Iron / activated carbon electrode for removing oxysalts including perchlorate in water as well as preparation method and application of iron / activated carbon electrode

Abstract

The invention discloses an iron / activated carbon composite electrode for removing oxysalts including perchlorate in water as well as a preparation method and application of the iron / activated carbon composite electrode, and belongs to the field of water treatment technologies and environmental functional materials. According to the electrode, activated carbon (AC) serves as a substrate, nanoscale zero-valent iron particles are loaded through an impregnation-calcination method, and the iron / activated carbon (Fe / AC) composite electrode is obtained. The electrode realizes electro-adsorption enrichment of target anions (such as ClO4 <->) by periodically switching an external potential, firstly applying a positive potential, then converting the target anions into a negative potential, and efficiently reducing the target anions into non-toxic and harmless chloride ions through the synergistic effect of direct electron transfer (DET) and hydrogenation reduction. The Fe / AC electrode prepared by the method has the characteristics of low cost, high catalytic activity, good stability and the like, has an excellent removal effect on persistent inorganic pollutants including low-concentration perchlorate in water, and is particularly suitable for deep purification of underground water and drinking water.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electrochemical water treatment and environmental functional materials, and particularly relates to an iron / activated carbon composite electrode for removing oxygen-containing acid salts including perchlorate in water as well as a preparation method and application thereof. BACKGROUND

[0002] Oxygen-containing acid salts, such as perchlorate (ClO4 - ), are persistent, highly toxic inorganic pollutants widely existing in surface water and groundwater, which are mainly derived from natural processes and human activities such as military, aerospace, fireworks and agricultural activities. Perchlorate has stable chemical properties, is difficult to degrade, and is easy to migrate, and can be enriched through drinking water and food chain, competitively inhibits the absorption of iodine by the thyroid gland, interferes with the endocrine system of the human body, and causes serious threats to the development of children's brains. The reference index of perchlorate has been listed in the “Drinking Water Health Standards” (GB5749-2022) of China, and the limit value is 70 μg / L, but the concentration of perchlorate in tap water in some areas still exceeds the standard, such as a research report with a concentration of 152 μg / L. Therefore, it is urgent to develop efficient, stable and environmentally friendly perchlorate deep purification technology.

[0003] At present, there are many methods for removing perchlorate (ClO4 - ) in water, including biological reduction method, adsorption method and chemical reduction method. Biological treatment needs to preferentially remove nitrate, because it is a more acceptable electron acceptor, and the application of this technology in drinking water plants is limited by the risk of microbial pathogen contamination. Common adsorbents, such as activated carbon and ion exchange resin, have weak adsorption capacity for ClO4 - , and the salt water generated in the regeneration process contains high concentration of ClO4 - , which needs further treatment and disposal. Heterogeneous catalysis and electrocatalytic reduction technology have attracted much attention in the degradation of oxidative pollutants. Heterogeneous catalysis technology using nickel, platinum, palladium / carbon and ruthenium supported catalysts has shown excellent ClO4 - reduction performance, but the reaction kinetics is slow under neutral pH conditions, and protons are needed. In contrast, electrocatalytic reduction can utilize the protons generated by water electrolysis, which is a promising alternative for the reduction of oxygen-containing acid salts including perchlorate in water.

[0004] In the past few decades, researchers have developed single-metal and double-metal catalysts for the hydrogenation reduction of ClO4 - . In these systems, the adsorbed hydrogen atoms generated by the cathode surface hydrogen evolution reaction (HER) react with oxidative pollutants including perchlorate, and finally generate chloride ions (Cl - ). Double-metal catalysts usually exhibit more excellent activity, which is attributed to the synergistic effect of the two metals in the catalyst. -Synergistic co-localization of adsorption sites and hydrogenation sites. For example, Wang reported that using a stainless steel cathode loaded with Rh-Cu catalyst can convert 78% of ClO4 - to Cl - in 6 hours, while the conversion rate of single metal catalysts (molybdenum, ruthenium, rhodium, copper, palladium) is only 17% to 56% under the same conditions. However, the complexity of synthesis and high cost of bimetallic catalysts restrict their application in the reduction of ClO4 in actual water. Therefore, it is a technical problem to be solved in the field to develop a simple, efficient, stable and low-cost non-noble metal electrode material to achieve efficient reduction and removal of oxyacid salts including perchlorate under near-neutral conditions. SUMMARY

[0005] The purpose of the present application is to provide an iron / activated carbon composite electrode for removing oxyacid salts including perchlorate in water and its preparation method and application. The electrode realizes efficient and rapid removal of oxyacid salts including trace amounts of perchlorate in actual water through a unique "electrosorption-electroreduction" coupling process, using a dual mechanism of direct electron transfer and hydrogenation reduction.

