Microfluidic chip for measuring COD by TiO2 photocatalytic oxidation method and its preparation method

Abstract

A microfluidic chip for measuring COD by TiO2 photocatalytic oxidation method and its preparation method, comprising a single-crystalline silicon substrate, a quartz upper cover covering the single-crystalline silicon substrate, a working electrode, a reference electrode and a counter electrode arranged on the single-crystalline silicon substrate, wherein the working electrode comprises a titanium transition layer arranged on the single-crystalline silicon substrate and an anatase TiO2 film arranged on the titanium transition layer. Functional structures with nano- to micron-sized and liquid flow paths are fabricated into the substrate and upper cover structures, and a chip body with complete analysis and detection functions and capable of outputting detection signals is obtained through packaging technology, which is beneficial to further reducing the sample usage amount, reducing energy consumption, shortening the analysis time, and forming a high-cost-effective chip-based COD detection mode.

Description

Technical Field

[0001] The present invention relates to a microfluidic chip for measuring COD by TiO2 photocatalytic oxidation method and a preparation method thereof. Background Art

[0002] Chemical Oxygen Demand (COD) is used to characterize the concentration of reducing substances in water by measuring the amount of oxygen, in mg / L, required for the complete oxidation of reducing substances in the water body, and thus to evaluate the degree of water body pollution.

[0003] Currently, the commonly used methods for detecting COD are the chromium method, the manganese method, and the ultraviolet absorbance method. In the first two methods, strong chemical oxidants, potassium dichromate and potassium permanganate, are used. Under high temperature and with heavy metal salts as catalysts, oxidation reflux is carried out for 2 - 3 hours. Finally, the amount of potassium dichromate and potassium permanganate consumed is calculated by back titration, and then the corresponding theoretical oxygen consumption is calculated. For the ultraviolet absorbance method, the absorbance of the water body at a certain wavelength of ultraviolet light is measured, and the COD value of the water body is indirectly calculated through the linear correlation between the absorbance and COD.

[0004] The chromium method and the manganese method have poor oxidation ability and cannot completely oxidize reducing substances, resulting in large errors in the obtained COD values. The ultraviolet absorbance method needs to be correlated with ultraviolet absorbance and cannot directly obtain the COD value. There are differences in the numerical conversion of the two measurement systems. Moreover, the current methods for detecting COD on the market can only perform detection. The detection results need to be recorded and then analyzed by other instruments. In addition, the detection sample consumption is large, the energy consumption is high, the analysis time is long, and the cost performance is low.

[0005] Therefore, there is a need for a microfluidic chip that can reduce the consumption of detection samples and has low energy consumption, short analysis time, and high cost performance to complete the measurement of COD. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a microfluidic chip for measuring COD by TiO2 photocatalytic oxidation method.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A microfluidic chip for measuring COD by TiO2 photocatalytic oxidation method, comprising a single-crystalline silicon substrate, a quartz upper cover covering the single-crystalline silicon substrate, a working electrode, a reference electrode, and a counter electrode provided on the single-crystalline silicon substrate. The working electrode includes a titanium transition layer provided on the single-crystalline silicon substrate and anatase TiO2 film provided on the titanium transition layer. Fabricating functional structures with nano- to micron-sized and liquid flow paths onto the substrate and obtaining a chip body with complete analytical and detection functions and capable of outputting detection signals through packaging technology is conducive to further reducing the sample usage amount, reducing energy consumption, shortening the analysis time, and forming a high-cost-effective COD detection mode.

[0008] Preferably, a microfluidic channel is formed between the single-crystalline silicon substrate and the quartz upper cover. The sample usage amount is reduced, and the energy consumption is decreased.

[0009] Preferably, a liquid outlet interface and a liquid inlet interface for liquid inlet and outlet are provided on the quartz upper cover.

[0010] Preferably, the liquid outlet interface and the liquid inlet interface are respectively conical hollow columns. It is convenient for sample liquid to enter and exit.

[0011] Preferably, pins connected to the gold wires led out from the working electrode, the reference electrode, and the counter electrode are provided on the quartz upper cover, and the pins are provided at the edge inside the quartz upper cover.

[0012] Preferably, annular reinforcing ribs corresponding to the working electrode, the reference electrode, and the counter electrode are provided inside the quartz upper cover, and the center of the annular reinforcing rib is directly above the center of the working electrode.

