A method for preparing a solid calcium ion selective electrode based on calcium manganese oxide

Abstract

The invention relates to the field of ion analysis sensors and discloses a preparation method of a solid-state calcium ion selective electrode based on calcium manganese oxide. The method comprises the following steps: using MnNO3 and NH4HCO3 as raw materials to obtain newly prepared MnCO3, washing by centrifugation, and drying; dispersing MnCO3 and CaCO3 in a 0.5M HNO3 solution, adding (NH4)2CO3 powder after solid dissolution, washing by centrifugation to obtain a precursor, adding graphene oxide (GO) during stirring, and pyrolyzing at high temperature to obtain a Ca-Mn-O material (Ca-Mn-O) loaded with reduced graphene oxide. x Mn y O z ‑rGO); a glassy carbon electrode with a diameter of 5 mm was used as the working electrode. x Mn y O z ‑rGO was ground in a mortar for 3 min, and then dispersed in N‑methylpyrrolidone (NMP) solution with PVC and PVDF at a mass ratio of 10:1:1, and ultrasonically dispersed for 2 h at a concentration of 10 mg / ml to obtain substance 1. Finally, 10 μL of the dispersion was coated on the treated glassy carbon electrode, and the active material electrode loading was about 0.48 mg cm ‑2 , and dried to obtain electrode Ca x Mn y O z ‑rGO; counter electrode Ca x Mn y O z ‑rGO was tested.

Description

Technical Field

[0001] The invention relates to the field of ion analysis sensors, and in particular to a method for preparing a solid calcium ion selective electrode based on calcium manganese oxide. Background Art

[0002] Ca 2+ It is an indispensable ion in the growth and development of the body. It can act as a signal molecule to maintain normal nerve conduction function and participate in the growth and changes of muscles and bones. 2+ Real-time, accurate and persistent monitoring of Ca2+ helps people monitor in real time whether the water quality meets the calcium ion content required by organisms. However, traditional analytical methods (such as spectral analysis) for measuring Ca2+ 2+ In contrast, potentiometric sensors based on ion selective membranes (ISMs) have become a popular method for measuring Ca concentration in water over the past 20 years due to their simple structure, small size, and light weight. 2+ the main means.

[0003] All calcium ion potential sensors currently used are constructed based on ion selective membranes of calcium ion carriers. As we all know, solid-state ion selective electrodes selectively recognize ions based on ion selective membranes, and then convert ion signals into electronic signals by solid-state transduction layers. However, such electrodes generally face the following disadvantages:

[0004] 1) The ion-selective membrane components are toxic and are prone to leakage during long-term use, causing contamination of the analyte;

[0005] 2) The organic ion groups in the membrane components (including ion carriers, polymer matrices, ion exchangers, and plasticizers) are extremely expensive;

[0006] 3) The mechanical strength of ion-selective membranes is relatively fragile and can be easily damaged during use;

[0007] 4) The water layer formed at the interface between the ion-selective membrane and the solid-state transduction layer can easily cause potential fluctuations and reduce the reliability of electrode test data. To this end, we proposed a method for preparing a solid-state calcium ion selective electrode based on calcium manganese oxide. Summary of the invention

[0008] 1. Technical issues to be resolved

[0009] In view of the deficiencies in the prior art, the present invention provides a method for preparing a solid calcium ion selective electrode based on calcium manganese oxide to solve the above problems.

[0010] (II) Technical solution

[0011] To achieve the above-mentioned purpose, the present invention provides the following technical solution: a method for preparing a solid calcium ion selective electrode based on calcium manganese oxide, comprising the following steps:

[0012] Step 1: Using MnNO3 and NH4HCO3 as raw materials, obtain newly prepared MnCO3, centrifuge and wash, and vacuum dry overnight;

[0013] Step 2: Disperse the newly prepared MnCO3 and CaCO3 in 0.5M HNO3 solution, add (NH4)2CO3 powder after solid dissolution, centrifuge and wash to obtain the precursor, and add GO during stirring;

[0014] Step 3: High temperature pyrolysis to obtain Ca x Mn y O z -rGO;

[0015] Step 4: A glassy carbon electrode with a diameter of 5 mm was used as the working electrode, and a platinum wire and a saturated calomel electrode were used as the counter electrode and the reference electrode, respectively, for pretreatment;

