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Article

Adsorption and Desorption Characteristics of Nano-Metal-Modified Zeolite for Removal of Oxygenated Volatile Organic Compounds

by
Yue Wang
1,2,†,
Hairong Jiang
1,3,†,
Wenhui Wei
1,
Zhengao Zhang
1,
Xiaowei Wang
1,*,
Minglu Zhang
1,* and
Lianhai Ren
1
1
State Environmental Protection Key Laboratory of Food Chain Pollution Control, Beijing Technology and Business University, Beijing 100048, China
2
Foreign Talent Research Center, Ministry of Human Resources and Social Security of the People’s Republic of China, Beijing 100038, China
3
College of Environmental Science and Engineering, Beijing Forestry University, Beijing 100083, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Coatings 2025, 15(10), 1206; https://doi.org/10.3390/coatings15101206
Submission received: 9 September 2025 / Revised: 1 October 2025 / Accepted: 4 October 2025 / Published: 13 October 2025
(This article belongs to the Special Issue Surface Structure and Adsorption Properties of Mesoporous Materials for Pollutant Removal)
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Abstract

Oxygenated volatile organic compounds are key precursors of secondary photochemical pollutants. To enhance their removal, NaY–zeolite was modified with nano-sized metals (Fe, Ti, Si, or Ce) using impregnation and sol–gel methods. Dynamic adsorption experiments were conducted to evaluate the adsorption of ethanol, acetaldehyde, and ethyl acetate under various condition modifications, including of the impregnation concentration, treatment time, and calcination temperature. The structural and surface properties of the modified zeolites were characterized by N2 adsorption–desorption isotherm, X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FT-IR) analyses. The results indicated that the metal-loaded zeolites exhibited significantly higher adsorption capacities than the unmodified NaY–zeolite. Among them, silicon-modified zeolite showed the best performance, with its adsorption capacities for ethanol, acetaldehyde, and ethyl acetate increasing from 32.4, 72.4, and 123.0 mg·g−1 to 49.82, 88.94, and 207.02 mg·g−1, corresponding to improvements of 37%, 23%, and 70%. The optimal modification conditions involved the use of silicon as the modifier with a 7% impregnation concentration, a 12 h impregnation time, and calcination at 350 °C; the zeolite modified under these conditions was characterized by a good adsorption capacity and low preparation cost. This study suggests newly designed adsorber materials suitable for highly efficient treatment of oxygenated volatile organic compounds.

