes to the adsorption capacity through its own pore structure, while ensuring unobstructed water flow channels. This structural synergy significantly enhances the adsorption capacity and rate of the composite material for PFASs. Experimental data fully confirm these effects. Regarding adsorption kinetics, the adsorption process of substances such as PFOS conforms more closely to a pseudo-second-order kinetic model, indicating that it is primarily chemisorption. Furthermore, in a mixed competitive system containing multiple PFASs, it still exhibits preferential adsorption capacity and a faster adsorption rate for PFOS and PFNA, achieving a PFOS removal rate of 86.7% within 5 minutes. In terms of adsorption capacity, the material demonstrates excellent performance, with a theoretical maximum adsorption capacity of 1189.6 mg / g for PFHxS. More importantly, when this composite material is packed into an adsorption column with a specific multilayer unit structure for dynamic testing, its advantages are translated into stable and reliable treatment efficiency. The breakthrough curves show that the adsorption column can operate for a long time with extremely short empty bed contact time, continuously treating more than thousands of bed volumes of drinking water containing PFASs, and the effluent concentrations of various pollutants such as PFOA and PFOS can remain below the strict limits for a long time. Attached Figure Description

[0015] Figure 1 For materials LDH-MWCNTS / GAC 40-60 Adsorption kinetics of various PFASs (a) Single PFAS solution (b) Mixed PFAS solution

[0016] Figure 2 For materials LDH-MWCNTS / GAC 40-60Adsorption isotherms of various PFASs: (a) single PFOA solution; (b) single PFNA solution; (c) single PFHxS solution; (d) single PFOS solution; (e) PFOA in a mixed solution of PFASs; (f) PFNA in a mixed solution of PFASs; (g) PFHxS in a mixed solution of PFASs; (h) PFOS in a mixed solution of PFASs.

[0017] Figure 3 The adsorption effect of PFASs on layered bimetallic hydroxide modified multi-walled carbon nanotubes supported on granular activated carbon prepared in Example 1 and Comparative Examples 1-3 is shown.

[0018] Figure 4 The adsorption effect of PFASs on layered bimetallic hydroxide modified multi-walled carbon nanotubes supported on granular activated carbon prepared in Examples 1-2 and Comparative Example 4 is shown.

[0019] Figure 5 This is the breakthrough curve of the adsorption column. Detailed Implementation

[0020] This invention provides a composite adsorption material-filled adsorption column for purifying PFASs in drinking water, mainly comprising a column body and a composite adsorption material filled within the column body. The composite adsorption material is granular activated carbon supported on layered bimetallic hydroxide-modified multi-walled carbon nanotubes.

[0021] This invention provides a formulation for preparing layered bimetallic hydroxide-modified multi-walled carbon nanotubes supported on granular activated carbon, comprising the following raw materials: granular activated carbon, multi-walled carbon nanotubes, magnesium nitrate, aluminum nitrate, water, and ammonia. All raw materials are mixed and subjected to a co-precipitation-in-situ growth reaction. The specific steps can be referred to the co-precipitation-in-situ growth method disclosed in Example 1 of Chinese Invention CN115947339B to obtain granular activated carbon-supported layered bimetallic hydroxide-modified multi-walled carbon nanotubes.

[0022] In this invention, the granular activated carbon includes one or more of coconut shell activated carbon, coal-based activated carbon, and wood-based activated carbon; this invention does not specifically limit the type of granular activated carbon, but specifically, the type of granular activated carbon is coconut shell activated carbon.

[0023] In this invention, the average particle size of the granular activated carbon is preferably 10-100 mesh, more preferably 20-80 mesh, and even more preferably 40-60 mesh.

[0024] In this invention, the mass percentage of granular activated carbon in the raw material composition of the composite adsorption material is preferably 5%-30%, more preferably 15%-20%, and even more preferably 16%-18%.

