CN100546914C - A kind of sol-gel self-propagating burning preparation CaIn 2O 4The method of powder - Google Patents

Abstract

The invention provides a method for preparing CaIn ₂ O ₄ powder by sol-gel self-propagating combustion: the nitrate aqueous solution containing Ca(NO ₃ ) ₂ and In(NO ₃ ) ₃ is used as the initial reaction solution, slowly dripping Add an aqueous solution of citric acid as a sol-gel chelating agent and self-combustion fuel, heat and stir to obtain a sol-gel precursor, adjust the sol-gel precursor to a pH value of 2 to 3 with ammonia or _HNO3 , and heat Hydrolyze to form a sol, dry to obtain a xerogel, heat to ignite the xerogel, and fully self-propagating combustion to obtain a combustion product, heat-treat the combustion product at 550-600°C for 1-2 hours, and grind to obtain the CaIn ₂ O ₄ powder body. The beneficial effects of the present invention are mainly reflected in: (1) the reaction precursor is a solution or a suspension with a particle size of nanometer order, and the dispersion and uniformity between different components are good; (2) the particles forming xerogel The smaller size can realize sintering and phase formation at a lower temperature, which is beneficial to obtain smaller CaIn ₂ O ₄ powders, thereby improving the photocatalytic activity of the powders.

Description

A method for preparing CaIn2O4 powder by sol-gel self-propagating combustion

(1) Technical field

The invention relates to a method for preparing CaIn ₂ O ₄ powder by sol-gel self-propagating combustion.

(2) Background technology

The technology of using TiO ₂ semiconductor photocatalyst to photodecompose organic pollutants has attracted many scholars for its strong oxidation and utilization of sunlight. However, due to the wide band gap (Eg=3.2eV) of TiO ₂ , it can only exhibit catalytic activity under ultraviolet light which accounts for 4% of the total solar energy, thus greatly limiting its development.

CaIn ₂ O ₄ is a new type of semiconductor photocatalyst with a bandgap width of only 2.0eV. It can effectively degrade organic pollutants in water under the irradiation of visible light. It has made a great breakthrough in environmental purification and is extremely Application prospect. The currently reported CaIn ₂ O ₄ photocatalysts are all prepared by solid-state reaction method, that is, solid CaCO ₃ and In ₂ O ₃ powders are mixed, burned at 1050°C for 12 hours, and then ground. The disadvantage of this method is that the solid powder is difficult to mix uniformly, the reaction temperature is high, the time is long and insufficient, and the obtained product particles are relatively coarse.

(3) Contents of the invention

The purpose of the present invention is to provide a method for preparing CaIn ₂ O ₄ powder by using sol-gel self-propagating combustion, so as to solve the problems that the reactants are difficult to mix uniformly and high-temperature sintering is required in the existing solid-state reaction method.

The technical method scheme that the present invention adopts is:

A kind of sol-gel self-propagating combustion prepares the method for CaIn ₂ O ₄ powder, described method is: with the nitrate aqueous solution containing Ca(NO ₃ ) ₂ and In(NO ₃ ) ₃ as the reaction starting solution, slowly Aqueous solution of citric acid as sol-gel chelating agent and self-combustion fuel is added dropwise, heated and stirred properly to obtain sol-gel precursor. Adjust the sol-gel precursor with nitric acid or ammonia water to a pH value of 2 to 3, heat and hydrolyze the precursor to form a sol, dry the sol to obtain a xerogel, ignite the xerogel by heating, and obtain a combustion product through sufficient self-propagating combustion , the combustion product was heat-treated at 550-600°C for 1-2 hours, and ground to obtain the CaIn ₂ O ₄ powder. The mass ratio of Ca(NO ₃ ) ₂ and In(NO ₃ ) ₃ in the nitrate aqueous solution It is 1:2. The pH value of the sol-gel precursor is adjusted to 2 to 3 to control hydrolysis. If the pH value is too small, the hydrolysis speed will be slow and the production efficiency will be low; if the pH value is too high, the hydrolysis speed and colloid viscosity will be too high, which will easily lead to the spontaneous combustion Slow and insufficient, and the oxidation-reduction reaction cannot be carried out uniformly, and the product composition is not uniform. The gel formed by nitrate and citric acid has self-propagating combustion characteristics. Using the sol-gel self-propagating combustion method, the required phase can be obtained in one step without pre-calcination, which reduces the possible formation of hard particles during pre-calcination. Agglomeration and grain growth improve the activity of the powder.

