High-sensitivity rapid detection method for manganese ions in lake and reservoir water body based on phosphoric acid functionalized carbon dots

Abstract

The invention discloses a high-sensitivity rapid detection method for manganese ions in a lake and reservoir water body based on phosphoric acid functionalized carbon dots. The method comprises the steps of preparation of a phosphoric acid functionalized carbon dot fluorescent probe (A), pretreatment of a water sample (B), anti-interference treatment (C), fluorescence detection (D), data calibration (E) and the like. Through full-chain innovation of materials, methods and equipment, a limited phosphoric acid functionalized carbon dot synthesis process, a collaborative masking strategy and an intelligent calibration system are adopted, so that the long-standing problems of insufficient sensitivity, poor anti-interference performance, low efficiency and the like in the field of lake and reservoir manganese ion detection can be effectively solved; the method has remarkable technical advantages and market application value.

Description

Technical Field

[0001] The present invention relates to the field of lake and reservoir water quality detection, and in particular to a highly sensitive and rapid detection method for manganese ions in lake and reservoir water based on phosphoric acid-functionalized carbon dots. Background Art

[0002] Manganese (Mn²⁺), as an important indicator of water pollution, its excessive presence can lead to disorders in the metabolism of aquatic organisms (such as abnormal activities of AKP / ACP in the liver and kidneys of grass carp) and potential risks to drinking water safety (national standard limit: 0.1 mg / L). For medium and large-sized lakes and reservoirs, due to complex hydrology and diverse pollutant sources, the detection of manganese ions needs to take into account high sensitivity, anti-interference ability, and on-site rapid response ability. Existing detection technologies mainly include atomic absorption spectrometry, spectrophotometry, and modified enzyme-linked immunosorbent assay, but they still generally suffer from problems such as insufficient sensitivity, poor anti-interference ability, non-renewable materials, and scene limitations. For example, although atomic absorption spectrometry has high precision, it requires complex pretreatment (such as filtration and acid digestion), the instrument is bulky and cannot be used for on-site detection, and the sample collection standard is ambiguous (the controversy over static and filtration leads to poor data comparability); the formaldehyde oxime spectrophotometry improves the efficiency through a full-wavelength enzyme-linked immunosorbent assay (the speed is increased by 25 times for 24 samples per time), but the sensitivity is still limited (detection limit ≈ 1 μmol / L), and coexisting ions (Fe³⁺, Ca²⁺) require additional masking steps, and the anti-interference ability is insufficient; although the carbon dot composite materials in patents CN117568015A and CN117907278A have the potential for high sensitivity (such as the detection limit of phosphorus is 0.02 mg / L), the functional design is single, lacking specific recognition groups for Mn²⁺ (such as phosphoric acid groups), and is easily interfered by competitive ions such as Fe³⁺ (signal drift > 20%), the cost of single use of the probe is high, and some nanomaterials (such as quantum dots) have potential toxicity hazards and are difficult to be applied on a large scale; patent CN202311606701 proposes to use waste batteries to prepare porous carbon materials to adsorb phosphates, although it realizes "treating waste with waste", it does not involve the specific detection of manganese ions, and the material regeneration efficiency is low; patent CN116380876B uses nano-lanthanum hydroxide modified cellulose membrane to enrich phosphorus element, but the detection object is phosphorus rather than manganese, and it relies on complex instruments (such as laser-induced breakdown spectroscopy); patent CN119361660A inhibits the dissolution of manganese ions by carbon-coated manganese pyrophosphate to improve battery performance, but this technology focuses on material preparation and does not involve the detection of manganese ions in water. Therefore, there is an urgent need to develop a rapid detection method for manganese ions with high sensitivity, high specificity, and high efficiency to provide a reliable tool for water environment governance. Summary of the Invention

[0003] Aiming at the above key technical problems, the present invention provides a highly sensitive and rapid detection method for manganese ions in lake and reservoir water based on phosphoric acid-functionalized carbon dots. Through the functional design of high-performance materials, multi-parameter intelligent calibration, and the integration of portable devices, the highly sensitive and rapid detection of manganese ions in lake and reservoir water is realized.

