A red mud modified PHI type carbon nitride adsorbent, a preparation method and applications thereof

Abstract

This invention discloses a method for preparing red mud modified PHI-type carbon nitride adsorbent, which belongs to the field of environmental functional materials. The mass ratio of red mud powder to melamine is (0.01-0.08):1, and the mass ratio of chloride template to melamine is (5-20):1; S1. Mix the red mud powder, melamine, and chloride uniformly; S2. Place the mixture obtained in step S1 in a tube furnace, heat it to 550-600℃ at a heating rate of 2-5℃ / min under an inert atmosphere and hold it for 4-8 hours, and obtain the calcined product after cooling; S3. Wash the calcined product obtained in step S2 with deionized water to remove the chloride template, and then dry it. The drying is carried out under vacuum at 60 degrees to obtain the red mud modified PHI type carbon nitride adsorbent. This invention uses red mud and melamine as raw materials and combines chloride-assisted thermal polycondensation to prepare red mud modified PHI type carbon nitride adsorbent. The process is simple, the raw materials are readily available, and it is beneficial to the resource utilization of industrial solid waste red mud.

Description

Technical Field

[0001] This invention relates to the field of environmental functional materials technology, and in particular to red mud modified PHI-type carbon nitride adsorbent, its preparation method and application. Background Technology

[0002] Organic pollutants have become a global concern due to their widespread sources and potential harm to the ecological environment and human health. These pollutants originate not only from industrial production processes but are also widely present in industrial wastewater, agricultural runoff, and various wastes generated in daily life. For example, organic compounds such as dyes, pesticides, drug residues, and phenolic compounds, if discharged directly without effective treatment, will cause serious pollution to water bodies and soil, and may even enter the food chain, threatening biodiversity and human health. Therefore, the development of efficient, economical, and environmentally friendly organic pollutant removal technologies is urgently needed. Against this backdrop, adsorption technology, due to its advantages of simple operation, low cost, and wide applicability, is considered one of the important means of treating organic pollutants.

[0003] Traditional adsorbent materials such as activated carbon, while exhibiting good adsorption performance, suffer from high costs and difficulties in regeneration. Red mud, a major industrial solid waste generated during alumina production, contains abundant iron and aluminum oxides, making it a potential adsorbent matrix. However, when raw red mud is used directly as an adsorbent, it suffers from drawbacks such as small specific surface area and insufficient adsorption sites.

[0004] Graphitic carbon nitride (g-C3N4) and its composites with industrial waste red mud have shown great potential. As a metal-free polymer semiconductor material, g-C3N4 has become a research hotspot in adsorption and photocatalysis due to its unique physicochemical properties, such as a suitable band gap, good chemical stability, excellent biocompatibility, and visible light response characteristics, especially showing broad application prospects in the removal of organic pollutants. Although g-C3N4 has a layered structure and abundant nitrogen atom sites, which are beneficial to the adsorption process, its preparation via thermal polymerization of precursors (such as melamine) often results in bulk and surface defects due to incomplete polymerization. These defects easily become charge recombination centers, thus limiting its photocatalytic efficiency and adsorption performance. To overcome these shortcomings, researchers are actively exploring the synthesis of carbon nitride with higher structural regularity and crystallinity. Currently, the chloride salt template method is widely used in materials preparation due to its advantages such as easy removal and low cost. This method can effectively reduce material defect sites, promote charge separation, and provide uniform adsorption sites, thereby significantly improving the performance of the material in photocatalysis and adsorption applications. However, there is still a lack of mature and feasible technical solutions for controlling the structure of red mud-modified carbon nitride materials using the chloride salt template method, which requires further research and improvement.

[0005] Based on the above problems, the present invention aims to develop a new PHI-type carbon nitride adsorbent modified from red mud that is highly active, has excellent performance, and is low cost. Summary of the Invention

[0006] The purpose of this invention is to provide a simple and low-cost method for preparing red mud modified PHI-type carbon nitride adsorbent, so as to prepare a composite adsorbent with optimized surface structure and interface properties, and to use it to remove organic pollutants in water.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing red mud modified PHI-type carbon nitride adsorbent, using red mud powder and melamine as raw materials, is carried out by a chloride salt template-assisted method.

[0009] Preferably, the mass ratio of the red mud powder to melamine is (0.01-0.08):1, and the mass ratio of the chloride template to melamine is (5-20):1.

[0010] Furthermore, it includes the following steps: S1. Mix the red mud powder, melamine and chloride salt evenly; S2. Place the mixture obtained in step S1 in a tube furnace, heat it to 550-600℃ at a heating rate of 2-5℃ / min under an inert atmosphere and hold it for 4-8 hours. After cooling, the calcined product is obtained. S3. The calcined product described in step S2 is washed with deionized water to remove the chloride template, and then dried using vacuum drying at 60 degrees Celsius to obtain red mud modified PHI type carbon nitride adsorbent.

