CN116459799A - Alginic acid composite adsorbent for efficiently removing tetracycline and its preparation and use method - Google Patents

Abstract

The invention discloses an alginic acid composite adsorbent for efficiently removing tetracycline and a preparation and use method thereof, which is characterized in that graphene oxide is ultrasonically dispersed in water to form a suspension, then sodium alginate is added, mechanical stirring is carried out to obtain a uniformly mixed GO/SA solution, and then the solution is added to Fe ³⁺ /Ca ²⁺ And (3) standing and cleaning the mixed solution at room temperature to obtain the product. The invention is nontoxic and environment-friendly, and is prepared by a simple one-step ionic crosslinking strategy; has specific adsorption sites for tetracycline pollutants and has extraordinary adsorption effect on TCThe adsorption capacity of TC is up to 2568.72 mg.g ^‑1 The surface of the adsorbent is remarkably higher than most adsorbents reported in literature, and the adsorbent has great practical application potential.

Description

Alginic acid composite adsorbent for efficiently removing tetracycline and its preparation and use method

technical field

The invention belongs to the technical field of tetracycline adsorption for wastewater treatment, and in particular relates to an alginic acid composite adsorbent for efficiently removing tetracycline and a preparation and use method thereof.

Background technique

As a broad-spectrum antibacterial agent, antibiotics have been widely used in the prevention and treatment of infectious diseases in humans and poultry. Tetracycline (TC) is mostly used in animal husbandry and aquaculture to kill pathogenic microorganisms mainly by inhibiting the synthesis of proteins in bacteria. Tetracycline cannot be completely absorbed and metabolized by the body, and more than 70% of tetracycline enters the environment through excretion in the form of the parent compound. Tetracycline is currently one of the antibiotics with the highest detection frequency and concentration in natural water bodies, and its ecological and environmental risks have attracted widespread attention. However, at present, the treatment technology for tetracycline pollution is still relatively lacking. Therefore, the development of high-efficiency, low-consumption, and environmentally friendly tetracycline wastewater treatment technology has extremely profound practical significance for alleviating the environmental and health risks caused by tetracycline residues and preventing and controlling antibiotic resistance problems that may be caused by tetracycline residues in the water environment.

Adsorption is the basis for the separation, migration and transformation of pollutants from the water environment. Compared with coagulation, precipitation, advanced oxidation, membrane filtration and other processes, the adsorption method is suitable for treating different types and concentrations of pollutants due to its advantages of no need for additional expensive chemical reagents, easy operation, and stable treatment effect. Therefore, it has attracted widespread attention. In recent years, graphene oxide (GO), a two-dimensional honeycomb nano-carbon material, has attracted extensive attention in the field of adsorption wastewater treatment due to its strong pollutant enrichment ability and anti-interference ability of coexisting components. However, graphene oxide is prone to agglomeration in the actual wastewater treatment process, and the specific surface area of the agglomerated graphene oxide decreases, and the treatment efficiency also decreases, which is not conducive to the large-scale application of graphene oxide. At the same time, graphene oxide is also cytotoxic and genotoxic, which can induce oxidative stress, trigger various inflammatory responses in the human body, and cause cell damage. Graphene oxide that has not been completely separated remains in the water environment, which will pose a great threat to human health and the ecological environment. If graphene oxide nanosheets can be embedded, encapsulated, or loaded on a millimeter-scale macroscopic carrier, while utilizing the excellent adsorption properties of graphene oxide, it can also solve the problems of reduced adsorption effect and ecological toxicity caused by incomplete separation during the application process of graphene oxide.

