Improved method for rapid determination of cod of catalyst systems

Abstract

The present application relates to the technical field of catalyst chemical oxygen demand COD determination, in particular to a COD rapid determination method for improving catalyst system, the chemical oxygen demand COD is a key index for measuring the content of reducing substances in water, after potassium dichromate oxidation treatment, the mass concentration of oxygen corresponding to the amount of potassium dichromate consumed by the oxidized reducing pollutants in the water sample, the determination result directly reflects the degree of water pollution. COD is one of the core parameters of water environment monitoring and treatment, the traditional COD determination method takes potassium dichromate oxidation method as the benchmark, but there are problems such as low reaction efficiency, long time consumption, incomplete oxidation caused by single catalyst, weak anti-interference ability, etc., relying on manual operation, large amount of reagent, high risk of secondary pollution, which is difficult to meet the demand of modern environmental monitoring for rapid, accurate and automatic, for complex water sample, the traditional method is easy to appear determination deviation, the data sharing and remote monitoring ability is insufficient, which restricts the intelligent development of water environment monitoring.

Description

Technical Field

[0001] This invention relates to the field of catalyst COD determination technology, specifically to an improved method for rapid COD determination of catalyst systems. Background Technology

[0002] Chemical oxygen demand (COD) is a key indicator for measuring the content of reducing substances in water bodies. Its measurement results directly reflect the degree of water pollution and are one of the core parameters for water environment monitoring and treatment. Traditional COD measurement methods use potassium dichromate oxidation as the benchmark, but they have problems such as low reaction efficiency, long time consumption, incomplete oxidation due to single catalyst, and weak anti-interference ability.

[0003] Traditional COD determination methods rely on potassium dichromate oxidation as a baseline, but these methods suffer from low reaction efficiency, long processing times (traditional digestion requires 2-3 hours), incomplete oxidation due to a single catalyst, and weak resistance to interference. Furthermore, they are reliance on manual operation, involving cumbersome procedures, large reagent consumption (e.g., traditional methods require significant amounts of potassium dichromate and sulfuric acid per test), high risk of secondary pollution, and slow data processing, failing to meet the demands of modern environmental monitoring for speed, accuracy, and automation. In addition, traditional methods are prone to measurement errors in complex water samples (such as those with high chloride ion and suspended solids levels), and their data sharing and remote monitoring capabilities are insufficient, hindering the intelligent development of water environment monitoring. Therefore, developing a COD determination method that combines high-efficiency catalysis, strong resistance to interference, rapid measurement, and integrated intelligent monitoring has become an important direction for addressing the pain points of existing technologies. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] To address the shortcomings of existing technologies, this invention provides an improved method for rapid COD determination using a catalyst system, which offers the advantage of fast determination speed and solves the problem of excessively long COD determination time in traditional methods.

[0006] (II) Technical Solution

[0007] To address the issue of excessively time-consuming traditional methods for COD determination, this invention provides the following technical solution: an improved catalyst system for rapid COD determination, comprising the following steps: S1, raw material selection.

[0008] Select potassium dichromate as the reference material, nano-titanium dioxide, palladium and manganese salts, and potassium hydrogen phthalate. During raw material selection, careful control should be exercised over the purity and appearance of the raw materials to avoid affecting the actual performance due to quality issues. S2. Material Preparation: Accurately weigh the dried potassium dichromate reference material, dissolve it in distilled water meeting the requirements of GB / T 6682 Grade I water, transfer it to a 500-1000 mL volumetric flask, dilute to the mark, and shake well to prepare a potassium dichromate standard solution. A 0.500 mol / L solution is used for high-concentration COD water sample determination; a 0.160 mol / L or lower concentration standard solution is used for low-concentration COD water sample determination. The amount of potassium dichromate should be 1.5-3 times the theoretical amount required for oxidation. For high-concentration water samples, use 0.25 mol / L potassium dichromate solution, adding 10-15 mL per 10-20 mL of water sample; for low-concentration water samples, use 0.025 mol / L potassium dichromate solution, adding 10-20 mL per 10-20 mL of water sample, to ensure that reducing substances in the water sample are fully oxidized.

