Transition metal hydroxyl oxide, method for preparing the same, and use thereof

Abstract

The application belongs to the field of sewage treatment, and particularly relates to a double transition metal hydroxyl oxide as well as a preparation method and application thereof. x Co y OOH; wherein x represents a proportion of Ni in total molar content of transition metals, y represents a proportion of Co in total molar content of transition metals, x+y=1, x is 0.25-0.75, and y is 0.25-0.75. The double transition metal hydroxyl oxide can effectively enhance ammonia adsorption performance, and when applied to ammonia-nitrogen wastewater treatment, in a chlorine-free mediated electrocatalytic system, ammonia can be enriched on the anode surface with H as an adsorption end, and ammonia can be induced to gradually dehydrogenate through a valence state cycle between high-valence metals in the electrode, and then ammonia-nitrogen in the solution is mineralized into nitrogen. In actual ammonia-nitrogen wastewater treatment, good feasibility is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of sewage treatment, and particularly relates to a transition metal oxide and a preparation method and application thereof. BACKGROUND

[0002] With the industrial emissions and the inefficient use of agricultural fertilizers, a large amount of nitrogen elements are lost and discharged into natural water bodies, causing water eutrophication and black odor. Therefore, effective removal of ammonia-nitrogen wastewater is the focus of attention. At present, the treatment technologies for ammonia-nitrogen wastewater mainly include air stripping, chemical precipitation, breakpoint chlorination, ion exchange, biological nitrification / denitrification, and electro-catalytic oxidation, but these technologies have the disadvantages of poor treatment effect, high cost, and high operation requirement. Among them, the electro-catalytic oxidation technology has gradually developed due to its advantages of high energy efficiency, small occupation, and mild reaction conditions.

[0003] At present, electro-catalytic oxidation can be divided into direct oxidation and active component-mediated indirect oxidation. Indirect ammonia oxidation is based on the basic principle of industrial breakpoint chlorination, and realizes efficient removal of ammonia-nitrogen by generating active chlorine (HClO, ClO-) through in-situ chlorine evolution of the anode, but in the system containing high concentration of chloride ions, chloramine and other halogenated organic by-products will be generated, causing secondary pollution. Therefore, under the condition of no chlorine mediation, direct mineralization of ammonia into nitrogen through three-electron transfer is a more ideal way.

[0004] Direct ammonia oxidation refers to the adsorption of ammonia (NH3) on the anode surface and then oxidation into nitrogen gas under the condition of no chlorine mediation. The key to solving the problems of low ammonia-nitrogen removal rate and low mineralization rate lies in the design of anode catalyst. When N is used as an adsorption site, although the activity can be improved and the overpotential can be reduced, noble metals such as Pt, Ir and Pd-based metals are used, but their cost is high, and there is a risk of catalyst poisoning. If H is used as an adsorption site, the risk of poisoning can be avoided, so it is more conducive to direct combination with H to improve the ammonia-nitrogen mineralization effect. Transition metal oxyhydroxides can effectively mineralize ammonia-nitrogen because they contain high-valence metals and rich-electron O, and are the best candidate catalysts to replace noble metal-based catalysts. However, the low density of electron centers is not conducive to ammonia adsorption, and with the ammonia dehydrogenation reaction, the high-valence metal is reduced to low-valence metal and deactivated, resulting in poor ammonia oxidation performance. Therefore, the present application provides a double transition metal oxyhydroxide, which can induce NH3 to gradually dehydrogenate by the valence state circulation between high-valence metals in the electrode in a chlorine-free mediated electro-catalytic system, and selectively mineralize ammonia-nitrogen in the solution into nitrogen gas. SUMMARY

[0005] The purpose of the present application is to provide a double transition metal hydroxyl oxide, which is constructed by introducing Co element with lower electronegativity than Ni element into Ni element hydroxyl oxide to build electron-rich center, and which is used for treating ammonia-nitrogen wastewater in a chlorine-free mediated electrocatalytic system.

[0006] Another purpose of the present application is to provide a preparation method of the double transition metal hydroxyl oxide.

[0007] Another purpose of the present application is to provide an application of the double transition metal hydroxyl oxide in wastewater treatment.

