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Magnetic iron-based MOF immobilized on Sephadex: A reusable catalyst for hydrogen generation and pesticide hydrolysis
*Corresponding author: E-mail address: n_elmetwaly00@yahoo.com (N. El-Metwaly)
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Received: ,
Accepted: ,
Abstract
Development of efficient and reusable catalysts for environmental remediation and clean energy production has gained significant attention. In the current work, the generation of hydrogen gas, as green energy, and pesticide degradation were concurrently performed in the presence of Fe-BDC-NH2@Sephadex as an effective recyclable catalyst. Formerly, the Fe-BDC-NH2@Sephadex composite was directly synthesized by the in-situ growth of Fe-BDC-NH2 within the polymeric matrix of Sephadex. The point of innovation in the current approach is to immobilize Sephadex within Fe-BDC-NH₂ to prepare a recyclable composite as a catalyst that can be concurrently exploited in the generation of hydrogen gas and pesticide degradation. Scanning electron microscope (SEM) images reveal that spherical particles of Sephadex macromolecules were fully covered with Fe-BDC-NH2 particles. Data on catalytic generation of hydrogen proclaimed that the increment in catalyst dose, borohydride concentration, and temperature was accompanied by a significant enhancement in the hydrogen production. After 20 min, the amount of generated hydrogen was raised from 167 to 308 mL by using 10% NaOH. While the volume of generated hydrogen reached 403 mL within 20 min by raising the Fe-BDC-NH2@Sephadex dose to 40 mg. The prothiofos hydrolysis was significantly improved in the presence of the Fe-BDC-NH2@Sephadex catalyst, and 98.4% of prothiofos was hydrolyzed in 150 min. Catalytic hydrolysis of sodium borohydride and prothiofos was lowered by 19.4% and 9.4% after six reusing hydrolysis cycles, respectively. Fe-BDC-NH2@Sephadex showed good stability and reusability against repetitive use cycles in the hydrolysis of sodium borohydride and prothiofos, and can easily separate from the medium by magnet.
Keywords
Fe-BDC-NH2
H2 production
Hydrolysis
NaBH4
Prothifos
Recyclable
1. Introduction
The exploitation of fossil fuels as a source of energy causes different problems with dangerous effects on human health, limiting their applications, and affecting their price and worldwide distribution [1]. Additionally, rapid consumption results in excessive greenhouse gas emission [2]. As a result, hydrogen has been newly identified as a promising source of energy. Hydrogen gas is stored in the form of “atomic hydrogen” or “molecular hydrogen” [3]. One of the most applicable hydrides for hydrogen storage is sodium borohydride, owing to cost effectiveness, rich source of hydrogen, safer storage, and the simplicity of hydrolysis & recyclability for borate [4]. Sodium borohydride could produce hydrogen gas at ambient conditions and can proceed spontaneously and exothermically [5], and it is ascribed as a water-splitting laborer, due to the affinity for liberating 50% hydrogen from H2O [6]. About 7-8% of sodium borohydride is only exploited for the production of hydrogen. Hydrolysis is quite slow and can be discontinued [7]. Therefore, the design of reactive catalysts is in high demand. The challenge for sodium borohydride hydrolysis is for high production of hydrogen by reaction acceleration [1].
Sodium borohydride hydrolysis can be catalyzed by homogeneous or heterogeneous catalysts [8]. The latter include metal nanoparticles [9], carbon-based materials, and biopolymer-based nanocomposites [10]. Heterogeneous catalysts are preferred due to easy separation from the reaction medium. Nanomaterials offer high catalytic activity due to their large surface area, but tend to agglomerate, requiring support templates. Metal-organic frameworks (MOFs), porous crystalline materials with large surface areas, are widely used in adsorption [11], electrochemical applications [12], catalysis [13], and hydrogen storage [14]. While MOFs have been well studied for hydrogen production via photo-catalysis and electro-catalysis, their application in sodium borohydride hydrolysis has only recently been reported [15], highlighting the need for further investigation in this promising area.
On the other hand, the persistence of pesticides is a major cause of organic environmental pollution [16]. Organophosphorus pesticides (OPPs), widely used as insecticides and herbicides, are esters of phosphoric or thio-phosphoric acid. Initially introduced as alternatives to hazardous chlorinated pesticides [17], OPPs gained global popularity [18]. Conventional degradation methods, such as chemical treatment and incineration, pose risks of secondary exposure and are often economically unviable. Therefore, increasing attention has been directed toward developing environmentally friendly and cost-effective techniques for OPP degradation or hydrolysis [19]. Research continues to explore safer and more efficient approaches for mitigating their environmental impact.
Various bio-composites have been synthesized and applied in industrial, medical, and environmental fields. Their advanced properties, largely determined by size and surface features, have led to an increase in interest in water treatment applications [20]. Incorporating metals into biopolymer matrices enhances their functionality, enabling broader applications. Two main techniques are used for metal incorporation: solvent intercalation and melt intercalation. In the solvent method, biopolymers like polysaccharides are dissolved in a solvent before mixing with metal precursors, allowing polymer chain intercalation. Melt intercalation is preferable for its simplicity. It involves mixing the metal and biopolymer directly in the reaction medium [21]. Several metal@biopolymer composites have shown effective removal of pesticides such as atrazine, dichlorvos, and organophosphates [22]. Though limited, these studies highlight the potential of bio-composites as promising materials for pesticide degradation, offering an eco-friendly and efficient alternative to conventional methods.
