CN115096969A - Cadmium (II) ion detection method based on composite material modified electrode and application - Google Patents
Cadmium (II) ion detection method based on composite material modified electrode and application Download PDFInfo
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Abstract
The invention discloses a cadmium (II) ion detection method based on a composite material modified electrode and application thereof, belonging to the technical field of water quality detection. The invention prepares polyaniline-coated graphite-phase carbon nitride (PANI @ g-C) 3 N 4 ) The composite is used for modifying a Glassy Carbon Electrode (GCE) to prepare PANI @ g-C 3 N 4 @ GCE, PANI @ g-C obtained 3 N 4 @ GCE is used as a working electrode and is used for detecting cadmium (II) ions in water environment; compared with the prior design, the PANI @ g-C provided by the invention 3 N 4 The @ GCE has a lower detection limit and a wider linear range, and has better anti-interference performance, reproducibility and stability; the method is used for detecting an actual water sample, and has the advantages of small relative standard deviation, accurate measurement and high reliability; also based on PANI @ g-C 3 N 4 @ GCE proposes a componentized sensor, the design volume of which is compared with that of a conventional systemThe three-electrode system has the advantages of being small, high in integration degree, convenient to carry and use, capable of effectively solving the problems that a three-electrode system is easy to collide with a wall and mutually collide, short circuit is caused, and an electric wire is easy to wind, and wide in application range.
Description
Technical Field
The invention relates to the technical field of water body detection, in particular to a cadmium (II) ion detection method based on a composite material modified electrode and application thereof.
Background
In recent years, with the rapid development of society, heavy metal pollution in water environment also becomes a global problem, and heavy metal is toxic to organisms and can seriously harm the health of human bodies even if the concentration of heavy metal is very low. Therefore, it is necessary to find reliable and sensitive substances and methods for detecting heavy metals in water environments.
Cadmium, heavy nonferrous metal elements, cadmium and cadmium compounds are one of toxic and harmful water pollutant lists, cadmium is high in toxicity, and cadmium is listed as a human carcinogen by international cancer research institution in 1993. .
At present, the determination of cadmium ions in water environment in the market is usually realized by an analytical instrument in a chemical laboratory, and although the method can obtain more accurate measurement results, the operation is complex and the use cost is higher. Therefore, the electrochemical sensor based on the electrochemical workstation is produced, compared with the traditional laboratory analysis instrument, the electrochemical workstation has the advantages of small volume, high speed and accuracy in detection and capability of being used for field detection, but the prior electrochemical detection generally adopts a three-electrode system, different electrodes are required to be respectively placed into containers such as beakers and the like of substances to be detected in the detection process, each electrode is easy to touch the wall or cause short circuit in the test process, and more troubles and inconvenience are caused to a user in the actual field operation. In order to solve the problems, the invention provides a cadmium (II) ion detection method based on a composite material modified electrode and a device sensor matched with the method, which can more conveniently and quickly complete the determination of cadmium (II) ions in a water environment.
Disclosure of Invention
The invention aims to provide a method for detecting cadmium (II) ions in a water environment based on a composite material modified electrode, and device design and application in a sensor preparation process, which are used for solving the problems of complex operation and inconvenient use of the existing determination method and the existing determination device in the background art.
In order to achieve the purpose, the invention adopts the following technical scheme:
the cadmium (II) ion detection method based on the composite material modified electrode specifically comprises the following steps:
s1, pretreating a Glassy Carbon Electrode (GCE): polishing the bare Glassy Carbon Electrode (GCE), polishing the surface of the bare Glassy Carbon Electrode (GCE) with the diameter of 2-5 mm to a mirror surface, and storing in a vacuum box for later use;
s2 preparation of PANI @ g-C 3 N 4 The compound is as follows: dispersing the prepared graphite-phase carbon nitride in hydrochloric acid, stirring, slowly dropwise adding aniline during stirring, then adding ammonium persulfate, stirring, washing and removing impurities to obtain the polyaniline-coated graphite-phase carbon nitride composite material, namely PANI @ g-C 3 N 4 A complex;
s3 preparation of PANI @ g-C 3 N 4 @ GCE: the PANI @ g-C prepared in S2 is added 3 N 4 Dripping the composite on the surface of a Glassy Carbon Electrode (GCE) pretreated in S1, drying under infrared light or naturally airing to obtain PANI @ g-C 3 N 4 @GCE；
S4, determination of cadmium (II) ion and PANI @ g-C 3 N 4 @ GCE interface characterization: the PANI @ g-C prepared in S3 3 N 4 @ GCE is used as a working electrode, and cadmium (II) ions in a solution to be detected are detected by adopting an anodic stripping voltammetry (DPASV); after the measurement is completed, the PANI @ g-C 3 N 4 The interface characterization is carried out by @ GCE, and the effect of the modified electrode is proved;
s5, optimizing experimental conditions and determining optimal experimental parameters: a control experiment is designed by combining the operation in S4, and the PANI @ g-C in the experiment is measured on cadmium (II) ions by adopting a controlled variable method 3 N 4 Optimizing the compound modification amount, the enrichment potential, the enrichment time and the pH value of the solution to determine a group of optimal experimental parameters;
S6、PANI@g-C 3 N 4 the testing effect of @ GCE cadmium (II) ion is verified: based on the ability to make PANI @ g-C obtained in S5 3 N 4 Under the experimental condition that the @ GCE performance reaches the optimum, the following steps are carried outPANI@g-C 3 N 4 @ GCE as a working electrode, and measuring cadmium (II) ions in tap water and underground water by adopting anodic stripping voltammetry (DPASV); after the determination is finished, the concentration of the cadmium (II) ions in the solution is calculated according to a current-concentration linear equation, the standard recovery rate and the standard deviation coefficient of the cadmium (II) ions are further calculated by combining the obtained concentration data, and the PANI @ g-C is verified 3 N 4 The reliability of @ GCE in cadmium (II) ion determination in an actual water environment.
