Preparation method of activated carbon electrode material for selectively removing phosphate ions

Abstract

The application discloses a preparation method of an activated carbon electrode material for selectively removing phosphate ions, and belongs to the technical field of capacitive deionization. The preparation method comprises the following steps: preparing a first mixed solution, preparing an alkaline solution, preparing a solid powder of iron trioxide loaded activated carbon through reaction, preparing a second mixed solution, and preparing an electrode. The activated carbon electrode material loaded with trivalent iron has strong capturing capacity and high selectivity for species phosphate ions.

Description

Technical Field

[0001] This invention relates to a method for preparing an activated carbon electrode material that selectively removes phosphate ions, belonging to the field of capacitive deionization technology. Background Technology

[0002] Currently, the main inorganic byproduct of the degradation of difficult-to-treat organic compounds such as organophosphorus pesticides in water is nitrate ions (NO3). - ), nitrite ions (NO2) - ), phosphate ions (PO4) 3- How to further remove these inorganic compounds is also a hot topic in research reports. - NO2 - and PO4 3- Nitrogen and phosphorus ions are common oxyacid anions in water. In addition, organic matter in the environment can also be oxidized and degraded to produce the aforementioned nitrogen- and phosphorus-containing inorganic substances. Excessive concentrations of these substances can have varying degrees of adverse effects on human health and the aquatic ecosystem. The presence of excessive nitrates and phosphates has a significant impact on the quality of freshwater worldwide, causing eutrophication, a sharp decline in oxygen levels, harming wildlife and even causing them to die from oxygen deprivation, worsening water quality, and increasing the cost and difficulty of drinking water treatment.

[0003] With the increasing severity of water pollution, national standards for wastewater discharge are constantly being raised. The current "Sichuan Province Minjiang and Tuojiang River Basin Water Pollution Discharge Standard (DB51 / 2311-2016)" and "Urban Wastewater Treatment Plant Pollutant Discharge Standard (GB 18918-2002)" require wastewater treatment plants to meet Class A standards (total phosphorus ≤ 0.5 mg / L), and in some cases, even Class III standards (total phosphorus ≤ 0.3 mg / L). These stricter requirements for effluent quality from phosphorus-containing wastewater treatment pose a significant challenge to phosphorus removal technologies. Currently, commonly used methods such as chemical phosphorus removal, biological phosphorus removal, adsorption, and electrolysis can effectively remove PO4 from water. 3- However, these methods are susceptible to the effects of reaction conditions and competing substances, and suffer from drawbacks such as high processing costs and low processing efficiency. Capacity Deionization (CDI) is a water desalination and purification technology based on the theory of double-layer capacitance. Compared with traditional deionization methods, it has advantages such as high energy utilization, simple system regeneration, and convenient reaction operation, overcoming the shortcomings of traditional methods and effectively removing PO4 from water. 3- However, wastewater contains complex components and interferes with PO4. 3- There are many substances that can be effectively removed; therefore, how to overcome the numerous interfering substances in the environment and improve PO4 removal efficiency is crucial. 3- Selective removal is very important. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing an activated carbon electrode material that selectively removes phosphate ions.

[0005] The first aspect of the present invention provides a method for preparing an activated carbon electrode material that selectively removes phosphate ions, comprising the following steps:

[0006] Preparation of the first mixture: Dissolve ferric chloride hexahydrate in a mixed solution of polyethylene glycol and ethanol. After complete dissolution, add activated carbon powder in a mass ratio of ferric chloride hexahydrate to activated carbon powder of 1.5 to 3:1. After ultrasonic dispersion, the first mixture is formed.

[0007] Preparation of alkaline solution: Dissolve the alkaline compound in deionized water to form an alkaline solution;

[0008] Preparation of solid powder of ferric oxide supported activated carbon by reaction: an alkaline solution was added to the first mixture and reacted at 150-200℃ for 12-16 h; after the reaction, the mixture was cooled, the precipitate was washed, and dried to obtain solid powder of ferric oxide supported activated carbon.

