Comparative Analysis of the Efficiencies of Two Low Cost Adsorbents for Carbon Dioxide Capture

Comparative Analysis of the Efficiencies of Two Low Cost Adsorbents for Carbon Dioxide Capture | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Comparative Analysis of the Efficiencies of Two Low Cost Adsorbents for Carbon Dioxide Capture Romana Khan, Sayyaf Yousaf, Haris Abdullah Noor, Muhammad Wajid Ullah, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4372373/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 09 Jul, 2025 Read the published version in International Journal of Environmental Research → Version 1 posted 5 You are reading this latest preprint version Abstract Global warming, climate change and associated threats have motivated research to look for cost effective adsorbents for Carbon dioxide (CO 2 ) capture at source. This study focused on CO 2 adsorption using a polymer- and a mineral-based adsorbent (chitosan and zeolite, respectively) modified with monoethanolamine (MEA). Chitosan beads were prepared by insolubilisation in NaOH whereas hollow zeolites were prepared by hydrothermal synthesis. Both adsorbents were successfully impregnated with MEA in different weight percent. Various physicochemical properties were studied using X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), and Fourier Transform Infrared spectroscopic (FTIR) techniques confirming the successful formation of the designed adsorbents. Both the sorbents were studied for CO 2 adsorption from a simulated flue gas mixture comprising nitrogen and CO 2 using a fixed-bed flow reactor. Observations showed that the CO 2 adsorption capacity enhanced with amine loading for both the adsorbents. The adsorbents were found to be very active and promising, and the maximum adsorption found was 19 mg/g of modified chitosan. Compared to hollow zeolites, the modified chitosan beads showed better adsorption. The stability of the adsorbents was tested and observed that the same material can be recycled for three adsorption-desorption cycles and no significant change in CO 2 adsorption capabilities. Global warming Greenhouse gases CO2 adsorption CO2 capture Polymer and mineral based adsorbents Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction The conviction that the world is warming because of a human-enhanced greenhouse effect has been backed up by current scientific observations (Demiral et al., 2021 ; Ozturk et al., 2022 ). The planet's average temperature increased by 0.6 to 0.9°C annually between 1906 and 2006. This change is linked with the enhanced emission of carbon dioxide (CO 2 ) which is considered a major anthropogenic greenhouse gas (GHG) after which methane, nitrous oxide, and water vapors also belong to the same group. The global monitoring reported that the average concentration of CO 2 was 338.8 ppmv in 1980 which increased to 405.02 ppmv in 2018 (Vorokhta et al., 2019 ). Undoubtedly, CO 2 levels are higher than in at least the past 800,000 years (Ramirez et al., 2019 ). CO 2 emission results from human activities such as the combustion of carbon-based fuels (e.g., oil, natural gas, and coal), soil erosion, animal agriculture, deforestation, etc. (Lin & Raza, 2020 ). Furthermore, the Intergovernmental Panel on Climate Change (IPCC) investigated that CO 2 concentration will increase up to 570 ppmv, consequently increasing the global mean temperature by 2°C, which will cause a 3 m increase in sea level (Yaumi et al., 2017 ) and other major environmental changes (such as melting of glaciers and increasing ocean acidity) by the year 2100. In the year 2010, the energy sector alone contributed about 68% of global GHGs emissions to the atmosphere (Lamb et al., 2021 ). An unceasing increase in its concentration in the air is of great concern to the scientific community due to its environmental impacts (Modak & Jana, 2019 ). This significant environmental concern motivated researchers and governments in the direction of the development of more efficient carbon capture techniques (Morales-Ospino et al., 2020 ; Yaumi et al., 2017 ). Carbon capture and storage (CCS) technologies are designed to capture, transport, and store CO 2 . Post-combustion CO 2 capture technology is the most easily adaptable of the currently known technologies to existing emission sources (Lee & Park, 2015 ). Among these methods, the preparation of sorbent material and adsorption technique is one of the best choices and has proven to be inexpensive and practical, owing to its easy and cheap process (Alkayal et al., 2022 ; Ibrahim et al., 2022 ). Wet/dry sorbents are used to segregate gases and collect CO 2 via a sorption/desorption process (Zhang et al., 2010 ). Each adsorption technique (wet or dry) possesses its benefits and shortcomings. Wet adsorption needs high energy and suffers from erosion and sluggish solid-to-gas reaction while it can treat large volumes of combustion emissions (Ben-Mansour et al., 2016 ). Dry adsorption possesses a high level of environmental and energy efficiency and requires only a basic device, yet it does not perform well for huge quantities of emissions and has a low separation efficiency (Kim et al., 2016 ). The most appropriate adsorbents should have the ability to capture CO 2 from a gas stream with fast kinetics, selectivity, resilience, and an excellent adsorption capacity (Tan et al., 2015 ; Wang et al., 2015 ). It is almost impossible to find adsorbent with all the above stated qualities however, it is optimistic that the properties of adsorbents could be altered with small quantities of other materials, which makes composites adsorbents. These composites are expected to perform well compared to the parent material. A study of such materials’ efficiency under identical experimental conditions will help in selecting and comparing different adsorbents. Chitosan (CS) is a biological waste product that is a main derivative of chitin, the second most prevalent natural polysaccharide after cellulose on the earth. Chitin is a -(1–4)-linked 2-acetamido-deoxy-d-glucose (N-acetyl glucosamine) that is structurally like cellulose except for the acetamide groups in the C-2 position, which in cellulose are replaced by hydroxyl groups. CS has several advantages, including easy availability, low cost, renewability, lower energy consumption, environmentally friendly nature, non-toxicity, biocompatibility, and biodegradability (Irani et al., 2017 ). Given the acidic nature of CO 2 and the basic nature of the nitrogen-containing polymer, will eventually lead to acid-base interaction between acidic CO 2 molecules and the basic site of CS polymer. CS has been utilized to generate functional derivatives by chemical modification, graft reaction, and ionic contact to increase its adsorption efficiency. The name zeolite refers to a tetrahedrally coordinated network of atoms (Abdullahi et al., 2017 ). The zeolites are aluminosilicates with a microporous crystalline structure that occur naturally and/or are synthesized. Two essential structural components make up the Zeolite framework: aluminum or silicon atoms linked to four oxygen atoms to produce a tetrahedral shape, and an oxygen atom coupled to two tetrahedral atoms (usually bent 145°) (Busca, 2014 ). Aluminum (Al) present in zeolites induces a negative charge that is compensated by exchangeable cations (often alkali) in the pore spaces. These alkali cations cause zeolites to adsorb acidic gases such as CO 2 (Spigarelli & Kawatra, 2013 ). Zeolite-based adsorbents are divided into various categories based on their pore size, including zeolite A, zeolite X, zeolite Y, ZSM-5, zeolite P, etc. (Sodha et al., 2022 ). Hollow zeolites (HZ) are a form of hierarchical zeolites with a low density and large surface area, as well as a changeable shell thickness and macropores in the core of the particles. Because of their great thermal stability, homogeneous structure of porosity, and good performance in mass transfer, these materials have garnered a lot of attention (Zhang & Che, 2019 ). Compared to hierarchical zeolites or ordinary nanocrystals, they offer numerous advantages, such as a crystalline structure that outperforms amorphous silica analogs in terms of hydrothermal and chemical stability, and a system of micropores functioning like a shape-selective membrane. Furthermore, their characteristics may be continually adjusted by altering the composition, notably the aluminum framework (Pagis et al., 2016 ). The advantages of the amine-modified adsorbents are all the same other than that they are less expensive and can reduce the amount of energy required for regeneration, improve adsorption capability, CO 2 selectivity, corrosion resistance, and cause minimal pollution to the environment (Fashi et al., 2019 ; Pagis et al., 2016 ; Wang et al., 2019 ). In the present study, two classes of adsorbents i.e. polymer-based chitosan and mineral-based zeolite both modified with monoethanolamine (MEA), have been developed and compared to study CO 2 adsorption capacity of these adsorbents under similar reaction conditions. The amines are known to possess an affinity for CO 2 and hence are selected to enhance the selectivity of adsorbents. An amine solution has higher capture selectivity to CO 2 than other gases and it is not affected strongly by the CO 2 partial pressure. This study will be helpful to compare the performance of MEA-modified chitosan beads and hollow zeolites as promising CO 2 adsorbents evaluated under similar conditions. 