CN114923967B - Laminated electrochemical sensing device based on carbon paper electrode and application of laminated electrochemical sensing device in heavy metal detection - Google Patents
Laminated electrochemical sensing device based on carbon paper electrode and application of laminated electrochemical sensing device in heavy metal detection Download PDFInfo
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Abstract
The invention discloses a laminated electrochemical sensing device based on a carbon paper electrode and application thereof in heavy metal detection, and belongs to the technical field of electrochemistry. The invention selects the carbon paper CPE as the working electrode to replace the traditional glassy carbon electrode and modifies AuNPs and Co-MOF-NH 2 Preparation of Co-MOF-NH 2 and/AuNPs/CPE working electrode, and constructing a laminated electrochemical sensing device with a miniature electrolytic cell to form a simple micro-field. The laminated electrochemical sensing device of the invention is used for detecting metal ions, and remarkably improves Cd 2+ And Pb 2+ Is used for quantitatively detecting Cd in the concentration range of 0.75-35 mug/L 2+ The detection limit reaches 0.11 mug/L; quantitative detection of Pb within the concentration range of 0.5-20. Mu.g/L 2+ The detection limit reaches 0.07 mug/L.
Description
Technical Field
The invention relates to a laminated electrochemical sensing device based on a carbon paper electrode and application thereof in heavy metal detection, and belongs to the technical field of electrochemistry.
Background
Heavy metals mainly refer to Pb, cd, hg, metalloid As and other heavy elements, and mainly exist in the form of ions with obvious biotoxicity in the environment. Heavy metal ions are difficult to degrade and are easy to enrich along with food chains, thereby causing the problems of environmental pollution and food safety. Even very low doses of heavy metal ions can cause acute and chronic poisoning after long-term accumulation in the human body, causing health hazard. Therefore, a sensitive detection method for trace heavy metal ions in food is established, and the portable device is utilized to realize on-site detection, so that the method has extremely important significance for food quality evaluation, ecological environment examination and human health protection.
Conventional methods for detecting heavy metals include inductively coupled plasma mass spectrometry (ICP-MS), atomic Absorption Spectrometry (AAS), atomic Emission Spectrometry (AES). The methods can accurately measure, but the instrument has complex structure and high cost, and are difficult to realize miniaturization and portability. The electrochemical method is a method for qualitatively and quantitatively analyzing substances by utilizing the electrical and electrochemical properties of the substances, and has the advantages of convenient operation of instruments and devices, low price and easy portability. How to improve the sensitivity of the miniature electrochemical device, reduce the detection limit of the method, and be favorable for realizing accurate and convenient field detection of heavy metal ions.
The modification of the functional nano material can effectively improve the sensitivity and selectivity of the miniaturized electrochemical device to heavy metal ions to be detected. The metal organic framework materials (Metal organic Framework, MOFs) are formed by assembling metal clusters and organic ligands, have the characteristics of high surface area, porosity, large pore volume, adjustable structure, open metal sites and the like, and are widely focused and applied in the fields of gas/energy storage, adsorption, separation, sensing, catalysis and the like. However, the introduction of organic ligands into MOFs reduces the conductivity of MOFs, and under a specific potential, metal nodes or organic ligands undergo oxidation-reduction reaction to cause chemical bond breakage and structural collapse, so that the stability of MOFs is affected and the catalytic effect of MOFs is reduced. Therefore, development of MOFs materials with excellent conductivity and electrocatalytic activity, modified in micro electrochemical devices, to realize ultra trace detection of heavy metal ions, is urgently needed.
Electrode matrices are another element affecting the performance of miniaturized electrochemical sensors. Screen-printed electrodes integrate a three-electrode system in one 2-3 cm 2 On the micro-plane of (2), the working electrode surface area is about 0.12cm 2 And the electrolyte is reduced to about 100 mu L, which is compared with the traditional sensor based on the glassy carbon electrode (effective electrode area is 0.07cm 2 5-10 mL of electrolyte) is used, but conductivity and detection sensitivity are reduced. Therefore, the selection of an electrode substrate having a high specific surface area and strong conductivity is of great importance for further improving the performance of miniaturized electrochemical devices and for reducing the detection limit of metal ions.
