Nickel-doped iron oxide catalysts rich in oxygen vacancies and hydroxyl groups, methods of making and applications

Abstract

In order to solve the problems of low activity of iron oxide catalyst and large energy consumption in calcination preparation in the prior art, the application provides a nickel-doped iron oxide catalyst rich in oxygen vacancies and hydroxyl groups, and the general formula is α-Fe 2‑2x Ni 2x O3H, x=0.05, 0.1, 0.2, 0.3, Ni 2+ The catalyst is doped in the iron oxide crystal in the form of isomorphism substitution, Ni-O-Fe bonds are formed, the catalyst surface contains rich oxygen vacancies and active structure hydroxyl groups, and the preparation method is as follows: one, inorganic divalent nickel salt and inorganic trivalent iron salt are dissolved in deionized water, ammonia water is added, stirring is conducted, and pH is adjusted to 9.0-11.0 to obtain a suspension; two, the suspension obtained in the step one is placed in a semi-closed container, so that the crystal is completely developed, and the target product is obtained. The iron oxide catalyst prepared by the application introduces oxygen vacancies and retains active surface hydroxyl groups, and the catalytic efficiency is further improved, the efficiency of activating persulfate to degrade pollutants in water is significantly improved, and the catalyst still has high catalytic activity in the process of multiple cycles.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, specifically relating to a nickel-doped iron hydroxyl oxide catalyst, its preparation method, and its application. Background Technology

[0002] Water pollution has been a pressing and undeniable global problem for decades. Advanced oxidation processes (AOPs) offer rapid degradation, high oxidation efficiency, and effective degradation of various environmental pollutants, making them promising for widespread application. In recent years, research based on sulfate (SO4)... ·- Advanced oxidation processes, particularly persulfate, are gaining increasing attention due to their efficient degradation of organic compounds. Persulfate can be activated to generate sulfate radicals (SO42-). ·- ). Using sulfate free radicals (SO4) ·- Advanced oxidation technologies, primarily based on SO4, are used to address SO4 pollution. ·- Its strong oxidizing properties have been extensively studied.

[0003] Therefore, how to activate persulfate to produce SO4 ·- Photoactivation is currently a hot research topic, and various activation strategies for persulfate have been extensively explored. Known persulfate activation methods include ultraviolet activation, thermal activation, alkaline activation, transition metal ion activation, transition metal oxide activation, and activation using carbon materials and natural minerals. In homogeneous system activation methods, photoactivation and thermal activation rely on external energy, while transition metal ions such as Mn... 2+ Fe 2+ Co 2+ Ag + and Au + While these methods can effectively activate persulfate to generate sulfate radicals, these metal ions are difficult to separate effectively from water, easily causing secondary pollution, and elements such as Ag and Au are relatively expensive. To address the drawbacks of the above methods in activating persulfate, heterogeneous catalysts such as transition metal oxides (e.g., Fe₂O₃, MnO₂, CuO, and Co₂O₃), carbon materials (e.g., activated carbon, carbon nanotubes, graphene, or carbon nitride), and molecular sieves (e.g., MCM-41, ZSM-5, and zeolites) have been extensively studied. Among these, multivalent transition metal oxides (TMOs) have advantages such as low energy input, specific pH conditions, high efficiency, and excellent recovery performance, and are widely used in the isomerization activation of persulfate.

[0004] α-Fe₂O₃, also known as hematite, is widely found in nature, abundant in resources, inexpensive, and safe and non-toxic. Due to these advantages, it is widely used in advanced oxidation processes in water treatment (catalytic ozone oxidation, Fenton-like oxidation, photocatalytic oxidation, etc.). However, because the orbital spin of Fe(III) is relatively stable, it is difficult to achieve orbital crossover and electron transfer between the oxygen atoms at both ends of the peroxy bond in persulfate. Therefore, hematite (α-Fe₂O₃) has relatively low efficiency as a catalyst for activating persulfate, leaving considerable room for improvement. Oxygen vacancies (OVs) are anionic defects formed under specific conditions by the separation of lattice oxygen at the oxide surface, resulting in low binding energies. The introduction of oxygen vacancies can effectively improve the physicochemical properties of materials, enhance the adsorption of oxidants, induce electron rearrangement, improve the orbital spin state of metal atoms, and accelerate the redox cycle between high-valence and low-valence metal ions, thereby strengthening the activation of persulfate. Introducing oxygen vacancies into metal oxides mainly employs the following methods: temperature control—by altering heating temperature, heating rate, elemental ratio, compound ratio, and protective gas residence time, oxygen vacancies are controlled by exposing and adjusting crystal facets or lattice defects in the catalyst; atomic doping substitution—by using dopant ions, metal oxides, and nanoparticles to maintain charge balance, different concentrations of vacancies can be generated by changing the dopant material and type. Temperature control is energy-intensive, and protective gases are expensive, resulting in high overall costs. Forming oxygen vacancies and constructing bimetallic active sites through low-valence metal ion doping in the catalyst structure is an effective strategy for improving material performance.