[0004] The object of the present invention is achieved by the following technical solutions: A highly sensitive and rapid detection method for manganese ions in lake and reservoir water based on phosphoric acid-functionalized carbon dots, characterized by comprising the following steps: (A) Preparation of phosphoric acid-functionalized carbon dot fluorescent probe: Using citric acid as the carbon source and diammonium hydrogen phosphate as the phosphorus source, carbon dots with phosphoric acid groups on the surface are synthesized by hydrothermal method, with a particle size range of 2 - 5 nm and a fluorescence emission peak located at 450 - 480 nm; (B) Pretreatment of water sample: After filtering the water sample of the lake or reservoir to be measured through a 0.45 μm filter membrane, a pH regulator is added to stabilize the pH of the water sample at 6.0 - 7.5; (C) Anti-interference treatment: Add ascorbic acid (AA) and ethylenediaminetetraacetic acid (EDTA) to the pretreated water sample to mask the interference of Fe³⁺, Ca²⁺, and Mg²⁺ respectively; (D) Fluorescence detection: Mix the phosphoric acid-functionalized carbon dot probe prepared in step (a) with the water sample treated in step (c), and use a portable fluorescence spectrometer to measure the fluorescence quenching intensity at an excitation wavelength of 360 nm, and calculate the Mn²⁺ concentration through a standard curve; (E) Data calibration: Combine a turbidity sensor to collect the turbidity value of the water sample in real time, and correct the fluorescence signal deviation through an algorithm model, where the turbidity correction factor α satisfies α = 1 / (1 + 0.023×NTU), and NTU is the value measured by the turbidity sensor.

[0005] The synthesis conditions of the phosphoric acid-functionalized carbon dots are as follows: the molar ratio of citric acid to diammonium hydrogen phosphate is 1:1.5 - 2.5, the hydrothermal reaction temperature is 180 - 200 °C, the reaction time is 4 - 6 hours, and after dialysis purification, it is stored by freeze-drying. Moreover, the density of phosphoric acid groups on the surface of the carbon dots is 0.8 - 1.2 mmol / g, which is measured by X-ray photoelectron spectroscopy (XPS).

[0006] In the anti-interference treatment, the addition amount of ascorbic acid (AA) is 0.1 - 0.5 mmol / L, the addition amount of EDTA is 0.05 - 0.2 mmol / L, the masking time is 5 - 10 minutes, and the molar concentration ratio of EDTA to ascorbic acid is 1:(2 - 4).

[0007] The portable fluorescence spectrometer integrates a micro optical fiber probe, a 405 nm laser diode light source and a CCD detection module, with a detection limit of 0.05 - 0.1 μmol / L, a response time ≤ 3 minutes, the dynamic range of the CCD detection module is 10 4 -10 6 counts, and the signal-to-noise ratio ≥ 50 dB.

[0008] The algorithm model is constructed based on machine learning. The input parameters include fluorescence intensity, turbidity, water sample temperature, and pH value, and the output is the corrected Mn²⁺ concentration value. The model training dataset covers lake and reservoir water samples with turbidity of 0 - 100 NTU, temperature of 5 - 35 °C, and pH of 5.0 - 9.0. The model uses the random forest algorithm, and the feature weight distribution is 60% for fluorescence intensity, 25% for turbidity, 10% for temperature, and 5% for pH.

[0009] The high-sensitivity and rapid detection method for manganese ions in lake and reservoir water based on phosphoric acid-functionalized carbon dots further includes a probe regeneration step: soaking the used carbon dot probe in a 0.1 mol / L sodium citrate solution, performing ultrasonic treatment for 10 - 15 minutes, then centrifuging for recovery. The number of recycling times is ≥5 times, and the fluorescence intensity recovery rate after regeneration is ≥90%.

[0010] The method for establishing the standard curve is as follows: Prepare Mn²⁺ standard solutions with concentrations of 0 - 10 μmol / L, mix them with the phosphoric acid-functionalized carbon dot probe respectively, and then measure the fluorescence intensity. Perform linear fitting on the logarithm of the Mn²⁺ concentration with ΔF / F0 (ΔF is the fluorescence quenching value, and F0 is the initial fluorescence intensity). The correlation coefficient R²≥0.995, and the fitting equation is ΔF / F0 = 0.256×lg[Mn²⁺] + 0.018.

[0011] A detection device for implementing the method according to any one of claims 1 - 7, characterized by comprising: (1) An integrated sampling module: integrating a filtration unit, a pH adjustment unit, and an automatic anti-interference agent adding unit, where the adding error of the anti-interference agent is ≤±5%; (2) A detection module: internally provided with a storage bin for phosphoric acid-functionalized carbon dot probes, a mixing reaction pool, and a micro fluorescence spectrometer. The volume of the mixing reaction pool is 2 mL, and the temperature control accuracy is ±0.5 °C; (3) A data processing module: equipped with an embedded system, which can display the Mn²⁺ concentration and turbidity calibration results in real time and support 4G / 5G wireless data transmission; (4) A power supply module: adopting a dual power supply system of solar cells and lithium batteries, with a standby time of ≥72 hours.