[0008] To achieve the above purposes, the present application is implemented by the following technical solutions:

[0009] A double transition metal hydroxyl oxide, which is a hydroxyl oxide Ni x Co y OOH formed by Ni salt and Co salt.

[0010] Wherein, x represents the proportion of Ni in the total molar content of transition metals, y represents the proportion of Co in the total molar content of transition metals, x+y=1, and x is 0.25-0.75, y is 0.25-0.75.

[0011] In the present application, by introducing Co element with lower electronegativity than Ni element to build electron-rich center, the adsorption performance to ammonia is enhanced, and the double transition metal hydroxyl oxide is applied to wastewater treatment, so that in a chlorine-free mediated electrocatalytic system, ammonia can be enriched on the anode surface with H as the adsorption end, and through the valence state cycle between high-valence metals in the electrode, ammonia is induced to gradually dehydrogenate, and then the ammonia-nitrogen in the solution is mineralized into nitrogen. In actual ammonia-nitrogen wastewater treatment, it has good feasibility.

[0012] Further, x is 0.5, and y is 0.5.

[0013] The preparation method of the double transition metal hydroxyl oxide comprises the following steps:

[0014] Mixing Ni salt and Co salt, adding them into water, and then adding urea and ammonium fluoride to stir to obtain the double transition metal hydroxyl oxide.

[0015] Specifically, the Ni salt is Ni(CH3COO)2·4H2O.

[0016] The Co salt is Co(NO3)2·6H2O.

[0017] Further, the molar ratio of the Ni salt to the Co salt is 1:3-3:1.

[0018] Further, the molar ratio of the Ni salt to the Co salt is 1:1.

[0019] The application also protects the application of the double transition metal oxyhydroxide in wastewater treatment.

[0020] A method for mineralizing ammonia-nitrogen wastewater, comprising the following steps:

[0021] S1. Using the double transition metal oxyhydroxide described above to treat a nickel foam substrate to obtain an electrode material;

[0022] S2. Using the electrode material prepared in step S1. as an anode material, using a platinum sheet as a cathode material, and using an electrocatalytic reaction to treat ammonia-nitrogen wastewater.

[0023] Further, the electrolyte of the electrocatalytic reaction is a sodium sulfate solution.

[0024] Further, the pH of the electrocatalytic reaction is 9-13.

[0025] Further, the voltage of the electrocatalytic reaction is 0.7-1.2 V.

[0026] Further, the time of the electrocatalytic reaction is 6-12 h.

[0027] Compared with the prior art, the application has the following beneficial effects:

[0028] The application provides a double transition metal oxyhydroxide, which introduces a Co element with lower electronegativity into a Ni element oxyhydroxide to construct an electron-rich center, enhances the adsorption performance of an electric anode to ammonia, uses the double transition metal oxyhydroxide as an anode material in a chlorine-free mediated electrocatalytic system, and uses the electric anode with a metal electron-rich center to enrich ammonia on the surface of the anode with H as an adsorption end, and gradually induces NH3 to dehydrogenate through the valence state circulation between high-valence metals in the electrode, and selectively mineralizes ammonia-nitrogen in the solution into nitrogen; in actual ammonia-nitrogen wastewater treatment, the ammonia-nitrogen removal rate of the ammonia-nitrogen wastewater treatment reaches 95%, and the nitrogen mineralization rate reaches 39%. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 Performance diagram of different nickel-cobalt metal ratio anodes in the electrocatalytic system for degrading ammonia-nitrogen;

[0030] Figure 2 Proportion diagram of ammonia-nitrogen and N-containing products changing with time when four kinds of transition metal (Mn, Fe, Co, Ni) prepared double transition metal oxyhydroxides are used as anode materials to treat ammonia-nitrogen wastewater;

[0031] Figure 3 Proportion diagram of ammonia-nitrogen and N-containing products changing with time when Co 0.5 Ni 0.5 OOH is used as an anode material to treat ammonia-nitrogen wastewater;

[0032] Figure 4 XPS spectra of O 1s orbitals before and after Co was introduced to NiOOH;

[0033] Figure 5 XPS spectra of Ni 2p orbitals before and after NiOOH reaction;

[0034] Figure 6 XPS spectra of Co 2p orbitals before and after CoOOH reaction. 0.5 Ni 0.5 XPS spectra of Ni 2p orbitals before and after NiOOH reaction;

[0035] Figure 7 XPS spectra of Co 2p orbitals before and after CoOOH reaction. 0.5 Ni 0.5 XPS spectra of Co 2p orbitals before and after CoOOH reaction. DETAILED DESCRIPTION

[0036] The application will be further described in conjunction with specific examples, which are only used to explain the application and not intended to limit the scope of the application. The test methods used in the following examples are conventional methods unless otherwise specified; the materials, reagents, etc. used are commercially available reagents and materials unless otherwise specified.

