A NiFe2O4 / C heterojunction photocatalyst and its preparation method and application

Abstract

The present invention discloses a NiFe2O 4 / C heterojunction photocatalyst and its preparation method and application belong to the technical field of pollutant emission reduction. 4 / C heterojunction photocatalyst, comprising a carbon rod and NiFe2O4 crystals distributed on the surface of the carbon rod; the NiFe2O 4 / The preparation method of C heterojunction photocatalyst comprises: calcining nickel-containing electroplating sludge, wherein the oxygen concentration in the calcining atmosphere is preferably not higher than 85%. The present invention uses nickel-containing electroplating sludge as raw material, and can prepare NiFe2O3 with stable crystal form and high adsorption through calcination. 4 / C heterojunction photocatalyst, which can not only effectively ensure the photoelectric performance and catalytic performance of the photocatalyst, but also realize the resource utilization of nickel-containing electroplating sludge.

Description

Technical Field

[0001] The present invention belongs to the technical field of pollutant emission reduction, and particularly relates to a method for preparing a NiFe2O4 / C heterojunction photocatalyst by utilizing nickel-containing sludge and application of the catalyst in degrading organic dyes. Background Art

[0002] Over the past few decades, organic dyes have become indispensable materials in the textile, leather, and paper industries, and are also widely used in food processing and agricultural research. This widespread use has led to the generation of large amounts of dye wastewater. These dyes are chemically stable and difficult to decompose in water, causing serious environmental problems.

[0003] Nickel-containing electroplating sludge is a by-product of the electroplating waste liquid treatment process and is classified as HW46 hazardous waste. Solidification landfill and thermal treatment are commonly used to treat electroplating sludge. However, solidification landfill not only occupies a large amount of land resources, but also the metal ions in the electroplating sludge are easily leached during the stacking process, which can easily cause secondary pollution. Although the thermal treatment method can effectively reduce the floor space occupied by electroplating sludge, it can also cause air pollution during the incineration process. Electroplating sludge contains a large amount of transition metal elements, such as Fe, Ni and Zn, which are valuable elements that can be recycled for secondary use. Therefore, the resource utilization of electroplating sludge has become a research hotspot, and there is an urgent need to find a suitable method for treatment. Summary of the Invention

[0004] One of the purposes of the present invention is to provide a NiFe2O 4 / C heterojunction photocatalyst and its preparation method, thereby effectively realizing the resource utilization of nickel-containing electroplating sludge, and preparing the obtained NiFe2O 4 / C heterojunction photocatalyst has high adsorption capacity and can be used in photocatalytic fields such as the photocatalytic degradation of high-concentration and difficult-to-handle organic dyes and the photocatalytic reduction of carbon dioxide.

[0005] The second object of the present invention is to provide a NiFe2O 4 / The application of C heterojunction photocatalyst in the field of photocatalysis can simultaneously realize photocatalysis and resource utilization of nickel-containing electroplating sludge, and can effectively ensure the photocatalytic effect.

[0006] In order to achieve the above object, the technical solution provided by the present invention is:

[0007] The present invention provides a NiFe2O 4 / C heterojunction photocatalyst, the catalyst comprises a carbon rod and NiFe2O4 crystals distributed on the surface of the carbon rod. 4 / The C heterojunction photocatalyst has a stable crystal form, high adsorption, strong photoelectric properties and photocatalytic ability, and can be effectively applied in many photocatalytic fields, such as the photocatalytic degradation of high-concentration and difficult-to-handle organic dyes, and the photocatalytic reduction of carbon dioxide.

[0008] Furthermore, the catalyst's Raman spectrum exhibits distinct D and G bands, with an intensity ratio (ID / IG) of 1.05. This demonstrates the catalyst's high degree of graphitization, which provides active sites during catalysis and exhibits a strong affinity for aromatic compounds, significantly impacting the efficiency of RhB degradation.

[0009] Furthermore, the specific surface area of ​​the catalyst is 80-500m 2 ·g -1 The diameter of the carbon rod is 10-25μm, and the particle size of the NiFe2O4 crystal is 0.8-1.0μm. The catalyst has a large specific surface area, and the carbon rod and NiFe2O4 crystal are large in size, which helps to further ensure the adsorption performance, photoelectric performance and catalytic performance of the catalyst.