[0012] The beneficial effects of the present invention are as follows: The present invention provides a highly sensitive and rapid detection method for manganese ions in lake and reservoir water based on phosphoric acid-functionalized carbon dots. By defining the synthesis parameters and fluorescence response mechanism of the phosphoric acid-functionalized carbon dots, accurate capture and analysis of low-concentration signals can be ensured, significantly improving the detection sensitivity. Through the "ascorbic acid + EDTA" synergistic masking strategy and the random forest algorithm combined with the turbidity correction factor α, the present invention obtains excellent anti-interference performance and is suitable for the rapid detection of manganese ions in complex water environments. Through a portable fluorescence spectrometer (response time ≤ 3 minutes), an integrated sampling module (automatic filtration and filling), modular design of the device, probe regeneration and utilization, etc., real-time field monitoring can be achieved, greatly improving the detection efficiency and practicability, and adapting to the monitoring needs of different scales of lakes and reservoirs. Through the full-chain innovation of materials, methods, and equipment, the present invention can effectively solve the long-existing problems of insufficient sensitivity, poor anti-interference ability, and low efficiency in the field of lake and reservoir manganese ion detection, and has significant technical advantages and market application value. Brief Description of the Drawings

[0013] Figure 1 It is a schematic flow chart of a highly sensitive and rapid detection method for manganese ions in lake and reservoir water based on phosphoric acid-functionalized carbon dots. Detailed Embodiments

[0014] The present invention will be further described in conjunction with the following embodiments, but the present invention is not limited to the embodiments. Embodiment

[0015] Preparation of phosphoric acid-functionalized carbon dot fluorescent probe: Dissolve citric acid (1.92 g) and diammonium hydrogen phosphate (3.96 g, molar ratio 1:2) in 50 mL of deionized water, perform hydrothermal reaction at 180 °C for 6 hours, dialyze and purify, and then freeze-dry to obtain carbon dots with a particle size of 3.2 ± 0.5 nm. The density of the phosphate group is determined by XPS to be 1.0 mmol / g.

[0016] In this embodiment, water samples from the Three Gorges Reservoir area are collected for detection. The collected water samples are filtered through a 0.45 μm filter membrane and the pH is adjusted to 6.8. Then, 0.3 mmol / L ascorbic acid (AA) and 0.1 mmol / L EDTA (molar ratio 3:1) are added and left standing for 8 minutes. Then, 2 mL of the treated water sample is mixed with the carbon dot probe (0.1 mg / mL), and a portable fluorescence spectrometer (CCD dynamic range 10 5counts, the fluorescence intensity was measured at a signal-to-noise ratio of 52 dB. The signal was corrected by a correction factor α = 1 / (1 + 0.023×25) = 0.64 in combination with a turbidity sensor (NTU = 25). The concentration of Mn²⁺ was measured to be 0.12 μmol / L (standard curve equation ΔF / F0 = 0.256×lg[Mn²⁺] + 0.018). After use, the probe was sonicated in 0.1 mol / L sodium citrate solution for 12 minutes, centrifuged for recovery, and the fluorescence intensity recovery rate was 92% after 5 cycles. The whole process of manganese ion detection took 15 minutes, the detection limit was 0.08 μmol / L, and the interference rates of Fe 3+ (10 μmol / L) and Ca 2+ (50 μmol / L) were < 5%.

[0017] Example 2: This example mainly conducts on-site test applications on the integrated detection device. The integrated sampling module automatically filters (0.45 μm filter element), adjusts the pH (phosphate buffer filling error ±3%), and adds anti-interference agents (AA 0.3 mmol / L, EDTA 0.1 mmol / L); the temperature-controlled reaction pool of the detection module is 2 mL (25 ± 0.5 °C), with an internal carbon dot probe storage bin (probe concentration 0.1 mg / mL), and a micro fluorescence spectrometer (405 nm laser light source); the data processing module uses an embedded system to run the random forest algorithm in real time (feature weights: fluorescence intensity 60%, turbidity 25%, temperature 10%, pH 5%), and uploads data to the cloud platform through 4G; the power supply uses solar energy + lithium battery, with a continuous standby time of 80 hours. The detection device can work stably in the range of pH 5.0 - 8.5 and turbidity 0 - 80 NTU; the device has good portability, weighs 2.5 kg, and does not require an external power supply for field deployment; compared with ICP-MS, the relative error is < 8% (n = 50).

