KR102577399B1 - Method for producing uniform high porosity cellulose beads and cellulose beads prepared according to the method - Google Patents

Abstract

The present invention includes the steps of forming cellulose/solvent droplets in a molten state (M) or solid state (S) using a mixture containing cellulose and an oxide-based solvent; solidifying the cellulose/oxide solvent droplet in the molten state (M) or solid state (S) to form a cellulose bead in the molten state (M) or solid state (S) inside the droplet; and the step of cross-linking cellulose to contain an amidoxime group in the porous cellulose beads.
The cellulose bead manufacturing method of the present invention is effective in manufacturing cellulose beads with a uniform and porous internal structure by controlling the concentration and temperature of cellulose using microfluidics. In addition, the cellulose beads of the present invention have an excellent ability to adsorb metal ions due to their uniform and porous internal structure, and can be used as a metal filter to remove harmful heavy metal ions.

Description

Method for producing uniform high porosity cellulose beads and cellulose beads prepared according to the method}

The present invention relates to a method for producing highly porous cellulose beads of uniform size and to cellulose beads produced thereby. In detail, the present invention relates to the concentration ratio of a mixture containing cellulose and an oxide-based solvent and the solidification temperature of the cellulose/oxide-based solvent droplet. Accordingly, it relates to a method for manufacturing cellulose beads that form a uniform porous structure and to cellulose beads manufactured thereby.

Contamination of water resources with harmful metals such as lead, mercury, cadmium, copper, iron and chromium is a serious threat to humans. Therefore, detecting and removing these harmful metals from water is very important for modern society. Various efficient but expensive methods have been proposed to remove heavy metal ions from industrial wastewater using ion exchange, reverse osmosis and electrodialysis techniques. Chemical precipitation is promising, but the production of precipitated bulky hydroxides is often a major drawback.

Meanwhile, cellulose, a linear polysaccharide, is the most abundant and renewable biopolymer in nature, and due to its unique properties such as biocompatibility, biodegradability, environmental friendliness, cost-effectiveness and ease of mixing with organic and inorganic compounds, it can be used as a biocompatible adsorbent for water treatment. It is being applied, and in particular, research is being conducted on the use of porous cellulose beads.

Cellulose beads, which are used as metal ion adsorbents, can affect the shape, size, internal surface area, and pore size distribution of cellulose beads depending on the concentration, composition, and coagulation temperature of cellulose during manufacture. Recently, microfluidic methods for producing particles of uniform size, such as those in Korean Patent No. 10-1937399, have become common, but technological development on specific processes for forming uniform surfaces and porous structures is insufficient. Therefore, it is necessary to find optimized conditions every time the concentration or coagulation temperature of cellulose is changed.

Republic of Korea Patent No. 10-1937399

In order to solve the above problems, the purpose of the present invention is to provide a method for manufacturing cellulose beads that form a uniform porous structure.

Another object is to provide cellulose beads manufactured using the above cellulose bead manufacturing method.

In order to achieve the above object, the present invention,

A first step of forming cellulose/solvent droplets in a molten state (M) or solid state (S) using a mixture containing cellulose and an oxide-based solvent;

A second step of coagulating the cellulose/oxide solvent droplets in the molten state (M) or solid state (S) to form cellulose beads in the molten state (M) or solid state (S) inside the droplets; and

The porous cellulose beads provide a method for producing porous cellulose beads, comprising a third step in which the cellulose is crosslinked to contain an amidoxime group.

In the process of solidifying the droplet, it is preferable that the droplet is entirely homogeneous or forms a core/shell structure depending on the temperature.

The oxide-based solvent preferably contains N -Methylmorpholine- N -oxide monohydrate (NMMO).

In order to achieve the above other objects, the present invention,

A mixture containing cellulose and an oxide solvent is used to form cellulose/solvent droplets in a molten state (M) or solid state (S), and the cellulose/oxide solvent liquid in the molten state (M) or solid state (S) is formed. A porous cellulose bead comprising a step of coagulating the droplet to form a cellulose bead in a molten state (M) or solid state (S) inside the droplet, wherein the porous cellulose bead is crosslinked and contains an amidoxime group. manufacture,

It provides a porous cellulose bead, characterized in that the diameter ratio (D ₃ /D ₂ ) of the diameter when the bead is dried ( _{D 2} ) and the diameter when the bead is re-swollen (D 3 ) is 1.8 to 4.0.

The cellulose beads preferably adsorb one or more metal ions selected from the group consisting of Pb ²⁺ , Cu ²⁺ , Zn ²⁺ , Ni ²⁺ , Cd ²⁺ , Fe ³⁺ , Ca ²⁺ , and Cr ³⁺ do.

The method for manufacturing cellulose beads of the present invention can manufacture cellulose beads with a uniform and porous internal structure by controlling the concentration and temperature of cellulose using microfluidics.

In addition, the cellulose beads of the present invention have excellent adsorption capacity for metal ions due to their uniform and porous internal structure, and can be used as a metal filter to remove harmful heavy metal ions.

Figure 1 shows (a) the manufacturing process and (b) the functionalization process of cellulose beads according to an embodiment of the present invention.
Figure 2 is a plan view and CPD circuit design photo of a CPD container according to an embodiment of the present invention.
Figure 3 is a graph showing the UV-vis spectrum of Cu(NO ₃ ) ₂ , KHP, and Cu ²⁺ /phthalate composite aqueous solution according to an example of the present invention.
Figure 4 is a matrix graph showing three regions of conditions for producing (a) cellulose beads, (b) M cell/NMMO droplets, and (c) cellulose solidified from S cell/NMMO droplets according to an embodiment of the present invention. This is an optical microscope image of the bead.
Figure 5 shows (a) cellulose (SS), (b) cellulose (SM), (c) cellulose (MS), and (d) cellulose (MM) beads prepared at Q _d = 4 μL min according to an embodiment of the present invention. Size distribution graph and photo.
Figure 6 shows (a) SEM images of the fractured surface of cellulose beads, (b) D _c /D _T of cellulose beads as a function of coagulation temperature (T _coa ), according to an embodiment of the present invention.
Figure 7 is an SEM image of cellulose beads prepared from (a) S cell/NMMO droplets and (b) M cell/NMMO droplets according to an embodiment of the present invention.
Figure 8 is an optical microscope image of cellulose (MM) beads prepared at a concentration of 4 wt% cellulose in a dope according to an embodiment of the present invention.
Figure 9 shows FTIR spectra, (b) and (c) of (a) (i) cellulose, (ii) SEM images of (b) the exterior and (c) the fractured surface of cellulose (MM) beads dried using the CPD method.
Figure 10 is an amide for calculating the degree of conversion from -OH to -CN group (x) in the case of CN-cellulose beads and from -CN to oxime group (z) in the case of O-cellulose beads according to an embodiment of the present invention. The oxime functionalization process is shown.
Figure 11 shows q _t of Cu ²⁺ /phthalate complex on O-cellulose beads as a function of elapsed time (t _elapse ) at different concentrations according to an embodiment of the present invention.
Figure 12 shows isothermal curves for Cu ²⁺ /phthalate complex adsorption on O-cellulose beads according to an example of the present invention and linear curve fitting for (a, c) Langmuir and (b, d) Freundlich models.
Figure 13 shows (a) adsorption capacity (q _t ) of O-cellulose beads, (b) concentration reduction of Cu ²⁺ /phthalate composite aqueous solution, (c) adsorption of Cu ²⁺ /phthalate/ according to an embodiment of the present invention. (d) Adsorption capacity (q _t ) of O-cellulose and (d) adsorption efficiency of O-cellulose according to the number of cycles during desorption.
Figure 14 is a photograph of a column filled with O-cellulose beads according to an embodiment of the present invention.
Figure 15 shows the adsorption capacity of metal ions using O-cellulose beads according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail.