[0025] This invention provides granular activated carbon supported on layered bimetallic hydroxide modified multi-walled carbon nanotubes, as described in the above-mentioned technical solution, or granular activated carbon supported on layered bimetallic hydroxide modified multi-walled carbon nanotubes prepared according to the above-mentioned technical solution, as a composite adsorption material for purifying PFASs in drinking water, which is then packed into an adsorption column. The specific processing method is as follows:

[0026] The adsorption column is made of polypropylene, which does not adsorb PFASs in drinking water and does not introduce PFASs; the adsorbent is granular activated carbon supported on layered bimetallic hydroxide modified multi-walled carbon nanotubes as described in the above technical solution or granular activated carbon supported on layered bimetallic hydroxide modified multi-walled carbon nanotubes prepared by the preparation formula described in the above technical solution.

[0027] In this invention, the adsorption column has a multi-layer stacked internal filling structure. Its construction method involves defining "a support layer and the adsorbent layer it supports" as a structural unit, and repeatedly stacking multiple units along the axial direction of the adsorption column. Accordingly, the filling structure of the adsorption column preferably consists of 7-15 structural units, more preferably 8-13 structural units, and even more preferably 9-11 structural units. In terms of column structure, the innovative multi-layer stacked design replaces the traditional uniform filling. Each structural unit of "support layer + adsorbent layer" serves as an independent adsorption and filtration module. The support layer not only fixes the adsorbent but also has a pre-filtration function, intercepting suspended solids in the water and protecting the downstream adsorbent layer. Multiple units connected in series enable tiered utilization of adsorption capacity, extending the overall breakthrough time and improving treatment efficiency. This invention, through its innovative multi-layer stacked unitized structure, physically eliminates the inherent channeling and compaction problems of traditional adsorption beds, achieving a leap in adsorption efficiency and operational stability.

[0028] In this invention, the average particle size of the granular activated carbon-supported layered bimetallic hydroxide-modified multi-walled carbon nanotubes is preferably 10-200 mesh, more preferably 40-100 mesh, and even more preferably 80-100 mesh.

[0029] In this invention, the mass of the adsorbent granular activated carbon-supported layered bimetallic hydroxide modified multi-walled carbon nanotubes in each structural unit is preferably 0.1-0.5 g, more preferably 0.2-0.4 g, and even more preferably 0.2-0.3 g.

[0030] In this invention, the support layer of the adsorbent is a precision filter layer, which may be PP cotton sheet, non-woven fabric, stainless steel filter screen, hollow fiber filter membrane or ceramic membrane, etc. The number of precision filter material sheets contained in each support layer is preferably 1-10 sheets, more preferably 2-7 sheets, and even more preferably 3-5 sheets.

[0031] In this invention, the column is connected to the inlet and outlet ends via detachable threads, snaps, or flanges, and a sealing structure is provided at the connection point. The sealing structure is an O-ring, silicone gasket, or PTFE tape. The design of the connection and sealing structure improves the modularity and ease of maintenance of the equipment, ensuring sufficient connection strength and sealing performance, facilitating periodic replacement or replenishment of the adsorbent material, and reducing manufacturing costs.

[0032] In this invention, primary protection components are installed on the inner sides of both the inlet and outlet ends. These primary protection components include a stainless steel filter screen and a perforated plate with through holes, arranged sequentially from the outside to the inside. The combination of the stainless steel filter screen and the perforated plate at the inlet and outlet ends constitutes a dual protection and water distribution system. The filter screen primarily intercepts any fine particles that may escape, while the perforated plate supports and evenly distributes the water flow, preventing channeling or dead zones.

[0033] In this invention, the drinking water to be treated is passed through an adsorption column for a certain empty bed contact time, preferably 0.1-1 min, more preferably 0.1-0.5 min, and even more preferably 0.1-0.3 min. The concentration of PFASs in the PFASs-containing drinking water is preferably 0.010-0.050 μg / L, more preferably 0.010-0.025 μg / L, and even more preferably 0.020-0.025 μg / L. The concentration of the high-concentration PFASs-polluted water body is preferably 0.05-50000 μg / L, more preferably 5-40000 μg / L, and even more preferably 100-40000 μg / L. In this invention, the PFASs preferably include perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), and perfluorooctanesulfonyl compounds (PFOS).

