A chitosan-manganese oxide composite photocatalyst for activating PMS, a preparation process and application thereof

Abstract

This invention discloses a preparation process for a chitosan-manganese oxide composite photocatalyst for activating PMS, comprising the following steps: (1) adding chitosan to a mixture of ethanol and water, and ultrasonically dispersing it to obtain a uniform dispersion, denoted as solution A; (2) adding KOH to solution A under stirring, and stirring to obtain a solution denoted as solution B; (3) dissolving KMnO4 in water, and obtaining a solution denoted as solution C; (4) adding solution B to solution C under stirring, and performing a synthesis reaction using an oil bath method or a hydrothermal method. After the product cools to room temperature, it is washed several times to obtain a solid, dried overnight, and the dried solid is ground to obtain the photocatalyst. This invention combines a low-cost, environmentally friendly, and easily prepared photocatalyst with advanced oxidation technology, utilizing the photocatalyst to activate PMS to form a system with strong oxidizing properties, which has great application potential in degrading dye pollutants in actual water bodies.

Description

Technical Field

[0001] This invention belongs to the field of photocatalyst preparation technology, specifically relating to a chitosan-manganese oxide composite photocatalyst for activating PMS, its preparation process, and its application. Technical Background

[0002] In recent years, researchers have found that removing organic dyes from industrial wastewater is becoming increasingly difficult. To address this, various physical, chemical, and biological methods have been employed, such as adsorption, membrane filtration, advanced oxidation processes (AOPs, including photocatalytic oxidation, Fenton oxidation, and Fenton-like processes), ion exchange, and catalytic reduction. Among these methods, advanced oxidation processes offer advantages over others, including higher redox potentials, lower costs, higher efficiency, environmentally friendly photo-oxidation processes, sustainable solar energy harvesting, and high reaction selectivity.

[0003] Advanced oxidation processes (AOPs) generate reactive oxygen species (ROS) with high redox potentials to degrade pollutants in wastewater. Photocatalytic oxidation, in particular, utilizes abundant sunlight for degradation and produces no other harmful gases, making it widely used. Photocatalysis involves providing activation regions to the surface of semiconductor materials under ultraviolet or visible light radiation, allowing redox reactions to occur on the semiconductor material. The products of the redox cycle are OH· and SO42-. -• The radical, in which reactive oxygen species (ROS) are generated, can effectively oxidize and degrade target pollutants. Therefore, a series of studies have been conducted on how to improve the degradation rate of target pollutants. Among the many elements used to prepare photocatalysts, transition metals are usually chosen for the following reasons: First, transition metals have a wide light absorption range, which can effectively utilize light energy; second, they have multiple valences, which can create defects on the surface or change its crystallinity, prolonging the recombination time of electrons and holes; third, doping with transition metal elements can improve their adsorption performance on reactants; and fourth, AOPs can utilize transition metals to activate peroxymonosulfate to degrade dyes. Researchers have studied the degradation of dyes under certain conditions using transition metal oxides, represented by cobalt, magnesium, bismuth, and cobalt-manganese bimetals, among many transition metal elements. Manganese is abundant in the Earth's crust, second only to iron, and has multiple oxidation forms. Furthermore, it has advantages such as low cost, good stability, environmental friendliness, and high catalytic activity, making it a major research material today. Among transition metal oxides, manganese oxides include MnO, MnO2, and Mn2O3, which have unique structures and compositions among oxides. The high stability and physicochemical properties of MnO2 in the environment have attracted widespread attention from researchers. Moon SA et al. showed that MnO2's degradation ability for Congo red is higher than that of Ag and CuO nanoparticles. Liu et al. used a hydrothermal method to prepare rod-shaped MnO2, achieving a degradation rate of up to 89.5% for methyl violet. Rabani I et al. found that the α-MnO2-Fe3O4 flower-like structure achieved a degradation rate of over 93% for MB and CV under visible light irradiation. Dong et al.'s research showed that MnO2, under light irradiation, activates PS, thereby effectively degrading bisphenol A. Sdy et al. found that different crystal phases of MnO2, when activating PMS to degrade phenol, follow the order α-MnO2 > β-MnO2 > γ-MnO2. Therefore, how to utilize the structure and metal oxides of MnO2 to activate PMS for dye degradation requires further investigation.

[0004] Chitosan (CS) is the only known alkaline polysaccharide in nature. It boasts advantages such as a large specific surface area, abundant active groups, and a stable crystal structure. Therefore, some studies have shown that the TiO2 / H2O2 system with added CS has a higher degradation efficiency for methylene blue than the traditional TiO2 / H2O2 system. Traditional photocatalysts suffer from limited photoresponsiveness, insufficient adsorption capacity, and easy aggregation, which restricts their application. However, combining CS with semiconductor materials can effectively increase active sites, reduce band gap energy, and enhance structural stability, significantly promoting the degradation of dyes in wastewater. Summary of the Invention

[0005] The purpose of this invention is to provide a chitosan-manganese oxide composite photocatalyst for activating PMS, its preparation process and its application, in order to solve the technical problem that existing oxidants have poor degradation effects and cannot meet application requirements.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A process for preparing a chitosan-manganese oxide composite photocatalyst for activating PMS includes the following steps:

[0008] (1) Weigh a certain amount of chitosan, add it to a mixture of ethanol and water, and sonicate it to obtain a uniform dispersion system, which is denoted as solution A.

