A method for analyzing the adsorption mechanism of amino-functionalized magnetic graphene oxide on methylene blue in wastewater

Abstract

The present invention relates to a method for analyzing the adsorption mechanism of amino-functionalized magnetic graphene oxide on methylene blue in wastewater, belonging to the technical field of wastewater treatment. In the present invention, kinetic adsorption experiments and isothermal adsorption experiments of amino-functionalized magnetic graphene oxide on methylene blue are respectively carried out in water bodies, and the adsorption kinetic model and isotherm model are respectively analyzed; the equilibrium thermodynamic parameters in the process of amino-functionalized magnetic graphene oxide adsorbing methylene blue are calculated, and the heat transfer mode of the adsorption reaction of amino-functionalized magnetic graphene oxide on methylene blue is determined according to the equilibrium thermodynamic parameters; FTIR spectral analysis is carried out on amino-functionalized magnetic graphene oxide before and after adsorbing methylene blue, and the adsorption mechanism of amino-functionalized magnetic graphene oxide on methylene blue in wastewater is determined in combination with the kinetic model. During the adsorption process of methylene blue, there are electrostatic interaction, hydrogen bond interaction and π-π conjugate interaction between amino-functionalized magnetic graphene oxide and methylene blue.

Description

Technical Field

[0001] The present invention relates to a method for analyzing the adsorption mechanism of amino-functionalized magnetic graphene oxide on methylene blue in wastewater, belonging to the technical field of wastewater treatment. Background Art

[0002] At present, there are many methods for treating methylene blue (MB) dye wastewater. Among them, the adsorption method is considered to be one of the most promising water treatment technologies for treating dye wastewater due to its advantages such as high efficiency, low cost, simple operation, and no secondary pollution. Although there are many studies on the treatment of methylene blue (MB), there are still problems such as small adsorption capacity and difficulty in separating the adsorbent from the aqueous solution. For example, Han et al. (2021) synthesized a 3D hydrogel, and the maximum adsorption capacity for methylene blue (MB) was only 135.17 mg·g -1 , Yu et al. (2021) prepared zinc oxide / biochar nanomaterials with a maximum adsorption capacity for methylene blue (MB) of 160 mg·g -1 , Jiang et al. (2021) prepared graphene oxide-based composites with a maximum adsorption capacity for methylene blue (MB) of 558.66 mg·g -1 , but there are problems such as difficult separation.

[0003] Graphene oxide (GO) has a layered structure, a large surface area, many oxygen-containing functional groups, and a negative charge between the layers, which easily attracts positively charged particles. It has excellent solubility, high chemical reactivity, and intelligent self-assembly performance. However, the carbon skeleton of GO is hydrophobic and the oxygen-containing functional groups are hydrophilic, so it has good dispersibility in solvents and is not easy to separate when dispersed in the solution, which is not conducive to its large-scale use. And the maximum adsorption capacity of pure GO for MB is only 224 mg·g -1 . In order to improve the adsorption capacity of GO for methylene blue (MB) and the recovery ability of the adsorbent, designing GO-based composites with adjustable structure and function and studying their adsorption mechanism are crucial for the field of wastewater treatment. Summary of the Invention

[0004] In view of the problems of low adsorption capacity of graphene oxide for methylene blue, poor recovery ability and unclear adsorption mechanism, the present invention provides a method for analyzing the adsorption mechanism of amino-functionalized magnetic graphene oxide for methylene blue in wastewater. The magnetic nanoparticles Fe3O4 are modified on the surface of graphene oxide (GO) by the co-precipitation method, and triethylenetetramine (TETA) is grafted onto the surface of MGO by the amidation reaction, that is, the nucleophilic reaction between amino groups and epoxy groups, to prepare an amino-functionalized magnetic graphene oxide adsorbent with high adsorption capacity, high recovery ability and spontaneous endothermic adsorption of methylene blue. Through the adsorption kinetic model, isotherm model, equilibrium thermodynamic parameters and infrared spectrum detection, it is determined that there are electrostatic interaction, hydrogen bond interaction and π-π conjugate interaction between the amino-functionalized magnetic graphene oxide MGO-TETA adsorbent and methylene blue MB during the adsorption process.

[0005] A method for analyzing the adsorption mechanism of amino-functionalized magnetic graphene oxide for methylene blue in wastewater, the specific steps are as follows:

[0006] (1) Conduct a kinetic adsorption experiment of amino-functionalized magnetic graphene oxide for methylene blue in water, and analyze the adsorption kinetic data of methylene blue by using the pseudo-first-order kinetic model, pseudo-second-order kinetic model, intraparticle diffusion model and liquid film diffusion model respectively to obtain the optimal kinetic model and analyze the control factors of the kinetic adsorption rate of methylene blue;