Specifically, the method includes:

(1) Add In ₂ O ₃ into concentrated nitric acid, heat at 40-50°C until In ₂ O ₃ is completely dissolved, the solution is clear and transparent, then add CaCO ₃ to obtain a nitrate solution containing Ca ²⁺ and In ³⁺ (ie Containing Ca(NO ₃ ) ₂ and In(NO ₃ ) ₃ nitrate aqueous solution); described concentrated nitric acid is analytically pure; described nitrate aqueous CaCO ₃ , In ₂ O ₃ , HNO The ratio of the amount of substance is ₁ :1:8;

(2) Slowly add aqueous citric acid solution dropwise to the nitrate solution obtained in step (1), heat and stir at 40 to 50° C. to obtain a sol-gel precursor; ₃ The ratio of the amount of substances is 2.22～11:1;

(3) Use nitric acid or ammonia water to adjust the pH of the sol-gel precursor to 2-3, hydrolyze at 60-70°C to obtain a sol, and dry the sol at 60-70°C to obtain a xerogel;

(4) Heating and igniting the xerogel at 400° C., and obtaining combustion products through sufficient self-propagating combustion. The combustion products are heat-treated at 550-600° C. for 1-2 hours, and ground to obtain the CaIn ₂ O ₄ powder.

Compared with the solid-state reaction, the sol-gel self-propagating combustion method does not require high reaction temperature and long reaction time. This method cleverly combines the sol-gel method and the self-propagating combustion method. It does not require pre-calcination, and the required phase can be obtained in one step, which reduces the hard agglomeration and grain growth that may be formed during the pre-calcination process. The activity of the powder is improved, and the prepared nanomaterial has uniform composition, small particle size, large specific surface area and high reactivity.

The beneficial effects of the present invention are mainly reflected in: (1) the reaction precursor is a solution or a suspension with a particle size of nanometer order, and the dispersion and uniformity between different components are good; (2) the particles forming xerogel The smaller size can realize sintering and phase formation at a lower temperature, which is beneficial to obtain smaller CaIn ₂ O ₄ powders, thereby improving the photocatalytic activity of the powders.

(4) Description of drawings

Fig. 1 is a schematic diagram of the main process flow of the present invention.

Fig. 2 is a concentration-time diagram of photocatalytic degradation of methylene blue by CaIn ₂ O ₄ powder prepared by the method provided by the present invention.

Fig. 3 is a concentration-time diagram of photocatalytic degradation of methylene blue by CaIn ₂ O ₄ powder prepared by the method provided by the present invention.

(5) Specific implementation methods

The present invention is further described below in conjunction with specific embodiment, but protection scope of the present invention is not limited thereto:

Example 1:

Take 0.555g In ₂ O ₃ and dissolve it in 1.2ml analytically pure concentrated HNO ₃ . After the In ₂ O ₃ is fully dissolved, add 0.2g CaCO ₃ to make a nitrate solution. Take 4.62g of citric acid (C ₆ H ₈ O ₇ ·H ₂ O) and fully dissolve it in 100mL of distilled water, slowly add it into the prepared nitrate solution, heat and stir at 40-50°C to obtain a sol-gel precursor; Adjust the pH value to 3 with ammonia water and nitric acid, heat to 60°C for hydrolysis, and place to form a sol. After the sol is formed, continue to heat up to 70°C to form a xerogel. Heating and igniting the xerogel at 400°C makes it fully self-propagating and burning. Burn the black product obtained from self-combustion at 600°C for 2 hours to obtain a yellow-white powder. After grinding, the CaIn ₂ O ₄ photocatalytic powder can be obtained. The photocatalytic degradation of methylene blue by CaIn ₂ O ₄ powder is shown in Figure 2. Contain _1.8g /l CaIn ₂ O The methylene blue solution (Sample1) of powder is degraded completely in 2 hours under natural light _{conditions ;} ) The concentration was only reduced from the original 10.1mg/l to 8mg/l. The CaIn ₂ O ₄ powder prepared by the sol-gel self-propagating combustion method has the performance of catalytic decomposition of organic matter under visible light.