Disclosure of Invention
Technical problems:
in order to solve the above problems, the present study prepared carbon paper electrodes (Carbon paper electrode, CPE) on which to electroprecipitationGold-accumulating nano particles (AuNPs) and dripping modified amino functionalized cobalt-based MOF material Co-MOF-NH 2 To produce Co-MOF-NH 2 An AuNPs/CPE working electrode; provides a laminated miniaturized electrochemical sensing device which is built by using a flattened electrode and a micron-sized self-made electrolytic cell and is used for trace Cd 2+ And Pb 2+ Is detected simultaneously with the detection of (a).
The technical scheme is as follows:
the invention provides a laminated electrochemical sensing device for heavy metal detection, which comprises three layers: co-MOF-NH of carbon paper working electrode with top layer modified by cobalt amide-based metal organic framework material and electrodeposited with gold nanoparticles 2 AuNPs/CPE and platinum sheet; the middle is a miniature electrolytic cell; the bottom layer is a bottom electrode plate containing a carbon counter electrode and an Ag/AgCl reference electrode;
the concrete composition comprises:
a hole is formed in the middle of the lamination of the bottom electrode plate containing the carbon counter electrode and the Ag/AgCl reference electrode, the waterproof double-sided tape with the thickness of 1mm is laminated on the bottom electrode plate, and the counter electrode and the reference electrode on the bottom electrode plate penetrate out of the hole to form a miniature electrolytic cell; relatively stacking platinum sheet pore diameters with the same pore diameter on an electrolytic cell; after the sample solution is added into the electrolytic cell, the working electrode Co-MOF-NH is added 2 The AuNPs/CPE is covered on the platinum sheet to form a laminated electrochemical sensing device. The device is further used in conjunction with an electrochemical workstation for detection.
In one embodiment of the invention, the aperture of the holes in the waterproof double-sided tape is 6-10mm, and particularly 8mm is optional.
In one embodiment of the invention, co-MOF-NH 2 The preparation method of the AuNPs/CPE comprises the following steps:
(1) Dispersing cobalt nitrate hexahydrate and 2-amino terephthalic acid in DMF solution, uniformly mixing, and sealing for solvothermal reaction; after the reaction is finished, solid-liquid separation is carried out to collect solid, and the solid is washed and dried to obtain Co-MOF-NH 2 ；
(2) Pretreating carbon paper electrode CPE, and then placing in HAuCl 4 Electrodepositing the solution to obtain CPE deposited by gold nanoparticles, and recording the CPE as AuNPs/CPE; and then the step (1) is carried outCo-MOF-NH 2 Dispersing in a mixed solution of absolute ethanol and water to prepare Co-MOF-NH 2 Dispersion of Co-MOF-NH 2 The dispersion is dripped on AuNPs/CPE to obtain Co-MOF-NH 2 /AuNPs/CPE。
In one embodiment of the invention, the molar ratio of cobalt nitrate hexahydrate to 2-amino terephthalic acid in step (1) is 1:1.
In one embodiment of the present invention, the concentration of 2-amino terephthalic acid in DMF in step (1) is 0.02mmol/mL.
In one embodiment of the invention, the solvothermal reaction in step (1) is at 130℃for 18 hours.
In one embodiment of the present invention, step (1) is washed 2-3 times with washing DMF and absolute ethanol, respectively.
In one embodiment of the present invention, HAuCl in step (2) 4 The concentration of the solution was 0.1% w/v, g/mL.
In one embodiment of the invention, the electrodeposition conditions in step (2) are at-0.2V for 120s for deposition.
In one embodiment of the present invention, co-MOF-NH in step (2) 2 The concentration of the dispersion was 1mg/mL.
In one embodiment of the present invention, the volume ratio of absolute ethanol to water in the mixed solution of absolute ethanol and water in step (2) is 1:3.
In one embodiment of the present invention, 20. Mu.L of 1mg/mL Co-MOF-NH is used in step (2) 2 The dispersion (absolute ethanol: water=1:3) was applied drop-wise to AuNPs/CPE.
In one embodiment of the present invention, the process of pre-treating CPE in step (2) includes:
cutting the carbon cloth, and then respectively treating the cut carbon cloth with dilute nitric acid solution (HNO 3 ：H 2 O=1: 1) Ultrasonic washing in acetone, absolute ethyl alcohol and ultrapure water, and drying for standby.
In one embodiment of the invention, co-MOF-NH 2 The AuNPs/CPE is covered on the electrolyte tank, and the whole surface of the modification area needs to be covered with holes.
