Allochroic silica gel drying agent, preparation method thereof and allochroic silica gel

Abstract

The invention belongs to the technical field of allochroic silicagel, and provides an allochroic silicagel drying agent, a preparation method thereof and allochroic silicagel. The preparation method comprises the following steps: performing microwave radiation treatment on silica gel particles; after microwave radiation treatment is finished, the silica gel particles are soaked in an ethanol solution containing metal salt for ultrasonic oscillation; carrying out heat treatment on the silica gel particles in a protective atmosphere; after the heat treatment is finished, dipping the silica gel particles in an aqueous solution of an organic ligand for reaction to obtain a reaction product; mixing the reaction product with the natural plant fiber dispersion liquid, and carrying out spray drying molding to obtain a drying agent crude product; and loading the photocatalytic material on the inner wall of the drying agent crude product by using a sol-gel method to obtain the allochroic silicagel drying agent. The indicator is formed through in-situ complexation of the metal salt and the organic ligand, a traditional cobalt chloride system is replaced, the toxicity problem is solved, and remarkable technical advantages and wide market prospects are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of discoloring silica gel, and in particular to a discoloring silica gel desiccant, a preparation method thereof, and a discoloring silica gel. Background Art

[0002] In current industrial production and daily life, desiccants play a crucial role, especially in fields that require a dry environment, such as the industries of precision instruments, electronic devices, pharmaceuticals, foods, and leather. As a desiccant with a unique indicating function, the discoloring silica gel desiccant can not only adsorb moisture but also intuitively reflect the change of environmental humidity through color change, thus attracting much attention.

[0003] The discoloring silica gel desiccant is an indicator adsorbent made from high-activity adsorbent material, fine-pore silica gel, through deep processing, and belongs to high-grade adsorption desiccants. Its main component is silicon dioxide. The commonly used production method at home and abroad is to combine cobalt chloride on the surface of the internal pores of silica gel through certain technological steps, and utilize the characteristic that the number of crystal water of cobalt chloride changes with the moisture absorption amount to make the silica gel show different colors, so as to realize the indication of environmental humidity. For example, it is blue before moisture absorption and gradually turns into light red as the moisture absorption amount increases.

[0004] However, traditional discoloring silica gel desiccants have some obvious disadvantages. On the one hand, cobalt chloride commonly used in the manufacture of discoloring silica gel has been listed as a carcinogenic substance polluting the environment by Western countries. On the other hand, there are many problems in the production process of the existing technology. For example, in the production of some cobalt-containing discoloring silica gels, the control is not strict, and backward technologies are adopted, resulting in a high cobalt content, toxicity, and potential safety hazards. Moreover, in order to achieve stable and uniform colors for common discoloring silica gels, excessive dyes and simple devices are often used for dipping. After dipping, the dipping solution is not completely filtered dry, resulting in non-uniform color appearance of the product and after moisture absorption, making it difficult to achieve large-scale production. In addition, the existing disclosed one-step dipping production process of cobalt-free dyeing solution has the problem of non-recycling of the dyeing solution, which will cause environmental protection problems in wastewater treatment; there is also a process using bromide salts and cobalt salts as dyeing agents, in which the cobalt salt concentration in the dyeing solution is relatively high, and the cobalt content of the prepared cobalt-containing discoloring silica gel is high, with great safety risks.

[0005] Therefore, it is of great practical significance and broad market prospects to develop a preparation method of a discoloring silica gel desiccant that is environmentally friendly, safe, green and efficient in the production process, and has stable and uniform colors, and use it to prepare discoloring silica gels with excellent performance. Summary of the Invention

[0006] In view of this, the present invention provides a discoloring silica gel desiccant, a preparation method thereof, and a discoloring silica gel, aiming to solve technical problems such as the relatively high toxicity of the cobalt chloride system used in the preparation of traditional discoloring silica gel desiccants.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for preparing a color-changing silica gel desiccant, comprising the following steps:

[0009] S1. Subject the silica gel particles to microwave radiation treatment;

[0010] S2. After the microwave radiation treatment, immerse the silica gel particles in an ethanol solution containing a metal salt and perform ultrasonic oscillation;

[0011] S3. Subject the silica gel particles to heat treatment in a protective atmosphere;

[0012] S4. After the heat treatment, immerse the silica gel particles in an aqueous solution of an organic ligand and react to obtain a reaction product;

[0013] S5. Mix the reaction product and a natural plant fiber dispersion liquid, and spray-dry and form to obtain a crude desiccant;

[0014] S6. Use the sol-gel method to load the photocatalytic material on the inner wall of the crude desiccant to obtain the color-changing silica gel desiccant.

