A single-atom iron-modified MXene membrane electrode and its preparation and application; an electrocatalytic device and method for nitrate reduction to ammonia production.

Abstract

This invention provides an iron-modified MXene membrane electrode, its preparation and application, and an electrocatalytic device and method for nitrate reduction to ammonia production, belonging to the fields of water treatment and resource utilization technology. The iron-modified MXene membrane electrode prepared by this invention possesses isolated iron active sites, exhibiting high electrochemical activity, excellent nitrate electrocatalytic reduction performance, extremely high ammonia selectivity and ammonia production Faradaic efficiency, and extremely low byproduct yield. This invention employs a flow-through operation mode, which significantly enhances intramembrane mass transfer and electron transfer efficiency during the reaction, accelerating the kinetics of nitrate reduction. Using the FeSA / MXene membrane electrode for the electrochemical reduction of nitrate to ammonia production demonstrates high nitrate removal efficiency and ammonia production rate, which is of great significance for the harmlessness and resource utilization of nitrate.

Description

Technical Field

[0001] This invention relates to the fields of water treatment technology and resource utilization technology, and in particular to an iron single-atom modified MXene membrane electrode and its preparation and application, and an electrocatalytic nitrate reduction ammonia production device and method. Background Technology

[0002] The overuse of eutrophication has led to the inevitable accumulation of nitrogenous pollutants in the environment. For example, surface runoff increases nitrate concentrations in natural water bodies to 60–300 mg / L, prompting stringent global regulations to limit nitrate concentrations. While various physical, chemical, and biological methods are widely used and technically mature for nitrate removal, electrochemical nitrate reduction remains a focus of attention. Generally, the final products of electrochemical nitrate reduction are nitrogen or ammonia. However, the conversion to harmless nitrogen is kinetically slow. Conversely, ammonia is an important chemical feedstock, serving as a medium for energy transfer and storage. Therefore, the electroreduction of nitrate to ammonia has been identified as a "two birds with one stone" strategy, providing a sustainable pathway for pollutant removal and the recovery of high-value substances.

[0003] In the field of electrocatalytic nitrate reduction, iron-based catalysts have become a research focus due to their natural abundance, high activity, and low nitrite selectivity. However, traditional iron-based electrocatalysts face challenges such as low atom utilization, high energy consumption, and poor long-term stability. A promising approach to overcome these shortcomings is the use of single-atom catalysts. Compared to bulk catalysts, single-atom catalysts possess higher atom utilization, unique activity, and selectivity, showing the potential for efficient conversion of nitrates to ammonia. However, current electrocatalytic degradation of nitrates still suffers from low conversion rates, low Faradaic efficiency in ammonia production, and low ammonia production rates. Importantly, the electrocatalytic reduction of nitrates to ammonia using single-atom catalysts typically requires an alkaline environment or a high concentration of nitrate feedstock (>0.1M), limitations that are too stringent for most water treatment systems. Summary of the Invention

[0004] The purpose of this invention is to provide an iron single-atom modified MXene membrane electrode and its preparation and application, as well as an electrocatalytic nitrate reduction ammonia production device and method, which can achieve high ammonia production rate and conversion, extremely high ammonia selectivity and ammonia production Faraday efficiency in a neutral environment.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing an iron single-atom modified MXene film electrode, comprising the following steps:

[0007] The MXene aqueous dispersion was mixed with a ferric salt solution to obtain a mixed dispersion.

[0008] The mixed dispersion was filtered onto a polymer-supported membrane to obtain an iron single-atom modified MXene membrane electrode.

[0009] Preferably, the concentration of the MXene aqueous dispersion is 1-3 mg / mL, and the MXene in the MXene aqueous dispersion includes Ti3C2T. x .

[0010] Preferably, the concentration of the ferric salt solution is 0.5–4 mg / mL, and the mass ratio of MXene to ferric salt in the ferric salt solution is (20–30):(1–5).

[0011] Preferably, the mixing is carried out under ultrasonic or stirring conditions, wherein the stirring speed is 500-800 rpm, the temperature is 20-25℃, and the time is 0.5-1h; the ultrasonic power is 100-500W, the temperature is 20-30℃, and the time is 0.5-1h.