In one embodiment of the present invention, the stacked electrochemical detection sensor is used in the following manner: adding the sample solution into the electrolyte tank completely, adding Co-MOF-NH 2 and/AuNPs/CPE is covered on the electrolyte tank and is communicated with a three-electrode system, and an electric signal is obtained through detection.
The invention also provides a quantitative detection method for heavy metal Cd 2+ And Pb 2+ Comprises the following steps:
the sample is treated by buffer solution to obtain a series of standard sample solutions with known concentration, the standard sample solutions are taken to be fully filled in the electrolyte tank of the laminated electrochemical sensing device, and then Co-MOF-NH is carried out 2 The AuNPs/CPE is covered on the electrolyte tank and is communicated with a three-electrode system to carry out enrichment detection, thus obtaining a corresponding response current value I p The method comprises the steps of carrying out a first treatment on the surface of the Using the concentration of the standard sample solution and the response current value I thereof p And (5) performing linear correlation to construct a quantitative detection model.
In one embodiment of the invention, the buffer is a 0.1M HAc-NaAc buffer, pH 5.0.
In one embodiment of the invention, the enrichment detection voltage is-1.3V; the enrichment time was 60s.
In one embodiment of the present invention, the standard sample solution is added in an amount of 60 to 80. Mu.L.
The beneficial effects are that:
1. the carbon paper is selected as a working electrode to replace the traditional glassy carbon electrode, so that the laminated electrochemical sensor with a miniature electrolytic cell and a simple micro-field is constructed, as shown in figure 1.
2. The electrochemical effects of the different modified electrodes were compared by Cyclic Voltammetry (CV) and alternating impedance (EIS), and AuNPs and Co-MOF-NH were found 2 Has good synergy, improves the surface performance of the electrode and accelerates the electron transfer rate, as shown in figure 2.
3.Co-MOF-NH 2 The modification of (c) resulted in a 20% increase in the electrochemically active area of the AuNP/CP electrode compared to before modification, as shown in fig. 3.
4. Use of Differential Pulse Voltammetry (DPV) in combination with Anodic Stripping Voltammetry (ASV) for metal ionsAuNPs and Co-MOF-NH 2 Is obviously improved in Cd 2+ And Pb 2+ As shown in fig. 4.
5. The invention is used for electrochemical detection of Cd 2+ And Pb 2+ Oxidation peak current with Cd 2+ And Pb 2+ The concentration increases and increases. Cd (cadmium sulfide) 2+ The linear equation is I in the concentration range of 0.75-35 mug/L p ＝-3.1188C Cd(Ⅱ) +1.0193(R 2 ＝0.997)；Pb 2+ The linear equation is I in the concentration range of 0.5-20 mug/L p ＝-4.8506C Pb(Ⅱ) +0.8849(R 2 =0.994). Cd can be obtained by calculation 2+ And Pb 2+ The detection limits of (a) are 0.11. Mu.g/L and 0.07. Mu.g/L (S/N=3), respectively, as shown in FIG. 6.
Drawings
FIG. 1 construction of Co-MOF-NH based 2 Schematic flow diagram of a stacked electrochemical detection sensor of AuNPs/CPE.
FIG. 2 is a bare carbon paper (bare CPE), electrodeposited gold nanoparticle carbon paper (AuNPs/CPE) and further drop coated modified Co-MOF-NH 2 Is used as a working electrode at 0.1mM [ Fe (CN) 6 ] 3-/4- (A) cyclic voltammogram and (B) AC impedance curve in (containing 0.2M KCl) probe solution.
FIG. 3 shows (A) electrodeposited gold nanoparticle carbon paper (AuNPs/CPE) and (C) further drop coating of modified Co-MOF-NH 2 Is used as a working electrode at 0.1mM [ Fe (CN) 6 ] 3-/4- A cyclic voltammetric superposition curve (containing 0.2M KCl) with a scan rate of 10-200 mV/s in the probe solution; (B) Aunps/CP and (D) Co-MOF-NH 2 AuNPs/CPE redox peak current and scan rate 1/2 Linear relationship between the two.
FIG. 4 is a bare carbon paper (bare CP), electrodeposited gold nanoparticle carbon paper (AuNPs/CPE) and further drop coated modified Co-MOF-NH 2 Is used as a working electrode for 2.5 mug/L Cd 2+ And Pb 2+ And mixing standard solutions to detect differential pulse voltammograms.
Fig. 5 is a schematic flow chart of a sample detection using a stacked electrochemical detection sensor.
