Preparation method of carbon-based visible light photocatalytic material

Abstract

The invention discloses a preparation method of a carbon-based visible light photocatalytic material, and relates to the technical field of photocatalytic material preparation. Abandoned tobacco leaves are used as a carbon source, biochar is obtained through ethanol decoloration and low-temperature carbonization at 180-220 DEG C, the biochar is soaked in a ferric nitrate cobalt mixed solution after pretreatment, a chemical vapor deposition reaction is regulated and controlled through a multi-dimensional cooperative control system, and the carbon-based visible light photocatalytic material is obtained. And finally removing the catalyst by using nitric acid and purifying. The method solves the problems that a traditional photocatalyst depends on ultraviolet light, carbon-based material preparation has many side reactions, waste resources are wasted and the like. The prepared material has a high specific surface area and a uniform carbon coating layer, and is high in visible light absorption capacity, high in photon-generated carrier separation efficiency, capable of efficiently degrading dye wastewater and good in cycling stability. According to the invention, waste is turned into wealth, the process is green, and a low-cost and high-performance photocatalytic material and a preparation scheme are provided for treatment of dye pollution.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic material preparation technology, specifically a method for preparing a carbon-based visible light photocatalytic material. Background Technology

[0002] Dye pollution primarily originates from industries such as textiles, leather processing, and printing. These industries use large quantities of dyes and chemicals in their production processes and often discharge untreated wastewater directly into natural water bodies due to a lack of effective wastewater treatment facilities. The organic pollutants and pigments in dye wastewater not only cause water discoloration and reduce light transmittance, affecting the photosynthesis of aquatic organisms, but the high concentrations of chemicals they contain can also poison aquatic life and even endanger plant growth through soil infiltration. More seriously, some dye components (such as carcinogens) can have negative impacts on human health after long-term exposure.

[0003] Photocatalysis, as an emerging method for treating dye pollution, utilizes photocatalysts to generate strong oxidizing species such as hydroxyl radicals (・OH) and superoxide anions (・O2⁻) under light irradiation, degrading organic dyes into carbon dioxide and water. However, existing photocatalysis technologies have significant drawbacks: First, traditional photocatalysts, such as titanium dioxide (TiO2) and zinc oxide (ZnO), mostly rely on ultraviolet light excitation, requiring special light sources and significantly increasing the cost of practical applications. Second, some photocatalysts experience a decline in photostability over long-term use, leading to a decrease in catalytic efficiency. Third, in the existing preparation processes of carbon-based photocatalytic materials, high-temperature carbonization easily damages the carbon structure, making it difficult to control chemical vapor deposition side reactions (such as tar formation and catalyst sintering), and resulting in high catalyst residues, further limiting the improvement of visible light catalytic activity.

[0004] Therefore, developing novel photocatalytic materials that can respond to visible light, have high stability, and are prepared using environmentally friendly processes has become an urgent need to solve the pollution of dye wastewater. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing carbon-based visible light photocatalytic materials, solving the problems of waste resource utilization and catalyst residue pollution.

[0007] (II) Technical Solution

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for preparing a carbon-based visible light photocatalyst material includes the following steps:

[0010] Step 1: Select discarded tobacco leaves as a suitable carbon source and decolorize them with ethanol for 24 hours to obtain tobacco biomass;

[0011] Step 2: Under nitrogen atmosphere, heat the tobacco biomass to 180℃-220℃ and react at a constant temperature for 1-2 hours to form biochar;

[0012] Step 3: After the reaction is complete, cool the biochar, remove unreacted substances by centrifugation and filtration, and then wash with deionized water or alcohol solvent until neutral to complete the pretreatment.

[0013] Step 4: Prepare a mixed solution of ferric nitrate and cobalt nitrate as a catalyst precursor, with an iron:cobalt mass ratio of 1:0.5-2 and a solution mass fraction of 8% to 10%. Soak biochar in this solution for 48 hours at room temperature.