Example 2:

Take 0.555g In ₂ O ₃ and dissolve it in 1.2ml analytically pure concentrated HNO ₃ . After the In ₂ O ₃ is fully dissolved, add 0.2g CaCO ₃ to make a nitrate solution. Dissolve 0.92g of citric acid (C ₆ H ₈ O ₇ ·H ₂ O) in 100mL of distilled water to make a citric acid solution, slowly add it to the prepared nitrate solution, heat and stir at 40-50°C to obtain a sol- Gel precursor;. Use ammonia water and nitric acid to adjust the pH to 3, heat to 65°C for hydrolysis, and place to form a sol. After the sol is formed, continue to heat up to 70°C to form a xerogel. Heating and igniting the xerogel at 400°C makes it fully self-propagating and burning. Burn the black product obtained from self-combustion at 550°C for 2 hours to obtain a yellow-white powder. After grinding, the CaIn ₂ O ₄ powder can be obtained. The photocatalytic degradation of methylene blue by CaIn ₂ O ₄ powder is shown in Figure 3. The methylene blue solution (Sample 2) containing 1.8g/l CaIn ₂ O ₄ powder was completely degraded within 150min under natural light conditions; while the methylene blue solution (Blank) without CaIn ₂ O ₄ powder The concentration was only reduced from the original 10mg/l to 6mg/l. The CaIn ₂ O ₄ powder prepared by the sol-gel self-propagating combustion method has the performance of catalytic decomposition of organic matter under visible light.

Claims (2)

1. a kind of sol-gel self-propagating combustion prepares CaIn ₂ O ₄ method of powder, described method is: with containing Ca(NO ₃ ) ₂ and In(NO ₃ ) ₃ nitrate aqueous solution is reaction initiation solution , drop an aqueous solution of citric acid as a sol-gel chelating agent and self-combustion fuel, heat and stir to obtain a sol-gel precursor, adjust the sol-gel precursor to a pH value of 2 to 2 with ammonia or _HNO3 3. Heating and hydrolyzing the precursor to form a sol, drying the sol to obtain a xerogel, heating and igniting the xerogel, and fully self-propagating combustion to obtain a combustion product, heat-treating the combustion product at 550-600°C for 1-2 hours, grinding, The CaIn ₂ O ₄ powder is obtained; the molar ratio of Ca(NO ₃ ) ₂ and In(NO ₃ ) ₃ in the nitrate aqueous solution is 1:2. 2. The method of claim 1, wherein said method comprises: (1) Add In ₂ O ₃ into concentrated nitric acid, heat at 40-50°C until In ₂ O ₃ is completely dissolved, then add CaCO ₃ to obtain an aqueous solution containing Ca(NO ₃ ) ₂ and In(NO ₃ ) ₃ ; (2) Add dropwise citric acid aqueous solution to step (1) gained aqueous solution, 40～50 ℃ heat and stir, obtain sol-gel _precursor ; The ratio of the quantity is 2.22～11:1; (3) Use nitric acid or ammonia water to adjust the pH of the sol-gel precursor to 2-3, hydrolyze at 60-70°C to obtain a sol, and dry the sol at 60-70°C to obtain a xerogel; (4) Heating and igniting the xerogel at 400° C., and obtaining combustion products through sufficient self-propagating combustion. The combustion products are heat-treated at 550-600° C. for 1-2 hours, and ground to obtain the CaIn ₂ O ₄ powder.

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