Preferably, the pretreatment operation of the glassy carbon electrode in S1 specifically includes the following steps:
a1, respectively carrying out ultrasonic treatment on a bare Glass Carbon Electrode (GCE) with the diameter of 2-5 mm in an ethanol solution and deionized water for 2-5 minutes;
a2, using coarse grain Al with diameter of 0.2-0.5 μm 2 O 3 Polishing powder and fine grain diameter Al with the diameter of 30-70 nm 2 O 3 Polishing the bare Glass Carbon Electrode (GCE) treated in A1 by using polishing powder until the polished bare glass carbon electrode is a mirror surface, and then washing the mirror surface by using deionized water;
a3, sequentially carrying out ultrasonic treatment on the washed naked GCE in deionized water, ethanol and deionized water for 5 minutes, airing, and placing in a vacuum box for later use.
Preferably, the PANI @ g-C mentioned in said S2 3 N 4 The preparation of the compound specifically comprises the following steps:
b1, dispersing the prepared graphite-phase carbon nitride in 200-400 mu g in hydrochloric acid, and carrying out ultrasonic treatment in an ultrasonic cleaning machine for 0.5-1.5 hours;
b2, stirring the graphite-phase carbon nitride solution treated in the B1 by using a magnetic stirrer, and slowly dripping 20-40 mu L of aniline in the stirring process;
b3, stirring for 20-30 minutes, adding 0.100-0.200 g of sodium persulfate into the solution, and then continuously stirring for 10-15 hours;
b4, after stirring, respectively washing with ethanol and deionized water for 3 times to remove oligomers, and finally obtaining the graphite-phase carbon nitride composite material comprising polyaniline, namely PANI @ g-C 3 N 4 And (c) a complex.
Preferably, said pair PANI @ gC mentioned in S4 3 N 4 The interface characterization was performed at @ GCE, and specifically included morphology observation by SEM, hydrophilicity analysis by CA, conductivity analysis by tafel, and elemental composition, and structure analysis by XRD and FTIR.
The invention further provides PANI @ g-C 3 N 4 Application of @ GCE in preparation of cadmium (II) ion sensors in water environment.
The cadmium (II) ion sensor based on the composite material modified electrode comprises a wire storage bridge, an electrode fixing device and a sample cell, wherein the top end of the wire storage bridge is spirally connected with a terminal, the electrode fixing device comprises a connecting pipe, the top end and the bottom end of the connecting pipe are both fixedly connected with threaded pipes, the connecting pipe is spirally and fixedly connected with one end, far away from the terminal, of the wire storage bridge through the threaded pipe at the top end, and the connecting pipe is fixedly connected with the top spiral of the sample cell through the threaded pipe at the bottom end; the connecting pipe is characterized in that a circular fixing block is clamped inside the connecting pipe, three fixing holes are formed in the circular fixing block, and a silver/silver chloride electrode, a platinum wire electrode and a replaceable glassy carbon electrode are respectively inserted into the three fixing holes.
Preferably, the wire storage bridge is made of polytetrafluoroethylene materials and used for placing a wire harness connected with the electrode; the terminal is made of stainless steel materials and used for concentrating and fixing the wire harnesses in the wire storage bridge and realizing connection with an external workstation; the sample cell is made of transparent polycarbonate materials and is used for containing a sample to be detected.
Preferably, the replaceable glassy carbon electrode adopts PANI @ g-C 3 N 4 @ GCE for determination of cadmium (II) ions in a sample to be detected.
Compared with the prior art, the invention provides a cadmium (II) ion detection method based on a composite material modified electrode and application thereof, and the method has the following beneficial effects:
(1) the detection method provided by the invention is implemented by PANI @ g-C 3 N 4 GCE is modified by the compound to prepare PANI @ g-C 3 N 4 @ GCE; compared with the GCE modified by common composite materials on the market, the surface area is increased, the active sites for reaction are increased, the conductivity is enhanced, the hydrophilicity is improved to a certain extent, and the improvement of oxidation peak current is facilitated when the concentration of cadmium (II) ions is detected by an electrochemical method; in addition, compared with electrodes prepared in other documents, the PANI @ g-C prepared by the invention 3 N 4 The @ GCE has a lower detection limit and a wider linear range, and has better anti-interference performance, reproducibility and stability; the method is used for detecting the actual water sample, and has the advantages of small relative standard deviation, accurate measurement and high reliability.