[0014] Step 5: In a high-temperature furnace, a chemical vapor deposition (CVD) reaction is carried out using methane gas. Through a multi-dimensional collaborative control system, the impact of CVD side reactions on the normal preparation of the catalytic material is offset. Throughout the preparation process, green processes such as low-temperature carbonization and multi-dimensional collaborative control of CVD side reactions are adopted, reducing high-temperature energy consumption and pollutant emissions. This aligns with the concept of sustainable development and promotes the greening process in the field of photocatalytic material preparation. The multi-dimensional collaborative control system covers multiple modules such as process parameter regulation, catalyst management, and gas composition adjustment, precisely controlling the CVD process and effectively suppressing side reactions such as tar formation and catalyst sintering, ensuring the integrity of the material structure and the consistency of its performance.

[0015] Step 6: Remove catalyst particles with nitric acid, wash repeatedly with deionized water and dry to obtain carbon-based photocatalyst. The catalyst removal and purification process can remove residual metal ions, avoid secondary pollution, ensure the stability and recyclability of the material, and greatly improve the reliability of the preparation process and its potential for industrial application.

[0016] Preferably, in step one, during the ethanol decolorization treatment, the discarded tobacco leaves are washed, chopped, and the chopped pieces are immersed in an ethanol aqueous solution with a volume fraction of 75%–95% for 24 hours at 20–30°C. Solid-liquid separation is then performed by filtration or centrifugation, and the decolorized tobacco biomass is collected. Using the discarded tobacco leaves as a carbon source effectively solves the problem of tobacco waste disposal, achieves high-value-added conversion of waste resources, and significantly reduces raw material costs. Compared to traditional biomass raw materials, discarded tobacco leaves are widely available and inexpensive. The ethanol decolorization pretreatment technology not only removes pigment impurities that affect photocatalytic performance but also retains the carbonaceous components in the tobacco leaves, providing high-quality raw materials for subsequent preparations.

[0017] Preferably, in step two, the temperature is increased to 180℃-220℃ in a tube furnace at a rate of 5℃ / min-10℃ / min, nitrogen gas with a purity ≥99.99% and a flow rate of 50-100mL / min is introduced, and air is continuously purged for 10-15 minutes. The reaction is then carried out at a constant temperature for 1-2 hours, with nitrogen gas continuously flowing during the reaction to form an inert atmosphere.

[0018] Preferably, in step three, after the biochar has cooled, the cooled mixture is added to deionized water to form a suspension, centrifuged at 2000-3000 rpm for 5-10 minutes, the precipitate is collected, and the precipitate is vacuum filtered through a mixed cellulose membrane with a pore size of 0.45 μm, with the vacuum degree maintained at -0.06 to -0.1 MPa. The biochar on the filter membrane is washed 2-3 times with 5-10 mL of deionized water to remove residual impurities.

[0019] Preferably, the biochar is washed with deionized water 2-3 times, and centrifuged or filtered after each wash. The pH of the washing solution is measured. When the pH of the washing solution reaches 6.5-7.5, the washing is stopped. If organic impurities are still present, the biochar is washed once more with 75%-95% ethanol (by volume). Finally, the biochar is rinsed with deionized water until the pH of the washing solution is stable at 6.5-7.5 and the conductivity is <10μS / cm.

[0020] Preferably, in step four, during soaking, the carboxyl groups (-COOH) and phenolic hydroxyl groups (-OH) on the surface of biochar undergo coordination reactions with Fe³⁺ and Co²⁺ to form R-COO-Fe²⁺ and RO-Co⁺ bonded structures, with a coordination density of 0.5–1.0 mmol / g. Fe³⁺ partially hydrolyzes to generate [Fe(OH)(H₂O)₅]²⁺, which is deposited on the surface of biochar to form an amorphous FeOOH precursor. The reducing groups on the surface of biochar reduce 15%–25% of Fe³⁺ to Fe²⁺, forming a Fe²⁺ / Fe³⁺ mixed valence state.