[0009] A composite catalyst was prepared by mixing nano-titanium dioxide, palladium salt, and manganese salt in a ratio of 85:2:13 via a sol-gel method. The catalyst was then dissolved in sulfuric acid to prepare a catalyst solution of a specific concentration, which was stored in the dark. This composite catalyst provides ample active sites for the reaction through its high specific surface area, while simultaneously acting as an electron transport bridge to lower the activation energy and accelerate the transfer of electrons from organic matter to hexavalent chromium ions, thus significantly improving reaction efficiency.

[0010] Potassium hydrogen phthalate is dissolved in 500-1000 mL of concentrated sulfuric acid to prepare a sulfuric acid-potassium hydrogen phthalate masking solution, which is used to eliminate the interference of chloride ions in the water sample. The mass ratio of chloride ions to potassium hydrogen phthalate should be strictly controlled to be ≥1:10. When the chloride ion concentration in the water sample exceeds 1000 mg / L, the amount of sulfuric acid-potassium hydrogen phthalate masking solution added should be appropriately increased to maintain the mass ratio above 1:10, ensuring that chloride ions and potassium hydrogen phthalate form a stable soluble complex and avoiding the oxidation of chloride ions by potassium dichromate, which would lead to a higher COD measurement value. S3, Water Sample Pretreatment and Material Heating Preparation: Water sample pretreatment: Collect no less than 100 mL of water sample and store it in a clean glass bottle. Immediately after collection, add sulfuric acid to acidify to pH ≤2 to inhibit microbial activity and prevent the decomposition of organic matter in the water sample. If the water sample is turbid, large interfering particles need to be removed through a filter membrane to avoid interference with subsequent absorbance monitoring; the chloride ion concentration in the water sample is determined by silver nitrate titration or a rapid qualitative method, and the amount of sulfuric acid-potassium hydrogen phthalate masking solution to be added is determined based on the results; S4, Determination Procedure

[0011] Using the fully automated sampling device of the intelligent COD analyzer, accurately aspirate 5.00 mL of pretreated water sample and inject it into the digestion tube. At the same time, add 1.00 mL of sulfuric acid-potassium hydrogen phthalate masking solution, shake well, and let stand for 10 minutes to fully eliminate chloride ion interference.

[0012] Add 5.00 mL of potassium dichromate standard solution and 3.00 mL of modified catalyst solution to the reaction tube in sequence. After accurately adding the samples with a manual pipette, mix thoroughly to ensure that the reaction system is homogeneous.

[0013] Place the reaction tube into the microwave heating module preheated to the set temperature, and start the heating program for 15-30 minutes. During the reaction, the fiber optic spectral sensor of the intelligent measuring instrument monitors the absorbance changes of the reaction system in real time. The high-range sensor monitors trivalent chromium at a wavelength of 600nm±20nm, and the low-range sensor monitors hexavalent chromium at a wavelength of 440nm±20nm, transmitting the data to the data processing system.

[0014] Pipette potassium hydrogen phthalate standard series working solutions of different concentrations into reaction tubes, dilute with distilled water to 5.00-10 mL, and perform the operation according to steps 2-4 above. Plot a calibration curve with COD value on the x-axis and the corresponding absorbance change value on the y-axis. The calibration curve must meet the linear correlation coefficient R²≥0.999.

