Color-changing material for early warning of residual chlorine in water body and preparation method of color-changing material

Abstract

The invention belongs to the technical field of water quality detection, and particularly relates to an off-color material for early warning residual chlorine in a water body and a preparation method of the off-color material. The color-changing material for early warning of the residual chlorine in the water body comprises an inner core and an encapsulation layer, the inner core is polyacrylamide / calcium alginate gel particles embedded with a residual chlorine color developing agent, and the encapsulation layer is calcium alginate. The color-changing material for residual chlorine early warning is placed at the water inlet front end of an electrodeionization or reverse osmosis system, when residual chlorine higher than 0.02 ppm exists in water, the polyacrylamide / calcium alginate gel particles embedded with the residual chlorine color developing agent can be changed from colorless to red, and the early warning effect on the residual chlorine in the water is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of water quality detection, and particularly relates to a discoloration material for residual chlorine warning of water bodies and a preparation method thereof. BACKGROUND

[0002] Chlorine-containing disinfectants are widely used in water disinfection processes in fields such as wastewater treatment plants, power plants, and waterworks, but residual chlorine in water bodies will also have serious adverse effects on water treatment facilities. For example, in an electrodeionization (EDI) system, residual chlorine in the influent will induce the oxidation and fragmentation of ion exchange resins packed in the EDI membrane stack, thereby causing the EDI flow channel to be blocked, the influent pressure to increase rapidly, and the water production flow to decrease. Therefore, it is of great positive significance to detect and warn residual chlorine in water treatment systems.

[0003] Currently, the ORP (Oxidation-Reduction Potential) electrode is used to detect residual chlorine in the influent of the EDI. However, the surface state of the ORP electrode has a great influence on the measurement, and there is a relatively obvious non-specific response problem. The DPD (N,N-diethyl-1,4-phenylenediamine) spectrophotometry is another important method for detecting residual chlorine in water bodies, which has high sensitivity and experimental repeatability, but it is difficult to achieve real-time monitoring.

[0004] Therefore, how to realize real-time monitoring and warning of residual chlorine in water bodies has attracted more and more widespread attention. SUMMARY

[0005] The present application aims to at least partially solve one of the technical problems in the related art. To this end, an embodiment of the present application proposes a discoloration material for residual chlorine warning of water bodies.

[0006] The discoloration material for residual chlorine warning of water bodies according to the embodiment of the present application comprises: a core and an encapsulation layer, the core is a polyacrylamide / calcium alginate gel particle embedding a residual chlorine developing agent, and the encapsulation layer is calcium alginate.

[0007] The water body residual chlorine early warning color-changing material has the following advantages and technical effects: 1. In the embodiment, the covalently cross-linked polyacrylamide network and the ionically cross-linked calcium alginate network in the gel particle core are interpenetrated to form a double network structure, the amino groups and the hydroxyl groups in the double network structure interact with each other through hydrogen bonds to embed the color developing agent, thereby effectively inhibiting the leakage of the color developing agent from the cross-linked network, and further weakening the escape of the color developing agent through the action of the external packaging layer, so that the residual chlorine early warning color-changing material has better stability; 2. Compared with the traditional DPD spectrophotometric method or residual chlorine test paper, the water body residual chlorine early warning color-changing material can be placed in the water body pipeline to realize real-time specific detection and early warning of residual chlorine; 3. The polyacrylamide / calcium alginate structure in the water body residual chlorine early warning color-changing material is rich in carboxyl functional groups, and the strong complexing ability between the carboxyl functional groups and ferric ions can effectively avoid the interference of ferric ions in the water body on the detection of residual chlorine; 4. In the embodiment, the residual chlorine early warning color-changing material is placed at the front end of the water inlet of an electrodeionization (EDI) or reverse osmosis (RO) system, and when the residual chlorine in the water body is higher than 0.02 ppm, the gel particles embedded with the color developing agent will change from colorless to red, thereby playing a warning role for the residual chlorine in the water body and having high sensitivity and accuracy.