[0016] Step 5: First, Ca x Mn y O z -rGO was ground in a mortar for 3 min, and then dispersed in NMP solution with PVC and PVDF at a mass ratio of 10:1:1, and ultrasonically dispersed for 2 h at a concentration of 10 mg / ml to obtain substance 1;

[0017] Step 6: Finally, take 10 μL of the dispersion and coat it on the treated glassy carbon electrode. The active material electrode loading is about 0.48 mg cm -2 , and dried to obtain electrode Ca x Mn y O z -rGO;

[0018] Step 7: Counter Electrode Ca x Mn y O z -rGO for testing.

[0019] Preferably, the ratio of the three materials in the second step should satisfy (1)n(Ca 2+ +Mn 2+ ):n(CO3 2- )=1 / 5,n(NH4)2CO3=0.5.

[0020] Preferably, the specific content of the pretreatment in the fourth step is: the glassy carbon electrode needs to be polished on a nylon cloth with 0.3 μm Al2O3 polishing powder first, then polished with 0.05 μm Al2O3 polishing powder after cleaning, and finally washed with clean water and ethanol several times.

[0021] Preferably, the drying treatment condition in the sixth step is to place in an oven at 60° C. and dry for 6 hours.

[0022] Preferably, the high temperature pyrolysis condition in the third step is to place the alumina porcelain boat in a tubular furnace and calcine it under an argon atmosphere.

[0023] Preferably, the electrode needs to be pretreated before the test in the seventh step, Ca x Mn y O z -rGO electrodes were heated to 10 -4 Soak in M ​​CaCl2 solution overnight.

[0024] (III) Beneficial effects

[0025] Compared with the prior art, the present invention provides a method for preparing a solid calcium ion selective electrode based on calcium manganese oxide, which has the following beneficial effects:

[0026] 1. The preparation method of the solid-state calcium ion selective electrode based on calcium manganese oxide breaks the limitation that the traditional solid-state calcium ion selective electrode needs to be based on the ion selective membrane (ISM) to identify external ions. While reducing the cost, it avoids the interference of the water layer and improves the stability of the electrode.

[0027] 2. The preparation method of the solid-state calcium ion selective electrode based on calcium manganese oxide. Both calcium manganese oxide and reduced graphene oxide have good biocompatibility, low price and excellent chemical stability. Based on this, we constructed an analytical sensor for real-time monitoring of calcium ion changes in hydroponic plants.

[0028] 3. The preparation method of the solid-state calcium ion selective electrode based on calcium manganese oxide has for the first time constructed a solid-state calcium ion selective electrode based on calcium manganese oxide-reduced graphene oxide. This sensor has the advantages of low cost, high sensitivity, good selectivity, etc., and has great application potential and commercial prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Ca x Mn y O z Schematic diagram of X-ray diffraction (XRD) pattern;

[0030] Figure 2 Ca x Mn yO z Scanning electron microscope (SEM) images of

[0031] Figure 3 (a) Ca x Mn y O z Electrode for Ca 2+ (a) Schematic diagram of the corresponding potential-calcium ion activity calibration curve; (c) Ca x Mn y O z Correction curve of electrode potential response to interfering ions; (d) Ca x Mn y O z pH interference test of the electrode.

[0032] Figure 4 Ca x Mn y O z -Schematic diagram of X-ray diffraction (XRD) pattern of rGO;

[0033] Figure 5 Ca x Mn y O z -Scanning electron microscopy (SEM) image of rGO;

[0034] Figure 6 (a) Ca x Mn y O z -rGO electrode for Ca 2+ (b) Schematic diagram of the corresponding potential-calcium ion activity calibration curve;

[0035] Figure 7 It is a schematic diagram of potential comparison, selectivity coefficient, potential response curve comparison and pH interference test;

[0036] Figure 8 This is a comparison chart of the results of actual sample testing through ion chromatography and ion selective electrode testing. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] See also Figure 1-6, a method for preparing a solid calcium ion selective electrode based on calcium manganese oxide, comprising the following steps:

[0039] 1) Calcium manganese oxide-reduced graphene oxide (Ca x Mn y O z -rGO) to construct a solid-state calcium ion-selective electrode without an ion-selective membrane and verify the online analysis of calcium ion concentration in hydroponic plants.