[0009] Preparation of the second mixture: Polyvinyl alcohol is dissolved in deionized water under constant temperature heating conditions, and then glutaraldehyde is added to obtain the second mixture;

[0010] Electrode preparation: Add solid powder of ferric oxide-supported activated carbon to the second mixture, adjust the mass fraction of solid powder of ferric oxide-supported activated carbon to 30-60%, and mix evenly to obtain a slurry; coat the slurry onto graphite paper, let it stand for 30-60 min, and then carry out a cross-linking reaction at 70-85℃ to obtain the electrode material.

[0011] Preferably, the first mixture consists of 1 gram of ferric chloride hexahydrate mixed with 6-12 mL of polyethylene glycol 400 and 32-64 mL of ethanol.

[0012] Preferably, the concentration of the alkaline solution is 1 mol / L.

[0013] Preferably, the alkaline compound used in the alkaline solution is sodium hydroxide or potassium hydroxide.

[0014] Preferably, in the step of preparing the solid powder of ferric oxide-supported activated carbon by reaction, the mixing volume ratio of the alkaline solution to the first mixed liquid is 6 to 12:50.

[0015] Preferably, the mass percentage of polyvinyl alcohol in the second mixture after dissolving in deionized water is 5.5% to 7.5%.

[0016] Preferably, the molar ratio of glutaraldehyde to polyvinyl alcohol monomer in the second mixture is 3.1 to 6.4%.

[0017] Preferably, in the electrode preparation step, the mass fraction of the solid powder of ferric oxide-supported activated carbon is adjusted by adding deionized water.

[0018] Preferably, in the electrode preparation step, the coating thickness of the slurry coated on the graphite paper is 250 μm, and the coating speed is 1 mm / s.

[0019] A second aspect of the present invention provides the application of the activated carbon electrode material prepared by the above-described preparation method in the treatment of phosphate ions in wastewater.

[0020] The beneficial effects of this invention are:

[0021] The activated carbon electrode material prepared in this invention is loaded with ferric iron. The preparation method is simple and rapid. By loading ferric iron onto the activated carbon electrode, the strong capture ability of ferric iron for phosphate ions in the environment is utilized. Combined with capacitive deionization technology, this improves the selective removal capability of capacitive deionization technology for phosphate ions in water. When other inorganic anions are present in the water, the anti-interference ability of capacitive deionization technology for removing phosphate ions is enhanced, enabling simple, rapid, and efficient removal of phosphate ions from water. When a mixed solution containing phosphate ions and other inorganic anions such as chloride ions enters the capacitive deionization device, phosphate ions can be attracted to the anode through two pathways: firstly, by forming coordination compounds with ferric iron through Fe-OP bonds and adsorbing onto the iron surface; secondly, activated carbon has a large specific surface area, which can form a strong electric double layer with the mixed solution, adsorbing and storing a large number of phosphate ions. Other inorganic anions such as chloride ions can only be adsorbed onto the anode surface through the second pathway. Therefore, compared to common activated carbon electrodes, the electrode material of this invention not only possesses the advantages of traditional capacitive deionization technology, but also provides coordination sites for phosphate ions, enhancing their selective adsorption capacity. Simultaneously, the electrode material can be rapidly regenerated and recycled through discharge, making the electrode regeneration method easy and its reuse efficiency high. Attached Figure Description

[0022] Figure 1 This is a scanning electron microscope image of the electrode material prepared in Embodiment 1 of the present invention.

[0023] Figure 2 This is a scanning electron microscope image of the electrode material prepared in Embodiment 1 of the present invention.

[0024] Figure 3 This is a scanning electron microscope image of the electrode material prepared in Embodiment 1 of the present invention.

[0025] Figure 4 The image shows an X-ray energy dispersive spectrometer image of the electrode material prepared in Embodiment 1 of the present invention.

[0026] Figure 5 The image shows the X-ray energy dispersive spectrometer pattern of the electrode material prepared in Example 1 of this invention.

[0027] Figure 6 The image shows the X-ray diffraction pattern of the electrode material prepared in Example 1 of this invention. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0029] Example 1

[0030] This embodiment provides a method for preparing an activated carbon electrode material that selectively removes phosphate ions, including the following steps:

[0031] Preparation of the first mixture: Dissolve 1g of ferric chloride hexahydrate in a mixture of 7.5mL of polyethylene glycol 400 and 40mL of ethanol. After complete dissolution, add 0.5g of activated carbon powder, sonicate for 5min, and disperse evenly to form the first mixture.

