1. The super-hydrophilic pH thick film sensor based on the chemical corrosion method is characterized by comprising a substrate (2), a working electrode (1) and a reference electrode (5);

the working electrode (1) comprises a titanium sheet (11) attached to one side of the substrate (2), a titanium dioxide sensitive layer (12) covers the front part of the outer side surface of the titanium sheet (11), and the tail part of the titanium sheet (11) is connected with the first lead (3); a conductive layer (21) is attached to the other side of the substrate (2), the tail part of the conductive layer (21) is connected with a second lead (4), a reference electrode (5) is positioned on the conductive layer (21), and a naphthol layer (53) is coated on the surface of the reference electrode (5); the substrate (2) is wrapped by the insulating glue (6), and only the areas of the working electrode (1) and the reference electrode (5) are reserved, so that part of the titanium dioxide sensitive layer (12) and the naphthol layer (53) are in direct contact with the outside; the first lead (3) and the second lead (4) are led out through the insulating layer (6).

2. The chemical etching method-based superhydrophilic pH thick film sensor according to claim 1, wherein the substrate (2) is a glass sheet (22), and the conductive layer (21) is indium tin oxide; the reference electrode (5) comprises a silver layer (51), a silver chloride layer (52) and a naphthol layer (53); a silver layer (51) is provided on the conductive layer (21), a silver chloride layer (52) is provided on the silver layer (51), and a naphthol layer (53) is provided on the silver chloride layer (52).

3. The chemical corrosion method based ultra-hydrophilic pH thick film sensor according to claim 1, wherein the substrate (2) is an alumina ceramic sheet (23), and the conductive layer (21) is made of silver; the reference electrode (5) comprises a silver chloride layer (52) and a naphthol layer (53); the silver chloride layer (52) covers the front part of the conductive layer (21), and the naphthol layer (53) covers the silver chloride layer (52).

4. A method for preparing a super-hydrophilic pH thick film sensor based on a chemical etching method according to any one of claims 1 to 3, comprising the following preparation steps:

inserting the titanium sheet (11) into a sodium hydroxide solution for reaction to prepare the titanium sheet (11) with a single-side titanium dioxide sensitive layer (12);

covering one side of the substrate (2) with a conductive layer (21), and manufacturing a reference electrode (5) in the front area of the conductive layer (21);

dropping naphthol on the surface of the reference electrode (5), and drying; repeating the steps for three times to obtain a naphthol layer (53);

bonding a titanium sheet (11) to the other side of the substrate (2), and respectively connecting the first lead (3) and the second lead (4) with the titanium sheet (11) and the tail part of the conductive layer (21); and coating an insulating glue (6) on the periphery of the substrate (2), and only reserving areas of the working electrode (1) and the reference electrode (5), so that part of the titanium dioxide sensitive layer (12) and the naphthol layer (53) are in direct contact with the outside, and the first lead (3) and the second lead (4) penetrate out of the insulating glue (6).

5. The method for preparing the super-hydrophilic pH thick film sensor based on the chemical corrosion method is characterized in that the titanium sheet (11) is inserted into a sodium hydroxide solution for reaction, and the preparation of the titanium sheet (11) with the single-side titanium dioxide sensitive layer (12) is specifically as follows: covering one side of a clean titanium sheet (11) with a protective film, then inserting the titanium sheet into a sodium hydroxide solution, reacting for a period of time at the temperature of 80 ℃, taking out the titanium sheet, and tearing off the protective film to obtain the titanium sheet (11) with the single-side titanium dioxide sensitive layer (12).

6. The method for preparing the ultra-hydrophilic pH thick film sensor based on the chemical etching method as claimed in claim 5, wherein the concentration of the sodium hydroxide solution is 0.5 mol/L-4 mol/L, and the reaction time is 15 minutes-180 minutes.

7. The method for preparing the ultra-hydrophilic pH thick film sensor based on the chemical etching method as claimed in claim 4, wherein the substrate (2) is a glass sheet (22), the conductive layer (21) is an indium tin oxide layer, a silver layer (51) is deposited in a designated area of the indium tin oxide layer, 1 wt% of sodium hypochlorite solution is dripped on the surface of the silver layer (51), and after the silver layer (51) is turned into light purple, the silver chloride layer (52) is obtained by washing with deionized water.

8. The method for preparing a low-cost pH sensor with a super-hydrophilic surface according to claim 4, wherein the substrate (2) is an alumina ceramic plate (23), silver is deposited on one side of the substrate (2) to prepare the conductive layer (21), 1 wt% of sodium hypochlorite solution is dripped on the front area of the surface of the conductive layer (21), and the area is washed by deionized water after being changed to light purple to prepare the silver chloride layer (52).

