A carbon-based magnesium-iron layered double hydroxide adsorbent, its preparation method and application

Abstract

The present invention relates to a carbon-based magnesium-iron layered double hydroxide adsorbent, its preparation method and application. The specific steps are as follows: First, pretreat activated carbon fiber (ACF) with an acid-modified solution, wash it until the pH value of the filtrate is 6.50 - 7.00, and then dry it under vacuum; then dissolve magnesium chloride and iron chloride in deionized water, stir magnetically until completely dissolved, add urea, and then add the pretreated ACF for hydrothermal reaction. After washing, dry it under vacuum to obtain the adsorbent (MFLA). The adsorbent of the present invention can efficiently adsorb the typical quinolone antibiotic ciprofloxacin (CIP) in water, with a large adsorption capacity, strong stability and recyclability.

Description

Technical Field

[0001] The invention relates to a carbon-based magnesium-iron layered double metal hydroxide adsorbent, a preparation method and application thereof, and belongs to the field of efficient removal of ciprofloxacin (CIP) from medical wastewater and domestic wastewater, and composite materials and preparation thereof. Background Art

[0002] Antibiotics are a class of secondary metabolites that interfere with the developmental functions of living cells and have the function of resisting pathogenic microorganisms and other activities. After these drugs enter the body, some of them are directly discharged into the sewage discharge system with body fluids without being metabolized. After being treated in sewage treatment plants, they flow into surface water and groundwater. A large number of expired antibiotics are discarded at will and enter the water body to cause environmental pollution. More importantly, they will pose a serious threat to human health and ecological security. Ciprofloxacin (CIP), as a commonly used and typical quinolone antibiotic drug, is widely detected in the environment. Studies have found that CIP is the most frequently used and largest type of quinolone antibiotic in hospitals, and the concentration of CIP is the highest among the residual chemicals in aquatic products. Therefore, it is very important to develop efficient and cost-effective treatment technologies to remove residual CIP in water environments.

[0003] At present, the main methods used to treat CIP in water include biological methods, chemical precipitation methods, membrane separation methods, adsorption methods, etc. Among them, the biological method is limited by the concentration of pollutants, and has disadvantages such as high power consumption, high treatment cost, and easy sludge bulking. In contrast, the adsorption method is a relatively efficient and simple treatment method, which can be used as a supplement to the biological method or as a separate deep removal method for CIP. Compared with other technologies, the adsorption method shows better performance because the adsorbent used in the adsorption method is widely available, low cost, simple process, easy operation, small footprint, and no secondary pollution. Therefore, the development of adsorbents for efficient removal of CIP in wastewater remains a research focus.

[0004] Activated carbon has a well-developed pore structure and has the characteristics of super strong adsorption capacity, stable chemical properties and high mechanical strength. It is one of the most commonly used adsorbents for treating wastewater containing antibiotics. Activated carbon is divided into powdered activated carbon, granular activated carbon (GAC) and activated carbon fiber (ACF). ACF is the third generation of activated carbon products after powdered and granular activated carbon. Compared with traditional GAC, ACF has the following advantages: (1) The pore distribution of ACF is basically monodisperse, mainly composed of micropores less than 2.00nm, with a small amount of mesopores and no macropores, and the pores open directly on the fiber surface. The diffusion path of the adsorbate to reach the adsorption site is short, and the fiber diameter is thin, so the contact area with the adsorbed substance is large, which increases the adsorption efficiency and can be in uniform contact. (2) The specific surface area of ​​ACF (1000-3000m 2 ·gˉ 1)Larger than GAC (500 - 1700 m 2 ·gˉ 1 ), with faster adsorption and desorption rates. (3) ACF is easier to regenerate and can be made into various products such as yarn, cloth, felt, and paper, with greater process flexibility. However, due to the limited functional groups on the surface of ACF, the adsorption effect of ACF on CIP needs to be improved. Therefore, the present invention provides ACF as a carrier to prepare an adsorbent with high adsorption capacity and recyclability.

