Polyethyleneimine-modified jute and preparation method and application thereof

Abstract

The application provides a polyethylene imine modified jute, a preparation method and application thereof, and belongs to the technical field of adsorption materials. The polyethylene imine modified jute is prepared by cross-linking polyethylene imine on the surface of jute biomass, the number of metal ion binding sites such as secondary amine, tertiary amine group and newly generated imino group of the polyethylene imine is increased, the polyethylene imine is rich in N element, the N element content of the biomass surface is increased by grafting on the surface of the biomass, the porous structure of the jute surface is increased, and thus the adsorption capacity of the biomass is greatly improved, and the jute can be used as an adsorbent with high Pd(II) loading capacity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of adsorption materials, and particularly relates to a polyethyleneimine modified jute, a preparation method and application thereof. BACKGROUND

[0002] The platinum group metals, namely ruthenium, rhodium, palladium and osmium, iridium and platinum, which are arranged in the 5th and 6th periods of the 8th group of the periodic table, are a group of natural elements with complex symbiotic characteristics. The content of platinum (Pt) and palladium (Pd) in the earth's crust is higher than that of the other four elements and they are more widely used, and are also known as "main platinum group metals". Platinum group metals have many unique and superior physical and chemical properties and have important and irreplaceable special applications in modern industry and high-tech industries.

[0003] The platinum group metal resources have low grade, complex composition and are difficult to extract, and the emission of platinum group metals from different sources can cause the increase of platinum and palladium concentrations in air particulate matter, soil, surface water and sewage sludge samples, so the enrichment and recovery of platinum group metals from a multi-metal solution containing platinum group metals becomes a key problem in the recycling of platinum group resources.

[0004] At present, the industrial conventional process for recovering platinum group metals is ion exchange, reverse osmosis, coprecipitation, etc. In the ion exchange method, the price of ion exchange resin is high, and it needs to be replaced frequently, so the operation cost is high, and it cannot realize the separation and purification of various platinum group metals, and the obtained product is still a mixed solution with complex composition, which has no recycling value; the reverse osmosis technology needs very high osmotic pressure, has no selectivity, and has huge energy consumption; in the process of treating wastewater by coprecipitation technology, an external precipitant is needed, and the composition of the generated precipitate is complex and difficult to handle. SUMMARY

[0005] The purpose of the present application is to provide a modified jute and a preparation method and application thereof, which can be used as an adsorbent with high Pd(II) loading capacity, and the method is simple and low in cost.

[0006] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical scheme:

[0007] The present application provides a preparation method of polyethyleneimine modified jute, comprising the following steps:

[0008] Mixing polyethyleneimine, jute and water, modifying to obtain a modified product;

[0009] Mixing the modified product with a crosslinking agent, crosslinking to obtain polyethyleneimine modified jute.

[0010] Preferably, the mass ratio of the jute to the polyethyleneimine is 1:1 to 1:10.

[0011] Preferably, the modification temperature is 15-30℃, and the time is 12-48h.

[0012] Preferably, the crosslinking agent comprises glutaraldehyde.

[0013] Preferably, the mass ratio of the jute to the crosslinking agent is 1:0.1-5.

[0014] Preferably, the crosslinking temperature is 15-30℃, and the time is 0.5-5h.

[0015] The application provides the polyethylene imine modified jute prepared by the preparation method.

[0016] The application provides application of the polyethylene imine modified jute in adsorbing palladium.

[0017] Preferably, the application method comprises:

[0018] Mixing the Pd(II) containing solution with the polyethylene imine modified jute to perform adsorption.

[0019] Preferably, the concentration of the polyethylene imine modified jute in the Pd(II) containing solution is 0.1-5g / L; and the adsorption temperature is 15-50℃.

