KR102289633B1 - Method of manufacturing for cellulose nanofibers having functional group for heavy metal adsorption - Google Patents

Abstract

An embodiment of the present invention provides a method of manufacturing a cellulose nanofiber introduced with a functional group for adsorption of heavy metals. A mixed solution of N,N-dimethylacetamide (DMAc) solution, 3,3'-dithiodipropionic acid (DTDPA) and 1,1-carbonyldiimidazole (CDI) was added to the cellulose nanofiber and heated to double preparing sulfur cellulose nanofibers; and immersing the double sulfur cellulose nanofiber in an ammonium thioglycolate (AmTG) solution to prepare a sulfur cellulose nanofiber; includes According to an embodiment of the present invention, the cellulose nanofibers introduced with the functional group for adsorption of heavy metals have an excellent function of adsorbing heavy metals, and thus can be widely used in adsorption materials such as membranes or filters.

Description

Manufacturing method of cellulose nanofibers introduced with a functional group for heavy metal adsorption {Method of manufacturing for cellulose nanofibers having functional group for heavy metal adsorption}

The present invention relates to a method for manufacturing cellulose nanofibers, and more particularly, to a method for manufacturing cellulose nanofibers into which a functional group for adsorbing heavy metals is introduced.

Cellulose is a representative natural polymer material, and has great practical utility thanks to its unique properties such as biodegradability, eco-friendliness, high thermal stability and mechanical strength. Because of these excellent properties, cellulose is receiving the most market attention among many eco-friendly biomass materials, and the global market size of cellulose is increasing every year. Currently, cellulose is also in the spotlight in life sciences and medicine, and in particular, nano-cellulose materials provide properties that can increase interaction with water, organic and polymeric materials, nanoparticles, and living cells due to the increased surface area.

However, cellulose contains many hydroxy groups inside and strong hydrogen bonds are formed, so it is not easily soluble in solvents, thus limiting its use. Therefore, research is being conducted to modify the surface of cellulose to increase its utility, and many methodologies for imparting functionality to cellulose have been proposed.

In particular, nanofibers can be used as materials for membrane filters or dressings because they have a large specific surface area compared to their weight and many small pores. However, due to the low solubility of cellulose, it is difficult to directly form nanofibers, and currently, methods for nanofiberization using cellulose derivatives have been proposed.

In addition, in order to extend the utility of cellulose by imparting desired functionality to the cellulose material, it is required to impart the functionality of cellulose through direct surface modification.

Japanese Laid-Open Patent Publication No. 2018-533660

The technical problem to be achieved by the present invention is to provide a method for manufacturing a cellulose nanofiber into which a functional group for adsorption of heavy metals is introduced.

In addition, it is to provide a cellulose nanofiber into which a functional group for adsorption of heavy metals is introduced.

In addition, it is to provide an adsorbent comprising cellulose nanofibers introduced with a functional group for adsorbing heavy metals.

The technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by those of ordinary skill in the art to which the present invention belongs from the description below. There will be.

In order to achieve the above technical object, an embodiment of the present invention provides a method for manufacturing a cellulose nanofiber introduced with a functional group for adsorption of heavy metals.

In an embodiment of the present invention, the method for producing a cellulose nanofiber into which a functional group for adsorbing heavy metals is introduced is a N,N-dimethylacetamide (DMAc) solution, 3,3'-dithiodipropionic acid ( DTDPA) and adding a mixed solution of 1,1-carbonyldiimidazole (CDI) and heating to prepare a double sulfur cellulose nanofiber; and immersing the double sulfur cellulose nanofiber in an ammonium thioglycolate (AmTG) solution to prepare a sulfur cellulose nanofiber; includes

In an embodiment of the present invention, in the step of preparing the double sulfur cellulose nanofiber, the cellulose nanofiber may be prepared by electrospinning a cellulose acetate solution and then immersing it in a basic aqueous solution.

In an embodiment of the present invention, in the step of preparing the double sulfur cellulose nanofiber, the DTDPA and CDI may be mixed in a molar ratio of 1:1 to 5:1.