In the current work, the catalytic activity of Fe-BDC-NH2@Sephadex as an effective recyclable catalyst was concurrently performed for the generation of hydrogen gas as green energy and for pesticide degradation. Formerly, Fe-BDC-NH2@Sephadex composite was directly synthesized by the in-situ growth of Fe-BDC-NH2 within the polymeric matrix of Sephadex. The point of innovation in the current approach is to immobilize Sephadex within Fe-BDC-NH₂ to prepare the recyclable active catalyst that can be concurrently exploited in the generation of hydrogen gas and pesticide degradation. Fe-BDC-NH₂ MOF was prepared in situ within the Sephadex matrix to form the composite. The synthesized material was characterized using various techniques, including scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). The catalytic activity of Fe-BDC-NH₂@Sephadex was then evaluated in the hydrolysis of sodium borohydride for hydrogen generation, as well as in the degradation of prothiofos. Kinetic studies were conducted for both reactions, and the reusability of the catalyst was also assessed.
2. Materials and Methods
2.1. Materials
Ferric chloride hexahydrate (FeCl3.6H2O, 97%,), 2-aminoterephethalic acid (C8H7NO4, NH2-BDC, 99%), Sephadex (Sephadex LH-20, bead size = 25-100 μm), sodium hydroxide (NaOH, 98%), and ethanol (C2H6O, ≥ 99.9%) were all acquired from Sigma-Aldrich and used as received.
2.2. Preparation of Fe-BDC-NH2
Fe-BDC-NH2 was synthesized as follows: 0.71 g of 2-aminoterephethalic acid (3.95 mM) was dissolved in 100 mL NaOH (1 M) and stirred for 5 min to obtain solution A. Solution B was prepared by dissolving 2.14 g of ferric chloride in 48.6 mL of distilled H2O. After the two solutions became completely clear, solution A was added to solution B gradually, under continuous stirring at room temperature. After 24 h, the obtained product was filtered off and washed several times with distilled water, followed by ethanol to remove the residual organic ligand. Finally, the obtained brown powder was dried at 60°C overnight prior to use.
2.3. Preparation of Fe-BDC-NH2@Sephadex
Fe-BDC-NH2@Sephadex composite was synthesized through the direct formation of Fe-BDC-NH2 within the matrix of Sephadex. Initially, 1.0 g of Sephadex was dispersed in 50 mL of distilled water at room temperature under continuous stirring. Secondly, 2.14 g of ferric nitrate was dissolved in distilled water, followed by the addition to the Sephadex solution, and then the mixture was heated at 50°C for 2 h. NH2–BDC (0.71 g) was dissolved in 50 mL of sodium hydroxide (1 M) and then drop-wise added to the previous mixture. The mixture was stirred overnight at 50°C, and the final product was carefully collected. The collected complex was washed with water, followed by ethanol, and dried at 60°C.
2.4. Characterization and analysis
The geometrical and topographical features for Sephadex and the prepared Fe-BDC-NH2@Sephadex were examined using an SEM (HRSEM, JEM-1200 – JEOL, Japan) attached with the field emission (FE) gun. The infrared spectral analysis was investigated by using an FTIR 6100 Jasco spectrometer using the attenuated total reflection (ATR) unit. The spectral data were collected in the transmission (T%) mode in the wavenumber range of 500–4000 cm–1. The XRD analysis was measured by using the X'Pert MPD Philips diffractometer at room temperature in the 2θ° region of 3°–40°. The applied parameters were Cu Kα X-radiation at 40 kV and λ = 1.5406 Å. The surface properties presented in Brunauer-Emmett-Teller (BET) surface area, pore size, and pore volume were all estimated for Sephadex, Fe-BDC-NH2, and Fe-BDC-NH2@Sephadex. The measurements were performed using NOVA touch 2LX Quantachrome version 1.2, while samples were primarily degassed at 70°C under vacuum. The magnetic properties for the synthesized Fe-BDC-NH2@Sephadex were recorded by using a vibrating sample magnetometer (VSM) analyzer (VSM 7410 Series).
2.5. Hydrogen generation process
The experiment of hydrogen generation was carried out using the displacement of water method by using the catalytic hydrolysis of NaBH4. In a sealed bottle attached with a temperature controller, 10 mL of the solution containing 1% NaOH and 1% NaBH4 was kept at 30°C; 10 mg of the prepared Fe-BDC-NH2@Sephadex catalyst was dispersed in the solution bottle. The outlet tube was connected to the bottle to collect the generated hydrogen gas. The other side of the connected tube was located under an inverted water-filled gas burette, which was submerged in a water-filled container. The volume of water displaced inside the burette was measured, referring to the volume of the produced hydrogen gas from the system.
