Carboxymethyl cellulose modified nano zero-valent iron material, preparation method and application thereof

Abstract

This invention relates to a carboxymethyl cellulose-modified nanomaterial of zero-valent iron, its preparation method, and its application in the remediation of trichloroethylene-contaminated water or groundwater. The material is prepared by mixing sodium carboxymethyl cellulose with a water-soluble ferrous salt in a deoxygenated aqueous phase, followed by reduction with an oxygen-free sodium borohydride aqueous solution under nitrogen protection. The sodium carboxymethyl cellulose forms a coating layer on the surface of the zero-valent iron through carboxylate groups, distributing the zero-valent iron particles on the carboxymethyl cellulose framework or the coating layer surface. Scanning electron microscopy analysis shows that the zero-valent iron particles are mainly distributed in the range of 80-150 nm; the zeta potential measured in anhydrous ethanol dispersion is -47 mV. The material is added at 0.5-5.0 g / L to trichloroethylene-contaminated water or groundwater and reacted under sealed, light-protected conditions at pH 6.0-8.0 and a temperature of 20-35°C for the reduction and dechlorination treatment of trichloroethylene.

Description

Technical Field

[0001] This invention belongs to the technical field of groundwater pollution remediation and environmental functional materials, specifically relating to a carboxymethyl cellulose modified nano-zero-valent iron material, its preparation method, and its application in the remediation of trichloroethylene-contaminated water bodies or groundwater. Background Technology

[0002] Trichloroethylene (TCE) is a typical chlorinated hydrocarbon pollutant that can persist in groundwater environments for extended periods. Nanoscale zero-valent iron (nZVI), due to its high specific surface area and reducing activity, can treat chlorinated organic compounds such as TCE through reductive dechlorination.

[0003] However, unmodified nZVI particles exhibit strong magnetic dipole and van der Waals interactions, making them prone to aggregation and sedimentation in aqueous and porous media, resulting in short effective migration distances and insufficient exposure of active sites. Furthermore, nZVI readily reacts with dissolved oxygen, anions in water, or other non-targeting components to form an iron oxide passivation layer, reducing electron utilization efficiency and long-term reactivity.

[0004] Sodium carboxymethyl cellulose (CMC-Na) is an anionic, water-soluble polymer containing carboxyl and hydroxyl groups. Its dispersion stability can be improved through steric hindrance and electrostatic repulsion. Previous studies have disclosed CMC-stabilized iron nanoparticles and their applications in dechlorination of chlorinated hydrocarbons or groundwater remediation. Therefore, there is still a need to develop a CMC-nZVI material and its processing method based on existing CMC-stabilized iron nanoparticles, possessing well-defined preparation parameters, reproducible material fingerprints, and TCE treatment data under complex groundwater conditions, in order to improve the aggregation, passivation, and reusability of unmodified nZVI. Summary of the Invention

[0005] Technical problems to be solved The technical problem to be solved by the present invention is to provide a carboxymethyl cellulose modified nano-zero-valent iron material and its preparation method, so that the material has dispersion stability and surface coordination structure that can be characterized by Zeta potential, sedimentation experiment and spectral characterization results, and can be used for reduction dechlorination treatment of TCE-containing water bodies or groundwater.

[0006] Technical solution To address the aforementioned technical problems, this invention provides a method for preparing carboxymethyl cellulose modified nano-zero-valent iron materials, comprising: first preparing a sodium carboxymethyl cellulose solution; then mixing deoxygenated water, the sodium carboxymethyl cellulose solution, and ferrous salt under nitrogen protection; subsequently adding an oxygen-free aqueous solution of sodium borohydride at a controlled dropping rate for reduction to generate zero-valent iron particles; and finally obtaining CMC-nZVI material through oxygen-free separation, washing, ultrasonic dispersion, and optional freeze-drying.

[0007] In the preparation process, the concentration of sodium carboxymethyl cellulose solution is preferably 8-20 g / L; the volume ratio of deoxygenated water to sodium carboxymethyl cellulose solution is preferably (3-5):1; Fe 2+ The preferred concentration is 0.05-0.15 mol / L; sodium borohydride and Fe 2+ The preferred molar ratio is (1.5-3.0):1; the preferred reducing agent dropping rate is 0.5-2.0 mL / min.