In an embodiment of the present invention, in the step of preparing the double sulfur cellulose nanofiber, the heating may be performed at 60°C to 120°C.

In an embodiment of the present invention, the heavy metal may include copper, cadmium, or lead.

In order to achieve the above technical object, another embodiment of the present invention provides a cellulose nanofiber introduced with a functional group for adsorbing heavy metals.

In order to achieve the above technical object, another embodiment of the present invention provides an adsorbent comprising cellulose nanofibers into which a functional group for adsorbing heavy metals is introduced.

According to an embodiment of the present invention, the cellulose nanofibers introduced with the functional group for adsorption of heavy metals have an excellent function of adsorbing heavy metals, and thus can be widely used in adsorption materials such as membranes or filters.

It should be understood that the effects of the present invention are not limited to the above-described effects, and include all effects that can be inferred from the configuration of the invention described in the detailed description or claims of the present invention.

1 is a flowchart of a cellulose nanofiber manufacturing method in which a functional group for adsorption of heavy metals is introduced, according to an embodiment of the present invention.
2 is a schematic diagram of a cellulose nanofiber manufacturing method in which a functional group for adsorption of heavy metals is introduced, according to an embodiment of the present invention.
3 is an SEM image of (a) cellulose acetate nanofibers, (b) cellulose nanofibers, and (c) sulfur cellulose nanofibers according to an embodiment of the present invention.
4 is (a) FT-IR spectra of cellulose acetate nanofibers, cellulose nanofibers and sulfur cellulose nanofibers, and (b) to (d) XPS spectra of sulfur cellulose nanofibers according to an embodiment of the present invention.
5 is an adsorption graph for Cu (II), Cd (II) and Pb (II) of sulfur cellulose nanofibers according to an embodiment of the present invention.
6 is a Langmuir linear regression isotherm for Cu (II), Cd (II) and Pb (II) of sulfur cellulose nanofibers, according to an embodiment of the present invention.
7 is a Freundlich linear regression isotherm for Cu (II), Cd (II) and Pb (II) of sulfur cellulose nanofibers, according to an embodiment of the present invention.
8 is a Langmuir and Freundlich linear regression isotherm for Cu (II), Cd (II) and Pb (II) of sulfur cellulose nanofibers, according to an embodiment of the present invention.
Figure 9 is, according to an embodiment of the present invention, Cu (II), Cd (II) and Pb (II) of sulfur cellulose nanofibers on (a) the effect of the contact time and (b) the secondary reaction rate model It is a kinetic model of heavy metal ions based on

Hereinafter, the present invention will be described with reference to the accompanying drawings. However, the present invention may be embodied in several different forms, and thus is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification, when a part is said to be “connected (connected, contacted, coupled)” with another part, it is not only “directly connected” but also “indirectly connected” with another member interposed therebetween. "Including cases where In addition, when a part "includes" a certain component, this means that other components may be further provided without excluding other components unless otherwise stated.

The terms used herein are used only to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In this specification, terms such as "comprises" or "have" are intended to designate that the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification exist, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

In addition, in the present invention, the cellulose nanofiber into which the functional group for adsorption of heavy metal is introduced includes sulfur cellulose nanofiber.

A method of manufacturing a cellulose nanofiber into which a functional group for adsorption of heavy metals is introduced according to an embodiment of the present invention will be described.

1 is a flowchart of a cellulose nanofiber manufacturing method in which a functional group for adsorption of heavy metals is introduced, according to an embodiment of the present invention.

2 is a schematic diagram of a cellulose nanofiber manufacturing method in which a functional group for adsorption of heavy metals is introduced, according to an embodiment of the present invention.

1 and 2, the method for manufacturing cellulose nanofibers introduced with a functional group for adsorption of heavy metals according to an embodiment of the present invention, N,N-dimethylacetamide (DMAc) solution, 3,3 in cellulose nanofibers '-A mixed solution of dithiodipropionic acid (DTDPA) and 1,1-carbonyldiimidazole (CDI) is added and heated to prepare a double sulfur cellulose nanofiber (S100); and immersing the double sulfur cellulose nanofiber in an ammonium thioglycolate (AmTG) solution to prepare a sulfur cellulose nanofiber (S200); It is characterized in that it includes.