1. Introduction

As a major group of volatile organic compounds (VOCs), oxygenated volatile organic compounds (OVOCs) mainly comprise aldehydes, alcohols, ketones, and low-molecular-weight organic acids. OVOCs tend to be more reactive than the alkanes they are derived from [1]. Ethanol, acetaldehyde, and ethyl acetate are important OVOCs. Although their concentrations are generally lower than 500 mg·m−3 in exhaust gases, they can be observed at trace levels [1]. Long-term exposure to ethanol concentrations as low as 25.0 mg/L is known to harm human health [2]. The American Conference of Governmental Industrial Hygienists (ACGIH) instructs that the threshold exposure limit valve for acetaldehyde should be 25 mg/L, and should not be surpassed at any time [3]. Ethyl acetate is a flammable and transparent volatile organic compound (VOC) with an aromatic odor [4]. Due to the strong volatility of odorous pollutants, they mainly spread and diffuse through the atmosphere, not only threatening human health, but also polluting the environment [5]. Thus, the removal of OVOCs from the air is essential due to the health issues it can cause.
Various technologies based on recovery and destruction have been developed for OVOC abatement [6]. In general, recovery technologies (i.e., adsorption, absorption, condensation, and membrane separation) based on physical and/or chemical interactions can separate OVOCs by controlling process conditions such as temperature and pressure [7,8]. Destruction technologies decompose OVOCs into harmless products (e.g., CO2 and H2O), and include thermal incineration, catalytic oxidation, photocatalytic decomposition, biofiltration, non-thermal plasma oxidation, and plasma catalysis [9,10,11]. Adsorption is one of the most promising recovery technologies because of its cost-effectiveness, flexible operation, and low energy consumption [12,13]. Selective adsorption-based technologies have especially high potential, and a wide range of OVOCs can be captured from exhaust gases due to the widespread use of adsorbent materials [14,15]. Adsorbents such as MOFs (metal–organic frameworks) [16], cellulose-supported materials [17], and molecular sieves [18] have been used for the removal of OVOCs. These adsorbents have a relatively small surface area and have been effectively utilized as fillers in various systems, such as drip filtration towers and adsorption towers, enhancing their versatility and efficiency in OVOC removal processes. Activated carbons are the most effective adsorbents for OVOC uptake [19]. Nevertheless, problems such as their difficult regeneration and high flammability limit their practical applications [12]. Hence, a non-toxic adsorbent with a high specific surface area, significant thermal stability, and easy regeneration is highly needed. Zeolite-type materials have all of these features, as well as tailorable surface hydrophobicity, which makes them perfect candidates as adsorbents [20,21]. Another important factor is the zeolite pore size, which differs among zeolitic frameworks, representing an interesting tunable property. Indeed, proper tuning of the size of these pores allows for selective adsorption [22,23]. Zeolite structures are highly porous, with a large surface area and good adsorption capacity. Furthermore, they cost only USD 0.070–0.120 per kilogram, depending on the mineral type and quality [24,25]. Various surface modifications can be performed to boost their adsorption capacity, such as metal oxide impregnation and organic modification, which work by enhancing the number of active sites available for adsorption [24].
In recent years, research on advanced OVOC adsorbents has increasingly focused on the use of structural regulation and surface functionalization to enhance adsorption capacity, selectivity, and regeneration performance. Surface functionalization is considered a key approach for improving adsorption performance. Studies have shown that heteroatom or metal doping in porous carbons can tune pore structures and surface properties to enhance VOC/OVOC adsorption [26]. In recent years, extensive research has been conducted on materials, such as MOFs, which offer high surface areas and tunable channels but face application limits due to their powder form. However, PVA-composited Zr-based MOF microspheres, achieved selective adsorption of polar VOCs with good cyclic stability, offering strategies to overcome these bottlenecks [27].
Existing research on the adsorption of metal-modified zeolites focuses mainly on pollutant adsorption in water. Nguyen Le Minh Tri et al. investigated the adsorbent feasibility of Fe-nano zeolite for the treatment of phenolic compounds in wastewaters. Fe-NZ exhibited high adsorption capacities for phenol (Ph), 2-chlorophenol (2-CP), and 2-nitrophenol (2-NP), with maximum values of 138.7, 158.9, and 171.2 mg/g, respectively, and the potential for multiple reuses [28]. Only a few reports have been published on OVOC elimination with nano-metal oxide modified zeolite. Studies have shown that modifying the surface of zeolites with metals, such as Fe, Ti, or Ce, is an excellent way to increase their acidity, leading to higher adsorption [29,30]. The evaporation-induced self-assembly (EISA) method was used by Yin et al. to load metal oxide nanoparticles onto a NaY zeolite that could then be used to remove OVOCs. The results of this study revealed that NaY–zeolite loaded with metal oxide nanoparticles demonstrated a considerably improved OVOC adsorption capacity [14]. Abdullah et al. [31] studied the effect of the amount of the zinc oxide loaded onto NaA-zeolite on hydrogen sulfide (H2S) adsorption using a fixed-bed reactor. They found that the H2S adsorption capacity was highest (15.75 mg S/g Adsorbent) when 20 wt% ZnO was loaded onto Na-A zeolite. A reduction in the adsorption capacity was observed when the wt% of ZnO was increased above 20 wt%. Another study was conducted by Lv et al. on Dimethyl Disulfide (DMDS) removal using NaY–zeolite (Ag2O/NaY, CuO/NaY, ZnO/NaY, CeO2/NaY, and NiO/-NaY). Of these adsorbents, Ag2O/NaY (5 wt%) showed the highest breakthrough adsorption capacity due to direct S-Ag+ interaction [32]. Therefore, modifications to reaction conditions have the potential to exert a great effect on the adsorption properties of zeolite.
In this study, NaY–zeolite with a large specific surface area, high average pore size, and low cost was selected as an adsorbent. The sol–gel and impregnation methods were implemented to modify the zeolite with the addition of different nano-metal (Fe, Ti, Si, and Ce) layers. The performance of the modified zeolite in dynamic OVOC (ethanol, acetaldehyde, and ethyl acetate) adsorption was evaluated under different modification conditions. Most existing studies focus on the removal of aqueous-phase pollutants, while systematic research on the adsorption of gaseous OVOCs remains limited. In particular, there is a lack of studies that systematically compare the loading of multiple nano-metal oxides (Fe, Ti, Si, Ce) onto the same NaY zeolite support using different modification methods (sol–gel and impregnation) and directly correlate surface chemical characterization results with OVOC adsorption performance. Our study aimed to develop novel OVOC adsorbents and evaluate their adsorption capacity, as well as to explore the mechanisms of interaction between metal oxides and OVOCs. Key insights will be provided for the development of efficient and cost-effective adsorbents for air pollution control, laying the essential groundwork for their application in odor removal through packed bed towers.

2. Materials and Methods

2.1. Materials

All the chemicals were of reagent grade and were obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). The zeolite used (200 mesh) was manufactured in Chaoyang Xinhe Zeolite Technology Co., Ltd. (Chaoyang, China). The OVOC (ethanol, acetaldehyde, and ethyl acetate; 500 mg/L) gas cylinders used were purchased from Beijing Ao kang Shuang Quan Energy Technology Co., Ltd. (Beijing, China).