The present invention includes the steps of forming cellulose/solvent droplets in a molten state (M) or solid state (S) using a mixture containing cellulose and an oxide-based solvent; solidifying the cellulose/oxide solvent droplet in the molten state (M) or solid state (S) to form a cellulose bead in the molten state (M) or solid state (S) inside the droplet; and the step of cross-linking cellulose to contain an amidoxime group in the porous cellulose beads.

First, a mixture containing cellulose powder and an oxide-based solvent is prepared, and droplets of cellulose and oxide-based solvent are formed. Cellulose beads are prepared using microfluidics. CP and DP are connected using two separate syringe pumps.

The syringe containing cellulose and oxide-based solvent dope and the T-junction microfluidic chip are placed inside a bath filled with an organic solvent, such as ethylene glycol. The flow rates of DP and CP are controlled to an appropriate level to form droplets. When the cellulose powder and the oxide-based solvent dope meet at the edge of the T-junction, droplets of cellulose/oxide-based solvent are formed. Four cellulose beads can be formed depending on the state of the cellulose/solvent droplets and the coagulation temperature during coagulation. During solidification, the cellulose/solvent droplets can be in the solid state (S) or the molten state (M).

The oxide-based solvent is not limited thereto, but preferably includes N -Methylmorpholine- N -oxide monohydrate (NMMO). In the case of NMMO, it can be used as a solvent for cellulose in the form of breaking the intermolecular and intramolecular hydrogen bonds of the -OH group in cellulose due to the dipole moment of NO, so it is used to form droplets with cellulose in the present invention.

Melt-state (M) cellulose/oxide-based solvent droplets were solidified using the following method. CP hot mineral oil containing M cellulose/oxide-based solvent droplets from the microfluidic chip was mixed with a THF/water mixture at low temperature (e.g., 20 to 50 °C) (S) or at high temperature (e.g., 60 °C). ~75°C) (M) directly dropwise into the THF/water mixture. The THF/water mixture is used during coagulation because CP mineral oil containing cellulose/oxide-based droplets cannot be removed from the water bath due to the immiscibility between water and mineral oil. Therefore, when solidified in a THF/water mixture at a low temperature (S), cellulose beads (M-S) may be formed, and when solidified in a THF/water mixture at a high temperature (M), cellulose beads (M-M) may be formed.

Solid-state (S) cellulose/oxide solvent droplets are mixed with a significant amount of cold mineral oil in a beaker placed in an ice-water bath during the process in which the droplets generated at the T-junction are discharged to the outside. It can be manufactured by cooling cellulose/oxide-based solvent droplets in a molten state (M) in the CP of hot mineral oil. Cellulose/oxide-based solvent droplets remove CP with THF and solidify in water at low temperature (20 ~ 40℃) or water at high temperature (40 ~ 75℃), showing a solid state (S) or liquid state (M). . Therefore, when solidified in water at a low temperature (S), cellulose beads (S-S) can be formed, and when solidified in water at a high temperature (M), cellulose beads (S-M) can be formed.

The coagulated cellulose spherical beads were filtered using filter paper and washed several times with water. The cellulose beads produced can be designated as cellulose (S-S), (S-M), (M-S) and (M-M) beads.

According to one embodiment of the present invention, in the process of solidifying cellulose/oxide-based solvent droplets, the droplets may be formed homogeneously depending on the coagulation temperature, and on the other hand, they may form a core/shell structure. It may be possible. In other words, four types of cellulose beads can be made by controlling the state of the droplet and the solidification temperature, and the thickness of the shell in the core/shell structure can also be adjusted.

In the step of forming cellulose/solvent droplets, they may be formed in a molten state (M) or in a solid state (S). The formation of cellulose beads in the molten state (M) or solid state (S) can then vary depending on the solidification temperature.

Therefore, if the solidification temperature (T _coa ) of the molten state (M) droplet is controlled to about 20°C to 50°C, solid state (S) cellulose beads will be formed, so the cellulose (MS) beads can exhibit a core/shell structure. there is. However, if the solidification temperature (T _coa ) of the molten state (M) droplet is controlled to about 60°C or higher, molten state (M) cellulose beads will be formed, so the core/shell structure of the cellulose (MM) beads will not be formed and the entire can exhibit a homogeneous open structure.

On the other hand, if the solidification temperature (T _coa ) of the liquid droplet in the solid state (S) is controlled to below 40°C, cellulose beads in the solid state (S) will be formed, so the cellulose (SS) beads) have an overall homogeneous and compact structure. can represent. However, if the solidification temperature (T _coa ) of the liquid droplet in the solid state (S) is controlled to a temperature exceeding 40°C, cellulose beads in the molten state (M) will be formed, so the cellulose (SM) beads will exhibit a core/shell structure. You can.

The porous cellulose beads of the present invention may contain an amidoxime group by crosslinking cellulose. Cellulose beads are cellulose crosslinked and functionalized with acrylonitrile (CN) and hydroxylamine (NH ₂ OH) to contain amidoxime groups. Specifically, the cellulose beads are crosslinked, and the ECH reacting with the hydroxyl groups of cellulose introduces some oxide groups that can further react with the hydroxyl groups of the same or other cellulose chains nearby. Cellulose beads are dispersed in NaOH aqueous solution under stirring and ECH/MeOH is added dropwise to form cross-linked cellulose (X-cellulose) beads and dried. The dried Then, CN-functionalized cellulose (CN-cellulose) beads can be introduced with an amidoxime group to form cellulose beads functionalized with an oxime group (hereinafter referred to as 'O-cellulose beads').

According to the production method of the present invention, the formed cellulose beads can be represented by cellulose (S-S), (S-M), (M-S) and (M-M) beads, among which cellulose (S-S), (S-M) and (M-S) beads. represents an oval shape, and cellulose (M-M) beads may exhibit a spherical shape. Uniformly sized oval cellulose (S-S), (S-M) and (M-S) beads exhibit a narrow size distribution with a long axis of 1,000 to 1,500 μm and a minor axis of 700 to 850 μm.