2.6. Catalytic hydrolysis of methyl parathion
The hydrolysis of prothiofos pesticide was catalytically studied in the presence of Fe-BDC-NH2@Sephadex as a catalyst. The catalytic hydrolysis was carried out in a 10 mL screw-capped vial at room temperature under dark conditions. In the vials, 30 mg of Fe-BDC-NH2@Sephadex catalyst was added to 3 mL of prothiofos aqueous solution (3.5 g L-1). The mixture was maintained under magnetic stirring for 4 h. The suspension was centrifuged at 12000 rpm, and UV-vis spectra of the supernatant solutions were measured using the UV2400 Shimadzu instrument. The catalytic hydrolysis activity was estimated based on the residual concentration of prothiofos, while the maximum absorbance varied from 277 nm to 292 nm.
3. Results and discussion
3.1. Preparation of Fe-BDC-NH2@Sephadex composite
Fe-BDC-NH2@Sephadex composite was prepared using the in-situ growth technique, while Fe-BDC-NH2 was formed and directly incorporated within the polymeric matrix of Sephadex, as schematically shown in Figure 1. Firstly, by adding Fe3+ ions to PUS, coordination interactions between ferric ions (Fe3+) and the hydroxyl groups in Sephadex macromolecules can be formed. By the addition of BDC-NH2 as an organic linker, many interactions may take place between BDC-NH2 and Fe@Sephadex, forming the final composite of Fe-BDC-NH2@Sephadex. Hydrogen bonding and coordination bonding can be created between the hydroxyl & amine groups in BDC-NH2 and the hydroxyl groups & Fe3+ in Fe@Sephadex. Herein, Fe3+ may act as a cross-linker and interact with BDC-NH2 from one side and with Sephadex from another side, obtaining Fe-BDC-NH2@Sephadex, while both BDC-NH2 and Sephadex acted as mixed linkers [23].
- Schematic for synthesis of Fe-BDC-NH2@Sephadex.
The morphological features and geometry of the synthesized Fe-BDC-NH2@Sephadex composite were investigated with two different magnifications, as shown in Figure 2. For Sephadex, ideal spherical particles like balls were clearly observed under a microscope with an estimated diameter of 40–60 µm. After the direct incorporation of Fe-BDC-NH2, the spherical particles of Sephadex were completely covered with the particles of Fe-BDC-NH2. Furthermore, the signal of Fe (at 6.2 keV) was recorded beside those of C and O for Sephadex. The data confirmed the successful immobilization of Fe-BDC-NH2 within the matrix of Sephadex.
- Micro images at two different magnifications and EDS spectral analysis for; (a, b, c) Sephadex and (d, e, f) Fe-BDC-NH2@Sephadex.
The spectral results of infrared for the synthesized Fe-BDC-NH2@Sephadex have been presented in Figure 3(i). Sephadex, as a polysaccharide macromolecule, showed five characteristic transmission bands at 3366, 2892, 1674, 1546, and 1155 cm-1, which are assigned for the hydroxyl groups, CH2 aliphatic, carboxylate group, carbonyl groups, and C-O-C group, respectively. Fe-BDC-NH2 exhibited five distinctive bands at 3262 cm-1 for the hydroxyl group, 1716 cm-1 for the carboxylate group, 1644 cm-1 for the C=C aromatic bond, 1434/1456 cm-1 for the NH2 group,1258 cm-1 for the C–O bond, and 778 cm-1 for the O-Fe bond [24]. In the case of Fe-BDC-NH2@Sephadex composite, all bands of Fe-BDC-NH2 were recorded beside that of Sephadex and confirmed the successful immobilization of Fe-BDC-NH2.
![[i] XRD spectral data and [ii] FTIR analysis for (a) Sephadex, (b) Fe-BDC-NH2, and (c) Fe-BDC-NH2@Sephadex.](/content/184/2026/0/1/img/AJC_1049_2025-g3.png)
- [i] XRD spectral data and [ii] FTIR analysis for (a) Sephadex, (b) Fe-BDC-NH2, and (c) Fe-BDC-NH2@Sephadex.
The results of diffraction (Figure 3ii) indicated that Sephadex had one broad diffraction peak at 2θ° = 18.8°. The pure Fe-BDC-NH2 exhibited many diffraction peaks at 2θ° = 5.2°, 6.1°, 8.1°, 9.0°, and 18.2°, which are related to the crystalline structure as reported in literature [25]. The main diffraction of Fe-BDC-NH2 was clearly detected alongside the diffraction of Sephadex. So, as the broad band centered at 18.8° for Sephadex is shifted to about 12.5° for Fe-BDC-NH2@Sephadex, this could be attributed to the effect of uploading of MOF within the crystalline networked structure of Sephadex. However, it could be mentioned that the crystalline structure of Fe-BDC-NH2 was not significantly changed after immobilization within Sephadex matrix.
