Abstract
The contamination of water sources by pharmaceutical pollutants presents significant environmental and health hazards, making the development of effective photocatalytic materials crucial for their removal. This research focuses on the synthesis of a novel Ag/CuS/Fe₃O₄ nanocomposite and its photocatalytic efficiency against tetracycline (TC) and diclofenac contaminants. The nanocomposite was created through a straightforward and scalable precipitation method, integrating silver nanoparticles (AgNPs) and copper sulfide (CuS) into a magnetite framework. Various analytical techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR),ultraviolet–visible spectrophotometry (UV–Vis) and energy-dispersive X-ray spectroscopy (EDS), were employed to characterize the structural and morphological properties of the synthesized material. The photocatalytic activity was tested by degrading tetracycline and diclofenac under visible light. Results indicated a marked improvement in the photocatalytic performance of the Ag/CuS/Fe₃O₄ nanocomposite (98%photodegradation of TC 60 ppm in 30 min) compared to both pure magnetite and CuS/Fe₃O₄. The enhanced photocatalytic efficiency is attributed to the synergistic interaction between AgNPs, CuS, and Fe3O4, which improves light absorption and charge separation, thereby increasing the generation of reactive oxygen species (ROS) and promoting the degradation of the pollutants. The rate constant k of photodegradation was about 0.1 min−1 for catalyst dosages 0.02 g. Also the effect of photocatalyst dose and concentration of TC and pH of solution was tested. The modified photocatalyst was also used for simultaneous photodegradation of TC and diclofenac successfully. This study highlights the potential of the Ag/CuS/Fe₃O₄ nanocomposite as an efficient and reusable photocatalyst for eliminating pharmaceutical pollutants from water.
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Discover the latest articles, news and stories from top researchers in related subjects.Introduction
The rapid urbanization and industrialization of modern society have significantly increased contamination of groundwater, air, and fossil fuels through conventional industrial waste disposal methods1,2. This has led to major environmental issues like pollution and climate change, threatening ecosystems and human health3,4,5,6,7,8. The World Health Organization reports that environmental pollution has caused 3.7 million deaths in the twenty-first century, with 92% of the global population living in areas with severe air and water pollution9,10. Thus, the safe disposal of hazardous waste has become a critical priority11,12,13,14. Advanced Oxidation Processes (AOPs), particularly heterogeneous photocatalysis, are promising for removing organic contaminants from water and air due to their efficiency in degrading organic pollutants15,16. Semiconductor-based photocatalysts, especially metal oxides, are widely studied for their efficiency and cost-effectiveness in water pollution treatment17,18,19,20,21,22,23,24. Titanium dioxide (TiO2) is notable for its low cost, non-toxicity, and chemical inertness but is limited to UV light activity, necessitating the development of visible-light-driven photocatalysts25,26,27,28,29. Various metal oxides, including La2O3, CdO, CeO2, CaO, and ZnO, have been explored to enhance TiO2’s activity30,31,32. Incorporating magnetic nanoparticles like hematite, maghemite, magnetite, and various ferrites into photocatalysts imparts magnetic properties, allowing easy separation from solutions with a magnet33. These nanoparticles do not significantly affect the surface area or dispersion of the photocatalyst and can also absorb visible light, enhancing pollutant degradation34. One promising frontier in combating water pollution is the development of magnetic visible-light-active nanocomposites for photocatalytic environmental cleanup.
Covellite CuS, a p-type semiconductor with a narrow bandgap (1.2–2.0 eV), is notable for its low cost, non-toxicity, easy production, and excellent stability. It absorbs broad visible light, plasmon, and near-infrared (NIR) radiation, making it an effective photocatalyst35,36. However, its efficiency is limited by factors like morphology, size, and rapid recombination of photoexcited charges, which researchers are addressing by creating CuS-based nanoheterostructures. For example, embedding CuS nanospheres within an MCM-41 matrix has shown enhanced performance in degrading methylene blue under visible light37. Additionally, silver (Ag) doping enhances the photocatalytic activity of semiconductors by lowering the recombination rate of holes and electron pairs and modifying the band gap energy, making the material more active under visible light, which is particularly advantageous for wastewater treatment applications38,39,40. These advancements position CuS and Ag-doped nanocomposites as powerful photocatalysts for clean water applications.