On the other hand, spherical cellulose (M-M) beads exhibit a narrow size distribution and have a diameter of 700 to 850 μm. Cellulose beads (Cellulose (S-M) and (M-M)) solidified to the molten state (M) at high temperatures (above 60°C) and beads (Cellulose (S-S) and (M-S) solidified to the solid state (S) at low temperatures. ), the color is whiter than that, which means that the internal structure of the beads solidified in the molten state (M) is different from the internal structure of the beads solidified in the solid state.

The present invention relates to porous cellulose beads functionalized with amidoxime groups formed from cellulose and solvent droplets, wherein the beads have a diameter when dried (D ₂ ) and a diameter when re-swollen (D ₃ ). Provided are porous cellulose beads in which the ratio (D ₃ /D ₂ ) represents a specific ratio.

The cellulose beads coagulated in water before drying have almost the same size as the cellulose/oxide solvent droplets. Dried cellulose beads shrink significantly from cellulose beads in water because the solids content of the mixture is very low. When dried cellulose beads are put back into water to be applied as an adsorbent, re-swelling of the dried cellulose beads is important for use as an adsorbent with a large surface area inside the cellulose beads.

Cellulose beads cross-linked according to the manufacturing method of the present invention are completely dried and then re-swell to the original cellulose beads in water, indicating that cross-linking prevents hydrogen bonding after drying. Therefore, crosslinking cellulose beads promotes both stability and reswelling ability. Therefore, according to the manufacturing method of the present invention, the re-swelling ability is excellent, showing excellent adsorption ability when used as a metal ion adsorbent.

It is preferable that the diameter ratio (D ₃ /D ₂ ) of the diameter when the porous cellulose beads of the present invention are dried ( _D 2 ) and the diameter when they are re-swollen (D ₃ ) is 1.8 to 4.0. This diameter ratio (D ₃ /D ₂ ) is possible because the expansion volume when re-swelled becomes very large, and when the diameter ratio is less than 1.0 or more than 5.0, more preferably less than 1.8 or more than 4.0. It is not desirable because the reswelling results are poor and it is difficult to achieve excellent adsorption performance. According to the existing cellulose bead manufacturing method, re-swelling after drying is difficult to occur, so the diameter (D ₃ ) at the time of re-swelling remains at 0 to 1.0, so the diameter (D ₂ ) and the diameter when re-swelled (D ₃ ) It can be said that it is difficult for the diameter ratio (D ₃ /D ₂ ) to exceed 1.0.

The internal structure of O-cellulose beads prepared according to the present invention can determine the adsorption capacity. The cellulose/oxide-based solvent droplets solidified to a molten state (M) at a high temperature (above 60°C) and the O-cellulose beads functionalized with an amidoxim group have a very uniform, rough, spherical, open internal structure. indicates.

Therefore, O-cellulose beads made from these cellulose (M-M) beads have the highest adsorption capacity because they have the highest porous structure, and cellulose (S-S) solidified into a solid state (S) at low temperature (below 60°C). On the contrary, O-cellulose beads prepared from beads show the lowest adsorption capacity. O-cellulose beads prepared from cellulose (S-M) and (M-S) beads exhibit adsorption capacity between them.

The porous cellulose beads prepared by the method of the present invention are one selected from the group consisting of Pb ²⁺ , Cu ²⁺ , Zn ²⁺ , Ni ²⁺ , Cd ²⁺ , Fe ³⁺ , Ca ²⁺ , and Cr ³⁺ It can adsorb more metal ions. The O-cellulose beads of the present invention can be used as a filler in a column for metal adsorption. Among metal ions, it can be seen that the adsorption capacity is excellent in that order: Pb ²⁺ , Cu ²⁺ , Zn ²⁺ , Ni ²⁺ , Cd ²⁺ , Fe ³⁺ , Ca ²⁺ , and Cr ³⁺ .

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. However, these examples are for illustrating the present invention in more detail, and it will be apparent to those skilled in the art that the scope of the present invention is not limited thereto.

<Example>

ingredient

Cellulose powder and NMMO monohydrate used as a solvent were purchased from KOLON (Korea), and epichlorohydrin (ECH) and acrylonitrile (AN) were purchased from Daejung (Korea).

Sodium hydroxide (NaOH), sodium carbonate (NaCO ₃ ), hydroxylamine hydrochloride (NH ₂ OH·HCl), tetrahydrofuran (THF), methanol (MeOH), and potassium hydrogen phthalate (KHP) were purchased from Deoksan. Tetramethylammonium (TMA) chloride ((CH ₃ ) ₄ N ⁺ Cl ^- ), copper (II) nitrate hexahydrate (Cu(NO ₃ ) ₂ ·6H ₂ O), cadmium (II) nitrate (Cd (NO ₃ ) ₂ ) and iron(III) chloride hexahydrate (FeCl ₃ ·6H ₂ O) were purchased from Junsei, Japan. Lead(II) nitrate (Pb(NO ₃ ) ₂ ), nickel(II) nitrate hexahydrate (Ni(NO ₃ ) ₂ ·6H ₂ O), calcium(II) nitrate tetrahydrate (Ca(NO ₃ ) ₂ ·4H ₂ O), zinc(II) nitrate hexahydrate (Zn(NO ₃ ) ₂ ·6H ₂ O) and chromium(II) chloride hexahydrate (Cr(NO ₃ ) ₂ ·6H ₂ O) were from Sigma Aldrich (USA). Purchased. All chemicals were used without further purification.

Fabrication of uniformly sized cellulose droplets

Figure 1(a) summarizes the overall circuit diagram for producing cellulose beads using microfluidics. NMMO monohydrate (100 g) was melted in a round-bottom glass tube (outer diameter = 60 mm, length = 180 mm) at 80 °C, and cellulose powder (4 g) was melted in a screw-type propeller (diameter = 125 mm, pitch = 35 mm) at 80 °C for 2 h. The resulting cell/NMMO dope was degassed by maintaining it at 90°C for 2 hours using a rubber cap on top to prevent moisture evaporation from the NMMO monohydrate. The degassed dope was transferred to a plastic syringe (inner diameter = 20.05 mm) and used as DP in microfluidics. Mineral oil containing EM90 (3 wt%) was used as CP in a plastic syringe (internal diameter = 15.90 mm). CP and DP were connected to a T-junction microfluidic chip (PEEK, P-713, IDEX, USA) (through hole diameter = 1.25 mm) using two separate syringe pumps (LEGATO 100, KD Scientific, USA). .

The syringe containing the cell/NMMO dope and the T-junction microfluidic chip are placed in a bath filled with ethylene glycol at 85°C (Figure 1(a)). The flow rates (Q _d and Q _c ) of DP and CP were controlled to 2.0 and 23 μL min ^{-1 ,} respectively. When the cell/NMMO dope met at the edge of the T-junction, a cell/NMMO droplet was formed. Four cellulose bead samples were prepared according to the state of the cell/NMMO droplets and coagulation temperature during coagulation. During solidification, cell/NMMO droplets can be in the solid state (S) or molten state (M).