Background

"phase" is a basic concept of thermodynamics, and refers to a part of a system that has uniform physical and chemical properties, distinct boundaries, and can be separated mechanically, such as a solid phase, a liquid phase, a gas phase, etc. Heterogeneous systems are systems containing more than one phase in a space with distinct interfaces between the phases, e.g. Ca (OH)₂Flocculent precipitates appear in the water, at which point water and Ca (OH)₂Together forming a heterogeneous system. In life, some heterogeneous systems have very complex compositions, such as soil, agricultural cultivation substrates, solid-liquid mixed waste, sand-seawater intersection areas of coastlines, and the like. In these systems, the solid phase, the liquid phase and the gas phase are irregularly staggered and have a very complicated internal structure, and it is usually very difficult to determine physicochemical parameters (such as pH value, conductivity value and the like) in these systems: the accuracy of the relevant parameters measured by a laboratory method is high, but the method is time-consuming, labor-consuming and low in efficiency; the sensor is used for direct online detection, although the speed is high and the efficiency is high, the accuracy of the result is poor and the practicability is low.

Zhang Xiliang, Xukun, et al, in Chinese patent CN201610301183.X, a micro-nano textured graphene-based bionic pH sensor and a preparation method thereof, disclose a pH sensor suitable for soil and culture medium, which enriches water in the surrounding environment through a super-hydrophilic surface and spreads on the surface of the sensor. For the sensor, the contact environment at the moment is converted into a simple liquid phase system from a complex heterogeneous system, and the electrode surface has a microenvironment suitable for detection, so that the rapid and accurate detection of the pH value in the heterogeneous system is realized. The super-hydrophilicity of the electrode surface is realized by preparing micron or nano-scale pits or grooves on the electrode sensitive material layer by femtosecond laser, the cost is high, the processing cost of a single electrode is thousands of yuan, and the application and popularization in agricultural production are limited.

At present, there are very many means for preparing the super-hydrophilic surface, such as a chemical etching method, a sol-gel method, a layer-by-layer self-assembly method, an anodic oxidation method, an ultraviolet irradiation method and the like besides femtosecond laser processing, and the methods can obviously reduce the preparation cost of the super-hydrophilic surface,as pointed out in the research on preparing TiO2 film by treating Ti sheet with strong alkali, TiO with nanoflower microtexture can be obtained by soaking the Ti sheet in hot NaOH₂A surface. In addition, some metal oxides may also exhibit superhydrophilicity under specific conditions, such as hydrophic properties of nano-TiO₂When the annealing temperature is 400 ℃ found in thin films deposited by RF magnetrons sputtering, the TiO prepared by magnetron sputtering₂The film will be transformed into anatase crystals, where the material is super hydrophilic.

However, none of the above documents mentions whether the material under study has a hydrogen ion concentration response characteristic, because the electrochemical properties of the metal oxide are closely related to the crystal structure, the surface atomic state, and the electronic energy state in the atom, and the rule is very complex. For example TiO prepared likewise by anodic oxidation₂Surface of the TiO at pH sensor based on₂In the report of nanotube array modified Ti electrode, the TiO produced thereby₂The nanotube can obtain better pH response performance and present better hydrophilicity, the hydrophilicity is further enhanced after ultraviolet irradiation, and the pH detection sensitivity of the sensor is further improved. However, the anodic oxidation of TiO by the anodic oxidation method is reported in Electrochemical measurements on Pt, Ir, and Ti oxides as pH probes₂The electrode had little pH response. In addition, in Investination on the sensitivity of TiO₂TiO prepared by magnetron sputtering in Ru pH sensor by Taguchi design of experiment₂The sensitivity of the layer is only around 30mV/pH, with a large gap from the theoretical value of 59.6 mV/pH. In this regard, the researchers thought that TiO₂The final crystal type and the surface accumulation form can influence the capability of oxygen atoms in surface Ti-O-Ti bonds for capturing electrons, thereby influencing the hydrogen ion concentration response performance of the crystal; generally speaking, anatase and amorphous TiO₂The hydrogen ion concentration response performance can be shown, but performance parameters such as sensitivity, response time and the like can be influenced by the preparation process, and specific influence rules and mechanisms are not clear and can only be determined through experiments.

