Manganese dioxide rich in oxygen vacancies and surface hydroxyl groups, preparation and application

Abstract

The present invention relates to a manganese dioxide rich in oxygen vacancies and surface hydroxyl groups, preparation and application, and belongs to the technical field of new material preparation. The present invention utilizes the mechanical force effect to trigger the redox reaction between Mn(VII) and Mn(II) to generate an octahedral [Mn(IV)O6] structural unit, and then generates MnO2, and prepares MnO2 rich in oxygen vacancies and surface hydroxyl groups, and uses it for catalytic oxidation and degradation of organic pollutants. Oxygen vacancies can increase the coordination of unsaturated Mn 3+ Content, and Mn 3+ OH ‑ It has a strong affinity, so that the prepared MnO2 has abundant oxygen vacancies and surface OH ‑ The preparation process is simple and rapid, and the reaction conditions are mild and no organic solvent is required; the prepared MnO2 has the performance of highly efficient activation of persulfate and can generate a large amount of active oxygen species to oxidatively degrade organic pollutants.

Description

Technical Field

[0001] The present invention belongs to the technical field of novel material preparation, and more specifically, relates to a manganese dioxide rich in oxygen vacancies and surface hydroxyl groups, and its preparation and application, and in particular to a method for preparing a highly active catalyst by ball milling mechanochemical method and using the catalyst for degrading phenols, antibiotics and dyes in water. Background Art

[0002] MnO2 is abundant in nature and non-toxic. It is often used to activate persulfate, H2O2 and O3 to oxidize and degrade organic pollutants. The catalytic performance of MnO2 is related to its crystal form, crystallinity, morphology, crystal face, surface chemical composition and specific surface area. Different researchers have reported different or even contradictory results on the effects of crystal form, crystallinity and morphology. Nevertheless, many studies have confirmed that Mn on the surface of MnO2 x+ The oxidation states and oxygen vacancies (V O ) content is a key factor affecting the catalytic performance of MnO2. In particular, V O Not only will it change Mn x+ The electronic structure of Mn x+ It has a strong affinity for electrophilic reagents such as peroxymonosulfate (PMS), which can significantly enhance the catalytic performance of MnO2. O Regulation has received widespread attention.

[0003] V O It is an anion defect in metal oxides, which can increase V by deoxidizing from anion sites or doping low-valent metal ions into cation sites. O The prepared MnO2 can be treated by reduction etching, heat treatment or mechanochemical post-treatment to remove its lattice oxygen (O L For example, by changing the annealing conditions (such as atmosphere, temperature and time) and the parameters of the mechanochemical method (such as ball milling time and rotation speed), the MnO2 can be made to have a moderate V O The content of MnO2 can greatly improve the catalytic activity. In addition, the introduction of low-valent metal ions such as Fe 3+ 、Ce 3+ Cu 2+ The prepared MnO2 not only has surface / subsurface V O , and contains body type V O However, this method usually requires long-term post-calcination treatment (>12h) and / or the use of organic templates, which will reduce the specific surface area of ​​MnO2 or cause secondary pollution. 3+ With Mn 4+ With structural compatibility, Mn 3+can easily enter the MnO2 lattice. However, dissolved Mn 3+ It is extremely unstable in aqueous solution, which makes it difficult to prepare Mn by solvent method. 3+ Doped MnO2. Adding oxalate ions or 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid as a capping agent can inhibit crystal growth and promote Mn 3+ and V O However, organic additives inevitably bring about secondary pollution. Summary of the invention