[0032] To prepare an alkaline solution: Dissolve 2g of sodium hydroxide in 30mL of deionized water. After complete dissolution, dilute to 50mL with deionized water to form an alkaline solution.

[0033] Preparation of ferric oxide-supported activated carbon solid powder by reaction: 8 mL of alkaline solution was added to 50 mL of the first mixture, and then transferred to a polytetrafluoroethylene reaction vessel. The mixture was reacted at 160 °C for 12 h. After the reaction, the mixture was naturally cooled to room temperature. The precipitate was washed three times with deionized water and ethanol. In other embodiments, it could be washed four to five times. The precipitate was dried in an oven for 10 h to obtain ferric oxide-supported activated carbon solid powder, which was then sealed and stored.

[0034] Preparation of the second mixture: Add 6.4 g of polyvinyl alcohol to 100 mL of deionized water, stir at 100 °C until completely dissolved, and then cool to room temperature. Then add 1.4 mL of glutaraldehyde to obtain the second mixture.

[0035] Electrode preparation: 6g of ferric oxide-supported activated carbon solid powder and 4mL of deionized water were added to 10g of the second mixture. The mixture was stirred continuously until fully homogeneous, resulting in a slurry. A 10cm×10cm piece of graphite paper was fixed on a coating apparatus. An appropriate amount of slurry was drawn up using a dropper and evenly coated onto the graphite paper, controlling the coating thickness to 250μm and the coating speed to 1mm / s. After coating, the mixture was allowed to air dry at room temperature for 30min, then placed in a vacuum drying oven at 70℃ for a crosslinking reaction to obtain the electrode material.

[0036] The solid powder of ferric oxide-supported activated carbon was scanned using a scanning electron microscope (SEM, Hitachi SU-8000, accelerating voltage 5.0 kV). The scanned images are shown below. Figures 1-3 As shown, some ferric oxide particles are uniformly dispersed on the surface of the activated carbon. The solid powder of ferric oxide-supported activated carbon was characterized using an X-ray energy dispersive spectroscopy (EDS) instrument configured with an SEM setup. The characterization results are as follows: Figure 4 and Figure 5 As shown, its iron content is approximately 5.3%. The X-ray diffraction pattern is as follows. Figure 6 As shown, the ferric oxide crystal structure of the solid powder on the surface is complete and consistent with the standard spectrum.

[0037] Example 2

[0038] The main difference between this embodiment and Embodiment 1 is that in this embodiment, each gram of ferric chloride hexahydrate is mixed with 6 mL of polyethylene glycol 400 and 32 mL of ethanol in the first mixture, and the mass ratio of ferric chloride hexahydrate to activated carbon powder is 1.5:1. In the step of preparing the solid powder of ferric oxide-supported activated carbon, the volume ratio of the alkaline solution to the first mixture is 6:50. In the second mixture, the mass percentage of polyvinyl alcohol is 5.5%, and the molar ratio of glutaraldehyde to polyvinyl alcohol monomer is 3.1%.

[0039] Example 3

[0040] The main difference between this embodiment and Embodiment 1 is that in this embodiment, each gram of ferric chloride hexahydrate is mixed with 12 mL of polyethylene glycol 400 and 64 mL of ethanol in the first mixture, and the mass ratio of ferric chloride hexahydrate to activated carbon powder is 3:1. In this embodiment, the alkaline compound used in the alkaline solution is potassium hydroxide. In the step of preparing the solid powder of ferric oxide-supported activated carbon, the mixing volume ratio of the alkaline solution to the first mixture is 12:50. The mass percentage of polyvinyl alcohol in the second mixture is 7.5%, and the molar ratio of glutaraldehyde to polyvinyl alcohol monomer is 6.4%.

[0041] Example 4

[0042] This embodiment provides the application of the activated carbon electrode material prepared by the above preparation method in the treatment of phosphate ions in wastewater.

