Adsorbent as well as preparation method and application thereof

Abstract

The invention relates to the technical field of adsorption materials, in particular to an adsorbent and a preparation method and application thereof. According to the specific technical scheme, the adsorbent is calcined dolomite. According to the invention, experiments and molecular simulation are combined, and the mechanism that dolomite adsorbs PFOA through hydrogen bonds under the action of electrostatic repulsion is disclosed. Further, electrostatic attraction is generated on the surface of the calcined dolomite, so that the adsorption performance is enhanced; in the prior art, high-cost materials such as MOF (Metal Organic Framework) and activated carbon are mostly paid attention to, but in the invention, the high-cost materials are converted into natural minerals, and the key function of Mg (OH) 2 is accidentally found through The invention verifies the emergency application potential of the PFOA in pollution accidents or industrial wastewater aiming at the PFOA concentration of 100mg / L (far exceeding the common environment ng / L level).

Description

Technical Field

[0001] This invention relates to the field of adsorption materials technology, specifically to an adsorbent, its preparation method, and its application. More particularly, it relates to the removal of perfluorooctane acid (PFOA) pollutants from water, using calcined dolomite (CDL) as the adsorbent material to conduct experimental research on the adsorption of PFOA in aquatic environments. Background Technology

[0002] Per- and polyfluoroalkyl substances (PFAS) are classified as typical organic pollutants due to their persistent nature. Perfluorooctanoic acid (PFOA) is one of the main compounds in PFAS and is widely used in numerous industries, including leather goods, cosmetics, food packaging, outdoor cooking utensils, surface coatings, fire-fighting foams, and surfactants. Currently, PFOA has been detected in human serum, groundwater, and wildlife tissues. Studies show that PFOA levels in rainwater samples worldwide exceed the drinking water safety standards set by the U.S. Environmental Protection Agency. Long-term exposure to PFOA may cause various diseases and even increase the risk of cancer. Therefore, PFOA has been listed as an emerging pollutant, and the need for remediation technologies is urgent.

[0003] The physicochemical stability of PFOAs allows them to persist in the environment for centuries. Furthermore, the robust nature of short-chain and ether-based alternatives poses a long-term challenge to traditional treatment technologies. Therefore, various methods for removing or degrading PFOAs in water have been explored, including advanced oxidation processes (AOPs), thermal / non-thermal degradation processes, physicochemical processes, and synergistic processes. However, these methods are costly and unsuitable for use in economically disadvantaged or underdeveloped regions. Adsorption methods, on the other hand, have become one of the preferred technologies for water pollution control due to their simplicity, low cost, versatility, and manageable post-treatment waste.

[0004] Many studies have reported the use of materials such as MOFs (metal-organic frameworks), mineral materials, activated carbon, resins, biomaterials, and molecularly imprinted polymers (MIPs) to adsorb PFOA. Although these materials have good adsorption performance, they are expensive to use, and most of these technologies require pretreatment, making them unsuitable for practical environmental applications. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an adsorbent, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] The present invention provides an adsorbent, wherein the adsorbent is calcined dolomite, and the surface of the calcined dolomite has active phases of Mg(OH)2 and Ca(OH)2.

[0008] This invention provides a method for preparing an adsorbent, which involves calcining dolomite in air at 950-1050℃ for 2.5-3.5 hours and then naturally cooling it to room temperature.

[0009] This invention provides an application of an adsorbent in the treatment of wastewater containing perfluorooctanoic acid (PFOA).

[0010] Preferably, the application method is as follows: place the adsorbent in wastewater containing perfluorooctanoic acid and adsorb for 4-5 hours.

[0011] Preferably, the wastewater has a pH value of 2-11 and a temperature of 303K-333K.

[0012] Preferably, the concentration of perfluorooctanoic acid in the wastewater is ≤200 mg / L.

[0013] Preferably, the concentration of NaCl in the wastewater is 0.001-1M.

[0014] Preferably, the solid-liquid ratio of the adsorbent to the wastewater is 1:20.