S cell/NMMO droplets were prepared by cooling M cell/NMMO droplets in CP of hot mineral oil by mixing them with a significant amount of cold mineral oil in a beaker previously placed in an ice-water bath. The cell/NMMO droplets solidified at low S and high M solidification temperatures, which represent the S and M of NMMO monohydrate, respectively. Remove the mineral oil from the beaker containing the S cell/NMMO droplets, fill the beaker with THF to mix with the remaining mineral oil, remove the THF, and place in the beaker at 30°C (S) or 60°C ( M) was refilled with water and kept for 30 minutes to solidify.

M cell/NMMO droplets were solidified using the following method. CP hot mineral oil (85 °C) containing M cell/NMMO droplets coming from a microfluidic chip was dropped directly into a THF/water mixture (50/50, v/v) at 30 °C (S) or 60 °C (M). I dropped it. The THF/water mixture was used during coagulation because the CP mineral oil containing cell/NMMO droplets could not be removed from the water bath due to the immiscibility between water and mineral oil.

The solidified cellulose spherical beads were filtered using filter paper (Advantec, 110 mm) and washed several times with water. The produced cellulose beads are denoted as cellulose (S-S), (S-M), (M-S) and (M-M) beads, where the first S and M represent the solid and melt states of the cell/NMMO droplet, respectively, and the second S and M represents the low and high solidification temperatures, respectively.

O ^- Preparation of cellulose beads

Cellulose beads were cross-linked with ECH (Figure 1(b)). ECH reacting with the hydroxyl groups of cellulose introduces a portion of ethylene oxide that can further react with hydroxyl groups of the same or other nearby cellulose chains. Cellulose beads (0.1 g) were dispersed in aqueous NaOH solution (3 wt%, 20 mL) under magnetic stirring for 30 min. ECH/MeOH (3.08 g, 1.54 g each) was added dropwise under magnetic stirring at 60°C for 1 hour. After the reaction, the reaction medium was washed with water until pH reached 7. The cross-linked cellulose (X-cellulose) beads were dried at 25°C in a vacuum oven for 2 hours. Amidoxime groups were introduced into cellulose beads (Figure 1(b)).

The dried X-cellulose beads (0.1 g (0.55 mM)) were dispersed in 20 mL AN supplemented with 0.56 mL MeOH solution containing 5 wt% TMA chloride. 0.75 mL MeOH solution containing 10% by weight sodium hydroxide was added dropwise at 0°C. The reaction was maintained at 25°C for 2 hours under magnetic stirring and finally washed with water until the pH of the medium reached 7. CN-functionalized cellulose (CN-cellulose) beads were further reacted with NH ₂ OH·HCl to introduce amidoxime groups. NH ₂ OH·HCl (8 g), Na ₂ CO ₃ (6 g), and CN-cellulose beaker (0.1 g) were added to a 250 mL beaker, to which 100 mL of water was added and sealed. The reaction was maintained at 70°C for 12 hours. After the reaction, the O-cellulose beads were washed with water several times to remove remaining salt. The water was replaced with MeOH and the O-cellulose beads were dried in a vacuum oven at 25°C.

critical point drying

A CPD method using liquid CO ₂ was used to prepare cellulose bead samples for scanning electron microscopy (SEM) and porosity/internal surface area measurements. This is because simple water evaporation by vacuum, heating, and air drying results in keratinization of the bead surface and significant loss of porosity and surface area.

Freeze-drying also causes water volume swelling and the growth of ice crystals upon freezing, resulting in the collapse of micro- and mesopores in cellulose beads. For CPD with liquid _CO2 , water must be exchanged stepwise with ethanol, acetone and liquid _CO2 , which are removed under supercritical conditions. Figure 2 is a plan view and CPD circuit design photo of a CPD container according to an embodiment of the present invention. Referring to Figure 2, a CPD container was handmade to investigate the internal structure of cellulose beads manufactured using the CPD method.

<Experimental example>

measurement

Attenuated total reflection (ATR)-Fourier transform infrared (FTIR) (ATR-FTIR) spectra were recorded in the range of 500-4000 cm ^-1 over an average of 64 scans using a FTIR spectrometer (Frontier, PerkinElmer, USA). The dried sample was ground into a fine powder using a mortar and pestle. Field emission (FE)-SEM (FE-SEM; SU8220, Hitachi, Japan) images of cellulose beads were obtained from the fractured surface of platinum-coated epoxy molded samples. Samples for SEM were dried using the CPD method with liquid CO ₂ .

Epoxy molding was performed by placing the beads into the cap (Cavity Embedding Mold, Ted Pella, USA), which was then covered with an epoxy mixture of EPON (2 mL), DDSA (1.25 mL), NMA (1.25 mL), and DMP (0.075 mL). This was done by filling, curing at 60°C for 24 hours, and splitting it in half with a vise. Cellulose beads were observed using an optical microscope (ANA-006, Leitz, Germany) equipped with a digital camera with transmission mode. Cu ²⁺ /phthalate solution concentration was measured using ultraviolet (UV)-visible (UV-vis) spectroscopy (UV-2401PC, Shimadzu, Japan). The chemical composition of cellulose beads was studied using an elemental analyzer (EA, Flash 2000, ThermoFisher, USA). The concentration of metal ions in water was investigated using an inductively coupled plasma spectrometer (ICP, Optima 7300DV, PerkinElmer, USA). The surface area of cellulose beads (SS, MM) was measured using a surface area and pore size analyzer (Quadrasorb Evo, Quantachrome, Austria) using the Brunauer-Emmett-Teller (BET) method. Samples for BET analysis were dried using the CPD method with liquid CO ₂ and pretreated at 100°C for 12 hours in a vacuum oven.

(1) Adsorption of metal ions

The Cu ²⁺ /phthalate composite aqueous solution was used to demonstrate the performance of O-cellulose beads for Cu ²⁺ ion detection using UV-vis spectroscopy. It was prepared by dissolving Cu(NO ₃ ) ₂ (adjusted to 50 to 1000 ppm) and KHP (4.08 g, 0.2 M, excess) in water (100 mL). Figure 3(a) shows the UV-vis spectrum of a complex aqueous solution of Cu(NO ₃ ) ₂ (1000ppm), KHP (0.2M), and Cu ²⁺ /phthalate (1000ppm/0.2M). The UV-vis spectrum of Cu(NO ₃ ) ₂ aqueous solution shows a small peak at 780 nm. However, the UV-vis spectrum of the Cu ²⁺ /phthalate composite aqueous solution shows a strong absorption peak at 730 nm with a hypochromatic shift, consistent with the reported results. The calibration curve (730 nm) of the Cu ²⁺ /phthalate composite aqueous solution was obtained at various concentrations as a linear regression curve (r ² = 0.998) (Figure 3(b)). Each adsorption experiment was performed three times to investigate the adsorption behavior of metal ions on the cellulose bead adsorbent. The concentration of the metal ion aqueous solution before and after adsorption was measured in the wavelength range of 400-800 nm using a UV-vis spectrophotometer. The adsorption capacity (q _t ) for Cu ²⁺ /phthalate complex was evaluated using the following equation (1):

[Equation 1]

where C ₀ (mg L ^-1 ) and C _t (mg L ^-1 ) are the dye concentration at initial time and time t, respectively, V(L) is the volume of dye solution, and m(g) is the dried adsorbent. is the weight of

(2) Desorption of metal ions

For desorption experiments, O-cellulose beads loaded with metal ions were immersed in 8 mL of 2 M HCl for 30 min under magnetic stirring at 25 °C, and the O-cellulose beads were rinsed several times with water and pH 6 buffer and then regenerated to their initial form. did. The adsorption test was again performed with magnetically stirred regenerated O-cellulose beads (4 mg) in Cu ²⁺ /phthalate solution (4 mL, 1000 ppm) at pH 7 for 2 h. The recyclability of O-cellulose beads was investigated by repeating the adsorption/desorption cycle five times.