First, a mixed solution of N,N-dimethylacetamide (DMAc) solution, 3,3'-dithiodipropionic acid (DTDPA) and 1,1-carbonyldiimidazol (CDI) is added to the cellulose nanofiber and heated to prepare a double sulfur cellulose nanofiber (S100).

The cellulose nanofiber may be used by using a ready-made nanofiber or by directly manufacturing it. When the cellulose nanofiber is directly manufactured, for example, it may be carried out by immersing in a basic aqueous solution, for example, sodium hydroxide aqueous solution after electrospinning a cellulose acetate solution, but is not limited thereto.

The cellulose nanofiber may be immersed in a mixed solution of N,N-dimethylacetamide (DMAc) solution, 3,3'-dithiodipropionic acid (DTDPA) and 1,1-carbonyldiimidazole (CDI). . In the mixed solution, DTDPA and CDI may be mixed in a molar ratio of 1:1 to 5:1, for example, 2:1.

DMAc in the mixed solution is utilized as a solvent to provide an environment in which cellulose and DTDPA can chemically bond, and to be used in excess so that cellulose can be sufficiently immersed, for example, 20 times or more of the moles of cellulose unit units. can

DTDPA in the mixed solution is a molecule having a sulfur functional group, and may form a chemical bond with a hydroxyl group (-OH) of cellulose, for example, 1 to 20 times the number of moles of the cellulose unit unit, for example, 10 Can be used as a boat.

The hydroxyl group may react with DTDPA to cut the disulfide group of DTDPA, and then functionalize the sulfur functional group to the cellulose nanofiber.

CDI in the mixed solution activates the carboxyl (-COOH) of DTDPA to form an environment to easily react with the hydroxy group (-OH) of cellulose, for example, 1 to 10 times the number of moles of the cellulose unit unit , for example, 5 times.

After immersing the cellulose nanofibers in the mixed solution, heating may be performed at 60° C. to 120° C., for example at 80° C. The heating may be performed for 18 to 30 hours, for example, 22 hours. Through this, double sulfur cellulose nanofibers are manufactured.

Next, the double sulfur cellulose nanofiber is immersed in an ammonium thioglycolate (AmTG) solution to prepare a sulfur cellulose nanofiber (S200).

Since the double sulfur cellulose nanofiber contains a sulfur-sulfur double bond, the sulfur-sulfur cellulose nanofiber into which only a thiol group (-SH) is introduced is prepared by breaking the sulfur-sulfur double bond using an AmTG solution.

Cellulose nanofibers introduced with a functional group for adsorption of heavy metals may have improved reactivity of the cellulose nanofibers by introduction of highly reactive thiol groups on the surface.

The functional group for adsorbing heavy metals may include a thiol group, and the thiol group of the prepared sulfur cellulose nanofiber may adsorb heavy metals.

The heavy metal may include copper, cadmium or lead.

A cellulose nanofiber into which a functional group for adsorption of heavy metals is introduced according to another embodiment of the present invention will be described.

The functional group for adsorbing heavy metals may include a thiol group. That is, the sulfur cellulose nanofiber is surface-modified with a thiol group.

The cellulose nanofiber into which the functional group for adsorbing heavy metals is introduced can easily introduce various functional groups to the surface of the cellulose nanofiber by using a click reaction because of its high reactivity.

In addition, the thiol group of the cellulose nanofiber into which the functional group for adsorbing heavy metals is introduced has high reactivity, so it can be an excellent adsorbent because it interacts with heavy metal ions to generate activity.

An adsorbent comprising cellulose nanofibers into which a functional group for adsorption of heavy metals is introduced according to another embodiment of the present invention will be described.

The functional group for adsorbing heavy metals includes a thiol group, and the thiol group adsorbs heavy metals, for example, copper, cadmium, or lead to function as an adsorbent.

