CN103235019A - Cyclodextrin/grapheme nanometer compound modified electrode, preparation method and usage - Google Patents

Abstract

The invention relates to the preparation of a cyclodextrin/graphene nanocomposite modified electrode and its use for simultaneous trace detection of heavy metal ions, belonging to the fields of nanocomposite materials and environmental monitoring. The present invention mainly uses the cyclodextrin/graphene nanocomposite modified glassy carbon electrode as the working electrode, the saturated calomel electrode as the reference electrode, and the platinum wire electrode as the counter electrode, and the trace Heavy metal ions were simultaneously quantitatively analyzed and determined. The electrode prepared by the invention has good reproducibility and stability, and the operation process is simple and fast, and the detection sensitivity is greatly improved, and the limit value of detecting heavy metal ions reaches 10 ^-11 M level.

Description

A cyclodextrin/graphene nanocomposite modified electrode and its preparation method and application

Technical field:

The invention belongs to the field of nanocomposite materials and environmental monitoring, and in particular relates to a preparation method of a cyclodextrin/graphene nanocomposite modified glassy carbon electrode and a method for detecting trace heavy metal ions.

Background technique:

With the rapid development of industry and agriculture, the pollution of heavy metal ions is increasing year by year. Heavy metals can not only exist in the environment for a long time, but also accumulate in humans, animals and plants through the food chain. In recent years, heavy metal pollution has attracted great attention all over the world because of its increasingly serious threat to the environment and human health.

At present, the methods for detecting heavy metal ions mainly include: atomic absorption spectrometry, fluorescence spectrometry, inductively coupled plasma mass spectrometry and electrochemical analysis. Compared with traditional methods, electrochemical analysis has been more widely used because of its simplicity, rapidity, sensitivity, and accuracy. The present invention detects based on anodic stripping voltammetry (Anodic Stripping Voltammetry ASV) in the electrochemical analysis method. It mainly includes two processes of deposition and stripping, namely: first, the detected ions are deposited and reduced on the surface of the working electrode under a certain potential. Then, when the electrode potential is reversely scanned, the deposited substance undergoes an oxidation reaction and dissolves, and the stripping voltammetry curve is recorded at the same time. The sensitivity of anodic stripping voltammetry depends on the electrical activity of the sensing material, so the present invention uses graphene composites to modify electrodes.

Graphene is a new type of carbon material with a two-dimensional honeycomb lattice structure stacked by sp ² hybridized carbon atoms. Its thickness is only 0.35nm, which is the thinnest two-dimensional material in the world. Graphene is widely used in new composite materials, photoelectric functional materials and devices, solar cells and sensor materials because of its excellent physical and chemical properties such as large specific surface area, fast carrier migration, good thermal conductivity and high mechanical strength. application prospects. However, the agglomeration of graphene reduces its specific surface area, further reduces its adsorption capacity, and limits its further widespread application. The invention uses cyclodextrin to modify graphene, which not only overcomes the influence of agglomeration, but also increases its selection and adsorption capacity for heavy metal ions. Using this nanocomposite as a sensing material, a method for detecting trace heavy metal ions with fast detection, high sensitivity and good reproducibility was invented, and the method is non-toxic and harmless to the environment and human health.

Invention content:

The object of the present invention is to provide a cyclodextrin/graphene nanocomposite modified glassy carbon electrode and a method for detecting trace heavy metal ions, specifically comprising the preparation of a cyclodextrin/graphene nanocomposite modified glassy carbon electrode, and using This electrode is used as the working electrode, and the purchased saturated calomel electrode is used as the reference electrode, and the platinum wire electrode is used as the counter electrode. The trace detection of heavy metal ions is completed through the constituted three-electrode system. Square wave anodic stripping voltammetry was used in the detection process.

A method for preparing a cyclodextrin/graphene nanocomposite modified glassy carbon electrode of the present invention comprises the following steps:

1. Pretreatment of the glassy carbon electrode: the glassy carbon electrode (3 mm in diameter) is polished to a mirror surface with 0.05 micron Al ₂ O ₃ powder on a polishing cloth. After polishing, ultrasonic cleaning was performed in ultrapure water for 2 minutes, followed by absolute ethanol and ultrapure water for 5 minutes, and finally dried with nitrogen gas for later use.

