Experimental study on modified fruit shell carbon for methane adsorption and decarbonization

Abstract

Modification of activated carbon has the potential to improve its adsorption and separation capacity. Different concentrations of ammonia (6%, 9%, 12%, 15%) and treatment times (4 h, 6 h, 8 h, 10 h) were used to modify jujube shell carbon and coconut shell carbon in ultrasonic washing equipment. Biogas adsorption experiments were carried out with modified activated carbon to study the effect of adsorption and decarbonization on activated carbon surface functional groups. After modification, the surface alkaline functional groups of activated carbon increased, the acidic functional groups decreased, and the adsorption performance of CO₂ was enhanced. In addition, the specific surface area and total pore volume of activated carbon decreased, the average pore size increased, and the degree of graphitization increased. In the experimental research range, under ultrasonic conditions, jujube shell carbon impregnated with 12% ammonia water for 4 h and coconut shell carbon impregnated with 9% ammonia water for 10 h had the best modification effect. The adsorption capacity for CO₂ was 1.83 and 1.745 mmol/g, respectively, which increased by 0.8 mmol/g and 0.599 mmol/g, respectively, compared with the unmodified sample.

Full Article

Experimental Study on Modified Fruit Shell Carbon for Methane Adsorption and Decarbonization

Yan Mao,^a,b,c,d Li Huang,^a,b,c,d,* Zhiqiang Hao,^a,b,c,d Hongge Tao,^a,b,c,d Chunyao Qing,^a,b,c,d Shengyong Liu,^a,b,c,d Guangtao Wang,^a,b,c,d and Qingyan Ma ^a

Modification of activated carbon has the potential to improve its adsorption and separation capacity. Different concentrations of ammonia (6%, 9%, 12%, 15%) and treatment times (4 h, 6 h, 8 h, 10 h) were used to modify jujube shell carbon and coconut shell carbon in ultrasonic washing equipment. Biogas adsorption experiments were carried out with modified activated carbon to study the effect of adsorption and decarbonization on activated carbon surface functional groups. After modification, the surface alkaline functional groups of activated carbon increased, the acidic functional groups decreased, and the adsorption performance of CO₂ was enhanced. In addition, the specific surface area and total pore volume of activated carbon decreased, the average pore size increased, and the degree of graphitization increased. In the experimental research range, under ultrasonic conditions, jujube shell carbon impregnated with 12% ammonia water for 4 h and coconut shell carbon impregnated with 9% ammonia water for 10 h had the best modification effect. The adsorption capacity for CO₂ was 1.83 and 1.745 mmol/g, respectively, which increased by 0.8 mmol/g and 0.599 mmol/g, respectively, compared with the unmodified sample.

DOI: 10.15376/biores.19.1.195-209

Keywords: Activated carbon; Ammonium hydroxide; Ultrasonic wave; Modified; Decarbonization

Contact information: a: College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou, 450002; b: Key Laboratory of New Materials and Equipment for Rural Renewable Energy, Ministry of Agriculture and Rural Affairs, Zhengzhou, 450002; c: International Joint Laboratory of Biomass Energy and Nanomaterials in Henan Province, Zhengzhou, 450002; d: Henan Provincial Key Laboratory of Rural Renewable Energy, Zhengzhou, 450002;

* Corresponding author: huangliyf@henau.edu.cn

INTRODUCTION

It is necessary to transition from carbon-based fossil fuels to renewable and clean energy in order to maintain sustainable development and economic growth. Biogas is a high-quality renewable energy source with advantages such as renewability, low pollution, and wide distribution. However, biogas has not yet achieved high-quality utilization in China, mainly due to its high content of carbon dioxide. Biogas decarbonization and quality improvement has potential to alleviate the energy crisis.