[0008] In some embodiments, the residual chlorine color developing agent is N,N'-diethyl-1,4-phenylenediamine. And / or, the embedding amount of the residual chlorine color developing agent in the core is 1.0-2.7 wt%.

[0009] In some embodiments, the mass ratio of polyacrylamide to calcium alginate in the core is (4-25):1. And / or, the particle size of the core is 4-8 mm. And / or, the thickness of the packaging layer is 2-45 μm.

[0010] The embodiment of the present application also provides a preparation method of a water body residual chlorine early warning color-changing material, which comprises the following steps: (1) Dissolve sodium alginate and acrylamide in deionized water, and then add a residual chlorine color developing agent, a cross-linking agent and an initiator under the conditions of nitrogen protection and ice water bath to perform free radical polymerization, so as to obtain a polyacrylamide / sodium alginate gel block body embedded with the residual chlorine color developing agent, and then crush the gel block body to obtain gel particles; (2) Disperse the gel particles prepared in the step (1) in a calcium chloride solution to perform a first soaking treatment, and then perform filtration treatment and deionized water cleaning treatment to obtain polyacrylamide / calcium alginate gel particles embedded with the residual chlorine color developing agent; (3) The polyacrylamide / calcium alginate gel particles encapsulated with residual chlorine colorimetric agent obtained in step (2) are dispersed in sodium alginate solution for a second soaking treatment. After leaching off the excess sodium alginate solution on the surface, a third soaking treatment is performed with calcium chloride solution to form a calcium alginate encapsulation layer.

[0011] The advantages and technical effects of the preparation method of this invention are as follows: 1. In the preparation process of this invention, acrylamide undergoes free radical polymerization under the action of a crosslinking agent and an initiator to form a covalently crosslinked polyacrylamide first network. Sodium alginate molecules interspersed in the three-dimensional crosslinked polyacrylamide network form an ionicly crosslinked second network through coordination with calcium ions. Through the reinforcement of the double network, high-strength and high-toughness gel particles can be obtained, so that the prepared residual chlorine warning color-changing material has good mechanical strength; 2. The residual chlorine warning color-changing material prepared by the method of this invention has good comprehensive performance, the process is mature, and it is easy to promote and apply in industrial production.

[0012] In some embodiments, in step (1), the mass fraction of sodium alginate is 4-25% of the mass fraction of acrylamide, and the solid-liquid ratio of acrylamide to deionized water is 0.12-0.15 g / mL.

[0013] In some embodiments, in step (1), the residual chlorine colorimetric agent is N,N'-diethyl-1,4-phenylenediamine hydrochloride, and the mass fraction of the residual chlorine colorimetric agent is 3-5% of the mass fraction of acrylamide; And / or, in step (1), the crosslinking agent is N,N'-methylenebisacrylamide, and the mass fraction of the crosslinking agent is 0.03~0.40% of the mass fraction of acrylamide; And / or, in step (1), the initiator is an ammonium persulfate-sodium bisulfite redox system, wherein the mass fraction of ammonium persulfate is 0.1~0.3% of the mass fraction of acrylamide, and the molar ratio of sodium bisulfite to ammonium persulfate is (0.5~2):1.

[0014] In some embodiments, in step (1), the temperature of the free radical polymerization is 10~50℃ and the time of the free radical polymerization is 2~5h; And / or, in step (1), the particle size of the gel particles is 4~8 mm.

[0015] In some embodiments, in step (2), the concentration of the calcium chloride solution is 0.05~0.20 mol / L, and the first soaking treatment time is 1~3 h.

[0016] In some embodiments, in step (3), the concentration of the sodium alginate solution is 0.2~0.6 wt%, and the second soaking treatment time is 10~30 min.

[0017] In some embodiments, in step (3), the concentration of the calcium chloride solution is 0.05~0.20 mol / L, and the time for the third soaking treatment is 10~30 min. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the chemical composition of the color-changing material for water residual chlorine early warning described in this invention at different preparation stages. Detailed Implementation

[0019] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0020] The water residual chlorine warning color-changing material of the present invention includes: a core and an encapsulation layer, wherein the core is a polyacrylamide / calcium alginate (PAM / SACa) gel particle encapsulating a residual chlorine colorimetric agent, and the encapsulation layer is calcium alginate (SACa).

