A cadmium ion selective adsorbent and a method for preparing the same

Abstract

The application relates to the technical field of adsorbents, and discloses a cadmium ion selective adsorbent and a preparation method thereof, which is prepared from the following raw materials in parts by weight: 2-3 parts of aminoundecanoic acid, 2-3 parts of citric acid, 0.45-0.6 parts of NaOH, 4-6 parts of cellulose, 4-6 parts of thiocyanogen, 4-6 parts of nano silicon dioxide, 450-650 parts of MES buffer solution, 500 parts of PBS buffer solution, 8-12 parts of a coupling agent, 8-12 parts of a crosslinking agent, 0.4-0.6 parts of metallothionein and 20-30 parts of water. The application bonds the metallothionein and the carbon dot surface carboxyl through an amide reaction, and combines the modified cellulose through a large number of hydrogen bonds, so that the combination capacity of the two is greatly enhanced, and the stability of the adsorbent is improved. The prepared adsorbent has excellent selective adsorption for cadmium, excellent tolerance for some common coexisting interfering ions in water bodies, and excellent industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of adsorbent technology, and in particular to a cadmium ion selective adsorbent and its preparation method. Background Technology

[0002] Cadmium (Cd) is a highly toxic heavy metal and one of the main pollutants causing heavy metal pollution in the environment. The vast majority of cadmium pollution originates from human activities, such as battery manufacturing, fuel production, metal plating, and chemical fertilizer production, all of which generate cadmium pollutants, causing the cadmium content in the natural environment to rise year by year. Cadmium exists primarily in ionic form in polluted water bodies, making it a difficult-to-degrade pollutant that readily enters organisms through the food chain and accumulates, causing serious harm. Currently, the use of cadmium in water bodies... 2+ Methods for cadmium removal include chemical precipitation, biological methods, adsorption, and membrane separation, each with its own advantages and disadvantages. Finding efficient and environmentally friendly methods for the selective removal of cadmium from natural water bodies remains a critical issue and is of great significance for addressing heavy metal pollution in the environment.

[0003] Metallothioneins (MTs) are low-molecular-weight, high-metal-content, cysteine-rich metal-binding proteins widely distributed in the biological world. MTs readily bind to heavy metals and can be used for the recovery and removal of heavy metal pollutants from the environment, or as biomarkers to assess the degree of heavy metal pollution in environmental systems. Metallothioneins exhibit adsorption selectivity for specific metal ions; specifically, MTs have different affinities for different metal ions. + Ca + Mg 2+ At high plasma concentrations, specific metal ions, such as Cd, can be selectively adsorbed. 2+ .

[0004] Carbon quantum dots (carbon dots) refer to carbon nanomaterials with a size of less than 10 nm. They are generally composed of a central carbon core and surrounding modifiers. The central carbon core is typically sp. 2 Hybridized nanocrystalline carbon or amorphous carbon. Carbon dots themselves contain a large number of oxygen-containing groups on their surface, have good water solubility, and their surface is easily functionalized by various organic, inorganic, or polymer substances, thus replacing highly toxic metal quantum dots. Compared with traditional semiconductor quantum dots or organic dyes, carbon dots have better water solubility, lower toxicity, and better biocompatibility.

[0005] CN102716719A discloses a heavy metal adsorbent for in vitro perfusion and its preparation method, which features low preparation cost, simple synthesis process, large adsorption capacity, and fast adsorption rate. It can be used for in vitro whole blood perfusion to remove heavy metals from the human body and treat heavy metal poisoning. However, the binding of this adsorbent's thiol reagent with the medium is not stable enough, and it will dissolve and lose its original effect after repeated use, failing to meet users' industrial needs for cadmium adsorption. In addition, its adsorption of heavy metal ions is not selective and is easily interfered with by other metal ions. Summary of the Invention

[0006] To overcome the shortcomings and deficiencies of the prior art, the present invention aims to provide a cadmium ion selective adsorbent and its preparation method. The prepared selective adsorbent has high stability and excellent selectivity and adsorption capacity for cadmium.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] A cadmium ion selective adsorbent, the raw materials of which, by weight, comprise: 2-3 parts aminoundecanoic acid, 2-3 parts citric acid, 0.45-0.6 parts NaOH, 4-6 parts cellulose, 4-6 parts thiourea, 4-6 parts nano silica, 450-650 parts MES buffer solution, 500 parts PBS buffer solution, 8-12 parts coupling agent, 8-12 parts crosslinking agent, 0.4-0.6 parts metallothionein, and 20-30 parts water.