The textural properties for the synthesized Fe-BDC-NH2 and Fe-BDC-NH2@Sephadex composite were measured, and the obtained data were inserted in Table 1. The results show that the BET surface area is significantly enlarged from 83.12 m2 g-1 for Sephadex to 816.91 m2 g-1 for Fe-BDC-NH2@Sephadex composite. This significant increase can be attributed to the successful incorporation and uniform distribution of the Fe-BDC-NH₂ framework within the porous structure of Sephadex, leading to the exposure of a larger number of active sites. The high surface area of Fe-BDC-NH₂ is known to arise from its crystalline and microporous MOF nature, which provides numerous accessible pores and channels that facilitate molecular diffusion and adsorption. Furthermore, the pore diameter is reduced from 4.11 nm for Sephadex to 2.62 nm in the composite. This reduction in pore size suggests that Fe-BDC-NH₂ nanoparticles partially occupied or modified the original Sephadex pores, resulting in a more compact and fine-textured structure. The combination of a higher surface area and reduced pore diameter is beneficial for enhancing the adsorption efficiency, as it increases the availability of adsorption sites and improves the interaction between the adsorbent surface and pollutant molecules.
| Catalyst |
BET surface area (m2 g-1) |
Pore volume (cm3 g-1) |
Pore diameter (nm) |
|---|---|---|---|
| Sephadex | 83.12 | 1.11 | 4.11 |
| Fe-BDC-NH2 | 775.72 | 0.054 | 1.52 |
| Fe-BDC-NH2@Sephadex | 816.91 | 1.09 | 2.62 |
Magnetic properties for the synthesized Fe-BDC-NH2@Sephadex were estimated by measuring the magnetism using the VSM analyzer. The obtained results reveal that the Fe-BDC-NH₂@Sephadex composite exhibits a saturation magnetization value of 8.2 emu g-1, indicating the successful incorporation of iron species within the hybrid framework. Although the magnetization is moderate compared to pure iron oxides, it is sufficient to impart a distinct magnetic response to the composite material. Importantly, the absence of a hysteresis loop and the coercive force approaching zero confirm the paramagnetic nature of the Fe-BDC-NH₂@Sephadex composite. These magnetic properties reflect that the obtained composite exhibited good magnetic character, which is quite sufficient to easily separate the composite from the polluted solution by an external magnet (Figure 4).
- VSM magnetism for Fe-BDC-NH2@Sephadex composite.
3.2. Catalytic performance for hydrogen production
A comparable overview for the catalytic performance in the hydrogen production via hydrolysis of sodium borohydride, for Fe-BDC-NH2@Sephadex composite versus Sephadex, was demonstrated. The generated hydrogen gas (mL) from the prepared system was estimated via the evaluation of the volume of water that is displaced by the evolved hydrogen gas. The effect of duration on the production of hydrogen has been plotted in Figure 5, and from the obtained data, it can be seen that the volume of the generated hydrogen gas gradually increased with the prolongation of the duration. After 20 min, the generated hydrogen gas was 173 mL in the case of Sephadex and reached 362 mL for Fe-BDC-NH2@Sephadex. This could declare that the generation of hydrogen was enhanced by a factor of 2.1 using the synthesized catalyst of Fe-BDC-NH2@Sephadex.
- Hydrogen generation from NaBH4 (10 mg catalyst, 1.5% NaBH4, 7% NaOH, at 30 ͦC).
Figure 6(a) shows the effect of NaOH concentration on the volume of the generated hydrogen gas, as it can be seen that, using Fe-BDC-NH2@Sephadex as a catalyst, an increase in the percentage of sodium borohydride is reflected in the increase in the volume of the liberated gas over time. Additionally, 167 mL of hydrogen gas was generated after 20 min without sodium hydroxide, whereas 308 mL of hydrogen was generated using 10% NaOH. On the other hand, using Sephadex as a catalyst (Figure S1a), an increment of NaOH from 0% up to 10% resulted in an increase in the amount of the evolved gas from 81 mL to 254 mL after 20 min. The data revealed the vital role of sodium hydroxide in catalyzing the reaction of hydrogen generation from borohydride via hydrolysis. As it was reported that [26] sodium hydroxide, a strong alkaline, acts in keeping sodium borohydride more stable.
- Hydrogen generation in the presence of Fe-BDC-NH2@Sephadex at different effects: (a) NaOH concentration, (b) NaBH4 concentration, (c) catalyst dose, and (d) Temperature.
Figure 6(b) represents the effect of NaBH4 concentration on the hydrogen generation. Using Sephadex as a catalyst, and from the plotted data, it could be decided that increasing the concentration of NaBH4 significantly increased the amount of the liberated hydrogen to be significantly raising it from 181 mL to 338 mL within 20 min, using 1.5% & 5% of NaBH4 (Figure S1b), respectively. Similarly, in the case of using Fe-BDC-NH2@Sephadex as a catalyst, an increment of NaBH4 concentration resulted in an extreme increment in the volume of generated hydrogen, which was raised from 282 mL (1.5% NaBH4) to 409 mL (5% NaBH4). This finding could be logically explained by increasing sodium borohydride as a hydrogen source, consequently reflecting an increase in the possibility of hydrogen generation.