[0007] (2) Conduct an isothermal adsorption experiment of amino-functionalized magnetic graphene oxide for methylene blue in water, fit the adsorption isotherm by using the Langmuir isotherm model, Freundlich isotherm model and Temkin adsorption isotherm model respectively, calculate the linear correlations of the Langmuir isotherm model, Freundlich isotherm model and Temkin adsorption isotherm model respectively to obtain the optimal isotherm model; calculate the maximum adsorption capacity of amino-functionalized magnetic graphene oxide for methylene blue at the preset adsorption temperature according to the optimal isotherm model;

[0008] (3) Through the isothermal adsorption experiment, calculate the equilibrium thermodynamic parameters of the process of amino-functionalized magnetic graphene oxide adsorbing methylene blue, where the equilibrium thermodynamic parameters include the standard Gibbs free energy change ΔG 0 、standard enthalpy change ΔH 0 and standard entropy change ΔS 0 [[ID=]](18); determine the heat transfer mode of the adsorption reaction of amino-functionalized magnetic graphene oxide for methylene blue according to the equilibrium thermodynamic parameters;

[0009] (4) FTIR spectroscopy was performed on both the amino-functionalized magnetic graphene oxide before adsorbing methylene blue and the amino-functionalized magnetic graphene oxide after adsorbing methylene blue. Combining with the optimal kinetic model in step (1), the adsorption mechanism of methylene blue on amino-functionalized magnetic graphene oxide in wastewater was determined.

[0010]

[0011] Where q e is the equilibrium adsorption capacity mg.g -1 ; V is the volume of the solution L; C0 is the initial concentration mol.L before methylene blue adsorption -1 ; C e is the equilibrium concentration mg.L after methylene blue adsorption -1 ; m is the mass of the adsorbent g;

[0012] The linear expression of the pseudo-first-order kinetic model in step (1) is

[0013] ln(q e -q t ) = ln q e，cal -k1t

[0014] The linear expression of the pseudo-second-order kinetic model is

[0015]

[0016] The linear expression of the intraparticle diffusion model is

[0017]

[0018] Liquid film diffusion model

[0019]

[0020] Where q e is the adsorption capacity at adsorption equilibrium mg.g -1 ; q t is the adsorption capacity at adsorption time t mg.g -1 ; q e,cal is the theoretical equilibrium adsorption capacity of the fitting model mg.g -1 ; k1 is the rate constant of the pseudo-first-order kinetic model min -1 ; k2 is the rate constant of the pseudo-second-order kinetic model g.mg -1 .min -1 ; k id is the rate constant of different stages of the intraparticle diffusion model mg.g -1 .min -0.5 ; k FD is the liquid film diffusion rate constant min-1 ; C is a constant related to the boundary layer, mg / g -1 ; C1 is the constant of the liquid film diffusion model, g / mg -1 .

[0021] The method for determining the optimal kinetic model:

[0022] Calculate the fitting correlation coefficients R of the pseudo-first-order kinetic model, pseudo-second-order kinetic model, intraparticle diffusion model, and liquid film diffusion model respectively 2 , the fitting correlation coefficient R 2 The model with the R value closest to 1 is the optimal isotherm model

[0023] The linear equation expression of the Langmuir isotherm model in step (2) is

[0024]

[0025] In the formula, C e is the adsorption equilibrium concentration of the solution, mg / L -1 ; q e is the adsorption capacity at adsorption equilibrium, mg / g -1 ; q max is the maximum monolayer adsorption capacity of the Langmuir model, mg / g -1 ; K L is the adsorption equilibrium constant of the Langmuir model, L / mg -1 ;

[0026] Determine the applicability and shape of the adsorption isotherm according to the separation factor R of the Langmuir isotherm model; the separation factor R L ; the expression of the separation factor R L is

[0027]

[0028] In the formula, C0 is the concentration of the methylene blue solution before adsorption, mg / L -1 ; K L is the adsorption equilibrium constant of the Langmuir model, L / mg -1 ;

[0029] The linear equation expression of the Freundlich isotherm model is

[0030]

[0031] In the formula, q e is the adsorption capacity at adsorption equilibrium, mg / g -1 , Ce is the adsorption equilibrium concentration of the solution, mg / L -1, n is the Freundlich empirical parameter related to adsorption intensity; K F is the adsorption equilibrium constant Lg of the Freundlich model -1 ;

[0032] The linear equation expression of the Temkin adsorption isotherm model is:

[0033] q e =BlnK T +BlnC e

[0034] Where q e is the adsorption capacity at adsorption equilibrium mg.g -1 , the adsorption equilibrium concentration of Ce solution mg.L -1 , B is the number of mg.g related to the adsorption heat -1 ;K T is the adsorption equilibrium constant Lg of the Temkin adsorption isotherm model -1 .

[0035] The standard Gibbs free energy change ΔG 0 The expression is

[0036] ΔG 0 =-RTlnK c

[0037] Standard enthalpy change ΔH 0 The expression is

[0038]

[0039] Standard entropy change ΔS 0 The expression is

[0040] ΔG 0 =ΔH 0 -TΔS 0

[0041] Where K c is the equilibrium constant at each temperature; where K c The expression is

[0042]

[0043] Where q e is the equilibrium adsorption capacity of methylene blue, and Ce is the concentration of methylene blue at adsorption equilibrium.