(2) The invention also provides the compound of the formula and PANI @ g-C 3 N 4 Compared with a common electrochemical workstation in the market, the electrochemical sensor with the devices matched with the @ GCE is smaller in size, more convenient to carry and use, and capable of effectively solving the problems that a three-electrode system detection product is easy to touch a wall, collide with each other, cause short circuit and easily wind wires during detection; in addition, the GCE in the sensor provided by the invention adopts a replaceable design, and when the sensor is used for measuring cadmium (II) ions in a water environment, the replaceable glassy carbon electrode adopts PANI @ g-C 3 N 4 In the same way, in the actual use process, the replaceable glassy carbon electrode can be replaced by other working electrodes required by the determination of corresponding heavy metal ions according to the actual detection requirement, and the sensor provided by the invention has wider application range by utilizing the design.
Drawings
FIG. 1 shows PANI @ g-C in example 1 of the present invention 3 N 4 @ GCE schematic diagram for detection of cadmium ions;
FIG. 2 shows (AD) PANI, (BE) g-C in example 1 of the present invention 3 N 4 、(CF)PANI@g-C 3 N 4 Surface SEM image of (a);
FIG. 3 is a schematic view showing the change in contact angle between front and rear electrodes after modification in example 1 of the present invention, wherein (A) represents GCE; (B) denotes g-C 3 N 4 @ GCE; (C) represents PANI @ g-C 3 N 4 @GCE；
FIG. 4 is a schematic view of Tafel curves of different electrodes in example 1 of the present invention;
FIG. 5 is an XRD and FTIR patterns for example 1 of the present invention, wherein FIG. 4(A) shows PANI, g-C 3 N 4 、PANI@g-C 3 N 4 XRD pattern of (a); FIG. 4(B) shows PANI and g-C 3 N 4 、PANI@g-C 3 FTIR plot of N;
FIG. 6 shows PANI @ g-C in example 1 of the present invention 3 N 4 A load amount of (a);
FIG. 7 is a graph of an optimized DPASV plot and a plot of the dissolution peak to peak current for the enrichment potential of example 1 of the present invention;
FIG. 8 is a graph of the optimized DPASV profile and the plot of the peak current of the dissolution peaks for the enrichment time in example 1 of the present invention;
FIG. 9 is a DPASV graph and a histogram of dissolution peak current as a function of solution pH for example 2 of the present invention;
FIG. 10 is a graph of cyclic voltammograms and impedances according to example 2 of the present invention, in which FIG. 10(A) shows graphs of CV curves of different electrodes; FIG. 10(B) shows EIS diagrams of different electrodes;
FIG. 11 is a schematic view showing the linear range and detection limit of detection in example 3 of the present invention, in which FIG. 11(A) shows PANI @ g-C 3 N 4 @ GCE DPASV plots for detection of cadmium (II) ions at different concentrations; FIG. 11(B) shows PANI @ g-C 3 N 4 The @ GCE detects a current-concentration linear relation graph at different cadmium (II) ion concentrations;
FIG. 12 is a diagram showing the results of the anti-interference test in example 4 of the present invention;
FIG. 13 shows PANI @ g-C in example 5 of the present invention 3 N 4 Reproducibility and stability profiles of @ GCE;
FIG. 14 is a schematic structural diagram of a cadmium (II) ion sensor based on a composite material modified electrode according to the present invention;
FIG. 15 is an exploded view of a cadmium (II) ion sensor based on a composite material modified electrode according to the present invention;
fig. 16 is a schematic structural diagram of an electrode fixing device of a cadmium (II) ion sensor based on a composite material modified electrode according to the present invention.
The reference numbers in the figures illustrate:
1. a wire storage bridge frame; 2. an electrode fixing device; 201. a connecting pipe; 202. a round fixed block; 203. a fixing hole; 204. a silver/silver chloride electrode; 205. a platinum wire electrode; 206. a replaceable glassy carbon electrode; 3. a sample cell; 4. a terminal block.
Detailed Description
The invention is further described below in conjunction with specific embodiments, and the advantages and features of the invention will become more apparent as the description proceeds. These examples are illustrative only and do not limit the scope of the present invention in any way. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention, and that such changes and modifications may be made without departing from the spirit and scope of the invention.
It is emphasized that, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods, devices, and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods, devices, and materials are now described.
Example 1:
referring to fig. 1-9, the method for detecting cadmium (II) ions based on the composite material modified electrode specifically includes the following steps:
s1, pretreating a Glassy Carbon Electrode (GCE): respectively carrying out ultrasonic treatment on the naked GCE with the diameter of 3mm in an ethanol solution and deionized water for 3 minutes; then, coarse-grain-size Al having a diameter of 0.3 μm was used 2 O 3 Polishing powder and fine grain diameter Al with diameter of 50nm 2 O 3 Polishing the naked GCE by using polishing powder until the naked GCE is polished to a mirror surface, and then washing the mirror surface clean by using deionized water; finally, the cleaned naked GCE is sequentially subjected to ultrasonic treatment in deionized water, ethanol and deionized water for 5 minutes respectively, and the naked GCE is placed in a vacuum box for standby after being dried.
S2 preparation of PANI @ g-C 3 N 4 The compound is as follows: mixing the prepared graphite 300 mugDispersing phase carbon nitride in hydrochloric acid, and carrying out ultrasonic treatment in an ultrasonic cleaning machine for 1 hour; then stirring the graphite phase carbon nitride solution treated in the B1 by using a magnetic stirrer, and slowly dripping 30 mu L of aniline in the stirring process; after stirring for 30 minutes, 0.114g of sodium persulfate was added to the solution, followed by further stirring for 12 hours; after stirring is finished, washing for 3 times by using ethanol and deionized water respectively, removing oligomers, and finally obtaining the graphite-phase carbon nitride composite material comprising polyaniline, namely PANI @ g-C 3 N 4 And (c) a complex.