Similarly, the amount of evolved hydrogen was progressively enlarged by increment of the catalyst dose (Figure 6c). The generated hydrogen in 20 min was greatly raised from 74 mL to 357 mL, using 10 mg and 40 mg of Sephadex, respectively (Figure S1c). Whereas, in the case of using Fe-BDC-NH2@Sephadex as a catalyst (Figure 6c), 218 mL and 403 mL of hydrogen gas were liberated within 20 min when the applied catalyst dose was raised from 10 mg to 40 mg, respectively. These affirm the role of Fe-BDC-NH2@Sephadex as a catalyst in accelerating the production of hydrogen from borohydride. Raising the reaction temperature was accompanied by an enhancement of the amount of generated hydrogen. In case of using Sephadex as a catalyst (Figure S1d), the evaluated amount of hydrogen was increased from 106 mL to 328 mL after 20 min by elevation of reaction temperature from 20°C to 50°C. However, using Fe-BDC-NH2@Sephadex with rising the reaction temperature up to 50°C resulted in liberation of 363 mL of hydrogen gas after 20 min (Figure 6d). This could be attributed to the effect of temperature elevation to help in increasing the rate of collision between the reactants, and hence, the liberated hydrogen is raised.
Kinetic studies for any reaction are quite important in order to understand the reaction behavior. Herein, the kinetic study of hydrogen generation from borohydride in the presence of Fe-BDC-NH2@Sephadex was performed at different temperatures via the linear relationship for zero-order, first-order, and Langmuir-Hinshelwood (as presented in Figure 7). The kinetic results have been presented in Figure 6 and (Figure S2), while the kinetic parameters were all estimated and presented in Table 2. From the fitted data and the estimated parameters, the best fitting of hydrogen generation results was recorded for the zero-order kinetic model, with R2 = 0.97-0.99. The hydrogen generation rate was higher in the case of using Fe-BDC-NH2@Sephadex as a catalyst rather than Sephadex. In the case of Fe-BDC-NH2@Sephadex, the reaction rate of hydrogen generation was gradually increased with temperature from 20°C to 50°C, as the value of K0 was considerably enlarged from 8.46 M L-1 min-1 to 13.20 M L-1 min-1. The increment in the hydrogen generation kinetics was 1.6 times related to raising the temperature of the medium. Based on the previous studies [4], the hydrolysis reaction of sodium borohydride normally obeys the zero-order model, while the linear increase in hydrogen generation was observed with time at a certain concentration of borohydride. Additionally, the linearity of kinetic data for hydrogen production was not recorded for either the first-order or the Langmuir-Hinshelwood models.
- Linear regression for the hydrogen generation in the presence of Fe-BDC-NH2@Sephadex at different temperatures; (a) zero-order, (b) first-order, and (c) Langmuir-Hinshelwood.
| Catalyst |
Temperature (°C) |
Zero-order | First-order | Langmuir-Hinshelwood | |||
|---|---|---|---|---|---|---|---|
| K0 (M L-1 min-1) | R2 | K1 x 10-2 (1 min-1) | R2 | KL-H x 10-6 (M L-1 min-1) | R2 | ||
| Sephadex | 20 | 7.54 ± 0.39 | 0.98 | 3.36 ± 0.01 | 0.99 | 5.03 ± 0.19 | 0.99 |
| 30 | 7.17 ± 0.20 | 0.99 | 2.78 ± 0.18 | 0.97 | 4.18 ± 0.27 | 0.97 | |
| 40 | 8.51 ± 0.31 | 0.99 | 3.11 ± 1.2 | 0.99 | 4.66 ± 0.18 | 0.99 | |
| 50 | 4.60 ± 0.20 | 0.97 | 1.34 ± 0.08 | 0.99 | 2.01 ± 0.11 | 0.98 | |
| Fe-BDC-NH2@Sephadex | 20 | 8.46 ± 0.22 | 0.99 | 5.89 ± 0.72 | 0.89 | 8.85 ± 1.07 | 0.89 |
| 30 | 9.68 ± 0.21 | 0.99 | 6.53 ± 0.95 | 0.87 | 9.79 ± 1.43 | 0.87 | |
| 40 | 12.34 ± 0.29 | 0.99 | 7.39 ± 1.21 | 0.88 | 11.09 ± 1.81 | 0.88 | |
| 50 | 13.20 ± 0.83 | 0.97 | 6.27 ± 1.01 | 0.90 | 9.41 ± 1.52 | 0.90 | |
3.3. Mechanism for hydrogen generation
The catalytic generation of hydrogen gas from sodium borohydride was carried out through the hydrolysis action, and subsequently, the mechanism of hydrolysis could be proposed herein. At the beginning, sodium borohydride molecules were suggested to adsorb onto the surface of Fe-BDC-NH2@Sephadex catalyst. Some weak interactions presented hydrogen bonds may be easily formed between the hydroxyl/amine groups in Fe-BDC-NH2@Sephadex and the hydrogen of borohydride, which in turn are advisable for releasing and generating hydrogen gas [1]. Based on the formerly obtained data, the hydrogen generation is largely increased with the sodium borohydride concentration (Figure 6b). This may be explained by the presence of a higher amount of existing sodium metaborate (NaBO2) due to the hydrolysis of sodium borohydride [27]. Importantly, the iron centers (Fe3⁺/Fe2⁺) within the Fe-BDC-NH₂ framework play a pivotal catalytic role in the hydrolysis reaction. The Fe sites act as active catalytic centers that facilitate the heterolytic cleavage of the B–H bond in NaBH₄ through electron transfer processes. During the reaction, Fe3⁺ can interact with hydride species (H⁻) from BH₄⁻, forming transient Fe–H intermediates. These intermediates subsequently react with water molecules adsorbed on the catalyst surface, leading to the formation of hydrogen gas (H₂) and regeneration of the active Fe3⁺ sites. This redox cycling between Fe2⁺ and Fe3⁺ significantly enhances the reaction kinetics by providing multiple electron transfer pathways.