[0011] Preferably, the chloride template is selected from one or more of lithium chloride, sodium chloride, and potassium chloride.

[0012] Preferably, the red mud is Bayer process red mud, which is washed with water, dried, and then ground to 100-200 mesh.

[0013] Furthermore, the inert atmosphere is argon or nitrogen.

[0014] A red mud-modified PHI-type carbon nitride adsorbent, characterized in that it is prepared by the preparation method described in claim 1, wherein the PHI-type carbon nitride adsorbent comprises a red mud component and a PHI-type carbon nitride component.

[0015] Preferably, the red mud modified PHI-type carbon nitride adsorbent comprises PHI-type carbon nitride and metal oxide components in red mud, and the metal oxide components are dispersed in the interlayer regions such as the surface of the PHI carbon nitride framework to form a heterogeneous composite structure.

[0016] An application of the aforementioned PHI-type carbon nitride adsorbent in the adsorption and removal of methylene blue from water, wherein the PHI-type carbon nitride adsorbent exhibits removal efficacy for methylene blue within a pH range of 3-11. Compared with existing technologies, it has the following beneficial effects: (1) This invention uses red mud and melamine as raw materials and combines them with chloride-assisted thermal polycondensation to prepare red mud modified PHI type carbon nitride adsorbent. The process is simple, the raw materials are readily available, and it is conducive to the resource utilization of industrial solid waste red mud.

[0017] (2) The present invention uses a chloride-assisted thermal polycondensation method, which is beneficial to control the material formation process and surface structure. The resulting adsorbent retains the characteristics of the PHI-type carbon nitride skeleton, and Fe and Al oxides from red mud are dispersed and introduced into the surface of the adsorbent, thereby forming a heterogeneous interface composite structure, increasing the specific surface area of ​​the material and having more accessible interfaces.

[0018] (3) The Fe and Al oxygen-containing components derived from red mud form a heterogeneous interface composite structure with the PHI-type carbon nitride matrix, which is beneficial to improve the chemical environment of the material surface and increase the adsorption active sites, thereby improving its adsorption and removal performance for methylene blue. Attached Figure Description

[0019] Figure 1 This is a comparison chart of the removal effects of different samples of methylene blue (MB) in this invention.

[0020] Figure 2 This is a graph showing the effect of the dosage of 4RM-PHI in this invention on MB removal efficiency.

[0021] Figure 3 This is a graph showing the effect of pH on the adsorption of MB by 4RM-PHI according to the present invention.

[0022] Figure 4 This diagram illustrates the effect of initial MB concentration of 4RM-PHI on the adsorption effect of the present invention.

[0023] Figure 5 This invention provides pseudo-first-order and pseudo-second-order kinetic models for the adsorption of MB by 4RM-PHI.

[0024] Figure 6 This is a diagram showing the cyclic regeneration performance of the 4RM-PHI of the present invention; Figure 7 This is a schematic diagram of the preparation process of the present invention. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0026] Example 1: A method for preparing a red mud modified PHI type carbon nitride adsorbent, (1) Bayer red mud is washed with water and dried at 110°C and then ground to 100-200 mesh and kept for later use; (2) Preparation of Na-PHI: Weigh 1g of melamine, 10g of sodium chloride template and 20mg of Bayer red mud, and grind them thoroughly in an agate mortar. (3) Transfer the mixed powder to a crucible, place it in a tube furnace, and heat it to 600°C at a heating rate of 2.5°C / min under constant inert gas protection (argon is used in this embodiment) and hold it for 4 hours. Then, let it cool naturally to room temperature.

[0027] (4) Take out the calcined product, wash it with deionized water and filter to separate the solid; repeat the washing and rinse the filter and solid with an appropriate amount of deionized water to remove the chloride template; finally, dry it at 60°C for 12 hours under vacuum to obtain PHI type carbon nitride adsorbent (2RM-PHI).

[0028] Example 2: A method for preparing a red mud modified PHI-type carbon nitride adsorbent, which is basically the same as that in Example 1, except that the mass of Bayer red mud added is 40 mg, to obtain 4RM-PHI.

[0029] Example 3: A method for preparing a red mud modified PHI-type carbon nitride adsorbent, which is basically the same as that in Example 1, except that the mass of Bayer red mud added is 60 mg, to obtain 6RM-PHI.

[0030] Example 4: A method for preparing a red mud modified PHI-type carbon nitride adsorbent, which is basically the same as that in Example 1, except that the mass of Bayer red mud added is 80 mg, to obtain 8RM-PHI.