[0009] (2) Under continuous stirring, KOH is added to solution A. The solution obtained after KOH is fully dissolved is called solution B.

[0010] (3) Dissolve KMnO4 in water and the resulting solution is denoted as solution C;

[0011] (4) Place solution C on a magnetic stirrer and add the solution B obtained above to solution C under stirring to obtain a brownish-black liquid. Continue stirring at room temperature and transfer to an oil bath or hydrothermal reactor to react for a certain period of time. After the reaction is completed, wait for the liquid to cool to room temperature, pour off the clear liquid on the top of the reactor, wash the solid at the bottom of the reactor several times with water and ethanol alternately, put the obtained solid into an oven to dry overnight, grind the dried solid, and obtain the chitosan-manganese oxide composite photocatalyst for activating PMS.

[0012] Preferably, the mass of CS in step (1) is 50-200 mg.

[0013] Preferably, in step (1), the volume of ethanol is 15.3 mL, the volume of water is 18 mL, and the ultrasonic time is 5 min.

[0014] Preferably, the mass of KOH in step (2) is 6.1g, and the stirring time is 1h.

[0015] Preferably, in step (3), 1.58 g of KMnO4 is dissolved in 25 mL of deionized water, and the resulting solution is denoted as C.

[0016] Preferably, in step (4), after stirring at room temperature for 4 hours, the mixture is transferred to an oil bath at 80°C and stirred for 24 hours. After cooling the liquid to room temperature, it is washed several times with deionized water and ethanol alternately. The resulting solid is placed in a 60°C oven and dried overnight. The dried solid is then ground to obtain the chitosan-manganese oxide composite photocatalyst for activating PMS.

[0017] Preferably, after stirring at room temperature for 4 hours in step (4), the brownish-black liquid is transferred to a 100mL reactor and reacted hydrothermally at 160℃ for 12 hours. After cooling the reactor to room temperature, it is washed several times with water and ethanol alternately. The collected solid is placed in a 60℃ oven to dry overnight. The dried solid is then ground to obtain the chitosan-manganese oxide composite photocatalyst for activating PMS.

[0018] This invention also provides an application of a chitosan-manganese oxide composite photocatalyst for activated PMS in dye degradation in water.

[0019] Preferably, the dye includes one or more of MB and TB.

[0020] Compared with existing technologies, this invention exhibits significant technical advantages, specifically in the following aspects. These advantages not only deepen the understanding of relevant chemical reaction mechanisms but also bring progress to practical applications:

[0021] (1) In terms of innovative photocatalyst preparation, this invention ingeniously utilizes the chemical reaction between CS (chitosan) and potassium permanganate to successfully synthesize a chitosan-modified manganese oxide photocatalyst. This innovation not only enriches the types of photocatalysts but also achieves efficient degradation of MB (methylene blue) and TB (toluidine blue) under mild conditions. The introduction of chitosan greatly optimizes the pore size distribution of manganese oxide, making the pore size of the CS-AM and CS-CM samples about 4-5 times larger than that of the unmodified AM. This structural optimization directly improves the catalyst's adsorption capacity and degradation efficiency for dyes, resulting in a degradation rate of over 92% for both dyes. Through detailed single-factor experimental analysis, this invention further clarifies the optimal range of CS addition amount and PMS (peroxymonosulfate) concentration, providing a scientific basis for parameter control in practical applications. Kinetic studies show that the degradation of MB follows a first-order kinetic model, while TB conforms more to a second-order kinetic model. This finding helps this invention to more accurately predict and control the degradation process. Furthermore, the strong alkalinity of the photocatalyst itself further enhances the degradation efficiency of dyes, which is of immeasurable value for improving the flexibility and economy of actual production processes.

[0022] In exploring the degradation mechanism, this invention discovered that PMS, upon photoactivation, can generate SO4-· (sulfate radicals). ·OH (hydroxyl radicals) and SO4-· together constitute the dominant radicals in the CS-AM / PMS system. These radicals not only significantly accelerate the dye degradation process but also effectively promote the redox cycle between Mn(III) and Mn(IV). This discovery provides a new perspective for enhancing the activity of photocatalysts. Therefore, this invention's strategy of activating PMS using CS-AM photocatalysts demonstrates great application potential in dye degradation in water, marking a significant step forward in addressing environmental pollution issues.

[0023] (2) In terms of the preparation process of nanomaterials, this invention has also made breakthrough progress. Chitosan-manganese oxide (CS-AM, CS-CM) nanomaterials prepared by oil bath method or hydrothermal method, through advanced characterization methods, this invention clearly observed that the introduction of CS significantly improved the specific surface area and pore structure of the catalyst. This structural optimization directly led to a significant increase in pore volume. Compared with pure manganese oxide (AM), its pores increased by about 4-5 times, which is crucial for improving the adsorption and catalytic performance of the catalyst.