The hydrogen generation performance of the Fe-BDC-NH₂@Sephadex catalyst during NaBH₄ hydrolysis was compared with that of various catalysts reported in previous studies, and the comparative results have been summarized in Table 3. This comparison provides valuable insight into the catalytic efficiency of Fe-BDC-NH₂@Sephadex in relation to other cobalt- and iron-based materials previously used for similar purposes. Taking into account the concentration of NaBH₄ employed in each case, it was observed that the Fe-BDC-NH₂@Sephadex catalyst exhibited a significantly higher hydrogen generation rate than other recently reported catalysts, such as Co@activated carbon [28], Co@γ-Al2O3 [28], and Co-DABCO-TPA@C [27] (Figure 7). This enhanced activity can be attributed to the synergistic interaction between the Fe-BDC-NH₂ metal-organic framework and the Sephadex polymer support, which offers many accessible active sites and improved dispersion of Fe centers, thereby promoting rapid hydrolysis of NaBH₄. Although some studies have reported higher hydrogen yields using larger catalyst dosages, the superior activity of Fe-BDC-NH₂@Sephadex under comparable or milder reaction conditions highlights its high intrinsic catalytic efficiency. In contrast, the catalyst Fe₃O₄@C–Co demonstrated a higher hydrogen generation rate, which can be logically related to the use of a fivefold higher NaBH₄ concentration in that study [29]; such conditions naturally favor greater hydrogen evolution but do not necessarily indicate better catalytic efficiency. Therefore, when the NaBH₄ concentration and other parameters are normalized, Fe-BDC-NH₂@Sephadex displays competitive or even superior catalytic behavior. These findings confirm that Fe-BDC-NH₂@Sephadex is an efficient and promising catalyst for NaBH₄ hydrolysis, combining high catalytic activity with structural stability and reusability, and performing comparably or better than all the catalysts listed in Table 3.
3.4. Recyclability of Fe-BDC-NH2@Sephadex in NaBH4 hydrolysis
The stability of the synthesized Fe-BDC-NH2@Sephadex catalyst in the generation of hydrogen was studied through investigation of the repetitive use cycles to check the wide-scale applicability. After the first cycle, the applied Fe-BDC-NH2@Sephadex catalyst was collected from the system by magnet, followed by washing with distilled water and drying in air. The regenerated Fe-BDC-NH2@Sephadex was then applied in the next catalytic cycle for the generation of hydrogen. The generation of hydrogen gas was gradually lowered by an increment in the recyclability of Fe-BDC-NH2@Sephadex catalyst (Figure 8a). The maximum volume of generated hydrogen was reduced from 386 mL after the first cycle to 311 mL after six reusing cycles. The decrement in the generation of hydrogen by the regeneration of the catalyst is logically owing to the leaching of some Fe-BDC-NH2 particles to the surroundings during the washing and application process. In general, the reduction in hydrogen generation is quite low, while the decrement percentage was 19.4 % after six recycling processes. The obtained results revealed the substantial stability of the synthesized catalyst of Fe-BDC-NH2@Sephadex with effective activity in the catalytic generation of hydrogen gas with several cycles, reflecting its ability in the large-scale applicability.
- (a) Effect of recyclability of Fe-BDC-NH2@Sephadex on the hydrogen generation from NaBH4. (b) Effect of the hydrogen production on the crystallinity of Fe-BDC-NH2@Sephadex.
The stability of the applied Fe-BDC-NH2@Sephadex as a catalyst after the hydrogen generation was examined through analyzing the XRD. The results in Figure 8(b) declared that there is no observable change in the patterns of XRD for Fe-BDC-NH2@Sephadex after the catalytic application in hydrogen generation. Consequently, the data suggested the stability of Fe-BDC-NH2@Sephadex towards the repetitive catalytic hydrogen generation. The leaching of Fe from the surface of Fe-BDC-NH2@Sephadex to the medium during the catalytic reaction was measured using ICP. The leached Fe after each catalytic cycle was less than 12 ppm, which is quite acceptable and insignificant to affect the stability of the catalyst.