[0005] However, traditional heteroatom-doped α-Fe₂O₃ often uses α-FeOOH as a precursor for ion doping, forming isomorphously substituted α-FeOOH, which is then calcined to obtain the α-Fe₂O₃ crystal form. This method is not only energy-intensive but also consumes valuable surface hydroxyl groups during calcination, resulting in low pollutant removal rates in activated persulfate-degraded water. Compared to α-Fe₂O₃, which is the most stable crystal structure among iron oxides, α-FeOOH, as its precursor, has an unstable crystal structure. The appearance of oxygen vacancies is often accompanied by changes in the internal electronic structure. If suitable dopant ions are selected and the degree of this electron rearrangement is skillfully controlled, the phase transformation to α-Fe₂O₃ can be achieved at low temperatures, and the valuable surface hydroxyl groups that would otherwise be lost during calcination can be retained, thereby further enhancing its synergistic effect in the activated persulfate-degraded water pollutant degradation. Summary of the Invention

[0006] To address the problems of low activity and high energy consumption in the calcination preparation of existing iron oxide catalysts, this invention proposes a nickel-doped iron oxide catalyst rich in oxygen vacancies and hydroxyl groups, along with its preparation method and application.

[0007] A nickel-doped iron oxide catalyst rich in oxygen vacancies and hydroxyl groups, with the general formula α-Fe 2-2x Ni 2x O3H, x=0.05,0.1,0.2,0.3, Ni 2+ The catalyst is doped into iron oxide crystals by isomorphic substitution to form Ni-O-Fe bonds. The catalyst surface contains abundant oxygen vacancies and active structural hydroxyl groups.

[0008] The catalyst has a specific surface area of ​​120–180 m². 2 / g.

[0009] The catalyst has a magnetic flux density of 20–30 emu / g.

[0010] A method for preparing a nickel-doped iron oxide catalyst rich in oxygen vacancies and hydroxyl groups includes the following steps:

[0011] 1. Dissolve inorganic divalent nickel salt and inorganic trivalent iron salt in deionized water, add ammonia water, stir and adjust the pH to 9.0-11.0 to obtain a suspension;

[0012] 2. Place the suspension obtained in step one in a semi-closed container to allow the crystals to develop completely, and obtain the target product.

[0013] The inorganic divalent nickel salt mentioned in step one is NiCl2, NiSO4, or Ni(NO3)2, and the inorganic trivalent iron salt is FeCl3, Fe2(SO4)3, or Fe(NO3)3.

[0014] In step one, the sum of inorganic divalent nickel salt and inorganic divalent nickel salt and inorganic trivalent iron salt (Ni 2+ :(Ni 2+ +Fe 3+ The molar ratios of )) are 0.05, 0.1, 0.2, and 0.3:1.

[0015] In step two, the crystal development temperature is 50–80℃ and the time is 24–96 hours.

[0016] A method for applying a nickel-doped iron oxide catalyst rich in oxygen vacancies and hydroxyl groups, specifically as follows:

[0017] A. Add the iron oxide catalyst to the aqueous solution containing the pollutants and stir to mix it evenly;

[0018] B. Add NaOH solution and persulfate solution to the above solution simultaneously to adjust the pH of the solution to neutral to initiate the reaction;

[0019] C. After the reaction is complete, the catalyst is recovered and regenerated using a magnet.

[0020] In step A, the catalyst dosage is 50–200 mg / L.

[0021] The persulfate mentioned in step B is one of permonosulfate and perdisulfate, or a mixture of both.