[0009] Preferably, the MES buffer solution has a concentration of 0.5 mol / L and a pH of 6.0.

[0010] Preferably, the PBS buffer solution has a concentration of 0.1 mol / L and a pH of 7.4.

[0011] Preferably, the coupling agent is EDC.

[0012] Preferably, the crosslinking agent is NHS.

[0013] The method for preparing a cadmium ion selective adsorbent includes the following steps:

[0014] (1) Thiourea and nano-silica were thoroughly mixed, thermally polymerized at high temperature under nitrogen protection, and then sonicated for 1 hour, washed and dried to obtain intermediate 1, which is a composite of carbon nitride and nano-silica.

[0015] (2) Dissolve aminoundecanoic acid in 10 times its weight of water, then add NaOH to neutralize it, filter out the insoluble matter, and then slowly add citric acid in batches under vigorous stirring for 10-15 min. Filter to collect the precipitate, wash with deionized water, dry, and obtain carbon dot precursor.

[0016] (3) Mix the carbon dot precursor and intermediate 1 evenly, place them in a quartz tube furnace and calcine them, then cool them to room temperature, pass the product through a 100μm sieve, collect the solid inside the sieve, wash them with deionized water 4-5 times, and dry them in a 60℃ oven for 2h to obtain intermediate 2, which is a composite of carbon dots, carbon nitride, and nano silica.

[0017] (4) Dissolve cellulose and intermediate 2 in 2 times their weight of ethanol, add sodium hydroxide solution and stir for 1 hour, then add chloroacetic acid ethanol solution, heat, and after the reaction is complete, neutralize with hydrochloric acid to pH 7, filter, wash with ethanol, and dry to obtain modified cellulose loaded with intermediate 2.

[0018] (5) Add the modified cellulose, coupling agent and crosslinking agent to 10 times the weight of MES buffer solution, stir at room temperature for 1 hour to activate, then centrifuge, filter and wash 2-3 times with MES buffer solution, then add to PBS buffer solution, then add metallothionein, stir overnight at 20°C in the dark, after the reaction is complete, wash 4-5 times with deionized water, dry to obtain selective adsorbent.

[0019] Preferably, the high-temperature thermal polymerization in step (1) is a thermal polymerization reaction at 550°C for 4 hours.

[0020] Preferably, the drying in step (2) is performed in a vacuum drying oven at 85°C for 2 hours.

[0021] Preferably, the burning in step (3) is burning at 300°C for 2 hours.

[0022] Preferably, in step (4), the centrifugation is performed at 10000 rpm for 5 minutes.

[0023] The beneficial effects of this invention are:

[0024] This invention prepares immobilized carbon quantum dots in a one-step process, loads them onto modified cellulose, and then uses an amide reaction to bond metallothionein to the carboxyl groups on the carbon dot surface. The numerous amino groups on the metallothionein also form hydrogen bonds with the hydroxyl groups on the modified cellulose, greatly enhancing the binding capacity and improving the stability of the adsorbent without affecting the structure and bioactivity of the metallothionein. The intermediate 1 prepared in this invention is composed of carbon nitride and nano-silica, possessing a large specific surface area, abundant adsorption sites, and a stable structure, further improving the adsorption capacity of the adsorbent.

[0025] The adsorbent prepared by this invention exhibits excellent selective adsorption of cadmium and excellent tolerance to some common coexisting interfering ions in water. It also shows good resistance to common metal cations such as K+. + Na + Ca 2+ Mg2+ Al 3+ Fe 3+ Pb 2+ Zn 2+ Cu 2+ Their allowable tolerance concentrations are all much higher than the concentrations present in actual water samples, indicating excellent prospects for industrial applications. Detailed Implementation

[0026] The following will describe the concept and technical effects of the present invention clearly and completely with reference to the embodiments, so as to fully understand the purpose, features and effects of the present invention.