[0010] Furthermore, the carbon rod surface is distributed with pores, the pore diameter is 2-4nm, and the pore volume is 0.05-0.3cm 3 ·g -1 The pores on the surface of the carbon rod can adsorb the substances to be reacted, thereby improving the photocatalytic effect of the catalyst.

[0011] Furthermore, the photocatalyst has a saturation magnetization intensity of 17.41-25emu / g and has strong magnetism, so it is easy to separate after use and is convenient for secondary use.

[0012] The present invention also provides a NiFe2O 4 / A method for preparing a C heterojunction photocatalyst, comprising:

[0013] The nickel-containing electroplating sludge is roasted, and the oxygen concentration in the roasting atmosphere is not higher than 85%.

[0014] The present invention uses nickel-containing electroplating sludge as raw material and prepares NiFe2O by roasting. 4 / C heterojunction photocatalyst, on the one hand, the prepared NiFe2O 4 / The C heterojunction photocatalyst has high adsorption capacity and excellent photoelectric and photocatalytic properties, and can therefore be well applied in the field of photocatalysis, such as the photocatalytic degradation of organic dyes and the photocatalytic reduction of carbon dioxide. On the other hand, the present invention can achieve effective resource utilization of nickel-containing electroplating sludge, solving the technical problem of the existing technology that nickel-containing electroplating sludge is difficult to effectively utilize as a resource.

[0015] It should be noted that the control of oxygen concentration in the calcination atmosphere plays a vital role in calcining nickel-containing electroplating sludge. It not only affects the overall structure of the resulting catalyst, but also affects the specific surface area and volume of the carbon rod and NiFe2O4 crystals, as well as the crystallinity of NiFe2O4. Specifically, when the oxygen concentration is too high (greater than 85%), the carbon rod structure will disappear, causing the NiFe2O4 particles to easily agglomerate, affecting the photoelectric performance and catalytic effect of the catalyst; and as the oxygen concentration decreases, the crystallinity of NiFe2O4 will decrease, especially when the oxygen concentration is lower than 10%, Ni 0.4 Fe 2.6 Low-valent iron-nickel oxides such as O4 and Fe3O4 can affect the catalytic ability of the resulting catalyst. In summary, when calcining nickel-containing electroplating sludge, the oxygen concentration in the calcining atmosphere is preferably controlled at 10%-30%, and more preferably at 10%-15%. This ensures that NiFe2O4 crystals are evenly attached to the surface of the carbon rod and that there are obvious pores on the carbon rod surface, thereby optimizing the adsorption, photoelectric, and catalytic properties of the catalyst.

[0016] Furthermore, the calcination conditions include a calcination temperature of 800-1100°C and a calcination time of 4-6 hours. The higher the calcination temperature and the longer the calcination time, the higher the crystallinity of the resulting catalyst. Therefore, considering the crystallinity of the resulting catalyst and production cost, the calcination temperature is controlled to be 800-1100°C and the calcination time is controlled to be 4-6 hours.

[0017] Furthermore, the method further comprises: drying and / or crushing the nickel-containing electroplating sludge, wherein the particle size of the electroplating sludge obtained after crushing is 200-400 meshes.

[0018] Furthermore, the nickel-containing electroplating sludge comprises the following components by mass percentage: Fe2O3: 35.34%-37.62%, NiO: 20.6%-23.02%, SO3: 35.26%-38.26%, SiO2: 5.69%-5.82%, and a carbon content of 25.62%-35.23% (the carbon content is determined by an industrial analytical combustion method using an infrared carbon-sulfur analyzer. The carbon in the nickel-containing electroplating sludge is primarily derived from organic substances such as carbon fiber polymer filter cloth in the electroplating sludge). It should be noted that the mass percentages of the various components in the nickel-containing electroplating sludge in this application are not subject to specific limitations on the aforementioned sludge components, as long as the requirements for Fe, Ni elements, and the formation of a carbon rod structure for the prepared catalyst are met.

[0019] The present invention also provides a NiFe2O as described in the present invention or prepared by any method of the present invention.4 / The application of C heterojunction photocatalysts in the field of photocatalysis specifically includes but is not limited to the photocatalytic degradation of organic dyes and the photocatalytic reduction of carbon dioxide.