[0021] Preferably, in step five, the multi-dimensional collaborative control system includes a process parameter control module, a catalyst management module, a gas component adjustment module, an equipment monitoring module, and a post-treatment purification module. The process parameter control module uses stepped heating to avoid low-temperature tar formation and pulsed gas supply to reduce local CH4 over-concentration, thus reducing amorphous carbon deposition. The catalyst management module uses a core-shell structured SiO2 protective layer to inhibit Fe-Co sintering. The gas component adjustment module reacts H2 with excess carbon to generate CH4, converting amorphous carbon into an active carbon source. Real-time monitoring and flow linkage provide tar warnings. The equipment monitoring module employs a dual-temperature zone design, using upstream pre-activated CH4 to reduce tar precursors and downstream carbon layer deposition to reduce pore blockage. The post-treatment purification module uses high-temperature annealing to improve carbon layer electron mobility and extend photogenerated carrier lifetime, supercritical extraction to remove tar and restore porosity, and low-temperature carbonization to maximize the retention of oxygen-containing functional groups on the biochar surface, providing abundant active sites for catalyst loading.

[0022] Preferably, in step six, a nitric acid aqueous solution is prepared, and the chemically vapor-deposited material is immersed in it at a solid-liquid mass ratio of 1:10-1:20. The solution is then stirred at 20-25°C for 0.5-2 hours to dissolve the Fe-Co catalyst through the following reaction: The filter cake was obtained by membrane filtration, and the carbon-based photocatalyst material generated after chemical vapor deposition reaction was separated from the acid solution.

[0023] The synergistic effect of the Fe-Co bimetallic catalyst and the formation of a uniform carbon coating layer significantly improve the material's absorption capacity for visible light and the separation efficiency of photogenerated carriers, giving the carbon-based photocatalytic material excellent photocatalytic performance.

[0024] Preferably, the carbon-based photocatalytic material generated after chemical vapor deposition includes a carbon-based main structure, residual catalyst particles, unreacted carbon precursor fragments, and metal oxides. Subsequently, the pH of the filter cake is adjusted to 5-6 with 5% NaOH solution to neutralize residual acid, and then washed 3-5 times with 5-10 mL of deionized water until the conductivity of the washing solution is <10 μS / cm and the pH is 6.5-7.5. If drying is required, it is washed once more with 95% ethanol by volume fraction to reduce pore structure shrinkage through displacement dehydration. Inductively coupled plasma spectroscopy is used to detect and control the Fe and Co ion concentrations in the final material to be <0.1 ppm.

[0025] (III) Beneficial Effects

[0026] This invention provides a method for preparing a carbon-based visible light photocatalyst material. It has the following beneficial effects:

[0027] 1. This invention innovatively uses discarded tobacco leaves as a carbon source, effectively solving the problem of tobacco waste disposal, achieving high-value-added conversion of waste resources, and significantly reducing raw material costs. Compared to traditional biomass raw materials, discarded tobacco leaves are widely available and inexpensive. Through ethanol decolorization pretreatment technology, not only are pigment impurities affecting photocatalytic performance removed, but the carbonaceous components in the tobacco leaves are also retained, providing high-quality raw materials for subsequent preparation. Throughout the preparation process, green processes such as low-temperature carbonization and multi-dimensional synergistic control of chemical vapor deposition side reactions are employed, reducing high-temperature energy consumption and pollutant emissions, aligning with the concept of sustainable development, and promoting the greening process in the field of photocatalytic material preparation.

[0028] 2. The low-temperature carbonization process maximizes the preservation of oxygen-containing functional groups on the biochar surface, providing abundant active sites for catalyst loading. Combined with the synergistic effect of the Fe-Co bimetallic catalyst and the formation of a uniform carbon coating layer, the material's absorption capacity for visible light and the separation efficiency of photogenerated carriers are significantly improved, giving the carbon-based photocatalytic material excellent photocatalytic performance. Simultaneously, the multi-dimensional collaborative control system encompasses multiple modules, including process parameter regulation, catalyst management, and gas composition adjustment, precisely controlling the chemical vapor deposition process and effectively suppressing side reactions such as tar formation and catalyst sintering, ensuring the integrity of the material structure and the consistency of its performance. Furthermore, the efficient catalyst removal and purification process eliminates residual metal ions, avoiding secondary pollution and ensuring the stability and recyclability of the material, significantly improving the reliability of the preparation process and its potential for industrial application. Attached Figure Description