[0015] The present invention has the following beneficial effects:

[0016] 1. This invention enhances the adsorption capacity of dolomite through calcination. After the calcined dolomite reaches adsorption saturation, its self-hardening properties allow for direct solidification and landfill disposal, completely avoiding the high energy consumption and secondary pollution risks associated with traditional high-temperature regeneration of adsorbents. Furthermore, this invention elucidates the main adsorption mechanism of PFOA by dolomite using molecular simulations and other methods. By calcining the dolomite and comparing the adsorption differences before and after calcination, this invention provides mechanistic insights into the removal of PFOA from water by dolomite and supports scalable water treatment solutions for real-world environmental conditions.

[0017] 2. This invention, through a combination of experimental research and molecular simulation, delves into the adsorption mechanism of PFOA by dolomite, thus filling a research gap in this field. Simultaneously, this invention will compare the changes in PFOA adsorption performance of dolomite before and after calcination, providing a novel strategy for the targeted optimization of natural minerals and further promoting the practical application of dolomite in environmental pollution control. Given dolomite's low cost, abundant reserves, and wide availability, it shows great promise for removing PFOA from polluted water. This invention will provide crucial parameter support for achieving a simple, low-environmentally impactful, low-cost, and highly scalable removal technology.

[0018] 3. This invention not only elucidates the adsorption mechanism through theoretical calculations but also emphasizes that although dolomite has a lower adsorption capacity compared to many high-capacity materials, it possesses advantages such as low cost, high availability, abundant production, and the ability to adsorb PFOA, demonstrating its significant potential in environmental remediation. Furthermore, this invention not only confirms that dolomite can serve as an adsorbent for removing perfluorooctanoic acid (PFOA) pollutants but also fills a gap in the research on the mechanism of PFOA removal from unmodified natural minerals. The method is simple to operate and easily applied on a large scale in environmental remediation. In summary, this invention provides a low-cost, easy-to-operate, and widely applicable adsorbent for water pollution treatment.

[0019] Furthermore, molecular simulations indicate that hydrogen bonding is the primary adsorption mechanism for PFOA on dolomite. Fitting experimental data using Langmuir and Freundlich isotherm models revealed that it is a surface monolayer adsorption with uniform adsorption sites. The adsorption mechanisms of PFOA on DL and CDL differ. CDL forms MgOH in water. + Dolomite interacts with PFOA through electrostatic attraction, thereby enhancing its adsorption capacity. The study also found that dolomite particles in CDL undergo structural fragmentation after calcination, completely losing their original morphology and forming irregularly shaped structures with a larger surface area. Furthermore, the study revealed that the adsorption mechanism of dolomite may not be limited to surface adsorption but also includes the important pathway of anion exchange, especially at medium to high concentrations. Therefore, in multi-pollutant systems, the adsorption performance of dolomite needs to consider factors such as solution conditions (e.g., pH, ionic strength), pollutant concentration, and the type and concentration of interfering substances. Optimizing operating conditions (e.g., pH and ionic strength), pretreatment to remove interfering substances (e.g., NOM and competing anions), and surface modification of dolomite (calcination) can effectively improve adsorption efficiency under complex environments.

[0020] 4. This invention combines experiments with molecular simulations to reveal the mechanism by which dolomite adsorbs PFOA via hydrogen bonding under electrostatic repulsion. Further findings indicate that electrostatic attraction occurs on the surface of dolomite after calcination, thereby enhancing its adsorption performance. While existing technologies often focus on high-cost materials such as MOFs and activated carbon, this invention turns to natural minerals and unexpectedly discovers the crucial role of Mg(OH)₂ through calcination. This invention verifies its potential for emergency application in pollution incidents or industrial wastewater at a PFOA concentration of 100 mg / L (far exceeding the common environmental level of ng / L). Furthermore, experiments were conducted to determine the ionic strength (Na₂O₂...). +The study found that the adsorption of PFOA by dolomite had no effect, and pH changes did not alter the material structure of dolomite and calcined dolomite. The study systematically compared the differences in adsorption performance of dolomite before and after calcination modification, providing a new strategy for the targeted optimization of natural minerals. In addition, dolomite is abundant and has a mature raw material supply chain, making it suitable for large-scale water treatment projects. Attached Figure Description

[0021] Figure 1 The figures show the isothermal adsorption curves of dolomite and calcined dolomite; the solid line represents the Langmuir model fitting the observed data, and the dashed line represents the Freundlich model fitting the observed data.

