Bimolecular modified straw adsorbent as well as preparation method and application thereof

Abstract

The invention relates to a bimolecular modified straw adsorbent as well as a preparation method and application thereof. The preparation method comprises the following steps: cleaning, drying and grinding straws, and sieving by a 100-mesh sieve; adding a polyethylene diamine solution, and carrying out stirring reaction at normal temperature; adding L-cysteine, adjusting the pH value to 4.5-5.5, and continuously stirring to react for 6-10 hours; and filtering, washing and drying to obtain the product. The preparation method has the advantages of simple steps, easily available raw materials and low requirements on equipment; the prepared bimolecular modified straw adsorbent has good removal effect and selectivity on Sb (III) and Sb (V), and is wide in pH value adaptation range. And a new technical means is provided for high-value conversion of straws and removal of antimony in water.

Description

Technical Field

[0001] The present invention relates to a method for preparing an adsorbent for antimony in water, and in particular to a bimolecular modified straw adsorbent, a preparation method thereof, and an application thereof. Background Art

[0002] Antimony (Sb) is considered a strategically important mineral due to its widespread industrial and military applications. However, industrial activities such as smelting, mining, fuel combustion, and sewage sludge incineration lead to antimony contamination of water bodies. Selective removal of Sb(III / V) from Sb-contaminated wastewater is crucial for protecting water quality and recovering antimony resources.

[0003] Adsorption has become an attractive method for treating antimony-contaminated wastewater due to its cost-effectiveness and simple operation. Straw, an agricultural waste found throughout rural areas, is mainly composed of cellulose, hemicellulose, and lignin, and is a potential low-cost, sustainable matrix for heavy metal remediation. In addition, biomass adsorbents modified by grafting organic molecules have advantages in terms of enhanced selectivity, tunable properties, and improved reversibility of the adsorption-desorption process. For example, Huang et al. designed a polyethyleneimine (PEI)-modified lignin-based porous biochar (PPLB), which had a maximum adsorption capacity of 371.7 mg / g for Sb(III); the strong selective adsorption capacity for Sb(III) was attributed to the protonated secondary amine groups. However, no research has yet been reported on its effectiveness in removing Sb(V). Summary of the Invention

[0004] The first technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a method for preparing a bimolecular modified straw adsorbent that can selectively and effectively adsorb Sb(III) and Sb(V) in water.

[0005] The second technical problem to be solved by the present invention is to provide a bimolecular modified straw adsorbent (abbreviated as "CPRS").

[0006] The third technical problem to be solved by the present invention is to provide a method for removing antimony in water by using the bimolecular modified straw adsorbent.

[0007] The technical solution adopted by the present invention to solve the first technical problem is a method for preparing a bimolecular modified straw adsorbent, which includes the following steps: washing, drying, grinding the straw, and passing it through a 100-mesh sieve; adding a polyethylene diamine (PEI) solution, stirring and reacting at room temperature; adding L-cysteine, adjusting the pH value to 4.5-5.5, and continuously stirring and reacting for 6-10 hours; filtering, washing, and drying to obtain the adsorbent.

[0008] Preferably, the mass volume concentration of the polyethylene diamine solution is 4-6%.

[0009] Preferably, the stirring speed is 500-800 rpm.

[0010] Preferably, the mass ratio of straw, polyethylene diamine and L-cysteine ​​is 1-2:1-2:2-4.

[0011] More preferably, the mass ratio of straw, polyethylene diamine and L-cysteine ​​is 2:1.5:3.

[0012] Preferably, the straw is any one or more of corn straw, wheat straw, cotton straw, and rice straw.

[0013] Preferably, the stirring reaction time at room temperature is 20-28 hours.

[0014] The technical solution adopted by the present invention to solve the second technical problem is a bimolecular modified straw adsorbent prepared by the above preparation method.

[0015] The technical solution adopted by the present invention to solve the third technical problem is a method for removing antimony in water, using the bimolecular modified straw adsorbent as an adsorbent for antimony in water.