Among the existing methods for capturing CO₂, adsorption is the most promising technology for industrial applications due to its high efficiency, low cost, and ease of operation over a relatively wide temperature range. The adsorption effect mainly depends on the choice of adsorbent, and the commonly used carbon dioxide adsorption materials are carbon molecular sieves, activated carbon, zeolite, calcium oxide, and metal organic frameworks (MOFs). Activated carbon has the advantages of low price, large specific surface area, high porosity, stable chemical structure, and controllable surface functionalization, etc. It is widely used in industrial adsorption fields. Activated carbon is a non-polar adsorbent, so it is often used to adsorb non-polar substances, and its adsorption capacity for polar substances is weak. The adsorption capacity of activated carbon mainly depends on its pore structure and surface chemical properties. Research has shown that the adsorption of CO₂ gas is greatly influenced by the structure of the adsorbent, mainly by the volume of micropores. The larger the proportion of micropores, the better the adsorption effect (Sanchez et al. 2014). Liu et al. studied the influence of surface functional groups of activated carbon on the adsorption process (Liu and Wilcox 2012). When the hydroxyl and carboxyl groups of surface oxygen-containing functional groups exist, the adsorption of activated carbon on CO₂ will be enhanced. These oxygen-containing functional groups have high electronegativity, which enables them to serve as basic adsorption sites. Therefore, the modification of activated carbon will introduce new chemical functional groups, which can significantly improve the adsorption capacity of activated carbon and enhance its selective adsorption. Currently, common modification methods include acid modification, alkali modification, loaded metal modification, and ultrasonic modification (Zheng et al. 2019). By modification, the chemical properties of the surface of activated carbon can be changed, making it a more targeted adsorbent. Research has shown that the introduction of Lewis bases can increase the affinity of materials for carbon dioxide, as carbon dioxide can act as a Lewis acid. Therefore, introducing nitrogen containing functional groups on the surface of activated carbon through modification can significantly enhance its adsorption capacity for CO₂ (Petrobic et al. 2021).

Waralee Dilokekunakul used bamboo waste as raw material to prepare activated carbon through heat treatment. The activated carbon was then modified to nitrogen rich and oxygen rich carbon through urea, air oxidation, and KOH activation. The results showed that nitrogen rich carbon exhibits the strongest CO₂ affinity and maximum CO₂ adsorption capacity. Under certain conditions of pore width and functional groups, the higher the temperature, the lower the CO₂ affinity (Dilokekunakul et al. 2020). Ipeaiyeda et al. (2020) studied the effects of ammonia and ammonium acetate on the physical and chemical properties, morphology, and porous structure of activated carbon produced from coconut shells and palm fruit shells. The results showed that the surface area of activated carbon ranged from 934 to 1646 m²/g. After modification, the pores of activated carbon were slightly widened, the BET surface area slightly increased, and the pore size increased. Zhang et al. (2010) modified high specific surface area activated carbon (AC) using ammonia solution immersion and microwave radiation under N₂ or H₂, respectively. The results showed that after surface modification, the content of C and N elements in the sample increased compared to the original AC, while the content of O elements decreased. Compared with the original activated carbon, the more alkaline groups on the surface of activated carbon, the higher its adsorption capacity for CO₂. The adsorption capacity of CO₂ by microwave irradiation modified AC in N₂ atmosphere was 3.75 mmol/g at 1 atm and 293 K, which increased by 28% compared to the original AC (Zhang et al. 2010). Zhang studied the effects of non-cavitating and cavitating states on pore volume, surface area, surface functional groups and microscopic morphology. The results showed that ultrasonic enlarges the surface area and pore size of activated carbon, which mainly affected the pore volume. Ultrasonic cavitation also promoted the increase of activated carbon porosity, mainly affecting the increase of specific surface area and micropore volume, but excessive cavitation would lead to the decrease of activated carbon porosity (Zhang et al. 2019). In summary, both alkali modification and ultrasonic modification can change the pore structure of activated carbon, which is conducive to adsorption. However, few scholars have combined the two modification methods to study the adsorption separation of CO₂/CH₄.

In this study, coconut shell activated carbon and date shell activated carbons were used as raw materials. The materials were soaked with ammonia and modified by ultrasonic oscillation. The purpose of this study was to introduce nitrogenous functional groups on the surface of activated carbon through ammonia modification to enhance the adsorption capacity of CO₂ and expand the pore channels of activated carbon and increase its porosity through ultrasonic cavitation. Through a self-made adsorption device, the physical and chemical properties of the modified activated carbon and its adsorption and separation effect on CO₂/CH₄ are studied, providing reference for the preparation of high CO₂/CH₄ separability modified activated carbon.

