CN103940882B - Trace copper ion sensor and construction method in a kind of water sample - Google Patents

Abstract

The invention discloses a trace copper ion sensor in a water sample and a construction method thereof. The invention uses a self-assembly method to modify a large amount of sodium phytate functionalized carbon nanotubes to the surface of an ITO electrode, thereby forming an interlaced network of carbon nanotubes structure, providing a large amount of surface area for depositing metal ions. At the same time, sodium phytate exposed on the surface of carbon nanotubes contains a large number of phosphate groups, which can easily capture metal ions in water samples and form complexes with them, and the prepared electrode has a good response to copper (II) ions , and has the advantages of low detection limit, high sensitivity, good selectivity, etc., it is an excellent sensor for detecting metal copper ions in water samples. In addition, the preparation method of the invention is simple, environmentally friendly and low in cost.

Description

A sensor for trace copper ions in water samples and its construction method

technical field

The invention belongs to a kind of "environmental green" phytic acid sodium salt with a higher coordination stability constant for copper ions to prepare a trace copper ion sensor in water samples.

Background technique

Copper element is a kind of metal element in water, which is essential for the human body, but excessive copper is very harmful to the human body. Free copper ions are much more harmful to the human body than complex copper. Excessive copper ions have a great negative effect on many aquatic organisms. The reason is that it combines with the sulfhydryl group in the protein and interferes with the activity of thiol enzymes. For example, if there are excessive copper ions in ecological tanks such as corals and aquatic plants, the Kill the beloved creature. Copper pollution mainly comes from electroplating, metallurgy, chemical industry and other industries. Therefore, in order to monitor the quality of water timely and accurately and ensure that people can obtain safe drinking water, it is of great significance to determine the content of copper ions in water. At present, the techniques for detecting heavy metals mainly include spectroscopic and electrochemical methods. Spectroscopic methods include atomic absorption spectrometry, atomic emission spectrometry, atomic fluorescence, mass spectrometry, etc.; electrochemical methods include voltammetry, polarography, and potential analysis. , conductometric analysis, etc. In recent years, more studies have been made on the detection of heavy metal ions by anodic stripping voltammetry, which is a very sensitive analytical method with a detection limit of 10 ^-11 molL ^-1 . At the same time, the current research on the detection of copper ions focuses on the preparation of a modified electrode that can specifically recognize metal ions. The selective recognition substances commonly used in chemically modified electrodes include crown ether, cyclodextrin, calixarene, cysteine, phenanthroline and its derivatives, chitosan and ethylenediaminetetraacetic acid disodium salt, etc. , these compounds have a strong ability to complex metal ions. However, most of the modified materials used in these modified electrodes will pollute the environment, or the preparation of these modified electrodes is relatively complicated. Therefore, how to have high sensitivity and high selectivity in the precise detection of metal copper ions, and at the same time, the sensor is non-toxic, non-polluting to the environment, and the preparation method is simple, will be the goal that researchers are constantly striving for. The P electrons of carbon atoms on multi-walled carbon nanotubes form a wide range of delocalized π bonds. Due to the significant conjugation effect, multi-walled carbon nanotubes have good electrical conductivity, and their specific surface area is large, so they are considered to be good electrical conductors. polymer composites. Sodium phytate has strong hydrophilicity, good biocompatibility, non-toxicity, and is environmentally friendly. There are six phosphate bonds in its structure, which has a strong coordination ability for copper ions and has a strong coordination ability for copper ions in the water phase. Medium-hydrophobic carbon nanotubes have good dispersibility. Sodium phytate is used to functionalize multi-walled carbon nanotubes to prepare modified electrode composite materials. The electrode modified by this composite material has good conductivity of carbon nanotubes, large specific surface area and strong effect of sodium phytate on copper ions. Coordination ability and other properties, combined with anodic stripping voltammetry at the same time to achieve high sensitivity and high selectivity detection of metal copper ions.

