KR20240062557A - Coffee waste derived caffeine adsorbent and manufacturing method of the same - Google Patents

Abstract

The present invention relates to a caffeine adsorbent containing a nitrogen-doped carbon material and a method for manufacturing the same. The carbon material is graphitized carbon and can be manufactured using coffee waste, and the prepared adsorbent can be used in target solutions such as beverages. The caffeine it contains can be removed, and it can be reused after a simple regeneration process.

Description

Coffee waste derived caffeine adsorbent and manufacturing method of the same}

The present invention relates to a caffeine adsorbent capable of adsorbing and removing caffeine contained in a solution and a method for producing the same.

Pharmaceutical and personal care products (PPCP) are classified as a type of emerging contaminants (EC) that cause water pollution even at low concentrations (ng/L and ㎍/L). Recently, caffeine has emerged as the most common personal drug found in rivers and wastewater, with ~0.034 ppb of caffeine detected in the Mississippi River in the United States and ~0.268 ppb in the Han River in Korea. Caffeine has the potential to cause soil or water pollution and disrupt the physiological activities of not only microscopic organisms but also macroscopic organisms, including humans. In addition, caffeine is included in beverages such as coffee and is used in human daily life to cause an awakening effect, but if contained in excessive amounts, it can cause side effects such as headache, tachycardia, and muscle tremors. Accordingly, there is a need to develop a means to prevent caffeine from entering and contaminating the aquatic environment or to remove caffeine contained in the solution in response to the increasing demand for decaffeinated beverages.

Adsorption has been mainly used to remove caffeine contained in water. Adsorption has been widely used because the caffeine removal process is simple and low cost. Conventionally, porous materials with a high active surface area and pore structure, such as carbon materials such as activated carbon, clay minerals, zeolite, and MOF, have been used to adsorb and remove caffeine. Various attempts have been made to improve the adsorption performance of adsorbents containing carbon materials by increasing the surface area or modifying the surface.

Meanwhile, in response to the increasing need to remove contaminants such as caffeine contained in water, there is a demand for the development of adsorbents manufactured from eco-friendly materials that can be reused through simple reprocessing for industrial and economic applications.

The purpose of the present invention is to provide a caffeine adsorbent made from coffee waste (CW; Coffee Waste) remaining after making coffee, a method for producing the same, and a method for removing caffeine contained in a solution using the same.

The caffeine adsorbent according to one aspect of the present invention is a caffeine adsorbent containing a nitrogen-doped carbon material, wherein the carbon material includes graphitized carbon, and the adsorbent contains pyridinic nitrogen (pyridinic-N) and pyridonic It contains nitrogen (pyridonic-N).

The carbon material may be a product of calcining coffee waste under nitrogen gas.

The adsorbent may contain the pyridonic nitrogen in a larger amount than the pyridinic nitrogen.

Another aspect of the present invention relates to a method for producing a caffeine adsorbent comprising calcining a mixture of coffee waste and potassium hydroxide under nitrogen gas.

The mixture may be a ground mixture of dried coffee waste and potassium hydroxide.

The weight ratio of the potassium hydroxide and the coffee waste may be 1:0.5 to 1:2.

The calcining step may include carbonizing at 600 to 800° C. under nitrogen gas to form carbide, and leaching the carbide into inorganic acid to produce a caffeine adsorbent.

Another aspect of the present invention relates to a method for adsorbing and removing caffeine including the step of contacting a solution with the caffeine adsorbent according to the above aspect.

The caffeine adsorbent may be added in an amount of 0.1 to 0.2 g per 1 L of the solution.

The solution is one or more beverages selected from the group consisting of coffee, black tea, green tea, oolong tea, white tea, pu-hong tea, black tea, herbal tea, flower tea, mate tea, chai, maca, energy drinks, alcoholic drinks, soda, and cocoa. It can be.

The caffeine adsorbent according to the present invention is environmentally friendly by reusing coffee waste that would be discarded after being used to produce coffee, and can be repeatedly used to adsorb caffeine by adsorbing and removing the caffeine contained in the target solution and then regenerating it in a simple method.