Introducing Fe₃O₄ (magnetite) as a base material for photocatalysts adds significant functionality. Magnetite, a naturally occurring iron oxide with magnetic properties, serves as a stable and robust support for semiconductor photocatalysts like CuS41,42. In CuS-based nanocomposites, Fe₃O₄ provides a high surface area and facilitates the dispersion of CuS nanoparticles, enhancing reactant accessibility to catalytic sites. Additionally, Fe₃O₄’s magnetic properties allow for easy separation and recovery of the catalyst using an external magnetic field, reducing operational costs and simplifying retrieval processes, making it more environmentally friendly. Fe₃O₄ also exhibits excellent stability and biocompatibility, making it suitable for environmental remediation and biomedical applications. Its chemical inertness ensures no interference with CuS’s catalytic activity, while its biocompatibility is advantageous for potential biomedical uses, such as drug delivery systems.Combining Fe₃O₄ with CuS and Ag to form ternary nanocomposites (CuS/Fe₃O₄/Ag) enhances photocatalytic performance and provides multifunctionality. The synergy between CuS, Fe₃O₄, and Ag improves charge separation efficiency, extends light absorption range, and boosts catalytic activity. This combination holds significant promise for addressing environmental pollution and advancing various technological applications43,44. Incorporating silver into CuS magnetite (CuS/Fe₃O₄) nanocomposites further enhances photocatalytic activity and imparts magnetic properties for easy separation and recycling of the catalyst. This dual functionality makes CuS/Fe₃O₄/Ag nanocomposites highly desirable for environmental remediation applications44. In this study, we incorporate Ag NPs and CuS into the Fe₃O₄ matrix to enhance light absorption and charge separation, improving photocatalytic performance. The magnetic properties of the nanocomposite facilitate easy separation and recyclability, making it a promising candidate for water treatment applications. This research contributes to the development of efficient and recyclable photocatalysts for removing pharmaceutical contaminants from water resources.
Experimental
Chemical materials and instruments
Commercially available chemicals were sourced from Merck and Sigma Aldrich and used directly without further purification. The materials used in this study included copper(II) chloride dihydrate (CuCl₂·2H₂O, 99%), magnetite (Fe₃O₄, 99%), sodium sulfite (Na₂SO₃, 99%), silver nitrate (AgNO₃, 99%), sodium hydroxide (NaOH, 98%), and deionized water. Characterization techniques were performed using a Panalytical X'Pert Pro Holland diffractometer for X-ray diffraction (XRD), a Shimadzu model 8700 spectrometer for Fourier transform infrared (FT-IR) spectroscopy, a Mira 3-XMU microscope for field emission scanning electron microscopy (FESEM), and a Photonix AR spectrometer for UV–vis diffuse reflectance spectroscopy.
Synthesis of Ag/ CuS@Fe3O4 photocatalyst
First, 3 mmol of CuCl₂ was dissolved in 25 mL of deionized water. Subsequently, 1 g of magnetite powder was added to the solution and stirred for 90 min. In a separate beaker, 8 mmol of sodium sulfite was dissolved in 10 mL of deionized water. This sodium sulfite solution was then added to the CuCl₂/magnetite mixture, and the combined solution was stirred for an additional hour. The resulting CuS/Fe₃O₄ nanoparticles were isolated, thoroughly washed with deionized water, dried in an oven at 60 °C for 24 h, and finally calcined in a furnace at 550 °C for 2 h. To prepare the Ag/CuS/Fe₃O₄ photocatalyst, 1 mmol of AgNO₃ was dissolved in 25 mL of deionized water. Then, 0.3 g of the prepared CuS/Fe₃O₄ nanoparticles were added to the AgNO₃ solution and stirred for 90 min. Following this, 3 mmol of NaOH was dissolved in 5 mL of water and added to the mixture, with further stirring for 15 min. The Ag/CuS/Fe₃O₄ nanoparticles were then separated, thoroughly washed with deionized water, and dried in an oven for 24 h (Scheme 1).
Evaluation of photocatalytic activity
To assess the photocatalytic performance of the synthesized nanomaterials, a degradation experiment of tetracycline (TC) under visible light illumination was conducted. First, 0.01 g of the nanocomposite was dispersed in 40 mL of a 50 ppm TC solution. The mixture was then stirred for 15 min to allow for adsorption–desorption equilibrium to be reached. Following this, the solution was exposed to visible light irradiation using a 60W low consumption fluorescent lamp.
At various time intervals, samples were withdrawn from the solution and centrifuged to separate the photocatalyst. The supernatant was then analyzed using a UV–Vis spectrophotometer to measure the absorbance of tetracycline. The degradation efficiency was calculated using the following formula:
where A0 and At are the initial absorbance and absorbance of tetracycline at time t, respectively.
Results and discussions
Characterization
XRD and FESEM characterization
X-ray diffraction (XRD) analysis was performed to investigate the crystallographic structure of the synthesized materials, including Fe3O4 (magnetite) and Ag/CuS/Fe3O4 nanocomposites. The XRD patterns of Fe3O4 and the doped nanocomposites revealed distinct diffraction peaks, indicating the crystalline nature of the materials.
