g-C3N4/Fe3O4 composites synthesized via solid-state reaction and photocatalytic activity evaluation of methyl blue degradation under visible light irradiation

This study applied the solid-state reaction technique to synthesize g-C₃N₄, Fe₃O₄, and g-C₃N₄/Fe₃O₄ composites in various ratios. XRD confirmed the formation of g-C₃N₄, Fe₃O₄, and a g-C₃N₄/Fe₃O₄ heterostructure. SEM confirmed the rod-shaped structure of Fe₂O₃ and the layered-like fabrication of g-C₃N₄. The E_g of g-C₃N₄/Fe₃O₄ was approximately 1.9 eV, making it a beneficial composite material for visible response in photocatalysis activity, which was confirmed by UV-Vis spectroscopy. Dielectrics were used to study ferrite nanoparticles and provide information on the mechanism of conductivity in the parts of the dielectric that responded to an applied alternating electric field. In polycrystalline ceramics, the resistive and capacitive grains, contributions, electrode specimen interfaces, and grain boundaries may all be distinguished using impedance analysis, a crucial tool for the study of complicated electrical performance. The g-C₃N₄/Fe₃O₄ composite material showed high photocatalytic activity against methylene blue (MB) dye.

1 Introduction

Water pollution has greatly increased due to industrialization, urbanization, and the absolute discharge of industrial and organic pollutants into water sources (Goel, 2006; Hussain et al., 2021). The large amounts of wastewater from many types of dyeing enterprises contain unused dyes and other chemicals (Shindhal et al., 2021). These pigments are mostly toxic and non-biodegradable (Najar and Najar, 2019). Pigment waste pollutes both subsurface and surface water, with negative consequences on vegetation and animals (Chowdhary et al., 2020). Methylene blue (MB) is the most widely used thiazine stain in the fabric industry. Its harmful effects include gastrointestinal irritation, cyanosis, and skin irritation (Khan et al., 2022). Many chemical and physical techniques, including flocculation-coagulation, ion exchange, surface adsorption, degradation of photocatalytic systems, and chemical precipitation, have been used to solve the challenge of the elimination of the dye from contaminated water (Vishnu et al., 2022). Among these, photodegradation is better than alternative techniques. In the context of the fundamental investigational technique and the existence of semiconductors under adequate light exposure, organic dye particles decompose into straightforward non-toxic byproducts (Som et al., 2020). TiO₂, CuO, ZnO, and other materials have been extensively utilized as photocatalysts for semiconductor-assisted photocatalytic processes (Nemiwal et al., 2021). However, owing to their significant band gaps, which account for only approximately 3%–5% of sunlight, they only function as photocatalysts when exposed to ultraviolet (UV) light (Arora et al., 2022). Therefore, highly efficient visible-light catalysts remain the subject of extensive research due to their potential for numerous applications, including energy consumption and environmental pollution control.

The band gap of 2.7 electron volts (eV) of graphite-like carbon nitride (two-dimensional) (g-C₃N₄), which can absorb visible light, is a typical semiconductor; moreover, it is polymeric and a non-metal material (Hu et al., 2020). Owing to its proper band gap, high stability, and simple preparation method, g-C₃N₄ is mostly used in applications related to pollution degradation (Liu et al., 2021). Furthermore, researchers have worked hard to improve the effectiveness of g-C₃N₄ photocatalysis by doping it with non-metallic or metallic elements (Chi, 2021) or coupling it with other organic dyes (Gurylev, 2021), halides (Zhang et al., 2020), or semiconductors.

However, in nature, g-C₃N₄ nanomaterials are highly dissolved. They cannot be recycled or reused due to a lack of catalyst-friendly environments. Fe₃O₄ nanoparticles with an outer magnetic field in a solution can be easily removed as they exhibit super-para-magnetism. Fe₃O₄ synthesis is easy and has good magnetic properties compared to all other super-paramagnetic materials. The conduction and valence band edges of Fe₃O₄ were −0.24 eV and 1.44 eV, and −1.61 eV and 1.73 eV for g-C₃ N₄ (Hussain et al., 2023a; Hussain et al., 2023b). Therefore, it was suitable for making a heterostructure and suppressing the recombination rate. Both Fe₃O₄ and g-C₃N₄ have band gap energies in the visible region. Therefore, they cover a broad spectrum of light, resulting in increased photocatalytic activity (Hussain et al., 2022a; Hussain et al., 2022b). Consequently, Fe₃O₄-based nanoparticles have been used in different research fields, including drug distribution procedures (Li et al., 2011), solid-phase extraction [26], and lithium storage in lithium-ion batteries (Yang et al., 2014). Magnetic nanocomposites of Fe₃O₄ and TiO₂ are regularly used for pollutant degradation (Xuan et al., 2009; Jing et al., 2013). Therefore, combining Fe₃O₄ with g-C₃N₄ may increase nanomaterial durability and make it easier to extract Fe₃O₄/g-C₃N₄ nanocomposites from suspensions in external magnetic fields. By encouraging the charge carrier’s separation, the heterostructure of g-C₃N₄ and Fe₃O₄ increases visible light absorption and suppresses the electron and hole recombination rates. Numerous amino groups have been identified on the edges and surfaces of g-C₃N₄ and form coordination compounds with metal ions. Therefore, the edges or surfaces of g-C₃N₄ can be doped with coordination doping caused by metal ions (Lai et al., 2023). Different photocatalysts have been used for contaminant removal, such as the methylene blue dye with g-C₃N₄ and Fe₃O₄. Comparative studies on the degradation of MO using g-C₃N₄ and Fe₃O₄ are listed in Table 1.