[0043] This embodiment utilizes an electrochemical workstation (CH1660E) to verify the selective removal efficiency of phosphate ions by the CDI method using the electrode material prepared in this invention. The anode is the electrode material prepared in Example 1 or a conventional activated carbon electrode, and the cathode is an activated carbon electrode with a cation exchange membrane to prevent phosphate ions from being adsorbed by the cathode. The electrode size is 1 cm × 2 cm. The adsorption voltage is 1.2 V / 30 min, and the desorption voltage is -1.2 V / 30 min. The peristaltic pump speed is 1.0 mL / min, using a continuous flow water feed mode. The initial concentrations of phosphate and chloride ions in the water are both 5 mmol / L. The pH is 7. The conductivity of the effluent is monitored in real time using a micro-conductivity meter (eDAQ, ET908).

[0044] This embodiment uses "S" i / j The selectivity of ion "i" relative to ion "j" is represented by the following formula:

[0045]

[0046] Where Q is the influent flow rate (mL / min), C is the ion concentration (mmol / L), and t is the reaction time (min); the numerator represents the ratio of the amount of i ions adsorbed on the electrode to the amount remaining in the solution, and the denominator represents the ratio of the amount of j ions adsorbed on the electrode to the amount remaining in the solution. The ratio is the selectivity of i ions relative to j ions, denoted by S. i / j express.

[0047] Based on the above formula, the selective adsorption capacities of the electrode material of this invention and the ordinary activated carbon electrode for phosphate ions, relative to chloride ions, can be calculated during the adsorption stage. When treating a mixed solution of phosphate and chloride ions with an ordinary activated carbon electrode, during the adsorption stage, the concentrations of phosphate and chloride ions in the effluent decreased to a minimum of 2.76 mmol / L and 2.81 mmol / L, respectively, after 6 minutes of reaction. After 30 minutes of reaction, the adsorption capacities of phosphate and chloride ions by the ordinary activated carbon electrode were 0.4 mmol / L and 0.38 mmol / L, respectively, indicating that the adsorption effect of the ordinary activated carbon electrode on the two ions was basically the same. When treating a mixed solution of phosphate and chloride ions with the electrode material of this invention, during the adsorption stage, the concentrations of phosphate and chloride ions in the effluent decreased to a minimum of 2.23 mmol / L and 3.42 mmol / L, respectively, after 6 minutes of reaction. After 30 minutes of reaction, the adsorption capacities of phosphate and chloride ions by the electrode material of this invention were 0.52 mmol / L and 0.25 mmol / L, respectively, indicating that the removal effect of phosphate ions was significantly better than that of chloride ions. When Fe is incorporated, the removal capacity of the activated carbon electrode for phosphate ions increases by 29.3% and the removal capacity for chloride ions decreases by 35.34% when phosphate ions and chloride ions are present simultaneously. Furthermore, during the adsorption stage, the selectivity of the electrode material of this invention for phosphate ions and that of the ordinary activated carbon electrode are 2.7 and 1.1, respectively. The electrode material of this invention improves the selective removal capacity for phosphate ions.

[0048] Phosphate ions are not only a major inorganic degradation byproduct of recalcitrant organic pollutants such as organophosphorus pesticides, but also one of the most common inorganic anions in water. The content and ratio of inorganic ions vary among different types of wastewater. This study investigated the changes in the selective adsorption of phosphate ions by electrode materials by adding different concentrations of chloride ions at pH 7 and an initial phosphate ion concentration of 5 mmol / L. When PO4... 3- Cl - When the molar concentration ratio changes from 1:0.5 to 1:5, as Cl... - As the concentration increases, the electrode material reacts to PO4. 3- The adsorption capacity gradually decreases, and the adsorption capacity for Cl... - The adsorption capacity of Cl is constantly improving, but - Increasing the concentration will not cause the electrode material to lose its resistance to PO4. 3- The adsorption and desorption capacity of PO4. 3- Cl - When the molar concentration ratios are 1:0.5, 1:1, 1:2 and 1:5, PO4 3- The adsorption capacities were 0.687 mmol / g, 0.519 mmol / g, 0.424 mmol / g, and 0.37 mmol / g, respectively, showing a decreasing trend; for Cl...- The adsorption capacity showed an increasing trend, reaching 0.126 mmol / g, 0.247 mmol / g, 0.432 mmol / g, and 1.208 mmol / g, respectively. Furthermore, the selectivity of the electrode material of this invention for phosphate ions was affected to some extent, reaching ~6.0, ~3.0, ~2.5, and ~1.8, respectively. This indicates that the selectivity for PO4+ was affected. 3- Selectivity due to Cl - Even when the concentration of PO4 is increased and suppressed, the electrode material of the present invention still maintains a high selectivity, indicating that it is effective against PO4. 3- It has a strong selective adsorption capacity.