The XRD pattern of pure Fe3O4 exhibited characteristic peaks at 2θ values of around 30.1°, 35.5°, 43.1°, 53.4°, 57.0°, and 62.7°, corresponding to the (220), (311), (400), (422), (511), and (440) crystal planes of cubic-phase magnetite, respectively45. These peaks are consistent with the standard data for magnetite (JCPDS card no. 96-900-5839), confirming the formation of pure magnetite in the synthesized sample (Figs. 1, 2).
In contrast, the XRD patterns of the Ag/CuS/Fe3O4 nanocomposites exhibited shifts and changes in the diffraction peaks compared to pure Fe3O4. These shifts and changes suggest alterations in the crystal structure due to the doping of Ag and CuS. The appearance of additional peaks or shifts in the XRD patterns of the doped nanocomposites indicates the formation of new phases or crystal structures. The presence of peaks corresponding to Ag (JCPDS card no. 96-901-1609) and CuS (JCPDS card no. 96-153-6219) in the doped nanocomposites confirms the successful incorporation of Ag and CuS into the magnetite matrix. The shifts in diffraction peaks suggest changes in lattice parameters and crystal symmetry due to the doping. Furthermore, the broadening of peaks in the XRD patterns of the nanocomposites compared to pure Fe3O4 indicates a reduction in crystallite size or the presence of smaller crystallites. This reduction in crystallite size may be attributed to the incorporation of Ag and CuS, which can affect the nucleation and growth of magnetite nanoparticles. Overall, the XRD analysis confirms the successful synthesis of pure magnetite and the doped Ag/CuS/Fe3O4 nanocomposites, providing valuable insights into their crystallographic structures and phases (Figs. 1, 2).
The observed differences in XRD patterns between Fe3O4 and Ag/CuS/Fe3O4 nanocomposites can be attributed to several factors. Firstly, the doping of Ag and CuS into the Fe3O4 lattice may lead to lattice distortion or strain, resulting in shifts and broadening of diffraction peaks. Additionally, the presence of Ag and CuS phases contributes to the appearance of new peaks corresponding to these materials. The presence of different phases in the nanocomposites suggests the formation of heterostructures, where Ag and CuS nanoparticles are dispersed on the surface or embedded within the Fe3O4 matrix. These heterostructures could enhance the photocatalytic properties of the nanocomposites by facilitating charge separation and promoting the generation of reactive oxygen species under visible light irradiation. The shifts in diffraction peaks may also indicate changes in the crystalline structure of Fe3O4 induced by doping. For example, the incorporation of Ag and CuS may lead to the formation of solid solutions or the introduction of defects in the Fe3O4 lattice, affecting its crystallographic parameters. Furthermore, the presence of impurities or secondary phases in the doped nanocomposites could influence their properties. These impurities may arise from incomplete doping reactions or the presence of residual reactants. Careful analysis of the XRD patterns allows for the identification and quantification of these impurities, providing insights into the purity and composition of the synthesized materials. Overall, XRD analysis provides valuable information about the structural characteristics of Fe3O4 and Ag/CuS/Fe3O4 nanocomposites, shedding light on their crystallographic phases, crystallite sizes, and structural changes induced by doping. This understanding is crucial for tailoring the properties of these materials for various applications, particularly in photocatalysis and environmental remediation.
Field Emission Scanning Electron Microscopy (FESEM) was employed to investigate the surface morphology and microstructure of magnetite (Fe₃O₄) and Ag/CuS/Fe₃O₄ nanocomposites (Fig. 3). The FESEM images of pure magnetite revealed irregularly shaped, aggregated particles with a broad size distribution. The surface of the magnetite appeared rough and uneven, indicating the presence of individual particles clustering together to form larger aggregates. In contrast, the FESEM images of the Ag/CuS/Fe₃O₄ nanocomposites displayed a noticeable alteration in morphology compared to pure magnetite. The Ag/CuS nanoparticles were clearly visible on the surface of the Fe₃O₄ particles, appearing as small, irregular clusters that were dispersed throughout the surface. This indicates the successful deposition of Ag/CuS onto the magnetite. Furthermore, the Ag/CuS nanoparticles contributed to a significant increase in surface roughness and complexity of the nanocomposites compared to pure magnetite.