[0004] The present invention solves the technical problems in the prior art that the preparation of MnO2 rich in oxygen vacancies requires high-temperature calcination, which reduces the specific surface area, and that organic compound additives cause secondary pollution. The present invention provides a method for preparing highly active manganese dioxide at room temperature and pressure and for catalytic degradation of organic pollutants. Permanganate and manganese sulfate are used as raw materials, or permanganate, divalent manganese salt and inorganic anion salt are added to a ball mill for ball milling. The divalent manganese salt is manganese nitrate, manganese chloride, manganese carbonate, manganese oxalate or manganese phosphate, and the inorganic anion salt is sodium sulfate, potassium sulfate, sodium fluoride, potassium fluoride, sodium phosphate or potassium phosphate. The inorganic anion salt is used as a grinding aid, and the high-energy collision between the grinding balls and between the grinding balls and the reactants during the ball milling process is utilized to promote the tetrahedral MnO4 - The Mn(VII) in the octahedral metal center undergoes a redox reaction with the Mn(II) and is converted into an octahedral [Mn(IV)O6] with the participation of H2O adsorbed on the surface; the inorganic anion SO4 2- PO4 3- and F - It can adsorb H2O through hydrogen bonding, thus affecting the reactivity of H2O. In addition, SO4 2- and PO4 3- The structure and ion size of MnO4 - Similarly, it will also affect MnO4 - Therefore, the MnO2 prepared in the presence of these anions has abundant oxygen vacancies and surface OH - The material can efficiently activate peroxymonosulfate to generate active oxygen species, which can then oxidize and degrade organic pollutants in water.

[0005] According to the first aspect of the present invention, a method for preparing manganese dioxide by ball milling mechanochemical method is provided, wherein permanganate and manganese sulfate are added to a ball milling tank for ball milling to make MnO4 - With Mn 2+ Oxidation-reduction reaction occurs to generate Mn 4+ , and at the same time, it is converted into MnO2 with the participation of crystal water of manganese sulfate, permanganate and H2O adsorbed on the surface of manganese sulfate;

[0006] Alternatively, permanganate, divalent manganese salt and inorganic anion salt are added into a ball mill for ball milling, wherein the divalent manganese salt is manganese nitrate, manganese chloride, manganese carbonate, manganese oxalate or manganese phosphate, and the inorganic anion salt is sodium sulfate, potassium sulfate, sodium fluoride, potassium fluoride, sodium phosphate or potassium phosphate, so that MnO4 - With Mn 2+ Oxidation-reduction reaction occurs to generate Mn 4+ At the same time, it is converted into MnO2 with the participation of crystal water of divalent manganese salt, permanganate and adsorbed H2O on the surface of divalent manganese salt.

[0007] Preferably, the molar ratio of the permanganate to manganese sulfate is 0.25-3, or the molar ratio of the permanganate to divalent manganese salt is 0.25-3.

[0008] Preferably, the molar ratio of the divalent manganese salt to the inorganic anion salt is 2:(1-6).

[0009] Preferably, the rotation speed of the ball mill is 200 rpm to 500 rpm, and the ball milling time is 0.1 h to 4.0 h.

[0010] According to another aspect of the present invention, there is provided manganese dioxide prepared by any one of the methods, wherein the manganese dioxide contains oxygen vacancies and surface hydroxyl groups.

[0011] According to another aspect of the present invention, there is provided a use of the manganese dioxide for catalyzing persulfate or ozone to produce singlet oxygen.

[0012] Preferably, the singlet oxygen is used to degrade organic pollutants.

[0013] Preferably, the application is specifically as follows: adding the manganese dioxide to an organic pollutant solution, mixing thoroughly, and then adding persulfate, wherein the manganese dioxide catalyzes the persulfate to produce singlet oxygen, thereby degrading the organic pollutants.

[0014] Preferably, the organic pollutants are phenols, antibiotics and / or organic dyes; and the persulfates are peroxymonosulfate and peroxydisulfate.

[0015] Preferably, the peroxymonosulfate is potassium peroxymonosulfate or sodium peroxymonosulfate.

[0016] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0017] (1) The present invention uses permanganate and divalent manganese salt as raw materials, and inorganic anion salt as grinding aid (when the divalent manganese salt is manganese sulfate, no additional inorganic anion salt is needed), and prepares MnO2 by mechanical ball milling. The reaction conditions are mild, and high temperature, high pressure and organic additives are not required. In this solid phase preparation method, not only can a large amount of MnO2 be prepared simply and quickly, but also the oxygen vacancies in MnO2 and the surface OH can be increased by regulating the types of inorganic anions. - content, promoting PMS adsorption, valence cycle of metal center Mn and lattice oxygen release, and enhancing the performance of activated PMS.