[0008] This invention also provides a CMC-nZVI material prepared by the above method. In this material, FeO particles are distributed on the surface of the carboxymethyl cellulose backbone or coating layer; according to scanning electron microscopy, the particle size is mainly distributed in the range of 80-150 nm; the Zeta potential measured in anhydrous ethanol dispersion system is -30 mV to -60 mV; its FTIR spectrum shows characteristic peaks of carboxylate groups and COC, and the carboxylate groups are coordinated with the nZVI surface.

[0009] This invention also provides a method for treating TCE-contaminated water or groundwater, wherein the above-mentioned CMC-nZVI material is added at a concentration of 0.5-5.0 g / L to TCE-containing water or groundwater, and the reaction is carried out under conditions of closed, light-protected environment, pH 6.0-8.0, and temperature 20-35°C. The water or groundwater may contain Ca. 2+ Mg 2+ and / or typical environmental factors such as humic acid.

[0010] Beneficial effects Compared with the prior art, the present invention has at least the following beneficial effects: Since CMC coordinates with the surface of zero-valent iron through carboxylate groups to form a coating layer, the examples show that nZVI particles are transformed from obvious agglomeration to nanoparticles distributed on the CMC framework or coating layer surface, and the main distribution range of FeO particle size is adjusted from 150-250 nm of unmodified nZVI to 80-150 nm.

[0011] In the anhydrous ethanol dispersion system, the Zeta potential of CMC-nZVI changed from +20 mV of unmodified nZVI to -47 mV; at the same time, the aqueous sedimentation experiment showed that CMC-nZVI remained in a suspended dispersion state after standing for 600 s, indicating that there is a corresponding relationship between CMC modification and the improvement of liquid phase dispersion stability.

[0012] Under the conditions of an initial TCE concentration of 100 mg / L, pH 7.0, 30℃, and 150 r / min, the examples showed that adding 2.0 g / L or higher of CMC-nZVI could reduce the TCE concentration within 24 h, with some samples dropping to near the detection limit. The limit of detection was 1.2 μg / L, and the limit of quantitation was 4.8 μg / L.

[0013] In Ca 2+ Mg 2+ Under conditions of coexistence with humic acid, the examples show that CMC-nZVI still maintains reactivity with TCE; in the reuse experiment, the second 5-day removal rate of recovered CMC-nZVI was 78.56%, which is higher than that of unmodified nZVI.

[0014] The detection results of Example 9 show that C2H2 is the main non-chlorinated product in the CMC-nZVI system, with a total molar percentage of DCE of 4.37%. This effect corresponds to the fact that the CMC coating or coordination structure improves particle dispersibility and affects the distribution of intermediate products in the reaction pathway. The relevant qualitative / quantitative basis is shown in Example 9 and Tables 5 to 8.

[0015] Table 1. Detection parameters for TCE and volatile intermediates Attached Figure Description

[0016] Figure 1 Schematic diagram of the CMC-nZVI preparation apparatus.

[0017] Figure 2 SEM images and particle size distributions of nZVI and CMC-nZVI are shown, where (a) is nZVI, (b) is CMC-nZVI, and (c) is the particle size distribution.

[0018] Figure 3 XRD patterns of nZVI and CMC-nZVI.

[0019] Figure 4 XPS spectra of nZVI and CMC-nZVI, where (a) is the full spectrum and (b) is the Fe 2p spectrum.

[0020] Figure 5 The FTIR spectra are for nZVI, CMC-nZVI, and CMC.

[0021] Figure 6 The results show the dispersion stability test results of nZVI and CMC-nZVI, where (a) is the sedimentation photograph from 0 to 600 s and (b) is the absorbance curve from 0 to 2000 s.

[0022] Figure 7 Zeta potential diagrams for nZVI and CMC-nZVI.

[0023] Figure 8 The degradation effects of different dosages of nZVI and CMC-nZVI on TCE in an ultrapure water system were investigated, where (a) represents nZVI and (b) represents CMC-nZVI.

[0024] Figure 9 The degradation effects of different dosages of nZVI and CMC-nZVI on TCE were investigated in a simulated groundwater system, where (a) represents nZVI and (b) represents CMC-nZVI.