[0012] The present invention provides an iron single-atom modified MXene film electrode prepared by the preparation method described above, comprising a polymer support film and iron single-atom anchored MXene nanosheets loaded on the polymer support film.

[0013] This invention provides the application of the iron single-atom modified MXene membrane electrode described above in the electrocatalytic reduction of nitrate to ammonia.

[0014] This invention provides an electrocatalytic nitrate reduction ammonia production flow filtration device, comprising an iron single-atom modified MXene membrane electrode and a porous titanium sheet arranged sequentially; the iron single-atom modified MXene membrane electrode and the porous titanium sheet are in a flow state.

[0015] Preferably, it also includes an Ag / AgCl reference electrode, and an insulating silicone block is disposed between the iron single-atom modified MXene film electrode and the porous titanium sheet.

[0016] This invention provides a method for electrocatalysis using the electrocatalytic nitrate reduction ammonia production flow filtration device described above, comprising the following steps:

[0017] The electrocatalytic nitrate reduction ammonia production flow filter is externally connected to an electrochemical workstation. Using nitrate as raw material, the nitrate-containing raw material liquid is passed through the electrocatalytic nitrate reduction ammonia production flow filter for electrocatalysis.

[0018] Preferably, the potential of the external power supply for the electrocatalysis is -1.2 to -1.6V; the concentration of sodium nitrate in the nitrate-containing raw material solution is 300 to 1200 mg / L; the pH value of the nitrate-containing raw material solution is 2 to 10; and the flow rate is 0 to 6 mL / min.

[0019] This invention involves filtering a mixed dispersion of MXene aqueous solution and ferric salt onto a polymer substrate membrane to prepare an iron-modified MXene membrane electrode (FeSA / MXene) with uniformly distributed iron single atoms. The iron-modified MXene membrane electrode prepared by this invention possesses isolated iron active sites and exhibits high electrochemical activity. Compared to particulate catalysts, the FeSA / MXene membrane electrode of this invention improves the utilization rate of iron active sites due to the uniform distribution of iron single atoms, atomic scale effect, and electronic state regulation. Therefore, it possesses excellent nitrate electrocatalytic reduction performance, extremely high ammonia selectivity and ammonia production Faradaic efficiency, and extremely low byproduct yield.

[0020] The synthesis method of the iron single-atom modified MXene membrane electrode of the present invention is simple and easy to operate. Since it is used to prepare a membrane electrode, it solves the problem that particulate catalysts are difficult to recover and reuse.

[0021] This invention provides a flow-through filtration device for the electrocatalytic reduction of nitrate to ammonia. The device comprises an iron-modified MXene membrane electrode and a porous titanium sheet, allowing for efficient electrocatalytic reduction of nitrate to ammonia by introducing the nitrate feedstock. The flow-through operation continuously transmits the solution from the membrane electrode to the porous titanium sheet, significantly enhancing mass transfer and electron transfer efficiency within the membrane, thus accelerating the kinetics of nitrate reduction. Under an applied auxiliary electric field, the FeSA / MXene membrane electrode generates highly reducing active hydrogen during cathode electrolysis of water, suppressing the generation of hydrogen gas as a byproduct. This active hydrogen can be used for efficient nitrate reduction to ammonia, improving ammonia selectivity and Faraday efficiency. Moreover, the FeSA / MXene membrane electrode exhibits high nitrate removal efficiency and extremely high tolerance in complex systems (pH (acidic and alkaline environments), inorganic salts) because the isolated distribution of iron single atoms can avoid iron aggregation and oxidation. Thus, it can effectively and selectively convert low concentrations of nitrate (sodium nitrate concentration 300-1200 mg / L) into ammonia in different environments.

[0022] Therefore, this invention uses the FeSA / MXene membrane electrode for the electrochemical reduction of nitrate to ammonia, which has high nitrate removal efficiency and ammonia production rate, while also having good cycle stability and practicality, which is of great significance for the harmlessness and resource utilization of nitrate. Attached Figure Description

[0023] Figure 1 This is a plan view of the electrocatalytic nitrate reduction ammonia production flow filtration device described in this invention;

[0024] Figure 2 TEM images of the FeSA / MXene membrane electrode in Example 1 and the FeNP / MXene membrane electrode in Comparative Example 1;

[0025] Figure 3 HAADF-STEM image of the FeSA / MXene film electrode prepared in Example 1;

[0026] Figure 4 The graph shows the results of electrocatalytic nitrate reduction to ammonia production using the FeSA / MXene membrane electrode described in Example 1 and the FeNP / MXene membrane electrode described in Comparative Example 1, respectively, through the electrocatalytic flow-through filtration device of the present invention.