[0018] (2) In the process of preparing MnO2 from the bottom up, the structural unit [Mn(IV)O6] is usually composed of tetrahedral permanganate (MnO4 - ) reduction and octahedral Mn 2+ Oxidation of MnO4 and MnO4 - and H2O. Since each Mn 2+ Surrounded by six anions, H2O interacts with adjacent hydrogen donors / acceptors, so Mn 2+ The chemical environment of H2O will affect the formation of [Mn(IV)O6]. 2+ The spatial structure and size of the surrounding anions (sulfate or phosphate) are similar to those of MnO4 - Similar, favoring Mn 2+ With MnO4 - contact and the redox reaction between the two; Inorganic anions (sulfate, phosphate or fluoride) have strong hydrogen bonding with H2O, which will hinder the O 2- Enter [Mn(IV)O6], thereby generating more oxygen vacancies. Oxygen vacancies can increase the coordination unsaturated Mn 3+ Content, and Mn 3+ OH - It has a strong affinity, so that the prepared MnO2 has abundant oxygen vacancies and surface OH - .

[0019] (3) Ball milling mechanochemical method uses the high-energy collision between the grinding balls and the materials to trigger chemical reactions, which has the advantages of simple process, low cost, high efficiency and easy industrialization. In view of this, the present invention has developed a method for regulating MnO2 oxygen vacancies by mechanochemical method assisted by sulfate, phosphate or fluoride ions, and uses MnO2 for catalytic degradation of organic pollutants.

[0020] (4) The MnO2 prepared by the present invention has the performance of efficiently activating persulfate or ozone to produce singlet oxygen, and the pseudo-first-order apparent rate constant of oxidative degradation of organic pollutants is 2.1 times that of MnO2 prepared by hydrothermal method, and has good recycling performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The invention adopts potassium permanganate and divalent manganese salt as raw materials and prepares MnO2 by ball milling method, and shows X-ray diffraction, infrared absorption spectrum and electron paramagnetic resonance spectrum.

[0022] Figure 2 The invention adopts potassium permanganate and divalent manganese salt as raw materials, sodium sulfate as grinding aid, and the X-ray diffraction, infrared absorption spectrum and electron paramagnetic resonance spectrum of MnO2 prepared by ball milling.

[0023] Figure 3 The figure shows the effect of the MnO2 prepared in the present invention in the absence of a grinding aid to catalyze the degradation of ofloxacin by PMS and the pseudo-first-order rate fitting diagram of the degradation reaction.

[0024] Figure 4 The graph shows the pseudo-first-order reaction rate constant of the degradation of ofloxacin by PMS catalyzed by MnO2 prepared in the presence or absence of sodium sulfate, sodium fluoride or sodium phosphate as a grinding aid and its relationship with the oxygen vacancy concentration.

[0025] Figure 5 This is a diagram showing the effect of using the MnO2 prepared in the present invention as a catalyst and repeatedly using it to catalyze the degradation of ofloxacin by PMS.

[0026] Figure 6 This is a diagram showing the effect of MnO2 prepared in the present invention catalyzing PMS to degrade tetrabromobisphenol A and rhodamine B.

[0027] Figure 7 This is a diagram showing the effect of the degradation of ofloxacin by PMS catalyzed by MnO2 prepared by the present invention and the hydrothermal method in the comparative example. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0029] The present invention provides a method for preparing manganese dioxide and its application in catalytic degradation of organic pollutants, which specifically comprises the following steps:

[0030] Step 1: adding permanganate and manganese sulfate into a ball mill for ball milling, or adding permanganate, divalent manganese salt and inorganic anion salt into a ball mill for ball milling, wherein the inorganic anion salt is sodium sulfate, potassium sulfate, sodium fluoride, potassium fluoride, sodium phosphate or potassium phosphate, wherein the molar ratio of permanganate to manganese sulfate or divalent manganese salt is 1:4-3:1, and the molar ratio of divalent manganese salt to inorganic anion salt is 2:1-1:3; then, adding grinding balls into the ball mill, wherein the ratio of the inner diameter of the ball mill mouth to the diameter of the grinding balls is set at 5:1-40:1, and the mass ratio of the grinding balls to the reaction materials is 10:1-100:1; at normal temperature and pressure, starting a planetary ball mill, wherein the revolution speed of the ball mill is set at 200 rpm to the maximum speed of the ball mill (generally ≤500 rpm), and the ball milling time is 0.10-4.0 h. The product prepared in step 1 is washed with water, dried, and then collected for later use.

[0031] Step 2: Add the MnO2 prepared in the above step 1 to the organic pollutant solution, and set the mass ratio of organic pollutants to MnO2 to 5:1-1:50; adsorb and balance for 30 minutes at normal temperature and pressure with magnetic stirring, and then add an appropriate amount of persulfate to start the degradation reaction of organic pollutants.

[0032] In some embodiments, the divalent manganese salt is one of manganese nitrate, manganese chloride, manganese carbonate, manganese oxalate, manganese phosphate, etc.;

[0033] In some embodiments, the inorganic anion salt is further configured to be sodium sulfate or potassium sulfate.

[0034] In some embodiments, the mass ratio of the grinding balls to the reaction materials is 30:1 to 60:1; and the revolution speed of the ball mill is set to 200 rpm to 400 rpm.

[0035] Example 1

[0036] (1) Add 2.0 g potassium permanganate and divalent manganese salt (one of manganese sulfate, manganese nitrate, manganese chloride or manganese carbonate) in a molar ratio of 2:3 into a dry, clean 250 mL ball mill; add grinding balls so that the mass ratio of grinding balls to reactants is about 47:1; the ball mill and the ball mill cover are connected with a sealing ring. Fix the ball mill on the ball mill, set the speed of the ball mill to 350 rpm, and perform ball milling reaction at room temperature and pressure. After 90 minutes of reaction, remove the ball mill and collect the solid powder. Wash the obtained solid mixture with distilled water and dry it at 60°C to obtain MnO2. According to the different types of anions (X) in the divalent manganese salt, the obtained MnO2 is abbreviated as MnO2-X.

[0037] (2) X-ray diffractometer (XRD) test shows (such as Figure 1When manganese nitrate is used, the obtained MnO2-NO3 is a mixed phase of pyrolusite and ramsdellite (curve 1); MnO2 prepared by using manganese sulfate, manganese chloride or manganese carbonate as divalent manganese salt (i.e. MnO2-CO3 (curve 2), MnO2-Cl (curve 3) and MnO2-SO4 (curve 4)) are all α-MnO2. Fourier transform infrared spectrometer (FT-IR) test shows (such as Figure 1 (b), MnO2-NO3 (curve 1) at 584 and 533 cm -1 The characteristic stretching vibration peaks of Mn-O and Mn-O-Mn of γ-MnO2 appear at 718, 582, 528 and 472 cm -1 The characteristic stretching vibration peaks of Mn-O and Mn-O-Mn of α-MnO2 appear at 1118 and 970 cm -1 The bending vibration peak of Mn(III)-OH appeared, indicating that MnO2-SO4 is rich in Mn(III)-OH. Electron paramagnetic resonance spectroscopy (EPR) test shows (such as Figure 1 (c): The four MnO2-X have a characteristic peak at a g value of about 2.010, which can be attributed to the oxygen vacancy that captures a single electron (V O ·), and V O The EPR intensity of the samples decreases in the following order: MnO2-SO4>MnO2-Cl>MnO2-CO3>MnO2-NO3, indicating that MnO2-SO4 has richer V than the other three MnO2 O ·.