[0016] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0017] The preparation method of the bimolecular modified straw adsorbent of the present invention has readily available raw materials, simple steps and no need for complex reaction conditions.

[0018] The bimolecular modified straw adsorbent of the present invention can selectively adsorb Sb(III) and Sb(V) in water with high removal efficiency and good adsorption performance. It has a good removal effect on both Sb(III) and Sb(V) in a wide pH range (pH=2-8).

[0019] The bimolecular modified straw adsorbent of the present invention has good adsorption-desorption performance, can be used multiple times, and greatly reduces the use cost of the adsorbent. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The synthetic route and characteristic diagram of CPRS of the present invention;

[0021] Among them, (a) synthesis route of CPRS; (b) XRD patterns of RS and CPRS; (c) FTIR spectrum; (d) XPS full spectrum; (e) C 1s spectrum.

[0022] Figure 2Dendrogram comparing the removal efficiency of Sb(III) and Sb(V) by different adsorption materials.

[0023] Figure 3 Dendrogram showing the effects of pH value (a) and dosage (b) on the removal of Sb(III) and Sb(V) by CPRS;

[0024] The experimental conditions are as follows: pH 0 = 3 ± 0.1, CPRS dosage = 1.0 g / L, [Sb(III)] 0 or [Sb(V)] 0 = 40 mg / L, and response time = 2 h.

[0025] Figure 4 Dendrogram showing the effect of different initial concentrations on the removal of Sb(III) and Sb(V) by CPRS;

[0026] The experimental conditions were as follows: pH 0 = 3 ± 0.1, and CPRS dosage = 1.0 g / L.

[0027] Figure 5 Dendrogram showing the selectivity of CPRS for Sb(III / V) adsorption in the presence of different heavy metal ions.

[0028] Figure 6 Dendrogram showing the reusability of CPRS for adsorption of Sb(III / V). DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with specific embodiments. It should be noted that, unless otherwise specified, the reagents used in the examples are all common commercially available products.

[0030] In the following embodiments, rice straw is used as an example of straw and was collected from Heshan District, Yiyang City, Hunan Province, China (112°5' E, 28°4' N). Other straws (such as corn straw, wheat straw, or cotton straw) have similar structures and compositions to rice straw. Bimolecularly modified straw adsorbents made from these materials can also exhibit the same or similar adsorption properties as bimolecularly modified straw adsorbents made from rice straw.

[0031] Example 1

[0032] The preparation method of the PEI and L-cysteine ​​bimolecular modified straw adsorbent (CPRS) in this embodiment includes the following steps: washing rice straw with ultrapure water, then drying and grinding, and then passing through a 100-mesh sieve to obtain undersize straw (abbreviated as RS) powder; then, mixing 30 ml of a 5% (w / v) PEI solution with 2.0 g of RS powder, and stirring the resulting mixture at 600 rpm at room temperature for 24 hours; then, adding 3.0 g of L-cysteine, and reducing the pH value to 5; the reaction is continued under stirring for 8 hours; finally, separating the solid by filtration, washing with ultrapure water to a neutral pH value, and then drying in an oven at 60°C. The synthesis route is as follows: Figure 1 As shown in (a).

[0033] Example 2

[0034] The preparation method of the PEI and L-cysteine ​​bimolecular modified straw adsorbent of this embodiment includes the following steps: washing rice straw with ultrapure water, then drying, grinding and passing through a 100-mesh sieve to obtain straw powder; then, mixing 20 ml of a 5% (w / v) PEI solution with 1.0 g of straw powder, and stirring the resulting mixture at 800 rpm at room temperature for 16 hours; then, adding 2.0 g of L-cysteine, and lowering the pH value to 5; the reaction is continued for 6 hours under stirring; finally, the solid is separated by filtration, thoroughly washed with ultrapure water to achieve a neutral pH value, and then dried in an oven at 60°C. The synthesis route is as follows Figure 1 As shown in (a).