[0005] In recent years, more and more modified layered double hydroxide materials have been found to have good adsorption effects. Layered double hydroxide (LDH), also known as hydrotalcite, is composed of divalent and trivalent metal hydroxides and has a layered crystal structure. The chemical composition of LDH is variable. By changing the metal ions and their composition ratios, as well as the types, quantities, and crystal sizes of the interlayer anions, materials with special structures and properties with different physical and chemical properties can be obtained, making LDH a very promising multifunctional material; there are hydrogen bonds and weak electrostatic forces between the interlayer anions and the layer plates of LDH, and ion exchange can occur with other anions in the external aqueous solution. Generally speaking, the more charges the interlayer anions carry, the greater their affinity with the interlayer, and they are more likely to enter the interlayer through ion exchange behavior with the interlayer anions in the solution to form a stable structure; LDH is alkaline due to the presence of OHˉ in its structure, and the strength of its alkalinity is consistent with the divalent metal cations on the layer plates. Since its specific surface area is generally small, its alkalinity is weak. The calcined product has an increased specific surface area due to dehydration, exposing more basic sites and increasing the alkalinity. LDH also has acidic characteristics. The strength of the acidity of LDH is not only related to the acidity of the divalent and trivalent metal cations on the layer plates but also related to the interlayer anions. As a typical representative of inorganic layered particles, while it has unique physical and chemical properties similar to clay minerals, it also shows good adsorption potential due to its good chemical activity, strong mechanical stability, high specific surface area, and excellent ion exchange performance. However, the problem of easy aggregation and poor water dispersibility of single LDH leads to low adsorption performance for antibiotics. Therefore, the application of LDH is limited, and LDH can be modified to make its application range wider and have better adsorption performance. The method of combining ACF with high strength, high temperature resistance, and corrosion resistance with LDH with good chemical activity, strong mechanical stability, high specific surface area, and excellent ion exchange performance to prepare a composite material with good adsorption performance can provide a new method for the adsorption and removal of SMX.

[0006] In the research field of the adsorption of antibiotics by modified hydrotalcite-like materials, Baichuan Tang et al. prepared hydrotalcite monomer adsorbents with various different metal combinations through a one-step hydrothermal synthesis method. It was screened and found that the MgCuZn-LDH adsorbent exhibited excellent adsorption performance. The removal rate of tetracycline (TC) with an initial concentration of 100 mg·gˉ 1 was up to 99.5%, and the removal rate reached more than 80% within the first 2 h; Yaling Gao et al. prepared Mg / Al / CO3-LDH by ultrasonic-assisted coprecipitation method. Under the optimal experimental conditions, the removal rate of TC reached more than 90% within 60 min; Yingrui Huang et al. prepared magnetic modified magnesium-aluminum carbonate hydrotalcite (Mag-LDO) by coprecipitation method. When the pH of the TC solution was 5 and the dosage of Mag-LDO was 200 mg·Lˉ 1 , the higher the initial concentration of TC, the higher the equilibrium adsorption capacity of Mag-LDO; Yi Song et al. synthesized MgZnAl-CLDH / NiFe2O4 by hydrothermal method. The maximum equilibrium adsorption capacities for congo red and doxycycline were 480.2296 mg·gˉ 1 and 387.6812 mg·gˉ 1 . SUMMARY OF THE INVENTION

[0007] The purpose of the present invention is to provide a carbon-based magnesium-iron layered double hydroxide adsorbent MgFe-LDH / ACF (MFLA) to solve the problems that single layered double metal hydroxides are prone to agglomeration and have poor water dispersibility. Another purpose of the present invention is to provide a preparation method of the above adsorbent. Still another purpose of the present invention is to provide the application of the above adsorbent in removing and adsorbing typical quinolone antibiotic CIP in wastewater.

[0008] The technical solution of the present invention is as follows: A carbon-based magnesium-iron layered double hydroxide adsorbent, characterized in that the adsorbent is composed of a carrier and a layered double metal hydroxide; wherein the carrier is activated carbon fiber ACF, and the layered double metal hydroxide is magnesium-iron layered double metal hydroxide; the mass percentage of Mg element loaded in the adsorbent is 20.42 - 32.95%, and the molar ratio of Fe 3+ and Mg 2+ is 1:(1 - 4); the total specific surface area of the adsorbent is 1500 - 1700 m 2 ·gˉ 1 , the pore volume is 0.55 - 0.65 cm 3 ·gˉ 1 , and the average pore diameter is 1.60 - 1.90 nm.