[0031] The adsorption performance of the material of this invention is verified as follows: Methylene blue (MB) was used as the model pollutant in the adsorption experiment. The concentration of methylene blue was determined using ultraviolet light. The absorbance was measured at 664 nm using a visible spectrophotometer and the concentration was calculated.

[0032] Adsorption experiments were conducted on the adsorbents from Examples 1-5. 20 mg of the adsorbent was added to 150 mL of a 60 mg / L methylene blue aqueous solution, and the reaction was carried out at 25°C and pH 7 for 6 hours. During this period, samples were taken, with 3-5 mL of solution taken using a disposable syringe, filtered through a 0.45-micron aqueous filter, and then subjected to ultraviolet light. The absorbance of the solution (664 nm) was measured using a visible spectrophotometer to assess the removal effect of methylene blue and calculate the removal rate. Results are shown below. Figure 1 .

[0033] Depend on Figure 1 The adsorption experiment results show that as the amount of red mud increases, the methylene blue removal rate first increases and then decreases, indicating that there is an optimal range for the amount of red mud modified.

[0034] The sample from Example 2 was selected for subsequent adsorption condition studies.

[0035] Adsorption experiments were conducted using the adsorbent from Example 2 within the range of 5 mg to 25 mg. Different weights of adsorbent were added to 150 mL of a 60 mg / L methylene blue aqueous solution, and reacted for 6 hours at 25°C and different pH values. Samples were taken during this period; 3-5 mL of solution was taken using a disposable syringe, filtered through a 0.45-micron aqueous filter, and then subjected to ultraviolet light. The absorbance of the solution was measured using a visible spectrophotometer (664 nm). The removal effect on methylene blue was assessed, and the removal rate was calculated. Results are shown below. Figure 2 .

[0036] like Figure 2 As shown, the MB removal rate increased significantly as the adsorbent dosage increased from 5 mg to 25 mg; when the dosage reached 20 mg, the removal rate was close to stable and remained at a high level.

[0037] Considering both removal effectiveness and dosage, the optimal dosage is 20mg.

[0038] Methylene blue solutions with pH values ​​of 3, 5, 7, 9, and 11 were prepared using HCl or NaOH. Adsorption experiments were conducted using the adsorbent from Example 2. 20 mg of the adsorbent was added to 150 mL of a 60 mg / L methylene blue aqueous solution, and the reactions were carried out at 25°C and different pH values ​​for 6 hours. During this period, samples were taken, with 3-5 mL of solution taken using a disposable syringe. After filtration through a 0.45-micron aqueous filter, the solution was subjected to ultraviolet light. The absorbance of the solution was measured using a visible spectrophotometer (664 nm). The removal effect on methylene blue was assessed, and the removal rate was calculated. Results are shown below. Figure 3 .

[0039] like Figure 3 As shown, the material of this invention exhibits high removal efficiency for methylene blue within a pH range of 3-11, with a relatively higher removal rate under near-neutral conditions. This is to facilitate the standardization of experimental conditions and engineering applications.

[0040] Subsequent experiments of this invention were conducted at pH=7. Different initial concentrations of methylene blue solution were used: 10 mg / L, 30 mg / L, 60 mg / L, 90 mg / L, and 110 mg / L. Adsorption experiments were conducted using the adsorbent from Example 2. 20 mg of the adsorbent was added to 150 mL of methylene blue aqueous solution of different concentrations, and the reaction was carried out at 25°C and pH 7 for 6 hours. During this period, samples were taken; 3-5 mL of solution was taken using a disposable syringe, filtered through a 0.45-micron aqueous filter, and then subjected to ultraviolet light. The absorbance of the solution (664 nm) was measured using a visible spectrophotometer to assess the removal effect of methylene blue and calculate the removal rate. Results are shown below. Figure 4 .

[0041] like Figure 4 As shown, an MB concentration of 60 mg / L exhibits a removal efficiency of 99.08% and an adsorption capacity of 445.86 mg / g. This indicates that the removal rate remains high within a low initial concentration range (10-60 mg / L); however, the removal rate decreases when the initial concentration increases to 90 mg / L and 110 mg / L. Based on the experimental results, an initial MB concentration of 60 mg / L was selected as one of the optimal conditions, at which point the removal rate is 99.08%, corresponding to an adsorption capacity of 445.86 mg / g.

[0042] The following is an adsorption kinetics analysis. The linear expression for the intraparticle diffusion model is:

[0043] The linear expression for the pseudo-first-order dynamics model is:

[0044] The linear expression of the pseudo-second-order dynamics model is:

[0045] In the formula, q t —Adsorption capacity after t minutes, mg g -1 ; k ip —Internal diffusion rate constant; t —Adsorption time, min; C —Considers constants related to thickness and boundary layers; q e —Adsorption capacity at adsorption equilibrium, mg g -1 ; k 1 — Pseudo-first-order reaction adsorption rate constant, min -1 ; k 2 — Pseudo-second-order reaction adsorption rate constant, g mg -1 min-1 .