[0020] Specifically, Fe and Ni in the catalyst, as transition metal elements, have strong catalytic ability, while the carbon structure has good electrical conductivity, which can accelerate the transfer of electrons during the catalytic process, thereby improving the degradation effect of high-concentration organic dyes and the reduction effect of carbon dioxide.

[0021] In summary, the technical solution provided by the present invention can achieve the following beneficial effects compared with the prior art:

[0022] (1) NiFe2O of the present invention 4 / C heterojunction photocatalyst uses carbon rods as carriers, and NiFe2O4 crystals are evenly distributed on the surface of the carbon rods. This catalyst has high adsorption and excellent photoelectric and catalytic properties, so it can be well applied in the field of photocatalysis, such as the photocatalytic degradation of organic dyes and the photocatalytic reduction of carbon dioxide.

[0023] (2) NiFe2O of the present invention 4 / C heterojunction photocatalyst, the carbon rod surface is distributed with pores, which can further improve the adsorption performance of the catalyst. For example, it can adsorb the organic matter to be treated and then degrade it, which is beneficial to improve its photocatalytic effect.

[0024] (3) The present invention uses nickel-containing electroplating sludge as raw material and prepares NiFe2O3 with stable crystal form and high adsorption capacity by roasting. 4 / C heterojunction photocatalyst, thereby effectively ensuring the photoelectric and catalytic properties of the photocatalyst, while also realizing the resource utilization of nickel-containing electroplating sludge. At the same time, the preparation process of the present invention is simple and can fully utilize the carbon-containing substances and transition metals in the nickel-containing electroplating sludge without adding any chemical reagents.

[0025] (4) The photocatalyst prepared by the present invention can be applied in the field of photocatalysis, for example, it can be used to treat high-concentration, difficult-to-treat organic dyes. When treating high-concentration, difficult-to-treat organic dyes, the persulfate can be directly catalyzed to degrade the organic dyes. The conditions are easy to achieve and the process is green and environmentally friendly.

[0026] (5) The photocatalyst prepared by the present invention can be applied to the photocatalytic reduction of carbon dioxide, thereby effectively solving the problem of relatively high preparation cost of existing CO2 photocatalysts and realizing resource utilization of electroplating sludge. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1(a), Figure 1(b), and Figure 1(c) are scanned images of the catalysts prepared in Example 1, Example 2, and the comparative example of the present invention, respectively;

[0028] Figure 2 The phase composition of the catalysts prepared in Example 1, Example 2 and the comparative example of the present invention;

[0029] Figure 3 The Raman spectra of the catalysts prepared in Example 1, Example 2 and the comparative example of the present invention are shown;

[0030] Figure 4 The photoelectric performance test comparison results of the catalysts prepared in Example 1, Example 2 and the comparative example of the present invention are shown;

[0031] Figure 5 This is a comparison chart of the adsorption and degradation effects of the catalysts prepared in Example 1, Example 2 and the comparative example on RhB;

[0032] Figure 6 The magnetic properties of the catalyst in Example 1 are tested.

[0033] Figure 7 is the catalytic reduction efficiency of carbon dioxide by the catalyst in Examples 9-11. DETAILED DESCRIPTION

[0034] The present invention provides a photocatalyst comprising a carbon rod structure and NiFe2O4 crystals distributed on the surface of the carbon rod. Specifically, the photocatalyst is prepared by calcining a raw material containing electroplating sludge at a temperature of 800-1100°C and a calcination time of 4-6 hours. The Fe2O3 in the electroplating sludge reacts with NiO to form NiFe2O4 crystals upon calcination. The organic polymer in the electroplating sludge is calcined to form a porous carbon rod structure, with the NiFe2O4 crystals distributed on the surface of the carbon rod.

[0035] The present invention uses a raw material containing electroplating sludge as a reaction raw material and calcines it to produce a photocatalyst. The photocatalyst can be used for the photocatalytic degradation of organic dyes, the photocatalytic reduction of carbon dioxide, and other photocatalytic fields. The choice of calcination temperature and time affects the structural morphology and phase composition of the resulting catalyst. When the calcination temperature is too low, NiFe2O4 crystals cannot form. When the calcination temperature is too high, the NiFe2O4 crystals will sinter and agglomerate. A calcination time that is too short will also affect the crystallinity of the NiFe2O4 crystals.

