1. The flexible formaldehyde electrochemical sensor is characterized by comprising a conductive sponge and a nano material layer attached to the surface of the conductive sponge, wherein the nano material layer is formed by compounding silver nanowires and carbon nanotubes.

2. The preparation method of the flexible formaldehyde electrochemical sensor is characterized by comprising the following steps:

1) cleaning the conductive sponge: shearing a conductive sponge into samples with certain sizes, sequentially placing the samples into deionized water and absolute ethyl alcohol for ultrasonic cleaning, and then airing or drying at low temperature for later use;

2) preparing an ethanol solution of silver nanowires: preparing a uniform silver nanowire ethanol solution with a certain concentration;

3) preparing carbon nano tube ethanol solution: preparing a uniform carbon nanotube ethanol solution with a certain concentration;

4) and (3) dripping: and (3) sequentially and uniformly dripping the dispersed silver nanowire ethanol solution and the carbon nanotube ethanol solution on clean conductive sponge alternately, wherein each layer is dried after being dripped, the next layer is dripped, multiple layers can be dripped, and both sides of the conductive sponge are dripped.

3. The preparation method according to claim 2, wherein the concentration of the ethanol solution of silver nanowires in the step 2) is 0.05mg/ml to 5 mg/ml.

4. The method according to claim 2, wherein the concentration of the carbon nanotube ethanol solution in the step 3) is 0.05mg/ml to 5 mg/ml.

5. The preparation method of claim 2, wherein in the step 4), the number of the dripping layers on each surface of the conductive sponge can be 2-12.

6. The preparation method according to claim 2, wherein in the step 1), the conductive sponge is placed in deionized water for ultrasonic cleaning for 20-30 minutes, then placed in absolute ethyl alcohol for ultrasonic cleaning for 20-30 minutes, and the cleaned conductive sponge is placed in a culture dish for natural drying or placed in a vacuum oven for drying at 40-60 ℃ for 1 hour.

Background

Formaldehyde is a toxic substance of protoplasts that can react with proteins and is harmful to humans. Formaldehyde has the preservative effect and can prolong the shelf life of the goods, so that the formaldehyde can be added into the food as a preservative by many illegal merchants. Therefore, the detection of formaldehyde in food is deeply concerned by experts of scholars at home and abroad. Along with the progress of the times and the continuous updating of the technology, the detection method of formaldehyde also develops endlessly.

Currently, methods for detecting formaldehyde are commonly used, such as spectrophotometry, chromatography, spectrometry, and electrochemical methods. And measuring the formaldehyde by adopting an indirect detection mode. The principle of spectrophotometry is that formaldehyde reacts with a certain compound to generate a certain substance with color, and the measurement is carried out at a specific wavelength. The chromatography mainly converts formaldehyde into a gas-phase or liquid-phase analyzable compound through derivatization, and generally adopts an organic solvent for extraction and enrichment and then carries out chromatographic determination. Gas chromatography is a common method of chromatography. The gas chromatography comprises a headspace gas chromatography and a derivatization gas chromatography, the direct headspace method is only suitable for samples with higher formaldehyde concentration, and the derivatization method can detect low-concentration or even trace formaldehyde. Spectroscopy is a method established on the basis of the selective absorption or emission of electrical radiation by substances of different molecular structures. The spectroscopic method can be classified into ultraviolet-visible absorption spectroscopy (UV-Vis), infrared spectroscopy (IR), fluorescence spectroscopy (FD), Phosphorescence Spectroscopy (PS), and the like, depending on the wavelength used. However, the conventional formaldehyde detection method has problems of poor sensitivity, long detection time, expensive instrument, and the like.

