CN106732588A - Catalyst of Cr (VI) and its preparation method and application in one kind conversion aqueous solution - Google Patents

Abstract

The invention relates to a catalyst for converting Cr(VI) in aqueous solution, its preparation method and application. The technical scheme adopted is: NaTaO ₃ and Er ³⁺ :YAlO ₃ are synthesized into Er ³⁺ :YAlO ₃ /NaTaO ₃ by means of ultrasonic dispersion and liquid boiling. Finally, dissolve the NaTaO ₃ /Er ³⁺ :YAlO ₃ powder obtained above and chloroauric acid, chloroplatinic acid or silver nitrate in ethanol, and synthesize X/NaTaO ₃ /Er ³⁺ by ultrasonic dispersion and liquid boiling: YAlO ₃ (X=Ag, Au and Pt). Under the irradiation of sunlight, X/NaTaO ₃ /Er ³⁺ :YAlO ₃ (X=Ag, Au and Pt) is used as a catalyst to photocatalytically convert Cr(VI). The method of the invention is simple and novel, has low cost, does not generate by-products and does not cause environmental pollution.

Description

Catalyst for converting Cr(VI) in aqueous solution and its preparation method and application

technical field

The invention belongs to the field of chemical catalysis, and in particular relates to the synthesis of a novel catalyst and a method for using the catalyst to convert Cr(VI) in water.

Background technique

With the development of modern industry, hexavalent chromium (Cr(VI)) in natural water bodies and industrial wastewater has become a major hazard to the environment. Cr(VI) mainly comes from industries such as mining, electroplating, metal surface treatment, tanning, printing and dyeing, and foundry. Under different concentration or pH conditions, Cr(VI) is expressed as ^chromate ( _HCrO ^4- ) and dichromate (Cr ₂ O ₇ ^2- ) into the environment. Studies have shown that Cr(VI) is 1000 times more carcinogenic than Cr(III), and generally has higher solubility, toxicity, instability and biological activity. If drinking water contains Cr(VI), it will increase the possibility of human body suffering from liver cancer, skin cancer and bladder cancer. On the contrary, an appropriate amount of Cr(III) is an essential element for the human body, therefore, it is very necessary to reduce Cr(VI) to Cr(III).

Photocatalytic technology has attracted widespread attention because it can directly use the absorbed light to remove pollutants in water, and is easy to separate and reuse. For example, TiO ₂ is widely used because of its relatively high catalytic activity and stable physical and chemical properties. For the removal of Cr(VI) in water, we need to choose a semiconductor with strong oxidizing and reducing power to convert Cr(VI) into Cr(III), which requires us to choose a relatively high conduction band and relatively Broadband semiconductors with lower valence bands. After investigation, perovskite NaTaO ₃ is a new type of non-metallic broadband semiconductor material with high photocatalytic reduction performance. However, because of its wide energy band gap, NaTaO ₃ can only absorb ultraviolet light for photocatalytic reaction. Ultraviolet light accounts for only 4% of the solar spectrum, which makes the utilization of solar energy extremely small. In order to obtain higher solar energy utilization, it is necessary to develop catalysts that can utilize visible light.

Contents of the invention

The purpose of the present invention is to design and synthesize a novel catalyst X/NaTaO ₃ /Er ³⁺ :YAlO ₃ (X=Ag, Au and Pt) which can be used to convert Cr(VI) in aqueous solution. The compound involved in the invention belongs to a novel rare metal catalyst, and the method is simple and pollution-free when applied to the conversion of Cr(VI), and the catalyst is stable and easy to separate.

The technical scheme adopted in the present invention is as follows: a catalyst for converting Cr(VI) in aqueous solution, the catalyst is X/NaTaO ₃ /Er ³⁺ :YAlO ₃ , wherein X=Ag, Au or Pt.

