Ca-k / nio-zno photocatalyst, and preparation method and application thereof

Abstract

This invention discloses a Ca-K / NiO-ZnO photocatalyst, its preparation method, and its application, belonging to the field of photocatalysis technology. The technical solution includes the following steps: 1) Adding Ni(NO3)2·6H2O and Zn(NO3)2·6H2O to water to obtain solution one; 2) Adding calcium oxide and potassium carbonate to water and stirring to obtain a homogeneous solution two; 3) Adding solution one to a reaction vessel for hydrothermal reaction; then calcining to obtain a NiO-ZnO catalyst; 4) Adding the NiO-ZnO catalyst to solution two, stirring, adding citric acid, heating the reaction, naturally cooling to room temperature, centrifuging to collect the precipitate, washing, and drying; then placing it in a high-temperature tube furnace for two calcinations to obtain the Ca-K / NiO-ZnO photocatalyst. The catalyst prepared by the method of this invention significantly improves its light absorption capacity and carrier separation efficiency under visible light.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis technology, specifically relating to a Ca-K / NiO-ZnO photocatalyst, its preparation method, and its application. Background Technology

[0002] Aniline, a typical aromatic amine organic pollutant, is widely found in the production wastewater of industries such as chemical, printing and dyeing, pharmaceutical, and rubber processing. It is highly toxic, difficult to biodegrade, and easily accumulates in water bodies and soil. It not only causes serious damage to aquatic ecosystems but also enters the human body through the food chain, causing health problems such as liver damage, blood diseases, and even cancer. Therefore, it is listed as one of the priority water pollutants for control. Thus, developing efficient and environmentally friendly aniline wastewater treatment technologies has become a key research focus in the field of water environment management.

[0003] Photocatalytic oxidation technology has become one of the ideal technologies for treating recalcitrant organic wastewater due to its advantages such as mild reaction conditions, no secondary pollution, and the ability to utilize solar energy for deep mineralization of pollutants. The core lies in the development of high-performance photocatalysts. Currently, various semiconductor photocatalysts, such as TiO2, g-C3N4, Bi-based oxides, MOFs-based composite semiconductors, and traditional ZnO-based single / two-component catalysts, have been applied to aniline degradation research. Although some progress has been made, due to factors such as the intrinsic properties of materials, preparation processes, and catalytic mechanisms, various catalysts still have significant shortcomings in practical applications, making it difficult to simultaneously meet the requirements of degradation efficiency, visible light utilization, stability, and large-scale application. Zinc oxide (ZnO), as a typical n-type semiconductor photocatalyst, is theoretically applicable to the field of organic pollutant degradation, but its material stability is poor, and it is prone to photocorrosion in photocatalytic reactions, leading to catalyst deactivation. Furthermore, single-component ZnO has weak adsorption capacity for aniline, and intermediate products tend to accumulate during the degradation process, resulting in poor deep mineralization effects, which limits its practical application.

[0004] Therefore, developing semiconductor photocatalysts that combine wide and efficient carrier separation, strong surface adsorption capacity, and stable lattice oxygen activation mechanism, while optimizing the preparation process to achieve large-scale production, and combining them with efficient photocatalytic reaction devices and catalyst recovery technology, has become a key direction for solving practical problems in aniline wastewater treatment. Summary of the Invention

[0005] This invention provides a Ca-K / NiO-ZnO photocatalyst, its preparation method, and its application. The catalyst prepared by the method of this invention significantly improves its light absorption capacity and carrier separation efficiency under visible light.

[0006] The technical solution of this invention is as follows:

[0007] In the first aspect, a method for preparing Ca-K / NiO-ZnO photocatalysts is disclosed, including the following steps:

[0008] 1) Add Ni(NO3)2·6H2O and Zn(NO3)2·6H2O to water to obtain solution one;

[0009] 2) Add calcium oxide and potassium carbonate to water and stir to obtain a homogeneous solution.

[0010] 3) Add solution one to the reactor, place the reactor in an oven at 100-120℃ for 18-24h for hydrothermal reaction; cool the reaction system to room temperature, wash, dry, and calcine at 350-450℃ for 5-7h to obtain NiO-ZnO catalyst;

[0011] 4) Add the NiO-ZnO catalyst to solution 2, stir, add citric acid, and continue stirring to obtain a suspension. Transfer the suspension to a reactor and heat at 100-150℃ for 4-5 hours. Allow it to cool naturally to room temperature, centrifuge to collect the precipitate, wash, and dry. Then place it in a high-temperature tube furnace and calcine it once at 200-300℃ for 2-3 hours, and then calcine it a second time at 500-600℃ for 5-8 hours to obtain the Ca-K / NiO-ZnO photocatalyst.