[0018] Example 3: This example mainly conducts optimization and calibration of machine learning algorithms. 1000 groups of lake and reservoir water samples (turbidity 0 - 100 NTU, temperature 5 - 35 °C, pH 5.0 - 9.0) were collected, covering a Mn²⁺ concentration range of 0.05 - 10 μmol / L, and a data set was established; a random forest model (feature weight allocation: fluorescence intensity 60%, turbidity 25%, temperature 10%, pH 5%) was used, with an accuracy of 98.7% for the training set and RMSE = 0.04 μmol / L for the test set. For high-turbidity samples (NTU = 80) tested, the error was +35% before calibration and < 5% after calibration, and the influence of temperature fluctuations (10 - 30 °C) on the results decreased from ±12% to ±3%.

[0019] Comparative Example 1: In this comparative example, the water sample of Example 1 was detected by the traditional potassium permanganate method. 100 mL of the collected water sample was taken, 10 mL of 1:5 H2SO4 was added, and after boiling, 10 mL of 0.002 mol / L KMnO4 was added and heated for 10 minutes; then titration analysis was carried out. An excessive amount of Na2C2O4 standard solution was added and back-titrated to the faint red end point. The calculated COD value was 2.37 mg / L (corresponding Mn²⁺ concentration ≈ 1.5 μmol / L). The COD value reflects the total reducing substances and cannot distinguish the interference of Mn²⁺ from other organic substances, with an error > 30%; the detection limit of this method is 1.0 μmol / L, which cannot meet the low-concentration detection requirements, and the pretreatment and titration time require 2 hours, and laboratory equipment support is also needed.

[0020] Comparative Example 2: In this comparative example (where the unclarified parts are carried out according to Example 1), citric acid and urea were used for hydrothermal synthesis of carbon dots (without phosphoric acid functionalization), with a particle size of 4.5 nm; the directly collected ones were taken and mixed with the probe without adding an anti-interference agent, and there was no linear relationship between the fluorescence intensity decline rate and the Mn²⁺ concentration. At this time, the detection limit of manganese ions was only 1.2 μmol / L, and Fe³⁺ (5 μmol / L) caused a 40% increase in false positive signals.

[0021] Comparative Example 3: In this comparative example (where the unclarified parts are carried out according to Example 1), only 0.2 mmol / L of EDTA was added during the water sample treatment, and ascorbic acid was not used. Fe 3+ (10 μmol / L) caused a deviation in the fluorescence quenching rate of +22%, and Ca 2+ (50 μmol / L) caused an interference of +15%. It shows that a single masking agent cannot effectively distinguish Mn²⁺ from Fe³⁺ / Ca²⁺.

[0022] Through the comparison between the examples and the comparative examples, the present invention adopts the defined phosphoric acid functionalized carbon dot synthesis process, the synergistic masking strategy and the intelligent calibration system, which are significantly superior to the traditional method (potassium permanganate method) and the unoptimized probe scheme in terms of sensitivity, anti-interference ability, operation efficiency and environmental adaptability. It is applicable to a wide pH / turbidity range, with a detection limit of 0.05 - 0.1 μmol / L, and the interference rates of Fe 3+ and Ca 2+ are < 5%, the detection time ≤ 15 minutes, and the fluorescence intensity recovery rate is ≥ 90% after the probe is cycled 5 times, having significant technical advantages and market application value.

[0023] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention. The scope of protection required by the present invention is defined by the appended claims and their equivalents.

Claims

1. A highly sensitive and rapid detection method for manganese ions in lake and reservoir water based on phosphoric acid-functionalized carbon dots, characterized in that, It includes the following steps: (A) Preparation of phosphoric acid-functionalized carbon dot fluorescent probe: Using citric acid as the carbon source and diammonium hydrogen phosphate as the phosphorus source, carbon dots with phosphoric acid groups on the surface are synthesized by a hydrothermal method, with a particle size range of 2 - 5 nm and a fluorescence emission peak located at 450 - 480 nm; (B) Pretreatment of water sample: After filtering the water sample of the lake or reservoir to be measured through a 0.45 μm filter membrane, a pH regulator is added to stabilize the pH of the water sample at 6.0 - 7.5; (C) Anti-interference treatment: Ascorbic acid (AA) and ethylenediaminetetraacetic acid (EDTA) are added to the pretreated water sample to mask the interference of Fe³⁺, Ca²⁺, and Mg²⁺ respectively; (D) Fluorescence detection: The phosphoric acid-functionalized carbon dot probe prepared in step (a) is mixed with the water sample treated in step (c), and the fluorescence quenching intensity is measured using a portable fluorescence spectrometer at an excitation wavelength of 360 nm, and the Mn²⁺ concentration is calculated through a standard curve; (E) Data calibration: Combining with a turbidity sensor to collect the turbidity value of the water sample in real time, and correcting the fluorescence signal deviation through an algorithm model, where the turbidity correction factor α satisfies α = 1 / (1 + 0.023×NTU), and NTU is the value measured by the turbidity sensor.