A kind of preparation method of the catalyst of above-mentioned conversion Cr(VI) in the aqueous solution, the method is as follows:

1) Mix Er ³⁺ :YAlO ₃ and NaTaO ₃ , add deionized water, ultrasonically disperse for 15-25min; heat at boiling point for 30-40min, and stir magnetically, reactants are filtered and cleaned with distilled water, and placed in a muffle furnace Heat at 500°C for 2-3 hours to get NaTaO ₃ /Er ³⁺ :YAlO ₃ ;

2) Dissolve NaTaO ₃ /Er ³⁺ :YAlO ₃ and chloroauric acid, chloroplatinic acid or silver nitrate in ethanol, disperse ultrasonically for 30-40 minutes to obtain a suspension, heat the suspension to the boiling point, and heat it for 30 After -40 minutes, the reactant was filtered and washed with distilled water, calcined at 350°C for 1-2h, and ground to obtain X/NaTaO ₃ /Er ³⁺ :YAlO ₃ ; where X=Ag, Au or Pt.

In the above preparation method of a catalyst for converting Cr(VI) in aqueous solution, the mass ratio is Er ³⁺ :YAlO ₃ :NaTaO ₃ =3:7.

In the above method for preparing a catalyst for converting Cr(VI) in aqueous solution, the added amount of the chloroauric acid, chloroplatinic acid or silver nitrate is 1-2% of the mass of NaTaO ₃ /Er ³⁺ :YAlO ₃ .

The above-mentioned preparation method of a catalyst for converting Cr(VI) in an aqueous solution, the preparation method of _NaTaO3 is: _Ta2O5 and _NaOH are added with water and stirred evenly, then transferred to a hydrothermal reaction kettle, and heated at 180 Treat at ℃ for 15-17 hours, cool to room temperature, discard the supernatant, wash the precipitate with deionized water until neutral, centrifuge, and dry to obtain NaTaO ₃ .

The preparation method of the above-mentioned catalyst for converting Cr(VI) in aqueous solution, the molar ratio is Ta:Na=1:10.

The above-mentioned preparation method of a catalyst for converting Cr(VI) in an aqueous solution, the preparation method of the Er ³⁺ : YAlO ₃ is: Er ₂ O ₃ and Y ₂ O ₃ are dissolved in concentrated nitric acid, and then sequentially added Al(NO ₃ ) ₃ aqueous solution and citric acid aqueous solution, heat and stir at 50-60°C, stop when the solution is viscous, and obtain a foaming viscous solution, heat the foaming viscous solution at 75-85°C Heating for 35-40 hours to obtain a foam sol. After heating the foam sol at 500°C for 50-60 minutes, calcining at 1100°C for 2-3 hours, cooling to obtain Er ³⁺ : YAlO ₃ .

The above-mentioned catalyst is used in the conversion of Cr(VI) in aqueous solution. The method is as follows: add the above-mentioned catalyst X/NaTaO ₃ /Er ³⁺ :YAlO ₃ into a solution containing Cr(VI), and irradiate under sunlight at room temperature.

The beneficial effects of the present invention are:

1. The present invention, in order to improve the photocatalytic efficiency of NaTaO ₃ , and then convert hexavalent chromium ions more effectively, the light conversion agent Er ³⁺ : YAlO ₃ is combined with NaTaO ₃ , in this photocatalyst combination, Er ³⁺ : YAlO ₃ can convert the absorbed visible light into ultraviolet light that can be directly utilized by NaTaO ₃ , so that NaTaO ₃ with a wider energy band gap can use sunlight more effectively for photocatalytic reactions.

2. In the present invention, in order to achieve the purpose of improving photocatalytic efficiency by using sunlight to stimulate electron-hole pairs, a small amount of precious metals such as gold and silver are added to the surface of the semiconductor, and a triple heterojunction photocatalytic system can be used. Enhanced visible light absorption and photocatalytic efficiency, exhibiting the best photocatalytic reduction efficiency for hexavalent chromium.

3. On the basis of a variety of photocatalytic technologies, the present invention studies the technology for Cr(VI) conversion with NaTaO ₃ composite up-conversion luminescent material and adding a cocatalyst. Through the method of the invention, the concentration of Cr(VI) can be reduced to below 0.05ppm without affecting other quality indicators. Compared with other photocatalytic technologies, the process of the present invention is simple, carried out at normal temperature and pressure, with mild conditions, solar energy can be utilized, and the conversion rate can reach more than 97%.

