Green synthesis of zinc ferrite nanoparticles in Limonia acidissima juice: Characterization and their application as photocatalytic and antibacterial activities

Highlights

• Zinc ferrite nanoparticles were prepared by microwave-assisted method using Limonia acidissima juice

• Zinc ferrite nanoparticles were characterized by structural, morphological, optical and magnetic studies.

• It showed promising photocatalytic activity against Evans blue and Methylene blue under visible light irradiation.

• Antibacterial activity (foodborne pathogens) of zinc ferrite nanoparticles is evaluated.

Abstract

The zinc ferrite (ZnFe₂O₄) nanoparticles were prepared by a green method using Limonia acidissima (wood apple) juice. The synthesized ZnFe₂O₄ samples were characterized by XRD, FTIR, SEM with EDAX, TEM, UV-DRS and luminescence. X-ray diffraction confirms the formation of the cubic spinel crystal structure of ZnFe₂O₄ nanoparticles with an average crystallite size of 20 nm. The prepared nanoparticles showed the agglomerated and spherical shaped particles from the SEM and TEM. The EDAX confirms the pure phase with all the elemental compositions present in the ZnFe₂O₄ nanoparticles. FTIR confirmed the characteristic functional groups present in the spinel ferrite. The VSM study shows the high saturation magnetization of prepared nanoparticles. The ZnFe₂O₄ nanoparticles showed effective photodegradation for Evans blue and Methylene blue under visible light irradiation. Moreover, the antibacterial activity of the prepared nanoparticles was carried out by agar well diffusion method against both gram-positive and gram-negative bacterial strains.

Introduction

Spinel ferrites (MFe₂O₄; M = Zn, Cu, Co, Ni, and Mn) are the ferromagnetic materials which gained much interest because of their unique optical, electrical and magnetic properties [1,2]. These materials have been widely used in many applications including magnetic recording and fluids, catalysis, sensors, magnetically guided drug delivery, pigments, etc. [[3], [4], [5], [6]]. For environmental remediation, ferrites have become the promising materials due to their narrow bandgap (1.1–2.3 eV), low cost, non-toxicity, thermal and chemical stability [[7], [8], [9]]. A variety of methods have been adopted for the preparation of ferrite nanoparticles such as ball milling, ultrasonication, microwave-assisted, co-precipitation, combustion, sol-gel and mechanical alloying etc., [[10], [11], [12]]. Over these conventional methods, the microwave-assisted method is used as an efficient method for the synthesis of ferrites, because this is a friendly method and by superheating it reduces the reaction time and produces products with high yield. Microwave generates the heat within the material on a molecular level and the heat will be rapidly and evenly distributed outside and inside when compared to classical heating. This method leads to a quick and homogeneous reaction instead of originating from external sources. This method is more efficient for producing homogeneity and highly pure sample, small particle size, less external energy and takes shorter time period [13,14].

Semiconductor photocatalysis has attracted the scientific society due to its wide variety of applications for reducing the contaminants from air and water. It is used for water splitting (H₂ production), odor control, bacterial inactivation and cancer cell inactivation. The contaminants (organic compounds) released into the environment need to be potentially photodegraded with no additional waste and byproducts into CO₂ and water [[15], [16], [17], [18]]. Worldwide, with an increase in population growth, water pollution is a challenging issue. Dyes play a major role in the contamination of water and are highly toxic which are frequently used in various industries such as textile, paper, food, cosmetics and plastics; in fact, textile industry ranks first in dyes usage [19,20]. Because of their complex structure, it is difficult to degrade naturally. Various semiconductor photocatalysts have been developed in recent years to degrade the organic contaminants present in the wastewater [[21], [22], [23], [24]].

Several metals and metal oxide nanoparticles like Ag, TiO₂, ZnO, Al₂O₃ have been widely used in biological applications. Among these different types of nanoparticles, magnetic nanoparticles have attracted the attention of researchers due to their magnetic behavior, chemical stability, and biocompatibility. These magnetic nanoparticles are being used for targeted drug delivery, metabolic or enzymatic degradation, pathogen detection, tissue repair, hyperthermia, and antigen diagnosis [[25], [26], [27], [28]].

Among ferrites, the inverse type is predominantly captivating due to its great magnetocrystalline anisotropy, high saturation magnetization from a characteristic crystal and magnetic structure. In general, zinc ferrite (ZnFe₂O₄) is a well-known inverse spinel ferrite with Zn²⁺ in B (octahedral) sites and Fe³⁺ ions that are divided equally among A (tetrahedral) and B (octahedral) sites. Thereafter, ZnFe₂O₄ nanoparticles have attracted extensively due to their excellent phase stability, high magnetic permeability, high electronic conductivity, low eddy current loss, bandgap (~1.9 eV), low cost of production and non-toxicity [29]. ZnFe₂O₄ nanoparticles have also attracted the attention because of their potential applications in the field of drug delivery, magnetic hyperthermia, sensing applications, magnetic resonance imaging (MRI), antibacterial and photocatalytic activity [30].

Generally, magnetic properties of the magnetic nanoparticles mainly depend on their diameter. Unluckily, several preparation methods of nanoparticles contain high energy requirements or hazardous chemicals, which are somewhat difficult and having wasteful purifications. Currently, for the synthesis of nanoparticles using naturally occurring reagents such as fruits, microorganisms as reductants and capping agents, biodegradable polymers (chitosan, etc.), marine algae, sugars, plant parts (roots, seed, leaf, stem, and latex) could be evaluated as preferable materials for nanotechnology. Furthermore, green synthesis of nanoparticles offers advancement over other conventional methods as they are one step, simple, cost-effective, environmental friendly and frequently lead to preparing more stable materials and relatively reproducible [31,32]. However, only a few researchers have reported the green synthesized (plant extracts and fruit juices) ZnFe₂O₄ nanoparticles by different methods (Table 1).

This work designates the preparation of ZnFe₂O₄ nanoparticles using Limonia acidissima juice as a novel fuel by microwave-assisted route. The Limonia acidissima is a fleshy fruit and contains a considerable amount of carbohydrate (18.1 g), protein (7.1 g), fat (3.7 g), ferus (6 mg) and Vitamin C (3 mg). These contents act as a reducing agent and metal nitrates as oxidizers which are useful for the microwave process. Further, the prepared nanoparticles used for structural, optical, morphological, magnetic, photocatalytic (Evans blue and Methylene blue) and antibacterial (foodborne pathogens) studies.