[0027] Figure 5 The linear sweep voltammetry curve of the FeSA / MXene membrane electrode described in Example 1 is shown below.

[0028] Figure 6 The graph shows the changes in the concentrations of nitrate, nitrite, and ammonia over time during the electrocatalytic reduction of nitrate using the FeSA / MXene membrane electrode in Application Example 1.

[0029] Figure 7 The electron paramagnetic resonance spectrum of the FeSA / MXene membrane electrode when DMPO is added as a trapping agent in Application Example 1;

[0030] Figure 8 The effect of FeSA / MXene membrane electrode in Application Examples 1-2 on the electrocatalytic reduction of nitrate to ammonia under different pH conditions;

[0031] Figure 9 The graph shows the results of the Faraday efficiency and nitrate removal rate of the FeSA / MXene membrane electrode under different potentials in Application Examples 1 and 3. Detailed Implementation

[0032] This invention provides a method for preparing an iron single-atom modified MXene film electrode, comprising the following steps:

[0033] The MXene aqueous dispersion was mixed with a ferric salt solution to obtain a mixed dispersion.

[0034] The mixed dispersion was filtered onto a polymer-supported membrane to obtain an iron single-atom modified MXene membrane electrode.

[0035] In this invention, unless otherwise specified, all raw materials required for preparation are commercially available products well known to those skilled in the art.

[0036] In this invention, the concentration of the MXene aqueous dispersion is preferably 1-3 mg / mL, more preferably 2-2.5 mg / mL; the MXene in the MXene aqueous dispersion preferably includes Ti3C2T. x The present invention does not impose any special limitations on the preparation process of the MXene aqueous dispersion; a uniform dispersion can be obtained by following a process well known in the art.

[0037] In this invention, the ferric salt in the ferric salt solution preferably includes FeCl3, and the concentration of the ferric salt solution is preferably 0.5-4 mg / mL, more preferably 1-2 mg / mL.

[0038] In this invention, the preferred mass ratio of MXene to ferric salt in the ferric salt solution is (20-30):(1-5), and more preferably 25:(2-4).

[0039] In this invention, a ferric salt solution is preferably added dropwise to the MXene aqueous dispersion. The present invention does not have a particular limitation on the rate of addition, and the addition can be carried out according to a process known in the art.

[0040] In this invention, the mixing is preferably carried out under ultrasonic or stirring conditions. The stirring speed is preferably 500-800 rpm, the temperature is preferably 20-25°C, and the time is preferably 0.5-1 h. The ultrasonic power is preferably 100-500 W, more preferably 200-300 W, the temperature is 20-30°C, more preferably 25°C, and the time is preferably 0.5-1 h, more preferably 30-40 min.

[0041] In this invention, the preferred method of filtration is vacuum filtration. This invention does not impose any special limitations on the conditions for vacuum filtration; filtration can be performed according to a process well known in the art.

[0042] In this invention, the polymer support film is preferably a polytetrafluoroethylene film.

[0043] This invention provides an iron-modified MXene film electrode prepared by the method described above, comprising a polymer support film and iron-anchored MXene nanosheets loaded on the polymer support film. Specifically, the iron single atoms form Fe-O coordination bonds with oxygen in MXene; the iron has valence states of +2 and +3; the MXene surface contains numerous terminal "T" groups, including -O, -OH, and -F groups, which can adsorb metal precursors through electrostatic attraction; and MXene contains reducing Ti vacancy defects, which can reduce trivalent iron to divalent iron.

[0044] This invention provides the application of the iron single-atom modified MXene membrane electrode described above in the electrocatalytic reduction of nitrate to ammonia.

[0045] like Figure 1 As shown, the present invention provides an electrocatalytic nitrate reduction ammonia production flow filtration device, comprising an iron single-atom modified MXene membrane electrode and a porous titanium sheet arranged sequentially; the iron single-atom modified MXene membrane electrode and the porous titanium sheet are in a flow state.