TABLE 1

TABLE 1. Comparisons of MB degradation analysis reported in various studies.

However, this study used a photocatalysis process to degrade the pollutants, utilizing optimized photocatalyst composites to achieve higher photocatalytic activity. We applied a facile approach for the synthesis of g-C₃N₄/Fe₃O₄ composites with different ratios, such as 1:1, 60:40, 70:30, 80:20, and 90:10. While different studies have reported the composites of g-C₃N₄/Fe₃O₄, ours is the first study to determine the optimized ratio for enhanced photocatalytic activity. We have largely increased the quantity of one material and decreased the quantity of the second material. In the 1:1 ratio, both materials show good structural, optical, and photocatalytic properties. These are magnetic and electrical materials; therefore, at a 1:1 ratio, these materials can be used in other optical, magnetic, and electronic instruments to increase efficiency and reduce device costs.

2 Experiments

Materials: Urea, iron chloride, iron sulfate FeSO₄.7H₂O (99–100%), FeCl₃.6H₂O (99.0%), ammonia (25–28%), and distilled water. All other solvents were purchased from Sigma-Aldrich and were 99.6% pure. The materials were used without further modification.

2.1 Fabrication of g-C₃N₄

g-C₃N₄ was synthesized at 550°C for 5 h during thermal polymerization (pyrolysis) using urea as a precursor, at a temperature of 5°C/min. After cooling, powdered g-C₃N₄ was obtained by grinding.

2.2 Fabrication of Fe₃O₄ and g-C₃N₄/Fe₃O₄ composite

By default, g-C₃N₄ (0.68 g) was dispersed in 90.0 mL of distilled water mixed with FeCl₃ (0.94 g) and FeSO₄ (1 g) before being added to 10 mL NH₄OH and stirring for 1 h at 70°C. Next, until the pH reached 10.0, the ammonia solution was added dropwise to the reaction mixture. The powder was obtained after centrifuging and washing three times with ethanol and distilled water. The particles were dehydrated at 70°C for 12 h. Composites of g-C₃N₄/Fe₃O₄ were prepared in ratios of 1:1, 50:50, 60:40, 70:30, 80:20, and 90:10 to study the effect on this change on the energy band gap (in eV) and its effect on MB dye degradation. Pellets were fabricated using the hydraulic press (Apex) from each composition’s final product. By applying a pressure of 4 tons, each pellet’s diameter was 10 mm. The pellets were then sintered in a muffle furnace for 2 h at 310°C. These pellets were used for the assessment of dielectric properties.

2.3 Characterizations

The crystal structure and phase development of the samples were assessed using a Rigaku D/MAX-IIA X-ray diffractometer (XRD). The wavelength was 1.5406 A° and ranged from 10 to 70°. A Nova-Nano scanning electron microscope (SEM) 450-FESEM was used to examine the morphological features of the produced specimens. The frequency-dependent dielectric characteristics of the present specimens were explored on a Wayne Kerr (6500 B) precision impedance analyzer with copper electrodes through 20 Hz to 20 MHz. The original synthesized material was in powder form. For dielectric measurements, pellets with diameters of 1.01 cm and thicknesses of 0.1 cm were made from powder using an Apex hydraulic press under a pressure of 4 tons for 2 min in each case. All processes were performed at room temperature.

2.4 Photocatalytic tests

The photocatalytic performances of the Fe₃O₄/g-C₃N₄ composites were tested in glass reactors. In an MB aqueous solution (60 mL, 5 mg L^-1), 0.020 g of the sample was dispersed in each experiment. The Xe lamp (500 W output) served as the light source. The chemical solution was agitated magnetically in the dark for 65 min to attain MB saturation absorption onto the catalyst before irradiation. The following equation was used to determine the percentage of MB degradation.

$\eta =\frac{A_o-A_t}{A_o}\times 100\%(1)$

In Eq. 1, η, А_t, and А₀ represent the degradation efficiency, verified concentration at time “t”, and initial concentration at “t = 0”, respectively.