[0037] The content change of ammonia nitrogen in the reaction system was determined by using Nash reagent spectrophotometry.

[0038] The content change of total nitrogen in the reaction system was determined by using alkaline potassium persulfate digestion method.

[0039] The content change of NO2 - and NO3 - in the reaction system was determined by using spectrophotometry.

[0040] The structure of the material was analyzed by using X-ray photoelectron spectroscopy (XPS), and the model of the XPS used was PHI, USA.

[0041] Example 1

[0042] A preparation method of a double transition metal hydroxyl oxide, comprising the following steps:

[0043] Ni(CH3COO)2·4H2O and Co(NO3)2·6H2O were sequentially added to 50 mL of deionized water in a molar ratio of 1:3 (the amount used was 1 mol and 3 mol, respectively), then urea (0.9007 g) and ammonium fluoride (0.1388 g) were added and stirred for 30 minutes to form a uniform transparent solution, obtaining Ni 0.25 Co 0.75 OOH.

[0044] Example 2

[0045] A method for preparing a double transition metal hydroxyl oxide, comprising the following steps:

[0046] Ni(CH3COO)2·4H2O and Co(NO3)2·6H2O were added into 50 mL deionized water in a molar ratio of 1:1 (amounts of 2 mol and 2 mol, respectively), then urea (0.9007 g) and ammonium fluoride (0.1388 g) were added and stirred for 30 minutes to form a uniform transparent solution, obtaining Ni 0.5 Co 0.5 OOH.

[0047] Example 3

[0048] A method for preparing a double transition metal hydroxyl oxide, comprising the following steps:

[0049] Ni(CH3COO)2·4H2O and Co(NO3)2·6H2O were added into 50 mL deionized water in a molar ratio of 3:1 (amounts of 3 mol and 1 mol, respectively), then urea (0.9007 g) and ammonium fluoride (0.1388 g) were added and stirred for 30 minutes to form a uniform transparent solution, obtaining Ni 0.75 Co 0.25 OOH.

[0050] Comparative Example 1

[0051] A method for preparing a double transition metal hydroxyl oxide, comprising the following steps:

[0052] 4 mM Ni(CH3COO)2·4H2O was added into 50 mL deionized water, then urea (0.9007 g) and ammonium fluoride (0.1388 g) were added and stirred for 30 minutes to form a uniform transparent solution, which was NiOOH.

[0053] Comparative Example 2

[0054] A method for preparing a double transition metal hydroxyl oxide, comprising the following steps:

[0055] 4 mM Co(NO3)2·6H2O was added into 50 mL deionized water, then urea (0.9007 g) and ammonium fluoride (0.1388 g) were added and stirred for 30 minutes to form a uniform transparent solution, which was CoOOH.

[0056] Comparative Example 3

[0057] A method for preparing a double transition metal hydroxyl oxide, comprising the following steps:

[0058] Mn(CH3COO)2-4H2O and FeCl2-4H2O were added into 50 mL deionized water in the molar ratio of 1:1 (the amount of addition was 2 mol and 2 mol, respectively), and then urea (0.9007 g) and ammonium fluoride (0.1388 g) were added and stirred for 30 minutes to form a uniform transparent solution, which was Fe 0.5 Mn 0.5 OOH.

[0059] Comparative Example 4

[0060] A method for preparing a double transition metal oxyhydroxide, comprising the following steps:

[0061] Mn(CH3COO)2-4H2O and Co(NO3)2-6H2O were added into 50 mL deionized water in the molar ratio of 1:1 (the amount of addition was 2 mol and 2 mol, respectively), and then urea (0.9007 g) and ammonium fluoride (0.1388 g) were added and stirred for 30 minutes to form a uniform transparent solution, which was Co 0.5 Mn 0.5 OOH.