[0021] In the water residual chlorine early warning color-changing material of this invention, the covalently cross-linked polyacrylamide network and the ionically cross-linked calcium alginate network in the core of the gel particles interpenetrate to form a double network structure. The amino and hydroxyl groups in the double network structure interact through hydrogen bonds to encapsulate the colorimetric agent, thereby effectively inhibiting the leakage of the colorimetric agent from the cross-linked network. Furthermore, the external encapsulation layer further weakens the escape of the colorimetric agent, enabling the water residual chlorine early warning color-changing material to have better stability. In this embodiment of the invention, the water residual chlorine early warning color-changing material differs from traditional polyacrylamide and calcium alginate networks. Compared to spectrophotometry or residual chlorine test paper, this method can be placed in water pipelines for real-time, specific detection and early warning of residual chlorine. In this embodiment, the polyacrylamide / calcium alginate structure of the residual chlorine warning color-changing material is rich in carboxyl functional groups. Through its strong complexing ability with ferric ions, it can effectively avoid the interference of ferric ions in the water on residual chlorine detection. In this embodiment, when the residual chlorine warning color-changing material is placed at the inlet of an electro-deionization (EDI) or reverse osmosis (RO) system, when the residual chlorine in the water is higher than 0.02 ppm, the gel particles containing the colorimetric agent will change from colorless to red, providing an early warning of residual chlorine in the water with high sensitivity and accuracy.

[0022] In some embodiments, preferably, the residual chlorine colorimetric agent is N,N'-diethyl-1,4-phenylenediamine; And / or, the amount of residual chlorine colorimetric agent embedded in the core is 1.0 ~ 2.7 wt%.

[0023] In this embodiment of the invention, the optimal amount of residual chlorine colorimetric reagent encapsulation is selected to achieve high sensitivity for early warning of residual chlorine in water. If the amount of residual chlorine colorimetric reagent encapsulation is too low, the concentration of the colorimetric substance generated by the reaction with residual chlorine will be too low, reducing the detection sensitivity; if the amount of residual chlorine colorimetric reagent encapsulation is too high, it will result in waste of colorimetric reagent and increased cost.

[0024] In some embodiments, preferably, the mass ratio of polyacrylamide to calcium alginate in the core is (4~25):1.

[0025] In this embodiment of the invention, the dual-network structure formed by polyacrylamide and calcium alginate ensures the encapsulation of residual chlorine colorimetric agent and the strength of the color-changing material. If the amount of polyacrylamide is high, the mechanical properties (toughness and stiffness) of the gel particles are poor; if the amount of polyacrylamide is low, the gel particles are brittle and prone to breakage.

[0026] In some embodiments, preferably, the kernel has a particle size of 4-8 mm; And / or, the thickness of the encapsulation layer is 2~45 μm.

[0027] In this embodiment of the invention, the thickness of the encapsulation layer is optimized. This not only effectively suppresses the escape of residual chlorine colorimetric reagent but also ensures that the internal colorimetric reagent has sufficient contact with the residual chlorine in the water, guaranteeing the sensitivity of the early warning. If the thickness of the encapsulation layer is too thin, it will not effectively suppress the leakage of the colorimetric reagent; if the thickness of the encapsulation layer is too thick, it will hinder the mass transfer and diffusion of residual chlorine molecules, resulting in a prolonged response time and making it difficult to meet the needs of real-time detection.

[0028] This invention also provides a method for preparing a color-changing material for water residual chlorine early warning, comprising the following steps: (1) Sodium alginate (SA) and acrylamide (AM) were dissolved in deionized water. After nitrogen deoxygenation, residual chlorine colorimetric agent, crosslinking agent and initiator were added in sequence under the conditions of ice water bath and nitrogen protection to carry out free radical polymerization to obtain polyacrylamide / sodium alginate gel (PAM / SA) block embedded with residual chlorine colorimetric agent. After crushing, gel particles were obtained. (2) The gel particles obtained in step (1) are dispersed in calcium chloride solution for a first soaking treatment, and then filtered and deionized to obtain polyacrylamide / calcium alginate (PAM / SACa) gel particles with residual chlorine colorimetric agent. (3) The polyacrylamide / calcium alginate (PAM / SACa) gel particles encapsulated with residual chlorine colorimetric agent obtained in step (2) are dispersed in sodium alginate (SA) solution for a second soaking treatment. After leaching off the excess sodium alginate (SA) solution on the surface, a third soaking treatment is performed with calcium chloride solution to form a calcium alginate encapsulation layer.

