In this study, Undoped and Cu-doped Ni0.6-x Zn0.4CuxFe2O4 (x = 0, 0.3) ferrite nanoparticles were synthesized using the sol-gel auto combustion method. The nanoparticles exhibited a single-phase spinel crystal structure as confirmed by XRD analysis. The crystallite sizes were determined to be in the range of 20 to 30 nm. SEM revealed the nanoparticles to have a spherical morphology. EDS confirmed the elemental composition and purity of the nanoparticles. FTIR analysis provided insights into the vibrational modes and bonding characteristics of the nanoparticles. UV-VIS was employed to investigate the optical properties of the nanoparticles, revealing band gap energies ranging from 2.80 to 3.5 eV. The photocatalytic activity of the nanoparticles was evaluated through the degradation of methylene blue under sunlight irradiation, demonstrating their effectiveness as photocatalysts. These findings contribute structural and optical properties of undoped and Cu-doped Ni-Zn ferrite nanoparticles, emphasizing their potential as efficient photocatalysts for environmental applications.
Research Article
Tuning Photocatalytic Efficiency through Cu Doping in Ni-Zn Ferrite Nanoparticles: Structural and Optical Characteristics
https://doi.org/10.21203/rs.3.rs-3130637/v1
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Sol-gel
XRD
SEM
EDS
FTIR
UV-VIS
Photocatalytic activity
Nanoscale materials are gaining scientific interest due to their distinct characteristics in recent times. The distinctive physical and chemical characteristics of nanoparticles have attracted considerable interest in diverse areas of research and technology, presenting novel prospects for advanced materials and applications [1]. Ferrite nanoparticles are a type of nanoparticle that possess unique magnetic, electrical, and optical properties, making them highly attractive for a variety of technological applications such as catalysis, electronics, and environmental remediation. Their potential in these areas has been widely recognized, making them a promising area of research [2]. AB2O4 spinel ferrites are receiving significant attention owing to their diverse properties and potential applications [3]. Here, A and B denote distinct metal ions, and the general formula for spinel ferrites is AB2O4. The Ni-Zn ferrite, which belongs to the spinel ferrite family, has been extensively researched due to its exceptional electrical and magnetic characteristics [4]. The introduction of dopant ions into the ferrite structure can effectively augment their characteristics and change their use for particular applications. The element Copper (Cu) exhibits fascinating dopant characteristics as it has the capacity to change the electronic and magnetic attributes of ferrite nanoparticles [5].
The synthesis and analysis of undoped and Cu-doped Ni-Zn ferrite nanoparticles have become a topic of interest in recent times, specifically in relation to their potential use as photocatalysts for the purpose of environmental remediation [6]. The utilization of semiconductor materials for photocatalysis has surfaced as a propitious technique for the disintegration of organic contaminants in air and water. This method employs solar energy as an eco-friendly and sustainable source. The sol-gel auto combustion technique has shown effectiveness and range in the synthesis of nanoparticles with controlled composition, size, and morphology. The process of combustion offers a prompt and effective means for the preparation of uniform nanoparticles possessing raised crystalline properties [7].
The aim of the present study is to produce undoped and Cu-doped Ni-Zn ferrite nanoparticles through the sol-gel auto combustion technique and analyze their structural and optical characteristics. The nanoparticles are subjected to characterization through various scientific techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), and ultraviolet-visible (UV-VIS) spectroscopy. The nanoparticles after an evaluation of their photocatalytic abilities in the degradation of organic pollutants, specifically methylene blue dye, when exposed to sunlight irradiation. The results obtained from this investigation will enhance the comprehension of the properties and potential uses of undoped and Cu-doped Ni-Zn ferrite nanoparticles as effective photocatalysts for the purpose of environmental remediation.
2.1. Materials and Preparation
Analytical grade nickel nitrate, zinc nitrate, copper nitrate, and ferric nitrate were used for the synthesis of the ferrite compositions Ni0.6-x Zn0.4CuxFe2O4 (x = 0, 0.3). The synthesis procedure was initiated by solubilizing citric acid and metal nitrates in deionized water. The nitrate solutions underwent standardization via chemical analysis. A mixture of nitrates and citric acid in a 1:3 molar ratio was heated to a temperature of 280°C, resulting in the formation of a gel-like substance. Subsequently, the gel went through drying and combustion, leading to the formation of dark brown powders for the Ni-Zn and Ni-Cu-Zn compositions. The powders were subjected to calcination at a temperature of 1000°C for a duration of 5 hours, then the powders were granulated to obtain a fine powder.