[0034] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0035] Example 1

[0036] Granular activated carbon (GAC) was passed through 40-mesh and 60-mesh sieves, respectively. 10 g of 40-60 mesh granular activated carbon was weighed and mixed evenly with 2 g of multi-walled carbon nanotubes (MWNTS). 30.72 g of magnesium nitrate hexahydrate, 15.00 g of aluminum nitrate nonahydrate, and 100 mL of ultrapure water were stirred until the inorganic salts were completely dissolved, yielding a mixed salt solution. The granular activated carbon and MWNTS were added to the mixed salt solution and stirred for 1 h. 50 mL of 30 wt.% ammonia solution was diluted to 100 mL to prepare a 6 mol / L ammonia solution. Subsequent material preparation steps can be performed according to the co-precipitation-in-situ growth method disclosed in Example 1 of Chinese Invention CN115947339B, and the material is designated as LDH-MWCNTS / GAC. 40-60 .

[0037] Comparative Example 1

[0038] Granular activated carbon (GAC) was passed through 10-mesh and 20-mesh sieves, respectively. 10 g of granular activated carbon (between 10-20 mesh) was weighed and mixed evenly with 2 g of multi-walled carbon nanotubes (MWNTS). 30.72 g of magnesium nitrate hexahydrate, 15.00 g of aluminum nitrate nonahydrate, and 100 mL of ultrapure water were stirred until the inorganic salts were completely dissolved, yielding a mixed salt solution. The granular activated carbon and MWNTS were added to the mixed salt solution and stirred for 1 h. 50 mL of 30 wt.% ammonia solution was diluted to 100 mL to prepare a 6 mol / L ammonia solution. Subsequent material preparation steps can be performed according to the co-precipitation-in-situ growth method disclosed in Example 1 of Chinese Invention CN115947339B, and the material is designated as LDH-MWCNTS / GAC. 10-20 .

[0039] Comparative Example 2

[0040] Granular activated carbon (GAC) was passed through 20-mesh and 40-mesh sieves, respectively. 10 g of granular activated carbon (between 20-40 mesh) was weighed and mixed evenly with 2 g of multi-walled carbon nanotubes (MWNTS). 30.72 g of magnesium nitrate hexahydrate, 15.00 g of aluminum nitrate nonahydrate, and 100 mL of ultrapure water were stirred until the inorganic salts were completely dissolved, yielding a mixed salt solution. The granular activated carbon and MWNTS were added to the mixed salt solution and stirred for 1 h. 50 mL of 30 wt.% ammonia solution was diluted to 100 mL to prepare a 6 mol / L ammonia solution. Subsequent material preparation steps can be performed according to the co-precipitation-in-situ growth method disclosed in Example 1 of Chinese Invention CN115947339B, and the material is designated as LDH-MWCNTS / GAC. 20-40 .

[0041] Comparative Example 3

[0042] Granular activated carbon (GAC) was passed through 60-mesh and 80-mesh sieves, respectively. 10 g of 60-80 mesh granular activated carbon was weighed and mixed evenly with 2 g of multi-walled carbon nanotubes (MWNTS). 30.72 g of magnesium nitrate hexahydrate, 15.00 g of aluminum nitrate nonahydrate, and 100 mL of ultrapure water were stirred until the inorganic salts were completely dissolved, yielding a mixed salt solution. The granular activated carbon and MWNTS were added to the mixed salt solution and stirred for 1 h. 50 mL of 30 wt.% ammonia solution was diluted to 100 mL to prepare a 6 mol / L ammonia solution. Subsequent material preparation steps can be performed according to the co-precipitation-in-situ growth method disclosed in Example 1 of Chinese Invention CN115947339B, and the material is designated as LDH-MWCNTS / GAC. 60-80 .