Figure 1 is a conceptual diagram showing the process of manufacturing a caffeine adsorbent using coffee waste according to an embodiment of the present invention.
Figure 2 shows Comparative Example 3 (CW-C-0-800), Example 1-3 (CW-C-0.5-800), Example 2-3 (CW-C-1-800), Example 3- These are SEM images of the surfaces of Example 3 (CW-C-1.5-800), Example 2-1 (CW-C-1-600), and Example 2-2 (CW-C-1-700).
Figure 3 shows (a) Example 1-3 (CW-C-0.5-800), (b) Example 2-3 (CW-C-1-800), and (c) Example 3-3 (CW- Nitrogen adsorption curves measured using (d) Example 2-1 (CW-C-1-600), (e) Example 2-2 (CW-C-1-700) am.
Figure 4 is a nitrogen adsorption curve measured using Comparative Example 3 (CW-C-0-800).
Figure 5(a) is the normalized Raman distribution of Example 2-3 (CW-C-1-800) and Comparative Example 3 (CW-C-0-800), and (b) is the normalized Raman distribution of Comparative Example 3 (CW- (c) is the deconvoluted Raman distribution of Example 2-3 (CW-C-1-800), (d) is the deconvoluted Raman distribution of Example 2-3 (CW-C-1-800), and (d) is the deconvoluted Raman distribution of Example 2-3 (CW-C-1-800). FTIR spectra of Example 1-3 (CW-C-0.5-800) and Comparative Example 3 (CW-C-0-800), and (e) is Example 2-3 (CW-C-1) under different pH conditions. This is the result of confirming the surface charge (zeta potential) of -800).
Figure 6 shows FTIR spectra of Example 1-3 (CW-C-0.5-800), Example 2-3 (CW-C-1-800), and Example 3-3 (CW-C-1.5-800). am.
Figure 7(a) shows Example 1-3 (CW-C-0.5-800), Example 2-3 (CW-C-1-800), and Example 3-3 (CW-C-1.5-800). and XPS spectra deconvoluted for C1s of Comparative Example 3 (CW-C-0-800), (b) is the XPS spectra deconvoluted for N1s, and (c) is the -C-1-600), the deconvoluted XPS spectra for C1s, (d) is the deconvolved XPS spectra for N1s.
Figure 8 shows Example 1-3 (CW-C-0.5-800), Example 2-3 (CW-C-1-800), Example 3-3 (CW-C-1.5-800), and Comparative Examples. This is an XPS spectra for the carbon row of 3 (CW-C-0-800).
Figure 9(a) shows the TGA of Example 1-3 (CW-C-0.5-800), Example 2-3 (CW-C-1-800), and Comparative Example 3 (CW-C-0-800). is a curve, and (b) is Example 2-1 (CW-C-1-600), Example 2-2 (CW-C-1-700), and Example 2-3 (CW-C-1-800) ) is the TGA curve.
Figure 10 shows Example 2-1 (CW-C-1-600; 600°C), Example 2-2 (CW-C-1-700; 700°C), and Example 2-3 (CW-C-1). This is a graph showing the correlation between pyrolysis temperature (-800; 800℃) and specific surface area (BET) and removal efficiency (Removal).
11 shows Comparative Example 3 (CW-C-0-800; KOH:CW=0), Example 1-3 (CW-C-0.5-800; KOH:CW=0.5), and Example 2-3 (CW) -C-1-800; KOH:CW=1) and Example 3-3 (CW-C-1.5-800; KOH:CW=1.5) KOH:CW ratio (KOH/CW) and specific surface area (BET) ) and removal efficiency (Removal) are graphs showing the correlation.
Figure 12(a) shows Comparative Example 3 (CW-C-0-800), Example 1-3 (CW-C-0.5-800), Example 2-3 (CW-C-1-800), and Example Removal efficiency (Removal) of Example 3-3 (CW-C-1.5-800), Example 2-1 (CW-C-1-600) and Example 2-2 (CW-C-1-700) and It is a graph showing the adsorption capacity (q _e ), and (b) is the adsorption capacity (q _e ) according to pH (2~10) during the adsorption performance test using Example 2-3 (CW-C-1-800). and removal efficiency (Removal), and (c) is a graph showing the adsorption capacity (q _e ) and removal efficiency (Removal), and (d) is a graph showing the adsorption capacity (q _e ) and removal efficiency (Removal) according to the time of administration of Example 2-3 (CW-C-1-800) to the caffeine solution. ) is a graph that confirms, and (e) plots the results (Experimental data) of (d) together with the pseudo first order model and pseudo second order model, and (f) is the result of fitting the result in (d) to the intramolecular diffusion model.
Figure 13(a) is a graph confirming the adsorption capacity (q _e ) of the adsorbent of Example 2-3 (CW-C-1-800) according to the temperature and caffeine concentration of the caffeine solution, and (b) is a graph of (a) The graph is a plot of the Langmuir model and the Freundlich model, (c) is a graph confirming the adsorption capacity (q _e ) of the adsorbent of Example 2-3 (CW-C-1-800) according to the caffeine solution temperature, and (d) ) is the result of testing the removal efficiency (Removal) according to reuse (1 to 3 times) of the adsorbent of Example 2-3 (CW-C-1-800) in Experimental Example 8.
Figure 14 is a conceptual diagram showing a nitrogen-doped carbon adsorbent prepared according to an embodiment of the present invention and the position where the adsorbent interacts with caffeine.

Hereinafter, each configuration of the present invention will be described in more detail so that those skilled in the art can easily implement it. However, this is only an example, and the scope of rights of the present invention is determined by the following contents. Not limited.

As used herein, the term “comprising” is used to list materials, compositions, devices, and methods useful in the present invention and is not limited to the listed examples.

Hereinafter, “carbonization” may be referred to as thermal decomposition as a process of thermally decomposing organic matter to produce carbon-rich carbide, and “graphitic carbon” is amorphous carbon with at least a portion of the graphite structure. means to include.

One embodiment of the present invention is a caffeine adsorbent including a nitrogen-doped carbon material, wherein the carbon material includes graphitized carbon, and the adsorbent includes pyridinic nitrogen and pyridonic nitrogen.

The carbon material may be a product of calcination of coffee waste under nitrogen gas. Coffee waste refers to by-products, including solids, remaining after coffee roasting and extraction of coffee beverages through drip. Preferably, coffee waste refers to the solids remaining after extraction of the coffee beverage. Carbonization or graphitization may occur during the process of calcining coffee waste. The calcination product of coffee waste may be comprised of more than half carbon based on element content, and at least a portion of the carbon may be graphitized. A product obtained by calcining coffee waste under nitrogen gas may have a structure in which nitrogen is doped into a carbon material containing graphitized carbon.

The nitrogen of the nitrogen-doped carbon material may be substituted with one or more of carbon included in the graphite structure of the carbon material or amorphous carbon that does not form a graphite structure. For example, part of the carbon included in the graphite structure of the carbon material may be replaced with nitrogen, and the nitrogen may be pyridinic nitrogen, pyridonic nitrogen, or oxidized nitrogen.

Figure 14 is a conceptual diagram showing the interaction between a portion of a caffeine adsorbent and caffeine according to an embodiment of the present invention. Referring to FIG. 14, the caffeine adsorbent includes a graphite structure in at least a portion of the carbon material and may further include pyridinic nitrogen, pyridonic nitrogen, and oxidized nitrogen. In addition, the carbon material may further include functional groups such as hydroxy groups and carboxyl groups. The nitrogen and functional groups may be mainly distributed at the edges of the carbon material.