[0020] The application provides a preparation method of polyethylene imine modified jute, which adopts the polyethylene imine modified jute, crosslinks the polyethylene imine on the surface of jute biomass, increases the number of metal ion binding sites such as secondary amine, tertiary amine group of the polyethylene imine and newly generated imino group of the crosslinking reaction, and increases the N element content of the jute by grafting the polyethylene imine on the surface of the biomass, so that the porous structure of the jute surface is increased, thereby greatly improving the adsorption capacity of the biomass, and the jute can be used as an adsorbent with high Pd(II) loading capacity. The method provides a reference for the biosorption of platinum group metals (especially Pd) and the innovative use of jute and other plant materials. According to the Langmuir model, the theoretical adsorption capacity of the polyethylene imine modified jute for Pd(II) is 687.01mg / g, which is 4.26 times that of the unmodified jute. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The SEM-EDS diagrams of the jute before and after modification are shown in (a), (c), (e) and (b), (d), (f);

[0022] Figure 2 The FTIR diagrams of the jute before and after modification in Example 1 are shown in (a), (c), (e) and (b), (d), (f);

[0023] Figure 3XPS spectra of unmodified jute and modified jute with different glutaraldehyde addition amounts;

[0024] Figure 4 XPS spectra of unmodified jute and modified jute with different glutaraldehyde addition amounts;

[0025] Figure 5 Effect of polyethyleneimine and glutaraldehyde addition amounts on adsorption of Pd by modified jute, and results are shown in Figure 5 wherein (a) represents polyethyleneimine addition amount, and (b) represents glutaraldehyde addition amount;

[0026] Figure 6 Nonlinear kinetic fitting graph of jute before and after modification in Example 1;

[0027] Figure 7 Nonlinear isotherm adsorption model fitting graph of jute before and after modification in Example 1; (a) is unmodified jute, and (b) is modified jute;

[0028] Figure 8 SEM-EDS graph of modified jute after adsorption of Pd (II) in Example 1, wherein (a) and (b) are SEM graphs of modified jute at different magnifications, (c) is an EDS element mapping selected area, (d), (e) and (f) are C, N and Pd element mapping graphs, respectively;

[0029] Figure 9 FTIR graph of modified jute before and after adsorption of Pd (II) in Example 1;

[0030] Figure 10 XPS graph of modified jute before and after adsorption of Pd (II) in Example 1;

[0031] Figure 11 Pd 3d high-resolution spectrum. DETAILED DESCRIPTION

[0032] The application provides a preparation method of polyethyleneimine modified jute, and comprises the following steps:

[0033] Polyethyleneimine, jute and water are mixed to perform modification, so as to obtain a modified product;

[0034] The modified product is mixed with a crosslinking agent to perform crosslinking, so as to obtain polyethyleneimine modified jute.

[0035] In the application, if no special description is given, the required raw materials or reagents are all commercially available goods which are well known to those skilled in the art.

[0036] In the present application, the jute is preferably the leaf part of jute plant; the present application does not have special limitation on the source of the jute, and the jute obtained by means well known in the art is acceptable.

[0037] The present application preferably freeze-dries the jute, grinds it to pass through a 200-mesh sieve, and then modifies it with polyethyleneimine.

[0038] In the present application, the mass ratio of the jute to polyethyleneimine (PEI) is preferably 1:1-1:10, and more preferably 1:7.

[0039] In the present application, the polyethyleneimine is preferably dissolved in water, and the jute is added to the obtained polyethyleneimine aqueous solution to modify it under oscillation in a constant-temperature incubator at a rotation speed of 180 rpm.

[0040] In the present application, the mass concentration of the polyethyleneimine aqueous solution is preferably 5%-10%, and more preferably 7%.

[0041] In the present application, the modification temperature is preferably 15-30℃, and more preferably 25℃, and the time is preferably 12-48h, and more preferably 24h.

[0042] After the modification, the present application preferably does not perform any treatment, and directly mixes the obtained modified product with a crosslinking agent.

[0043] In the present application, the crosslinking agent preferably includes glutaraldehyde (GA); the glutaraldehyde is a commercially available glutaraldehyde solution, and the mass concentration of the glutaraldehyde solution is preferably 5%-50%, and more preferably 25%.

[0044] In the present application, the mass ratio of the jute to the crosslinking agent (calculated based on glutaraldehyde) is preferably 1:0.5-5, and more preferably 1:1.25-1.75, and further preferably 1:1.5.

[0045] In the present application, the crosslinking temperature is preferably 15-30℃, and more preferably 25℃, and the time is preferably 0.5-5h, and more preferably 2h; and the crosslinking is preferably performed under oscillation at 150-180 rpm.

[0046] After the crosslinking is completed, the present application preferably centrifuges the obtained product at 5000 rpm for 5 min, washes it with deionized water for 3 times to remove the uncrosslinked reagent, and then performs vacuum freeze-drying on the obtained product, grinds it, and passes it through a 200-mesh sieve to obtain polyethyleneimine-modified jute.