The significant difference between thick film sensors and thin film sensors is the significant increase in the thickness of the electrode sensitive layer, typically from 100 nm to several microns, which is usually prepared by chemical etching, sol-gel methods. The advantages of thick film sensors over thin film sensors, including higher reliability, durability, lower drift and hysteresis, longer service life, and lower manufacturing cost, are summarized in Metal oxides based electrochemical pH sensors, which have long response times and are difficult to fabricate directly in integrated circuits. Agricultural sensors typically have higher requirements for reliability, environmental suitability and cost control, and therefore thick film sensors are more suitable for agricultural applications.

Disclosure of Invention

Based on the technical problems and relevant research conclusions, the invention provides a super-hydrophilic pH thick film sensor based on a chemical corrosion method and a preparation method thereof, aiming at the problems of high manufacturing cost, complex flow and the like of the current super-hydrophilic pH sensor.

The technical scheme of the invention is as follows: a super-hydrophilic pH thick film sensor based on a chemical corrosion method comprises a substrate, a working electrode and a reference electrode;

the working electrode comprises a titanium sheet attached to one side of the substrate, a titanium dioxide sensitive layer covers the front part of the outer side surface of the titanium sheet, and the tail part of the titanium sheet is connected with a first lead; a conductive layer is attached to the other side of the substrate, a second lead is connected to the tail of the conductive layer, the reference electrode is located on the conductive layer, and a naphthol layer is coated on the surface of the reference electrode; the substrate is wrapped by the insulating glue, and only the areas of the working electrode and the reference electrode are reserved, so that part of the titanium dioxide sensitive layer and the naphthol layer are in direct contact with the outside; the first and second wires are led out through the insulating layer.

In the scheme, the substrate is a glass sheet, and the conductive layer is made of indium tin oxide; the reference electrode comprises a silver layer, a silver chloride layer and a naphthol layer; the silver layer is arranged on the conducting layer, the silver chloride layer covers the silver layer, and the naphthol layer covers the silver chloride layer.

In the scheme, the substrate is an aluminum oxide ceramic wafer, and the conductive layer is made of silver; the reference electrode comprises a silver chloride layer and a naphthol layer; the silver chloride layer covers the front part of the conducting layer, and the naphthol layer covers the silver chloride layer.

A preparation method of the super-hydrophilic pH thick film sensor based on the chemical corrosion method comprises the following preparation steps:

inserting the titanium sheet into a sodium hydroxide solution for reaction to prepare the titanium sheet with a unilateral titanium dioxide sensitive layer;

covering one side of the substrate with a conductive layer, and manufacturing a reference electrode in the front area of the conductive layer;

dropping naphthol on the surface of the reference electrode, and drying in the air; repeating the steps for three times to obtain a naphthol layer;

bonding the titanium sheet to the other side of the substrate, and respectively connecting the first lead and the second lead with the titanium sheet and the tail part of the conductive layer; and coating insulating glue on the periphery of the substrate, and only reserving areas of the working electrode and the reference electrode, so that part of the titanium dioxide sensitive layer and the naphthol layer are in direct contact with the outside, and the first lead and the second lead penetrate out of the insulating glue.

In the scheme, the step of inserting the titanium sheet into a sodium hydroxide solution for reaction to prepare the titanium sheet with the unilateral titanium dioxide sensitive layer specifically comprises the following steps: covering a layer of protective film on one side of a clean titanium sheet, then inserting the titanium sheet into a sodium hydroxide solution, reacting for a period of time at the temperature of 80 ℃, taking out the titanium sheet, and tearing off the protective film to obtain the titanium sheet with the unilateral titanium dioxide sensitive layer.

In the scheme, the concentration of the sodium hydroxide solution is 0.5-4 mol/L, and the reaction time is 15-180 minutes.

In the scheme, the substrate is a glass sheet, the conducting layer is an indium tin oxide layer, a silver layer is deposited in a designated area of the indium tin oxide layer, 1 wt% of sodium hypochlorite solution is dripped on the surface of the silver layer, and the silver layer is washed by deionized water after being converted into light purple to obtain a silver chloride layer.

In the scheme, the substrate is an aluminum oxide ceramic wafer, silver is deposited on one side of the substrate to prepare the conducting layer, 1 wt% of sodium hypochlorite solution is dripped into a region close to the front part of the surface of the conducting layer, and the conducting layer is washed by deionized water after the region is changed into light purple to obtain the silver chloride layer.