The Energy Dispersive X-ray (EDX) analysis was conducted to determine the elemental composition of Fe3O4 and Ag/CuS/Fe3O4 nanocomposites (Fig. 4). The results are presented below:
For Fe3O4:Oxygen (O): The dominant presence of oxygen is confirmed, with a weight percent (W%) of approximately 59.19%. Iron (Fe): Iron is present in the sample, constituting about 40.81% of the composition. Other Elements: No other significant elements were detected, indicating a composition primarily consisting of Fe3O4. For Ag/CuS/Fe3O4: Oxygen (O): The presence of oxygen is confirmed, although slightly lower than in pure Fe3O4, with a weight percent of approximately 64.21%. Sulfur (S): Sulfur is detected, indicating the incorporation of CuS into the nanocomposite, with a weight percent of about 1.45%. Iron (Fe): Iron is still present in the nanocomposite, although in a lower proportion compared to Fe3O4 alone, constituting about 33.97% of the composition. Copper (Cu): The presence of copper suggests the incorporation of CuS into the nanocomposite, with a weight percent of approximately 0.29%. Silver (Ag): Silver is detected, indicating successful doping into the nanocomposite, with a weight percent of about 0.09%. The EDX analysis confirms the presence of oxygen, sulfur, iron, copper, and silver in the Ag/CuS/Fe3O4 nanocomposite, suggesting successful doping and incorporation of these elements into the Fe3O4 matrix. The slight differences in elemental composition between Fe3O4 and the nanocomposite indicate changes in the chemical composition due to doping and incorporation of additional elements.
UV–Vis analysis
The UV–Vis spectra provide valuable insights into the optical properties and bandgap energy of nanocomposites (Fig. 5). In the case of Fe3O4, a characteristic peak was observed at 580 nm, corresponding to its absorption of visible light.
Upon the incorporation of CuS into Fe3O4 to form CuS/ Fe3O4 nanocomposites, a redshift in the UV–Vis spectrum was observed, with the peak shifting to 610 nm. This redshift indicates a narrowing of the bandgap energy and enhanced absorption of visible light. The redshift can be attributed to the presence of CuS, which has a lower bandgap energy compared to Fe3O4. The introduction of CuS nanoparticles alters the electronic structure of the nanocomposite, leading to improved light absorption and thus enhanced photocatalytic activity.
Similarly, in the Ag/CuS/Fe3O4 nanocomposites, a further redshift in the UV–Vis spectrum was observed, with the peak shifting even more towards longer wavelengths. This indicates a further narrowing of the bandgap energy and enhanced light absorption compared to CuS/Fe3O4 nanocomposites. The incorporation of silver (Ag) into the CuS/Fe3O4 nanocomposites likely contributes to this redshift, as Ag nanoparticles can efficiently trap and transfer photogenerated charge carriers, leading to increased photocatalytic efficiency. The band gap of Fe3O4, CuS/Fe3O4 and Ag/CuS/ Fe3O4 nanocomposites were calculated using Einstein equation (Eg = 1242/ lambda onset) and were obtained 2.03,2.00 and 1.97 eV respectively.
Overall, the UV–Vis spectra of the nanocomposites reveal the modification of their optical properties, with the redshift indicating enhanced light absorption and improved photocatalytic activity. These results are crucial for understanding the mechanisms underlying the photocatalytic performance of the nanocomposites and for optimizing their synthesis for various environmental remediation applications.
FTIR analysis
FTIR spectra of the Fe3O4 and Ag/CuS/Fe₃O₄ is shown in Fig. 6. The infrared (IR) spectra of Fe3O4 and Ag/CuS@Fe3O4 provide valuable information about their chemical composition and structural properties.
In the spectral range of 400 to 1000 cm−1, Fe3O4 exhibits multiple peaks, likely due to the presence of impurities such as SiO2 and alumina in the mineral46,47. These peaks indicate the presence of different chemical bonds and vibrational modes associated with these impurities. In contrast, Ag/CuS/Fe₃O₄ shows fewer peaks in this range, suggesting a simpler chemical composition with fewer impurities.
At 1000 cm−1, Ag/CuS/Fe₃O₄ displays a strong peak, indicating the presence of specific chemical bonds associated with the doping process48,49. This peak is more intense compared to Fe3O4, suggesting a higher concentration of these bonds in the doped material.
In the range of 1376–1478 cm−1, Fe3O4 exhibits a strong peak, likely related to the presence of Fe–O bonds in the magnetite structure50. However, in the doped material, this peak appears with lower intensity at 1427 and 1632 cm−1, indicating alterations in the bonding environment due to the doping of Ag/CuS51.
Moreover, in Fe3O4, a broad peak is observed at 3165 cm−1, indicating the presence of O–H stretching vibrations, possibly due to surface hydroxyl groups or absorbed water molecules52. In contrast, the doped material shows a lower and narrower peak at 3437 cm−1, suggesting a decrease in the abundance of hydroxyl groups or water molecules on the surface53.