[0044] The preparation method of the amino-functionalized magnetic graphene oxide comprises the following specific steps:

[0045] Under stirring conditions, FeCl3·6H2O and FeCl2·4H2O were dissolved in ultrapure water to obtain a mixed solution A, and then a graphene oxide aqueous suspension was added, and magnetic stirring was carried out for 2 - 3 min to obtain a mixed solution B; at a temperature of 65 - 90 °C, NH3·H2O was added dropwise to the mixed solution B to maintain the solution pH at 9 - 12 and react for 48 - 68 min to obtain a magnetic graphene oxide solution. TETA was added to the magnetic graphene oxide solution and reacted at a constant temperature for 12 - 36 h, cooled to room temperature, and solid-liquid separation was carried out. The solid was washed successively with ethanol and ultrapure water, and vacuum dried to obtain amino-functionalized magnetic graphene oxide;

[0046] The molar ratio of Fe 3+ to Fe 2+ in the mixed solution A is 1:1 - 5, the volume ratio of the graphene oxide aqueous suspension to the mixed solution A is 1:3 - 6, the concentration of graphene oxide in the graphene oxide aqueous suspension is 1 - 50 mg / mL, and the volume ratio of TETA to the magnetic graphene oxide solution is 1:20 - 40.

[0047] The beneficial effects of the present invention are as follows:

[0048] (1) The present invention prepares an amino-functionalized magnetic graphene oxide adsorbent MGO-TETA with high adsorption capacity, high recovery ability and spontaneous endothermic adsorption of methylene blue MB by an amidation one-pot method;

[0049] (2) The present invention proves through the study of the adsorption kinetic model that the adsorption kinetic behavior of the amino-functionalized magnetic graphene oxide adsorbent for methylene blue is chemisorption, that is, the rate-determining step of MB adsorption on MGO-TETA is jointly controlled by intraparticle diffusion and liquid film diffusion;

[0050] (3) The present invention can calculate the maximum adsorption capacity of amino-functionalized magnetic graphene oxide for methylene blue at a preset adsorption temperature through the isotherm model; it is proved through the study of thermodynamic parameters that the adsorption of the amino-functionalized magnetic graphene oxide adsorbent for methylene blue is a spontaneous and feasible endothermic process, and the degree of disorder increases continuously during the adsorption process;

[0051] (4) There are electrostatic interactions, hydrogen bond interactions, and π-π conjugate interactions between the amino-functionalized magnetic graphene oxide MGO-TETA adsorbent and methylene blue MB. Description of the Drawings

[0052] Figure 1 is the adsorption curve of methylene blue adsorption amount vs. time in Example 1;

[0053] Figure 2 is the pseudo-first-order kinetic model diagram;

[0054] Figure 3It is the graph of the pseudo-second-order kinetic model;

[0055] Figure 4 It is the graph of the intraparticle diffusion model;

[0056] Figure 5 It is the graph of the liquid film diffusion model;

[0057] Figure 6 It is the effect of temperature on the adsorption of MB by MGO-TETA;

[0058] Figure 7 It is the graph of the Langmuir isotherm model

[0059] Figure 8 It is the graph of the Freundlich isotherm model;

[0060] Figure 9 It is the graph of the Temkin isotherm model

[0061] Figure 10 It is the adsorption thermodynamics graph;

[0062] Figure 11 It is the infrared spectrum graph of graphene oxide, amino-functionalized magnetic graphene oxide before adsorbing methylene blue, and amino-functionalized magnetic graphene oxide after adsorbing methylene blue;

[0063] Figure 12 It is the Raman spectrum graph of graphene oxide, amino-functionalized magnetic graphene oxide before adsorbing methylene blue, and amino-functionalized magnetic graphene oxide after adsorbing methylene blue;

[0064] Figure 13 It is the adsorption mechanism graph of amino-functionalized magnetic graphene oxide to methylene blue;

[0065] Figure 14 It is the effect of pH value in Example 2 on the adsorption of MB by MGO-TETA (initial concentration is 100mg.L -1 )

[0066] Figure 15 It is the measurement of the pH of the MGO-TETA adsorbent by the ΔpH drift method in Example 2 pzc ;

[0067] Figure 16 It is the effect of ionic strength on the adsorption of methylene blue by the amino-functionalized magnetic graphene oxide adsorbent in Example 3;

[0068] Figure 17 It is the effect of the adsorbent dosage on the adsorption of methylene blue by the amino-functionalized magnetic graphene oxide adsorbent in Example 3. Specific implementation mode

[0069] The present invention will be further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the content described above.