S3 preparation of PANI @ g-C 3 N 4 @ GCE: the PANI @ g-C prepared in S2 is added 3 N 4 Dripping the compound on the surface of GCE pretreated in S1, and drying under infrared light or naturally airing to obtain PANI @ g-C 3 N 4 @GCE。
S4, determination of cadmium (II) ion and PANI @ g-C 3 N 4 @ CE interface characterization: the PANI @ g-C prepared in S3 is added 3 N 4 @ GCE is used as a working electrode, cadmium (II) ions in a solution to be detected are measured by adopting anodic stripping voltammetry (DPASV), and the specific flow is shown in figure 1; after the measurement is completed, the PANI @ g-C 3 N 4 The interface characterization of @ GCE specifically comprises the steps of carrying out morphology observation through SEM, carrying out hydrophilicity analysis through CA, carrying out conductivity analysis through Tafel and carrying out element composition, composition and structure analysis through XRD and FTIR, and the specific characterization contents prove the effects of the modified electrode;
4.1SEM characterization
SEM is a method of scanning the surface of a sample by a focused electron beam to produce an image of the surface of the sample. The appearance, size and distribution of the sample can be visually shown. Prepared PANI, g-C 3 N 4 、PANI@g-C 3 N 4 The topography of (a) is shown in fig. 2.
Referring to FIG. 1, wherein A, D are 2 μm and 200nm electron micrographs of polyaniline, respectively, it can be seen that the PANI prepared by the experiment is in a linear structure, B, E are g-C 3 N 4 The electron microscope images of 1 μm and 100nm show that the graphite phase carbon nitride prepared by the experiment is in a blocky structure, and the side surface is in a laminated structure; C. f is respectivelyPANI@g-C 3 N 4 2 μm, 200nm, it can be seen that the linear PANI is wrapped in the massive g-C 3 N 4 As shown above, the successful preparation of PANI @ g-C is also demonstrated 3 N 4 A composite material. Effectively increasing the specific surface area and adsorbing more cadmium (II).
4.2 contact Angle characterisation
The contact angle is that a drop of deionized water is dropped on the surface of a solid, so that a gas-liquid-solid three-phase interface is formed, and the included angle of tangent lines of the interfaces between every two of the gas, the liquid and the solid is the contact angle. The size of the contact angle reflects the wettability of the solid by the liquid, i.e., the hydrophilicity and hydrophobicity of the solid surface. The change in contact angle before and after electrode modification may indicate whether the electrode is in better contact with the solution. Contact angle characterization was therefore performed on the electrodes before and after modification. The contact angle changes before and after electrode modification are shown in FIG. 3.
Referring to fig. 3, wherein fig. 3(a) is the contact angle of bare GCE, fig. 3(B) is the contact angle of modified graphite-phase carbon nitride, and fig. 3(C) is the contact angle of polyaniline and graphite-phase carbon nitride composite modified electrode, the magnitude of the contact angle is used to illustrate the change of hydrophilicity. The smaller the contact angle, the better the hydrophilicity. As can be seen from fig. 3(a), the contact angle (θ) of the bare GCE is large (72.77 °), and the hydrophilicity is poor, which affects the wettability between the solution and the electrode: as can be seen from fig. 3(B), the contact angle (θ) of the graphite-phase carbon nitride-modified electrode is small (48.42 °); FIG. 3(C) shows PANI @ g-C 3 N 4 The contact angle of the electrode after the composite modification of the electrode (θ: 32.14 °) was the smallest, the hydrophilicity was the best, and the wettability between the solution and the electrode was also the best. The electrode modified by the polyaniline-coated graphite-phase carbon nitride is well improved in hydrophilicity, and the wettability of the electrode is greatly improved.
4.3 Tafel Curve characterization
By PANI @ g-C 3 N 4 The modified electrode can effectively enhance the adsorption capacity of the electrode, improve the electronic conductivity of the electrode, and obtain the current density passing through the surface of the electrode through calculation of a tafel curve, so that a tafel experiment is carried out, as shown in fig. 4.
Referring to the contents shown in fig. 4, the data is analyzed according to the relation in the tafel curve, so as to obtain: the passing current value of the bare GCE before modification is 4.56 muA, and the reaction area of the electrode is 0.3cm 2 So that the current density was 15.2. mu.A/cm 2 (ii) a Modified by PANI @ g-C 3 N 4 The electrode passing current value was 9.39. mu.A, and the reaction area of the electrode was 0.3cm 2 So that the current density was 31.3. mu.A/cm 2 (ii) a After treatment, the current density is improved by about 2 times. By applying pair PANI @ g-C 3 N 4 Improvement of electron transfer on the surface of @ GCE electrode can improve the sensitivity of the electrode and enhance PANI @ g-C 3 N 4 The response speed of the @ GCE electrode.
4.4 characterization by X-ray diffraction (XRD) and Infrared Spectroscopy (FTIR)
The XRD technique is a study of X-ray diffraction of a substance, i.e. an electromagnetic wave with a shorter wavelength, which reacts with atoms in a crystal to form a diffraction pattern. Information about the molecular structure can be obtained by calculation. The FTIR technique is to analyze the molecular structure and chemical composition of materials by absorption of infrared light of different wavelengths. To further prove the successful preparation of PANI @ g-C 3 N 4 Composite, for prepared PANI, g-C 3 N 4 、PANI@g-C 3 N 4 The composite of (a) was characterized by XRD and FTIR as shown in fig. 5.
