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DOI: 10.1039/D5NJ02521D (Paper) New J. Chem., 2025, Advance Article

Regular growth of MOF crystals in restricted networks to prepare chitosan/polyvinylpyrrolidone/ZIF-8 gel beads for adsorbing CO2

Tingting Shia, Zongjie Lia, Miao Zhenga, Wen Lia, Wenwen Wua and Naipu He*abc
aSchool of Chemistry and Chemical Engineering, Lanzhou Jiaotong University, Anning Xilu 88#, Lanzhou 730070, P. R. China. E-mail: henaipu@mail.lzjtu.cn
bSchool of Environmental and Municipal Engineering, Lanzhou Jiaotong University, Lanzhou 730070, P. R. China
cGansu Provincial Dust Control and Environmentally Friendly Technology Innovation Center, Lanzhou Jiaotong University, Lanzhou 730070, P. R. China

Received 18th June 2025 , Accepted 4th August 2025

First published on 5th August 2025

Abstract

Chitosan (CS) and polyvinylpyrrolidone (PVP) were crosslinked by glutaraldehyde and Zn2+ to fabricate polymer networks. Subsequently, CS/PVP sols were dropped into an alkaline solution, resulting in deionization of hydrophilic groups and contraction of polymer networks to form CS/PVP beads with restricted networks. ZIF-8 crystals were incubated in restricted networks to prepare ZIF-8@CS/PVP gel beads (CPZxB). The growth of ZIF-8 crystals in the restricted networks showed a more regular morphology. Meanwhile, the size of ZIF-8 crystals in beads was modulated by the molar ratio of 2-MeIM to Zn2+. Specifically, the size of ZIF-8 crystals decreased with an increase in the ratio of 2-MeIM to Zn2+. Additionally, the equilibrium adsorption capacity of beads for CO2 was 3.13 mmol g−1 under an initial pressure of 400 kPa at 288.15 K, and increased by 23% compared to ZIF-8 crystals. The adsorption mechanism was explored using the kinetic model and Langmuir model, and the adsorption thermodynamic parameters were calculated using the van't Hoff equation. The results indicated that the adsorption of CO2 on gel beads primarily depended on chemisorption and was a spontaneous exothermic process. As a result, growing MOF crystals in confined networks can be an effective strategy to obtain more regular morphology.

1. Introduction

Carbon dioxide, a major component of greenhouse gases, is one of the main causes of global warming due to its massive emissions.1 Carbon capture and storage (CCS) technology using liquid solvents or solid adsorbents is considered one of the most promising methods for reducing the concentration of CO2 in the atmosphere.2 In particular, solid adsorbents have attracted increasing attention in recent years due to advantages, such as low cost, high adsorption capacity and easy industrial scale-up.3,4 As solid adsorbents, gel beads have the advantages of uniform size and large specific surface area.5 Additionally, they have excellent thermal stability, low cost and easy separation.6

Solid materials containing amines were important candidates for CO2 adsorbents.7 Chitosan (CS) is a cationic polysaccharide derived from a natural polymer.8,9 Its structure was characterized by the presence of a large number of amino and hydroxyl groups in the main chain, which could enhance the adsorption of carbon dioxide by chitosan.10 However, the use of hydrogels with a single component was limited due to their inadequate mechanical properties, and CS was usually combined with other materials through various methods.11 Polyvinylpyrrolidone (PVP) can be combined with chitosan through cross-linking as it contains a large number of N-containing groups, and can also serve as ideal adsorption sites for CO2.12

Zeolitic imidazolate framework-8 (ZIF-8) is a type of zeolite-like material with a sodalite topology, formed by the coordination self-assembly of metal ions (Zn2+) and 2-methylimidazole (2-MeIM) into a periodic three-dimensional crystalline porous material.13,14 The pore size of ZIF-8 was comparable to the kinetic diameter of CO2 molecules, and 2-MeIM rings were also the locations for CO2 adsorption.15 This was due to the strong hydrogen bonds between imidazole and CO2, involving the –NH– groups, as well as strong intramolecular dispersion π–π stacking interactions.16 Thus, ZIF-8 exhibited excellent adsorption capacity for CO2.17 However, due to their weak mechanical strength, they tended to aggregate and were difficult to recycle, which limited the application of ZIF-8.13,14 Rigid MOF nanocrystals combined with flexible materials such as polymers and gels could enhance the flexibility, recyclability and processability of MOFs.18,19 Generally, the hydroxy groups and amine groups of polymers coordinated with metal ions to anchor MOF crystals on the polymer chains. Additionally, emulsification of amphiphilic polymers directed the in situ growth of MOFs and modulated the morphology and distribution on polymer substrates.20,21

In our previous works, ZIF-8@CS/PVP composite hydrogels were prepared through the in situ growth of ZIF-8 on the polymer networks consisting of amphiphilic polymers chitosan (CS) and polyvinylpyrrolidone (PVP).22 PVP played a key role in guiding the growth of ZIF-8 crystals and preventing the aggregation of ZIF-8 crystals in the network of the CS/PVP hydrogel. The inherent regular shapes were not observed because the MOF crystals were coated with flexible polymer chains.

