Synthesis of zinc oxide nanoparticles and their optical and morphological characterization

Introduction

Nanotechnology has emerged as a transformative technology for developing advanced nutrient delivery systems in agriculture (Ayenew et al., 2025) [2] . Materials engineered at the nanoscale possess unique physicochemical properties, including a high surface-area-to-volume ratio, enhanced surface reactivity and improved interaction with biological systems, making them suitable for efficient nutrient delivery. Among various nanomaterials, metal oxide nanoparticles have attracted considerable attention because of their stability, ease of synthesis and potential to improve fertilizer-use efficiency while minimizing nutrient losses to the environment (Ravishankar et al., 2025) [5] . Zinc is an essential plant micronutrient involved in numerous physiological, biochemical and metabolic processes. It acts as a structural and catalytic component of several enzymes and proteins and plays a crucial role in chlorophyll synthesis, photosynthetic activity, auxin metabolism, membrane integrity and reproductive growth. However, the agronomic efficiency of conventional zinc fertilizers is often reduced by adsorption, precipitation and fixation reactions in soil, particularly under alkaline conditions, resulting in poor zinc availability to crops. (Abegunde et al., 2026) [1] . The development of nanoscale zinc fertilizers has therefore gained considerable interest as an alternative approach to enhance zinc availability and nutrient-use efficiency. Zinc oxide nanoparticles (ZnO NPs) have emerged as one of the most promising nanomaterials for agricultural applications because of their high chemical stability, biocompatibility, large specific surface area and controlled nutrient-release behaviour. The physicochemical characteristics of ZnO nanoparticles are largely governed by the synthesis route and reaction conditions, including precursor concentration, pH, temperature, calcination conditions and reaction time (Swain et al., 2025; Rani et al., 2025) [6,4] . Consequently, optimization of the synthesis process together with detailed characterization is essential for obtaining nanoparticles with desirable properties suitable for agricultural applications. Reliable characterization is indispensable for confirming nanoparticle formation and understanding their properties. Ultraviolet-Visible (UV-Vis) spectroscopy is widely employed to verify the composition formation through their characteristic optical absorption behaviour. Fourier Transform Infrared (FT-IR) spectroscopy provides information on the functional groups and chemical bonding associated with the synthesized nanoparticles and confirms the removal of precursor compounds after synthesis. Scanning Electron Microscopy (SEM) enables direct visualization of particle morphology, surface texture and aggregation characteristics.

Materials and Methods

Synthesis of nanoscale ZnO and boron Preparation of nanoscale

ZnO: Nanoscale ZnO was prepared by using the oxalate decomposition technique as described by Prasad et al., 2012 [3] . In brief, equimolar concentrations of zinc acetate and oxalic acids were mixed thoroughly for 3 hrs at 60 centigrade. The solution was then filtered and the obtained precipitation was air dried and calcined at 500 degree centigrade for 1 hr. The collected zinc oxide nano powder was used in the further experiments.

Characterization of nanoscale ZnO UV -Vis (UV-Visible spectra) analysis

Ultraviolet-Visible (UV-Vis) spectroscopic analysis was carried out to confirm the formation and optical properties of the synthesized zinc oxide nanoparticles. The absorption spectrum was recorded using a UV-Visible spectrophotometer (UV-1800, Shimadzu, Kyoto, Japan). The nanoparticle suspension was prepared by dispersing the synthesized ZnO nanoparticles in distilled water, and the absorbance was measured over the wavelength range of 300-600 nm using a quartz cuvette with a 1 cm path length. The characteristic absorption maximum (λmax) was recorded to confirm the formation of ZnO nanoparticles.