[0040] 2) Ammonium carbonate (ultrapure) ((NH4)2CO3), calcium carbonate (99%+) (CaCO3), manganese (II) nitrate tetrahydrate (MnNO3), nitric acid (HNO3), N-methylpyrrolidone (NMP) and tris(hydroxymethyl)aminomethane (Tris) were purchased from Beijing Inokai Technology Co., Ltd.; polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl), and calcium chloride (CaCl2) were purchased from Sigma-Aldrich Co., Ltd.; ammonium bicarbonate (NH4HCO3) and hydrochloric acid (HCl) were purchased from China National Pharmaceutical Group Co., Ltd.; Ca x Mn y O z Self-synthesized.

[0041] 3) Using MnNO3 and NH4HCO3 as raw materials, first prepare MnCO3, centrifuge and wash, and vacuum dry overnight. Then disperse the newly prepared MnCO3 and CaCO3 in 0.5M HNO3 solution, add a certain amount of (NH4)2CO3 powder after the solid is dissolved, and the ratio of the three materials must meet (1)(1)n(CaCO3) 2+ +Mn 2+ ):n(CO3 2- )=1 / 5n(NH4)2CO3=0.5, centrifuge and wash to obtain the precursor (Ca x Mn y CO3). The precursor was placed in an alumina porcelain boat in a muffle furnace and sintered at 950°C for 10 h. After cooling, Ca x Mn y O z The final product.

[0042] 4) X-ray diffraction (XRD) was used to characterize the synthesized Ca x Mn y O z The crystal structure was analyzed, such as Figure 1 As shown, after comparison with the PDF standard card, it belongs to the orthorhombic crystal type.

[0043] 5) Scanning electron microscope (SEM) test ( Figure 2), Ca x Mn y O z The microscopic morphology is nanoparticles with a particle size of 100 nm, which are aggregated into loose microspheres with a unique porous spherical shape ( Figure 2 ).

[0044] 6) A glassy carbon electrode (GCE) with a diameter of 5 mm was used as the working electrode, and a platinum wire and a saturated calomel electrode were used as the counter electrode and the reference electrode, respectively; before use, the glassy carbon electrode was polished on a nylon cloth with 0.3 μm Al2O3 polishing powder, then cleaned and polished with 0.05 μm Al2O3 polishing powder, and finally washed several times with clean water and ethanol.

[0045] 7) All electrochemical tests were completed using a Gamry electrochemical workstation and EMF6 multi-channel potentiometer.

[0046] 8) Preparation of solid calcium ion selective electrode: First, Ca x Mn y O z The powder was ground in a mortar for 3 min, and then dispersed in NMP solution with PVC and PVDF at a mass ratio of 10:1:1, and ultrasonically dispersed for 2 h, with a concentration of 10 mg / ml. Finally, 10 μL of the dispersion was coated on the treated glassy carbon electrode, and the active material electrode loading was about 0.48 mg cm -2 Place in a 60℃ oven and dry for 6h. The electrode is recorded as Ca x Mn y O z .

[0047] 9) Use the electrochemical open circuit potential test method to test Ca x Mn y O z Ca 2+ The potential response of Figure 3 As shown in a and b, it can be seen that Ca x Mn y O z -rGO electrode for Ca 2+ The sensitivity is 26.47mV dec -1 , detection limit 10 -4.53 M. Ca x Mn y O z The potential response of the electrode to the interfering ions is as follows Figure 3 As shown in c, it can be seen that the potential curves of all interfering ions are also within the target ion Ca 2+ The curve is shown below. The CaCl2 concentration in Tris-HCl buffers ranging from pH 4 to 8 was 0.1 M.x Mn y O z Perform pH interference test, the test results are as follows Figure 3 As shown in d, the potential fluctuates greatly with the change of pH, indicating that pH has an important effect on Ca x Mn y O z There is a big interference.