[0025] Figure 10 For Ca 2+ Mg 2+ The effects of humic acid on the degradation of TCE by nZVI and CMC-nZVI, where (a) and (b) are Ca 2+ The effects, (c) and (d) are Mg 2+ The effects are shown in (e) and (f), which represent the effects of humic acid.

[0026] Figure 11 The ability of nZVI and CMC-nZVI to repeatedly degrade TCE.

[0027] Figure 12 A schematic diagram of the reaction pathway for the degradation of TCE by nZVI and CMC-nZVI. Detailed Implementation

[0028] The following examples are for illustrative purposes only and should not be construed as limiting the scope of protection of this invention. Without departing from the technical concept of this invention, those skilled in the art can make conventional adjustments to the formula and reaction conditions based on the actual water properties, TCE concentration, and dosing method. In this specification, deoxygenated water or oxygen-free water refers to water that has been aerated with nitrogen for at least 30 minutes or treated using an equivalent deoxygenation method; unless otherwise stated, the amount of materials added is based on the total volume of the reaction system, and the percentage is a mass percentage.

[0029] Example 1: Preparation of CMC-nZVI material Comparative Example 1 nZVI was prepared as follows: 400 mL of ultrapure water and 100 mL of anhydrous ethanol were placed in a three-necked flask, nitrogen gas was introduced for 30 min and mechanically stirred at 400-500 r / min, and 13.9 g of FeSO4·7H2O was added until completely dissolved; 3.8 g of NaBH4 and 0.1 g of NaOH were dissolved in 100 mL of oxygen-free ultrapure water and added dropwise at 1.0 mL / min. After the addition was completed, stirring was continued for 30 min; after sedimentation, the sample was washed three times alternately with anhydrous ethanol and oxygen-free ultrapure water, and then dispersed by sonication in oxygen-free ultrapure water for 1 h. If necessary, it was freeze-dried and sieved according to the example.

[0030] Weigh 1.2 g of sodium carboxymethyl cellulose (molecular weight 90-150 kDa, degree of substitution DS=0.7, viscosity 200-500 mPa·s, 2% aqueous solution, 25℃), and slowly add it to 100 mL of ultrapure water. Stir at 60-80℃ and 500 r / min until completely dissolved to obtain a CMC solution with a mass concentration of 12 g / L. Mix 400 mL of deoxygenated ultrapure water with 100 mL of CMC solution and place the mixture in a three-necked flask. Purge with nitrogen and aerate for 30 min to remove dissolved oxygen, while mechanically stirring at 400-500 r / min.

[0031] Under nitrogen protection and stirring, 13.9 g of FeSO4·7H2O was added to a three-necked flask and stirred continuously until completely dissolved. Separately, 3.8 g of NaBH4 was dissolved in 100 mL of oxygen-free ultrapure water, and 0.1 g of NaOH was added to improve the stability of the reducing agent. The NaBH4 solution was added dropwise to the above system at a rate of 1.0 mL / min using a peristaltic pump. During the addition, the color of the system changed from dark green to black; after the addition was complete, stirring was continued for 30 min. Under this feeding condition, Fe... 2+ The concentration is approximately 0.10 mol / L, NaBH4 and Fe 2+ The molar ratio is approximately 2.0:1, the theoretical FeO yield is approximately 2.79 g, and the mass ratio of CMC-Na to theoretical FeO is approximately 0.43:1.

[0032] After the reaction, the mixture was allowed to settle under nitrogen protection. The supernatant was discarded and transferred to a centrifuge tube. Anhydrous ethanol was added to redisperse the precipitate, and the mixture was centrifuged. The precipitate was then washed three times with anhydrous ethanol and oxygen-free ultrapure water, respectively. The washed material was then ultrasonically dispersed in oxygen-free ultrapure water for 1 h to obtain a CMC-nZVI suspension. When powder samples were needed, the material was frozen at -80°C, then freeze-dried at -50°C and a relative pressure of approximately -0.08 MPa for 24 h, and passed through a 100-mesh sieve to obtain CMC-nZVI powder. A schematic diagram of the preparation apparatus used in this embodiment is shown below. Figure 1 As shown.