[0024] In advanced oxidation / photocatalytic synergistic degradation experiments, this invention systematically studied the degradation of MB and TB dyes using PMS as the oxidant and CS-manganese oxide as the photocatalyst. The results showed that the addition of CS increased the adsorption sites on the surfaces of CS-AM and CS-CM, thereby promoting the effective capture and degradation of dye molecules. Under optimal conditions (CS addition of 167 mg, PMS concentration of 10 mg / L, pH 11), CS-AM achieved degradation rates of 94.5% and 92.2% for MB and TB, respectively, within just 150 min, a performance far exceeding that of similar catalysts. Furthermore, CS-AM exhibited excellent cycling stability; even after five cycles, its degradation rates for MB and TB remained above 82%, fully demonstrating the durability and economic efficiency of the catalyst of this invention.

[0025] Free radical quenching experiments further revealed the singlet oxygen in the CS-AM / PMS system ( 1 O2 plays a central role in the dye degradation process. The decomposition of PMS under light and the generation of sulfate and hydroxyl radicals after activation with Mn(III) jointly promote the degradation of PMS. 1The generation of O2, and the superoxide anions produced by the photoexcitation of manganese oxide in CS-AM, effectively replenish the consumption in the Mn(III) / Mn(IV) cycle, ensuring the continuous generation of singlet oxygen. This discovery not only deepens the understanding of the synergistic mechanism of advanced oxidation / photocatalysis in this invention, but also provides new ideas and approaches for developing more efficient and environmentally friendly water treatment technologies.

[0026] In summary, this invention has made significant progress in the preparation, performance optimization, and degradation mechanism exploration of photocatalysts, providing strong technical support for solving environmental pollution problems. Attached Figure Description

[0027] Figure 1 A schematic diagram of the synthesis of CS-AM and CS-CM;

[0028] Figure 2 SEM images of AM(a), CS-AM(b), and CS-CM(c);

[0029] Figure 3 EDS plots for AM(a), CS-AM(b), and CS-CM(c);

[0030] Figure 4 Infrared spectra of CS, CS-AM, and CS-CM;

[0031] Figure 5 XRD spectra of CS, AM, CS-AM, and CS-CM;

[0032] Figure 6 The images are XPS spectra AM(a), CS-AM(b), CS-CM(c), Mn2p and O1p full spectrum AM(a1) and (a2), CS-AM(b1) and (b2), and CS-CM(c1) and (c2).

[0033] Figure 7 The BJH aperture distribution curves for CS-AM(a), CS-CM(b), and AM(c) are shown.

[0034] Figure 8 The degradation performance of AM, CS-AM, and CS-CM on MB(a) and TB(b) is compared. The degradation curves of MB(c) and TB(d) with different CS additions under oil bath method at 80℃ and the degradation curves of MB(e) and TB(f) with different CS additions under hydrothermal method at 160℃ are also shown.

[0035] Figure 9A comparison of the degradation performance of PMS, PMS+CS-AM, and PMS+CS-CM on MB(a) and TB(b), and degradation curves of MB(c) and TB(d) at different PMS concentrations;

[0036] Figure 10 Degradation curves of MB(a) and TB(b) by CS-AM at different pH values;

[0037] Figure 11 Degradation curves of CS-AM at different initial concentrations of MB(a) and TB(b);

[0038] Figure 12 Figures show the catalytic kinetic model (a) for MB and the kinetic model (b) for TB;

[0039] Figure 13 The degradation cycle diagram of MB and TB by CS-AM;

[0040] Figure 14 The diagram shows the effect of free radical quenching on the CS-AM / PMS system. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to specific embodiments. It should be emphasized that the following description is merely exemplary and not intended to limit the scope or application of the invention. 1. Experimental Section

[0042] 1.1 Chemicals and reagents

[0043] Chitosan, potassium permanganate, potassium hydroxide, sodium hydroxide, hydrochloric acid, ethanol, potassium persulfate, methylene blue, toluidine blue. All solutions were prepared using deionized water.

[0044] 1.2 Catalyst Preparation

[0045] Oil bath method MnO xPreparation of the composite material (CS-AM). First, weigh out certain amounts of CS (50 mg, 84 mg, 167 mg, 200 mg), add the weighed CS to a mixture of 15.3 mL ethanol and 18 mL deionized water, and sonicate for 5 min to obtain a uniform dispersion, denoted as solution A. Under continuous stirring, add 6.1 g of KOH to solution A, and stir for 1 h to obtain solution B. Then, dissolve 1.58 g of KMnO4 in 25 mL of deionized water to obtain solution C. Finally, place solution C on a magnetic stirrer, and add the above-obtained solution B to solution C at a certain stirring speed to obtain a brownish-black liquid. Continue stirring at room temperature for 4 h, then transfer to an oil bath at 80 °C and continue stirring for 24 h. After cooling the liquid to room temperature, wash several times alternately with deionized water and ethanol. Place the obtained solid in a 60 °C oven and dry overnight. Grind the dried brown solid and store for later use. In addition, pure amorphous MnO without the addition of CS... x This is denoted as AM. The reaction mainly utilizes the redox reaction between potassium permanganate and ethanol to reduce manganese to manganese(III) and manganese(IV).

[0046] Hydrothermal MnO x Preparation of the composite material (CS-CM). To account for the influence of different crystal forms on catalyst performance, the amounts of CS, KMnO4, and KOH were kept constant during the preparation of CS-CM. The reaction conditions were changed from oil bath to hydrothermal. Solution B obtained above was added to solution C to obtain a brownish-black liquid. After stirring at room temperature for 4 hours, the brownish-black liquid was transferred to a 100 mL reactor and reacted at 160 °C for 12 hours. After cooling the reactor to room temperature, it was washed several times alternately with deionized water and ethanol. The collected solid was dried overnight in a 60 °C oven. The dried brown solid was ground and stored for later use. A schematic diagram of the synthesis steps is shown below. Figure 1 .