[0015] The water sample is measured following the same operating steps as those used for plotting the calibration curve. If the digestion solution is turbid or has precipitation affecting the colorimetric determination, it should be centrifuged until clear before measurement; if the digestion solution has an abnormal color or cannot be clarified after centrifugation, the sample is not suitable for this method. The COD value of the sample is calculated from the calibration curve based on the absorbance change of the water sample. If the water sample has been diluted, water is used instead of the sample, and its absorbance value is measured according to steps 10.1.1 to 10.1.7. The blank test should be performed simultaneously with the sample to eliminate the influence of the background absorption of the reagent itself on the results; S5, Data Analysis: Turn on the power of the intelligent COD analyzer, start the matching data analysis software, perform instrument self-check and initialization to ensure that each module is working properly, and set parameters such as reaction temperature, heating time, and detection wavelength in the software. Preferably, in step S1, potassium dichromate needs to be dried to constant weight at 120℃±2℃, and potassium hydrogen phthalate needs to be dried to constant weight at 105-110℃ to ensure the accuracy of subsequent solution preparation.

[0016] Preferably, in step S2, dried potassium hydrogen phthalate is weighed, dissolved in distilled water meeting the requirements of Grade I water in GB / T 6682, transferred to a 500-1000 mL volumetric flask (Grade A), diluted to the mark, and shaken well to prepare a potassium hydrogen phthalate COD standard solution. The solution with a COD value of 5000 mg / L is used as the standard stock solution. It can be stored at 2-8℃ or, before volume adjustment, with approximately 10 mL of sulfuric acid solution (1 + 9) added and stored at room temperature, and can be stably stored for one month. Different concentrations of standard working solutions are obtained by diluting as needed for method calibration and verification, and for plotting calibration curves.

[0017] Preferably, step S3 is equipped with a fully automated sample introduction device, a microwave heating module (with automatic constant temperature heating and timing functions; the heating hole diameter matches the digestion tube to ensure close contact between the digestion tube and the heating wall; the heating hole depth is not less than or more than 5 mm above the height of the reaction liquid in the digestion tube), a fiber optic spectral sensor, and a data processing and transmission system, enabling automatic sample processing, real-time monitoring of the reaction process, and automatic calculation of results. The heating module is preheated, with the heating temperature controlled between 120-140℃. The heating time is adjusted according to the type and concentration of organic matter in the water sample. For water samples with a high content of recalcitrant organic matter, the temperature can be increased to 140℃ and the time extended to 30 minutes to ensure complete oxidation of the organic matter.

[0018] Preferably, in step S4, if the water sample has been diluted, it needs to be multiplied by the dilution factor n. The calculation formula is as follows: when measured at a wavelength of 600nm ± 20nm: ρ(COD) = n[k(As Ab)+a]

[0019] When measured at a wavelength of 440nm ± 20nm: ρ(COD) = n[k(Ab) [As)+a] Where: ρ(COD)—— COD value of water sample, in mg / L; n—— dilution factor of water sample; k—— sensitivity of calibration curve, in (mg / L) / 1; As—— absorbance value of sample, in L; Ab—— absorbance value of blank test, in L; a—— intercept of calibration curve, in mg / L. COD measurement values ​​are generally retained to three significant figures.

[0020] Preferably, in step S5, the instrument automatically collects absorbance data during the reaction process, and the software analyzes the data through a built-in machine learning algorithm, automatically identifies the reaction endpoint, and calculates the COD value based on the calibration curve. At the same time, the system automatically records sample information, measurement parameters, and results, and generates a measurement report. Through Internet of Things (IoT) technology, the measurement results are transmitted to a cloud server, and authorized personnel can view the data through mobile terminals or computer clients, realizing real-time data sharing and remote monitoring, and meeting the information needs of modern environmental monitoring.

[0021] (III) Beneficial Effects

[0022] Compared with existing technologies, this invention provides an improved method for rapid COD determination using a catalyst system, which has the following advantages:

[0023] 1. A composite catalyst was prepared by sol-gel method using a ratio of nano-titanium dioxide:palladium salt:manganese salt of 85:2:13. Nano-titanium dioxide provides abundant active sites and enhances catalytic efficiency. The introduction of palladium and manganese forms an electron transfer bridge, which significantly reduces the reaction activation energy and accelerates the oxidation of organic matter. By using the composite catalyst and microwave heating technology, the digestion time is shortened from 2-3 hours in the traditional method to 15-30 minutes, which greatly improves the detection efficiency and meets the needs of rapid monitoring.