[0022] Principle of this invention:

[0023] This invention utilizes low-valence metal ions (Ni) 2+ The isomorphic substitution strategy introduces oxygen vacancies into α-FeOOH. Due to the instability of the α-FeOOH crystal structure, under the influence of electron rearrangement caused by oxygen vacancies, it undergoes a phase transformation into the more stable α-Fe₂O₃. Furthermore, because the material preparation is carried out at a relatively low temperature, the structural hydroxyl groups on the surface of α-FeOOH are retained, ultimately synthesizing α-Fe₂O₃ rich in oxygen vacancies and surface hydroxyl groups. 2-2x Ni 2x O3H catalytic material. Its activation of persulfate generates reactive oxygen species (ROS) that can efficiently degrade pollutants. Due to the low cost of Ni... 2+ The introduction of oxygen vacancies creates oxygen vacancies on the material surface and exposes more Lewis acid sites, enhancing the complexation with the oxidant. The hydrogen bonding between the H atoms in the surface hydroxyl groups and the O atoms in the oxidant also enhances the adsorption of the oxidant. Furthermore, the introduction of oxygen vacancies enhances the spin of the 3d orbitals of Fe, making it easier for electron transfer to occur between Fe atoms and oxygen atoms in the oxidant, generating ROS (SO42-). ·- ,·OH,O2 ·- , 1 O2 and SO5 ·- ROS attacks pollutants, ultimately transforming them into smaller molecules. During the reaction, metal ions (Ni)... 2+ / Ni 3+ Fe 2+ / Fe 3+ The cycle between them makes α-Fe 2-2x Ni 2x O3H maintains excellent catalytic performance even after multiple cycles of use.

[0024] Beneficial effects

[0025] 1. This invention utilizes Ni 2+ The doping method with α-FeOOH introduces oxygen vacancies, which, under the influence of electron rearrangement, directly transform the substance into α-Fe2O3 while retaining active surface hydroxyl groups. Due to the abundance of surface hydroxyl groups, the adsorption of persulfate is enhanced. The abundance of oxygen vacancies increases the number of active sites, enhancing the complexation and electron transfer with persulfate. Furthermore, the synergistic effect of the bimetallic active sites further improves the catalytic efficiency. The efficiency of activating persulfate to degrade pollutants in water is significantly improved, and it still maintains high catalytic activity during multiple cycles.

[0026] 2. The synthesis of α-Fe in this invention 2-2x Ni 2x O3H materials also have advantages such as easy separation and recycling, and convenient storage and transportation. Attached Figure Description

[0027] Figure 1 The XRD patterns of Example 1, Comparative Example 1, and Comparative Example 2 are shown below.

[0028] Figure 2 The ESR spectra of Example 1, Comparative Example 1, and Comparative Example 2 are shown below.

[0029] Figure 3 The Raman spectra of Example 1, Comparative Example 1, and Comparative Example 2 are shown below.

[0030] Figure 4 The FTIR spectra of Example 1, Comparative Example 1, and Comparative Example 2 are shown below.

[0031] Figure 5 HRTEM images of Example 1, Comparative Example 1, and Comparative Example 2;

[0032] Figure 6 The magnetic curves are those of Example 1, Comparative Example 1, and Comparative Example 2.

[0033] Figure 7 The nitrogen adsorption-desorption curves for Example 1, Comparative Example 1, and Comparative Example 2 are shown.

[0034] Figure 8 This demonstrates the effectiveness of activated PMS in removing CLO from water in Examples 1, 1, and 2.

[0035] Figure 9 To demonstrate the effectiveness of activated PMS in removing CLO from water for recycling purposes;

[0036] Figure 10 The adsorption spectra of pyridine are shown for Example 1 and Comparative Example 2.

[0037] Figure 11 The temperature-dependent dimagnetic susceptibility is shown for Example 1 and Comparative Example 2.

[0038] Figure 12 The ATR-FTIR spectra of Example 1 and PMS in D2O and H2O, respectively;

[0039] Figure 13 The XRD spectra of Example 1, Comparative Example 3, Comparative Example 4 and Comparative Example 5 are shown below.

[0040] Figure 14 The ESR spectra of Example 1, Comparative Example 3, Comparative Example 4 and Comparative Example 5 are shown.

[0041] Figure 15 The FTIR spectra of Example 1, Comparative Example 3, Comparative Example 4, and Comparative Example 5 are shown below.

