Method for measuring chemical oxygen demand of seawater based on bias voltage photoelectric oxidation

Abstract

The invention discloses a seawater chemical oxygen demand determination method based on bias voltage photoelectric oxidation, and relates to the technical field of water quality monitoring. The method comprises the following steps: collecting seawater and performing pretreatment to obtain a seawater sample; adding supporting electrolyte into the seawater sample to obtain an electrolytic water sample; the method comprises the following steps: injecting an electrolysis water sample into a photoelectrochemical reaction tank, applying bias voltage to a working electrode by taking Ag / AgCl as a reference electrode, and turning on a light source with a specific wavelength for irradiation; carrying out an oxidation reaction in the photoelectrochemical reaction tank, and after the oxidation reaction of the organic matter is complete, obtaining a steady-state photocurrent with a stable current signal; according to a preset steady-state light current-COD concentration curve, a COD measured value is obtained, the COD standard concentration value is corrected according to the water temperature and the salinity, and a COD corrected value is obtained. An adjustable tiny external bias voltage is introduced to cooperate with light source irradiation, so that rapid, accurate and high-anti-interference measurement of COD in seawater is realized.

Description

Technical Field

[0001] This invention relates to the field of water quality monitoring technology, and in particular to a method for determining the chemical oxygen demand (COD) of seawater based on bias photoelectric oxidation. Background Technology

[0002] Chemical oxygen demand (COD) is a crucial indicator of organic pollution levels in water quality monitoring. Existing COD measurement methods, especially traditional chemical methods and some spectroscopic analysis methods, while providing accurate data, are complex and time-consuming, and are often highly sensitive to factors such as salinity and chloride ions in seawater, making them susceptible to interference. Furthermore, these methods are often ill-suited for the requirements of unmanned surface vessels (USVs), failing to achieve rapid, long-term, and automated marine water quality monitoring.

[0003] However, existing photoelectrochemical methods have inherent drawbacks in seawater applications: 1) Photogenerated electron-hole pairs recombine easily, resulting in low quantum efficiency, limited oxidation capacity, and incomplete oxidation of recalcitrant organic matter; 2) In a high chloride ion environment, chloride ions compete with organic matter for photogenerated holes, leading to the chloride evolution reaction (2Cl₂). - →Cl2+2e - This not only consumes the effective holes used for oxidizing organic matter, but the chlorine gas produced may also further oxidize the electrode or react with water to generate hypochlorous acid, introducing measurement errors and corroding the electrode; 3) The reaction rate is greatly affected by the seawater matrix, and the measurement stability and accuracy are difficult to guarantee. Summary of the Invention

[0004] The purpose of this invention is to provide a method for determining the chemical oxygen demand of seawater based on bias photoelectric oxidation, aiming to solve or improve at least one of the above-mentioned technical problems.

[0005] To achieve the above objectives, the present invention provides the following solution: A method for determining the chemical oxygen demand (COD) of seawater based on bias-voltage photoelectric oxidation includes: Seawater was collected and pretreated to obtain seawater samples; A supporting electrolyte was added to the seawater sample to obtain an electrolyzed water sample; An electrolyzed water sample is injected into a photoelectrochemical reaction cell. Using Ag / AgCl as the reference electrode, a bias voltage is applied to the working electrode, and a light source of a specific wavelength is turned on for irradiation. An oxidation reaction is carried out in a photoelectrochemical reactor. After the organic matter is completely oxidized, a stable steady-state photocurrent with a stable current signal is obtained. Based on the preset steady-state photocurrent-COD concentration curve, the COD measurement value is obtained, and the COD standard concentration value is corrected according to water temperature and salinity to obtain the COD correction value.

[0006] Furthermore, the pretreatment involves removing suspended particulate matter by filtration using a filter membrane with a pore size of 0.45 μm.

[0007] Furthermore, the electrolyte is Na2SO4 with a concentration of 0.1-0.5 mol / L.

[0008] Furthermore, the bias voltage is 0.1-0.8V.

[0009] Furthermore, a light source with a specific wavelength of 365 nm.

[0010] Furthermore, the steady-state photocurrent-COD concentration curve was obtained by measuring different COD concentrations and plotting the concentration value on the x-axis and the average potential value on the y-axis.

[0011] Furthermore, the COD standard concentration value is corrected based on water temperature and salinity to obtain the corrected COD value, including: Based on different temperature and salinity gradients, standard samples were measured, and the COD measurement values ​​were corrected according to the standard sample values ​​to obtain the corrected COD value, expressed as: In the formula, This is a COD correction value; This is a correction factor; This is the measured COD value.