2. Materials and Methods 2.1. Materials All reagents used in this study were analytical grade and utilized without purifying them any further. Sodium hydroxide (NaOH), Aluminium isopropoxide (C 9 H 21 O 3 Al), Monoethanolamine (MEA), Methanol, Chitosan powder, Acetic acid, and Sodium dodecyl sulphate, Tetra-n-propylammonium Bromide (C 12 H 28 BrN) from Qingdao BZ Oligo Biotech Co, Ltd., Tetraethyl-orthosilicate from DAEJUNG. CO 2 cylinder and N 2 Cylinder were used as a source of CO 2 and N 2 and purchased from local vendors. 2.2. Preparation of Adsorbents 2.2.1. Preparation of Chitosan Beads Chitosan solution was prepared by dissolving 3.5 grams of chitosan powder in 5% acetic acid solution (50 mL). The mixture was then stirred for 3 hours on a magnetic stirrer until the complete dissolution of chitosan powder. The chitosan solution was added dropwise into a solution of sodium hydroxide and sodium dodecyl sulphate under slow stirring conditions (Zhao et al., 2020). Chitosan beads thus formed are thoroughly washed with distilled water several times until the pH of the filtrate turned neutral. 2.2.2. Preparation of Modified Chitosan Beads MEA was added in the formation stage of chitosan beads that is in chitosan solution. The MEA were added in 1 wt %, 2 wt%, and 3 wt% to be designated as CA1, CA2, and CA3, respectively. The remaining procedure was the same as described in the previous section. 2.2.3. Crosslinking of Chitosan Beads For crosslinking of chitosan microspheres, 30 ml methanol was taken to which chitosan microspheres were added and stirred for 15 min. Then 0.5 ml of glutaraldehyde was added as a crosslinker and stirred for 30 min. After that, 0.5 ml glutaraldehyde was added again and stirred for 30 min. Finally, 1 ml of glutaraldehyde was added to the mixture and stirred for another 1 h. After the completion of the reaction, microspheres were filtered, washed with deionized water, placed in open-air to dry, and then stored in a clean container. 2.2.4. Synthesis of Hollow Zeolite The preparation of microspheres of hollow zeolite (HZ-S5) was carried out by a facile hydrothermal method. In the synthesis procedure sodium hydroxide 0.09 g and Aluminum Isopropoxide (Al[O-CH(CH 3 ) 2 ] 3 0.082 g, were dissolved in 7.20 g of distilled water with vigorous magnetic stirring for 30 min. A templating agent such as tetra-n-propylammonium Bromide (TPABr) 3.20 g was added to the above solution and stirred for one hour till homogenized. Following the thorough dissolution, 1.66 g of Tetraethyl-orthosilicate (TEOS) was added dropwise to the above homogeneous solution. This resulted in a molar composition of 30 TPABr: 20 SiO 2 : 0.5 Al 2 O 3 : 5.7 NaOH: 1000 H 2 O. The resulting mixture was stirred sturdily in an oil bath at 60°C for 12 hours to obtain a homogeneous gel. The gel thus formed was transferred to a Teflon-lined stainless-steel autoclave and heated on a hotplate at 90 ℃ for 24 h with the stirring condition. After 24 h heating, the autoclave was placed in an oven at 140 ℃ for 45 h. It was taken out and allowed to cool. The product thus obtained was filtered and washed several times with distilled water to reduce pH to 7 and then dried overnight at 90°C. All synthesized adsorbents were calcined at 550°C for 8 h to remove organic components. 2.2.5. Synthesis of Hollow Zeolite-Amines (HZA) Composites Wet-impregnation method was performed for amine-based modifications of hollow zeolites (HZA) according to the literature (Didas et al., 2012 ; Rezaei & Jones, 2013 ) with different amine concentrations using MEA as an amine source. Briefly, the HZ sample was degassed at 250°C overnight. Then 1 ml of MEA was dissolved in 5 ml methanol at room temperature. After stirring methanol and amine solution for an hour, HZ was added to a liquid (amine). The amines were added as 1 wt %, 2 wt %, and 3 wt % designated as HZA1, HZA2, and HZA3, respectively. The adsorbent was then dried for 8 h at 110 ℃ under nitrogen flow to eliminate the solution phase. 2.3. Characterization The crystallinity of the prepared materials was determined by the powder XRD diffractometer (Model: JDX3532 JEOL Japan), which was equipped with Cu-Ka radiation, where the signal background was eliminated. The surface morphology of the samples was determined through scanning electron microscopy (Model: JEOL JSM 5910).Particle size was determined by the dynamic light scattering (DLS) method for zeolites. FTIR spectra were recorded with a Perkin Elmer FTIR spectrophotometer (Spectrum GX & Autoimage, USA) with spectral range 4000–400 cm − 1 ; beam splitter Ge coated on KBr; detector DTGS; and resolution 0.25 cm − 1 . The CO 2 concentration was determined using a CO 2 meter (model: AZ- 7755), at 303 K under constant gas flow. 2.4. Adsorption Set-up and CO 2 Measurement The experimental setup for the CO 2 capture reactor is shown in the schematic diagram (Fig. 1 ). The experimental set-up consists of a Pyrex glass adsorbent reactor 12 cm x 2.5 cm and a Pyrex glass mixing chamber 80 mm x 20 mm connected by silicon tubing of 0.5 cm inner diameter. Adsorbents are placed in the reactor mixed with silica sand while the mixing chamber is to mix CO 2 and N 2 gas to attain the desired concentration of CO 2 . The CO 2 and N 2 sources were gas cylinders with a controlled flowmeter. The CO 2 meter was used to calculate the gas flow at the inlet and outlet. The setup was calibrated and carefully observed to ensure no leakage. The adsorption properties of adsorbents were measured on 303 K. In the process, the CO 2 and N 2 were introduced in the mixing chamber at the ratio of 1:3 and then allowed to enter the reactor containing the adsorbent with a flow rate of 0.6 L/min. The prepared sorbent was degassed at 150°C before the adsorption experiment. Before adsorption, feed gas was designed to bypass the reactor with the adsorbent. Capture was initiated by switching the feed gas to the reactor with the help of valves. A CO 2 analyzer was used to calculate the incoming and outgoing gas properties. The setup was calibrated with an empty tank, and to observe and eliminate leakages. First, the N 2 was permitted to flow through the reactor for the adsorption process and then was followed by CO 2 and N 2 mixture. The chitosan beads were air dried and then mixed with the silica sand in a ratio of 1:4 and a total of 5 g mixture was added to the glass column. In a typical adsorption study, N 2 and CO 2 gases are allowed to enter the mixing chamber in a ratio of 3:1. After stabilizing the CO 2 concentration, the gas from the mixing chamber is allowed to enter the adsorption column. The decrease in concentration with time was carefully noted. The experiment was repeated thrice to get constant results. The stability of the adsorbents was studied by using the same material after degassing for three consecutive cycles. 3. Results and Discussion 3.1. Physicochemical Characterization of the Adsorbents The XRD graphs of pristine and MEA modified chitosan bead are shown in Fig. 2 a. Chitosan membrane patterns showed two characteristic broad diffraction peaks at 2θ = 10° and 20° which are typical fingerprints for semi-crystalline chitosan (Madni et al., 2019 ). In all modified samples no sharp peak for MEA was observed. This is because as compared to chitosan, the amount of amine was very low. The location of their reflection line remained constant indicating that the structure was well preserved even with the different loading of MEA. It is observed that the introduction of MEA improves the crystallinity of the chitosan. Depending on the interaction a dopant can enhance the crystalline phase of the parent material and vice versa. The XRD results showed that the reflection line of both HZ and modified HZA well resolved, and the location of their reflection line remained constant indicating that the structure was well preserved even with the different loading of MEA. Comparison of HZ and HZA3 was presented in characterization data. A micrograph of HZ and HZA3 is displayed in Fig. 2 b showing high purity and high crystalline phase. HZ has diffraction peaks at 2θ = 7.9°, 8.8°, 20.85°, 23.5°, and 23.85° positions which represent 443, 328, 116, 457, and 246 planes, respectively. The results agreed with the literature (Kumar et al., 2020 ; Wang et al., 2015 ) revealing all the characteristic peaks of the zeolites were replicated confirming the successful formation of hollow zeolites. Nevertheless, the crystalline hollow zeolitic structure remained nearly intact, which suggests that the impregnation procedure did not affect the crystal framework structure of the other impregnated samples of HZA. However contrary to Chitosan the modification reduced the crystallinity of HZ and more amorphous phase may have been resulted. It was also observed that the in the hydrothermal synthesis, temperature and time are have a crucial effect