阅读说明：本技术 一种基于LDHs的阴离子选择性膜的营养液离子浓度检测方法 (Method for detecting ion concentration of nutrient solution based on LDHs anion selective membrane ) 是由 应义斌 刘雅倩 平建峰 于 2021-08-20 设计创作，主要内容包括：本发明公开了一种基于LDHs的阴离子选择性膜的营养液浓度检测方法。基于LDHs的阴离子选择性的纳米流体通道薄膜,具有这样的特征：阳极氧化铝膜层,作为基底；以及LDHs纳米片层,均匀分布在阳极氧化铝薄膜的表面及纳米通道内,该纳米流体通道薄膜的通道尺寸为10-20nm；本发明制得的纳米流体通道薄膜对阴离子具有很好的选择性,能将盐差能转换为电能。将薄膜放置在营养液及固定离子浓度水平的溶液间,输出电流的大小反馈了营养液与溶液间离子浓度梯度的高低,输出的电流信号即可实时反馈营养液浓度水平。(The invention discloses a nutrient solution concentration detection method based on an LDHs anion selective membrane. An LDHs-based anion selective nanofluidic channel film having the characteristics of: an anodic aluminum oxide film layer as a substrate; and LDHs nanosheet layers uniformly distributed on the surface of the anodic alumina thin film and in the nanochannels, wherein the channel size of the nanofluid channel thin film is 10-20 nm; the nano fluid channel film prepared by the method has good selectivity on anions, and can convert salt difference energy into electric energy. The film is placed between the nutrient solution and the solution with the fixed ion concentration level, the magnitude of the output current feeds back the ion concentration gradient between the nutrient solution and the solution, and the output current signal can feed back the nutrient solution concentration level in real time.)

1. A method for detecting the ion concentration of nutrient solution based on an LDHs anion selective membrane is characterized in that: the detection method adopts a nutrient solution concentration detection device, the nutrient solution concentration detection device comprises a water culture box, a container box embedded with an anion selective membrane, an Ag/AgCl electrode and a data acquisition circuit board, deionized water is filled in the water culture box, nutrient solution is filled in the container box, the container box is placed in the water culture box, the anion selective membrane is adopted to seal holes after the side surface of the container box is provided with holes, and an Ag/AgCl electrode connected with the data acquisition circuit board is respectively inserted into the liquid at two sides of the membrane;

the data acquisition circuit board comprises an I/V conversion circuit, an amplifying circuit, an STM32 microprocessor and a lithium battery which are sequentially connected.

2. The method for detecting the ion concentration of the nutrient solution based on the anion selective membrane of the LDHs as claimed in claim 1, wherein the anion selective membrane is fixed on the side surface of the container box through epoxy resin; silicon films with 3 × 10 openings are packaged on both sides of the anion selective membrane^-8m²And (4) a small hole.

3. The method for detecting the ion concentration of the nutrient solution based on the LDHs anion selective membrane as claimed in claim 1, wherein current signals generated by the ion concentration difference at two sides of the membrane are transmitted to a data acquisition circuit board for processing through Ag/AgCl electrodes, the current signals are converted into voltage signals through an I/V conversion circuit, the voltage signals are amplified through an amplifying circuit, then an STM32 microprocessor is used for AD acquisition, the acquired signals are subjected to low-pass filtering through a low-pass filtering module in the microprocessor and then are sent to an upper computer, the upper computer converts the received voltage signals into current values through a built-in ADC, and the current values are drawn into a time-current curve in real time.

4. The method for detecting the ion concentration of the nutrient solution based on the anion selective membrane of LDHs as claimed in claim 3, wherein the method for detecting the concentration of the nutrient solution by adopting the nutrient solution concentration detection device comprises the following steps:

1) nutrient solutions with different concentrations and known concentrations are placed in the container box, and a nutrient solution concentration detection device is adopted to measure corresponding current values, so that a relation curve of the current and the concentration is obtained;

2) and monitoring the nutrient solution with unknown concentration in real time by adopting a nutrient solution concentration detection device to obtain a real-time change curve of a current value, and feeding back the concentration change of the nutrient solution in real time according to a relation curve of the current and the concentration.

5. The method for detecting the ion concentration of the nutrient solution based on the LDHs anion selective membrane as claimed in claim 1, which is characterized in that: the anion selective membrane is prepared by the following method:

1) preparing a nitrate solution with the concentration of 0.1-1mol/L, and adjusting the pH value of the nitrate solution to 5-6 by using a nitric acid solution and an ammonia water solution;

2) vertically placing an anodic aluminum oxide film in the nitrate solution obtained in the step 1), heating the nitrate solution, and growing layered double hydroxides on the surface of the anodic aluminum oxide film;

3) and taking out the anodic alumina film with LDHs, fully soaking in deionized water, and drying at room temperature for 24h to obtain the nano fluid channel film with anion selectivity based on LDHs, namely the anion selective film.