EXPERIMENTAL

Materials and Instruments

The adsorption material had been prepared using a pyrolysis temperature of 1200 °C, to make steam-activated coconut shell activated carbon (1-2 mm) and date shell activated carbon (1 to 2 mm). The activated carbon was purchased from Gongyi City Sanle water purification materials factory. The aqueous ammonia, used as modifier, was purchased from Yantai Shuangshuang Chemical Co., Ltd. The mixture used as an artificial biogas with a volume ratio of 60% CO₂ and 40% CH₄, was purchased from Henan Yuanzheng Special Gas Co., Ltd. The instruments used are shown in Table 1.

Table 1. Experimental Instruments

Methods

The mass concentration of the ammonia modifiers was set to 4 levels (6%, 9%, 12%, 15%), the modification time was set to 4 durations (4 h, 6 h, 8 h, 10 h), and the modification temperature was set to 30 ℃. Each group took 8 g carbon, put it in a 100 mL conical bottle, and 100 mL of ammonia solution of different concentrations was poured in and sealed. After modification, the sample was placed in the oven and dried at 105 ℃ for 12 h. After that, the BET specific surface area analyzer, Fourier transform infrared spectrometer and Raman spectrometer were used to characterize the sample. The adsorption experiment was conducted by self-made adsorption device (Fig. 1) to determine the adsorption and separation effect of the sample on CO₂/CH₄.

The adsorption and desorption curves of AC on N₂ before and after modification were measured by BELSORP-mini II automatic specific surface area and micropore analyzer at 77K, and the total pore volume was calculated by the MP method. The functional groups of AC surface were measured by IR-960 Fourier transform infrared spectrometer with wavenumber ranging from 4000 to 400 cm^-1. The degree of AC carbonization was determined by HR-Evolution laser confocal micro-Raman spectrometer. The wavelength of excitation source was 532 mm, and the wavenumber range was 2000 to 500 cm^-1.

Fig. 1. Diagram of adsorption device. 1 – Biogas bottle; 2 – Pressure reducing valve; 3 – Valve; 4 – Adsorption column; 5 – Gas collecting bag; and 6 – Vacuum pump

Sample Screening Markers

Based on the results of sample adsorption and separation of methane and carbon dioxide, certain unmodified samples and samples with better adsorption effect were selected after modification, and they were labeled separately. Unmodified coconut shell carbon was labeled as AC0, coconut shell carbon soaked in 12% ammonia for 4 h was labeled as AC1, coconut shell carbon soaked in 9% ammonia for 6 h was labeled as AC2, coconut shell carbon soaked in 9% ammonia for 8 h was labeled as AC3, and coconut shell carbon soaked in 9% ammonia for 10 h was labeled as AC4. Unmodified jujube shell charcoal was labeled as AC5, jujube shell charcoal soaked in 12% ammonia for 4 h was labeled as AC6, jujube shell charcoal soaked in 12% ammonia for 6 h was labeled as AC7, jujube shell charcoal soaked in 9% ammonia for 8 h was labeled as AC8, and jujube shell charcoal soaked in 9% ammonia for 10 h was labeled as AC9.

RESULTS AND DISCUSSION

Adsorption Results of Modified Activated Carbon on Carbon Dioxide in Biogas

The device shown in Fig. 1 was used for the adsorption experiment, and the content of CH₄ and CO₂ in the gas after passing the adsorption column was detected by gas chromatograph. The results are shown in Figs. 2 to 5.

The adsorption and decarbonization effect of modified activated carbon samples on simulated biogas was better than that of unmodified activated carbon. When the modification time was the same, the decarbonization effect of activated carbon on biogas was first enhanced and then weakened with the increase of ammonia concentration in the range of 6 to 15% mass fraction. Taking jujube shell charcoal soaked in ammonia water for 4 h under ultrasonic oscillation conditions as an example, the modified sample showed the best decarbonization effect on biogas when the ammonia water concentration was 12%, and the CH₄ content in biogas increased from 60% to 89.2%. After the unmodified sample adsorbs and decarbonizes biogas, the CH₄ content in biogas was only 73.6%.