So far, there is no sensor for detecting metal copper ions in water samples prepared by using "green" phytate sodium salt at home and abroad. Therefore, inventing a sensor with low detection limit, high sensitivity and good selectivity to detect copper ions is an important technical problem that needs to be solved urgently.

Contents of the invention

The object of the invention is to provide a sensor with low detection limit, high sensitivity and good selectivity for detecting trace copper ions in water samples.

The purpose of the present invention is achieved like this:

A method for constructing a trace copper ion sensor in a water sample, comprising the following steps:

(1) Weigh multi-walled carbon nanotubes, add concentrated sulfuric acid and concentrated nitric acid mixed acid with a volume ratio of 3:1, sonicate for 4 to 4.5 hours, dilute, filter, wash until neutral, and dry to obtain activated multi-walled carbon Nanotubes; the dosage ratio of multi-walled carbon nanotubes and mixed acid is 2.5-6.5g/mL;

(2) The activated multi-walled carbon nanotubes were added to the sodium phytate solution with a concentration of 1.0×10 ^-2 mol/L at a ratio of 1 mg/mL, and ultrasonically mixed for 7 to 8 hours to obtain stable and uniform phytic acid Sodium functionalized multi-walled carbon nanotube suspension;

(3) After cleaning and activating the ITO (indium tin oxide glass) electrode, control the conductive area of ITO to 1cm×1cm, and seal the remaining area with nail polish, dry it, and set aside;

(4) Dip the dried ITO electrode into the sodium phytate-functionalized multi-walled carbon nanotube suspension, self-assemble in a refrigerator at 4°C for three hours, then take it out and wash it with deionized water to obtain the plant. Sodium acid functionalized carbon nanotubes modified ITO electrodes.

The environment-friendly reagent sodium phytate (Na-IP ₆ ), also known as sodium phytate, contains 6 non-coplanar phosphate bonds in its molecular structure, which makes it have a strong ability to chelate multivalent metal ions The ability of its coordination with copper (II) ions is more stable than that of other metal ions. Sodium phytate is an important pure natural green additive, the most notable feature is that it has a strong chelation effect with metal ions, strong anti-oxidation and color protection. Widely used as antioxidant and color-protecting agent for fruit and vegetable juice drinks, meat products and seafood. In this paper, sodium phytate is mainly used to functionalize multi-walled carbon nanotubes, and sodium phytate is adsorbed on the surface of carbon nanotubes. Using sodium phytate, it has a strong effect on the surface of ITO. Using self-assembly technology, a large amount of carbon The nanotubes are modified to the surface of the ITO electrode, thereby forming an interlaced network structure of carbon nanotubes, which provides a large surface area for depositing metal ions. At the same time, the sodium phytate exposed on the surface of carbon nanotubes contains a large number of phosphate groups, which can easily capture metal copper ions in water samples and form complexes with them, and the prepared electrode has a good effect on copper (II) ions. Response, and has the advantages of low detection limit, high sensitivity, good selectivity, etc., it is an excellent sensor for detecting metal copper ions in water samples.

The invention uses a self-assembly method to modify a large amount of sodium phytate functionalized carbon nanotubes on the surface of an ITO electrode, thereby forming an interlaced network structure of carbon nanotubes and providing a large amount of surface area for depositing metal ions. At the same time, sodium phytate exposed on the surface of carbon nanotubes contains a large number of phosphate groups, which can easily capture metal ions in water samples and form complexes with them, and the prepared electrode has a good response to copper (II) ions , and has the advantages of low detection limit, high sensitivity, good selectivity, etc., it is an excellent sensor for detecting metal copper ions in water samples.

The advantages of the present invention are:

1. The preparation method is simple, environmentally friendly and low in cost.

2. The coordination ratio between phytic acid sodium salt and Cu(II) ions is stable with that of other metal ions, so the phytic acid sodium salt modified on the ITO electrode can better improve the electrode pair in the process of anodic stripping voltammetry. Selectivity for copper ions.