The cyclic voltammetry for measuring formaldehyde by an electrochemical method has the advantages of high sensitivity, good selectivity, simple instrument, quick measurement, low cost, wide application range, accurate and reliable measurement result, simultaneous measurement of multiple elements and strong superiority in the aspect of formaldehyde measurement. Common electrochemical methods for formaldehyde determination include stripping voltammetry, cyclic voltammetry, laser-induced decomposition spectroscopy, and the like. Further exploration and research are needed for electrochemical detection techniques that are more accurate, have lower detection limits, and are less costly. Therefore, the formaldehyde electrochemical sensor with excellent performance and low cost has certain application prospect and practical significance.

Disclosure of Invention

Based on the needs, the invention provides the preparation method of the flexible formaldehyde electrochemical sensor, which is low in cost, simple in preparation and easy for large-scale production.

The flexible formaldehyde electrochemical sensor is based on the combination of conductive sponge, silver nanowires and carbon nanotubes as a substrate layer and an active layer. The conductive sponge, the silver nanowires and the carbon nanotubes are all purchased and obtained directly in the market. The conductive sponge is purchased from Shenzhen Huayue Source electronics Limited company, has the thickness of 3mm, takes polyurethane foam sponge as a matrix, and is subjected to PVD (physical vapor deposition) conductive treatment and electro-deposition of metal nickel, copper and other thickening treatments, so that the sponge is conductive in all directions, has the characteristics of good conductivity, strong bonding force, high shielding efficiency, good rebound resilience, stable performance and the like, and is an EMI/ESD (electro-magnetic interference/static discharge) material widely applied at present.

The preparation method of the flexible formaldehyde electrochemical sensor comprises the following steps:

1) cleaning the conductive sponge: shearing the conductive sponge into samples with certain sizes, sequentially placing the samples into deionized water and absolute ethyl alcohol for ultrasonic cleaning, and then airing or drying at low temperature for later use.

2) Preparing an ethanol solution of silver nanowires: preparing a uniform silver nanowire ethanol solution with a certain concentration.

3) Preparing carbon nano tube ethanol solution: preparing a uniform carbon nano tube ethanol solution with a certain concentration.

4) And (3) dripping: uniformly and sequentially dripping the dispersed silver nanowire ethanol solution and the carbon nanotube ethanol solution on clean conductive sponge, wherein each layer is dried after being dripped, and then the next layer is dripped, so that multiple layers can be dripped; both sides of the conductive sponge are coated by dripping. The silver nanowire and carbon nanotube composite conductive sponge is expected to produce a synergistic effect, and the sensitivity of the sensor is enhanced in the force application process. And (3) dropping and coating the silver nanowires and the conductive sponge of the carbon nanotubes to obtain the flexible formaldehyde electrochemical sensor.

Further, in the step 2), the concentration of the silver nanowire ethanol solution is 0.05 mg/ml-5 mg/ml.

Further, in the step 3), the concentration of the carbon nano tube ethanol solution is 0.05 mg/ml-5 mg/ml.

Furthermore, in the step 4), the number of the dripping layers on each surface of the conductive sponge can be 2-12.

Further, in the step 1), the conductive sponge is firstly placed in deionized water for ultrasonic cleaning for 20-30 minutes, then placed in absolute ethyl alcohol for ultrasonic cleaning for 20-30 minutes, and the cleaned conductive sponge is placed in a culture dish for natural airing or is placed in a vacuum oven for drying for 1 hour at the temperature of 40-60 ℃.

Compared with the prior art, the invention has the following beneficial effects:

1) the formaldehyde electrochemical sensor prepared by compounding the silver nanowires and the carbon nanotubes on the conductive sponge has the advantages that the silver nanowires and the carbon nanotubes are effectively combined on the porous loose structure of the conductive sponge, so that a synergistic effect is expected to be generated, and the electrochemical catalytic oxidation of formaldehyde is promoted.

2) The porous shape of the conductive sponge has larger specific surface area, which is beneficial to enhancing the electrochemical catalytic oxidation of formaldehyde.