Compared with the prior art, the invention has the beneficial effects that:

on one hand, the sensor disclosed by the invention is simple in structure and compact in volume, and the thick film electrode has better environmental adaptability for detecting the pH of heterogeneous systems such as cultivation soil and cultivation medium. When the substrate is glass, the manufacturing cost can be reduced, the titanium sheet bonded with the glass and the wrapped insulating glue can improve the shock resistance of the glass, and the mechanical strength of the glass can meet the requirement of conventional detection, such as pH test of culture mediums of laboratories, plant factories and the like; when the substrate is alumina ceramic, the sensor has better mechanical strength and environmental adaptability, and can be used for detecting the pH value of the cultivation soil and the like.

On the other hand, the pH sensor with the super-hydrophilic surface is prepared by reacting the titanium sheet with the NaOH solution, and compared with the preparation method of processing the micro-texture by magnetron sputtering in the prior art, the preparation method has the advantages of simpler process flow and obviously reduced cost; compared with the anodic oxidation method which needs precise instruments to control factors such as reaction current, electrolytic cell ion concentration, electrolytic cell temperature and the like, the method only needs to control the concentration, reaction time and reaction temperature of the NaOH solution, has low process difficulty, is beneficial to large-scale production, and further reduces the production and use cost; the sensor of the invention has safe and environment-friendly preparation and production process, lower energy consumption, no high-pollution intermediate product, and is beneficial to reducing pollution and energy consumption.

Drawings

FIG. 1 is a cross-sectional view of a super-hydrophilic pH thick film sensor structure based on a chemical etching method.

FIG. 2 is a cross-sectional view of another ultra-hydrophilic pH thick film sensor structure based on chemical etching method according to the present invention.

In the figure, 1 is a working electrode, 11 is a titanium sheet, 12 is a titanium dioxide sensitive layer, 2 is a substrate, 21 is a conductive layer, 3 is a first lead, 4 is a second lead, 5 is a reference electrode, 51 is a silver layer, 52 is a silver chloride layer, 53 is a naphthol layer, and 6 is an insulating layer.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.

In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

As shown in fig. 1, which is an embodiment of the super-hydrophilic pH thick film sensor based on the chemical etching method, the super-hydrophilic pH thick film sensor based on the chemical etching method includes a substrate 2, and a working electrode 1 and a reference electrode 5 which cover the surface of the substrate 2, the working electrode 1 includes a titanium sheet 11 attached to one side of the substrate 2, the front portion of the outer side surface of the titanium sheet 11 is covered with a titanium dioxide sensitive layer 12, and the tail portion of the titanium sheet 11 is connected with a first lead 3; a conducting layer 21 is attached to the other layer of the substrate 2, the tail part of the conducting layer 21 is connected with a second lead 4, a reference electrode 5 is positioned on the conducting layer 21, and a naphthol layer 53 is coated on the surface of the reference electrode 5; the substrate 2 is wrapped by the insulating glue 6, and only the areas of the working electrode 1 and the reference electrode 5 are reserved, so that part of the titanium dioxide sensitive layer 12 and the naphthol layer 53 are in direct contact with the outside; the first wire 3 and the second wire 4 are led out through the insulating layer.

As shown in fig. 1, the substrate 2 is a glass plate, the conductive layer 21 is made of indium tin oxide, the reference electrode 5 includes a silver layer 51 connected to the conductive layer 21, a silver chloride layer 52 covers the silver layer 51, and a naphthol layer 53 covers the silver chloride layer 52.

As shown in fig. 2, the substrate 2 is an alumina ceramic sheet, the conductive layer 21 is made of silver, the reference electrode 5 includes a silver chloride layer 52 covering the front portion of the conductive layer 21, and a naphthol layer 53 covers the silver chloride layer 52.

A preparation method of the super-hydrophilic pH thick film sensor based on the chemical corrosion method comprises the following steps:

covering a layer of protective film on one side of a clean titanium sheet 11, then inserting the titanium sheet into a sodium hydroxide solution, reacting for a period of time at 80 ℃, taking out the titanium sheet and tearing off the protective film to obtain the titanium sheet 11 with the unilateral titanium dioxide sensitive layer 12; the concentration of the sodium hydroxide solution ranges from 0.5mol/L to 4mol/L, and the reaction time ranges from 15 minutes to 180 minutes.