[0029] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Please see Figure 1 The present invention provides a technical solution:

[0032] A method for preparing a carbon-based visible light photocatalyst material includes the following steps:

[0033] Step 1: Select discarded tobacco leaves as a suitable carbon source and decolorize them with ethanol for 24 hours to obtain tobacco biomass;

[0034] Step 2: Under nitrogen atmosphere, heat the tobacco biomass to 180℃-220℃ and react at a constant temperature for 1-2 hours to form biochar;

[0035] Step 3: After the reaction is complete, cool the biochar, remove unreacted substances by centrifugation and filtration, and then wash with deionized water or alcohol solvent until neutral to complete the pretreatment.

[0036] Step 4: Prepare a mixed solution of ferric nitrate and cobalt nitrate as a catalyst precursor, with an iron:cobalt mass ratio of 1:0.5-2 and a solution mass fraction of 8% to 10%. Soak biochar in this solution for 48 hours at room temperature.

[0037] Step 5: In a high-temperature furnace, a chemical vapor deposition reaction is carried out using methane gas. Through a multi-dimensional collaborative control system, the impact of the side reactions of the chemical vapor deposition reaction on the normal preparation of the catalytic material is offset.

[0038] Step 6: Remove catalyst particles with nitric acid, wash with deionized water multiple times, and then dry to obtain carbon-based photocatalyst.

[0039] In step one, during the ethanol decolorization process, the discarded tobacco leaves are washed, chopped, and the chopped pieces are immersed in an ethanol aqueous solution with a volume fraction of 75% to 95% for 24 hours at 20-30°C. Solid-liquid separation is then performed by filtration or centrifugation to collect the decolorized tobacco biomass.

[0040] In step two, the temperature is increased to 180℃-220℃ in a tube furnace at a rate of 5℃ / min-10℃ / min. Nitrogen gas with a purity of ≥99.99% and a flow rate of 50-100mL / min is introduced. After continuously purging the air for 10-15 minutes, the reaction is carried out at a constant temperature for 1-2 hours. During the reaction, nitrogen gas is continuously circulated to form an inert atmosphere.

[0041] In step three, after the biochar cools, the cooled mixture is added to deionized water to form a suspension. The suspension is centrifuged at 2000-3000 rpm for 5-10 minutes, and the precipitate is collected. The precipitate is then vacuum filtered through a mixed cellulose membrane with a pore size of 0.45 μm, maintaining the vacuum at -0.06 to -0.1 MPa. The biochar on the filter membrane is washed 2-3 times with 5-10 mL of deionized water to remove residual impurities.

[0042] Wash the biochar 2-3 times with deionized water. After each wash, centrifuge or filter to separate the biochar and measure the pH of the washing solution. Stop washing when the pH of the washing solution reaches 6.5-7.5. If organic impurities are still present, wash once more with 75%-95% ethanol (v / v). Finally, rinse with deionized water until the pH of the washing solution is stable at 6.5-7.5 and the conductivity is <10μS / cm.

[0043] In step four, during soaking, the carboxyl groups (-COOH) and phenolic hydroxyl groups (-OH) on the surface of biochar undergo coordination reactions with Fe³⁺ and Co²⁺ to form R-COO-Fe²⁺ and RO-Co⁺ bond structures with a coordination density of 0.5–1.0 mmol / g. Fe³⁺ partially hydrolyzes to generate [Fe(OH)(H₂O)₅]²⁺, which is deposited on the surface of biochar to form an amorphous FeOOH precursor. The reducing groups on the surface of biochar reduce 15%–25% of Fe³⁺ to Fe²⁺, forming a Fe²⁺ / Fe³⁺ mixed valence state.