FIG. 6 shows (A) sensor versus gradient concentration Cd 2+ And Pb 2+ Mixing the oxidation peak response current and Cd of the differential pulse voltammogram (B) of the standard solution 2+ And Pb 2+ Relationship of concentration and linear equation.
FIG. 7 is an optimization of (A) pH, (B) enrichment potential, and (C) enrichment time.
FIG. 8 is a schematic diagram of interfering ion pairs 15 μg/L Pb 2+ And Cd 2+ Influence of the electrochemical sensor response of the mixed label solution.
FIG. 9 is Co-MOF-NH 2 Repeatability verification of/AuNPs/CPE.
FIG. 10 is a schematic representation of Co-MOF-NH 2 AuNP/CPE as working electrode, 2.5. Mu.g/L Cd in a three electrode solution system (calomel electrode as reference) and a layered device with a micro-cell, respectively 2+ And Pb 2+ And mixing standard solutions to detect differential pulse voltammograms.
Detailed Description
The invention relates to an instrument and equipment: CHI660C electrochemical workstation, saturated calomel electrode, platinum electrode, shanghai Chen Hua instruments company; KQ-100DB model numerical control ultrasonic cleaner, kunshan ultrasonic instruments Inc.
The invention relates to a reagent: cobalt nitrate hexahydrate (Co (NO) 3 ) 2 ·6H 2 O), sodium acetate, glacial acetic acid, sodium bicarbonate, sodium carbonate, sodium sulfate, silver nitrate, sodium chloride, ferric chloride, ferrous chloride, magnesium chloride, calcium chloride, zinc chloride, N-dimethyl sulfoxide (DMF), nitric acid, acetone, absolute ethanol, national medicine Shanghai test; cadmium chloride, lead chloride, copper chloride, mercury chloride, mikrin biol, inc (Shanghai, china); tetrachloroauric acid trihydrate (HAuCl) 4 ·3H 2 O, GR), shanghai taitan technologies, inc; 2-amino terephthalic acid (NH) 2 -H 2 BDC), beijing enokic technologies limited; ultrapure water.
Dongli carbon paper (TGP-H-60), shanghelsen electric; double-sided tape (1 mm thick), 3M company, usa; waterproof baking varnish sticker; customizing a screen printing electrode and a post technology; 3D printing die SimpNeed 3D technology; platinum sheet.
Example 1: working electrode preparation and construction of stacked electrochemical sensor
(1)Co-MOF-NH 2 Is synthesized by (a)
Co-MOF-NH 2 Synthesizing by a hydrothermal method: after 2mmol of cobalt nitrate hexahydrate and 2mmol of 2-amino terephthalic acid are dissolved in 100mL of DMF solution in an ultrasonic dispersion way, the solution is poured into a polytetrafluoroethylene reaction kettle and put into a stainless steel tube sleeve to be sealed, and the reaction is carried out for 18h at 130 ℃. After cooling to room temperature, washing Co-MOF-NH with DMF and absolute ethanol in sequence 2 3 times each, 10min at 10000rpm, the unreacted monomers were removed. Centrifuging, collecting precipitate, and drying at 60deg.C overnight to obtain Co-MOF-NH 2 。
(2)Co-MOF-NH 2 Preparation of AuNPs/CPE
Cutting 0.19mm thick carbon paper into 1.5X1 cm pieces 2 Size of the tablets in the presence of dilute nitric acid solution (HNO 3 ∶H 2 O=1:1), acetone, absolute ethanol, ultra-pure water for 30min each to remove surface impurities and activate, and then dried at 60 ℃ for standby. Cutting waterproof baking varnish decal to 2×1cm 2 The size is folded in half and 1X 1cm 2 One end of the carbon paper is perforated with a hole with the diameter of 8mm, and the sticker is folded and stuck on two sides of the carbon paper to prepare the carbon paper electrode. Placing a carbon paper electrode at 0.1% (w/v) HAuCl 4 In the aqueous solution (ensuring that the exposed carbon paper with the diameter of 8mm, namely the modification area, is partially completely immersed), the AuNPs are deposited under the three-electrode system at-0.2V for 120 s. And washing off redundant deposition solution on the surface of the electrode by ultrapure water, and drying by nitrogen. Subsequently, 20. Mu.L of 1mg/mL Co-MOF-NH 2 Dripping the dispersion (absolute ethanol: water=1:3) on a modification region with a carbon paper electrode diameter of 8mm, and drying at 60deg.C for 30min to obtain Co-MOF-NH 2 /AuNPs/CPE。
(3) Construction of stacked electrochemical detection sensor
1mm thick double-sided tape was cut into 1.2X1.2 cm pieces 2 Punching in the middle with 8mm punch, attaching one end to the bottom electrode sheet printed with counter electrode and AgCl reference electrode (the counter electrode and reference electrode penetrate out of the hole), and attaching the other end to platinum sheet (1.5X1 cm) with hole of 8mm diameter 2 ) To form a micro electrolyte bath; 60 mu LThe electrolyte tank is completely filled with the sample liquid, so that a solution passage communicated with the three electrodes is formed. The prepared Co-MOF-NH 2 the/AuNPs/CPE modification area is aligned with the electrolyte pool and covered on the top layer, and is communicated with a three-electrode system to form a sensing device for detection.