In recent years, hydrogels with a three-dimensional network structure prepared with hydrophilic polymers (sodium alginate, chitosan, carboxymethyl cellulose, etc.) as matrix materials have been widely used in the field of wastewater treatment through a simple one-step ion cross-linking reaction. Sodium alginate has the advantages of wide sources, low extraction cost, and no environmental toxicity, so it is considered to be a raw material for the preparation of adsorbents with practical application prospects. Although the molecular chain of sodium alginate contains abundant oxygen-containing functional groups (-COOH, -OH), which can chelate heavy metals and combine with various organic pollutants through hydrogen bonds or electrostatic mechanisms, the hydrogel formed after cross-linking with multivalent metal ions often has a reduced number of adsorption sites and poor mechanical strength, which limits its large-scale application in actual wastewater treatment. If graphene oxide nanosheets can be introduced into its network structure, it can not only increase the adsorption active sites to improve the adsorption effect, but also achieve the purpose of enhancing the mechanical strength of the adsorbent itself so that it has better environmental adaptability.

Therefore, in order to solve the shortcomings of graphene oxide nanosheets that are easy to agglomerate in actual water treatment, difficult to recover after use, and sodium alginate microspheres have poor mechanical strength and low adsorption capacity, a green and efficient adsorbent for tetracycline removal was proposed in this paper.

Contents of the invention

In order to solve the above technical problems, the present invention provides an alginic acid composite adsorbent for efficiently removing tetracycline and its preparation and use method. The invention is green, non-toxic and environmentally friendly, and the GO/SA-Fe ³⁺ -Ca ²⁺ composite adsorbent can be successfully prepared only through simple mixing and cross-linking reactions; the obtained GO/SA-Fe ³⁺ -Ca ²⁺ composite adsorbent can efficiently remove tetracycline through mechanisms such as cation π bond, π-πEDA interaction and hydrogen bond interaction.

In order to achieve the above-mentioned technical effects, the present invention is achieved through the following technical solutions: an alginic acid composite adsorbent for efficiently removing tetracycline, characterized in that the chemical formula is: GO/SA-Fe ³⁺ -Ca ²⁺ .

Another object of the present invention is to provide a method for preparing an alginic acid composite adsorbent that efficiently removes tetracycline, which is characterized in that it comprises the following steps:

Step1: Add graphene oxide (GO) into water, and disperse it uniformly to form a suspension by ultrasonic/stirring; then weigh sodium alginate (SA) and add it to the above-mentioned GO suspension, and mechanically stir at 400rpm for 24h at room temperature to obtain a uniform GO/SA mixed solution;

Step2: Use a medical syringe to add the mixed solution obtained in Step1 dropwise to the Fe ³⁺ /Ca ²⁺ mixed solution for cross-linking reaction to obtain alginic acid composite hydrogel; then continue to stand for at least 24h;

Step3: Wash the product obtained in Step2, and freeze-dry to obtain GO/SA-Fe ³⁺ -Ca ²⁺ composite microspheres.

Further, in the Step 1, the specific ratio of the GO/SA solution is as follows: 0.2 g of graphene oxide (GO) and 1.2 g of sodium alginate (SA) are dissolved in 100 mL of ultrapure water.

Further, in the Step 2, the total mass concentration of the Fe ³⁺ /Ca ²⁺ mixed solution is 1 wt%. The specific preparation method of the Fe ³⁺ /Ca ²⁺ mixed solution is as follows: Weigh 0.9g Fe(NO ₃ ) ₃ ·9H ₂ O and 0.1g CaCl ₂ ·2H ₂ O powders and dissolve them in 100mL ultrapure water.

Further, in the Step3, wash with deionized water, and freeze-dry at -49°C for 24 hours.

Another object of the present invention is to provide a method for using an alginic acid composite adsorbent for efficiently removing tetracycline, which is characterized in that it includes the following steps:

Add adsorbent to the waste liquid at 0.3-0.8g/L, adjust the initial pH to 6-8 with NaOH solution and HCl solution, and shake in the temperature range of 20-35°C for 48-72h to achieve efficient removal of TC.

Further, 0.5g/L of adsorbent was added to the waste liquid, the initial pH was adjusted to 7 with 0.1M NaOH solution and HCl solution, and the high-efficiency removal of TC could be achieved by shaking in the temperature range of 30°C for 72h.