[0036] It should be noted that the above-mentioned raw materials containing electroplating sludge may contain only electroplating sludge, or other substances may be added as needed; at the same time, the above-mentioned roasting temperature includes any numerical range within the above-mentioned numerical range, such as 800-900℃, 850-950℃, 900-950℃ or 950-1100℃, etc., and also includes any specific numerical value within the range of 800-1100℃, such as 800℃, 850℃, 870℃, 890℃, 900℃, 930℃, 970℃ or 1100℃, etc.; similarly, the roasting time can also be selected as 4-5h, 4.5-5.5h, 5-6h, 4h, 4.5h, 5h, 5.5h or 6h, etc.

[0037] In addition, the oxygen concentration in the calcination atmosphere has an important influence on the structural morphology of the prepared catalyst. When the oxygen concentration in the calcination atmosphere is too high (volume concentration is higher than 85%), the obtained catalyst is mainly composed of NiFe2O4 particles. As the oxygen concentration decreases (lower than 85%), a carbon rod structure exists in the catalyst, and NiFe2O4 crystals (particles) are distributed on the surface of the carbon rod, and pores are formed on the surface of the carbon rod. The pores can adsorb the catalytic substance, such as carbon dioxide, which is beneficial to the subsequent reaction and can effectively improve the efficiency of the catalytic reaction. However, when the oxygen concentration in the calcination atmosphere is reduced to a certain level, the pores on the surface of the carbon rod are significantly reduced, and the specific surface area of ​​the obtained catalyst is reduced, thereby affecting the photocatalytic effect. The oxygen concentration in the calcination atmosphere in the present invention is preferably 0-85%, more preferably 10-40%, and even more preferably 10-15%.

[0038] In order to further understand the content of the present invention, the present invention is now described in detail in conjunction with specific embodiments. However, it should be noted that the following embodiments only represent some examples of the present invention, and the actual protection scope is not limited by the embodiments.

[0039] Example 1

[0040] This embodiment provides a NiFe2O 4 / The preparation method of C heterojunction photocatalyst comprises the following steps:

[0041] Step 1: Prepare the raw materials

[0042] (1) Drying the nickel-containing electroplating sludge; in this embodiment, the nickel-containing electroplating sludge comprises the following components by weight: Fe2O3: 37.62%, NiO: 21.3%, SO3: 35.26%, SiO2: 5.82%, and a carbon content of 30.05%. In this embodiment, the electroplating sludge is nickel-containing electroplating sludge generated during the production process of Baosteel Zhanjiang Iron and Steel Co., Ltd., but the type and source of the electroplating sludge are not limited.

[0043] (2) The nickel-containing electroplating sludge is crushed by a crusher and sieved to obtain nickel-containing electroplating sludge with a particle size of 200 mesh.

[0044] Step 2: Calcination

[0045] (1) The nickel-containing electroplating sludge powder was placed in a crucible and calcined at 1000°C for 4 hours in an atmosphere with an oxygen concentration of 15% to obtain NiFe2O 4 / C heterojunction photocatalyst.

[0046] The catalyst prepared in this example was applied to the photocatalytic degradation of organic dyes. The specific application experimental process is as follows:

[0047] (1) Rhodamine b (RhB) and deionized water were mixed in a beaker to prepare a 100 ppm RhB solution;

[0048] (2) The NiFe2O4 / C catalyst prepared in this example was added to a beaker and reacted in the dark for 60 minutes, and the change in the concentration of RhB was recorded. Then, 5 mg of persulfate was added to the beaker, and the concentration change was recorded every 20 minutes. The reaction lasted for 120 minutes.

[0049] Example 2

[0050] The NiFe2O 4 / The preparation method of C heterojunction photocatalyst is basically the same as that of Example 1, except that the oxygen concentration in the calcination atmosphere in this embodiment is 0%.

[0051] Comparative Example

[0052] The NiFe2O 4 / The preparation method of C heterojunction photocatalyst is basically the same as that of Example 1, except that the oxygen concentration in the calcination atmosphere in this comparative example is 90%.