When the concentration of the modifier was the same, as the modification time increased, the effect of activated carbon on biogas decarbonization also first increased and then it deteriorated. Taking coconut shell charcoal soaked in 9% ammonia water under ultrasonic oscillation conditions as an example, after 10 h of modification, the sample showed the highest decarbonization effect on biogas. The CH₄ content in biogas increased from 60% to 87.3%, while the unmodified sample adsorbed and decarbonized biogas, resulting in a CH₄ content of 75.5%.

The experimental data also showed that when the ammonia concentration was 15% and the modification time was 10 h, the decarbonization effect of coconut shell charcoal and jujube shell charcoal on simulated biogas was not as good as that of unmodified activated carbon. This is due to the fact that high modifier concentration and long modification time can cause damage to the pore structure of activated carbon, which is irreversible. The pore collapses, the pore is blocked, and the pore volume and specific surface area of the micropores decrease, resulting in poor adsorption and decarbonization effect (Ma et al. 2022).

Fig. 2. Adsorption and separation of CO₂ by biogas from jujube shell carbon treated with ammonia impregnation and ultrasonic oscillation

Fig. 3. Adsorption and separation of CO₂ by biogas from coconut shell carbon treated with ammonia impregnation and ultrasonic oscillation

Fig. 4. Adsorption and separation of CO₂ from biogas by ammonia modified jujube shell carbon

Fig. 5. Adsorption and separation of CO₂ from biogas by ammonia modified coconut shell carbon

When the ammonia concentration was 6% and the modification time was 4 h, the decarbonization effect of coconut shell charcoal and jujube shell charcoal on biogas was not ideal. This may be due to the short modification time, which leads to incomplete physical adsorption, or it may be due to the low ammonia concentration, which introduces fewer alkaline functional groups on the surface of activated carbon during the modification process and weak chemical adsorption. By comparing and analyzing the Fourier transform infrared spectra, it was found that the functional group absorption peak of jujube shell activated carbon was significantly stronger than other conditions at an ammonia concentration of 12% and an ultrasonic immersion time of 4 h, and the stretching vibration of carbonyl and O-H bonds was stronger; Coconut shell activated carbon exhibited strong absorption peaks of functional groups, especially the stretching vibration of O-H groups in hydroxyl groups, when the ammonia concentration is 9% and the ultrasonic immersion time was 10 h. The higher specific surface area can be expected to enhance the adsorption capacity of the mixture, but it is not conducive to gas separation. That is, the adsorption capacity of activated carbon for methane was also enhanced, reducing the adsorption selectivity of modified activated carbon.

Sample Functional Group Analysis

Activated carbon adsorption can be divided into physical adsorption and chemical adsorption. The surface of activated carbon can be rich in functional groups, including oxygen containing functional groups and nitrogen containing functional groups, such as carboxyl, hydroxyl, carbonyl, lactone, aldehyde, ether, lactam, pyridinamide, etc. (Li 2018). These functional groups play an important role in the adsorption of activated carbon. Generally speaking, the acid groups in oxygen containing functional groups have strong affinity for polar substances, Alkaline groups have a strong affinity for non-polar substances (Lei 2013).

The modified jujube shell carbon and coconut shell carbon were detected by FTIR spectrum. Several groups of samples with better CO₂/CH₄ separation effect after modification were selected. The infrared spectra are shown in Figs. 6 and 7.

The absorbance peaks of functional groups of unmodified activated carbon were small and weak, while the modified activated carbon exhibited a strong absorbance peak between 3480 and 3270 cm^-1, which is due to the hydrogen bond generated by O-H groups in the alcohol hydroxyl group and phenolic hydroxyl group, and the O-H group is stretched and vibrated to form a peak with a wide spectral band. At the same time, the stretching vibration of N-H enhances this peak, because the wave number range of both is roughly the same (Shafeeyan et al. 2011). The absorbance peak at 1100 to 1000 cm^-1 is the stretching vibration of the C-O bond, the absorbance peak at 1125 to 1110 cm^-1 is the C-O-C antisymmetric stretching vibration of the ether, the absorbance peak at 1180 to 1160 cm^-1 is the stretching vibration of C-N, and the peak at 1280 to 1150 cm^-1 may be caused by the stretching vibration of C-OH in phenols. The absorbance peak at 850 to 780 cm^-1 is related to the C-H group at the edge of the Simple aromatic ring. The absorbance peak at 1730 to 1630 cm^-1 is the stretching vibration of quinone carbonyl and ester carbonyl C=O, and there may also be the presence of lactone groups. The stretching vibration of carbonyl C=O in carboxylic acids may occur in the range 1760 to 1660 cm^-1 (Dizbay-Onat et al. 2018).

