KR20200039994A - Hybrid bead using persimmon leaf and chitosan for the treatment of aqueous solution contaminated with toxic heavy metal ions and method of the same - Google Patents

Abstract

The present invention relates to a method for preparing a hybrid bead for a heavy metal ion adsorbent using persimmon leaf and chitosan, and a hybrid bead prepared thereby. The method, as a method for preparing a hybrid bead for a heavy metal ion adsorbent to remove heavy metal ions contained in an aqueous solution, comprises: a pre-treatment step of preparing persimmon leaves in a powder form; a culture step of mixing the powder-form persimmon leaves in a chitosan solution and culturing the mixture in a bead form; a first washing step of washing the prepared beads using a first solvent; an aging step of preparing hybrid beads by adding a crosslinking agent to the beads and aging the same; a second washing step of primarily washing the hybrid beads with a second solvent different from the first solvent, and secondarily washing the same with the first solvent; and a drying step of drying the hybrid beads.

Description

Hybrid beads for heavy metal ion adsorbents using persimmon leaves and chitosan and their manufacturing method {Hybrid bead using persimmon leaf and chitosan for the treatment of aqueous solution contaminated with toxic heavy metal ions and method of the same}

The present invention relates to a hybrid bead for heavy metal ion adsorbent using persimmon leaf and chitosan and a method for manufacturing the same, and more specifically, it can effectively adsorb and remove harmful heavy metal ions contained in an aqueous solution phase, and separate post-treatment. The present invention relates to hybrid beads for heavy metal ion adsorbents using persimmon leaves and chitosan, which are not required, and a method for manufacturing the hybrid beads.

Harmful heavy metal contaminants cause physical or chemical changes in the aquatic environment that result in qualitative changes in the aquatic environment, and the use of contaminated water adversely affects the survival of life. In particular, Pb (II) and Cd (II) can cause fatal effects on living organisms inhabiting aquatic ecosystems in small amounts (He et al. 2014; Lee & Choi, 2018). In order to remove heavy metals, various treatment methods such as adsorption, tangle-aggregation, membrane filtration, membrane separation, electrochemical treatment, ion exchange, biosorption, etc. have been studied and have been applied directly to the field (Barsbay et al. 2018; Bacelo et al. 2016; Choi & Lee 2015; Ali et al. 2016). Some of these methods are expensive and inefficient in controlling the concentration of heavy metal ions contained in wastewater (Lee & Choi, 2018). In addition, there is a problem that other methods are not efficient or environmentally friendly, and other methods require separate post-treatment (Abdelfattah et al. 2016).

Recently, various studies have been conducted to remove or adsorb heavy metals that are inexpensive and have high efficiency when removed using agricultural by-products or biomaterials (Bacelo et al. 2016; Ali et al. 2016; Abdelfattah et al. 2016 ; Chen et al. 2010; Lee & Choi 2018; Garg et al. 2008). On the other hand, in the case of using agricultural by-products or biomaterials as adsorbents, it is necessary to separate them from wastewater due to a decrease in the removal rate of heavy metals due to a decrease in diffusion resistance and surface active sites, and there is a problem of generating additional contamination (Xu et al. 2017).

Accordingly, it is inexpensive and does not require a separate post-treatment, and various studies have been conducted to remove heavy metals from the aqueous solution with eco-friendliness and high efficiency.

The object of the present invention is a hybrid bead for heavy metal ion adsorbent using eco-friendly persimmon leaf and chitosan that does not require a separate post-treatment and does not require high cost and can effectively remove harmful heavy metal ions contained in an aqueous solution, and its preparation It is to provide a method.

In addition, another object of the present invention is to investigate the adsorption mechanism of heavy metal ions contained in an aqueous solution, and to provide a hybrid bead for heavy metal ion adsorbents using persimmon leaves and chitosan that can be effectively applied to a contaminated environment using the same, and to provide a method for manufacturing the hybrid beads It is to do.

In addition, another object of the present invention is a heavy metal ion adsorbent using persimmon leaf and chitosan that can efficiently remove lead and cadmium ions in aqueous solution using hybrid beads having a new structure using persimmon leaf and chitosan It is to provide a hybrid bead and its manufacturing method.

According to an aspect of the present invention, embodiments of the present invention are a method for preparing a hybrid bead for heavy metal ion adsorbent for removing heavy metal ions contained in an aqueous solution, a pre-treatment step of preparing persimmon leaves in powder form; A culture step of mixing persimmon leaves provided in a powder form in a chitosan solution and culturing in a bead form; A first washing step of washing the prepared beads using a first solvent; An aging step of preparing a hybrid bead by aging after adding a crosslinking agent to the bead; A second washing step in which the hybrid beads are first washed with a second solvent different from the first solvent, and then second washed with the first solvent; And a drying step of drying the hybrid beads; a method of manufacturing hybrid beads for heavy metal ion adsorbents using persimmon leaves and chitosan.

The pre-treatment step includes washing the persimmon leaf with deionized water to remove organic substances and contaminants; Cutting the washed persimmon leaf to a square size; Drying the cut persimmon leaf in an oven at a temperature of 75 ° C to 90 ° C for 70 to 74 hours; And crushing the dried persimmon leaf to prepare in powder form having a particle size of 50 mesh to 70 mesh.

The culturing step comprises preparing a chitosan solution having a pH of 6.2 to 6.5 by mixing chitosan and an acidic solution; Preparing the mixture by adding 1 g to 2 g of the persimmon leaf in 100 mL to 200 mL of the chitosan solution at a temperature of 20 ° C to 30 ° C, followed by stirring for 2 to 6 hours to homogenize; Preparing a coagulation solution by mixing 150 mL to 250 mL of distilled water, 250 mL to 350 mL of methanol and 50 g to 70 g of sodium hydroxide (NaOH); Preparing a bead form by dropping the mixture dropwise in the coagulation solution using a burette; And placing the coagulation solution in which the beads are dispersed in a culture medium and incubating at 60 ° C to 80 ° C for 20 to 30 hours to become a tan.

The chitosan, the acidic solution has a pH of 1 to 3, acetic acid, tartaric acid, salicylic acid, citric acid, hydroxyacetic acid, lingoic acid, propionic acid, lactic acid, glycerin, L-ascorbic acid, xenoic acid, sulfonic acid And it may be one or more selected from the group consisting of formic acid organic acid and hydrochloric acid, sulfuric acid and inorganic acid of phosphoric acid.

In the step of preparing the chitosan solution, further comprising adding a bacterial biomass having an average size of 7 μm to the chitosan solution, the bacterial biomass is Corynebacterium sp., Escherichia sp. .), Bacillus (Bacillus sp.) And Serratia (Serratia sp.).

The aging step includes the steps of preparing a crosslinking agent by mixing 50 mL to 150 mL of methanol and 0.5 mL to 15 mL of glutaraldehyde; Adding the prepared crosslinking agent to the beads; And aging the beads to which the crosslinking agent is added at 60 ° C. to 80 ° C. for 5 to 8 hours in an incubator.

In the second washing step, the first solvent may include distilled water, and the second solvent may include ethanol.

The drying step may be maintained at room temperature for 4 to 8 hours and then stored in a desiccator.

The heavy metal ions may be Pb (II) and Cd (II).

According to another aspect of the present invention, the present invention is manufactured by the above-described method for manufacturing a hybrid bead, includes a plurality of pores therein, and includes a hybrid bead for heavy metal ion adsorbents for removing heavy metal ions contained in an aqueous solution. .

The hybrid beads may have an average specific surface area of 16.65 m ² / g, and an average pore size of the adsorbent pore may be 4.65 nm.

The heavy metal ions are Pb (II) and Cd (II), and the hybrid beads can adsorb Pb (II) and Cd (II) in the aqueous solution according to Langmuir isothermal adsorption.

The heavy metal ions are Pb (II) and Cd (II), the pH of the aqueous solution containing the heavy metal ions is 5, and the removal efficiency by adsorption of the Pb (II) and Cd (II) is 98% and 90, respectively. %.