2.2. Photocatalytic Activity Experiments
The photocatalytic activity of Ni-Zn and Ni-Cu-Zn ferrite spinel ferrites was assessed by studying the degradation of methylene blue (MB) under sunlight exposure. A 50 mL solution containing MB at a concentration of 10 mg L-1 was mixed with 10 mg of the catalyst powders. The solution was stirred in darkness for one hour to establish absorption-desorption equilibrium. Then, the solution was exposed to sunlight. Samples of 3 mL were collected at specific time intervals during the photocatalytic degradation process. The residual MB concentration was determined by measuring the absorption peak at 554 nm using a UV-Visible spectrometer. The degradation efficiency was determined using the following equation [8]:
Where, Ct represents the dye concentration at time t, and C0 is the initial dye concentration. By monitoring the degradation efficiency over time, the effectiveness of the Ni-Zn and Ni-Cu-Zn ferrite nanoparticles as photocatalysts for MB degradation can be assessed.
3.1. XRD Analysis
X-ray diffraction (XRD) analysis was used to examine the crystal structure and studies of purity of the synthesized samples. The X-ray diffraction (XRD) pattern obtained showed miller indices and peak positions that closely corresponded to the characteristic XRD pattern of spinel ferrite. This suggests that a pure phase was formed, and there were no apparent impurity peaks present. The validation of the spinal cubic configuration corresponds with the seen crystal structure for spinel ferrite, as indicated by the corresponding hkl planes (220), (311), (400), (422), (333), and (440) that are related to the Fd3m space group [9]. The X-ray diffraction (XRD) data provided interplanar spacing (d) values that were compatible with the JCPDS card number 96-153-2574. The reference peak for calculating the lattice parameter (a) has been chosen as the primary (311) peak of the cubic spinel structure. On comparative analysis of the undoped (x = 0.00) and Cu-doped (x = 0.30) ferrite samples, noticeable differences in their respective properties were detected. The incorporation of Cu ions in the sample doped with Cu resulted in a slight increase in the lattice parameter (a), indicating lattice distortion. Furthermore, the sample doped with Copper showed higher crystallite size calculated using Scherrer's formula [10], with an increase of 26.40 nm in comparison to 19.43 nm in the non-doped sample. This observation implies that the addition of Cu dopants had an impact on the formation and receiving of the crystallographic domains. The X-ray density (dx) of both undoped and Cu-doped samples exhibited minimal variation, suggesting that the mass per unit volume did not undergo substantial change on Cu doping. The Cu-doped sample exhibited a slightly higher bulk density (db), which could be attributed to the incorporation of Cu ions which resulted in an increase in overall mass.
3.2. FTIR (Fourier Transform Infrared) Analysis
FTIR was conducted to further investigate the formation of functional groups in the samples. The obtained spectra, as depicted in Fig. 3, provide valuable insights into the chemical composition and bonding characteristics of the materials. In the spectra, distinctive absorption bands were observed, confirming the presence of specific functional groups. Notably, the stretching vibrations of metal ions at the tetrahedral site A and octahedral site B were identified within the frequency ranges of 541–555 cm-1 and 403–412 cm-1, respectively [11]. The variations in the band positions between the two samples were anticipated due to the differences in the distances between the octahedral and tetrahedral ions. It is important to note that the size of the resulting nanoparticles and alterations in the interaction between oxygen and cations have a significant influence on these absorption bands. Changes in the lattice parameter, which can be influenced by factors such as dopants or variations in the synthesis process, contribute to the observed apparent shift in frequencies. These modifications in the lattice parameter can result in changes in bond lengths and strengths, thereby affecting the absorption characteristics of the functional groups. The observed absorption bands and their variations in position can be attributed to the presence of metal ions at specific sites, the size of the nanoparticles, and alterations in the oxygen-cation interaction [12].
3.3. FESEM Analysis
FESEM was conducted to investigate the morphology of the samples. The obtained morphological images, as shown in Fig. 5, provide visual information about the surface structure and particle distribution. The FESEM images reveal the presence of spherical nanoparticles with a uniform distribution across the surface. The grain sizes of the nanoparticles were measured and found to range between 22 and 33 nm, as indicated in Table 1. This indicates a relatively narrow size distribution and suggests a controlled synthesis process. The Energy-Dispersive X-ray (EDX) pattern was analyzed to determine the elemental composition of the samples. The EDX analysis detected the presence of Ni, Fe, Cu, and O elements, which are the expected constituents of the ferrite material. Importantly, no additional peaks corresponding to impurity elements were observed in the EDX pattern, indicating that the samples were pristine and free from contamination [13].
The FESEM analysis provides valuable insights into the morphology and elemental composition of the investigated samples. The spherical nanoparticle morphology with well-dispersed grain sizes indicates a homogeneous structure. The absence of impurity peaks in the EDX pattern further confirms the purity of the samples. These findings enhance our understanding of the structural and elemental characteristics of the investigated ferrite nanoparticles.
3.4. UV-VIS Analysis
UV-Vis analysis was employed to explore the optical properties of the synthesized Ni-Zn nanoparticles, including both undoped and Cu-doped Ni-Zn ferrite nanoparticles. The analysis aimed to determine the bandgap energy (Eg) using the maximum transmittance wavelength, according to the equation Eg = 1240/λmax (in eV) [14]. The obtained UV-Vis spectra provided insights into the absorption behaviour of the samples across the ultraviolet and visible regions of the electromagnetic spectrum. By analyzing the wavelength at which maximum transmittance occurred, the corresponding bandgap energy was calculated [15].