Fourier Transform Infrared (FT-IR) spectroscopy

Fourier Transform Infrared (FT-IR) spectroscopic analysis was carried out to identify the functional groups and chemical bonds associated with the synthesized zinc oxide nanoparticles. The FT-IR spectrum was recorded in the range of 400-4000 cm⁻¹ using an ATR-FTIR spectrometer (IRTracer-100 AH, Shimadzu, Japan) operated at a resolution of 4 cm⁻¹. The synthesized ZnO nanoparticles were directly placed on the diamond ATR crystal and the spectra were recorded in transmittance mode. The obtained absorption bands were analysed to confirm the characteristic functional groups associated with ZnO nanoparticles.

Scanning Electron Microscopy and EDAX analysis

The surface morphology and elemental composition of the synthesized zinc oxide nanoparticles were examined using a Scanning Electron Microscope (SEM) (EVO 10, Carl Zeiss Microscopy, Cambridge, UK). A small quantity of the dried ZnO nanoparticle sample was uniformly mounted on an aluminium stub using conductive carbon tape and coated with a thin layer of gold-palladium using a sputter coater to improve electrical conductivity. The sample was subsequently observed under suitable accelerating voltage and magnification to evaluate particle shape, surface texture and aggregation pattern.

Results

Synthesis of nanoscale ZnO

Nanoscale zinc oxide particles were synthesized following the procedure described in the Materials and Methods section. The major steps involved in their preparation are schematically presented in Fig. 1. The synthesized nanonutrients were subjected to various characterization techniques and the results concerning particle size, morphology and dispersibility indicated that the prepared nanoparticles possessed suitable properties for foliar application and subsequent agricultural investigations.

Characterization of nanoscale ZnO UV-Visible spectral analysis of nanoscale ZnO

The UV-Visible absorption spectrum of the synthesized nanoscale zinc oxide exhibited a distinct absorption maximum at approximately 370 nm (Fig. 2). This characteristic absorption band was associated with the electronic transition of electrons from the valence band to the conduction band, thereby verifying the formation of ZnO nanoparticles. The occurrence of this absorption maximum further demonstrated the nanoscale characteristics and pronounced optical response of the synthesized particles. Hence, UV-Visible spectroscopic analysis established the successful preparation of nanoscale ZnO.

Fourier Transform Infrared spectroscopy (FT-IR)

The FTIR spectrum of the synthesized zinc oxide nanoparticles was recorded in the range of 400-4000 cm⁻¹ using 100 scans at a resolution of 4 cm⁻¹ (Fig. 3). The spectrum exhibited high transmittance throughout most of the region, indicating the presence of only a small quantity of surface-bound organic residues. A weak absorption band observed at 2345.44 cm⁻¹ was attributed to the asymmetric stretching vibration of atmospheric or surface-adsorbed CO₂. The absence of prominent O-H, C-H and C=O absorption bands suggested the effective removal of moisture and organic precursor residues during nanoparticle preparation. A pronounced reduction in transmittance below approximately 650 cm⁻¹, extending towards 400 cm⁻¹, was associated with the stretching vibrations of Zn-O bonds in the ZnO crystal lattice. The characteristic absorption in the lower wavenumber region therefore supported the successful formation of ZnO nanoparticles with comparatively low organic contamination.

Scanning Electron Microscopy

The SEM image (Fig. 4) revealed that the synthesized nano zinc particles were predominantly irregular to nearly spherical in shape, with rough and uneven surface morphology. The particles were closely associated with one another and formed compact agglomerated clusters. The particle dimensions marked in the micrograph were 37.95, 40.08, 45.28 and 59.55 nm, indicating a size range of approximately 37.95-59.55 nm, with an average particle size of about 45.72 nm. The observed aggregation may be attributed to the high surface energy of the nanoparticles, which promotes attractive forces among the particles and leads to cluster formation. The SEM image was captured using a ZEISS scanning electron microscope at a magnification of 15,000×, an accelerating voltage of 10.00 kV and a working distance of 13.5 mm, using a secondary electron detector (SE1). The nanoscale dimensions and characteristic clustered morphology observed in the micrograph supported the successful formation of nano zinc particles. These morphological characteristics may influence their surface reactivity, dispersion, dissolution and zinc-release behaviour when used for agricultural applications.

References

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