Characterization of electrochemical performance of the device:
the electrochemical performance of the modified electrode was characterized using Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). The CV method scanning range in potassium ferricyanide solution is-0.2-0.6V, and the scanning speed is 50mV/s. The Electrochemical Impedance (EIS) parameters were: the frequency is 0.01 Hz-100 kHz, and the signal amplitude is 5mV. The electrochemical detection adopts an Anodic Stripping Voltammetry (ASV), deposition of heavy metal ions to be detected is carried out for 60s at 1.30V, differential Pulse Voltammetry (DPV) curves are recorded within the range of-1.2 to-0.4V in 0.1M acetic acid-sodium acetate buffer solution with pH value of 5.0, and anode current value is read for Pb 2+ And Cd 2+ The measurement was performed.
As shown in FIG. 2A, fe on bare carbon paper 2+ /Fe 3+ Not significant, the redox peak potential difference (Δep) was 478mV. After electrodeposition of AuNPs, a pair of relatively symmetrical and pronounced redox peaks appear, with redox peak currents of 280.6 μa and 262.4 μa, respectively, and a redox peak potential difference (Δep) of 78mV. Co-MOF-NH modification 2 Thereafter, fe 2+ /Fe 3+ The oxidation-reduction peak currents of (a) were reduced to 224.3. Mu.A and 217.4. Mu.A, respectively, but were still Fe on bare carbon paper 2+ /Fe 3+ About 20 times the redox peak current value, and the redox peak potential difference (Δep) was 83mV. In addition, co-MOF-NH 2 The material produced redox peaks at 0.46V and 0.44V. The EIS curve results correspond to the CV curve (fig. 2B): carbon paper electrode charge transfer resistor (R after electrodeposition of AuNPs ct ) Reducing from 1600 omega to 50 omega, and further dripping and coating modified Co-MOF-NH 2 After that, R ct 55 omega. The above results demonstrate that electrodeposition of AuNPs improves the conductivity of carbon paper electrodes and accelerates electron transfer on the electrode surfaces; and, in the modification of Co-MOF-NH 2 The electrode still has excellent conductivity after that.
Next, CV method is used to scan the redox probe at different ratesThe electrochemically active area of the electrode was examined for each modification step (fig. 3). The oxidation-reduction peak current of the modified electrode increases linearly along with the increase of the sweeping speed within the range of 10-200 mV/s, and the response current value and v 1/2 Linear, indicating that the reaction process at the electrode surface is diffusion controlled. Redox peak current and v of AuNPs/CPE 1/2 The linear equation of (a) is respectively I pa (μA)＝711.13ν 1/2 +26.68(R 2 ＝0.999)，I pc (μA)＝-771.81ν 1/2 -25.74(R 2 ＝0.999)；Co-MOF-NH 2 Redox peak current vs. v of AuNPs/CPE 1/2 The linear equation of (a) is respectively I pa (μA)＝849.04ν 1/2 +8.80(R 2 ＝0.999)，I pc (μA)＝-932.28ν 1/2 –8.23(R 2 =0.999). Wherein I is pa Is an oxidation response current; i pc To restore the response current.
The electroactive area of the modified electrode was calculated according to the randes-sevick equation:
oxidation peak current I pa (A)＝268600n 2/3 AD 1/2 Cv 1/2
Wherein n is the electron transfer number of the redox reaction (n=1), and a is the electroactive area (cm 2 ) C is [ Fe (CN) 6 ] 3-/4- Concentration of solution (mol/cm) 3 ) D is the diffusion coefficient (7.60×10 -6 cm 2 S), V represents (V/s). Calculated from the equation, when Co-MOF-NH is modified 2 And then, the electroactive surface area of the electrode is improved by 20% compared with that before modification, which is beneficial to enrichment and reaction of the object to be detected on the surface of the electrode.