In the current study, ZIF-8 crystals were grown in restricted networks to control the morphology of nanocrystals. As shown in Scheme 1, chitosan (CS) and polyvinylpyrrolidone (PVP) were firstly crosslinked by glutaraldehyde and Zn2+ to prepare CS/PVP sols with semi-interpenetrating networks. In particular, CS/PVP sols were incubated in an alkaline solution to achieve deionization of hydrophilic groups, resulting in contraction of the polymer networks to form gel beads. Then, MOF crystals were in situ grown in the constrained polymer networks to fabricate ZIF-8@CS/PVP gel beads (CPZxB, where x is the molar ratio of 2-MeIM to Zn2+during preparation). Meanwhile, the effect of the concentration of 2-MeIM on the morphology and distribution of ZIF-8 in the restricted polymer networks was investigated. Furthermore, the adsorption behavior of the adsorbent for CO2 was explored using the adsorption kinetics model and the Langmuir model.


image file: d5nj02521d-s1.tif
Scheme 1 Diagram of the synthesis of ZIF-8@CS/PVP gel beads (CPZxB, where x is the molar ratio of 2-MeIM to Zn2+ during preparation).

2. Experimental

2.1. Materials

Chitosan (CS, deacetylation: 90–95%, viscosity: 50–800 mPa) was purchased from Sangon Biotech. Polyvinylpyrrolidone (PVP, molecular weight: 40[thin space (1/6-em)]000 g mol−1) and acetic acid (AR) were purchased from Beijing Chemical Factory. Sodium hydroxide (AR) and acetic acid (AR) were purchased from Damao Chemical Reagent Factory. Zinc nitrate hexahydrate (AR) was purchased from Sinopharm Group. Dimethylimidazole (AR) was purchased from Aladdin.

2.2. Preparation of ZIF-8@CS/PVP gel beads (CPZxB)

ZIF-8@CS/PVP gel beads (CPZxB, where x is the molar ratio of 2-MeIM to Zn2+ during preparation) were prepared by adjusting the molar ratio of 2-MeIM to Zn2+. Typically, chitosan (CS) solution was prepared by completely dissolving 0.2 g of chitosan powder in 20 mL of 2% acetic acid solution. 2 g of polyvinylpyrrolidone (PVP) was dissolved in 10 mL of distilled water and sonicated to obtain PVP solution. 10 mL of PVP solution and 5 mL of 1% glutaraldehyde solution were added to 20 mL of CS solution with stirring at room temperature for 4 hours. 1.318 g of Zn (NO3)2·6H2O was dissolved in advance in 30 mL of methanol, and added to the CS/PVP mixtures with stirring for 1 hour. The resulting sols were dropped into 1 M NaOH solution to obtain off-white CS/PVP gel beads, which were collected and washed with 300 ml deionized water until the pH of final eluate was close to neutral. 2-MeIM solution was prepared in advance by ultrasonically dissolving 2-MeIM in 30 mL of methanol. The CS/PVP gel beads were immersed in the methanol solution of 2-MeIM with a predetermined concentration at 60 °C for 3 hours. The resulting beads were collected and rinsed with 300 ml deionized water 3 times and dried under vacuum at 100 °C for 24 hours to obtain ZIF-8@CS/PVP gel beads (CPZxB, where x is the molar ratio of 2-MeIM to Zn2+ during preparation) with a diameter of 2 mm (Table 1).
Table 1 Preparation of CPZxB by adjusting the molar ratio of 2-MeIM to Zn2+
CPZxBa Zn2+ (mmol) 2-MeIM[thin space (1/6-em)]:[thin space (1/6-em)]Zn2+ (mol[thin space (1/6-em)]:[thin space (1/6-em)]mol)
a CPZxB (where x is the molar ratio of 2-MeIM to Zn2+ during preparation) was prepared by immersing CS/PVP gel beads in the methanol solution of 2-MeIM and changing the concentration of 2-MeIM.
CPZ4B 4.438 4
CPZ16B 16
CPZ64B 64

