Potassium-doped carbon nitride / activated carbon composite material and preparation method thereof

Abstract

The application discloses a kind of potassium-doped carbon nitride / activated carbon composite material and preparation method thereof, comprising: dissolving urea and potassium chloride in water in proportion, after stirring and dissolving, heating to water evaporation and drying to obtain solid precursor;The dried precursor is calcined in nitrogen atmosphere, grinds after cooling, to obtain potassium-doped carbon nitride powder;Activated carbon powder is treated by soaking with dilute nitric acid, washed to neutral after centrifugation and dried, to obtain pretreated activated carbon;Potassium-doped carbon nitride powder and pretreated activated carbon are added to water in proportion, mixed uniformly to obtain a mixture;The mixture is heated to water evaporation, dried to obtain composite precursor;Secondary calcination is carried out under nitrogen protection, grinds after cooling, to obtain potassium-doped carbon nitride / activated carbon composite material.The composite material of the application has both adsorption and catalytic functions, not only can efficiently degrade formaldehyde, but also can effectively capture CO2.

Description

Technical Field

[0001] This invention belongs to the technical field of environmental functional materials, specifically relating to a potassium-doped carbon nitride / activated carbon composite material and its preparation method. Background Technology

[0002] Formaldehyde is a common indoor air pollutant, mainly originating from decoration materials, furniture, and paints. Long-term exposure can cause serious harm to human health, such as respiratory diseases, immune system abnormalities, and even cancer. Currently, formaldehyde treatment methods mainly include adsorption, catalytic oxidation, and photocatalysis. Among these, adsorption is widely used due to its simplicity and low cost, but traditional adsorption materials such as activated carbon have problems such as limited adsorption capacity, easy saturation, and difficulty in regeneration.

[0003] Carbon nitride (g-C3N4), as a non-metallic polymer semiconductor material, exhibits good chemical stability and visible light response characteristics, showing potential in photocatalytic degradation of pollutants. However, pure-phase carbon nitride suffers from drawbacks such as small specific surface area, high charge recombination rate, and weak formaldehyde adsorption capacity. Doping with metallic or non-metallic elements can modulate its electronic structure, enhancing light absorption and carrier separation efficiency. Potassium ion doping not only broadens the photoresponse range of carbon nitride but also introduces basic sites, promoting formaldehyde adsorption and activation.

[0004] Activated carbon (AC) possesses a well-developed pore structure and a large specific surface area, making it an excellent adsorbent, but its catalytic performance is relatively weak. Combining activated carbon with catalytic materials can achieve synergistic adsorption and catalysis, improving overall degradation efficiency. Furthermore, acid treatment of activated carbon can increase the number of oxygen-containing functional groups on its surface, improve its hydrophilicity and dispersibility, and enhance its interfacial bonding with carbon nitride.

[0005] Therefore, developing a potassium-doped carbon nitride / activated carbon composite material with both high adsorption capacity and high catalytic activity is of great significance for achieving efficient and continuous purification of formaldehyde. Summary of the Invention

[0006] One objective of this invention is to address the shortcomings of existing technologies by providing a method for preparing potassium-doped carbon nitride / activated carbon composite materials. This method forms strong -CO-NH- covalent bonds at the interface during secondary calcination. These covalent bonds can undergo nucleophilic addition with formaldehyde, thereby efficiently degrading formaldehyde.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for preparing a potassium-doped carbon nitride / activated carbon composite material includes the following steps: Step 1: Dissolve urea and potassium chloride in water in a certain proportion, stir until dissolved, heat until the water evaporates and dry to obtain a solid precursor; Step 2: Calcine the dried precursor in a nitrogen atmosphere, cool it, and then grind it to obtain potassium-doped carbon nitride powder. Step 3: Soak the activated carbon powder in dilute nitric acid, centrifuge, wash until neutral, and dry to obtain pretreated activated carbon; Step 4: Add potassium-doped carbon nitride powder and pretreated activated carbon to water in a certain proportion and mix evenly to obtain a mixture. Step 5: Heat the mixture until the water evaporates, and dry to obtain the composite precursor; Step 6: The composite precursor is calcined a second time under nitrogen protection, cooled and then ground to obtain potassium-doped carbon nitride / activated carbon composite material.