3) The method is simple and easy to implement, low in cost and easy for large-scale production.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a scanning electron micrograph of a conductive sponge electrochemical sensor according to example 1 of the present invention, the magnification of which is 700 times;

FIG. 2 is a 2 ten thousand times scanning electron micrograph of the conductive sponge electrochemical sensor of example 1 of the present invention;

FIG. 3 is a cyclic voltammogram of different concentrations of formaldehyde tested in accordance with an embodiment of the present invention;

FIG. 4 specificity curves for different substances in the examples of the present invention.

Detailed Description

The technical solutions of the present invention are further described below with reference to the drawings and the specific embodiments, but the present invention is not limited to the embodiments in any way. In the examples, unless otherwise specified, the experimental methods are all conventional methods; unless otherwise indicated, the experimental reagents and materials were commercially available.

A flexible formaldehyde electrochemical sensor comprises a conductive sponge and a nanometer material layer attached to the surface of the conductive sponge, wherein the nanometer material layer is formed by compounding silver nanowires and carbon nanotubes. The preparation method of the flexible formaldehyde electrochemical sensor provided by the embodiment of the invention comprises the following steps:

firstly, cleaning the conductive sponge. Shearing the conductive sponge into a sample with a certain size, firstly placing the sample in deionized water for ultrasonic cleaning for 20-30 minutes, then placing the sample in absolute ethyl alcohol for ultrasonic cleaning for 20-30 minutes, placing the cleaned conductive sponge in a culture dish for natural drying or placing the culture dish in a vacuum oven for drying at 40-60 ℃ for 1 hour.

And step two, preparing an ethanol solution of the silver nanowires. Preparing ethanol solution (0.05 mg/ml-5 mg/ml) of silver nanowires with a certain concentration, and performing ultrasonic treatment for 10-15 minutes after preparation to fully disperse the silver nanowires in the ethanol and stabilize the silver nanowires into uniform solution.

And step three, preparing carbon nano tube ethanol solution. Preparing carbon nano tube ethanol solution (0.05 mg/ml-5 mg/ml) with a certain concentration, and performing ultrasonic treatment for 10-15 minutes after preparation to fully disperse the silver nano wires in the ethanol to obtain uniform solution stably.

And fourthly, dripping. And (3) sequentially and uniformly dripping the dispersed silver nanowire ethanol solution and the carbon nanotube ethanol solution on a clean conductive sponge in an alternating manner, wherein 2-12 layers of the silver nanowire ethanol solution and the carbon nanotube ethanol solution can be dripped on each surface of the conductive sponge, and after one layer of the silver nanowire ethanol solution and the carbon nanotube ethanol solution are dripped, the conductive sponge is placed in a cool and dry place to be naturally dried and then dripped one layer. The silver nanowire and the carbon nanotube composite nano layer generate a synergistic effect to promote the electrochemical catalytic oxidation of formaldehyde, and the conductive sponge has high specific surface area, so that the formaldehyde electrochemical sensor with high sensitivity is expected to be obtained.