3 Results and discussion

3.1 X-ray diffraction

The XRD patterns of g-C₃N₄, Fe₃O₄, and their composites are shown in Figure 1A. The g-C₃N₄ nanosheets exhibited two stable peaks along with g-C₃N₄, indicating that the crystal structures of the nanosheets and bulk g-C₃N₄ were essentially the same. The reflection peak at 13.1° with an hkl value of (100), originating from lattice planes along the c-axis (Figure 1A), was less apparent in nano-sheets. The peak occurs due to the commonly decreasing layer planar size during the thermal oxidation etch of bulk g-C₃N₄. The g-C₃N₄ nanoparticles showed the same effect (Niu et al., 2012). Compared to bulk g-C₃N₄, the peak initiating from the repeated layering in nanosheets moved from 27.23° to an hkl value of (002), indicating closer spacing between the sheets. The individual layers in bulk g-C₃N₄ are said to be fluctuating but might be made planar by additional heating, leading to compact stacking. Since the gallery distance decreased due to annealing during thermal oxidation, a denser packing should have formed in our situation (Zhou and Qiu, 2019). In previous studies, the g-C₃N₄ pure XRD spectrum showed two prominent peaks at 2θ of 2.23 and 13.1° (Yang et al., 2020). Therefore, the normal distribution of the (002) interfacial diffraction peak high value may be the cause of the strong height of 27.23°, while the interlayer structure’s (13.1°) significant value (100) may be the cause of the peak’s strong height (Tang et al., 2018). The characteristic peaks (Figure 1A) of the g-C₃N₄ were prepared by urea, as shown by the aforementioned data and the crystal database JCPDS 87–1,526, which have no additional impurity peaks, showing that g-C₃N₄ was effectively synthesized. Because of the long-range interplanar layering of the aromatic structure, the sharp peak at 27.23° belongs to d = 0.324 nm and is identified as the (002) plane of bulk g-C₃N₄. The minor peak at 13.1° belongs to the (100) plane with d = 0.676 nm.

FIGURE 1

FIGURE 1. (A) XRD pattern and (B) Raman spectra of g-C₃N₄, g-C₃N₄ nano sheets, Fe₃O₄, and g-C₃N₄/Fe₃O₄ composites.

Figure 1A shows the formation of the Fe₃O₄ nanoparticles. The peak position hkl values of (220), (311), (400), (422), (511), and (440) are clearly visible, showing the presence of a crystalline spinel phase composed of magnetite (Fe₃O₄) iron oxide. In the composite 1:1 of g-C₃N₄/Fe₃O₄, the peak of g-C₃N₄ shows low intensity. This confirmed the formation of a heterostructure.

The Fe₂O₃@g-C₃N₄ (1:1) NCs’ Raman spectra are depicted in Figure 1B. Fe₂O₃-NPs showed distinctive Raman bands with Raman shifts of 607, 410, 294, and 221 cm^-1, which corresponded to the E_1g, E_1g, E_1g, and A_1g Raman modes, respectively. Raman peaks were likewise examined at ∼480, ∼708, and ∼760 for g-C₃N₄. The s-triazine ring was indicated by the strongest peak of g-C₃N₄ at 708 cm^-1 (Kang et al., 2018). The production of an NC of g-C₃N₄ and Fe₃O₄ was confirmed by the presence of both g-C₃N₄ and Fe₃O₄ peaks.

3.2 UV-Vis spectroscopy and Raman analysis

The band gap energy (E_g) of the produced sample was derived by the following Tauc equation to fit the investigation’s absorption data (Pareek et al., 2018; Zhu and Zhou, 2021).

${\left(\mathrm{\alpha }\mathrm{h}\mathrm{v}\right)}^2=\mathrm{A}\left(\mathrm{h}\mathrm{v}-{\mathrm{E}}_{\mathrm{g}}\right),(2)$

where hν and α are the photon energy and adsorption coefficient, respectively. The contact of the extended linear component of the (αhν) (Hussain et al., 2021) against the curve axis of the (hν) axis yields the E_g value. The E_g values of the g-C₃N₄/Fe₃O₄ nanocomposite, g-C₃N₄, and Fe₃O₄ are 1.9 eV, 2.7 eV, and 2.4 eV, respectively (Figure 2). These E_g values indicate that each compound and its nanocomposites were semiconductors in nature (Usman et al., 2019; Zhu and Zhou, 2021).

FIGURE 2

FIGURE 2. Tauc plot of g-C₃N₄, g-C₃N₄ nano sheets, Fe₃O₄, and g-C₃N₄/Fe₃O₄ composites.

Figure 2 shows that the Eg of the composite g-C₃N₄/Fe₃O₄ prepared in the ratios of 1:1, 50:50, 60:40, 70:30, 80:20, and 90:10 decreased gradually to less than that of pure g-C₃N₄. Hence, the absorbance value of a pure g-C₃N₄ sample was lower than that for the composite g-C₃N₄/Fe₃O₄ ratios, which signified that composites were good photo-absorbers and photocatalysts.