[0070] In the embodiment of the present invention, the preparation method of amino-functionalized magnetic graphene oxide is as follows:

[0071] Weigh 2.7 g of FeCl3·6H2O and 1.0 g of FeCl2·4H2O into a 250 mL beaker, add 200 mL of ultrapure water to dissolve to obtain a mixed solution A. Transfer the mixed solution A to a 500 mL round-bottom flask, add 85 mL of graphene oxide aqueous suspension (the concentration of graphene oxide in the graphene oxide aqueous suspension is 10 mg / mL) under stirring, and continue magnetic stirring for 3 min to obtain a mixed solution B. Transfer the mixed solution B to an oil bath and stir at a temperature of 85 °C for 5 min. Dropwise add NH3·H2O to maintain the pH of the mixed solution B at 10 ± 0.5 and react for 48 min to obtain a magnetic graphene oxide solution; then add 3 mL of TETA to the magnetic graphene oxide solution and continue the constant-temperature reaction for 12 h; after the reaction is completed, cool to room temperature, wash 5 times with ethanol first, and then wash 5 times with ultrapure water. Put the washed product into a vacuum drying oven and dry at 60 °C for 24 h to finally obtain a TETA-MGO solid, that is, amino-functionalized magnetic graphene oxide.

[0072] Example 1: A method for analyzing the adsorption mechanism of amino-functionalized magnetic graphene oxide on methylene blue in wastewater is as follows:

[0073] (1) Conduct a kinetic adsorption experiment of amino-functionalized magnetic graphene oxide on methylene blue in water: In 150 mL of methylene blue solutions with initial concentrations of 100, 150, and 200 mg·L -1 , add 150 mg of amino-functionalized magnetic graphene oxide adsorbent. At times 0, 2, 4, 6, 8, 10, 15, 20, 25, 30, 40, 50, 60, 120, 180, 240, 300, 360, and 420 min, separate the amino-functionalized magnetic graphene oxide adsorbent and the methylene blue MB solution by a magnet, and take samples to detect the concentration of methylene blue MB in the solution;

[0074]

[0075] In the formula, q e is the equilibrium adsorption capacity mg·g -1 ; V is the volume of the solution L; C0 is the initial concentration before methylene blue adsorption mol·L -1 ; C e is the equilibrium concentration after methylene blue adsorption mg·L -1 ; m is the mass of the adsorbent g;

[0076] Draw the adsorption curve of methylene blue adsorption capacity versus time (see Figure 1 );

[0077] Analyze the adsorption kinetic data of methylene blue using the pseudo-first-order kinetic model, pseudo-second-order kinetic model, intraparticle diffusion model, and liquid film diffusion model respectively;

[0078] Among them, the linear expression of the pseudo-first-order kinetic model is

[0079] ln(q e -q t ) = ln q e，cal -k1t

[0080] The linear expression of the pseudo-second-order kinetic model is

[0081]

[0082] The linear expression of the intraparticle diffusion model is

[0083]

[0084] Liquid film diffusion model

[0085]

[0086] In the formula, q e is the adsorption capacity at adsorption equilibrium mg.g -1 ; q t is the adsorption capacity at adsorption time t mg.g -1 ; q e,cal is the theoretical equilibrium adsorption capacity of the fitting model mg.g -1 ; k1 is the rate constant of the pseudo-first-order kinetic model min -1 ; k2 is the rate constant of the pseudo-second-order kinetic model g.mg -1 .min -1 ; k id is the rate constant of different stages of the intraparticle diffusion model mg.g -1 .min -0.5 ; k FD is the liquid film diffusion rate constant min -1 ; C is a constant related to the boundary layer mg.g -1 ; C1 is the liquid film diffusion model constant g.mg -1 ;

[0087] The fitting curve graphs of the pseudo-first-order kinetic model, pseudo-second-order kinetic model, intraparticle diffusion model, and liquid film diffusion model are shown in Figures 2 - 5; The kinetic parameters of the pseudo-first-order kinetic model, pseudo-second-order kinetic model, intraparticle diffusion model, and liquid film diffusion model are shown in Table 1.

[0088] Table 1 Kinetic parameters of MB on MGO-TETA

[0089]

[0090]

[0091] The correlation coefficient R 2 fitted by the pseudo-first-order kinetic model is 0.9083, and the correlation coefficient R 2 fitted by the pseudo-second-order kinetic model is 0.9999, which is closer to 1 and has better correlation; the theoretical equilibrium adsorption capacity q e,cal calculated by the pseudo-second-order kinetic model is 95.79 mg·g -1 , which is closer to the actual maximum adsorption capacity q e,exp = 96.46 mg·g -1 . Therefore, the pseudo-second-order kinetic model is the optimal kinetic model, which can more accurately describe the adsorption kinetics of MB on MGO-TETA, indicating that chemical adsorption is the control step of the whole adsorption process, and the kinetic adsorption rate of methylene blue is jointly controlled by intraparticle diffusion and liquid film diffusion;