2.2. Preparation of Adsorbents

Gelatinous ferric hydroxide was selected as a ferric precursor and incorporated into zeolite using the sol–gel method. An iron hydroxide colloid was obtained through the following procedure. A solution of Fe3+ was first prepared by dissolving Fe(NO3)3·9H2O in 10 mL of distilled water, and this was then added dropwise to 40 mL of boiling distilled water (heated on an electric heater and kept at a boil), with occasional stirring, By controlling the amount of Fe(NO3)3⋅9H2O, different colloid concentrations (0.01–0.30 mol/L) were obtained. ensuring that the reaction was taking place adequately between drops [33]. The solution was continuously heated until it turned brown to ensure that iron hydrolysis had been completed. The iron hydroxide colloid solution was then cooled to room temperature [34]. TiO2 sol–gel was synthesized through hydrolysis of tetrabutyl titanate (TBT) [35,36]. SiO2 sol–gel was synthesized through hydrolysis of tetraethyl orthosilicate (TEOS, 99%) [37]. CeO2 sol–gel was synthesized through hydrolysis of cerium nitrate hexahydrate solution [38]. The desired amount of zeolite was added to each X colloid solution (X = Fe(OH)3, TiO2, SiO2, or CeO2). After dipping for a certain time, the mixture was collected by suction filtration. The product was dried at 105 °C overnight. Finally, the concentrated mixture was calcined in a muffle furnace at a suitable temperature for 2 h, and then cooled to room temperature; the resulting product was named M-zeolite (M = Fe, Ti, Si, or Ce).
Under various conditions, with modifications made to the metal (Fe, Ti, Si, and Ce), calcination temperature (200 °C, 350 °C, 500 °C, and 650 °C), impregnation concentration (3%, 5%, 7%, and 10%), and impregnation time (6, 12, 24, and 36 h) used, a dynamic adsorption experiment was conducted to determine the optimal conditions for OVOC adsorption.

2.3. Characterization Method

The Pan Analytical X′Pert-Pro X-ray diffractometer (Malvern Panalytical, Almelo, The Netherlands) was utilized to explore the XRD patterns of zeolite, Fe–zeolite, Ti–zeolite, Si–zeolite, and Ce–zeolite using Cu-Kα emission, a 30 kV/15 mA current, and a kβ-filter in the 2θ range of 10–90° (speed: 5° per minute). The Tescan MIRA LMS (Brno, Czech Republic) was used for examination of elemental composition, color mapping, and surface morphology analysis with the SEM-EDS technique (Tokyo, Japan). The Micromeritics ASAP 2460 (Norcross, GA, USA) instrument was employed to determine the BET surface area and the mean diameter and volume of pores and to construct a BJH plot for the pore size distribution of zeolite, Fe–zeolite, Ti–zeolite, Si–zeolite, and Ce–zeolite through N2 adsorption–desorption isotherms at 77 K by means of the BET (Brunauer–Emmett–Teller) and BJH (Barrett–Joyner–Halenda) methods. To confirm the composition of the prepared materials, Fourier transform infrared (FTIR) spectroscopy (Thermo Scientific Nicolet iS20, Waltham, MA, USA) was also conducted at room temperature using the KBr disk technique in the wavenumber range of 4000–400 cm−1 with 32 scans at 4 cm−1 resolution.

2.4. Experiment to Investigate Dynamic Adsorption of OVOCs Using Modified Zeolites

The fixed-bed OVOC dynamic adsorption break-through tests were carried out in a quartz adsorption column (15 cm × 2 cm); the experimental system is illustrated in Figure 1. The feed gas was provided by gas cylinders of ethanol, acetaldehyde, and ethyl acetate (500 mg/L, balanced by N2), respectively. Approximately 0.50 g of modified zeolite was weighed in the adsorption column, then it was fixed in the center of the adsorption column with 60-mesh quartz sand and both ends of the adsorption column were plugged with cotton and single-hole rubber. OVOCs were fed into the quartz adsorption column at a fixed flow rate (500 mL·min−1), and the gas flow was controlled by a rotor flowmeter. The gas outlet was connected to an OVOC analyzer (Model:MOT5-M-YX Shenzhen Keernuo Electronic Technology Co., Ltd., Bao’an District, Shenzhen, Guangdong Province, China). The outlet concentration was measured every 5 min until adsorption saturation was reached, then connect to the tail gas absorption device. The gas concentration at the outlet of the adsorption column was adopted as the adsorption penetration point when the ratio of the outlet concentration Cout to the intake concentration Cin of the adsorption column was 0.05. When the ratio was 0.95, the adsorption equilibrium was reached. At this point, the gas adsorption capacity represented the dynamic saturated adsorption capacity of modified zeolite for ethanol, acetaldehyde, or ethyl acetate, which was an essential parameter used to screen the modified zeolite in this experiment. The OCOV removal percentage and adsorption capacity were calculated using the following equations, Equations (1) and (2):
R e m o v a l   e f f i c i e n c y   ( % ) = C i n − C o u t C i n × 100
q = Q · C i n m t − ∫ 0 t C o u t C i n d t
where q is the breakthrough OVOC capacity (mg-OVOCs/100 g-adsorbent), Q is the inlet gas flow rate (L·min−1), t is the breakthrough time (min), Cin and Cout are the inlet and outlet concentrations of OVOCs (mg·L−1), respectively, and m is the weight of the adsorbent (g).