[0024] 2. Based on the COD concentration of the water sample, prepare potassium dichromate solutions of 0.500 mol / L (high concentration) and 0.160 mol / L or lower (low concentration). The amount of potassium dichromate used should be 1.5–3 times the theoretical amount required for oxidation to ensure that the reducing substances are fully oxidized. Dry the potassium dichromate to constant weight at 120℃±2℃ to ensure accurate solution concentration. Strictly control the mass ratio of chloride ions to potassium hydrogen phthalate ≥1:10 to ensure masking effect. Intelligent instruments and sensor systems improve operational consistency and reduce human error. Heating is uniform and rapid, and the temperature can be controlled at 120–140℃ to adapt to different water samples.

[0025] 3. The composite catalyst significantly reduces the activation energy through the synergistic effect of high specific surface area and electron transfer, promoting the complete oxidation of organic matter. The measured results are closer to the theoretical value, and the relative error is lower than that of traditional methods. The sulfuric acid-potassium hydrogen phthalate masking solution effectively eliminates chloride ion interference, making it suitable for high-chlorine water bodies and avoiding the problem of high COD values ​​caused by chloride ion oxidation.

[0026] 4. It integrates a fully automated sample introduction, microwave heating, real-time spectral monitoring and intelligent data analysis system to achieve full automation of sample processing, reaction monitoring, result calculation and report generation, reduce manual intervention and improve data reliability.

[0027] 5. By precisely preparing and optimizing dosages, the use of harmful reagents such as potassium dichromate and sulfuric acid can be reduced, thereby lowering the risk of secondary pollution. It also supports IoT data transmission and cloud storage, enabling real-time sharing and remote monitoring of test results, and promoting the intelligent and information-based development of water environment monitoring. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the process structure of the present invention. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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.

[0030] Example 1:

[0031] Please see Figure 1 A rapid COD determination method with an improved catalyst system includes the following steps: S1, raw material selection.

[0032] Select potassium dichromate as the reference material, nano-titanium dioxide, palladium and manganese salts, and potassium hydrogen phthalate. During raw material selection, careful control should be exercised over the purity and appearance of the raw materials to avoid affecting the actual performance due to quality issues. S2. Material Preparation: Accurately weigh the dried potassium dichromate reference material, dissolve it in distilled water meeting the requirements of GB / T 6682 Grade I water, transfer it to a 500-1000 mL volumetric flask, dilute to the mark, and shake well to prepare a potassium dichromate standard solution. A 0.500 mol / L solution is used for high-concentration COD water sample determination; a 0.160 mol / L or lower concentration standard solution is used for low-concentration COD water sample determination. The amount of potassium dichromate should be 1.5-3 times the theoretical amount required for oxidation. For high-concentration water samples, use 0.25 mol / L potassium dichromate solution, adding 10-15 mL per 10-20 mL of water sample; for low-concentration water samples, use 0.025 mol / L potassium dichromate solution, adding 10-20 mL per 10-20 mL of water sample, to ensure that reducing substances in the water sample are fully oxidized.

[0033] A composite catalyst was prepared by mixing nano-titanium dioxide, palladium salt, and manganese salt in a ratio of 85:2:13 via a sol-gel method. The catalyst was then dissolved in sulfuric acid to prepare a catalyst solution of a specific concentration, which was stored in the dark. This composite catalyst provides ample active sites for the reaction through its high specific surface area, while simultaneously acting as an electron transport bridge to lower the activation energy and accelerate the transfer of electrons from organic matter to hexavalent chromium ions, thus significantly improving reaction efficiency.