The adsorbent may be applied without limitation as long as it can use cellulose nanofibers that adsorb heavy metals. For example, it may be used as a functional membrane or filter.

manufacturing example

1. Preparation of cellulose acetate nanofibers

DMF/acetone (4/6, v/v) is prepared by dissolving cellulose acetate solution for spinning (19wt% based on total weight) at room temperature for 24 hours. Cellulose acetate nanofibers were prepared by electrospinning a sufficiently dissolved cellulose acetate solution.

2. Cellulose Nanofiber Manufacturing

A deacetylation reaction was induced by immersing the cellulose acetate nanofibers in 0.05M sodium hydroxide solution at room temperature to prepare cellulose nanofibers.

3. Manufacturing of double sulfur cellulose nanofibers

3,3'-dithiodipropionic acid (DTDPA) in N,N-dimethylacetamide (DMAc) 10 times and 1 times the number of moles of cellulose unit units, 1-carbonyldiimidazole (1,1-carbonyldiimidazole, CDI) was added to 5 times the number of cellulose unit unit moles to prepare a solution, and the cellulose nanofibers were added to the solution and left at 80° C. for 22 hours. . Next, the unreacted material was washed with ethanol and water to obtain double sulfur cellulose nanofibers.

4. Sulfur Cellulose Nanofiber Manufacturing

By immersing the double sulfur cellulose nanofiber in an ammonium thioglycolate (AmTG; 60%) solution, the double sulfur structure is broken and a thiol group (-SH) is left on the surface of the sulfur cellulose nanofiber (the functional group for adsorbing heavy metals is introduced cellulose nanofiber) was obtained.

Experimental example

Inductively coupled plasma-optical emission spectrometry ICP-MS (SPS 3100, Hitachi) for the variables of pH, heavy metal ion concentration, and heavy metal ion contact time for cellulose nanofibers introduced with heavy metal adsorption functional groups for copper, cadmium, and lead. High-Tech Science Corporation, Tokyo, Japan).

3 is an SEM image of (a) cellulose acetate nanofibers, (b) cellulose nanofibers, and (c) sulfur cellulose nanofibers according to an embodiment of the present invention.

Referring to FIG. 3, FIGS. 3(a) to 3(c) were taken using a scanning electron microscope (JSM-6010LA SEM, JEOL, Japan), and it can be seen that they have a general nanofiber shape. Cellulose is very difficult to make using electrospinning due to strong hydrogen bonding. Therefore, it is possible to manufacture cellulose nanofibers after electrospinning cellulose acetate first and undergoing a deacetylation process. As shown in Fig. 3(a), the cellulose acetate nanofiber has a smooth surface and a bead-free structure. The diameter of the prepared nanofiber is 379±90 nm, and a uniform nanofiber is prepared. Cellulose nanofibers from which acetyl groups have been removed are prepared through deacetylation treatment in which cellulose acetate nanofibers are immersed in NaOH aqueous solution. 3(b) shows the surface structure of cellulose nanofibers, and nanofibers with almost no shape change even after deacetylation of 388±109 nm are prepared. Cellulose nanofibers were further modified with CDI esterification and DTDPA to impart sulfur functional groups to the cellulose chain. In this case, DTDPA reacts with OH groups in the cellulose chain by esterification and CDI acts as a catalyst. The result after the introduction of the sulfur functional group is as shown in Fig. 3 (c), the shape of the sulfur cellulose nanofiber (cellulose nanofiber introduced with a functional group for adsorbing heavy metals) does not change much and is well preserved, whereas the diameter is cellulose acetate and cellulose nanofiber compared to 418±68 nm, which is slightly increased.

4 is (a) FT-IR spectra of cellulose acetate nanofibers, cellulose nanofibers and sulfur cellulose nanofibers, and (b) to (d) XPS spectra of sulfur cellulose nanofibers according to an embodiment of the present invention.

