Preparation and application method of a three-dimensional hydrogel particle electrode capable of selectively removing and enriching heavy metals

Abstract

The present invention provides a three-dimensional hydrogel particle electrode capable of selectively removing and enriching heavy metals, the three-dimensional hydrogel particle electrode comprising an enrichment layer and an excitation core embedded in the enrichment layer, the enrichment layer being a semi-interpenetrating porous network structure, the semi-interpenetrating porous network structure being formed by a polymer network and a conductive line running through it, the three-dimensional hydrogel particle electrode having excellent electrochemical reaction activity and stability, adsorption selectivity, and structural strength. The present invention also discloses a method for preparing the three-dimensional hydrogel particle electrode capable of selectively removing and enriching heavy metals, wherein the excitation core is connected to the conductive line through a sulfonamide process, a polymer network is formed through a physical crosslinking process, and a three-dimensional hydrogel particle electrode having a semi-interpenetrating porous network structure is formed by the polymer network and the conductive line through hydrogen bonding. The present invention also discloses the application of the three-dimensional hydrogel particle electrode.

Description

Technical Field

[0001] The invention relates to the technical field of electrochemical water treatment, and in particular to a preparation and application method of a three-dimensional hydrogel particle electrode capable of selectively removing and enriching heavy metals. Background Art

[0002] Water is the essential material basis for human survival and development.

[0003] How to achieve the standard discharge of industrial wastewater and realize the recycling of water resources is imminent.

[0004] Treatment methods such as adsorption, membrane separation, and advanced oxidation require the addition of chemical agents during the treatment process, which will cause secondary pollution. The regeneration of adsorbents and membranes is a complex process. These traditional wastewater treatment methods have long treatment times, low treatment efficiency, and a typical phenomenon of efficiency dependence on pollutant concentration, making it difficult to achieve standard discharge of industrial wastewater.

[0005] Particle electrode technology is an emerging technology in electrochemical oxidation. It adds particle electrodes to traditional electrochemical technology. Particle electrode technology is simple to operate, does not require the addition of harmful chemical reagents, and is not prone to secondary pollution. The added particle electrodes greatly increase the reaction area, which is beneficial to pollution treatment and can also achieve the recovery of heavy metals. However, problems such as low electrochemical activity, weak selectivity, and poor stability of particle electrodes still restrict the development and application of 3D technology. Solving the above problems will further promote the development and application of particle electrode technology in water pollution control and provide new guarantees for the discharge and reuse of industrial wastewater. Summary of the invention

[0006] A three-dimensional hydrogel particle electrode capable of selectively removing and enriching heavy metals, the three-dimensional hydrogel particle electrode comprising an enrichment layer in which excitation cores are embedded;

[0007] The enriched layer is a semi-interpenetrating porous network structure, which is formed by a polymer network and conductive lines running through it through hydrogen bonding; the polymer network is formed by cross-linking alginate and metal ions; the conductive lines are conductive polymers rich in sulfonic acid groups;

[0008] The excitation core is connected to the conductive wire through an interface reaction and is firmly fixed in the enrichment layer; the interface reaction is achieved by the sulfonic acid group of the conductive wire and the excitation core through a sulfonamide process; the excitation core can quickly and wirelessly excite oxidation and reduction reactions at both ends under the drive of an external electric field.

[0009] In particular, the preparation process of the three-dimensional hydrogel particle electrode has the following steps:

[0010] Step a: adding alginate to 100 mL of the conductive wire aqueous solution and stirring continuously to obtain a uniform suspension solution A;

[0011] Step b: preparing the excited nuclei into a suspension solution B, slowly adding 100 mL of the suspension solution B into the suspension solution A, adding an acid solution and stirring at high temperature to obtain a uniform suspension solution C;

[0012] Step c: adding the suspension solution C to the cross-linking solution by a peristaltic pump, stirring slowly, and then standing for cross-linking;

[0013] Step d: The hydrogel particle electrode obtained in step c is washed with deionized water and stored at low temperature.

[0014] In particular, in step a, the mass of alginate is controlled to be 1.5-3.0 g; the conductive wire is a perfluorosulfonic acid polymer, and its mass fraction is controlled to be 3%-10%; the stirring speed is controlled to be 100-200 rpm, and the stirring time is controlled to be 24-36 h.

[0015] In particular, the mass fraction of the suspension solution B in step b is controlled to be 0.8% to 1.5%; the acid solution added is 2 to 5 mL of concentrated hydrochloric acid; the stirring temperature is maintained at 90 to 120° C., the stirring speed is controlled to be 100 to 200 rpm, and the stirring time is controlled to be 36 to 48 hours.

[0016] In particular, the cross-linking solution in step c contains calcium ions (Ca 2+ ), iron ions (Fe 3+ ), ferrous ions (Fe 2+ ), manganese ion (Mn 2+ ), the mass fraction of the cross-linking solution is controlled to be 2-6%; the peristaltic pump flow rate is controlled to be 1-3 mL / min, the stirring speed is controlled to be 50-100 rpm, the stirring time is controlled to be 1-3 h, and the static cross-linking time is controlled to be 2-6 h; the sample storage temperature in step d is controlled to be 2-8 ° C.