<Evaluation and results>

Production of cellulose beads using microfluidics

To find the optimal Q _d and Q _c in microfluidics, cellulose (4 wt%)/NMMO dope was evaluated at different Q _d and Q _c in a T-junction microfluidic chip.

Figure 4(a) shows the matrix diagram of processability at different Q _d and Q _c . The matrix graph can be divided into three regions representing unprocessed conditions (zone I) and conditions for producing asymmetric prolate (zone II) and symmetric spherical (zone III) cellulose beads.

The photo on the inset graph shows a representative light microscopy image of cellulose beads. Symmetric spherical cellulose beads were produced when Q _c > ~10.0 μL min ^-1 and Q _d > ~1.0 μL min ^-1 (zone III). For 6.0 μL min ^-1 < Q _c <10.0 μL min ^-1 (zone II), asymmetrically extended extended cellulose beads were produced. No droplets were generated at Q _c < 6.0 μL min ^-1 (zone I).

At low capillary numbers (low Q _c ) in the T-junction chip, droplets form in a squeezing mode, creating a global pressure gradient as the droplet forms. In squeezing mode, the generated water droplet moves through the channel with a plug trapped in the channel wall. When Q _c increases (i.e., the capillary number increases), droplet production switches from the squeezing mode to the water droplet mode. For clarity, cellulose/NMMO droplets generated at Q _d = 4 μL min ⁻¹ and Q _c = 30 μL min ⁻¹ (high Q _c in zone III) were evaluated at different solidification temperatures.

Figures 4(b) and (c) show optical microscopy images of cellulose beads solidified from M and S cell/NMMO droplets at different temperatures, respectively. At the T junction of the microfluidic chip, the M and S cell/NMMO droplets are identical. In the case of M cell/NMMO droplets ((b) in Figure 4), spherical cellulose beads were present at T _coa > 50°C, but elliptical cellulose beads were produced at T _coa = 10°C, 20°C, 30°C, and 40°C. Cellulose beads prepared at T _coa > 50°C represent cellulose (MM) beads. The oval shape of the cellulose beads generated at low T _coa indicates that the cell/NMMO droplets at the T-junction were generated in a squeezing mode.

In the case of cellulose (MM) beads, due to the high temperature solidification of M cell/NMMO droplets, the shear stress generated at the T-junction of the microfluidic chip during droplet production can be easily released during solidification. Therefore, cellulose (MM) beads were formed in compression mode, but spherical cellulose can be observed. The squeezing mode is evident in the S cell/NMMO droplet (Figure 4(c)). Oval cellulose beads were produced at all studied T _coa because the oval shape of the cell/NMMO droplet at the T-junction was fixed during cooling of the cell/NMMO droplet to produce the S cell/NMMO droplet. Therefore, the cell/NMMO droplet at the T junction is in a squeezing mode.

Size distribution of cellulose beads produced under various coagulation conditions.

Figure 5 shows (a) cellulose (SS), (b) cellulose (SM), (c) cellulose (MS), and (d) cellulose (MM) beads prepared at Q _d = 4 μL min according to an embodiment of the present invention. Size distribution graph and photo. Oval shapes are observed for cellulose (SS), (SM) and (MS) beads, while spherical shapes are observed for cellulose (MM) beads.

Uniformly sized elliptical cellulose (S-S), (S-M), and (M-S) beads had a narrow size distribution, yielding beads with a long axis of 1219.3 ± 78.7 μm and a short axis of 779.4 ± 42.9 μm.

Spherical cellulose (M-M) beads were obtained with a narrow size distribution and a diameter of 784 ± 24.8 μm. Cellulose beads solidified in the molten state (cellulose (S-M) and (M-M)) are white compared to beads solidified in the solid state (cellulose (S-S) and (M-S)), which indicates that the internal structure of the beads solidified in the molten state is solid. This indicates that it is different from the solidified bead.

Coagulation occurs through water diffusion into the cell/NMMO droplets. Therefore, the solidification temperature is important in controlling the internal porous structure of cellulose beads because the resulting solidification structure is determined by the water diffusion rate, which is highly dependent on the solidification temperature.

Structure of cellulose beads

The morphology of the prepared cellulose beads was analyzed using the CPD method with dried samples. Figure 6 shows (a) SEM images of the fractured surface of cellulose beads, (b) D _c /D _T of cellulose beads as a function of coagulation temperature (T _coa ), according to an embodiment of the present invention. (a) is an SEM image of the fractured surface of cellulose (SS), (SM), (MS), and (MM) beads. During coagulation, water dilutes the NMMO content of cell/NMMO droplets, and the diluted NMMO has a low solvation power of cellulose, leading to phase separation. For cellulose (SS) (a(i) in Figure 6) and (MM) (a(iv) in Figure 6) beads, cellulose (MM) beads are coarser and more porous than cellulose (SS) beads, but their internal structure is homogeneous. do. This is because the cellulose chains dissolved in the M cell/NMMO droplets coagulate (phase separate) with high mobility, forming large phase-separated fiber bundles in the case of cellulose (MM) beads.

The surface areas of cellulose (SS) and (MM) beads measured using the BET method are 196 and 218 m ² g ^-1 , respectively, which means that cellulose (MM) beads have a more porous structure, which is consistent with the morphology data from SEM. It indicates that there is.

For cellulose (M-S) beads (a(iii) in Figure 6 ), M cell/NMMO droplets were dropped directly into a THF/water mixture (30°C) during coagulation. The outer surface of the molten cell/NMMO droplet is contacted with a cold THF/water mixture in a coagulation beaker. Therefore, the outer part of the cell/NMMO droplet becomes solid, but the inner part is still molten because it cannot be cooled enough to become solid during the initial solidification. Therefore, the structure of the outer part of the cellulose (M-S) bead is different from that of the inner part. The outer and inner parts were solidified into a solid state and a molten state, respectively, and the core structure became rougher than the shell structure, as shown in (a) (i) and (iv) of Figure 6.