[0047] The preparation principle of this invention:

[0048] Oil bath method for preparing MnO x The detailed process and technical analysis of the composite material (CS-AM) are as follows. First, precise amounts of chitosan (CS) were weighed out at concentrations of 50 mg, 84 mg, 167 mg, and 200 mg. These different dosages of CS were intended to explore their impact on the properties of the composite material. Then, the precisely weighed CS was slowly added to a carefully prepared mixture of 15.3 mL of ethanol and 18 mL of deionized water. The addition of ethanol facilitated the dissolution and dispersion of CS, while the deionized water ensured the purity of the reaction system. After ultrasonic treatment for 5 minutes, CS formed a uniform dispersion in the mixture, which this invention designates as solution A. This step ensured the thorough dispersion of CS, laying a solid foundation for subsequent reactions.

[0049] Under continuous stirring, 6.1 g of potassium hydroxide (KOH) was slowly added to solution A. KOH, as an alkaline catalyst, not only promoted the dissolution of CS, but also participated in subsequent redox reactions, affecting MnO. x The formation and structure of [the substance] are significantly affected. After stirring for 1 hour, the resulting solution is denoted as B. At this point, KOH has been fully mixed with CS and the solvent, forming a mixture favorable for MnO. x The microenvironment for growth.

[0050] Next, 1.58 g of potassium permanganate (KMnO4) was dissolved in 25 mL of deionized water, and the resulting solution was denoted as C. KMnO4 is a form of MnO. x The main source of MnO, its concentration and solubility directly affect x The amount and structure of the product were determined. Solution C was placed on a magnetic stirrer, and solution B obtained above was slowly added to solution C at a certain stirring speed. During this process, complex redox reactions occurred between CS, KOH, and KMnO4, forming a brownish-black liquid mixture. Stirring was continued at room temperature for 4 hours to ensure the reaction proceeded fully.

[0051] The mixture was then transferred to an oil bath at 80°C and stirred for another 24 hours. The oil bath method provides a stable heating environment, which is beneficial for the formation and stabilization of the composite material structure. After 24 hours, the liquid was cooled to room temperature and washed several times alternately with deionized water and ethanol to remove unreacted raw materials and byproducts. The resulting solid was then dried overnight in a 60°C oven to completely remove moisture and solvent. The dried brown solid was then ground to obtain the composite photocatalyst CS-AM.

[0052] In exploring the preparation process of composite photocatalysts, controlling the dosage of each raw material and optimizing process parameters are crucial. The dosage of CS affects the structure and properties of the composite material; the amount of KOH directly relates to the reaction rate and MnO. x The amount of MnO produced; while the concentration of KMnO4 determines the amount of MnO produced. x The purity and structure of the composite material are also important factors. Furthermore, parameters such as oil bath temperature, stirring speed, and reaction time significantly affect the performance of the composite material. Through careful design and optimization, this invention successfully prepared a high-performance composite photocatalyst, CS-AM, achieving unexpected technical results.

[0053] Next, this invention shifts to the hydrothermal method for preparing MnO. xDetailed process of preparing the composite material (CS-CM). To further investigate the influence of different crystal forms on catalyst performance, in the preparation of CS-CM, this invention kept the amounts of CS, KMnO4, and KOH constant, but changed the reaction conditions from oil bath to hydrothermal. Solution B obtained above was added to solution C, again yielding a brownish-black liquid mixture. After stirring at room temperature for 4 hours, the brownish-black liquid was transferred to a 100 mL reactor and reacted at 160°C for 12 hours. The hydrothermal method provides a high-temperature and high-pressure environment, which is conducive to the formation of MnO4 with specific crystal forms. x After the reaction was completed, the reactor was cooled to room temperature and washed several times alternately with deionized water and ethanol. The collected solid was then dried overnight in a 60°C oven. The dried brown solid was then ground to obtain the composite photocatalyst CS-CM.

[0054] By comparing composite photocatalysts prepared by oil bath and hydrothermal methods, this invention reveals that different crystal forms of MnOx significantly affect the performance of the catalysts. This discovery not only enriches our understanding of the composite photocatalyst preparation process but also provides valuable experience for the design and optimization of subsequent catalysts.

[0055] 1.3 Photocatalytic Degradation Experiment

[0056] Degradation experiments were conducted under a 300W xenon lamp light source (PLS-SXE300+ / UV, Beijing Pofila Technology Co., Ltd., China). All photodegradation experiments were performed in 100mL beakers. PMS was added to a mixture of dye solution and catalyst, and the beaker was placed under a xenon lamp for degradation. The degradation of the dye by catalysts with different CS contents was studied, while several factors were varied: different amounts of CS added, initial dye concentration, PMS concentration, and pH. The stirring speed was kept constant at 600rpm. The addition of PMS and pH adjustment were completed before degradation. Before degradation began, the suspension was placed in the dark for 60 minutes to reach adsorption-desorption equilibrium.