In FIG. 5(A), PANI and g-C are represented from bottom to top, respectively 3 N 4 、PANI@g-C 3 N 4 XRD patterns of (A) and (B) are combined according to related data, and g-C is compared 3 N 4 ，PANI，PANI@g-C 3 N 4 The XRD pattern of the compound can be seen that PANI @ g-C 3 N 4 Exhibit PANI and g-C 3 N 4 All characteristic peaks. The diffraction peaks at 21.1 ° and 25.6 ° were assigned to the (020) and (200) crystallographic planes of the carborundum salt (ES) form of PANI; the peak at 27.21 ℃ is attributed to g-C 3 N 4 The interfacial stacking peak of the conjugated aromatic system (2). This also indicates the successful preparation of PANI @ g-C 3 N 4 And (c) a complex.
As shown in FIG. 5(B), the top-to-bottom lines represent PANI and g-C, respectively 3 N 4 、PANI@g-C 3 N 4 FTIR spectrum of the complex, 807cm -1 The absorption peak is the out-of-plane stretching vibration of the C-N ring; at 1118cm -1 、1484cm -1 Is due to the stretching vibration of C-H, C ═ C; 1250-1639 cm -1 In the range of C-N aromatic ring stretching vibration; it can be seen that PANI @ g-C 3 N 4 The spectrum of the composite material comprises PANI and g-C 3 N 4 C-H stretching vibration in the combined PANI, moving to long wave direction, g-C 3 N 4 The vibration peak of the C-N ring in (A) becomes strong, indicating that g-C 3 N 4 There is an interaction with PANI.
S5, optimizing experimental conditions and determining optimal experimental parameters: a control experiment is designed by combining the operation in S4, and the PANI @ g-C in the experiment is measured on cadmium (II) ions by adopting a controlled variable method 3 N 4 Optimizing the compound modification amount, the enrichment potential, the enrichment time and the pH value of the solution, and determining a group of optimal experimental parameters, which specifically comprises the following contents:
5.1PANI@g-C 3 N 4 optimization of modification amounts
The amount of modification is such that the PANI @ g-C is affected 3 N 4 An important condition for detecting cadmium ions in water by the electrode is that the modification amount of the electrode is optimized, and the following figure 6 shows.
Referring to fig. 6, it can be seen from fig. 6 that the optimal modification amount is 8 μ L, and when the modification amount is increased again, the oxidation peak current of cadmium (II) ions does not increase any more, but rather shows a decreasing trend, which is mainly because the modification amount affects the active area of the electrode, the larger the active area of the electrode is, the higher the electrostatic adsorption capacity is, the peak current is increased, and as the modification amount is increased again, the too much load is added, so that PANI @ g-C on the surface of the electrode is formed 3 N 4 The film is too thick, so that the resistance of electron transfer is large; thus, the optimum amount of modification was determined to be 8. mu.L.
5.2 optimization of the enrichment potential
According to the principle of electrochemical deposition, the embodiment uses overpotential deposition, that is, when it is desired to reduce and enrich a certain metal element on the surface of an electrode, the deposition potential is set to be less than the oxidation potential of the metal. In the embodiment, experiments are carried out on the change condition of the oxidation peak current of the cadmium ions when the enrichment potential is-0.9-1.4 v, and the change condition of the oxidation peak current of the cadmium ions (II) is shown in FIG. 7.
As can be seen from fig. 7, the peak current value gradually increases when the enrichment potential of cadmium (II) ions is from-0.9V to-1.2V, reaches the maximum value when the enrichment potential is set to-1.2V, but decreases when the enrichment potential continues to increase negatively. This is because a more negative potential results in better enrichment of cadmium (II) ions to the electrode surface. However, when the enrichment potential exceeds-1.2V, hydrogen evolution reaction can occur on the surface of the electrode, so that the dissolution peak current of cadmium is reduced. The optimal enrichment potential of cadmium (II) ions is determined to be-1.2V by comprehensive consideration.
5.3 optimization of enrichment time
The enrichment time is very important to the effect of the electrode, and this example performed experiments on the change of the oxidation peak current of cadmium (II) ions when the enrichment times were 60s, 120s, 180s, 240s, 300s, and 360s, respectively, as shown in fig. 8.
As can be seen from FIG. 8, when the deposition time of the cadmium (II) ion solution is from 60 to 240s, the dissolution peak value of the cadmium (II) ion is continuously increased, and when the enrichment time of the detection process is continuously increased, the dissolution peak value shows a gentle trend. This is because the longer the enrichment time of cadmium (II) ions, the more saturated the cadmium that is enriched on the electrode, and the flatter the current response. And comprehensively considering the detection time and the cadmium dissolution peak current, and determining the optimal enrichment time to be 240 s.
5.4 optimization of solution pH
The pH of the solution is also an important parameter affecting the detection effect of the electrode, so that the optimization experiment of the pH of the solution is carried out, as shown in FIG. 9.