[0043] Example 2

[0044] Granular activated carbon (GAC) was passed through 40-mesh and 60-mesh sieves, respectively. 4 g of 40-60 mesh granular activated carbon was weighed and mixed evenly with 2 g of multi-walled carbon nanotubes (MWNTS). 30.72 g of magnesium nitrate hexahydrate, 15.00 g of aluminum nitrate nonahydrate, and 100 mL of ultrapure water were stirred until the inorganic salts were completely dissolved, yielding a mixed salt solution. The granular activated carbon and MWNTS were added to the mixed salt solution and stirred for 1 h. 25 mL of 30 wt.% ammonia solution was diluted to 50 mL to prepare a 6 mol / L ammonia solution. Subsequent material preparation steps can be performed according to the co-precipitation-in-situ growth method disclosed in Example 1 of Chinese Invention CN115947339B, and the material is designated as LDH-MWCNTS / GAC. 40-60-4 , where 4 represents the weight of granular activated carbon in grams.

[0045] Comparative Example 4

[0046] Granular activated carbon (GAC) was passed through 40-mesh and 60-mesh sieves, respectively. 16 g of 40-60 mesh granular activated carbon was weighed and mixed evenly with 2 g of multi-walled carbon nanotubes (MWNTS). 30.72 g of magnesium nitrate hexahydrate, 15.00 g of aluminum nitrate nonahydrate, and 100 mL of ultrapure water were stirred until the inorganic salts were completely dissolved, yielding a mixed salt solution. The granular activated carbon and MWNTS were added to the mixed salt solution and stirred for 1 h. 50 mL of 30 wt.% ammonia solution was diluted to 100 mL to prepare a 6 mol / L ammonia solution. Subsequent material preparation steps can be performed according to the co-precipitation-in-situ growth method disclosed in Example 1 of Chinese Invention CN115947339B, and the material is designated as LDH-MWCNTS / GAC. 40-60-16 16 represents the weight in grams of granular activated carbon.

[0047] Application Example 1

[0048] LDH-MWCNTS / GAC prepared in Example 1 40-60 Pass the sample through a 100-mesh sieve and collect the material remaining on the sieve for later use. Add PFOA, PFNA, PFHxS, and PFOS to ultrapure water to prepare single PFASs solutions and mixed PFASs solutions with a concentration of 1 mg / L, respectively. Take two 40 mL portions of the above PFASs solutions and add 5.5 mg of the LDH-MWCNTS / GAC prepared in Example 1 to each. 40-60 The samples were placed in a constant-temperature shaker and adsorbed for 3, 5, 10, 30, 60, 120, 720, and 1440 min, respectively. Samples were removed at the corresponding time points and filtered through a 0.22 µm PTFE hydrophilic filter. A total of 5 mL of sample was filtered. The first 3.5 mL was discarded to reduce the influence of the filter membrane on PFAS adsorption. The remaining 1.5 mL was placed in a sample vial, and the concentrations of each PFAS were determined using high-performance liquid chromatography-tandem mass spectrometry. The experimental results are shown in Table 1.

[0049] Table 1. LDH-MWCNTS / GAC at different adsorption times 40-60 Comparison of PFOS removal rates of LDHs / MWNTS with Chinese invention CN115947339B

[0050]

[0051] Compared with existing technologies in this field (LDHs / MWNTS materials in Chinese invention CN115947339B), the LDH-MWCNTS / GAC provided by this invention... 40-60 The material exhibits unique advantages in PFOS adsorption performance. Although the adsorption rate of the comparative material in a single PFOS solution is slightly higher, the material of this invention performs better under actual mixed pollution conditions: its PFOS removal rate in the mixed system is not only consistently higher than its performance in a single system, but also reaches 86.7% in the rapid adsorption phase within 5 minutes, demonstrating excellent competitive adsorption selectivity and environmental adaptability.

