Preparation method of potassium-doped nitrogen oxidation phosphorescent catalyst

Abstract

The invention discloses a preparation method of a potassium-doped nitrogen oxidation phosphorescent catalyst, and belongs to the technical field of photocatalytic material preparation. The method comprises the following steps: by taking phosphorus oxynitride and potassium thiocyanate as raw materials, grinding and mixing, carrying out molten salt reaction at 400-600 DEG C for 1-5 hours, and cooling, washing and drying a reaction product to obtain the potassium-doped phosphorus oxynitride crystal. The method is simple in process, mild in reaction condition, low in cost and easy for large-scale production. Through potassium element doping, the visible light absorption range of phosphorus oxynitride is effectively widened, the recombination rate of photo-induced electron-hole pairs is remarkably reduced, and the carrier separation and transmission efficiency is improved, so that the photocatalytic activity of the material is greatly improved. The prepared K-PON photocatalyst has wide application prospects in the fields of photocatalytic reduction of uranium-containing wastewater, degradation of organic pollutants, energy conversion and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photocatalytic material preparation, and in particular to a preparation method of a potassium-doped phosphorus oxynitride photocatalyst. BACKGROUND

[0002] Photocatalytic technology, as a green technology that utilizes solar energy to drive chemical reactions and solves environmental and energy problems, has received extensive attention in recent years. An ideal photocatalyst should have strong visible light response ability, high photo-generated carrier separation efficiency, good chemical stability, and low cost. Therefore, developing new types of efficient visible light response photocatalysts is a research hotspot and difficulty in the field.

[0003] Phosphorus oxynitride (PON) is an inorganic non-metallic material composed of phosphorus, oxygen, and nitrogen elements, which usually exists in a cristobalite phase structure at normal temperature and pressure. Due to its excellent thermal and chemical stability, PON has been widely used in flame retardants and other fields in the early days. Recent studies have found that PON has a certain response to visible light due to its unique electronic band structure, showing potential as a new type of photocatalytic material. For example, Chinese patent documents CN113307239B and CN113477267B and related academic research disclose the application of phosphorus oxynitride in photocatalytic reduction of uranium-containing wastewater, showing its application prospects in nuclear environmental pollution control.

[0004] However, pure-phase phosphorus oxynitride without modification has a key bottleneck problem that restricts its photocatalytic performance: the recombination rate of its photo-generated electron-hole pairs is extremely high. Under light conditions, PON can generate photo-generated carriers (electrons and holes), but these carriers recombine in the bulk or surface before migrating to the material surface to participate in redox reactions, resulting in a significant reduction in the number of carriers available for catalytic reactions. This fundamental defect causes the electron transport efficiency of pure-phase PON to be low, and the photocatalytic activity is difficult to meet the requirements of practical applications, which seriously limits its in-depth application and promotion in the field of photocatalysis. SUMMARY

[0005] The purpose of the present application is to solve the defects existing in the prior art and provide a preparation method of a potassium-doped phosphorus oxynitride photocatalyst.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: A preparation method of a potassium-doped phosphorus oxynitride photocatalyst, comprising the following steps: Step 1, mixing raw materials: grinding phosphorus oxynitride powder and potassium thiocyanate powder to obtain a uniform mixed precursor; Step 2, melt salt reaction: the mixed precursor is placed in a high-temperature resistant crucible, and is programmed to be heated at a certain heating rate to a reaction temperature of 400-600 DEG C, and is kept at the temperature for 1-5 hours to perform the melt salt reaction; Step 3, post-treatment: the product after reaction is naturally cooled to room temperature, and then is filtered and washed using a washing solvent to remove by-products and unreacted raw materials, and finally is dried to obtain black potassium-doped phosphorus oxynitride crystals, i.e., K-PON photocatalyst.

[0007] Further, in step 1, the mass ratio of the phosphorus oxynitride to potassium thiocyanate is 1:(0.5-4).

[0008] Further, in step 2, the reaction temperature is 400-600 DEG C.

[0009] Further, in step 2, the programmed heating rate is 10-20 DEG C / min.

[0010] Further, in step 2, the melt salt reaction is performed in a tube furnace.