[0038] Under the mechanical action of ball milling, MnO4 - With Mn 2+ Oxidation-reduction reaction occurs to generate Mn 4+ , and at the same time, it is converted into the structural unit of MnO2 [Mn(IV)O6] with the participation of the crystal water of divalent manganese salt, and / or permanganate and H2O adsorbed on the surface of divalent manganese salt, and finally generates MnO2 (Formula 1). 2+ The surrounding anionic species will affect the Mn 2+ With MnO4 - The reaction with NO3 - 、CO3 2- and Cl - In comparison, SO4 2- The spatial structure and size of MnO4 - Similar, favoring Mn 2+ With MnO4 -In addition, SO4 2- It can adsorb H2O through hydrogen bonding, hindering the O 2- In order to supplement the unbalanced charge caused by the oxygen vacancies, the Mn connected to the oxygen vacancies 4+ will be reduced to the unsaturated Mn 3+ , thereby promoting OH - Therefore, MnO2 prepared by manganese sulfate has abundant oxygen vacancies and Mn(III)-OH.

[0039] 2MnO4 - + 3Mn 2+ + 2H2O → 5MnO2 + 4H + (1)

[0040]

[0041] Example 2

[0042] (1) Add 2.0g potassium permanganate and divalent manganese salt (one of manganese nitrate, manganese chloride or manganese carbonate) in a molar ratio of 2:3 to a dry, clean 250mL ball mill; add sodium sulfate so that the molar ratio of sodium sulfate to divalent manganese salt is 1:1; add grinding balls so that the mass ratio of grinding balls to reactants is about 47:1; the ball mill and the ball mill cover are connected with a sealing ring. Fix the ball mill on the ball mill, set the speed of the ball mill to 350rpm, and perform ball milling reaction at room temperature and pressure. After 90 minutes of reaction, remove the ball mill and collect the solid powder. Wash the obtained solid mixture with distilled water and dry it at 60℃ to obtain MnO2.

[0043] (2) XRD test shows (such as Figure 2 In the presence of sodium sulfate, MnO2-NO3 (curve 1), MnO2-CO3 (curve 2) and MnO2-Cl (curve 3) prepared using manganese nitrate, manganese chloride or manganese carbonate as divalent manganese salts are all α-MnO2. FT-IR and EPR tests show that (as shown in Figure 2 b and c), compared with the case without sodium sulfate (curves 1'-3'), the MnO2-NO3 (curve 1), MnO2-CO3 (curve 2) and MnO2-Cl (curve 3) prepared in the presence of sodium sulfate not only have higher -1 The bending vibration peaks of Mn(III)-OH appeared, and the g value was about 2.010 with a stronger V O · peak, indicating that sodium sulfate as a grinding aid can make the prepared MnO2-X rich in Mn(III)-OH and V O ·.

[0044] Example 3

[0045] (1) In order to evaluate the effect of the type of divalent manganese salt on the catalytic performance of the prepared MnO2, the product obtained in step (1) of Example 1 was collected. 15 mg of MnO2 was added to 50 mL of 10 mg L -1 The solution of ofloxacin was placed on a magnetic stirrer for 30 min. After ofloxacin was in adsorption-desorption equilibrium on the catalyst surface, 100 μL of 50 g L -1 PMS solution (add HCl or NaOH dilute solution to the PMS stock solution to adjust the initial pH to 7.0 ± 0.2) was used to start the degradation reaction of oxafloxacin. When the reaction lasted for a certain period of time, 1 mL of the degradation solution was taken out and mixed with 100 μL of 0.5 mol L -1 The sodium thiosulfate solution was mixed and shaken vigorously to terminate the reaction. After filtering out the catalyst with a 0.22 μm water filter membrane, the concentration of ofloxacin remaining in the degradation solution was determined by high performance liquid chromatography (HPLC). Figure 3 As shown in a: After 15 minutes of reaction, the degradation rate of ofloxacin by PMS or MnO2-X alone is almost negligible, while the combination of PMS and MnO2-X can almost completely degrade ofloxacin, and MnO2-SO4 has the highest catalytic performance. The degradation of ofloxacin conforms to the pseudo-first-order reaction kinetics, and the formula is ln(c t / c0)=-kt+m, where c0 and c t are the concentrations of ofloxacin (mg L) at reaction time 0 and t (min) respectively. -1 ), k is the apparent rate constant (min -1 ), m is a constant. By t / c0) and time t are linearly fitted, such as Figure 3 As shown in b, the k of the PMS and MnO2-X system for the degradation of ofloxacin increases in the following order: MnO2-NO3 (0.14min -1 ) <MnO2-CO3(0.20min -1 ) <MnO2-Cl(0.27min -1 ) <MnO2-SO4(0.48min -1 ), indicating that divalent manganese salts affect the catalytic performance of the prepared MnO2-X, where manganese sulfate is used as the Mn 2+ The catalytic performance of MnO2-X prepared by precursor is the highest.