[0047] The present application provides polyethyleneimine-modified jute prepared by the preparation method of the above technical solution.

[0048] The present application provides the application of the polyethyleneimine-modified jute of the above technical solution in adsorbing palladium.

[0049] In the present application, the method of application preferably comprises: mixing Pd(II) containing solution with polyethyleneimine modified jute for adsorption.

[0050] In the present application, the method of preparing Pd(II) containing solution preferably comprises: weighing PdCl2, dissolving in 0.1M dilute hydrochloric acid solution, adding deionized water to constant volume, obtaining Pd(II) containing solution with specific concentration. The present application does not have special limitation on the concentration of Pd(II) in the Pd(II) containing solution, which can be determined according to the actual sample or simulated sample.

[0051] In the present application, the concentration of polyethyleneimine modified jute in Pd(II) containing solution is preferably 0.1-5g / L, more preferably 1.0g / L; the temperature of adsorption is preferably 15-50℃, more preferably 25-30℃.

[0052] The technical solutions provided by the present application will be described in detail below in combination with examples, but they should not be understood as limiting the scope of protection of the present application.

[0053] Example 1

[0054] Freeze-drying jute, grinding to pass 200 mesh sieve, obtaining unmodified jute;

[0055] Taking 100mL deionized water, adding 7g polyethyleneimine, obtaining polyethyleneimine aqueous solution with mass concentration of 7%; weighing 1g unmodified jute and adding into the polyethyleneimine aqueous solution, incubating in a constant temperature incubator with temperature of 30℃ and rotation speed of 180rpm for 24h; adding 6mL glutaraldehyde solution with mass concentration of 25%, so that the final concentration of glutaraldehyde in the reaction system is 1.5%, i.e. the mass ratio of jute to glutaraldehyde is 1:1.5; then crosslinking at 30℃ with 150rpm for 2h, centrifuging at 5000rpm for 5min, washing with deionized water for 3 times to remove uncrosslinked reagents, vacuum freeze-drying the obtained product, grinding and passing 200 mesh sieve, obtaining polyethyleneimine modified jute.

[0056] Example 2

[0057] Freeze-drying jute, grinding to pass 200 mesh sieve, obtaining unmodified jute;

[0058] Taking 100mL deionized water, adding 5g polyethyleneimine, obtaining polyethyleneimine aqueous solution with mass concentration of 5%; other steps are the same as example 1.

[0059] Example 3

[0060] The difference from Example 1 is only that 100 mL of deionized water is taken, 6 g of polyethyleneimine is added to obtain a polyethyleneimine aqueous solution with a mass concentration of 6%, and the rest is the same as in Example 1.

[0061] Example 4

[0062] The difference from Example 1 is only that 100 mL of deionized water is taken, 8 g of polyethyleneimine is added to obtain a polyethyleneimine aqueous solution with a mass concentration of 8%, and the rest is the same as in Example 1.

[0063] Example 5

[0064] The difference from Example 1 is only that 100 mL of deionized water is taken, 9 g of polyethyleneimine is added to obtain a polyethyleneimine aqueous solution with a mass concentration of 9%, and the rest is the same as in Example 1.

[0065] Example 6

[0066] The difference from Example 1 is only that 100 mL of deionized water is taken, 10 g of polyethyleneimine is added to obtain a polyethyleneimine aqueous solution with a mass concentration of 10%, and the rest is the same as in Example 1.

[0067] Example 7

[0068] The jute is freeze-dried and ground to pass through a 200-mesh sieve to obtain unmodified jute;

[0069] 100 mL of deionized water is taken, 7 g of polyethyleneimine is added to obtain a polyethyleneimine aqueous solution with a concentration of 7%, 1 g of unmodified jute is weighed and added to the polyethyleneimine aqueous solution, and the mixture is incubated in a constant-temperature incubator at a temperature of 30°C and a rotation speed of 180 rpm for 24 h. Then 3 mL of a glutaraldehyde solution with a mass concentration of 25% is added to make the final concentration of glutaraldehyde in the reaction system 0.75%, i.e. the mass ratio of jute to glutaraldehyde is 1:0.75. Subsequently, the mixture is crosslinked at 30°C and 150 rpm for 2 h, and then centrifuged at 5000 rpm for 5 min. The obtained product is washed with deionized water for 3 times, and then vacuum freeze-dried, ground and passed through a 200-mesh sieve to obtain polyethyleneimine-modified jute.