2. The highly sensitive and rapid detection method for manganese ions in lake and reservoir water based on phosphoric acid-functionalized carbon dots according to claim 1, wherein, The synthesis conditions of the phosphoric acid-functionalized carbon dots are as follows: the molar ratio of citric acid to diammonium hydrogen phosphate is 1:1.5 - 2.5, the hydrothermal reaction temperature is 180 - 200 °C, the reaction time is 4 - 6 hours, after dialysis purification, it is stored by freeze-drying, and the density of phosphoric acid groups on the carbon dot surface is 0.8 - 1.2 mmol / g, which is measured by X-ray photoelectron spectroscopy (XPS).

3. A highly sensitive and rapid detection method for manganese ions in lake and reservoir water based on phosphoric acid-functionalized carbon dots according to claim 1, characterized in that, In the anti-interference treatment, the addition amount of ascorbic acid (AA) is 0.1 - 0.5 mmol / L, the addition amount of EDTA is 0.05 - 0.2 mmol / L, the masking time is 5 - 10 minutes, and the molar concentration ratio of EDTA to ascorbic acid is 1:(2 - 4).

4. A highly sensitive and rapid detection method for manganese ions in lake and reservoir water based on phosphoric acid-functionalized carbon dots according to claim 1, characterized in that, The described portable fluorescence spectrometer integrates a micro optical fiber probe, a 405 nm laser diode light source, and a CCD detection module. The detection limit is 0.05 - 0.1 μmol / L, the response time is ≤ 3 minutes, and the dynamic range of the CCD detection module is 10 4 -10 6 counts, and the signal-to-noise ratio is ≥ 50 dB.

5. A highly sensitive and rapid detection method for manganese ions in lake and reservoir water based on phosphoric acid-functionalized carbon dots according to claim 1, characterized in that, The algorithm model is constructed based on machine learning. The input parameters include fluorescence intensity, turbidity, water sample temperature, and pH value, and the output is the corrected Mn²⁺ concentration value. The model training dataset covers lake and reservoir water body samples with turbidity of 0 - 100 NTU, temperature of 5 - 35 °C, and pH of 5.0 - 9.

0. The model uses the random forest algorithm, and the feature weight distribution is 60% for fluorescence intensity, 25% for turbidity, 10% for temperature, and 5% for pH.

6. A highly sensitive and rapid detection method for manganese ions in lake and reservoir water based on phosphoric acid-functionalized carbon dots according to claim 1, characterized in that, It also includes a probe regeneration step: The used carbon dot probe is immersed in a 0.1 mol / L sodium citrate solution, ultrasonically treated for 10 - 15 minutes and then centrifuged for recovery. The number of recycling times is ≥5 times, and the fluorescence intensity recovery rate after regeneration is ≥90%.

7. A highly sensitive and rapid detection method for manganese ions in lake and reservoir water based on phosphoric acid-functionalized carbon dots according to claim 1, characterized in that, The method for establishing the standard curve is as follows: Prepare a Mn²⁺ standard solution with a concentration of 0 - 10 μmol / L, mix it with the phosphoric acid-functionalized carbon dot probe respectively and then measure the fluorescence intensity. Perform a linear fitting on the logarithm of ΔF / F0 (ΔF is the fluorescence quenching value, F0 is the initial fluorescence intensity) and the Mn²⁺ concentration, with the correlation coefficient R²≥0.995, and the fitting equation is ΔF / F0 = 0.256×lg[Mn²⁺] + 0.

018.

8. A detection device for implementing the method according to any one of claims 1-7, characterized in that, It includes: (1)Integrated sampling module: integrating a filtering unit, a pH adjustment unit and an automatic anti-interference agent dosing unit, where the dosing error of the anti-interference agent is ≤ ±5%; (2)Detection module: internally equipped with a storage bin for phosphoric acid-functionalized carbon dot probes, a mixing reaction pool and a micro fluorescence spectrometer, the volume of the mixing reaction pool is 2 mL, and the temperature control accuracy is ±0.5 °C; (3)Data processing module: equipped with an embedded system, real-time display of the Mn²⁺ concentration and turbidity calibration results, supporting 4G / 5G wireless data transmission; (4)Power supply module: adopting a dual power supply system of solar cells and lithium batteries, standby time ≥ 72 hours.

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