[0015] Further, in the step S1, the frequency of the microwave radiation treatment is 300 MHz to 3 GHz, and the time of the microwave radiation treatment is 5 to 30 min.

[0016] Further, in the step S2, the metal salt includes one or more of ferric chloride, copper sulfate, and cobalt nitrate; the mass concentration of the ethanol solution containing the metal salt is 1 to 20%; the time of the ultrasonic oscillation is 10 to 60 min.

[0017] Further, in the step S3, the protective atmosphere includes nitrogen, argon, helium, or neon; the temperature of the heat treatment is 150 to 300 °C, and the time of the heat treatment is 30 to 120 min.

[0018] Further, in the step S4, the organic ligand includes one or more of o-phenanthroline, 8-hydroxyquinoline, and carboxylic acid compounds; the mass concentration of the aqueous solution of the organic ligand is 0.01 to 0.5%.

[0019] Further, in the step S4, the temperature of the reaction is 40 to 80 °C, and the time of the reaction is 1 to 5 h.

[0020] Further, in the step S5, the natural plant fiber includes bamboo fiber, coconut shell fiber, or wood pulp fiber; the mass of the natural plant fiber is 1 to 10% of the mass of the reaction product; the particle size of the crude desiccant is 1 to 5 mm.

[0021] Furthermore, in step S6, the photocatalytic material includes nano titanium dioxide or zinc oxide; the mass of the photocatalytic material is 0.1-1% of the mass of the coarse desiccant.

[0022] The invention provides a color-changing silica gel desiccant prepared by the preparation method of the color-changing silica gel desiccant.

[0023] The present invention also provides a color-changing silica gel, which is prepared according to the preparation method of the color-changing silica gel desiccant mentioned above;

[0024] The color of the color-changing silica gel is blue when it is not damp, and is pink when it is damp.

[0025] It can be seen from the above technical solution that compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] The present invention effectively activates the surface of silica gel particles through microwave radiation treatment, significantly enhancing their adsorption performance. Microwave radiation can uniformly heat silica gel particles in a short time, break the stability of their surface structure, increase surface active sites, and thus improve moisture absorption efficiency. The present invention forms an indicator through in-situ complexation of metal salts and organic ligands, replacing the traditional cobalt chloride system, and solving the toxicity problem.

[0027] The present invention also introduces natural plant fibers, which not only improve the mechanical strength of the desiccant, but also enhance its environmental performance. The degradability of natural plant fibers reduces environmental pollution and conforms to the development trend of green environmental protection. In addition, the photocatalytic material loads and utilizes nano titanium dioxide or zinc oxide, which further improves the environmental protection and regeneration performance of the desiccant. The photocatalytic material can decompose organic pollutants and reduce the secondary pollution that may be generated by the desiccant during use. By loading the photocatalytic material, the color-changing silica gel desiccant can be regenerated by light after being saturated with moisture absorption to restore its moisture absorption performance. This feature greatly extends the service life of the desiccant, reduces the cost of use, and reduces the environmental burden of the discarded desiccant.

[0028] In summary, the present invention successfully prepares a silica gel desiccant with high moisture absorption and obvious color change effect through a series of refined process steps, solves many deficiencies in the prior art, and has significant technical progress and practical value. Its positive effects in improving moisture absorption efficiency, enhancing color change effect, improving environmental protection performance, and extending service life make the present invention have important application value and market prospects in the field of silica gel desiccant. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a comparison chart of the color reversible change retention rate of the color-changing silica gel prepared by the method of Examples 1 to 3 after 20 cycles of moisture absorption-desorption. DETAILED DESCRIPTION

[0030] The present invention provides a preparation method of a color-changing silica gel desiccant, comprising the following steps:

[0031] S1. Subject the silica gel particles to microwave radiation treatment;

[0032] S2. After the microwave radiation treatment ends, immerse the silica gel particles in an ethanol solution containing a metal salt and perform ultrasonic oscillation;

[0033] S3. Subject the silica gel particles to heat treatment in a protective atmosphere;

[0034] S4. After the heat treatment ends, immerse the silica gel particles in an aqueous solution of an organic ligand to carry out a reaction to obtain a reaction product;

[0035] S5. Mix the reaction product and a natural plant fiber dispersion liquid, and obtain a crude desiccant through spray drying and forming;

[0036] S6. Load a photocatalytic material onto the inner wall of the crude desiccant by using a sol-gel method to obtain the color-changing silica gel desiccant.