The adsorbent may be a porous material including mesopores with an average pore diameter of 2 nm to 50 nm and micropores with an average pore diameter of less than 2 nm. The adsorbent may include walls made of a nitrogen-doped carbon material, and pores may be formed between the walls. By adjusting the calcination conditions of the carbon material, the thickness of the wall and the formation of pores can be controlled. Preferably, the adsorbent may include the pyridonic nitrogen in a larger amount than the pyridinic nitrogen, and the adsorbent may form a more stable porous structure and provide improved adsorption performance.

The adsorbent may have a total volume of micro pores larger than the total volume of meso pores, and the average diameter of the total pores may be 1 to 2 nm. When the average diameter of all pores is within the above range, excellent adsorption performance for caffeine can be provided.

The specific surface area of the adsorbent may be 500 to 1500 m ² /g.

Another embodiment relates to a method for producing a caffeine adsorbent according to the above embodiment, which includes calcining a mixture of coffee waste and potassium hydroxide under nitrogen gas.

The mixture of coffee waste and potassium hydroxide may be a ground mixture of dried coffee waste and potassium hydroxide. The calcination process of the mixture can be broadly divided into two stages. The first reaction is when potassium hydroxide reacts with carbon during calcination to produce potassium carbonate. The second reaction is that the produced potassium carbonate is decomposed into potassium oxide and carbon dioxide, carbon dioxide containing the produced carbon dioxide reacts with carbon to produce carbon monoxide, and the potassium carbonate reacts with carbon to produce potassium and carbon monoxide. It includes producing potassium oxide and reacting with carbon to produce potassium and carbon monoxide. The second reaction includes a plurality of steps as described above, and may occur sequentially or simultaneously after the first reaction. Potassium hydroxide reacts with carbon to produce carbon monoxide, and the generated carbon monoxide escapes from the carbonized carbon material. As potassium carbonate and potassium diffuse into the pores of the carbon material formed at the beginning of the carbonization process, they distort the pore structure and contribute to increasing the adsorption active sites contained in the adsorbent.

Potassium hydroxide and coffee waste can be mixed in a weight ratio of 0.5:1 to 2:1. If potassium hydroxide is not used, the desired porous structure is not formed, and if potassium hydroxide is used in excessive amounts, the pore volume becomes excessively large and the adsorption performance deteriorates. Preferably, the weight ratio of coffee waste and potassium hydroxide may be 0.5:1 to 1.5:1, and most preferably, the weight ratio of coffee waste and potassium hydroxide may be 1:1.

The calcining step may include carbonizing at 600 to 800° C. under nitrogen gas to form carbide and leaching the carbide into inorganic acid to produce a caffeine adsorbent.

Calcination (pyrolysis) temperature can determine the physicochemical properties of the adsorbent by controlling the decomposition rate of potassium hydroxide and potassium carbonate. If the calcination temperature is less than 600°C, potassium carbonate is not produced, and if the calcination temperature exceeds 800°C, the wall structure of the formed adsorbent collapses and the porous structure cannot be maintained.

The step of preparing a caffeine adsorbent by leaching the carbide with an inorganic acid may involve adding carbide to an inorganic acid such as nitric acid to remove metallic potassium and other impurities generated during the carbonization process. Leaching can be repeated several times, but the number of times is not limited.

Another embodiment relates to a method for removing caffeine contained in a target solution by adsorption using the caffeine adsorbent according to the above embodiment.

The method for removing caffeine by adsorption may include contacting a caffeine adsorbent with the solution. For example, the caffeine adsorbent may be added to the solution in a tea bag or container, and then removed after caffeine adsorption, but is not limited to this. The caffeine adsorbent may also be manufactured in the form of a filter.

The step may be adding 0.1 to 0.2 g of the caffeine adsorbent per 1 L of the solution. Even if the caffeine adsorbent is administered in an amount greater than 0.2 g, the removal efficiency does not increase significantly.

The solution is not limited as long as it contains caffeine. For example, the solution is selected from the group consisting of coffee, black tea, green tea, oolong tea, white tea, black tea, black tea, herbal tea, flower tea, mate tea, chai, maca, energy drinks, alcoholic drinks, soda and cocoa. It may be one or more beverages, or wastewater collected in rivers, streams, oceans, or wastewater treatment plants.

The pH of the target solution from which the adsorbent can adsorb and remove caffeine may be 2 to 10, and is not limited to this, so it is possible to treat a wide range of targets, from beverages to contaminated water and sewage sources.

The caffeine adsorbent used according to the above caffeine adsorption removal method can be recovered and regenerated by dispersing it in alcohol. Preferably, the alcohol may be ethanol, but is not limited thereto. For example, an adsorbent saturated with adsorbed caffeine can be regenerated by dispersing it in ethanol and stirring, and then the regenerated caffeine adsorbent can be recovered and reused through filtration and drying.

Below, the present invention will be described in more detail through specific examples and experimental examples. The following examples and experimental examples are intended to illustrate the present invention, and the present invention is not limited by the following examples and experimental examples.

Examples 1 to 4. Preparation of adsorbent derived from coffee waste

Figure 1 is a conceptual diagram showing the manufacturing process and use method of an adsorbent derived from coffee waste according to an embodiment. Referring to Figure 1, the adsorbent is made up of coffee waste (CW) and potassium hydroxide (KOH) in the following order: physical mixing, carbonization, and leaching.

Coffee waste collected from the coffee machine was dried in a convection oven at 80°C overnight to remove water absorbed by the coffee waste. Potassium hydroxide (Showa, 85% flake) and dried coffee waste were mixed in the weight ratio shown in Table 1 below and ground in a mortar to prepare a mixture of coffee waste and potassium hydroxide.