Overall, these results suggest that the doping of Ag/CuS into magnetite leads to structural and chemical modifications, altering the vibrational modes and intensities observed in the IR spectra. These changes may be attributed to the incorporation of Ag/CuS nanoparticles into the magnetite structure, which influences the chemical bonding and surface properties of the material.
Evaluation of photocatalytic activity of CuS/Fe3O4 and Ag/CuS/Fe3O4photocatalyst
The synthesized Ag/CuS/Fe3O4 nanocomposite exhibited significantly enhanced photocatalytic performance compared to pure Fe3O4 and CuS/Fe3O4. The discussion focuses on the observed differences in photocatalytic activity and the factors contributing to these outcomes.
In the photocatalytic degradation of tetracycline (TC), Ag/CuS/Fe3O4 demonstrated remarkable efficiency, achieving complete degradation of 20 ppm TC within just 30 min of visible light irradiation. In contrast, pure Fe3O4 exhibited a much lower degradation efficiency, with only 21% TC degradation under the same conditions. CuS/Fe3O4, while showing improved performance compared to Fe3O4, achieved a TC degradation efficiency of 27% within 30 min.
The superior photocatalytic activity of Ag/CuS/Fe3O4 can be attributed to several factors. Firstly, the incorporation of silver (Ag) and copper sulfide (CuS) onto the Fe3O4 surface increases the availability of active sites for photocatalytic reactions. Ag acts as a co-catalyst, enhancing the separation of photogenerated electron–hole pairs and improving charge carrier mobility54,55. Similarly, CuS functions as a sensitizer, extending the absorption range of the photocatalyst into the visible region and enhancing light utilization efficiency56,57.
Furthermore, the presence of Ag and CuS modifies the band structure of Fe3O4, leading to a reduction in the band gap energy and an increase in the absorption of visible light58,59. This modification facilitates the generation of more reactive oxygen species (ROS) and promotes the photocatalytic degradation of organic pollutants60,61.
The synergistic effect between Ag, CuS, and Fe3O4 is also crucial in enhancing photocatalytic performance. The combination of these materials creates a heterojunction structure, which facilitates efficient charge transfer and inhibits charge carrier recombination62,63. The unique electronic and optical properties of Ag/CuS/Fe3O4 nanocomposites contribute to the improved photocatalytic activity observed in this study.
Effect of catalyst dose
The effect of catalyst dose on the photocatalytic degradation of tetracycline (TC) was investigated by varying the amount of Ag/CuS/Fe3O4 nanocomposite from 0.002 to 0.02 g while keeping the TC concentration constant at 20 ppm. The results revealed a clear correlation between the catalyst dose and the photocatalytic efficiency.
At the lowest catalyst dose of 0.002 g, approximately 60% of TC was degraded after 30 min of visible light irradiation64. Increasing the catalyst dose to 0.005 g resulted in a slight improvement in the degradation efficiency, with around 60–70% degradation observed65. Further increasing the catalyst dose to 0.007 g significantly enhanced the photocatalytic activity, achieving approximately 84% degradation of TC within the same time frame66.
Interestingly, a dose of 0.02 g of Ag/CuS/Fe3O4 nanocomposite led to the highest photocatalytic efficiency, with approximately 95% degradation of TC achieved in just 30 min67. This indicates that the photocatalytic performance is highly dependent on the amount of catalyst present in the reaction system. The observed trend suggests that an optimal catalyst dose is crucial for achieving maximum photocatalytic activity. At lower doses, insufficient active sites may limit the degradation rate, resulting in lower efficiency. On the other hand, excessively high doses may lead to aggregation of catalyst particles, reducing the available surface area for photocatalytic reactions. The enhanced photocatalytic activity at higher catalyst doses can be attributed to the increased number of active sites available for TC adsorption and photocatalytic reactions. Moreover, higher catalyst doses may also promote more efficient light absorption and utilization, leading to improved charge carrier generation and separation (Fig. 7).
These findings emphasize the importance of optimizing the catalyst dose to maximize photocatalytic performance and underscore the potential of Ag/CuS/Fe3O4 nanocomposites for environmental remediation applications.
Effect of tetracycline concentration
The effect of TC concentration on the photodegradation efficiency using Ag/CuS/Fe3O4 nanocomposites was investigated. The concentration of TC varied from 25 to 100 ppm (Fig. 8).
At lower concentrations (25 ppm, 30 ppm, and 40 ppm), the photodegradation efficiency exhibited an increasing trend. Specifically, at 25 ppm, 30 ppm, and 40 ppm, the degradation efficiencies were 94%, 96%, and 97%, respectively. This suggests that lower concentrations of TC lead to more efficient photodegradation, possibly due to better accessibility of the photocatalytic sites on the nanocomposites.