[0042] Figure 16 The ATR-FTIR spectra of Example 1, Comparative Example 3, Comparative Example 4 and Comparative Example 5 in D2O are shown below.

[0043] Figure 17 Examples 1, 3, 4 and 5 show the activation of PMS to degrade CLO. Detailed Implementation

[0044] A nickel-doped iron oxide catalyst rich in oxygen vacancies and hydroxyl groups, with the general formula α-Fe 2-2x Ni 2x O3H, x=0.05,0.1,0.2,0.3, Ni 2+ The catalyst is doped into iron oxide crystals via isomorphous substitution to form Ni-O-Fe bonds. The catalyst surface contains abundant oxygen vacancies and active hydroxyl groups, and the catalyst specific surface area is 120–180 m². 2 / g, with a magnetic strength of 20-30 emu / g.

[0045] A method for preparing a nickel-doped iron oxide catalyst rich in oxygen vacancies and hydroxyl groups includes the following steps:

[0046] I. Dissolve inorganic divalent nickel salts and inorganic trivalent ferric salts in deionized water, add ammonia, and stir to adjust the pH to 9.0–11.0 to obtain a suspension. The inorganic divalent nickel salt is NiCl2, NiSO4, or Ni(NO3)2, and the inorganic trivalent ferric salt is FeCl3, Fe2(SO4)3, or Fe(NO3)3. The sum of the inorganic divalent nickel salt and the inorganic divalent nickel salt and inorganic trivalent ferric salt (Ni 2+ :(Ni 2+ +Fe 3 + The molar ratios of )) are 0.05, 0.1, 0.2, and 0.3:1;

[0047] 2. Place the suspension obtained in step 1 in a semi-closed container to allow the crystals to develop completely, and obtain the target product. The crystal development temperature is 50-80℃ and the time is 24-96h.

[0048] A method for applying a nickel-doped iron oxide catalyst rich in oxygen vacancies and hydroxyl groups, specifically as follows:

[0049] A. Add the iron oxide catalyst to the aqueous solution containing pollutants and stir to mix it evenly. The catalyst dosage is 50-200 mg / L.

[0050] B. Add NaOH solution and persulfate solution to the above solution simultaneously, adjust the pH of the solution to neutral, and start the reaction. The persulfate is one of permonosulfate (PMS) and perdisulfate (PDS) or a mixture of both.

[0051] C. After the reaction is complete, the catalyst is recovered and regenerated using a magnet.

[0052] Example 1:

[0053] A nickel-doped iron oxide catalyst rich in oxygen vacancies and hydroxyl groups (α-Fe 1.6 Ni 0.4 O3H) material (x=0.2, i.e. (Ni 2+ :(Ni 2+ +Fe 3+ Preparation method of 0.2:1 molar ratio of ))

[0054] 1. Dissolve 0.58g Ni(NO3)2·6H2O and 3.23g Fe(NO3)3·9H2O in a beaker containing 100mL deionized water, stir for 30min to mix the nickel and iron ions evenly, slowly add ammonia water (wt. 25%) dropwise to the mixture until the pH of the solution is 11.0, and continue stirring for 30min.

[0055] 2. Seal the beaker containing the suspension with plastic wrap and place it in a forced-air drying oven at 60°C for 72 hours. Then, separate the precipitate from the suspension by vacuum filtration. Wash the obtained precipitate repeatedly with deionized water until the supernatant is neutral. Finally, dry the precipitate at 60°C for 6 hours to obtain a nickel-doped iron oxide catalyst (α-Fe) rich in oxygen vacancies and hydroxyl groups. 1.6 Ni 0.4 O3H). Specific surface area is 171 m². 2 / g, with a magnetic strength of 24.4 emu / g.

[0056] Example 2:

[0057] Hematite α-Fe, rich in oxygen vacancy-type metal doped material, was prepared using the method described in Example 1. 1.9 Ni 0.1 O3H(x=0.05, that is (Ni 2+ :(Ni 2+ +Fe 3+ The molar ratio of Ni(NO3)2·6H2O and Fe(NO3)3·9H2O was 0.15 g and 3.84 g, respectively, and the remaining preparation conditions were the same as in Example 1. The specific surface area was 123 m². 2 / g, with a magnetic strength of 6.0 emu / g.