3.3 Scanning electron microscopy (SEM) analysis

SEM micrographs of Fe₃O₄, g-C₃N₄, and their composites are shown in Figure 3. Fe₃O₄ showed a rod-like structure in SEM images. This structure is good for photocatalysis due to its high electron mobility. Regarding the weak van der Waals among layers in the graphite, g-C₃N₄ has a layered structure, while the assembly of the planar bonding is completely different.

FIGURE 3

FIGURE 3. SEM micrographs of (A–C) Fe₃O₄, (D) g-C₃N₄/Fe₃O₄, and (E–I) g-C₃N₄.

The tri-s-triazine (heptazine) rings, which are connected to the structure’s hypothesized aggregated mlem, are the energetically preferred form of g-C₃N₄. The composite materials showed both rod-like and layered structures, which confirmed the formation of composite materials.

Chemical mixing draws graphite with fewer or more pages while maintaining its composite structure. The main structure was composed of thick micron-sized particles evenly distributed throughout the sample area. Most of the particles had many full layers and hard surfaces.

3.4 Dielectric properties

Evaluation of the dielectric characteristics of ferrite nanoparticles provides information about the mechanism of conductivity in the parts of the dielectric that respond to an applied alternating electric field. These properties are dependent on various factors, such as the mode of production, chemical composition, stoichiometry, porosity of the ion charge, particle size, and cation distribution between the octahedral and tetrahedral structures (Khan et al., 2020). In the current study, dielectric parameters, such as capacitance, and the dielectric loss angle (tan δ) were assessed using an LCR meter at room temperature. The real part of the permittivity (ε′), the imaginary part of the permittivity (ε") or dielectric loss factor, and AC conductivity (${\sigma }_{ac}$) are given by the following relationships (Hossen and Hossain, 2012; Zidi et al., 2015; Şaşmaz Kuru, 2020):

${\epsilon }^{\prime }=\frac{C_{P}d}{{\epsilon }_{°}A},(3)$

${\epsilon }^{″}=\frac{{\sigma }_{ac}}{\omega {\epsilon }_{°}},(4)$

$\mathit{tan}\delta =\frac{{\epsilon }^{″}}{{\epsilon }^{\prime }},(5)$

${\sigma }_{ac}\frac{d}{Z΄A}.(6)$

The capacitance of the pellet is represented by “C”. Its unit is the farad. The thickness of the pellet is measured in meters, and its symbol is d. The cross-sectional area of the flat pellet surface is A. ε_o is the permeability of free space, and f is the frequency. Figures 4A–D show the behavior of ε′, tan δ, and ε'', respectively, at the applied frequency. The stored energy can be described by the permittivity (ε′). ε′ has a higher value in the lower-frequency range and decreases with increasing frequency, consistent with the default behavior in most ferrite materials. The reduced ε′ with greater frequency occurs because at higher frequencies, there is a time delay for each detected security. It also contributes to the polarization of the applied field (polarization cartridge damping), which leads to a reduced ε′, and is assigned to the contribution to the electric polarizability (Prakash and Vasudevan, 2020). The reason for this change may be related to the g-C₃N₄ concentration, in which there is less of a chance to jump on grain boundaries. This will increase the grain boundary charge and, thus, the value of ε′ changes (Patnaik et al., 2020). If the amount of iron ions is high, then the permittivity is high due to the presence of Fe ions in the S octahedral region (Khorsandi et al., 2021). Therefore, these ions can produce high polarization.

FIGURE 4

FIGURE 4. (A–D): Behaviors of the (A) dielectric constant (ε′), (B) dielectric loss angle (tanδ), (C) dielectric loss factor (ε''), and (D) AC conductivity (${\mathit{\sigma }}_{\mathit{a}\mathit{c}}$) for the applied material frequencies.