[0037] In the present invention, in the step S1, the frequency of the microwave radiation treatment is 300 MHz to 3 GHz, and the time of the microwave radiation treatment is 5 to 30 min.

[0038] In the present invention, in the step S2, the metal salt includes one or more of ferric chloride, copper sulfate and cobalt nitrate; the mass concentration of the ethanol solution containing the metal salt is 1 to 20%, preferably 5 to 15%, and more preferably 10%; the time of the ultrasonic oscillation is 10 to 60 min, preferably 20 to 40 min, and more preferably 30 min.

[0039] In the present invention, in the step S3, the protective atmosphere includes nitrogen, argon, helium or neon; the heat treatment temperature is 150 to 300 °C, preferably 180 to 260 °C, and more preferably 200 to 220 °C; the heat treatment time is 30 to 120 min, preferably 50 to 100 min, and more preferably 60 to 80 min.

[0040] In the present invention, in the step S4, the organic ligand includes one or more of o-phenanthroline, 8-hydroxyquinoline and carboxylic acid compounds, and the carboxylic acid compounds are preferably one or more of salicylic acid, citric acid, glycine and glutamic acid; the mass concentration of the aqueous solution of the organic ligand is 0.01 to 0.5%, preferably 0.05 to 0.4%, and more preferably 0.1 to 0.3%.

[0041] In the present invention, in step S4, the reaction temperature is 40 to 80 °C, preferably 50 to 70 °C, and more preferably 60 °C; the reaction time is 1 to 5 h, preferably 2 to 4 h, and more preferably 3 h.

[0042] In the present invention, in step S5, the natural plant fiber includes bamboo fiber, coconut shell fiber or wood pulp fiber; the mass of the natural plant fiber is 1 to 10% of the mass of the reaction product, preferably 2 to 8%, and more preferably 4 to 6%; the length of the natural plant fiber is preferably 0.1 to 2 mm, and more preferably 0.5 to 1 mm; the diameter of the natural plant fiber is preferably 10 to 50 μm, and more preferably 20 to 40 μm; the particle size of the crude desiccant is 1 to 5 mm, preferably 2 to 4 mm.

[0043] In the present invention, in step S6, the photocatalytic material includes nano-titanium dioxide or zinc oxide, the particle size of the photocatalytic material is preferably 10 to 100 nm, and more preferably 30 to 80 nm; the mass of the photocatalytic material is 0.1 to 1% of the mass of the crude desiccant, preferably 0.2 to 0.8%, and more preferably 0.4 to 0.6%.

[0044] The present invention provides a discolorable silica gel desiccant prepared by the above preparation method of the discolorable silica gel desiccant.

[0045] The present invention also provides a discolorable silica gel, which is prepared according to the above preparation method of the discolorable silica gel desiccant;

[0046] The color of the discolorable silica gel is blue when not damp, and pink after being damp.

[0047] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0048] Example 1

[0049] Take 500 g of commercially available silica gel particles and spread them flat in a microwave - specific container. Set the microwave frequency to 2.45 GHz and perform radiation treatment for 15 min. Prepare a copper sulfate ethanol solution with a mass concentration of 10%. Immerse the silica gel after microwave treatment in the copper sulfate ethanol solution and place it in an ultrasonic cleaner (frequency 40 kHz) and oscillate for 30 min to allow metal ions to fully enter the pores of the silica gel. Transfer the silica gel to a tube furnace, introduce nitrogen, heat it to 200 °C at a rate of 5 °C / min and hold for 60 min. The heat treatment decomposes the metal salt into copper oxide, which combines with the silica gel framework to form a stable structure. Prepare a 0.3% aqueous solution of o - phenanthroline and heat it to 60 °C. Immerse the heat - treated silica gel in the o - phenanthroline aqueous solution and react for 3 h, and adjust the solution pH to 6.5. Take bamboo fiber and mix it with the reaction product at a ratio of 5% (25 g), add deionized water to make a dispersion with a solid content of 20%. Use a centrifugal spray dryer (inlet temperature 180 °C, outlet temperature 90 °C), control the particle size to be 1 - 5 mm, and obtain a porous crude product after drying. Prepare a nano - TiO2 sol by mixing tetrabutyl titanate, ethanol, and nitric acid in a molar ratio of 1:10:0.3, and age for 24 h to form a stable sol. Immerse the crude desiccant in the sol for 10 min, dry it at 150 °C and then calcine it at 500 °C for 1 h. The TiO2 loading is 0.5%, forming a uniform photocatalytic layer, and thus obtaining the color - changing silica gel desiccant.