[0092] (2) Isothermal adsorption experiment of amino-functionalized magnetic graphene oxide on methylene blue in water: Add 15 mg of amino-functionalized magnetic graphene oxide adsorbent into 15 mL of methylene blue solutions with different concentrations (40 - 2000 mg·L -1 ). After adsorption at 25, 35, and 45 °C for 6 h, separate the adsorbent and methylene blue solution by a magnet, and sample to test the concentration of the methylene blue solution;

[0093] The influence of temperature on the adsorption of MB (initial concentration is 100 mg·L -1 ) by MGO-TETA (see Figure 6 ), the maximum equilibrium adsorption capacities of the adsorbent for MB at 25, 35, and 45 °C are 394.71, 414.67, and 638.90 mg·g -1 ;

[0094] The relationship between the amount of methylene blue adsorption and the initial concentration of methylene blue: within a certain range, with the increase of the initial concentration of methylene blue, the amount of methylene blue adsorption also increases;

[0095] The adsorption isotherms were respectively fitted by the Langmuir isotherm model, Freundlich isotherm model, and Temkin adsorption isotherm model (see Figures 7 - 9 ).

[0096] The linear equation expression of the Langmuir isotherm model is

[0097]

[0098] Where C e is the adsorption equilibrium concentration of the solution, mg / L -1 ; q e is the adsorption capacity at adsorption equilibrium, mg / g -1 ; q max is the maximum monolayer adsorption capacity of the Langmuir model, mg / g -1 ; K L is the adsorption equilibrium constant of the Langmuir model, L / mg -1 ;

[0099] According to the separation factor R of the Langmuir isotherm model L to determine the applicability and shape of the adsorption isotherm; the separation factor R L The expression of is

[0100]

[0101] Where C0 is the concentration of the methylene blue solution before adsorption, mg / L -1 ; K L is the adsorption equilibrium constant of the Langmuir model, L / mg -1 ;

[0102] The linear equation expression of the Freundlich isotherm model is

[0103]

[0104] Where q e is the adsorption capacity at adsorption equilibrium, mg / g -1 , Ce is the adsorption equilibrium concentration of the solution, mg / L -1 , n is the Freundlich empirical parameter related to the adsorption intensity; K F is the adsorption equilibrium constant of the Freundlich model, L / g -1 ;

[0105] The linear equation expression of the Temkin adsorption isotherm model is

[0106] q e = BlnK T + BlnC e

[0107] Where q e is the adsorption capacity at adsorption equilibrium, mg / g-1 , the adsorption equilibrium concentration of the Ce solution, mg·L -1 , B is a number related to the adsorption heat, mg·g -1 ; K T is the adsorption equilibrium constant of the Temkin adsorption isotherm model, L·g -1 ;

[0108] The linear correlations of the Langmuir isotherm model, Freundlich isotherm model, and Temkin adsorption isotherm model were calculated respectively (see Table 2).

[0109] Table 2 Isotherm parameters of MB on MGO-TETA

[0110]

[0111] The Langmuir adsorption isotherm has a better linear correlation than the Freundlich adsorption isotherm and Temkin adsorption isotherm models, and its R 2 = 0.9873. At the same time, the maximum monolayer adsorption capacity (q max，25℃ = 392.16 mg·g -1 , q max，35℃ = 411.52 mg·g -1 , q max，45℃ = 628.93 mg·g -1 ) calculated by the Langmuir isotherm model is closer to the actual maximum adsorption amount (q e,25℃ = 394.71 mg·g -1 , q e,35℃ = 414.67 mg·g -1 , q e,45℃ = 638.90 mg·g -1 ), indicating that the adsorption mode of MB on MGO-TETA is more suitable to be described by the Langmuir isotherm model, which is a monolayer uniform adsorption at specific positions;

[0112] Therefore, the Langmuir adsorption isotherm model is the optimal isotherm model; the maximum adsorption amount of amino-functionalized magnetic graphene oxide for methylene blue at the preset adsorption temperature can be calculated according to the optimal isotherm model;

[0113] (3) Through the isothermal adsorption experiment, for MB with an initial concentration of 100 mg·L -1 , by plotting InK c against 1000 / T (see Figure 10 ), from Figure 10It can be seen that InKc has a good linear relationship with 1000 / T, indicating that the adsorption conforms to the temperature coefficient method formula; then ΔH is calculated from the slope and intercept of the straight line in the figure. 0 and ΔS 0 thermodynamic parameters (see Table 3), where the equilibrium thermodynamic parameters include the standard Gibbs free energy change ΔG 0 、standard enthalpy change ΔH 0 and standard entropy change ΔS 0 ;

[0114] The expression for the standard Gibbs free energy change ΔG 0 is

[0115] ΔG 0 =-RTlnK c

[0116] The expression for the standard enthalpy change ΔH 0 is

[0117]

[0118] The expression for the standard entropy change ΔS 0 is

[0119] ΔG 0 =ΔH 0 -TΔS 0

[0120] In the formula, K c is the equilibrium constant at each temperature; where the expression for K c is