[0013] Preferably, the working electrode is located between the counter electrode and the reference electrode.

[0014] Preferably, the counter electrode includes the titanium transition layer provided on the single-crystalline silicon substrate and a gold layer provided on the titanium transition layer.

[0015] Preferably, the reference electrode includes the titanium transition layer provided on the single-crystalline silicon substrate and a silver-silver chloride layer on the gold layer provided on the titanium transition layer.

[0016] The technical problem to be solved by the present invention is to provide a preparation method for a microfluidic chip for measuring COD by TiO2 photocatalytic oxidation method.

[0017] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for preparing a microfluidic chip for measuring COD by TiO2 photocatalytic oxidation method, specifically including the following steps: S1, prepare a single crystal silicon substrate, and form a titanium transition layer on the single crystal silicon substrate by electron sputtering method; S2, form an anatase TiO2 film on the titanium transition layer by electron beam thermal evaporation coating technology, and form the external shape structure of the working electrode by photolithography and etching methods to complete the preparation of the working electrode; S3, use a mask plate to mask the working electrode, and then form a gold layer on the titanium transition layer by sputtering method, and obtain the external shape structure of the counter electrode and the reference electrode gold layer by photolithography and etching methods, and remove the connection of the titanium transition layer between the three electrodes to complete the preparation of the counter electrode; S4, use a mask plate to mask the working electrode and the counter electrode, and deposit a silver-silver chloride layer on the reference electrode gold layer by electrochemical deposition method and partial oxidation method to complete the preparation of the reference electrode; S5, use a low-temperature anodic bonding method to cover the quartz upper cover on the single crystal silicon substrate to form a packaging structure.

[0018] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art: 1. The present invention combines the TiO2 photocatalytic oxidation method for measuring water body COD with MEMS technology in the form of a microfluidic chip, which is beneficial to further reducing the sample usage, reducing energy consumption, shortening the analysis time, and forming a cost-effective chip-based COD detection mode;

[0019] The TiO2 photocatalytic oxidation method can oxidize reducing substances more thoroughly. The obtained COD value is closer to the definition of COD itself. Moreover, hydroxyl radicals are generated online at room temperature, the oxidation reaction is rapid, no chemical reagents are used, and it is more convenient to realize on-line, real-time and green detection;

[0020] The TiO2 photocatalytic oxidation method can directly measure the COD value without the need to correlate with COD through other data, avoiding the differences in the numerical conversion of the two measurement systems. Description of the Drawings

[0021] Figure 1 Schematic diagram of the microfluidic chip for measuring water body COD by TiO2 photocatalytic oxidation method provided by the present invention;

[0022] Figure 2a To form an anatase TiO2 film on the titanium layer by electron beam thermal evaporation coating technology;

[0023] Figure 2b To obtain the external shape structure of the working electrode by photolithography and etching methods;

[0024] Figure 2c To mask the working electrode with a mask plate and then obtain a gold layer on the titanium layer by sputtering method;

[0025] Figure 2d To obtain the outer shape structures of the counter electrode and the reference electrode on the titanium layer by photolithography and etching methods

[0026] Figure 2e To remove the titanium transition layer connection between the three electrodes by etching method;

[0027] Figure 2f First, mask the working electrode and the counter electrode with a mask plate, and then obtain a silver-silver chloride layer on the gold layer of the reference electrode by electrochemical deposition method and partial oxidation method;

[0028] Figure 2g For the microfluidic channel between the upper cover and the substrate after encapsulation;

[0029] Figure 3 For the overall structure diagram of the chip;

[0030] Wherein: 1. Single crystal silicon substrate; 2. Quartz upper cover; 21. Liquid outlet interface; 22. Liquid inlet interface; 3. Titanium transition layer; 4. Anatase TiO2 film; 5. Gold layer; 6. Silver-silver chloride layer; 7. Microfluidic channel; 8. Annular reinforcing rib. Specific embodiments

[0031] The present invention uses MEMS technology for fabricating a microfluidic chip, including sputtering, photolithography, electrochemical deposition and oxidation, electron beam thermal evaporation coating technology and low-temperature anodic bonding method, and realizes the measurement of water body COD by TiO2 photocatalytic oxidation method in a microfluidic chip.

[0032] Through the microfluidic chip, the amount of sample for time analysis in the process of measuring water body COD by TiO2 photocatalytic oxidation method is less, the detection time is shorter, and it can form an integrated chip detection system with other functional microfluidic chips.