2.3. Characterization

X-ray diffractions (XRD) patterns were measured using an X-ray diffractometer (D/max-2400x, Rigaku Electric, Japan) with a scanning range of 5–60°. Fourier transform infrared spectroscopy (FT-IR) was performed using a VERTEX 70FT-IR spectrometer (Bruker, Switzerland) with a scanning wavelength range of 4000–400 cm−1. The scanning electron microscopy (SEM) image was observed using a JSM-6701F microscope (Japan Electron Optics Co., Ltd) with an accelerating voltage of 5 kV. The transmission electron microscopy (TEM) images were observed using a field emission transmission electron microscope (TECNI G2, FEI, USA) with an accelerating voltage of 120 kV. The thermogravimetric analysis curve (TGA) was recorded using a thermogravimetric analyzer (NETZSCH, STA 449C, Germany) under a nitrogen atmosphere, and the temperature was increased from 30 °C to 800 °C with a heating rate of 10 °C min−1. After degassing the sample at 100 °C under vacuum for 3 hours, N2 adsorption–desorption was conducted using an ASAP 2020 analyzer (American Mac Physical Adsorbent Apparatus).

2.4. Experiments of CO2 adsorption

The experiments of CO2 adsorption were performed using a homemade device according to the method described in our previous paper.22–25 Additionally, the adsorption kinetics was simulated using pseudo-first order (PFO, eqn (1)) and pseudo-second order (PSO, eqn (2)) kinetic models.
 
qt = qe(1 − e−k1t) (1)
 
image file: d5nj02521d-t1.tif(2)
where t (minute) is the adsorbent time, qt and qe (mmol g−1) are the adsorption capacity of the sample for CO2 at instant time (t) and the equilibrium time, respectively. k1 (min−1) and k2 (g mmol−1 min−1) are the rate constants of PFO and PSO, respectively.

Adsorption isotherms were fitted by the Langmuir model using eqn (3).

 
image file: d5nj02521d-t2.tif(3)
where qe is the adsorbed quantity at the equilibrium pressure (P) and temperature (T). qmax (mmol g−1) is the limit adsorption capacity when the pressure tends to infinity; and K (kPa−1) is the Langmuir constant.26–28

The adsorption thermodynamics parameters (ΔGθ, ΔHθ, and ΔSθ) were calculated using the van’t Hoff equation (eqn (4) and (5)).

 
image file: d5nj02521d-t3.tif(4)
 
image file: d5nj02521d-t4.tif(5)
where T (K) is the temperature, and R = 8.314 J mol−1 K−1.

3. Results and discussion

3.1. Preparation of ZIF-8@CS/PVP gel beads (CPZxB)

ZIF-8@CS/PVP gel beads (CPZxB) were prepared as follows in three key stages (Scheme 2). Firstly, chitosan (CS) and polyvinylpyrrolidone (PVP) were mixed with Zn2+ to prepare CS/PVP sols. Specifically, CS was cross-linked by glutaraldehyde to form a three-dimensional network structure. Simultaneously, the pyrrolidone ring in PVP formed hydrogen bonds between the hydroxyl groups and amino groups in the side chains of CS, creating a semi-interpenetrating network. In addition, the coordination interactions between Zn2+ and the amino groups of CS as well as the tertiary amine groups of PVP immobilized the metal ions in the polymer networks. Secondly, CS/PVP sols were dropped into NaOH solution to form gel beads. When CS/PVP networks were dropped into an alkaline solution, the NaOH solution acted as the receiving phase to neutralize acetic acid and solidify chitosan. Meanwhile, deprotonation of hydroxyl groups and amino groups as well as contraction of polymer chains led to phase separation and solidified the gel.29 Finally, gel beads were immersed in the methanol solution of 2-MeIM to in situ growth of ZIF-8 crystals in polymer networks. By controlling the concentration of 2-MeIM, the morphology and size of ZIF-8 crystals in polymer networks was investigated.
image file: d5nj02521d-s2.tif
Scheme 2 Preparation of ZIF-8@CS/PVP gel beads (CPZxB, where x is the molar ratio of Zn2+ to 2-MeIM during preparation).

As shown in Fig. 1, the crystal data of the simulated ZIF-8 was sourced from the CCDC database (CCDC number: 602542). The simulated ZIF-8 card exhibited the characteristic diffraction peaks at 7.3°, 10.4°, 12.7°, 14.7°, 16.4° and 18.0° corresponding to the (011), (002), (112), (022), (013) and (222) crystal planes of ZIF-8, respectively.30,31 The X-ray diffraction (XRD) revealed that the diffraction peaks of CPZxB was consistent with that of simulated ZIF-8. The diffraction peaks of CPZxB at 18.0° gradually increased with increasing the concentration of organic ligands, suggesting that the concentration of organic ligands affected on the nucleation rate of ZIF-8 crystals.32 In the methanol solution of ligand (2-MeIM) with the lower concentration, the ZIF-8 crystals tended to aggregate, resulting in irregular crystal shapes and weaker diffraction peak intensity. On increasing the concentration of 2-MeIM, the diffraction peaks of CPZ64B became stronger, demonstrating that the higher ligand concentration increased the supersaturation of the system, accelerated the nucleation rate of ZIF-8 and promoted crystal growth, which was manifested as a significant enhancement in peak intensity.


image file: d5nj02521d-f1.tif
Fig. 1 XRD of CPZxB.

