2025 Volume 66 Issue 1 Pages 130-135
Nickel-based zeolitic imidazolate framework (Ni-ZIF) nanoparticles were prepared by dissolving nickel nitrate hexahydrate (Ni(NO3)2·6H2O) and 2-methylimidazole (C4H6N2) in methanol (CH3OH) and stirring the resulting solution for 6 h at 60°C. The resulting precipitate was collected by centrifugation and dried at 60°C for 24 h to afford solid-state Ni-ZIF nanoparticles. Next, a Ni-ZIF-C60 fullerene nanowhisker (FNW) composite was prepared by liquid-liquid interfacial precipitation using a solution of Ni-ZIF nanoparticles, C60-saturated toluene, and 2-propanol (C3H8O). In comparison to the Ni-ZIF nanoparticles, the hybrid Ni-ZIF-C60FNW composite exhibited higher photocatalytic activity in the degradation of tetracycline hydrochloride under ultraviolet (UV) irradiation at 254 and 365 nm. The kinetics of the photocatalytic degradation of tetracycline hydrochloride using both the Ni-ZIF nanoparticles and the Ni-ZIF-C60FNW composite under UV irradiation followed the pseudo-first-order reaction rate law.
Over the past few centuries, industrial development has led to the creation and production of many chemicals, many of which have been studied for their environmental impact [1]. New trace pollutants, which were previously not well known, have been detected owing to advances in analytical technology [2]. Some of these pollutants do not readily decompose in nature, and trace amounts remain in water, as their removal rates during the water treatment process are very low [3–5]. In addition, the possibility that the persistence of these substances in water may pose a threat to the underwater ecosystem and potentially endanger human health has been investigated [6].
Approximately 200,000 tons of newly emerging contaminants are used annually for human and agricultural purposes [7–9]. Among these, tetracycline (TC), which is used as both a therapeutic agent and growth promoter in the medical and livestock industries, is discharged at a high rate due to its structural stability and incomplete metabolism [10]. It then enters water systems through various channels and has been detected both in wastewater and drinking water sources [11–16]. When an antibiotic like tetracycline is present in an aquatic ecosystem, it can be absorbed by organisms and accumulated in the food chain, posing a risk to both aquatic life and humans [17]. Therefore, various studies (adsorption, membrane filtration, photocatalysts in advanced oxidation processes, etc.) have been conducted to effectively remove antibiotics from wastewater [18–20]. Among these, adsorption methods have attracted attention due to their cost efficiency, low energy consumption, simple operation, and eco-friendliness. Nevertheless, challenges remain in the manufacturing of highly efficient and low-cost adsorbent materials [21–24].
Owing to their large specific surface area, easily modifiable structure, and stable pore structure, metal-organic frameworks (MOFs) have drawn significant attention as adsorption materials. However, their large-scale use is often limited by their instability in aqueous solutions. Recently, carbon compounds produced by the high-temperature carbonization of MOFs have been identified as promising adsorbents because of their inherent porosity and durability [25–27].
Among these carbon materials, C60 fullerene nanowhiskers were discovered in 2001 by Miyazawa using a lead zirconate colloidal solution containing C60 fullerene [28]. These materials were prepared using a liquid-liquid interfacial precipitation method and exhibited higher light transmittance and charge carrier mobility than pure C60 fullerene [29–31]. Furthermore, they have been used in many different applications, including photocatalysis and catalysis [32–35].
Previous studies using C60 fullerene nanowhiskers as photocatalysts have focused on the water treatment of dyes such as rhodamine B and methylene blue [36, 37]. Therefore, there is a need for investigating the use of these materials for the removal of trace pollutants such as antibiotics from water. In this study, a nanocomposite with a heterojunction structure, including C60 fullerene nanowhiskers (Ni-ZIF-C60FNW), was designed and synthesized to evaluate its applicability in the photocatalyst for water treatment of TC under ultraviolet light conditions. In particular, the photocatalytic activity and kinetics of TC antibiotic degradation of both Ni-ZIF nanoparticles and hybrid Ni-ZIF-C60FNW composite were evaluated by UV-Vis spectrophotometry under irradiation at 254 and 365 nm.