[0008] Furthermore, in step 1, the mass ratio of urea to potassium chloride is (5-20):1.

[0009] Furthermore, a water bath heating method is used to evaporate the water until it is dry, with the water bath temperature being 60-90℃.

[0010] Furthermore, in step 2, the precursor is calcined at a temperature of 400-600℃, with a heating rate of 2-10℃ / min and a holding time of 2-6 h.

[0011] Furthermore, in step 3, the concentration of dilute nitric acid is 0.8-1.3 mol / L, the soaking time is 2-6 h, and after treatment, it is washed with water until neutral.

[0012] Furthermore, in step 4, the mass ratio of potassium-doped carbon nitride to pretreated activated carbon is 1:0.5-5.

[0013] Furthermore, in step 4, ultrasound or stirring is used to mix the two evenly.

[0014] Furthermore, in step 6, the secondary calcination temperature is 350-550℃, and the holding time is 1-4 h.

[0015] Another object of the present invention is to provide a potassium-doped carbon nitride / activated carbon composite material, which is prepared by the above-described method for preparing potassium-doped carbon nitride / activated carbon composite material.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) The secondary calcination of this invention promotes a dehydration condensation reaction between the -COOH groups on the surface of activated carbon AC and the terminal -NH2 groups on K-CN, forming a strong -CO-NH- covalent bond at the interface. The nitrogen atom in this covalent bond (-CO-NH-) (especially the unbonded lone pair electrons) can act as a nucleophilic site, while the carbonyl carbon of formaldehyde is electron-deficient and easily attacked by nucleophiles. As a result, the formaldehyde molecules adsorbed on the AC surface undergo nucleophilic addition with the amide groups at the interface to form hydroxymethylated amide intermediates. This reaction converts gaseous formaldehyde into surface-bonded species, thereby "removing" it from the gas phase, greatly improving the degradation efficiency of formaldehyde and avoiding the problem of formaldehyde desorption from activated carbon due to temperature increases. In addition, the composite material can not only catalyze the polymerization of formaldehyde into polyoxymethylene through alkaline sites, but also effectively capture CO2. 2) The preparation process of this invention is simple, requires no complex equipment, and the raw materials are readily available, making it suitable for large-scale production; 3) Potassium doping effectively modulates the band structure of carbon nitride, enhances the absorption of visible light and even near-infrared light, and improves catalytic activity; at the same time, acid treatment of activated carbon increases surface functional groups, improves the bonding strength with carbon nitride and the stability of composite materials. 4) The materials are environmentally friendly, with no secondary pollution, and are suitable for indoor air purification devices, building material coatings, and other fields. Attached Figure Description

[0017] Figure 1 SEM image of the potassium-doped carbon nitride / activated carbon composite material prepared in Example 1; Figure 2 The curve showing the formaldehyde degradation efficiency of the composite material in Example 1 over time; Figure 3 The curve showing the change in carbon dioxide removal concentration of the composite material in Example 1 over time; Figure 4 The image shows the in-situ diffuse reflectance infrared Fourier transform (DRIFTS) spectrum of formaldehyde degradation by the composite material in Example 1 at room temperature. Figure 5 The XPS full spectrum of the composite material in Example 1; Figure 6 The N 1s, C 1s, O 1s, and K 2p spectra of the composite material in Example 1 are shown, where (a) is the N 1s spectrum, (b) is the C 1s spectrum, (c) is the O 1s spectrum, and (d) is the K 2p spectrum. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0020] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0021] Example 1