As shown in SEM images (Fig. 2), gel pores were observed, and the ZIF-8 crystals with regular shape were mounted in the pores of CPZxB. These gel pores were like an incubator to cultivate in situ growth of MOF crystals. Additionally, with increasing concentrations of the organic ligand, more and more crystals were observed, and some came together to form aggregates. The higher concentration of 2-MeIM helped to accelerate the reaction rate, which promoted the rapid formation and growth of ZIF-8 crystals. The ZIF-8 crystals with regular rhombic dodecahedral in CPZxB were also observed in the TEM images (Fig. 2).


image file: d5nj02521d-f2.tif
Fig. 2 SEM images of (a) and (d) CPZ4B, (b) and (e) CPZ16B, (c) and (f) CPZ64B and TEM images of (g), (h) and (j) CPZ64B.

Specifically, the size of the ZIF-8 crystal decreased with the increase in the ratio of 2-MeIM to Zn2+. The crystal size of CPZ4B, CPZ16B and CPZ64B was 1000–1500, 500–1000, and 250–800 nm, respectively, which was consistent with the results reported by Kida et al.33 Generally, increasing the concentration of 2-MeIM accelerated the nucleation rate of crystals. An excessively high nucleation rate was conducive to forming the smaller-sized crystals.34 As the concentration of 2-MeIM increased, the number of 2-MeIM molecules available for coordination with Zn2+ ions in the solution increased, which significantly increased the collision probability between 2-MeIM and Zn2+, thereby speeding up the crystallization rate. In the early stage of crystallization, a large number of 2-MeIM molecules rapidly reacted with Zn2+ to form nuclei. At that time, the number of nuclei formed was relatively large, however, due to the deprotonation of the amino groups (–NH2) under alkaline conditions, which resulted in the formation of deprotonated amines and thus reduced the positive charge, the electrostatic repulsion between the polymer chains was decreased. This allowed the polymer chains to pack more closely together, making the growth space available for each nucleus relatively small, which ultimately led to a reduction in crystal size.35–37

As shown in Fig. 3, FT-IR spectra of CPZxB revealed that the peak at 1590 cm−1 was the N–H bending vibration of the amino groups in CS.38 The characteristic absorption peak at 1659 cm−1 was attributed to the C[double bond, length as m-dash]O stretching of the pyrrolidone rings in PVP, the peak at 3421 cm−1 was caused by –OH stretching, and the peak at 3022 cm−1 was the stretching vibration of –CH2 in PVP.39 The FT-IR spectra of ZIF-8 exhibited the characteristic absorption peaks of the imidazole unit: the overall ring-stretching and in-plane ring-bending vibrations appeared at 990–1150 and 1420–1510 cm−1, respectively.40 The characteristic absorption peak at 424 cm−1 was assigned to the Zn–N stretching vibration.41 The Zn–N peak appeared in the spectra of CPZxB, confirming that coordination has occurred between the metal ions and the nitrogen-containing groups. Additionally, the intensity of the characteristic absorption peak at 1590 cm−1 gradually decreased, which was attributed to coordination interaction between Zn2+ and N-containing groups.


image file: d5nj02521d-f3.tif
Fig. 3 FT-IR spectra of CPZxB.

Thermogravimetric analyses (TGA) of CPZxB were carried out under N2 atmosphere (Fig. 4). The weight of CPZxB was lost about 10% at 125–135 °C, which was attributed to a small amount of water in gel beads. After that, the weight of CPZxB was gradually lost, which was attributed to the decomposition of polymer networks and the collapse of MOF skeleton.42 When the temperature was raised to 800 °C, organic polymers such as CS and PVP were decomposed.43 Similarly, the organic ligand of ZIF-8 was completely decomposed at high temperatures.44 The final residual mass of CPZ4B, CPZ16B and CPZ64B was 19%, 23% and 8.7%, respectively.


image file: d5nj02521d-f4.tif
Fig. 4 TGA of CPZxB.

N2 adsorption–desorption isotherms revealed that the specific surface area of CPZ4B, CPZ16B and CPZ64B was 798.76, 992.71 and 4.83 m2 g−1, respectively (Fig. 5). The adsorption–desorption curves of CPZ4B and CPZ16B exhibited typical type I isotherms with H4 hysteresis loop, indicating that the pores in these materials were primarily distributed between 0 and 50 nm, with a predominance of micropores and mesopores. The adsorption–desorption curve of CPZ64B was a typical type IV isotherm with an H4 hysteresis loop. CPZxB had micropores and mesopores.45 Meanwhile, the specific surface area of CPZ64B was lower than that of CPZ4B and CPZ16B. When the concentration of 2-MeIM was too high, it may be formed additional coordination bonds or accumulate within the pores, thereby reducing the pore volume available for adsorption.46,47


image file: d5nj02521d-f5.tif
Fig. 5 N2 adsorption–desorption isotherms of CPZxB.