[0050] Example 2

[0051] Take 500 g of commercially available silica gel particles and spread them flat in a microwave - specific container. Set the microwave frequency to 1 GHz and perform radiation treatment for 20 min. Prepare a ferric chloride ethanol solution with a mass concentration of 5%. Immerse the silica gel after microwave treatment in the ferric chloride ethanol solution and place it in an ultrasonic cleaner (frequency 40 kHz) and oscillate for 40 min to allow metal ions to fully enter the pores of the silica gel. Transfer the silica gel to a tube furnace, introduce nitrogen, heat it to 250 °C at a rate of 5 °C / min and hold for 50 min. Prepare a 0.1% aqueous solution of 8 - hydroxyquinoline and heat it to 50 °C. Immerse the heat - treated silica gel in the 8 - hydroxyquinoline aqueous solution and react for 4 h. Take coconut shell fiber and mix it with the reaction product at a ratio of 5% (25 g), add deionized water to make a dispersion with a solid content of 20%. Use a centrifugal spray dryer (inlet temperature 180 °C, outlet temperature 90 °C), control the particle size to be 1 - 5 mm, and obtain a porous crude product after drying. Prepare a nano - TiO2 sol by mixing tetrabutyl titanate, ethanol, and nitric acid in a molar ratio of 1:10:0.3, and age for 24 h to form a stable sol. Immerse the crude desiccant in the sol for 10 min, dry it at 150 °C and then calcine it at 500 °C for 1 h. The TiO2 loading is 0.4%, forming a uniform photocatalytic layer, and thus obtaining the color - changing silica gel desiccant.

[0052] Example 3

[0053] Take 500 g of commercially available silica gel particles and spread them flat in a microwave - specific container. Set the microwave frequency to 1.5 GHz and perform radiation treatment for 25 min. Prepare a cobalt nitrate ethanol solution with a mass concentration of 15%. Immerse the silica gel after microwave treatment in the cobalt nitrate ethanol solution, place it in an ultrasonic cleaner (frequency 40 kHz) and oscillate for 40 min to allow metal ions to fully enter the pores of the silica gel. Transfer the silica gel to a tube furnace, introduce nitrogen, heat it to 220 °C at a rate of 5 °C / min and hold for 70 min. Prepare a 0.4% glycine aqueous solution and heat it to 60 °C. Immerse the heat - treated silica gel in the glycine aqueous solution and react for 2 h. Take 5% (25 g) of coconut shell fiber and mix it with the reaction product, add deionized water to make a dispersion with a solid content of 20%. Use a centrifugal spray dryer (inlet temperature 180 °C, outlet temperature 90 °C), control the particle size to be 1 - 5 mm, and obtain a porous crude product after drying. Prepare a nano - TiO2 sol by mixing tetrabutyl titanate, ethanol, and nitric acid in a molar ratio of 1:10:0.3, and age for 24 h to form a stable sol. Immerse the crude desiccant in the sol for 10 min, dry it at 150 °C and then calcine it at 500 °C for 1 h. The TiO2 loading is 0.6%, forming a uniform photocatalytic layer, and thus obtaining the color - changing silica gel desiccant.

[0054] Place the color - changing silica gel desiccants prepared in Examples 1 - 3 in an environment with a relative humidity of 90% at room temperature for a water absorption performance test experiment. Record the adsorption amount and the color change of the color - changing silica gel desiccant at different times. The results are shown in Table 1.