[0070] Example 8

[0071] The difference from Example 7 is only that 4 mL of a glutaraldehyde solution with a mass concentration of 25% is added to make the final concentration of glutaraldehyde in the reaction system 1%, i.e. the mass ratio of jute to glutaraldehyde is 1:1, and the rest is the same as in Example 7.

[0072] Example 9

[0073] The only difference from Example 7 is that 5 mL of 25% glutaraldehyde solution is added to make the final concentration of glutaraldehyde in the reaction system 1.25%, that is, the mass ratio of jute to glutaraldehyde is 1:1.25; otherwise, it is the same as Example 7.

[0074] Example 10

[0075] The only difference from Example 7 is that 7 mL of 25% glutaraldehyde solution is added to make the final concentration of glutaraldehyde in the reaction system 1.75%, that is, the mass ratio of jute to glutaraldehyde is 1:1.75; otherwise, it is the same as Example 7.

[0076] 1. Characterization

[0077] 1) Figure 1 The images show SEM-EDS images of jute before and after modification; (a), (c), and (e) represent unmodified jute, while (b), (d), and (f) represent modified jute. Figure 1 It can be observed that before polyethyleneimine modification, jute has a relatively smooth surface with fewer wrinkles and retains a regular surface structure. Figure 1 (a, c); After modification with polyethyleneimine, jute is composed of irregular biomass fragments of different sizes, with a rough surface full of pores and wrinkles. Figure 1 (b, d). The rough surface has a larger specific surface area, providing ample adsorption sites for metal ions. The surface morphology of jute modified with polyethyleneimine shows significant changes, indicating that surface modification with polyethyleneimine can alter the basic structure and morphology of biomass. EDS energy dispersive spectroscopy analysis revealed (… Figure 1 Both before and after modification, jute contains the basic elements that constitute living organisms, such as C, N, O, P, and S.

[0078] 2) The elemental composition of the micro-regions on the surface of jute was analyzed, and the results are shown in Table 1.

[0079] Table 1. Relative elemental content of jute surface before and after polyethyleneimine modification.

[0080]

[0081] From Table 1, after modification by polyethyleneimine, the mass ratio of N element changed significantly, the mass ratio of N element increased from 8.40% to 21.74%, and the atomic ratio increased from 7.80% to 20.23%. While the mass ratio of C element decreased from 68.55% to 61.65%, and the atomic ratio decreased from 74.29% to 66.91%; at the same time, the proportions of O, P and S elements decreased to varying degrees. Polyethyleneimine modification significantly increased the content of N element in jute, which may be because polyethyleneimine as a surface modifier itself is rich in N element, and grafting it to the surface of jute leads to an increase in the content of N element in modified jute. It can be seen that polyethyleneimine has successfully modified the surface of jute.

[0082] 3) CHNS element composition analysis method was used, and the contents of CO2, H2O, N2 and SO2 gas products produced after sample combustion were quantitatively analyzed by gas chromatograph detector, and the contents of C, H, N and S elements in the sample were calculated, and the results are shown in Table 2.

[0083] Table 2 CHNS element composition analysis of jute before and after modification

[0084]

[0085] From Table 2, compared with unmodified jute, the contents of C, H and N elements in modified jute were increased. The mass fractions of C, H and N elements were increased from 40.42%, 5.97% and 4.31% to 49.67%, 9.83% and 19.36% respectively. The contents of C and H elements were 1.23 and 1.65 times of those before modification respectively. It is worth noting that the mass fraction of N element in modified jute increased most significantly, which increased by 3.49 times compared with that before modification, which may be due to a large number of nitrogen-containing groups in polyethyleneimine molecules being grafted and modified on the surface of jute, further indicating that polyethyleneimine successfully crosslinked with jute. After modification by polyethyleneimine, the content of S element was lower than that of biomass before modification, which may be due to the content being lower than the detection limit and not being detected. The CHNS element composition analysis results show that polyethyleneimine modification may increase the number of nitrogen-containing groups on the surface of jute, thereby providing more adsorption sites.