3. Results and Discussion

3.1. Adsorbent Characterization

3.1.1. N2 Adsorption–Desorption Isotherms

Figure 2 shows the N2 adsorption–desorption isotherms of Fe–zeolite, Ti–zeolite, Si–zeolite, and Ce–zeolite, respectively. All the modified zeolites showed a type-IV isotherm, along with a H2-type hysteresis loop, signifying the presence of mesopores in the modified zeolites [39]. The mesopores present in the modified zeolites contributed to better adsorption of organic pollutants. The metal-loading modifications resulted in changes to the adsorption sites on the surface of the carrier material, including pores and surface functional groups. The modifications also increased the material’s specific surface area and porosity, and an increased number of surface functional groups were detected. In most cases, the formation of numerous metal flakes, a well-developed carbon skeleton, and a honeycomb structure was observed in the carrier, which caused a significant increase in the number of adsorption sites for contaminants [40,41]. The BET surface areas (S.A.s) of Fe–zeolite, Ti–zeolite, and Ce–zeolite were 363.31, 429.71, and 406.14 m2/g, respectively, and were greater than that of unmodified zeolite (314.82 m2/g), as can be seen in Table 1. Due to Si–zeolite’s larger surface area (439.33 m2/g) and higher pore volume, it exhibited the highest percentage of adsorptive removal among the various adsorbents, resulting in the maximum OVOC removal. Yang et al. [42] discovered that the synthesized MOF-177 material captures VOCs through a pore-filling mechanism. Due to its enormous specific surface area and pore volume, the porous MOF-177 material exhibits a significant capacity for VOC adsorption. According to previous studies, a larger specific surface area typically implies the presence of more available adsorption sites, while the pore size and distribution determine how easily molecules can enter pores [43], this observation is consistent with our conclusion.

3.1.2. XRD Pattern

The X-ray diffraction (XRD) patterns of the freshly prepared modified zeolites are given in Figure 3. Fe-Zeolite shows less intense peaks than unmodified zeolite, revealing a decrease in the zeolite’s crystalline structure after the implementation of the exchange method and calcination. All the samples show the typical diffraction peaks that characterize NaY–zeolite topology. No changes can be observed in their XRD peak positions, indicating that the zeolites’ structures were well preserved after the development of mesoporosity and the impregnation of metallic particles. This result has also been found by other authors, who have reported that the intracrystalline structure of zeolites is conserved after desilication, dealumination, or acid washing [44,45,46]. No characteristic signals of Fe, Ti, Si, or Ce metal particles or of iron oxide, titanium oxide, silicon oxide, or cerium oxide were detected, although the peak XRD intensity gradually decreased with an increase in the amount of metal incorporated. Among the different metals incorporated, the peak XRD intensity decreased significantly with an increase in the content of Fe and Ti. Therefore, it can be concluded that these metal species were highly uniformly distributed on the surface of NaY–zeolite, and they did not destroy the zeolite’s crystal structure. This is further confirmed by SEM measurements, which show that the morphology and particle size of Fe–zeolite, Ti–zeolite, Si–zeolite, and Ce–zeolite were similar to those of unmodified NaY–zeolite (Figure 4). The increases in the metal content established by EDS testing provide additional evidence that the Fe, Ti, Si, and Ce metal species were quite small and well dispersed across the surface of the NaY–zeolite.

3.1.3. SEM-EDS Spectra

Scanning electron microscopy (SEM) was used to investigate the morphology of the unmodified zeolite and the M-zeolites (Figure 4). These observations provided information regarding the topography and composition of the samples. It was clear that both the raw and modified zeolites had similar morphology with typical smooth surfaces, implying that no structural changes were induced during the modification process. In addition, the zeolite composites loaded with different metals maintained the same morphology, suggesting that no collapse of the NaY–zeolite structure occurred due to the loading of different metals. This result agrees with the XRD structural results. A slightly matte appearance can be observed on the surface of the composite, as reported in previous studies [47,48], a small number of metal oxide particles were highly and uniformly dispersed on the surfaces. However, the micropores of the modified zeolite composites were not blocked by the metal oxide particles attached to their surfaces. On the contrary, these particles changed the surface properties of the modified zeolites in a way that was beneficial to the adsorption of OVOCs [14]. The attachment of metal nanoparticles to the surface of the NaY–zeolite support was vital because it reduced the level of nanoparticle aggregation, thereby increasing the roughness of the zeolite surface. Studies have shown that crystals with high roughness exhibit a higher surface area than that of crystals with lower roughness [49]. The modified zeolites exhibited highly porous structures with uniformly shaped crystals and a higher surface area, ensuring maximum adsorption capacity.
Energy-dispersive spectroscopy (EDS) analysis was conducted to further investigate the composition of the unmodified and modified zeolites (Figure 4). The elemental peaks confirmed the presence of carbon (C), aluminum (Al), silicon (Si), oxygen (O), iron (Fe), titanium (Ti), and cerium (Ce) in these modified zeolites. After evaluating the regions under the peaks of individual elements, the corresponding elemental composition was determined. The peaks of these different metals in the EDS spectra also support the notion that modification took place in the crystal lattices of the various zeolites. A similar study utilizing EDS also confirmed the presence of distinct metal peaks (Fe, Ti, Si, Ce), further supporting this notion [50]. The peaks of C, O, Si, and Al were observed in the EDS spectra, confirming that the basic composition of the parent zeolite remained intact even after the modifications were applied. This result also revealed that neither the sol–gel method nor the impregnation method affected the zeolite framework, thereby promoting the adsorption process. Moreover, the elemental content distribution revealed by EDS confirmed that the theoretical metal loadings (Fe, Ti, Si, and Ce) were approximately 5 wt% in relation to the unmodified zeolites.

