Harnessing the Effects of CD-Doped and Ag-Coated CeO2 (IV) Nanoparticles for Enhanced Nitrophenol Reduction, Photocatalytic Degradation, and Other Potential Biological Applications

Inorganic Chemistry Inorganic Non-Metallic Materials Engineering Nanoscience Environmental Engineering Chemistry Materials Science Bioengineering Materials Chemistry Environmental Chemistry Life Sciences

Academic Background

With the rapid development of nanotechnology, the potential applications of nanomaterials in environmental remediation, biomedicine, and energy conversion have garnered increasing attention. Among these, cerium oxide (CeO₂) nanoparticles have become a research hotspot due to their unique redox properties, high stability, and excellent biocompatibility. However, traditional chemical synthesis methods often use toxic reagents and produce harmful byproducts, negatively impacting the environment. Therefore, developing an environmentally friendly and sustainable method for nanoparticle synthesis has become a key focus of current research.

Green synthesis utilizes plant extracts as reducing and capping agents, reducing reliance on harmful chemicals while enhancing the biocompatibility of nanoparticles. This study aims to prepare CeO₂ nanoparticles using a green synthesis method and enhance their photocatalytic, catalytic reduction, and biomedical properties through cadmium (Cd) doping and silver (Ag) coating, exploring their potential applications in environmental remediation and biomedicine.

Source of the Paper

This paper was co-authored by Pranali S. Parab, Aniket A. Pawanoji, Komal R. Jarhad, and Amol S. Pawar, all from the Department of Chemistry at K. J. Somaiya College of Science and Commerce in Mumbai, India. The paper was accepted on March 18, 2025, and published in the journal Bionanoscience with the DOI 10.1007/s12668-025-01909-3.

Research Process

1. Green Synthesis of Nanoparticles

This study used lemongrass (Cymbopogon citratus) leaf extract as a reducing and capping agent to synthesize undoped CeO₂ nanoparticles, Cd-doped CeO₂ nanoparticles (Cd-CeO₂), and Ag-coated CeO₂ nanoparticles (CeO₂-Ag). The specific steps are as follows:

  • Preparation of Lemongrass Leaf Extract: 50 grams of lemongrass leaves were finely chopped, added to 250 ml of distilled water, heated to 80-90°C, stirred for 15-20 minutes, filtered, and stored in a refrigerator for future use.
  • Synthesis of Undoped CeO₂ Nanoparticles: 20 ml of 0.1 M cerium nitrate solution was mixed with lemongrass leaf extract, stirred at 60-70°C for 2 hours, dried, and then calcined at 600°C for 2 hours.
  • Synthesis of Ag-Coated CeO₂ Nanoparticles: A 5% silver nitrate solution was added to the reaction mixture during the synthesis of undoped CeO₂ nanoparticles, stirred for 12 hours, centrifuged, and dried.
  • Synthesis of Cd-Doped CeO₂ Nanoparticles: A 5% cadmium sulfate solution was added to the reaction mixture during the synthesis of undoped CeO₂ nanoparticles, stirred for 4 hours, centrifuged, and calcined at 500°C for 2 hours.

2. Characterization of Nanoparticles

The synthesized nanoparticles were characterized using various techniques, including ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and energy-dispersive X-ray spectroscopy (EDAX). The results showed that the bandgap of undoped CeO₂ nanoparticles was 2.91 eV, while those of Cd-CeO₂ and CeO₂-Ag decreased to 2.64 eV and 2.38 eV, respectively, indicating that doping and coating effectively modulated the optoelectronic properties of the nanoparticles. XRD analysis confirmed the high purity and cubic fluorite structure of the nanoparticles, while SEM and HRTEM images revealed spherical nanoparticles with sizes ranging from 3 to 20 nm.

3. Catalytic Reduction and Photocatalytic Degradation Experiments

  • Catalytic Reduction of 4-Nitrophenol (4-NP): Undoped and Ag-coated CeO₂ nanoparticles were used as catalysts to reduce 4-NP to 4-aminophenol (4-AP) in the presence of sodium borohydride (NaBH₄). The results showed that the catalytic efficiency of CeO₂-Ag nanoparticles reached 96.53%.
  • Photocatalytic Degradation of Methylene Blue (MB): Undoped and Cd-doped CeO₂ nanoparticles were used as photocatalysts to degrade MB dye under UV light. The results showed that the degradation efficiency of Cd-CeO₂ nanoparticles was 89.56%.

4. Biomedical Applications

  • Antioxidant Activity: The antioxidant properties of the nanoparticles were evaluated using a DPPH radical scavenging assay, showing an antioxidant activity of 70% ± 2%.
  • Antibacterial Activity: The antibacterial activity of the nanoparticles against Gram-positive bacteria (e.g., Staphylococcus aureus) and Gram-negative bacteria (e.g., Escherichia coli) was assessed using the agar diffusion method, showing inhibition zones exceeding 17 ± 2 mm.
  • Hemolysis Assay: The hemolytic activity of the nanoparticles was evaluated, showing a hemolysis rate of less than 5%, indicating good biocompatibility.

Key Results and Conclusions

This study successfully prepared CeO₂ nanoparticles using a green synthesis method and significantly enhanced their catalytic, photocatalytic, and biomedical properties through Cd doping and Ag coating. The specific conclusions are as follows:

  1. Catalytic Performance: Ag-coated CeO₂ nanoparticles exhibited high efficiency in the catalytic reduction of 4-NP, achieving a conversion rate of 96.53%; Cd-doped CeO₂ nanoparticles showed excellent performance in the photocatalytic degradation of MB, with a degradation efficiency of 89.56%.
  2. Biomedical Performance: The nanoparticles demonstrated significant antioxidant and antibacterial activities, with low hemolysis rates, indicating their potential for biomedical applications.
  3. Advantages of Green Synthesis: The use of lemongrass leaf extract as a reducing and capping agent not only simplified the synthesis process but also improved the biocompatibility and environmental friendliness of the nanoparticles.

Research Highlights

  1. Green Synthesis Method: This study is the first to use lemongrass leaf extract to synthesize CeO₂ nanoparticles and modulate their properties through doping and coating, providing a new approach to the green synthesis of nanomaterials.
  2. Multifunctional Nanoparticles: The synthesized nanoparticles exhibited excellent performance in catalysis, photocatalysis, and biomedicine, demonstrating broad application potential.
  3. Environmental Friendliness: The green synthesis method reduced reliance on harmful chemicals, aligning with the principles of sustainable development.

Research Significance and Value

This study not only provides a new method for the green synthesis of CeO₂ nanoparticles but also significantly enhances their performance through doping and coating, offering efficient and environmentally friendly solutions for environmental remediation and biomedical applications. Future research could further optimize synthesis parameters and explore the potential applications of nanoparticles in more fields.

Through this detailed report, we can see that green-synthesized nanoparticles not only hold scientific value but also demonstrate immense potential in practical applications, providing new directions for the future development of nanotechnology.