[0046] (2) In order to evaluate the effect of sodium sulfate as a grinding aid on the catalytic performance of the prepared MnO2, the product obtained in step (1) of Example 2 was collected and ofloxacin was degraded according to the method of step (1) of Example 3. The results are shown in FIG. Figure 4 As shown in a: Compared with the case without sodium sulfate, the k of the MnO2-X prepared by using sodium sulfate as a grinding aid to activate PMS to degrade ofloxacin has increased, for example, MnO2-NO3, MnO2-CO3 and MnO2-Cl increased by 2.6, 1.7 and 1.4 times, respectively. In addition, similar phenomena can be observed when sodium sulfate is replaced by potassium sulfate, indicating that the presence of sulfate ions will improve the catalytic performance of the prepared MnO2-X.

[0047] (3) In order to explore the relationship between the structure of the catalyst and its catalytic performance, the apparent rate constant k of the activation of PMS for OFX degradation by MnO2-X was compared with the V of MnO2-X observed by EPR. O The results are shown in Figure 2. Figure 4 As shown in b: k and V O The EPR signal intensity of · shows a positive correlation, indicating that the oxygen vacancy concentration of MnO2-X is the main factor affecting the catalytic performance. O It can not only enhance the adsorption of PMS by the catalyst, but also be beneficial to the adsorption of Mn 4+ / Mn 3+ circulation and the release of lattice oxygen, thereby improving the catalytic performance of MnO2.

[0048] (4) In order to explore the influence of other anionic inorganic salts, sodium fluoride or sodium phosphate was used as a grinding aid. MnO2-NO3, MnO2-CO3 and MnO2-Cl were prepared according to step (1) of Example 2. Compared with the case where no grinding aid was present, the k of the three MnO2-X activated PMS for degradation of ofloxacin prepared by using sodium fluoride as a grinding aid was increased by 30%-60%, respectively; the k of the MnO2-NO3 activated PMS for degradation of ofloxacin prepared by using sodium phosphate as a grinding aid was increased by 70% (e.g. Figure 4 (as shown in c in Figure 1).

[0049] Example 4

[0050] In order to evaluate the reusability of MnO2. Using MnO2-SO4 prepared in step (1) of Example 1 as a catalyst, a degradation experiment of ofloxacin was carried out. The volume of the reaction solution was expanded 10 times (500 mL), and the concentrations of the catalyst, ofloxacin, PMS and other conditions remained unchanged. After the degradation was completed, the used catalyst was collected and washed with water and ethanol, and then dried at 60°C for the next cycle experiment. Since the sampling test resulted in a loss of catalyst mass, the volume of the reaction solution used in the 2nd to 5th cycle experiments was reduced to 400, 300, 200 and 100 mL, respectively, and other conditions such as the catalyst concentration remained unchanged. The results are as follows Figure 5The results show that in 5 uses, ofloxacin can be almost completely degraded after a reaction time of 10 min, and the relative standard deviation of k is about 3.8%, indicating that MnO2 has good recycling performance.