[0006] The present application provides an iron / activated carbon composite electrode for removing oxyacid salts including perchlorate in water, wherein the composite electrode uses activated carbon as a conductive substrate, and nano zero-valent iron particles are loaded on the activated carbon; the mass loading of iron is 1 to 20 wt% of the activated carbon; and the particle size of the nano zero-valent iron particles is 2 to 50 nm.

[0007] The present application provides a preparation method of an iron / activated carbon composite electrode for removing oxyacid salts including perchlorate in water, and the specific steps are as follows:

[0008] (1) adding powdered activated carbon (AC) into a water solution of soluble iron salt, stirring and mixing uniformly, and performing impregnation;

[0009] (2) drying the mixture obtained in step (1) at 60 to 100°C to obtain a solid product;

[0010] (3) calcining the dried solid product under inert atmosphere (such as N2 or Ar) protection at 300 to 600°C for 1 to 10 hours to decompose and reduce the iron salt into zero-valent iron, and firmly load the zero-valent iron on the surface of the activated carbon to obtain a Fe / AC composite material;

[0011] (4) mixing the Fe / AC composite material obtained in step (3) with a binder at a mass ratio of (85 to 95):(5 to 15), coating on a graphite current collector, pressing into shape, and drying to obtain the Fe / AC composite electrode. In the present application, the soluble iron salt in step (1) is FeSO4·7H2O or FeCl3.

[0012] In the present application, the binder in step (3) is polyvinyl alcohol (PVA).

[0013] The application of the Fe / AC composite electrode for removing oxygen-containing acids in water to remove perchlorate in water adopts a mode of operation with periodically switched potentials.

[0014] (a) Electric adsorption stage: a positive potential is applied to the Fe / AC electrode, the positive potential is +0.4V to +1.0V relative to the standard hydrogen electrode (SHE), and the duration is 10 to 120 minutes, so that the negatively charged oxygen-containing acid salt (such as ClO4 - ) is enriched and adsorbed on the electrode surface by electrostatic action;

[0015] (b) Electric reduction stage: the potential applied to the Fe / AC electrode is switched to a negative potential, the negative potential is -1.2V to -1.8V relative to SHE, and the duration is 10 to 120 minutes, at this potential, the pollutants adsorbed on the electrode surface are reduced by receiving electrons directly (direct electron transfer, DET), on the other hand, the atomic hydrogen (H*) produced by the electrolysis of water also hydrogenates and reduces them, the two mechanisms work together to gradually reduce ClO4 - to Cl - ;

[0016] (c) Steps (a) and (b) constitute a cycle, which is repeated until the target pollutants in the water body are sufficiently removed.

[0017] In the present application, the specific conditions of the application are: the pH value of the water body is 6.0 to 8.5; the initial concentration of the target pollutant is 0.01mM to 1.0mM, and the perchlorate is 1μg / L to 100mg / L.

[0018] In the present application, the duration of the electric adsorption stage and the electric reduction stage is 10 to 120 minutes, and the two stages are alternately cycled.

[0019] In the present application, the oxygen-containing acid salt is any one of perchlorate, nitrate, chlorate, chlorite or bromate. In the present application, the pH value of the water body during application is 6.0 to 8.0; the initial concentration of the oxygen-containing acid salt is 0.01mM to 1.0mM. In the present application, the application is used to treat the persistent inorganic pollutant perchlorate in groundwater or drinking water.

[0020] The beneficial effects of the present application are:

[0021] 1. Cost advantage: replace the noble metals Pd and Pt with cheap and readily available iron as the active component, greatly reducing the manufacturing cost of the electrode material, laying the foundation for large-scale application of the technology.

[0022] 2. Dual function: innovatively integrating the functions of "electric adsorption enrichment" and "electrocatalytic reduction" in the same electrode, enriching first and then reducing through polarity switching, solving the mass transfer limitation problem at low concentration, and significantly improving the reaction efficiency and removal rate.

[0023] 3. Dual mechanism: revealing that the Fe / AC electrode reduces oxyacid salts through both direct electron transfer (DET) and atomic hydrogen hydrogenation, and achieving efficient reaction at near neutral conditions, avoiding the step of adjusting the pH of the water body.