[0012] Preferably, the mass ratio of calcium oxide, potassium carbonate, Ni(NO3)2·6H2O and Zn(NO3)2·6H2O is 1:(1-3):(40-50):(50-60).

[0013] Preferably, the ratio of the mass of added citric acid to the total mass of Ni(NO3)2·6H2O and Zn(NO3)2·6H2O is 1:(15-20).

[0014] Preferably, in step 3), the product is washed with ethanol and deionized water, and then dried at 55-65°C for 1-2 hours.

[0015] Preferably, in step 4), the product is washed with ethanol and deionized water, and then dried at 55-80°C for 12-15 hours.

[0016] Secondly, the preparation method described above discloses the Ca-K / NiO-ZnO photocatalyst.

[0017] Thirdly, the application of the catalyst in the degradation of aniline is disclosed, including the following steps:

[0018] 1) The catalyst is placed in the photoreactor, and the set temperature of the photoreactor is 120-200℃ and the pressure is 0.1-0.3MPa;

[0019] 2) Add an aniline solution with a concentration of 10-20 mg / L to the photoreactor, ensuring the solution volume does not exceed the composite catalyst.

[0020] 3) After reacting for 8-10 hours under visible light, the concentration of aniline at the end of the reaction was measured.

[0021] The reaction mechanism of this invention is as follows:

[0022] 1. In traditional photocatalysis, it is generally believed that holes directly oxidize pollutants, or react with H2O / OH adsorbed on the surface. - The reaction generates hydroxyl radicals (·OH) to oxidize pollutants. However, this process involves lattice oxygen (O₂). 2- lattice Within the mechanism of ), there exists a different path:

[0023] Hole trapping and lattice oxygen activation: photogenerated holes (h + After migrating to the catalyst surface, they do not always react immediately with the adsorbate. They may be reacted with the lattice oxygen (O2) on the catalyst surface. 2- lattice ) was captured.

[0024] O 2- lattice +h + →O - lattice ;

[0025] The O here - lattice It is a highly reactive monovalent oxygen substance (equivalent to an oxygen ion with a positively charged hole, belonging to a bound state vacancy or active lattice oxygen). Oxygen vacancy formation and replenishment: When lattice oxygen participates in a reaction as an active substance, oxygen vacancies are left on the surface. These oxygen vacancies are crucial for subsequent reactions. Oxygen in the gas phase is captured by oxygen vacancies, forming superoxide radicals, while the oxygen vacancies are refilled, restoring the lattice structure. This forms a cycle of lattice oxygen → oxygen vacancy → re-oxidation.

[0026] 2. Degradation pathway of aniline

[0027] Aniline (C6H5NH2) molecules interact with the catalyst surface through their amino groups (-NH2) and benzene rings. Under the combined action of active lattice oxygen and free radicals, the degradation process is as follows:

[0028] Step 1: Benzene ring attack and ring opening

[0029] Active lattice oxygen (O 2- lattice ) or generated OH radicals attack the electron cloud on the benzene ring.

[0030] Because -NH2 is a strong electron-donating group, the ortho and para electron clouds on the benzene ring are highly dense and easily attracted by electrophilic reagents (such as O-). lattice , The hydroxyl group (OH) attacks the hydroxyl group, resulting in the formation of intermediates such as hydroquinone and catechol.

[0031] Step 2: Conversion of amino groups

[0032] The amino group (-NH2) can be oxidized by holes or reactive oxygen species to form a nitro group (-NO2) or further deaminated to form phenols, or NH4 can be released during ring opening. + and NO3 - ion.

[0033] Step 3: Loop Opening and Mineralization

[0034] The aromatic ring is opened, generating small molecule organic acids (such as maleic acid and oxalic acid).

[0035] It is eventually completely oxidized into CO2 and H2O.

[0036] Ca 2+ Oxygen vacancies can enter the crystal lattice and cause lattice distortion, increasing the concentration of oxygen vacancies. The more oxygen vacancies there are, the higher the activity of lattice oxygen tends to be, and the easier it is for it to participate in reactions.

[0037] K + Typically used as an electronic additive or structural modifier, it may adjust the acidity or alkalinity of the catalyst surface, enhance the adsorption capacity for aniline (alkaline), and make it easier for pollutants to come into contact with the active lattice oxygen on the surface.

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] 1. This invention modifies NiO-ZnO heterojunction catalysts by co-doping with Ca and K, utilizing Ca... 2+ Introducing lattice distortion increases oxygen vacancy concentration, K + Adjusting the surface acidity / alkalinity and electronic structure significantly improves the catalyst's light absorption capacity and carrier separation efficiency under visible light.