[0027] Example 1:

[0028] A cadmium ion selective adsorbent comprises: 2 parts aminoundecanoic acid, 2 parts citric acid, 0.45 parts NaOH, 4 parts cellulose, 4 parts thiourea, 4 parts nano silica, 450 parts MES buffer solution, 500 parts PBS buffer solution, 8 parts EDC, 8 parts NHS, 0.4 parts metallothionein, and 20 parts water.

[0029] The preparation method of the cadmium ion selective adsorbent described in this embodiment, based on parts by weight, includes the following steps:

[0030] (1) Thiourea and nano-silica were thoroughly mixed and thermally polymerized at 550°C for 4 hours under nitrogen protection. Then, the mixture was sonicated for 1 hour, washed and dried to obtain intermediate 1, which is a composite of carbon nitride and nano-silica.

[0031] (2) Dissolve aminoundecanoic acid in 10 times its weight of water, then add NaOH to neutralize it, filter out the insoluble matter, and then slowly add citric acid in batches under vigorous stirring for 10-15 min. Filter and collect the precipitate, wash it with deionized water, and dry it in a vacuum drying oven at 85℃ for 2 h to obtain the carbon dot precursor.

[0032] (3) Mix the carbon dot precursor and intermediate 1 evenly, place them in a quartz tube furnace and calcine at 300°C for 2 hours, then cool to room temperature, pass the product through a 100μm sieve, collect the solid inside the sieve, wash with deionized water 4-5 times, and dry in an oven at 60°C for 2 hours to obtain intermediate 2, which is a composite of carbon dots, carbon nitride, and nano silica.

[0033] (4) Dissolve cellulose and intermediate 2 in 2 times their weight of ethanol, add sodium hydroxide solution and stir for 1 hour, then add chloroacetic acid ethanol solution, heat, and after the reaction is complete, neutralize with hydrochloric acid to pH 7, filter, wash with ethanol, and dry to obtain modified cellulose loaded with intermediate 2.

[0034] (5) Add modified cellulose, EDC and NHS to 10 times the weight of MES buffer solution, stir at room temperature for 1 hour to activate, then centrifuge at 10000 rpm for 5 minutes, filter and wash 2-3 times with MES buffer solution, then add to PBS buffer solution, then add metallothionein, stir overnight at 20°C in the dark, after the reaction is complete, wash 4-5 times with deionized water, dry to obtain selective adsorbent.

[0035] Example 2:

[0036] A cadmium ion selective adsorbent comprises: 2.5 parts aminoundecanoic acid, 2.5 parts citric acid, 0.53 parts NaOH, 5 parts cellulose, 5 parts thiourea, 5 parts nano silica, 550 parts MES buffer solution, 500 parts PBS buffer solution, 10 parts EDC, 10 parts NHS, 0.5 parts metallothionein, and 25 parts water.

[0037] The preparation method of the cadmium ion selective adsorbent described in this embodiment, based on parts by weight, includes the following steps:

[0038] (1) Thiourea and nano-silica were thoroughly mixed and thermally polymerized at 550°C for 4 hours under nitrogen protection. Then, the mixture was sonicated for 1 hour, washed and dried to obtain intermediate 1, which is a composite of carbon nitride and nano-silica.

[0039] (2) Dissolve aminoundecanoic acid in 10 times its weight of water, then add NaOH to neutralize it, filter out the insoluble matter, and then slowly add citric acid in batches under vigorous stirring for 10-15 min. Filter and collect the precipitate, wash it with deionized water, and dry it in a vacuum drying oven at 85℃ for 2 h to obtain the carbon dot precursor.

[0040] (3) Mix the carbon dot precursor and intermediate 1 evenly, place them in a quartz tube furnace and calcine at 300°C for 2 hours, then cool to room temperature, pass the product through a 100μm sieve, collect the solid inside the sieve, wash with deionized water 4-5 times, and dry in an oven at 60°C for 2 hours to obtain intermediate 2, which is a composite of carbon dots, carbon nitride, and nano silica.

[0041] (4) Dissolve cellulose and intermediate 2 in 2 times their weight of ethanol, add sodium hydroxide solution and stir for 1 hour, then add chloroacetic acid ethanol solution, heat, and after the reaction is complete, neutralize with hydrochloric acid to pH 7, filter, wash with ethanol, and dry to obtain modified cellulose loaded with intermediate 2.