According to the present invention as described above, a hybrid for heavy metal ion adsorbent using eco-friendly persimmon leaf and chitosan that does not require separate post-treatment and does not require high cost and can effectively remove harmful heavy metal ions contained in the aqueous solution Beads and methods of making the same can be provided.

In addition, according to the present invention, it is possible to provide a hybrid bead for a heavy metal ion adsorbent using persimmon leaves and chitosan that can be effectively applied to a contaminated environment by identifying the adsorption mechanism of heavy metal ions contained in an aqueous solution and using the same, and a method for manufacturing the same. have.

In addition, according to the present invention, a hybrid bead having a new structure is manufactured using persimmon leaf and chitosan, and heavy metal ion adsorbent using persimmon leaf and chitosan which can efficiently remove lead and cadmium ions in an aqueous solution using the persimmon leaf and chitosan It is possible to provide a hybrid bead and a method for manufacturing the same.

1 is a flowchart illustrating a method of manufacturing a hybrid bead according to an embodiment of the present invention.
Figure 2 is a graph showing the FT-IR spectrum of chitosan, persimmon leaves and hybrid beads prepared according to this embodiment.
3A is a graph showing adsorption rates of Pb (II) and Cd (II) according to initial concentrations using hybrid beads prepared according to the present embodiment.
3B is a graph showing adsorption rates of Pb (II) and Cd (II) according to pH using hybrid beads prepared according to the present embodiment.
3C is a graph showing the adsorption rates of Pb (II) and Cd (II) according to the amount of the adsorbent, which is a hybrid bead prepared according to this embodiment.
3D is a graph showing the adsorption equilibrium of Pb (II) and Cd (II) according to the contact time of the hybrid beads prepared according to the present embodiment.
4A to 4C are graphs using the pseudo-first model and the pseudo-secondary model for the adsorption removal process of the hybrid beads and Pb (II) and Cd (II) prepared according to the present embodiment.

Specific details of other embodiments are included in the detailed description and drawings.

Advantages and features of the present invention, and methods for achieving them will be clarified with reference to embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms. In the following description, when a part is connected to another part, it is only directly connected. It also includes cases where other media are connected in the middle. In addition, in the drawings, parts not related to the present invention are omitted in order to clarify the description of the present invention, and like parts are given the same reference numerals throughout the specification.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

1 is a flowchart illustrating a method of manufacturing a hybrid bead according to an embodiment of the present invention.

One embodiment of the present invention is a method of manufacturing a hybrid bead for heavy metal ion adsorbents for removing heavy metal ions contained in an aqueous solution, a pre-treatment step of preparing persimmon leaves in powder form; A culture step of mixing persimmon leaves provided in a powder form in a chitosan solution and culturing in a bead form; A first washing step of washing the prepared beads using a first solvent; An aging step of preparing a hybrid bead by aging after adding a crosslinking agent to the bead; A second washing step in which the hybrid beads are first washed with a second solvent different from the first solvent, and then second washed with the first solvent; And a drying step of drying the hybrid beads; a method of manufacturing hybrid beads for heavy metal ion adsorbents using persimmon leaves and chitosan.

Persimmon trees are mainly produced in Asia, especially in China, Japan and Korea, accounting for more than 90% of global production (Lee & Choi, 2018). Persimmon in Korea is a kind of fruit mainly found in rural areas where environmental conditions suitable for various types of persimmon trees are formed due to climatic conditions.

In an embodiment of the present invention, the hybrid beads can be removed by adsorbing heavy metal ions in an aqueous solution. The hybrid beads may be made of persimmon leaves and chitosan, whereby it can act as an inexpensive heavy metal ion adsorbent that is environmentally friendly and capable of efficiently removing heavy metals in an aqueous solution with high efficiency without additional post-treatment.

The heavy metal ions may be Pb (II) and Cd (II). The Pb (II) and Cd (II) induce a fatal effect even in small amounts to living organisms inhabiting aquatic ecosystems. On the other hand, the techniques conventionally used to remove the Pb (II) and Cd (II) are expensive or low efficiency, and other methods require treatment of the adsorbent adsorbing the Pb (II) and Cd (II). There is a problem that requires an ancillary process. The hybrid beads according to the embodiment of the present invention can effectively remove the Pb (II) and Cd (II) at low cost by using persimmon leaves and chitosan. In addition, the hybrid beads according to this embodiment do not require eco-friendly and ancillary treatment, and the hybrid beads can adsorb and remove Pb (II) and Cd (II) optimally and efficiently in the environment of the actual ecosystem. Even when applied to a real environment, it can be used immediately without having to control separate conditions.

nez-Las Heras et al. 2016). 반면, 종래 기술에 의하면 예컨대, Pb(II) 및 Cd(II)와 같은 중금속 이온을 제거하는 경우 Pb(II) 및 Cd(II)에 대한 각각의 최대 흡착량은, 천연 타닌은 53.37 mg/g 및 51.85 mg/g이고 (Xu et al. 2017), 키토산은 80.23 내지 118.00 mg/g 및 60.85 mg/g이다 (Li et al. 2016).Persimmon leaf is a by-product of persimmon tree and can act as a kind of natural adsorbent easily obtained in Korean farms. The persimmon leaf contains a large amount of tannin and polyphenol compounds capable of binding to metal ions by a chelating reaction, whereby it can be removed by binding to toxic substances such as heavy metals and alkaloids (Shen et al. 2004) ; Mart

nez-Las Heras et al. 2016). On the other hand, according to the prior art, for example, when removing heavy metal ions such as Pb (II) and Cd (II), the maximum adsorption amount for each of Pb (II) and Cd (II) is 53.37 mg / g for natural tannin. And 51.85 mg / g (Xu et al. 2017), and chitosan 80.23 to 118.00 mg / g and 60.85 mg / g (Li et al. 2016).

Chitosan is a type of natural cationic polysaccharide obtained by N-deacetylation of chitin obtained by extraction from shells of shrimp, crab, and shellfish (Sargin et al. 2016). In such natural cationic polysaccharide natural polymers, the matrix structure is provided with a large amount of free amine groups (-NH ₂ ) and hydroxy groups, whereby chitosan can efficiently adsorb and remove heavy metal ions in wastewater (Liu et. al. 2014). The chitosan is an adsorbent with high efficiency against cationic contaminants, while chitosan is a cationic natural polymer. The adsorption amount of these cations has a lower adsorption amount than the anion (Zhao et al. 2013; Sargin & Arslan 2015). In addition, when heavy metals are adsorbed and removed using unmodified tannins, considerable time is required to reach adsorption equilibrium (Bacelo et al. 2016; Yurtsever & Sengil 2009). On the other hand, the phenolic group of tannin is ion-exchanged with a metal ion, and the ammonia group and hydroxy group of chitosan function as a chelating reaction site coordinated with the metal ion. In addition, when the pH value is increased, the efficiency of the ion exchange and coordination reaction is improved. The adsorption process of heavy metals in aqueous solution is greatly influenced by pH. That is, adsorption of Pb (II) in an aqueous solution can be promoted in a high pH region rather than a low pH.

For this reason, when tannin and chitosan contained in persimmon leaves are combined, it is possible to improve the adsorption efficiency of heavy metals. Therefore, in an embodiment of the present invention, it is an object of the present invention to improve the adsorption and removal efficiency of Pb (II) and Cd (II) in an aqueous solution using hybrid beads made of persimmon leaves containing cationic polymer tannin and chitosan. In the present embodiment, the experimental results for the adsorption removal efficiency were analyzed by applying to the isothermal adsorption formula of Langmuir, Freundlich and Dubinin-Radushkevich (DR). The kinetic analysis was confirmed by performing an adsorption experiment according to the temperature change. In addition, the present invention was analyzed by a number of experiments using tannin and chitosan, the quasi-first-order kinematic model, pseudo-secondary kinetics model, and intraparticle diffusion were confirmed by simple numerical values.

In the pre-treatment step, the persimmon leaf may be prepared in powder form. The pre-treatment step includes washing the persimmon leaf with deionized water to remove organic substances and contaminants; Cutting the washed persimmon leaf to a square size; Drying the cut persimmon leaf in an oven at a temperature of 75 ° C to 90 ° C for 70 to 74 hours; And crushing the dried persimmon leaf to prepare a powder having a particle size of 50 mesh to 70 mesh.