[0017] In particular, the preparation of the excitation core in step b comprises the following steps:

[0018] Step ① The reed biomass is carefully cleaned with deionized water, cut into small pieces, soaked in a mixed solution of iron, manganese salt and ethylenediamine, then oven dried, and sieved after drying;

[0019] Step ②: placing the reed biomass obtained in step ① in a crucible, placing it in a tubular furnace, purging nitrogen in advance, pyrolyzing it in a nitrogen atmosphere, and cooling it to room temperature after pyrolysis to obtain the desired excitation nuclei.

[0020] In particular, in step ①, Fe 3+ and Mn 2+The molar ratio is 1:3-3:1, the total concentration is controlled to be 60-100 g / L, the amount of ethylenediamine added is controlled to be 0.5-1.0 mL / 1 g of reed biomass; the soaking time is 12-24 h; the drying temperature is controlled to be 50-80° C., the drying time is controlled to be 18-24 h; the sieving mesh is controlled to be 80-100 mesh; the mass of the reed biomass in the crucible in step ② is controlled to be 3-6 g, the nitrogen pre-purge time is controlled to be 5-10 min, the tubular furnace heating rate is controlled to be 3-6° C. / min, the pyrolysis temperature is controlled to be 400-600° C., and the pyrolysis time is controlled to be 2-4 h.

[0021] In particular, a method for applying a three-dimensional hydrogel particle electrode capable of selectively removing and enriching heavy metals comprises the following application steps:

[0022] Step 1: adding the prepared three-dimensional hydrogel particle electrode to the wastewater to adjust the pH value of the solution;

[0023] Step 2: Place the anode plate and cathode plate in the solution, stir continuously, and apply voltage for reaction.

[0024] In particular, the wastewater in step 1 contains one of monovalent thallium (Tl(Ⅰ)) and hexavalent chromium (Cr(Ⅳ)); the added mass of the three-dimensional hydrogel particle electrode is controlled to be 0.5-1.2 g / 1L of wastewater; when the pollutant is Tl(Ⅰ), the solution pH is controlled to be 11-13, and when the pollutant is Cr(Ⅵ), the solution pH is controlled to be 1-3.

[0025] In particular, the anode plate and cathode plate in step 2 are any one of graphite plates, boron-doped corundum electrode plates, platinum electrode plates, and stainless steel electrode plates; the stirring speed is controlled to be 50-100 rpm; the applied voltage is controlled to be 1.5-3 V / cm; and the reaction time is controlled to be 30-60 min.

[0026] The method of the present invention is easy to operate. The excitation core is connected to the conductive wire through a sulfonamide process, a polymer network is formed through a physical crosslinking process, and a three-dimensional hydrogel particle electrode with a semi-interpenetrating porous network structure is formed by the polymer network and the conductive wire through hydrogen bonding. This structure enables the three-dimensional hydrogel particle electrode to have excellent electrochemical reaction activity and stability, adsorption selectivity, and structural strength.

[0027] The present invention also provides an application of the three-dimensional hydrogel particle electrode, which is specifically applied to electrochemical water treatment to improve water treatment efficiency.

[0028] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings constituting part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0030] Figure 1 A cross-sectional view of a three-dimensional hydrogel particle electrode that can selectively remove and enrich heavy metals;

[0031] Figure 2 is the effect of pH on the morphology of Tl(Ⅰ);

[0032] Figure 3 The effect of the enrichment layer on different forms of Tl(Ⅰ) (the dotted line in the figure represents hydrogen bonding).

[0033] Among them, (1) enrichment layer, (2) excitation core, (3) polymer network, (4) conductive line, and (5) sulfonamide process of excitation core and conductive line. DETAILED DESCRIPTION

[0034] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0035] Example 1

[0036] like Figure 1 A three-dimensional hydrogel particle electrode capable of selectively removing and enriching heavy metals, the three-dimensional hydrogel particle electrode comprising an enrichment layer (1), wherein an excitation core (2) is embedded in the enrichment layer (1);

[0037] The enrichment layer (1) is a semi-interpenetrating porous network structure, which is formed by a polymer network (3) formed by cross-linking sodium alginate and Ca2+ and a conductive line (4) running through the semi-interpenetrating porous network structure through hydrogen bonding; the conductive line (4) is a perfluorosulfonic acid polymer;

[0038] The excitation core (2) is connected to the perfluorosulfonic acid polymer through a sulfonation process (see the attached Figure 1 (5)), which is firmly fixed in the enrichment layer (1); the excited core can rapidly and wirelessly excite oxidation and reduction reactions at its two ends under the drive of an external electric field.

[0039] In this embodiment, the preparation of the three-dimensional hydrogel particle electrode capable of selectively removing and enriching heavy metals comprises the following steps:

[0040] Step a: 1.5 g of sodium alginate was added to 100 mL of a 3% aqueous solution of a perfluorosulfonic acid polymer and stirred at 100 rpm for 24 h to obtain a uniform suspension solution A;

[0041] Step b: preparing the excited nuclei (2) into a suspension solution B with a mass fraction of 0.8%, slowly adding 100 mL of the suspension solution B to the suspension solution A, adding 2 mL of concentrated hydrochloric acid, stirring at 100 rpm for 36 h at 90° C., and obtaining a uniform suspension solution C;

[0042] Step c: Add 2% Ca2+ into the suspension C at a rate of 1 mL / min by a peristaltic pump. 2+ The solution was stirred at 50 rpm for 1 h and then allowed to stand for cross-linking for 2 h;

[0043] Step d: The hydrogel particle electrode obtained in step c is washed with deionized water and stored at 2°C.