Description of drawings

Figure 1a is the XRD pattern of Er ³⁺ : YAlO ₃ .

Figure 1b is the SEM image of Er ³⁺ : YAlO ₃ .

Figure 2a is the XRD pattern of _NaTaO3 .

Figure 2b is the SEM image of _NaTaO3 .

Fig. 3a is the XRD pattern of NaTaO ₃ /Er ³⁺ :YAlO ₃ .

Fig. 3b is a SEM image of NaTaO ₃ /Er ³⁺ :YAlO ₃ .

Fig. 4a is the XRD pattern of Ag/NaTaO ₃ /Er ³⁺ :YAlO ₃ .

Fig. 4b is a SEM image of Ag/NaTaO ₃ /Er ³⁺ :YAlO ₃ .

Fig. 5a is the XRD pattern of Au/NaTaO ₃ /Er ³⁺ :YAlO ₃ .

Fig. 5b is a SEM image of Au/NaTaO ₃ /Er ³⁺ :YAlO ₃ .

Fig. 6a is an XRD pattern of Pt/NaTaO ₃ /Er ³⁺ :YAlO ₃ .

Fig. 6b is a SEM image of Pt/NaTaO ₃ /Er ³⁺ :YAlO ₃ .

detailed description

Example 1 Catalyst Ag/NaTaO ₃ /Er ³⁺ : YAlO ₃

(1) Preparation method

1. Preparation of NaTaO ₃ : Add 1.7540g Ta ₂ O ₅ and 3.1750g NaOH (Ta/Na molar ratio 1:10), add 25mL of distilled water and stir evenly, then transfer to a hydrothermal kettle and treat at 180°C for 15h Let cool to room temperature. After the hydrothermal kettle is completely cooled, take it out and discard the supernatant to obtain a white powder, which is centrifuged and washed with deionized water until the eluate is neutral, and then rinsed twice with absolute ethanol. Finally, the product was dried in an oven at 60°C for 12 hours to obtain NaTaO ₃ , which was used for future use.

2. Preparation of Er ³⁺ :YAlO ₃ : Dissolve 0.0232g Er ₂ O ₃ and 1.3640g Y ₂ O ₃ in concentrated nitric acid, and heat and stir with magnetic force until it is colorless and transparent to obtain a rare earth ion solution. Then take another beaker, weigh 4.5316g Al(NO ₃ ) ₃ ·9H ₂ O and dissolve it in distilled water, stir it with a glass rod at room temperature and slowly add it into the above rare earth ion solution. Weigh 15.2325g citric acid as chelating agent and cosolvent and dissolve with distilled water, then add in the above-mentioned solution. Then heat and stir at 50-60°C, and stop when the solution is viscous. No precipitate formed during this process and a foamy viscous solution was finally obtained. Put the foamed viscous solution into an oven and heat at a constant temperature of 80°C for 36h. During the drying process, no precipitate was formed until the solvent was evaporated to dryness, and finally a foamy sol was obtained. The obtained foam sol was heated at 500 °C for 50 min, and then calcined at 1100 °C for 2 h. Finally, the sintered mass was taken out from the high temperature furnace and cooled to room temperature in air to obtain Er ³⁺ :YAlO ₃ powder.

3. Preparation of NaTaO ₃ /Er ³⁺ :YAlO ₃ : Mix Er ³⁺ :YAlO ₃ and NaTaO ₃ (mass ratio 3:7). Then place it in a beaker, pour 50mL of deionized water into it, and carry out ultrasonic dispersion for more than 15min. Heat at boiling point for 30 min with magnetic stirring. The reactant was filtered and washed with distilled water, put into a crucible, and baked in a muffle furnace at 500°C for 2h with a heating rate of 2°C/min to obtain the target product NaTaO ₃ /Er ³⁺ :YAlO ₃ .