3.5. Catalytic hydrolysis of prothiofos pesticide
The catalytic degradation of prothiofos pesticide via the hydrolysis process was investigated in the presence of Fe-BDC-NH2@Sephadex composite, while the Sephadex was applied as a blank. During the catalytic hydrolysis, prothiofos was degraded to 2,4 2,4-dichlorophenol and O-ethyl-S-propyl phosphorodithioate. Consequently, the characteristic absorbance peak of prothiofos at 277 nm (assigned for π-π* transitions) diminished, and the characterized peak of 2,4-dichlorophenol appeared at 292 nm. Hence, the catalytic hydrolysis of prothiofos was estimated by recording the absorbance, and the hydrolysis percentage was subsequently calculated as presented in Figure 9. The relation between hydrolysis percentage and the time intervals is shown in Figure 9(a), and the absorbance spectra for prothiofos before and after hydrolysis have been presented in Figure 9(b). The data revealed that the hydrolysis of prothiofos was stepwise increased with interval time, and 11.6% of prothiofos was only hydrolyzed within 150 min without a catalyst. While the hydrolysis percentage reached 41.2% in the case of using Sephadex, this may be due to the adsorption effect of prothiofos onto the surface of Sephadex macromolecule. For Fe-BDC-NH2, the hydrolysis of prothiofos was 91.2% within 100 min, which may be attributed to the catalytic effect of Fe-BDC-NH2. While in the presence of Fe-BDC-NH2@Sephadex composite, the hydrolysis percentage of prothiofos was 82.7% after only 40 min and surpassed 98.4% within 100 min. This reflects the effective catalytic and adsorptive role of Fe-BDC-NH2@Sephadex in the hydrolysis of prothiofos, while the catalytic effect may be related to the incorporated Fe-BDC-NH2. Comparing without a catalyst, the use of Fe-BDC-NH2@Sephadex significantly enhances the hydrolysis of prothiofos by 10 times.
- Catalytic hydrolysis of prothiofos in the presence of Fe-BDC-NH2@Sephadex; (a) hydrolysis percentage. (b) UV-Vis absorbance spectra for prothiofos before and after hydrolysis. (c) First-order kinetics for the catalytic hydrolysis of prothiofos.
The kinetics of catalytic hydrolysis in the presence of the applied catalyst were studied, and the data showed the best fit to the pseudo-first order. The first-order constant (k) results have been presented in Figure 9(c). The estimated rate constant was significantly enlarged from 1.2 × 10-3 h-1 without a catalyst to 16.8 × 10-3 h-1 when using Sephadex and to 42.3 × 10-3 h-1 when using Fe-BDC-NH2@Sephadex as a catalyst. The catalytic hydrolysis rate of prothiofos was increased by a factor of 35.3 when Fe-BDC-NH2@Sephadex was applied as a catalyst. While the immobilization of Fe-BDC-NH2 within Sephadex matrix enhanced the catalytic hydrolysis by a factor of 2.5, rather than Sephadex. The hypothesis of pseudo-first order kinetics declared that the prothiofos hydrolysis depends on only one factor of the applied catalyst dose, and subsequently, a faster hydrolysis rate and further enhancement in prothiofos hydrolysis could be attained by exploitation of a higher catalyst dose.
Based on the former studies, hydrolysis of different OPPs using different applied catalysts has been collected in Table 4. The catalytic hydrolysis of prothifos, as one of the OPPs, was compared with the results obtained in the literature. The catalytic hydrolysis of prothiofos was significantly faster than the enzymatic hydrolysis results for parathion, methyl parathion, paraoxon, diazinon, triasophos, fenitrothion, and cyanophos [30,31]. Moreover, using a tri-metallic-based composite catalyst (Pd@Au@Ag@Chitin) showed a lower reduction rate (24.5 × 10-5 m-1) than that of using Fe-BDC-NH2@Sephadex (70.5 × 10-5 m-1) [32]. This means that using a similar hydrolysis process, using Fe-BDC-NH2@Sephadex showed faster catalytic hydrolysis than that of Pd@Au@Ag@Chitin with a 2.9 factor, which reflects the effective catalytic effect of the synthesized Fe-BDC-NH2@Sephadex in prothiofos hydrolysis.