The absorbance peak of ammonia modified activated carbon in the range of this wave number in the figure is significantly weakened. The reason is that ammonia reacts with the acidic functional groups on the surface of activated carbon, resulting in a decrease in the number of acidic functional groups, such as carbonyl C=O in carboxylic acid, which indicates that ammonia modification can change the number of functional groups on the surface of activated carbon.

Fig. 6. Functional group analysis of jujube shell activated carbon

Fig. 7. Functional group analysis of coconut shell activated carbon

After modification with ammonia solution, the surface of activated carbon has more alkaline functional groups, which can enhance the adsorption and separation effect of CH₄ and CO₂. From Figure 6, it can be seen that as the modification time increases, the absorbance peak of functional groups gradually weakens, which is particularly evident at 3480 to 3270 cm^-1, which may be due to the excessive reaction time leading to the collapse of activated carbon pores, the destruction of pore structure, and a decrease in the number of surface functional groups.

Analysis of Structural Properties of Samples

Raman spectroscopy is now considered to be a very important technical means to characterize the relationship between the structure and properties of carbon materials. For carbon materials, the most studied are peak D and peak G, which are located at 1300 and 1560 cm^-1, respectively, where peak D represents SP³ (disordered carbon) and peak G represents SP² (graphitic carbon). There are many different types of defects in carbon materials, such as holes and cracks, etc. Peak D reflects the degree of irregularity of the crystal, peak G represents the degree of regularity of the crystal, and their ratio I_D/I_G reflects the degree of disorder of the crystal structure. The greater the ratio, the lower the degree of graphitization. Conversely, the smaller the ratio, the more regular crystal structure, the higher the degree of graphitization (Schuepfer et al. 2020). In this experiment, the wavelength of excitation light source was selected to be 532 mm, and the wave number range was 2000 to 500 cm^-1. The spectra of date shell activated carbon and coconut shell activated carbon detected by Raman spectroscopy are shown in Figs. 8 and 9.

Fig. 8. Raman spectrum analysis of jujube shell activated carbon

The I_D/I_G of unmodified date shell carbon was 6.240, and the I_D/I_G of unmodified coconut shell carbon was 3.152. The I_D/I_G value of the unmodified sample was greater than that of similar modified samples for both date shell carbon and coconut shell carbon, indicating that the modification process increases the regular crystal structure of activated carbon and enhances the degree of graphitization of activated carbon. Compared with the two activated carbons, the I_D/I_G value of coconut shell activated carbon is small on the whole, and the graphitization degree is higher. Among them, the sample AC4 has the highest graphitization degree, and the I_D/I_G is 2.036. It also has the best adsorption effect on CO₂ in biogas, and the CH₄ content after adsorption was 87.3%.

Fig. 9. Raman spectrum analysis of coconut shell activated carbon

Analysis of Specific Surface Area and Pore Size

The pore structure parameters of activated carbon before and after modification are shown in Table 2. The pore size distribution of the optimized sample of modified activated carbon is shown in Figs. 10 and 11.

Table 2. Pore Structure Parameters of Activated Carbon Before and After Modification

The adsorption performance of activated carbon materials depends on their pore structure, especially micropores and mesopores. From Table 2, it can be seen that the average pore size of coconut shell carbon was less than 2 nm. Combined with the pore size distribution map of coconut shell carbon, the proportion of micropores was the highest at about 0.7 nm, indicating that coconut shell carbon contained a very rich amount of micropores. The pore size of jujube shell charcoal was slightly larger than that of coconut shell charcoal, with the largest proportion of micropores at about 1 nm, and jujube shell charcoal with relatively small specific surface area had a larger pore size.