[0048] 10) To solve the problem of Ca x Mn y O z To solve the pH interference problem, we added rGO (rGO accounts for m% of the theoretical product) and Ca x Mn y O z -rGO was prepared by adding rGO (rGO accounted for m% of the theoretical product) during the stirring process of the precursor, and replacing the muffle furnace with a tube furnace placed in an alumina porcelain boat under an argon atmosphere to obtain Ca x Mn y O z -rGO. The synthesized Ca x Mn y O z -rGO crystal structure was analyzed, such as Figure 4 As shown, it is also an orthorhombic crystal. Scanning electron microscopy (SEM) test ( Figure 5 ), Ca x Mn y O z -rGO surface becomes smooth.

[0049] 11) Electrode Ca can be obtained by the same method as in step 8 x Mn y O z -rGO.

[0050] 12) Use the electrochemical open circuit potential test method to test Ca x Mn y O z -rGO for Ca 2+ The potential response of Figure 6 As shown, it can be seen that Ca x Mn y O z -rGO electrode for Ca 2+ The sensitivity is 27.99mV dec -1 , detection limit 10 -4.2 M.

[0051] 13) Test Ca x Mny O z -rGO for Ca 2+ Selectivity of response. Ca x Mn y O z The potentials of interfering ions and target ions of rGO at 0.1 M are shown in Figure 2. Figure 7 As shown in a, it can be seen that the potentials of all interfering ions are above the target ion Ca 2+ The potential is below that of Ca x Mn y O z -rGO for Ca 2+ It has a certain selectivity. The selectivity coefficient for each interfering ion is calculated by the selectivity coefficient formula, as shown in Figure 7 b. + 、Na + , Li + and Mg 2+ The selectivity coefficient is calculated to obtain logK ij ≤–2. This is comparable to the selectivity of calcium ion carriers reported so far. x Mn y O z The potential response of the rGO electrode to interfering ions is shown in Figure 7 As shown in c, it can be seen that the potential curves of all interfering ions are also within the target ion Ca 2+ Below the curve, it is again proved that Ca x Mn y O z -rGO for Ca 2+ It has a certain selectivity. And in the 0.1M CaCl2 background solution, from pH 4 to 8 in Tris-HCl buffer, x Mn y O z -rGO was tested for pH interference, and the test results were as follows Figure 7 As shown in (d), when the pH changes, the potential fluctuates slightly, proving that the addition of rGO is beneficial to reducing the interference of pH.

[0052] 14) Use Ca x Mn y O z -rGO calcium ion selective electrode, testing Ca in 3 mineral waters and 3 soil leachates 2+ Each sample consists of 3 Ca 2+ -SC-ISEs individual test. The test results are compared with the ion chromatography test results. Figure 8 a, b. It can be seen that the two measurement results are basically consistent, proving that the ion selective electrode has good analytical performance.x Mn y O z -rGO electrode for online testing of Ca in hydroponic garlic 2+ changes, such as Figure 8 c. During the test, Ca x Mn y O z -rGO test curve is consistent with the change trend of IC test results. Due to ion stress (the calcium ion content in the culture solution is higher than that of garlic), when garlic is first put into the culture solution, calcium ions will be released to the outside world, causing the calcium ion content in the solution to increase, and then the calcium ion potential tends to remain unchanged. But in fact, the concentration change range obtained by the test is much larger than the actual concentration change range. This is mainly due to the CO2 produced during plant growth and Ca x Mn y O z There is a certain complexation effect, which makes the potential change greatly. Therefore, general plant culture media need flowing water to ensure that the culture media is rich in oxygen for plant growth. However, in order to ensure that the real-time calcium ion changes during plant growth can be measured, the test was not conducted under flowing conditions. During the test, Ca x Mn y O z The -rGO test curve is consistent with the changing trend of the IC test results, which to a certain extent makes it possible to apply this material to water quality testing and realize real-time testing in actual production and life.