A mixture of coffee waste and potassium hydroxide was injected into a tubular furnace, calcined (carbonized) with nitrogen gas at the temperature shown in Table 1 below, then leached with nitric acid and dried to obtain an adsorbent from which potassium was removed. Hereinafter, when examples or comparative examples are described as CW-C-X-T, it will be understood that X is the content of potassium hydroxide in the coffee waste and T is the calcination temperature.

Potassium hydroxide:coffee waste mixing ratio Calcination temperature
(℃) Example 1-1 (CW-C-0.5-600) 0.5:1 600 Example 1-2 (CW-C-0.5-700) 0.5:1 700 Example 1-3 (CW-C-0.5-800) 0.5:1 800 Example 2-1 (CW-C-1-600) 1:1 600 Example 2-2 (CW-C-1-700) 1:1 700 Example 2-3 (CW-C-1-800) 1:1 800 Example 3-1 (CW-C-1.5-600) 1.5:1 600 Example 3-2 (CW-C-1.5-700) 1.5:1 700 Example 3-3 (CW-C-1.5-800) 1.5:1 800 Example 4-1 (CW-C-2-600) 2:1 600 Example 4-2 (CW-C-2-700) 2:1 700 Example 4-3 (CW-C-2-800) 2:1 800

Comparative example

In a comparative example, only dried coffee waste was ground in a mortar, injected into a tubular furnace, and calcined with nitrogen gas. Comparative Example 1 (CW-C-0-600), Comparative Example 2 (CW-C-0-700), and Comparative Example 3 (CW-C-) according to the calcination temperature (600 ℃, 700 ℃, 800 ℃), respectively. 0-800).

Experimental Example 1. Confirmation of pore structure of adsorbent

The adsorbents prepared in Examples and Comparative Examples were confirmed by SEM (S-3500N, Hitachi) and are shown in Figure 2.

Referring to Figure 2, Example 1-3 (CW-C-0.5-800), Example 2-1 (CW-C-1-600), Example 2-2 (CW-C-1-700) , Example 2-3 (CW-C-1-800) and Example 3-3 (CW-C-1.5-800), a uniformly distributed interconnected pore structure is formed as a result of activation using potassium hydroxide. It was confirmed that In contrast, Comparative Example 3 (CW-C-0-800), which did not use potassium hydroxide, was confirmed to have a non-uniform macroporous structure.

The surface area, pore structure, and pore size distribution of the adsorbent were confirmed through nitrogen adsorption curves (see Figures 3 and 4) and BET analysis (Belsorp miniX), and the results are shown in Table 2 below.

SA ( ^m2 /g) PV( ^cm3 /g) Dia
(nm) V _micro V _meso V _total Comparative Example 3
(CW-C-0-800) 3.22 1.5*10 ^-4 8.7*10 ^-4 1.6*10 ^-2 17.2 Example 1-3 (CW-C-0.5-800) 1070 0.93 0.25 1.18 1.6 Example 2-1 (CW-C-1-600) 504 0.42 0.085 0.51 1.72 Example 2-2 (CW-C-1-700) 754 0.89 0.15 1.04 1.97 Example 2-3 (CW-C-1-800) 1212 0.95 0.33 1.28 1.67 Example 3-3 (CW-C-1.5-800) 1340 1.07 0.49 1.56 1.63 SA: BET specific surface area
PV: pore volume
V _micro : volume of micropore
V _meso : Volume of macropore (mesopore)
V _total : total pore volume
Dia: average diameter of pores

Referring to Figure 2, in examples with the same potassium hydroxide and coffee waste content ratios, the thickness of the pore walls formed decreases as the carbonization temperature increases. Referring to Table 1, it was confirmed that in the adsorbent according to the example, micropores were formed in the process of reducing the wall thickness.

The pore structure of the adsorbent is formed during the activation of coffee waste using potassium hydroxide. As the relative content of potassium hydroxide increases, the rate of carbonate formation among the carbon contained in the coffee waste increases, allowing pore formation to become more active. As the heat treatment temperature increases, more carbon volatilizes, increasing the specific surface area, total pore volume, and micropore volume.

Figures 3 and 4 show nitrogen adsorption/desorption isotherms and pore size distribution curves for adsorbents according to Examples and Comparative Examples, respectively. Except for the comparative example in FIG. 4, type I isotherm lines appeared in all examples in FIG. 3, and the average pore diameter of each example in Table 1 was shown to be less than 2 nm, indicating that the adsorbent of the example had a microporous structure. It has been confirmed that it has. Referring to Table 1, it was confirmed that the average diameter of pores formed in the adsorbent was dependent on temperature.

Experimental Example 2. Confirmation of surface characteristics of adsorbent

Determination of relationship between potassium hydroxide use and graphitization

Raman spectrum analysis was performed on the carbon contained in the adsorbent of Example 2-3 (CW-C-1-800) and Comparative Example 3 (CW-C-0-800), and the graphite of the carbon contained in the adsorbent was determined. The degree of anger was confirmed.

Figure 5(a) is the normalized Raman distribution (Raman spectra) of each sample of Examples and Comparative Examples. In both samples, disordered carbon (D) and graphitized sp ² carbon (G) among sp ² hybridized carbons are shown, respectively. Peaks appeared at ~1340cm ^-1 and ~1590cm ^-1 . In Example 2-3, the ID/IG value was found to be as low as 0.88, which indicates higher graphite properties compared to the comparative example, meaning that the use of potassium hydroxide affects graphitization.