The beneficial effects of the present invention are:

In the present invention, GO/SA- ^{Fe 3+} -Ca ²⁺ composite microspheres are prepared by embedding graphene oxide nanosheets in alginic acid microspheres through a one-step ion cross-linking reaction ^of Fe ³⁺ . The composite material has the advantages of single graphene and alginic acid at the same time, and can realize the efficient removal of tetracycline in water. The + ^{-Ca 2+} composite adsorbent can efficiently remove tetracycline through cation π bond, π-πEDA interaction and hydrogen bond mechanism, and the maximum adsorption capacity of tetracycline can reach 2568.72mg/g.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the accompanying drawings required for the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative work.

Fig. 1 is the SEM figure of sample;

Fig. 2 is the adsorption capacity under different initial pH conditions and the pH value of the solution after adsorption;

Figure 3 shows the effect of GO/SA-Fe ³⁺ -Ca ²⁺ on the adsorption capacity of tetracycline under different contact times, the fitting of pseudo-first-order and pseudo-second-order adsorption kinetic models, and the intra-particle diffusion model;

Figure 4 shows the adsorption capacity of GO/SA-Fe ³⁺ -Ca ²⁺ for different initial concentrations of tetracycline and the fitting of Langmuir isotherm model, Freundlich isotherm model, Liu isotherm model and Temkin isotherm model;

Figure 5 shows the effect of different salt concentrations on the adsorption effect of TC;

Figure 6 shows the N ₂ adsorption-desorption isotherms of SA-Fe ³⁺ -Ca ²⁺ , SA-Ca ²⁺ and GO/SA-Fe ³⁺ -Ca ²⁺ .

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

Example 1

A preparation method of an alginic acid composite adsorbent for efficiently removing tetracycline, comprising the following steps:

Step 1: Weigh 0.2 g of graphene oxide (GO) and dissolve it in 100 mL of ultrapure water, and obtain a uniform GO aqueous solution by ultrasonication and stirring for about 10 minutes; then weigh 1.2 g of sodium alginate (SA) and add it to the above solution, and mechanically stir for 24 hours to obtain a uniform GO/SA mixed solution.

Step 2: Weigh 0.9g Fe(NO ₃ ) ₃ 9H ₂ O and 0.1g CaCl ₂ 2H ₂ O to prepare a Fe ³⁺ /Ca ²⁺ solution with a total mass concentration of 1wt%, and use a 10mL medical syringe to slowly drop the GO/SA solution into the Fe ³⁺ /Ca ²⁺ solution for cross-linking reaction, and leave the obtained functionalized alginic acid composite to react at room temperature for at least 24 hours.

Step 3: Wash away excess Fe ³⁺ and Ca ²⁺ with deionized water, and dry the washed material in a freeze dryer at -49°C for 24 hours to obtain GO/SA-Fe ³⁺ -Ca ²⁺ composite adsorbent.

Example 2

Usage method: add GO/SA-Fe ³⁺ -Ca ²⁺ material to the tetracycline solution to be treated to form a suspension, and shake it in the shaker for 72 hours, so that the adsorbent can reach the adsorption equilibrium of the pollutants in the water body, and the tetracycline can be removed.

Example 3

A preparation method of an alginic acid composite adsorbent for efficiently removing tetracycline, comprising the following steps:

Step 1: Dissolve 0.2 g of graphene oxide (GO) in 100 mL of ultrapure water, and prepare a uniform GO aqueous solution (solution 1) by ultrasonication and stirring for about 10 minutes; add 1.2 g of sodium alginate into solution 1, and mechanically stir for 24 hours to obtain a GO/SA mixed solution (solution 2); weigh 1.2 g of sodium alginate and dissolve it in 100 mL of ultrapure water to prepare an SA solution (solution 3).

Step 2: Weigh 0.9g Fe(NO ₃ ) ₃ .9H ₂ O and 0.1g CaCl ₂ .2H ₂ O to prepare a Fe ³⁺ /Ca ²⁺ solution (solution 4) with a total mass concentration of 1 wt%. Solution 2 and solution 3 were dropped into solution 4 with a 10mL syringe, and allowed to stand for 24 hours to achieve complete crosslinking of the material.