| Catalyst | Pesticides |
Qe (mg g-1) |
Hydrolysis (%) |
K1 × 10-5 (min-1) |
References |
|---|---|---|---|---|---|
| Enzyme | Triazophos | 255.7/ 10 h | [30] | ||
| Parathion | 72.7/ 10 h | ||||
| Methyl parathion | 55.9/ 10 h | ||||
| Diazinon | 36.5/ 10 h | ||||
| Paraoxon | 82.6/ 10 h | ||||
| Cyanophos | 8.5/ 10 h | ||||
| Fenitrothion | 36.1/ 10 h | ||||
| Hexahistidine@ organophosphorus hydrolase | Diazinon | 60 %/24 h | [31] | ||
| Paraoxon | 60 %/24 h | ||||
| Parathion | 62 %/24 h | ||||
| Pd@Au@Ag@Chitin | Prothiofos | 346.5/ 2.5 h | 24.5 | [32] | |
| Fe-BDC-NH2@Sephadex | Prothiofos | 70.5 | Current study |
The decomposition (hydrolysis and degradation) of OPPs in the presence of a catalyst was carried out through cleavage of the O-P bonds [33]. Emam et al. reported and confirmed that prothiofos was hydrolyzed in the presence of Pd@Au@Ag@Chitin through O-P bond fission, producing 2,4-dichlorophenol and O-ethyl-S-propyl-phosphorodithioate [32]. Consequently, the same as literature, hydrolysis of prothiofos using Fe-BDC-NH2@Sephadex may result in the same compounds of 2,4-dichlorophenol and O-ethyl-S-propyl-phosphorodithioate. While Fe-BDC-NH2@Sephadex acts as a potential intermediate, it helps in the reduction of the bond dissociation energy (BDE) of the O-P bond and accelerates the transfer of electrons [32]. It could be supposed that Fe-BDC-NH2@Sephadex forms an intermediate complex primarily with the prothiofos molecules via a coordination bonding between the Fe metal in the catalyst and the S of the pesticide. The performed Fe-S intermediate complex is followed by the bond cleavage, forming much stable fragments (O-ethyl-S-propyl-phosphorodithioate and 2,4-dichlorophenol).
Reusability is a critical factor in determining the practical application of any catalyst, especially in environmental remediation processes. To estimate the recyclability of the synthesized Fe-BDC-NH2@Sephadex catalyst, a series of regeneration and reusing experiments was conducted for the catalytic hydrolysis of prothiofos. After completion of every catalytic hydrolysis cycle, the catalyst Fe-BDC-NH2@Sephadex was separated from the mixture via centrifugation, thoroughly washed with distilled water to remove the residual hydrolysed products, and then washed with ethanol to eliminate any residual. The cleaned/dried catalyst was then reused in subsequent hydrolysis cycles, while the recycling process was performed over 6 consecutive hydrolysis cycles to assess the stability and reusability of the catalyst. As illustrated in Figure 10, the catalytic efficiency showed a gradual marginal decrease with each cycle. This lowering in catalytic activity may be attributed to the minor losses of catalyst material during recovery or potential surface fouling. Despite this, the catalyst retained a high degree of activity, with the hydrolysed percentage of prothiofos decreasing from 98.4% in the first cycle to 89.2% after six cycles, representing a modest 9.4% only. These findings confirm the robust nature and excellent reusability of the Fe-BDC-NH2@Sephadex, indicating its strong potential as an effective and recyclable catalyst for multiple cycles in environmental applications such as pesticide degradation.
- Effect of recyclability of Fe-BDC-NH2@Sephadex on the catalytic hydrolysis of prothiofos.
4. Conclusions
In the current work, the generation of hydrogen gas, as green energy, and pesticide degradation were concurrently performed in the presence of Fe-BDC-NH2@Sephadex as an effective recyclable catalyst. Formerly, Fe-BDC-NH2@Sephadex composite was directly synthesized by the in-situ growth of Fe-BDC-NH2 within the polymeric matrix of Sephadex. The point of innovation in the current approach is to immobilize Sephadex within Fe-BDC-NH₂ in order to prepare a recyclable composite as a catalyst that can be concurrently exploited in the generation of hydrogen gas and pesticide degradation. The obtained results showed that the generation of hydrogen gas was gradually increased with the concentration of borohydride, NaOH concentration, catalyst dose, and temperature. Within only 20 min, the volume of generated hydrogen was enlarged by a factor of 1.8 by using 10% NaOH, while a further increment in the generated hydrogen by a factor of 1.3 was obtained by increasing the catalyst dose to 40 mg. The kinetic parameters show the best fit to the data, which explains the linear growth in hydrogen generation with time at a certain concentration of borohydride. After six reusing cycles of Fe-BDC-NH2@Sephadex, the total evolved hydrogen was reduced by only 19.4%. The catalytic hydrolysis of prothiofos was significantly enhanced in the presence of Fe-BDC-NH2@Sephadex catalyst, while 98.4% of prothiofos was hydrolyzed within 150 min.
As a conclusion, Fe-MOF@Sephadex composite showed a potential for sustainable environmental and energy-related applications. Compared with the conventional catalysts, the synthesized Fe-BDC-NH2@Sephadex catalyst showed some advantages, including good stability in the catalytic hydrolysis of sodium borohydride and prothiofos pesticide against repetitive cycles, and easy removal from the system by a magnetic bar, and consequently can be widely applicable.
Data availability
All relevant data are within the manuscript and available from the corresponding author upon request.
CRediT authorship contribution statement
Salhah H. Alrefaee, Ibrahim S. S. Alatawi: Data curation, formal analysis, methodology, and software; Nada M. Alatawi, Mona Alhasani: Investigation and writing – review & editing; Abdullah A. A. Sari, Abdulkarim Albishri: formal analysis, investigation, writing-original draft. Amal T. Mogharbel and Nashwa el-Metwaly: Supervision and administration of research group.
Declaration of competing interest
There are no conflicts of interest.
Declaration of generative AI and AI-assisted technologies in the writing process
The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.
Supplementary data
Supplementary material to this article can be found online at https://dx.doi.org/10.25259/AJC_1049_2025.
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