2. Preparation of cyclodextrin/graphene nanocomposite modified glassy carbon electrode:

First, graphene oxide was prepared by the modified Hummers method through graphite oxidation, mechanical exfoliation, flocculation drying and other steps. The specific operation steps are as follows: in a 50-5000 milliliter round bottom flask, add 10-100 milliliters of concentrated sulfuric acid with a mass concentration of 95-98% and 20-100 milliliters of concentrated nitric acid with a mass concentration of 65-68%. Stir under magnetic force for 5-50 minutes, then add 2-200 grams of natural flake graphite, stir vigorously to prevent agglomeration, after the dispersion is uniform, add 10-100 grams of potassium chlorate, and finally remove the ice bath and react at room temperature for 20-150 hours, until the reaction is complete Finally, the product is washed, ultrasonically stripped, flocculated with sodium hydroxide, dried at 20-80° C. for 2-10 hours, and ground to obtain graphene oxide solid powder.

-环糊精， 最后于30-120℃下真空干燥2-20小时，即得产物环糊精/石墨烯纳米复合物。 Dissolve graphene oxide in deionized water, add excess hydroxypropyl- -Cyclodextrin, ultrasonically dispersed for 10-60 minutes, reacted with microwave assistance for 10 minutes-2 hours, microwave power 100-800 watts, reaction temperature 20-80°C, then add reducing agent, at 50-100°C React for 10-120 minutes. After the reaction is completed, centrifuge at a speed of 3000-10000 rpm and wash repeatedly with absolute ethanol to remove unreacted hydroxypropyl-

- Cyclodextrin, and finally vacuum drying at 30-120° C. for 2-20 hours to obtain the product cyclodextrin/graphene nanocomposite.

Dissolve the cyclodextrin/graphene nanocomposite prepared in the above steps with a solvent, control its concentration to be 0.5-50 mg/ml, and then add 5% of the cyclodextrin/graphene nanocomposite solution volume 0.1-10% For Nafion, ultrasonically disperse for 10-60 minutes to obtain a uniform dispersion. Use a micropipette to pipette 3-10 microliters of the above dispersion, drop-coat it on the surface of the treated glassy carbon electrode, and dry it at room temperature to obtain a cyclodextrin/graphene nanocomposite modified electrode. For comparison, graphene-modified glassy carbon electrodes and cyclodextrin-modified glassy carbon electrodes were prepared by the same method.

The invention also provides a method for detecting trace heavy metal ions, which is suitable for trace detection of heavy metal ions in environmental detection and water quality analysis. The specific measurement method is as follows: the cyclodextrin/graphene nanocomposite modified electrode prepared above is used as the working electrode, the saturated calomel electrode is used as the reference electrode, and the platinum wire electrode is used as the counter electrode, thus forming a three-electrode system. When measuring heavy metal ions, first place the three-electrode system in 20 ml of 0.1 mol/L buffer solution with a pH of 3.0-6.0, and use cyclic voltammetry to scan several times until a smooth curve is obtained to complete the activation of the working electrode surface . Then, under stirring conditions, use a micropipette to add a certain concentration of heavy metal ion solution to the above buffer solution in sequence, enrich at a potential of -0.4 to -1.8 volts for 30-600 seconds, and then use square wave anodic stripping voltammetry Reverse scanning, while recording the stripping voltammetry curve.

The reducing agent used in the present invention is one or more of ammonia water, hydrazine hydrate, sodium hydroxide, sodium borohydride and vitamin C.

The solvent used in the present invention is one or more of deionized water, ethanol, acetone and N,N-dimethylformamide.

The buffer solution used in the present invention is one of acetic acid-sodium acetate, ammonium chloride-hydrochloric acid, sodium monohydrogen phosphate-sodium dihydrogen phosphate buffer solution.

The heavy metal ion solution used in the present invention is one or more of lead, cadmium, mercury, silver, chromium, copper, zinc and bismuth solutions.

The beneficial effects of the present invention are as follows:

The cyclodextrin/graphene nanocomposite provided by the invention has both the host-guest recognition ability and enrichment performance of the cyclodextrin and the excellent conductivity and large specific surface area of the graphene. The modification of water-soluble cyclodextrin molecules not only overcomes the agglomeration of graphene, but also facilitates the selective capture of heavy metal ions.

In addition, the present invention uses the cyclodextrin/graphene nanocomposite-modified glassy carbon electrode as the working electrode to simultaneously detect trace heavy metal ions through electrochemical stripping voltammetry. The operation process is simple and fast, and the detection method is reproducible. , good stability, and greatly improved the detection sensitivity. The modification of cyclodextrin has a good detection effect on heavy metal ions, especially the detection limits of lead ion and cadmium ion reached 9.42×10 ^-11 mol/L and 6.73×10 ^-11 mol/L, respectively.