Step 3: Wash the excess Fe ³⁺ and Ca ²⁺ with deionized water, put the washed material into a freeze dryer at -49°C for 24 hours, and collect the target materials: GO/SA-Fe ³⁺ -Ca ²⁺ and SA-Fe ³⁺ -Ca ²⁺ .

From the SEM image in Figure 1, it can be seen that the outer surface of GO/SA-Fe ³⁺ -Ca ²⁺ microspheres has irregular wrinkles and fine cracks on the surface. The GO/SA-Fe ³⁺ -Ca ²⁺ microspheres are granular, and the inside is a porous network structure with a large pore size. But SA-Fe ³⁺ -Ca ²⁺ microspheres have fewer channels inside. Compared with the SA-Fe ³⁺ -Ca ²⁺ microspheres without GO doping, the GO/SA-Fe ³⁺ -Ca ²⁺ microspheres doped with GO had a denser network structure and more folds, which was beneficial to increase its specific surface area and facilitate the mass transfer in the adsorption process.

Example 4

To explore the effect of initial pH on TC adsorption, the specific steps include:

(1) Prepare a TC solution with a concentration of 50mg/L, and adjust the pH with 1M NaOH and 1M HCl, and the initial pH range is 2 to 9;

(2) Weigh 0.02 g each of the GO/SA-Fe ³⁺ -Ca ²⁺ , SA-Fe ³⁺ -Ca ²⁺ and SA-Ca ²⁺ materials prepared in Example 3, put them into a ground-mouth Erlenmeyer flask, and set 2 parallel samples under different pH conditions;

(3) Pour the solution of (1) into (2), the volume is 40mL, put it in a constant temperature shaker, the oscillation time is 24h, and the rotation speed is 180r/min;

The experimental results show that: under different pH conditions, the adsorption capacity of SA-Fe ³⁺ -Ca ²⁺ on TC is higher than that of SA-Ca ²⁺ ; the adsorption capacity of GO/SA-Fe ³⁺ -Ca ²⁺ on TC is much higher than that of SA-Fe ³⁺ -Ca ²⁺ ; and the effect is relatively stable in the range of pH = 5-8, indicating that the adsorbent has excellent pH adaptability. Wherein the adsorption capacity q _t =47.03mg/g at pH=7.

Measurement method of residual concentration: specific measurement steps of residual concentration of TC: After filtering the solution with a 0.45 μm filter membrane, measure the absorbance at a wavelength of 270 nm with a UV-visible spectrophotometer, and calculate the residual concentration according to the marked line.

Example 5

To explore the effect of adsorption time on the adsorption of tetracycline, the specific steps include:

(1) Configure the TC solution with an initial concentration of 20 and 50 mg/L, and adjust the pH with 1M NaOH and 1M HCl to make the initial pH of the solution=7;

(2) Weigh 0.02 g of each GO/SA-Fe ³⁺ -Ca ²⁺ material prepared in Example 1, put it into a ground-mouth Erlenmeyer flask, and set up two parallel samples at different adsorption times;

(3) Pour 40mL of the solution in (1) into (2), put it in a constant temperature shaker (25°C), the shaking time is 0.5, 1, 2, 3, 4, 6, 8, 10, 12, 18, 24, 30, 36, 42, 48, 60, 72h, and the rotation speed is 180rpm;

The experimental results show that the adsorption of TC by GO/SA-Fe ³⁺ -Ca ²⁺ material basically reaches the adsorption equilibrium after about 48 hours.

Measurement method of residual concentration: specific measurement steps of residual concentration of TC: After filtering the solution with a 0.45 μm filter membrane, measure the absorbance at a wavelength of 270 nm with a UV-visible spectrophotometer, and calculate the residual concentration according to the marked line.