[0029] In the preparation method of this invention, acrylamide undergoes free radical polymerization under the action of a crosslinking agent and an initiator to form a covalently crosslinked polyacrylamide first network. Sodium alginate molecules interspersed in the three-dimensional crosslinked polyacrylamide network form an ionicly crosslinked second network through coordination with calcium ions. The reinforcement of the two networks can obtain high-strength and high-toughness gel particles, giving the prepared residual chlorine warning color-changing material good mechanical strength. The method of this invention produces a residual chlorine warning color-changing material with good comprehensive performance, and the process is mature and easy to promote and apply in industrial production.

[0030] In some embodiments, preferably, in step (1), the mass fraction of sodium alginate (SA) is 4-25% of the mass fraction of acrylamide (AM), and the solid-liquid ratio of acrylamide (AM) to deionized water is 0.12-0.15 g / mL.

[0031] In some embodiments, preferably, in step (1), the residual chlorine colorimetric agent is N,N'-diethyl-1,4-phenylenediamine (DPD) hydrochloride, and the mass fraction of the residual chlorine colorimetric agent is 3-5% of the mass fraction of acrylamide (AM); And / or, in step (1), the crosslinking agent is N,N'-methylenebisacrylamide (MBA), and the mass fraction of the crosslinking agent is 0.03~0.40% of the mass fraction of acrylamide (AM); And / or, in step (1), the initiator is an ammonium persulfate (APS)-sodium bisulfite (SBS) redox system, wherein the mass fraction of ammonium persulfate (APS) is 0.1~0.3% of the mass fraction of acrylamide (AM), and the molar ratio of sodium bisulfite (SBS) to ammonium persulfate (APS) is (0.5~2):1.

[0032] In some embodiments, preferably, in step (1), the temperature of the free radical polymerization is 10~50℃ and the time of the free radical polymerization is 2~5h.

[0033] In this embodiment of the invention, the free radical polymerization conditions are preferred, under which acrylamide can form a relatively complete network structure at a suitable reaction rate. If the reaction temperature is too low or the reaction time is too short, it is difficult to form an effective polyacrylamide covalent crosslinking network, resulting in poor mechanical strength of the PAM / SACa@DPD gel particles. If the reaction temperature is too high or the reaction time is too long, it will increase energy and time costs, and excessively high reaction temperatures will cause explosive polymerization, resulting in poor uniformity of the internal network of PAM / SACa@DPD gel particles and reduced mechanical strength.

[0034] In some embodiments, preferably, in step (1), the particle size of the gel particles is 4~8 mm.

[0035] In some embodiments, preferably, in step (2), the concentration of the calcium chloride solution is 0.05~0.20 mol / L, and the first soaking treatment time is 1~3 h.

[0036] In some embodiments, preferably, in step (3), the concentration of the sodium alginate (SA) solution is 0.2~0.6 wt%, and the time for the second soaking treatment is 10~30 min.

[0037] In some embodiments, preferably, in step (3), the concentration of the calcium chloride solution is 0.05~0.20 mol / L, and the time for the third soaking treatment is 10~30 min.