Description of drawings:

Fig. 1 Schematic diagram of the synthesis principle of cyclodextrin/graphene nanocomposite and the interaction between the complex and heavy metal ions.

Fig. 2 TEM images of graphene oxide (a) and cyclodextrin/graphene nanocomposite (b).

Fig. 3 Thermogravimetric curves of graphene, graphene oxide, cyclodextrin, and cyclodextrin/graphene nanocomposites.

Figure 4 In 0.1 mol/L pH 4.5 acetic acid-sodium acetate buffer solution containing lead and cadmium (1.0×10 ^-7 mol/L), bare glassy carbon electrode, graphene-modified glassy carbon electrode, cyclodextrin-modified glassy carbon electrode Square-wave anodic stripping voltammograms of electrode and cyclodextrin/graphene nanocomposite modified glassy carbon electrode.

Figure 5 Square-wave anodic stripping voltammogram (a) of various concentrations of lead and cadmium solutions, the peak current represents the concentration of metal ions. Linear plots of peak current versus (b) lead and (c) cadmium ion concentrations.

Detailed ways:

The present invention will be further described in detail through the accompanying drawings and specific embodiments below.

Example 1 The first step is the preparation of a cyclodextrin/graphene nanocomposite modified glassy carbon electrode.

(1) Pretreatment of the glassy carbon electrode: the glassy carbon electrode (3 mm in diameter) was polished to a mirror surface with 0.05 micron Al ₂ O ₃ powder on a polishing cloth. After polishing, ultrasonically clean in ultrapure water for 2 minutes, followed by ultrasonic cleaning with absolute ethanol and ultrapure water for 5 minutes, and finally blow dry with nitrogen gas for use.

(2) Preparation of cyclodextrin/graphene nanocomposite modified glassy carbon electrode:

First, graphene oxide was prepared by the modified Hummers method through graphite oxidation, mechanical exfoliation, flocculation drying and other steps. The specific operation steps are as follows: add 72 milliliters of concentrated sulfuric acid with a mass concentration of 95-98% and 36 milliliters of concentrated nitric acid with a mass concentration of 65-68% in a 500 milliliter round bottom flask, and magnetically stir for 15 minutes under 0 ° C ice bath conditions , then add 4 grams of natural flake graphite, stir vigorously to prevent agglomeration, after the dispersion is uniform, add 44 grams of potassium chlorate, and finally remove the ice and react at room temperature for 96 hours. After the reaction was completed, the product was washed, ultrasonically stripped, flocculated with sodium hydroxide and dried at 40° C. for 6 hours to obtain graphene oxide solid powder.

Weigh 40 mg of graphene oxide and dissolve in 80 ml of deionized water, then add 1.0 g of hydroxypropyl- -Cyclodextrin, ultrasonically dispersed for 20 minutes; reacted for 30 minutes under the assistance of microwave, the microwave power is 450 watts, and the reaction temperature is 50°C; then add 500 μl of ammonia water and 100 μl of hydrazine hydrate, and react at 75°C for 30 minutes , After the reaction is complete, pour the mixture into a centrifuge tube, centrifuge at 8000 rpm for 15 minutes, and wash repeatedly with a large amount of absolute ethanol to remove unreacted hydroxypropyl- - Cyclodextrin, and finally vacuum-dried at 70° C. for 6 hours to obtain the product cyclodextrin/graphene nanocomposite. The preparation principle is shown in Figure 1, and the morphology and thermal stability are shown in Figure 2 and Figure 3, respectively.

Dissolve 1 mg of the cyclodextrin/graphene nanocomposite prepared in the above steps with 1 ml of N,N-dimethylformamide, then add 20 microliters of 5% Nafion, and ultrasonically disperse to obtain a uniform dispersion. Use a micropipette to pipette 5 microliters of the above dispersion, drop-coat it on the surface of the treated glassy carbon electrode, and dry it at room temperature to obtain a cyclodextrin/graphene nanocomposite modified electrode. For comparison, graphene-modified glassy carbon electrodes and cyclodextrin-modified glassy carbon electrodes were prepared by the same method. It can be seen from Figure 4 that the performance of the cyclodextrin/graphene nanocomposite modified glassy carbon electrode is much better than other electrodes.