[0051] Example 5

[0052] In order to evaluate the catalytic performance of MnO2 activated PMS in degrading other organic pollutants, 10 mg of MnO2-SO4 prepared in step (1) of Example 1 was added to 50 mL of tetrabromobisphenol A (40 mg L -1 ) or rhodamine B (10 mg L -1 ) solution. Place it on a magnetic stirrer to react for 30 minutes. After the organic pollutants are in adsorption-desorption equilibrium on the catalyst surface, add 100 μL 50 g L -1 PMS solution was used to start the degradation reaction. After a certain period of reaction, 1 mL of the degradation solution was taken out and mixed with 100 μL of 0.5 mol L -1 The sodium thiosulfate solution was mixed and shaken vigorously to terminate the reaction. After filtering out the catalyst with a 0.22 μm water filter membrane, the concentration of tetrabromobisphenol A or rhodamine B remaining in the degradation solution was measured at 310 nm and 554 nm respectively by UV-visible spectrophotometry. The results are as follows: Figure 6 As shown in a and b: PMS or MnO2-SO4 alone can hardly degrade tetrabromobisphenol A and rhodamine B; when PMS and MnO2-SO4 are used at the same time, tetrabromobisphenol A and rhodamine are almost completely degraded after 30 and 45 minutes of reaction respectively, indicating that the MnO2 / PMS system can efficiently degrade a variety of organic pollutants.

[0053] Example 6

[0054] In order to better reflect the advantages of the present invention, Figure 7 The degradation of ofloxacin by MnO2-SO4 and MnO2 activated PMS prepared by hydrothermal method is shown. As can be seen from the figure, when MnO2-SO4 is used as a catalyst (curve 1), ofloxacin can be completely degraded within 10 minutes, and the pseudo-first-order apparent degradation reaction rate is 0.48min -1 ; The hydrothermal method for preparing MnO2 (curve 2) requires 20 min, and the pseudo-first-order apparent degradation reaction rate is 0.23 min -1 , which is 47.9% of that of the MnO2-SO4 system. The above indicates that the MnO2 prepared by the present invention has the performance of highly efficient catalysis of PMS.

[0055] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A ball milling mechanochemical method for preparing nanostructured ... − A method for producing manganese dioxide, characterized in that Permanganate, divalent manganese salt and inorganic anion salt are added into a ball mill for ball milling. The divalent manganese salt is manganese nitrate, manganese chloride, manganese carbonate, manganese oxalate or manganese phosphate. The inorganic anion salt is sodium sulfate, potassium sulfate, sodium fluoride, potassium fluoride, sodium phosphate or potassium phosphate. − With Mn 2+ Oxidation-reduction reaction occurs to generate Mn 4+ , and at the same time, it is converted into MnO2 with the participation of crystal water of divalent manganese salt, permanganate and H2O adsorbed on the surface of divalent manganese salt; The inorganic anion salt is a grinding aid, which utilizes the high-energy collision between the grinding balls and between the grinding balls and the reactants during the ball milling process to promote the tetrahedral MnO4 − The Mn(VII) in the octahedral metal center undergoes a redox reaction with the Mn(II) and is converted into an octahedral [Mn(IV)O6] with the participation of H2O adsorbed on the surface; the inorganic anion SO4 2− PO4 3− or F − It is used to adsorb H2O through hydrogen bonding, thereby affecting the reactivity of H2O.

2. The ball mill mechanochemical method as claimed in claim 1 is used to prepare a nanostructured ... − A method for producing manganese dioxide, characterized in that The molar ratio of the permanganate to the divalent manganese salt is 0.25-3.

3. The ball mill mechanochemical method as claimed in claim 1 is used to prepare a nanostructured ... − A method for producing manganese dioxide, characterized in that The molar ratio of the divalent manganese salt to the inorganic anion salt is 2:(1-6).

4. The ball mill mechanochemical method as claimed in claim 1 for preparing a nanostructured carbon nanotube having abundant oxygen vacancies and surface OH − A method for producing manganese dioxide, characterized in that The rotation speed of the ball mill is 200 rpm to 500 rpm, and the ball milling time is 0.1 h to 4.0 h.

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