In order to further understand the adsorption process and adsorption mechanism, the kinetic data were fitted using the pseudo-first-order kinetic model, pseudo-second-order kinetic model and intra-particle diffusion model (Weber-Morris model):

Pseudo-first-order adsorption kinetic equation:

Pseudo-second-order adsorption kinetic equation:

In-particle diffusion model (Weber-Morris model):

q _t =k _i ·t ^0.5 +C

Among them, q _t (mg·g ^-1 ) and q _e (mg·g ^-1 ) are the adsorption amount of the target pollutant at time t and equilibrium, respectively. k ₁ (min ^-1 ) and k ₂ (g·mg ^-1 min ^-1 ) are pseudo-first-order and pseudo-second-order kinetic adsorption rate constants, respectively. _ki (mg·g ^-1 min ^-1/2 ) represents the intra-particle diffusion rate constant.

Example 6

Explore the effect of initial concentration of tetracycline on adsorption, including:

(1) Prepare tetracycline solutions with initial concentrations of 20, 50, 100, 200, 300, 400, 500, 600, and 800 mg/L respectively, and adjust the pH of the solution with 1M NaOH and 1M HCl to make the initial pH of the solution = 7;

(2) Weigh 0.02 g of each of the GO/SA-Fe ³⁺ -Ca ²⁺ materials prepared in Example 1, put them into a ground-mouth Erlenmeyer flask, and set up two parallel samples under different initial concentration conditions;

(3) Pour the solution in (1) into (2) with a volume of 40mL, put it in a constant temperature shaker (20, 25, 30°C), the oscillation adsorption time is 48h, and the rotation speed is 180rpm;

The experimental results show that the correlation coefficient ^R2 of the Liu isotherm model is the largest under different temperature conditions. The maximum adsorption capacity obtained in the experiment is 810.86 mg/g, and the maximum adsorption capacity calculated according to the Liu isotherm model is 2568.72 mg/g.

Measurement method of residual concentration: specific measurement steps of residual concentration of TC: After filtering the solution with a 0.45 μm filter membrane, measure the absorbance at a wavelength of 270 nm with a UV-visible spectrophotometer, and calculate the residual concentration according to the marked line.

In order to further describe the adsorption behavior of GO/SA-Fe ³⁺ -Ca ²⁺ on TC, the experimental data were fitted nonlinearly by Langmuir, Freundlich, Liu (combination of Langmuir and Freundlich) and Temkin isotherm models. The equations for each model are as follows:

Langmuir isotherm model:

Freundlich isotherm model:

Liu isotherm model:

Temkin isotherm model:

q _e ＝B ₁ lnK _T +B ₁ lnC _e

Among them, C _e (mg/L) and q _e (mg/g) represent the equilibrium concentration and equilibrium adsorption capacity of TC, respectively. q _max (mg/g) is the maximum adsorption capacity of the adsorbent; K _L (L/mg), K _F (mg ^(1-1/n) L ^1/n g ^-1 ) and K _g (L/mg) are Langmuir, Freundlich, Liu equilibrium constants, respectively. n _F and n _L are dimensionless constants in the Freundlich and Liu isotherm models, respectively.