On a built laminated electrochemical sensor by utilizing a differential pulse voltammetry, the electrode is verified to be Cd after modifying materials 2+ And Pb 2+ The selectivity and sensitivity of the detection are improved (fig. 4). Adding Cd with the concentration of 2.5 mug/L into a sample cell 2+ And Pb 2+ Mixing standard solution, using bare carbon paper electrode, using Differential Pulse Voltammetry (DPV), -almost no Cd is observed in the range of 1.1-0.4V 2+ And Pb 2+ Is not limited, and the elution peak of (a) is not limited. Detection by AuNPs/CPE and Cd 2+ Is significantly increased in response peak current valueAs shown by-3.12. Mu.A, auNPs enhanced Cd 2+ Enrichment and Cd at electrode surface 2+ →Cd 0 Electron transfer of the process. By Co-MOF-NH 2 When detecting/AuNPs/CPE, cd 2+ And Pb 2+ The peak current values of the response of (C) are significantly increased to-4.12. Mu.A and-14.6. Mu.A, indicating Co-MOF-NH 2 Is Cd 2+ /Pb 2+ Enrichment and diffusion at the electrode surface provides more sites.
Example 2 detection of heavy metals Using stacked electrochemical detection apparatus
The detection process is shown in fig. 5.
The samples were diluted with 0.1M HAc-NaAc buffer (ph=5) to obtain a series of known cds 2+ And Pb 2+ Standard sample solution of concentration; adding standard sample liquid into electrolytic cell completely filled with sensor to form solution passage for connecting three electrodes, and adding Co-MOF-NH 2 The AuNPs/CPE electrode modification area is aligned with the electrolytic cell to cover the top layer, and is communicated with a three-electrode system for detection.
Cd by Anodic Stripping Voltammetry (ASV) 2+ And Pb 2+ And (3) detecting: first, the solution was maintained at a constant enrichment voltage of-1.3V for 60s, so that the Cd in the solution 2+ And Pb 2+ Enriching to the surface of the working electrode and reducing to Cd 0 And Pb 0 Scanning from negative potential to positive potential to enrich Cd on electrode 0 And Pb 0 The oxidation reaction is carried out to re-dissolve, and the corresponding response current value I is obtained after detection p . Respectively utilize Cd 2+ And Pb 2+ Concentration and corresponding response current value I p And (5) performing linear correlation to construct a quantitative model.
FIG. 6A shows the concentration of Cd of 0-35. Mu.g/L 2+ And Pb 2+ Stripping voltammogram of the assay performed by mixing the standards. 0.1M HAc-NaAc buffer (pH 5.0) was used as a blank for Cd detection using standard curve method according to the optimal detection conditions selected 2+ And Pb 2+ The linear range was measured. Along with, cd 2+ And Pb 2+ The increase in concentration forms an electric double layer structure between the solution and the metal, resulting in an increase in polarization potential and anodic passivation, resulting in two typesThe ion elution potential was positively shifted. As shown in FIG. 6B, cd 2+ The linear equation is I in the concentration range of 0.75-35 mug/L p ＝-3.1188C Cd(Ⅱ) +1.0193(R 2 ＝0.997)；Pb 2+ The linear equation is I in the concentration range of 0.5-20 mug/L p ＝-4.8506C Pb(Ⅱ) +0.8849(R 2 =0.994). Cd can be obtained by calculation 2+ And Pb 2 + The detection limit of (C) was 0.11. Mu.g/L and 0.07. Mu.g/L, respectively (S/N=3).
Example 3 detection Condition optimization
In the detection process, the pH of the buffer solution can influence the dissolution potential of the object to be detected, and the enrichment voltage and the enrichment time can influence the response current value, so that the three factors are required to be subjected to single-factor experiments to obtain the optimal detection condition.
Optimization was performed in the pH range of 3.0 to 6.0 (fig. 7A): when the pH is too low, system H + More active sites of electrode surface electricity are occupied, and the electrostatic effect is strong and Cd is resisted 2+ And Pb 2+ Near, the enrichment amount is small; with the increase of the pH value, protons in the solution are reduced, so that metal ions to be detected are more combined with active sites on the surface of the electrode, and enrichment detection of the metal ions is facilitated; at a pH greater than 5.5, the metal ions hydrolyze resulting in a decrease in the response current value.