[0009] The present invention also provides a method for preparing the above-mentioned carbon-based magnesium-iron layered double hydroxide adsorbent, and the specific steps are as follows:

[0010] (1) Carrier pretreatment: Put activated carbon fiber ACF into an acid-modified solution and stir. After filtration, wash with deionized water until the pH value of the filtrate is 6.50 - 7.00, and then dry under vacuum to obtain the pretreated ACF.

[0011] (2) Loading layered double hydroxide: Dissolve magnesium chloride MgCl2 and iron chloride FeCl3 in deionized water. After magnetic stirring until completely dissolved, add urea to obtain a mixed solution. Then add the ACF pretreated in step (1) to the mixed solution and stir magnetically. Then carry out a hydrothermal reaction on the mixed solution. Finally, wash with deionized water until the pH value of the filtrate is 6.50 - 7.00, and dry under vacuum to prepare the carbon-based magnesium-iron layered double hydroxide adsorbent MgFe-LDH / ACF (MFLA).

[0012] Preferably, the acid-modified solution described in step (1) is hydrochloric acid or sulfuric acid, and the concentration of the acid-modified solution is 1.0 - 2.5 mol·Lˉ 1 ; the stirring speed is 250 - 300 rpm, and the stirring time is 4 - 8 h; the mass ratio of the added activated carbon fiber ACF to the volume of the acid-modified solution is 15.00 - 25.00 g·Lˉ 1 ; the vacuum drying temperature is 60 - 80 °C, and the vacuum drying time is 12 - 18 h.

[0013] Preferably, the mass ratio of the pretreated ACF, MgCl2, FeCl3, and urea added in step (2) to the volume of deionized water is 5.00 - 15.00 g·Lˉ 1 、2.00 - 8.00 g·Lˉ 1 、3.00 - 10.00 g·Lˉ 1 and 3.00 - 5.00 g·Lˉ 1 .

[0014] Preferably, in step (2), the magnetic stirring speed when MgCl2 and FeCl3 are dissolved in water is 250 - 300 rpm, and the stirring time is 20 - 40 min; the magnetic stirring speed when the pretreated ACF is added to the mixed solution is 250 - 300 rpm, and the stirring time is 5 - 15 min; the hydrothermal reaction time is 12 - 16 h, and the temperature is 120 - 140 °C; the vacuum drying temperature is 60 - 80 °C, and the vacuum drying time is 12 - 18 h.

[0015] Preferably, in both step (1) and step (2), wash with deionized water until the pH value of the filtrate is 6.50 - 7.00.

[0016] The present invention also provides an application of the above-mentioned carbon-based magnesium-iron layered double metal hydroxide adsorbent in the degradation of ciprofloxacin (CIP) in wastewater. The specific steps are as follows: Add the MFLA adsorbent to the simulated wastewater with a CIP concentration of 20.00 - 40.00 mg·Lˉ 1 and a pH of 2.00 - 12.00, place it in a constant temperature shaking incubator for reaction, where the set rotation speed is 150 - 250 rpm, the temperature is 20 - 30 °C, and the reaction time is 3 - 6 h; the mass ratio of the added MFLA adsorbent to the volume of the wastewater is 0.60 - 1.20 g·Lˉ 1 .

[0017] Beneficial effects:

[0018] (1) By means of the hydrothermal synthesis method, the present invention simply and efficiently prepares a carbon-based magnesium-iron layered double metal hydroxide adsorbent (MFLA) with a unique structure using activated carbon fiber (ACF) as a carrier;

[0019] (2) The preparation process of the adsorbent of the present invention is simple, the reaction conditions are relatively low, the process is easy to control, and the operation is convenient;

[0020] (3) The adsorbent of the present invention can be recycled for adsorption, is easy to recycle, and ensures its practical application value. Specific embodiments

[0021] To better understand the present invention, the following further illustrates the present invention through examples. The examples are only used to explain the present description and will not constitute any limitation to the invention.