3. Low detection limit and high sensitivity.

Description of drawings

Figure 1 is a schematic diagram of the sensor preparation process.

Fig. 2 is the FESEM image of the multi-walled carbon nanotubes modified ITO electrode and the sodium phytate functionalized carbon nanotubes modified ITO electrode and the XPS characterization of the IP ₆ -MWCNTs-ITO electrode.

Figure 3 is the cyclic voltammetry curves of different electrodes responding to 0.01molL ^-1 CuCl ₂ .

Fig. 4 is the differential conventional pulsed anodic stripping voltammogram of the target sensor to different concentrations of Cu(II) ions.

detailed description

The present invention will be further described below through specific embodiments.

The electrochemical experiment of the present invention is carried out on the CHI660D type electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd.); the field emission scanning electron microscope spectrum adopts HitachiS-4800 (Tokyo, Japan) field emission scanning electron microscope, and other instruments are FE20 laboratory pH meter (Mettler-Toledo Instruments Shanghai Co., Ltd.); SK2200H ultrasonic instrument (Shanghai Kedao Ultrasonic Instrument Co., Ltd.).

The preparation process of IP ₆ -MWCNTs-ITO electrode is shown in Fig. 1 . Phytate-functionalized carbon nanotubes modified ITO to prepare trace copper ion sensors in water samples: Weigh 0.9-1.5 grams of multi-walled carbon nanotubes, add concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 3:1 mixed acid 24 mL, sonicated for 4-4.5 hours, then diluted, filtered, washed until neutral, and dried to obtain activated multi-walled carbon nanotubes. Add 0.017～0.02g of activated multi-walled carbon nanotubes to 17～20mL of sodium phytate solution with a concentration of 1.0×10 ^-2 mol/L, and ultrasonically mix for 7 to 8 hours to obtain stable and uniform phytic acid Sodium-functionalized multi-walled carbon nanotube suspensions. After the ITO electrode is cleaned and activated, the ITO conductive area is controlled to 1cm×1cm, and the remaining area is sealed with nail polish, dried and set aside. Dip the dried ITO electrode into the suspension of sodium phytate-functionalized multi-walled carbon nanotubes, self-assemble in a refrigerator at 4°C for three hours, then take it out and wash it with deionized water to obtain the sodium phytate-functionalized multi-walled carbon nanotubes suspension. Carbon nanotubes modified ITO electrodes.

Field emission scanning electron microscopy (FESEM) is an effective means to study the microscopic morphology of electrode surfaces. X-ray photoelectron spectroscopy is a commonly used surface composition analysis method. Fig. 2 is the characterization of the prepared modified ITO electrode by field emission scanning electron microscopy and X-ray photoelectron spectroscopy. Figure 2A is a FESEM image of a modified electrode without sodium phytate-functionalized carbon nanotubes self-assembled into ITO. It can be seen that only a few carbon nanotubes are assembled on the surface of the ITO electrode; The FESEM image of the self-assembly of nanotubes to the ITO modified electrode shows that a large number of carbon nanotubes are assembled on the surface of the ITO electrode to form an interlaced network structure. Thus, it shows that sodium phytate-functionalized carbon nanotubes are easier to assemble on the surface of ITO electrodes and provide a larger specific surface area. Figure 2C is the X-ray photoelectron spectrum of the IP ₆ -MWCNTs-ITO electrode. It is found that the electron binding peak of the 2P orbital of phosphorus appears at the electron binding energy of 133.5eV, which proves the existence of sodium phytate.