[0052] Figure 1 For LDH-MWCNTS / GAC 40-60 The adsorption kinetics of PFOA, PFNA, PFHxS and PFOS in single PFASs solutions and mixed PFASs solutions are shown in Table 2, with the corresponding kinetic fitting parameters presented.

[0053] Table 2 LDH-MWCNTS / GAC 40-60 Adsorption kinetic fitting parameters in single PFASs solutions and PFASs mixed solutions

[0054]

[0055] Material LDH-MWCNTS / GAC 40-60 The adsorption process of PFASs conforms more closely to the pseudo-second-order kinetic model (R² ≥ 0.95), indicating that chemisorption is the dominant process. In the mixed PFASs system, the adsorption capacities of PFOS and PFNA are largely unaffected by competitive adsorption, with equilibrium adsorption capacities of 6.86 mg / g and 6.04 mg / g, respectively, exhibiting strong adsorption selectivity; while the equilibrium adsorption capacities of PFOA and PFHxS decrease. Notably, the pseudo-second-order adsorption rate constant of PFOS in the mixed system (K² = 0.35 g·mg⁻¹) is [not specified in the original text]. -1 ·min -1 The improvement compared to the single system indicates that the material LDH-MWCNTS / GAC has been significantly enhanced. 40-60 Even in complex water conditions, it still exhibits rapid and high-capacity adsorption of PFOS. In summary, the material LDH-MWCNTS / GAC... 40-60 It is suitable for efficient treatment of wastewater containing multiple PFASs.

[0056] Application Example 2

[0057] LDH-MWCNTS / GAC prepared in Example 1 40-60 Pass the sample through a 100-mesh sieve and collect the material remaining on the sieve for later use. Add PFOA, PFNA, PFHxS, and PFOS to ultrapure water to prepare single PFASs solutions and mixed PFASs solutions with concentrations of 0.1, 0.5, 1, 5, 10, 20, and 40 mg / L, respectively. Take two 40 mL portions of each of the above PFASs solutions and add 5.5 mg of the LDH-MWCNTS / GAC prepared in Example 1 to each. 40-60 The samples were placed in a constant-temperature shaker and removed after 24 h of adsorption. They were then filtered through a 0.22 µm PTFE hydrophilic filter, for a total of 5 mL. The first 3.5 mL of sample was discarded to reduce the influence of the filter membrane on PFASs adsorption. The remaining 1.5 mL of sample was placed in a sample vial, and the concentrations of each PFASs were determined using high-performance liquid chromatography-tandem mass spectrometry. The experimental results are shown in Table 3.

[0058] Table 3 LDH-MWCNTS / GAC 40-60 Removal rate of each PFAS in single PFAS solution and mixed PFAS solution

[0059]

[0060] PFOS and PFNA maintained the highest removal rates at most concentrations. With increasing initial concentration, the removal rates of all PFAS decreased, especially in mixed systems. When the concentration reached 5-10 mg / L, the removal rates of PFOA, PFNA, and PFHxS all showed a sharp decline. At the same initial concentration, the removal rates of PFAS in all mixed solutions were lower than their removal rates in single solutions, and this inhibitory effect intensified with increasing concentration.

[0061] LDH-MWCNTS / GAC 40-60 The adsorption behavior of PFHxS in a single system conforms to the Langmuir isotherm adsorption model, indicating that monolayer adsorption is dominant, and the calculated theoretical maximum adsorption capacity is 1189.6 mg / g. However, in mixed solutions of PFASs, the adsorption behavior of PFHxS is more appropriately described by the Redlich-Peterson model, reflecting that its adsorption mechanism tends to be more complex under competitive adsorption conditions, possibly involving the superposition of adsorption sites, making it difficult to accurately predict using a simple model.