Example 7

It can be obtained from Figure 1: Figure 1(f) shows the surface topography of sodium alginate. It can be observed that sodium alginate is in the form of flakes, stacked with each other to form an irregular shape, and the surface is dense and difficult to form adsorption sites. Figure 1(a) is the topography of the outer surface of GO/SA-Fe ³⁺ -Ca ²⁺ . There are irregular wrinkles and cracks on the outer surface of the microspheres, which can be attributed to the dehydration process of the material during freeze-drying. The irregular structure of the outer surface can increase the contact area between the adsorbent and the pollutants, and the small cracks also provide channels for the pollutants to enter the interior of the composite material, which is conducive to the occurrence of the adsorption process. Figure 1(b) is the cross-sectional microscopic morphology of GO/SA-Fe ³⁺ -Ca ²⁺ respectively enlarged by 100 times. There is an obvious sheet structure inside GO/SA-Fe ³⁺ -Ca ²⁺ , which may be GO nanosheets embedded in it. In addition to the layered structure, the dark black appearance of the material can also explain the successful entrapment of graphene oxide. The results of SEM show that GO/SA-Fe ³⁺ -Ca ²⁺ is a porous network structure with large pore size. This is in contrast to SA-Fe ³⁺ -Ca ²⁺ . As shown in Figure 1(d), the surface of SA-Fe ³⁺ -Ca ²⁺ is relatively smooth, and almost no irregular structures such as wrinkles can be observed. Figure 1(e) is the cross-sectional microscopic morphology of SA-Fe ³⁺ -Ca ²⁺ respectively enlarged by 100 times. Compared with the composite material doped with GO, the interior of the undoped GO adsorbent does not show obvious layered structure, and the interior is relatively smooth. Figure 1(c) is the topography of graphene oxide. From the appearance, graphene oxide is a fluffy floc of brownish yellow, with wrinkled appearance and obvious lamellar structure. Combining the appearance and morphology of the existing materials, it can be concluded that the composite microspheres with porous network structure and rough inner surface can be obtained by embedding graphene oxide in sodium alginate microspheres in a gentle way, which increases the contact area between microspheres and TC, which is conducive to the adsorption of pollutants.

It can be seen from Figure 2 that under the condition of pH = 3-9, the adsorption effect of SA-Fe ³⁺ -Ca ²⁺ on TC is better than that of SA-Ca ²⁺ , indicating that Fe ³⁺ can be used as the active site for binding TC in the process of adsorbing TC. Under different pH conditions, the adsorption effect of GO/SA-Fe ³⁺ -Ca ²⁺ on TC was better than that of SA-Fe ³⁺ -Ca ²⁺ , which indicated that the addition of GO improved the adsorption capacity of the adsorbent. According to the existing experimental results, GO/SA-Fe ³⁺ -Ca ²⁺ has a weak adsorption effect on TC under acidic conditions, but has a relatively stable and excellent adsorption effect on TC near neutral pH, and the maximum adsorption capacity is 47.26 mg/g at pH=8. Under acidic conditions, a large amount of H ⁺ competes with positively charged TC molecules for active sites, so the removal effect is relatively low at low pH. At the same time, strong acidic conditions will destroy the skeleton structure of the composite microsphere itself, and the Fe ³⁺ on the material will be dissolved, the active sites of the adsorbent will be reduced, and the adsorption effect will also decrease. As the pH continued to increase (pH = 6-8), the adsorption effect of TC also continued to increase; in this pH range, TC mainly existed in the form of neutral molecules, and the electrostatic interaction between the adsorbent and the adsorbate was weak in this range, indicating that the electrostatic mechanism was not the dominant mechanism for TC adsorption. Under the condition of pH=6～8, GO/SA-Fe ³⁺ -Ca ²⁺ composite adsorbent can remove TC through the mechanism of π-πEDA, cation-π bond and hydrogen bond. As the pH further increased (pH = 9), TC mainly existed in the form of anions. At this time, the surface of the adsorbent was also negatively charged, and there was an electrostatic repulsion between the adsorbent and the adsorbate, which inhibited the adsorption of TC. Combined with the existing experimental results, it can be shown that both Fe ³⁺ and GO are effective binding sites for TC removal, and the π-πEDA and cation-π bonds have the strongest interaction near neutral pH, and the adsorbent has the best removal effect on pollutants.

It can be seen from Figure 3 that the nonlinear fitting curves of the pseudo-first-order and pseudo-second-order equations are shown in Figure 3(a-d). It can be seen from the calculation that the relevant parameters of the pseudo-second-order kinetic model (R ² =0.988,0.995) are slightly higher than the correlation coefficients of the pseudo-first-order kinetic equation (R ² =0.971,0.993), indicating that the pseudo-second-order kinetic model can better describe the adsorption process of GO/SA-Fe ³⁺ -Ca ²⁺ on TC.