Referring to fig. 9, the experiment explored the current response at different pH, pH range 3.5-6.0. At a solution pH of 5, the value of the elution peak current of cadmium (II) ions reached an optimum value, which wasIs due to the lower pH, PANI @ g-C 3 N 4 The @ GCE can react with hydrogen ions in water to cause PANI @ g-C 3 N 4 The enrichment amount of cadmium (II) ions on the surface of @ GCE is reduced, so that the dissolution peak current is reduced; when the pH value of the solution is too high, cadmium (II) is easy to undergo hydrolysis reaction to form precipitate, and the PANI @ g-C is influenced finally 3 N 4 Detection Effect of @ GCE. Thus, the optimum pH of the cadmium (II) ion solution was determined to be 5.0.
S6、PANI@g-C 3 N 4 The testing effect of @ GCE cadmium (II) ion is verified: based on the ability to make PANI @ g-C obtained in S5 3 N 4 Under the experimental condition that the @ GCE performance reaches the optimum, PANI @ g-C 3 N 4 @ GCE as a working electrode, and measuring cadmium (II) ions in tap water and underground water by adopting anodic stripping voltammetry (DPASV); after the determination is finished, the concentration of the cadmium (II) ions in the solution is calculated according to a current-concentration linear equation, the standard recovery rate and the standard deviation coefficient of the cadmium (II) ions are further calculated by combining the obtained concentration data, and the PANI @ g-C is verified 3 N 4 The reliability of the @ GCE in the determination of cadmium (II) ions in an actual water environment specifically comprises the following steps: selecting three concentrations with different sizes, namely 10 mug/L, 20 mug/L and 40 mug/L respectively, preparing cadmium (II) ion solutions by using underground water and tap water respectively to carry out DPASV measurement on the cadmium (II) ion solutions, calculating the concentration of the cadmium (II) ions in the solutions according to a current-concentration linear equation, and measuring the content of the cadmium (II) ions in the underground water and the tap water as shown in Table 1.
TABLE 1 PANI @ g-C 3 N 4 @ GCE detection of relative deviation and recovery rate of cadmium (II) ions in actual sample
The data in the table 1 are combined for calculation, the standard addition recovery rate is close to 91.75% -105.88%, and the RSD is close to<4.07 percent. Good recovery rate and RSD (reduced pressure swing chromatography) confirm that the PANI @ g-C prepared in experiment 3 N 4 The @ GCE has certain reliability in the application of actual water samples.
The invention further relates toPut forward PANI @ g-C 3 N 4 Application of @ GCE in preparation of cadmium (II) ion sensors in water environment.
Referring to fig. 14-16, the cadmium II ion sensor based on the composite material modified electrode includes a wire storage bridge 1, an electrode fixing device 2 and a sample cell 3, wherein a terminal 4 is spirally connected to a top end of the wire storage bridge 1, the electrode fixing device 2 includes a connecting tube 201, both a top end and a bottom end of the connecting tube 201 are fixedly connected with threaded tubes, the connecting tube 201 is fixedly connected with a end of the wire storage bridge 1 far from the terminal 4 through the top threaded tube, and the connecting tube 201 is fixedly connected with a top spiral of the sample cell 3 through the bottom threaded tube; a circular fixing block 202 is clamped inside the connecting pipe 201, three fixing holes 203 are formed in the circular fixing block 202, and a silver/silver chloride electrode 204, a platinum wire electrode 205 and a replaceable glassy carbon electrode 206 are respectively inserted into the three fixing holes 203.
The wire storage bridge frame 1 is made of polytetrafluoroethylene materials and is used for placing a wire harness connected with the electrodes; the terminal 4 is made of stainless steel materials and is used for concentrating and fixing the wire harnesses in the wire storage bridge frame 1 and realizing connection with an external workstation; the sample cell is made of transparent polycarbonate material and is used for containing a sample to be detected.
The replaceable glassy carbon electrode 206 adopts PANI @ g-C 3 N 4 @ GCE for determination of cadmium (II) ions in a sample to be detected.
The invention provides the compound with PANI @ g-C 3 N 4 Compared with a common electrochemical workstation in the market, the electrochemical sensor with the devices matched with the @ GCE is smaller in size, more convenient to carry and use, and capable of effectively solving the problems that a three-electrode system detection product is easy to touch a wall, collide with each other, cause short circuit and easily wind wires during detection; in addition, the GCE in the sensor provided by the invention adopts a replaceable design, and the replaceable glassy carbon electrode 206 adopts PANI @ g-C when the cadmium (II) ions in the water environment are measured 3 N 4 @ GCE, like this, in the in-service use, can be according to actual detection needs, will change formula glassy carbon electrode 206 and replace other corresponding heavy metal ion surveyThe required working electrode makes the sensor of the invention have wider application range by using the design.
Example 2:
comparison of Performance before and after electrode modification
2-1, cyclic voltammogram and impedance plot
Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) were used to study different modified electrodes (bare GCE, g-CN) 4 @ GCE and PANI @ g-C 3 N 4 ) To examine the effect of the modified electrode, the experiment was conducted as shown in FIG. 10, and CV and EIS were conducted in a 5.0mmol/L potassium ferricyanide solution containing 0.1mol L-1 KCl.