[0022] Example 1:

[0023] (1) Prepare simulated wastewater containing CIP, with a CIP concentration of 30.00 mg·Lˉ 1 and a pH value of 12.00.

[0024] (2) Prepare the adsorbent MFLA, and the steps are as follows:

[0025] ① Carrier pretreatment: First, measure 400 mL of 1.0 mol·Lˉ 1 hydrochloric acid solution and pour it into a beaker, then add 7.00 g of ACF and stir at 250 rpm for 8 h. Finally, wash it with deionized water until the pH value of the filtrate is 6.50, and vacuum dry it at 60 °C for 18 h to obtain the pretreated ACF;

[0026] ② Supported layered double metal hydroxides: 0.40 g of MgCl2 and 0.30 g of FeCl3 were dissolved in 100 mL of deionized water and magnetically stirred at 250 rpm for 40 min. After complete dissolution, 0.30 g of urea was added to obtain a mixed solution. Then, 0.50 g of pretreated ACF was added to the mixed solution and magnetically stirred at 250 rpm for 15 min. The mixed solution was then hydrothermally treated at 140 °C for 12 h. Finally, it was washed with deionized water until the pH value of the filtrate was 6.50 and vacuum dried at 60 °C for 18 h to prepare MFLA. The total specific surface area of the prepared adsorbent MFLA was measured to be 1678.10 m 2 ·gˉ 1 , the pore volume was 0.55 cm 3 ·gˉ 1 , the average pore diameter was 1.78 nm, in which the molar ratio of Fe 3+ and Mg 2+ was 1:2, and the elemental content of Mg was 27.65%.

[0027] Weighed 0.06 g of the adsorbent prepared in this example and put it into 100 mL of the above-prepared simulated wastewater containing CIP. It was placed in a constant-temperature shaking incubator and shaken at 150 rpm at 20 °C for 6 h to reach the reaction equilibrium. The adsorption capacity and removal rate of CIP were 17.14 mg·gˉ 1 and 85.72% respectively.

[0028] Example 2:

[0029] (1) Prepare simulated wastewater containing CIP with a CIP concentration of 20.00 mg·Lˉ 1 and a pH value of 2.00.

[0030] (2) Prepare the adsorbent MFLA, and the steps are as follows:

[0031] ① Carrier pretreatment: First, measure 400 mL of 1.5 mol·Lˉ 1 sulfuric acid solution and pour it into a beaker. Then add 6.00 g of ACF and stir at 260 rpm for 6 h. Finally, wash it with deionized water until the pH value of the filtrate is 6.80 and vacuum dry it at 70 °C for 16 h to obtain the pretreated ACF;

[0032] ②Supported layered double metal hydroxide: 0.20 g of MgCl2 and 0.50 g of FeCl3 were dissolved in 100 mL of deionized water and magnetically stirred at 270 rpm for 35 min. After complete dissolution, 0.40 g of urea was added to obtain a mixed solution. Then, 1.00 g of pretreated ACF was added to the mixed solution and magnetically stirred at 270 rpm for 12 min. The mixed solution was then hydrothermally treated at 130 °C for 16 h. Finally, it was washed with deionized water until the pH value of the filtrate was 6.70 and vacuum dried at 70 °C for 16 h to prepare MFLA. The total specific surface area of the prepared adsorbent MFLA was measured to be 1501.15 m 2 ·gˉ 1 , and the pore volume was 0.59 cm 3 ·gˉ 1 , and the average pore diameter was 1.83 nm. Among them, the molar ratio of Fe 3+ and Mg 2+ was 1:1, and the elemental content of Mg was 20.42%.

[0033] Weighed 0.08 g of the adsorbent prepared in this example and put it into 100 mL of the above-prepared simulated wastewater containing CIP. It was placed in a constant-temperature shaking incubator and shaken at 180 rpm at 25 °C for 4 h to reach the reaction equilibrium. The adsorption capacity and removal rate of CIP were 19.31 mg·gˉ 1 and 96.54% respectively.