[0033] In this embodiment, DS represents the degree of substitution of sodium carboxymethyl cellulose; the viscosity specification is based on the nominal viscosity measured by the supplier in a 2% aqueous solution at 25°C. The mass ratio of CMC-Na to theoretical FeO for different batches of material can be calculated based on the actual feed amount and the theoretical FeO yield.

[0034] Example 2: Main Reagents and Detection Equipment Experimental reagents included TCE standards (Aladdin, GC grade, purity ≥99.5%), FeSO4·7H2O, sodium carboxymethyl cellulose (molecular weight 90-150 kDa, degree of substitution DS=0.7, viscosity 200-500 mPa·s), NaBH4, KBr, anhydrous ethanol, humic acid, glacial acetic acid, MgSO4, CaCl2, NaCl, KCl, (NH4)2SO4, hydrogen peroxide, etc.; unless otherwise specified, all reagents were of analytical grade. 2+ Provided by CaCl2, Mg 2+ Provided by MgSO4. The main experimental instruments are shown in Table 2.

[0035] The composition of the inorganic salt medium (MSM) is as follows: Na₂HPO₄ 2440.0 mg / L, KH₂PO₄ 1520.0 mg / L, (NH₄)₂SO₄ 500.0 mg / L, MgSO₄ 98.0 mg / L, CaCl₂ 37.8 mg / L, EDTA-2Na 5.0 mg / L, FeSO₄·7H₂O 2.0 mg / L, ZnSO₄·7H₂O 0.1 mg / L, MnCl₂·4H₂O 0.03 mg / L, H₃BO₃ 0.3 mg / L, CuCl₂·2H₂O 0.01 mg / L, CoCl₂·6H₂O 0.2 mg / L, NiCl₂·6H₂O 0.02 mg / L, Na₂MoO₄·2H₂O 0.03 mg / L, biotin 0.02 mg / L, vitamin B9. 0.02 mg / L, Vitamin B6 0.1 mg / L, Vitamin B1 0.05 mg / L, Vitamin B2 0.05 mg / L, Vitamin B3 0.05 mg / L, Vitamin B5 0.05 mg / L, Vitamin B 12 0.001 mg / L, Vitamin K3 / menaquinone 1.0 mg / L, Vitamin K1 0.22 mg / L, para-aminobenzoic acid 0.05 mg / L, lipoic acid 0.05 mg / L.

[0036] Table 2 Main Experimental Instruments Example 3 Material Characterization The microstructure of nZVI and CMC-nZVI was observed using scanning electron microscopy. Samples were dispersed in anhydrous ethanol, ultrasonically dispersed, and then dropped onto the sample stage. SEM images were acquired at a working voltage of 5 kV, and particle size was statistically analyzed using ImageJ. At least 50 particles were counted in each of the three fields of view. The average particle size of unmodified nZVI was 200 ± 50 nm, and the average particle size of CMC-nZVI was 115 ± 35 nm. The results are as follows: Figure 2 As shown, the particle size of unmodified nZVI is concentrated in 150-250 nm, and the particles are obviously aggregated; the FeO particles in CMC-nZVI are mainly distributed in the range of 80-150 nm, and are distributed on the surface of the relatively clear CMC framework or coating layer.

[0037] Crystal structure analysis of the material was performed using Co-target XRD, with a 2θ scan range of 10°–80°. The results are as follows: Figure 3 As shown, both nZVI and CMC-nZVI have Fe0 characteristic peaks near 2θ=52.8° and smaller Fe0 diffraction peaks near 2θ=77.6°; CMC-nZVI shows amorphous broad peaks in the range of 2θ=10°-30°, indicating the presence of an organic coating layer in CMC.

[0038] XPS analysis was used to analyze the elemental composition of the material surface. The results are as follows: Figure 4 As shown in Table 3, both materials contain Na, Fe, O, C, and S elements on their surfaces; the Fe content on the CMC-nZVI surface is lower than that on the nZVI surface, indicating that the CMC coating weakens the Fe signal detected by XPS. Fe 2p fitting shows the presence of Fe0 and Fe2O3 in the material. 3+ The signal indicates that there is a certain oxide layer on the surface of the material.