on the structure of the hollow zeolite. At the lowest synthesis temperature (100–130°C), all the samples remain in the amorphous state. When the synthesis temperature was increased to 140°C, the formation of hollow zeolite occurred in the crystalline structure, and crystallinity was 73% as calculated from the peaks and total area of the XRD graph. The formation of a hollow zeolite was amorphous at lower temperatures, the reason is TPABr which acts as a structure-directing agent of the hollow zeolite and requires appropriate temperature (Yaumi et al., 2017 ). Scanning Electron Microscopy (SEM) is used to analyze the morphology of chitosan polymeric materials as well as their surface characteristics as displayed in Fig. 3 . SEM micrographs revealed that the shape of the chitosan beads is roughly spherical (Fig. 3 a-h). In order to compare pristine chitosan with MEA modified chitosan the images of same magnification have been selected so that Fig. 3 a can be compared with Fig. 3 e and so on. The surface is rough and porous. Both micro and macro pores are visible on the surface of pristine chitosan microbead Fig. 3 (a-d). All modified compositions containing amine depicted slight change in surface morphology as well as porosity Fig. 3 (e-h). The results of SEM analysis of chitosan beads and modified chitosan beads ranged from roughly 800 mm to 950 mm. To study the size and surface morphology, both HZ and HZA3 nanoparticles were examined through SEM. SEM analysis depicted roughly spherical morphology in the typical images of the HZ and HZA3 as shown in Fig. 4 . Figures of same resolution of HZ and HZA3 are placed for comparison. The surface seems smooth and only slightly aggregated. The samples appear to be mesoporous. The average crystal size of the nanoparticles was found 712 nm. Further, the morphology of the obtained hollow zeolite particles was found to be like that of zeolites prepared from other sources (Wang et al., 2015 ). The SEM images further confirmed the successful synthesis of our desired sorbent. The modified HZ size was found to be smaller which is also clear by Fig. 4 a and 4 e comparison. It may be due to phase change from crystalline to amorphous in MEA modified zeolites as shown by XRD analysis Fig. 2These slight changes between HZ and HZA3 (Fig. 4 ) confirmed that the MEA was loaded successfully. The size reduction was also confirmed by Dynamic Light Scattering (DLS) and the results are shown in Fig. 5 . It was observed that HZ and modified HZ particle size distribution ranged between 615–955 nm with a size of 712 nm exhibited by the maximum particles that are 45.4% while, for modified hollow zeolite it ranged between 615–712 nm exhibited by about 67.5% particles. The FTIR spectrum of simple chitosan (Fig. 6 ) represented by C showed stretching vibrations of OH, NH, and CH groups that appeared at 3100–3400 and 2900– 3000 cm –1 , respectively. Figure 6 showed characteristic peaks of chitosan at 1100, 1360, 1470, and 1680 cm –1 due to C–O ether linkage, bending vibration of CH 3 and CH 2 and stretching vibration of amide carbonyl groups (Madni et al., 2019 ). The C-O stretching vibration was confirmed by the band at 1096 cm -1 . The peak of 1634 cm -1 is due to bending (H-O-H) water, while the peak of 3409 cm -1 is due to O-H stretching. Chitosan's spectra showed a broad band at 3356cm -1 , which is due to the presence of hydroxyl/amine groups in the chitosan. C-H groups in chitosan are shown by the peak at 2925cm -1 and 2853cm -1 . NH and C = O stretch caused the bands at 1589 and 1652cm -1 . The antisymmetric stretching of the C–O–C Bridge can be seen in the band at 1150cm -1 . The peak at 1020cm -1 is caused by the C-O stretching vibration. The peak at 1643 cm -1 indicated that C = N is produced because of crosslinking with glutaraldehyde. The same peaks were identified for modified chitosan with amine; however, due to changes in surface chemistry in modified samples, a little shift in frequency was observed. MEA have been included in the chitosan, as seen by the shift. 3.2 Adsorption Studies The breakthrough curves were produced as shown in Fig. 7 to estimate the CO 2 capture capacity of prepared adsorbents and details are presented in Table 1 . It is observed that as compared to pure chitosan and hollow zeolite sorbents, their composites showed almost 2–3 times better adsorption efficiency. It appeared that the amine doping on porous adsorbents favored CO 2 capture. The affinity of amine toward CO 2 capture is known for some time and it is believed to follow either the zwitterions mechanism or the termolecular mechanism (Chen et al., 2021 ). Zwitterions mechanism summarized carbamate formation, bicarbonate formation, and carbamate reversion as the key steps that result in the formation of Zwitterion species (CO 2 + RNH 2 ↔ RNH 2 + CO 2 - ). The termolecular mechanism suggests that amine reacts with CO 2 and a base at the same time and forms a complex. That trend is also observed in the present study with adsorbents and their composites. Among different amine groups, literature suggested MEA is the best in terms of CO 2 capture efficiency possibly due to the presence of hydroxyl groups, which possess the capability to form a hydrogen bond with CO 2 (Luis, 2016 ). Between chitosan and hollow zeolite, it is observed that the performance of chitosan was slightly better. Both the adsorbents are roughly spherical in shape and porous in nature. The difference in surface chemistry may be due to surface adsorbed groups and the mode of adsorption. In the case of chitosan composites, the role of single-walled carbon nanotubes can’t be overlooked. These are attached to chitosan through one end while the other end forms a dandling appearance and as MEA is attached to them hence, they are more exposed to approaching CO 2 gas. Composites show stability when recycled up to three cycles of use. Table 1 Breakthrough curve and CO 2 capture capacity of prepared adsorbents Adsorbents Breakthrough time (min) CO 2 capture capacity (mg/g) CS 8.5 12.24 CA1 10.5 15.12 CA2 11.5 17 CA3 13 19 HZ 5.2 7.5 HZA1 7.7 11 HZA2 8.2 12 HZA3 9.2 13 4. Conclusions In this study, the CO 2 capturing efficiency of a polymer- and a mineral-based adsorbent (chitosan and zeolite, respectively) modified with monoethanolamine (MEA) was assessed and compared. Chitosan beads were prepared and modified with amine in different amounts for the first time to study CO 2 adsorption. Hollow zeolite-based sorbents were successfully produced using a hydrothermal technique and then the sorbent was doped using MEA. The characterization studies (XRD and SEM analysis) confirmed the formation of the designed material. CO 2 adsorption was studied from a simulated flue gas mixture comprising nitrogen and carbon dioxide using a fixed-bed flow reactor. The results showed that the composites exhibit better adsorption performance compared to pure parent sorbents. Between chitosan and hollow zeolite composites, the former was found better. Among the prepared adsorbents, all show significant affinity to adsorb CO 2 but CA3 was found to have better efficiency with an adsorption capacity of 19 mg/g. The shape of beads and the combination of Chitosan-MEA has influenced the adsorption ability of the adsorbent. The adsorbents could be successfully used for the adsorption of CO 2 , they are easy to synthesize and are cost-effective. This study showed that the newly developed sorbents can be used for CO 2 capture applications. A detailed adsorption study with different parameters such as temperature and CO 2 pressure is recommended for further implications. Declarations Compliance with Ethical Standards Funding: This research was funded by the Pakistan Science Foundation with Grant number PSF-MSRT II/PHY/KP-COMSATS-ABT (16). Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results. Acknowledgments: Authors are grateful to the Environmental Sciences Laboratory of COMSATS University Islamabad, Abbottabad Campus for providing the materials, equipment and space used in this study. 