[0022] Figure 2 The kinetic adsorption curves of dolomite and calcined dolomite are shown under the condition of initial concentration of 100 mg / L and no pH adjustment.

[0023] Figure 3 XRD patterns of dolomite before and after adsorption at different pH values ​​in the equilibrium solution under an initial concentration of 100 mg / L; (a) adsorption capacity of PFOA at different pH values, with insets showing X-ray diffraction (XRD) patterns of dolomite samples after adsorption at pH values ​​of 2–11; (b) X-ray diffraction patterns of dolomite samples treated at pH values ​​of 8–11, with accompanying sample photographs showing significant changes in sample appearance at different pH values.

[0024] Figure 4 Potential analysis diagrams of dolomite (a) and calcined dolomite (b);

[0025] Figure 5 To investigate the effect of equilibrium solution pH on the removal of PFOA by dolomite and calcined dolomite under an initial concentration of 100 mg / L;

[0026] Figure 6 The effect of temperatures of 303 K, 318 K, and 333 K on the removal of PFOA by dolomite and calcined dolomite under an initial concentration of 100 mg / L was investigated.

[0027] Figure 7 FTIR spectra of primary dolomite, primary calcined dolomite, and adsorbed samples at different initial concentrations;

[0028] Figure 8 The XRD patterns of dolomite (a) and calcined dolomite (b) at different initial PFOA concentrations are shown; among them, magnesium hydroxide (Mg(OH)2), magnesium oxide (MgO), calcium hydroxide (Ca(OH)2) and calcium oxide (CaO) are the XRD patterns of standard samples.

[0029] Figure 9TGA(a) and DTG(b) analyses of dolomite and calcined dolomite; the numbers in the figures represent the initial perfluorooctanoic acid (PFOA) concentrations.

[0030] Figure 10 SEM images of raw dolomite, raw calcined dolomite, and adsorbed samples, along with their surface energy distribution (SED) spectra and spot patterns; among them, SEM images of raw dolomite (a), raw calcined dolomite (b), and their respective adsorbed samples (c, d) at an initial concentration of 200 mg / L; their surface energy distribution (SED) spectra and spot scan patterns (e).

[0031] Figure 11 Molecular simulation of PFOA adsorption in dolomite; where the formation of hydrogen bonds between perfluorooctanoic acid (PFOA) molecules and the surface of dolomite is shown (a, b), and polarization analysis shows charge accumulation (red) and charge loss (blue) in PFOA and dolomite (c, d).

[0032] Figure 12 This is a diagram illustrating the mechanism of PFOA adsorption. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Unless otherwise specified, the technical means used in the implementation examples are conventional means well known to those skilled in the art.

[0035] This invention provides an adsorbent, namely calcined dolomite, the surface of which has active phases of Mg(OH)₂ and Ca(OH)₂. The adsorbent is obtained by calcining the dolomite in a muffle furnace at 950-1050℃ for 2.5-3.5 hours in air atmosphere, followed by natural cooling to room temperature. It should be noted that calcination of the dolomite causes the formation of MgOH on its surface. + This enhances the electrostatic attraction and adsorption capacity for PFOA. Specifically, after calcination, active phases of Mg(OH)2 and Ca(OH)2 are formed on the surface, and the zeta potential changes to +9.07mV.

[0036] This invention uses calcined dolomite as an adsorbent to treat wastewater, especially to adsorb perfluorooctanoic acid (PFOA) pollutants in water, thereby eliminating and reducing the concentration of PFOA in the water.

[0037] The application method is as follows: The adsorbent is placed in wastewater containing perfluorooctanoic acid (PFOA) and adsorbed for 4-5 hours. After adsorption is complete, dolomite powder is separated. The wastewater has a pH of 2-11 and a temperature of 303K-333K. The concentration of PFOA in the wastewater is ≤200 mg / L. The solid-liquid ratio of the adsorbent to the wastewater is 1:20 g / mL. The concentration of NaCl in the wastewater is 0.001-1 M.

[0038] Dolomite, as an important carbonate mineral, has shown significant application potential in industrial and environmental fields. This invention demonstrates that the adsorption mechanism of dolomite under electrostatic repulsion conditions possesses unique adaptability. This discovery not only deepens our understanding of the adsorption behavior of natural minerals but also provides new design ideas for green environmental remediation materials for treating complex water bodies (such as industrial wastewater or groundwater containing multiple pollutants) through mechanism innovation and performance optimization strategies.