[0086] 4) Figure 2 The FTIR spectra of jute before and after modification in Example 1 are shown in Figure 2 It can be found by comparison that in the range of 4000-400 cm -1 Although there are differences in the positions and intensities of some characteristic peaks, the overall peak shape of the biomass before and after modification is consistent. Therefore, it can be considered that after modification by polyethyleneimine, the main structure and components of jute remain intact. Specifically, from 3200 to 3600 cm -1The broad and strong vibration band is caused by the overlap of the stretching vibration bands of O-H and N-H. The band shift from 2927 cm -1 to 2938 cm -1 is due to the stretching of C-H in alkane, while 2844 cm -1 is caused by the stretching of O-H and C-H in carboxylic acid. It is worth noting that after modification by polyethyleneimine, the peak at 1651 cm -1 is slightly shifted to 1655 cm -1 due to the stretching vibration of amide band I. In addition, the significant change in the peak at 1386-1465 cm -1 is caused by the N-H bending during the stretching of amide II band. The above results show that the modification of polyethyleneimine does not change the basic chemical structure and functional group composition of jute, but introduces new functional groups on the surface of jute, which may help to enhance the affinity of jute for metal ions.

[0087] 5) Figure 3 XPS spectra of unmodified jute and modified jute with different amounts of polyethyleneimine; as shown in Figure 3 , the N1s spectrum of jute before modification can be deconvoluted into two peaks at 400.3 eV and 399.8 eV, representing primary amine groups (-NH2) and secondary amine groups (-NH-), respectively. After modification, the deconvoluted spectrum of jute can be divided into two peaks representing different functional groups. These peaks at 398.8 eV and 398.4 eV of N1s signal correspond to tertiary amine groups (>N-) or imino groups ( = N-), secondary amine groups (-NH-), respectively. After modification by polyethyleneimine, the peak position of secondary amine groups moves from 399.8 eV to 398.4 eV.

[0088] Polyethyleneimine and the amino groups on the surface of jute can undergo Schiff base reaction with the aldehyde groups at both ends of glutaraldehyde, forming covalent imine bonds. Therefore, the peak of imino group at 398.8 eV is the characteristic peak of imino group formed by the crosslinking reaction of polyethyleneimine and glutaraldehyde, and the degree of crosslinking reaction can be judged according to the peak area and proportion.

[0089] Table 3 Proportion of N1s fine spectrum peaks of jute under different amounts of polyethyleneimine

[0090]

[0091] As shown in Table 3, as the amount of polyethyleneimine increased from 5% to 7% and then to 10%, the peak area ratio representing imino groups at 398.8 eV increased from 43.15% to 57.40%, and then decreased to 43.28%. Correspondingly, the peak area ratio of primary amine groups decreased from 7.02% to trace amounts, and the ratio of secondary amine groups gradually decreased from 56.85% to 42.60%, and then increased to 56.72%. This indicates that within the 0–7% range, with the increase of polyethyleneimine content, more primary and secondary amine groups from polyethyleneimine cross-link with groups on the microbial surface, forming imino groups with characteristic peaks at 398.8 eV; with further increases in polyethyleneimine content, the number of imino groups no longer increases, while the ratio of secondary amine groups increases.

[0092] 6) Figure 4 XPS plots of unmodified jute and modified jute with different glutaraldehyde additions are shown; Figure 4 As shown, with the increase of glutaraldehyde used for crosslinking, the peak areas representing tertiary amine groups or imino groups in the N1s fine spectrum of polyethyleneimine-modified microorganisms also increase. Correspondingly, the peak areas representing primary and secondary amine groups decrease.

[0093] Table 4. Ratio of N1s fine peaks in modified jute under different glutaraldehyde addition levels.

[0094]

[0095] As shown in Table 4, when the crosslinking agent glutaraldehyde was used at 0.75% and 1.5%, the primary amine groups were reduced to trace amounts. The above analysis confirms that polyethyleneimine molecules containing a large number of primary, secondary, and tertiary amine groups were successfully grafted onto biomass, and the grafting led to a significant increase in the number of newly generated imino groups. This increase in the number of amino groups indicates that the binding sites for metal ions also increase, resulting in an increase in the amount of metal ions adsorbed by polyethyleneimine-modified jute.