[0058] Using α-Fe 1.9 Ni 0.1 O3H activated PMS to degrade thiamethoxam (CLO), CLO concentration 1.0 mg / L, PMS concentration 100 mg / L, α-Fe 1.9 Ni 0.1 With an O3H dosage of 200 mg / L and a pH of 7.0, CLO achieved a removal rate of 86.3% within 30 minutes.

[0059] Example 3:

[0060] Hematite α-Fe, rich in oxygen vacancy-type metal doped material, was prepared using the method described in Example 1. 1.8 Ni 0.2 O3H(x=0.1, that is (Ni 2+ :(Ni 2+ +Fe 3+ The molar ratio of Ni(NO3)2·6H2O and Fe(NO3)3·9H2O was 0.29 g and 3.64 g, respectively, and the remaining preparation conditions were the same as in Example 1. The specific surface area was 140 m². 2 / g, magnetic strength is 8.4 emu / g

[0061] Using α-Fe 1.8 Ni 0.2 O3H activated PMS to degrade CLO, CLO concentration 1.0 mg / L, PMS dosage 100 mg / L, α-Fe 1.8 Ni 0.2 With an O3H dosage of 200 mg / L and a pH of 7.0, CLO achieved a removal rate of 88.0% within 30 minutes.

[0062] Example 4:

[0063] Hematite α-Fe, rich in oxygen vacancy-type metal doped material, was prepared using the method described in Example 1. 1.4 Ni 0.6 O3H(x=0.3, that is (Ni 2+ :(Ni 2+ +Fe 3+ The molar ratio of Ni(NO3)2·6H2O and Fe(NO3)3·9H2O was 0.87 g and 2.83 g, respectively, and the remaining preparation conditions were the same as in Example 1. The specific surface area was 152 m². 2 / g, with a magnetic strength of 10.4 emu / g.

[0064] Using α-Fe 1.4 Ni 0.6O3H activated PMS to degrade CLO, CLO concentration 1.0 mg / L, PMS dosage 100 mg / L, α-Fe 1.4 Ni 0.6 With an O3H dosage of 200 mg / L and a pH of 7.0, CLO achieved a removal rate of 83.7% within 30 minutes.

[0065] Comparative Example 1:

[0066] The synthesis process of Comparative Example 1 was the same as that of Example 1, but Ni(NO3)2·6H2O was not added.

[0067] Comparative Example 2:

[0068] Comparative Example 2 was obtained by calcining Comparative Example 1 in a muffle furnace at a high temperature of 400°C for 2 hours.

[0069] Comparative Example 3:

[0070] Comparative Example 3 was obtained by calcining Example 1 in a muffle furnace at a high temperature of 200°C for 2 hours.

[0071] Comparative Example 4:

[0072] Comparative Example 4 was obtained by calcining Example 1 in a muffle furnace at a high temperature of 400°C for 2 hours.

[0073] Comparative Example 5:

[0074] Comparative Example 5 was obtained by calcining Example 1 in a muffle furnace at a high temperature of 600°C for 2 hours.

[0075] Example 5:

[0076] A method for applying a nickel-doped iron oxide catalyst rich in oxygen vacancies and hydroxyl groups includes the following steps:

[0077] 1. The α-Fe prepared in Example 1 1.6 Ni 0.4 O3H material was added to water containing pollutants and mixed evenly using magnetic stirring to obtain a mixture; α-Fe 1.6 Ni 0.4 The O3H catalyst dosage was 200 mg / L, and the target pollutant was thiamethoxam (CLO) at a concentration of 1.0 mg / L.

[0078] 2. Add NaOH solution and persulfate solution to the above solution simultaneously to adjust the pH of the solution to neutral to start the reaction. The persulfate solution is a PMS solution with a concentration of 100 mg / L, and the NaOH solution has a concentration of 0.2 mol / L.

[0079] 3. After the catalytic reaction is complete, the catalyst is recovered using a magnet, washed with distilled water, and dried at 60°C.

[0080] Testing and Analysis:

[0081] Figure 1 The XRD patterns of Example 1, Comparative Example 1, and Comparative Example 2 are shown below. Figure 1 It can be seen that without Ni 2+ In the doped case, Comparative Example 1 exhibits the standard α-FeOOH crystal form, perfectly matching the standard crystal form PDF#29-0713; through Ni 2+ After isomorphic substitution doping, Example 1 exhibits the α-Fe₂O₃ crystal form, consistent with the standard crystal form PDF#33-0664. Simultaneously, Comparative Example 2, formed after calcination of Comparative Example 1, also exhibits the standard α-Fe₂O₃ crystal form. This demonstrates that Ni... 2+ Following isomorphic substitution doping, electron rearrangement occurred within α-FeOOH, resulting in a phase transformation to α-Fe2O3. Detailed tests and analyses were conducted regarding the changes in its electronic structure and physicochemical properties.