3.1.4. FTIR Spectra

The results of Fourier transform infrared spectroscopy (FT-IR) analysis of the composition of unmodified zeolite, Fe–zeolite, Ti–zeolite, Si–zeolite, and Ce–zeolite are illustrated in Figure 5. The broad band within the range of 3500–3100 cm−1 is assigned to the stretching vibration of a hydroxyl group from Si-OH hydrogen-bonded to water on the surface of the zeolite [51]. In the lower-frequency region of the IR spectrum (1800–400 cm−1), the main peaks of the samples can be seen at wavelengths of 440, 540, 795, and 980–1090 cm−1. The FT-IR peaks at wavelengths of 440 and 550 cm−1 can be attributed to T-O-T and microporous zeolites, respectively. However, the presence of absorption bands at around 440 cm−1 and 1100 cm−1 confirms the presence of the Si-O functional group [52]. The FT-IR bands at 550 cm−1 are indicative of the Si-O-Al group [53]. The observed bands at approximately 795 cm−1 are due to the –OH (Al–OH) translational vibration. Major changes were observed in the shape of the strongest adsorption bands at 1100 cm−1, associated with a change in the modified NaY–zeolite. The relative intensity of the Si–O stretching vibration (1107 cm−1) increased with the amount of metal loading. NaY–zeolite has the chemical composition TO4 (T = Si or Al). The Si/Al ratio affects the vibration power of the bands. In Fe-modified zeolites, the band near 1100 cm−1 becomes sharper and more intense, indicating the formation of Si–O–M (M = Fe, Ti) bonds [54]; in Si-modified zeolite, a more pronounced Si–O–Si vibration is observed, reflecting a higher Si/Al ratio and enhanced hydrophobicity.