4. Preparation of Ag/NaTaO _{3 /Er 3+ :YAlO 3: Dissolve 1g of NaTaO 3 /Er 3+ :YAlO 3} ^powder _{and 0.01g} ^of _silver nitrate in 200mL of ethanol, and fully disperse for 30 minutes by ultrasonic (80kHZ, ultrasonic output The power is 50W) to obtain a suspension, which is heated to the boiling point and kept at a constant temperature for 30 minutes at the boiling point. After the reactant is filtered and washed, the separated powder is calcined at 350°C for 1 hour, and finally ground to obtain Ag/NaTaO ₃ /Er ³⁺ :YAlO ₃ .

(2) Characterization data

The XRD of the prepared Er ³⁺ : YAlO ₃ is shown in Figure 1a. It can be seen from Figure 1a that the diffraction peak position of the sample is basically consistent with the data of JCPDS standard card 33-0040, which shows that the samples after heat treatment are all single Body-centered cubic structure, no other impurity phases appear. This shows that the doping of Er ³⁺ ions has no obvious effect on the crystal structure.

The SEM of the prepared Er ³⁺ :YAlO ₃ is shown in Figure 1b. It can be seen from Figure 1b that the obtained crystals are spherical or quasi-spherical, with a particle size of 40-60nm, relatively uniform size distribution, and good dispersion. Indicates that the sample preparation was successful.

The XRD of the prepared _NaTaO3 is shown in Figure 2a, as can be seen from Figure 2a, _{NaTaO3Characteristic} peaks 2θ=22.85°(100), 2θ=32.55°(110), 2θ=40.23°(111), 2θ=46.67° (200) and 2θ=52.58°(210), which are basically consistent with the data of the NaTaO ₃ standard card (JCPDS card 74-2488), which indicates that the sample after heat treatment has a single cubic structure and no other impurities appear.

The SEM of the prepared NaTaO ₃ is shown in Figure 2b. It can be seen from Figure 2b that NaTaO ₃ is a cube with a length of 220nm, which indicates that the prepared NaTaO ₃ crystals show (100) and (110) planes.

The XRD and SEM of the prepared NaTaO ₃ /Er ³⁺ :YAlO ₃ are shown in Figures 3a and 3b. It can be seen from Figure 3a that NaTaO ₃ /Er ³⁺ :YAlO ₃ has both NaTaO ₃ and Er ³⁺ :YAlO ₃ characteristic peaks, and no other impurity phases appear, which shows that the composite of NaTaO ₃ and Er ³⁺ :YAlO ₃ There was no obvious effect on the crystal structure. It can be seen from Figure 3b that NaTaO ₃ appears as a 220nm-long cube, and the light conversion agent Er ³⁺ : YAlO ₃ appears as a spherical shape and is uniformly distributed on the surface of the NaTaO ₃ cube, indicating that the composite catalyst was successfully prepared.

The XRD and SEM of the prepared Ag/NaTaO ₃ /Er ³⁺ :YAlO ₃ are shown in Figures 4a and 4b. It can be seen from Figure 4a that Ag/NaTaO ₃ /Er ³⁺ :YAlO ₃ has the characteristic peaks of NaTaO ₃ and Er ³⁺ :YAlO ₃ at the same time, and no characteristic peak of Ag is found, which shows that the amount of Ag as a promoter is very small And evenly distributed on the surface of NaTaO ₃ /Er ³⁺ :YAlO ₃ , resulting in no characteristic peaks being detected. It can be seen from Figure 4b that on the surface of the NaTaO ₃ cube, in addition to some spherical light-changing agents evenly distributed, some fine particles were also observed, which indicated that a small amount of promoter Ag was successfully attached to the surface of the catalyst.

(3) Cr(VI) conversion method

Add 50mL Cr(VI) solution (1ppm) and 50mgAg/NaTaO ₃ /Er ³⁺ :YAlO ₃ into the test tube of the photocatalytic reaction instrument, turn on the magnetic stirring under normal temperature simulated sunlight, and react for 120min. Catalyst and solution are separated.

The concentration of Cr(VI) is measured by diphenylcarbazide spectrophotometry, and the conversion rate reaches more than 95%.