[0035] Example 3

[0036] The preparation method of the PEI and L-cysteine ​​bimolecular modified straw adsorbent of this embodiment includes the following steps: washing the rice straw with ultrapure water, then drying, grinding, and passing through a 100-mesh sieve to obtain straw powder; then, mixing 40 ml of a 5% (w / v) PEI solution with 2.0 g of straw powder, and stirring the resulting mixture at 500 rpm for 28 hours at room temperature. Subsequently, L-cysteine ​​(4.0 g) was added, and the pH value was reduced to 5. The reaction continued for 10 hours under stirring. Finally, the solid was separated by filtration, thoroughly washed with ultrapure water to reach a neutral pH value, and then dried in an oven at 60°C. The synthesis route is as follows Figure 1 As shown in (a).

[0037] Comparative Example 1

[0038] The rice straw was rinsed with ultrapure water, then dried, ground and passed through a 100-mesh sieve to obtain straw (named RS) powder. Then, a 5% (w / v) PEI solution (30 ml) was mixed with 2.0 g of RS powder. The resulting mixture was stirred at 600 rpm for 28 hours at room temperature. The solid was separated by filtration, thoroughly washed with ultrapure water to reach a neutral pH value, and then dried in an oven at 60°C. A PEI-modified straw adsorbent (abbreviated as RS-PEI) was obtained.

[0039] Comparative Example 2

[0040] Rice straw was rinsed with ultrapure water, dried, ground, and passed through a 100-mesh sieve to obtain straw powder (designated RS). 30 ml of water and 3.0 g of L-cysteine ​​were added, and the mixture was stirred at 600 rpm for 8 hours at room temperature. This yielded an L-cysteine-modified straw adsorbent (abbreviated as RS-cysteine).

[0041] The crystal structures of RS and CPRS prepared in Example 1 were analyzed by X-ray diffraction (XRD). Figure 1 (b) shows its crystal structure. The X-ray diffraction curve of RS shows characteristic reflections at 15.2°, 22.0° and 40.5°, corresponding to the (110), (021) and (004) crystal planes of cellulose, respectively. After the introduction of PEI and cysteine ​​molecules, the CPRS spectrum shows characteristic peaks at 18.8°, 28.4° and 33°, which are very consistent with the (100), (0018) and (112) crystal planes of cystine (PDF#37-1802). This observation indicates that crystalline cystine has been successfully loaded onto the surface of straw through cysteine ​​modification. At the same time, by Fourier transform infrared spectroscopy (FTIR), as shown Figure 1 (c), at 4000-400 cm -1 The functional groups of RS and CPRS were clearly identified within the range. The overlapping stretching modes of -OH, -NH2 and -NH- functional groups are at 3428 cm -1 The main reason for the large peak at 2922 cm is that the CPRS surface has both hydroxyl and amine functional groups. -1 The peak intensity at 2585 cm-1 was significantly reduced, indicating that the content of polycyclic sugars in the surface cellulose and hemicellulose components was reduced. The stretching vibration of the cysteine-SH group explains the peak at 2585 cm-1 in the CPRS spectrum. -1 The vibration peak at 1728 cm is the direct evidence that the thiol group is successfully fixed on the straw surface. In addition, the stretching mode of the C=O group on the side chain of the lignin structural unit is the peak at 1728 cm in the RS spectrum. -1 The source of the band. After the molecular modification with PEI and L-cysteine, the 1728cm -1The disappearance of the peaks indicates that the lignin side chains have been changed or destroyed. In addition, the peaks at 1488 and 1412 cm -1 The enhanced absorption signal observed at 1055 cm is from the carboxylate (-COO-) of grafted cysteine. -1 The peak at is the symmetric stretching vibration of the Si-O-Si linkage associated with silicon dioxide (SiO2) on the RS surface.