In Figure 4(a), the cellulose acetate nanofiber is shown at the bottom, the cellulose nanofiber is shown in the middle, and the sulfur cellulose nanofiber is shown at the top. In addition, FIG. 4(b) is _{the full spectrum of the C 1s} and S _2s peaks, FIG. 4(c) is _{the core-level spectrum of the C 1s} peak, and FIG. 4(d) is the core-level spectrum of the _{S 2s peak.}

Referring to FIG. 4, first, the sulfur cellulose nanofibers in FIG. 4(a) were analyzed by FT-IR and XPS spectroscopy. Cellulose acetate nanofibers ^{show two typical peaks at 1720 cm -1} and 1230 cm ^-1 , which show carbonyl and ester bond absorption peaks in the acetate group. ^{Cellulose nanofibers showed a wide peak in the region of 3100-3600 cm -1} of the hydroxyl group through deacetylation, and it was confirmed that the acetate peak disappeared. The hydroxyl group of the cellulose nanofiber reacts with DTDPA to cut the disulfide group of DTDPA, and then functionalizes the sulfur functional group on the cellulose nanofiber. This surface modification allows the cellulose nanofibers introduced with the functional group for adsorption of heavy metals ^{to again show carbonyl and ester peaks at 1720 cm -1} and 1230 cm ^-1 , and it can be confirmed that the peak of the hydroxyl group is reduced compared to the cellulose nanofibers. can However, since various peaks cover the sulfur peak in FT-IR, the sulfur peak that ^{should appear at 2560 cm -1} is not observed. This can be confirmed through XPS analysis of cellulose nanofibers introduced with a functional group for adsorption of heavy metals. _{The appearance of a peak at 227.5 eV in S 2} of sulfur in Figure 4(b) can confirm the sulfur functional group on the cellulose nanofiber. The carbon to sulfur ratio was determined by analyzing multiple spectra _{of C 1} and S ₂ of cellulose nanofibers introduced with a functional group for adsorption of heavy metals. _{The C 1s} peak shown in Fig. 4(c) is five different peaks: CC at 284.5 eV, CO at 286.0 eV, C=O at 287.4 eV, OC=O at 289.0 eV, and CS at 285.5 eV. . In the case of sulfur in FIG. 4(d), _{the peak of S 2} is divided into two peaks. It shows a peak of 228.0 eV for the SH bond and 231.5 eV for the SS bond. Quantification of carbon and sulfur was calculated using the peak areas _{of C 1 and S bonds.} Theoretically, the value of [C]/[S] is calculated to be 15 when one mercaptopropionic acid reacts with one repeating cellulose unit. The experimentally calculated [C]/[S] value is 16.23, which is very consistent. Therefore, the above results can be seen that the sulfur functional group was successfully applied to the surface of the cellulose nanofiber by the chemical transformation reaction.

5 is an adsorption graph for Cu (II), Cd (II) and Pb (II) of sulfur cellulose nanofibers according to an embodiment of the present invention.

The pH solution was a phosphate buffered saline (PBS) solution (pH 7.4) at a pH of 2 to 7, the contact time was set in the range of 10 minutes to 24 hours, and the concentration of heavy metal ions was in the range of 20 to 400 ppm. set to evaluate the heavy metal adsorption performance.

After each adsorption test, the residual concentration of metal ions in the heavy metal solution was investigated by ICP-MS, followed by evaluation of isotherms and kinetic models. The adsorption capacity (q _e ) in the adsorption equilibrium state was calculated as in Equation 1 below.

Equation 1:

In Equation 1, V is the volume of the solution, C ₀ is the initial concentration of heavy metal ions, C _f is the equilibrium concentration of heavy metal ions (mg·L ^-1 ), and m is the mass (g) of the adsorbent.