As shown in FIG. 10(A), Fe [ (CN) is observed in the CV curve of GCE 6 ] 3- A redox peak potential difference (Δ Ep) of approximately 108 mV; is modified with g-C 3 N 4 The electrode of (a) Ep is increased, but the peak current value is also increased because of g-C 3 N 4 Is relatively poor, which also demonstrates that g-C 3 N 4 The surface of the electrode is successfully modified; while g-C coated with PANI is modified 3 N 4 The delta Ep of the modified electrode is reduced to 68mV, the oxidation-reduction peak potential difference is reduced, and the dissolution peak current is obviously improved, which indicates that the reversibility of the electrode is improved, and the modified electrode has faster electron transfer. Fig. 10(B) shows a graph of different electrode impedances. It can be observed that the bare GCE before modification has a semi-circle with a relatively large radius (Rct ≈ 730 Ω), indicating the electrode pair Fe [ (CN) in the electrolyte solution containing KCl 6 ] 3- The redox electron transfer resistance of (2) is large; is modified with g-C 3 N 4 The electrode of (A) has a larger semicircle (Rct. apprxeq.1450. omega.) because of the poorer conductivity of the graphite phase carbon nitride, which also indicates that g-C 3 N 4 The surface of the electrode is modified. Modifying polyaniline-coated g-C 3 N 4 The electrode then has a semi-circle with a smaller radius (Rct 270 Ω). After PANI modification, the semicircular radius of the electrode is reduced (Rct ≈ 450 Ω). The results showed that the modified electrode had low impedance and low resistance to electron transfer, indicating modificationThe electrochemical signal of the electrode in water can be effectively improved, because the conductivity of the electrode is improved, and the electron transfer speed is accelerated.
Example 3:
PANI@g-C 3 N 4 detection Linear Range and detection Limit of @ GCE
Through experiments, when the performance of the electrode reaches the optimum, the detection limit of the linear range of detection is measured on the electrode. At PANI @ g-C 3 N 4 The cadmium (II) ion solution containing an acetic acid buffer solution at pH 5.0 was selected for detection under conditions of a supported amount of 8 μ L, an enrichment time of 240s, and an enrichment potential of-1.2V. The detection results of the DPASV measurements on the cadmium (II) solutions of different concentrations are shown in fig. 11 below.
Referring to fig. 11, we can observe that the concentration of cadmium (II) ion and the oxidation peak current of cadmium (II) ion are in a linear increasing trend, the linear working range is 0.1-140 μ g/L, and the detection limit is 0.05 μ g/L. The linear regression equation obtained by linear fitting is: 0.10541x +0.55901, and the linear correlation coefficient is R 2 0.9978, indicating good linearity, PANI @ g-C, versus electrodes prepared in other literature and prior art 3 N 4 @ GCE has a lower detection limit and a wider linear range, as shown in Table 2:
TABLE 2 detection Range and detection Limit for detection of cadmium (II) ions by different electrodes
Example 4:
PANI@g-C 3 N 4 anti-interference of @ GCE
Anti-interference experiment
To evaluate Sn/g-C 3 N 4 The anti-interference performance of the/GCE sensor when measuring the solution containing cadmium (II) ions is that under the best experimental conditions, the DPASV detection is firstly carried out on the cadmium ions, and the detection result is shown in figure 12.
When the concentration to be measured is 100 mu g/L, adding100 times of common anion and cation (K) + 、Ca 2+ 、Na + 、Cl - 、SO 4 2- 、NO 3 - ) In time, as shown in FIG. 12, we can see that the relative deviation of the dissolution peak current is about 6%, the experimental results are not changed much, and the investigated sensor does not show significant interference from most common ions, indicating PANI @ g-C 3 N 4 The @ GCE has strong anti-interference capability.
Example 5:
PANI@g-C 3 N 4 reproducibility and stability of @ GCE
To evaluate the reproducibility of the proposed sensor, a series of repeated DPASV experiments were performed on the same electrode in 0.2M sodium acetate buffer solution (pH 5.0) containing 100 μ g of cadmium (II) ions. As shown in fig. 13(a), the peak current did not change significantly. The Relative Standard Deviation (RSD) of the cadmium (II) ion was 5.2%. In addition, the manufactured PANI @ g-C was also investigated on one electrode by examining the change in dissolution peak current of Cd (II) 3 N 4 Stability of @ GCE. As shown in fig. 13(B), the Relative Standard Deviation (RSD) of cadmium (II) ions for the stability experiment was determined to be 6.7%. The high repeatability and good reproducibility indicate that the developed PANI @ g-CN @ GCE has great advantages in future practical application.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.