The persimmon leaf is prepared in powder form and mixed with the chitosan solution. At this time, the persimmon leaf can be dried in an oven at a temperature of 75 ° C to 90 ° C for 70 to 74 hours. When the temperature is lower than 75 ° C, moisture remains on the surface of the persimmon leaf, thereby deteriorating the binding force with heavy metal ions, and when the temperature is higher than 90 ° C, the performance of functional groups present in the persimmon leaf may be reduced. In addition, by drying for 70 to 74 hours, it can be prepared in an easy state to manufacture in powder form without deteriorating the performance of persimmon leaves. Preferably, the persimmon leaves can be cut into squares of 5 cm (width) x 5 cm (length) and then dried at 80 ° C. for 72 hours using a magnetic container.

The persimmon leaf is pulverized in a powder form of 50 mesh to 70 mesh, and if it is less than 50 mesh, the heavy metal ion adsorption capacity of the hybrid beads prepared by mixing with the chitosan solution is reduced, and if it is more than 70 mesh, the mixing with the chitosan is uneven. It becomes a problem. Persimmon leaf is prepared in the form of a hybrid bead by being provided in the above-described range to improve the adsorption efficiency of heavy metal ions and to be well mixed with chitosan. Preferably, the gamma leaf is provided with a size of 65 mesh.

The culturing step comprises preparing a chitosan solution having a pH of 6.2 to 6.5 by mixing chitosan and an acidic solution; Preparing the mixture by adding 1 g to 2 g of the persimmon leaf in 100 mL to 200 mL of the chitosan solution at a temperature of 20 ° C to 30 ° C, followed by stirring for 2 to 6 hours to homogenize; Preparing a coagulation solution by mixing 150 mL to 250 mL of distilled water, 250 mL to 350 mL of methanol and 50 g to 70 g of sodium hydroxide (NaOH); Preparing a bead form by dropping the mixture dropwise in the coagulation solution using a burette; And placing the coagulation solution in which the beads are dispersed in a culture medium and incubating at 60 ° C to 80 ° C for 20 to 30 hours to become a tan.

The chitosan may be prepared as a chitosan solution of pH 6.2 to pH 6.5 by mixing an acidic solution. The acidic solution has a pH of 1 to 3, and is an organic acid of acetic acid, tartaric acid, salicylic acid, citric acid, hydroxyacetic acid, lingoic acid, propionic acid, lactic acid, glycerin, L-ascorbic acid, xenoic acid, sulfanoic acid and formic acid. And hydrochloric acid, sulfuric acid, and phosphoric acid. Preferably, the acidic solution is hydroxyacetic acid having a pH of 2.8, and the chitosan solution may have a pH of 6.2. The chitosan solution is mixed with hydroxyacetic acid having a pH of 2.8 to produce a pH of 6.2, so that mixing with persimmon leaves in powder form is uniform, and the performance of functional groups present in chitosan and persimmon leaves is further improved to adsorb heavy metal ions. Improve it.

The chitosan solution may be mixed with persimmon leaves prepared in powder form, and stably manufactured in a bead form by mixing in the above-described range, and it is possible to improve heavy metal adsorption power by controlling the surface area and pore size of the prepared hybrid beads. . Preferably, after 1.5 g of the persimmon leaf is added in 150 mL of a chitosan acidic solution, the mixture can be stirred at 24 ° C. for 4 hours until the mixture is homogenized. Subsequently, the mixture of chitosan and persimmon leaves can be transferred to a burette and added dropwise to a coagulation solution, a mixture consisting of 200 mL of water, 300 mL of methanol and 60.0 g of NaOH.

The coagulation solution in which the beads are dispersed may be placed in a culture vessel and cultured at 60 ° C to 80 ° C for 20 to 30 hours to become a tan. When the temperature is less than 60 ° C, the size of the bead is not uniformly formed, which is a problem. If the temperature is higher than 80 ° C, the bead form is not maintained. In addition, if it is less than 20 hours, a problem such as the shape of the beads being deformed by a weak external force occurs. Preferably, the culture can be incubated for 24 hours in an incubator at a temperature of 72 ° C.

Alternatively, the step of preparing the chitosan solution may further include adding bacterial biomass having an average size of 7 μm to the chitosan solution. The bacterial biomass may be one or more selected from the group consisting of Corynebacterium sp., Escherichia sp., Bacillus sp. And Serratia sp. By adding the bacterial biomass in the chitosan solution, the bacterial biomass is inserted into the pores of the hybrid beads and the bacterial biomass is stably settled on the hybrid beads, thereby improving the adsorption capacity of heavy metal ions. Preferably, the bacterial biomass may be included in 5 parts by weight relative to the total 100 parts by weight of the mixture of the persimmon leaf powder and the chitosan solution by the surface area of the hybrid beads, functional groups of chitosan and persimmon leaves, and pore size.

Subsequently, the prepared beads may be washed a plurality of times using a first solvent, for example, distilled water, in the first washing step to remove residues. The distilled water is prepared 5 times compared to the volume of the beads, and the beads can be washed 5 to 10 times, preferably 9 times. After washing, the water is removed by filtration through filter paper.

In the aging step, a crosslinking agent may be added to the washed beads to combine the beads to produce hybrid beads. The aging step includes the steps of preparing a crosslinking agent by mixing 50 mL to 150 mL of methanol and 0.5 mL to 15 mL of glutaraldehyde; Adding the prepared crosslinking agent to the beads; And aging the beads to which the crosslinking agent is added at 60 ° C. to 80 ° C. for 5 hours to 8 hours in an incubator.

The crosslinking agent may be added to the beads to be more firmly fixed by crosslinking the beads consisting of the persimmon leaf and chitosan. The cross-linking agent may be prepared by mixing methanol and glutaraldehyde, preferably 90 mL methanol and 0.9 mL glutaraldehyde solution. The beads to which the crosslinking agent is added can be aged for 5 to 8 hours at 60 ° C to 80 ° C in an incubator. If the temperature is less than 60 ° C, the crosslinking reaction by the crosslinking agent is delayed, and if it is greater than 80 ° C, it is a problem by changing the functional groups of the hydride beads during the crosslinking process. Also, if it is less than 5 hours, some incomplete crosslinking reactions are present and 8 hours is sufficient, so if it exceeds this, production efficiency is reduced. Preferably it can be aged at 70 ° C. for 6 hours in an incubator.

The aging hybrid beads can be washed in the second washing step. In the second washing step, glutaraldehyde remaining unreacted may be removed by first washing with a second solvent, such as ethanol, and second washing with a first solvent, such as distilled water. The second solvent is added in a volume of 2 times the volume of the hybrid beads, and the hybrid beads are washed 5 times or more in total, and the first solvent, such as distilled water, is used in a volume of 2.5 times the volume of the hybrid beads. The hybrid beads can be washed twice.

In the second washing step, by washing in the order of the second solvent and the first solvent, unreacted reactants can be completely removed while preventing damage to structures such as the shape, functional group, and pore shape of the hybrid beads.

Subsequently, the hybrid beads may be removed from the first solvent using a filter, and maintained at room temperature for 4 to 8 hours, and then stored in a desiccator. If the time is less than 4 hours, it is difficult to completely remove the solvent remaining inside the hybrid pore, and since 8 hours is sufficient, the process efficiency is reduced when it exceeds.

According to another aspect of the present invention, the present invention is prepared by the hybrid bead manufacturing method and includes a plurality of pores therein, and includes a hybrid bead for a heavy metal ion adsorbent for removing heavy metal ions contained in an aqueous solution.

The average specific surface area of the hybrid beads may be 16.65 m ² / g, and the average size of the pores may be 4.65 nm.

In addition, the heavy metal ions are Pb (II) and Cd (II), and the hybrid beads can adsorb Pb (II) and Cd (II) in the aqueous solution according to Langmuir isothermal adsorption.