3.2. Gas Adsorption Performance for Ethanol, Acetaldehyde, and Ethyl Acetate

To investigate the differences in OVOC adsorption performance of the metal-modified zeolites, the dynamic adsorption of ethanol, acetaldehyde, and ethyl acetate by the modified zeolites was investigated under constant room temperature (20 °C) (Figure 6). The adsorption capacities of the modified samples are presented in Figure 6a. The adsorption capacity of the parent NaY–zeolite was low due to its microporous structure. The adsorption capacity values for ethanol, acetaldehyde, and ethyl acetate were measured to be 32.4, 72.4, and 123.0 mg·g−1, respectively. The modified zeolites exhibited a particularly high adsorption capacity for ethyl acetate. Yu et al. [21] reported that ethyl acetate can be readily and tightly adsorbed on pore walls and, regardless of the zeolite type, can access narrow pore apertures. Compared with toluene, ethyl acetate appears to possess a greater number of available adsorption sites within zeolite adsorbents and induces more pronounced changes in electronic density, indicating stronger interactions with the zeolite framework. These factors may account for the higher adsorption capacity of ethyl acetate among the three investigated OVOCs. For all the modified samples, the saturation adsorption capacity increased for ethanol and ethyl acetate, in addition to the adsorption of acetaldehyde (Figure 6a). These results can be attributed to the interaction between metal ions or their oxides and OVOCs [12,20]. Notably, the adsorption capacities for ethanol, acetaldehyde, and ethyl acetate of Si–zeolite increased from 32.4, 72.4, and 123 mg·g−1 to 49.8, 88.9, and 207 mg·g−1, representing improvements of 37%, 23%, and 70%, respectively. Studies have shown that due to hydrogen bonding and polar interactions with oxygen-containing organics, silica-rich or silica-modified zeolites generally exhibit stronger adsorption toward polar OVOCs. Research has found that acetone forms stable hydrogen-bonding complexes with surface hydroxyl groups on both nonporous and mesoporous silica [55]. Comparative studies on silica–alumina fixed-bed reactors further showed that acetone’s equilibrium adsorption capacity was about four times higher than that of nonpolar toluene, underscoring the dominant role of molecular polarity [56]. Consequently, in multicomponent gas systems, more polar OVOCs preferentially occupy adsorption sites in silica-modified zeolites, enhancing selective adsorption.
All the modified zeolites showed some improvement in their adsorption of these three kinds of OVOCs, except for the Ti- and Ce-modified zeolites, which exhibited a slight decrease in their adsorption of acetaldehyde. The adsorption capacity of the modified zeolites for these three kinds of OVOCs increased by 5%–70%. As the SBET and VTotal pore of all the zeolites increased after modification, the improvement observed in the adsorption performance of the modified zeolites can be seen as a result of the larger surface area, larger pore volume, and rougher surface structure of the newly developed metal-modified zeolites (Table 1). The most important effect of the mesoporous channels was the improved mass transfer rate of the adsorbents or reactants in the zeolites [57,58,59]. This indicates that for microporous zeolites with a micron-scale crystal size, a limited mass transfer rate is one of the most important factors affecting their adsorption capacity. Compared with the unmodified NaY–zeolite, the modified zeolites had a flatter breakthrough curve, suggesting that the adsorption process in the modified zeolites was slow to reach an equilibrium state. Hence, the modified zeolites had a longer life cycle. When microporous zeolite crystals possess relatively large particle sizes, VOC molecules must diffuse through longer pathways to reach the internal micropores, which results in mass transfer limitations. When adsorption saturation was reached, the inlet and outlet concentrations of OVOCs were equal. However, mass transfer limitations may lead to the distribution of OVOC concentration in zeolites being non-uniform. The introduction of mesoporous structures led to a more uniform distribution of OVOC concentration, and the higher number of adsorption sites in the modified zeolites increased their adsorption effectiveness.
The breakthrough times for ethanol, acetaldehyde, and ethyl acetate with the modified zeolites were observed to be longer than those with the unmodified zeolites, with respective ranges of 8–12 min, 2–20 min, and 12–44 min (Figure 6b–d). Additionally, the saturation times were extended by 10–15 min, 10–20 min, and 15–50 min compared to those for the unmodified zeolites. Notably, Si–zeolite exhibited the longest saturation times, reaching 145 min for ethanol, 70 min for acetaldehyde, and 130 min for ethyl acetate. These results have practical value, as they indicate that this adsorbent can be used for a certain length of time before it reaches breakthrough or near-breakthrough adsorption and requires replacement or regeneration to meet emission standards. Metal-modified zeolites show great application potential owing to their low cost, high adsorption performance, and favorable physicochemical properties such as fast adsorption and gas selectivity. Their high thermal stability allows for efficient regeneration by thermal desorption or inert gas purging, and the materials retain high activity after multiple cycles, highlighting their excellent reusability.

3.3. Effect of Impregnation Concentration

Generally, the purpose of metal ion impregnation is to increase zeolite’s adsorption capacity for OVOCs. In this study, the adsorption capacities of unmodified zeolite, Fe–zeolite, Ti–zeolite, Si–zeolite, and Ce–zeolite for ethanol, acetaldehyde, and ethyl acetate were compared. We ultimately chose to apply SiO2 sol–gel impregnation to modify the zeolites. However, different concentrations of impregnation solution led to differences in the amounts of metal ions or their oxides loaded onto the zeolite surface. These variations greatly affected the OVOC adsorption capacity of the modified zeolites. The effect of the impregnation concentration on the adsorption capacities of the samples is described in Figure 7. The adsorption capacity for ethanol follows the sequence of 7%-Si > 10%-Si > 5%-Si > 3%-Si > unmodified zeolites. For acetaldehyde, the sequence is 7%-Si > 5%-Si > 10%-Si > 3%-Si > unmodified zeolites, while for ethyl acetate, the sequence is 5%-Si > 10%-Si > 7%-Si > 3%-Si > unmodified zeolites. For the three kinds of OVOCs, the adsorption capacity of the modified zeolites was increased by 70%, 30%, and 55%, respectively. However, this high adsorption capacity was associated with long breakthrough and saturation times. Compared to the unmodified zeolites, the modified zeolites demonstrated increased saturation times by 22 min for ethanol, 25 min for acetaldehyde, and 50 min for ethyl acetate. Previous research has shown that a higher Si/Al ratio in a metal-modified zeolite framework enhances the framework’s hydrophobicity and reduces its number of polar sites, thereby weakening the competitive adsorption of water vapor while strengthening the selective binding of OVOCs [60,61]. During the synthesis of the zeolites, the zeolite framework became negatively charged due to the substitution of Al for Si. These negative charges were compensated for by non-framework cations (such as Na) [62]. The cations located on the surface of the zeolites formed coordinated covalent bonds with water [63]. H2O molecules were arranged within the hydrophilic pore spaces in the well-defined structures of the pore wall surface through both electrostatic interactions and hydrogen bonding [63]. Therefore, a higher Si impregnation concentration may lead to a higher capacity of zeolites for OVOC adsorption under humid conditions. Modification through SiO2 sol–gel impregnation more effectively prevents the loss of elemental Si on the surface of zeolites compared to other modification methods (e.g., alkali modification). In view of cost considerations, 7% Si was chosen as the optimum impregnation concentration for our subsequent studies.