[0034] Potassium hydrogen phthalate is dissolved in 500-1000 mL of concentrated sulfuric acid to prepare a sulfuric acid-potassium hydrogen phthalate masking solution, which is used to eliminate the interference of chloride ions in the water sample. The mass ratio of chloride ions to potassium hydrogen phthalate should be strictly controlled to be ≥1:10. When the chloride ion concentration in the water sample exceeds 1000 mg / L, the amount of sulfuric acid-potassium hydrogen phthalate masking solution added should be appropriately increased to maintain the mass ratio above 1:10, ensuring that chloride ions and potassium hydrogen phthalate form a stable soluble complex and avoiding the oxidation of chloride ions by potassium dichromate, which would lead to a higher COD measurement value. S3, Water Sample Pretreatment and Material Heating Preparation: Water sample pretreatment: Collect no less than 100 mL of water sample and store it in a clean glass bottle. Immediately after collection, add sulfuric acid to acidify to pH ≤2 to inhibit microbial activity and prevent the decomposition of organic matter in the water sample. If the water sample is turbid, large interfering particles need to be removed through a filter membrane to avoid interference with subsequent absorbance monitoring; the chloride ion concentration in the water sample is determined by silver nitrate titration or a rapid qualitative method, and the amount of sulfuric acid-potassium hydrogen phthalate masking solution to be added is determined based on the results; S4, Determination Procedure

[0035] Using the fully automated sampling device of the intelligent COD analyzer, accurately aspirate 5.00 mL of pretreated water sample and inject it into the digestion tube. At the same time, add 1.00 mL of sulfuric acid-potassium hydrogen phthalate masking solution, shake well, and let stand for 10 minutes to fully eliminate chloride ion interference.

[0036] Add 5.00 mL of potassium dichromate standard solution and 3.00 mL of modified catalyst solution to the reaction tube in sequence. After accurately adding the samples with a manual pipette, mix thoroughly to ensure that the reaction system is homogeneous.

[0037] Place the reaction tube into the microwave heating module preheated to the set temperature, and start the heating program for 15-30 minutes. During the reaction, the fiber optic spectral sensor of the intelligent measuring instrument monitors the absorbance changes of the reaction system in real time. The high-range sensor monitors trivalent chromium at a wavelength of 600nm±20nm, and the low-range sensor monitors hexavalent chromium at a wavelength of 440nm±20nm, transmitting the data to the data processing system.

[0038] Pipette potassium hydrogen phthalate standard series working solutions of different concentrations into reaction tubes, dilute with distilled water to 5.00-10 mL, and perform the operation according to steps 2-4 above. Plot a calibration curve with COD value on the x-axis and the corresponding absorbance change value on the y-axis. The calibration curve must meet the linear correlation coefficient R²≥0.999.

[0039] Determine the water sample following the same operating procedures as those used for plotting the calibration curve. If the digestion solution is turbid or has precipitation affecting the colorimetric determination, centrifuge it to clarify before measurement; if the digestion solution has an abnormal color or cannot become clear after centrifugation, the sample is not suitable for this method. Calculate the COD value of the sample based on the absorbance change value of the water sample using the calibration curve. If the water sample has been diluted, use water instead of the sample and determine its absorbance value according to steps 10.1.1 to 10.1.7. The blank test should be performed simultaneously with the sample to eliminate the influence of background absorption of the reagent itself on the results; S5, Data Analysis: Turn on the power of the intelligent COD analyzer, start the matching data analysis software, perform instrument self-check and initialization to ensure that all modules are working properly, and set parameters such as reaction temperature, heating time, and detection wavelength in the software;

[0040] Furthermore, in step S1, potassium dichromate needs to be dried to constant weight at 120℃±2℃, and potassium hydrogen phthalate needs to be dried to constant weight at 105-110℃ to ensure the accuracy of subsequent solution preparation.