Alternatively, the heavy metal ions are Pb (II) and Cd (II), the pH of the aqueous solution containing the heavy metal ions is 5, and the removal efficiency by adsorption of the Pb (II) and Cd (II) is 98 respectively. % And 90%.

Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are only preferred embodiments of the present invention, and the scope of the present invention is not limited by the following embodiments.

Substance and manufacturing method

1. Adsorbent and adsorbent

Persimmon leaves collected from persimmon farms in Korea, Gangwon-do and Gangneung were prepared. After washing persimmon leaves with deionized water to remove organic substances and contaminants, the washed persimmon leaves are cut into squares of 0.5 cm (width) x 0.5 cm (length), and then have a larger width than the persimmon leaves. In a porcelain container, and dried in an oven at 80 ° C. for 72 hours (Lee & Choi, 2018). The dried persimmon leaves were pulverized into powder, and stored in a desiccator. The hybrid beads used in this experiment were prepared in the following manner.

After adding 1.5 g of persimmon leaf prepared in powder form in 150 mL of a chitosan acidic solution, the mixture was stirred at 24 ° C. for 4 hours until the mixture was homogenized. The mixture of chitosan and persimmon leaves was transferred to a burette and dropped dropwise into a coagulation solution (a mixture consisting of 200 mL of water, 300 mL of methanol and 60.0 g of NaOH). The hybrid beads formed in the form of beads in the coagulation solution were incubated for 24 hours in the incubator until the coagulation solution became a tan. After washing the hybrid beads multiple times with distilled water and removing the water by filtration, a crosslinking agent (90 mL methanol and 0.9 mL glutaraldehyde solution) was added to maintain the spherical shape of the hybrid beads. The mixture was aged in the incubator at 70 ° C. for 6 hours. Finally, crosslinked hybrid beads were again obtained, washed with ethanol, and then washed with water multiple times to remove unreacted glutaraldehyde molecules. The prepared hybrid beads were dried at room temperature for 5 hours, and then stored in a desiccator for use in experiments.

Stock solutions of 1000 mg / L of Pb (II) and Cd (II) are Pb (NO ₃ ) ₂ (Duksan Pure Chem., Co. Ltd. Korea, purity = 99%) and Cd (NO ₃ ) · H ₂ O (Sigma Aldrich, Japan, purity = 99%) was prepared by dissolving each in deionized water. The stock solution was diluted with distilled water and prepared and used as a solution using deionized water to meet the concentration required for the experiment.

2. Experiment and analysis

The experiment for removing heavy metal ions in an aqueous solution using hybrid beads was performed as a batch test that was added to 1 L of a solution containing each heavy metal ion. As for the initial concentration effect of Pb (II) and Cd (II), experiments were conducted by changing to 0.5 to 50 mg / L, contact time was changed to 0 to 120 min, pH was changed to 2 to 10, and adsorbent The dose of adsorbent was changed to 0.5 to 20 g / L, the particle size of persimmon leaf was 50-70 mesh, and the temperature was 25 to 45 ° C to adsorb heavy metal ions using hybrid beads. Was evaluated. The pH was adjusted from 2 to 10 using NaOH and HCl, and the temperature was controlled using a shaking incubator thermostat. The sample solution for each condition prepared by mixing the hybrid beads and the aqueous solution containing heavy metal ions was stirred at 120 rpm in a shaking incubator, and sampled at a predetermined time.

The collected sample was centrifuged at 3000 rpm for 20 minutes, filtered using a 0.45 μm Whatman filter, and then measured using an atomic absorption spectrometer (AAS, Perkin Elmer, AAS 3300). All experiments were repeated 5 times, and the average value of the experiment results was used. The specific surface area and pore volume of persimmon leaf, chitosan and hybrid beads were measured by Brynauer-Emmett-Teller (BET) and specific surface area analyzer (Model ASAP, 2020), and the molecular structure and composition of the surface functional groups were Fourier transform infrared spectrometry ( FT-IR; Jasco, FT-IR 4100) (Lee & Choi, 2018). The particle size and the amount of persimmon leaf, chitosan and hybrid beads were measured with a particle size analyzer (Laser Diffraction Master class 3 & 4, Malvern, England), respectively, and an electronic balance (XP26, Mettler Toledo, Swiss) was used. Other parameters were fixed in each experiment. Persimmon leaf content was measured by an electronic balance (XP26, Mettler Toledo, Swiss). The adsorption amount (q _t ) and removal efficiency (R,%) of the heavy metal adsorbed on the hybrid beads were calculated by the following equations (1) and (2) (Lee & Choi, 2018).

식 (1)

Equation (1)

식 (2)

Equation (2)

analysis

1. Characteristics of hybrid beads

Physical properties of persimmon leaf, chitosan and hybrid beads

Evaluation of the surface area, which is one of the methods for evaluating the adsorbent performance, was performed as an index of the space in the adsorption by calculating the total pore surface area per 1 g of the adsorbent (Choi & Lee 2015; Lee & Choi 2018). In general, as the surface area size increases, the adsorption amount also increases (Bacelo et al. 2016; Liu et al. 2014). The pore size affects the reduction rate of adsorption and contaminants. The larger the micropore size, the larger the specific surface area and the higher the adsorption amount (Pangeni et al. 2014; Wan & Hanafiah 2008). On the other hand, if the pore size is too small, the substance adsorbed on the pore is difficult to penetrate into the inside of the adsorbent through the pore, and as a result, the number of available pores is reduced (Choi 2014). Therefore, when a single substance is adsorbed and removed, it is preferable that the distribution of pores is provided so as not to concentrate (concentrate) on a specific pore, but various pore distributions are advantageous when removing various substances such as water treatment (Bacelo et. al. 2016; Wan & Hanafiah 2008). Table 1 below shows the physical properties of persimmon leaf, chitosan, and hybrid beads. The specific surface area and pore size of the hybrid beads are 16.65 m ² / g and 4.66 nm, respectively.

Parameters Surface Area (m ² / g) Pore volume (m ³ / g) Pore size (nm) Particle size (mm) Single point at p / po BET Langmuir t-Plot Miscropore Persimmon leaves 0.2010 0.8530 1.1395 1.1663 0.0543 1.4753 0.297-0.210 Chitosan 0.5162 2.0562 12.6852 1.8623 0.1624 2.6583 - Hybrid bead 4.2632 16.653 22.6324 23.5637 0.2986 4.6598 1 ± 0.12

According to the related literature, persimmon leaves contain a large amount of hydroxyl groups (-OH), tannins and catechins effective for removing heavy metals (Lee & Choi 2018; Martinez-Las Heras et al. 2014). Persimmon leaves contain 6.65% of tannins with higher content than Platanos (5.12%) and Ginkgo (2.02%) (Wi et al. 2012). The mechanism of adsorption and binding of tannins to heavy metal ions is that two H ⁺ are generated in the hydroxy group in the phenol group contained in the tannin compound, and combines with the divalent metal cation to form a ring, and the catemon ring of phenol monomer It is a chelation reaction with a metal ion within (Liu et al. 2014; Xu et al. 2016). Therefore, the adsorption process of tannins has a very high bond strength due to chemical ion exchange, not physical bonding.

FT-IR analysis

Figure 2 is a graph showing the FT-IR spectrum of chitosan, persimmon leaves and hybrid beads prepared according to this embodiment. 2 shows the FT-IR spectrum of chitosan, persimmon leaves, and hybrid beads. Persimmon leaves are basically 480 to 650 cm ^-1 N-containing bioligand, 950 to 1150 cm ^-1 PO ₄ ^3- (stretching), 1300 to 1450 cm ^-1 CO stretching, 1500 to 1600 cm ^-1 Carboxyl group and NH bending, 1640 to 1670 cm ^-1 carboxyl group, 1680 to 1740 cm ^-1 carboxyl group C = O, 2800 to 2900 cm ^-1 CH stretching and OH carboxylic acid, and 3000 to 3500 cm ^-1 -OH group. In addition, the tannin component of persimmon leaf contains a large amount of phenol hydroxy groups (hydroxy groups, -OH-) and has heavy metal adsorption power (Abdelfattah et al. 2016).