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Spigarelli BP, Kawatra SK (2013) Opportunities and challenges in carbon dioxide capture. Journal of CO 2 Utilization 1: 69-87. doi: https://doi.org/10.1016/j.jcou.2013.03.002 Tan LS, Shariff AM, Lau KK, Bustam MA (2015) Impact of high pressure on high concentration carbon dioxide capture from natural gas by monoethanolamine/N-methyl-2-pyrrolidone solvent in absorption packed column. International Journal of Greenhouse Gas Control 34:25-30. doi: https://doi.org/10.1016/j.ijggc.2014.12.020 Vorokhta M, Morávková J, Řimnáčová, D, Pilař R, Zhigunov A, Švábová M, Sazama P (2019) CO 2 capture using three-dimensionally ordered micromesoporous carbon. Journal of CO 2 Utilization, 31:124-134. doi: https://doi.org/10.1016/j.jcou.2019.03.001 Wang X, Guo Q, Kong T (2015) Tetraethylenepentamine-modified MCM-41/silica gel with hierarchical mesoporous structure for CO 2 capture. Chemical Engineering Journal 273:472-480. doi: https://doi.org/10.1016/j.cej.2015.03.098 Wang X, Zeng W, Song M, Wang F, Hu X, Guo Q, Liu Y (2019) Polyetheramine improves the CO 2 adsorption behavior of tetraethylenepentamine-functionalized sorbents. Chemical Engineering Journal 364:475-484. doi: https://doi.org/10.1016/j.cej.2019.02.008 Yaumi AL, Bakar MZA, Hameed BH (2017) Recent advances in functionalized composite solid materials for carbon dioxide capture. Energy 124:461-480. doi: https://doi.org/10.1016/j.energy.2017.02.053 Zhang L, Liu H, Li X, Xie S, Wang Y, Xin W, . . . Xu L (2010) Differences between ZSM-5 and ZSM-11 zeolite catalysts in 1-hexene aromatization and isomerization. Fuel Processing Technology 91(5):449-455. doi: https://doi.org/10.1016/j.fuproc.2009.12.003 Zhang Y, Che S (2019) One-Pot Synthesis and Formation Mechanism of Hollow ZSM-5. Chemistry – A European Journal 25(24):6196-6202. doi: https://doi.org/10.1002/chem.201900193 Supplementary Files Highlights.docx Cite Share Download PDF Status: Published Journal Publication published 09 Jul, 2025 Read the published version in International Journal of Environmental Research → Version 1 posted Editorial decision: Major revisions 17 Jul, 2024 Reviewers agreed at journal 02 Jun, 2024 Reviewers invited by journal 08 May, 2024 Editor assigned by journal 06 May, 2024 First submitted to journal 05 May, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4372373","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":300080595,"identity":"fcc03a88-0892-420b-b649-1d6500df4bb4","order_by":0,"name":"Romana Khan","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABA0lEQVRIiWNgGAWjYPCChAQGBuYDDAwGQDaQkmCAMAlpYUsAqZMgRQsPWBFhLebt3YmfC2rS8vhn93z8zFNgV8d3gPngbR6GO8a4tMicObtZesaxnGKJO0AGj0GyhOQBtmRrHoZnZri0SEjkbpDmYatIbLiRu42Zx4BZwuAAj5k0D8NhGzxaNv/m+VeROP9GzjOglnqgFv5vhLRsk+Zty0nccCOHDajlMMgWNpAW3A7jObvNmrcvLXHjjTRjyTkGxyVnHmYztpxj8Ayn9yXYezff5vmWnDjvRvLDD2/+VPPzHW9+eONNxR3DBlx6MAEziDA4QLwGGCBDyygYBaNgFAxXAABCeFVL8cbXSgAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0003-2760-0914","institution":"COMSATS University Islamabad - Abbottabad Campus","correspondingAuthor":true,"prefix":"","firstName":"Romana","middleName":"","lastName":"Khan","suffix":""},{"id":300080596,"identity":"fe55b418-fca9-4ae2-89ce-5abfe92ef43e","order_by":1,"name":"Sayyaf Yousaf","email":"","orcid":"","institution":"COMSATS University Islamabad - Abbottabad Campus","correspondingAuthor":false,"prefix":"","firstName":"Sayyaf","middleName":"","lastName":"Yousaf","suffix":""},{"id":300080597,"identity":"7c8c45f2-6dbc-469b-8f43-c6c168e294b9","order_by":2,"name":"Haris Abdullah Noor","email":"","orcid":"","institution":"COMSATS University Islamabad - Abbottabad Campus","correspondingAuthor":false,"prefix":"","firstName":"Haris","middleName":"Abdullah","lastName":"Noor","suffix":""},{"id":300080598,"identity":"0ffd17e1-a624-4d60-bc02-89d0eecda306","order_by":3,"name":"Muhammad Wajid Ullah","email":"","orcid":"","institution":"Jiangsu University","correspondingAuthor":false,"prefix":"","firstName":"Muhammad","middleName":"Wajid","lastName":"Ullah","suffix":""},{"id":300080599,"identity":"ef2f5c7e-0ceb-40e6-9f66-8074917f27f7","order_by":4,"name":"Alireza Noorpoor","email":"","orcid":"","institution":"University of Tehran","correspondingAuthor":false,"prefix":"","firstName":"Alireza","middleName":"","lastName":"Noorpoor","suffix":""},{"id":300080600,"identity":"b855041a-0c17-4744-981c-4c01c55ecd01","order_by":5,"name":"Adnan Ahmad Tahir","email":"","orcid":"","institution":"COMSATS University Islamabad - Abbottabad Campus","correspondingAuthor":false,"prefix":"","firstName":"Adnan","middleName":"Ahmad","lastName":"Tahir","suffix":""},{"id":300080601,"identity":"5aab7607-d454-497d-9898-1dd5aecbde8b","order_by":6,"name":"Maria Siddique","email":"","orcid":"","institution":"COMSATS University Islamabad - Abbottabad Campus","correspondingAuthor":false,"prefix":"","firstName":"Maria","middleName":"","lastName":"Siddique","suffix":""}],"badges":[],"createdAt":"2024-05-05 15:52:02","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4372373/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4372373/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s41742-025-00833-4","type":"published","date":"2025-07-09T15:57:24+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":56620221,"identity":"04b814a5-2051-4402-927e-175ec9a0fcc7","added_by":"auto","created_at":"2024-05-16 17:51:58","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":39002,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of adsorption set-up.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4372373/v1/b0da7a1eee00fe9f97a44771.png"},{"id":56620228,"identity":"c1cb38c4-cae1-481b-b410-47c8965e2818","added_by":"auto","created_at":"2024-05-16 17:51:59","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":180209,"visible":true,"origin":"","legend":"\u003cp\u003eXRD analysis of (a) Chitosan and modified chitosan, and (b) Hollow zeolite, HZ and amine modified hollow zeolite, HZA3.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4372373/v1/68abfab5bf31b387c7b38eae.jpg"},{"id":56620226,"identity":"5f0a12d2-ef8e-4a65-83a3-b98748d4e638","added_by":"auto","created_at":"2024-05-16 17:51:59","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":512648,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of (\u003cstrong\u003ea\u003c/strong\u003e) CS (a-d), (\u003cstrong\u003eb\u003c/strong\u003e) CA3 (e-f).\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4372373/v1/17af8e4acae6ee49a07e92fa.jpg"},{"id":56620225,"identity":"c838e343-f55b-4d1e-b567-24902e99c6b4","added_by":"auto","created_at":"2024-05-16 17:51:59","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":380124,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of (\u003cstrong\u003ea\u003c/strong\u003e) HZ (a-d), and (\u003cstrong\u003eb\u003c/strong\u003e) HZA3 (e-f).\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4372373/v1/dd40982702149798be7245f4.jpg"},{"id":56620223,"identity":"23c0e327-c5d2-43ed-b78c-f997ab89c90b","added_by":"auto","created_at":"2024-05-16 17:51:59","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":253975,"visible":true,"origin":"","legend":"\u003cp\u003eParticle size distribution of (\u003cstrong\u003ea\u003c/strong\u003e) HZ, and (\u003cstrong\u003eb\u003c/strong\u003e) HZA3\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4372373/v1/963bcbb0fd75ead9dff58826.jpg"},{"id":56620227,"identity":"f72f02b4-b7ad-4d90-97cb-45e30b52a437","added_by":"auto","created_at":"2024-05-16 17:51:59","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":176834,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR results of chitosan and modified chitosan.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4372373/v1/5fc2c264588e40bfbba58dde.jpg"},{"id":56620229,"identity":"fc1e4f1c-f404-48a3-bc2c-3c3eee7b61b8","added_by":"auto","created_at":"2024-05-16 17:51:59","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":185663,"visible":true,"origin":"","legend":"\u003cp\u003eBreakthrough curves of prepared adsorbents (a) chitosan and modified chitosan composites, and (b) HZ and modified HZA composites\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4372373/v1/4021f3fa96230759d8467c9e.jpg"},{"id":86700111,"identity":"8251d871-2bb4-48b5-a1dc-9910eb349b66","added_by":"auto","created_at":"2025-07-14 16:11:44","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2433485,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4372373/v1/79ef09f9-7323-475d-af15-47e225e88b90.pdf"},{"id":56620222,"identity":"e3ae7b0e-1a13-442b-95ed-e48e0b6d64b6","added_by":"auto","created_at":"2024-05-16 17:51:58","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":14383,"visible":true,"origin":"","legend":"","description":"","filename":"Highlights.docx","url":"https://assets-eu.researchsquare.com/files/rs-4372373/v1/bb9f3daaaca2fdce78adfdab.docx"}],"financialInterests":"","formattedTitle":"Comparative Analysis of the Efficiencies of Two Low Cost Adsorbents for Carbon Dioxide Capture","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe conviction that the world is warming because of a human-enhanced greenhouse effect has been backed up by current scientific observations (Demiral et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Ozturk et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The planet's average temperature increased by 0.6 to 0.9\u0026deg;C annually between 1906 and 2006. This change is linked with the enhanced emission of carbon dioxide (CO\u003csub\u003e2\u003c/sub\u003e) which is considered a major anthropogenic greenhouse gas (GHG) after which methane, nitrous oxide, and water vapors also belong to the same group. The global monitoring reported that the average concentration of CO\u003csub\u003e2\u003c/sub\u003e was 338.8 ppmv in 1980 which increased to 405.02 ppmv in 2018 (Vorokhta et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Undoubtedly, CO\u003csub\u003e2\u003c/sub\u003e levels are higher than in at least the past 800,000 years (Ramirez et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). CO\u003csub\u003e2\u003c/sub\u003e emission results from human activities such as the combustion of carbon-based fuels (e.g., oil, natural gas, and coal), soil erosion, animal agriculture, deforestation, etc. (Lin \u0026amp; Raza, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Furthermore, the Intergovernmental Panel on Climate Change (IPCC) investigated that CO\u003csub\u003e2\u003c/sub\u003e concentration will increase up to 570 ppmv, consequently increasing the global mean temperature by 2\u0026deg;C, which will cause a 3 m increase in sea level (Yaumi et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) and other major environmental changes (such as melting of glaciers and increasing ocean acidity) by the year 2100. In the year 2010, the energy sector alone contributed about 68% of global GHGs emissions to the atmosphere (Lamb et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). An unceasing increase in its concentration in the air is of great concern to the scientific community due to its environmental impacts (Modak \u0026amp; Jana, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThis significant environmental concern motivated researchers and governments in the direction of the development of more efficient carbon capture techniques (Morales-Ospino et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Yaumi et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Carbon capture and storage (CCS) technologies are designed to capture, transport, and store CO\u003csub\u003e2\u003c/sub\u003e. Post-combustion CO\u003csub\u003e2\u003c/sub\u003e capture technology is the most easily adaptable of the currently known technologies to existing emission sources (Lee \u0026amp; Park, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Among these methods, the preparation of sorbent material and adsorption technique is one of the best choices and has proven to be inexpensive and practical, owing to its easy and cheap process (Alkayal et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Ibrahim et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWet/dry sorbents are used to segregate gases and collect CO\u003csub\u003e2\u003c/sub\u003e via a sorption/desorption process (Zhang et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Each adsorption technique (wet or dry) possesses its benefits and shortcomings. Wet adsorption needs high energy and suffers from erosion and sluggish solid-to-gas reaction while it can treat large volumes of combustion emissions (Ben-Mansour et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Dry adsorption possesses a high level of environmental and energy efficiency and requires only a basic device, yet it does not perform well for huge quantities of emissions and has a low separation efficiency (Kim et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The most appropriate adsorbents should have the ability to capture CO\u003csub\u003e2\u003c/sub\u003e from a gas stream with fast kinetics, selectivity, resilience, and an excellent adsorption capacity (Tan et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). It is almost impossible to find adsorbent with all the above stated qualities however, it is optimistic that the properties of adsorbents could be altered with small quantities of other materials, which makes composites adsorbents. These composites are expected to perform well compared to the parent material. A study of such materials\u0026rsquo; efficiency under identical experimental conditions will help in selecting and comparing different adsorbents.\u003c/p\u003e \u003cp\u003eChitosan (CS) is a biological waste product that is a main derivative of chitin, the second most prevalent natural polysaccharide after cellulose on the earth. Chitin is a -(1\u0026ndash;4)-linked 2-acetamido-deoxy-d-glucose (N-acetyl glucosamine) that is structurally like cellulose except for the acetamide groups in the C-2 position, which in cellulose are replaced by hydroxyl groups. CS has several advantages, including easy availability, low cost, renewability, lower energy consumption, environmentally friendly nature, non-toxicity, biocompatibility, and biodegradability (Irani et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Given the acidic nature of CO\u003csub\u003e2\u003c/sub\u003e and the basic nature of the nitrogen-containing polymer, will eventually lead to acid-base interaction between acidic CO\u003csub\u003e2\u003c/sub\u003e molecules and the basic site of CS polymer. CS has been utilized to generate functional derivatives by chemical modification, graft reaction, and ionic contact to increase its adsorption efficiency.\u003c/p\u003e \u003cp\u003eThe name zeolite refers to a tetrahedrally coordinated network of atoms (Abdullahi et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The zeolites are aluminosilicates with a microporous crystalline structure that occur naturally and/or are synthesized. Two essential structural components make up the Zeolite framework: aluminum or silicon atoms linked to four oxygen atoms to produce a tetrahedral shape, and an oxygen atom coupled to two tetrahedral atoms (usually bent 145\u0026deg;) (Busca, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Aluminum (Al) present in zeolites induces a negative charge that is compensated by exchangeable cations (often alkali) in the pore spaces. These alkali cations cause zeolites to adsorb acidic gases such as CO\u003csub\u003e2\u003c/sub\u003e (Spigarelli \u0026amp; Kawatra, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Zeolite-based adsorbents are divided into various categories based on their pore size, including zeolite A, zeolite X, zeolite Y, ZSM-5, zeolite P, etc. (Sodha et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Hollow zeolites (HZ) are a form of hierarchical zeolites with a low density and large surface area, as well as a changeable shell thickness and macropores in the core of the particles. Because of their great thermal stability, homogeneous structure of porosity, and good performance in mass transfer, these materials have garnered a lot of attention (Zhang \u0026amp; Che, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Compared to hierarchical zeolites or ordinary nanocrystals, they offer numerous advantages, such as a crystalline structure that outperforms amorphous silica analogs in terms of hydrothermal and chemical stability, and a system of micropores functioning like a shape-selective membrane. Furthermore, their characteristics may be continually adjusted by altering the composition, notably the aluminum framework (Pagis et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The advantages of the amine-modified adsorbents are all the same other than that they are less expensive and can reduce the amount of energy required for regeneration, improve adsorption capability, CO\u003csub\u003e2\u003c/sub\u003e selectivity, corrosion resistance, and cause minimal pollution to the environment (Fashi et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Pagis et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the present study, two classes of adsorbents i.e. polymer-based chitosan and mineral-based zeolite both modified with monoethanolamine (MEA), have been developed and compared to study CO\u003csub\u003e2\u003c/sub\u003e adsorption capacity of these adsorbents under similar reaction conditions. The amines are known to possess an affinity for CO\u003csub\u003e2\u003c/sub\u003e and hence are selected to enhance the selectivity of adsorbents. An amine solution has higher capture selectivity to CO\u003csub\u003e2\u003c/sub\u003e than other gases and it is not affected strongly by the CO\u003csub\u003e2\u003c/sub\u003e partial pressure. This study will be helpful to compare the performance of MEA-modified chitosan beads and hollow zeolites as promising CO\u003csub\u003e2\u003c/sub\u003e adsorbents evaluated under similar conditions.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n\u003ch2\u003e2.1. Materials\u003c/h2\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eAll reagents used in this study were analytical grade and utilized without purifying them any further. Sodium hydroxide (NaOH), Aluminium isopropoxide (C\u003csub\u003e9\u003c/sub\u003eH\u003csub\u003e21\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003eAl), Monoethanolamine (MEA), Methanol, Chitosan powder, Acetic acid, and Sodium dodecyl sulphate, Tetra-n-propylammonium Bromide (C\u003csub\u003e12\u003c/sub\u003eH\u003csub\u003e28\u003c/sub\u003eBrN) from Qingdao BZ Oligo Biotech Co, Ltd., Tetraethyl-orthosilicate from DAEJUNG. CO\u003csub\u003e2\u003c/sub\u003e cylinder and N\u003csub\u003e2\u003c/sub\u003e Cylinder were used as a source of CO\u003csub\u003e2\u003c/sub\u003e and N\u003csub\u003e2\u003c/sub\u003e and purchased from local vendors.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n\u003ch2\u003e2.2. Preparation of Adsorbents\u003c/h2\u003e\n\u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\n\u003ch2\u003e2.2.1. Preparation of Chitosan Beads\u003c/h2\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eChitosan solution was prepared by dissolving 3.5 grams of chitosan powder in 5% acetic acid solution (50 mL). The mixture was then stirred for 3 hours on a magnetic stirrer until the complete dissolution of chitosan powder. The chitosan solution was added dropwise into a solution of sodium hydroxide and sodium dodecyl sulphate under slow stirring conditions (Zhao et al., 2020). Chitosan beads thus formed are thoroughly washed with distilled water several times until the pH of the filtrate turned neutral.