[0039] Specifically, dolomite's unique adsorption capacity provides important theoretical and practical basis for its future application in treating pollutants such as PFOA (perfluorooctanoic acid) in real-world environments. The research results broaden the potential application scope of dolomite in environmental remediation and provide theoretical support for the development of novel composite materials (such as dolomite / sodium alginate composites). These new materials are expected to play an important role in water pollution control.

[0040] From an environmental perspective, this research aims to address the urgent need for environmental equity and global sustainable governance. It advocates shifting the remediation of hazardous substances such as PFAS from traditional, energy-intensive methods to low-cost, green governance strategies. This not only helps reduce the release risks of short-chain PFAS but also promotes the synergistic achievement of pollution control and sustainable development through the recycling of mineral resources.

[0041] Furthermore, this invention possesses significant academic and practical value. It not only provides new research ideas and methods for the field of environmental science, but also offers a low-cost, simple, and highly scalable selection of excellent adsorbents for practical environmental remediation. This innovative research method and its application prospects are of great importance in promoting the development of environmental science and technology.

[0042] The present invention will be further described in detail below with reference to specific embodiments.

[0043] Example

[0044] This study explores the effects of calcined and uncalcined dolomite on the adsorption process under various factors (such as temperature and pH). The dolomite used in this invention is sourced from Linshiyu Mineral Resources Co., Ltd., Guzhangshan, Hunan Province, China. Its CAS number is 16389-88-1, and its purity is greater than 99% (composed of 99.5% dolomite, 0.3% quartz, and 0.5% calcite). Calcined dolomite (CDL) is prepared by calcining dolomite (DL) in a muffle furnace at 1000°C in air atmosphere, followed by natural cooling to room temperature.

[0045] The specific method is as follows: place the sample (dolomite or calcined dolomite) in water to adsorb PFOA, and then separate the dolomite powder after the adsorption is complete.

[0046] During PFOA adsorption, the PFOA concentration was adjusted to maximize the adsorption capacity. The pH value of the adsorbed liquid was measured after 24 hours, and the solid sample sediment was obtained.

[0047] During PFOA adsorption, the adjustment time is used to determine the adsorption equilibrium time of PFOA.

[0048] During PFOA adsorption, the pH of the water was adjusted to 2-11, and the changes before and after adsorption were analyzed by XRD.

[0049] When adsorbing PFOA, the ionic strength of the water is adjusted to 0.001, 0.01, 0.1, and 1 M NaCl.

[0050] During PFOA adsorption, the temperature was adjusted to 303K, 318K, and 333K.

[0051] The solid samples were further characterized by dynamic molecular simulation analysis, XRD analysis, FTIR analysis, TGA analysis, and SEM analysis.

[0052] The equipment used in the characterization process is as follows:

[0053] (1) The equilibrium concentration of PFOA was determined using a Shimadzu LC-30A liquid chromatograph and an LCMS-8050 mass spectrometer. The analytical apparatus included key components such as an FCV-20AH2 valve unit, a SIL-30AC autosampler, a CTO-20AC column furnace, and a DGU-20A5R degassing unit. Separation was performed using a Shim-pack GIST-HP C18-AQ column (2.1×100mm, 1.9μm). The mobile phase consisted of water, 2mM ammonium acetate (phase A), and acetonitrile (phase B).

[0054] (2) The crystal structures of DL and CDL after PFOA adsorption were analyzed by X-ray diffraction (XRD), equipped with Cu target radiation, D / teX Ultra detector, step size of 0.01, and scan rate of 2° / min. The samples were measured in the range of 15-65°2θ at 45kV and 40mA.

[0055] (3) FTIR analysis was performed using the KBr particle suppression method on a Nexus FTIR spectrometer (Thermo Nicolet, Waltham, USA). The wavenumbers for spectral acquisition were 400-4000 cm⁻¹. -1 Between, with a resolution of 4cm -1 An average of 256 scans were performed.