Referring to Figures 5(b) and (c), the D band and G band can be deconvoluted into four peaks (Peak I to IV) through Gaussian simulation. ~1200 cm ^-1 (Peak I) and ~1500 cm ^-1 (Peak III) correspond to sp ³ carbon, and ~1350 cm ^-1 (Peak II) and ~1590 cm ^-1 (Peak IV) correspond to graphitized carbon. It may correspond to carbon. The degree of graphitization of carbon can be determined by calculating the area ratio of sp ³ carbon and sp ² carbon (A _sp ³ /A _sp ² ). While the ratio in Examples 2-3 was 0.91, Comparative Example 3 It was confirmed that the graphitized carbon content in the adsorbent of the example was high at the level of 0.61.

Determination of the relationship between the use of potassium hydroxide and the surface functionality of the carbon contained in the adsorbent.

Fourier transform infrared spectroscopy (FT-IR, Nicolet iS5, Thermo Scientific) analysis of the adsorbents of Examples and Comparative Examples was performed using KBr pellets to identify functional sites present in the CW samples. Figure 5(d) is the FTIR spectra of Example 1-3 (CW-C-0.5-800) and Comparative Example 3 (CW-C-0-800), and Figure 6 is the FTIR spectra of Example 1-3 (CW-C) -0.5-800), Example 2-3 (CW-C-1-800), and Example 2-3 (CW-C-1.5-800). Referring to these, in the spectra of Examples and Comparative Examples A clear difference appears in the fingerprint area (1500~900 cm ^-1 ).

Referring to Figure 5(d), when the relative content of potassium hydroxide increases from 0 to 0.5, CC stretching moves from ~1629 cm ^-1 to ~1626 cm ^-1 , Example 1-3 (CW-C-0.5 -800) showed new peaks at ~1698 and 1383 cm ^-1 corresponding to C=N and NO stretching, respectively.

Referring to Figure 6, it was confirmed that the relative content of potassium hydroxide had a significant effect on the surface properties of the adsorbent.

XPS analysis of adsorbents

For the Example and Comparative Example adsorbents, the chemical state of the surface of each sample was confirmed through X-ray photoelectron spectroscopy (XPS, Thermo Electron).

Figure 7(a) shows Example 1-3 (CW-C-0.5-800), Example 2-3 (CW-C-1-800), and Example 3-3 (CW-C-1.5-800). and the deconvoluted XPS spectra for C1s of Comparative Example 3 (CW-C-0-800), (b) is the deconvoluted XPS spectra deconvoluted for C1s in Example 2-1 (CW-C-1-600), (d) is the XPS spectra deconvolved for N1s in Example 2-1 above. Figure 7 shows the presence of carbon, oxygen and nitrogen in all samples used for analysis.

Referring to Figure 7, the deconvoluted C 1s peak shows two peaks resulting from sp ² and sp ³ hybridization, respectively. The peak at ~283 eV corresponds to CC and C=C, the other represents a higher binding energy (~291.7 eV) belonging to the π-π* transition by bonding with nitrogen or oxygen (CN, CO) .

Figure 8 shows Example 1-3 (CW-C-0.5-800), Example 2-3 (CW-C-1-800), Example 3-3 (CW-C-1.5-800), and Comparative Examples. This is an XPS spectra for the carbon row of 3 (CW-C-0-800). According to the XPS results in Figure 8, it was confirmed that both the relative content of potassium hydroxide and temperature had a significant effect on carbon species. For example, when the potassium hydroxide ratio increased from 0.5 to 1, the peak at the lower binding energy shifted from 283.88 to 283.63 eV, indicating an increase in the degree of sp ² hybridization of carbon and consistent with the graphitization degree analysis discussed earlier. . On the other hand, when the temperature increases from 600 °C to 800 °C, the peak shifts to a lower binding energy by 0.2 eV.

Referring to Figure 7, the deconvoluted N 1s peak indicated that all nitrogen species form a 6-ring nitrogen moiety. However, there were differences in the specific type and content depending on the relative content of potassium hydroxide. For example, in Comparative Example 3, peaks appeared at 398 and 403.32 eV, which represent Pyridinic-N and Graphitic-N, respectively, which means that they are more stable nitrogen species when not chemically activated. Upon undergoing activation with calcium hydroxide, three different nitrogen species appeared at ~398.4, ~400.5, and ~405.37 eV, with the first and third peaks being attributed to Pyridinic-N and Oxidated-N, respectively, and the second peak being It is found in the Pyrrolic-N and Pyridonic-N regions, but Pyridonic-N is more stable under synthetic conditions. These results show that potassium hydroxide goes beyond simply contributing to the formation of pores in the adsorbent, and changes and determines the type of nitrogen species contained in the adsorbent.

Table 3 below summarizes the content of nitrogen species contained in the Example and Comparative Example adsorbents used in the analysis of FIGS. 7 and 8.

nitrogen species Element content (%) Comparative Example 3
(CW-C-0-800) Pyridinic-N 57.82 Graphic-N 42.18 Example 1-3
(CW-C-0.5-800) Pyridinic-N 43.48 Pyridonic-N 11.45 Oxidized-N 45.07 Example 2-3
(CW-C-1-800) Pyridinic-N 13.16 Pyridonic-N 48.43 Oxidized-N 38.41 Example 3-3
(CW-C-1.5-800) Pyridinic-N 12.62 Pyridonic-N 37.10 Oxidized-N 50.28 Example 2-1
(CW-C-1-600) Pyridinic-N 41.71 Pyridonic-N 18.6 Oxidized-N 39.69

Referring to Table 3, when the ratio of potassium hydroxide increased from 0.5 to 1, the content of Pyridonic-N increased from 11.45% to 48.43%, and the contents of Oxidized-N and Pyridinic-N decreased, but potassium hydroxide When the ratio further increased, the opposite trend was observed. This means that in chemical activation of coffee waste, a 6-ring nitrogen moiety linked to an oxygenated functional group is more likely to be formed.