[0012] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects: This invention discloses a method for determining the chemical oxygen demand (COD) of seawater based on bias-voltage photoelectric oxidation. The method introduces a controllable micro external bias voltage, which, together with the illumination of a light source, constitutes a highly efficient and stable photoelectric chemical sensing system, thereby realizing rapid, accurate, and highly interference-resistant measurement of COD in seawater. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a schematic flowchart of the method of the present invention; Figure 2 This is a schematic diagram of the photocurrent signal attenuation rate in this embodiment. Detailed Implementation

[0015] 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.

[0016] The purpose of this invention is to provide a method for determining the chemical oxygen demand of seawater based on bias photoelectric oxidation, aiming to solve or improve at least one of the above-mentioned technical problems.

[0017] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] like Figure 1 As shown, this invention provides a method for determining seawater chemical oxygen demand based on bias-voltage photoelectric oxidation, comprising: Step 1: Collect seawater using an automated platform, filter it with a filter membrane to remove suspended particulate matter, and obtain a seawater sample; wherein the pore size of the filter membrane is 0.45μm.

[0019] Step 2: Add 0.1-0.5 mol / L of supporting electrolyte Na2SO4 to the seawater sample to obtain an electrolyzed water sample; By adding a supporting electrolyte to maintain the stability of the ionic strength of the reaction system, measurement errors caused by fluctuations in seawater conductivity are reduced.

[0020] Step 3: Inject the electrolyzed water sample into the photoelectrochemical reaction cell, use Ag / AgCl as the reference electrode, apply a bias voltage of 0.1-0.8V to the working electrode, and turn on a light source with a specific wavelength of 365 nm for irradiation; wherein, the Ag / AgCl reference electrode is saturated KCl.

[0021] The bias voltage is output and controlled by a potentiostat.

[0022] In the above steps, the applied external bias voltage effectively drives the photogenerated electrons to flow directionally to the counter electrode, greatly suppressing electron-hole recombination and thus significantly increasing the concentration and lifetime of photogenerated holes, thereby enhancing the system's oxidation capacity for organic matter. Simultaneously, precise control of the bias voltage using a potentiostat maintains the working electrode potential below the chlorine evolution reaction potential, effectively suppressing the oxidative side reaction of chloride ions thermodynamically and improving the selectivity and accuracy of the reaction.

[0023] Step 4: Perform the oxidation reaction in the photoelectrochemical reaction cell. After the organic matter is completely oxidized, obtain a stable steady-state photocurrent with a stable current signal. In the above steps, the steady-state photocurrent is directly proportional to the rate at which organic matter in the electrolyzed water sample is oxidized, and a linear relationship can be established with the COD value. Step 5: Based on the preset steady-state photocurrent-COD concentration curve, obtain the COD measurement value, and correct the COD standard concentration value according to water temperature and salinity to obtain the COD correction value, including: By configuring different COD concentrations (0, 2, 5, 10, 20, 50, 100 mg / L) for measurement, the steady-state photocurrent-COD concentration curve was obtained by plotting the concentration value on the x-axis and the average value of the potential value on the y-axis. Based on different temperature and salinity gradients, standard samples were measured, and the COD measurement values ​​were corrected according to the standard sample values ​​to obtain the corrected COD value, expressed as: In the formula, This is a COD correction value; This is a correction factor; This is the measured COD value.

[0024] This invention provides an apparatus for performing the above-described method, specifically comprising: The three-electrode system includes a working electrode using a TiO2 nanotube array / Ti electrode and WO3 / conductive glass; a counter electrode using platinum wire or carbon rod; and a reference electrode using Ag / AgCl. A potentiostat is used to apply a bias voltage of 0.1-0.8V to the working electrode; LED light sources emit ultraviolet or visible light and are tightly integrated above the working electrode; The photoelectrochemical reaction cell, used for photoelectrochemical oxidation reactions, is made of corrosion-resistant materials and has a volume of <1mL, which facilitates rapid response and reagent conservation.

[0025] The signal detection and processing module is used to detect the steady-state photocurrent signal in the photoelectro-oxidation reaction and calculate the COD measurement value. Specifically, it includes: The current detection circuit, integrated with a potentiostat, is used to measure and amplify the steady-state photocurrent signal.

[0026] The data processing unit stores the steady-state photocurrent-COD concentration curve and corrects the measured COD value to obtain the corrected COD value.

[0027] Auxiliary modules are used to control power supply, fluid flow, and communication.

[0028] Specifically, it includes: The power supply and management unit uses lithium batteries or solar cells in conjunction with the BMS to power the potentiostat, LED light source and data processing unit; The fluid control unit, including a micro-pump, valve, and flow path, enables automatic injection, reaction, and evacuation of seawater samples; A wireless communication unit for data transmission via 4G / 5G / LoRa.