[0011] Further, in step 2, the high-temperature resistant crucible is one of a quartz crucible, a corundum crucible or an alumina crucible.

[0012] Further, in step 3, the washing solvent is anhydrous ethanol.

[0013] The present application has the following advantages: first, in the aspect of preparation process, the method has the advantages of short process, simple operation, mild conditions and easy scale-up production. The core process adopts the classical melt salt reaction method, only needs to physically grind and mix the raw materials phosphorus oxynitride and potassium thiocyanate, and then performs a single step of heat treatment at a moderate temperature range of 400-600 DEG C to complete the reaction. The whole process does not need to introduce complex synthesis equipment, tedious intermediate steps or harsh reaction conditions, significantly reduces the complexity of the production process and the technical requirements for the operator. At the same time, the raw materials are easy to obtain, the production cost is low, the process has high repeatability and good stability, which lays a solid technical foundation for subsequent industrialized production and commercial application.

[0014] Secondly, in terms of material modification, the method successfully realizes the efficient and uniform doping of potassium elements in the phosphorus oxynitride lattice. The application innovatively selects potassium thiocyanate (KSCN) as the potassium source and molten salt medium, which melts to form a liquid phase environment at the reaction temperature, greatly promoting the mass transfer and diffusion of reactant ions. This unique molten salt environment not only ensures the full progress of the chemical reaction, but also more effectively drives the potassium atoms into the crystal framework of phosphorus oxynitride, realizing deep bulk doping. This essential modification from the inside of the crystal structure is more stable and thorough than the physical loading or simple modification on the surface.

[0015] Thirdly, in terms of product performance, the comprehensive performance of the K-PON photocatalyst prepared by the method has been revolutionarily improved. The successful doping of potassium elements first effectively modulates the energy band structure of phosphorus oxynitride, significantly widening its absorption range of visible light. More crucially, the introduced potassium species can act as an efficient electron capture center, preferentially attracting photo-generated electrons, thereby greatly hindering and delaying the recombination process of photo-generated electron-hole pairs. This is confirmed by the characterization data: the photoluminescence spectrum (PL) shows that the fluorescence emission intensity of K-PON is significantly weakened compared to pure PON, directly proving the effective inhibition of electron-hole recombination rate; while the electrochemical impedance spectroscopy (EIS) shows that its charge transfer resistance is significantly reduced, indicating that the separation and migration rate of photo-generated carriers has been greatly improved. These improvements in micro properties directly translate into a leap in macro photocatalytic performance, enabling the catalyst to produce more effective photo-generated electrons to participate in surface reactions under visible light irradiation.

[0016] Fourthly, in terms of the stability and application prospects of the prepared product, the application also shows great value. The K-PON catalyst prepared by the method perfectly inherits the excellent thermal stability and chemical stability of phosphorus oxynitride, and can maintain its crystal structure and catalytic activity stability in long-term use and harsh reaction environment. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0018] Figure 1 is the XRD pattern of K-PON prepared in Example 1.

[0019] Figure 2 is the photoluminescence spectrum of K-PON prepared in Example 2.

[0020] Figure 3 This is the electrochemical impedance spectroscopy of the K-PON prepared in Example 2. Detailed Implementation

[0021] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1: Mass ratio 1:1, reaction at 450℃ Weigh 0.4 g of phosphorus oxynitride (PON) powder and 0.4 g of potassium thiocyanate (KSCN) powder (mass ratio 1:1), place them in an agate mortar, and grind and mix thoroughly for 30 minutes until the mixture is homogeneous. Transfer the homogeneous precursor to a 50 mL quartz crucible and place it in the center of the reaction chamber of a tube furnace.

[0023] After sealing the tube furnace, the temperature was programmed to rise from room temperature to 450°C at a rate of 12°C / min. Once the target temperature was reached, the furnace was held at that temperature for 3 hours to carry out the molten salt reaction.

[0024] After the reaction was complete, heating was stopped, and the sample was allowed to cool naturally to room temperature within the tube furnace. The reaction product was removed and transferred to a beaker containing sufficient anhydrous ethanol. It was washed using magnetic stirring and ultrasonic assistance, followed by vacuum filtration. This washing and filtration process was repeated three times to thoroughly remove soluble byproducts. Finally, the filtered solid product was dried in a vacuum oven at 80°C for 6 hours to obtain black potassium-doped phosphorus oxynitride (K-PON) powder.