[0040] 2. The present invention employs a two-step hydrothermal combined segmented calcination preparation method, and the resulting Ca-K / NiO-ZnO photocatalyst has uniform grain distribution, good interfacial contact and excellent thermal stability, with fully exposed active sites, and aniline degradation efficiency is significantly better than that of undoped or single-doped systems.

[0041] 3. The catalyst of this invention follows a lattice oxygen activation mechanism during the degradation of aniline, where photogenerated holes are preferentially captured by surface lattice oxygen to generate highly active O. - latticeBy combining oxygen vacancy cycling and free radical oxidation pathways, efficient ring-opening and deep mineralization of aniline can be achieved, avoiding the accumulation of toxic intermediates.

[0042] 4. The preparation process of this invention is simple, reproducible, and mild, making it suitable for large-scale production and promising for application in the field of organic wastewater treatment. Attached Figure Description

[0043] Figure 1 This is a scanning electron microscope (SEM) image of the catalyst prepared in Example 1 of this invention.

[0044] Figure 2 This is a morphology image of the catalyst prepared in Example 1 of the present invention under a high magnification microscope.

[0045] Figure 3 This is the XRD pattern of the catalyst prepared in Example 1 of this invention. Detailed Implementation

[0046] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions will be clearly and completely described below in conjunction with the embodiments of this invention.

[0047] Example 1

[0048] The preparation method of Ca-K / NiO-ZnO photocatalyst includes the following steps:

[0049] 1) Add 4.5g of Ni(NO3)2·6H2O and 5.5g of Zn(NO3)2·6H2O to 100mL of water to obtain solution one;

[0050] 2) Add 0.1g of calcium oxide and 0.2g of potassium carbonate to 100mL of water and stir to obtain a homogeneous solution.

[0051] 3) Add solution one to the reaction vessel, place the reaction vessel in an oven at 110℃ for 20h for hydrothermal reaction; cool the reaction system to room temperature, wash with ethanol and deionized water, dry at 60℃ for 2h, and calcine at 400℃ for 6h to obtain NiO-ZnO catalyst;

[0052] 4) The NiO-ZnO catalyst was added to solution two and stirred. 0.56 g of citric acid was added, and stirring continued to obtain a suspension. The suspension was transferred to a reaction vessel and heated at 120℃ for 4.5 h. After natural cooling to room temperature, the precipitate was collected by centrifugation and washed with deionized water and ethanol. It was then dried at 70℃ for 13 h. Next, it was placed in a high-temperature tube furnace and calcined once at 250℃ for 2.5 h, followed by a second calcination at 550℃ for 6 h to obtain the Ca-K / NiO-ZnO photocatalyst. The morphology of the photocatalyst under a scanning electron microscope is shown below. Figure 1As shown, the morphology under high magnification is as follows: Figure 2 As shown, the XRD test pattern is as follows: Figure 3 As shown, the successful synthesis of the Ca-K / NiO-ZnO photocatalyst is demonstrated.

[0053] The application of the catalyst in the degradation of aniline includes the following steps:

[0054] 1) Place 0.2g of catalyst in the photoreactor, with the set temperature of the photoreactor at 150℃ and the pressure at 0.2MPa;

[0055] 2) Add an aniline solution with a concentration of 15 mg / L to the photoreactor, ensuring the solution volume does not exceed the composite catalyst.

[0056] 3) The concentration of aniline was measured after the reaction was completed 9 hours under visible light.

[0057] Example 2

[0058] The preparation method of Ca-K / NiO-ZnO photocatalyst includes the following steps:

[0059] 1) Add 4g of Ni(NO3)2·6H2O and 5g of Zn(NO3)2·6H2O to 100mL of water to obtain solution one;

[0060] 2) Add 0.1g of calcium oxide and 0.1g of potassium carbonate to 100mL of water and stir to obtain a homogeneous solution.

[0061] 3) Add solution one to the reaction vessel, place the reaction vessel in a 100℃ oven for 24 hours for hydrothermal reaction; cool the reaction system to room temperature, wash with ethanol and deionized water, dry at 55℃ for 2 hours, and calcine at 350℃ for 7 hours to obtain NiO-ZnO catalyst;

[0062] 4) Add the NiO-ZnO catalyst to solution 2, stir, add 0.6g of citric acid, continue stirring to obtain a suspension, transfer the suspension to a reactor, heat at 100℃ for 5h, cool naturally to room temperature, centrifuge to collect the precipitate, wash with deionized water and ethanol, dry at 55℃ for 15h; then place it in a high-temperature tube furnace, calcine at 200℃ for 3h, and then calcine at 500℃ for 8h to obtain the Ca-K / NiO-ZnO photocatalyst.