For cellulose (S-M) beads ((a)(ii) in Figure 6), S cell/NMMO droplets were dropped into hot water (60°C) during coagulation. Therefore, the S cell/NMMO droplets were changed into M cell/NMMO droplets by heating with hot water. However, although the thickness of the shell was small, the outer part quickly solidified (phase separated) in the solid state before reaching the melting temperature of the S cell/NMMO droplet (Figure 6(a)(ii)). Therefore, similar to cellulose (M-S) beads, coagulation between the outer and inner parts is different to form the core/shell structure. Therefore, the outer and inner parts solidify into solid and molten states, respectively.

Effect of solidification temperature on shell thickness

Figure 6(b) shows D _c /D _T of cellulose beads (prepared from S and M cell/NMMO droplets) as a function of solidification temperature (T _coa ), where D _c means the diameter of the core, and D _T represents the total diameter. Figure 7 is an SEM image of cellulose beads prepared from (a) S cell/NMMO droplets and (b) M cell/NMMO droplets according to an embodiment of the present invention. _DT and D _c were measured using an optical microscope and SEM images, respectively. When D _c /D _T = 0 or 1, the cellulose beads are entirely homogeneous, compact, and fibrous without a core/shell structure.

40℃(셀룰로오스(S-S)비드)에서 균질하고 컴팩트한 구조(D_c/D_T = 0)를 나타내고, T_coa > 40℃에서 코어/쉘 구조(셀룰로오스(S-M) 비드)를 나타낸다.Cellulose beads in S cell/NMMO droplets are T _coa

It exhibits a homogeneous and compact structure (D _c /D _T = 0) at 40°C (cellulose (SS) beads) and a core/shell structure (cellulose (SM) beads) at T _coa > 40°C.

Cellulose beads in M cell/NMMO droplets exhibit a core/shell structure at T _coa = 20°C - 50°C (cellulose (MS) beads) and a homogeneous open structure (cellulose (MM) beads) at T _coa = 60°C (cellulose (MM) beads). D _c /D _T = 1).

Therefore, four types of cellulose beads can be made by controlling the state and coagulation temperature of the cell/NMMO droplet, and T _coa can control the thickness of the shell.

Preparation of O-cellulose beads

The cellulose beads coagulated in water before drying had almost the same size as the cell/NMMO droplets. Dried cellulose beads shrink significantly from cellulose beads in water because the solids content of the mixture is very low. When the dried cellulose beads are inserted back into water for adsorption applications, reswelling of the dried cellulose beads is important for use as an adsorbent with a large surface area inside the cellulose beads.

Figure 8(a) shows optical microscopy images of cellulose beads without crosslinking (M-M) before and after drying and reswelling of the dried cellulose beads (in water). Completely dried cellulose did not swell to the original cellulose beads in water, indicating that hydrogen bonds formed after drying prevent reswelling of the dried cellulose beads.

Figure 8 (b) shows an optical microscope image of cross-linked cellulose (M-M) beads. Completely dried cellulose beads reswell to the original cellulose beads in water, indicating that crosslinking prevents hydrogen bond formation after drying. Therefore, crosslinking cellulose beads promotes both stability and reswelling ability. The degree of reswelling of the cellulose beads depends on the cellulose concentration of the dope.

Table 1 shows the diameters of X-cellulose beads prepared with different cellulose concentrations in the dope before drying (in water) and after drying and after reswelling of the dried cellulose beads. The diameters of swollen, dried and re-swollen X-cellulose beads are denoted as D ₁ , D ₂ and D ₃ , respectively.

이 증가함에 따라 cell/NMMO 액적의 고체 함량이 증가하기 때문에

이 증가함에 따라 증가한다. 그러나,

이 증가하면 재팽윤된 셀룰로오스 비드(D₃/D₂)의 비율이 감소한다. 낮은

에서 가교가 수행되면 수소 결합을 효과적으로 차단한다. 따라서 작은 붕괴 건조 X-셀룰로오스 비드(낮은

로 인해)는 건조 전 원래 크기보다 훨씬 부풀어 오를 수 있다. 따라서

가 감소하면 D₃/D₂가 커진다. 그러나,

= 2 및 3 wt%에서 제조된 X-셀룰로오스 비드는 물에서 원래 크기로 재팽윤될 수 없지만,

= 4 및 5 wt%에서는 재팽윤되어 원래 크기(D₁)에 가깝다(D₃/D₁ = 0.5, 0.7, 0.9, 1 각각

= 2, 3, 4, 5 wt %에서).The diameter of the dried X-cellulose beads (D ₂ ) is

Because the solid content of the cell/NMMO droplet increases as this increases,

It increases as this increases. however,

As this increases, the ratio of re-swollen cellulose beads (D ₃ /D ₂ ) decreases. low

When crosslinking is performed, hydrogen bonds are effectively blocked. Therefore, small collapsing dried X-cellulose beads (low

(due to this) may swell significantly beyond its original size before drying. thus

As decreases, D ₃ /D ₂ increases. however,

= X-cellulose beads prepared at 2 and 3 wt% cannot reswell to their original size in water;

= 4 and 5 wt%, it re-swells and is close to its original size (D ₁ ) (D ₃ /D ₁ = 0.5, 0.7, 0.9, 1, respectively)

= at 2, 3, 4, 5 wt%).

)
(wt%)Dope Concentration
(

)
(wt%) Swollen
X-cellulose
(D ₁ )
(

) Dried
X-cellulose
(D ₂ )
(

) Reswollen
X-cellulose
(D ₃ )
(

) Diameter Ratio
(D ₃ /D ₂ )
(Volume Ratio) 2 800 100 400 4
(64) 3 750 200 500 2.5
(16) 4 650-750 250 580-700 2.3
(12.2) 5 550-650 300 550-600 1.8
(5.8)

X-cellulose beads were functionalized with AN to create intermediate CN-cellulose beads and further functionalized with NH ₂ OH to make final O-cellulose beads. FTIR spectroscopy confirmed the functionalization of X-, CN-, and O-cellulose.

Figure 9(a) shows FTIR spectra of cellulose, X-cellulose, CN-cellulose, and O-cellulose beads. The FTIR spectrum of X-cellulose beads is close to that of cellulose due to the similarity of functional groups. The FTIR spectrum of CN-cellulose shows a characteristic CN stretching band at 2260 cm ^-1 . The FTIR spectrum of O-cellulose shows additional peaks at ~920, 1610 and 1670 cm ^-1 due to stretching vibration bands of -NO, -NH and -C=N bonds in amidoxime.

The porous structure was studied using SEM with cellulose (M-M) beads and functionalized cellulose beads (X-, CN-, and O-cellulose beads).

Figures 9(b) and (c) show SEM images of the external and fractured surfaces of cellulose, X-cellulose, CN-cellulose, and O-cellulose beads dried using the CPD method, respectively. The internal structure of all cellulose beads (broken surface, Figure 9 (c)) is porous regardless of functionalization, but the external surface is small and shows a closed structure (Figure 9 (b)). The cellulose structure can easily collapse during drying due to strong hydrogen bonds. CPD is one of the best ways to preserve swollen structures during drying. Therefore, the open fiber structure of the cellulose beads can be observed.