Claims (8)
1. The cadmium (II) ion detection method based on the composite material modified electrode is characterized by comprising the following steps:
s1, pretreating a glassy carbon electrode: polishing the bare glassy carbon electrode, polishing the surface of the bare glassy carbon electrode to a mirror surface, and storing in a vacuum box for later use;
s2 preparation of PANI @ g-C 3 N 4 The compound is as follows: dispersing the prepared graphite-phase carbon nitride in hydrochloric acid, stirring, slowly dropwise adding aniline during stirring, then adding ammonium persulfate, stirring, washing and removing impurities to obtain the polyaniline-coated graphite-phase carbon nitride composite material, namely PANI @ g-C 3 N 4 A complex;
s3 preparation of PANI @ g-C 3 N 4 @ GCE: the PANI @ g-C prepared in S2 is added 3 N 4 Dripping the composite on the surface of a glassy carbon electrode pretreated in S1, and drying or naturally airing under infrared light to obtain PANI @ g-C 3 N 4 @GCE；
S4, determination of cadmium (II) ion and PANI @ g-C 3 N 4 @ GCE interface characterization: the PANI @ g-C prepared in S3 is added 3 N 4 @ GCE is used as a working electrode, and cadmium (II) ions in a solution to be detected are detected by adopting an anodic stripping voltammetry method; after the measurement is completed, the PANI @ g-C 3 N 4 The interface characterization is carried out by @ GCE, and the effect of the modified electrode is proved;
s5, optimizing experimental conditions and determining optimal experimental parameters: a control experiment was designed in conjunction with the procedure in S4, using a controlled variable method, for the determination of PANI @ g-C in the experiment for cadmium (II) ions 3 N 4 Optimizing the modification amount, the enrichment potential, the enrichment time and the pH value of the solution of the compound to determine a group of optimal experimental parameters;
S6、PANI@g-C 3 N 4 the effect of @ GCE on detecting cadmium (II) ions is verified: based on the ability to make PANI @ g-C obtained in S5 3 N 4 Under the experimental condition that the @ GCE performance reaches the optimum, PANI @ g-C 3 N 4 @ GCE is used as a working electrode, and cadmium (II) ions in tap water and underground water are measured by adopting an anodic stripping voltammetry method; after the determination is finished, the concentration of the cadmium (II) ions in the solution is calculated according to a current-concentration linear equation, the standard recovery rate and the standard deviation coefficient of the cadmium (II) ions are further calculated by combining the obtained concentration data, and the PANI @ g-C is verified 3 N 4 The reliability of @ GCE in cadmium (II) ion determination in an actual water environment.
2. The method for detecting cadmium (II) ions based on a composite material modified electrode as claimed in claim 1, wherein the glassy carbon electrode pretreatment operation mentioned in S1 specifically includes the following steps:
a1, respectively carrying out ultrasonic treatment on the bare glassy carbon electrode in an ethanol solution and deionized water for 2-5 minutes;
a2 using Al of coarse and fine particle sizes 2 O 3 Polishing the bare glass carbon electrode treated in the A1 by using polishing powder until the bare glass carbon electrode is polished into a mirror surface, and then washing the mirror surface by using deionized water;
a3, sequentially carrying out ultrasonic treatment on the washed bare glassy carbon electrode in deionized water, ethanol and deionized water, airing, and placing in a vacuum box for later use.
3. The method for detecting cadmium (II) ions based on composite material modified electrode as claimed in claim 1, wherein PANI @ g-C mentioned in S2 3 N 4 The preparation of the compound specifically comprises the following steps:
b1, dispersing the prepared graphite-phase carbon nitride in hydrochloric acid, and carrying out ultrasonic treatment in an ultrasonic cleaning machine;
b2, stirring the graphite-phase carbon nitride solution treated in the B1 by using a magnetic stirrer, and slowly dropwise adding a certain amount of aniline in the stirring process;
b3, stirring for 20-30 minutes, adding a certain amount of sodium persulfate into the solution, and then continuously stirring for 10-15 hours;
b4, after stirring, washing for 3 times by using ethanol and deionized water respectively, removing oligomers, and finally obtaining the graphite-phase carbon nitride composite material containing polyaniline, namely PANI @ g-C 3 N 4 And (c) a complex.
4. The method for detecting cadmium (II) ions based on composite material modified electrode as claimed in claim 1, wherein the pair PANI @ g-C mentioned in S4 3 N 4 The interface characterization is carried out by @ GCE, and specifically comprises the steps of carrying out morphology observation through SEM, carrying out hydrophilicity analysis through CA and carrying out tafelConductivity analysis and elemental composition, composition and structure analysis by XRD and FTIR.
5. The PANI @ g-C as in claim 1 3 N 4 Application of @ GCE in preparation of cadmium (II) ion sensors in water environment.
6. The cadmium (II) ion sensor based on the composite material modified electrode is characterized by comprising a wire storage bridge (1), an electrode fixing device (2) and a sample pool (3), wherein the top end of the wire storage bridge (1) is spirally connected with a terminal (4), the electrode fixing device (2) comprises a connecting pipe (201), the top end and the bottom end of the connecting pipe (201) are both fixedly connected with threaded pipes, the connecting pipe (201) is spirally and fixedly connected with one end, far away from the terminal (4), of the wire storage bridge (1) through the top threaded pipe, and the connecting pipe (201) is spirally and fixedly connected with the top of the sample pool (3) through the bottom threaded pipe; the connecting pipe is characterized in that a circular fixing block (202) is clamped inside the connecting pipe (201), three fixing holes (203) are formed in the circular fixing block (202), and a silver/silver chloride electrode (204), a platinum wire electrode (205) and a replaceable glassy carbon electrode (206) are respectively inserted into the three fixing holes (203).
7. The cadmium (II) ion sensor based on the composite material modified electrode as claimed in claim 6, wherein the wire storage bridge (1) is made of polytetrafluoroethylene material and is used for placing a wire harness connected with the electrode; the wiring terminal (4) is made of stainless steel materials and is used for concentrating and fixing the wiring harness in the wire storage bridge frame (1) and realizing connection with an external workstation; the sample cell is made of transparent polycarbonate materials and is used for containing a sample to be detected.
8. The composite-modified-electrode-based cadmium (II) ion sensor of claim 6, wherein the replaceable glassy carbon electrode (206) employs PANI @ g-C 3 N 4 @ GCE for determination of cadmium (II) ions in a sample to be detected.
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