[0057] During the illumination process, samples were taken at regular intervals, centrifuged (10000 rpm, 10 min), and filtered through a 0.22 μm polyethersulfone membrane filter. The optical absorbance of the dye at the maximum absorption wavelength was measured using a UV-Vis spectrophotometer (UV-2600, Shanghai Shimadzu Global Laboratory Consumables Co., Ltd, China). The formula for calculating the photodegradation efficiency is (Eq.(1)):

[0058] Dye removal rate (%) = (1-C) t / C0)×100 (1)

[0059] In the formula, C0 is the initial concentration of the dye, C t These are the corresponding concentrations of dye after exposure to light at different times.

[0060] In the repeatability experiments, after each cycle, the catalyst was not washed; instead, the reacted catalyst was collected and dried in a 60°C oven for use in the next cycle. All experiments were repeated 5 times.

[0061] 1.4 Characterization and Analysis Methods

[0062] The morphology and structure of the photocatalyst surface were observed using scanning electron microscopy (SEM, SUPRA 55Sapphire, GRE) after platinum-sprayed pretreatment. Fourier transform infrared spectroscopy was used to study the functional groups on the photocatalyst surface. X-ray diffraction (X-Pert PRO, MiniFlex600) was used to analyze the XRD spectra of the photocatalyst under the conditions of 40 kV voltage, 15 mA current, a scan rate of 0.02° / s, and a scan angle of 5–80°. X-ray photoelectron spectroscopy was used to analyze the carbon, oxygen, and manganese elements present in the photocatalyst. Ultraviolet spectrophotometry was used to analyze the absorbance of MB and TB at 664 nm and 640.4 nm.

[0063] 2. Results and Discussion

[0064] 2.1 Material Characterization

[0065] Using scanning electron microscopy to study MnO x The morphology was analyzed, and the surface structure and mapping images of AM, CS-AM, and CS-CM were shown in the figure. Figure 2 and Figure 3 As shown. In Figure 2 AM can be seen in Figure 2 (a) The sample exhibits a sheet-like structure. The morphology of the samples prepared by both methods changes significantly after the addition of CS, but the morphology also differs due to temperature variations. CS-AM ( Figure 2 (b) The sample exhibits a sheet-like stacked, porous structure; CS-CM ( Figure 2 Sample (c) exhibits a coexistence of sheet-like and rod-like structures. The figure also shows that all three samples exist at the nanoscale. The thickness of the nanosheets is approximately 2–5 nm.

[0066] exist Figure 3 The EDS images showed that the distribution of C elements in the CS-AM and CS-CM samples was consistent with the distribution of O and Mn elements in the AM sample, indicating that CS was successfully introduced into the composite material and was uniformly modified on the surface of manganese oxide.

[0067] (1)FT-IR

[0068] FT-IR spectra such as Figure 4 As shown, 1653cm -1 The corresponding peak is the amide group of CS, at 1434 cm⁻¹. -1 It is an alcohol group (CH-OH), but after CS undergoes a redox reaction with KMnO4, the above peak position shifts, and at 522 cm⁻¹... -1 The characteristic peaks of manganese oxide (Mn-O) are observed. The figure also shows that CS-AM and CS-CM peak at 522 cm⁻¹. -1 and 3000cm -1 The characteristic peaks on the left and right sides are more intense than those on AM, and the peak intensities also vary at different temperatures.

[0069] (2) XRD

[0070] The structures of CS, AM, CS-AM, and CS-CM were analyzed using XRD patterns, such as... Figure 5 As shown. Based on the XRD pattern, this invention shows that 12.9 0 25.1 0 MnO x The characteristic diffraction peaks at 20.4°, attributed to CS, disappeared, and other new peaks appeared. The peak intensities of CS-added manganese oxide were higher than those of manganese oxide itself, indicating that the addition of CS improved the MnO₂ content. x The crystallinity of CS-AM is improved, and the characteristic peaks of CS-AM prepared by the oil bath method are sharper and have higher intensity than those of CS-CM prepared by the hydrothermal method.

[0071] (3) XPS

[0072] XPS spectra were used to analyze the complete spectra of CS-AM and CS-CM, as well as the spectral regions and corresponding contents of O and Mn. Figure 6 As shown in the spectrum, the peak intensities of C1s and O1s in CS-AM and CS-CM are both higher than those in AM, indicating an increase in the content of both elements and demonstrating the successful introduction of CS. Figure 6 As shown in (a1, b1, and c1), the XPS spectrum of O1s can be divided into two peaks, corresponding to Mn-O and Mn-OH bonds, respectively. This indicates that the main components of the sample are manganese oxides and manganese hydroxides, and the contents of Mn-O and Mn-OH change in the presence of CS. The graphs also reveal that the manganese oxides may be heavily coated with hydroxyl groups, and that the hydroxides formed from the oxides are consumed to promote electron exchange at the interface between the manganese oxides and water. Figure 6As shown in (a2, b2, and c2), manganese in CS-AM and CS-CM is mainly Mn(Ⅳ), with Mn(Ⅳ) content of 46.27% and 56.26% in the two samples, and Mn(Ⅲ) content of 37.5% and 29.94% in the two samples, respectively. The presence of CS promotes the interconversion of Mn(Ⅲ) and Mn(Ⅳ).