[0041] Further, in step S2, weigh the dried potassium hydrogen phthalate, dissolve it in distilled water that meets the requirements of Grade I water in GB / T 6682, transfer it to a 500-1000 mL volumetric flask (Grade A), dilute to the mark, shake well, and prepare a potassium hydrogen phthalate COD standard solution. The solution with a COD value of 5000 mg / L is used as the standard stock solution. It can be stored at 2-8℃ or, before volume adjustment, with the addition of approximately 10 mL of sulfuric acid solution (1 + 9) and stored at room temperature, and can be stably stored for one month. Different concentrations of standard working solutions are obtained as needed for method calibration and validation, and calibration curves are plotted.

[0042] Furthermore, step S3 is equipped with a fully automated sample introduction device, a microwave heating module (with automatic constant temperature heating and timing functions; the heating hole diameter matches the digestion tube to ensure close contact between the digestion tube and the heating wall; the heating hole depth is no less than or more than 5 mm above the height of the reaction liquid inside the digestion tube), a fiber optic spectral sensor, and a data processing and transmission system. This enables automatic sample processing, real-time monitoring of the reaction process, and automatic calculation of results. The heating module is preheated, and the heating temperature is controlled at 120-140℃. The heating time is adjusted according to the type and concentration of organic matter in the water sample. For water samples with a high content of recalcitrant organic matter, the temperature can be increased to 140℃ and the time extended to 30 minutes to ensure complete oxidation of organic matter.

[0043] Furthermore, in step S4, if the water sample has been diluted, it needs to be multiplied by the dilution factor n. The calculation formula is as follows: when measured at a wavelength of 600nm ± 20nm: ρ(COD) = n[k(As Ab)+a]

[0044] When measured at a wavelength of 440nm ± 20nm: ρ(COD) = n[k(Ab) [As)+a] Where: ρ(COD)—— COD value of water sample, in mg / L; n—— dilution factor of water sample; k—— sensitivity of calibration curve, in (mg / L) / 1; As—— absorbance value of sample, in L; Ab—— absorbance value of blank test, in L; a—— intercept of calibration curve, in mg / L. COD measurement values ​​are generally retained to three significant figures.

[0045] Furthermore, in step S5, the instrument automatically collects absorbance data during the reaction process. The software analyzes the data using a built-in machine learning algorithm, automatically identifies the reaction endpoint, and calculates the COD value based on the calibration curve. Simultaneously, the system automatically records sample information, measurement parameters, and results, generating a measurement report. Through IoT technology, the measurement results are transmitted to a cloud server, and authorized personnel can view the data via mobile terminals or computer clients, achieving real-time data sharing and remote monitoring, thus meeting the information needs of modern environmental monitoring.

[0046] Results of COD standard solutions at different concentrations (n=5)

[0047]

[0048] Under acidic conditions, potassium dichromate is used as an oxidant, and with the synergistic effect of a composite catalyst, the oxidation reaction of organic matter in water samples can be efficiently accelerated. Finally, the COD value is accurately calculated by monitoring the concentration changes of hexavalent chromium and trivalent chromium. The specific process and key control details are as follows:

[0049] The core mechanism of the composite catalyst is reflected in two aspects: First, its high specific surface area provides ample active sites for the reaction, enabling organic matter and potassium dichromate molecules in the water sample to be adsorbed more efficiently onto the catalyst surface, significantly increasing the collision probability; second, the catalyst lowers the activation energy of the reaction through electron transfer bridging, accelerating the transfer of electrons from organic matter to hexavalent chromium ions, thereby significantly shortening the reaction time. At a reaction temperature of 120-140℃, the oxidation reaction that originally required 2-3 hours can be completed within 15-30 minutes, and the oxidation rate of organic matter can reach over 95%.

[0050] Controlling interference in the reaction system is crucial for accurate results. Chloride ions, commonly found in water samples, are easily oxidized to chlorine gas by potassium dichromate, leading to higher COD readings. Therefore, a mixture of potassium hydrogen phthalate and concentrated sulfuric acid is needed for masking. Potassium hydrogen phthalate combines with chloride ions to form a stable complex, preventing them from participating in the oxidation reaction. Furthermore, the mass ratio of potassium hydrogen phthalate to chloride ions must be strictly controlled to be above 1:10. Simultaneously, concentrated sulfuric acid not only maintains the system's strong acidity (pH ≤ 2) but also enhances the stability of the complex.