3.4.1 Variations in dielectric loss tangent (tanδ) and dielectric loss factor (ε'') with frequency

Dielectric loss occurs due to energy dissipation in the dielectric materials and is explained in terms of tan δ and ε''. It appears as a result of impurities and poor crystal lattice in the material, leading to polarization lagging of the supplied alternating field (Liu et al., 2020). Figures 4A, B show the variation in tan δ and ε'', respectively, as a function of $logf$ at 27°C. The tan δ and ε'' decrease with increasing frequency, which is the normal behavior of ferrites. The decreased ε'' and tan δ values with the frequency were associated with the Maxwell–Wagner model and Koop’s theory (Ünal et al., 2021). The sudden decline in dielectric constant, according to Kumar et al., is caused by inertia, which prevents immediate dipolar polarization. Polarizations with longer relaxation durations are frozen over a certain frequency (only electronic polarization mainly contributes); thus, the imaginary dielectric constant (ε'') is decreased. The hopping of electrons between adjacent Fe ions (Fe³⁺ and Fe²⁺) in the octahedral region requires only a tiny amount of energy in the high-frequency zone, which correlates with a small resistance (due to grains). Additionally, the grain boundaries are responsive and offer a high level of resistance in the low-frequency range. Consequently, significant energy is required to transfer electrons between two Fe ions. The energy lost in dielectrics is known as dielectric loss. Dielectric loss (tan δ) occurs because of crystal flaws such as secondary phases, defects, and delayed polarization with the applied field. As shown in Figure 4C, the tan δ values of Fe₃O₄, g-C₃N₄, and composite g-C₃N₄/Fe₃O₄ ratio systems demonstrated minimum and maximum values at high and low f, respectively. Koop’s phenomenology theory explains why the dielectric energy loss and constant become frequency-independent at higher $f$. Substitution of g-C₃N₄ in the Fe₃O₄ sites increased both tan δ and ε''. The trends shown by the samples in the current study design might be attributed to the combined influence of g-C₃N₄/Fe₃O₄ doping in composite ratios. The enhanced dielectric properties displayed by the specimens in later examination occurred due to the doping of g-C₃N₄ nanoparticles at Fe₃O₄ sites in the composite as the amount of g-C₃N₄ differed among the current compositions. Therefore, g-C₃N₄ can be used to improve the dielectric characteristics of the composites.

3.4.2 AC conductivity

The frequency-dependent AC conductivity (σ_ac) spectra of Fe₃O₄, g-C₃N₄, and composite g-C₃N₄/Fe₃O₄ are explained in Figure 4D. The spectra demonstrated that all samples have very low σ_ac values at low frequencies, indicating considerable resistance. After a certain high frequency, conductivity steadily increased. These types of processes are explained in Koop’s model. This concept states that low conductivity at lower f is caused by weakly conducting grain boundaries, while strong conductivity at higher f is caused by highly conducting grains (Guo et al., 2021). The electron-hopping frequencies between Fe³⁺ and Fe²⁺ are severely hampered at lower frequencies (Wu and Zhu, 2019). Therefore, the observed conductivity of the material at a lower frequency is lower. However, as the frequency of the applied field rises, the conductive grain becomes highly active by promoting electron hopping between nearby ions and enhancing the interaction between ferrous iron (Fe²⁺) and ferric iron (Fe³⁺) ions on the octahedral sites. Consequently, the electrical conductivity increases with the frequency. The AC conductivity of g-C₃N₄ was low because the conductivity of polycrystalline materials declines with reducing grain size. Smaller grains contain more insulating grain borders and a smaller contact area between grains, which inhibit electron flow and, in turn, increase conductivity (Xi and Chung, 2021). In general, conductivity and permittivity are significantly influenced by grain size, stoichiometry, porosity, grain borders, and crystal defects.

3.4.3 Impedance analysis

In polycrystalline ceramics, impedance analysis is a crucial technique for separating resistive and capacitive grains, grain boundaries, and contributions, as well as electrode specimen interfaces, when studying complex electrical performances (Tiwari et al., 2020). The boundaries between grains are typically of a distinct conducting nature. This will depend on the nature of the sample used, and the temperature and frequency range of the test. The present study used dielectric materials with dipolar rotation in their electrical properties, as well as materials used in electronic conduction, for impedance spectroscopy studies.

Figures 5A–D show the impedance spectroscopy output characteristics as a sequence of semi-circles with various radii and/or origins. The electrical phenomena representation occurs because of the grain boundaries, grains, and interface polarization when their graph is drawn in the complex plane (Mazen et al., 2021). The electrical conductivity was measured using AC-impedance analysis, which showed that depending on their chemical composition, a wide range of materials with electric, anti-ferroelectric, or paraelectric phases and slightly different dielectric properties formed crystal structures of varying sizes. Understanding the electrical conductivity of this type of ferroelectric and its physical characteristics is crucial (Fu et al., 2021). The internal defects in the material, such as the A-site vacancy, electron space charges, or oxygen, have significant effects on the electrical conductivity of the material. Therefore, it is important to have a basic understanding of their mechanics and the methods in the context of the defect mechanisms because of the different types of faults that are recommended for the relaxation of insulation material in high temperature ranges (Krauskopf et al., 2020). The formulas for impedance are as follows (Jha, 2013):

$Z΄=\frac{R}{1+\left(\omega RC\right)˄2},(7)$

$Z΄΄=\frac{\omega R˄2C}{1+\left(\omega RC\right)˄2}.(8)$

FIGURE 5

FIGURE 5. (A–D) Frequency dependence for real and imaginary parts of the electric impedance for Fe₃O₄, g-C₃N₄, and composite g-C₃N₄/Fe₃O₄ with different ratios.