[0096] 2. Adsorption performance test

[0097] Weigh 1.25 g of PdCl2 and dissolve it in 1 mol / L dilute hydrochloric acid. Transfer the solution to a 1 L volumetric flask and dilute to 1 L with deionized water to obtain a Pd(II) solution with a concentration of 750 mg / L. Adjust the pH to 3 using 1 mol / L sodium hydroxide aqueous solution. Take 30 mL of polyethyleneimine-modified jute and add 1.0 g / L for adsorption testing. The adsorption test was carried out in a constant temperature incubator at 30 ± 1 °C with a rotation speed of 150 rpm. After adsorption for 6 h, the concentration of Pd(II) in the solution before and after adsorption was determined by inductively coupled plasma optical emission spectrometry (ICP-OES), and the adsorption amount and adsorption rate were calculated.

[0098] Adsorption capacity (q) eThe calculation method for (mg / g) is given in formula (2-1):

[0099]

[0100] The adsorption rate (A%) is calculated using formula (2-2):

[0101]

[0102] Among them, C0 (mg / L) and C e (mg / L) represents the initial concentration of Pd(II) solution and the final concentration at adsorption equilibrium, respectively; V(L) represents the volume of Pd(II) solution; and m(g) represents the mass of polyethyleneimine-modified jute.

[0103] Within the range of 5%–10% polyethyleneimine and 0.75%–1.75% glutaraldehyde, the effects of the addition amounts of these two substances on the Pd adsorption effect of modified jute are shown in the following results. Figure 5 , where (a) represents the amount of polyethyleneimine added and (b) represents the amount of glutaraldehyde added.

[0104] Depend on Figure 5 As shown in Figure a, within the range of 5%–10% polyethyleneimine addition, the adsorption capacity of modified jute for Pd(II) exhibits a trend of first increasing and then decreasing. When the polyethyleneimine addition is 5%, 6%, 7%, 8%, 9%, and 10%, the adsorption capacity of modified jute for Pd(II) is 644.77, 666.62, 670.84, 670.91, 665.70, and 640.14 mg / g, respectively. When the polyethyleneimine addition is 7% or 8%, the adsorption capacity of Pd(II) approaches and reaches its maximum; when the polyethyleneimine addition exceeds 8%, the adsorption capacity of modified jute for Pd(II) decreases due to agglomeration.

[0105] Depend on Figure 5 As shown in Figure b, within the range of 0.75%–1.75% glutaraldehyde addition, the adsorption capacity of modified jute for Pd(II) exhibits a trend of first increasing and then decreasing. When the glutaraldehyde addition is 0.75%, 1.00%, 1.25%, 1.50%, and 1.75%, the adsorption capacities of modified jute for Pd(II) are 648.69, 657.23, 662.44, 670.84, and 640.50 mg / g, respectively. When the glutaraldehyde addition increases to 1.75%, the modified jute agglomerates, and the adsorption capacity decreases.

[0106] The decrease of adsorption capacity when the addition amount of polyethyleneimine and glutaraldehyde is high can be due to the over-crosslinking of jute, polyethyleneimine and glutaraldehyde, which leads to the agglomeration of the modified jute, resulting in the decrease of the adsorption sites of the modified jute exposed to the solution. Meanwhile, the adsorption effect can be unstable when the addition amount of polyethyleneimine is high due to the uneven agglomeration. Considering the stability of the adsorption effect and the cost, the optimal conditions for preparing the modified jute are that the addition amount of polyethyleneimine is 7% and the addition amount of glutaraldehyde is 1.5%.

[0107] 3. Analysis of adsorption kinetics model

[0108] The adsorption kinetics model is used to study the relationship between the adsorption rate and the adsorption capacity of jute and time during the adsorption process, and the time for reaching the adsorption reaction equilibrium.

[0109] Figure 6 The nonlinear kinetic fitting graphs of jute before and after modification in Example 1 are shown in Figure 6 It can be seen that the adsorption rate is high at the beginning of the reaction, but gradually decreases as the adsorption reaction continues. The initial rapid adsorption indicates that the adsorption of Pd(II) on jute (modified jute or unmodified jute) can be caused by the rapid electrostatic adsorption reaction between the positively charged groups on the surface of jute and the negatively charged Pd(II) chloride complex ions.

[0110] The adsorption capacity of jute for Pd(II) increases rapidly within 60 min, and the adsorption capacity increases at a low rate after 100 min, and remains basically unchanged after 240 min, indicating that the adsorption reaction reaches equilibrium; it indicates that Pd(II) almost occupies all the metal ion adsorption sites on the surface of jute at this time, or the Pd(II) content on the surface of jute is high, which hinders the continuation of adsorption due to the electrostatic repulsion between ions. Therefore, in order to ensure that the adsorption reaction reaches equilibrium, all adsorption tests are carried out for 6 h.