The degree of conversion from -OH to -CN group for CN-cellulose beads and from -CN to amide oxime group for O-cellulose beads was calculated using EA.

Table 2 summarizes the EA results of cellulose, CN-cellulose and O-cellulose beads. The content of N is 4.31 and 10.05 wt% for CN-cellulose and O-cellulose beads, respectively, but the content of C is ∼44 ± 3 wt% for all cellulose beads. From the EA data, the degree of conversion to -CN groups for CN-cellulose beads and to amide oxime groups for O-cellulose beads was calculated:

Atom Cellulose CN-Cellulose O-Cellulose N 0 4.31 10.05 C 42.37 46.39 43.86 H 6.21 6.06 6.18 O 51.42 43.24 39.91

Figure 10 is an amide for calculating the degree of conversion from -OH to -CN group (x) in the case of CN-cellulose beads and from -CN to oxime group (z) in the case of O-cellulose beads according to an embodiment of the present invention. The oxime functionalization process is shown. where x, y and z are the number of -CN groups converted between three -OH groups, the number of -CN groups converted to amide oxime groups and unconverted -CN groups, respectively, x = z + y. The molecular weights of one unit of CN- and O-cellulose are 180 + 54x and 180 + 54y + 87z, respectively, where 54 and 87 are -CH ₂ CH ₂ CN and amide oxime (-CH ₂ CH ₂ C(= NOH)NH, respectively. ₂ ) is the molecular weight (per mole).

The nitrogen content in weight percentage is 14x/(180 + 54x) × 100 and (28z + 14y)/(180 + 54y + 87z) × 100 for CN- and O-cellulose beads, respectively. The measured nitrogen content is 4.31 and 10.05 wt% for CN- and O-cellulose beads, respectively, so the calculated x, y, and z values (with x = y + z) are 1.5, 1.0, and 0.5, respectively. Therefore, the degree of conversion from -OH to -CN group (x) for CN-cellulose beads is 50% (1.5/3 × 100) and for O-cellulose, the degree of conversion from -CN to amide oxime group is 33% ( 0.5/1.5 × 100).

The degree of conversion of amide oxime groups is similar to the reported value of 40% for amide oxime functionalized poly(acrylonitrile) (PAN) nanofibers, although produced by various reaction conditions with different NH ₂ OH·HCl concentrations.

Metal ion isotherm of O-cellulose beads

O-cellulose beads were used as an adsorbent for Cu ²⁺ /phthalate complex in water. Cu ²⁺ /phthalate complex enhances the intensity of Cu ²⁺ in UV-vis spectroscopy, as previously discussed.

Figure 11 shows the q _t of Cu ²⁺ /phthalate complex on O-cellulose beads as a function of elapsed time (t _elapse ) at different concentrations. Curve-fitting was performed using equation (3) of pseudo-first-order dynamics (Figure 11a) and equation (5) of pseudo-second-order dynamics (Figure 11b). The curve fitting data for q _e and k are the amount of adsorbed material at equilibrium and adsorption kinetic coefficient, respectively. The parameters of q _e1 (and k ₁ ) for first-order dynamics and q _e2 (and k ₂ ) for second-order dynamics are given by plots of ln(q _e -q _t ) vs t and t/q _t vs t It was calculated using modified equations (4) and (6).

Table 3 summarizes the curve fitting results using parameters q _e , k and r ² . The observed data fits the second-order equation (5) better than the first-order equation (3). r ² is 0.9610 and 0.9919 for the first and second equations, respectively. These results indicate that the adsorption mechanism is due to the chelating reaction between the transition metal ion and the amide oxime group:

[Equation 3]

[Equation 4]

[Equation 5]

[Equation 6]

initial
conc.
(ppm) First order Second order k ₁
(min ^-1 ) q _e1
(m·gg ^-1 ) r ²

10^-3
(g·mg^-1·min^-1)k ₂

10 ^-3
(g·mg ^-1 ·min ^-1 ) q _e2
(mg·g ^-1 ) h
(m·gg ^-1 ·min ^-1 ) r ² 47.4 0.0019 21.0094 0.9500 0.1171 28.7356 0.0966 0.9948 80.5 0.0020 35.2815 0.9783 0.0657 41.4938 0.1131 0.9996 167.4 0.0027 42.3281 0.9835 0.0915 51.3347 0.2411 0.9998 261.9 0.0034 42.4981 0.9802 0.1280 53.5906 0.3677 0.9995 358.7 0.0034 45.9402 0.9674 0.1191 61.0874 0.4446 0.9995 461.5 0.0039 50.2847 0.9712 0.1205 68.4932 0.5654 0.9998 729.0 0.0041 51.1632 0.8660 0.1348 70.4722 0.6696 0.9997 1010.3 0.0049 50.6678 0.9526 0.1692 81.3008 1.1186 0.9992

Isotherms were performed using the Langmuir (equation (7)) and Freundlich (equation (9)) models, where q _m is the adsorption capacity (related to the number of available binding sites) and C _e is the aqueous phase at equilibrium. The concentration, K _L and K _F are the affinity constants for adsorption in the Langmuir (equation (7)) and Freundlich (equation (9)) models, respectively, and n is the heterogeneity index. The parameters of equations (7) and (9) are linear to the Langmuir and Freundlich isotherm equations (8) and (10) modified using Cu ²⁺ /phthalate complex in the concentration range of 25-1000 ppm at 25°C. Calculations were made by performing curve fitting (Figure 12).

Table 4 summarizes the calculated q _m , K , and n . The r ² values of the Langmuir and Freundlich isotherm curves are 0.99 and 0.95, respectively, which indicates that the Langmuir model fits the observed data well and that a saturated monolayer (not a multilayer) of solute molecules on the adsorbent surface was formed during adsorption. The affinity constant of KL is 0.013 L·mg ^-1 , which is similar to the reported value of poly(amidoxime) cellulose powder (0.014 L·mg ^-1 ). The calculated q _m is ~ 81.30 mg g ^-1 , which is larger than the reported value (52.70 mg g ^-1 ) for amidoxime-functionalized poly(acrylonitrile) (PAN) nanofibers with 25% oxime group conversion. Therefore, O-cellulose beads prepared from cellulose (MM) beads have a high adsorption capacity of metal ions:

[Equation 7]

[Equation 8]

[Equation 9]

[Equation 10]

Langmuir Freundich q _m (mg·g ^-1 ) 82.3 - K(L·mg ^-1 ) 0.013 0.015 r ² 0.99 0.95 n ^-1 - 0.25

Relationship between internal structure and adsorption properties

The relationship between internal porous structure and adsorption properties was evaluated by measuring O-cellulose beads made from cellulose (SS), (SM), and (MS) beads as adsorbents for Cu ²⁺ /phthalate complexes in water.