According to FT-IR analysis of chitosan, the peak of 3300 to 3500 cm ^-1 means the bond of the -OH group, the peak of 1640 to 1670 cm ^-1 is the carboxyl group, and the peak of 1500 to 1600 cm ^-1 is the bending carboxyl group And NH bending machine. In addition, the peaks of 1424 and 1380 cm ^-1 indicate CH bending of the alkyl group, and the peaks of 1310 and 1253 cm ^-1 indicate CN bending and NH group, respectively. 1148 and 1027 cm ^-1 indicate the asymmetry and CO vibration of the COC group, respectively, and the peak at 897 cm ^-1 is due to the β-1,4-glycosidic bond.

Hybrid bead (hybrid bead) contains a mixture of tannin and chitosan peaks, and contains many carboxyl and carbonyl groups for heavy metal adsorption. In general, the functional group with the best adsorption capacity for heavy metals is known as the carboxyl group. The carboxyl group dissociates into -COO- and H + in aqueous solution, and is mostly -COO-form above a certain pK value, so that cationic heavy metals are efficiently adsorbed ( Xu et al. 2016; Choi 2016). In addition, although there is no document in which the mechanism of adsorption of heavy metals by various biological materials has been clarified, the reason why adsorption occurs is that functional groups in the polymer material in the cell tissue are coordinated with heavy metals. Such functional groups include ^{_{-COOH, NH 2 -, -PO 4}} , -SO 4, C 6 H 5 -,> CO, (NH 2) a ₃ C-NH-, -OH. Therefore, it is thought that -OH, -CH ₂ OSO ₃ ^- and -COOH, -OH, etc., which are involved in coordination with heavy metals contained in the hybrid bead, and a large amount of carboxyl groups and carbonyl groups have a significant effect on the removal of heavy metals. .

2. Parameters (Parametric study)

Figure 3a is a graph showing the adsorption rates of Pb (II) and Cd (II) according to the initial concentration using the hybrid beads prepared according to this embodiment ((a) Effect of initial concentration), Figure 3b is the present embodiment It is a graph showing the adsorption rates of Pb (II) and Cd (II) according to pH using hybrid beads prepared according to an example ((b) Effect of various pH levels). 3c is a graph showing the adsorption rates of Pb (II) and Cd (II) according to the amount of the adsorbent, which is a hybrid bead prepared according to the present embodiment ((c) Effect of adsorbent dose), FIG. 3d is the present embodiment It is a graph showing the adsorption equilibrium of Pb (II) and Cd (II) according to the contact time of the hybrid beads prepared according to ((d) Effect of contact time on the hybrid beads for Pb (II) and Cd (II) removal ).

3A to 3D, in order to investigate the effect of various parameters on the adsorption efficiency of Pb (II) and Cd (II) using hybrid beads in aqueous solution, the initial concentration of various heavy metals, aqueous solutions of various pH, various Experiments were conducted for positive adsorbent and contact time.

Effect of initial heavy metal concentration

Regarding the effect of the concentration of the initial heavy metal related to the removal efficiency, it was carried out by varying the heavy metal concentration to 0.5 to 20 mg / L, and the results are shown in FIG. 3 (a). Since the amount of adsorbent and the time of adsorption depend on the initial concentration of the heavy metal, the effect of the concentration of the initial heavy metal on the removal efficiency is based on the basic formula derived from the optimum conditions of the adsorption process. As a result, Pb (II) and Cd (II) were determined to have a higher removal efficiency than the initial concentration of less than 2 mg / L of 98%. The adsorption efficiency decreases as the concentration of the initial heavy metal increases. The removal efficiency at the initial heavy metal concentration of 20 mg / L was 62.3% for Pb (II) and 40.7% for Cd (II). Additionally, removal efficiency at 10 mg / L of Pb (II) and 5 mg / L of Cd (II) was measured to 90%. The removal efficiency of Pb (II) using hybrid beads is higher than that of Cd (II). In addition, the removal efficiency of Cd (II) is higher than that of Pb (II) as the concentration of heavy metals increases. As a result, it was confirmed that the adsorption amount of Pb (II) and Cd (II) was affected by the concentration of the initial heavy metal. In addition, as the concentration of the initial heavy metal increased, the amount of adsorption adsorbed on the adsorbent increased, but the adsorption rate decreased.

pH effect

It was confirmed that the pH of the aqueous solution had a significant effect on heavy metal removal. The ionic form of the heavy metal in the aqueous solution differs depending on the pH. In order to investigate the effect of pH on the removal efficiency of Pb (II) and Cd (II), the pH was controlled by changing to 2-10. The removal efficiency of Pb (II) and Cd (II) was 98.2% and 90.3% at pH 5, respectively. On the other hand, it was confirmed that the removal efficiency of Pb (II) and Cd (II) was 43.4% to 64.2% at low pH (2.0 to 3.0). In FT-IR analysis, the carbonyl and carboxyl groups on the surface of the hybrid beads play an important role in heavy metal adsorption. According to previous studies, the adsorption mechanism on the heavy metal surface is generally influenced by the pH in the reaction medium, the surface properties of the adsorbent, and the intrinsic properties of the heavy metal (Bacelo et al. 2016; Lee & Choi 2018).

The adsorption of heavy metals by hybrid beads increases at pH 2 to 5, which is believed to be related to the ion exchange mechanism. At low pH values (pH 4.0 and below), high concentrations of H ⁺ ions compete for cation ion exchange with Pb (II) and Cd (II) at the adsorbent surface, resulting in Pb (II) at the surface of the hybrid beads. And Cd (II) adsorption is inhibited. On the other hand, when the pH value is increased, H ⁺ ions decrease on the surface of the adsorbent, and competition between the cations and H ⁺ ions capable of ion exchange on the surface of the adsorbent decreases. Accordingly, Pb (II) and Cd (II) exchanged with Pb (OH) ₂ and Cd (OH) ₂ or Pb (OH) ₃ and Cd (OH) ₃ rapidly adsorb hybrid beads as the pH value increases. Is adsorbed on. (Barsbay et al. 2018). In general, heavy metals in aqueous solutions are formed as hydroxides when the pH rises, and exist in the form of Cd (OH) ⁺ and Pb (OH) ⁺ (Yurtsever & Sengil 2009). In addition, it is precipitated in the form of Cd (OH) ₂ and Pb (OH) ₂ at neutral or alkaline pH (Choi et al. 2016; Lee & Choi 2018). Therefore, the increased pH affects the removal efficiency of Pb (II) and Cd (II). The adsorption of Pb (II) by hybrid beads has a higher value than that of Cd (II). Under conditions of pH 5 or higher, Pb (II) forms hydroxymetal (MeOH ⁺ ) stronger than Cd (II). These hydroxy compounds were strongly bound to functional groups on the surface of the hybrid beads. The preferred selectivity of heavy metals on adsorbents is related to various factors such as, for example, the hydrated ion radius and hydration energy of the heavy metal. Coordination bonds of Pb (II) and Cd (II) are known as 6 and 4, respectively (Choi et al. 2016; Li et al. 2016). According to the results, the movement of hydrated Cd (II) within the pores of the hybrid beads is similar to the stereo-chemically hindered effect (Choi et al. 2016). In addition, pore size distribution is an important factor in determining the fraction for the total volume of particles in accessing the size and shape of a given molecule. Pb (II), a class with minimal hydration energy (1481 kJ / mol), is compared to Cd (II) (1807 kJ / mol) (Choi et al. 2016), and hydrated compared to Cd (II) metal It can be seen that the Pb (II) ion is more easily introduced into the passage of the hybrid bis. Therefore, the selectivity of Pb (II) is higher than that of Cd (II). As a result of the above-described experiment, it was confirmed that both of Pb (II) and Cd (II) showed high removal efficiency at pH 6 or higher. Considering that the pH at the time of microbial treatment is approximately 6 to 8, when the heavy metal is adsorbed and removed from the aqueous solution using a hybrid bead as an adsorbent, the hybrid bead can be applied directly without adjustment to a separate pH. This reduces the use of chemicals, does not require post-treatment according to the use of chemicals, is a very useful resource reproduction, and environmentally friendly.