[0111] Table 5 lists the parameters in the kinetic model fitting.

[0112] Table 5: Adsorption kinetics model parameters of jute before and after modification in Example 1

[0113]

[0114] As can be seen from Table 5, the correlation coefficient R 2 of the pseudo-second-order kinetics model of jute adsorbing Pd(II) is 0.9970 and 0.9526, which is higher than the R 2values (0.9969, 0.1847), indicating that the pseudo-second-order model fits the adsorption behavior of jute to Pd(II) better. Therefore, the adsorption behavior of jute to Pd(II) is more in line with the pseudo-second-order kinetic model rather than the pseudo-first-order kinetic model. Since the pseudo-second-order kinetic adsorption model is based on the assumption of electron pair transfer, sharing or exchange between the adsorbent and metal ions, it can be inferred that there is the formation of new chemical bonds in the adsorption process of jute, and the chemical interaction determines the adsorption reaction rate.

[0115] 4、 Figure 7 The nonlinear isotherm adsorption model fitting graphs of jute before and after modification in Example 1; (a) is unmodified jute, (b) is modified jute. All data are based on the adsorption reaction reaching equilibrium. From the isotherm adsorption model fitting results, it can be seen that with the increase of equilibrium concentration, the adsorption capacity of jute to Pd(II) increases, and gradually tends to adsorption reaction equilibrium, that is, the adsorption capacity of jute to metal ions cannot be further increased with the continuous increase of Pd(II) concentration in the solution.

[0116] Table 6 Isotherm adsorption model parameters of jute before and after modification in Example 1

[0117]

[0118] From Table 6, it can be seen that the correlation coefficient R 2 values (0.9972, 0.9995) of using Langmuir model to fit the adsorption of Pd(II) by jute before and after modification are higher than the R 2 values (0.9883, 0.9975) of using Freundlich model to fit. It indicates that the adsorption behavior of jute to Pd(II) conforms to Langmuir model. That is, the adsorption of jute to Pd(II) is carried out by uniform monolayer adsorption. With the progress of adsorption reaction, the metal ion adsorption sites on the surface of jute are gradually occupied, until the adsorption equilibrium is reached.

[0119] Langmuir constant (K L ) as a parameter representing the affinity between adsorbent and adsorbate is greatly improved after modification by polyethyleneimine. The K L value (0.43) of Pd(II) by modified biomass is 53 times of the K L value (0.008) of unmodified jute. Therefore, it can be concluded that the affinity of jute to Pd(II) is significantly improved after modification by polyethyleneimine, and accordingly, the adsorption capacity is also significantly improved. Langmuir model can also be used to evaluate the theoretical maximum adsorption capacity of adsorption material. The theoretical maximum adsorption capacity of Pd(II) by modified jute increases from 161.24 mg / g to 687.01 mg / g compared with unmodified jute.

[0120] 5、Figure 8 The images shown are SEM-EDS images of modified jute after adsorbing Pd(II) in Example 1. (a) and (b) are SEM images at different magnifications after Pd(II) adsorption in modified jute, (c) is the selected region of the EDS elemental mapping, and (d), (e), and (f) are the elemental mapping images of C, N, and Pd, respectively. Figure 8 As shown in (a), the jute adsorbed with Pd(II) consists of irregular fragments. Magnification observation reveals that the surface of the jute adsorbed with Pd(II) is rough and covered with wrinkles. Figure 8 (b) This is because the jute used in the experiment consisted of fragmented cell pieces, and this surface morphology matched the characteristics. Observation Figure 8 The mapping image shows that, in addition to the uniform distribution of C and N elements originating from jute itself on its surface, Pd is also distributed very evenly on the jute surface after adsorption of Pd(II).

[0121] Table 7. Relative elemental contents of jute surface before and after Pd(II) adsorption.

[0122]

[0123] As shown in the semi-quantitative data in Table 7, the contents of Pd and Cl in jute after adsorption of Pd(II) both increased, with the mass ratios increasing from 0 and 1.36% to 31.67% and 12.60%, respectively, indicating that jute effectively adsorbed PdCl2.