Toluene (C7H8), 2-propanol (C3H8O), and nickel nitrate hexahydrate (Ni(NO3)2·6H2O) were supplied by Daejung Chemicals. Polyvinylpyrrolidone (PVP, M.W. ∼10,000), tetracycline hydrochloride (C22H24N2O8·HCl), and sodium borohydride (NaBH4) were obtained from Sigma-Aldrich. C60 fullerene and 2-methylimidazole (C4H6N2) were purchased from Alfa Aesar. Powder X-ray diffraction (XRD; D8 Advance, Bruker, Germany) was used to investigate the crystal structures of the hybrid nanocomposites. Cu Kα radiation was used at 40 kV and 40 mA in a 2θ range from 5 to 90°, with a scan speed of 0.2 s/step. Raman spectroscopy (B&W Tek i-Raman Plus instrument, BWS465-532S, USA) was used to examine the lattice vibrations of the samples excited by a 532 nm radiation from a 40 mW Nd:YAG laser. The surfaces of the hybrid nanocomposites were examined using a scanning electron microscope (SEM; JSM-6510, JEOL Ltd., Japan) at a magnification of 5000× and an accelerating voltage of 10–30 kV. UV–Vis spectrophotometry (Shimadzu, UV-1691 PC, Japan) was used to evaluate the photocatalytic activity and kinetics of both the synthesized Ni-ZIF nanoparticles and C60FNW–Ni-ZIF composite for the degradation of TC under UV light irradiation at 254 and 365 nm. A UV lamp (6 W, 254 nm/365 nm, 77202 Marne La Vallee-Cedex 1, France) was used for irradiation.
2.2 Synthesis of Ni-ZIF nanoparticlesNickel-based zeolitic imidazolate framework (Ni-ZIF) nanoparticles were synthesized using the following procedure. Specifically, 0.582 g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O) and 0.985 g of 2-methylimidazole (C4H6N2) were dissolved in 20 mL of methanol, and the mixture was stirred for 30 min. The stirring was continued for 6 h at 60°C. The yellowish precipitate was isolated by centrifugation at 4000 rpm for 30 min and washed numerous times with methanol. Subsequently, the product was dried at 60°C for 24 h [38].
2.3 Synthesis of Ni-ZIF-C60FNW compositeFirst, a solution of Ni-ZIF nanoparticles was prepared. 0.015 g of powdered Ni-ZIF and 0.003 g of PVP were added to 30 mL of distilled water, sonicated for 30 min to promote dispersion, and stirred for 1 h. The C60FNW-Ni-ZIF composite was prepared using a liquid-liquid interfacial precipitation (LLIP) method at a volume ratio of 1:2:10 starting form a Ni-ZIF solution, C60-saturated toluene, and 2-propanol (C3H8O). The obtained mixture was stored at 5°C for 48 h. Subsequently, the precipitate was filtered and dried in an oven at 60°C for 2 h to afford a solid powder sample.
2.4 Photocatalytic activity and kinetics study of Ni-ZIF nanoparticle and Ni-ZIF-C60FNW composite for tetracycline hydrochloride degradation under UV light irradiationThe Ni-ZIF nanoparticles and Ni-ZIF-C60FNW composites (1 mg/mL) were used for the photocatalytic degradation of tetracycline hydrochloride in an aqueous solution and evaluated using UV light irradiation at 254 and 365 nm at room temperature. To establish an adsorption-desorption equilibrium between the 5 mL solution of tetracycline hydrochloride (0.2 mg/mL) and photocatalysts (0.5 mg/mL), we first stirred the solution for 30 min in the dark condition. UV light irradiation was used for the photodegradation of tetracycline hydrochloride, and 3 mL of the sample was drawn from the photoreactor vessel every 15 min. The absorption peak of tetracycline hydrochloride was measured by using a UV-Vis spectrophotometer (Shimadzu UV-1691 PC) at a maximum wavelength of 365–380 nm.