3.4. Effect of Impregnation Time

Solution impregnation is a method that involves altering the properties of the packing material, contributing to enhanced performance and efficiency in gas adsorption processes. The carrier material is fully impregnated with a metal ion solution and then pyrolyzed at high temperatures to form a composite adsorbent [64]. However, a suitable impregnation time not only enables the successful loading of zeolites with more Si and enhances their adsorption capacity, but also prevents the accumulation of excessive SiO2 on the surface of zeolites and the subsequent clogging of pores [65,66]. In this study, different impregnation times were investigated based on a 7 wt% impregnation concentration of Si. For ethanol and ethyl acetate, 12 h impregnation produced the greatest improvement in adsorption capacity, with this capacity reaching 59.4 mg·g−1 and 198 mg·g−1, respectively (Figure 8). The impregnation time of 12 h substantially extended the penetration and equilibrium adsorption time for ethyl acetate (Figure 8d). The optimum impregnation time for the SiO2 sol–gels was 12 h, ensuring saturation of the zeolite surface loading without causing a reduction in the specific surface area due to pore blockage.

3.5. Effect of Calcination Temperature

As previously reported, calcination increased the zeolites’ OVOC removal performance by removing hydrated water and broadening their pore size [67,68]. Negative effects of calcination are probably caused by the use of zeolites with various components and structural characteristics and different calcination temperatures [69,70]. Functional group modifications on the surface of zeolites occur due to variations in calcination temperature, resulting in pore collapse and surface area reduction [71]. Various calcination temperatures were investigated in this study (Figure 9). With an increase in the calcination temperature, the adsorption capacities for the three kinds of OVOCs showed a trend of increasing and then decreasing, whereas the increase in the calcination temperature for ethanol was not significant. The zeolites’ adsorption capacity for acetaldehyde peaked at 350 °C with 94.4 mg·g−1, and their ethanol and ethyl acetate adsorption capacities reached their maximum at 500 °C (59.4 mg·g−1 and 200 mg·g−1, respectively). Furthermore, an increase in the calcination time substantially extended the penetration and equilibrium adsorption time for ethanol and ethyl acetate (Figure 9c,d). This effect was probably due to the collapse of the pore walls of the zeolites at high calcination temperatures, which destroyed their pore structure and led to a reduced adsorption capacity [72]. At calcination temperatures of 350 °C and 500 °C, the SiO2 sol–gels were not only successfully loaded onto the surface of the zeolites, but also chemically reacted with the zeolites to enrich their pore channels. This resulted in complete activation of the zeolites and high adsorption capacities. Previous studies have shown that the structure and framework of the stretching vibration band of Si (Al)–O can be destroyed by an increase in the calcination temperature [73]. Furthermore, the BET specific surface area decreased with elevation of the calcination temperature beyond a certain threshold (500 °C). Increasing the temperature under which the SiO2 sol–gels were loaded onto the surface of the zeolites from 350 °C to 500 °C increased the specific surface area of the zeolites and changed their surface structure. The XRD, BET, and SEM analysis results confirm these findings.

4. Conclusions

In conclusion, the modification of NaY–zeolite using various nano-metals (Fe, Ti, Si, or Ce) through sol–gel and impregnation methods enhanced its OVOC adsorption. The high adsorption capacities of Si–zeolite for ethanol, acetaldehyde, and ethyl acetate were attributed to its elevated surface area, unique morphology, and high Si/Al ratio, which ensured the stability of zeolite. Conditions of 7% Si impregnation with a 12 h impregnation time and a 350 °C calcination temperature not only optimized costs, but also yielded significant improvements in performance, making these the optimal conditions for multifaceted applications. In summary, nano-metal modification significantly influenced the adsorption capacity of zeolite, with the impregnation concentration and calcination temperature being crucial factors. These adjustments not only altered the zeolite’s pore size and distribution but also enhanced its adsorption performance. The chemisorption of metal oxides with oxygen functional groups in OVOCs, combined with physical adsorption across a high specific surface area, collectively contributed to a notable improvement in adsorption capacity. These results provide detailed insight into the potential of metal-modified zeolites to selectively adsorb OVOCs, highlighting the importance of optimizing processes for the decontamination of oxygenated volatile organic pollutants. The metal-modified zeolite process employed in this study is simple and cost-effective, demonstrating feasibility for large-scale implementation and significant practical application potential.

Author Contributions

Y.W.: methodology, formal analysis, writing—original draft. H.J.: conceptualization, investigation, data curation, writing—review and editing. W.W.: investigation, data curation. Z.Z.: investigation, data curation. X.W.: investigation, data curation. M.Z.: supervision, investigation, visualization, resources. L.R.: supervision, visualization, resources. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Key R&D Program of China [2019YFC1906004].