[0025] The obtained product was characterized by X-ray diffraction (XRD), and the results are as follows: Figure 1 As shown, the diffraction peaks of the product correspond to the peak positions of the standard cards for phosphorus oxynitride (PDF#80-0869) and potassium metal (PDF#40-0995), and no obvious impurity peaks were observed. This indicates that the matrix crystal structure of the material after the reaction is still quartz-phase PON, and potassium has been successfully doped into the crystal lattice, forming the K-PON photocatalyst of this invention.

[0026] Example 2: Mass ratio 1:2, reaction at 550℃ Take 0.4 grams of phosphorus oxide-nitride (PON) powder and 0.8 grams of potassium thiocyanate (KSCN) powder (mass ratio of 1:2), program the temperature to rise to 550℃ at a temperature rise rate of 15℃ / min, and react at this temperature for 2 hours. After the reaction is completed, the same is subjected to furnace cooling, anhydrous ethanol washing, filtration and 80℃ vacuum drying to obtain the final product K-PON.

[0027] The obtained product is subjected to photoluminescence spectrum (PL) and electrochemical impedance (EIS) tests. The results are shown in Figure 2 and Figure 3 . Figure 2 The PL spectrum of K-PON prepared by the present application shows that the fluorescence emission intensity of K-PON is significantly reduced compared with pure phase PON (see Comparative Example 1). Figure 3 The EIS spectrum of K-PON shows that the impedance arc radius of K-PON is much smaller than that of pure phase PON, indicating that the charge transport resistance is smaller, and the separation and migration efficiency of photo-generated carriers is higher. The two tests together prove that potassium doping effectively improves the photoelectrochemical performance of the material.

[0028] In summary, the present application successfully prepares a high-performance K-PON photocatalyst by a simple molten salt method, which is controllable in process, low in cost, and exhibits excellent performance in the field of photocatalysis.

[0029] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent substitutions for part or all of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the present application.

Claims

1. A method for preparing a potassium-doped nitrogen-oxidizing phosphorus photocatalyst, characterized in that, Includes the following steps: Step 1, Raw material mixing: Grind phosphorus oxynitride powder and potassium thiocyanate powder to obtain a uniform mixed precursor; Step 2, Molten Salt Reaction: The mixed precursor is placed in a high-temperature resistant crucible and heated to a reaction temperature of 400-600℃ at a certain heating rate, and held at this temperature for 1-5 hours to carry out the molten salt reaction. Step 3, Post-processing: The reaction product is naturally cooled to room temperature, then filtered and washed with a washing solvent to remove byproducts and unreacted raw materials. Finally, it is dried to obtain black potassium-doped phosphorus oxide crystals, i.e., K-PON photocatalyst.

2. The method for preparing the potassium-doped nitrogen-oxidizing phosphorus photocatalyst according to claim 1, characterized in that, In step 1, the mass ratio of nitrogen-oxidized phosphorus to potassium thiocyanate is 1:(0.5-4).

3. The method for preparing the potassium-doped nitrogen-oxidizing phosphorus photocatalyst according to claim 1, characterized in that, In step 2, the reaction temperature is 400-600℃.

4. The method for preparing the potassium-doped nitrogen-oxidizing phosphorus photocatalyst according to claim 1, characterized in that, In step 2, the programmed heating rate is 10-20℃ / min.

5. The method for preparing the potassium-doped nitrogen-oxidizing phosphorus photocatalyst according to claim 1, characterized in that, In step 2, the molten salt reaction is carried out in a tube furnace.

6. The method for preparing the potassium-doped nitrogen-oxidizing phosphorus photocatalyst according to claim 1, characterized in that, In step 2, the high-temperature resistant crucible is one of a quartz crucible, a corundum crucible, or an alumina crucible.

7. The method for preparing the potassium-doped nitrogen-oxidizing phosphorus photocatalyst according to claim 1, characterized in that, In step 3, the washing solvent is anhydrous ethanol.

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