Hydrothermal Production of Multifunctional Zinc Ferrite Nanoparticles as Fertilizer, Supercapacitor Electrode, and NPK Sensor

Academic Background

With the continuous growth of the global population, the world population is expected to reach 10 billion by 2050, particularly in developing countries, where the demand for food will significantly increase. As the most populous country in the world, India needs to increase its crop production by 50% to meet the demand for food, fuel, and other commodities. However, farmers face challenges such as limited resources and insufficient expertise, making it a pressing issue to improve crop yields under constrained conditions. Although the use of traditional fertilizers has increased yields to some extent, it has also led to problems such as over-fertilization, environmental pollution, and resource waste. Therefore, the development of new and efficient fertilizers has become an important direction in agricultural research.

Meanwhile, energy storage technology is also rapidly advancing. Supercapacitors, as high-efficiency energy storage devices, have attracted significant attention due to their high power density and long cycle life. However, the performance of traditional electrode materials still needs improvement. Nanomaterials, owing to their unique physical and chemical properties, have shown great potential in both agriculture and energy storage. Zinc ferrite (ZnFe₂O₄), as a spinel ferrite, has excellent electrochemical and magnetic properties and has been widely studied in various fields in recent years. However, how to apply zinc ferrite nanoparticles in agricultural fertilizers, supercapacitor electrodes, and soil nutrient sensors remains a subject that requires further exploration.

Source of the Paper

This paper was co-authored by M. Ajitha, K. Selvarani, Subash C. B. Gopinath, and T. Theivasanthi, affiliated with the Graphene Solutions Laboratory and the School of Agricultural Sciences at Kalasalingam Academy of Research and Education in India, as well as the Faculty of Chemical Engineering & Technology and the Institute of Nano Electronic Engineering at Universiti Malaysia Perlis. The paper was accepted on April 2, 2025, and published in the journal Bionanoscience, with the DOI 10.1007/s12668-025-01925-3.

Research Process

1. Synthesis and Characterization of Zinc Ferrite Nanoparticles

The study first synthesized ZnFe₂O₄ nanoparticles using the hydrothermal method. The specific steps are as follows: 1. Material Preparation: Zinc nitrate (Zn(NO₃)₂), ferric nitrate (Fe(NO₃)₃), sodium hydroxide (NaOH), and cetyltrimethylammonium bromide (CTAB) were used as precursors. 2. Hydrothermal Reaction: The precursors were dissolved in double-distilled water, stirred, and then transferred to a 100 mL Teflon-lined autoclave, where they were reacted at 165°C for 16 hours. 3. Centrifugation and Drying: After the reaction, the dark brown powder was obtained through centrifugation and drying.

The synthesized nanoparticles were characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDAX). XRD analysis confirmed the cubic spinel structure of the nanoparticles, with a crystallite size of 40.11 nm. FTIR spectroscopy revealed the functional groups in the sample, SEM images displayed the morphology of the nanoparticles, and EDAX analysis confirmed the atomic percentages of Zn and Fe.

2. Application of Nanoparticles in Agriculture

The study evaluated the effects of ZnFe₂O₄ nanoparticles as nano-fertilizers on the growth of tomatoes, spinach, and several types of millet. The specific experimental steps are as follows: 1. Nano-fertilizer Preparation: ZnFe₂O₄ nanoparticles were suspended in double-distilled water at a concentration of 5 µM and sonicated to ensure uniform distribution. 2. Plant Treatment: The nano-fertilizer was applied to the soil of tomatoes, millet, and spinach, and plant growth was periodically recorded. 3. Growth Parameter Measurement: After 5 weeks, root length, shoot length, leaf count, and dry weight of the plants were measured.

The experimental results showed that plants treated with ZnFe₂O₄ nano-fertilizer significantly outperformed the control group in growth parameters. For example, the shoot length of tomatoes increased from 68 cm to 102 cm, root length increased from 20 cm to 23.5 cm, and leaf count increased from 92 to 164. The nano-fertilizer enhanced the absorption efficiency of zinc and iron, promoting plant growth and yield.

3. Application of Nanoparticles in Supercapacitors

The study also explored the performance of ZnFe₂O₄ nanoparticles as supercapacitor electrodes. The specific experimental steps are as follows: 1. Electrode Preparation: 80 wt% ZnFe₂O₄ nanoparticles were mixed with 5 wt% polyvinylidene fluoride (PVDF) and 15 wt% acetylene black, coated onto nickel foil, and dried for electrochemical testing. 2. Electrochemical Testing: The electrode performance was evaluated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) in a 1 M KOH electrolyte.

The experimental results showed that the ZnFe₂O₄ nanoparticle electrode exhibited a specific capacitance of 360 F/g at a current density of 1 A/g and maintained 93.1% cyclic stability after 2400 cycles. This indicates that ZnFe₂O₄ nanoparticles have excellent electrochemical performance and long-term stability, making them suitable for supercapacitors.

4. Application of Nanoparticles in Soil Nutrient Sensors

The study also developed a soil nutrient sensor based on ZnFe₂O₄ nanoparticles for detecting nitrogen (N), phosphorus (P), and potassium (K) content. The specific experimental steps are as follows: 1. Sensor Preparation: ZnFe₂O₄ nanoparticles were mixed with different concentrations of N, P, and K solutions, sonicated, and subjected to UV-Vis spectroscopy analysis. 2. Spectral Analysis: Absorption spectra in the wavelength range of 200-800 nm were recorded, and spectral changes at different concentrations were analyzed.

The experimental results showed that the peak intensity of the UV-Vis absorption spectra increased with the concentration of N, P, and K. This indicates that ZnFe₂O₄ nanoparticles can serve as an efficient soil nutrient sensor for real-time monitoring of nutrient content in soil.

Research Results and Conclusions

ZnFe₂O₄ nanoparticles were successfully synthesized using the hydrothermal method, and their structure, morphology, and performance were thoroughly characterized. The study found that ZnFe₂O₄ nanoparticles exhibited excellent performance in agriculture, energy storage, and soil nutrient detection: 1. Agricultural Application: As a nano-fertilizer, ZnFe₂O₄ significantly promoted the growth of tomatoes, millet, and spinach, improving nutrient absorption efficiency and yield. 2. Energy Storage: As a supercapacitor electrode, ZnFe₂O₄ nanoparticles demonstrated high specific capacitance and excellent cyclic stability, making them suitable for high-efficiency energy storage devices. 3. Soil Detection: As an NPK sensor, ZnFe₂O₄ nanoparticles enabled real-time monitoring of nitrogen, phosphorus, and potassium content in soil through UV-Vis spectroscopy.

Research Highlights

1. Multifunctional Application: This study is the first to simultaneously apply ZnFe₂O₄ nanoparticles in agricultural fertilizers, supercapacitor electrodes, and soil nutrient sensors, demonstrating their broad application potential across multiple fields.
2. High Efficiency: ZnFe₂O₄ nanoparticles significantly improved plant growth efficiency in agriculture, exhibited high specific capacitance and long cycle life in energy storage, and achieved real-time monitoring in soil detection.
3. Green Synthesis: The hydrothermal method used to synthesize ZnFe₂O₄ nanoparticles is simple and cost-effective, making it suitable for large-scale production.

Research Significance

This study provides new solutions for agriculture, energy storage, and soil detection. The multifunctional application of ZnFe₂O₄ nanoparticles not only enhances agricultural production efficiency but also offers high-performance electrode materials for energy storage devices while enabling real-time monitoring of soil nutrients. These achievements are of great significance for promoting sustainable agriculture and clean energy technologies.