[0049] At pH=7 and an initial phosphate ion concentration of 5 mmol / L, 5 mmol / L Cl was added respectively. - NO3 - CO3 2- SO4 2- The electrode material of the present invention was examined for its effect on PO4. 3- Selective changes. The results showed that the four anions reacted selectively to PO4. 3- The order of influence removal is NO3. - ≈Cl - <SO4 2- <CO3 2- Among them, NO3 - and Cl - The existence of PO4 3- The removal effect is minimal and essentially the same for PO4. 3- The adsorption capacities were 0.576 mmol / g and 0.519 mmol / g, respectively, for NO3. - and Cl - The adsorption capacity was 0.247 mmol / g for all samples.

[0050] PO4 was treated with the electrode material of the present invention 10 times consecutively. 3- Solution, PO4 3- The adsorption capacity remained at around 0.6 mmol / g, and the treatment effect on salt solutions was stable and reliable.

[0051] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for preparing an activated carbon electrode material that selectively removes phosphate ions, characterized in that: Includes the following steps: Preparation of the first mixture: Dissolve ferric chloride hexahydrate in a mixed solution of polyethylene glycol and ethanol. After complete dissolution, add activated carbon powder in a mass ratio of ferric chloride hexahydrate to activated carbon powder of 1.5 to 3:

1. After ultrasonic dispersion, the first mixture is formed. Preparation of alkaline solution: Dissolve the alkaline compound in deionized water to form an alkaline solution; Preparation of solid powder of ferric oxide supported activated carbon by reaction: an alkaline solution was added to the first mixture and reacted at 150-200℃ for 12-16 h; after the reaction, the mixture was cooled, the precipitate was washed, and dried to obtain solid powder of ferric oxide supported activated carbon. Preparation of the second mixture: Polyvinyl alcohol is dissolved in deionized water under constant temperature heating conditions, and then glutaraldehyde is added to obtain the second mixture; Electrode preparation: Add solid powder of ferric oxide-supported activated carbon to the second mixture, adjust the mass fraction of solid powder of ferric oxide-supported activated carbon to 30-60%, and mix evenly to obtain a slurry; coat the slurry onto graphite paper, let it stand for 30-60 min, and then carry out a cross-linking reaction at 70-85℃ to obtain the electrode material.

2. The preparation method according to claim 1, characterized in that: The first mixture consists of 1 gram of ferric chloride hexahydrate mixed with 6-12 mL of polyethylene glycol and 32-64 mL of ethanol.

3. The preparation method according to claim 1, characterized in that: The concentration of the alkaline solution is 1 mol / L.

4. The preparation method according to claim 1, characterized in that: The alkaline compound used in the alkaline solution is sodium hydroxide or potassium hydroxide.

5. The preparation method according to claim 1, characterized in that: In the step of preparing solid powder of ferric oxide supported activated carbon by reaction, the mixing volume ratio of the alkaline solution to the first mixed liquid is 6 to 12:

50.

6. The preparation method according to claim 1, characterized in that: In the second mixture, the mass percentage of polyvinyl alcohol after dissolving in deionized water is 5.5% to 7.5%.

7. The preparation method according to claim 1, characterized in that: The molar ratio of glutaraldehyde to polyvinyl alcohol monomer in the second mixture is 3.1 to 6.4%.

8. The preparation method according to claim 1, characterized in that: In the electrode preparation step, the mass fraction of the solid powder of ferric oxide-supported activated carbon is adjusted by adding deionized water.

9. The preparation method according to claim 1, characterized in that: In the electrode preparation step, the coating thickness of the slurry on the graphite paper is 250 μm, and the coating speed is 1 mm / s.

10. The application of activated carbon electrode material prepared by the preparation method according to any one of claims 1-9 in the treatment of phosphate ions in wastewater.

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