The enrichment potential was optimized in the range of-1.1 to-1.5V (FIG. 7B), cd at-1.3V 2+ And Pb 2+ The enrichment effect of the ion-exchange membrane is best, and the hydrogen evolution reaction of the system is aggravated when the potential is negative, so that the response peak current value of the ion to be detected is reduced.
When the enrichment time is increased from 15s to 60s, cd 2+ And Pb 2+ The response current value of (C) gradually increases, and then reaches the plateau (fig. 7C).
In summary, pH 5.0, enrichment voltage-1.3V and enrichment time 60s were chosen as optimal detection conditions.
Example 4: anti-interference and repeatability test
To verify Co-MOF-NH 2 Detection of Pb by AuNPs/CPE 2+ And Cd 2+ Is 15 mug/L Pb 2+ And Cd 2+ Adding interfering ions with the concentration of 10 times: ag (silver) + 、Ca 2+ 、Cu 2+ 、Fe 3+ 、Fe 2+ 、Zn 2+ 、Mg 2+ 、Hg 2+ 、NO 3 - 、HCO 3 - 、CO 3 2- 、SO 4 2- . As shown in fig. 8. It can be found that when Cu removal is added 2+ Pb after the external interfering cation 2+ And Cd 2+ The stripping voltammetric currents of (a) are reduced to some extent, but the error is within an acceptable range (within 6%). Cu (Cu) 2+ Maximum test error of Pb 2+ And Cd 2+ The response current values of (a) are reduced by 49% and 31%, respectively, due to Cu 2+ Competing for Pb 2+ And Cd 2+ Binding sites on the electrode, cu can be inhibited by adding potassium ferrocyanide to the system 2+ Is to be used in the future). In interfering anions, HCO 3 - 、CO 3 2- 、SO 4 2- Easy mixing with Pb 2+ And Cd 2+ The insoluble or insoluble salt is formed by combination, so that detection errors are caused, but the anions are easy to remove by digestion of the sample, so that interference is not easy to generate.
To examine the repeatability of the device detection, 6 Co-MOF-NH were prepared using the same modification method 2 AuNPs/CPE and for 15. Mu.g/L Pb 2+ And Cd 2+ And (3) detecting the mixed standard solution of the above. As shown in FIG. 9, the obtained Cd 2+ The relative standard deviation of the response current value was 3.45%, pb 2+ 3.24% indicates good reproducibility of the sensor.
Example 5: actual sample detection and labeling recovery test
Pb in 8 samples of tea, fruit, vegetables, fish and shrimp and animal livers by the method of example 2 2+ And Cd 2 + Detection was performed and Pb was added at 5. Mu.g/L and 10. Mu.g/L, respectively 2+ And Cd 2+ And (5) calculating the adding standard recovery rate by mixing the standard. Pb 2+ Positive results were obtained with the exception of the pear and radish samples, with a labeling recovery of 92.6% -103.4% (n=5). Cd (cadmium sulfide) 2+ Positive results were obtained except for the tea and fruit samples, with a labeled recovery of 93.0% -102.3% (n=)5) (Table 1) shows that the electrochemical sensor is specific to Pb in an actual sample 2+ And Cd 2+ The detection is accurate and reliable.
TABLE 1 Pb in different food samples 2+ And Cd 2+ Concentration (mg/Kg), recovery (%) and RSD (%) (n=5)
Comparative example 1
A traditional common three-electrode system sensor with a non-laminated structure is constructed by taking a calomel electrode as a reference electrode:
by Co-MOF-NH 2 When detecting in a common three-electrode system with calomel electrode as reference electrode, using/AuNPs/CPE as working electrode, cd 2+ And Pb 2+ The peak current values of the response of (C) are-1.34. Mu.A and-5.03. Mu.A, respectively. While the detection was performed using the stacked electrochemical sensor with micro-cell of example 1, cd 2+ And Pb 2+ The peak current values of the response of (a) increased to-4.12. Mu.A and-14.6. Mu.A. As shown in fig. 10
Detecting Cd in a traditional three-electrode system by adopting a standard curve method 2+ And Pb 2+ The linear equation is I in the concentration range of 0.5-20 mug/L p ＝-0.4929C Cd(Ⅱ) +0.1077(R 2 =0.998) and I p ＝-2.1147C Pb(Ⅱ) +0.2567(R 2 =0.997). Cd can be obtained by calculation 2+ And Pb 2+ The detection limit of (a) is 0.25 mug/L and 0.15 mug/L (S/N=3), which is higher than Cd using the device of the invention 2+ And Pb 2+ The detection limit of (2) is 0.11. Mu.g/L and 0.07. Mu.g/L (S/N=3). Therefore, compared with the traditional three-electrode solution system, the device effectively improves the relative contact area of the solution to be tested and the working electrode, is beneficial to the enrichment of metal ions to be tested on the working electrode, simultaneously effectively saves the use amount of electrolyte and reduces the detection limit.