[0024] 4. High efficiency and stability: the removal rate of perchlorate by the prepared Fe / AC electrode can reach more than 90%, the reaction rate constant is 1-2 orders of magnitude higher than that of the traditional system, and the electrode has good stability, with extremely low iron dissolution rate (<1.0 μg / L) and no secondary pollution.

[0025] 5. Strong practicality: the electrode and method also have excellent removal effect on perchlorate in actual water bodies (such as groundwater and tap water), have strong resistance to complex water matrix interference, and have good practical application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 SEM and TEM images of the Fe / AC composite material prepared in Example 1 of the present application, wherein: a is a SEM image, and b is a TEM image.

[0027] Figure 2 A schematic diagram of the system device for removing oxyacid salts in water by using the Fe / AC electrode described in the present application. Wherein: a is an electrochemical reactor, b is a photo of the detailed configuration thereof, and c is a schematic diagram of a three-electrode system.

[0028] Figure 3 Concentration-time curve of the Fe / AC electrode prepared in Example 1 of the present application when treating 1.0 mM perchlorate solution under periodic potential (+0.72 V and -1.48 V vs SHE alternately). Wherein: a is the change of voltage with time; b is the change of current with time, and c is the removal performance of Pd / AC electrode and AC electrode on perchlorate in water.

[0029] Figure 4 Application of the Fe / AC electrode in actual water bodies.

[0030] Figure 5 A schematic diagram of the reduction mechanism of perchlorate on the surface of the Fe / AC electrode proposed in the present application (DET and hydrogenation pathways).

[0031] Markings in the figure:

[0032] 1. Electrochemical reactor; 2. Titanium sheet; 3. Fe / AC working electrode; 4. Counter electrode (Pt sheet); 5. Reference electrode (Ag / AgCl); 6. DC power supply / potentiostat; 7. Water outlet / sampling port; 8. Ion exchange membrane. DETAILED DESCRIPTION

[0033] The present application will be described in detail below with reference to examples and drawings, but the scope of protection of the present application is not limited thereto.

[0034] Example 1: Preparation of Fe / AC electrode

[0035] 1. 1.0 g of commercial activated carbon powder (AC) was weighed and added to 10 mL of 0.1 M FeSO4 aqueous solution, and magnetically stirred for 6 h for sufficient impregnation.

[0036] 2. The mixture was then dried in a vacuum oven at 80 °C for 12 h.

[0037] 3. The dried solid was transferred to a tube furnace and heated to 450 °C at a rate of 5 °C / min under N2 atmosphere, and kept for 2 h.

[0038] 4. After naturally cooling to room temperature, the activated carbon composite material loaded with nano zero-valent iron (Fe / AC) was obtained.

[0039] 5. 90 mg of the obtained Fe / AC material was mixed with 10 mg of polyvinyl alcohol (PVA) binder, and an appropriate amount of deionized water was added to make a slurry, which was uniformly coated on a 1 cm x 1 cm graphite sheet, and a certain pressure was applied to make it tightly adhere. The Fe / AC composite electrode was prepared by drying and curing at 60 °C.

[0040] 6. TEM observation ( Figure 1 ) showed that the nano iron particles were uniformly distributed on the surface of the activated carbon, with a particle size of about 10-30 nm. Example 2: Fe / AC electrode for removal of perchlorate in water

[0041] 1. A double-chamber electrolytic cell (separated by a cation exchange membrane in the middle) was used for electrochemical experiments. The Fe / AC electrode prepared in Example 1 was used as the working electrode, a platinum sheet was used as the counter electrode, and Ag / AgCl was used as the reference electrode.

[0042] 2. 15 mL of NaClO4 solution with an initial concentration of 1.0 mM (~100 mg / L) (10 mM Na2SO4 as background electrolyte, initial pH = 7.0) was added to the cathode chamber (working electrode chamber).

[0043] 3. The operation mode adopts periodic switching of potential: +0.72V (vs SHE) for 2 hours (adsorption stage) and then -1.48V (vs SHE) for 2 hours (reduction stage), and so on.

[0044] 4. As shown in Figure 3 , after 20 hours (5 cycles) of treatment, the removal rate of perchlorate by the Fe / AC electrode reaches 90.1%, and the reaction conforms to the pseudo-first-order kinetic model, with a rate constant k of 0.14h -1 . Ion chromatography detection shows that the reduction product is mainly chloride ion (Cl-), and intermediate products (ClO3 - , ClO2 - ) are generated in small amounts and are eventually reduced.