[0056] (4) Thermogravimetric analysis (TGA) was performed on the Netzsch STA 449F3 system under nitrogen atmosphere at a heating rate of 10 °C / min to evaluate its thermal stability and weightlessness behavior. Characterization was performed using a scanning electron microscope (SEM) with an SU8010, and energy-dispersive X-ray spectroscopy (EDS) was performed using an X-Max N silicon drift detector.

[0057] (5) The adsorption mechanism of dolomite and PFOA was theoretically analyzed through molecular dynamics simulations. AIMD simulations were performed using the Quickstep module of the CP2K software package. These simulations employed density functional theory (DFT), and wavefunction optimization was achieved using the orbital transformation method. To ensure numerical accuracy, a strict 1×10⁻⁶ spectral density was used. -6 The convergence criteria for Au were established. Core electrons were described using the Goedecker-Teter-Hutter (GTH) pseudopotential, while intermolecular dispersion forces were modeled using the Perdew-Burke-Ernzerhof (PBE) exchange correlation function combined with Grime's DFT-D3 dispersion correction. The basis set used was the GTH double ζ-valence polarization (DZVP) with an energy cutoff of 500 Ry to address the computational challenges associated with large electron densities in AIMD simulations. A time step of 0.5 fs was used, and temperature control was achieved using a Nosé-Hoover thermostat, maintaining a constant temperature of 330 K within the specification (NVT) set. The total simulation duration was approximately 5885 fs (11770 frames), providing a robust dataset for subsequent evaluations.

[0058] The adsorption effects of CD and CDL were validated and their adsorption mechanisms analyzed under isothermal, kinetic, different pH values, ionic strengths, and temperature conditions. All experiments were performed in triplicate to ensure reproducibility. Each sample consisted of 20 mL of solution mixed with 1.00 g of solid adsorbent in a 50 mL centrifuge tube. The mixture was shaken at 150 rpm using a vibrating sieve at room temperature. In the isothermal adsorption experiments, the initial PFOA concentration ranged from 0 to 200 mg / L, and the mixing time was 24 hours. The final pH of DL was 8.0, and the final pH of CDL was approximately 12.5. The initial PFOA concentration for all other experiments was maintained at 100 mg / L.

[0059] (1) Isothermal adsorption experiment

[0060] The equilibrium (q) was calculated based on the mass balance equation. e The adsorption capacity of PFOA is calculated using the following formula:

[0061] q e =(C0-C e )v / m (1)

[0062] In the formula, C0 and C e q represents the concentration of PFOA (mg / L) at time 0 and equilibrium, respectively; v is the volume of the PFOA solution (L); and m is the mass of the adsorbent (g). At equilibrium, q e The equilibrium PFOA adsorption capacity (mg / L) is given, where Ce is the equilibrium concentration.

[0063] Linear regression was used to fit the PFOA adsorption data to the Freundlich isotherm and Langmuir model. The empirical equations are detailed below:

[0064] Freundlich isotherm: q e =K f C e 1 / n (2)

[0065] In the formula, K f : Adsorption equilibrium constant, which represents the strength of the adsorption surface [(mg / g)(L / mg)1 / n]; 1 / n: Frendelsch constant (L / g) under the exponential factor.

[0066] Langmuir model: q e =q max K L C e / (1+K L C e (3)

[0067] In the formula, q eq represents the amount of PFOA adsorbed per unit mass of DL under equilibrium conditions (mg / g). max K represents the maximum adsorption capacity of DL for PFOA (mg / g), and K represents the theoretical maximum adsorption capacity of the adsorbent. L C is the Langmuir constant. e The equilibrium concentration (mg / L) represents the concentration of residual PFOA in the solution.

[0068] The obtained Langmuir isotherm adsorption curve is as follows: Figure 1 As shown, the isotherm model calculations can be obtained. The maximum adsorption capacities (qx) of DL and CDL are 2.16 mg / g and 2.58 mg / g, respectively. The maximum adsorption capacity of CDL is slightly higher than that of DL. The K values ​​of DL and CDL are 0.14 and 0.33, respectively, indicating that CDL has a stronger adsorption affinity for PFOA.

[0069] (2) Dynamics Experiment

[0070] Given an initial PFOA concentration of 100 mg / L, samples were taken for analysis after 0.25, 0.5, 1, 2, 4, 8, 16, and 24 hours to determine the PFOA adsorption equilibrium time.