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data is contained within the article.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Figure 1. Schematic diagram of fixed-bed OVOC dynamic adsorption test system.
Figure 1. Schematic diagram of fixed-bed OVOC dynamic adsorption test system.
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Figure 2. Nitrogen adsorption–desorption BET loops of four zeolites.
Figure 2. Nitrogen adsorption–desorption BET loops of four zeolites.
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Figure 3. XRD pattern of different modified zeolites.
Figure 3. XRD pattern of different modified zeolites.
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Figure 4. SEM-EDS results of different modified zeolites.
Figure 4. SEM-EDS results of different modified zeolites.
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Figure 5. FT-IR results of modified zeolites.
Figure 5. FT-IR results of modified zeolites.
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Figure 6. (a) Adsorption capacities (20 °C). Breakthrough curves of different metal-modified zeolites for (b) ethanol, (c) acetaldehyde, and (d) ethyl acetate.
Figure 6. (a) Adsorption capacities (20 °C). Breakthrough curves of different metal-modified zeolites for (b) ethanol, (c) acetaldehyde, and (d) ethyl acetate.
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Figure 7. (a) OVOC adsorption capacities. Breakthrough curves of zeolites modified with different impregnation concentrations for (b) ethanol, (c) acetaldehyde, and (d) ethyl acetate. Notes: Si is used as a modifier, with different impregnation concentrations (3%, 5%, 7%, 10%).
Figure 7. (a) OVOC adsorption capacities. Breakthrough curves of zeolites modified with different impregnation concentrations for (b) ethanol, (c) acetaldehyde, and (d) ethyl acetate. Notes: Si is used as a modifier, with different impregnation concentrations (3%, 5%, 7%, 10%).
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Figure 8. (a) OVOC adsorption capacities. Breakthrough curves of zeolites modified under different impregnation times for (b) ethanol, (c) acetaldehyde, and (d) ethyl acetate. Notes: Si is used as a modifier, and the impregnation concentration is 7%, with different impregnation times (6 h, 12 h, 24 h, 36 h).
Figure 8. (a) OVOC adsorption capacities. Breakthrough curves of zeolites modified under different impregnation times for (b) ethanol, (c) acetaldehyde, and (d) ethyl acetate. Notes: Si is used as a modifier, and the impregnation concentration is 7%, with different impregnation times (6 h, 12 h, 24 h, 36 h).
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Figure 9. (a) OVOC adsorption capacities. Breakthrough curves of zeolites modified at different calcination temperatures for (b) ethanol, (c) acetaldehyde, and (d) ethyl acetate. Notes: Si is used as a modifier, and the impregnation concentration is 7%, impregnation time is 12 h, with different calcination temperatures (200 °C, 350 °C, 500 °C, 650 °C).
Figure 9. (a) OVOC adsorption capacities. Breakthrough curves of zeolites modified at different calcination temperatures for (b) ethanol, (c) acetaldehyde, and (d) ethyl acetate. Notes: Si is used as a modifier, and the impregnation concentration is 7%, impregnation time is 12 h, with different calcination temperatures (200 °C, 350 °C, 500 °C, 650 °C).
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Table 1. Surface properties of adsorbents used.
Table 1. Surface properties of adsorbents used.
AdsorbentBET Surface Area S.A. (m2/g)Total Pore Volume
(cm3/g)		Mean Pore Diameter
(nm)
Zeolite3150.211.93
Fe-zeolite3630.252.79
Ti-zeolite4300.211.96
Si-zeolite4390.271.95
Ce-zeolite4060.201.98
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Wang, Y.; Jiang, H.; Wei, W.; Zhang, Z.; Wang, X.; Zhang, M.; Ren, L. Adsorption and Desorption Characteristics of Nano-Metal-Modified Zeolite for Removal of Oxygenated Volatile Organic Compounds. Coatings 2025, 15, 1206. https://doi.org/10.3390/coatings15101206

AMA Style

Wang Y, Jiang H, Wei W, Zhang Z, Wang X, Zhang M, Ren L. Adsorption and Desorption Characteristics of Nano-Metal-Modified Zeolite for Removal of Oxygenated Volatile Organic Compounds. Coatings. 2025; 15(10):1206. https://doi.org/10.3390/coatings15101206

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Wang, Yue, Hairong Jiang, Wenhui Wei, Zhengao Zhang, Xiaowei Wang, Minglu Zhang, and Lianhai Ren. 2025. "Adsorption and Desorption Characteristics of Nano-Metal-Modified Zeolite for Removal of Oxygenated Volatile Organic Compounds" Coatings 15, no. 10: 1206. https://doi.org/10.3390/coatings15101206

APA Style

Wang, Y., Jiang, H., Wei, W., Zhang, Z., Wang, X., Zhang, M., & Ren, L. (2025). Adsorption and Desorption Characteristics of Nano-Metal-Modified Zeolite for Removal of Oxygenated Volatile Organic Compounds. Coatings, 15(10), 1206. https://doi.org/10.3390/coatings15101206

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