[0082] Figure 2 The ESR spectra of Example 1, Comparative Example 1, and Comparative Example 2 are shown. The ESR spectra reveal the formation of oxygen vacancies. As can be seen from the figures, no oxygen vacancy signal was observed in Comparative Example 1 or the calcined Comparative Example 2. However, in Ni-doped samples… 2+ The catalyst in Example 1 exhibited a distinct ESR signal belonging to oxygen vacancies, indicating that low-valence Ni... 2+ The isomorphous material replaced the Fe in the original structure. 3+ This leads to a charge imbalance within the structure, causing oxygen atoms on the catalyst surface to escape in order to balance the charge, resulting in abundant oxygen vacancies. The electron rearrangement caused by oxygen vacancies is also the main reason for the phase transformation of α-FeOOH to α-Fe2O3.

[0083] Figure 3 The images show the Raman spectra of Example 1, Comparative Example 1, and Comparative Example 2. Raman spectroscopy is highly sensitive to disorder in crystal structures; changes in Raman characteristic peaks often correspond to increases or decreases in electron density within the crystal structure. Figure 3 As shown, Example 1 exhibits a blue shift of its characteristic peak compared to Comparative Examples 1 and 2. This indicates that oxygen vacancies lead to an increase in local electron density, thereby increasing the vibrational frequency, which is also a manifestation of electron rearrangement.

[0084] Figure 4 The images show the FTIR spectra of Example 1, Comparative Example 1, and Comparative Example 2. Figure 4It can be seen that, compared with Comparative Example 1, the peak position corresponding to the Fe-O bond in Example 1 has shifted, and the shift direction is towards the peak position corresponding to the Fe-O bond in Comparative Example 2. This indicates that Ni doping caused a change in the Fe-O intensity, forming Fe-O-Ni, making the Fe-O intensity in Example 1 between Comparative Example 1 and Comparative Example 2. At the same time, it was observed that, compared with Comparative Example 2, Example 1 retained some of the surface structure hydroxyl groups because it was not subjected to high-temperature calcination.

[0085] Figure 5 These are high-resolution transmission electron microscope (HRTEM) images of Example 1, Comparative Example 1, and Comparative Example 2. Figure 5 It can be seen that the main exposed crystal plane of Comparative Example 1 is the (111) plane, and the interplanar spacing is 0.245 nm. However, Ni 2+ In Example 1, the main exposed crystal plane after doping is the (110) plane, which is the same as the exposed crystal plane in Comparative Example 2. However, the interplanar spacing is 0.250 nm, slightly smaller than that of Comparative Example 2 (0.252 nm). This indicates that Ni 2+ Doping not only changes the Fe-O strength and bond length, but also further alters the characteristics of the exposed crystal planes.

[0086] In summary, Ni 2+ Introducing charge doping into α-FeOOH leads to the formation of oxygen vacancies, altering the Fe... 3+ With O 2- The vibrations of the overlapping orbitals even trigger the rearrangement of the electronic structure in its crystal structure, thus lowering the energy barrier of the phase transition and allowing α-FeOOH to transform into the more stable crystalline phase α-Fe2O3 under non-high temperature conditions. The phase transition also improves other physicochemical properties of the catalyst.

[0087] Figure 6 The magnetic curves for Example 1, Comparative Example 1, and Comparative Example 2 are obtained from... Figure 6 It can be seen that the magnetic properties of Example 1 are significantly improved compared to Comparative Example 1 and Comparative Example 2, which is more conducive to magnetic separation and recovery.

[0088] Figure 7 The N2 adsorption-desorption curves for Example 1, Comparative Example 1, and Comparative Example 2 are obtained from... Figure 7 Analysis shows that the specific surface area of ​​Example 1 is 171 m². 2 / g compared to Comparative Example 1 (84m 2 / g) and Comparative Example 2 (39m) 2 The ratios ( / g) are significantly improved, which is more conducive to the contact reaction with PMS.