[0042] like Figure 1 As shown in (d), in the measured spectra of RS and CPRS, the signals of C and O elements were observed, while the obvious N and S signals in CPRS clearly confirmed the effective grafting of PEI and cysteine. Figure 1 As shown in (e), characteristic peaks for RS appear at binding energies of 284.8 eV (CC), 286.6 eV (CO), and 288.1 eV (OC=O). Compared to the RS spectrum, the C1s spectrum of CPRS exhibits significant changes, with the binding energy of the CO component shifting from 286.6 eV to 286.0 eV. Furthermore, new components attributed to CN and CS bonds appear, consistent with the effective interaction of PEI and cysteine.

[0043] It should be noted that the PEI and L-cysteine ​​bimolecular modified straw adsorbents prepared in Examples 2 and 3 also have the same or similar characterization data as the CPRS prepared in Example 1.

[0044] Application Example 1

[0045] Simulation of antimony-containing wastewater:

[0046] Potassium antimony tartrate and potassium pyroantimonate were dissolved in ultrapure water to prepare Sb(III) and Sb(V) stock solutions (1000 mg / L). These stock solutions were diluted to prepare each test solution. Batch adsorption experiments were performed by adding the synthesized adsorbent (1.0 g / L) to 100 mL of Sb(III) or Sb(V) solution (40 mg / L) in an Erlenmeyer flask. The Erlenmeyer flask was maintained at 25°C and stirred at 220 rpm in a thermostatic shaker. To analyze the reaction solutions at different stages, aliquots were filtered using a membrane filter (0.45 μm) after 5, 10, 15, 30, 45, 60, and 120 minutes. The filtrates were analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES) to quantify the residual levels of Sb(III) and Sb(V). Each experiment was performed in triplicate.

[0047] The removal efficiency of Sb(III) and Sb(V) was compared and evaluated using original straw (RS), PEI-modified straw (RS-PEI), L-cysteine-modified straw (RS-cysteine) and CPRS. Figure 2 As shown, RS-PEI achieved a removal efficiency of 66.4% for Sb(III), but the removal efficiency for Sb(V) was almost negligible. In contrast, both pristine RS and RS-cysteine ​​showed no significant removal ability for either Sb(III) or Sb(V). Interestingly, CPRS achieved removal efficiencies of 83.9% and 84.3% for Sb(III) and Sb(V), respectively. These results together indicate that dual modification of rice straw with PEI and cysteine ​​can effectively enhance its ability to remove Sb(III) and Sb(V).

[0048] Figure 3 (a) shows the removal ability of CPRS for Sb(III) and Sb(V) in the pH range of 2 to 8. At pH 3, the removal efficiency of CPRS for Sb(III) and Sb(V) was 83.9% and 84.3%, respectively, within 120 minutes. The efficiency gradually decreased with increasing pH. In the pH range of 2-8, Sb(III) mainly exists in the form of neutral Sb(OH)3 molecules. The amine groups on CPRS are simultaneously protonated to form positively charged -NH3 + and -NH2 + -. These protonated amines show strong complexing ability for Sb(III). Sb(V) mainly binds to negatively charged Sb(OH)6 in the pH range of 3-8. - In the presence of ions, the protonated amine groups promote their migration to the CPRS surface through electrostatic attraction. The elimination of Sb(III) by CPRS mainly depends on the strong complexing ability provided by its protonated amine groups. For the removal of Sb(V), the positively charged protonated amine groups in CPRS first attract the negatively charged Sb(OH)6 - Then, the thiol groups on the surface further promote the complexation of Sb(V).

[0049] like Figure 3 As shown in (b), at an initial concentration of 40 mg / L and a pH of 3, the amount of CPRS used affects the removal efficiency of Sb(III) and Sb(V). Increasing the dosage from 0.5 g / L to 2.5 g / L increases the removal efficiency of Sb(III) from 68.6% to 87.7%, and the removal efficiency of Sb(V) from 70.4% to 89.5%. This improvement in Sb removal efficiency is attributed to the high CPRS dosage and the abundance of effective adsorption sites. At a concentration of 1.0 g / L, the removal efficiency of both Sb(III) and Sb(V) reaches approximately 84%.