[0062] For the remaining PFASs, whether in single or mixed systems, their adsorption isotherms better conform to the Sips model. The non-uniformity index obtained from this model fitting is distributed between 0.5 and 0.8, indicating that the adsorption energy distribution of these PFASs on the material surface exhibits significant non-uniformity. This demonstrates the effectiveness of the LDH-MWCNTS / GAC model. 40-60 The adsorption of PFASs is not controlled by a single mechanism, but is contributed by a variety of adsorption interactions with different energies, which may include synergistic mechanisms such as ion exchange, electrostatic attraction, hydrophobic interactions and pore filling. The adsorption mechanism dynamically evolves between monolayer homogeneous adsorption and multilayer heterogeneous adsorption based on the target molecule structure and solution composition.

[0063] Application Example 3

[0064] The granular activated carbon-supported layered bimetallic hydroxide-modified multi-walled carbon nanotubes prepared in Examples 1 and 1-3 were passed through a 100-mesh sieve, and the material remaining on the sieve was collected for later use. PFOA, PFNA, PFHxS, and PFOS were added to ultrapure water to prepare mixed PFASs solutions with a concentration of 25 ng / L. Two 1000 mL portions of the above PFASs solutions were taken, and 0.14 g of the granular activated carbon-supported layered bimetallic hydroxide-modified multi-walled carbon nanotubes prepared in Examples 1 and 1-2 were added to each. The samples were placed in a constant-temperature shaker and subjected to adsorption at 25°C and 160 rpm. After 24 h, the filter material was removed, and the samples were pretreated by solid-phase extraction (SPE) and placed in a sample vial. The concentrations of each PFASs were determined by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS / MS). The experimental results are shown below. Figure 3 As shown.

[0065] Depend on Figure 3 It can be seen that the particle size of GAC has a significant impact on the adsorption effect of the composite adsorbent material on PFASs. The material LDH-MWCNTS / GAC prepared in Example 1... 40-60 The material LDH-MWCNTS / GAC showed the best removal rates for PFOA, PFNA, and PFHxS. For PFOS, its removal rate was only 0.05% lower than that of the control group (2), which showed the best removal performance. Overall, the material LDH-MWCNTS / GAC... 40-60 The adsorption effect is optimal.

[0066] Application Example 4

[0067] The granular activated carbon-supported layered bimetallic hydroxide-modified multi-walled carbon nanotubes prepared in Examples 1-2 and Comparative Example 4 were passed through a 100-mesh sieve, and the material remaining on the 100-mesh sieve was collected for later use. PFOA, PFNA, PFHxS, and PFOS were added to ultrapure water to prepare mixed PFASs solutions with a concentration of 25 ng / L. Two 1000 mL portions of the above PFASs solutions were taken, and 0.14 g of the granular activated carbon-supported layered bimetallic hydroxide-modified multi-walled carbon nanotubes prepared in Examples 1-2 and Comparative Example 3 were added to each. The samples were placed in a constant-temperature shaker and subjected to adsorption at 25°C and 160 rpm. After 24 h, the filter material was removed, and the samples were pretreated by solid-phase extraction (SPE) and placed in sample vials. The concentrations of each PFASs were determined by high-performance liquid chromatography-tandem mass spectrometry. The experimental results are shown below. Figure 4 As shown.

[0068] Depend on Figure 4 It can be seen that the material LDH-MWCNTS / GAC 40-60 The adsorption effect was optimal, with removal rates of 88.20%, 81.72%, 98.56%, and 97.41% for PFOA, PFNA, PFHxS, and PFOS, respectively.

[0069] Application Example 5

[0070] In Example 1, the granular activated carbon-supported layered bimetallic hydroxide-modified multi-walled carbon nanotubes were passed through a 100-mesh sieve, and the material remaining on the sieve was used for later use. PFOA, PFNA, PFHxS, and PFOS were added to ultrapure water to prepare mixed PFASs solutions with a concentration of 25 ng / L. The adsorption column consisted of 10 structural units, each of which contained a support layer composed of 3 layers of PP cotton discs and an adsorbent layer composed of 0.2-0.3 g of granular activated carbon-supported layered bimetallic hydroxide-modified multi-walled carbon nanotubes. Stainless steel filter screens and perforated plates with through holes were installed sequentially from the outside to the inside of both the inlet and outlet ends of the column. The column and the inlet / outlet ends were connected by detachable threads and sealed with O-rings and PTFE tape. The water inlet unit consists of a storage tank and a peristaltic pump. The storage tank, peristaltic pump, adsorption column, and sampling area are all connected by silicone tubing. 1 L of sample is taken at corresponding time intervals. After solid-phase extraction (SPE) pretreatment, the sample is placed in a sample vial, and the concentrations of each PFASs are determined using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS / MS). The results are as follows: Figure 5 As shown.