Referring to FIG. 5 , the intermediate rapid adsorption capacity test under pH conditions may affect the solubility of the adsorbent, the concentration of counter ions in the adsorbent, and the degree of ionization of the adsorbent. That is, it has a great influence on the adsorption capacity of heavy metal adsorbing ions. Therefore, when investigating the adsorption behavior, pH experiments are usually conducted first. The pH of the initial solution for adsorption behavior was investigated in the range of 2 to 7. This range is generally chosen to prevent precipitation of metal particles formed in basic conditions. For each metal ion, Cu (II), Cd (II) and Pb (II), 0.01 g sulfur cellulose nanofibers were immersed in 50 mL of 200 ppm metal solution for 12 hours. Figure 5 shows the adsorption behavior for Cu (II), Cd (II) and Pb (II) ions at different pH conditions. At low pH, H ⁺ ions prefer adsorption sites, so metal ions compete with ^{H + ions to occupy adsorption sites.} Therefore, the adsorption efficiency was the lowest at pH 2, but slightly increased at pH 3. Conversely, this phenomenon can also be used to leach metal ions from the adsorbent into solution. The adsorption behavior showed maximum efficiency at pH 4 for all tested metal ions. The experimental adsorption amounts for Cu(II), Cd(II) and Pb(II) at pH4 were 38.64, 30.41 and 19.2 mg/g, respectively. This is due to the oxidation reaction of sulfur and the intermolecular disulfide bonds formed by disulfide exchange, since the disulfide exchange reaction is favored at high pH and inhibited at low pH. That is, as the pH increases from 5 to 7, it can be expected that the formation of disulfide bonds or oxidation of sulfur results in loss of heavy metal adsorption sites in sulfur cellulose nanofibers.

6 is a Langmuir linear regression isotherm for Cu (II), Cd (II) and Pb (II) of sulfur cellulose nanofibers, according to an embodiment of the present invention.

7 is a Freundlich linear regression isotherm for Cu (II), Cd (II) and Pb (II) of sulfur cellulose nanofibers, according to an embodiment of the present invention.

Table 1 shows the Langmuir and Freundlich isotherm parameters for sulfur cellulose nanofibers of three heavy metal ions, Cu(II), Cd(II) and Pb(II).

heavy metal ions Langmuir isotherm Freundlich isotherm q _max (mg g ^-1 ) K _L (L mg ^-1 ) R ² K _F (mg g ^-1 ) n ^-1 R ² Cu (II) 49.0 0.016 0.999 7.51 0.5284 0.926 Cd(II) 45.9 0.011 0.011 2.17 0.6023 0.935 Pb (II) 22.0 0.052 0.994 2.68 0.3937 0.822

The adsorption capacity of heavy metals can be expressed using the Langmuir and Freundlich isotherm models, which are the most widely used isotherm models. The Langmuir model assumes that adsorption occurs uniformly on the adsorbent surface with adsorption energy. The general form of the Langmuir isotherm can be calculated by Equation 2 as follows.

Equation 2:

In Equation 2, q _e is the amount of material adsorbed to the equilibrium state (mg·g ^-1 ), q _max is the maximum adsorption capacity (mg·g ^-1 ), and C _e is the equilibrium concentration of the adsorbent in the aqueous phase (mg·g -1 ). L ^-1 ) and K _L (L·mg ^-1 ) are Langmuir constants related to the free energy of adsorption. In particular, K _L is a value for predicting the affinity between the adsorbate and the adsorbent. This value is used to calculate R _L , called the separation factor. R _L provides important information about the adsorption strength as shown in Equation 3: Equation 3:

In Equation 3, C ₀ (mg L ^-1 ) is the initial concentration of the adsorbate, and R _L is an irreversible state when the value is R _L =0, a good adsorption state when 0 < R _L <1, R _L Poor state when >1 Finally , when R _L =1, it is theoretically linear, indicating the affinity between the adsorbent and the adsorbent.

6, 7 and Table 1, the adsorption behavior was analyzed with two isotherm models, namely, the Langmuir isotherm and the Freundlich isotherm model. Experiments were performed on 0.01 g of sulfur cellulose nanofibers in 50 mL of metal solution for three heavy metal ions Cu (II), Cd (II) and Pb (II), and the contact time was 10 hours at a pH of 4 was fixed with . 6 and 7 are calculated and plotted by linear regression of (C _e / q _e ) versus C _e for the Langmuir isotherm, log qe versus log Ce for the Freundlich isotherm. According to the regression correlation coefficient (R ² values), the Langmuir model shows a higher correlation coefficient than the Freundlich model. ^{The values of R 2} extracted from Langmuir linear regression for the three heavy metal ions Cu(II), Cd(II) and Pb(II) were 0.999, 0.995 and 0.994, respectively, whereas the values of the Freundlich model were 0.926, 0.935 and 0.822, respectively. am. The parameters of the isotherm model are shown in Table 1 for which linear regression was calculated. These results indicate that the Langmuir model is more suitable for explaining equilibrium data than the Freundlich model. In other words, since the metal adsorption results particularly fit the Langmuir isotherm model, it can be explained that the sulfur functionalization reaction occurs uniformly on the nanofiber surface, and the metal adsorption mainly occurs on the nanofiber surface.