Since the GO/SA-Fe ³⁺ -Ca ²⁺ composite adsorbent is a porous material, the rate of the adsorption process may be controlled by intraparticle diffusion. The kinetic data were further analyzed by an intraparticle diffusion model. As shown in Fig. 4(d), the fitting plot is divided into three straight lines, which means that the adsorption of TC involves multiple steps, and the intraparticle diffusion is not the only rate-limiting step. Taking the solution with an initial concentration of 20 mg/LTC as an example, the largest value of ki _,1 = 12.31 corresponds to the first stage of adsorption, that is, the first 8 hours. In this stage, TC molecules diffuse to the surface of the adsorbent, and the adsorption rate is the fastest; the second stage (ki _,2 = 2.90) is the internal diffusion stage, that is, TC molecules gradually occupy the active sites inside the adsorbent; the slope of the fitted curve obtained in the final stage (ki _,3 = 0.36) is close to 0, which indicates that the adsorption has reached equilibrium. The experimental results for solutions with an initial concentration of 50mg/LTC can also be interpreted in a similar way. The above experimental results show that the adsorption of TC by GO/SA-Fe ³⁺ -Ca ²⁺ is a relatively complicated process, which is divided into multiple steps.

It can be seen from Figure 4 that under different temperature conditions (293, 298 and 303K), the equilibrium adsorption capacity q _e increases with the increase of _Ce , but this increase is not linear, indicating that intra-particle diffusion is not the controlling factor of the adsorption process. In addition, as the temperature increased, the equilibrium adsorption capacity q _e also increased significantly, indicating that the adsorption process of TC was an endothermic reaction. The correlation coefficients of different isotherm models were obtained by fitting, and the correlation coefficient R ² corresponding to the Liu isotherm model was the largest under different temperature conditions, indicating that the Liu model can best describe the adsorption process of TC on GO/SA-Fe ³⁺ -Ca ²⁺ . Based on the Liu model calculation, the maximum adsorption capacity is 2568.72 mg/g at 303K, which shows a very high removal effect on TC.

The above phenomenon shows that the present invention is non-toxic and environmentally friendly, and the GO/SA-Fe ^{3 +} -Ca ²⁺ composite material is prepared through simple mixing and cross-linking. The new adsorbent GO/SA-Fe ³⁺ -Ca ²⁺ has a specific enrichment site for tetracycline pollutants, and achieves a fast and efficient adsorption effect on TC, with an adsorption capacity as high as 2568.72mg/g.

It can be obtained from Figure 5 that three salts (NaCl, KCl, and CaCl ₂ ) with concentration gradients of 0.005, 0.01, 0.02, 0.05, and 0.10 mol/L were set, the initial concentration of TC was 50 mg/L, and the initial pH=7. The possible effects of different cations on TC adsorption were investigated. Combined with the existing results, NaCl, KCl, and CaCl ₂ all have different degrees of inhibition on the adsorption of TC, and Ca ²⁺ has the greatest inhibitory effect on the adsorption process of TC. The presence of salt inhibited the adsorption of TC, indicating that there is a certain correlation between the adsorption process and the electrostatic interaction. Combined with the results of the pH measurement of the solution after adsorption, it was found that the pH of the solution after adsorption was around 4; that is, the acidity of the solution gradually increased as time went by during the adsorption process. Under acidic conditions, some TC molecules exist in the form of cations; TC in the cationic state can be removed by electrostatic interaction with negatively charged adsorbents. In addition, the Fe ³⁺ centers in the composite adsorbent may have a strong coordination effect with the N and O-containing groups in TC. As the concentration of cations (Na ⁺ , K ⁺ , Ca ²⁺ ) increased, the cations could compete with TC for active sites on the adsorbent through receptor interaction, thus weakening the removal effect of TC. At the same time, Ca ²⁺ contributed more to the increase of ionic strength, and because of its larger ionic radius and more coordination numbers occupied more adsorption sites, it had a stronger inhibitory effect on the TC adsorption process. When the salt concentration reached 0.10mol/L, GO/SA-Fe ³⁺ -Ca ^{2 +} still maintained a high removal rate of TC, which indicated that the electrostatic mechanism was not the dominant mechanism involved in the adsorption process. Based on the above experimental results, it can be deduced that the priority of coordination, π-πEDA interactions, etc. is higher than that of electrostatic interactions in the TC adsorption process.