[0038] The technical solution of the present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0039] Example 1 (1) In a three-necked flask, 0.5686 g of sodium alginate (SA, 4.00 wt% of AM) and 14.2160 g of acrylamide (AM) were dissolved in 95 mL of deionized water and nitrogen was passed through for 15 min to remove oxygen. The three-necked flask containing the sodium alginate and acrylamide solution was placed in an ice-water bath. Under the conditions of ice-water bath and nitrogen protection, 0.7108 g of N,N'-diethyl-1,4-phenylenediamine (DPD) hydrochloride colorimetric reagent (5.00 wt% of AM), 4.26 mg of N,N'-methylenebisacrylamide (MBA, 0.03 wt% of AM), 42.65 mg of ammonium persulfate (APS, 0.30 wt% of AM) and 17.77 mg of sodium bisulfite (SBS, with a molar ratio of SBS to APS of 1:2) were added and mixed thoroughly. Then, the mixed solution was placed in a 10°C water bath to initiate the polymerization and chemical cross-linking of acrylamide monomers. After 5 h, polyacrylamide / sodium alginate (PAM / SA) gel blocks embedded with DPD were obtained. The DPD-embedded PAM / SA gel blocks were broken into gel particles with a particle size of approximately 8 mm to obtain DPD-embedded polyacrylamide / sodium alginate (PAM / SA@DPD) gel particles.

[0040] (2) PAM / SA@DPD gel particles were dispersed in 0.05 mol / L calcium chloride solution and soaked for 1 h to achieve cross-linking between calcium ions and sodium alginate (SA) in PAM / SA gel particles, thus obtaining polyacrylamide / calcium alginate (PAM / SACa@DPD) gel particles with DPD encapsulation; then, PAM / SACa@DPD gel particles were filtered using a nylon filter with a pore size of 0.4 mm and washed with deionized water 3 to 5 times to remove unreacted components.

[0041] (3) Disperse PAM / SACa@DPD gel particles in 0.2 wt% sodium alginate solution, soak for 10 min, filter and drain excess solution from the surface of gel particles to obtain gel particles with sodium alginate solution coated on the surface; then, soak the gel particles with sodium alginate solution coated on the surface in 0.05 mol / L calcium chloride solution for 10 min to form a calcium alginate encapsulation layer on the surface of PAM / SACa@DPD gel particles; finally, wash the calcium alginate encapsulated PAM / SACa@DPD gel particles with deionized water to obtain the color-changing material for water residual chlorine warning.

[0042] The chemical composition of color-changing materials used for residual chlorine warning in water at different stages of preparation, such as... Figure 1 As shown.

[0043] The water residual chlorine warning color-changing material prepared in this embodiment of the invention has a core particle size of 8 mm and an encapsulation layer thickness of 2 μm; the amount of residual chlorine colorimetric agent embedded in the core is 1.02 wt%, and the mass ratio of polyacrylamide to calcium alginate is 25:1.

[0044] Example 2 (1) In a three-necked flask, 1.7770 g of sodium alginate (SA, 12.50 wt% of AM) and 14.2160 g of acrylamide (AM) were dissolved in 100 mL of deionized water and nitrogen was passed through for 15 min to remove oxygen. The three-necked flask containing the sodium alginate and acrylamide solution was placed in an ice-water bath. Under the conditions of ice-water bath and nitrogen protection, 0.6000 g of N,N'-diethyl-1,4-phenylenediamine (DPD) hydrochloride colorimetric reagent (4.22 wt% of AM), 14.22 mg of N,N'-methylenebisacrylamide (MBA, 0.10 wt% of AM), 28.43 mg of ammonium persulfate (APS, 0.20 wt% of AM) and 23.69 mg of sodium bisulfite (SBS, with a molar ratio of SBS to APS of 1:1) were added and mixed thoroughly. Then, the mixed solution was placed in a 30°C water bath to initiate the polymerization and chemical cross-linking of acrylamide monomers. After 3 hours, polyacrylamide / sodium alginate (PAM / SA) gel blocks embedded with DPD were obtained. The DPD-embedded PAM / SA gel blocks were broken into gel particles with a particle size of approximately 6 mm to obtain DPD-embedded polyacrylamide / sodium alginate (PAM / SA@DPD) gel particles.