[0044] In this embodiment, the preparation of the excitation core (2) includes the following steps:

[0045] Step 1: Clean the reed biomass with deionized water, cut it into small pieces, and soak it in Fe 3+ and Mn 2+ 0.5 mL / 1 g of ethylenediamine was added to a solution with a molar ratio of 1:3 and a total concentration of 60 g / L, and the solution was soaked for 12 h, then dried in an oven at 50°C for 18 h, and then passed through an 80-mesh sieve after drying.

[0046] Step ②: 3 g of reed biomass obtained in step ① is placed in a crucible and placed in a tubular furnace. Nitrogen is purged for 5 minutes in advance. The heating rate of the tubular furnace is set to 3°C / min. Pyrolysis is carried out at 400°C for 2 hours in a nitrogen atmosphere. After pyrolysis, it is cooled to room temperature to obtain the desired excitation nucleus (2).

[0047] The application method of the three-dimensional hydrogel particle electrode comprises the following steps:

[0048] Step 1: Add 0.5 g / 1 L of hydrogel particle electrode to 100 mL of Tl(Ⅰ) wastewater, and adjust the pH value of the solution to 11; add 0.5 g / 1 L of hydrogel particle electrode to 100 mL of Cr(Ⅵ) wastewater, and adjust the pH value of the solution to 1;

[0049] Step 2: Place the graphite anode plate and the graphite cathode plate in the solution, stir continuously at 50 rpm, and apply a voltage of 1.5 V / cm for 30 min.

[0050] Example 2

[0051] The difference between Example 2 and Example 1 is that:

[0052] 1. In step a, the amount of sodium alginate added was 2.25 g, the mass fraction of the perfluorosulfonic acid polymer aqueous solution was 6.5%, the stirring speed was 150 rpm, and the stirring time was 30 h; in step b, the mass fraction of the suspension solution B was 1.15%, the concentrated hydrochloric acid was 3.5 mL, the heating temperature was 105 ° C, the stirring speed was 150 rpm, and the stirring time was 42 h; in step c, the peristaltic pump flow rate was 2 mL / min, and the Ca content was 0.1%. 2+ The mass fraction of the cross-linking solution is 4%, the stirring speed is 75 rpm, the stirring time is 2 h, and the static cross-linking time is 4 h; the low-temperature storage temperature in step d is 5°C.

[0053] 2. Fe in step ① 3+ and Mn 2+ The molar ratio is 1:1, the total concentration is 80 g / L, the amount of ethylenediamine added is 0.75 mL / 1 g of reed biomass, the soaking time is 18 h, the drying temperature is 65 ° C, the drying time is 21 h, and after drying, it is sieved through a 90-mesh sieve; in step ②, the amount of reed biomass added is 4.5 g, the pre-purge time of nitrogen is 7.5 min, the tubular furnace heating rate is 4.5 ° C / min, the pyrolysis temperature is 500 ° C, and the pyrolysis time is 3 h.

[0054] 3. In step 1, 0.85 g / 1 L of hydrogel particle electrode was added to the wastewater; the pH value of Tl(Ⅰ) wastewater was 12, and the pH value of Cr(VI) wastewater was 2; in step 2, the stirring speed was 75 rpm, the applied voltage was 2.25 V / cm, and the reaction time was 45 min.

[0055] Example 3

[0056] The difference between Example 3 and Example 1 is that:

[0057] 1. In step a, the amount of sodium alginate added was 3.0 g, the mass fraction of the perfluorosulfonic acid polymer aqueous solution was 10%, the stirring speed was 200 rpm, and the stirring time was 36 h; in step b, the mass fraction of the suspension solution B was 1.5%, the concentrated hydrochloric acid was 5 mL, the heating temperature was 120 ° C, the stirring speed was 200 rpm, and the stirring time was 48 h; in step c, the peristaltic pump flow rate was 3 mL / min, and the Ca content was 0.1%. 2+ The mass fraction of the cross-linking solution is 6%, the stirring speed is 100 rpm, the stirring time is 3 hours, and the static cross-linking time is 6 hours; the low-temperature storage temperature in step d is 8°C.

[0058] 2. Fe in step ① 3+ and Mn 2+The molar ratio is 3:1, the total concentration is 100 g / L, the amount of ethylenediamine added is 1.0 mL / 1 g of reed biomass, the soaking time is 24 h, the drying temperature is 80 ° C, the drying time is 24 h, and the drying is passed through a 100 mesh sieve; the amount of reed biomass added in step ② is 6 g, the nitrogen pre-purge time is 10 min, the tubular furnace heating rate is 6 ° C / min, the pyrolysis temperature is 600 ° C, and the pyrolysis time is 4 h.

[0059] 3. In step 1, 1.2 g / 1 L of hydrogel particle electrode was added to the wastewater; the pH value of Tl(Ⅰ) wastewater was 13, and the pH value of Cr(VI) wastewater was 3; in step 2, the stirring speed was 100 rpm, the applied voltage was 3.0 V / cm, and the reaction time was 60 min.

[0060] Comparative Example 1

[0061] The difference between this comparative example and Example 1 is that the excitation core (2) is not immersed in the iron and manganese salt solution during preparation.

[0062] Comparative Example 2

[0063] The difference between this comparative example and Example 1 is that no ethylenediamine is added during the preparation of the excitation core (2).

[0064] Comparative Example 3

[0065] The difference between this comparative example and Example 1 is that this comparative example does not contain the excitation core (2).

[0066] Comparative Example 4

[0067] The difference between this comparative example and Example 1 is that this comparative example does not contain a conductive line (3).