Figure 1 shows the XRD patterns of the (a) Ni-ZIF nanoparticles and (b) Ni-ZIF-C60FNW composite. In Fig. 1(a), the peaks observed at 2θ = 13.42° indicated the Ni-ZIF nanoparticles structure. The Ni-ZIF nanoparticles exhibited low crystallinity with a wide diffraction peak due to their low coordination capacity, as previously reported [38]. The peaks at 2θ = 10.80°, 17.60°, 19.06°, 20.70°, 28.08°, 30.93°, and 32.85° in the XRD pattern corresponded to the (111), (220), (103), (311), (420), (422), and (333) planes of the C60 fullerene nanowhiskers, while those at 2θ = 13.38° were due to the Ni-ZIF nanoparticles, as shown in Fig. 1(b) [38]. The XRD data indicated the effective synthesis of the Ni-ZIF-C60FNW composite. Moreover, the mean crystallite size of the Ni-ZIF nanoparticles was calculated using the Scherrer’s formula, D = k · λ/β · cos θ, where D is the crystallite size, λ is the wavelength of the Cu-Kα radiation (λ = 0.154178 nm), k is a shape factor (taken as 0.9), 2θ is the angle between the incident and scattered X-rays, and β is the full width at half maximum (FWHM). The average crystallite size of the Ni-ZIF nanoparticles was determined to be 83.57 nm (Table 1). Figure 2 shows the Raman spectrum of the Ni-ZIF-C60FNW composite. The Raman spectrum of the Ni-ZIF-C60FNW composite revealed the presence of Hg (1) at 270 cm−1, Ag (1) at 491 cm−1, and Ag (2) at 1459 cm−1 due to the C60 FNW [35]. Furthermore, the bands at 684, 841, and 1309 cm−1 were likely attributable to the N-H bending, C-H stretching, and N-H wagging vibrations of the Ni-ZIF nanoparticles [39, 40].
XRD patterns of (a) Ni-ZIF nanoparticles and (b) Ni-ZIF-C60FNW composite. (online color)
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Raman spectrum of the Ni-ZIF-C60 FNW composite.
Figure 3 shows the SEM images of the (a) Ni-ZIF nanoparticles and (b) Ni-ZIF-C60FNW composite. Figure 3(a) shows a nanoflower-like morphology, mostly composed of interconnected petals. Moreover, Fig. 3(b) shows that these nanoflower-shaped Ni-ZIF nanoparticles were located on the rod-like structure of the C60 fullerene nanowhiskers.
SEM image of (a) Ni-ZIF nanoparticles and (b) Ni-ZIF-C60 FNW composite.
Figure 4 shows the TEM image of the Ni-ZIF-C60FNW composite. Ni-ZIF nanoparticles were arrayed and adhered to the C60 fullerene nanowhiskers. The size of the Ni-ZIF nanoparticles was 80–200 nm. In addition, the TEM image of the Ni-ZIF nanoparticles shows a nanoflower-like shape, similar to that observed in the SEM image. These nanoflowers were composed of interconnected nanosheets, such as petals. Furthermore, the petals were slightly curly and compactly interpenetrated, forming a nanoflower-like structure [41].
TEM image of (a) Ni-ZIF nanoparticles and (b) Ni-ZIF-C60 FNW composite.