[0121]

[0122] In the formula, q e is the equilibrium adsorption capacity of methylene blue, and Ce is the concentration of methylene blue at adsorption equilibrium;

[0123] Table 3 Adsorption thermodynamic parameters

[0124] [[ID=!65]]

[0125] At all the studied temperatures, ΔG 0 is negative, indicating that the adsorption of MB on MGO-TETA is a spontaneous and feasible process. The positive values of ΔH 0 show that the adsorption reaction is endothermic, and the positive values of ΔS 0 also indicate that the degree of disorder is increasing during the adsorption process; therefore, according to the equilibrium thermodynamic parameters, it is determined that the adsorption reaction of amino-functionalized magnetic graphene oxide to methylene blue is a spontaneous, feasible and endothermic process;

[0126] (4) Perform FTIR spectral analysis on both the amino-functionalized magnetic graphene oxide before adsorbing methylene blue and the amino-functionalized magnetic graphene oxide after adsorbing methylene blue;

[0127] Infrared spectra of graphene oxide, amino-functionalized magnetic graphene oxide before adsorbing methylene blue, and amino-functionalized magnetic graphene oxide after adsorbing methylene blue (see Figure 11 );

[0128] Combined with the optimal kinetic model in step (1), namely the pseudo-second-order kinetic model, is the optimal kinetic model, which can more accurately describe the adsorption kinetics of MB on MGO-TETA, indicating that chemical adsorption is the control step of the entire adsorption process. The kinetic adsorption rate of methylene blue is jointly controlled by intraparticle diffusion and liquid film diffusion, and the adsorption mechanism of amino-functionalized magnetic graphene oxide on methylene blue in wastewater is determined; The absorption peak appearing at 3421 cm -1 is formed by the stretching vibration of -OH and moves to 3414 cm after adsorbing MB -1 . During the adsorption process, the -COOH group on MGO-TETA and the H-donor groups (hydroxyl and carboxyl groups) on the surface of GO respectively form hydrogen bond interactions with the H-acceptor atom (N) of the MB molecule; The characteristic peaks of MGO-TETA at 1636 and 1543 cm -1 belong to the stretching vibration peaks of the amide group and move to 1650 and 1611 cm after adsorbing MB -1 , indicating that there is an electrostatic interaction between the carboxyl group in MGO-TETA and the cationic dye molecule; After adsorption, the stretching vibration of the benzene ring skeleton appears at 883 cm -1 , indicating that there may be π-π conjugate interactions between MGO-TETA and the cationic dye molecule during the adsorption process;

[0129] Raman spectra of graphene oxide, amino-functionalized magnetic graphene oxide before adsorbing methylene blue, and amino-functionalized magnetic graphene oxide after adsorbing methylene blue (see Figure 12 ); When the MB cationic dye molecule acts as an electron donor or acceptor, it will change the electronic structure of GO. The electron acceptor will cause an increase in the frequency of the G absorption band, while the electron donor will cause a decrease in the frequency of the absorption band. After MGO-TETA adsorbs MB, the G absorption band shifts, indicating that MB shows an electron-donating effect, confirming the existence of π-π conjugate interactions between the dye molecule and MGO-TETA;

[0130] Therefore, during the adsorption process, there are electrostatic interactions, hydrogen bond interactions, and π-π conjugate interactions between the MGO-TETA adsorbent and MB (the mechanism is shown in Figure 13 ).

[0131] Example 2: Investigate the effect of pH from 1 to 12 on the adsorption of methylene blue by the amino-functionalized magnetic graphene oxide adsorbent in water: At a temperature of 298 K, 15 mg of the amino-functionalized magnetic graphene oxide adsorbent was added to 15 mL of an MB solution with a concentration of 100 mg·L -1 . After 6 h of adsorption, the adsorbent and the methylene blue solution were separated by a magnet, and a sample was taken to measure the concentration of the methylene blue solution;

[0132] The effect of pH on the adsorption of MB (initial concentration of 100 mg·L -1 ) by MGO-TETA is shown in Figure 14 . As the initial pH of the solution increases, the adsorption capacity of MGO-TETA for MB gradually increases;

[0133] The zero-point charge of MGO-TETA was tested, and the pH of the MGO-TETA adsorbent was measured by the ΔpH drift method. pzc See Figure 15 . The pH at the zero point of charge of the TETA-MGO adsorbent is about 7.65. When the pH is less than 7.65, the surface of the adsorbent is easily protonated to obtain a positive charge, which is not conducive to the adsorption of cationic methylene blue molecules; when the pH is greater than 7.65, the surface of the adsorbent is easily deprotonated to obtain a negative charge, which is conducive to the adsorption of cationic dye methylene blue, and the absolute value of pH-pzc increases with the increase of the pH value, and remains basically unchanged when the pH is 10 - 12; the adsorption capacities at pH 10, 11, and 12 are 76.33, 87.15, and 86.45 mg·g -1 respectively, and pH = 11 is the optimal adsorption pH.