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\n\u003ch2\u003e2.2.2. Preparation of Modified Chitosan Beads\u003c/h2\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eMEA was added in the formation stage of chitosan beads that is in chitosan solution. The MEA were added in 1 wt %, 2 wt%, and 3 wt% to be designated as CA1, CA2, and CA3, respectively. The remaining procedure was the same as described in the previous section.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\n\u003ch2\u003e2.2.3. Crosslinking of Chitosan Beads\u003c/h2\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eFor crosslinking of chitosan microspheres, 30 ml methanol was taken to which chitosan microspheres were added and stirred for 15 min. Then 0.5 ml of glutaraldehyde was added as a crosslinker and stirred for 30 min. After that, 0.5 ml glutaraldehyde was added again and stirred for 30 min. Finally, 1 ml of glutaraldehyde was added to the mixture and stirred for another 1 h. After the completion of the reaction, microspheres were filtered, washed with deionized water, placed in open-air to dry, and then stored in a clean container.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\n\u003ch2\u003e2.2.4. Synthesis of Hollow Zeolite\u003c/h2\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eThe preparation of microspheres of hollow zeolite (HZ-S5) was carried out by a facile hydrothermal method. In the synthesis procedure sodium hydroxide 0.09 g and Aluminum Isopropoxide (Al[O-CH(CH\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e]\u003csub\u003e3\u003c/sub\u003e 0.082 g, were dissolved in 7.20 g of distilled water with vigorous magnetic stirring for 30 min. A templating agent such as tetra-n-propylammonium Bromide (TPABr) 3.20 g was added to the above solution and stirred for one hour till homogenized. Following the thorough dissolution, 1.66 g of Tetraethyl-orthosilicate (TEOS) was added dropwise to the above homogeneous solution. This resulted in a molar composition of 30 TPABr: 20 SiO\u003csub\u003e2\u003c/sub\u003e: 0.5 Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e: 5.7 NaOH: 1000 H\u003csub\u003e2\u003c/sub\u003eO. The resulting mixture was stirred sturdily in an oil bath at 60\u0026deg;C for 12 hours to obtain a homogeneous gel. The gel thus formed was transferred to a Teflon-lined stainless-steel autoclave and heated on a hotplate at 90 \u003cem\u003e℃\u003c/em\u003e for 24 h with the stirring condition. After 24 h heating, the autoclave was placed in an oven at 140 \u003cem\u003e℃\u003c/em\u003e for 45 h. It was taken out and allowed to cool. The product thus obtained was filtered and washed several times with distilled water to reduce pH to 7 and then dried overnight at 90\u0026deg;C. All synthesized adsorbents were calcined at 550\u0026deg;C for 8 h to remove organic components.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\n\u003ch2\u003e2.2.5. Synthesis of Hollow Zeolite-Amines (HZA) Composites\u003c/h2\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eWet-impregnation method was performed for amine-based modifications of hollow zeolites (HZA) according to the literature (Didas et al., \u003cspan class=\"CitationRef\"\u003e2012\u003c/span\u003e; Rezaei \u0026amp; Jones, \u003cspan class=\"CitationRef\"\u003e2013\u003c/span\u003e) with different amine concentrations using MEA as an amine source. Briefly, the HZ sample was degassed at 250\u0026deg;C overnight. Then 1 ml of MEA was dissolved in 5 ml methanol at room temperature. After stirring methanol and amine solution for an hour, HZ was added to a liquid (amine). The amines were added as 1 wt %, 2 wt %, and 3 wt % designated as HZA1, HZA2, and HZA3, respectively. The adsorbent was then dried for 8 h at 110 ℃ under nitrogen flow to eliminate the solution phase.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n\u003ch2\u003e2.3. Characterization\u003c/h2\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eThe crystallinity of the prepared materials was determined by the powder XRD diffractometer (Model: JDX3532 JEOL Japan), which was equipped with Cu-Ka radiation, where the signal background was eliminated. The surface morphology of the samples was determined through scanning electron microscopy (Model: JEOL JSM 5910).Particle size was determined by the dynamic light scattering (DLS) method for zeolites. FTIR spectra were recorded with a Perkin Elmer FTIR spectrophotometer (Spectrum GX \u0026amp; Autoimage, USA) with spectral range 4000\u0026ndash;400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e; beam splitter Ge coated on KBr; detector DTGS; and resolution 0.25 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The CO\u003csub\u003e2\u003c/sub\u003e concentration was determined using a CO\u003csub\u003e2\u003c/sub\u003e meter (model: AZ- 7755), at 303 K under constant gas flow.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n\u003ch2\u003e2.4. Adsorption Set-up and CO\u003csub\u003e2\u003c/sub\u003e Measurement\u003c/h2\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eThe experimental setup for the CO\u003csub\u003e2\u003c/sub\u003e capture reactor is shown in the schematic diagram (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). The experimental set-up consists of a Pyrex glass adsorbent reactor 12 cm x 2.5 cm and a Pyrex glass mixing chamber 80 mm x 20 mm connected by silicon tubing of 0.5 cm inner diameter. Adsorbents are placed in the reactor mixed with silica sand while the mixing chamber is to mix CO\u003csub\u003e2\u003c/sub\u003e and N\u003csub\u003e2\u003c/sub\u003e gas to attain the desired concentration of CO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003eThe CO\u003csub\u003e2\u003c/sub\u003e and N\u003csub\u003e2\u003c/sub\u003e sources were gas cylinders with a controlled flowmeter. The CO\u003csub\u003e2\u003c/sub\u003e meter was used to calculate the gas flow at the inlet and outlet. The setup was calibrated and carefully observed to ensure no leakage. The adsorption properties of adsorbents were measured on 303 K. In the process, the CO\u003csub\u003e2\u003c/sub\u003e and N\u003csub\u003e2\u003c/sub\u003e were introduced in the mixing chamber at the ratio of 1:3 and then allowed to enter the reactor containing the adsorbent with a flow rate of 0.6 L/min. The prepared sorbent was degassed at 150\u0026deg;C before the adsorption experiment.\u003c/p\u003e\n\u003cp\u003eBefore adsorption, feed gas was designed to bypass the reactor with the adsorbent. Capture was initiated by switching the feed gas to the reactor with the help of valves. A CO\u003csub\u003e2\u003c/sub\u003e analyzer was used to calculate the incoming and outgoing gas properties. The setup was calibrated with an empty tank, and to observe and eliminate leakages. First, the N\u003csub\u003e2\u003c/sub\u003e was permitted to flow through the reactor for the adsorption process and then was followed by CO\u003csub\u003e2\u003c/sub\u003e and N\u003csub\u003e2\u003c/sub\u003e mixture.\u003c/p\u003e\n\u003cp\u003eThe chitosan beads were air dried and then mixed with the silica sand in a ratio of 1:4 and a total of 5 g mixture was added to the glass column. In a typical adsorption study, N\u003csub\u003e2\u003c/sub\u003e and CO\u003csub\u003e2\u003c/sub\u003e gases are allowed to enter the mixing chamber in a ratio of 3:1. After stabilizing the CO\u003csub\u003e2\u003c/sub\u003e concentration, the gas from the mixing chamber is allowed to enter the adsorption column. The decrease in concentration with time was carefully noted. The experiment was repeated thrice to get constant results. The stability of the adsorbents was studied by using the same material after degassing for three consecutive cycles.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n\u003ch2\u003e3.1. Physicochemical Characterization of the Adsorbents\u003c/h2\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eThe XRD graphs of pristine and MEA modified chitosan bead are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea. Chitosan membrane patterns showed two characteristic broad diffraction peaks at 2\u0026theta;\u0026thinsp;=\u0026thinsp;10\u0026deg; and 20\u0026deg; which are typical fingerprints for semi-crystalline chitosan (Madni et al., \u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e). In all modified samples no sharp peak for MEA was observed. This is because as compared to chitosan, the amount of amine was very low. The location of their reflection line remained constant indicating that the structure was well preserved even with the different loading of MEA. It is observed that the introduction of MEA improves the crystallinity of the chitosan. Depending on the interaction a dopant can enhance the crystalline phase of the parent material and vice versa.