Additionally, the surface area of CPZxB was higher than that of ZIF-8@CS/PVP gels prepared in our previous paper.22 The results indicated that the deionization of hydrophilic groups and the contraction of polymer chains in an alkaline solution stiffened the skeleton of the CS/PVP networks, making the network structure more compact and thereby increasing the specific surface area.48 Moreover, the alkaline environment likely facilitated the dispersion of ZIF-8 particles. The poor encapsulation ability of the gel led to an increasing exposure of ZIF-8, which in turn increased the specific surface area of CPZxB.49

3.2. Adsorption of CPZxB for CO2

3.2.1. Equilibrium adsorption of CPZxB for CO2. The adsorption capacity of CS/PVP gels and CPZxB for CO2 was investigated under an initial pressure of 400 kPa at 288.15 K (Fig. 6). Equilibrium adsorption capacities of CS/PVP gels, CPZ4B, CPZ16B and CPZ64B were calculated as 1.55, 2.11, 3.13 and 2.69 mmol g−1, respectively (Fig. 7). The result indicated that the presence of ZIF-8 significantly enhanced the CO2 adsorption capacity of the composite materials. In particular, CPZ16B had the largest equilibrium adsorption capacity, which was attributed to its larger specific surface area.
image file: d5nj02521d-f6.tif
Fig. 6 Adsorption capacity of CS/PVP gels and CPZxB for CO2 under an initial pressure of 400 kPa at 288.15 K.

image file: d5nj02521d-f7.tif
Fig. 7 Equilibrium adsorption capacity of CS/PVP gels and CPZxB for CO2 under an initial pressure of 400 kPa at 288.15 K.
3.2.2. Adsorption kinetics of CPZxB for CO2. The pseudo-first order (PFO) and pseudo-second order (PSO) kinetic models were used to simulate adsorption of CS/PVP gels and CPZxB for CO2 (Fig. 8, Table 2). PFO only operates in the initial stage of the adsorption process, while PSO has a longer duration of action. As shown in Table 2, the adsorption kinetics for CPZxB for CO2 was more consistent with PSO kinetic models. The result indicated that the adsorption of CPZxB for CO2 was mainly chemisorption.
image file: d5nj02521d-f8.tif
Fig. 8 (a) PFO and (b) PSO curves of CS/PVP gels and CPZxB adsorption for CO2.
Table 2 Adsorption kinetic parameters of CS/PVP gels and CPZxB for CO2
Sample PFO PSO
k1 (min−1) R2 k2 (g mmol−1 min−1) R2
CS/PVP gels 0.018 0.9171 0.0147 0.9661
CPZ4B 0.022 0.9054 0.0150 0.9643
CPZ16B 0.014 0.9650 0.0045 0.9889
CPZ64B 0.021 0.9168 0.0119 0.9869

3.2.3. Adsorption thermodynamics of CPZxB for CO2. As shown in Fig. 9a, the adsorption isotherm of CPZ16B for CO2 was recorded at different temperatures (273.15, 288.15, 298.15 and 313.15 K) and different initial pressures (100, 200, 300 and 400 kPa). Fig. 9b indicates that the adsorption isotherm was fitted to the Langmuir model. The maximum adsorption capacity (qmax) and Langmuir constant (K) are listed in Table 3. Furthermore, the adsorption thermodynamic parameters were calculated using the van't Hoff equation (Table 4). When −ΔHθ was less than 20 kJ mol−1, the adsorption mechanism was typically physisorption. When −ΔHθ exceeds 40 kJ mol−1, the adsorption process involves a chemical change.50 In the present system, ΔHθ was calculated as −46.56 kJ mol−1, indicating that the adsorption was chemisorption with an exothermic process. ΔSθ was calculated as −124.71 J mol−1, indicating that the overall degree of disorder of the adsorption system decreased. ΔGθ indicated that the adsorption was a spontaneous process. As a result, the adsorption of CPZ16B for CO2 was a spontaneous chemical adsorption process.
image file: d5nj02521d-f9.tif
Fig. 9 (a) Adsorption isotherms of CPZ16B for CO2 at different temperatures and (b) fitting curves using the Langmuir model.
Table 3 Langmuir model fitting parameters of CPZxB for CO2 at different temperatures
Temperature (K) qmax (mmol g−1) K (kPa−1) R2
273.15 8.81262 0.06001 0.9816
288.15 6.55822 0.03729 0.9912
298.15 4.18801 0.00767 0.9831
313.15 7.55726 0.01678 0.9943