[0063] The application of the catalyst in the degradation of aniline includes the following steps:

[0064] 1) Place 0.2g of catalyst in the photoreactor, with the set temperature of the photoreactor at 120℃ and the pressure at 0.1MPa;

[0065] 2) Add a 10 mg / L aniline solution to the photoreactor, ensuring the solution volume does not exceed the composite catalyst.

[0066] 3) Under visible light, the concentration of aniline was measured after the reaction was completed 8 hours later.

[0067] Example 3

[0068] The preparation method of Ca-K / NiO-ZnO photocatalyst includes the following steps:

[0069] 1) Add 5g of Ni(NO3)2·6H2O and 6g of Zn(NO3)2·6H2O to 100mL of water to obtain solution one;

[0070] 2) Add 0.1g of calcium oxide and 0.3g of potassium carbonate to 100mL of water and stir to obtain a homogeneous solution.

[0071] 3) Add solution one to the reaction vessel, place the reaction vessel in a 120℃ oven for 18 hours for hydrothermal reaction; cool the reaction system to room temperature, wash with ethanol and deionized water, dry at 65℃ for 1 hour, and calcine at 450℃ for 5 hours to obtain NiO-ZnO catalyst;

[0072] 4) Add the NiO-ZnO catalyst to solution 2, stir, add 0.55g of citric acid, continue stirring to obtain a suspension, transfer the suspension to a reactor, heat at 150℃ for 4h, cool naturally to room temperature, centrifuge to collect the precipitate, wash with deionized water and ethanol, dry at 80℃ for 12h; then put it into a high-temperature tube furnace, calcine at 300℃ for 2h, and then calcine at 600℃ for 5h to obtain the Ca-K / NiO-ZnO photocatalyst.

[0073] The application of the catalyst in the degradation of aniline includes the following steps:

[0074] 1) Place 0.2g of catalyst in the photoreactor, with the set temperature of the photoreactor at 200℃ and the pressure at 0.3MPa;

[0075] 2) Add an aniline solution with a concentration of 20 mg / L to the photoreactor, ensuring the solution volume does not exceed the composite catalyst.

[0076] 3) The concentration of aniline was measured after the reaction was completed under visible light for 10 hours.

[0077] Comparative Example 1

[0078] Unlike Example 1, this comparative example does not contain Ca and K doping, but the rest of the preparation methods and steps are the same as in Example 1.

[0079] Comparative Example 2

[0080] Unlike Example 1, this comparative example does not contain Ca doping, but the rest of the preparation methods and steps are the same as in Example 1.

[0081] Comparative Example 3

[0082] Unlike Example 1, this comparative example does not contain K doping, but the rest of the preparation methods and steps are the same as in Example 1.

[0083] Comparative Example 4

[0084] Unlike Example 1, this comparative example uses a one-step hydrothermal method, including the following steps:

[0085] 1) Add 4.5g of Ni(NO3)2·6H2O, 5.5g of Zn(NO3)2·6H2O, 0.1g of calcium oxide and 0.2g of potassium carbonate to 200mL of water to obtain a solution;

[0086] 2) Add the above solution to the reaction vessel, add 0.56g of citric acid, and place the reaction vessel in an oven at 110℃ for 20h for hydrothermal reaction; cool the reaction system to room temperature, wash with ethanol and deionized water, and dry at 70℃ for 13h; then place it in a high-temperature tube furnace and calcine it once at 250℃ for 2.5h, and then calcine it a second time at 550℃ for 6h to obtain Ca-K / NiO-ZnO photocatalyst.

[0087] Comparative Example 5

[0088] Unlike Example 1, this comparative example does not include secondary calcination.

[0089] Comparative Example 6

[0090] Unlike Example 1, in step 2) of this comparative example, 0.08g of calcium oxide and 0.08g of potassium carbonate were added, while the rest of the preparation methods and steps were the same as in Example 1.

[0091] The catalysts prepared in the examples and comparative examples were subjected to performance testing, and the test results are shown in Table 1.

[0092] Table 1 Catalyst performance test results

[0093]

[0094] As can be seen from Table 1, the catalyst prepared by the present invention has a large average specific surface area and average pore size, and a large crushing strength, which is more conducive to improving catalytic performance.

[0095] The catalysts prepared in the above examples and comparative examples were used to catalytically degrade aniline, and the test results are shown in Table 2.

[0096] ;

[0097] η is the degradation rate of aniline, M 反应初 and M 反应后 These represent the aniline concentrations before and after the reaction, respectively.