[0039] Table 3. Surface element percentages of nZVI and CMC-nZVI FTIR analysis was used to analyze the functional groups on the material surface. The results are as follows: Figure 5 As shown, CMC-nZVI in COO appears - The antisymmetric stretching vibration peak is at 1352.81 cm⁻¹. -1 A COO- symmetric stretching peak appears at 1114.08 cm⁻¹. -1 A COC stretching vibration peak appears at approximately 3547.04 cm⁻¹. -1 An OH stretching vibration peak appears at 621.83 cm⁻¹; nZVI and CMC-nZVI peak at 621.83 cm⁻¹. -1 and 617.6 cm -1 A Fe-O vibrational peak appears nearby. According to the formula Δv=v as (COO)- -v s (COO) - ), COO - The peak difference between antisymmetric and symmetric stretching vibrations is Δv = 238.73 cm. -1 In the examples, it was inferred from the above-mentioned peak position changes that the carboxylate group of CMC is coordinated with nZVI.

[0040] Example 4: Dispersion Stability Test 200 mg of nZVI and CMC-nZVI were weighed separately and placed in serum bottles. 20 mL of water was added to prepare a 10 g / L suspension. The bottles were sealed, shaken to disperse, and allowed to stand. The sedimentation was recorded from 0 to 600 s. Simultaneously, the absorbance of the suspension was measured at 508 nm over time. The results are as follows: Figure 6 As shown, nZVI showed obvious solid-liquid separation at 60 s and almost completely settled at 600 s; CMC-nZVI still maintained a relatively uniform black dispersion at 600 s.

[0041] Weigh 200 mg of nZVI and CMC-nZVI and place them separately in 20 mL of anhydrous ethanol. Measure the zeta potential three times. The zeta potential test results are as follows: Figure 7 As shown, the average Zeta potential of nZVI is +20 mV, while the average Zeta potential of CMC-nZVI is -47 mV. This indicates that the surface electrical properties of particles changed after CMC modification in the anhydrous ethanol dispersion system, and the repulsive effect between particles was enhanced, which is beneficial to inhibiting agglomeration and sedimentation.

[0042] Example 5: Effect of different dosages on TCE degradation The degradation experiment was conducted in 100 mL sealed serum bottles, with a reaction volume of 50 mL, under light-protected, temperature-controlled shaking conditions. Material dosages were set at 0, 0.5, 1.0, 2.0, 3.0, and 5.0 g / L, with 0 g / L serving as a blank control. The initial TCE concentration was 100 mg / L, the initial pH was 7.0, the temperature was 30℃, and the shaking rate was 150 r / min. Three replicates were prepared for each group, and non-reaction losses such as TCE volatilization were subtracted using a blank control. TCE concentration was determined by headspace gas chromatography.

[0043] The headspace gas chromatography conditions were as follows: headspace vial heating temperature 60℃, injection needle temperature 80℃, transfer line temperature 120℃, vaporization chamber temperature 250℃, detector (ECD) temperature 320℃; column temperature program: 40℃ for 5 min, ramped up to 100℃ at 8℃ / min, then ramped up to 200℃ at 6℃ / min and held for 10 min; gas circulation time 30 min, vial equilibration time 30 min, pressure equilibration time 1 min; pressure 40.2 kPa, total flow rate 4.8 mL / min, column flow rate 1.20 mL / min, linear velocity 22.4 cm / s, split ratio 3.0.

[0044] During sampling, the syringe and headspace vial were dried at 105℃ for 1 h, and sodium chloride was ignited at 350℃ for 6 h. For each sample, 3 mL of reaction solution was taken, filtered through a 0.22 μm aqueous filter membrane, and added to a headspace vial containing 0.8 g NaCl. After sealing, headspace equilibration and detection were performed (no terminator, headspace vial specification 20 mL, gas-liquid ratio 17:3).