[0045] 1. The actual groundwater in a certain place was taken as the object, and perchlorate was added to a concentration of 0.01mM (995μg / L).

[0046] 2. The Fe / AC electrode of Example 1 and the operation condition (adsorption 2h / reduction 2h) of Example 2 were used for treatment.

[0047] 3. The results show that Figure 4 , after 12 hours of treatment, the removal rate of perchlorate in the groundwater by the electrode can still reach more than 75%, proving the effectiveness and applicability of the present application under actual water body conditions.

[0048] Comparative Example 1: Performance of pure AC electrode

[0049] 1. Under the same experimental conditions (Example 2), a pure AC electrode without iron loading was used to treat a perchlorate solution with an initial concentration of 1.0mM.

[0050] 2. After 20 hours of operation, the removal rate of perchlorate was only 20.5%, and the reaction rate constant k was 0.01h -1 , which was much lower than that of the Fe / AC electrode, proving the key role of nano zero-valent iron loading in improving the reduction activity of the electrode.

Claims

1. An iron / activated carbon composite electrode for removing an oxyanion salt in water, characterized by The composite electrode uses activated carbon as a conductive substrate, and has nano zero-valent iron particles loaded thereon; wherein the mass loading of iron is 1-20 wt% of the activated carbon; and the nano zero-valent iron particles have a particle size of 2-50 nm.

2. A method for producing the iron / activated carbon composite electrode for removing an oxyanion salt in water according to claim 1, characterized by The specific steps are as follows: (1) adding powdered activated carbon (AC) to a water solution of a soluble iron salt, stirring to mix uniformly, and performing impregnation; (2) drying the mixture obtained in step (1) at 60-100 ℃ to obtain a solid product; (3) calcining the dried solid product under inert atmosphere protection at 300-600 ℃ for 1-10 hours to decompose and reduce the iron salt to zero-valent iron and firmly load the zero-valent iron on the surface of the activated carbon, thereby obtaining a Fe / AC composite material; (4) mixing the Fe / AC composite material obtained in step (3) with a binder in a mass ratio of (85-95):(5-15), coating on a graphite current collector, and pressing to form a shape, and then drying to obtain a Fe / AC composite electrode.

3. The method of claim 2, wherein The soluble iron salt in step (1) is FeSO4·7H2O or FeCl3.

4. The method of claim 2, wherein The binder in step (3) is polyvinyl alcohol.

5. Use of the iron / activated carbon composite electrode for removing oxygenated acid salts from water according to claim 1, characterized in that An operating mode of periodic switching of potentials is adopted: (a) an electro-adsorption stage: a positive potential is applied to the Fe / AC electrode, the positive potential is +0.4 V to +1.0 V relative to a standard hydrogen electrode (SHE), and the duration is 10-120 minutes, so that negatively charged oxygen-containing acid salt anions are enriched and adsorbed on the electrode surface by electrostatic action; (b) an electro-reduction stage: the potential applied to the Fe / AC electrode is switched to a negative potential, between -1.2 V and -1.8 V with respect to the SHE, for a duration of between 10 and 120 minutes, at which potential the pollutants adsorbed on the surface of the electrode are reduced, on the one hand directly by receiving electrons, and on the other hand by hydrogenation reduction by the atomic hydrogen (H*) produced by electrolysis of water, the two mechanisms acting in synergy to reduce CIO4 - to CI - in stages. (c) steps (a) and (b) constitute a cycle, which is repeated until the target pollutants in the water body are sufficiently removed.

6. Use according to claim 5, characterized in that The specific conditions for the application are: the pH value of the water body is 6.0-8.5; the initial concentration of the target pollutants is 0.01 mM-1.0 mM, and the perchlorate salt is 1 μg / L-100 mg / L.

7. Use according to claim 5, characterized in that: The duration of the electro-adsorption stage and the electro-reduction stage is each 10-120 minutes, and the two stages are alternately and cyclically performed.

8. Use according to claim 6, characterized in that: The oxygen-containing acid salt is any one of a perchlorate salt, a nitrate salt, a chlorate salt, a chlorite salt, or a bromate salt.

9. Use according to claim 6, characterized in that: The pH value of the water body when applied is 6.0-8.0; and the initial concentration of the oxygen-containing acid salt anion is 0.01 mM-1.0 mM.

10. The use according to claim 6, characterized in that: The application is used for treating perchlorate salt pollution in groundwater or drinking water.

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