[0068] Comparative Example 5

[0069] The difference between this comparative example and Example 1 is that the perfluorosulfonic acid-based polymer of the conductive line (3) is replaced by non-conductive cellulose nanofibers.

[0070] Comparative Example 6

[0071] The difference between this comparative example and Example 1 is that this comparative example uses inorganic biochar particles of the same particle size as particle electrodes.

[0072] Comparative Example 7

[0073] The difference between this comparative example and Example 1 is that in this comparative example, the pH value of the Tl(Ⅰ) wastewater is 8, and the pH value of the Cr(VI) wastewater is 6.

[0074] Comparative Example 8

[0075] The difference between this comparative example and Example 1 is that no three-dimensional hydrogel particle electrode is added in step 1.

[0076] Comparative Example 9

[0077] The difference between this comparative example and Example 1 is that no voltage is applied in step 2.

[0078] In the present invention, Examples 1 to 3 and Comparative Examples 1 to 9 are used to verify the following effects, and the results are as follows:

[0079] 1. Verification of pollutant removal effect:

[0080] Artificial simulated wastewater was used in the verification. Among them, Tl(Ⅰ) wastewater contains 100~10000μg / L Tl + and 100 mg / L K + ; Cr(VI) wastewater contains 1-200 mg / L of Cr(VI) and 500 mg / L of NO-3.

[0081] Verification was performed according to the requirements of Examples 1 to 3 and Comparative Examples 1 to 9. The total Tl concentration was measured using ICP-MS; Cr(VI) was detected using diphenylaminourea spectrophotometry at a test wavelength of 540 nm.

[0082] The concentration of pollutants in the treated wastewater and the removal effect are shown in the following table.

[0083] Table 1 Concentration and removal rate of Tl(Ⅰ) and Cr(Ⅵ) after treatment of wastewater with different initial concentrations

[0084]

[0085]

[0086] The research on this effect verification has the following conclusions:

[0087] 1. According to Table 1, the removal effect of Tl(Ⅰ) and Cr(Ⅵ) after treatment in Example 1 is close to that in Example 2 and Example 3; at the same pollutant concentration, the standard deviation of the pollutant removal rate of the three embodiments is less than 1.5%; at different initial pollutant concentrations, the removal rates of Tl(Ⅰ) and Cr(Ⅵ) in the three embodiments are all greater than 94%. The experimental results show that within the parameter range required by the patent of the present invention, the three-dimensional hydrogel particle electrode has almost no difference in the removal effect of pollutants. Therefore, the products obtained within the parameter range required by the patent of the present invention can effectively treat pollutants in a competitive environment. Specifically, under the excitation of an external electric field, the three-dimensional hydrogel particles of the patent of the present invention can quickly and wirelessly excite oxidation and reduction reactions, and achieve efficient removal of pollutants through a direct electron transfer process. By treating wastewater with different initial pollutant concentrations, it was found that even in an environment with highly competitive ions, the product of the present invention can overcome the concentration-dependent effect and still maintain a high removal effect for low-concentration heavy metals, and is suitable for the treatment of wastewater with a wide range of pollutant concentrations (Tl(Ⅰ) (100-10000μg / L); Cr(VI) (1-200mg / L)).

[0088] 2. According to Table 1, the removal rates of Tl(I) in the solution treated in Comparative Example 1 are 60.45% (100 μg / L), 58.27% (1000 μg / L), and 55.46 (10000 μg / L), respectively, and the removal rates of Cr(VI) are 56.00% (1 mg / L), 58.27% (50 mg / L), and 50.42% (200 mg / L), respectively; the values ​​of each item are reduced by 38.77%, 39.41%, 38.79%, 41.00%, 43.46%, and 44.31% respectively compared with the embodiment. The experimental results show that the lack of iron and manganese modification in the excitation core weakens the ability of the excitation core to rapidly and wirelessly excite oxidation and reduction reactions at both ends, reduces the electron transfer ability of the three-dimensional hydrogel particle electrode, and is not conducive to the redox process of pollutants. On the contrary, the excitation cores with iron and manganese have more reaction sites, which are conducive to rapid wireless excitation of oxidation and reduction reactions, thereby achieving more efficient heavy metal removal. Therefore, it is necessary to load iron and manganese on the excitation cores.

[0089] 3. According to Table 1, the removal rates of Tl(Ⅰ) in the solution treated in Comparative Example 2 were 80.15% (100 μg / L), 79.22% (1000 μg / L), and 76.47 (10000 μg / L), and the removal rates of Cr(VI) were 81.00% (1 mg / L), 83.76% (55.26 mg / L), and 78.68% (200 μg / L), respectively; the values ​​were reduced by 19.07%, 18.46%, 17.78%, 16.00%, 14.96%, and 16.05% respectively compared with the embodiment. The experimental results show that the lack of ethylenediamine modification makes the excitation core lack amino groups, which makes it impossible for the excitation core to undergo sulfonation with the perfluorosulfonic acid polymer, and thus the excitation core cannot be firmly fixed in the enrichment layer, which may lead to the loss of active centers and the degradation of the performance of the three-dimensional hydrogel particle electrode; at the same time, the perfluorosulfonic acid polymer with strong conductivity cannot be connected to the excitation core, and the electroactive sites of the excitation core cannot be expanded. Therefore, the use of ethylenediamine to aminate the excitation core during the preparation process is necessary for the preparation of three-dimensional hydrogel particle electrodes with high heavy metal removal effects.