It can be obtained from Figure 6 that the N ₂ adsorption-desorption isotherms of GO/SA-Fe ³⁺ -Ca ²⁺ , SA-Fe ³⁺ -Ca ²⁺ and SA-Ca ²⁺ were tested at 77K, and the pore size distribution curves of the three samples were obtained. Graphene oxide has a large specific surface area (42.5323m ² /g); the specific surface areas of SA-Fe ³⁺ -Ca ²⁺ and SA-Ca ²⁺ are relatively low (respectively 15.7508m ² /g and 28.1637m ² /g); the GO/SA-Fe ³⁺ -Ca ²⁺ composite material doped with graphene oxide has a larger specific surface area (38.3689m ² /g), which can realize the efficient removal of tetracycline pollutants. In addition, the porous structure formed in the composite material is also conducive to the efficient enrichment of pollutants inside the material.

Claims (8)

1. An alginic acid composite adsorbent for efficiently removing tetracycline, characterized in that the chemical formula is: GO/SA-Fe ³⁺ -Ca ²⁺ . 2. a preparation method for efficiently removing the alginic acid composite adsorbent of tetracycline, is characterized in that, comprises the following steps: Step1: Add graphene oxide (GO) into water, and disperse it uniformly by ultrasonic/stirring to form a suspension; then weigh sodium alginate (SA) and add it to the above GO suspension, and mechanically stir at 400 rpm for 24 hours at room temperature to obtain a uniform GO/SA mixed solution; Step2: Use a medical syringe to add the mixed solution obtained in Step1 dropwise to the Fe ³⁺ /Ca ²⁺ mixed solution for cross-linking reaction to obtain alginic acid composite hydrogel; then continue to stand for at least 24 hours; Step3: Wash the product obtained in Step2, and freeze-dry to obtain GO/SA-Fe ³⁺ -Ca ²⁺ composite microspheres. 3. a kind of preparation method of the alginic acid composite adsorbent that efficiently removes tetracycline according to claim 2, is characterized in that: in described Step1, the concrete proportioning of GO/SA solution is as follows: the sodium alginate (SA) of the graphene oxide (GO) of 0.2g and 1.2g are dissolved in the ultrapure water of 100mL. 4. A method for preparing an alginic acid composite adsorbent for efficiently removing tetracycline according to claim 2, characterized in that: in the Step 2, the total mass concentration of the Fe ³⁺ /Ca ²⁺ mixed solution is 1 wt%. The specific preparation method of the Fe ³⁺ /Ca ²⁺ mixed solution is as follows: Weigh 0.9g Fe(NO ₃ ) ₃ ·9H ₂ O and 0.1g CaCl ₂ ·2H ₂ O powders and dissolve them in 100mL ultrapure water. 5. The preparation method of an alginic acid composite adsorbent for efficiently removing tetracyclines according to claim 2, characterized in that: in the Step3, wash with deionized water, and freeze-dry at -49°C for 24 hours. 6. A method for efficiently removing an alginic acid composite adsorbent for tetracycline, comprising the following steps: Add adsorbent to the waste liquid at 0.3-0.8g/L, adjust the initial pH to 6-8 with NaOH solution and HCl solution, and shake in the temperature range of 20-35°C for 48-72h to achieve efficient removal of TC. 7. the use method of a kind of alginic acid composite adsorbent that efficiently removes tetracycline according to claim 6, is characterized in that: Add adsorbent to the waste liquid at 0.5g/L, adjust the initial pH to 7 with 0.1M NaOH solution and HCl solution, and shake in the temperature range of 30°C for 72h to achieve efficient removal of TC. 8. The alginic acid composite adsorbent for efficiently removing tetracycline according to any one of claims 1 to 7 and its preparation and use method, which discloses the application of an alginate composite adsorbent for efficiently removing tetracycline in the field of wastewater treatment tetracycline adsorption technology.