[0053] The present invention firstly uses calcium manganese oxide-reduced graphene oxide (Ca x Mn y O z -rGO) was used to prepare Ca-free ion-selective membranes. 2+ Selective electrode, as far as we know, this is the first solid-state calcium ion selective electrode without ion selective membrane. The present invention breaks the limitation that traditional solid-state calcium ion selective electrodes need to be based on ion selective membranes (ISM) to identify external ions, while reducing costs and avoiding interference from the water layer, improving the stability of the electrode; it is worth mentioning that calcium manganese oxide and reduced graphene oxide have good biocompatibility, low price, and excellent chemical stability. Based on this, we have constructed an analytical sensor for real-time monitoring of calcium ion changes in hydroponic plants. In summary, the present invention has for the first time constructed a solid-state calcium ion selective electrode based on calcium manganese oxide-reduced graphene oxide. The sensor has the advantages of low cost, high sensitivity, good selectivity, etc., and has huge application potential and commercial prospects.

[0054] Explanation of the drawings

[0055] Figure 7 Medium(a)Cax Mn y O z -rGO electrode for 0.1M target ion concentration (Ca 2+ ) and its interfering ions potential comparison; (b) Ca x Mn y O z -rGO electrode selectivity coefficient for interfering ions; (c) Ca x Mn y O z -rGO electrode for target ion Ca 2+ Comparison of potential response curves of Ca and its interfering ions; (d) Ca x Mn y O z -rGO electrode was tested for pH interference in Tris-HCl buffer ranging from pH 4 to 8 in the presence of 0.1 M CaCl2 background solution.

[0056] Figure 8 (a) Based on Ca x Mn y O z -rGO calcium ion sensor test three kinds of mineral water and (a) three kinds of soil eluent test and ion chromatography test results comparison; (c) Ca-based x Mn y O z -rGO calcium ion sensor test of garlic calcium ion concentration changes during 3 days of growth and comparison with ion chromatography test results.

[0057] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a solid calcium ion selective electrode based on calcium manganese oxide, characterized in that: The following steps are involved: Step 1: Using MnNO3 and NH4HCO3 as raw materials, obtain newly prepared MnCO3, centrifuge and wash, and vacuum dry overnight; Step 2: Disperse the newly prepared MnCO3 and CaCO3 in 0.5M HNO3 solution, add (NH4)2CO3 powder after solid dissolution, centrifuge and wash to obtain the precursor, and add GO during stirring; Step 3: High temperature pyrolysis to obtain Ca x Mn y O z -rGO; Step 4: A glassy carbon electrode with a diameter of 5 mm was used as the working electrode, and a platinum wire and a saturated calomel electrode were used as the counter electrode and the reference electrode, respectively, for pretreatment; Step 5: First, Ca x Mn y O z -rGO was ground in a mortar for 3 min, and then dispersed in NMP solution with PVC and PVDF at a mass ratio of 10:1:1, and ultrasonically dispersed for 2 h to a concentration of 10 mg / ml to obtain a dispersion; Step 6: Finally, 10 μL of the dispersion was coated on the treated glassy carbon electrode. The active material electrode loading was 0.48 mg cm -2 , and dried to obtain electrode Ca x Mn y O z -rGO; Step 7: Counter Electrode Ca x Mn y O z -rGO for testing.

2. The method for preparing a solid calcium ion selective electrode based on calcium manganese oxide according to claim 1, characterized in that: In the second step, n(Ca 2+ +Mn 2+ ):n(CO3 2- )=1:

5.

3. The method for preparing a solid calcium ion selective electrode based on calcium manganese oxide according to claim 1, characterized in that: The specific content of the pretreatment in the fourth step is: the glassy carbon electrode needs to be polished with 0.3 μm Al2O3 polishing powder on nylon cloth first, then polished with 0.05 μm Al2O3 polishing powder after cleaning, and finally washed with clean water and ethanol several times.

4. The method for preparing a solid calcium ion selective electrode based on calcium manganese oxide according to claim 1, characterized in that: The drying treatment condition in the sixth step is to place the product in an oven at 60° C. and dry it for 6 hours.

5. The method for preparing a solid calcium ion selective electrode based on calcium manganese oxide according to claim 1, characterized in that: The high temperature pyrolysis condition in the third step is to place the alumina porcelain boat in a tube furnace under an argon atmosphere and calcine at 950° C. for 10 hours.

6. The method for preparing a solid calcium ion selective electrode based on calcium manganese oxide according to claim 1, characterized in that: Before the test in the seventh step, the electrode needs to be pretreated, Ca x Mn y O z -rGO electrodes were heated to 10 -4 Soak in M ​​CaCl2 solution overnight.

Images