[0071] The PFOA adsorption kinetics data were fitted to a pseudo-second-order model using linear regression. The empirical equation is as follows:

[0072] Pseudo-second order: dq t / dt=k(q max -q t ) 2 +h(4)

[0073] In the formula, q t Let q be the adsorption amount at time t (mg / g). max denoted as the maximum adsorption capacity (mg / g), k is the kinetic constant (g / mg·min), and h is a constant term.

[0074] The obtained adsorption kinetic curves are as follows Figure 2 As shown, DL exhibits a higher initial adsorption rate for PFOA compared to CDL. The pseudo-second-order adsorption kinetic model fits the experimental data well. The adsorption equilibrium times for PFOA by DL and CDL are 4 h and 5 h, respectively.

[0075] (3) pH effect experiment

[0076] The initial PFOA concentration was maintained at 100 mg / L, and the pH of the equilibrium solution was adjusted to 2-11 using 2M NaOH or 2M HCl. The effect of pH on adsorption capacity is as follows. Figure 3As shown, the adsorption capacity of DL for PFOA decreased with increasing pH. At pH 2-7, CDL underwent significant dissolution, leaving only a small amount of yellow precipitate. At pH 8-11, CDL became viscous with the formation of bubbles, but no yellow precipitate was observed. Figure 3 (b) Therefore, the effect of solution pH on CDL adsorption of PFOA was not evaluated in this invention. However, XRD results for DL ​​(pH 2-11) and CDL (pH 8-11) confirmed that the material structure remained unchanged. Both DL and CDL are highly sensitive to pH changes, resulting in partial solubility in water, with CDL showing greater solubility than DL.

[0077] Determining the zeta value of samples allows us to identify the potential changes at different pH levels, analyze the changes in surface charge characteristics of dolomite before and after calcination, and reveal the effect of calcination on the surface chemical properties of minerals. 5 mg of sample was dissolved in 30 mL of deionized water. The zeta potential of CDL at pH = 12.5 (+9.07 mV) indicates that the surface charge of DL changed from negative to positive after calcination. Figure 4 This positive property enables CDL to effectively capture PFOA through electrostatic attraction, significantly improving its adsorption capacity.

[0078] (4) Ion strength test

[0079] like Figure 5 The effect of changes in ionic strength on PFOA adsorption is negligible. PFOA adsorbs approximately 1.76 mg / g of DL and 1.94 mg / g of CDL. The presence of neutral ionic salts in solution has a limited effect on the adsorption of PFOA on solid surfaces.

[0080] (5) Temperature effect experiment

[0081] The initial concentration of PFOA was set at 100 mg / L, and the tests were conducted at 303 K, 318 K, and 333 K.

[0082] The thermodynamic equation is as follows:

[0083] lnK d =-ΔH° / RT+ΔS° / R(5)

[0084] ΔG°=ΔH°-TΔS°(6)

[0085] Where lnK d ΔH° represents the natural logarithm of the distribution coefficient, ΔS° represents the standard enthalpy change (kJ / mol), ΔG° represents the standard entropy change (kJ / (mol·K)), and ΔG° represents the standard Gibbs free energy change (kJ / mol). R is the gas constant (8.314 J / (mol·K)), and T is the absolute temperature (K).

[0086] The resulting temperature effect diagram is as follows Figure 6 This confirmed that the adsorption process is spontaneous and that the reaction is endothermic. Molecular simulations further confirmed this. Figure 11 It is known that the main adsorption mechanism of PFOA by dolomite is hydrogen bonding, and the formation of hydrogen bonds is an exothermic process. Therefore, it can be concluded that the adsorption process of PFOA by dolomite involves the coexistence of multiple adsorption mechanisms (hydrogen bonding, van der Waals forces, and electrostatic interactions).

[0087] After the adsorption experiment, all mixtures were centrifuged at 5000 rpm for 5 min. The supernatant was filtered through a 0.22 μm membrane filter, and the solids were collected for instrumental analysis.