[0053] The SEM structures and BET characterizations of the catalysts prepared in Example 1, Example 2, and the comparative example are shown in Figure 1 and Table 1, respectively. It can be seen from Figures 1(a), 1(b), and 1(c) that when the oxygen concentration is too high (greater than 85%), the carbon rod structure in the catalyst disappears, and the NiFe2O4 crystals undergo sintering and agglomeration. However, as the oxygen concentration decreases, the carbon rod structure is retained, and the NiFe2O4 crystals are evenly distributed on the carbon rod structure (the size of the NiFe2O4 crystals is 0.8-1.0 μm), and there are certain pores on the surface of the carbon rods. However, when the oxygen concentration decreases to a certain level (less than 10%), the carbon rods become smoother, and their surface pores are significantly reduced, resulting in a decrease in the specific surface area of ​​the catalyst. At the same time, it can be seen from Table 1 that the specific surface area and pore volume of the catalyst in Example 1 are greater than those in Example 2, and the pore diameter is smaller than that in Example 2.

[0054] Table 1 BET analysis of catalysts prepared in different examples

[0055]

[0056] The phase compositions (XRD patterns) of the catalysts prepared in Example 1, Example 2 and the comparative example are as follows: Figure 2 As shown by Figure 2 It can be seen that after the electroplating sludge was treated at high temperature, a clear crystalline phase appeared. Under high concentration of O2, the crystallinity of NiFe2O4 was the highest. However, in the absence of oxygen, Ni 0.4 Fe 2.6 The appearance of low-valent iron-nickel oxides such as O4 and Fe3O4 indicates that under the condition of insufficient oxygen supply, Fe and Ni ions are not completely oxidized to NiFe2O4, and its crystallinity is not high.

[0057] like Figure 3 Shown are Raman spectra of the catalysts prepared in Examples 1, 2, and the comparative example, further confirming the presence of carbon rod structures in Examples 1 and 2. Both Examples 1 and 2 exhibit distinct D and G bands, with an intensity ratio (ID / IG) of 1.05, indicating a high degree of graphitized structures in the samples. These graphitized structures serve as active sites in the catalytic process and exhibit a strong affinity for aromatic compounds, which is crucial for the efficient degradation of RhB.

[0058] The photoelectric properties of the catalysts prepared in Example 1, Example 2 and Comparative Example 1 were tested. Figure 4 As shown. Among them, Figure 4 -(a) is the transient photocurrent response. It can be seen from the figure that the photoelectric performance of Example 1 is the best, and the photoelectric performance of the catalyst prepared in the comparative example is the worst. Figure 4-(b) is the impedance of each catalyst. The smaller the radius, the smaller the impedance. It can be clearly seen from the figure that the radius of the catalyst prepared in Example 1 is the smallest, so its impedance is the smallest. Figure 4 (c) The conductivity of the different catalysts was tested using cyclic voltammetry. It can be observed that Example 1 has the largest area, while the comparative example has the smallest area. This analysis demonstrates that as the oxygen concentration in the calcination atmosphere decreases, the carbon rod structure in the resulting catalyst is preserved, effectively improving the catalyst's conductivity. However, when the oxygen concentration decreases to a certain level, the carbon rod radius increases, the NiFe2O4 crystal size also increases, and the porosity on the carbon rod surface decreases, leading to a decrease in the conductivity of the resulting catalyst. The photoelectric performance of the resulting catalyst is optimal when the oxygen concentration in the calcination atmosphere is between 10% and 15%.

[0059] The catalysts prepared in Example 1, Example 2 and Comparative Example 1 were used to photocatalytically degrade RhB, and the concentration change of RhB was detected, and the adsorption and degradation efficiency were calculated. The results are as follows: Figure 5 As shown in the figure, the comparative example and Example 2 have almost no adsorption capacity during the dark reaction phase, while Example 1 exhibits high adsorption characteristics, absorbing approximately 60% of the RhB within 60 minutes. During the light reaction phase, Examples 1 and 2 also have better photocatalytic persulfate degradation capabilities for RhB, with degradation rates reaching 97% and 90%, respectively.