[0062] Comparative Example 5

[0063] A method for preparing a double transition metal oxyhydroxide, comprising the following steps:

[0064] Mn(CH3COO)2-4H2O and Ni(CH3COO)2-4H2O were added into 50 mL deionized water in the molar ratio of 1:1 (the amount of addition was 2 mol and 2 mol, respectively), and then urea (0.9007 g) and ammonium fluoride (0.1388 g) were added and stirred for 30 minutes to form a uniform transparent solution, which was Ni 0.5 Mn 0.5 OOH.

[0065] Comparative Example 6

[0066] A method for preparing a double transition metal oxyhydroxide, comprising the following steps:

[0067] FeCl2-4H2O and Ni(CH3COO)2-4H2O were added into 50 mL deionized water in the molar ratio of 1:1 (the amount of addition was 2 mol and 2 mol, respectively), and then urea (0.9007 g) and ammonium fluoride (0.1388 g) were added and stirred for 30 minutes to form a uniform transparent solution, which was Ni 0.5 Fe 0.5 OOH.

[0068] Comparative Example 7

[0069] A method for preparing a double transition metal oxyhydroxide comprises the following steps:

[0070] FeCl2·4H2O and Co(NO3)2·6H2O were added into 50mL deionized water in a molar ratio of 1:1 (2 mol and 2 mol respectively), and then urea (0.9007g) and ammonium fluoride (0.1388g) were added and stirred for 30 minutes to form a uniform and transparent solution, which was Co 0.5 Fe 0.5 OOH.

[0071] Example 4

[0072] A 1.5 cm × 4 cm nickel foam (NF) substrate was ultrasonically cleaned with acetone, 5:4 hydrochloric acid, ethanol, and water for 15 min each. After drying, the substrate was immersed in the solutions prepared in the examples and comparative examples at 90°C for 7 hours. The substrate was then immersed in a 5% NaClO solution with a pH of 3-4 for 1 hour to obtain the corresponding electrode material.

[0073] Platinum sheet was used as cathode material, and Ni 0.25 Co 0.75 OOH、Ni 0.5 Co 0.5 OOH、Ni 0.75 Co 0.25 OOH, NiOOH, CoOOH and NF were used as anode materials to construct an electrocatalytic system. Ammonia nitrogen wastewater was treated, sodium sulfate solution was used as electrolyte, and NaOH was used to adjust the solution to alkalinity. The electrochemical reaction was carried out at a voltage of 1.1V for 6h. The results are as follows: Figure 1 As shown; using Ni 0.5 Co 0.5 OOH is used as the reaction system of the anode material. Samples are taken every 1 hour during the reaction and the product distribution in the sample is immediately measured. The catalytic performance of different double transition metal oxyhydroxides as anode materials is shown in Figure 2. Figure 2 As shown; by analyzing the changes in the content of various products in the solution, the catalytic degradation effect of the system on ammonia nitrogen was analyzed, and the results are shown as follows Figure 3 shown.

[0074] from Figure 1 It can be seen that after 6 hours of electrocatalytic reaction, when NiOOH and CoOOH were used as anode materials, the ammonia nitrogen removal rates were 33% and 100%, and the nitrogen mineralization rates were 16% and 0%, respectively. 0.5 Co 0.5 OOH has good comprehensive performance as anode material, high ammonia nitrogen removal rate, and can be converted into nitrogen; among them, Ni 0.5 Co 0.5OOH has the best performance as an anode material, with an ammonia nitrogen removal rate of 95% and a nitrogen mineralization rate of 39%.