[0051] In the reaction process monitoring stage, the fiber optic spectral sensor plays a core role: its probe is directly inserted into the reaction vessel to capture the changes in absorbance at a wavelength of 540 nm in real time. As the reaction proceeds, the concentration of hexavalent chromium gradually decreases, and the absorbance decreases linearly. The sensor converts the light signal into an electrical signal and transmits it to the data processing system. The system has a built-in working curve calibrated with a standard solution. Combined with machine learning algorithms, it automatically calculates the total oxygen content of the organic matter oxidized, i.e., the COD value, based on the consumption of hexavalent chromium and the stoichiometric relationship of the redox reaction.

[0052] To ensure the quality of the results, strict quality control measures must be implemented throughout the process: potassium dichromate solution must be added in excess; the pH of the water sample must be stabilized at ≤2 after acidification; calibration with a standard solution must be performed before each measurement to ensure that the error is within ±5%; and the final measurement results are uploaded to the cloud database in real time via the Internet of Things module, supporting remote viewing, data sharing, and historical trend analysis on multiple terminals, thus meeting the intelligent and information-based needs of environmental monitoring.

[0053] 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 rapid COD determination method for an improved catalyst system, characterized in that, Includes the following steps: S1. Raw material selection Selected materials include potassium dichromate, nano-titanium dioxide, palladium and manganese salts, and potassium hydrogen phthalate. S2. Material Preparation Accurately weigh the dried potassium dichromate, dissolve it in distilled water that meets the requirements of Grade I water in GB / T 6682, transfer it to a 500-1000mL volumetric flask, dilute to the mark, shake well, and prepare a potassium dichromate standard solution. A composite catalyst was prepared by mixing nano-titanium dioxide, palladium salt, and manganese salt in a ratio of 85:2:13 via a sol-gel method. The catalyst solution was then dissolved in sulfuric acid and stored in the dark. This composite catalyst provides ample active sites for the reaction through its high specific surface area and acts as an electron transport bridge, lowering the activation energy and accelerating the transfer of electrons from organic matter to hexavalent chromium ions, thus significantly improving reaction efficiency. Dissolve potassium hydrogen phthalate in 500-1000 mL of concentrated sulfuric acid to prepare a sulfuric acid-potassium hydrogen phthalate masking solution, which is used to eliminate the interference of chloride ions in water samples. The mass ratio of chloride ions to potassium hydrogen phthalate should be strictly controlled to be ≥1:

10. S3. Water sample pretreatment and material heating preparation Water sample pretreatment: Collect no less than 100 mL of water sample and store it in a clean glass bottle. Immediately after collection, add sulfuric acid to acidify to pH ≤ 2 to inhibit microbial activity and prevent the decomposition of organic matter in the water sample. If the water sample is turbid, large particulate matter should be removed through a filter membrane to avoid interference with subsequent absorbance monitoring. Use silver nitrate titration or rapid qualitative method to determine the chloride ion concentration in the water sample, and determine the amount of sulfuric acid-potassium hydrogen phthalate masking solution to be added based on the results. S4. Measurement Procedure Using the fully automatic sampling device of the intelligent COD analyzer, accurately aspirate 5.00 mL of pretreated water sample and inject it into the digestion tube. At the same time, add 1.00 mL of sulfuric acid-potassium hydrogen phthalate masking solution, shake well, and let stand for 10 minutes to fully eliminate chloride ion interference. Add 5.00 mL of potassium dichromate standard solution and 3.00 mL of modified catalyst solution sequentially to the reaction tube. After precise addition using a manual pipette, mix thoroughly to ensure a homogeneous reaction system. Place the reaction tube into the microwave heating module preheated to the set temperature, start the heating program, and heat for 15-30 minutes. During the reaction, the fiber optic spectral sensor of the intelligent measuring instrument monitors the absorbance changes of the reaction system in real time. The high-range sensor monitors trivalent chromium at a wavelength of 600nm±20nm, and the low-range sensor monitors hexavalent chromium at a wavelength of 440nm±20nm. The data is then transmitted to the data processing system. Pipette potassium hydrogen phthalate standard series working solutions of different concentrations into reaction tubes, dilute with distilled water to 5.00-10 mL, and perform the above steps S2-S4. Plot a calibration curve with COD value on the x-axis and the corresponding absorbance change value on the y-axis. The calibration curve must meet the linear correlation coefficient R²≥0.