[0042] (5) Add modified cellulose, EDC and NHS to 10 times the weight of MES buffer solution, stir at room temperature for 1 hour to activate, then centrifuge at 10000 rpm for 5 minutes, filter and wash 2-3 times with MES buffer solution, then add to PBS buffer solution, then add metallothionein, stir overnight at 20°C in the dark, after the reaction is complete, wash 4-5 times with deionized water, dry to obtain selective adsorbent.

[0043] Example 3:

[0044] A cadmium ion selective adsorbent comprises: 3 parts aminoundecanoic acid, 3 parts citric acid, 0.6 parts NaOH, 6 parts cellulose, 6 parts thiourea, 6 parts nano silica, 650 parts MES buffer solution, 500 parts PBS buffer solution, 12 parts EDC, 12 parts NHS, 0.6 parts metallothionein, and 30 parts water.

[0045] The preparation method of the cadmium ion selective adsorbent described in this embodiment, based on parts by weight, includes the following steps:

[0046] (1) Thiourea and nano-silica were thoroughly mixed and thermally polymerized at 550°C for 4 hours under nitrogen protection. Then, the mixture was sonicated for 1 hour, washed and dried to obtain intermediate 1, which is a composite of carbon nitride and nano-silica.

[0047] (2) Dissolve aminoundecanoic acid in 10 times its weight of water, then add NaOH to neutralize it, filter out the insoluble matter, and then slowly add citric acid in batches under vigorous stirring for 10-15 min. Filter and collect the precipitate, wash it with deionized water, and dry it in a vacuum drying oven at 85℃ for 2 h to obtain the carbon dot precursor.

[0048] (3) Mix the carbon dot precursor and intermediate 1 evenly, place them in a quartz tube furnace and calcine at 300°C for 2 hours, then cool to room temperature, pass the product through a 100μm sieve, collect the solid inside the sieve, wash with deionized water 4-5 times, and dry in an oven at 60°C for 2 hours to obtain intermediate 2, which is a composite of carbon dots, carbon nitride, and nano silica.

[0049] (4) Dissolve cellulose and intermediate 2 in 2 times their weight of ethanol, add sodium hydroxide solution and stir for 1 hour, then add chloroacetic acid ethanol solution, heat, and after the reaction is complete, neutralize with hydrochloric acid to pH 7, filter, wash with ethanol, and dry to obtain modified cellulose loaded with intermediate 2.

[0050] (5) Add modified cellulose, EDC and NHS to 10 times the weight of MES buffer solution, stir at room temperature for 1 hour to activate, then centrifuge at 10000 rpm for 5 minutes, filter and wash 2-3 times with MES buffer solution, then add to PBS buffer solution, then add metallothionein, stir overnight at 20°C in the dark, after the reaction is complete, wash 4-5 times with deionized water, dry to obtain selective adsorbent.

[0051] Comparative Example 1:

[0052] The only difference between this comparative example and Example 1 is that modified cellulose is not added in step (5), while the other raw materials and steps are the same as in Example 1.

[0053] Comparative Example 2:

[0054] The only difference between this comparative example and Example 1 is that carbon nitride and nano-silica are not added in step (1), while the other raw materials and steps are the same as in Example 1.

[0055] Comparative Example 3:

[0056] The only difference between this comparative example and Example 1 is that metallothionein is not added in step (5), while the other raw materials and steps are the same as in Example 1.

[0057] Adsorbent performance testing: Preparation of Cd 2+ Divide the 100 μg / L solution into equal volumes for later use.

[0058] Stability and adsorption rate test: The adsorbents prepared in Examples 1-3 and Comparative Examples 1-3 were added to a solution containing Cd. 2+ Adsorption experiments were conducted in the solution. The adsorbent was then filtered out, washed, and desorbed. The adsorption experiments were repeated 20 times in total.