[0046] Using the adsorbent from Example 2, 120 mg of the adsorbent was added to 900 mL of methylene blue aqueous solutions with concentrations of 30 mg / L, 60 mg / L, and 110 mg / L, respectively. The reactions were carried out at 25 °C and pH 7 for 6 h. During this period, samples were taken, with 3-5 mL of solution taken using a disposable syringe. After filtration through a 0.45-micron aqueous filter, the solution was subjected to ultraviolet light. The absorbance of the solution (664 nm) was measured using a visible spectrophotometer to assess the removal effect of methylene blue and calculate the removal rate. Results are shown below. Figure 5 .

[0047] The kinetic fitting parameters are shown in the table below. The results show that, under most experimental conditions, the pseudo-second-order kinetics has a higher fitting correlation, i.e., R0. 2 The result is closer to 1, and the calculated equilibrium adsorption amount is closer to the experimental result, indicating that the pseudo-second-order kinetic model can more accurately describe the adsorption kinetics of MB, and the adsorption process is mainly controlled by chemisorption.

[0048]

[0049] Cyclic performance test To evaluate the cyclic performance of the adsorbent of this invention, a two-step "desorption-regeneration" method was used to conduct a cyclic regeneration test. 4RM-PHI obtained in Example 2 was selected as the test sample. After completing one round of methylene blue adsorption experiments, the saturated adsorbent was filtered and separated.

[0050] Subsequent treatment was carried out according to a liquid-to-solid ratio of 40 mL of desorption solution or regeneration solution to 0.01 g of waste adsorbent. First, the saturated adsorbent was placed in an acidic ethanol solution with pH=2 for desorption for 2 h; then, the desorbed adsorbent was transferred to a 0.1 mol / L NaOH solution for regeneration for 1 h.

[0051] After the desorption-regeneration process, the adsorbent was repeatedly washed with deionized water until the washing solution was nearly neutral; then it was dried at 60 °C for 12 h to obtain the regenerated adsorbent, which was then used in the next round of adsorption experiments.

[0052] The adsorption-desorption-regeneration process was repeated five times, and the changes in methylene blue removal rate in each cycle were recorded to evaluate the regeneration performance and cycle stability of the adsorbent. (See attached diagram.) Figure 6 .

[0053] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a red mud-modified PHI-type carbon nitride adsorbent, characterized in that, It is prepared using red mud powder and melamine as raw materials via a chloride salt template-assisted method.

2. The preparation method of the red mud modified PHI-type carbon nitride adsorbent according to claim 1, characterized in that, The mass ratio of red mud powder to melamine is (0.01-0.08):1, and the mass ratio of chloride template to melamine is (5-20):

1.

3. The preparation method of red mud modified PHI-type carbon nitride adsorbent according to claim 2, characterized in that, Includes the following steps: S1. Mix the red mud powder, melamine and chloride salt evenly; S2. Place the mixture obtained in step S1 in a tube furnace, heat it to 550-600℃ at a heating rate of 2-5℃ / min under an inert atmosphere and hold it for 4-8 hours. After cooling, the calcined product is obtained. S3. The calcined product described in step S2 is washed with deionized water to remove the chloride template, and then dried to obtain red mud modified PHI type carbon nitride adsorbent.

4. The preparation method of red mud modified PHI-type carbon nitride adsorbent according to claim 1, characterized in that, The chloride template is selected from one or more of lithium chloride, sodium chloride, and potassium chloride.

5. The preparation method of red mud modified PHI-type carbon nitride adsorbent according to claim 1, characterized in that, The red mud is Bayer process red mud, which is washed with water, dried, and then ground to 100-200 mesh.

6. The preparation method of the red mud modified PHI-type carbon nitride adsorbent according to claim 3, characterized in that, The inert atmosphere is argon or nitrogen.

7. A red mud-modified PHI-type carbon nitride adsorbent, characterized in that, The PHI-type carbon nitride adsorbent, prepared by the method described in claim 1, comprises red mud components and PHI-type carbon nitride components.

8. The red mud-modified PHI-type carbon nitride adsorbent according to claim 7, characterized in that, The red mud modified PHI-type carbon nitride adsorbent contains PHI-type carbon nitride and metal oxide components from red mud, and the metal oxide components are dispersed in the interlayer regions such as the surface of the PHI carbon nitride framework, forming a heterogeneous composite structure.

9. An application of the PHI-type carbon nitride adsorbent as described in claim 7 in the adsorption and removal of methylene blue from water, characterized in that, The PHI-type carbon nitride adsorbent exhibits removal efficacy for methylene blue within a pH range of 3-11.

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