[0088] Figure 7 The image shows an FTIR spectrum, indicating that the typical absorption band of the original PFOA is around 1149-1238 cm⁻¹. -1 The peaks observed at 1400-1500 cm⁻¹ were dominated by stretching vibrations of hydrophobic CF₂ and CF₃ groups, suggesting possible hydrophobic interactions between the CF groups. The main characteristic peaks of DL were observed at 1400-1500 cm⁻¹. -1 881cm -1 and 729cm -1 A strong absorption band was observed at [location missing]. Its peak distribution is as follows: 1400-1500 cm⁻¹. -1 Broadband corresponds to CO3 2- Asymmetric stretching (v3); at 881cm -1 The spike at that point is due to CO3 2- Caused by out-of-plane bending (v2); at 729cm -1 The peak band at that point was assigned to CO3 2- The in-plane bending (v4) mode. FTIR spectra of the CDL after contact with water show that its main characteristic band shifts to 714 cm⁻¹. -1 874cm -1 and 1450cm -1 This indicates that CO3 2- The infrared intensity gradually increases, indicating that the dolomite underwent a structural transformation into calcite after high-temperature calcination. At 3642 cm⁻¹ -1 A faint spike observed at [location] is considered to be OH. - The vibration band is enhanced due to the formation of Ca(OH)2.

[0089] Figure 8 The XRD pattern shows that after dolomite was calcined in a muffle furnace at 1000℃ for 180 minutes, the characteristic diffraction peaks of powder DL completely disappeared, and new diffraction peaks appeared ( Figure 8b) The XRD pattern matches that of Ca(OH)₂, indicating that dolomite is converted to Ca(OH)₂ after high-temperature calcination, possibly due to its weak hydration resistance. Upon contact with water or PFOA solution, CDL exhibits distinct calcite peaks at 2θ = 23.12°, 29.48°, 36.06°, 39.56°, 43.3°, 47.74°, and 48.7°. Figure 8 (b) Clear diffraction peaks corresponding to Mg(OH)₂ appeared at 2θ = 18.56°, 37.62°, 50.96°, and 58.64°, while small peaks of Ca(OH)₂ appeared at 2θ = 29.62°, 33.96°, 47.22°, and 50.9°. Figure 8 b). This indicates that during the calcination process, CO3... 2- The dolomite underwent thermal decomposition, releasing CO2 into the air and forming CaO and MgO. This suggests that the presence of Mg(OH)2 may be due to its adsorption to PFOA molecules through electrostatic attraction.

[0090] (6) Thermogravimetric analysis experiment

[0091] In the DTG curve, PFOA exhibits an endothermic peak at 150 °C. According to the TGA results, at this temperature, the weight loss reaches its maximum of 95%. Figure 9 a) This significant weight loss may be due to the evaporation of molten or liquid PFOA molecules. DL peak decomposition occurs in the 600-800℃ range ( Figure 9 (b) The main weight loss was approximately 55%, which may be attributed to the decomposition of dolomite and the release of CO2. The TGA curve of DL after PFOA adsorption was similar to that of the original DL powder, and there was no PFOA thermogravimetric peak. The TG and DTG curves of CDL did not show obvious thermogravimetric peaks. After PFOA adsorption, the DTG curve showed three distinct thermogravimetric peaks, distributed in the ranges of 300-380℃, 380-500℃, and 500-800℃. The 10% weight loss observed at 300-380℃ was mainly attributed to the dehydration and decomposition of Mg(OH)2 and Ca(OH)2. The TG and DTG curves combined with XRD results confirmed that MgO / Mg(OH)2 plays a crucial role in the adsorption of PFOA by CDL.

[0092] Figure 10 SEM images of samples adsorbing different concentrations of PFOA are shown. It can be seen that the SEM images of DL before and after contact with PFOA exhibit similar characteristics. Figure 10 In contrast, the dolomite particles in CDL underwent structural fragmentation after calcination, completely losing their original morphology and forming irregularly shaped structures with a larger surface area. These structures are composed of nanoscale spherical particles with a size of approximately 0.1 μm (a, 10c). Figure 10b). EDS analysis ( Figure 10 e) This further confirms that carbonate minerals dominate the mineral composition. For example... Figure 10 As shown in Figure d, after adsorption of 200 mg / L PFOA, the spherical particles partially transformed into blocky and plate-like crystals with a certain thickness and a size of approximately 0.2 μm. Based on XRD and FTIR analysis, these crystals are likely Mg(OH)₂ and Ca(OH)₂.