When comparing the element contents of Examples 2-1 and 2-3, it was confirmed that Pyridonic-N was more likely to be formed than Pyridinic-N and Oxidized-N as the calcination temperature increased.

Thermogravimetric analysis

Thermogravimetric analysis (TGA, SINCON-1000, Korea) was performed with the adsorbents of Examples and Comparative Examples to confirm the thermal behavior of each sample.

Figure 9(a) shows the TGA of Example 1-3 (CW-C-0.5-800), Example 2-3 (CW-C-1-800), and Comparative Example 3 (CW-C-0-800). is a curve, and (b) is Example 2-1 (CW-C-1-600), Example 2-2 (CW-C-1-700), and Example 2-3 (CW-C-1-800) ) is the TGA curve.

Referring to Figure 9, all samples showed a pattern of decreasing weight (weight %), showing a two-stage deterioration pattern. In the first step, the weight loss at 25 to 110 °C is related to the evaporation of water molecules adsorbed on the surface of the carbon contained in the adsorbent, and in the second step, the larger weight loss (~70 to 80%) is related to the decomposition of the carbon. corresponds to This indicates that as the potassium hydroxide content increases, the stability of carbon decreases, creating a less stable functional group. Additionally, as the thermal decomposition temperature increases, the stability of carbon decreases, indicating that less stable bonds are formed.

Experimental Example 3. Confirmation of adsorption performance of adsorbent (1)

The adsorbent according to Examples or Comparative Examples was administered to 50 mL (pH 5.5) of a 25 ppm caffeine solution at room temperature (adsorbent dosage for solution 0.2 g/L), and the adsorption capacity (q _e ) and removal efficiency ( ϕ ) were measured. It was calculated as follows.

Equation (1) q _e = (C _o - C _e )V/m

Equation (2) ϕ = (C _o - C _e / C _o ) * 100(%)

In the above formulas (1) and (2), C _o and C _e are the caffeine concentration (mg/L) before and after adsorption, respectively, V is the volume of the caffeine solution, and m is the mass of the adsorbent (g).

Figure 10 is a graph showing the specific surface area (BET, m ² /g) and removal efficiency (Removal, %) of the adsorbents of Examples 2-1 to 2-3, and shows the difference between specific surface area and removal efficiency when the thermal decomposition temperature is different. It shows correlation. Figure 11 is a graph showing the specific surface area and removal efficiency of the adsorbents of Examples 1-3, 2-3, 3-3, and Comparative Example 3, showing the correlation between specific surface area and removal efficiency when the KOH/CW ratio is different. It is shown. Figure 12(a) is a graph showing the removal efficiency and adsorption capacity of the adsorbents of Examples 1-3, 2-3, 3-3, and Comparative Example 3. The removal efficiencies of the examples and comparative examples used are shown in Table 4 below.

Removal (%) Comparative Example 3
(CW-C-0-800) 16.7 Example 1-3
(CW-C-0.5-800) 68.5 Example 2-1
(CW-C-1-600) 27 Example 2-2
(CW-C-1-700) 54 Example 2-3
(CW-C-1-800) 90.4 Example 3-3
(CW-C-1.5-800) 86.5

Referring to Figures 10, 11 and Table 4, Example 2-3 treated at the highest calcination temperature (800°C) showed the highest removal efficiency (90.4%), followed by Example 3-3 (86.5%). %). In Figure 11, the specific surface area of the adsorbent of Comparative Example 3 (KOH:CW = 0) was shown to be approximately 3 m ² /g, but is not shown because the value is small. Example 2-3 (KOH:CW = 1) had a specific surface area of 1212 m ² /g and a removal efficiency of 90.4%, compared to the specific surface area (3 m ² /g) and removal efficiency (16.7%) of Comparative Example 3. It was confirmed that the adsorption performance increased significantly as the potassium hydroxide content increased. However, in Example 3-3, where the potassium hydroxide content was further increased, the removal efficiency decreased, indicating that not only the increase in specific surface area or the total volume of pores due to the increase in potassium hydroxide content affects the adsorption performance. Confirmed.

The results of comparing the physical properties of the adsorbent of Example 2-3 (CW-C-1-800) before and after caffeine adsorption are shown in Table 5 below.

SA ( ^m2 /g) PV( ^cm3 /g) Dia
(nm) V _micro V _meso V _total Example 2-3
(CW-C-1-800) 1212 0.95 0.33 1.28 1.67 Example 2-3 After adsorption of caffeine using (CW-C-1-800-caff) 590 0.39 0.19 0.58 1.04 SA: BET specific surface area
PV: pore volume
V _micro : volume of micropore
V _meso : Volume of macropore (mesopore)
V _total : total pore volume
Dia: average diameter of pores

Referring to Table 5, after adsorption, the micropore volume decreased by approximately 60%, and the mesopore volume decreased by approximately 42%. In this way, it was confirmed that the composition of the adsorbent structure, that is, the type of pores, also plays an important role in adsorption.

Experimental Example 4. Confirmation of adsorption performance of adsorbent (2)

The adsorption performance was compared using the adsorbent according to the example and carbon-based materials as conventionally used adsorbents. As carbon-based materials, glucose-derived carbon (GC), multi-walled carbon nanotubes (MWCNT), activated carbon (AC), and acid-treated activated carbon (A-AC) were used, and the adsorption performance was tested in the same manner as in Experimental Example 3. It was confirmed and shown in Table 6 below.