[0022] S1. Weigh 5 g of urea and 0.5 g of potassium chloride, dissolve them in 50 mL of deionized water, and stir for 30 min until completely dissolved to obtain a mixed solution. S2. The mixed solution was placed in an 80°C water bath and evaporated to dryness, then transferred to an oven and dried at 80°C for 12 h to obtain a solid precursor. S3. Place the dried solid precursor in a tube furnace, and... The temperature was increased to 500℃ at 2.3℃ / min under an atmosphere, held for 4 h, and then ground after natural cooling to obtain potassium-doped carbon nitride. S4. Take 5 g of activated carbon powder, add 50 mL of 1 mol / L dilute nitric acid, centrifuge, wash with deionized water until neutral, and then dry in an oven at 80℃ for 24 h to obtain pretreated activated carbon. S5. Weigh 1.0 g of potassium-doped carbon nitride and 1.0 g of pretreated activated carbon, add 50 mL of water, and sonicate for 1 h to mix them evenly. Evaporate the mixture in a 50°C water bath and then dry it at 50°C for 12 h. S6. The dried mixture is heated to 550°C at 5°C / min under N2 atmosphere, held at that temperature for 1.5 h, cooled, and then ground to obtain the desired composite material.

[0023] Example 2

[0024] S1. Weigh 5 g of urea and 0.25 g of potassium chloride, dissolve them in 50 mL of deionized water, and stir for 30 min until completely dissolved to obtain a mixed solution; S2. The mixed solution was evaporated to dryness in a 60°C water bath, and then transferred to an oven to dry at 80°C for 12 h to obtain a solid precursor. S3. Place the dry solid precursor in a tube furnace, heat it to 400℃ at 2℃ / min under N2 atmosphere, hold it at 400℃ for 6 h, and grind it after natural cooling to obtain potassium-doped carbon nitride. S4. Take 5 g of activated carbon powder, add 65 mL of 0.8 mol / L dilute nitric acid, centrifuge, wash with deionized water until neutral, and then dry in an oven at 80℃ for 24 h to obtain pretreated activated carbon. S5. Weigh 1.0 g of potassium-doped carbon nitride and 0.5 g of pretreated activated carbon, add 50 mL of water, stir to mix the two evenly to obtain a mixture, evaporate the mixture to dryness in a 60℃ water bath, and then dry it at 60℃ for 12 h. S6. The dried mixture is heated to 350°C at 3°C / min under N2 atmosphere, held at this temperature for 4 h, cooled, and then ground to obtain the desired composite material.

[0025] Example 3

[0026] S1. Weigh 5 g of urea and 1 g of potassium chloride, dissolve them in 50 mL of deionized water, and stir for 30 min until completely dissolved to obtain a mixed solution. S2. The mixed solution was placed in a 90°C water bath and evaporated to dryness, and then transferred to an oven and dried at 90°C for 12 h to obtain a solid precursor. S3. Place the dried solid precursor in a tube furnace, and... Under an atmosphere, the temperature was increased to 600℃ at 10℃ / min, held for 2 hours, and then ground after natural cooling to obtain potassium-doped carbon nitride. S4. Take 20 g of activated carbon powder, add 200 mL of 1.3 mol / L dilute nitric acid, centrifuge, wash with deionized water until neutral, and then dry in an oven at 80℃ for 24 h to obtain pretreated activated carbon. S5. Weigh 1.0 g of potassium-doped carbon nitride and 5.0 g of pretreated activated carbon, add 50 mL of water, and sonicate for 1 h to mix them evenly. Evaporate the mixture in a 60°C water bath and then dry it at 60°C for 12 h. S6. The dried mixture is heated to 450°C at 5°C / min under N2 atmosphere, held at that temperature for 1 h, cooled and then ground to obtain the desired composite material.

[0027] The surface morphology of the composite material prepared in Example 1 above was observed under a scanning electron microscope, and the results were as follows: Figure 1 The SEM image shown. From Figure 1 It can be seen that potassium-doped carbon nitride can adhere well to the surface of activated carbon. To illustrate the beneficial effects of this embodiment, the ability of the composite material prepared in this embodiment to degrade formaldehyde and remove carbon dioxide was tested under both light-free and light-illuminated conditions, and the results are as follows. Figure 2 The curves showing the formaldehyde degradation efficiency of the composite material over time are as follows: Figure 3 The curve showing the change in carbon dioxide removal concentration of the composite material over time is shown. Figure 2 It can be seen that the composite material achieved a formaldehyde gas degradation rate of 98% within 24 hours. After the light was turned on, the formaldehyde concentration remained basically unchanged because the composite material did not adsorb and degrade formaldehyde, while the formaldehyde concentration of pure activated carbon increased due to formaldehyde desorption caused by the increase in temperature inside the chamber. Figure 3 As can be seen, the carbon dioxide concentration dropped to 0 within 2 hours. In summary, the tests show that this composite material achieves a 90% degradation rate of formaldehyde gas within 120 minutes under dark conditions, enabling rapid capture and efficient degradation of formaldehyde.