[0090] 4. According to Table 1, the removal rates of Tl(Ⅰ) in the solution treated in Comparative Example 3 are 30.31% (100μg / L), 13.66% (1000μg / L), and 4.89 (10000μg / L), respectively, and the removal rates of Cr(VI) are 15.00% (1mg / L), 8.48% (50mg / L), and 3.57 (200mg / L), respectively; the values ​​of each item are reduced by 78.91%, 84.02%, 89.36%, 82.00%, 90.24%, and 91.16% respectively compared with the embodiment. The experimental results show that the three-dimensional hydrogel particle electrode lacks the excitation core and is difficult to quickly and wirelessly excite the oxidation reaction and reduction reaction at both ends, which significantly reduces the electron transfer ability of the three-dimensional hydrogel particle electrode and significantly inhibits the removal effect of pollutants. At this time, the removal effect shown is only the adsorption of heavy metals by the enrichment layer. Therefore, the preparation of a three-dimensional hydrogel particle electrode with high heavy metal removal performance cannot lack the excitation core.

[0091] 5. According to Table 1, the removal rates of Tl(Ⅰ) in the solution treated by Comparative Example 4 are 60.79% (100μg / L), 58.46% (1000μg / L), and 56.28 (10000μg / L), respectively, and the removal rates of Cr(VI) are 68.00% (1mg / L), 70.10% (50mg / L), and 58.47% (200mg / L), respectively; the values ​​of each item are reduced by 38.43%, 39.22%, 37.97%, 29.00%, 28.62%, and 36.26% respectively compared with the embodiment. The experimental results show that the perfluorosulfonic acid-based polymer lacking sulfonic acid groups and being conductive cannot expand the electroactive sites on the surface of the excitation core, which reduces the reactive active sites of heavy metals in the three-dimensional hydrogel particle electrode, thereby reducing the particle electrode's ability to remove heavy metals. Therefore, when preparing three-dimensional hydrogel particle electrodes with high heavy metal removal performance, conductive wires containing sulfonic acid groups and having good conductivity are indispensable.

[0092] 6. According to Table 1, the removal rates of Tl(Ⅰ) in the solution treated in Comparative Example 5 are 72.47% (100 μg / L), 68.47% (1000 μg / L), and 58.22 (10000 μg / L), and the removal rates of Cr(Ⅵ) are 76.00% (1 mg / L), 77.42% (50 mg / L), and 65.28% (200 mg / L), respectively; the values ​​of each item are reduced by 26.75%, 29.21%, 36.03%, 21.00%, 21.30%, and 29.45% respectively compared with the embodiment. The experimental results show that the use of non-conductive cellulose nanofibers instead of conductive perfluorosulfonic acid polymers cannot expand the electroactive sites of the excitation core, limiting the removal effect of the three-dimensional hydrogel particle electrode on heavy metals. Therefore, cellulose nanofibers cannot be used to replace perfluorosulfonic acid polymers when preparing three-dimensional hydrogel particle electrodes with high heavy metal removal performance.

[0093] 7. According to Table 1, the removal rates of Tl(Ⅰ) in the solution treated by Comparative Example 6 are 36.28% (100μg / L), 45.44% (1000μg / L), and 32.57 (10000μg / L), and the removal rates of Cr(VI) are 32.00% (1mg / L), 52.34% (50mg / L), and 38.49% (200mg / L), respectively; the values ​​of each item are reduced by 62.94%, 52.24%, 61.68%, 65.00%, 46.38%, and 56.24% respectively compared with the embodiment. The experimental results show that although the use of inorganic biochar particle electrodes of the same particle size instead of three-dimensional hydrogel particle electrodes can weakly stimulate oxidation and reduction reactions at both ends, due to the lack of a flexible enrichment layer, the inorganic biochar particle electrodes are easily worn and affect their application. In addition, unlike the embodiment, in a competitive environment, after the treatment of comparative example 6, the removal effect of low-concentration heavy metals is not good. This is because the inorganic biochar particle electrode lacks an enrichment layer, which reduces its selectivity for heavy metals. It can be seen that the enrichment layer protects the three-dimensional hydrogel particle electrode and is also the key to determining the selectivity of the three-dimensional hydrogel particle electrode for heavy metals. Therefore, the inorganic particle electrode cannot be used to replace the three-dimensional hydrogel particle electrode of the patent of the present invention.

[0094] 8. According to Table 1, the removal rates of Tl(I) in the solution treated in Comparative Example 7 are 43.25% (100 μg / L), 56.11% (1000 μg / L), and 37.95% (10000 μg / L), and the removal rates of Cr(VI) are 44.00% (1 mg / L), 62.08% (50 mg / L), and 42.77% (200 mg / L), respectively; the values ​​are reduced by 55.97%, 41.57%, 56.30%, 53.00%, 36.64%, and 51.96% respectively compared with the embodiment. Figure 2 As shown in Figure 2, the pH value of the wastewater solution will affect the existence form of heavy metals. The form affects the interaction between heavy metals and the enrichment layer, such as the Figure 3 , TlOH(aq) has hydrogen bonding with the enrichment layer, while Tl+ has no such effect. Combined with the experimental results, too high or too low solution pH values ​​are not conducive to the conversion of heavy metals into the form that is most easily selectively adsorbed by the enrichment layer, which leads to low heavy metals on the surface of the three-dimensional hydrogel particle electrode in a competitive environment, and cannot overcome the concentration-dependent effect, thereby reducing the heavy metal removal efficiency. Therefore, when using the three-dimensional hydrogel particle electrode of the present invention, the wastewater pH value must be controlled as required.