[0045] The method for constructing the TCE solution standard curve is as follows: Take five headspace vials, weigh 0.8 g of NaCl into each vial, and add appropriate amounts of TCE to make the TCE concentrations in the solutions 0, 10, 20, 50, and 100 mg / L. After gas chromatography determination, construct the concentration-peak area standard curve, and determine the linear correlation coefficient R. 2 Not less than 0.995. The TCE concentration in the experimental group was determined according to the standard curve, and the TCE removal rate was calculated according to formula (1): η=(C 0- C t ) / C0×100% (1) In the formula, η is the TCE removal rate (%), C0 is the initial TCE concentration in the solution (mg / L), and C t Let TCE be the concentration (mg / L) in the solution at time t.

[0046] The results are as follows Figure 8 As shown, the removal rate of TCE by both materials increased with increasing dosage. nZVI reached near-equilibrium after approximately 24 hours; CMC-nZVI exhibited a longer reaction duration at low dosages, with TCE concentrations decreasing within 24 hours at dosages of 2.0 g / L and above, with some samples reaching near the detection limit (LOD), which was 1.2 μg / L and 4.8 μg / L. Considering both material dosage and degradation efficiency, 2.0 g / L was selected as the optimal dosage for subsequent experiments.

[0047] Example 6: TCE Degradation in Simulated Groundwater Systems The MSM system described in Example 2 was used to simulate the groundwater environment. The initial TCE concentration was 100 mg / L, and the material dosage was 2.0 g / L or 3.0 g / L. Other conditions were the same as in Example 5.

[0048] The results are as follows Figure 9 As shown, the TCE removal rate of the materials in the MSM system was slower compared to the ultrapure water system. At a dosage of 2.0 g / L, the TCE removal rate of both materials was approximately 70% after 24 h of reaction; at a dosage of 3.0 g / L, the TCE concentration was still reduced after 144 h of reaction, with some samples dropping to near the detection limit (1.2 μg / L) and the quantitation limit (4.8 μg / L). These results indicate that coexisting ions and inorganic salts affect the surface reaction process of the materials, but CMC-nZVI still maintains its TCE reduction and dechlorination capability.

[0049] Example 7: The Influence of Environmental Factors on TCE Degradation Table 4 Environmental Factor Concentration Settings In a 50 mL anoxic ultrapure water system, the initial TCE concentration was 100 mg / L, the material dosage was 2.0 g / L, the initial pH was 7.0, the temperature was 30℃, and the shaking rate was 150 r / min. Ca was added separately. 2+ Mg 2+ And humic acid, to investigate the effects of typical groundwater factors on the degradation of TCE by nZVI and CMC-nZVI; among which Ca 2+ Provided by CaCl2, Mg 2+ Provided by MgSO4. See Table 4 for specific concentration settings.

[0050] The results are as follows Figure 10 As shown, Ca 2+ The effect on the short-term removal rate of CMC-nZVI was manifested as a change in the short-term removal rate, with a decrease in removal rate within 24 hours, but still maintaining a certain removal capacity within 48 hours; Mg 2+ Humic acid showed varying effects on the removal rate at different concentrations and time periods, but it did not completely inhibit the removal of TCE by CMC-nZVI. This result corresponds to the fact that the material of this invention still exhibits reactivity under typical groundwater coexistence conditions. The average values ​​and error bars at each time point were calculated from three parallel samples.

[0051] Example 8 Material Reusability After the first round of TCE degradation experiments, the reaction system containing solid materials was separated into solid and liquid components and then frozen at -20°C. It was then freeze-dried under vacuum at -50°C and a relative pressure of approximately -0.08 MPa for 72 hours to recover the nZVI and CMC-nZVI materials. The recovered materials were then added back into a freshly prepared reaction system, with the material concentration controlled at 2.0 g / L and the initial TCE concentration at 100 mg / L, for the second round of degradation experiments.

[0052] The results are as follows Figure 11 As shown, at a dosage of 2.0 g / L, the 5-day removal rate of TCE by recovered CMC-nZVI was 78.56%, which was 8.21 percentage points higher than that of recovered nZVI, with each group being repeated three times. This result indicates that, under the conditions of the examples, the CMC coating helps reduce the impact of particle agglomeration and surface passivation on reactivity after recycling.