[0029] The working principle of the above coefficients is as follows: Under the combined action of light and external bias, the working electrode (photoanode) generates a large number of holes with strong oxidizing properties (h). + These holes preferentially oxidize organic matter in seawater samples: Organics + h + →CO2+H2O.

[0030] At the same time, the external bias will generate photoelectrons (e - The electrode is quickly withdrawn to the counter electrode, where a reduction reaction (e.g., O₂ + 4H₂) occurs. + +4e - →2H₂O). The photocurrent generated in the entire circuit directly reflects the oxidation rate of organic matter. By precisely controlling the bias voltage, an optimal electrochemical window that preferentially oxidizes organic matter while suppressing chloride ion oxidation was obtained, achieving high-precision and highly interference-resistant COD determination. Specific Implementation Seawater COD measurement was conducted on an unmanned surface vessel platform, including: As shown in Table 1, the working electrode was a TiO2 nanotube array / Ti electrode, the reference electrode was Ag / AgCl (saturated KCl), and the counter electrode was a platinum wire. During measurement, a +0.5V bias voltage was applied to the potentiostat, and the 365nm UV-LED light source was turned on simultaneously. A linear calibration curve (R0) for "photocurrent-COD" was established using potassium hydrogen phthalate standard solution. 2 >0.995). Measurements were performed on actual seawater samples, and the results were compared with those obtained using the national standard potassium dichromate method, with a relative error of <±8%.

[0032] Table 1

[0033] Validation of resistance to chloride ion interference, including: As shown in Table 2, simulated water samples with the same COD concentration (50 mg / L) but different chloride ion concentrations (0, 10000, 20000 mg / L) were prepared. The conventional unbiased photochemical method and the bias-enhanced method of this invention were compared. The results show that the measured values ​​of the conventional method drift significantly with increasing chloride ion concentration (>±25%), while the measured values ​​of the method of this invention remain stable within ±5%, demonstrating its superior resistance to chloride ion interference.

[0034] Table 2

[0035] Rapid response and long-term stability testing, including: like Figure 2 As shown, the unmanned surface vessel platform operated continuously on a near-shore buoy for 30 days, automatically taking four measurements per day. During this period, the photocurrent signal attenuation rate was less than 10%, requiring no electrode replacement or complex maintenance, demonstrating the system's long-term operational stability in harsh marine environments. The single measurement cycle (from sample introduction to result output) was less than 5 minutes.

[0036] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0037] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for determining seawater chemical oxygen demand based on bias-voltage photoelectric oxidation, characterized in that, include: Seawater was collected and pretreated to obtain seawater samples; A supporting electrolyte was added to the seawater sample to obtain an electrolyzed water sample; An electrolyzed water sample is injected into a photoelectrochemical reaction cell. Using Ag / AgCl as the reference electrode, a bias voltage is applied to the working electrode, and a light source of a specific wavelength is turned on for irradiation. An oxidation reaction is carried out in a photoelectrochemical reactor. After the organic matter is completely oxidized, a stable steady-state photocurrent with a stable current signal is obtained. Based on the preset steady-state photocurrent-COD concentration curve, the COD measurement value is obtained, and the COD standard concentration value is corrected according to water temperature and salinity to obtain the COD correction value.

2. The method for determining seawater chemical oxygen demand based on bias-voltage photoelectric oxidation according to claim 1, characterized in that, The pretreatment involves removing suspended particulate matter by filtration using a filter membrane with a pore size of 0.45 μm.

3. The method for determining seawater chemical oxygen demand based on bias photoelectric oxidation according to claim 1, characterized in that, The supporting electrolyte is Na2SO4 with a concentration of 0.1-0.5 mol / L.

4. The method for determining seawater chemical oxygen demand based on bias photoelectric oxidation according to claim 1, characterized in that, The bias voltage is 0.1-0.8V.

5. The method for determining seawater chemical oxygen demand based on bias photoelectric oxidation according to claim 1, characterized in that, The light source has a specific wavelength of 365 nm.

6. The method for determining seawater chemical oxygen demand based on bias photoelectric oxidation according to claim 1, characterized in that, The steady-state photocurrent-COD concentration curve is obtained by measuring different COD concentrations and plotting the concentration value on the x-axis and the average potential value on the y-axis.

7. The method for determining seawater chemical oxygen demand based on bias-voltage photoelectric oxidation according to claim 1, characterized in that, The process of correcting the COD standard concentration value based on water temperature and salinity to obtain the corrected COD value includes: Based on different temperature and salinity gradients, standard samples were measured, and the COD measurement values ​​were corrected according to the standard sample values ​​to obtain the corrected COD value, expressed as: In the formula, This is a COD correction value; This is a correction factor; This is the measured COD value.

Images