[0046] In this invention, the "flow state" means that both the iron single-atom modified MXene membrane electrode and the porous titanium sheet can flow with the raw material liquid.

[0047] In this invention, the iron single-atom modified MXene film electrode serves as the working electrode (cathode), and the porous titanium sheet serves as the counter electrode (anode); an insulating silicone block is provided between the iron single-atom modified MXene film electrode and the porous titanium sheet to prevent short circuits caused by the connection of the anode and cathode.

[0048] The present invention does not have any particular limitations on the porous titanium sheet and the insulating silicone block, and any commercially available products well known in the art are acceptable.

[0049] In this invention, the electrocatalytic nitrate reduction ammonia production flow filtration device further includes an Ag / AgCl reference electrode.

[0050] This invention provides a method for electrocatalysis using the electrocatalytic nitrate reduction ammonia production flow filtration device described above, comprising the following steps:

[0051] The electrocatalytic nitrate reduction ammonia production flow filter is externally connected to an electrochemical workstation. Using nitrate as raw material, the nitrate-containing raw material liquid is passed through the electrocatalytic nitrate reduction ammonia production flow filter for electrocatalysis.

[0052] In this invention, the potential of the external power supply for the electrocatalysis is preferably -1.2 to -1.6V, more preferably -1.3 to -1.5V; the potential is preferably provided by an electrochemical workstation. This invention does not impose any particular limitation on the electrochemical workstation; any device well-known in the art is acceptable; in an application example of this invention, it is specifically a CHI 660E.

[0053] In this invention, the concentration of sodium nitrate in the nitrate-containing raw material solution is preferably 300-1200 mg / L, the pH value of the nitrate-containing raw material solution is preferably 2-10, more preferably 4.0-6.0, and the flow rate is preferably 0-6 mL / min.

[0054] In this invention, the nitrate-containing raw material solution is preferably nitrate wastewater; in an application example of this invention, a nitrate wastewater simulation solution prepared using sodium nitrate as a raw material is preferably used.

[0055] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0056] Example 1

[0057] 2 mL of a 1 mg / mL FeCl3 aqueous solution was added dropwise to 25 mL of a 1 mg / mL Ti3C2T solution. x In an aqueous dispersion, ultrasonic dispersion was performed to obtain a mixed dispersion, wherein the ultrasonic dispersion power was 200W, the ultrasonic dispersion time was 40min, and the ultrasonic dispersion temperature was 20℃.

[0058] The mixed dispersion was vacuum filtered onto a polytetrafluoroethylene membrane to obtain an iron single-atom modified MXene membrane electrode, denoted as FeSA / MXene membrane electrode.

[0059] Example 2

[0060] 2 mL of a 2 mg / mL FeCl3 aqueous solution was added dropwise to 15 mL of a 2 mg / mL Ti3C2T solution. x In an aqueous dispersion, ultrasonic dispersion was performed to obtain a mixed dispersion, wherein the ultrasonic dispersion power was 300W, the ultrasonic dispersion time was 30min, and the ultrasonic dispersion temperature was 25℃.

[0061] The mixed dispersion was vacuum filtered onto a polytetrafluoroethylene membrane to obtain a FeSA / MXene membrane electrode.

[0062] Example 3

[0063] 2 mL of a 2 mg / mL FeCl3 aqueous solution was added dropwise to 25 mL of a 1 mg / mL Ti3C2T solution. x In an aqueous dispersion, ultrasonic dispersion was performed to obtain a mixed dispersion, wherein the ultrasonic dispersion power was 100W, the ultrasonic dispersion time was 60min, and the ultrasonic dispersion temperature was 30℃.

[0064] The mixed dispersion was vacuum filtered onto a polytetrafluoroethylene membrane to obtain a FeSA / MXene membrane electrode.

[0065] Comparative Example 1

[0066] The amount of FeCl3 aqueous solution in Example 1 was increased to 20 mL, and 1 mL of hydrazine hydrate was added. The rest was the same as in Example 1, and FeNP / MXene membrane electrode was obtained.