[0089] Figure 8To assess the degradation efficiency of thiamethoxam in different systems, the reaction conditions were as follows: thiamethoxam concentration 1.0 mg / L, persulfate dosage 100 mg / L, and the dosages for Examples 1, 1 Comparative Example, and 2 were 200 mg / L, with a pH of 7.0. Figure 8 The results show that, compared with PMS alone, the activated PMS in Comparative Example 1 and the activated PMS in Comparative Example 2 can effectively improve the removal effect of CLO, and the removal rate of CLO can reach 100% within 30 minutes. Compared with other systems, the removal rates are increased by 70%, 58% and 25%, respectively.

[0090] Figure 9 Cyclic experiment for the degradation of thiamethoxam in Example 1: Continuing with CLO as the target compound, the α-Fe... 1.6 Ni 0.4 Catalytic efficiency of O3H during multiple cycles. Reaction conditions: thiamethoxam concentration 1.0 mg / L, persulfate dosage 100 mg / L (Example 1 dosage 200 mg / L), pH 7.0. Results showed that Example 1 maintained high catalytic efficiency during multiple cycles, with a CLO removal rate of up to 85% after 5 cycles, indicating strong catalyst reusability.

[0091] To analyze the superior catalytic performance of Example 1 (with the same crystal form) compared to Comparative Example 2, the following analytical tests were performed, and the results are as follows:

[0092] Figure 10 The images show the adsorption spectra of pyridine in Example 1 and Comparative Example 2. These spectra characterize Lewis acid sites on the material surface. Lewis acid sites are generally considered to be sites with an empty orbital that can accept a lone pair of electrons; on metal oxide surfaces, they typically represent exposed metal sites. Figure 10 It can be seen that the surface of Example 1 has more Lewis acid sites than that of Comparative Example 1, that is, more metal active sites are exposed on the surface, which can greatly enhance the complexation and electron transfer with PMS, mainly due to oxygen vacancies.

[0093] Figure 11 The temperature-dependent dimagnetic susceptibility of Example 1 and Comparative Example 2 is derived from... Figure 11 It can be seen that, compared with Comparative Example 2, Example 1 has a lower μ value. eff From 0.45μ B Increased to 0.66μ B This indicates that under the influence of oxygen vacancies, the 3d orbital spin of Fe is enhanced, the number of unpaired electrons increases, and the electron transfer ability to PMS is enhanced.

[0094] Figure 12 The images show the ATR-FTIR spectra of Example 1 and PMS in D2O and H2O, respectively. Figure 12As shown in Figure a, when Example 1 was added to deuterium water, the spectral value at 2467 cm⁻¹ was [value missing]. -1 A distinct Me-OD characteristic peak appears at the metal site, characterizing the formation of hydrolyzed hydroxyl groups. The intensity of this peak decreases significantly after the addition of PMS, indicating that PMS complexes with the surface metal sites by substituting surface hydroxyl groups. Figure 12 As shown in b, after adding HSO5 from Example 1 to the PMS solution, - The characteristic peaks of SO4 decreased significantly, while the characteristic peaks of SO4 decreased significantly. 2- The significantly enhanced characteristic peaks indicate that PMS dissociates from the metal sites after surface complexation, generating oxidatively active species. Therefore, this invention suggests that weakening the occupation of surface metal sites by hydrolyzed hydroxyl groups is beneficial for the adsorption and dissociation of PMS on its surface.

[0095] To verify the role of the structural hydroxyl group in Example 1, the present invention subjected Example 1 to high-temperature calcination at different temperatures (200℃, 400℃ and 600℃). Figure 13 and Figure 14 The XRD and ESR spectra of Examples 1, 3, 4 and 5 are shown respectively. As can be seen from the figure, the four catalysts have the same crystal form, all of which maintain the standard crystal form of α-Fe2O3, and the oxygen vacancy intensity is almost the same. Figure 15 The figures show the FTIR spectra of Example 1, Comparative Example 3, Comparative Example 4, and Comparative Example 5. As can be seen from the figures, the number of structural hydroxyl groups gradually decreases with increasing calcination temperature. Figure 16 The ATR-FTIR spectra of Examples 1, 3, 4 and 5 in D2O are shown in the figure. As can be seen from the figure, the more structural hydroxyl groups on the catalyst surface, the lower the intensity of the hydrolyzable hydroxyl groups formed on the surface. This indicates that the hydrogen bonding between structural hydroxyl groups and hydrolyzable hydroxyl groups can effectively reduce the bonding strength between hydrolyzable hydroxyl groups and metal sites, which will be more conducive to the bonding of PMS to hydrolyzable hydroxyl groups and metal sites. Figure 17 The figures show the efficiency of PMS activation in degrading CLO in Examples 1, 3, 4, and 5. As can be seen from the figures, with the decrease in the number of structural hydroxyl groups, the first-order degradation kinetic rate constant of PMS activation in CLO degradation gradually decreases, and the utilization efficiency of PMS also gradually decreases. In summary, the structural hydroxyl groups in Example 1 help to reduce the occupation of active sites by hydrolyzed hydroxyl groups, improve the complexation efficiency of PMS on the surface, thereby increasing the utilization rate of PMS and the generation efficiency of reactive oxygen species, and enhancing the degradation of pollutants.