Effect of adsorbent input

The amount of adsorbent input is a very important treatment parameter in terms of economy and environment. Regardless of the efficiency of the adsorbent, industrial use is hesitant if the economic aspect is poor. In other words, a large amount of heavy metal can be adsorbed in a small amount, and if the adsorbent is environmentally friendly, such an adsorbent can be applied immediately. The effect of the adsorbent amount according to the removal efficiency of Pb (II) and Cd (II) was fixed at pH 6 and the initial concentration of 5 ppm, and then the experiment was conducted while increasing the input amount of the adsorbent. In the measured experimental results, the removal efficiency of Pb (II) and Cd (II) increases as the input amount of the adsorbent increases (Fig. 3 (c)). This is because the surface area related to heavy metal adsorption increases as the input amount of the adsorbent increases, and thus the probability of adsorption of the adsorbent to the unit ion increases. The removal efficiency of Pb (II) and Cd (II) adsorbed into the interior of the hybrid beads was confirmed to be 95% and 92%, respectively, at 3 g / L of adsorbent.

3. Effect of contact time and adsorption speed

The conditions under which adsorption equilibrium can be reached in a short time are basic conditions of the adsorbent. Therefore, it is necessary to optimize the adsorption efficiency of heavy metals to adsorbents depending on the contact time. More than 90% of Pb (II) and Cd (II) adsorbed to the hybrid beads within 30 minutes of contact time, and the adsorption equilibrium reached 60 minutes of contact time (Figure 3 (d)). Tannin is an easy-to-use material, it is inexpensive and can be easily extracted from plants, and is an excellent candidate as a biomaterial adsorbent because it can be easily converted into an insoluble (tannin gel or tannin foam) or a fixed matrix. However, the adsorption rate of the unmodified natural tannin adsorbent is very low and the time to reach the adsorption equilibrium is very long (Bacelo et al. 2016; Xu et al. 2017). Luzardo et al. According to (2017), the result of adsorption removal of Pb (II) using mimosa tannin reported that adsorption equilibrium was reached after 24 h. To solve this problem, Xu et al. According to (2017), the adsorption equilibrium of Cr (III), Cu (II), and Pb (II) was reached after 4h contact time when tannin modified with tannin gel was used. Additionally, Sargin & Arslan (2015) prepared a microcapsule consisting of chitosan / sporopollenin, and confirmed that it reached the adsorption equilibrium for heavy metal removal after 6h. According to various studies, heavy metal adsorption by modified tannins may reduce adsorption equilibrium time compared to unmodified tannins, but it is reported that it still takes a long time to reach adsorption equilibrium compared to activated carbon (Bacelo et al. 2016; Xu et al. 2017; Yurtsever & Sengil 2009; Zhan & Zhao 2003; Sengil & Ozacar 2008). Hybrid beads according to an embodiment of the present invention reached adsorption equilibrium within 1 h. Therefore, the hybrid bead according to the present embodiment has an advantage of removing heavy metals present in the aqueous solution very quickly and efficiently within a shorter contact time than the prior art.

4A to 4C are graphs using the pseudo-first model and the pseudo-secondary model for the adsorption and removal process of hybrid beads and Pb (II) and Cd (II) prepared according to the present embodiment (Plot of the (a) Pseudo-first-order and (b) Pseudo-second-order kinetic model and (c) intra-particle diffusion plot of the for Pb (II) and Cd (II) removal on hybrid beads).

에 의하여 물리적인 흡착을 쉽게 확인할 수 있다 (Ali et al. 2016; Lee & Choi 2018). 다른 한편으로는, 화학적인 흡착은 속도제한단계이기 때문에 유사 2차 모델 (

에 의하여 화학흡착을 보다 쉽게 확인할 수 있다. 입자 내부 확산 모델은 입자 내에서의 확산을 위하여 속도제한단계로 사용된다 (Xu et al. 2017; Sengil & Ozacar 2009). 결정계수에 따르면, 하이브리드 비드를 이용한 Pb(II) 및 Cd(II)의 흡착 제거 과정은 유사 1차 모델보다는 유사 2차 모델이 보다 적절함을 확인할 수 있었다(도 4a 및 도 4b 참조). 하이브리드 비드를 이용한 입자 내부 확산 사이의 상관관계는 Pb(II)는 0.9779이고 Cd(II)는 0.9632임을 확인할 수 있었으며, 이는 유사 1차 모델 및 유사 2차 모델에 의한 값보다는 작다 (도 4c 참조). 즉, 이와 같은 결과는 입자 내에서의 확산은 흡착 과정에서 속도제한단계가 아님을 나타낸다. 전술한 실험 결과에 따르면, 하이브리드 비드를 이용한 Pb(II) 및 Cd(II)의 제거는 중금속의 흡착속도제한에 사용되는 물리흡착보다는 화학흡착이 보다 적절하게 사용됨을 확인할 수 있었다. Pb(II) 및 Cd(II) 양측 모두 접촉시간 및 ln (q_e-q₀)에 크게 관련되어 있다. 이는 중금속과 흡착제 사이의 친화력이 매우 높다는 것과, 본 반응에서 흡착 과정이 매우 빠르게 수행됨을 나타내었다. 또한, Pb(II)는 Cd(II)에 비하여 더 높은 상관계수를 나타내어 흡착 평형에 더 빠르게 도달하였고, 더 높은 흡착량을 갖음을 확인할 수 있었다. 좋은 흡착제의 가장 기본적인 조건은 짧은 접촉 시간 내에 많은 양의 오염물질을 흡착하고, 과 시간 (over time) 동안에도 탈착됨이 없이 강하게 흡착할 수 있어야 한다. 본 실시예에 따른 감나무잎 및 키토산을 이용한 하이브리드 비드는 짧은 접촉 시간 내에 다량을 흡착할 수 있는 친환경적인 흡착제임을 확인할 수 있었다.4A-4C, the adsorption rate can be used to describe the adsorption rate, adsorption mechanism and adsorption rate limit. Similar first-order models (

The physical adsorption can be easily confirmed by (Ali et al. 2016; Lee & Choi 2018). On the other hand, since chemical adsorption is a rate-limiting step, the pseudo-secondary model (

By this, chemical adsorption can be more easily confirmed. The intra-particle diffusion model is used as a rate limiting step for diffusion in particles (Xu et al. 2017; Sengil & Ozacar 2009). According to the coefficient of determination, the adsorption and removal process of Pb (II) and Cd (II) using hybrid beads was confirmed to be more appropriate than the quasi-first model (see FIGS. 4A and 4B). The correlation between intraparticle diffusion using hybrid beads was confirmed to be 0.9779 for Pb (II) and 0.9632 for Cd (II), which is smaller than the values obtained by the pseudo-first model and pseudo-secondary model (see FIG. 4C). . That is, these results indicate that diffusion in particles is not a rate limiting step in the adsorption process. According to the above-described experimental results, it was confirmed that the chemical adsorption is more appropriately used for the removal of Pb (II) and Cd (II) using hybrid beads than the physical adsorption used to limit the adsorption rate of heavy metals. Both Pb (II) and Cd (II) are highly related to the contact time and ln (q _e -q ₀ ). This indicates that the affinity between the heavy metal and the adsorbent is very high, and the adsorption process is performed very quickly in this reaction. In addition, Pb (II) showed a higher correlation coefficient than Cd (II), so it was confirmed that the adsorption equilibrium was reached faster and had a higher adsorption amount. The most basic condition of a good adsorbent should be able to adsorb a large amount of contaminants within a short contact time and be able to adsorb strongly without desorption even during over time. It was confirmed that the hybrid beads using persimmon leaf and chitosan according to this embodiment are eco-friendly adsorbents capable of adsorbing large amounts within a short contact time.