[0045] (2) PAM / SA@DPD gel particles were dispersed in 0.1 mol / L calcium chloride solution and soaked for 2 h to achieve cross-linking between calcium ions and sodium alginate (SA) in PAM / SA gel particles, thus obtaining polyacrylamide / calcium alginate (PAM / SACa@DPD) gel particles with DPD encapsulation; then, PAM / SACa@DPD gel particles were filtered using a nylon filter with a pore size of 0.4 mm and washed with deionized water 3 to 5 times to remove unreacted components.

[0046] (3) The calcium ion crosslinked PAM / SACa@DPD gel particles are dispersed in a 0.5 wt% sodium alginate solution and soaked for 15 min. The solution is filtered and excess solution is drained off the surface of the gel particles to obtain gel particles coated with sodium alginate solution. Then, the gel particles coated with sodium alginate solution are soaked in a 0.1 mol / L calcium chloride solution for 20 min to form a calcium alginate encapsulation layer on the surface of the PAM / SACa@DPD gel particles. Finally, the calcium alginate encapsulated PAM / SACa@DPD gel particles are washed with deionized water to obtain the color-changing material for water residual chlorine warning.

[0047] The water residual chlorine warning color-changing material prepared in this embodiment of the invention has a core particle size of 6 mm and an encapsulation layer thickness of 11 μm; the amount of residual chlorine colorimetric agent embedded in the core is 2.71 wt%, and the mass ratio of polyacrylamide to calcium alginate is 8:1.

[0048] Example 3 (1) In a three-necked flask, 3.5540 g of sodium alginate (SA, 25.00 wt% of AM) and 14.2160 g of acrylamide (AM) were dissolved in 118 mL of deionized water and nitrogen was passed through for 15 min to remove oxygen. The three-necked flask containing the sodium alginate and acrylamide solution was placed in an ice-water bath. Under the conditions of ice-water bath and nitrogen protection, 0.4265 g of N,N'-diethyl-1,4-phenylenediamine (DPD) hydrochloride colorimetric reagent (3.00 wt% of AM), 56.86 mg of N,N'-methylenebisacrylamide (MBA, 0.40 wt% of AM), 14.22 mg of ammonium persulfate (APS, 0.10 wt% of AM) and 23.69 mg of sodium bisulfite (SBS, with a molar ratio of SBS to APS of 2:1) were added and mixed thoroughly. Then, the mixed solution was placed in a 50°C water bath to initiate the polymerization and chemical crosslinking of acrylamide monomers. After 2 hours, polyacrylamide / sodium alginate (PAM / SA) gel blocks embedded with DPD were obtained. The DPD-embedded PAM / SA gel blocks were broken into gel particles with a particle size of approximately 4 mm to obtain DPD-embedded polyacrylamide / sodium alginate (PAM / SA@DPD) gel particles.

[0049] (2) PAM / SA@DPD gel particles were dispersed in 0.2 mol / L calcium chloride solution and soaked for 3 h to achieve cross-linking between calcium ions and sodium alginate (SA) in PAM / SA gel particles, thus obtaining polyacrylamide / calcium alginate (PAM / SACa@DPD) gel particles with DPD encapsulation; then, PAM / SACa@DPD gel particles were filtered using a nylon filter with a pore size of 0.4 mm and washed with deionized water 3 to 5 times to remove unreacted components.

[0050] (3) The PAM / SACa@DPD gel particles after calcium ion crosslinking are dispersed in a 0.6 wt% sodium alginate solution and soaked for 30 min. The solution is filtered and excess solution is drained off the surface of the gel particles to obtain gel particles with sodium alginate solution coated on the surface. Then, the gel particles with sodium alginate solution coated on the surface are soaked in a 0.2 mol / L calcium chloride solution for 30 min to form a calcium alginate encapsulation layer on the surface of the PAM / SACa@DPD gel particles. Finally, the calcium alginate encapsulated PAM / SACa@DPD gel particles are washed with deionized water to obtain the color-changing material for water residual chlorine warning.

[0051] The water residual chlorine warning color-changing material prepared in this embodiment of the invention has a core particle size of 4 mm and an encapsulation layer thickness of 45 μm; the amount of residual chlorine colorimetric agent embedded in the core is 1.84 wt%, and the mass ratio of polyacrylamide to calcium alginate is 4:1.