[0034] Example 3:

[0035] (1) Prepare simulated wastewater containing CIP with a CIP concentration of 40.00 mg·Lˉ 1 , and the pH value was 7.00.

[0036] (2) Prepare the adsorbent MFLA, and the steps are as follows:

[0037] ① Carrier pretreatment: First, measure 400 mL of 2.5 mol·Lˉ 1 sulfuric acid solution and pour it into a beaker. Then add 10.00 g of ACF and stir at 270 rpm for 4 h. Finally, wash it with deionized water until the pH value of the filtrate is 7.00 and vacuum dry it at 80 °C for 12 h to obtain the pretreated ACF;

[0038] ② Supported layered double metal hydroxide: 0.60 g of MgCl2 and 1.00 g of FeCl3 were dissolved in 100 mL of deionized water and magnetically stirred at 300 rpm for 20 min. After complete dissolution, 0.50 g of urea was added to obtain a mixed solution. Then, 1.50 g of pretreated ACF was added to the mixed solution and magnetically stirred at 300 rpm for 5 min. Subsequently, the mixed solution was hydrothermally treated at 120 °C for 15 h. Finally, it was washed with deionized water until the pH value of the filtrate was 7.00 and vacuum dried at 80 °C for 12 h to prepare MFLA. The total specific surface area of the prepared adsorbent MFLA was measured to be 1693.36 m 2 ·gˉ 1 , and the pore volume was 0.65 cm 3 ·gˉ 1 , and the average pore diameter was 1.90 nm. Among them, the metal molar ratio of Fe 3+ and Mg 2+ was 1:3, and the elemental content of Mg was 29.79%.

[0039] Weigh 0.12 g of the adsorbent prepared in this example and put it into 100 mL of the above-prepared simulated wastewater containing CIP. Place it in a constant-temperature shaking incubator and reach the reaction equilibrium at 30 °C and a rotation speed of 250 rpm in 5 h. The adsorption capacity and removal rate of CIP were 16.03 mg·gˉ 1 and 80.14% respectively.

[0040] Example 4:

[0041] (1) Prepare a simulated wastewater containing CIP with a CIP concentration of 30.00 mg·Lˉ 1 and a pH value of 4.00.

[0042] (2) Prepare the adsorbent MFLA, and the steps are as follows:

[0043] ① Carrier pretreatment: First, measure 400 mL of 2.0 mol·Lˉ 1 hydrochloric acid solution and pour it into a beaker. Then add 8.00 g of ACF and stir at 300 rpm for 5 h. Finally, wash it with deionized water until the pH value of the filtrate is 6.90 and vacuum dry it at 70 °C for 14 h to obtain the pretreated ACF;

[0044] ②Supported layered double metal hydroxide: 0.80 g of MgCl2 and 1.00 g of FeCl3 were dissolved in 100 mL of deionized water, magnetically stirred at 260 rpm for 30 min. After complete dissolution, 0.30 g of urea was added to obtain a mixed solution. Then, 1.20 g of pretreated ACF was added to the mixed solution, magnetically stirred at 260 rpm for 10 min. The mixed solution was then hydrothermally treated at 140 °C for 14 h. Finally, it was washed with deionized water until the pH value of the filtrate was 6.80 and vacuum dried at 60 °C for 12 h to prepare MFLA. The total specific surface area of the prepared adsorbent MFLA was measured to be 1643.48 m 2 ·gˉ 1 , and the pore volume was 0.62 cm 3 ·gˉ 1 , and the average pore diameter was 1.60 nm. Among them, the molar ratio of Fe 3+ to Mg 2+ was 1:4, and the elemental content of Mg was 32.95%.

[0045] In this example, to confirm the stability and recyclability of the adsorbent MFLA prepared according to the present invention for adsorbing SMX, a cyclic adsorption and regeneration experiment was carried out. 0.10 g of ACF and 0.10 g of the adsorbent MFLA prepared in this example were weighed and put into 100 mL of the simulated wastewater containing CIP prepared in this example, placed in a constant temperature shaking incubator, and reacted at 25 °C and 260 rpm for 3 h to reach the reaction equilibrium. After 9 cycles, the adsorption amounts of ACF and the adsorbent MFLA for SMX decreased from 11.68 mg·gˉ 1 and 19.43 mmol·gˉ 1 to 3.00 mg·gˉ 1 and 18.22 mmol·gˉ 1 respectively, and the removal rates decreased from 58.43% and 97.15% to 15.02% and 91.12% respectively.