[0073] (4) BET

[0074] As shown in Table 1, the addition of the biopolymer CS resulted in a significantly larger average particle size for both CS-AM and CS-CM samples compared to AM itself, with porosity approximately 4-5 times greater. This indicates that the addition of CS leads to a significant increase in the average particle size of MnO. X Particle aggregation occurred, but it increased the porosity of the catalyst. N2 adsorption-desorption isotherms and Barrett-Joyner-Halenda (BJH) pore size distribution curves were tested at 77 K for three samples, and the results are as follows: Figure 7 As shown, the N2 adsorption-desorption isotherms of the three samples can be classified as type IV adsorption isotherms. According to the IUPAC classification, the three samples have typical mesoporous structures and hysteresis loops. However, with the addition of CS and the increase of temperature, the mesoporous structure in the samples is damaged, causing the hysteresis loops to shift towards higher relative pressures.

[0075] Table 1

[0076]

[0077] 2.2 Catalytic performance

[0078] 2.2.1 Effect of CS addition amount on the two dyes

[0079] To investigate the role of CS in the samples, experiments were conducted to examine the effect of CS dosage on the dye. In these experiments, the present invention investigated the effects of excessive and insufficient CS dosage on the dye, as well as the effect of temperature on dye degradation. Figure 8 (a) Figure 8 In (b), a comparison of the degradation curves of MB and TB revealed that the sample performance was improved when CS was involved in the preparation processes of the two different methods. This indicates that the introduction of CS helps to improve the catalytic activity of samples prepared by the two different methods. Figure 8As shown in (cf), the amount of CS added needs to be within an appropriate range. The CS addition amounts were 0, 50 mg, 84 mg, 167 mg, and 200 mg. When the addition amount was 167 mg, the degradation rates of MB and TB were 94.5% and 92.2%, respectively. Therefore, the optimal addition amount was 167 mg; too high or too low a amount was detrimental to degradation. This may be because CS prevents electrons from returning and recombinizing with holes, thus hindering the reaction between electrons and PMS. When the CS addition amount is too high, after the redox reaction between CS and potassium permanganate, excessive CS will occupy the catalytic active sites of the catalyst; conversely, when the CS addition amount is too low, there will be insufficient adsorption sites on the catalyst, both of which will lead to a decrease in the dye degradation rate. Figure 8 (e) Figure 8 As observed in (f), the adsorption performance of CS-CM prepared from the same raw materials under hydrothermal conditions at 160℃ is worse than that of CS-AM prepared by the oil bath method at 80℃. Therefore, the temperature should be controlled during sample preparation. The temperature range is 60-100℃, and the temperature is best controlled at 80℃ in the oil bath.

[0080] 2.2.2 Effect of PMS concentration on dye degradation

[0081] In advanced oxidation processes, photocatalysts generate electron-hole pairs upon photoexcitation. The active substances formed by the combination of oxidant and catalyst are then used as a basis for dye degradation. Therefore, oxidants play a crucial role in dye degradation. Figure 9 (a) Figure 9 In (b), the comparison of the degradation curves of MB and TB verified that the addition of PMS promoted the degradation of the dyes in both samples. Similarly, through... Figure 9 (c) Figure 9 (d) It can be seen that when the PMS concentration increases to 10 mg / L, the degradation rate of both dyes reaches over 90%. However, when the PMS concentration increases from 10 mg / L to 20 mg / L, the degradation rate of both dyes gradually decreases. Therefore, the addition of PMS concentration should be appropriate, with the optimal concentration being 10 mg / L within the range of 0-20 mg / L. Too low a concentration will not produce sufficient PMS. 1 O2 promotes dye degradation, and this trend also reflects the synergistic effect of the samples prepared by the two methods with PMS. However, the reason for the decrease in dye degradation rate may be that the excessive oxidant quenched OH·.

[0082] 2.2.3 Effect of pH on dye degradation

[0083] To investigate the effect of pH on dye degradation, the influence of different pH values ​​on two dyes was examined. Figure 10 (a) Figure 10As shown in (b), strong alkaline and acidic conditions favor dye degradation. When the pH of the dye is strongly alkaline, the degradation rate of both dyes reaches over 90%, and when the pH is acidic, the degradation rate of both dyes is over 85%, because MB and TB are cationic dyes and will adsorb onto the negatively charged photocatalyst. In alkaline solutions, due to the increased electrostatic attraction, the photocatalyst surface becomes negatively charged, and the electrostatic attraction promotes the adsorption of positively charged dyes. When at lower pH, H... + It competes with cationic dyes, thus reducing the adsorption of dyes on the photocatalyst surface. However, under neutral pH conditions, due to the presence of amine and carboxyl groups on CS that strongly interact with protons, a small amount of sample is dissolved, leading to a reduction in adsorption sites on the material surface. Simultaneously, the decrease in pH also causes the charge on the manganese oxide surface to change from neutral to positive, resulting in reduced adsorption of cationic dyes. Therefore, the degradation rate of dyes is lower under neutral conditions. Within the pH range of 5-11, the sample itself is alkaline. At pH=11, the degradation rates of MB and TB are optimal, at 94.5% and 92.2%, respectively. Lowering the pH is detrimental to degradation.

[0084] 2.2.4 Effect of different initial concentrations on dye degradation

[0085] like Figure 11 (a) Figure 11 As shown in (b), the degradation rate of both MB and TB dyes decreased with increasing initial concentration. When the initial dye concentration was too high, a large number of dye molecules would be free in the solution due to the limited adsorption sites of the CS-AM sample, leading to a decrease in the dye degradation rate.