[0052] Comparative Example 1 The preparation method of this comparative example is the same as that of Example 2, except that step (3) is deleted, that is, only polyacrylamide / calcium alginate (PAM / SACa@DPD) gel particles encapsulating DPD are obtained, and no calcium alginate encapsulation layer is formed on its surface.

[0053] Comparative Example 2 The preparation method of this comparative example is the same as that of Example 2, except that sodium alginate is not added in step (1), that is, polyacrylamide gel particles encapsulated with DPD are prepared only by covalently cross-linked polyacrylamide.

[0054] The water residual chlorine warning color-changing materials prepared in Examples 1-3 and Comparative Examples 1-2 were tested for their compressibility using a universal testing machine. The compressive strain was set to 90%, and the compression rate was set to 1 mm / s. Furthermore, the effectiveness of the water residual chlorine warning color-changing materials of the present invention was evaluated using the following methods: (1) Preparation of a 0.02 ppm residual chlorine solution: A commercially available residual chlorine standard solution was diluted with deionized water to a residual chlorine solution of 0.02 ppm; (2) Detection of residual chlorine: The water residual chlorine warning color-changing material was placed in the residual chlorine solution, and its color change was recorded after 6 min. The results are shown in Table 1.

[0055] Table 1

[0056] *Note: "++" indicates a significant color change; "+" indicates a weaker color change; "-" indicates a subtle color change.

[0057] As shown in Table 1, the compressive strengths of the color-changing materials for water residual chlorine early warning prepared in Examples 1-3 were 0.765 MPa, 4.182 MPa, and 6.376 MPa, respectively, indicating that the chemical composition and preparation temperature of the gel particles have a significant impact on the mechanical properties. When the amount of crosslinking agent N,N'-methylenebisacrylamide (MBA) and sodium alginate (SA) component is small, and the reaction temperature is low (Example 1), the polymerization rate of acrylamide monomer (AM) is slow, the crosslinking density of the formed polyacrylamide covalent crosslinking network is small, and the contribution of the calcium alginate rigid network to the overall mechanical strength is also low. Therefore, the obtained PAM / SACa@DPD gel particles are relatively soft and have low compressive strength. When the amount of crosslinking agent N,N'-methylenebisacrylamide (MBA), sodium alginate (SA) component, and reaction temperature are too high (Example 3), the polymerization rate of acrylamide monomer (AM) is faster and side reactions are more likely to occur. The resulting polyacrylamide covalent crosslinked network has a high crosslinking density, and the excessively high proportion of calcium alginate rigid network leads to increased brittleness of PAM / SACa@DPD gel particles. Therefore, they are prone to breakage after being subjected to external compression. This invention evaluates the elastic recovery under relatively harsh compression conditions (compression strain of 90%), but in actual use, the color-changing material prepared in Example 3 can recover when the compression ratio is not too high, and can still meet the usage requirements. When only the polyacrylamide covalent crosslinked network exists (Comparative Example 2), the compressive strength of the gel particles decreases significantly, indicating that the presence of calcium alginate ionic crosslinked network plays an important role in the mechanical strength of the gel particles.

[0058] Furthermore, compared to Example 2, Examples 1 and 3 showed weakened detection performance for 0.02 ppm residual chlorine solution. The reduced sensitivity in Example 1 may be related to insufficient gel network formation under reaction conditions and a relatively lower effective DPD encapsulation amount. The reduced sensitivity in Example 3 may be related to the excessively thick encapsulation layer inhibiting the diffusion rate of residual chlorine molecules to some extent. In Comparative Example 1, the removal of the calcium alginate encapsulation layer also reduced its detection sensitivity for 0.02 ppm residual chlorine solution, which is related to the escape of the DPD chromogenic agent under unencapsulated conditions. In Comparative Example 2, the absence of a calcium alginate ion crosslinking network resulted in ineffective detection of 0.02 ppm residual chlorine solution, stemming from the significant swelling of the simple polyacrylamide gel and the excessively low effective encapsulation amount of the DPD chromogenic agent.