Claims

1. A carbon-based magnesium-iron layered double hydroxide adsorbent, characterized in that The adsorbent is composed of a carrier and a layered double metal hydroxide; wherein the carrier is activated carbon fiber ACF, and the layered double metal hydroxide is a magnesium-iron layered double metal hydroxide; the loading mass percentage of Mg element in the adsorbent is 20.42-32.95%, and the loading mass percentage of Fe 3+ and Mg 2+ The molar ratio is 1:(1-4); the total specific surface area of ​​the adsorbent is 1500-1700m 2 ·g -1 , pore volume is 0.55-0.65cm 3 ·g -1 , with an average pore size of 1.60-1.90 nm, is prepared by the following method, the specific steps of which are as follows: (1) Carrier pretreatment: Put activated carbon fiber (ACF) into an acid-modified solution and stir. After filtration, wash with deionized water until the pH value of the filtrate is 6.50 - 7.00, and then dry in vacuum to obtain pretreated ACF. (2) Loading of layered double metal hydroxide: Dissolve magnesium chloride (MgCl2) and iron(III) chloride (FeCl3) in deionized water. After magnetic stirring until completely dissolved, add urea to obtain a mixed solution. Then add the pretreated ACF obtained in step (1) to the mixed solution and stir magnetically. Next, carry out a hydrothermal reaction on the mixed solution. Finally, wash with deionized water until the pH value of the filtrate is 6.50 - 7.00, and dry in vacuum to prepare a carbon-based magnesium-iron layered double metal hydroxide adsorbent MFLA. The hydrothermal reaction time is 12 - 16 h, and the temperature is 120 - 140 °C.

2. The carbon-based magnesium-iron layered double hydroxide adsorbent according to claim 1, wherein The acid-modified solution described in step (1) is hydrochloric acid or sulfuric acid, and the concentration of the acid-modified solution is 1.0 - 2.5 mol·L -1 ; the stirring speed is 250 - 300 rpm, and the stirring time is 4 - 8 h; the mass ratio of the added activated carbon fiber ACF to the volume of the acid-modified solution is 15.00 - 25.00 g·L -1 ; the vacuum drying temperature is 60 - 80 °C, and the vacuum drying time is 12 - 18 h.

3. The carbon-based magnesium-iron layered double hydroxide adsorbent according to claim 1, wherein In step (2), the mass ratios of the added pretreated ACF, MgCl2, FeCl3, and urea to the volume of deionized water are 5.00 - 15.00 g·L -1 , 2.00 - 8.00 g·L -1 , 3.00 - 10.00 g·L -1 , and 3.00 - 5.00 g·L -1 .

4. The carbon-based magnesium-iron layered double hydroxide adsorbent according to claim 1, wherein (2) In step (2), the magnetic stirring speed of MgCl2 and FeCl3 dissolved in water is 250 - 300 rpm, and the stirring time is 20 - 40 min. The magnetic stirring speed of the pretreated ACF added to the mixed solution is 250 - 300 rpm, and the stirring time is 5 - 15 min. The vacuum drying temperature is 60 - 80 °C, and the vacuum drying time is 12 - 18 h.

5. Application of the carbon-based magnesium-iron layered double metal hydroxide adsorbent as described in claim 1 in the degradation of ciprofloxacin (CIP) in wastewater.

6. The application according to claim 5, wherein The specific steps are as follows: Add the MFLA adsorbent into the simulated wastewater with a ciprofloxacin (CIP) concentration of 20.00 - 40.00 mg·L -1 , a pH of 2.00 - 12.00, place it in a constant temperature shaking incubator for reaction, where the set rotation speed is 150 - 250 rpm, the temperature is 20 - 30 °C, and the reaction time is 3 - 6 h; the mass ratio of the added MFLA adsorbent to the volume of the wastewater is 0.60 - 1.20 g·L -1 .