In general, the performance of adsorbents can be evaluated by adsorption isotherms based on adsorption equilibrium. The adsorption isotherm is expressed as the relationship between the equilibrium concentration of the adsorbent at a constant temperature and the adsorption equilibrium amount per gram of adsorbent (Zhao et al. 2013). Various models such as Langmuir, Freundlich and Dubinin-Radushkevich (D-R) have been developed and developed to demonstrate the adsorption mechanism. Currently, these models are used to demonstrate the adsorption performance and adsorption mechanism of adsorbents or adsorbents. In the Langmuir adsorption isotherm, the binding force of adsorption is applied in a monolayer, and adsorption does not occur in other individual layers (Ali et al. 2016; Lee & Choi 2018). Thus, Langmuir adsorption is called monolayer adsorption. In Freundrich's isothermal adsorption, the heat of adsorption decreases exponentially according to the surface temperature applied by Langmuir adsorption isothermal (Choi et al. 2016; Chen et al. 2010). D-R adsorption isotherm is most widely used to understand adsorption mechanisms or to determine adsorption energy (Chen et al. 2010). In this example, the adsorption isotherm model analysis performed quantitative evaluation of absorption / sorption of metal ions related to isotherm.

According to the Langmuir isothermal adsorption, the adsorption amounts of Pb (II) and Cd (II) were 1.345 and 0.782 (mmol / g), respectively (see Table 2). It was confirmed that the difference in the adsorption amount in the hybrid beads was due to the difference in the affinity between the adsorbent and the adsorbent and the molecular size of the heavy metal ion related to the electronegative properties of the heavy metal ion. In addition, adsorption of heavy metal ions by bioabsorbable materials may be effective depending on the selectivity of heavy metal ions to functional groups of bioabsorbable materials (Choi 2014). The results of this study confirmed that the hybrid beads according to the examples of the present invention have more affinity for adsorption of Pb (II) and Cd (II).

The application of Freundrich's isothermal adsorption is appropriate when the adsorbed surface energy is irregularly dispersed, such as activated carbon. In the Freundrich model, the K _F value is the action of adsorption capacity, and 1 / n indicates the action of adsorption strength between particles and contaminants. For 1 / n, it was confirmed from the experimental results that Pb (II) was 0.475 and Cd (II) was 0.711. The adsorption constant of Pb (II) K _F is 14.316, and the adsorption constant of Cd (II) K _F is 12.137, which confirms that Pb (II) has a larger adsorption constant than Cd (II). In general, as the adsorption constant K _F value increases, the adsorption power of the adsorbent also increases (Ali et al. 2016). In addition, the results of adsorption of Pb (II) and Cd (II) using hybrid beads were confirmed through the experiments in which the Langmuir model was more suitable than the Freundrich model (see Table 2). Since the DR adsorption isotherm can be determined from adsorption energy, it is most widely used to understand adsorption mechanisms or to determine adsorption energy (Ali et al. 2016). Dubinin-Ladushkechwich (DR) adsorption isothermal model indicates that the adsorption process is either physical adsorption or ion exchange (He et al. 2014; Xu et al. 2017). The adsorption energies of Pb (II) and Cd (II) in hybrid beads were 11.215 and 8.432 kJ / mol, respectively, indicating that Pb (II) and Cd (II) in hybrid beads are close to selective chemical adsorption. It was confirmed that it appeared. Table 2 below shows parameters of Langmuir, Freundrich and DR adsorption isotherm for Pb (II) and Cd (II) using hybrid beads.

Models Parameters Pb (II) Cd (II)

Langmuir isotherm

q _m (mmol / g) 1.345 0.782 K _L (L / mmol) 1345.15 87.93 R ² 0.982 0.978 Freundlich isotherm

K _F (mmol / g) 14.316 12.137 n 2.102 1.404 R ² 0.842 0.826 Dubinin-Radushkevich isotherm

q _m (mmol / g) 1.928 1.901 k (mol ² / kJ ² ) 0.004 0.012 E (kJ / mol) 11.215 8.432 R ² 0.967 0.942

Table 3 shows the results of adsorbing heavy metals using persimmon leaves or chitosan. Ozmen et al. (2009) confirmed that the maximum adsorption amount of Pb (II) was 9.947 mg / g when using glass beads with glutaraldehyde. It was confirmed that the adsorption amount of the modified persimmon leaf and chitosan was higher than that of the unmodified persimmon leaf and chitosan. The removal of Pb (II) and Cd (II) using hybrid beads was confirmed to be higher than the adsorption amount of the modified persimmon leaf and the equilibrium adsorption amount by the modified chitosan. Hybrid beads made of persimmon leaf and chitosan according to this embodiment are not expensive, have high removal efficiency for heavy metals, and are environmentally friendly. In addition, hybrid beads are very economical when used as a heavy metal adsorbent in that no post-treatment is required. Table 3 below shows the results of comparing the maximum adsorption amount of heavy metals using biomaterial adsorbents.

Adsorbent Heavy metal q _m (mg / g) Reference Cinnamomum camphora Pb (II) 75.82 Chen et al . 2010 Glass bead Pb (II) 9.95 Ozmen et al. 2009 Dried persimmon leaf Pb (II)
Cd (II) 22.59
18.26 Lee & Choi 2018 Persimmon waste gel Cu (II) 7.18 Bacelo et al . 2016 Persimmon tannin gel Cd (II) 5.27 Bacelo et al . 2016 Modified quebracho tannin Pb (II) 86.207 Yurtsever & Sengil 2009 Mimosa tannin gel Cu (II) 43.71 Sengil & Ozacar 2008 Ca (II) imprinted chitosan microspheres Pb (II)
Cd (II) 47.10
49.90 Sankaramarkrishnan & Sanghi 2006 Xanthated chitosan Pb (II)
Cd (II) 283.00
420.00 He et al . 2014 Thiosemicarbazide modified chitosan Pb (II) Cd (II) 325.20
257.20 Li et al . 2016 EGTA-modified Chitosan Pb (II)
Cd (II) 103.60
83.18 Zhao et al . 2013 Hybrid bead Pb (II)
Cd (II) 278.68
87.91 This study

4. Thermodynamic interpretation

The adsorption process is affected by temperature because it appears as a thermodynamic equilibrium between the heavy metals adsorbed on the surface of the hybrid beads for heavy metals in aqueous solution. The effect of adsorption temperature of Pb (II) and Cd (II) on hybrid beads was investigated by controlling the temperature to 25-45 ° C. The experimental results were analyzed using the Gibbs free energy (ΔG ^o ) deviation.

The energy change of ΔG ^o measures the usefulness of a chemical reaction and determines the direction of the spontaneous change process in the chemical reaction. On the other hand, it is not related to the direction of change (Choi and Lee 2015; Ali et al. 2016). That is, the condition of ΔG ^o is useful when a chemical reaction system is changed from a single equilibrium state with a negative value to a new equilibrium state, giving confidence that the change occurs spontaneously (Heidari et al. 2013; Lee & Choi 2018). When the temperature increased in the experimental results for ΔG ^o , Pb (II) decreased from -7.86 to -8.17, and Cd (II) decreased from -2.86 to -2.94 (see Table 4). Therefore, it was confirmed that the adsorption process of Pb (II) and Cd (II) using hybrid beads is a spontaneous reaction in nature. In addition, the respective enthalpy values for Pb (II) and Cd (II) were (ΔH ^o ) -3.64 and -1.79. These results indicate that the heavy metal adsorption reaction using hybrid beads is an exothermic process. On the other hand, each entropy (ΔS ^o ) for Pb (II) and Cd (II) shows a positive value of 14.23 and 3.71, which means that the hybrid beads have effective affinity when used as an adsorbent. Table 4 shows the thermodynamic parameters for adsorption of Pb (II) and Cd (II) as hybrid beads.

Parameters Temperature Pb (II) Cd (II)

ΔG ^o (kJ / mol)
△ G ° = △ H ° -T △ S ° = -RT ln

298 K -7.86 -2.86 308 K -8.01 -2.90 318 K -8.17 -2.94 ΔH ^o (kJ / mol) -3.64 -1.76 ΔS ^o (J / molK) 14.23 3.71

Table 5 below shows the definitions of the characters used in this example.