6. The method for detecting the ion concentration of the nutrient solution with the LDHs-based anion selective membrane as claimed in claim 5, wherein the nitrate in the nitrate solution is nickel nitrate, cobalt nitrate or zinc nitrate;

the type of nitrate is selected according to the type of anion selective membrane to be prepared, and specifically comprises the following steps: the NiAl-LDH anion selective membrane is prepared by adopting a nickel nitrate solution, the CoAl-LDH anion selective membrane is prepared by adopting a cobalt nitrate solution, and the ZnAl-LDH anion selective membrane is prepared by adopting a zinc nitrate solution.

7. The method as claimed in claim 5, wherein the pore size of the anodic alumina in step 2) is controlled within the range of 160-200 nm.

8. The method for detecting the ion concentration of the nutrient solution based on the LDHs anion selective membranes as claimed in claim 5, wherein the heating temperature in the step 2) is 80 ℃ and the heating time is 4-20 h.

9. The method for detecting the ion concentration of the nutrient solution based on the LDHs anion selective membrane of claim 5, wherein the thickness of the anion selective membrane is 45-50 μm, and the size of the nanochannel is 10-20 nm; the anion selective membrane is positively charged, when anions and cations in the concentrated salt solution have a tendency of migrating to the dilute salt solution under the drive of the salt difference, the membrane allows the anions to pass through and blocks the migration of the cations, so that the directional movement of charges is generated, current is generated, and the conversion from the salt difference energy to the electric energy is realized.

Technical Field

The invention belongs to the technical field of water culture nutrient solution management, and particularly relates to a nutrient solution ion concentration detection method based on an LDHs anion selective membrane.

Background

Hydroponic production is the main production method in plant factories by virtue of its high yield per unit area and low resource consumption. In hydroponic production, nutrient solutions containing various ions are commonly used to provide necessary nutrients for crop growth, and when the ion concentration in the nutrient solution is too high or too low, the yield of crops is limited. In actual production, the ion concentration of the nutrient solution is generally detected by measuring the conductivity of the nutrient solution, but the conductivity test electrode has the problem of potential drift in the long-term use process, so that the accuracy of the conductivity measurement result is reduced. In addition, the use of a large number of sensors per unit area for detection also results in high economic costs. Therefore, a more accurate and convenient real-time monitoring mode is needed for water culture nutrient solution management.

Disclosure of Invention

In order to solve the problems in the background art, the invention provides a nutrient solution ion concentration detection method of an anion selective membrane based on LDHs, and the membrane has good stability and can realize real-time detection.

The technical scheme adopted by the invention is as follows:

a nutrient solution ion concentration detection method of an anion selective membrane based on LDHs adopts a nutrient solution concentration detection device, the nutrient solution concentration detection device comprises a water culture box, a container box embedded with the anion selective membrane, an Ag/AgCl electrode and a data acquisition circuit board, deionized water is filled in the water culture box, nutrient solution is filled in the container box, the container box is placed in the water culture box, the anion selective membrane is adopted to seal holes after the side surface of the container box is provided with holes, and the Ag/AgCl electrode connected with the data acquisition circuit board is respectively inserted into the liquid at two sides of the membrane; the data acquisition circuit board comprises an I/V conversion circuit, an amplifying circuit, an STM32 microprocessor and a lithium battery which are sequentially connected.

The anion selective membrane is fixed on the side surface of the container box through epoxy resin; silicon films with 3 × 10 openings are packaged on both sides of the anion selective membrane^-8m²Small holes to control the actual working area of the membrane.

Current signals generated by ion concentration differences on two sides of the membrane are transmitted to a data acquisition circuit board through an Ag/AgCl electrode to be processed, the current signals are converted into voltage signals through an I/V conversion circuit, the signals are amplified through an amplifying circuit, then AD acquisition is carried out by an STM32 microprocessor, the acquired signals are subjected to low-pass filtering through a low-pass filtering module in the microprocessor and then are sent to an upper computer, the upper computer converts the received voltage signals into current values through a built-in ADC, and the current values are drawn into a time current curve in real time.

The method for detecting the concentration of the nutrient solution by adopting the nutrient solution concentration detection device comprises the following steps:

1) nutrient solutions with different concentrations and known concentrations are placed in the container box, and a nutrient solution concentration detection device is adopted to measure corresponding current values, so that a relation curve of the current and the concentration is obtained;

2) and monitoring the nutrient solution with unknown concentration in real time by adopting a nutrient solution concentration detection device to obtain a real-time change curve of a current value, and feeding back the concentration change of the nutrient solution in real time according to a relation curve of the current and the concentration.