Functional groups included SA ( ^m2 /g) Removal(%) N-based O-based Example 2-3
(CW-C-1-800) NO ^- , C=N, NH -OH, -OOH 1212 90.4 Example 3-3 (CW-C-1.5-800) NO ^- , C=N, NH -OH, -OOH 1340 86.5 GC - -OH, -OOH 71.05 1.71 MWCNTs - -OH, -OOH 105.1 22.3 AC - -OH, -OOH 838.6 93.3 A-AC - -OH, -OOH 812.4 56.9 SA: BET specific surface area
Removal: Removal (adsorption) efficiency

Referring to Tables 2 and 6, carbon (GC) derived from glucose has a higher specific surface area than the adsorbent according to Comparative Example 3, but lower adsorption performance. Additionally, simply acid-treated activated carbon (A-AC) showed lower adsorption performance than pure activated carbon (AC).

In addition, the contact angle of activated carbon (AC) with water was 66.5°, and the contact angle with water of Example 2-3 (CW-C-1-800) was 47°, so the adsorbent of the example was more hydrophobic than activated carbon. The adsorption performance was similar. These results are known to increase the non-electrostatic attraction and electrostatic interaction as the content of acidic functional groups increases. However, as the content of acidic functional groups increases, hydrophobicity and minimum hydrophobic π-π interaction decrease, which is π-π for caffeine adsorption. This means that surface interactions have a greater impact than electrostatic and non-electrostatic interactions.

Referring to Table 6, it was confirmed that the adsorbent of the example rich in nitrogen-based functional groups showed better adsorption performance by Lewis basicity. Heterocyclic nitrogen improves the basicity of carbon materials, and the nitrogen-based functional group was shown to be a factor determining surface interaction in adsorption. As confirmed in Experimental Example 2, among nitrogen-based functional groups, Pyridonic-N contributed more to caffeine adsorption than Pyridinic-N.

Experimental Example 5. Confirmation of adsorption performance of adsorbent (3)

Check adsorption performance according to adsorbent content

The adsorption performance of Examples and Comparative Examples was confirmed in the same manner as in Experimental Example 3, except that 5 to 50 mg of adsorbent was included in 50 mL of caffeine solution, and adsorption performance according to adsorbent content was confirmed.

Figure 12(c) is a graph showing the adsorption capacity (q _e ) and removal efficiency (Removal, %) according to the content of adsorbent (Loading, g/L). At the lowest adsorbent content (5mg; Loading 0.1 g/L), the adsorption capacity was 134 mg/g, but the removal efficiency was low at 54.4%. When the adsorbent content was increased to 10 mg (Loading 0.2 g/L), the adsorption capacity decreased (109.87 mg/g), but the removal efficiency increased to 88%. Afterwards, when the adsorbent content was further increased, the removal efficiency did not increase significantly, but the adsorption capacity rapidly decreased. When the adsorbent content exceeded 0.2 g/L, not all active sites in the adsorbent were involved in adsorption, and the adsorption capacity decreased and the increase in removal efficiency decreased.

Check adsorption performance according to pH

The effect of pH on the adsorbent and its adsorption performance was confirmed.

The pH was adjusted to 2 to 8 using 0.1 M hydrochloric acid solution and ammonium hydroxide solution in the aqueous solution containing the adsorbent, and the change in surface charge of the adsorbent was confirmed.

Figure 5(e) shows the surface charge analysis (zeta potential, mV) results of the adsorbent of Example 2-3 (CW-C-1-800) according to pH concentration. Referring to Figure 5(e), the zero charge point of the adsorbent is pH 3.9, and as the pH increases, the negativity of the surface increases significantly.

The adsorption performance of Example 2-3 was confirmed in the same manner as Experimental Example 3, but the pH was adjusted to 2 to 10 using a 0.1 M hydrochloric acid solution and an ammonium hydroxide solution in the caffeine solution, and the adsorption performance according to pH was confirmed. .

Referring to Figure 12(b), the pH of the caffeine solution maintained the adsorption performance of the adsorbent at a level of 84% to 89%. From this, it was confirmed that pH affects the surface properties of the adsorbent but does not have a significant effect on the adsorption performance of the adsorbent, and that the adsorbent according to the example can be applied to contaminated water of various pH.

Experimental Example 6. Adsorption kinetics analysis of adsorbent

An adsorption experiment was performed with the adsorbent of Example 2-3 (CW-C-1-800) in the same manner as in Experimental Example 3, and the adsorption performance over time was confirmed.

Referring to Figure 12(d), approximately 71% of the caffeine was removed in the initial stage of adsorption (~ 1 min). After 5 minutes, the removal efficiency was more than 80%, and it was found to be saturated after 30 minutes.

The adsorption kinetic data was found to be suitable for Pseudo First Order (PFO), Pseudo Second Order (PSO), and Intra-particle diffusion kinetic models, and the correlation for each model was The relationship coefficients were shown in Table 7 below.

dynamics model correlation Coefficient PFO q _t = q _e (1 - e ^-k1t ) q _e (mg/g) k ₁ (min ^-1 ) R ² SD 108.4 0.48 >0.999 1.58 PSO q _t = [(k ₂ q ² _e )t]/[1 + k ₂ q _m t] q _e (mg/g) k ₁ (g/mg min) R ² SD 109.9 0.015 >0.999 0.94 Intra-particle diffusion q _t = k _id (t) ^0.5 + C _i k _id
(m/g min ^-1/2 ) C _i R ² SD Stage I 14.72 71.57 One 0 Stage II 4.5 87.7 ~0.97 1.74 Stage III 0.97 102.4 One 2.8 q _t : Adsorption capacity at time t (calculated as 110 mg/g)
q _e : Adsorption capacity when equilibrium is reached (mg/g)
k ₁ : Velocity coefficient in pseudo-first-order model
k ₂ : Velocity coefficient in pseudo-second-order model
k _id : diffusion coefficient within particles (m/g min ^-1/2 )
C _i : Coefficient reflecting boundary layer thickness

Referring to Table 7, both the PFO and PSO models showed high correlation (R ² ) values and low SD values, indicating that the adsorption of caffeine can include both physical and chemical adsorption (see Figure 12(e) ). However, the χ ² value of PFO (0.1) was lower than that of PSO (0.12), confirming that physical adsorption was more prominent than chemical adsorption.