8 is a Langmuir and Freundlich linear regression isotherm for Cu (II), Cd (II) and Pb (II) of sulfur cellulose nanofibers, according to an embodiment of the present invention.

The Freundlich model is an empirical equation based on the adsorption behavior that occurs on a surface with non-uniform energies at the adsorption site of the adsorbent, and is generally used to explain multilayer adsorption on a surface with a multilayer structure. The general form of the Freundlich isotherm can be calculated using Equations 4 and 5 as follows.

Equation 4:

Equation 5:

where K _f is the Freundlich capacity constant and n is the adsorption strength. q _e and C _e are the same as the Langmuir isotherm model.

Referring to Figure 8, the maximum adsorption capacity of heavy metal ions is extracted from the Langmuir isotherm model. The calculated maximum adsorption capacity values for Cu(II), Cd(II) and Pb(II) are 49.0, 45.9 and 22.0 mg g ^{−1 ,} respectively. Although these values are not much higher than those of other reported adsorbents due to the low adsorption properties of cellulose and limited adsorption sites on the surface, they are significant results in terms of the utilization of cellulose for metal adsorption, and the metal adsorption behavior of sulfur cellulose nanofibers is meaningful. show that there is

Figure 9 is, according to an embodiment of the present invention, Cu (II), Cd (II) and Pb (II) of sulfur cellulose nanofibers on (a) the effect of the contact time and (b) the secondary reaction rate model It is a kinetic model of heavy metal ions based on

Table 2 is the isothermal parameters of the primary and secondary kinetic models for sulfur cellulose nanofibers of Cu (II), Cd (II) and Pb (II) three heavy metal ions.

heavy metal ions q _{e, exp} (mg g ^-1 ) First-order reaction rate model Second order reaction rate model k ₁ (min ^-1 ) q _{e, cal} (mg g ^-1 ) R ² k ₂ (min ^-1 ) q _{e, cal} (mg g ^-1 ) R ² Cu (II) 39.63 0.003 39.30 0.941 1.09 × 10 ^-3 39.84 0.999 Cd(II) 30.00 0.002 27.79 0.915 6.16 × 10 ^-4 31.64 0.999 Pb (II) 19.64 0.001 24.51 0.910 5.33 × 10 ^-4 20.36 0.999

As a kinetic model, a pseudo-first-order model and a pseudo-second-order model are generally used to explain the kinetic behavior of adsorbents. do. The pseudo-first-order model was presented empirically to reveal the relationship between the reaction rate and the equilibrium adsorption amount between the adsorbent and the adsorbent. It is generally assumed that the occupancy of adsorbed sites is proportional to the number of non-adsorbed sites. That is, it is based on the relationship between the adsorption rate and the free site that the adsorbent can adsorb. The pseudo-second-order model is based on the adsorption equilibrium capacity of the solid phase. It is calculated under the assumption that the adsorption rate is related to the value of the square of the difference between the number of free sites the adsorbent can adsorb and the number of adsorbed sites. The general form of the first-order reaction rate model and the second-order reaction rate model isotherm can be calculated using Equations 6 and 7 as follows.

Equation 6:

Equation 7:

where q _e (mg g ^-1 ) is the adsorption capacity at equilibrium, q _t (mg g ^-1 ) is the adsorption amount on the adsorbent surface at the reaction time ( t , min), and k ₁ (1· min ^-1 ) and k ₂ (g·mg ^-1 ·min ^-1 ) are the kinetic rate constants of the first-order kinetic model and the second-order kinetic model, respectively.