The anion selective membrane is prepared by the following method:

1) preparing a nitrate solution with the concentration of 0.1-1mol/L, and adjusting the pH value of the nitrate solution to 5-6 by using a nitric acid solution and an ammonia water solution;

2) vertically placing an anodic aluminum oxide film in the nitrate solution obtained in the step 1), heating the nitrate solution, and growing Layered Double Hydroxides (LDHs) on the surface of the anodic aluminum oxide film;

3) and taking out the anodic alumina film with LDHs, fully soaking in deionized water, and drying at room temperature for 24h to obtain the nano fluid channel film with anion selectivity based on LDHs, namely the anion selective film.

The nitrate in the nitrate solution is nickel nitrate, cobalt nitrate or zinc nitrate;

the type of nitrate is selected according to the type of anion selective membrane to be prepared, and specifically comprises the following steps: the NiAl-LDH anion selective membrane is prepared by adopting a nickel nitrate solution, the CoAl-LDH anion selective membrane is prepared by adopting a cobalt nitrate solution, and the ZnAl-LDH anion selective membrane is prepared by adopting a zinc nitrate solution.

The aperture range of the anode alumina in the step 2) is controlled to be 160-200 nm.

The heating temperature in the step 2) is 80 ℃, and the heating time is 4-20 h.

The thickness of the anion selective membrane is 45-50 μm, and the size of the nano channel is 10-20 nm; the anion selective membrane is positively charged, when anions and cations in the concentrated salt solution have a tendency of migrating to the dilute salt solution under the drive of the salt difference, the membrane allows the anions to pass through and blocks the migration of the cations, so that the directional movement of charges is generated, current is generated, and the conversion from the salt difference energy to the electric energy is realized.

The invention has the beneficial effects that:

the nano fluid channel film prepared by the invention can convert salt difference energy into electric energy, the film is placed between nutrient solution and solution with fixed ion concentration level, the magnitude of output current feeds back the ion concentration gradient between the nutrient solution and the solution, and the output current signal can feed back the nutrient solution concentration level in real time.

Drawings

FIG. 1 is a scanning electron micrograph of a NiAl-LDH based nanofluidic channel thin film of example 1.

FIG. 2 is the BET test results of the NiAl-LDH based nanofluidic channel thin film of example 1; 2a is a nitrogen adsorption and desorption curve, and 2b is a pore size distribution curve.

FIG. 3 is a diagram of elemental analysis of NiAl-LDH based nanofluidic channel films in example 1; 3a is an elemental analysis diagram of chlorine, and 3b is an elemental analysis diagram of sodium.

Fig. 4 is a schematic diagram of an application device of the nanofluidic channel membrane in osmotic energy power generation in example 1.

FIG. 5 is a graph showing the relationship between the current density and the output power density and the external resistance obtained by the power generation method of example 1.

Fig. 6 is a graph showing the change of the output current density with time obtained by the power generation method in example 1.

FIG. 7 is a schematic view of the inside of the apparatus based on the nanofluidic channel membrane for detecting the ion concentration of the nutrient solution in example 2.

Fig. 8a is a graph of the current and conductivity of the nutrient solution as measured in example 2 versus nutrient solution concentration.

FIG. 8b is a schematic diagram of the system based on the nanofluidic channel membrane of example 2 for detecting the ionic concentration of the nutrient solution.

Fig. 8c is a schematic circuit diagram of the data acquisition board in embodiment 2.

FIG. 8d is a graph of current versus time obtained when different nutrient solution ion concentrations were tested as in example 2.

Detailed Description

The invention is further illustrated by the following figures and examples.

The invention provides application of a nanometer fluid channel film with anion selectivity based on LDHs in monitoring the ion concentration level of a nutrient solution in real time in water culture production. Hydroponic production is the main production method in plant factories by virtue of its high yield per unit area and low resource consumption. In hydroponic production, nutrient solutions containing various ions are commonly used to provide necessary nutrients for crop growth, and when the ion concentration in the nutrient solution is too high or too low, the yield of crops is limited. In actual production, the ion concentration of the nutrient solution is generally detected by measuring the conductivity of the nutrient solution, but the conductivity test electrode has the problem of potential drift in the long-term use process, so that the accuracy of the conductivity measurement result is reduced. In addition, the use of a large number of sensors per unit area for detection also results in high economic costs.

The anion selective nano fluid channel film based on LDHs has the following characteristics: an anodic aluminum oxide film layer as a substrate; and LDHs nanosheet layers which are uniformly distributed on the surface of the anodic alumina film and in the nano-channels, wherein the channel size of the nano-fluid channel film is 10-20 nm.

Preferably, the solution at the fixed ion concentration level in this application may be deionized water.