999. The water sample is measured following the same procedure as the calibration curve. If the digestion solution is turbid or has precipitate that affects the colorimetric determination, it should be centrifuged to clear the solution before measurement. If the digestion solution has an abnormal color or does not become clear after centrifugation, this method is not applicable to the water sample; the COD value of the water sample is calculated through the calibration curve based on the change in absorbance of the water sample. S5, Data Analysis Turn on the power of the intelligent COD analyzer, start the accompanying data analysis software, and perform instrument self-test and initialization to ensure that all modules are working properly. Set the reaction temperature, heating time, and detection wavelength parameters in the software. The instrument automatically collects absorbance data during the reaction process. The software analyzes the data through built-in machine learning algorithms, automatically identifies the reaction endpoint, and calculates the COD value based on the calibration curve. At the same time, the system automatically records sample information, measurement parameters, and results, and generates a measurement report. Through Internet of Things (IoT) technology, the measurement results are transmitted to a cloud server. Authorized personnel can view the data through mobile terminals or computer clients, realizing real-time data sharing and remote monitoring, meeting the information needs of modern environmental monitoring.

2. The method for rapid COD determination of an improved catalyst system according to claim 1, characterized in that, In step S1, potassium dichromate needs to be dried to constant weight at 120℃±2℃, and potassium hydrogen phthalate needs to be dried to constant weight at 105-110℃ to ensure the accuracy of subsequent solution preparation.

3. The method for rapid COD determination of an improved catalyst system according to claim 1, characterized in that, In step S2, weigh the dried potassium hydrogen phthalate, dissolve it in distilled water that meets the requirements of Grade I water in GB / T 6682, transfer it to a 500-1000 mL volumetric flask, dilute to the mark, shake well, and prepare a potassium hydrogen phthalate COD standard solution. The solution with a COD value of 5000 mg / L is used as the standard stock solution. It can be stored at 2-8℃ or, before volume adjustment, with approximately 10 mL of sulfuric acid solution added, stored at room temperature and can be stably stored for one month. Different concentrations of standard working solutions are obtained as needed for method calibration and verification, and calibration curves are plotted.

4. The method for rapid COD determination of an improved catalyst system according to claim 1, characterized in that, The S3 step is equipped with a fully automated sample introduction device, a microwave heating module, a fiber optic spectral sensor, and a data processing and transmission system, which can realize automatic sample processing, real-time monitoring of the reaction process, and automatic calculation of results. The microwave heating module is preheated and the heating temperature is controlled at 120-140℃. The heating time is adjusted according to the type and concentration of organic matter in the water sample.

5. The method for rapid COD determination of an improved catalyst system according to claim 1, characterized in that, In step S4, if the water sample has been diluted, it needs to be multiplied by the dilution factor n. The calculation formula is as follows: when measured at a wavelength of 600nm ± 20nm: ρ(COD) = n[k(As−Ab) + a] When measured at a wavelength of 440nm±20nm: ρ(COD)=n[k(Ab−As)+a] where: ρ(COD)—— COD value of water sample, in mg / L; n—— dilution factor of water sample; k—— sensitivity of calibration curve, in mg / L; As—— absorbance value of sample; Ab—— absorbance value of blank test; a—— intercept of calibration curve, in mg / L.

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