[0055] Table 1 Color change results of the color - changing silica gel desiccant

[0056]

[0057] Moisture absorption - desorption cycle experiment: Prepare the color - changing silica gel desiccant using the steps of Examples 1 - 3. Accurately weigh a certain amount of the color - changing silica gel with an electronic balance, record its initial mass m0, and measure the initial color of the color - changing silica gel using a colorimeter, recording its chromaticity value C0. Place the color - changing silica gel in a thermostatic and humidistatic chamber. At a relative humidity of 90% and a temperature of 25°C, observe and record the color change and mass change of the color - changing silica gel every 1 hour until its mass no longer increases significantly, that is, it reaches the moisture - absorption saturation state. Record the mass m1 and chromaticity value C1 at the moisture - absorption saturation. Take out the moisture - absorption - saturated color - changing silica gel from the thermostatic and humidistatic chamber and place it in an oven for desorption at 100°C, controlling the time within 3 hours. After desorption is completed, take out the color - changing silica gel and place it in a desiccator to cool to room temperature. Weigh its mass m2 with an electronic balance and measure its chromaticity value C2 using a colorimeter. Place the cooled color - changing silica gel back into the thermostatic and humidistatic chamber for moisture absorption, repeat the above steps, complete 20 moisture - absorption - desorption cycles, record the corresponding mass and chromaticity value for each cycle, and calculate the color reversible change retention rate after each cycle according to the following formula (1), and calculate the average value of the color reversible change retention rate after 20 cycles. Conduct the above experiments on the color - changing silica gel prepared by the methods of Examples 1 - 3 respectively. The experimental results are shown in Figure 1 , and it can be obtained from Figure 1 that the color reversible change retention rate of the color - changing silica gel prepared by the present invention is still above 95% after 20 moisture - absorption - desorption cycles.

[0058] R n =(C n - C0) / (C1 - C0)×100%... Formula (1).

[0059] In formula (1), n represents the number of cycles, and Cn is the chromaticity value at the completion of desorption after the nth cycle.

[0060] The above - mentioned is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a color-changing silica gel desiccant, characterized in that, The following steps are involved: S1, subjecting silica gel particles to microwave radiation treatment; S2, after the microwave radiation treatment, immersing the silica gel particles in an ethanol solution containing a metal salt and performing ultrasonic oscillation; S3, heat treating the silica gel particles in a protective atmosphere; S4, after the heat treatment is completed, immersing the silica gel particles in an aqueous solution of an organic ligand to react to obtain a reaction product; S5, mixing the reaction product and the natural plant fiber dispersion, and spray drying to obtain a desiccant crude product; S6. The photocatalytic material is loaded on the inner wall of the crude desiccant by the sol-gel method to obtain a color-changing silica gel desiccant.

2. The preparation method of the color-changing silica gel desiccant according to claim 1, wherein In the step S1, the frequency of the microwave radiation treatment is 300 MHz to 3 GHz, and the time of the microwave radiation treatment is 5 to 30 minutes.

3. The preparation method of the discoloring silica gel desiccant according to claim 2, characterized in that, In step S2, the metal salt includes one or more of ferric chloride, copper sulfate and cobalt nitrate; the mass concentration of the ethanol solution containing the metal salt is 1-20%; and the ultrasonic oscillation time is 10-60 minutes.

4. The preparation method of the color-changing silica gel desiccant according to any one of claims 1 to 3, characterized in that, In step S3, the protective atmosphere includes nitrogen, argon, helium or neon; the heat treatment temperature is 150-300° C., and the heat treatment time is 30-120 min.

5. The preparation method of the color-changing silica gel desiccant according to claim 4, characterized in that, In step S4, the organic ligand includes one or more of o-phenanthroline, 8-hydroxyquinoline and carboxylic acid compounds; and the mass concentration of the aqueous solution of the organic ligand is 0.01-0.5%.

6. The preparation method of the color-changing silica gel desiccant according to claim 5, wherein, In step S4, the reaction temperature is 40-80° C., and the reaction time is 1-5 hours.

7. The preparation method of the color-changing silica gel desiccant according to claim 1 or 6, characterized in that, In step S5, the natural plant fiber includes bamboo fiber, coconut shell fiber or wood pulp fiber; the mass of the natural plant fiber is 1-10% of the mass of the reaction product; and the particle size of the crude desiccant is 1-5 mm.

8. The preparation method of the color-changing silica gel desiccant according to claim 7, characterized in that, In the step S6, the photocatalytic material includes nano titanium dioxide or zinc oxide; the mass of the photocatalytic material is 0.1-1% of the mass of the coarse desiccant.

9. A color-changing silica gel desiccant prepared by the method for preparing the color-changing silica gel desiccant according to any one of claims 1 to 8.

10. A discoloring silica gel, characterized in that, The color-changing silica gel is prepared according to the preparation method of the color-changing silica gel desiccant according to any one of claims 1 to 8; The color of the color-changing silica gel is blue when it is not damp, and is pink when it is damp.

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