The second step. The cyclodextrin/graphene nanocomposite modified glassy carbon electrode is used for the detection of heavy metal ions. The cyclodextrin/graphene nanocomposite modified glassy carbon electrode prepared above was used as the working electrode, the saturated calomel electrode was used as the reference electrode, and the platinum wire electrode was used as the counter electrode, thus forming a three-electrode system. When measuring heavy metal ions, first place the three-electrode system in 20 ml of 0.1 mol/L acetic acid-sodium acetate buffer solution with a pH of 4.5, and use cyclic voltammetry to scan several times at a speed of 300 mV/s until a smooth curve to complete the activation of the working electrode surface. Then, under the condition of stirring, a certain amount of lead and cadmium standard solutions with different concentrations were sequentially added to the above solution with a micropipette, then enriched at a potential of -1.2 volts for 120 seconds, and reacted with square wave anodic stripping voltammetry. The stripping voltammetry curve was recorded simultaneously with the scan.

Example 2 According to the preparation method of Example 1, except that the reducing agent was changed from ammonia water and hydrazine hydrate to sodium hydroxide solution and sodium borohydride, the results shown in Figures 2 and 3 were also obtained.

Example 3 According to the preparation method of Example 1, except that the reducing agent was changed from ammonia water and hydrazine hydrate to sodium borohydride, the results shown in Figures 2 and 3 were also obtained.

Example 4 According to the preparation method of Example 1, except that the reducing agent was changed from ammonia water and hydrazine hydrate to sodium hydroxide solution and vitamin C, the results shown in Figures 2 and 3 were also obtained.

Example 5 According to the preparation method of Example 1, except that the reducing agent was changed from ammonia water and hydrazine hydrate to vitamin C, the results shown in Figures 2 and 3 were also obtained.

Example 6 According to the method of Example 1, except that the solvent was changed from N,N-dimethylformamide to ethanol, the results shown in Figures 4 and 5 were also obtained.

Example 7 Following the method of Example 1, except that the solvent was changed from N,N-dimethylformamide to acetone, the results shown in Figures 4 and 5 were also obtained.

Example 8 According to the method of Example 1, only the buffer solution was changed from acetic acid-sodium acetate buffer solution to ammonium chloride-hydrochloric acid buffer solution, and the results shown in Figures 4 and 5 were also obtained.

Example 9 According to the method of Example 1, the buffer solution was changed from acetic acid-sodium acetate buffer solution to sodium monohydrogen phosphate-sodium dihydrogen phosphate buffer solution. The results shown in Figures 4 and 5 are also obtained.

Example 10 According to the method of Example 1, the standard solution of heavy metal ions is changed from the standard solution of lead and cadmium ions to the standard solution of lead, cadmium and bismuth ions, and the results shown in Figures 4 and 5 are also obtained.

Example 11 According to the method of Example 1, the standard solution of heavy metal ions is changed from the standard solution of lead and cadmium ions to the standard solution of lead, cadmium and mercury ions, and the results shown in Figures 4 and 5 are also obtained.

)=0.281x(nM)-0.086,最低检出限为6.73×10^-11M。 It can be seen from Figure 5 that the cyclodextrin/graphene modified glassy carbon electrode has a good stripping voltammetry response to Pb ²⁺ and Cd ²⁺ , and with the increase of the concentration of Pb ²⁺ and Cd ²⁺ , the peak current response also gradually increased. The intensity of the peak current is linearly fitted with the corresponding concentration of metal ions for further analysis. It can be seen that in the range of 1×10 ^-10 to 9×10 ^-9 M, the peak current has a linear relationship with the concentration of Pb ²⁺ , and the linear The equation is y( )=0.223x(nM)+0.145, the lowest detection limit is 9.42×10 ^-11 M. In contrast, in the range of 5×10 ^-10 ~ 9×10 ^-9 M, the peak current has a linear relationship with the concentration of Cd ²⁺ , and the linear equation is y(

)=0.281x(nM)-0.086, the lowest detection limit was 6.73×10 ^-11 M.

The electrode prepared by the invention has good stability and reproducibility, and for the same modified electrode, the relative standard deviation of 10 repeated tests is 1.93%. And for the 6 parallel electrodes prepared at the same time, the relative standard deviation is also within 5%. In addition, the electrodes did not need to be re-prepared or activated during the whole testing process, which further proves the good stability and reproducibility of our prepared electrodes.