[0124] 6. Figure 9 The images shown are FTIR spectra of modified jute before and after adsorption of Pd(II) in Example 1; from Figure 9 It can be seen that in the range of 4000-400cm -1 Within the range, although the positions and intensities of some characteristic peaks differ, the overall peak shape of the absorption peaks of jute after Pd(II) adsorption is basically consistent with that of jute before adsorption. Therefore, it can be considered that the main structure and components of jute remain intact after Pd(II) adsorption. Jute after Pd(II) adsorption shows a peak shape at 1655 cm⁻¹. -1 The amide I band shifted to 1619 cm⁻¹ -1 ; at 1465cm -1 The amide II band shifted to 1449 cm⁻¹ -1 The former displacement is due to the stretching vibration of the CN bond in the amide, while the latter displacement is due to the deformation vibration of the NH group in -CO-NH-. At 1387 cm⁻¹ -1 The absorption peak shifted to 1385 cm⁻¹ -1The results show that the stretching vibration of N-H bond occurs in the adsorption process. The above results show that the nitrogen-containing groups on the surface of jute, especially the C-N bond and N-H bond, mainly participate in the adsorption of Pd(II) on jute. However, since FTIR can only detect the change of the chemical bond of the group on the surface of jute, it cannot determine the position of the group on the molecule, so further analysis of the structure of the group participating in the adsorption is needed.

[0125] 7、 Figure 10 XPS spectra of jute before and after the adsorption of Pd(II) in Example 1; Figure 10 The N1s signals at 399.8 eV and 398.4 eV correspond to secondary amine groups (-NH-), and the N1s signal at 398.8 eV corresponds to tertiary amine groups (>N-) or imine groups (=N-). Further analysis of the proportion of N1s fine spectrum peaks of jute before and after adsorption shows that the proportion of imine group peaks at 398.8 eV decreases from 57.40% to a trace amount, and the corresponding proportion of secondary amine group peaks at 399.8 eV increases from 42.60% to almost 100% after the adsorption of Pd(II). The decrease in the proportion of imine groups on the surface of jute and the increase in the proportion of secondary amine groups after the adsorption of Pd(II) show that the imine group on the surface of jute is the key group participating in the adsorption of Pd(II), and the imine group is mainly converted into secondary amine group after the reaction.

[0126] To analyze the occurrence form of Pd element on jute after the adsorption of Pd(II), further analysis of the Pd 3d high-resolution spectrum of jute after the adsorption of Pd(II) is carried out. As shown in Figure 11 , Figure 11 is a Pd 3d high-resolution spectrum; after deconvolution, Pd 3d can be divided into four peaks representing two valence states. The binding energies of Pd 3d5 / 2 and Pd 3d3 / 2 orbits are 338.0 eV and 342.6 eV, respectively, which directly prove that jute can adsorb Pd(II) in the solution. The peaks at binding energies of 336.0 eV and 340.6 eV are the characteristic peaks of Pd(0) 3d5 / 2 and 3d3 / 2, respectively. The existence of a small amount of Pd(0) may be due to the reduction of Pd(II) to Pd(0) by enzymes, proteins and some metabolites in jute under acidic conditions.

[0127] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A process for the preparation of polyethyleneimine-modified jute characterized in that, The method comprises the following steps: polyethyleneimine, jute and water are mixed to modify and obtain a modified product; the modified product is mixed with a crosslinking agent to crosslink and obtain polyethyleneimine modified jute; the mass ratio of the jute to the polyethyleneimine is 1:1-1:10; the modification temperature is 15-30℃ and the time is 12-48h; the mass ratio of the jute to the crosslinking agent is 1:0.5-5.

2. The production method according to claim 1, characterized by, the crosslinking agent comprises glutaraldehyde.

3. The preparation method according to claim 2, characterized in that, the crosslinking temperature is 15-30℃ and the time is 0.5-5h.

4. Polyethyleneimine modified jute prepared by the preparation method in any one of claims 1-3.

5. Application of the polyethyleneimine modified jute in claim 4 in adsorbing palladium.

6. Use according to claim 5, characterized in that, The application method comprises: a Pd(II) containing solution is mixed with the polyethyleneimine modified jute to adsorb.

7. Use according to claim 6, characterized in that, the concentration of the polyethyleneimine modified jute in the Pd(II) containing solution is 0.1-5g / L; and the adsorption temperature is 15-50℃.

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