[0060] The magnetic properties of Example 1 were measured using a vibrating sample magnetometer at room temperature. Figure 6 The catalyst prepared in Example 1 exhibited a saturation magnetization of 17.41 emu / g in the absence of a hysteresis loop or remanence, clearly demonstrating its superparamagnetic properties. This superparamagnetism makes it easier to recover after the reaction, thereby reducing separation costs and process complexity.

[0061] Example 3

[0062] The NiFe2O 4 / The preparation method of C heterojunction photocatalyst is basically the same as that of Example 1, except that the oxygen concentration in the calcination atmosphere in this embodiment is 13%. 4 / The structure and performance of the C heterojunction photocatalyst are relatively close to those in Example 1.

[0063] Example 4

[0064] The NiFe2O 4 / The preparation method of C heterojunction photocatalyst is basically the same as that of Example 1, except that the oxygen concentration in the calcination atmosphere in this embodiment is 10%. 4 / The structure and performance of the C heterojunction photocatalyst are relatively close to those of Example 1, and the grain size of its NiFe2O4 and the pore size on the carbon rod surface are slightly larger than those of Example 1.

[0065] Example 5

[0066] The NiFe2O 4 / The preparation method of C heterojunction photocatalyst is basically the same as that of Example 1, except that the oxygen concentration in the calcination atmosphere in this embodiment is 8%.

[0067] Example 6

[0068] The NiFe2O 4 / The preparation method of C heterojunction photocatalyst is basically the same as that of Example 1, except that the oxygen concentration in the calcination atmosphere in this embodiment is 5%.

[0069] NiFe2O prepared in Example 5 and Example 6 4 / The structure of the C heterojunction photocatalyst is similar to that of Example 1, but the diameter of the carbon rod becomes thicker, and the grain size of NiFe2O4 increases significantly. The pores on the surface of the carbon rod also decrease, and the pore diameter increases. The photoelectric performance and catalytic degradation effect of this catalyst are worse than those of Example 1.

[0070] Example 7

[0071] The NiFe2O 4 / The preparation method of C heterojunction photocatalyst is basically the same as that in Example 1, with the main differences being: in this embodiment, the calcination temperature is 800°C, the calcination time is 6 hours, the particle size of the nickel-containing electroplating sludge particles is 300 mesh, and the nickel-containing electroplating sludge in this embodiment contains the following components in percentage by mass: Fe2O3: 35.34%, NiO: 20.6%, SO3: 38.26%, SiO2: 5.8%, and the carbon content is 25.62%.

[0072] Example 8

[0073] The NiFe2O 4 / The preparation method of C heterojunction photocatalyst is basically the same as that in Example 1, with the main differences being: in this embodiment, the calcination temperature is 1100°C, the calcination time is 5 hours, the particle size of the nickel-containing electroplating sludge particles is 400 mesh, and the nickel-containing electroplating sludge in this embodiment contains the following components in percentage by mass: Fe2O3: 35.97%, NiO: 23.02%, SO3: 35.32%, SiO2: 5.69%, and the carbon content is 35.23%.

[0074] Example 9

[0075] The NiFe2O 4 / The preparation method of the C heterojunction photocatalyst was the same as in Example 1 and applied to the photocatalytic reduction of CO2. The specific process was as follows: 10 mg of NiFe2O4 / C catalyst, 100 μL of deionized water, and 5 ml of ethyl acetate were placed in a sealed glass bottle. The gas in the glass bottle was evacuated and then CO2 was injected. The reaction was then irradiated with a 350W xenon lamp. Samples were taken every hour and the reduction products were detected by gas chromatography. The efficiency of the products CO and CH4 obtained after four hours of photoreduction of CO2 was as follows: Figure 7 shown.

[0076] Example 10

[0077] The NiFe2O 4 / The preparation method of the C heterojunction photocatalyst is basically the same as that of Example 1, with the main difference being that the oxygen concentration in the calcination atmosphere in this embodiment is 100%, and the catalyst obtained is mainly a block structure formed by the accumulation of NiFe2O4 particles (similar to the structure of Comparative Example 1). It is applied to the photocatalytic reduction of CO2 under the same reaction conditions as in Example 9. The reduction product is detected by gas chromatography. The efficiency of the products CO and CH4 obtained after four hours of photoreduction of CO2 is shown as follows: Figure 7 shown.