[0050] Figure 4The removal capabilities of Sb(III) and Sb(V) were demonstrated over an initial concentration range of 5 to 100 mg / L. At 5 mg / L, the removal rates for Sb(III) and Sb(V) were 56.8% and 68.5%, respectively. When the concentration increased to 40 mg / L, the removal rate reached a maximum of approximately 84%. This phenomenon observed at lower concentrations may be due to the rapid adsorption equilibrium reached on the CPRS surface, which may limit the full utilization or effectiveness of the amine complexing capacity and driving force. In contrast, an initial concentration of 40 to 100 mg / L resulted in a decrease in the removal rate. This is because the adsorbent has a limited number of adsorption sites, which gradually approach saturation at higher initial concentrations.

[0051] In natural antimony-containing wastewater, antimony usually coexists with various heavy metal ions, including Cd 2+ 、Zn 2+ 、Cu 2+ , Pb 2+ , Ca 2+ and Mg 2+ .like Figure 5 As shown, in the presence of a single cation (40 mg / L, Cd 2+ 、Zn 2+ 、Cu 2+ , Pb 2+ , Ca 2+ or Mg 2+ ), the removal rates of Sb(III / V) by CPRS were 82.3%, 84.2%, 85.6%, 87.9%, 85.9% and 84.8%, respectively. This indicates that the presence of coexisting heavy metal ions did not significantly inhibit the removal of Sb(III / V) by CPRS.

[0052] To evaluate the reusability of CPRS for Sb(III / V) removal under simulated environmental conditions, adsorption-desorption cycles were performed using a mixed solution containing 10 mg / L Sb(III) and 10 mg / L Sb(V) (total concentration of 20 mg / L). A mixture of 5% thiourea and 0.5 M HCl was used as the eluent for antimony desorption. After each adsorption cycle, the spent CPRS adsorbent was washed with 100 mL of desorbent for 1 hour, then rinsed with ultrapure water at least three times and dried at 60°C for 6 hours.

[0053] like Figure 6 As shown, after 10 cycles, the CPRS still maintained 92.2% of its initial adsorption efficiency. This demonstrates the good reusability and structural stability of the CPRS during the adsorption-desorption process. The Sb(III / V) removal efficiency decreased slightly with increasing cycle number, likely due to the irreversible occupation of some active sites by the adsorbed Sb(III) and Sb(V). This demonstrates the good reusability of the CPRS of the present invention.

[0054] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of protection of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for preparing a bimolecular modified straw adsorbent, characterized in that: The following steps are involved: The straw is washed, dried, ground, and passed through a 100-mesh sieve; polyethylene diamine solution is added and stirred at room temperature for reaction; L-cysteine ​​is added and the pH value is adjusted to 4.5-5.5, and the reaction is continued with stirring for 6-10 hours; Filter, wash and dry to obtain the product.

2. The method for preparing the bimolecular modified straw adsorbent according to claim 1, wherein: The mass volume concentration of the polyethylene diamine solution is 4-6%.

3. The method for preparing the bimolecular modified straw adsorbent according to claim 1 or 2, characterized in that: The stirring speed is 500-800 rpm.

4. The method for preparing the bimolecular modified straw adsorbent according to claim 1 or 2, characterized in that: The mass ratio of the straw, the polyethylene diamine and the L-cysteine ​​is 1-2:1-2:2-4.

5. The method for preparing the bimolecular modified straw adsorbent according to claim 1 or 2, characterized in that: The straw is any one of corn straw, wheat straw, cotton straw or rice straw.

6. The method for preparing the bimolecular modified straw adsorbent according to claim 1 or 2, characterized in that: The stirring reaction time at room temperature is 16-28 hours.

7. The bimolecular modified straw adsorbent prepared by the preparation method of the bimolecular modified straw adsorbent according to any one of claims 1 to 6.

8. A method for removing antimony from water, using the bimolecular modified straw adsorbent according to claim 7 as an adsorbent for antimony.

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