Fig. 10. Pore size distribution of jujube shell activated carbon optimal sample

Fig. 11. Pore size distribution of coconut shell activated carbon optimal sample

The two samples with the best adsorption and separation performance for CO₂/CH₄: coconut shell carbon sample AC4 had a specific surface area of 395 m²/g, an average pore size of 1.57 nm, a total pore volume of 0.178 cm³/g, and a microporous volume of 0.175 cm³/g; The specific surface area of jujube shell charcoal sample AC6 was 75.2 m²/g, with an average pore size of 8.50 nm, a total pore volume of 0.0372 cm³/g, and a microporous volume of 0.0355 cm³/g. Overall, after modification with ammonia water, the specific surface area and total pore volume of activated carbon decrease, the average pore size increases, and the number of mesopores increases. CO₂ is a subcritical gas, and molecular condensation occurs in larger pores, resulting in an increase in CO₂ adsorption capacity (Li 2013). The decrease in the total pore volume of the specific surface area may be due to the excessive generation of oxygen-containing and nitrogen-containing groups, which block some narrow micropores. AC4 and AC6 are the samples with the smallest specific surface area in coconut shell charcoal and jujube shell charcoal, respectively, possibly due to the highest amount of alkaline functional groups generated after modification.

CONCLUSIONS

1. After being modified by ammonia immersion and ultrasonic oscillation, activated carbon exhibited the presence of N-containing functional groups, resulting in an increase in surface alkaline functional groups and a decrease in acidic functional groups. The modification enhanced the adsorption of non-polar substances and enhanced the adsorption and separation effect of CO₂ and CH₄.
2. The ultrasonic oscillation modification treatment with ammonia immersion resulted in an increase in the regular crystal structure and enhanced graphitization degree in the fruit shell activated carbon. The maximum I_D/I_G value of the experimental sample was 2.04.
3. After being modified with 6% to 15% ammonia water for 4 to 10 h, the specific surface area and total pore volume of activated carbon in the experiment decreased, while the average pore size increased. Among them, the coconut shell carbon sample AC4 with the best adsorption and separation effect for CO₂ and CH₄ in biogas had a specific surface area of 395 m²/g, an average pore size of 1.57 nm, a total pore volume of 0.178 cm³/g, and a microporous volume of 0.175 cm³/g. The specific surface area of jujube shell charcoal sample AC6 was 75.2 m²/g, with an average pore size of 8.50 nm, a total pore volume of 0.0372 cm³/g, and a microporous volume of 0.0355 cm³/g.
4. In the experiment of activated carbon samples adsorbing and decarbonizing biogas, the sample modified with 12% ammonia solution for 4 h in an ultrasonic oscillation environment showed the best adsorption and decarbonization effect, increasing the CH₄ content in simulated biogas from 60% to 89.2%. Compared with unmodified fruit shell carbon, it increased by 15.6%, with a unit adsorption capacity of 1.83 mmol/g and an increase of 0.8 mmol/g compared to unmodified samples; Coconut shell carbon showed the best adsorption and decarbonization effect in an ultrasonic oscillation environment after being modified with a concentration of 9% ammonia solution for 10 h, resulting in an increase in CH₄ content in simulated biogas from 60% to 87.29%. Compared with unmodified coconut shell carbon, it increased by 11.8%, with a unit adsorption capacity of 1.74 mmol/g and an increase of 0.599 mmol/g compared to unmodified samples.

ACKNOWLEDGMENTS

The authors are grateful for the support of the Henan Province science and technology research project 222102320290.

REFERENCES CITED

Dilokekunakul, W., Teerachawanwong, P., Klomkliang, N., Supasitmongkol, S., and Chaemchuen, S. (2020). “Effects of nitrogen and oxygen functional groups and pore width of activated carbon on carbon dioxide capture: Temperature dependence,” Chemical Engineering Journal 389, article 124413. DOI: 10.1016/j.cej.2020.124413

Dizbay-Onat, M., Vaidya, U. K., Balanay, J. A. G., and Lungu, C. T. (2018). “Preparation and characterization of flax, hemp and sisal fiber-derived mesoporous activated carbon adsorbents,” Adsorption science & technology 36, 441-457. DOI: 10.1177/0263617417700635

Ipeaiyeda, A. R., Choudhary, M. I., and Ahmed, S. (2020). “Ammonia and ammonium acetate modifications and characterisation of activated carbons from palm kernel shell and coconut shell,” Waste and Biomass Valorization 11, 983-993 DOI: 10.1007/s12649-018-0414-7

Lei, C. (2013). Normalized Experimental Study on Surface Structure and Functional Groups of Activated Carbon, Ph.D. Dissertation, Huazhong University of Science and Technology, Wuhan.