3.4.4 Modulus study

The modulus spectroscopy of graphs helps us identify the spectral components of the material; those showing a different capacitance but the same resistance. The e-modulus formula also has the benefit of suppressing the electrode effect (Oliveira et al., 2019). Therefore, this is the optimal method for learning the spectroscopy of complex moduli. The value of the electric modulus (M*) can be estimated based on the following: The formulas for real modulus and imaginary modulus are as follows (Joshi et al., 2017; Rayssi et al., 2018):

$M΄=\left({\epsilon }^{\prime }\right)/\left({\epsilon }^{\prime }˄2+{\epsilon }^{″}˄2\right),(9)$

$M΄΄=\frac{\left({\epsilon }^{″}\right)}{\left({\epsilon }^{\prime ˄2}+{\epsilon }^{″˄2}\right)}.(10)$

The complex electric module of formalization and analysis revealed the nature of polycrystalline and grain boundary effects. Figure 6 displays the complex modulus spectrum for M′ and M΄, in which the arc was the electrical phenomenon with the lowest capacity to perform in a high-voltage system. Arcs appearing in the spectra demonstrate the ceramic’s phase characteristics. In addition, the non-semi-circular arc proved that electrical relaxation phenomena existed in the Behera.

FIGURE 6

FIGURE 6. Frequency-dependent (A) real and (B) imaginary moduli of Fe₃O₄, g-C₃N₄, and composite g-C₃N₄/Fe₃O₄ with different ratios.

Figure 6A shows the relationship of M′ with frequency. Except for g-C₃N₄, for which the real modulus M′ stayed essentially the same over the whole frequency range, M′ increased to a maximum value with greater frequency for all samples. This clarified the large frequency range across which relaxation processes occur. For g-C₃N₄, Fe₃O₄ = 0, which verified that the real modulus Mʹ remained the same because of g-C₃N₄ and other composite samples as a result of Fe₃O₄ and g-C₃N₄. Owing to the charge carriers’ limited mobility, conduction phenomena may be present. Figure 6B depicts the frequency-dependent imaginary component of the electrical modulus M΄΄. As the frequency and Fe₃O₄ content increased (up to 90%), the imaginary modulus M shifted to the high-frequency side. This is considered a non-Debye type of relaxation because the maximum peaks on either side of M″ are asymmetric and wider, demonstrating the distribution of relaxation periods rather than a single time constant (Arya and Sharma, 2018). The real modulus M″ maximum shifted toward a small frequency area for sample 70:30, indicating greater conduction. Therefore, at lower and higher frequencies, charge carriers can travel over short and long distances, respectively. The maximum real modulus M″ indicates a change in mobility from long to short range. The asymmetric modulus peaks will move in the direction of a higher frequency, which demonstrated the relationship between the movements of the mobile ion charges. The non-Debye type is implied by the asymmetry in the peak broadening due to a spread in the relaxation time caused by various time constants. The presence of low-frequency peaks points to the possibility of long-distance ion transport, while high-frequency peaks point to the possibility of ion confinement in a potential well.

3.5 Photocatalytic activity

The photocatalytic activity (PCA) values of the degradation of the methylene blue dye under visible light for g-C₃N₄, Fe₃O₄, and g-C₃N₄/Fe₃O₄ composites (1:1, 60:40, 70:30, 80:20, and 90:10) were 53, 38, 89, 88, 83, 80, and 59, respectively.

3.5.1 Evaluation of the phоtо-catаlytic activity

The rate соnstаnt of the рhоtо-degrаdаtiоn kinetics of the MB is shown in Figures 7A–J). Fe₃О₄ has a small PCA compared to MB under visible light irradiation, while Fe₃О₄/g-С₃N₄ nаnо-соmроsites and g-С₃N₄ nanosheets were effective under the same соnditiоns. In the nаnо-соmроsite materials, the electrons migrated easily to Fe₃О₄ NPs due to the lower conduction band (СB) of Fe₃О₄ compared to g-С₃N₄. Thus, the PCA improved and the rate of photogenerated electrons and holes was effectively reduced. The 1:1 NC showed the highest PCA (89%). However, photogenerated electrons (e⁻) have strong reductive properties. Photogenerated holes (h⁺) possess high oxidizing characteristics and can interact with MB to produce CO₂ and H₂O. They form OH ions when they react with H₂О or О₂. Therefore, an improved PCA of the iron oxide and Fe₃О₄/g-С₃N₄ nаnо-соmроsite was obtained. Compared to the g-C₃N₄ nanosheets, the 1:1 nano-composites showed higher-level photocatalytic effects, which were attributed to their greater dispersibility when combined with Fe₃O₄ nanocomposites. Owing to the reduced amounts of g-C₃N₄ in the 80:20, 70:30, and 60:40 nanocomposites compared to the g-C₃N₄ nanosheets, they showed weaker catalytic effects.