[0095] 9. According to Table 1, the removal rates of Tl(Ⅰ) in the solution treated by Comparative Example 8 are 37.42% (100μg / L), 34.46% (1000μg / L), and 27.81 (10000μg / L), respectively, and the removal rates of Cr(VI) are 40.00% (1mg / L), 39.82% (50mg / L), and 32.44% (200mg / L), respectively; the values ​​of each item are reduced by 61.80%, 63.22%, 66.44%, 57.00%, 58.90%, and 62.29% respectively compared with the embodiment. The experimental results show that the traditional electrochemical technology cannot achieve excellent heavy metal removal effect in a high concentration competitive environment. The addition of the three-dimensional hydrogel particle electrode of the present invention to the traditional electrochemical technology greatly improves the heavy metal removal effect. It can be seen that the dual-maximum chemical effect produced by the three-dimensional hydrogel particle electrode of the present invention is the key to achieving heavy metal removal.

[0096] 10. According to Table 1, the removal rates of Tl(Ⅰ) in the solution treated in Comparative Example 9 are 15.42% (100μg / L), 6.42% (1000μg / L), and 2.30 (10000μg / L), and the removal rates of Cr(VI) are 13.00% (1mg / L), 4.36% (50mg / L), and 1.65% (200mg / L), respectively; the values ​​are reduced by 83.80%, 91.26%, 91.95%, 84.00%, 94.36%, and 93.08% respectively compared with the embodiment. The experimental results show that without applying an electric field, the three-dimensional hydrogel particle electrode cannot rapidly and wirelessly stimulate oxidation and reduction reactions, and at this time, it only shows a very low adsorption effect on heavy metals. Therefore, the electric field is the key to the rapid and wireless stimulation of oxidation and reduction reactions by the three-dimensional hydrogel particle electrode, and the electric field must be applied in the treatment process using the patented product of the present invention.

[0097] 2. Verification of the stability of three-dimensional hydrogel particle electrodes:

[0098] Artificial simulated wastewater was used in this verification. Among them, Tl(Ⅰ) wastewater contained 100μg / L Tl+ and 100mg / L K + ; Cr(VI) wastewater contains 50 mg / L of Cr(VI) and 500 mg / L of NO-3.

[0099] Verification was performed according to the requirements of Examples 1 to 3 and Comparative Examples 4 to 6. After seven cumulative treatments, the breakage of the particle electrode was counted to reflect the stability of the hydrogel particle electrode.

[0100] The fragmentation of the hydrogel particle electrode after treatment is shown in the following table.

[0101] Table 2 Breakage rate of three-dimensional hydrogel particle electrodes

[0102]

[0103] The research on this effect verification has the following conclusions:

[0104] 1. According to Table 2, it is easy to know that the breakage rate of the three-dimensional hydrogel particle electrode after treatment in Example 1 is close to that in Example 2 and Example 3. The standard deviation of the breakage rate of the three embodiments is less than 0.5%, and the average breakage rate is about 6.30%. The experimental results show that within the parameter range required by the patent of the present invention, the obtained three-dimensional hydrogel particle electrode that can selectively remove and enrich heavy metals has similar stability. The semi-interpenetrating porous network structure formed by the polymer network and the conductive line through hydrogen bonding significantly enhances the stability of the three-dimensional hydrogel particle electrode, thereby extending the service life of the particle electrode.

[0105] 2. According to Table 2, the breakage rate of the three-dimensional hydrogel particle electrode after the treatment of Comparative Example 4 is 51.43%, which is 45.13% higher than that of the embodiment. The experimental results show that the lack of conductive wires makes it impossible to form a semi-interpenetrating structure in the three-dimensional hydrogel particle electrode, which seriously weakens the stability of the hydrogel particle electrode and leads to a sharp increase in the breakage rate. Therefore, the conductive wire is an indispensable substance for maintaining the high stability of the hydrogel particle electrode.

[0106] 3. According to Table 2, the breakage rate of the three-dimensional hydrogel particle electrode after treatment in Comparative Example 5 is 8.21%, which is not significantly different from that in Example 5. The experimental results show that using cellulose nanofibers instead of perfluorosulfonic acid polymers can also form a semi-interpenetrating structure and enhance the stability of the hydrogel particle electrode.

[0107] 4. According to Table 2, the breakage rate of the inorganic biochar particle electrode after treatment in Comparative Example 6 is 82.52%, which is 76.2% higher than that in Example 6. The experimental results show that the inorganic biochar particle electrode lacks the protection of the flexible enrichment layer and is easily broken due to collision during the experiment, which greatly shortens the service life of the particle electrode. Therefore, the use of a flexible enrichment layer is conducive to maintaining the stability of the particle electrode and extending its service life.

[0108] 3. Verification of the effect of particle electrode in recovering heavy metals:

[0109] The wastewater used in this validation was the same as that used in Validation 2.