Figure 5 shows the UV-Vis spectra for the photocatalytic degradation of tetracycline hydrochloride using the Ni-ZIF nanoparticles and Ni-ZIF-C60 FNW composite. The percentage degradation of tetracycline hydrochloride was calculated using eq. (1) [42]:
| \begin{align} &\text{Tetracycline hydrochloride degradation %} \\ &\quad = \frac{\text{C}_{0} - \text{C}_{\text{t}}}{\text{C}_{0}} \times 100\% \end{align} | (1) |
where C0 is the initial concentration of tetracycline hydrochloride solution after adsorption-desorption equilibrium for 30 min and Ct is the concentration of tetracycline hydrochloride at time t. According to eq. (1), when Ni-ZIF nanoparticles were used, 79.296% of tetracycline hydrochloride was decomposed upon irradiation at 254 nm for 120 min (Fig. 6(a)), while 79.292% underwent decomposition when irradiated at 365 nm for 120 min (Fig. 6(c)). Figure 6(b) and Fig. 6(d) indicate that 97.187% and 91.245% of tetracycline hydrochloride were degraded in the presence of the Ni-ZIF-C60 FNW composite photocatalyst under 254 and 365 nm conditions, respectively.
UV-Vis spectra for tetracycline hydrochloride (TCH) photocatalytic degradation on Ni-ZIF nanoparticles and Ni-ZIF-C60 FNW composite under UV irradiation; (a) Ni-ZIF nanoparticles, (b) Ni-ZIF-C60 FNW composite at 254 nm, and (c) Ni-ZIF nanoparticles, (d) Ni-ZIF-C60 FNW composite at 365 nm. (online color)
Kinetic study of the photocatalytic degradation of TCH on Ni-ZIF nanoparticles and Ni-ZIF-C60 FNW composite under UV irradiation; (a) Ni-ZIF nanoparticles, (b) Ni-ZIF-C60 FNW composite at 254 nm, and (c) Ni-ZIF nanoparticles, (d) Ni-ZIF-C60 FNW composite at 365 nm. (online color)
Figure 6 illustrates the kinetics of the photocatalytic degradation of TCH using the Ni-ZIF nanoparticles and Ni-ZIF-C60 FNW composite under UV irradiation. The following equation (eq. (2)) was used for determining the kinetics of the first-order reaction [43]:
| \begin{equation} \ln(\mathrm{C}/\mathrm{C}_{0}) = - \mathrm{k}_{1}\mathrm{C} \end{equation} | (2) |
where k1 is the rate constant, C0 is the initial TCH concentration, and C is the concentration at time t. The photocatalytic degradation of TCH over the photocatalysts shown in Fig. 6 is a result of the linear behavior of the curves, which follows pseudo-first-order kinetics. The R2 values (coefficient of determination) for the pseudo-first-order reaction kinetics were 0.9988 in Fig. 6(a), 0.9909 in Fig. 6(b), 0.9854 in Fig. 6(c), and 0.9952 in Fig. 6(d).
A Ni-ZIF-C60FNW composite was synthesized using the LLIP method starting from a Ni-ZIF nanoparticles solution, C60 fullerene-saturated toluene solution, and 2-propanol. The characterization of the Ni-ZIF-C60FNW composite was confirmed using XRD, Raman spectroscopy, SEM, and TEM. Ni-ZIF nanoparticles and Ni-ZIF-C60FNW composites were used for the photocatalytic degradation of TCH under UV irradiation (254 and 365 nm). The photocatalytic degradation rates of TCH using the Ni-ZIF nanoparticles and Ni-ZIF-C60FNW composite under UV irradiation decreased in the following order of UV irradiation: 254 > 365 nm. Compared to Ni-ZIF nanoparticles alone, the Ni-ZIF-C60FNW composite exhibited higher photocatalytic activity for TCH degradation. Further more, kinetics study of the photocatalytic degradation of TCH using Ni-ZIF nanoparticles and Ni-ZIF-C60FNW composite as photocatalysts revealed a pseudo-first-order reaction rate law. In summary, we demonstrated the availability of Ni-ZIF-C60FNW composite as a photocatalyst and the potential for photocatalytic activity in the degradation of antibiotic residues such as TCH by using UV irradiation.
This work was supported by Research Foundation of Sahmyook University.