FIGURE 7

FIGURE 7. (A–G) Relationship between wavelength and absorbance. (H) Relationship between time and A₀/A. (I) Relationship between samples and degradation efficiency. (J) Relationship between log A₀/A and irradiation time.

4 Conclusion

In conclusion, this study used solid-state reactions and sol-gel techniques to synthesize g-C₃N₄, Fe₃O₄, and g-C₃N₄/Fe₃O₄ with diverse proportions of g-C₃N₄ and Fe₃O₄. The formation of nano-sheet structures of g-C₃N₄, the cubic phase of Fe₃O₄, and g-C₃N₄/Fe₃O₄ nano-composites were confirmed by XRD. In SEM, Fe₃O₄ showed a rod-like structure, g-C₃N₄ showed a layered-like structure, and the composites showed both rod-like and layered-like structures. The composites at the 1:1 ratio showed a small E_g, according to UV-Vis spectroscopy. This is due to the formation of defective sites at the junction of two semiconductors. The PCA of the magnetically separated g-C₃N₄/Fe₃O₄ catalysts under visible light illumination was up to 1.8 times greater for MB dye compared with the pure g-C₃N₄. Owing to the synergistic interactions between Fe₃O₄ and g-C₃N₄, which increase the migratory performance of photo-generated charge carriers, the PCA is boosted. Our findings indicate the new design possibilities of the solutions reported here open the field for recycled photocatalysts that are magnetically separable and have good visible light PCA.

Data availability statement

The raw data supporting the conclusion of this article will be made available by the authors, without undue reservation.

Author contributions

AA: writing original draft; MA: revision and methodology; MT: writing original draft; SA: supervision and project administration; AH: manuscript revision; IA: contribution to the structural properties; AM: funding and project administration; MUF: supervision and project administration; MAF: explanation of optical analysis.

Acknowledgments

The authors would like to acknowledge the Researchers Supporting Project number (RSP2023R43), King Saud University, Riyadh, Saudi Arabia.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

The handling editor FI declared a shared affiliation with author SA at the time of the review.

Publisher’s note

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References

Alharthi, F. A., Ali Alghamdi, A., Alanazi, H. S., Alsyahi, A. A., and Ahmad, N. (2020). Photocatalytic degradation of the light sensitive organic dyes: Methylene blue and rose bengal by using urea derived g-C3N4/ZnO nanocomposites. Catalysts 10 (12), 1457. doi:10.3390/catal10121457

CrossRef Full Text | Google Scholar

Arora, I., Chawla, H., Chandra, A., Sagadevan, S., and Garg, S. (2022). Advances in the strategies for enhancing the photocatalytic activity of TiO2: Conversion from UV-light active to visible-light active photocatalyst. Inorg. Chem. Commun. 143, 109700. doi:10.1016/j.inoche.2022.109700

CrossRef Full Text | Google Scholar

Arya, A., and Sharma, A. (2018). Structural, electrical properties and dielectric relaxations in Na+-ion-conducting solid polymer electrolyte. J. Phys. Condens. Matter 30 (16), 165402. doi:10.1088/1361-648x/aab466

PubMed Abstract | CrossRef Full Text | Google Scholar

Chi, Z. (2021). Prospects for the application of advanced oxidation technology in the treatment of pharmaceutical wastewaters.

Google Scholar

Chowdhary, P., Bharagava, R. N., Mishra, S., and Khan, N. (2020). “Role of industries in water scarcity and its adverse effects on environment and human health,” in Environmental concerns and sustainable development (Berlin, Germany: Springer), 235–256.

CrossRef Full Text | Google Scholar

Dwivedi, P., Jatrana, I., Khan, A. U., Satiya, H., and Khan, M. (2021). Photoremediation of methylene blue by biosynthesized ZnO/Fe3O4 nanocomposites using callistemon viminalis leaves aqueous extract: A comparative study. Nanotechnol. Rev. 10 (1), 1912–1925. doi:10.1515/ntrev-2021-0117

CrossRef Full Text | Google Scholar

Fu, D. W., Gao, J. X., Huang, P. Z., Ren, R., Shao, T., Han, L., et al. (2021). Observation of transition from ferroelasticity to ferroelectricity by solvent selective effect in anilinium bromide. Angew. Chem. Int. Ed. 60 (15), 8198–8202. doi:10.1002/anie.202015219

CrossRef Full Text | Google Scholar

Goel, P. (2006). Water pollution: Causes, effects and control. New Delhi: . New age international.