[0078] Example 11

[0079] The NiFe2O 4 / The preparation method of C heterojunction photocatalyst was the same as that of Example 2 (the oxygen concentration in the calcination atmosphere was 0), and it was applied to the photocatalytic reduction of CO2, and the reaction conditions were the same as those of Example 9. The reduction product was detected by gas chromatography, and the efficiency of the products CO and CH4 obtained after four hours of photoreduction of CO2 was as follows: Figure 7 shown.

[0080] according to Figure 7It can be seen that the catalyst obtained by calcining nickel-containing electroplating sludge can be effectively used in the photocatalytic reduction of CO2. When the oxygen concentration is greater than 85%, there is no carbon rod structure in the obtained catalyst, and the photocatalytic reduction effect of CO2 is the worst. As the oxygen concentration decreases, the carbon rod structure appears in the obtained catalyst, and the NiFe2O 4 / The C crystals adhere to the carbon rod surface, increasing the catalyst's specific surface area and making the NiFe2O4 crystals more evenly distributed. Pores appear on the carbon rod surface, allowing for carbon dioxide adsorption and further enhancing the photocatalytic reduction of carbon dioxide. However, when the oxygen concentration drops below 10%, the carbon rod surface porosity decreases, reducing the catalyst's specific surface area and leading to a decrease in the photocatalytic reduction of CO2. Therefore, the optimal oxygen concentration in the calcination atmosphere is 10-40%, and even more preferably 10-15%, for optimal results.

Claims

1. A NiFe2O4 / C heterojunction photocatalyst, characterized in that: The catalyst comprises a carbon rod and NiFe2O4 crystals distributed on the surface of the carbon rod; the Raman spectrum of the catalyst has obvious D band and G band, and the intensity ratio ID / IG of the two is 1.05; The preparation method of the NiFe2O4 / C heterojunction photocatalyst comprises the following steps: calcining nickel-containing electroplating sludge, wherein the oxygen concentration in the calcining atmosphere is lower than 85%.

2. The NiFe2O4 / C heterojunction photocatalyst according to claim 1, characterized in that: The specific surface area of ​​the catalyst is 80-500m 2 ·g -1 , the diameter of the carbon rod is 10-25 μm, and the particle size of the NiFe2O4 crystal is 0.8-1.0 μm.

3. The NiFe2O4 / C heterojunction photocatalyst according to claim 1, characterized in that: The carbon rod surface is distributed with pores, the pore diameter is 2-4nm, and the pore volume is 0.05-0.3cm 3 ·g -1 .

4. The NiFe2O4 / C heterojunction photocatalyst according to claim 1, characterized in that The saturation magnetization intensity of the photocatalyst is 17.41-25 emu / g.

5. A method for preparing a NiFe2O4 / C heterojunction photocatalyst according to any one of claims 1 to 4, characterized in that: include: The nickel-containing electroplating sludge is roasted, and the oxygen concentration in the roasting atmosphere is lower than 85%.

6. The method for preparing the NiFe2O4 / C heterojunction photocatalyst according to claim 5, characterized in that: The calcination conditions include: a calcination temperature of 800-1100° C., a calcination time of 4-6 hours, and an oxygen concentration in the calcination atmosphere of 10-15%.

7. The method for preparing the NiFe2O4 / C heterojunction photocatalyst according to claim 6, characterized in that: The method further comprises the steps of drying and / or crushing the nickel-containing electroplating sludge, wherein the particle size of the electroplating sludge obtained after crushing is 200-400 meshes.

8. The method for preparing the NiFe2O4 / C heterojunction photocatalyst according to any one of claims 5 to 7, characterized in that: The nickel-containing electroplating sludge contains the following components in percentage by mass: Fe2O3: 35.34%-37.62%, NiO: 20.6%-23.02%, SO3: 35.26%-38.26%, SiO2: 5.69%-5.82%, and a carbon content of 25.62%-35.23%.

9. Use of a NiFe2O4 / C heterojunction photocatalyst according to any one of claims 1 to 4, or prepared by the method according to any one of claims 5 to 8, in the field of photocatalysis, wherein the photocatalytic field includes the photocatalytic degradation of organic dyes and the photocatalytic reduction of CO2.

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