[0067] Characterization

[0068] Figure 2TEM images of the FeSA / MXene and FeNP / MXene film electrodes prepared in Example 1 and Comparative Example 1, from... Figure 2 No nanoparticles can be observed in FeSA / MXene. In contrast, iron nanoparticles are clearly visible in FeNP / MXene.

[0069] Figure 3 The image shown is a HAADF-STEM image of the FeSA / MXene film electrode prepared in Example 1. Figure 3 The bright spot is an iron single atom.

[0070] Application Example 1

[0071] Different membrane electrodes were used for the electrocatalytic reduction of nitrate to ammonia, with flow-through operation structures such as... Figure 1 As shown, the cathode is the FeSA / MXene film electrode prepared in Example 1.

[0072] The flow-through operating structure was connected to an electrochemical workstation (model CHI 660E). Before testing, the working electrode was connected to the FeSA / MXene membrane electrode (Example 1), the counter electrode was connected to a porous titanium sheet, and the Ag / AgCl electrode was used as the reference electrode. After assembly, 100 mL of a mixed aqueous solution of 0.1 mol / L Na₂SO₄ and 300 mg / L sodium nitrate (pH 7.0) saturated with argon gas was pumped into the filter device at a flow rate of 6 mL / min in the direction of the arrow, and flowed out of the outlet in the direction of the arrow after passing through the FeSA / MXene membrane electrode and the porous titanium sheet. The electrocatalytic experiment used the constant voltage method with an applied voltage of -1.4 V. The electrochemical measurement was performed using a linear voltammetric scan method with a scanning potential range of 0 to -1.60 V.

[0073] Application Example 2

[0074] The only difference between Application Example 2 and Application Example 1 is that: using 1 mol / L hydrochloric acid and / or sodium hydroxide solution, the pH of a mixed aqueous solution of 0.1 mol / L Na2SO4 and 300 mg / L sodium nitrate is adjusted to 2.0, 4.0 and 10.0 respectively to reduce nitrate to produce ammonia.

[0075] Application Example 3

[0076] The difference between Application Example 3 and Application Example 1 is that the applied potential is set to -1.2V, -1.3V, -1.5V and -1.6V respectively to reduce nitrate to produce ammonia.

[0077] Comparative Application Example 1

[0078] The only difference from Application Example 1 is that the FeNP / MXene membrane electrode prepared in Comparative Example 1 is used instead of the FeSA / MXene membrane electrode for electrocatalytic reduction of nitrate to ammonia.

[0079] Test Results

[0080] 1) Figure 4 The graph shows the results of electrocatalytic nitrate reduction to ammonia production using the FeSA / MXene membrane electrode described in Example 1 and the FeNP / MXene membrane electrode described in Comparative Example 1, respectively, through the electrocatalytic flow-through filtration device of the present invention. Figure 4 As can be seen, the FeSA / MXene membrane electrode exhibits excellent nitrate removal performance, ammonia production Faradaic efficiency, and selectivity. Furthermore, the FeSA / MXene membrane electrode with isolated iron active sites demonstrates even higher nitrate removal performance, ammonia selectivity, and Faradaic efficiency.

[0081] 2) Electrochemical linear sweep voltammetry was performed sequentially in aqueous solutions containing 0.1 mol / L Na₂SO₄ and 0.1 mol / L Na₂SO₄ + 600 mg / L NaNO₃, respectively. The results are shown in [Figure number missing]. Figure 5 ; Figure 5 The linear scan voltammetry curve (linear scan rate: 10 mV / s, voltage range: 0 V to -1.60 V) of the FeSA / MXene film electrode described in Example 1 is shown below. Figure 5 As can be seen, the addition of nitrate resulted in a higher reduction current density, and a new reduction peak appeared at -1.35V, confirming the occurrence of the nitrate reduction reaction.

[0082] 3) Figure 6 This is a graph showing the changes in the concentrations of nitrate, nitrite, and ammonia over time during the electrocatalytic nitrate reduction process using a FeSA / MXene membrane electrode in Application Example 1. Figure 6 It can be seen that as time increases, nitrates decrease continuously, ammonia concentration increases continuously, and nitrites are not detected.