Claims (9)
1. A stacked electrochemical sensing device comprising three layers: co-MOF-NH of carbon paper working electrode with top layer modified by cobalt amide-based metal organic framework material and electrodeposited with gold nanoparticles 2 AuNPs/CPE and platinum sheet; the middle is a miniature electrolytic cell; the bottom layer is a bottom electrode plate containing a carbon counter electrode and an Ag/AgCl reference electrode;
the concrete composition comprises: a hole is formed in the middle of the lamination of the bottom electrode plate containing the carbon counter electrode and the Ag/AgCl reference electrode, the waterproof double-sided tape with the thickness of 1mm is laminated on the bottom electrode plate, and the counter electrode and the reference electrode on the bottom electrode plate penetrate out of the hole to form a miniature electrolytic cell; relatively stacking platinum sheet pore diameters with the same pore diameter on an electrolytic cell; after the sample solution is added into the electrolytic cell, the working electrode Co-MOF-NH is added 2 The AuNPs/CPE is covered on the platinum sheet to form a laminated electrochemical sensing device;
the cobalt amide-based metal organic framework material modified carbon paper electrode Co-MOF-NH with electrodeposited gold nanoparticles 2 The preparation method of the AuNPs/CPE comprises the following steps:
(1) Dispersing cobalt nitrate hexahydrate and 2-amino terephthalic acid in DMF solution, uniformly mixing, and sealing for solvothermal reaction; after the reaction is finished, solid-liquid separation is carried out to collect solid, and the solid is washed and dried to obtain Co-MOF-NH 2 ；
(2) Pretreating carbon paper electrode, and then placing in HAuCl 4 Electrodepositing the solution to obtain a CP electrode deposited by gold nano particles, which is marked as AuNPs/CPE; then the Co-MOF-NH obtained in the step (1) is processed 2 Dispersing in a mixed solution of absolute ethanol and water to prepare Co-MOF-NH 2 Dispersion of Co-MOF-NH 2 The dispersion is dripped on AuNPs/CPE to obtain Co-MOF-NH 2 /AuNPs/CPE。
2. The stacked electrochemical sensor device of claim 1 wherein the molar ratio of cobalt nitrate hexahydrate to 2-amino terephthalic acid in step (1) is 1:1.
3. The stacked electrochemical sensor device of claim 1 wherein the concentration of 2-aminoterephthalic acid in DMF in step (1) is 0.02mmol/mL.
4. The stacked electrochemical sensor device of claim 1 wherein the solvothermal reaction in step (1) is at a temperature of 130 ℃ for a period of 18 hours.
5. The stacked electrochemical sensor device of claim 1, wherein the conditions for electrodeposition in step (2) are-0.2V for 120s for deposition.
6. The stacked electrochemical sensor device of any one of claims 1-5, wherein Co-MOF-NH in step (2) 2 The concentration of the dispersion was 1mg/mL.
7. Quantitative detection of heavy metal Cd based on laminated electrochemical sensing device as claimed in any one of claims 1-6 2+ Or Pb 2+ Is characterized by comprising the following steps:
treating a sample with a buffer solution to obtain a series of standard sample solutions with known concentrations, completely filling the standard sample solutions with the electrolytic cells of the laminated electrochemical sensing device according to any one of claims 1 to 6, and then adding Co-MOF-NH 2 The AuNPs/CPE is covered on the electrolyte tank and is communicated with a three-electrode system to carry out enrichment detection, thus obtaining a corresponding response current value I p The method comprises the steps of carrying out a first treatment on the surface of the Using the concentration of the standard sample solution and the response current value I thereof p And (5) performing linear correlation to construct a quantitative detection model.
8. The method of claim 7, wherein the buffer is 0.1M HAc-NaAc buffer, and the pH is 5.0.
9. The method of claim 7, wherein the enrichment detection voltage is-1.3V; the enrichment time was 60s.
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