[0044] In step five, the multi-dimensional collaborative control system includes a process parameter control module, a catalyst management module, a gas component adjustment module, an equipment monitoring module, and a post-treatment purification module. The process parameter control module uses stepped heating to avoid low-temperature tar formation and pulsed gas supply to reduce localized CH4 over-concentration, thus decreasing amorphous carbon deposition. The catalyst management module uses a core-shell structured SiO2 protective layer to inhibit Fe-Co sintering. The gas component adjustment module reacts H2 with excess carbon to generate CH4, converting amorphous carbon into an active carbon source. Real-time monitoring and flow linkage provide tar warnings. The equipment monitoring module employs a dual-temperature zone design, reducing tar precursors through upstream pre-activation of CH4 and downstream carbon layer deposition to reduce pore blockage. The post-treatment purification module improves carbon layer electron mobility and extends photogenerated carrier lifetime through high-temperature annealing and removes tar and restores porosity through supercritical extraction.

[0045] In step six, a nitric acid aqueous solution is prepared, and the chemically vapor-deposited material is immersed in it at a solid-liquid mass ratio of 1:10-1:20. The solution is then stirred at 20-25°C for 0.5-2 hours to dissolve the Fe-Co catalyst through the following reaction: The filter cake was obtained by membrane filtration, and the carbon-based photocatalyst material generated after chemical vapor deposition reaction was separated from the acid solution.

[0046] The carbon-based photocatalytic material generated after chemical vapor deposition includes a carbon-based main structure, residual catalyst particles, unreacted carbon precursor fragments, and metal oxides. The filter cake pH is then adjusted to 5-6 with 5% NaOH solution to neutralize residual acid. It is then washed 3-5 times with 5-10 mL of deionized water until the conductivity of the washing solution is <10 μS / cm and the pH is 6.5-7.5. If drying is required, it is washed once more with 95% ethanol by volume to reduce pore shrinkage through displacement dehydration. Inductively coupled plasma atomic emission spectrometry is used to detect the Fe and Co ion concentrations in the final material and control them to <0.1 ppm.

[0047] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0048] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a carbon-based visible light photocatalytic material, characterized in that, Includes the following steps: Step 1: Select discarded tobacco leaves as a suitable carbon source and decolorize them with ethanol for 24 hours to obtain tobacco biomass; Step 2: Under nitrogen atmosphere, heat the tobacco biomass to 180℃-220℃ and react at a constant temperature for 1-2 hours to form biochar; Step 3: After the reaction is complete, cool the biochar, remove unreacted substances by centrifugation and filtration, and then wash with deionized water or alcohol solvent until neutral to complete the pretreatment. Step 4: Prepare a mixed solution of ferric nitrate and cobalt nitrate as a catalyst precursor, with an iron:cobalt mass ratio of 1:0.5-2 and a solution mass fraction of 8% to 10%. Soak biochar in this solution for 48 hours at room temperature. Step 5: In a high-temperature furnace, a chemical vapor deposition reaction is carried out using methane gas. Through a multi-dimensional collaborative control system, the impact of the side reactions of the chemical vapor deposition reaction on the normal preparation of the catalytic material is offset. Step 6: Remove catalyst particles with nitric acid, wash with deionized water multiple times, and then dry to obtain carbon-based photocatalyst.

2. The method for preparing a carbon-based visible light photocatalytic material according to claim 1, characterized in that: In step one, during the ethanol decolorization process, the discarded tobacco leaves are washed, chopped, and the chopped pieces are immersed in an ethanol aqueous solution with a volume fraction of 75% to 95% for 24 hours at 20-30°C. Solid-liquid separation is then performed by filtration or centrifugation to collect the decolorized tobacco biomass.

3. The method for preparing a carbon-based visible light photocatalytic material according to claim 1, characterized in that: In step two, the temperature is increased to 180℃-220℃ in a tube furnace at a rate of 5℃ / min-10℃ / min. Nitrogen gas with a purity of ≥99.99% and a flow rate of 50-100mL / min is introduced. After continuously purging the air for 10-15 minutes, the reaction is carried out at a constant temperature for 1-2 hours. During the reaction, nitrogen gas is continuously circulated to form an inert atmosphere.