[0083] 4) Take 10 μL of DMPO and 50 μL of 0.1 mol / L Na₂SO₄ aqueous solution, and take 10 μL of DMPO and 50 μL of 0.1 mol / L Na₂SO₄ + 600 mg / L NaNO₃ aqueous solution. Place the two mixtures separately in centrifuge tubes, shake well, transfer to capillary tubes, and then transfer to specific quartz test tubes for electron paramagnetic spectroscopy testing. The results are shown in [Figure 1]. Figure 7 ; Figure 7 The electron paramagnetic resonance spectrum of the FeSA / MXene film electrode in Application Example 1 is shown (scavenger: DMPO, voltage: -1.4V). Figure 7The characteristic peak of active hydrogen can be observed. However, the signal of the characteristic peak weakens after the addition of nitrate, which confirms that the FeSA / MXene membrane electrode of the present invention can generate active hydrogen and that it acts on the reduction of nitrate.

[0084] 5) Figure 8 The graph shows the nitrate removal rate and ammonia production selectivity of the FeSA / MXene membrane electrode used in Examples 1-2 under different pH conditions. Figure 8 It can be seen that the FeSA / MXene membrane electrode of the present invention has excellent ammonia selectivity (>95%) under acidic, neutral and alkaline conditions. Therefore, it is shown that the FeSA / MXene membrane electrode prepared by the present invention is not affected by the pH value of the solution and has strong anti-interference ability.

[0085] 6) Figure 9 The graph shows the Faraday efficiency and nitrate removal rate of ammonia production at different potentials in Examples 1 and 3. Figure 9 It can be seen that when the applied potential is -1.4V, the rapid removal of nitrates can be promoted, thereby improving the Faraday efficiency of ammonia production.

[0086] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an iron single-atom modified MXene film electrode, characterized in that, Includes the following steps: The MXene aqueous dispersion was mixed with a ferric salt solution to obtain a mixed dispersion. The mixed dispersion was filtered onto a polymer-supported membrane to obtain an iron single-atom modified MXene membrane electrode. The concentration of the MXene aqueous dispersion is 1~3 mg / mL, and the MXene in the MXene aqueous dispersion is Ti3C2T. x ; The concentration of the ferric salt solution is 0.5~4 mg / mL; The mass ratio of MXene to ferric salt in the ferric salt solution is (20~30):(1~5).

2. The preparation method according to claim 1, characterized in that, The mixing is carried out under ultrasonic or stirring conditions, wherein the stirring speed is 500~800 rpm, the temperature is 20~25℃, and the time is 0.5~1h; the ultrasonic power is 100~500W, the temperature is 20~30℃, and the time is 0.5~1h.

3. The iron-modified MXene film electrode prepared by the preparation method according to any one of claims 1 to 2, characterized in that, It includes a polymer support film and iron single-atom anchored MXene nanosheets loaded on the polymer support film.

4. The application of the iron single-atom modified MXene membrane electrode according to claim 3 in the electrocatalytic reduction of nitrate to ammonia.

5. A flow-through filtration device for electrocatalytic nitrate reduction to produce ammonia, characterized in that, It includes an iron single-atom modified MXene film electrode and a porous titanium sheet arranged in sequence; an insulating silicone block is disposed between the iron single-atom modified MXene film electrode and the porous titanium sheet; the iron single-atom modified MXene film electrode and the porous titanium sheet are in a flow state; the iron single-atom modified MXene film electrode is the iron single-atom modified MXene film electrode as described in claim 3.

6. The electrocatalytic nitrate reduction ammonia production flow-through filtration device according to claim 5, characterized in that, It also includes the Ag / AgCl reference electrode.

7. A method for electrocatalysis using the electrocatalytic nitrate reduction ammonia production flow-through filtration device as described in claim 5 or 6, characterized in that, Includes the following steps: The electrocatalytic nitrate reduction ammonia production flow filter is externally connected to an electrochemical workstation. Using nitrate as raw material, the nitrate-containing raw material liquid is passed through the electrocatalytic nitrate reduction ammonia production flow filter for electrocatalysis.

8. The method according to claim 7, characterized in that, The potential of the external power supply for the electrocatalysis is -1.2 to -1.6V; the concentration of sodium nitrate in the nitrate-containing raw material solution is 300 to 1200 mg / L; the pH value of the nitrate-containing raw material solution is 2 to 10; and the flow rate is 0 to 6 mL / min and not 0.

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