[0096] The above are only some embodiments of the present invention. The scope of protection of the present invention is not limited thereto. Any changes made by those skilled in the art within the scope of the claims of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A nickel-doped iron oxide catalyst rich in oxygen vacancies and hydroxyl groups, with the general formula α-Fe 2-2x Ni 2x O3H, x=0.05,0.1,0.2,0.3, Ni 2+ The catalyst is doped into iron oxide crystals by isomorphous substitution to form Ni-O-Fe bonds. The catalyst surface contains abundant oxygen vacancies and active hydroxyl groups. The active hydroxyl group reduces the bonding strength between the hydrolyzed hydroxyl group and the metal site through hydrogen bonding, promoting the adsorption and dissociation of persulfate; the catalyst has a specific surface area of ​​120~180 m². 2 / g, with a magnetic field of 20~30 emu / g; the catalyst does not require high-temperature calcination, but is directly transformed from α-FeOOH to α-Fe2O3 by placing a nickel-iron mixed suspension in a semi-closed container and allowing crystals to develop at 50~80℃ for 24~96 h while retaining surface active hydroxyl groups.

2. The preparation method of the nickel-doped iron oxide catalyst rich in oxygen vacancies and hydroxyl groups according to claim 1 is as follows:

1. Dissolve inorganic divalent nickel salt and inorganic trivalent iron salt in deionized water, add ammonia water, stir and adjust the pH to 9.0~11.0 to obtain a suspension; 2. Place the suspension obtained in step one in a semi-closed container to allow the crystals to develop completely, and obtain the target product.

3. The method for preparing a nickel-doped iron oxide catalyst rich in oxygen vacancies and hydroxyl groups according to claim 2, characterized in that, The inorganic divalent nickel salt mentioned in step one is NiCl2, NiSO4, or Ni(NO3)2, and the inorganic trivalent iron salt is FeCl3, Fe2(SO4)3, or Fe(NO3)3.

4. The method for preparing a nickel-doped iron oxide catalyst rich in oxygen vacancies and hydroxyl groups according to claim 2, characterized in that, In step one, the molar ratio of the inorganic divalent nickel salt to the sum of the inorganic divalent nickel salt and the inorganic trivalent iron salt is 0.05:1, 0.1:1, 0.2:1, or 0.3:

1.

5. The method for preparing a nickel-doped iron oxide catalyst rich in oxygen vacancies and hydroxyl groups according to claim 2, characterized in that, In step two, the crystal development temperature is 50~80℃ and the time is 24~96 h.

6. A method for using the nickel-doped iron oxide catalyst rich in oxygen vacancies and hydroxyl groups as described in claim 1, specifically comprising: A. Add the iron oxide catalyst to the aqueous solution containing the pollutants and stir to mix it evenly; B. Add NaOH solution and persulfate solution to the above solution simultaneously to adjust the pH of the solution to neutral to initiate the reaction; C. After the reaction is complete, the catalyst is recovered and regenerated using a magnet.

7. The method for applying the nickel-doped iron oxide catalyst rich in oxygen vacancies and hydroxyl groups according to claim 6, characterized in that, In step A, the catalyst dosage is 50~200 mg / L.

8. The method for applying the nickel-doped iron oxide catalyst rich in oxygen vacancies and hydroxyl groups according to claim 6, characterized in that, The persulfate mentioned in step B is one of permonosulfate and perdisulfate, or a mixture of both.

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