Figure 3 is the cyclic voltammetry curves of bare ITO electrode, multi-walled carbon nanotube-modified ITO electrode and sodium phytate-functionalized multi-walled carbon nanotube-modified ITO electrode to 0.01molL ^-1 CuCl ₂ , respectively. Curve (a) is the cyclic voltammetry graph of the response of bare ITO electrode to copper ions. It can be observed from the figure that the oxidation peaks of copper ions appear at potentials 0.40V and 0.72V respectively; curve (b) is the sodium phytate functionalized carbon The cyclic voltammetry curve of the response of the nanotube-modified ITO electrode to copper ions, it can be observed that the oxidation peak of copper ions appears only at a potential of 0.29V; curve (c) is the cycle of the response of the multi-walled carbon nanotube-modified ITO electrode to copper ions In the voltammetry curve, it can be observed that the oxidation peaks of copper ions appear at the potentials of 0.32V and 0.59V, respectively. Comparing the cyclic voltammetry curves of the three electrodes, it can be seen that the sodium phytate functionalized multi-walled carbon nanotubes modified ITO electrode has a lower potential and a higher response current to copper ion oxidation, and has less background interference, showing the superiority of the IP ₆ -MWCNTs-ITO electrode for the detection of copper (Ⅱ) ions.

Next, the performance parameters of the sensor were quantitatively investigated by differential conventional pulsed anodic stripping voltammetry. Figure 4 is the IP ₆ -MWCNTs-ITO electrode at the working potential of -0.5V, using it curves to deposit different concentrations of CuCl ₂ in a 0.05molL ^-1 KNO ₃ solution with pH = 3.00, and then using differential conventional pulse voltammetry Method, stripping copper in the potential range of -0.5V-0.5V. As the concentration of copper ions increases, the oxidation peak current and peak area increase gradually. The inner illustration reflects the linear correction relationship of the sensor to the oxidation peak area at different Cu(II) ion concentrations, and it can be seen that the response peak area has a linear relationship with the concentration of Cu(II) ions, ranging from 1.00×10 ^-8 to 1.00× 10 ^-6 molL ^-1 range, the linear regression coefficient is 0.9976, and the lowest detection limit is 2.50×10 ^-9 molL ^-1 (signal-to-noise ratio S/N=3). Five IP ₆ -MWCNTs-ITO electrodes were prepared by the same method, and the relative standard deviation (RSD) was 3.2% for the determination of the same concentration of Cu(Ⅱ) solution (0.06μmolL ^-1 ). This shows that the IP ₆ -MWCNTs-ITO electrode has good reproducibility.

Experimental results show that the sensor has satisfactory reproducibility and sensitivity.

Table 1 is a comparison of the response current values of IP ₆ -MWCNTs-ITO electrodes to 1.00×10 ^-6 molL ^-1 Cu(Ⅱ) in the presence of various metal ions with an excess concentration of 100 times, showing that the IP ₆ -MWCNTs-ITO electrode pair Copper(Ⅱ) ion has better selectivity.

Table 1

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have modifications and changes. All modifications, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (2)

1. the construction method of trace copper ion sensor in water sample, comprises the following steps:

(1) take multi-walled carbon nano-tubes, add the nitration mixture that the concentrated sulphuric acid and red fuming nitric acid (RFNA) volume ratio are 3:1, ultrasonic 4 ~ 4.5 hours, dilution, filter, washing, to neutral, is drying to obtain the multi-walled carbon nano-tubes of activation; The amount ratio of multi-walled carbon nano-tubes and nitration mixture is 2.5-6.5g/mL;

(2) it is 1.0 × 10 that the multi-walled carbon nano-tubes activated joins concentration according to the ratio of 1mg/mL ^-2in the sodium phytate solution of mol/L, ultrasonic mixing 7 ~ 8 hours, obtains the functionalized multi-walled carbon nano-tubes suspending liquid of sodium phytate of stable uniform;

(3) by after ITO electrode cleaning activation, control ITO conductive area 1cm × 1cm, all the other areas nail polish is coated with envelope, dries, for subsequent use;

(4) immerse in the functionalized multi-walled carbon nano-tubes suspending liquid of sodium phytate by the ITO electrode of having dried, self assembly three hours in 4 DEG C of refrigerators, then, take out, by washed with de-ionized water, namely obtained sodium phytate functionalized carbon nanotubes modifies ITO electrode.

2. a trace copper ion sensor in water sample, is characterized in that, method preparation according to claim 1.