Referring to FIG. 12(f) and Table 7, the intra-particle diffusion fitting model showed that caffeine adsorption by the adsorbent according to the example included three stages (Stage I to III). In the first region with a steep slope, adsorption proceeded rapidly until approximately 2 min, indicating the adsorption of caffeine on the outer surface of the adsorbent, in the second region corresponding to intra-particle diffusion controlled by the pore structure inside the adsorbent, and in the third region. The region represents the final equilibration stage. Therefore, it was confirmed that the adsorption performance of the adsorbent is determined by its inherent surface properties and internal structure.

Experimental Example 7. Effect and thermodynamic analysis of adsorption temperature of adsorbent

Check adsorption performance according to adsorption temperature

An adsorption experiment was performed in the same manner as in Experimental Example 3 using the adsorbent of Example 2-3 (CW-C-1-800) under the conditions of pH 5.5 and adsorption time of 30 minutes, but the caffeine concentration (25 to 400 ppm) ) and temperature (25 ℃, 35 ℃, and 55 ℃) were confirmed for adsorption performance.

Figure 13(a) is a graph confirming the adsorption capacity (qe) of the adsorbent of Example 2-3 (CW-C-1-800) according to the temperature and caffeine concentration of the caffeine solution, and (b) is the graph of (a) and Langmuir model and Freundlich model are plotted.

Referring to Figure 13(a), the adsorption capacity was found to increase as the initial caffeine concentration (Ce, ppm) increased, and the adsorption capacity increased when the adsorption temperature was 35 ℃ compared to when the adsorption temperature was 25 ℃, making the adsorption endothermic. It turned out to be a reaction. However, it was confirmed that performance was slightly reduced at 55°C.

Figure 13(b) shows a comparison of the nonlinear isotherm model of Langmuir and Freundlich and the adsorption capacity of the adsorbent of Example 2-3 at each temperature. The Langmuir model assumes that adsorption occurs only in limited areas of the adsorbent, resulting in single-layer adsorption, while the Freundlich model assumes multi-layer adsorption due to surface heterogeneity. The adsorption model of the example was similar to the Langmuir model, confirming that it was monolayer adsorption, and it was confirmed that changes in temperature did not change the adsorption site.

Adsorption thermodynamics

An adsorption experiment was performed in the same manner as in Experimental Example 3 using the adsorbent of Example 2-3 (CW-C-1-800) under conditions of pH 5.5 and adsorption time of 30 minutes, but at temperatures (30°C, 50°C, and The adsorption performance at 60°C was confirmed and shown in Figure 13(c).

Referring to Figure 13(c), the adsorption performance improved by 7.7% when the temperature was 50 ℃ compared to when the temperature was 30 ℃. At 60 ℃, as the movement of caffeine in the solution became more active, the desorption rate became higher than the adsorption rate and the adsorption performance decreased. .

When the free energy (ΔG°=ΔH°-TΔS°) value is negative and the ΔH° value is -18.14 kJ/mol, the ΔS° value is found to be -27.52 J/molK. Caffeine adsorption on the example adsorbent. It was confirmed that it was spontaneous physical adsorption.

Experimental Example 8. Confirmation of reusability of adsorbent

After being used for caffeine adsorption (caffeine initial concentration 25 ppm, pH 5.5, adsorbent dosage 0.5 g/L), the saturated adsorbent of Example 2-3 was dispersed in ethanol and stirred for 12 hours to regenerate, then dried in an oven. It was reused. Adsorption performance was confirmed by repeating regeneration and reuse three times.

Referring to Figure 13(d), the removal efficiency was shown to remain constant during three reuses, confirming its applicability as an industrial adsorbent.

Claims (10)

A caffeine adsorbent comprising a nitrogen-doped carbon material, comprising:
The carbon material includes graphitized carbon,
The adsorbent is a caffeine adsorbent containing pyridinic nitrogen (pyridinic-N) and pyridonic nitrogen (pyridonic-N). According to paragraph 1,
The carbon material is a caffeine adsorbent that is a product of calcining coffee waste under nitrogen gas. According to paragraph 1,
The adsorbent is a caffeine adsorbent containing the pyridonic nitrogen in a larger amount than the pyridinic nitrogen. A method for producing a caffeine adsorbent comprising calcining a mixture of coffee waste and potassium hydroxide under nitrogen gas. According to paragraph 4,
A method for producing a caffeine adsorbent, wherein the mixture is a ground mixture of dried coffee waste and potassium hydroxide. According to paragraph 4,
A method for producing a caffeine adsorbent, wherein the weight ratio of the potassium hydroxide and the coffee waste is 0.5:1 to 2:1. According to paragraph 1,
The calcination step is,
Carbonizing at 600 to 800° C. under nitrogen gas to form carbide; and
A method for producing a caffeine adsorbent, comprising the step of producing a caffeine adsorbent by leaching the carbide with an inorganic acid. A method for removing caffeine by adsorption, comprising contacting a solution with the caffeine adsorbent according to any one of claims 1 to 3. According to clause 8,
A method for adsorbing and removing caffeine, wherein the caffeine adsorbent is added in an amount of 0.1 to 0.2 g per 1 L of the solution. According to clause 8,
The solution is,
Caffeine, one or more beverages selected from the group consisting of coffee, black tea, green tea, oolong tea, white tea, green tea, black tea, herbal tea, flower tea, mate tea, chai, maca, energy drinks, alcoholic drinks, soda and cocoa. Adsorption removal method.