[0110] Verification was carried out in accordance with the requirements of Implementation Examples 1 to 3, Comparative Examples 1 to 7, and Comparative Example 9, and the heavy metal recovery capacity was tested after seven cumulative treatments. Before the heavy metal concentration test, aqua regia was used to digest the particle electrode. The specific process of aqua regia digestion is as follows: the particles after the reaction were rinsed with ultrapure water three times to remove pollutants on the surface of the particles, and then placed in an oven at 60°C for 24 hours to remove moisture; the dried particles were placed in a 50mL conical flask, 10mL of aqua regia was added to the conical flask, and then the conical flask was placed in a fume hood for at least one night; when heating for digestion, the digestion temperature was set to 300°C. After the digestion was completed, ultrapure water was used to rinse the residue in the conical flask, and the washing liquid was filtered with medium-speed qualitative filter paper, the filtrate was collected, and filtered again with a 0.45μm filter head. The test method of heavy metal concentration detection using effect verification 1.

[0111] The heavy metal recovery of the particle electrode after treatment is shown in the following table.

[0112] Table 3 Heavy metal recovery of particle electrodes

[0113]

[0114]

[0115] The research on this effect verification has the following conclusions:

[0116] 1. According to Table 3, it is easy to know that the Tl and Cr contents in the gel ore formed after treatment in Example 1 are close to those in Example 2 and Example 3, and the standard deviation of the metal content in the gel ore formed in the three embodiments is less than 1%. The Tl content in the gel ore formed in the three embodiments is about 0.053% and the Cr content is about 23.45%. The experimental results show that within the parameter range required by the patent of the present invention, the obtained three-dimensional hydrogel particle electrode that can selectively remove and enrich heavy metals has a close recovery capacity for heavy metals. The conversion of the valence state of heavy metals is achieved through an electrochemical process, so that Tl (I) and Cr (VI) are respectively converted into more difficult to dissolve Tl (III) and Cr (III), which are deposited in the semi-interpenetrating porous network structure of the three-dimensional hydrogel particle electrode to achieve the enrichment and recovery of heavy metals. Although the Tl gel ore content is very low, it meets the standard of Tl minerals with mining value (0.050%).

[0117] 2. It is easy to know from Table 3 that the Tl contents in the gel ore formed after treatment in Comparative Examples 1 to 3, Comparative Example 5, Comparative Example 7 and Comparative Example 9 are 0.034%, 0.036%, 0.012%, 0.021%, 0.015% and 0.003%, respectively, and the Cr contents are 15.28%, 15.82%, 8.37%, 13.23%, 9.55% and 0.86%, respectively. Compared with the embodiment, the Tl contents are reduced by 0.019%, 0.017%, 0.041%, 0.032%, 0.038% and 0.050%, respectively, and the Cr contents are reduced by 8.17%, 7.60%, 15.08%, 10.22%, 13.90% and 22.59%, respectively. It can be seen from effect verification 1 that the rapid wireless excitation oxidation reaction and reduction reaction capabilities of Comparative Examples 1 to 3, Comparative Example 5 and Comparative Example 9 are all suppressed to varying degrees. The experimental results show that suppressing the rapid wireless excitation oxidation reaction and reduction reaction capabilities of the three-dimensional hydrogel particle electrode is not conducive to the change of the valence state of heavy metals, reduces the deposition of heavy metals in the particle electrode, and is not conducive to the formation of high-quality gel ore. Therefore, ensuring that the hydrogel particle electrode has good rapid wireless excitation oxidation reaction and reduction reaction capabilities is the key to forming high-quality gel ore.

[0118] 3. According to Table 3, the Tl content in the gel ore formed after the treatment of Comparative Example 4 and Comparative Example 6 is 0.018% and 0.005%, respectively, and the Cr content is 11.23% and 3.65%, respectively. Compared with the embodiment, the Tl content is reduced by 0.035% and 0.048%, respectively, and the Cr content is reduced by 12.22% and 19.80%, respectively. The experimental results show that since Comparative Example 4 does not contain a conductive line, it cannot form a semi-interpenetrating porous network structure, which weakens the ability of the three-dimensional hydrogel particle electrode to retain heavy metals, thereby affecting the formation of high-quality gel ore. Comparative Example 6 does not contain an enrichment layer with a semi-interpenetrating porous network structure, and it is difficult to retain heavy metals. Therefore, having a semi-interpenetrating porous network structure is a prerequisite for the three-dimensional hydrogel particle electrode to form a high-quality gel ore.

[0119] Based on the above results, we can draw the following conclusions:

[0120] The three-dimensional hydrogel particle electrode that can selectively remove and enrich heavy metals has a high electron transfer ability and can quickly and wirelessly stimulate oxidation and reduction reactions under the drive of an electric field to achieve efficient removal of pollutants. The excellent selectivity of the three-dimensional hydrogel particle electrode enables it to effectively overcome the concentration-dependent effect and adapt to the treatment of wastewater with a wide range of heavy metal concentrations; the semi-interpenetrating porous network structure formed by the polymer network and the conductive lines in the enrichment layer greatly enhances the stability of the three-dimensional hydrogel particle electrode and extends its service life; at the same time, the porous structure of the three-dimensional hydrogel particle electrode is conducive to the deposition and retention of heavy metals, which can achieve effective recovery of heavy metals.