[0033] Such as Figure 1The microfluidic chip for measuring COD by TiO2 photocatalytic oxidation method shown in the figure includes a single-crystalline silicon substrate 1, a quartz upper cover 2 covering the single-crystalline silicon substrate 1, a working electrode, a reference electrode, and a counter electrode disposed on the single-crystalline silicon substrate 1. The working electrode includes a titanium transition layer 3 disposed on the single-crystalline silicon substrate 1 and anatase TiO2 film 4 disposed on the titanium transition layer 3. A microfluidic channel 7 is formed between the single-crystalline silicon substrate 1 and the quartz upper cover 2. The quartz upper cover 2 is provided with a liquid outlet interface 21 and a liquid inlet interface 22 for liquid inlet and outlet. The liquid outlet interface 21 and the liquid inlet interface 22 are respectively conical hollow columns. The quartz upper cover 2 is provided with pins connected to the gold wires led out from the working electrode, the reference electrode, and the counter electrode. The pins are disposed at the edge inside the quartz upper cover 2. An annular reinforcing rib 8 corresponding to the working electrode, the reference electrode, and the counter electrode is disposed inside the quartz upper cover 2. The center of the annular reinforcing rib 8 is disposed directly above the working electrode. The working electrode is located between the counter electrode and the reference electrode. The counter electrode includes a titanium transition layer 3 disposed on the single-crystalline silicon substrate 1 and a gold layer 5 disposed on the titanium transition layer 3. The reference electrode includes a titanium transition layer 3 disposed on the single-crystalline silicon substrate 1 and a silver-silver chloride layer 6 disposed on the gold layer 5 on the titanium transition layer 3.

[0034] The TiO2 photocatalytic oxidation method can oxidize reducing substances more thoroughly. The obtained COD value is closer to the definition of COD itself. Moreover, hydroxyl radicals are generated online at room temperature, the oxidation reaction is rapid, no chemical reagents are used, and it is more convenient to realize on-line, real-time, and green detection.

[0035] The preparation method of the microfluidic chip provided by the present invention specifically includes: as Figure 2a - Figure 2b , prepare a single-crystalline silicon substrate, and form a titanium transition layer on the single-crystalline silicon substrate by electron sputtering method; form anatase TiO2 film on the titanium transition layer by electron beam thermal evaporation coating technology, and form the outer shape structure of the working electrode by photolithography and etching methods to complete the preparation of the working electrode.

[0036] As Figure 2c - Figure 2e , use a mask plate to mask the working electrode, and then form a gold layer on the titanium transition layer by sputtering method. Obtain the outer shape structure of the gold layer of the counter electrode and the reference electrode by photolithography and etching methods, and remove the connection of the titanium transition layer between the three electrodes to complete the preparation of the counter electrode.

[0037] As Figure 2f , use a mask plate to mask the working electrode and the counter electrode, and deposit a silver-silver chloride layer on the gold layer of the reference electrode by electrochemical deposition method and partial oxidation method to complete the preparation of the reference electrode.

[0038] As Figure 2g , use low-temperature anodic bonding method to cover the quartz upper cover on the single-crystalline silicon substrate to form a packaging structure.

[0039] This embodiment is implemented under the following implementation conditions and technical requirements:

[0040] Cleaning: Use a 500-micron-thick, 3-inch single-crystalline silicon as the substrate. First, ultrasonically clean it in an acetone solution for 10 minutes, then put it into absolute ethanol for ultrasonic cleaning for 10 minutes, and finally clean it with pure water and dry it with nitrogen; on the 3-inch single-crystalline silicon substrate, first sputter a titanium transition layer with a thickness of 30 - 50 nanometers as the connection layer on the cleaned substrate.

[0041] Anatase TiO2 film electrode: Form a 500 - 1000-nanometer-thick anatase TiO2 film on the titanium layer through electron beam thermal evaporation coating technology, and control the electron beam thermal evaporation temperature above 400 degrees to ensure obtaining anatase crystalline form.

[0042] Patterned TiO2 film electrode: On the sputtered titanium metal, use steps such as spin coating, exposure, development, and fixing in MEMS technology to pattern the TiO2 film electrode pattern.

[0043] Etching of TiO2 film electrode: Use TiO2 etchant to remove the excess TiO2, and then remove the excess photoresist.