Example 2 Catalyst Au/NaTaO ₃ /Er ³⁺ : YAlO ₃

(1) Preparation method

1.NaTaO ₃ preparation: with embodiment 1

2.Er ³⁺ : YAlO ₃ Preparation: Same as Example 1

3. Preparation of NaTaO ₃ /Er ³⁺ :YAlO ₃ : Same as Example 1

4. Preparation of Au/NaTaO _{3 /Er 3+ :YAlO 3 : Dissolve 1g of NaTaO 3 /Er 3+ :YAlO 3} ^powder _{and 0.01g} ^of _chloroauric acid in 200mL of ethanol, and fully disperse for 30 minutes using ultrasound (80kHZ, ultrasonic The output power is 50W) to obtain a suspension. The suspension is heated to the boiling point and kept at a constant temperature for 30 minutes at the boiling point. After filtering and washing, the separated powder is calcined at 350°C for 1 hour and finally ground to obtain Au/NaTaO ₃ / Er ³⁺ : YAlO ₃ .

(2) Characterization data

The XRD and SEM of the prepared Au/NaTaO ₃ /Er ³⁺ :YAlO ₃ are shown in Figures 5a and 5b. It can be seen from Figure 4a that Au/NaTaO ₃ /Er ³⁺ :YAlO ₃ has both NaTaO ₃ and Er ³⁺ :YAlO ₃ characteristic peaks, and no characteristic peaks of Au are found, which shows that the amount of Au as a promoter is very small And evenly distributed on the surface of NaTaO ₃ /Er ³⁺ :YAlO ₃ , resulting in no characteristic peaks being detected. It can be seen from Figure 4b that on the surface of the NaTaO ₃ cube, in addition to some spherical light-changing agents evenly distributed, some fine particles were also observed, which indicated that a small amount of promoter Au was successfully attached to the surface of the catalyst.

(3) Cr(VI) conversion method

Add 50mL of Cr(VI) solution (1ppm) and 50mg of catalyst Au/NaTaO ₃ /Er:YAlO ₃ into the test tube of the photocatalytic reaction apparatus, and turn on the magnetic stirring at room temperature under simulated sunlight, and react for 120min. Catalyst and solution are separated.

The concentration of Cr(VI) is measured by diphenylcarbazide spectrophotometry, and the conversion rate reaches above 98%.

Example 3 Pt/NaTaO ₃ /Er ³⁺ : YAlO ₃

(1) Preparation method

1.NaTaO ₃ preparation: with embodiment 1

2.Er ³⁺ : YAlO ₃ Preparation: Same as Example 1

3. Preparation of NaTaO ₃ /Er ³⁺ :YAlO ₃ : Same as Example 1

4. Preparation of Pt/NaTaO _{3 /Er 3+ :YAlO 3 : Dissolve 1g of NaTaO 3 /Er 3+ :YAlO 3} ^powder _{and 0.01g} ^of _{chloroplatinic} acid in 200mL of ethanol, and fully disperse for 30 minutes using ultrasound (80kHZ, ultrasonic The output power is 50W) to obtain a suspension. The suspension is heated to the boiling point and kept at a constant temperature for 30 minutes at the boiling point. After filtering and washing, the separated powder is calcined at 350°C for 1 hour and finally ground to obtain Pt/NaTaO ₃ / Er ³⁺ : YAlO ₃ .

(2) Characterization data:

The XRD and SEM of the prepared Pt/NaTaO ₃ /Er ³⁺ :YAlO ₃ are shown in Figures 6a and 6b. It can be seen from Figure 6a that Pt/NaTaO ₃ /Er ³⁺ :YAlO ₃ has the characteristic peaks of NaTaO ₃ and Er ³⁺ :YAlO ₃ at the same time, and no characteristic peak of Pt is found, which shows that the amount of Pt as a promoter is very small And evenly distributed on the surface of NaTaO ₃ /Er ³⁺ :YAlO ₃ , resulting in no characteristic peaks being detected. It can be seen from Figure 6b that on the surface of the NaTaO ₃ cube, in addition to some spherical light-changing agents evenly distributed, some fine particles were also observed, which indicated that a small amount of promoter Pt was successfully attached to the surface of the catalyst.