Nomenclature C _o Initial concentration of heavy metal ions (mg / L) C _e Equilibrium concentration of heavy metal ions (mg / L) C _t Concentration of heavy metal ion at time t (mg / L) E Sorption energy (kJ / mol) ΔG ^o Gibbs free energy (kJ / mol) ΔH ^o Enthalpy (kJ / mol) k _One Adsorption rate constants of the pseudo-first-order model (1 / min) k ₂ Adsorption rate constants of the pseudo-second-order model (mg / g / min) k _L Langmuir constant (L / mg) k _F Freundlich constants referring to the adsorption capacity (mg / g) m Quantity of adsorbent (g) n Freundlich isotherm constants, intensity of sorption (mg / g) / (mg / L) ^{1 / n} q _e Amount adsorbed per unit weight of adsorbent at equilibrium (mg / g) q _t Quantity of heavy metal ions adsorbed at time t (mg / g) q _m Langmuir monolayer maximum adsorption capacity (mg / g) R Removal efficiency (%) R Ideal gas constant, 8.314 (J / mol / K) R ² Correlation coefficient ΔS ^o Entropy (J / molK) t Time (min) T Absolute temperature (K) V Volume of solution (L) β Activity coefficient related to the mean sorption energy ε Polanyi potential

Evaluation results

As described above, the adsorption rate of Pb (II) and Cd (II) heavy metals contained in the aqueous solution was confirmed by using the hybrid beads according to this embodiment in a batch experiment. The FT-IR analysis confirmed that the hybrid beads according to the present embodiment had a structure of having a carboxyl group, a carbonyl group, CH stretching vibration, OH carboxylic acid, and a combined -OH group, and were easily adsorbed to heavy metals. As a result of the experiment, it was confirmed that the Pb (II) and Cd (II) adsorption rates of the hybrid beads were 90% or more with a contact time of 30 minutes. In the Pb (II) and Cd (II) adsorption process using hybrid beads according to the present embodiment, it was confirmed that a pseudo-second-order model is more appropriately applied, which is the pseudo secondary This is because the kinetic model corresponds more closely than the pseudo-first-order kinetic model. In addition, the adsorption of Pb (II) and Cd (II) by the hybrid beads is more appropriately applied by the Langmuir isothermal adsorption, and it is confirmed that the ion exchange reaction occurs in the heterogeneous adsorption surface layer. Could. The maximum adsorption using the Langmuir model was 278.68 mg / g for Pb (II) and 87.91 mg / g for Cd (II). 1 / n of Pb (II) and Cd (II) were 0.475 and 0.711, respectively. It was confirmed that the adsorption strength of Pb (II) and Cd (II) using the hybrid beads according to this embodiment was excellent as shown in the L-type isothermal adsorption properties. In the thermodynamic experiments, ΔG ^o and ΔH ^o represent values of (negative), and ΔS ^o represents values of (positive). The adsorption removal process of Pb (II) and Cd (II) using the hybrid beads according to this example was confirmed to be a spontaneous exothermic reaction, and the affinity of the adsorbed material was excellent. The hybrid beads according to the present embodiment are manufactured by mixing chitosan and persimmon leaves, do not consume high cost, have high removal efficiency for heavy metals, are environmentally friendly, and can be applied to various fields. In addition, adsorption of heavy metals using these is very economical since no post-treatment is required.

Those of ordinary skill in the art to which the present invention pertains will appreciate that the present invention may be implemented in other specific forms without changing its technical spirit or essential features. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. The scope of the present invention is indicated by the scope of the claims, which will be described later, rather than the detailed description, and all the changed or modified forms derived from the meaning and scope of the claims and their equivalent concepts are included in the scope of the present invention. Should be interpreted.

Claims (13)

A method for producing a hybrid bead for heavy metal ion adsorbents for removing heavy metal ions contained in an aqueous solution,
A pre-treatment step of preparing persimmon leaves in powder form;
A culture step of mixing persimmon leaves provided in a powder form in a chitosan solution and culturing in a bead form;
A first washing step of washing the prepared beads using a first solvent;
An aging step of preparing a hybrid bead by aging after adding a crosslinking agent to the bead;
A second washing step in which the hybrid beads are first washed with a second solvent different from the first solvent, and then second washed with the first solvent; And
Drying step of drying the hybrid beads; Method of manufacturing hybrid beads for heavy metal ion adsorbent using persimmon leaves and chitosan consisting of. According to claim 1,
The pre-treatment step,
Washing the persimmon leaf with deionized water to remove organic substances and contaminants;
Cutting the washed persimmon leaf to a square size;
Drying the cut persimmon leaf in an oven at a temperature of 75 ° C to 90 ° C for 70 to 74 hours; And
Method of manufacturing a hybrid bead for a heavy metal ion adsorbent comprising; crushing the dried persimmon leaf to prepare a powder having a particle size of 50mesh to 70mesh. According to claim 1,
The culture step,
Preparing a chitosan solution having a pH of 6.2 to 6.5 by mixing chitosan and an acidic solution;
Preparing the mixture by adding 1 g to 2 g of the persimmon leaf in 100 mL to 200 mL of the chitosan solution at a temperature of 20 ° C to 30 ° C, followed by stirring for 2 to 6 hours to homogenize;
Preparing a coagulation solution by mixing 150 mL to 250 mL of distilled water, 250 mL to 350 mL of methanol and 50 g to 70 g of sodium hydroxide (NaOH);
Preparing a bead form by dropping the mixture dropwise in the coagulation solution using a burette; And
A method of manufacturing a hybrid bead for a heavy metal ion adsorbent, comprising: placing the bead-dispersed coagulation solution in a incubator and incubating it at 60 ° C to 80 ° C for 20 to 30 hours to become a tan. According to claim 3,
In the chitosan solution,
The acidic solution has a pH of 1 to 3, organic acid of acetic acid, tartaric acid, salicylic acid, citric acid, hydroxyacetic acid, lingoic acid, propionic acid, lactic acid, glycerin, L-ascorbic acid, xenoic acid, sulfanoic acid and formic acid Method for producing hybrid beads for heavy metal ion adsorbents selected from the group consisting of inorganic acids of perchloric acid, sulfuric acid and phosphoric acid. According to claim 4,
In the step of preparing the chitosan solution further comprises adding a bacterial biomass having an average size of 7㎛ in the chitosan solution,
The bacterial biomass is at least one heavy metal ion adsorbent selected from the group consisting of Corynebacterium sp., Escherichia sp., Bacillus sp. And Serratia sp. Preparation method for hybrid beads. According to claim 1,
The aging step,
Preparing a crosslinking agent by mixing 50 mL to 150 mL of methanol and 0.5 mL to 15 mL of glutaraldehyde;
Adding the prepared crosslinking agent to the beads; And
Aging method for a heavy metal ion adsorbent comprising; aging the beads to which the crosslinking agent is added at 60 ° C. to 80 ° C. for 5 to 8 hours in an incubator. According to claim 1,
In the second washing step, the first solvent comprises distilled water, and the second solvent is a method for preparing a hybrid bead for a heavy metal ion adsorbent comprising ethanol. According to claim 1,
The drying step is a method of manufacturing a hybrid bead for a heavy metal ion adsorbent that is kept at room temperature for 4 to 8 hours and then stored in a desiccator. According to claim 1,
The heavy metal ions are Pb (II) and Cd (II). A hybrid bead for heavy metal ion adsorbents prepared by any one of claims 1 to 9 and including a plurality of pores therein to remove heavy metal ions contained in an aqueous solution. The method of claim 10,
The hybrid beads have an average specific surface area of 16.65 m ² / g and an average size of pores of 4.65 nm. The method of claim 10,
The heavy metal ions are Pb (II) and Cd (II), and the hybrid beads are hybrids for heavy metal ion adsorbents that adsorb Pb (II) and Cd (II) in the aqueous solution according to Langmuir isothermal adsorption. Bead. The method of claim 10,
The heavy metal ions are Pb (II) and Cd (II), the pH of the aqueous solution containing the heavy metal ions is 5, and the removal efficiency by adsorption of the Pb (II) and Cd (II) is 98% and 90, respectively. % Hybrid beads for heavy metal ion adsorbents.

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