[0044] Obtaining a gold layer on the titanium layer: First, mask the working electrode through a mask plate, and then obtain a gold layer on the titanium layer through sputtering.

[0045] Patterned gold electrode: First, mask the working electrode through a mask plate, and then use steps such as spin coating, exposure, development, and fixing in MEMS technology to pattern the gold electrode pattern.

[0046] Etching of gold electrode: Use gold etchant to remove the excess gold, and then remove the excess photoresist.

[0047] Removing the titanium layer between the three electrodes: First, cover a layer of photoresist on the surface of the three electrodes, then use Ti etchant to remove the titanium layer between the three electrodes, and finally remove the excess photoresist.

[0048] Fabrication of silver-silver chloride reference electrode: In the prepared silver electroplating solution, use a gold electrode as the cathode and a platinum wire as the anode for silver deposition reduction, and then use the obtained Ag-gold electrode as the anode and a platinum wire as the cathode for anodic oxidation to obtain a silver-silver chloride reference electrode.

[0049] Packaging and microfluidic channel preparation: Use low-temperature (200 °C) anodic bonding technology to package the prepared substrate containing three electrodes and the upper cover to form a microfluidic chip for measuring the COD of water by TiO2 photocatalytic oxidation method.

[0050] The above embodiments are only used to illustrate the technical concept and characteristics of the present invention. The purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and it cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A microfluidic chip for measuring COD by TiO2 photocatalytic oxidation method, characterized in that: It includes a single-crystal silicon substrate (1), a quartz upper cover (2) covering the single-crystal silicon substrate (1), a working electrode, a reference electrode, and a counter electrode disposed on the single-crystal silicon substrate (1). The working electrode includes a titanium transition layer (3) disposed on the single-crystal silicon substrate (1), the thickness of the titanium transition layer (3) is 30 - 50 nanometers, and it further includes an anatase TiO₂ film (4) disposed on the titanium transition layer (3), the thickness of the anatase TiO₂ film (4) is 500 - 1000 nanometers. A microfluidic channel (7) is formed between the single-crystal silicon substrate (1) and the quartz upper cover (2). An outlet interface (21) and an inlet interface (22) for liquid inlet and outlet are provided on the quartz upper cover (2). Pins connected to the gold wires led out from the working electrode, the reference electrode, and the counter electrode are provided on the quartz upper cover (2), and the pins are disposed at the edge inside the quartz upper cover (2). Annular reinforcing ribs (8) corresponding to the working electrode, the reference electrode, and the counter electrode are provided inside the quartz upper cover (2). The center of the annular reinforcing rib (8) is disposed directly above the center of the working electrode. The working electrode is located between the counter electrode and the reference electrode. The counter electrode includes the titanium transition layer (3) disposed on the single-crystal silicon substrate (1) and a gold layer (5) disposed on the titanium transition layer (3). The reference electrode includes the titanium transition layer (3) disposed on the single-crystal silicon substrate (1) and a silver-silver chloride layer (6) disposed on the gold layer (5) on the titanium transition layer (3).

2. The microfluidic chip for measuring COD by the TiO2 photocatalytic oxidation method according to claim 1, characterized in that: The outlet interface (21) and the inlet interface (22) are respectively conical hollow columns.

3. The preparation method of the microfluidic chip according to claim 2, characterized in that: Specifically, it includes the following steps: S1, Prepare a single-crystal silicon substrate, and form a titanium transition layer on the single-crystal silicon substrate by electron sputtering method; S2, Form an anatase TiO₂ film on the titanium transition layer by electron beam thermal evaporation coating technology, and form the outer shape structure of the working electrode through photolithography and etching methods to complete the preparation of the working electrode; S3, Mask the working electrode with a mask plate, then form a gold layer on the titanium transition layer by sputtering method, obtain the outer shape structures of the gold layers of the counter electrode and the reference electrode through photolithography and etching methods, and remove the connection of the titanium transition layer between the three electrodes to complete the preparation of the counter electrode; S4, Mask the working electrode and the counter electrode with a mask plate, and deposit a silver-silver chloride layer on the gold layer of the reference electrode by electrochemical deposition method and partial oxidation method to complete the preparation of the reference electrode; S5, Cover the quartz upper cover on the single-crystal silicon substrate by low-temperature anodic bonding method to form the overall chip packaging structure.

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