[0134] Example 3: Investigate the effect of ionic strength and adsorbent dosage on the adsorption of methylene blue by the amino-functionalized magnetic graphene oxide adsorbent:

[0135] Ionic strength: 15 mg of the adsorbent was added to MB solutions containing NaCl, CaCl2, and FeCl3 with concentrations of 0.01 - 0.12 mol·L -1 s respectively, where the original concentration of methylene blue was 100 mg·L -1 , the pH value was 11, and the volume was 15 mL; after 6 h of adsorption at a temperature of 298 K, the adsorbent and the methylene blue solution were separated by a magnet, and a sample was taken to measure the concentration of the methylene blue solution (see Figure 16 ); all three salts have an inhibitory effect on the adsorption of MB by TETA-MGO, among which the inhibitory effect of Na + is the lowest, and the inhibitory effects of Ca 2+ and Fe 3+The inhibitory effects are enhanced in sequence; due to the competitive adsorption formed between the cationic dye methylene blue molecules and the metal cations in the salt solution, with a higher charge number, the competitive adsorption of ions is stronger. Due to the existence of the charge shielding effect, the electrostatic interaction between the carboxylic acid groups on the adsorbent surface and the methylene blue molecules of the cationic dye is partially weakened, resulting in a decrease in the adsorption capacity;

[0136] Dosage of adsorbent: 10, 15, 20, 25, and 30 mg of adsorbent were respectively added to the MB solution with a concentration of 100 mg·L -1 After adsorption at 298 K for 6 h, the adsorbent and the methylene blue solution were separated by a magnet, and the concentration of the methylene blue solution was sampled and tested (see Figure 17 ); when the dosage of the adsorbent is less than 15 mg, with the increase in the dosage of the adsorbent, the removal rate of MB gradually increases because the increase in the amount of the adsorbent provides more adsorption sites; when the dosage of the adsorbent exceeds 15 mg, increasing the dosage of the adsorbent, the adsorption amount of the adsorbent for MB grows slowly and hardly changes. A large number of methylene blue molecules of the dye have been adsorbed by the adsorbent, and at a high dosage of the adsorbent, the existence of osmotic pressure makes the adsorption reach equilibrium.

[0137] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for analyzing the adsorption mechanism of amino-functionalized magnetic graphene oxide on methylene blue in wastewater, characterized in that, The specific steps are as follows: (1) Conduct kinetic adsorption experiments on methylene blue by amino-functionalized magnetic graphene oxide in water. Use the pseudo-first-order kinetic model, pseudo-second-order kinetic model, intraparticle diffusion model, and liquid film diffusion model to analyze the adsorption kinetic data of methylene blue, obtain the optimal kinetic model, and analyze the controlling factors of the kinetic adsorption rate of methylene blue. The determination method of the optimal kinetic model: Calculate the fitting correlation coefficients R of the pseudo-first-order kinetic model, pseudo-second-order kinetic model, intraparticle diffusion model, and liquid film diffusion model respectively 2 , and the model with the fitting correlation coefficient R 2 closest to 1 is the optimal isotherm model; The adsorption kinetic behavior of methylene blue by the amino-functionalized magnetic graphene oxide adsorbent is chemisorption, that is, the adsorption rate control step of methylene blue on the amino-functionalized magnetic graphene oxide is jointly controlled by intraparticle diffusion and liquid film diffusion; (2) Conduct an isothermal adsorption experiment of amino-functionalized magnetic graphene oxide on methylene blue in water. Fit the adsorption isotherm using the Langmuir isotherm model, Freundlich isotherm model, and Temkin adsorption isotherm model respectively, calculate the linear correlations of the Langmuir isotherm model, Freundlich isotherm model, and Temkin adsorption isotherm model respectively, and obtain the optimal isotherm model; Calculate the maximum adsorption capacity of amino-functionalized magnetic graphene oxide for methylene blue at the preset adsorption temperature according to the optimal isotherm model; (3) By means of isothermal adsorption experiments, the equilibrium thermodynamic parameters in the process of methylene blue adsorption by amino-functionalized magnetic graphene oxide were calculated, where the equilibrium thermodynamic parameters include the change in standard Gibbs free energy ΔG 0 , the change in standard enthalpy ΔH 0 and the change in standard entropy ΔS 0 ; According to the equilibrium thermodynamic parameters, the heat transfer mode of the adsorption reaction of methylene blue by amino-functionalized magnetic graphene oxide was determined; (4) Conduct FTIR spectral analysis on both the amino-functionalized magnetic graphene oxide before adsorbing methylene blue and the amino-functionalized magnetic graphene oxide after adsorbing methylene blue. Combine the optimal kinetic model in step (1) to determine the adsorption mechanism of amino-functionalized magnetic graphene oxide on methylene blue in wastewater. During the adsorption process of methylene blue, there are electrostatic interactions, hydrogen bond interactions, and π-π conjugate interactions between the amino-functionalized magnetic graphene oxide and methylene blue.