[0028] To investigate the room-temperature formaldehyde removal mechanism of potassium-doped carbon nitride / activated carbon (K-CN / AC) composite materials, in-situ infrared spectroscopy analysis under no-light conditions was performed in this embodiment. Figure 4 The infrared absorption spectrum of the material surface over time (0-60 min) under continuous formaldehyde atmosphere is shown. With increasing reaction time, a series of new absorption peaks appear and intensify, mainly located at 2940 cm⁻¹. -1 1143 cm -1 1053 cm -1 and 932 cm -1 This indicates that formaldehyde molecules have undergone chemical transformation on the material surface.

[0029] According to the literature, 2940 cm -1 The absorption peak at this point can be attributed to the CH stretching vibration, typically corresponding to the formation of methylene (-CH2-) or methyl (-CH3) species. 1143 cm⁻¹ -1 and 1053 cm -1 The peak is attributed to the stretching vibration of the CO single bond, a characteristic feature of alkoxy, alcohol, or polymeric ether species. 932 cm⁻¹ -1 The low-frequency absorption at these points may correspond to out-of-plane bending vibrations of CH or skeletal vibrations associated with surface-adsorbed species. The appearance and enhancement of these peaks indicate that the formaldehyde molecule has undergone the breaking of the C=O double bond and the formation of CO and CH bonds on the material surface, ruling out simple physical adsorption.

[0030] Based on material characterization, this invention suggests that the transformation process mainly involves the following two pathways: 1. Surface-induced polymerization: Potassium doping enhances the Lewis basic sites of carbon nitride (such as lone pairs of electrons on nitrogen atoms), which can catalyze the polymerization of formaldehyde to produce polyoxymethylene or oligooxymethylene (HO-(CH2O)). n -H). The characteristic vibrations of polyoxymethylene include exactly... v (CH) (~2940 cm -1 )and v (COC) (~1140, 1050 cm-1 This pathway immobilizes gaseous formaldehyde into a solid polymer, achieving efficient capture at room temperature; 2. Partial oxidation to formate: 1350-1550 cm⁻¹ in the spectrum. -1 The slight enhancement observed in the region (corresponding to carboxylate COO) - The symmetric and antisymmetric stretching vibrations suggest that a small amount of formaldehyde is oxidized to formate (HCOO) by active oxygen species (such as defective oxygen or doping-induced oxygen species) on the material surface. - However, 2300-2400 cm -1 The absence of CO2 characteristic peaks indicates that deep oxidation is inhibited at room temperature without light, and the reaction remains at the partial oxidation stage.

[0031] 3200-3600 cm -1 No significant changes were observed in the hydroxyl region, indicating that the hydroxyl groups on the material surface were not consumed in large quantities, and the concentration of OH groups at the polymer end groups was low, which is consistent with the structural characteristics of the polyoxymethylene backbone.

[0032] Interestingly, this embodiment also revealed that the K-CN / AC composite material can not only catalyze the polymerization of formaldehyde into polyoxymethylene through alkaline sites, but also effectively capture CO2. In-situ infrared studies showed that CO2 is mainly present on the material surface as bicarbonate (~1400 cm⁻¹). -1 and ~1220 cm -1 It is chemically adsorbed in the form of ).