4. The method for preparing a carbon-based visible light photocatalytic material according to claim 1, characterized in that: In step three, after the biochar has cooled, the cooled mixture is added to deionized water to form a suspension. The suspension is centrifuged at 2000-3000 rpm for 5-10 minutes, and the precipitate is collected. The precipitate is then vacuum filtered through a mixed cellulose membrane with a pore size of 0.45 μm, with the vacuum level maintained at -0.06 to -0.1 MPa. The biochar on the filter membrane is washed 2-3 times with 5-10 mL of deionized water to remove residual impurities.

5. The method for preparing a carbon-based visible light photocatalytic material according to claim 4, characterized in that: The biochar is washed 2-3 times with deionized water. After each wash, the biochar is separated by centrifugation or filtration. The pH of the washing solution is measured. When the pH of the washing solution reaches 6.5-7.5, the washing is stopped. If organic impurities are still present, the biochar is washed once more with 75%-95% ethanol (by volume). Finally, the biochar is rinsed with deionized water until the pH of the washing solution is stable at 6.5-7.5 and the conductivity is <10μS / cm.

6. The method for preparing a carbon-based visible light photocatalytic material according to claim 1, characterized in that: In step four, during soaking, the carboxyl and phenolic hydroxyl groups on the surface of biochar undergo coordination reactions with Fe³⁺ and Co²⁺ to form R-COO-Fe²⁺ and RO-Co⁺ bond structures with a coordination density of 0.5–1.0 mmol / g. Fe³⁺ is partially hydrolyzed to generate [Fe(OH)(H₂O)₅]²⁺, which is deposited on the surface of biochar to form an amorphous FeOOH precursor. The reducing groups on the surface of biochar reduce 15%–25% of Fe³⁺ to Fe²⁺, forming a Fe²⁺ / Fe³⁺ mixed valence state.

7. The method for preparing a carbon-based visible light photocatalytic material according to claim 1, characterized in that: In step five, the multi-dimensional collaborative control system includes a process parameter control module, a catalyst management module, a gas component adjustment module, an equipment monitoring module, and a post-treatment purification module. The process parameter control module uses stepped heating to avoid low-temperature tar formation and pulsed gas supply to reduce local CH4 over-concentration, thus decreasing amorphous carbon deposition. The catalyst management module uses a core-shell structured SiO2 protective layer to inhibit Fe-Co sintering. The gas component adjustment module reacts H2 with excess carbon to generate CH4, converting amorphous carbon into an active carbon source and providing tar warnings through real-time monitoring and flow rate linkage. The equipment monitoring module employs a dual-temperature zone design, reducing tar precursors through upstream pre-activation of CH4 and downstream carbon layer deposition to reduce pore blockage rate. The post-treatment purification module improves carbon layer electron mobility and extends photogenerated carrier lifetime through high-temperature annealing and removes tar and restores porosity through supercritical extraction.

8. The method for preparing a carbon-based visible light photocatalytic material according to claim 1, characterized in that: In step six, a nitric acid aqueous solution is prepared, and the chemically vapor-deposited material is immersed in it at a solid-liquid mass ratio of 1:10-1:

20. The solution is then stirred at 20-25°C for 0.5-2 hours to dissolve the Fe-Co catalyst through the following reaction: The filter cake was obtained by membrane filtration, and the carbon-based photocatalyst material generated after chemical vapor deposition reaction was separated from the acid solution.

9. The method for preparing a carbon-based visible light photocatalytic material according to claim 8, characterized in that: The carbon-based photocatalytic material generated after chemical vapor deposition includes a carbon-based main structure, residual catalyst particles, unreacted carbon precursor fragments, and metal oxides. The filter cake pH is then adjusted to 5-6 with 5% NaOH solution to neutralize residual acid. It is then washed 3-5 times with 5-10 mL of deionized water until the conductivity of the washing solution is <10 μS / cm and the pH is 6.5-7.

5. If drying is required, it is washed once more with 95% ethanol by volume to reduce pore shrinkage through displacement dehydration. Inductively coupled plasma atomic emission spectrometry is used to detect the Fe and Co ion concentrations in the final material and control them to be <0.1 ppm.

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