[0059] In summary, the calcium alginate-encapsulated PAM / SACa@DPD gel particles obtained in Example 2 have relatively ideal mechanical properties and are more suitable as a color-changing material for water residual chlorine warning in water treatment equipment inlet pipes.

[0060] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0061] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A color-changing material for early warning of residual chlorine in water, characterized in that, include: The core is a polyacrylamide / calcium alginate gel particle encapsulating residual chlorine colorimetric agent, and the encapsulation layer is calcium alginate.

2. The color-changing material for water residual chlorine early warning according to claim 1, characterized in that, The residual chlorine colorimetric reagent is N,N'-diethyl-1,4-phenylenediamine; And / or, the amount of residual chlorine colorimetric agent embedded in the core is 1.0~2.7 wt%.

3. The color-changing material for water residual chlorine early warning according to claim 1 or 2, characterized in that, The mass ratio of polyacrylamide to calcium alginate in the core is (4~25):1; And / or, the particle size of the kernel is 4~8mm; And / or, the thickness of the encapsulation layer is 2~45 μm.

4. The method for preparing the color-changing material for water residual chlorine early warning according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Sodium alginate and acrylamide were dissolved in deionized water, and after nitrogen deoxygenation, residual chlorine colorimetric agent, crosslinking agent and initiator were added in sequence under the conditions of ice water bath and nitrogen protection to carry out free radical polymerization to obtain polyacrylamide / sodium alginate gel block embedded with residual chlorine colorimetric agent, and then the gel particles were obtained after crushing. (2) The gel particles obtained in step (1) are dispersed in calcium chloride solution for a first soaking treatment, and then filtered and deionized to obtain polyacrylamide / calcium alginate gel particles with residual chlorine colorimetric agent. (3) The polyacrylamide / calcium alginate gel particles encapsulated with residual chlorine colorimetric agent obtained in step (2) are dispersed in sodium alginate solution for a second soaking treatment. After leaching off the excess sodium alginate solution on the surface, a third soaking treatment is performed with calcium chloride solution to form a calcium alginate encapsulation layer.

5. The method for preparing the color-changing material for water residual chlorine early warning according to claim 4, characterized in that, In step (1), the mass fraction of sodium alginate is 4-25% of the mass fraction of acrylamide, and the solid-liquid ratio of acrylamide to deionized water is 0.12-0.15 g / mL.

6. The method for preparing the color-changing material for water residual chlorine early warning according to claim 4, characterized in that, In step (1), the residual chlorine colorimetric agent is N,N'-diethyl-1,4-phenylenediamine hydrochloride, and the mass fraction of the residual chlorine colorimetric agent is 3-5% of the mass fraction of acrylamide; And / or, in step (1), the crosslinking agent is N,N'-methylenebisacrylamide, and the mass fraction of the crosslinking agent is 0.03~0.40% of the mass fraction of acrylamide; And / or, in step (1), the initiator is an ammonium persulfate-sodium bisulfite redox system, wherein the mass fraction of ammonium persulfate is 0.1~0.3% of the mass fraction of acrylamide, and the molar ratio of sodium bisulfite to ammonium persulfate is (0.5~2):

1.

7. The method for preparing the color-changing material for water residual chlorine early warning according to claim 4, characterized in that, In step (1), the temperature of the free radical polymerization is 10~50℃, and the time of the free radical polymerization is 2~5h; And / or, in step (1), the particle size of the gel particles is 4~8 mm.

8. The method for preparing the color-changing material for water residual chlorine early warning according to claim 4, characterized in that, In step (2), the concentration of the calcium chloride solution is 0.05~0.20 mol / L, and the first soaking treatment time is 1~3 h.

9. The method for preparing the color-changing material for water residual chlorine early warning according to claim 4, characterized in that, In step (3), the concentration of the sodium alginate solution is 0.2~0.6 wt%, and the second soaking treatment time is 10~30 min.

10. The method for preparing the color-changing material for water residual chlorine early warning according to claim 4 or 9, characterized in that, In step (3), the concentration of the calcium chloride solution is 0.05~0.20 mol / L, and the time for the third soaking treatment is 10~30 min.

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