\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003eThe XRD results showed that the reflection line of both HZ and modified HZA well resolved, and the location of their reflection line remained constant indicating that the structure was well preserved even with the different loading of MEA. Comparison of HZ and HZA3 was presented in characterization data. A micrograph of HZ and HZA3 is displayed in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb showing high purity and high crystalline phase. HZ has diffraction peaks at 2\u0026theta;\u0026thinsp;=\u0026thinsp;7.9\u0026deg;, 8.8\u0026deg;, 20.85\u0026deg;, 23.5\u0026deg;, and 23.85\u0026deg; positions which represent 443, 328, 116, 457, and 246 planes, respectively. The results agreed with the literature (Kumar et al., \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e; Wang et al., \u003cspan class=\"CitationRef\"\u003e2015\u003c/span\u003e) revealing all the characteristic peaks of the zeolites were replicated confirming the successful formation of hollow zeolites. Nevertheless, the crystalline hollow zeolitic structure remained nearly intact, which suggests that the impregnation procedure did not affect the crystal framework structure of the other impregnated samples of HZA. However contrary to Chitosan the modification reduced the crystallinity of HZ and more amorphous phase may have been resulted. It was also observed that the in the hydrothermal synthesis, temperature and time are have a crucial effect on the structure of the hollow zeolite. At the lowest synthesis temperature (100\u0026ndash;130\u0026deg;C), all the samples remain in the amorphous state. When the synthesis temperature was increased to 140\u0026deg;C, the formation of hollow zeolite occurred in the crystalline structure, and crystallinity was 73% as calculated from the peaks and total area of the XRD graph. The formation of a hollow zeolite was amorphous at lower temperatures, the reason is TPABr which acts as a structure-directing agent of the hollow zeolite and requires appropriate temperature (Yaumi et al., \u003cspan class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eScanning Electron Microscopy (SEM) is used to analyze the morphology of chitosan polymeric materials as well as their surface characteristics as displayed in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. SEM micrographs revealed that the shape of the chitosan beads is roughly spherical (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea-h). In order to compare pristine chitosan with MEA modified chitosan the images of same magnification have been selected so that Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea can be compared with Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ee and so on. The surface is rough and porous. Both micro and macro pores are visible on the surface of pristine chitosan microbead Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e (a-d). All modified compositions containing amine depicted slight change in surface morphology as well as porosity Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e (e-h). The results of SEM analysis of chitosan beads and modified chitosan beads ranged from roughly 800 mm to 950 mm.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eTo study the size and surface morphology, both HZ and HZA3 nanoparticles were examined through SEM. SEM analysis depicted roughly spherical morphology in the typical images of the HZ and HZA3 as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. Figures of same resolution of HZ and HZA3 are placed for comparison. The surface seems smooth and only slightly aggregated. The samples appear to be mesoporous. The average crystal size of the nanoparticles was found 712 nm.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eFurther, the morphology of the obtained hollow zeolite particles was found to be like that of zeolites prepared from other sources (Wang et al., \u003cspan class=\"CitationRef\"\u003e2015\u003c/span\u003e). The SEM images further confirmed the successful synthesis of our desired sorbent. The modified HZ size was found to be smaller which is also clear by Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea and \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ee comparison. It may be due to phase change from crystalline to amorphous in MEA modified zeolites as shown by XRD analysis Fig.\u0026nbsp;2These slight changes between HZ and HZA3 (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e) confirmed that the MEA was loaded successfully.\u003c/p\u003e\n\u003cp\u003eThe size reduction was also confirmed by Dynamic Light Scattering (DLS) and the results are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e. It was observed that HZ and modified HZ particle size distribution ranged between 615\u0026ndash;955 nm with a size of 712 nm exhibited by the maximum particles that are 45.4% while, for modified hollow zeolite it ranged between 615\u0026ndash;712 nm exhibited by about 67.5% particles.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eThe FTIR spectrum of simple chitosan (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e) represented by C showed stretching vibrations of OH, NH, and CH groups that appeared at 3100\u0026ndash;3400 and 2900\u0026ndash; 3000 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e, respectively. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e showed characteristic peaks of chitosan at 1100, 1360, 1470, and 1680 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e due to C\u0026ndash;O ether linkage, bending vibration of CH\u003csub\u003e3\u003c/sub\u003e and CH\u003csub\u003e2\u003c/sub\u003e and stretching vibration of amide carbonyl groups (Madni et al., \u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e). The C-O stretching vibration was confirmed by the band at 1096 cm\u003csup\u003e-1\u003c/sup\u003e. The peak of 1634 cm\u003csup\u003e-1\u003c/sup\u003e is due to bending (H-O-H) water, while the peak of 3409 cm\u003csup\u003e-1\u003c/sup\u003e is due to O-H stretching. Chitosan's spectra showed a broad band at 3356cm\u003csup\u003e-1\u003c/sup\u003e, which is due to the presence of hydroxyl/amine groups in the chitosan. C-H groups in chitosan are shown by the peak at 2925cm\u003csup\u003e-1\u003c/sup\u003e and 2853cm\u003csup\u003e-1\u003c/sup\u003e. NH and C\u0026thinsp;=\u0026thinsp;O stretch caused the bands at 1589 and 1652cm\u003csup\u003e-1\u003c/sup\u003e. The antisymmetric stretching of the C\u0026ndash;O\u0026ndash;C Bridge can be seen in the band at 1150cm\u003csup\u003e-1\u003c/sup\u003e. The peak at 1020cm\u003csup\u003e-1\u003c/sup\u003e is caused by the C-O stretching vibration. The peak at 1643 cm\u003csup\u003e-1\u003c/sup\u003e indicated that C\u0026thinsp;=\u0026thinsp;N is produced because of crosslinking with glutaraldehyde. The same peaks were identified for modified chitosan with amine; however, due to changes in surface chemistry in modified samples, a little shift in frequency was observed. MEA have been included in the chitosan, as seen by the shift.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n\u003ch2\u003e3.2 Adsorption Studies\u003c/h2\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eThe breakthrough curves were produced as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e to estimate the CO\u003csub\u003e2\u003c/sub\u003e capture capacity of prepared adsorbents and details are presented in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. It is observed that as compared to pure chitosan and hollow zeolite sorbents, their composites showed almost 2\u0026ndash;3 times better adsorption efficiency. It appeared that the amine doping on porous adsorbents favored CO\u003csub\u003e2\u003c/sub\u003e capture. The affinity of amine toward CO\u003csub\u003e2\u003c/sub\u003e capture is known for some time and it is believed to follow either the zwitterions mechanism or the termolecular mechanism (Chen et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e). Zwitterions mechanism summarized carbamate formation, bicarbonate formation, and carbamate reversion as the key steps that result in the formation of Zwitterion species (CO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;RNH\u003csub\u003e2\u003c/sub\u003e \u0026harr; RNH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e CO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e). The termolecular mechanism suggests that amine reacts with CO\u003csub\u003e2\u003c/sub\u003e and a base at the same time and forms a complex. That trend is also observed in the present study with adsorbents and their composites. Among different amine groups, literature suggested MEA is the best in terms of CO\u003csub\u003e2\u003c/sub\u003e capture efficiency possibly due to the presence of hydroxyl groups, which possess the capability to form a hydrogen bond with CO\u003csub\u003e2\u003c/sub\u003e (Luis, \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e). Between chitosan and hollow zeolite, it is observed that the performance of chitosan was slightly better. Both the adsorbents are roughly spherical in shape and porous in nature. The difference in surface chemistry may be due to surface adsorbed groups and the mode of adsorption. In the case of chitosan composites, the role of single-walled carbon nanotubes can\u0026rsquo;t be overlooked. These are attached to chitosan through one end while the other end forms a dandling appearance and as MEA is attached to them hence, they are more exposed to approaching CO\u003csub\u003e2\u003c/sub\u003e gas. Composites show stability when recycled up to three cycles of use.