[0033] To verify the effective combination of the two materials and the hypothesized conversion pathway, XPS tests were performed on the composite material, yielding the following results: Figure 5 The XPS full spectrum shown and as shown Figure 6 The N 1s, C 1s, O 1s, K 2p spectra are shown. Figure 5 The successful hybridization of K-doped g-C3N4 (K-CN) with activated carbon (AC) was macroscopically confirmed. AC exhibited a C 1s main peak at 284.8 eV and a significant O 1s signal at 532 eV, indicating its carbonaceous framework and abundant oxygen-containing functional groups. K-CN, on the other hand, showed an additional N 1s (398 eV) and characteristic K 2p (293 eV) and K 2s (377 eV) core levels, confirming the successful incorporation of potassium into the g-C3N4 matrix.

[0034] The spectra of the K-CN / AC composite clearly show the superposition of the characteristics of the two components, simultaneously displaying C 1s, O 1s, N 1s, and K 2p signals. This observation provides preliminary evidence for the coexistence of the two phases in the composite. Broad-spectrum testing results and... Figure 6The high-resolution XPS analysis of C 1s, N 1s, O 1s and K 2p confirmed the tight fusion of K-CN and AC, forming a heterostructure.

[0035] and Figure 6 (a) The XPS N 1s fine spectrum shows that potassium doping negatively shifts the nitrogen binding energy of the tertiary amines of carbon nitride (399.0 eV), confirming the K doping effect. + The electron-donating effect is observed. After being combined with activated carbon and subjected to secondary heat treatment, the N 1s spectrum exhibits a systematic positive shift of approximately 0.7 eV, with a new peak appearing at 403.3 eV. The former is attributed to charge rearrangement and electron transfer at the heterojunction interface between carbon nitride and activated carbon; the latter corresponds to the C–O–N covalent interfacial bond formed by the dehydration condensation of the two. This chemically bonded interface provides a high-speed channel for charge transfer.

[0036] Figure 6 (b) The XPS C 1s fine spectrum confirms the interfacial interaction. The characteristic peak at 288.9 eV in K-CN / AC undergoes a positive shift compared to K-CN (288.6 eV) and is close to the carbonyl carbon peak of pure activated carbon (288.8 eV). This is attributed to the increased binding energy of aromatic carbon (NC=N) due to the transfer of electrons from the carbon nitride skeleton to activated carbon after the two phases are covalently bonded via CON, as well as the superposition with the signal from the residual C=O group in activated carbon. This result is consistent with the positive shift observed in the N 1s spectrum and the formation of the 403.3 eV interfacial nitrogen peak, both pointing to the formation of a strongly electronically coupled heterojunction.

[0037] Figure 6 (c) shows the O 1s XPS spectrum, which provides evidence for the formation of interfacial covalent bonds. The characteristic peak of carbonyl oxygen at 531.9 eV in AC is a broadened main peak centered at 532.0 eV in K-CN / AC. This change indicates that the carboxyl / carbonyl functional groups on the activated carbon surface did not retain their original morphology during the secondary calcination process, but participated in the dehydration condensation reaction with the edge amino groups of carbon nitride, generating carbonyl oxygen (NC=O) in the amide bond (-CO-NH-), whose binding energy is located near 532.0 eV. This result is consistent with the amide nitrogen peak at 403.3 eV in the N 1s spectrum and the corresponding change in the C 1s spectrum, jointly confirming the successful construction of the CON covalent interfacial bridge.

[0038] Figure 6 The K 2p XPS spectrum shown in (d) further confirms the electronic structure reorganization caused by interfacial coupling. K in the composite material + 2p 3 / 2The binding energy shifted slightly positively from 293.1 eV to 293.4 eV. This change did not originate from a change in the chemical state of potassium itself, but rather from the transfer of electrons from the carbon nitride framework to the activated carbon after the formation of a covalent interface between carbon nitride and activated carbon, thus increasing the K binding energy. + The enhanced positive charge of the local electrostatic potential environment leads to an increase in the binding energy of its inner-shell electrons. This result is consistent with the positive shift in binding energy observed in the N 1s and C 1s spectra, together constituting a strong interfacial electron interaction.

[0039] In summary, secondary calcination promotes the dehydration condensation reaction between the -COOH groups on the AC surface and the terminal -NH2 groups on K-CN, forming a strong -CO-NH- covalent bond at the interface. This chemical bridging establishes a direct channel for efficient interfacial charge transfer, allowing electrons to migrate from the carbon nitride framework to the conductive AC matrix. The binding energy shifts of all core elements capture this charge redistribution, promoting charge separation and improving charge carrier dynamics.