[0059] Table 1. Adsorption Rate Test

[0060]

[0061]

[0062] As shown in Table 1, the adsorption rate of Comparative Example 1 gradually decreased in repeated experiments, while Example 1 consistently exhibited excellent adsorption rates. This is because modified cellulose was added to Example 1, which can effectively load carbon quantum dots and form hydrogen bonds with a large number of amino groups on metallothionein, greatly enhancing the binding ability of both and improving the stability of the adsorbent. The adsorption rate of Comparative Example 2 was worse than that of Example 1. This is because carbon nitride and nano-silica were added to Example 1, which have a large specific surface area, abundant adsorption sites, and stable structure, further improving the adsorption capacity of the adsorbent.

[0063] Selective testing: For Cd-containing 2+ Different concentrations of other metal ions were added to the solution, and the adsorption capacity of each adsorbent for Cd was tested. 2+ The adsorption rate.

[0064] Table 2. Selectivity Tests

[0065]

[0066] As can be seen from Table 2, Comparative Example 3 showed the effect of various metal ions on Cd. 2+ The adsorption rate of the other example was significantly reduced, while Example 1 exhibited excellent selective adsorption. This is because metallothionein was added to Example 1. Metallothionein has different affinities for different metal ions, and can selectively adsorb specific metal ions, such as Cd, even in the presence of other interfering ions. 2+ .

[0067] The above embodiments are only some embodiments of the present invention, and not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

Claims

1. A cadmium ion selective adsorbent, characterized in that, The raw materials, by weight, consist of: 2-3 parts aminoundecanoic acid, 2-3 parts citric acid, 0.45-0.6 parts NaOH, 4-6 parts cellulose, 4-6 parts thiourea, 4-6 parts nano silica, 450-650 parts MES buffer solution, 500 parts PBS buffer solution, 8-12 parts coupling agent, 8-12 parts crosslinking agent, 0.4-0.6 parts metallothionein, and 20-30 parts water; The MES buffer solution has a concentration of 0.5 mol / L and a pH of 6.

0. The PBS buffer solution has a concentration of 0.1 mol / L and a pH of 7.

4. The coupling agent is EDC; The crosslinking agent is NHS; The preparation method of the cadmium ion selective adsorbent includes the following steps: (1) Thiourea and nano-silica were thoroughly mixed, thermally polymerized at high temperature under nitrogen protection, and then sonicated for 1 hour, washed and dried to obtain intermediate 1, which is a composite of carbon nitride and nano-silica. (2) Dissolve aminoundecanoic acid in 10 times its weight of water, then add NaOH to neutralize it, filter out the insoluble matter, and then slowly add citric acid in batches under vigorous stirring for 10-15 min. Filter to collect the precipitate, wash with deionized water, and dry to obtain the carbon dot precursor. (3) Mix the carbon dot precursor and intermediate 1 evenly, place them in a quartz tube furnace and calcine them, then cool them to room temperature, pass the product through a 100μm sieve, collect the solid inside the sieve, wash them with deionized water 4-5 times, and dry them in a 60℃ oven for 2h to obtain intermediate 2, which is a composite of carbon dots, carbon nitride, and nano silica. (4) Dissolve cellulose and intermediate 2 in 2 times their weight of ethanol, add sodium hydroxide solution and stir for 1 hour, then add chloroacetic acid ethanol solution, heat, and after the reaction is complete, neutralize with hydrochloric acid to pH 7, filter, wash with ethanol, and dry to obtain modified cellulose loaded with intermediate 2. (5) Add the modified cellulose, coupling agent and crosslinking agent to 10 times the weight of MES buffer solution, stir at room temperature for 1 hour to activate, then centrifuge, filter and wash 2-3 times with MES buffer solution, then add to PBS buffer solution, then add metallothionein, stir overnight at 20°C in the dark, after the reaction is complete, wash 4-5 times with deionized water, dry to obtain selective adsorbent.

2. The cadmium ion selective adsorbent according to claim 1, characterized in that, In step (1), the high-temperature thermal polymerization is a thermal polymerization reaction at 550°C for 4 hours.

3. The cadmium ion selective adsorbent according to claim 1, characterized in that, In step (2), the drying process involves drying in a vacuum drying oven at 85°C for 2 hours.

4. The cadmium ion selective adsorbent according to claim 1, characterized in that, In step (3), the burning process involves burning at 300°C for 2 hours.

5. The cadmium ion selective adsorbent according to claim 1, characterized in that, In step (5), the centrifugation is performed at 10000 rpm for 5 minutes.

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