[0086] 2.2.5 Catalytic Kinetic Model

[0087] like Figure 11 (a) Figure 11 (b) The lower the initial concentration of the dye, the more favorable it is for degradation. This is also reflected in the kinetic models of MB and TB at different concentrations, such as... Figure 12 As shown. The catalytic kinetics conform to equations (2) and (3).

[0088] from Figure 12 It can be seen that a high initial dye concentration is detrimental to dye degradation, which is reflected in the kinetics: the lower the initial dye concentration, the higher the kinetic constant. Furthermore, it can be observed that the kinetic model of MB conforms to pseudo-first-order catalytic kinetics, while the kinetic model of TB conforms to pseudo-second-order catalytic kinetics.

[0089] ln(C t / C0)=-k1t (2)

[0090] In the formula, C0 is the initial concentration of the dye, Ct t represents the corresponding concentration of dye after illumination at different times t, and k1 is the degradation rate constant.

[0091] (1 / C t -1 / C0)=k2t (3)

[0092] In the formula, C0 is the initial concentration of the dye, C t t represents the corresponding concentration of dye after light exposure at different times t, and k2 is the degradation rate constant.

[0093] The fitting results show that the linear regression of CS-AM catalytic degradation of MB conforms to first-order catalytic kinetics, while the catalytic degradation of TB conforms to second-order catalytic kinetics.

[0094] 2.3 Recycling performance

[0095] Figure 13 This demonstrates the stability of CS-AM in the degradation of MB and TB dyes. The figure shows that in the first three cycles, the degradation rate for MB remained around 90%, and the degradation rate for TB remained around 87%. After five cycles, the degradation rates of both dyes decreased to around 82%, indicating the stability of CS-AM in the degradation of MB and TB dyes. The decrease in the degradation rates of MB and TB may be due to partial loss of the photocatalyst during the cycling experiments, or partial dissolution of CS. Comparing the experimental results with other reports (Table 2) proves that CS-AM has great potential for treating MB and TB dyes in wastewater and is superior to existing technologies.

[0096] Table 2 Comparison of the dye degradation capabilities of CS-AM and reported photocatalysts in the literature.

[0097]

[0098]

[0099] literature:

[0100] [1]Dawadi S, Gyawali K, Katuwal S, et al. Degradation of Methylene BlueUsing Hydrothermally Synthesized α-Manganese Oxide Nanostructures as aHeterogeneous FentonCatalyst[J]. Journal of Nanomaterials, 2022, 2022(1):3405066.

[0101] [2]LiY, Li M, Zhu C, et al. Main factors for photocatalytic degradation of rhodamine B byMoS2 activatedPMS[J]. Materials Letters, 2023, 341: 134191.

[0102] [3]Kiwaan HA, Atwee TM, Azab EA, et al. Photocatalytic degradation of organic dyes in the presence of nanostructured titanium dioxide [J]. Journal of Molecular Structure, 2020, 1200: 127115.

[0103] [4]Ramesh M.CuO as efficient photo catalyst for photocatalyticdecoloration of wastewater containing Azo dyes[J].Water Practice&Technology,2021,16(4):1078-1090.

[0104] 2.4 Degradation Mechanism

[0105] The advanced oxidation process used in this invention utilizes peroxymonosulfate (PMS) or peroxydisulfate (PDS) as oxidants to generate highly reactive sulfate free radicals (SO4). - · / SO5 - PMS is used to degrade target pollutants, and due to its asymmetric structure, it is more easily activated by light than PDS. Furthermore, hydroxyl radicals (OH·) can also be used to activate PMS. To verify the degradation of dyes by free radicals, 0.5 mL of quenchers (MeOH, IPA, FFA, KI) were introduced to quench the mixed solution of catalysts before experiments were conducted. Figure 14 It can be seen from this that ·O2 - , 1 O2, ·OH, SO4 - Together, they participate in the degradation of dyes as ROS, among which 1O2 plays a major role. Therefore, this invention proposes that the generation of reactive oxygen species not only promotes the degradation of dyes but also promotes the redox reaction of Mn(III) / Mn(IV). Meanwhile, studies by Shi et al. have shown that Mn(IV) (eg=0) is more likely to bind and adsorb with PMS than Mn(II) (eg=2) and Mn(III) (eg=1), which not only improves the recycling efficiency of Mn(IV) / Mn(III) but also further promotes the activation of PMS. In this invention, PMS is excited to generate SO4 under light irradiation. - · and OH - This leads to the formation of OH· and O2, with O2 gaining electrons to form O2. - Then, under the action of PMS, Mn(III) is oxidized to Mn(IV), and Mn(IV) is reacted with O2. - Under the influence of ·, it is reduced to Mn(Ⅲ), generating 1 O2 promotes both the degradation of the dye and the cyclic transformation of Mn(III) / Mn(IV) (Eq. 4 and 11). Simultaneously, SO4 generated during the degradation reaction... - The reason why · and OH· have little effect on dyes is mainly because they are converted into · 1 O2 and O2 - ·, and O2 - ·Then the reaction produces 1 O2. For 1 The specific reactions involved in the generation of O2 are as follows.