Covering one side of the substrate 2 with an upper conductive layer 21, and manufacturing a reference electrode 5 in the front area of the conductive layer 21;

dropping 0.5 wt% of naphthol on the surface of the reference electrode 5, and airing; repeating the steps for three times to obtain a naphthol layer 53;

bonding the titanium sheet 11 to the other side of the substrate 2, and respectively connecting the first lead 3 and the second lead 4 with the titanium sheet 11 and the tail part of the conductive layer 21; coating an insulating adhesive 6 on the periphery of the substrate 2, and reserving a part of the titanium dioxide sensitive layer 12 and a part of the naphthol layer 53 as reaction areas of the working electrode 1 and the reference electrode 5; and the first and second wires 3 and 4 are allowed to pass out of the insulating paste 6.

When the substrate 2 is a glass sheet 22 and the conducting layer 21 is made of indium tin oxide, when the reference electrode 5 is manufactured, a silver layer 51 is deposited in a designated area of the indium tin oxide layer, 1 wt% of sodium hypochlorite solution is dripped on the surface of the silver layer 51, and after the silver layer 51 is changed into light purple, the silver layer is washed by deionized water to obtain a silver chloride layer 52.

When the substrate 2 is an aluminum oxide ceramic sheet 23, silver is deposited on one side of the substrate 2 to prepare the conductive layer 21, when the reference electrode 5 is prepared, 1 wt% of sodium hypochlorite solution is dripped on the front area of the surface of the conductive layer 21, and after the area is changed into light purple, the area is washed by deionized water to obtain a silver chloride layer 52.

The working electrode of the super-hydrophilic pH thick film sensor based on the chemical corrosion method of the invention has the preparation parameters and the effects in the embodiment 1: the titanium dioxide sensitive layer 12 having a fine band-like microtexture was obtained by placing the titanium plate 11 in a 0.5mol/L sodium hydroxide solution, heating to 80 ℃ by a water bath method for 15 minutes, and the sensor produced at this time had a sensitivity of 52.59mV/pH and an average film thickness of about 130 nm.

The working electrode of the super-hydrophilic pH thick film sensor based on the chemical corrosion method of the invention is prepared with parameters and effects in example 2: the titanium plate 11 is put into 0.5mol/L sodium hydroxide solution, heated to 80 ℃ by a water bath method for 180 minutes, and the titanium dioxide sensitive layer 12 with obvious concave-convex microtexture can be obtained, wherein the sensitivity of the manufactured sensor is 50.12mV/pH, and the average film thickness is about 230 nm.

The working electrode of the super-hydrophilic pH thick film sensor based on the chemical corrosion method of the invention is prepared according to the parameters and the effects of the embodiment 3: the titanium plate 11 is put into 4mol/L sodium hydroxide solution, heated to 80 ℃ by a water bath method and kept for 15 minutes, so that the titanium dioxide sensitive layer 12 with obvious strip-shaped microtexture can be obtained, the sensitivity of the manufactured sensor is 52.43mV/pH, and the average film thickness is about 130 nm.

The working electrode of the super-hydrophilic pH thick film sensor based on the chemical corrosion method of the invention is prepared with parameters and effects in example 4: the titanium plate 11 is put into 4mol/L sodium hydroxide solution, heated to 80 ℃ by a water bath method for 180 minutes, and the titanium dioxide sensitive layer 12 with obvious net-shaped microtexture like a hill can be obtained, and the manufactured sensor has the lowest sensitivity in a test group and is 47.26mV/pH film thickness and is not tested.

The working electrode of the super-hydrophilic pH thick film sensor based on the chemical corrosion method of the invention is prepared with parameters and effects as example 5: the titanium dioxide sensitive layer 12 with the net microtexture was obtained by placing the titanium plate 11 in 1mol/L sodium hydroxide solution, heating to 80 ℃ by a water bath method for 30 minutes, and the sensor produced at this time had the highest sensitivity of the test group of 54.30mV/pH, and the average film thickness at this time was about 200 nm.

The working electrode 1 is obtained by soaking a titanium sheet 11 in 80 ℃ NaOH solution, and is integrated with a reference electrode 5 prepared on a substrate 2 into a pH thick film sensor. The super-hydrophilic pH thick film sensor has the advantages of simple structure, high detection sensitivity, good stability, capability of quickly and accurately measuring the pH value in a heterogeneous system, simple preparation process, easiness in control, low manufacturing cost, no toxic substance in the production process, safety, environmental friendliness and suitability for online detection of pH of cultivation soil, cultivation matrix and the like in agricultural production.

The above-listed detailed description is only a specific description of a possible embodiment of the present invention, and they are not intended to limit the scope of the present invention, and equivalent embodiments or modifications made without departing from the technical spirit of the present invention should be included in the scope of the present invention.