However, as the TC concentration increased to 50 ppm, 60 ppm, 80 ppm, and 100 ppm, the photodegradation efficiency relatively decreased. At 50 ppm, 60 ppm, 80 ppm, and 100 ppm, the degradation efficiencies were 97%, 98%, 81%, and 78%, respectively. This decrease in efficiency with higher TC concentrations could be attributed to factors such as increased competition for active sites on the nanocomposites, saturation of the photocatalytic surface, and reduced light penetration due to higher turbidity caused by increased TC concentration.
Overall, the photodegradation efficiency of TC using Ag/CuS/Fe3O4 nanocomposites is influenced by the initial concentration of TC, with lower concentrations demonstrating higher efficiencies, while higher concentrations exhibit a diminishing trend in efficiency.
Effect of pH solution
To investigate the effect of pH on the photocatalyst efficiency, first the isoelectric point (pHiep) of the photocatalyst was determined and then the effect of pH solution on it was investigated. pHiep was determined using a sodium chloride (NaCl) solution with varying pH values. The pHiep is a crucial parameter that indicates the pH at which the surface charge of the photocatalyst is neutral70,71.
In this experiment, NaCl solutions with pH values ranging from acidic to alkaline were prepared and used to suspend the photocatalyst. The suspensions were then stirred for 24 h to ensure equilibrium. Subsequently, the pH of the photocatalyst particles was measured.
The results revealed that the pHiep of the photocatalyst was determined to be 8.7 (Fig. 9). This indicates that at a pH of 8.7, the surface charge of the photocatalyst becomes neutral, and the material exhibits minimum electrostatic repulsion between particles.
The isoelectric pH is an essential parameter as it affects the surface chemistry and colloidal stability of the photocatalyst. Understanding the pHiep allows for the optimization of photocatalytic processes, as it influences the adsorption of reactants and intermediates onto the photocatalyst surface. By knowing the pHiep, appropriate pH conditions can be chosen to enhance the photocatalytic activity and stability of the material. Additionally, the pHiep value provides valuable insights into the surface properties of the photocatalyst, which are crucial for various applications, including pollutant degradation and water treatment.
The determination of the isoelectric pH of the photocatalyst provides fundamental information that can be utilized to optimize its performance and enhance its effectiveness in environmental remediation processes.
The effect of pH on the photocatalytic activity of Ag/CuS/Fe3O4 nanocomposites was systematically investigated to understand its impact on the degradation of tetracycline (Fig. 10). The results revealed a significant dependence of photocatalytic performance on pH levels. At pH 2, the photoactivity was observed to be relatively low, achieving only about 20% degradation of tetracycline. This decrease in activity at acidic pH can be attributed to several factors, including reduced adsorption of tetracycline molecules and hindered generation of reactive oxygen species (ROS) due to the protonation of surface hydroxyl groups. However, as the pH increased to 4, 6, 7, 11, and 12, a substantial enhancement in photocatalytic activity was observed. In these alkaline conditions, the photoactivity exceeded 95%, indicating a remarkable improvement in tetracycline degradation efficiency. The higher activity at alkaline pH can be attributed to the increased adsorption of tetracycline molecules and facilitated generation of ROS, both of which are crucial for the photocatalytic degradation process. The isoelectric pH of the photocatalyst was found to be 8.7, further confirming the pH-dependent behavior observed in the photocatalytic activity. Overall, the results emphasize the importance of pH in controlling the photocatalytic performance of Ag/CuS/Fe3O4 nanocomposites, with alkaline conditions being particularly favorable for efficient tetracycline degradation.
In Table 1 a comparison of the present work with the previous reports in photodegradation of tetracycline is reported. As can be seen from this Table the proposed photocatalyst has high photodegradation efficiency and kinetics in compare to pervious works.
Kinetic study
The photocatalytic degradation of tetracycline (TC) using Ag/CuS/Fe3O4 nanocomposites was investigated to understand the reaction kinetics. The study involved varying the dosage of the catalyst from 0.002 to 0.02 g and analyzing the degradation kinetics.
The degradation rate of TC was calculated using the following equation:
where C₀ is the initial concentration of TC (ppm); Cₜ is the concentration of TC at time t (ppm); k is the rate constant (L/min or cm3/min); t is the reaction time (min).
By measuring the TC concentration at different time intervals throughout the experiment, the rate constant (k) can be determined using this equation. The rate constant reflects the efficiency of the photocatalyst in degrading TC.
From the kinetic analysis, it was observed that increasing the dosage of the catalyst led to higher degradation rates of TC. The rate constant k ranged from 0.026 min−1 to 0.1 min−1 for catalyst dosages ranging from 0.002 to 0.02 g (Fig. 11). Specifically, at a catalyst dosage of 0.002 g, the rate constant was 0.026 min−1, whereas at a dosage of 0.02 g, the rate constant increased to 0.1 min−1.