Figure 13 (a) shows cellulose (SS), (SM), and (MS) 40 hours after inserting O-cellulose beads (4 mg) into a vial containing Cu ²⁺ /phthalate complex (1000 ppm, 4 mL). ) and (MM) show the q _t of O-cellulose beads made from beads. The measured q _ts are 61.2, 66.8, 69.9, and 83.0 mg g ^-1 for O-cellulose beads made from cellulose (SS), (SM), (MS), and (MM) beads, respectively.

O-cellulose beads made from cellulose (M-M) beads have the highest adsorption capacity because they have the highest porous structure, as discussed previously, while O-cellulose beads made from cellulose (S-S) beads have the opposite adsorption capacity. This is the lowest. O-cellulose beads made from cellulose (S-M) and (M-S) beads have adsorption capacity between them. Therefore, it can be confirmed that the internal structure of O-cellulose beads dominates the adsorption capacity.

Application from column to filler

O-cellulose beads were applied as a filler in the column as well as for application as a metal filter. O-cellulose beads of uniform size can be placed in the column (Figure 15).

Figure 13 (b) shows Cu ²⁺ /phthalate complex by passing the complex solution (4 mL) through a column (5.6 mm in diameter) filled with O-cellulose beads (70 mg) at a flow rate of 2.5 mL h ^-1 . Indicates a decrease in concentration of aqueous solution (initial concentration: 500 ppm). The Cu ²⁺ /phthalate complex aqueous solution was circulated for the circulation test using a syringe pump. The initial Cu ²⁺ /phthalate composite aqueous solution (500 ppm) concentration decreased to 324, 409, 442, and 470 ppm during the first, second, third, and fourth cycles. The reduction rates are 64.8%, 81.8%, 88.4%, and 94% for the first, second, third, and fourth cycles. The amount of O-cellulose beads contained in the column was only 0.07 g, and 94% of the metal ions were filtered out after the fourth cycle. The results indicate that O-cellulose beads can be successfully used as fillers in columns for metal adsorption.

The adsorption of different metal ions was studied using ICP. Pb ²⁺ , Cu ²⁺ , Zn ²⁺ , Ni ²⁺ , Cd ²⁺ , Fe ³⁺ , Ca ²⁺ , Cr ³⁺ and Mg ²⁺ aqueous solutions were prepared at the same concentration of 1000 ppm. Their concentration was measured for 24 hours after inserting O-cellulose beads (4 mg) into a vial containing metal ion solution (4 mL).

15 shows 125.0, respectively, of Pb ²⁺ , Cu ²⁺ , Zn ²⁺ , Ni ²⁺ , Cd ²⁺ , Fe ³⁺ , Ca ²⁺ , Cr ³⁺ and Mg ²⁺ ions according to an embodiment of the present invention. It shows adsorption capacity of 75.1, 62.5, 51.1, 34.5, 33.4, 11.1, and 0 mg g ^-1 values, which indicates that O-cellulose beads can remove hazardous metal ions. The order of adsorption amount is Pb ²⁺ > Cu ²⁺ > Zn ²⁺ > Ni ²⁺ > Cd ²⁺ > Fe ³⁺ > Ca ²⁺ > Cr ³⁺ = Mg ²⁺ (not adsorbed). Pb ²⁺ is adsorbed the most, and Mg ²⁺ is not adsorbed to O-cellulose beads.

Desorption and resorption of Cu ²⁺ /phthalate on O-cellulose beads were tested. O-cellulose beads (4 mg) in the vial were evaluated with Cu ²⁺ /phthalate aqueous solution. 1000 ppm Cu ²⁺ /phthalate aqueous solution was adsorbed on O-cellulose beads for 2 hours. The O-cellulose beads to which Cu ²⁺ /phthalate was adsorbed were treated with 2M HCl (8 mL) under stirring at 250 rpm for 30 minutes at 25°C to desorb Cu ²⁺ /phthalate from the O-cellulose beads.

The re-adsorption test was performed using HCl-treated O-cellulose beads after being thoroughly washed with water under the same conditions as the first adsorption. The adsorption amount of Cu ²⁺ /phthalate was measured again. The same adsorption and desorption tests were repeated for several cycles.

Figures 13c and 13d show the adsorption capacity and efficiency of O-cellulose as a function of cycle number during adsorption/desorption of Cu ²⁺ /phthalate, respectively. Efficiency is the relative amount of Cu ²⁺ /phthalate adsorption in the i ^th cycle compared to that in the (i-1) ^th cycle, defined by equation (11). The efficiency is constant at approximately ~88%, but the adsorption capacity continues to decrease as the number of cycles increases, indicating that the recovery rate of oxime groups is high enough for reuse. However, efficiency can be improved by optimizing desorption conditions.

[Equation 11]

The foregoing has described, rather broadly, the features and technical advantages of the present invention to enable a better understanding of the claims described below. Those skilled in the art to which the present invention pertains will understand that the present invention can be implemented in other specific forms without changing its technical idea or essential features. Therefore, the embodiments described above should be understood in all respects as illustrative and not restrictive. The scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modified forms derived from the claims and their equivalent concepts should be construed as being included in the scope of the present invention.

Claims (5)

A first step of forming cellulose/oxide solvent droplets in a molten state (M) or solid state (S) using a mixture containing cellulose and an oxide-based solvent;
A second step of coagulating the cellulose/oxide solvent droplets in the molten state (M) or solid state (S) to form cellulose beads in the molten state (M) or solid state (S) inside the droplets; and
The beads include a third step in which the cellulose is crosslinked to form porous cellulose beads functionalized with amidoxime groups,
In the second step, the shape of the bead is oval and the inside and outside of the bead are formed as any of (SS), (SM), and (MS), or the shape of the bead is spherical and the inside and outside of the bead are ( MM) A method for producing porous cellulose beads.
According to claim 1,
A method of producing porous cellulose beads, characterized in that the droplet is entirely homogeneous or forms a core/shell structure depending on the temperature in the process of solidifying the droplet.
According to claim 1,
A method for producing porous cellulose beads, wherein the oxide-based solvent includes N-methylmorpholine N-oxide (NMMO).
Porous cellulose beads produced by the method according to any one of claims 1 to 3,
The diameter ratio (D ₃ /D ₂ ) of the diameter _{when the bead is dried (D 2 ) and the diameter when it is re-swollen (D 3 )} is 1.8 to 4.0,
The shape of the bead is oval, and the inside and outside of the bead are formed as one of (SS), (SM), and (MS), or the shape of the bead is spherical, and the inside and outside of the bead are (MM). Porous cellulose beads.
According to claim 4,
The cellulose beads are characterized by adsorbing one or more metal ions selected from the group consisting of Pb ²⁺ , Cu ²⁺ , Zn ²⁺ , Ni ²⁺ , Cd ²⁺ , Fe ³⁺ , Ca ²⁺ , and Cr ³⁺ Porous cellulose beads.