The LDHs-based nano fluid channel film provided by the invention has good selectivity on anions due to the high surface charge density of the LDHs, and meanwhile, the nano channel size of the film is controllable due to the influence of the growth time and the pH of a reaction solution on the growth amount of the LDHs. The thickness of the film is 45-50 μm, so that the film resistance is low.

In combination with the power generation process, anions in the high-concentration salt solution are transferred into the low-concentration salt solution through the nano fluid channel film based on LDHs, and the directional transfer of a large amount of anions forms internal current. In the specific implementation, the membrane is placed between two semi-conductive cells containing salt solutions of different concentrations, with 3X 10 on either side of the membrane^-8m²The silicon film of the small hole is used for controlling the actual working area of the film. An Ag/AgCl electrode is respectively arranged in the two semi-conductive tanks to connect the circuit.

1. The preparation method of the nanofluidic channel film of the Ni-Al LDH comprises the following steps:

1) preparing a nickel nitrate solution with the concentration of 1mol/L, and adjusting the pH value of the solution to 5.5;

2) vertically placing an anodic alumina film with the aperture of 160-200nm and the diameter of 15mm in a nickel nitrate solution, and heating the nitrate solution in a water bath at the temperature of 80 ℃ for 16 h;

3) and taking out the anodic aluminum oxide film, fully moistening and washing the anodic aluminum oxide film by deionized water, and drying the anodic aluminum oxide film for 24 hours at room temperature to obtain the Ni-Al LDH-based anion selective nano fluid channel film.

FIGS. 1a and 1b are scanning electron micrographs of the surface and cross section of a film, respectively, from which it can be seen that LDH nanosheets grow uniformly and abundantly inside and on the surface of the anodized aluminum channels, and the thickness of the film is 49 μm (FIG. 1 b).

The resulting nanofluidic channel diameter was 17.8nm as shown in fig. 2.

And performing an EDX test on the cross section of the film to verify the selectivity of the film on anions. The prepared film is immersed in 0.5mol/L NaCl for 24h, and unbound ions are washed away by deionized water. The results of the test are shown in FIG. 3, Cl in the nanofluidic channel^-The content of (A) is far higher than that of Na⁺The content of (a) proves that the film prepared by the method has anion selectivity.

The device for applying the membrane in osmotic energy power generation is shown in figure 4, and the electrolyte solution is a neutral solution. FIG. 5 shows the measured current density and output power density changes under different external resistors, and it can be found that the nano-fluid channelThe maximum power density of the film can reach 2.86 W.m^-2. In addition, as shown in fig. 6, the present membrane can maintain a stable output for 7 hours without separately replenishing the electrolyte solution.

2. Nutrient solution concentration detection device based on nano fluid channel film

In this example, the test was performed using a Hoagland formula, and the concentration level corresponding to the recommended formula was expressed as 1S.

Figure 7 shows the inside of a specially designed hydroponic tank. Specifically, the film is fixed on the side face of a cuboid container box with a hole through epoxy resin, the box serves as a container of nutrient solution, the box is placed in deionized water, and at the moment, a certain ion concentration difference is formed on two sides of the film. Because the ion concentration in the deionized water is constant, the ion concentration gradient at the two sides of the membrane changes along with the change of the ion concentration in the nutrient solution. An Ag/AgCl electrode is placed on each side of the film to connect the data acquisition circuit board, and the graph of FIG. 8a records the corresponding conductivity and measured current changes of the nutrient solution in the boxes with different concentrations. The conductivity is directly proportional to the concentration, and the current is positively correlated with the concentration, indicating that feeding back the nutrient solution concentration with the current is feasible. Accordingly, the real-time monitoring system shown in fig. 8b is designed, current signals generated by the thin film are processed through the data acquisition board of fig. 8c, specifically, the current signals are firstly converted into voltage signals through the I/V conversion circuit, the voltage signals are amplified through the amplifying circuit, then the AD acquisition is carried out by the STM32 microprocessor, the acquired signals are subjected to low-pass filtering through a low-pass filtering module in the microprocessor and then are sent to the upper computer, the upper computer converts the voltage into the current through the built-in ADC, the current value is drawn into a curve to be displayed, and meanwhile, corresponding prompts are given according to the size of the current.

In this example, the currents 0.27 μ A and 0.10 μ A for the 1S and 0.25S nutrient solutions are used as the upper and lower limits, and FIG. 8d is a current-time curve shown for four concentration levels. Corresponding reminding can be given according to whether the current exceeds the preset upper limit and the preset lower limit, red warning is displayed when the concentration exceeds the upper limit, green warning is displayed when the concentration is too low and is lower than the lower limit, and yellow warning is displayed when the concentration is normally between the upper limit and the lower limit.