Referring to Figure 9 and Table 2, the first-order reaction rate model (pseudo-first-order model) and the second-order reaction rate model (pseudo-second-order model) are the most widely used models to explain the adsorption kinetics, Both models were applied to investigate the kinetic adsorption behavior of sulfur cellulose nanofibers (cellulose nanofibers introduced with functional groups for adsorption of heavy metals). The adsorption kinetic experiment was performed on 0.01 g of sulfur cellulose nanofibers in 50 mL of a metal solution for three heavy metal ions Cu (II), Cd (II) and Pb (II), and the initial concentration of metal ions was 200 ppm, It was carried out by fixing the contact time to 10 hours at a pH of 4. Figure 9(a) shows the removal performance of heavy metal ions according to the increase of the contact time, and the parameters of the linear model of two isotherms were calculated and shown in Table 2. By comparing the correlation coefficients, it can be seen that the second-order kinetics model is more suitable than the first-order kinetics model. The correlation coefficient values of Cu (II), Cd (II) and Pb (II) were 0.944, 0.88, and 0.91 for the first-order kinetic model, and 0.999 for all of the second-order kinetic models. The secondary reaction rate model of each metal ion is shown in Fig. 9(b). As mentioned above, the second-order kinetic model is related to the value of the square of the difference between the number of equilibrium adsorption sites and the number of occupied sites. Therefore, these results indicate that the adsorption process is mainly controlled by chemisorption, and electron sharing and exchange occurs between metal ions and sulfur functional groups of sulfur cellulose nanofibers. The saturation adsorption of heavy metal ions of sulfur cellulose nanofibers was found to be approximately 39.63, 30.00 and 19.64 mg·g ⁻¹ for Cu (II), Cd (II) and Pb (II). In addition, the sulfur cellulose nanofibers exhibit a fast adsorption rate for all heavy metal ions generated during the initial 1 hour. It can be seen that the heavy metal ion immediately reacts with the sulfur functional group on the surface of the nanofiber. This property can be an attractive property for practical applications of filtration or separation processes according to the method presented in the present invention.

According to an embodiment of the present invention, the cellulose nanofibers introduced with the functional group for adsorption of heavy metals have an excellent function of adsorbing heavy metals, and thus can be widely used in adsorption materials such as membranes or filters.

The above description of the present invention is for illustration, and those of ordinary skill in the art to which the present invention pertains can understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. For example, each component described as a single type may be implemented in a dispersed form, and likewise components described as distributed may be implemented in a combined form.

The scope of the present invention is indicated by the following claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included in the scope of the present invention.

Claims (8)

A mixed solution of N,N-dimethylacetamide (DMAc) solution, 3,3'-dithiodipropionic acid (DTDPA) and 1,1-carbonyldiimidazole (CDI) was added to the cellulose nanofiber and heated to double preparing sulfur cellulose nanofibers; and
Preparing a sulfur cellulose nanofiber by immersing the double sulfur cellulose nanofiber in an ammonium thioglycolate (AmTG) solution; including,
The thiol group of the sulfur cellulose nanofiber adsorbs heavy metals, wherein the heavy metals include copper, cadmium or lead. According to claim 1,
In the step of preparing the double sulfur cellulose nanofiber,
The cellulose nanofiber is a method of manufacturing a cellulose nanofiber introduced with a functional group for adsorbing heavy metals, characterized in that it is prepared by immersing in a basic aqueous solution after electrospinning a cellulose acetate solution. According to claim 1,
In the step of preparing the double sulfur cellulose nanofiber,
The DTDPA and CDI are a method of manufacturing a cellulose nanofiber introduced with a functional group for heavy metal adsorption, characterized in that it is mixed in a molar ratio of 1:1 to 5:1. According to claim 1,
In the step of preparing the double sulfur cellulose nanofiber,
The heating is a method of manufacturing a cellulose nanofiber introduced with a functional group for adsorption of heavy metals, characterized in that carried out to 60 °C to 120 °C. delete delete A cellulose nanofiber into which a functional group for adsorbing heavy metals prepared by the method according to claim 1 is introduced. An adsorbent comprising a cellulose nanofiber into which the functional group for adsorbing heavy metals of claim 7 is introduced.

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