The results revealed that at ambient temperature, both undoped and Cu-doped Ni-Zn ferrite samples exhibited a reduction in bandgap energy compared to the bulk material. Specifically, the bandgap energy decreased from 3.64 eV to 2.80 eV for the undoped and Cu-doped Ni-Zn ferrites, respectively. This decrease in bandgap energy suggests a shift towards lower energy levels, indicating a modification in the electronic structure of the materials. The incorporation of Cu dopants may have contributed to this shift, as dopants can introduce additional energy levels within the band structure, influencing the absorption properties.
The observed changes in bandgap energy have significant implications for the optical behaviour of the materials. A lower bandgap energy corresponds to a broader absorption range, allowing the samples to absorb a wider range of photons, including those in the visible region. This enhanced light absorption capability can have implications for various applications, such as solar energy conversion and photocatalysis. The UV-Vis analysis revealed a reduction in bandgap energy for both undoped and Cu-doped Ni-Zn ferrite nanoparticles compared to the bulk material. These findings provide valuable insights into the optical characteristics and electronic structure of the synthesized nanoparticles, suggesting potential applications in optoelectronic devices and light-harvesting technologies [16].
3.5. Photocatalytic Activity
The photocatalytic activity of Ni-Zn and Ni-Cu-Zn ferrite powders was studied to assess their potential for wastewater treatment. Specifically, the degradation of organic pollutants, such as heteropolyaromatic MB dye, was investigated under sunlight irradiation. The analysis involved monitoring the degradation process at regular 20-minute intervals.
Figure 5. illustrates the photocatalytic degradation of MB dye in the presence of the spinel ferrite catalysts. The degradation process is indicated by the shift in the absorbance peak at 464 nm, corresponding to the characteristic absorption of the dye. As the photocatalytic reaction progresses, the absorbance at this wavelength decreases, indicating the degradation and breakdown of the organic pollutant. To quantitatively assess the degradation rate, the ratio between the residual concentration of the dye and the initial concentration (C/C0) is calculated [17]. This ratio provides a measure of how quickly the organic dye pollutant degrades over time. By plotting this ratio as a function of time, the efficiency and effectiveness of the photocatalytic process can be evaluated.
The photocatalytic activity of the Ni-Zn and Ni-Cu-Zn ferrite powders relies on their ability to harness solar energy and generate reactive species, such as hydroxyl radicals (•OH), which are highly oxidative and capable of breaking down organic pollutants. Under sunlight irradiation, the ferrite nanoparticles absorb photons, exciting their electrons to higher energy levels. These energized electrons can then transfer to the oxygen molecules adsorbed on the catalyst surface, generating superoxide radicals (•O2-) and, subsequently, hydroxyl radicals (•OH). The generated hydroxyl radicals play a crucial role in the degradation of organic pollutants. They react with the pollutant molecules, leading to the cleavage of chemical bonds and the conversion of complex organic compounds into simpler and less harmful by-products [18]. This photocatalytic process offers an environmentally friendly approach to wastewater treatment, as it utilizes solar energy and does not rely on the use of additional chemicals.
By studying the photocatalytic activity of the Ni-Zn and Ni-Cu-Zn ferrite powders, their effectiveness in degrading organic pollutants under sunlight irradiation can be evaluated. Understanding the working mechanism of the photocatalytic process provides insights into the degradation kinetics and the potential application of these ferrite catalysts in wastewater treatment and environmental remediation.
The present study reports the successful synthesis of Ni0.6-x Zn0.4CuxFe2O4 (x = 0, 0.3) spinel ferrite through the sol-gel auto combustion technique. The observed nanoparticles showed a spinal cubic crystal structure, characterized by crystallite sizes that varied from 20 to 30 nm. The lattice constant was measured to be between 8.3721 and 8.3716. Based on morphological analysis, it was determined that there were small spherical particles present, with grain sizes ranging from 20 to 33 nm. The EDX analysis was conducted to confirm the elemental composition and purity of the samples. The analysis detected the presence of Ni, Zn, Cu, Fe, and O elements. The spinel ferrite structure was further characterized through FTIR analysis, which detected the stretching vibrations of tetrahedral and octahedral sites. The nanoparticles exhibited remarkable photocatalytic qualities, indicating their potential for the use in the treatment of wastewater and remediation of the environment. This research enhances comprehension concerning the synthesis, analysis, and possible uses of nanoparticles composed of Ni-Zn and Ni-Cu-Zn spinel ferrite. The results promote the significance of the correlation between the structure and properties of nanomaterials. This provides a basis for additional investigation and enhancement to fully utilize the abilities of these nanoparticles in tackling environmental issues and promoting sustainable progress.
Competing interests:
The authors declare no competing interests.
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