This result indicates that higher catalyst dosages promote faster degradation kinetics due to increased active sites available for the adsorption of TC molecules and subsequent generation of reactive species. The first-order kinetic behavior suggests that the degradation rate is directly proportional to the concentration of TC remaining in the solution.
Furthermore, the observed first-order kinetics imply that the photocatalytic degradation of TC by Ag/CuS/Fe3O4 nanocomposites is primarily controlled by the availability of active sites on the catalyst surface. As the dosage of the catalyst increases, the number of active sites also increases, leading to enhanced degradation rates.
Overall, the kinetic study demonstrates that the Ag/CuS/Fe3O4 nanocomposites exhibit efficient photocatalytic degradation of TC, and the process follows a first-order kinetic model across different catalyst dosages86.
Mechanism of photodegradation
The photocatalytic degradation of TC using Ag/CuS/Fe3O4 nanocomposites involves a complex series of reactions driven by the generation of reactive oxygen species (ROS) upon exposure to visible light87,88,89.
The positions of the VB and CB edges in Ag/CuS/Fe₃O₄ nanocomposites ensure that the photogenerated electrons and holes have sufficient energy to drive the redox reactions required for ROS formation. This effective separation and movement of charge carriers enhance the photocatalytic degradation of TC by producing a higher amount of ROS90,91,92.
The mechanism can be described as follows:
-
1.
Adsorption: Initially, tetracycline molecules adsorb onto the surface of the Ag/CuS/ Fe3O4 nanocomposites due to electrostatic interactions and hydrogen bonding between the TC molecules and the catalyst surface.
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2.
Generation of Reactive Species: Under visible light irradiation, the Ag/CuS/Fe3O4 nanocomposites absorb photons, leading to the excitation of electrons from the valence band to the conduction band. This excitation creates electron–hole pairs (e−–h+).
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3.
ROS Generation: The photogenerated electrons (e−) react with molecular oxygen (O2) adsorbed on the catalyst surface, leading to the formation of superoxide radicals (O2·−). Similarly, the photogenerated holes (h+) react with water molecules (H2O) to form hydroxyl radicals (OH·). These ROS are highly reactive and play a crucial role in the degradation of TC93,94.
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4.
TC Degradation: The ROS, including superoxide radicals and hydroxyl radicals, attack the adsorbed TC molecules, leading to the degradation of TC into smaller, less complex organic molecules, and eventually into harmless byproducts such as carbon dioxide and water.
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5.
Effect of Scavengers: The presence of scavengers such as hydrogen peroxide (H2O2), ethylenediaminetetraacetic acid (EDTA), ethanol (EtOH), and potassium chloride (KCl) significantly affects the photocatalytic degradation process (Fig. 12).
In the initial stages of photodegradation, scavengers compete with tetracycline (TC) molecules for the reactive oxygen species (ROS). H2O2, as a strong oxidizing agent, readily scavenges ROS, leading to a decrease in their concentration. EDTA, a strong chelating agent, also competes with TC for ROS, effectively reducing their availability for TC degradation. Ethanol (EtOH) acts as a sacrificial agent by absorbing photons and generating hydroxyl radicals (·OH), thus scavenging ROS. Potassium chloride (KCl) likely acts as an electron scavenger, intercepting electrons and reducing the formation of ROS.
As can be observed in Fig. 12, in the presence of H2O2 the degradation efficiency was increased. This is due to strong scavenging abilities. However, as the reaction progresses, the scavengers begin to saturate, and their scavenging capacities diminish. At this point, the differences in photodegradation efficiency between the scavenger-containing samples and the control diminish. Eventually, in the later stages of photodegradation, all scavengers and the control without scavenger exhibit similar high photodegradation efficiencies, typically around 95%. This behavior suggests that while scavengers initially hinder the degradation process by competing with TC for ROS, their effect diminishes over time, allowing the photocatalyst to efficiently degrade TC regardless of the scavenger present.
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6.
Later Stage Degradation: However, as the reaction progresses, the concentration of ROS decreases, and the availability of active sites on the catalyst surface becomes limiting. At this point, the presence of scavengers has a minimal effect on the degradation efficiency. Therefore, in the later stages of photodegradation, the photodegradation efficiency of the scavenger-containing solutions approaches that of the control (without scavenger).
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7.
Overall Efficiency: Despite the presence of scavengers, the overall photodegradation efficiency remains high (around 95%), indicating the robustness of the Ag/CuS/Fe3O4 nanocomposites in degrading TC under visible light irradiation.
This mechanism highlights the importance of ROS generation and scavenger effects in the photocatalytic degradation of tetracycline using Ag/CuS/Fe3O4 nanocomposites.