2. The method for analyzing the adsorption mechanism of amino-functionalized magnetic graphene oxide on methylene blue in wastewater according to claim 1, wherein: The linear expression of the pseudo-first-order kinetic model in step (1) is ln(q e -q t ) = lnq e，cal -k1t The linear expression of the pseudo-second-order kinetic model is The linear expression of the intraparticle diffusion model is Liquid film diffusion model Where q e is the adsorption capacity at adsorption equilibrium, mg / g -1 ; q t is the adsorption capacity at adsorption time t, mg / g -1 ; q e,cal is the theoretical equilibrium adsorption capacity of the fitting model, mg / g -1 ; k1 is the rate constant of the pseudo-first-order kinetic model, min -1 ; k2 is the rate constant of the pseudo-second-order kinetic model, g / (mg·min) -1 .min -1 ; k id is the rate constant at different stages of the intraparticle diffusion model, mg / (g·min) - 1 .min -0.5 ; k FD is the liquid film diffusion rate constant, min -1 ; C is a constant related to the boundary layer, mg / g -1 ; C1 is the liquid film diffusion model constant, g / mg -1 .

3. The method for analyzing the adsorption mechanism of amino-functionalized magnetic graphene oxide on methylene blue in wastewater according to claim 1, characterized in that: The linear equation expression of the Langmuir isotherm model in step (2) is Where, C e is the adsorption equilibrium concentration of the solution, mg / L -1 ; q e is the adsorption capacity at the adsorption equilibrium, mg / g -1 ; q max is the maximum monolayer adsorption capacity of the Langmuir model, mg / g -1 ; K L Adsorption equilibrium constant of the Langmuir model, L·mg -1 ; Separation factor R according to the Langmuir isotherm model L Determine the applicability and shape of the adsorption isotherm; separation factor R L The expression for where C0 is the concentration of methylene blue solution before adsorption, mg·L -1 ; K L is the adsorption equilibrium constant of the Langmuir model, L·mg -1 ; The linear equation expression of the Freundlich isotherm model is Where, q e is the adsorption capacity at adsorption equilibrium, mg / g -1 , Ce is the adsorption equilibrium concentration of the solution, mg / L -1 , n is the Freundlich empirical parameter related to the adsorption strength; K F is the adsorption equilibrium constant of the Freundlich model, L / g -1 ; The linear equation expression of the Temkin adsorption isotherm model is q e = BlnK T + BlnC e Where q e is the adsorption capacity at adsorption equilibrium, mg / g -1 , Ce is the adsorption equilibrium concentration of the solution, mg / L -1 , B is a number related to the heat of adsorption, mg / g -1 ; K T is the adsorption equilibrium constant of the Temkin adsorption isotherm model, L / g -1 .

4. The method for analyzing the adsorption mechanism of amino-functionalized magnetic graphene oxide on methylene blue in wastewater according to claim 1, characterized in that: Standard Gibbs free energy change ΔG 0 is expressed as ΔG 0 = -RTlnK c Standard enthalpy change ΔH 0 is expressed as Standard entropy change ΔS 0 The expression for ΔG 0 = ΔH 0 - TΔS 0 where K c is the equilibrium constant at each temperature; where the expression of K c is where q e is the equilibrium adsorption capacity of methylene blue, and Ce is the concentration of methylene blue at adsorption equilibrium.

5. The method for analyzing the adsorption mechanism of amino-functionalized magnetic graphene oxide on methylene blue in wastewater according to claim 1, characterized in that: The preparation method of the amino-functionalized magnetic graphene oxide, the specific steps are as follows: Under stirring conditions, dissolve FeCl3·6H2O and FeCl2·4H2O in ultrapure water to obtain a mixed solution A, then add the graphene oxide aqueous suspension, and magnetically stir for 2 - 3 min to obtain a mixed solution B; At a temperature of 65 - 90 °C, dropwise add NH3·H2O to the mixed solution B to maintain the solution pH at 9 - 12 and react for 48 - 68 min to obtain a magnetic graphene oxide solution. Add TETA to the magnetic graphene oxide solution and react at a constant temperature for 12 - 36 h, cool to room temperature, perform solid-liquid separation, wash the solid with ethanol and ultrapure water in sequence, and vacuum dry to obtain the amino-functionalized magnetic graphene oxide.

6. The method for analyzing the adsorption mechanism of amino-functionalized magnetic graphene oxide on methylene blue in wastewater according to claim 5, characterized in that: The molar ratio of Fe 3+ to Fe 2+ in the mixed solution A is 1:1 to 5, the volume ratio of the graphene oxide aqueous suspension to the mixed solution A is 1:3 to 6, the concentration of graphene oxide in the graphene oxide aqueous suspension is 1 to 50 mg / mL, and the volume ratio of TETA to the magnetic graphene oxide solution is 1:20 to 40.

Images