Claims (10)

1. the preparation method of cyclodextrin/graphene nanometer composite modified electrode comprises the steps:

The pre-service of glass-carbon electrode: with glass-carbon electrode at the Al of polishing cloth with 0.05 micron ₂O ₃Powder is polished to minute surface; Polishing back in ultrapure water ultrasonic 2 minutes is earlier used absolute ethyl alcohol, ultrapure water ultrasonic cleaning 5 minutes more successively, dries up with nitrogen at last, and is stand-by;

The preparation of cyclodextrin/graphene nanometer composite modified electrode:

A. the concentrated sulphuric acid and the 20-100 milliliter mass concentration that add 10-100 milliliter mass concentration and be 95-98% in 50-5000 milliliter round-bottomed flask are the red fuming nitric acid (RFNA) of 65-68%, stirred 5-50 minute at 0 ℃ of condition of ice bath lower magnetic force, add 2-200 gram natural flake graphite then, vigorous stirring prevents from reuniting; After waiting to be uniformly dispersed, add 10-200 gram potash chlorate, remove at last under the ice bath room temperature and reacted 20-150 hour; After question response was finished, with the product washing, ultrasonic peeling off with the NaOH flocculation and in 20-80 ℃ of dry 2-10 hour, ground, and gets the graphene oxide pressed powder;

B. graphene oxide is dissolved in the deionized water, add excessive hydroxypropyl-

-cyclodextrin, ultrasonic dispersion 10-60 minute; The auxiliary reaction down of microwave 10 minutes-2 hours, microwave power was 100-800 watt, and temperature of reaction is 20-80 ℃; Add reductive agent subsequently, centrifugal under 3000-10000 rev/min rotating speed after reaction finishes in 50-100 ℃ of down reaction 10-120 minute, and use the absolute ethyl alcohol cyclic washing, with remove unreacted hydroxypropyl-

-cyclodextrin in 30-120 ℃ of following vacuum drying 2-20 hour, namely gets product cyclodextrin/graphene nanometer composite at last;

C. cyclodextrin/graphene nanometer composite the dissolution with solvents that above-mentioned steps is made, controlling its concentration is the 0.5-50 mg/ml, add 5% the Nafion solution of cyclodextrin/graphene nanometer composite liquor capacity 0.1-10% again, ultrasonic dispersion 10-60 minute, obtain uniform dispersion liquid; Pipette the above-mentioned dispersion liquid of 3-10 microlitre with the micropipette rifle, drip and to be coated in the glass-carbon electrode surface of handling well, dry under the room temperature, obtain cyclodextrin/graphene nanometer composite modified electrode.

2. as the preparation method of the described cyclodextrin of claim 1/graphene nanometer composite modified electrode, it is characterized in that: step

In used reductive agent be in ammoniacal liquor, hydrazine hydrate, NaOH, sodium borohydride, the vitamin C one or more.

3. as the preparation method of the described cyclodextrin of claim 1/graphene nanometer composite modified electrode, it is characterized in that: step

Solvent for use is deionized water, ethanol, acetone, N, one or more in the dinethylformamide.

4. obtain cyclodextrin/graphene nanometer composite modified electrode by the described preparation method of claim 1.

5. the application of the described cyclodextrin of claim 4/graphene nanometer composite modified electrode in detecting heavy metal ion.

6. application as claimed in claim 5 is characterized in that: described detection refers to environment measuring or water analysis.

7. application as claimed in claim 5 is characterized in that:

As working electrode, saturated calomel electrode is as contrast electrode with cyclodextrin/graphene nanometer composite modified glassy carbon electrode, and platinum electrode is to electrode, constitutes three-electrode system thus; When measuring heavy metal ion, it is the buffer solution of 3.0-6.0 that three-electrode system is placed 20 milliliters 0.1 mol pH earlier, scans for several times until obtaining level and smooth curve, with the activation of the electrode surface of finishing the work with cyclic voltammetry; Then under stirring condition, in above-mentioned buffer solution, add certain density heavy metal ion solution with the micropipette rifle successively, enrichment 30-600 second under current potential-0.4～-1.8 volt, record the stripping volt-ampere curve simultaneously with the reverse scan of square wave anodic stripping voltammetry.

8. application as claimed in claim 7 is characterized in that: used buffer solution is acetic acid-sodium acetate, ammonium chloride-hydrochloric acid, a kind of in disodium-hydrogen-sodium dihydrogen phosphate buffer.

9. application as claimed in claim 7 is characterized in that: used metal ion solution is one or more in lead, cadmium, mercury, silver, chromium, copper, zinc, the bismuth solution.

10. application as claimed in claim 7 is characterized in that, the concentration of described heavy metal ion is 1 * 10 ^-4-1 * 10 ^-8Mol.

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