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab1\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eBreakthrough curve and CO\u003csub\u003e2\u003c/sub\u003e capture capacity of prepared adsorbents\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eAdsorbents\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eBreakthrough time (min)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eCO\u003csub\u003e2\u003c/sub\u003e capture capacity (mg/g)\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eCS\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e8.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e12.24\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eCA1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e15.12\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eCA2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e11.5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e17\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eCA3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e13\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e19\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eHZ\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e7.5\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eHZA1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e7.7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e11\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eHZA2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e8.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e12\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eHZA3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e9.2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e13\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eIn this study, the CO\u003csub\u003e2\u003c/sub\u003e capturing efficiency of a polymer- and a mineral-based adsorbent (chitosan and zeolite, respectively) modified with monoethanolamine (MEA) was assessed and compared. Chitosan beads were prepared and modified with amine in different amounts for the first time to study CO\u003csub\u003e2\u003c/sub\u003e adsorption. Hollow zeolite-based sorbents were successfully produced using a hydrothermal technique and then the sorbent was doped using MEA. The characterization studies (XRD and SEM analysis) confirmed the formation of the designed material. CO\u003csub\u003e2\u003c/sub\u003e adsorption was studied from a simulated flue gas mixture comprising nitrogen and carbon dioxide using a fixed-bed flow reactor. The results showed that the composites exhibit better adsorption performance compared to pure parent sorbents. Between chitosan and hollow zeolite composites, the former was found better. Among the prepared adsorbents, all show significant affinity to adsorb CO\u003csub\u003e2\u003c/sub\u003e but CA3 was found to have better efficiency with an adsorption capacity of 19 mg/g. The shape of beads and the combination of Chitosan-MEA has influenced the adsorption ability of the adsorbent. The adsorbents could be successfully used for the adsorption of CO\u003csub\u003e2\u003c/sub\u003e, they are easy to synthesize and are cost-effective. This study showed that the newly developed sorbents can be used for CO\u003csub\u003e2\u003c/sub\u003e capture applications. A detailed adsorption study with different parameters such as temperature and CO\u003csub\u003e2\u003c/sub\u003e pressure is recommended for further implications.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eCompliance with Ethical Standards\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e This research was funded by the Pakistan Science Foundation with Grant number PSF-MSRT II/PHY/KP-COMSATS-ABT (16).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest:\u003c/strong\u003e The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments:\u003c/strong\u003e Authors are grateful to the Environmental Sciences Laboratory of COMSATS University Islamabad, Abbottabad Campus for providing the materials, equipment and space used in this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e: The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAbdullahi T, Harun Z, Othman, MHD (2017) A review on sustainable synthesis of zeolite from kaolinite resources via hydrothermal process. 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Fuel Processing Technology 91(5):449-455. doi: https://doi.org/10.1016/j.fuproc.2009.12.003\u003c/li\u003e\n\u003cli\u003eZhang Y, Che S (2019) One-Pot Synthesis and Formation Mechanism of Hollow ZSM-5. Chemistry \u0026ndash; A European Journal 25(24):6196-6202. doi: https://doi.org/10.1002/chem.201900193\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"international-journal-of-environmental-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"IJER","sideBox":"Learn more about [International Journal of Environmental Research](https://www.springer.com/journal/41742)","snPcode":"41742","submissionUrl":"https://www.editorialmanager.com/ijer/default2.asp...\n","title":"International Journal of Environmental Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Global warming, Greenhouse gases, CO2 adsorption, CO2 capture, Polymer and mineral based adsorbents","lastPublishedDoi":"10.21203/rs.3.rs-4372373/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4372373/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eGlobal warming, climate change and associated threats have motivated research to look for cost effective adsorbents for Carbon dioxide (CO\u003csub\u003e2\u003c/sub\u003e) capture at source. This study focused on CO\u003csub\u003e2\u003c/sub\u003e adsorption using a polymer- and a mineral-based adsorbent (chitosan and zeolite, respectively) modified with monoethanolamine (MEA). Chitosan beads were prepared by insolubilisation in NaOH whereas hollow zeolites were prepared by hydrothermal synthesis. Both adsorbents were successfully impregnated with MEA in different weight percent. Various physicochemical properties were studied using X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), and Fourier Transform Infrared spectroscopic (FTIR) techniques confirming the successful formation of the designed adsorbents. Both the sorbents were studied for CO\u003csub\u003e2\u003c/sub\u003e adsorption from a simulated flue gas mixture comprising nitrogen and CO\u003csub\u003e2\u003c/sub\u003e using a fixed-bed flow reactor. Observations showed that the CO\u003csub\u003e2\u003c/sub\u003e adsorption capacity enhanced with amine loading for both the adsorbents. The adsorbents were found to be very active and promising, and the maximum adsorption found was 19 mg/g of modified chitosan. Compared to hollow zeolites, the modified chitosan beads showed better adsorption. The stability of the adsorbents was tested and observed that the same material can be recycled for three adsorption-desorption cycles and no significant change in CO\u003csub\u003e2\u003c/sub\u003e adsorption capabilities.\u003c/p\u003e","manuscriptTitle":"Comparative Analysis of the Efficiencies of Two Low Cost Adsorbents for Carbon Dioxide Capture","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-16 17:51:54","doi":"10.21203/rs.3.rs-4372373/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revisions","date":"2024-07-17T07:16:48+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2024-06-02T06:08:52+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-05-08T08:39:12+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-05-07T02:33:04+00:00","index":"","fulltext":""},{"type":"submitted","content":"International Journal of Environmental Research","date":"2024-05-05T11:51:53+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"international-journal-of-environmental-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"IJER","sideBox":"Learn more about [International Journal of Environmental Research](https://www.springer.com/journal/41742)","snPcode":"41742","submissionUrl":"https://www.editorialmanager.com/ijer/default2.asp...\n","title":"International Journal of Environmental Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"e0afee13-3740-4434-95e5-211745500551","owner":[],"postedDate":"May 16th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-07-14T16:10:12+00:00","versionOfRecord":{"articleIdentity":"rs-4372373","link":"https://doi.org/10.1007/s41742-025-00833-4","journal":{"identity":"international-journal-of-environmental-research","isVorOnly":false,"title":"International Journal of Environmental Research"},"publishedOn":"2025-07-09 15:57:24","publishedOnDateReadable":"July 9th, 2025"},"versionCreatedAt":"2024-05-16 17:51:54","video":"","vorDoi":"10.1007/s41742-025-00833-4","vorDoiUrl":"https://doi.org/10.1007/s41742-025-00833-4","workflowStages":[]},"version":"v1","identity":"rs-4372373","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4372373","identity":"rs-4372373","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}