[0093] Figure 11 The adsorption mechanism of PFOA on the dolomite surface was investigated using AIMD simulations. The simulations showed no evidence of hydrogen bonds between PFOA and the dolomite surface. Figure 11 a). However, as the simulation progressed, hydrogen atoms in the carboxyl group of PFOA formed hydrogen bonds with oxygen atoms on the surface of dolomite ( Figure 11 b). This indicates that hydrogen bonding is the primary mechanism driving adsorption. Furthermore, charge transfer involving fluorine atoms was observed in PFOA ( Figure 11 c, 11d). This indicates that, in addition to hydrogen bonding, polarization and charge transfer are identified as key factors in the adsorption process. Finally, this interaction was quantified, and the adsorption energy was calculated within a representative hydrogen bond simulation framework, yielding an adsorption energy of 0.99 eV ( Figure 11 d) This study is the first to quantitatively analyze the adsorption of PFOA by dolomite, excluding direct comparisons with previous literature.

[0094] XRD results of DL (pH 2-11) and CDL (pH 8-11) confirmed that the material structure remained unchanged. Zeta value determination revealed that calcination affected the surface chemical properties of the minerals, enabling CDL to effectively adsorb PFOA through electrostatic attraction, significantly improving its adsorption capacity. Furthermore, changes in ionic strength had a negligible effect on the adsorption of PFOA by dolomite. Therefore, it can be inferred that external factors have little impact on the removal of PFOA from water by dolomite, indicating that this invention is applicable to most water environment treatments. Furthermore, analysis using XRD, FTIR, and TGA showed that calcined dolomite decomposes into calcite, producing MgO and CaO, which in water are Mg(OH)₂ and Ca(OH)₂, increasing the electrostatic interaction between dolomite and PFOA. Combined with the maximum adsorption capacity of DL and CDL (…),… Figure 1 This indicates that modification (calcination) of dolomite increases its adsorption performance.

[0095] The above experimental results show that the maximum adsorption capacity of CDL is 19.4% higher than that of DL; PFOA reaches adsorption equilibrium on both DL and CDL within 4-5 hours; molecular simulations reveal the hydrogen bond adsorption of PFOA on DL; electrostatic attraction and hydrogen bonding are the main mechanisms of CDL; and DL, being green, natural, and abundant, is one of the candidate adsorbents for removing PFOA.

[0096] This invention elucidates the adsorption mechanism of PFOA by dolomite through a combination of experiments and molecular simulations. Leveraging the advantages of dolomite, such as low cost, high availability, abundant production, and good scalability, the effects of DL and CDL adsorption on PFOA under different factors (pH, stability, ionic strength, etc.) were simulated. Experimental data and the invention's advantages demonstrate that it meets practical application requirements due to its low cost, simple process, and applicability to various environmental changes, making it highly significant for global governance. Instrumental analysis and maximum adsorption capacity show that the adsorption of PFOA by dolomite involves multiple adsorption mechanisms (mainly hydrogen bonding and electrostatic interactions), and that modified dolomite exhibits increased adsorption performance for PFOA. Figure 12 ).

[0097] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. An adsorbent, characterized in that: The adsorbent is calcined dolomite, and the surface of the calcined dolomite has active phases of Mg(OH)2 and Ca(OH)2.

2. A method for preparing the adsorbent according to claim 1, characterized in that: Dolomite is obtained by calcining it in air at 950-1050℃ for 2.5-3.5 hours and then naturally cooling it to room temperature.

3. The application of the adsorbent of claim 1 in the treatment of wastewater containing perfluorooctanoic acid.

4. The application according to claim 3, characterized in that: The application method is as follows: place the adsorbent in wastewater containing perfluorooctanoic acid and adsorb for 4-5 hours.

5. The application according to claim 4, characterized in that: The wastewater has a pH of 2-11 and a temperature of 303K-333K.

6. The application according to claim 3, characterized in that: The concentration of perfluorooctanoic acid (PFOA) in wastewater is ≤200 mg / L.

7. The application according to claim 3, characterized in that: The concentration of NaCl in the wastewater is 0.001-1M.

8. The application according to claim 4, characterized in that: The solid-liquid ratio of the adsorbent to the wastewater is 1:20.

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