(3) Cr(VI) conversion method

In the test tube of the photocatalytic reaction instrument, add 50mL Cr(VI) solution (1ppm) and 50mg catalyst Pt/NaTaO ₃ /Er ³⁺ :YAlO ₃ , under normal temperature simulated sunlight, turn on magnetic stirring, react for 120min, and react After completion, the catalyst and the solution are separated.

The concentration of Cr(VI) is measured by diphenylcarbazide spectrophotometry, and the conversion rate reaches above 96%.

Claims (9)

1. one kind converts the catalyst of Cr (VI) in the aqueous solution, it is characterised in that the catalyst is X/NaTaO₃/Er³⁺: YAlO₃, wherein, X=Ag, Au or Pt.

2. the one kind described in claim 1 converts the preparation method of the catalyst of Cr (VI) in the aqueous solution, it is characterised in that method It is as follows：

1) by Er³⁺:YAlO₃And NaTaO₃Mixing, plus deionized water, ultrasonic disperse 15-25min；30- is heated at the boiling point 40min, and magnetic agitation, after reactant is with distillation water filtration and cleaning, 500 DEG C of heating 2-3h, obtain NaTaO in Muffle furnace₃/ Er³⁺:YAlO₃；

2) by NaTaO₃/Er³⁺:YAlO₃With the dissolving of gold chloride, chloroplatinic acid or silver nitrate in ethanol, ultrasonic disperse 30-40 minutes, Suspension is obtained, suspension is heated to boiling point, heated 30-40 minutes under boiling point, after reactant is used distillation water filtration and is washed, 1-2h is calcined at 350 DEG C, is ground, obtain X/NaTaO₃/Er³⁺:YAlO₃；Wherein X=Ag, Au or Pt.

3. one kind according to claim 2 converts the preparation method of the catalyst of Cr (VI) in the aqueous solution, it is characterised in that In mass ratio, Er³⁺:YAlO₃:NaTaO₃=3:7.

4. one kind according to claim 2 converts the preparation method of the catalyst of Cr (VI) in the aqueous solution, it is characterised in that The addition of described gold chloride, chloroplatinic acid or silver nitrate is NaTaO₃/Er³⁺:YAlO₃The 1-2% of quality.

5. one kind according to claim 2 converts the preparation method of the catalyst of Cr (VI) in the aqueous solution, it is characterised in that Described NaTaO₃Preparation method be：By Ta₂O₅And NaOH, add water after stirring, it is transferred in hydrothermal reaction kettle, 180 15-17h is processed at DEG C, room temperature is cooled to, supernatant is abandoned, sediment is washed with deionized to neutrality, and centrifugation is dried, obtained NaTaO₃。

6. one kind according to claim 5 converts the preparation method of the catalyst of Cr (VI) in the aqueous solution, it is characterised in that In molar ratio, Ta:Na=1:10.

7. one kind according to claim 1 converts the preparation method of the catalyst of Cr (VI) in the aqueous solution, it is characterised in that Described Er³⁺:YAlO₃Preparation method be：By Er₂O₃And Y₂O₃It is dissolved in concentrated nitric acid, then sequentially adds Al (NO₃)₃Water Solution and aqueous citric acid solution, in 50-60 DEG C of heating stirring, stop when solution is in thick, and must foam glutinous colloidal solution, will The glutinous colloidal solution of foaming obtains foam sol in 35-40h is heated at 75-85 DEG C, and foam sol is heated into 50- at 500 DEG C After 60min, 2-3h is calcined at 1100 DEG C, cooling obtains Er³⁺:YAlO₃。

8. application of the catalyst described in claim 1 in Cr (VI) in converting the aqueous solution.

9. application according to claim 8, it is characterised in that method is as follows：In the solution containing Cr (VI), power is added Profit requires the catalyst described in 1, is irradiated under normal temperature, solar irradiation.