[0075] Ammonia nitrogen removal performance and product distribution of six double transition metal hydroxyls Figure 2 As shown in the figure, Co 0.5 Mn 0.5 OOH can completely remove ammonia nitrogen, but its main product is NO3 - The main component is Fe, with a yield of 89% and a nitrogen mineralization rate of only 0.8%. 0.5 Mn 0.5 OOH、Ni 0.5 Mn 0.5 OOH、Co 0.5 Fe 0.5 OOH、Ni 0.5 Fe 0.5 The oxidation effect of the five hydroxyl oxides OOH is poor, and the ammonia nitrogen removal rate can only reach 49% (Ni 0.5 Mn 0.5 OOH); Compared with these bimetallic oxyhydroxides, Ni 0.5 Co 0.5 The OOH ammonia nitrogen removal effect is significantly enhanced, and the nitrogen mineralization rate can reach 39%. 0.5 Co 0.5 OOH can effectively remove ammonia nitrogen, and the selectivity of the product to nitrogen is higher. Therefore, compared with other bimetallic oxyhydroxides, Ni 0.5 Co 0.5 OOH is a more ideal catalyst material.

[0076] Ni 0.5 Co 0.5 The changes of ammonia nitrogen concentration and product over time within 6 hours of OOH reaction are as follows: Figure 3 As shown. Figure 3 It can be seen that within 2 hours of reaction, NO2 - The concentration gradually increases as the reaction time increases. - Oxidized and converted into NO3 - , so NO2 - During the reaction, ammonia nitrogen is gradually degraded, and the nitrogen concentration gradually increases as the ammonia nitrogen concentration decreases.

[0077] XPS tests were performed on NiOOH before and after the introduction of Co. The results are as follows: Figure 4 As shown. Figure 4 It can be seen that after the introduction of Co into NiOOH, the binding energy of O 1s orbital shifts to the high energy direction, indicating that Ni 0.5 Co 0.5The electron cloud around Ni in OOH moves further to O, indicating that the electron density of O is further improved.

[0078] NiOOH and Ni 0.5 Co 0.5 OOH were tested by XPS, and the results are shown in Figures 5-7 It can be seen that the peak value of Ni changes before and after the reaction of NiOOH, the peak value of Ni 3+ decreases after the reaction, the peak value of Ni 2+ increases, indicating that high-valence Ni is converted to Ni 2+ after reacting with ammonia; the valence state of Ni 0.5 in Co 0.5 OOH is different from that of NiOOH, the peak value of Ni 3+ increases after the reaction, and the peak value of Ni 2+ decreases, according to the analysis of Co 2p orbit, the peak value of Co 3+ decreases after the reaction, and the peak value of Co 2+ increases, which indicates that after high-valence Ni is converted to Ni 2+ , Ni 2+ can be oxidized to Ni 3+ to continue to react with ammonia. The above shows that the rich-electron O environment in double transition metal hydroxyl oxide can enrich ammonia with H as the binding site, and through the valence state cycle between high-valence metals, the ammonia nitrogen removal performance and selectivity of the double transition metal hydroxyl oxide can be further improved.

[0079] Obviously, the above examples of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. For those skilled in the art, other different forms of changes or variations can be made on the basis of the above description. Here, it is not necessary and impossible to exhaust all the embodiments. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. Use of a double transition metal hydroxyl oxide in waste water treatment, characterized in that, The double transition metal hydroxyl oxide is a hydroxyl oxide Ni x Co y OOH; Wherein, the x refers to the proportion of Ni in the total molar content of transition metals, and the y refers to the proportion of Co in the total molar content of transition metals, The x is 0.5, and the y is 0.5; The preparation method of the double transition metal hydroxyl oxide comprises the following steps: The Ni salt and the Co salt are mixed and added into water, and then urea and ammonium fluoride are added and stirred to obtain the double transition metal hydroxyl oxide; The application comprises the following steps: S1. treating a nickel foam substrate with the double transition metal hydroxyl oxide to obtain an electrode material; S2. treating ammonia-nitrogen wastewater by using an electro-catalytic reaction, with the electrode material obtained in step S1. as an anode material and a platinum sheet as a cathode material.

2. Use according to claim 1, characterized in that, The Ni salt is Ni(CH3COO)2·4H2O.

3. Use according to claim 1, characterized in that, The Co salt is Co(NO3)2·6H2O.

4. The use according to claim 1, characterized in that, The electrolyte of the electro-catalytic reaction is a sodium sulfate solution.

5. The use according to claim 1, characterized in that, The pH of the electro-catalytic reaction is 9-13.

6. The use according to claim 1, characterized in that, The voltage of the electro-catalytic reaction is 0.7-1.2 V.

Images