[0121] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A three-dimensional hydrogel particle electrode capable of selectively removing and enriching heavy metals, characterized in that: The invention comprises an enrichment layer (1), wherein an excitation core (2) is embedded in the enrichment layer (1); The enriched layer (1) is a semi-interpenetrating porous network structure, which is formed by a polymer network (3) and a conductive line (4) running through the network through hydrogen bonding; the polymer network is formed by cross-linking alginate and metal ions; the conductive line (4) is a conductive polymer rich in sulfonic acid groups; The excitation core (2) is connected to the conductive wire (4) through an interface reaction and is firmly fixed on the enrichment layer (1); the interface reaction is achieved by the sulfonic acid group of the conductive wire (4) and the excitation core (2) through a sulfonamide process; the excitation core (2) can rapidly and wirelessly excite oxidation and reduction reactions at both ends thereof under the drive of an external electric field; The preparation of the excitation core (2) comprises the following steps: Step ① The reed biomass is carefully cleaned with deionized water, cut into small pieces, soaked in a mixed solution of iron, manganese salt and ethylenediamine, then oven dried, and sieved after drying; Step ②: placing the reed biomass obtained in step ① in a crucible, placing it in a tubular furnace, purging nitrogen in advance, pyrolyzing it in a nitrogen atmosphere, and cooling it to room temperature after pyrolysis to obtain the desired excitation nuclei (2).

2. According to claim 1, a three-dimensional hydrogel particle electrode capable of selectively removing and enriching heavy metals, characterized in that: The preparation steps of the excitation core (2) are as follows: ① Fe in the mixed solution 3+ and Mn 2+ The molar ratio is 1:3-3:1, the total concentration is controlled to be 60-100 g / L, the amount of ethylenediamine added is controlled to be 0.5-1.0 mL / 1 g of reed biomass; the soaking time is 12-24 h; the drying temperature is controlled to be 50-80° C., and the drying time is controlled to be 18-24 h; the sieving mesh number is controlled to be 80-100 mesh; the mass of the reed biomass in the crucible of step ② is controlled to be 3-6 g, the nitrogen pre-purge time is controlled to be 5-10 min, the tubular furnace heating rate is controlled to be 3-6° C. / min, the pyrolysis temperature is controlled to be 400-600° C., and the pyrolysis time is controlled to be 2-4 h.

3. The three-dimensional hydrogel particle electrode capable of selectively removing and enriching heavy metals according to claim 1, characterized in that: The preparation process has the following steps: Step a: adding alginate to 100 mL of an aqueous solution containing a conductive wire (4), and continuously stirring to obtain a uniform suspension solution A; Step b: preparing the excited nuclei (2) into a suspension solution B, slowly adding 100 mL of the suspension solution B into the suspension solution A, adding an acid solution and stirring at high temperature to obtain a uniform suspension solution C; Step c: adding the suspension solution C to the cross-linking solution by a peristaltic pump, stirring slowly, and then standing for cross-linking; Step d: The three-dimensional hydrogel particle electrode obtained in step c is washed with deionized water and stored at low temperature.

4. A three-dimensional hydrogel particle electrode capable of selectively removing and enriching heavy metals according to claim 3, characterized in that: In the step a, the mass of alginate is controlled to be 1.5-3.0 g; the conductive wire (4) is a perfluorosulfonic acid polymer, and its mass fraction is controlled to be 3%-10%; the stirring speed is controlled to be 100-200 rpm, and the stirring time is controlled to be 24-36 hours.

5. The three-dimensional hydrogel particle electrode capable of selectively removing and enriching heavy metals according to claim 3, characterized in that: The mass fraction of the suspension solution B in step b is controlled to be 0.8% to 1.5%; the acid solution added is 2 to 5 mL of concentrated hydrochloric acid; the stirring temperature is maintained at 90 to 120° C., the stirring speed is controlled to be 100 to 200 rpm, and the stirring time is controlled to be 36 to 48 hours.

6. The three-dimensional hydrogel particle electrode capable of selectively removing and enriching heavy metals according to claim 3, characterized in that: The cross-linking solution in step c contains calcium ions (Ca 2+ ), iron ions (Fe 3+ ), ferrous ions (Fe 2+ ), manganese ion (Mn 2 + ), the mass fraction of the cross-linking solution is controlled to be 2-6%; the peristaltic pump flow rate is controlled to be 1-3 mL / min, the stirring speed is controlled to be 50-100 rpm, the stirring time is controlled to be 1-3 h, and the static cross-linking time is controlled to be 2-6 h; the sample storage temperature in step d is controlled to be 2-8 ° C.

7. An application method of a three-dimensional hydrogel particle electrode capable of selectively removing and enriching heavy metals, characterized in that: The application steps include: Step 1: adding the three-dimensional hydrogel particle electrode prepared according to claims 1 to 6 to wastewater, and adjusting the pH value of the solution; Step 2: Place the anode plate and cathode plate in the solution, stir continuously, and apply voltage for reaction.

8. The application method of the three-dimensional hydrogel particle electrode capable of selectively removing and enriching heavy metals according to claim 7, characterized in that: The wastewater in step 1 contains one of monovalent thallium (Tl(Ⅰ)) and hexavalent chromium (Cr(Ⅳ)); the added mass of the three-dimensional hydrogel particle electrode is controlled to be 0.5-1.2 g / 1L of wastewater; when the pollutant is Tl(Ⅰ), the solution pH is controlled to be 11-13, and when the pollutant is Cr(Ⅵ), the solution pH is controlled to be 1-3.

9. The application method of the three-dimensional hydrogel particle electrode capable of selectively removing and enriching heavy metals according to claim 7, characterized in that: In step 2, the anode plate and cathode plate are any one of graphite plate, boron-doped corundum electrode plate, platinum electrode plate, and stainless steel electrode plate; the stirring speed is controlled to be 50-100 rpm; the applied voltage is controlled to be 1.5-3 V / cm; and the reaction time is controlled to be 30-60 min.

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