[0098] Table 2 Detection results of photocatalytic degradation of aniline

[0099]

[0100] Comparative Example 1 did not add CaO or K2CO3, only pure NiO-ZnO was prepared. 2+ The absence of K leads to insufficient lattice distortion, which cannot effectively increase the oxygen vacancy concentration, resulting in a limited number of surface-active lattice oxygens and hindering the lattice oxygen activation pathway; + The absence of Ca-K co-doping results in a lack of alkaline regulation on the catalyst surface, reducing the adsorption capacity for aniline and decreasing the contact efficiency between pollutants and active sites. Without Ca-K co-doping, the band structure of the NiO-ZnO heterojunction is not further optimized, leading to a high recombination rate of photogenerated electron-hole pairs, low quantum efficiency, and a very low degradation rate.

[0101] In Comparative Example 2, without Ca doping, the lattice structure is relatively complete, the generation of active lattice oxygen is limited, the lattice oxygen activation pathway is insufficient, resulting in a low degradation rate.

[0102] In Comparative Example 3, K + The lack of [something] reduces the alkalinity of the catalyst surface, weakens the affinity for aniline, and makes it difficult for pollutants to effectively accumulate near the active sites, resulting in a low degradation rate.

[0103] In Comparative Example 4, a one-step hydrothermal method was used, which did not involve stepwise preparation. This resulted in uneven precipitation of the precursor. Since Ca and K could not be precisely located at oxygen vacancies or surface sites, the generation efficiency of active lattice oxygen was reduced, the lattice oxygen activation mechanism could not be fully utilized, and the complex interactions between the components may lead to particle agglomeration, a decrease in specific surface area, weak interparticle bonding after calcination, and a large number of internal defects. Therefore, the crushing strength decreased sharply.

[0104] In Comparative Example 5, the lack of secondary calcination resulted in insufficient crystallinity of the catalyst, leading to poor activity and stability of lattice oxygen.

[0105] In Comparative Example 6, the doping amount was too small to effectively induce lattice distortion, resulting in limited improvement in oxygen vacancy concentration and weak surface alkalinity regulation.

Claims

1. A method for preparing Ca-K / NiO-ZnO photocatalyst, characterized in that, Includes the following steps: 1) Add Ni(NO3)2·6H2O and Zn(NO3)2·6H2O to water to obtain solution one; 2) Add calcium oxide and potassium carbonate to water and stir to obtain a homogeneous solution. 3) Add solution one to the reactor, place the reactor in an oven at 100-120℃ for 18-24h for hydrothermal reaction; cool the reaction system to room temperature, wash, dry, and calcine at 350-450℃ for 5-7h to obtain NiO-ZnO catalyst; 4) Add the NiO-ZnO catalyst to solution 2, stir, add citric acid, and continue stirring to obtain a suspension. Transfer the suspension to a reaction vessel, heat at 100-150℃ for 4-5 hours, cool naturally to room temperature, collect the precipitate by centrifugation, wash, and dry. Then place it in a high-temperature tube furnace and calcine at 200-300℃ for 2-3 hours, and then calcine at 500-600℃ for 5-8 hours to obtain the Ca-K / NiO-ZnO photocatalyst. The mass ratio of calcium oxide, potassium carbonate, Ni(NO3)2·6H2O and Zn(NO3)2·6H2O is 1:(1-3):(40-50):(50-60).

2. The preparation method of the Ca-K / NiO-ZnO photocatalyst as described in claim 1, characterized in that, The ratio of the mass of added citric acid to the total mass of Ni(NO3)2·6H2O and Zn(NO3)2·6H2O is 1:(15-20).

3. The preparation method of the Ca-K / NiO-ZnO photocatalyst as described in claim 1, characterized in that, In step 3), wash with ethanol and deionized water, and dry at 55-65℃ for 1-2 hours.

4. The preparation method of the Ca-K / NiO-ZnO photocatalyst as described in claim 1, characterized in that, In step 4), wash with ethanol and deionized water, and dry at 55-80℃ for 12-15 hours.

5. The Ca-K / NiO-ZnO photocatalyst prepared by the preparation method according to any one of claims 1-4.

6. The application of the photocatalyst as described in claim 5 in the degradation of aniline, characterized in that, Includes the following steps: 1) The photocatalyst is placed in the photoreactor, and the set temperature of the photoreactor is 120-200℃ and the pressure is 0.1-0.3MPa; 2) Add an aniline solution with a concentration of 10-20 mg / L to the photoreactor, ensuring the solution volume does not completely submerge the photocatalyst. 3) After reacting for 8-10 hours under visible light, the concentration of aniline at the end of the reaction was measured.

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