Table 4 Adsorption thermodynamic parameters of CPZ16B for CO2
Temperature (K) ΔGθ (kJ mol−1) ΔHθ (kJ mol−1) ΔSθ (J mol−1)
273.15 −28.39 −46.56 −124.71
288.15 −27.39
298.15 −26.72
313.15 −25.73

Fig. 10 shows the FT-IR spectra of CPZ16B before and after CO2 adsorption. It was well known that the symmetric stretching vibration of the carboxylate group (–COO−) in esters typically appeared in the range of 1360–1400 cm−1.51 It was generally believed that the primary amine groups of CS and the tertiary amine groups of PVP were the adsorption sites for CO2. After CPZ16B adsorbed CO2, Fig. 10 showed that the characteristic absorption peak appeared at 1369 cm−1. During the adsorption, the lone pair of electrons on the nitrogen atoms of the primary and tertiary amine groups attacked the electron-deficient central carbon atom of the acidic gas CO2 molecule. This action forced the strong π bond of the carbon–oxygen double bond to break, and a new σ bond was formed between nitrogen and carbon, ultimately resulting in the formation of carbamate.52 The active hydrogen atoms in the hydroxyl groups formed ion pairs with adjacent amine groups through hydrogen bonds to stabilize the adsorption of CO2.


image file: d5nj02521d-f10.tif
Fig. 10 FT-IR of CPZ16B after CO2 adsorption.

Generally, the adsorption sites of materials for CO2, including zinc ion, the imidazole ring of ligand, the amine groups of CS, and the pyrrole of PVP, exhibited basicity, which interacted with CO2 to form Lewis acid–base pairs. In particular, the amine groups of CS reacted with CO2 to form carbamates, which enabled CO2 molecules by chemical bonding to firmly adsorb onto the networks of gel. There was also chemical bonding of the metal ions and the imidazole ligands of ZIF-8 with CO2 molecules. Additionally, the porous structure allowed CO2 molecules to be adsorbed into the pores of ZIF-8 through physical interactions such as van der Waals forces.

4. Conclusions

The polymers chitosan (CS) and polyvinylpyrrolidone (PVP) were cross-linked by Zn2+ and glutaraldehyde to form CS/PVP networks whose hydrophilic groups were deionized, resulting in contraction of polymer networks to form gel beads. ZIF-8 crystals were incubated in the restricted networks and had a regular shape. Meanwhile, the size and aggregation were tuned by the concentration of the organic ligand. Upon increasing the concentration of 2-MeIM, the shape of the crystal particles became more regular, presenting a rhombic dodecahedral structure, and the size was gradually decreased. Additionally, the equilibrium adsorption capacities of some gel beads for CO2 are higher that of pure ZIF-8 crystals under an initial pressure of 400 kPa at 288.15 K, and the equilibrium adsorption capacity of CPZ16B was increased by 23% compared with pure ZIF-8 crystals. The adsorption kinetic simulation results indicated that the adsorption process of CPZxB for CO2 was more consistent with the pseudo-second order (PSO) kinetic model. The adsorption isotherms were fitted to the Langmuir model, and the adsorption thermodynamic parameters were calculated using the van't Hoff equation. −ΔHθ was greater than 40 kJ mol−1, which indicated that the adsorption of CPZxB for CO2 was mainly chemisorption. As a result, adsorption of CPZxB for CO2 primarily relied on a spontaneous chemical adsorption process.

Author contributions

The manuscript was written through contributions from all authors. All authors have given approval to the final version of the manuscript.

Conflicts of interest

There are no conflicts to declare.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Acknowledgements

We gratefully acknowledge the Science and Technology Programs of Gansu Province, China (No. 20YF8GA032) for financial support.