Example 1

And immersing the conductive sponge cut into 30 multiplied by 10 multiplied by 3mm into deionized water, and ultrasonically cleaning for 20min to clean impurities on the surface of the conductive sponge. And after the deionized water cleaning is finished, soaking the glass substrate in absolute ethyl alcohol for ultrasonic cleaning for 20 min. And taking out the conductive sponge after the ultrasonic cleaning from the absolute ethyl alcohol, and drying in a vacuum drying oven at 50 ℃ for 20 min. And taking out after drying, standing and cooling. Using 200 mul pipette to transfer 0.05ml silver nano-wire solution with concentration of 10mg/ml into 1.5ml micro centrifuge tube, then using 1000 mul pipette to transfer 0.95ml deionized water into the same micro centrifuge tube, and oscillating the micro centrifuge tube to prepare 1ml silver nano-wire solution with concentration of 0.5 mg/ml. Preparing 0.5mg/ml carbon nano tube solution by the same operation of preparing the silver nano wire solution. Using a liquid transfer gun to transfer the silver nanowire solution with the concentration of 0.5mg/ml from the micro centrifugal tube, uniformly dripping and coating one surface of the dried and cooled conductive sponge, standing and drying, and thus finishing dripping and coating 1 layer of the sample; after the sample is dried, transferring the carbon nano tube solution with the concentration of 0.5mg/ml from the micro centrifugal tube by using a liquid transfer gun, uniformly dripping the carbon nano tube solution on the same surface, and standing and drying; so far, one side of the conductive sponge is coated with 1 layer of silver nanowire solution with the concentration of 0.5mg/ml and 1 layer of carbon nanotube solution with the concentration of 0.5mg/ml, and two nano layers are coated by dropping. The same operation was performed on the other side by turning the conductive sponge over, and then the above operation was repeated to prepare conductive sponges each coated with a total of 6 nano-layers each including 3 layers of silver nanowires and 3 layers of carbon nanotubes, and the microstructures of the samples were as shown in fig. 1 and 2. Fig. 1 is a conductive sponge with 6 nano-layers applied by dropping, and black spots distributed on the sponge are the silver nanowire and carbon nanotube composite nano-layers. Fig. 2 is a photograph magnified by 2 ten thousand times, and it can be seen that the interpenetrating and crosslinking of the silver nanowires and the carbon nanotubes forms a network, and this structure is favorable for two nanomaterials to generate a synergistic effect, thereby promoting electrochemical response and sensitivity.

Example 2 response experiment of Formaldehyde

The electrochemical response experiment of formaldehyde is carried out on Chenghua CHI660 electrochemical workstation, and a cyclic voltammetry method and a three-electrode system are adopted. Wherein the reference electrode is a silver/silver chloride electrode, the counter electrode is a platinum wire, and the working electrode is the flexible electrochemical sensor prepared according to embodiment 1 of the present invention. 0.2mol/L NaOH solution is taken as solvent to prepare formaldehyde NaOH solution with different concentrations to be used as cyclic voltammetry curve, the scanning range is-1.0V-2.0V, and the scanning speed is 100 mV/s. The experimental result is shown in figure 3, compared with the pure NaOH base solution, the cyclic voltammetry curve of 20-50mmol/L has obvious reduction peak, and the peak current changes obviously and regularly along with the change of the formaldehyde concentration, which shows that the electrochemical sensor has good electrochemical response to formaldehyde.

Example 3 specificity test of Formaldehyde

The formaldehyde specificity experiment was performed on Chenghua CHI660 electrochemical workstation, using a chronoamperometric method, setting the response potential to 0.8V according to the cyclic voltammetry curve of example 2, three-electrode system. Wherein the reference electrode is a silver/silver chloride electrode, the counter electrode is a platinum wire, and the working electrode is the flexible electrochemical sensor prepared according to embodiment 1 of the present invention, and the results are shown in fig. 4. The test was started in a blank NaOH base solution, and after the current curve was smoothed, the formaldehyde solution was added rapidly to bring the solution concentration to the range of 20-50mmol/L of the response of example 2, and a step drop in current was found, indicating that the sensor responded well to formaldehyde. After 30 seconds interval when the current curve again plateaus, the same amount of formic acid was added and no response was found. And adding methanol, ethanol, n-butanol and acetone in equal amount at equal intervals in turn to find that no response exists. When an equal amount of formaldehyde was added again, a rapid step-down in current was found. The results show that the sensor only has good response to formaldehyde, does not respond to other substances with similar structures, and has good specificity.

It should be noted that the above-mentioned embodiments are only preferred embodiments of the present invention, and the present invention is not limited thereto, and although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications and equivalents can be made in the technical solutions described in the foregoing embodiments, or equivalents thereof. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention. Although the present invention has been described with reference to the specific embodiments, it should be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.