[0040] The nitrogen atom in the amide bond (-CO-NH-) (especially the unbonded lone pair electrons) can act as a nucleophilic site. The carbonyl carbon of formaldehyde is electron-deficient and easily attacked by nucleophiles. Therefore, the degradation mechanism of the composite material is as follows: formaldehyde molecules adsorbed on the AC surface undergo nucleophilic addition with the amide group at the interface, forming a hydroxymethylated amide intermediate. This reaction converts gaseous formaldehyde into surface-bonded species, thus "removing" it from the gas phase.

[0041] Furthermore, the nitrogen atom in -CO-NH- exhibits a certain degree of basicity, while the carbonyl oxygen group possesses a certain degree of electronegativity. This polar structure can serve as a chemisorption site for CO2 (an acidic gas). The main mechanism is that CO2 molecules can reversibly insert into the NH site at the interface, forming a carbamate (-NH-COO-). - (or similar intermediates). This chemisorption is stronger than physical adsorption, which is beneficial for "capturing" CO2 in dark environments. AC itself has a huge specific surface area, which is responsible for enriching CO2 molecules. The -CO-NH- covalent bond ensures that the adsorbed CO2 will not easily desorb, thus achieving efficient "capture".

[0042] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A method for preparing a potassium-doped carbon nitride / activated carbon composite material, characterized in that, Includes the following steps: Step 1: Dissolve urea and potassium chloride in water in a certain proportion, stir until dissolved, heat until the water evaporates and dry to obtain a solid precursor; Step 2: Calcine the dried precursor in a nitrogen atmosphere, cool it, and then grind it to obtain potassium-doped carbon nitride powder. Step 3: Soak the activated carbon powder in dilute nitric acid, centrifuge, wash until neutral, and dry to obtain pretreated activated carbon; Step 4: Add potassium-doped carbon nitride powder and pretreated activated carbon to water in a certain proportion and mix evenly to obtain a mixture. Step 5: Heat the mixture until the water evaporates, and then dry it to obtain the composite precursor; Step 6: The composite precursor is calcined a second time under nitrogen protection, cooled and then ground to obtain potassium-doped carbon nitride / activated carbon composite material.

2. The method for preparing the potassium-doped carbon nitride / activated carbon composite material according to claim 1, characterized in that, In step 1, the mass ratio of urea to potassium chloride is (5-20):

1.

3. The method for preparing the potassium-doped carbon nitride / activated carbon composite material according to claim 1, characterized in that, The water is evaporated by a water bath heating method, with the water bath temperature being 60-90℃.

4. The method for preparing the potassium-doped carbon nitride / activated carbon composite material according to claim 1, characterized in that, In step 2, the precursor is calcined at a temperature of 400-600℃, with a heating rate of 2-10℃ / min and a holding time of 2-6 h.

5. The method for preparing the potassium-doped carbon nitride / activated carbon composite material according to claim 1, characterized in that, In step 3, the concentration of dilute nitric acid is 0.8-1.3 mol / L, the soaking time is 2-6 h, and after treatment, it is washed with water until neutral.

6. The method for preparing the potassium-doped carbon nitride / activated carbon composite material according to claim 1, characterized in that, In step 4, the mass ratio of potassium-doped carbon nitride to pretreated activated carbon is 1:0.5-5.

7. The method for preparing the potassium-doped carbon nitride / activated carbon composite material according to claim 1, characterized in that, In step 4, ultrasound or stirring is used to mix the two evenly.

8. The method for preparing the potassium-doped carbon nitride / activated carbon composite material according to claim 1, characterized in that, In step 6, the secondary calcination temperature is 350-550℃, and the holding time is 1-4 h.

9. A potassium-doped carbon nitride / activated carbon composite material, characterized in that, The potassium-doped carbon nitride / activated carbon composite material was prepared using the method described in any one of claims 1-8.

Images