[0053] Example 9 Intermediate Products and Reaction Path Analysis Volatile intermediates in the TCE degradation process were detected by GC-MS. A DB-5MS capillary column (30 m × 0.25 mm × 0.25 μm) was used; high-purity helium was used as the carrier gas at a flow rate of 1.0 mL / min; the injection port temperature was 250℃, and splitless injection was employed. The column temperature program was 35℃ for 5 min, increased to 120℃ at 5℃ / min, and then increased to 220℃ at 10℃ / min and held for 2 min. Mass spectrometry conditions included an EI ion source with an electron energy of 70 eV, an ion source temperature of 230℃, a quadrupole temperature of 150℃, a transfer line temperature of 280℃, and a scan range of m / z 0-300. Samples were injected after headspace equilibration, and qualitative analysis was performed using retention times of standards or NIST library matching results. Quantitative results were based on external standard method calculations. The relevant limits of detection, limits of quantitation, and matching thresholds are shown in Table 1.

[0054] Ion chromatography was used to determine the release of small-molecule organic acids such as formic acid, acetic acid, and oxalic acid, as well as chloride ions. An IonPac AS11-HC anion exchange column was used at 30℃, with gradient elution of KOH solution (1-30 mmol / L), a flow rate of 1.0 mL / min, and suppressed conductivity detection. The injection volume was 25 μL. The reaction was terminated with 6 mol / L analytical grade nitric acid solution, with 1.0 mL of 6 mol / L nitric acid solution added to every 50 mL of reaction system. After termination, the sample was centrifuged to remove solid particles, filtered through a 0.22 μm filter membrane, and appropriately diluted before injection.

[0055] The results of intermediate product analysis are shown in Tables 5 to 8. Table 5 lists the quantitative results of the products, Table 6 lists the chlorine mass balance, and Tables 7 and 8 list the intermediate products of the reaction pathways for the nZVI and CMC-nZVI systems, respectively. In the nZVI system, the total molar proportion of DCE was 25.12%, accompanied by a hydrogen evolution side reaction; in the CMC-nZVI system, the molar proportion of C2H2 was 89.87%, the total molar proportion of DCE was 4.37%, and H2 was approximately 21.8 μM. The chlorine mass balance results are shown in Table 6. In the CMC-nZVI system, the proportion of free chlorine in the aqueous phase was 96.42% of the initial total chlorine, and the total chlorine recovery rate was 99.22%. Under the above detection conditions, CMC modification helps to reduce the proportion of chlorinated intermediate products such as DCE. The total chlorine recovery rate of the nZVI group is shown in Table 6, serving as the mass balance result for the control system. The reaction pathway diagram is shown below. Figure 12 As shown.

[0056] Table 5 Quantitative results of TCE degradation products The chlorine recovery rate in Table 6 is calculated using the following formula: Chlorine recovery rate = (C TCE残留 ×3+C DCE总 ×2+C Cl- ) / (C TCE初始 ×3)×100% Table 6. Chlorine element mass balance results Table 7 Intermediate products in the nZVI degradation TCE reaction pathway Table 8 Intermediate products in the CMC-nZVI degradation TCE reaction pathway The above embodiments are only used to illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention; the scope of protection of the present invention is determined by the claims.

Claims

1. A method for preparing a carboxymethyl cellulose modified nanomaterial of zero valent iron, characterized in that, Includes the following steps: (1) Add sodium carboxymethyl cellulose to deoxygenated water or water that has been deoxygenated, and stir at 60-80℃ and 300-700 r / min to obtain a sodium carboxymethyl cellulose solution with a mass concentration of 8-20 g / L. (2) The deoxygenated water and the sodium carboxymethyl cellulose solution are mixed at a volume ratio of (3-5):1, stirred under nitrogen protection, and water-soluble ferrous salt is added to make Fe 2+ The concentration is 0.05-0.15 mol / L; (3) An oxygen-free aqueous solution containing sodium borohydride is added dropwise to the system obtained in step (2) at a rate of 0.5-2.0 mL / min, wherein the sodium borohydride reacts with Fe. 2+ The molar ratio is (1.5-3.0):

1. After the addition is complete, continue stirring for 20-60 min to obtain a black precipitate. (4) The black precipitate was separated under oxygen or nitrogen protection and washed with anhydrous ethanol and oxygen-free water and ultrasonically dispersed to obtain the carboxymethyl cellulose modified nano zero-valent iron material.