Li, F. R. (2013). Study on Adsorption and Separation of CO₂/CH₄ on Microwave Activated Carbon, Ph.D. Dissertation, Kunming University of Science and Technology, Kunming.

Li, Y. R. (2018). Preparation, In-situ Modification, and Adsorption Mechanism of Antibiotics and Heavy Metals on Cattail Activated Carbon, Ph.D. Dissertation, Shandong University, Qingdao, PR China.

Liu, Y. Y., and Wilcox, J. (2012). “Effects of surface heterogeneity on the adsorption of CO₂ in microporous carbons,” Environmental Science and Technology 46(03), 1940-1947. DOI: 10.1021/es204071g

Ma, J. Y., Liu, Y., Chen, S., Du, Y. J., and Wu, H. F. (2022). “Changes in the pore structure of modified sludge-activated carbon and its effect on the adsorption characteristics of CO₂ under high pressure,” Microporous and Mesoporous Materials 345, article 112255. DOI: 10.1016/j.micromeso.2022.112255

Petrobic, B., Gorbounov, M., and Soltan, S. M. (2021). “Influence of surface modification on selective CO₂ adsorption: A technical review on mechanisms and methods,” Microporous and Mesoporous Materials 312, 2-3. DOI: 10.1016/j.micromeso.2020.110751

Sanchez, S. Á., Suarez, G. F., Martinez, A. A., and Tascon, J. M. D. (2014). “Influence of porous texture and surface chemistry on the CO₂ adsorption capacity of porous carbons: Acidic and basic site interactions,” ACS Applied Materials & Interfaces 6(23), 21237-21247. DOI: 10.1021/am506176e

Schuepfer, D. B., Badaczewski, F., Guerra-Castro, J. M., Hofmann, D. M., Heiliger, C., Smarsly, B., and Klar, P. J. (2020). “Assessing the structural properties of graphitic and non-graphitic carbons by Raman spectroscopy,” Carbon 161, 359-372. DOI: 10.1016/j.carbon.2019.12.094

Shafeeyan, M. S., Daud, W. M. A. W., Houshamand, A., and Niya, A. A. (2011). “Ammonia modification of activated carbon to enhance carbon dioxide adsorption: Effect of pre-oxidation,” Applied Surface Science 257, 3936-3942. DOI: 10.1016/j.apsusc.2010.11.127

Zhang, Z. B., Liu, X. Y., Li, D. W., Lei, Y. Q., Gao, T. T., Wu, B. G., Zhao, J.W., Wang, Y. K., Zhou, G. Y., and Yao, H. M. (2019). “Mechanism of ultrasonic impregnation on porosity of activated carbons in non-cavitation and cavitation regimes,” Ultrasonics Sonochemistry 51, 206-213. DOI: 10.1016/j.ultsonch.2018.10.024

Zhang, Z. J., Xu, M. Y., Wang, H. H., Li, Z. (2010). “Enhancement of CO₂ adsorption on high surface area activated carbon modified by N₂, H₂ and ammonia,” Chemical Engineering Journal 160(2), 571-577. DOI: 10.1016/j.cej.2010.03.070.

Zheng, J., Qiao, J. L., and Lin, Z. F. (2019). “Progress in modification and adsorption of activated carbon,” Modern Chemical Industry 39(S1), 53-57. DOI: 10.16606/j.cnki.issn0253-4320. 2019. S. 012

Article submitted: September 11, 2023; Peer review completed: October 28, 2023; Revised version received and accepted: October 31, 2023; Published: November 10, 2023.

DOI: 10.15376/biores.19.1.195-209