[0106]

[0107] SO4 - ·+OH - →SO4 2- +OH· (2)

[0108] HSO5→SO5 - ·+H + +e - (3)

[0109] Mn(Ⅲ) + HSO5- → Mn(Ⅳ) + SO4 - ·+OH - (4)

[0110] HSO5 - →SO5 2- +H + (5)

[0111] HSO5 - +SO5 2- →HSO4 - +SO4 2- + 1 O2 (6)

[0112] HSO4 - +OH→SO4 - ·+H2O (7)

[0113] 2SO5 - +H₂O→2HSO₄ - +1.5 1 O2 (8)

[0114] 2SO4 - ·+2OH - →2SO4 2- +2OH·+O2 (9)

[0115] O2+e - →O2 - · (10)

[0116] Mn(Ⅳ)+O2 - ·→Mn(Ⅲ)+O2 (11)

[0117] O2 - ·+OH·→ 1 O2+OH - (12)

[0118] In summary, the main pathways for ROS generation in the CS-AM / PMS system include: ① PMS decomposition upon exposure to light to generate SO4. - ·, and SO4 - • After a series of reactions, it is finally generated 1 O2 (Eq.(1)-(6)). ② PMS reacts to generate SO4 after activation by Mn(Ⅲ). - · and OH· (Eq. 4 and 9). ③ Oxygen adsorbed on the CS-AM surface gains electrons to generate O2. - ·, then reacts with OH· to produce 1 O2 (Eq. 10 and 12).

[0119] The degradation mechanism of dyes by the CS-AM / PMS system is as follows: First, HSO5 in PMS... - It decomposes into SO4 under light. - ·, and then react with CS-AM to form Mn(Ⅲ)-HSO5 - In e - Under the acceptor, Mn(III) is oxidized to Mn(IV), SO42- - • After a series of reactions, O2 is generated, which acts as an e-fouling agent. - donor promotes O2 - The generation of · further promotes the reduction of Mn(Ⅳ) to Mn(Ⅲ) and the decomposition of PMS, and also promotes1 The generation of O2 and the valence cycle of Mn.

[0120] 3. Conclusion

[0121] This invention successfully prepared CS-AM and CS-CM nano-photocatalysts using an oil bath method or a hydrothermal method, with a simple synthesis process. CS serves as both a reactant and an important component of the catalyst, increasing the porosity of CS-AM and CS-CM, and expanding the adsorption sites on the catalyst surface, which is beneficial for dye adsorption on the catalyst surface, thereby improving the dye degradation rate. CS-AM exhibits a strong synergistic effect in the advanced oxidation / photocatalytic degradation of dyes by activating PMS, achieving degradation rates of 94.5% for MB and 92.2% for TB. CS-AM also demonstrates good recyclability and stability, which can reduce material costs in practical applications.

[0122] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A preparation process for a chitosan-manganese oxide composite photocatalyst for activating PMS, characterized in that, Includes the following steps: (1) Weigh a certain amount of chitosan, add it to a mixture of ethanol and water, and sonicate it to obtain a uniform dispersion system, which is denoted as solution A; (2) Under continuous stirring, KOH is added to solution A, and the solution obtained after KOH is fully dissolved is called solution B; (3) Dissolve KMnO4 in water and the resulting solution is denoted as solution C; (4) Place solution C on a magnetic stirrer. Under stirring, add the solution B obtained above to solution C to obtain a brownish-black liquid. Continue stirring at room temperature, transfer to an oil bath or hydrothermal reactor and react for a certain time. After the reaction is completed, wait for the liquid to cool to room temperature, pour off the clear liquid on the top of the reactor, wash the solid at the bottom of the reactor several times with water and ethanol alternately, put the obtained solid into an oven to dry overnight, grind the dried solid, and obtain the chitosan-manganese oxide composite photocatalyst. The mass of chitosan mentioned in step (1) is 50-200 mg; In step (1), the volume of ethanol is 15.3 mL, the volume of water is 18 mL, and the sonication time is 5 min. The mass of KOH mentioned in step (2) is 6.1g, and the stirring time is 1h; In step (3), 1.58 g of KMnO4 is dissolved in 25 mL of deionized water, and the resulting solution is denoted as C; In step (4), the process when reacting in an oil bath is as follows: after stirring at room temperature for 4 hours, the mixture is transferred to an oil bath at 80°C and stirred for 24 hours. After cooling the liquid to room temperature, it is washed several times with deionized water and ethanol alternately. The resulting solid is placed in a 60°C oven to dry overnight. The dried solid is then ground to obtain the chitosan-manganese oxide composite photocatalyst. In step (4), the process of reacting in the hydrothermal reactor is as follows: After stirring at room temperature for 4 hours, the brownish-black liquid is transferred to a 100mL reactor and reacted hydrothermally at 160℃ for 12 hours. After cooling the reactor to room temperature, it is washed several times with water and ethanol alternately. The collected solid is placed in a 60℃ oven to dry overnight. The dried solid is ground to obtain the chitosan-manganese oxide composite photocatalyst.

2. A chitosan-manganese oxide composite photocatalyst prepared according to the process described in claim 1.

3. An application of the chitosan-manganese oxide composite photocatalyst according to claim 2 in dye degradation in water.

4. The application of the chitosan-manganese oxide composite photocatalyst according to claim 3 in the degradation of dyes in water, characterized in that, The dyes mentioned include one or more of methylene blue and toluidine blue.

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