2. The preparation method according to claim 1, characterized in that, The sodium carboxymethyl cellulose solution in step (1) is prepared by adding 1.2 g of sodium carboxymethyl cellulose to 100 mL of deoxygenated water or deoxygenated water and stirring at 60-80℃; the deoxygenated water in step (2) is 400 mL, the sodium carboxymethyl cellulose solution is 100 mL, and the ferrous salt is 13.9 g of ferrous sulfate heptahydrate; the oxygen-free aqueous solution containing sodium borohydride in step (3) is prepared by dissolving 3.8 g of sodium borohydride and 0.1 g of sodium hydroxide in 100 mL of oxygen-free water; based on theoretical zero-valent iron, the mass ratio of sodium carboxymethyl cellulose to zero-valent iron is approximately 0.43:

1.

3. The preparation method according to claim 1, characterized in that, In step (2), the nitrogen aeration time shall not be less than 30 min and the stirring speed shall be 400-500 r / min.

4. The preparation method according to claim 1, characterized in that, The washing in step (4) involves alternating washing with anhydrous ethanol and oxygen-free water at least 3 times, and the ultrasonic dispersion time is 0.5-1.5 h.

5. The preparation method according to claim 1, characterized in that, Step (4) also includes storing the obtained material in oxygen-free water, or freezing it at -80°C and then freeze-drying it at -50°C and a relative pressure of about -0.08 MPa for 20-30 h, and then passing it through a 100-mesh sieve.

6. The preparation method according to claim 1, characterized in that, Based on the theoretical mass of zero-valent iron, the mass ratio of sodium carboxymethyl cellulose to zero-valent iron is (0.3-1.2):1, preferably (0.35-0.60):

1.

7. A carboxymethyl cellulose-modified nanomaterial of zero-valent iron, characterized in that, The material is prepared by the method according to any one of claims 1 to 6, and the material comprises zero-valent iron particles and a carboxymethyl cellulose layer coating or disposed on the surface of the zero-valent iron particles; according to scanning electron microscopy, the particle size of the zero-valent iron particles is mainly distributed in the range of 80-150 nm, and the zeta potential of the material measured in an anhydrous ethanol dispersion system is -30 mV to -60 mV.

8. The material according to claim 7, characterized in that, The material exhibited characteristic zero-valent iron diffraction peaks at 2θ = 52.8° ± 1.0° and 2θ = 77.6° ± 1.0° in cobalt target X-ray diffraction tests; and in Fourier transform infrared spectroscopy, it showed characteristic peaks at 1591 cm⁻¹ ± 10 cm⁻¹ and 1114 cm⁻¹ ± 10 cm⁻¹. -1 and 617 cm -1 An absorption peak is observed at ±10 cm⁻¹, where the carboxylate group is coordinated with the surface of zero-valent iron.

9. A method for treating trichloroethylene-contaminated water or groundwater, characterized in that, The carboxymethyl cellulose modified nano-zero-valent iron material according to claim 7 or 8 is reacted with trichloroethylene-containing water or groundwater under closed and light-protected conditions; wherein the dosage of the carboxymethyl cellulose modified nano-zero-valent iron material is 0.5-5.0 g / L, the initial pH of the trichloroethylene-containing water or groundwater is 6.0-8.0, and the reaction temperature is 20-35℃.

10. The processing method according to claim 9, characterized in that, The initial concentration of trichloroethylene in the trichloroethylene-containing water or groundwater is 50-150 mg / L, the dosage of the carboxymethyl cellulose-modified nano-zero-valent iron material is 2.0-3.0 g / L, and the contact reaction time is 24-144 h; and it meets at least one of the following conditions: the trichloroethylene-containing water or groundwater also contains 20-80 mg / L of Ca. 2+ 3-15 mg / L Mg 2+ And / or 5-20 mg / L humic acid; the treatment method further includes solid-liquid separation and recovery of the carboxymethyl cellulose modified nano zero-valent iron material after reaction, and after freezing at -20℃ and vacuum freeze-drying at -50℃ and a relative pressure of about -0.08 MPa for 48-72 h, it is then added to a newly prepared trichloroethylene-contaminated water body or groundwater system for treatment.

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