[0071] like Figure 5 As shown, during continuous operation, PFOA exceeded the US EPA limit of 4 ng / L when the bed volume reached 3990, while PFOS exceeded the same limit after the bed volume reached 4995. PFNA and PFHxS remained below the limit of 10 ng / L throughout the entire experiment. This indicates that in practical applications, this invention can stably and efficiently remove multiple PFAS contaminants simultaneously over a long period.

[0072] The specific embodiments of the present invention have been described in detail above. However, these embodiments are only used to illustrate the core advantages of the present invention and are not intended to limit the present invention. Those skilled in the art can modify or adjust the technical solutions of the present invention through appropriate improvements or combinations without departing from the concept and scope of the present invention, and these improvements and combinations should also be considered within the protection scope of the present invention.

Claims

1. A composite adsorption material-filled adsorption column for purifying PFASs in drinking water, comprising a column body, an inlet end disposed on the column body, and an outlet end disposed on the column body, characterized in that, The column is filled with a composite adsorbent material, which is granular activated carbon supported by layered bimetallic hydroxide modified multi-walled carbon nanotubes. The filling structure inside the column consists of at least two structural units that are repeatedly stacked along the axial direction. Each structural unit includes a support layer and an adsorbent layer directly supported thereon. The adsorbent layer is composed of the composite adsorbent material.

2. The adsorption column according to claim 1, characterized in that, The average particle size of the granular activated carbon is 10-100 mesh.

3. The adsorption column according to claim 1, characterized in that, In the raw materials constituting the composite adsorption material, the mass percentage of granular activated carbon is 1% to 10%.

4. The adsorption column according to claim 1, characterized in that, The number of structural units is 7 to 15.

5. The adsorption column according to claim 1, characterized in that, The mass of the adsorbent layer in each structural unit is 0.1–0.5 g.

6. The adsorption column according to claim 1, characterized in that, The support layer is a precision filter layer, selected from at least one of PP cotton sheets, non-woven fabric, stainless steel filter screen, hollow fiber filter membrane or ceramic membrane; each support layer is composed of 1 to 10 precision filter layers stacked together.

7. The adsorption column according to claim 1, characterized in that, Both the inlet and outlet ends are equipped with primary protection components, which include a stainless steel filter screen and a perforated plate with through holes arranged sequentially from the outside to the inside.

8. A method for preparing the composite adsorbent material in the adsorption column according to any one of claims 1-7, characterized in that, The process includes the following steps: mixing granular activated carbon, multi-walled carbon nanotubes, magnesium nitrate, aluminum nitrate, and water to obtain a mixture; then adding ammonia to the mixture to carry out a co-precipitation-in-situ growth reaction to obtain the granular activated carbon-supported layered bimetallic hydroxide-modified multi-walled carbon nanotubes; wherein the average particle size of the granular activated carbon is 10-100 mesh, and in the total mass of the raw materials, the granular activated carbon, multi-walled carbon nanotubes, magnesium nitrate, and aluminum nitrate are 5-30 parts, 3-4 parts, 45-60 parts, and 20-30 parts by mass, respectively.

9. The application of the adsorption column according to any one of claims 1-7 in the purification of drinking water, characterized in that, Drinking water containing PFASs is passed through the adsorption column with an empty bed contact time of 0.1 to 1 min.

10. The application according to claim 9, characterized in that, The PFASs in the drinking water include at least one of perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), and perfluorooctanesulfonyl compounds (PFOS).

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