References

  1. I. Hussain, A. Rehman and C. Işık, Environ. Sci. Pollut. Res., 2022, 29, 19378–19389 CrossRef PubMed .
  2. W. Zhang, X. Zhang, Y. Xu, Y. Xu, J. Qiao, T. Shi, Z. Huang, Y. Liu, M. Fang, X. Min and X. Wu, Polymer, 2021, 214, 123258 CrossRef CAS .
  3. Y. Wang, M. Wang, Z. Wang, S. Wang and J. Wang, Appl. Surf. Sci., 2020, 507, 145130 CrossRef CAS .
  4. T. Okumura, T. Yamaguchi, S. Nishibe, R. Numaguchi and Y. Kawajiri, Int. J. Greenhouse Gas Control, 2024, 133, 104094 CrossRef CAS .
  5. P. Qiu, B. Ma, C. T. Hung, C. W. Li and D. Zhao, Acc. Chem. Res., 2019, 52, 2928–2938 CrossRef CAS PubMed .
  6. X. Xu, B. Pejcic, C. Heath and C. Wood, J. Mater. Chem., 2018, 6(43), 21468–21474 RSC .
  7. B. Singh, Z. E. Gorji, R. Singh, V. Sharma and T. Pepo, Energy Environ. Mater., 2024, 8(1), e12832 CrossRef .
  8. Q. A. Al-Maqtari, A. A. S. Al-Gheethi, A. D. Ghaleb, A. A. Mahdi, W. Al-Ansi, A. E. Noman, A. Al-Adeeb, A. O. K. Odjo, Y. Du, M. Wei and W. Yao, Food Hydrocolloids, 2022, 129, 107624 CrossRef CAS .
  9. B. Wei, J. Zou, Q. Pu, K. Shi, B. Xu and Y. Ma, J. Sci. Food Agric., 2022, 102(9), 3826–3834 CrossRef CAS PubMed .
  10. F. Russo, F. Galiano, A. Iulianelli, A. Basile and A. Figoli, Fuel Process. Technol., 2021, 213, 106643 CrossRef CAS .
  11. M. Javed, H. Huang, Y. Ma, F. E. Ettoumi, L. Wang, Y. Xu, H. R. El-Seedi, Q. Ru and Z. Luo, Food Chem., 2024, 438, 137948 CrossRef CAS PubMed .
  12. O. Korepanov, O. Aleksandrova, D. Firsov, Z. Kalazhokov, D. Kirilenko, D. Kozodaev, V. Matveev, D. Mazing and V. Moshnikov, Nanomaterials, 2022, 12(14), 2357 CrossRef CAS PubMed .
  13. W. Wang, J. Liang, Y. Wu, W. Li, X. Huang, Z. Li, X. Zhang, X. Zou and J. Shi, Food Chem., 2025, 463, 141054 CrossRef CAS PubMed .
  14. Y. Wang, M. Shoaib, J. Wang, H. Lin, Q. Chen and Q. Ouyang, J. Food Compos. Anal., 2025, 137, 106864 CrossRef CAS .
  15. S. Wang, J. Cui, S. Zhang, X. Xie and W. Xia, Mater. Res. Express, 2020, 7, 025304 CrossRef CAS .
  16. R. A. Agarwal and N. K. Gupta, Coord. Chem. Rev., 2017, 332, 100–121 CrossRef CAS .
  17. W. Zheng, R. Ding, K. Yang, Y. Dai, X. Yan and G. He, Sep. Purif. Technol., 2019, 214, 111–199 CrossRef CAS .
  18. C. Li, Y. Qiao, Y. Li, J. Wen, N. He and B. Li, Prog. Chem., 2021, 33(11), 1964–1971 CAS .
  19. R. Zhao, T. Ma, S. Zhao, H. Rong, Y. Tian and G. Zhu, Chem. Eng. J., 2020, 382, 122893 CrossRef CAS .
  20. R. Freund, O. Zaremba, G. Arnauts, R. Ameloot, G. Skorupskii, M. Dincă, A. Bavykina, J. Gascon, A. Ejsmont, J. Goscianska, M. Kalmutzki, U. Lächelt, E. Ploetz, C. S. Diercks and S. Wuttke, Angew. Chem., Int. Ed., 2021, 60, 23975–24001 CrossRef CAS PubMed .
  21. A. Sathiyaseelan, X. Zhang, Y. Lu, N. A. Azeez, L. Zhang, G. S. Krishnakumar and M. Y. Wang, Prog. Mater. Sci., 2024, 101387 Search PubMed .
  22. N. He, W. Li, T. Shi, Z. Li, F. Guo, Z. Li and X. Zhao, ACS Appl. Polym. Mater., 2024, 6(5), 2814–2822 CrossRef CAS .
  23. C. Li, N. He, X. Zhao, X. Zhang, W. Li, X. Zhao and Y. Qiao, ChemistrySelect, 2022, 7, e202103927 CrossRef CAS .
  24. C. Li, F. Guo, Z. Li, N. He, W. Li and X. Zhao, Mol. Syst. Des. Eng., 2024, 9(2), 205–213 RSC .
  25. N. He, C. Li, X. Zhao, Y. Li, X. Zhang and Y. Qiao, Polym. Adv. Technol., 2022, 33(3), 750–759 CrossRef CAS .