Application of Ag/CuS/Fe3O4 nanocomposites in photodegradation of diclofenac
The photocatalyst demonstrated high efficiency in the degradation of diclofenac (Dic) when tested alone, achieving an impressive degradation rate of 84% (Fig. 13A). This indicates the excellent photocatalytic activity of the material in degrading this particular pharmaceutical compound under visible light illumination.
Furthermore, in a simultaneous photodegradation experiment involving both diclofenac (Dic) and tetracycline (TC), the photocatalyst exhibited remarkable performance. The degradation of tetracycline (TC) reached an impressive efficiency of 95%, indicating the photocatalyst’s strong capability to degrade this antibiotic compound. Moreover, despite the simultaneous degradation of both diclofenac (Dic) and tetracycline (TC), the photocatalyst also demonstrated substantial efficacy in degrading diclofenac (Dic), achieving a degradation efficiency of 50%. This highlights the versatility of the photocatalyst in simultaneously degrading multiple organic pollutants, even when present in complex mixtures (Fig. 13B).
Overall, the results underscore the potential of the photocatalyst for efficient photodegradation of pharmaceutical compounds, both individually and in complex mixtures, contributing to the mitigation of organic pollutant contamination in water bodies.
The efficiency of the photocatalyst for the photodegradation of diclofenac alone was found to be 84%. Diclofenac, a commonly used nonsteroidal anti-inflammatory drug, is known for its persistence in the environment and potential ecological risks.
However, when the photocatalyst was used for the simultaneous photodegradation of both diclofenac and tetracycline (TC), the results showed remarkable performance. The degradation efficiency for tetracycline was as high as 95%, indicating the excellent ability of the photocatalyst to break down this antibiotic compound efficiently.
Interestingly, despite the simultaneous degradation of both diclofenac and tetracycline, the efficiency for diclofenac was slightly lower, achieving a degradation rate of 50%. This suggests that while the photocatalyst is effective in degrading diclofenac, the presence of tetracycline may have a slight inhibitory effect on its degradation efficiency for diclofenac.
Overall, the simultaneous photodegradation of diclofenac and tetracycline demonstrates the potential of the photocatalyst for the efficient removal of these emerging contaminants from water sources. Further optimization of the photocatalytic process may enhance the degradation efficiency for diclofenac and other pharmaceutical compounds, contributing to the development of advanced water treatment technologies.
Conclusion
The study demonstrates that Ag/CuS/Fe₃O₄ nanocomposites are highly effective for the degradation of organic pollutants, specifically tetracycline (TC) and diclofenac, showing superior performance compared to Fe₃O₄ and CuS/Fe₃O₄ alone. The enhanced photocatalytic activity of the Ag/CuS/Fe₃O₄ nanocomposites is attributed to the synergistic effects between silver (Ag) and copper sulfide (CuS), which facilitate improved charge carrier separation and broaden the light absorption range. The incorporation of Ag notably reduces the bandgap energy of the photocatalyst, thereby enhancing its activity under visible light. Characterization techniques confirmed the successful synthesis and maintained structural integrity of the nanocomposites. The Ag/CuS/Fe₃O₄ photocatalyst achieved a remarkable 98% degradation of TC within just 30 min and exhibited broad-spectrum effectiveness in degrading multiple pollutants. Optimization of experimental conditions and kinetic studies further validated the efficiency of the photocatalyst. The successful application of this photocatalyst for the simultaneous photodegradation of tetracycline and diclofenac underscores its practical utility for environmental remediation. These findings not only demonstrate the substantial progress made in photocatalyst development but also highlight the promising potential of Ag/CuS/Fe₃O₄ nanocomposites for real-world applications in water treatment.
Future perspectives
Future research could focus on scaling up the synthesis of Ag/CuS/Fe₃O₄ nanocomposites for large-scale environmental applications. Additionally, exploring the incorporation of other metal nanoparticles or varying the ratios of the components could further enhance the photocatalytic efficiency. Investigating the long-term stability and recyclability of these nanocomposites in practical settings will be crucial for their commercial viability. Further studies may also evaluate their performance in different environmental matrices and with a broader range of pollutants to fully establish their applicability in diverse water treatment scenarios.
Data availability
All data generated or analysed during this study are included in this published article.
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Mohammadzadeh Kakhki, R., Bolandhemmat, H. Synthesis of Ag/CuS doped mineral magnetite nanocomposite with improved photocatalytic activity against tetracycline and diclofenac pollutants. Sci Rep 14, 19009 (2024). https://doi.org/10.1038/s41598-024-69644-5
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DOI: https://doi.org/10.1038/s41598-024-69644-5
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