  26. Z. Li, T. Shi, W. Wu, X. Zhao, M. Zheng and N. He, Langmuir, 2025, 40(29), 19505–19513 CrossRef PubMed .
  27. X. Du, W. Guang, Y. Cheng, Z. Hou, Z. Liu, H. Yin, L. Huo, R. Lei and C. Shu, Appl. Clay Sci., 2020, 192, 105631 CrossRef CAS .
  28. C. R. Girish, Chem. Pap., 2025, 1–20 Search PubMed .
  29. E. Luzzi, P. Aprea, M. Salzano de Luna, D. Caputo and G. Filippone, ACS Appl. Mater. Interfaces, 2021, 13, 20728–20734 CrossRef CAS PubMed .
  30. T. Lan, X. Ding, S. Xiao, Z. Yuan, T. Yan, Q. Chen, T. Li and W. Zheng, Discover Appl. Sci., 2025, 7(7), 728 CrossRef .
  31. C. Limtongnoi, S. Amnuaypanich, S. Naknonhan, B. Tharat, S. Suthirakun, T. Kleebmek, C. Saiyasombat, S. Chio-Srichan, N. Patdhanagul and S. Amnuaypanich, Chem. Eng. J. Adv., 2025, 23, 100801 CrossRef .
  32. T. Tsuruoka, K. Araki, K. Kawauchi, Y. Takashima and K. Akamatsu, Inorganics, 2024, 12(1), 21 CrossRef CAS .
  33. K. Kida, M. Okita, K. Fujita, S. Tanaka and Y. Miyake, CrystEngComm, 2013, 15, 1794–1801 RSC .
  34. S. Zhang, J. Wang, C. Wei, P. Liu, S. Qin, L. Cao, Y. Zhou, J. Zhang and S. Zhang, J. Environ. Chem. Eng., 2024, 12(6), 114839 CrossRef CAS .
  35. J. Nie, Z. Wang and Q. Hu, Sci. Rep., 2016, 6(1), 36053 CrossRef CAS PubMed .
  36. V. Armel, J. Hannauer and F. Jaouen, Catalysts, 2015, 5(3), 1333–1351 CrossRef CAS .
  37. J. Cravillon, S. Münzer, S. J. Lohmeier, A. Feldhoff, K. Huber and M. Wiebcke, Chem. Mater., 2009, 21, 1410–1412 CrossRef CAS .
  38. M. A. Taheri, M. Setoodehkhah and M. Moradian, Sci. Rep., 2025, 15(1), 19056 CrossRef CAS PubMed .
  39. M. Godino-Ojer, M. Shamzhy, J. Čejka and E. Pérez-Mayoral, Catal. Today, 2020, 345, 258–266 CrossRef CAS .
  40. J. Narimbi, S. Balakrishnan, T. S. Perova, G. Dee, G. F. Swiegers and Y. K. Gun’ko, Materials, 2023, 16(6), 2410 CrossRef CAS PubMed .
  41. X. Hou, W. Chen, M. Fan and C. Shi, RSC Adv., 2024, 14(48), 36063–36072 RSC .
  42. Y. Zhou, Y. Xu, J. Guo, S. Zhang and Y. Lu, Aust. J. Chem., 2019, 72(6), 450–459 CrossRef CAS .
  43. M. S. Pérez-Garibay, G. Á. Lara-Rodríguez and E. Bucio, Gels, 2025, 1(2), 147 CrossRef PubMed .
  44. S. AL-atawi, M. M. Aljohani, T. A. Hamdalla, S. A. Al-Ghamdi, A. M. Alsharari and S. Khasim, Catalysts, 2024, 14(10), 705 CrossRef CAS .
  45. D. M. Kabtamu, Y. N. Wu and F. Li, J. Hazard. Mater., 2020, 397, 122765 CrossRef CAS PubMed .
  46. S. Salamat, M. Hadavifar and H. Rezaei, J. Environ. Chem. Eng., 2019, 7, 103328 CrossRef CAS .
  47. A. Jomekian, B. Bazooyar and R. M. Behbahani, J. Solid State Chem., 2020, 289, 121532 CrossRef CAS .
  48. Y. Hu, S. Hu, S. Zhang, S. Dong, J. Hu, L. Kang and X. Yang, Sci. Rep., 2021, 11(1), 9142 CrossRef CAS PubMed .
  49. D. Behera, P. Priyadarshini and K. Parida, Dalton Trans., 2025, 54(7), 2681–2708 RSC .
  50. M. Mabuza, K. Premlall and M. O. Daramola, Int. J. Coal Sci. Technol., 2022, 9(1), 45 CrossRef CAS .
  51. A. Pragya, S. Mutalik, M. W. Younas, S. K. Pang, P. K. So, F. Wang, Z. Zheng and N. Noor, RSC Adv., 2021, 11(18), 10710–10726 RSC .
  52. R. B. Said, J. M. Kolle, K. Essalah, B. Tangour and A. Sayari, ACS Omega, 2020, 5(40), 26125–26133 CrossRef CAS PubMed .
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