Google Scholar

Guo, F., Zhang, X., Cai, H., Fan, X., Hu, L., Sun, W., et al. (2021). Effect of doping location induced anisotropy on thermophysical properties of dilute Fe2O3-Y2O3-ZrO2 solid solutions. J. Am. Ceram. Soc. 104, 4742–4758. doi:10.1111/jace.17858

CrossRef Full Text | Google Scholar

Gurylev, V. (2021). Nanostructured photocatalyst via defect engineering: Basic knowledge and recent advances. Berlin, Germany: Springer.

Google Scholar

Hossen, M. B., and Hossain, A. A. (2012). AC resistivity and frequency dependence of the dielectric properties for Al doped NiCuZn ferrites. United States: IEEE, 903–907.

Google Scholar

Hu, X., Hu, J., Peng, Q., Ma, X., Dong, S., and Wang, H. (2020). Construction of 2D all-solid-state Z-scheme g-C3N4/BiOI/RGO hybrid structure immobilized on Ni foam for CO2 reduction and pollutant degradation. Mater. Res. Bull. 122, 110682. doi:10.1016/j.materresbull.2019.110682

CrossRef Full Text | Google Scholar

Hussain, A., Ali, N., Ali, S., Hou, J., Aslam, I., Naeem, H., et al. (2022). Diverse morphological study for nonmetal-doped g-C3N4 composites with narrow bandgap for improved photocatalytic activity. Res. Chem. Intermed. 48 (7), 2857–2870. doi:10.1007/s11164-022-04750-5

CrossRef Full Text | Google Scholar

Hussain, A., Hou, J., Tahir, M., Ali, S., Rehman, Z. U., Bilal, M., et al. (2022). Recent advances in BiOX-based photocatalysts to enhanced efficiency for energy and environment applications. Catal. Rev. 22, 1–55. doi:10.1080/01614940.2022.2041836

CrossRef Full Text | Google Scholar

Hussain, A., Hou, J., Tahir, M., Wang, X., Qadri, M. U., Jiang, T., et al. (2021). Fine-tuning internal electric field of BiOBr for suppressed charge recombination. J. Environ. Chem. Eng. 9 (1), 104766. doi:10.1016/j.jece.2020.104766

CrossRef Full Text | Google Scholar

Hussain, A., Maqsood, S., Ji, R., Zhang, Q., Farooq, M. U., Boota, M., et al. (2023). Investigation of transition metal-doped graphitic carbon nitride for MO dye degradation. Diam. Relat. Mater. 132, 109648. doi:10.1016/j.diamond.2022.109648

CrossRef Full Text | Google Scholar

Hussain, A., Tahir, M., Yang, W., Ji, R., Zheng, K., Umer, M., et al. (2023). Synergic effect among activated carbon/sulphur-assisted graphitic carbon nitride for enhanced photocatalytic activity. Diam. Relat. Mater. 135, 109836. doi:10.1016/j.diamond.2023.109836

CrossRef Full Text | Google Scholar

Jha, A. (2013). Electrical characterization of zirconium substituted barium titanate using complex impedance spectroscopy. Bull. Mater. Sci. 36 (1), 135–141. doi:10.1007/s12034-013-0420-0

CrossRef Full Text | Google Scholar

Jing, J., Li, J., Feng, J., Li, W., and William, W. Y. (2013). Photodegradation of quinoline in water over magnetically separable Fe3O4/TiO2 composite photocatalysts. Chem. Eng. J. 219, 355–360. doi:10.1016/j.cej.2012.12.058

CrossRef Full Text | Google Scholar

Joshi, J., Kanchan, D., Joshi, M., Jethva, H., and Parikh, K. (2017). Dielectric relaxation, complex impedance and modulus spectroscopic studies of mix phase rod like cobalt sulfide nanoparticles. Mater. Res. Bull. 93, 63–73. doi:10.1016/j.materresbull.2017.04.013

CrossRef Full Text | Google Scholar

Kang, S., Jang, J., Pawar, R. C., Ahn, S-H., and Lee, C. S. (2018). Low temperature fabrication of Fe₂O₃ nanorod film coated with ultra-thin g-C₃N₄ for a direct z-scheme exerting photocatalytic activities. RSC Adv. 8, 33600–33613. doi:10.1039/c8ra04499f

PubMed Abstract | CrossRef Full Text | Google Scholar

Khan, I., Bilal, A., Shakeel, K., and Malik, F. T. (2022). Effects of nickel toxicity on various organs of the Swiss albino mice. Uttar Pradesh J. Zoology 43 (14), 1–12.

Google Scholar

Khan, M. Z., Gul, I. H., Baig, M. M., and Khan, A. N. (2020). Comprehensive study on structural, electrical, magnetic and photocatalytic degradation properties of Al3+ ions substituted nickel ferrites nanoparticles. J. Alloys Compd. 848, 155795. doi:10.1016/j.jallcom.2020.155795

CrossRef Full Text | Google Scholar

Khorsandi, K., Hosseinzadeh, R., Sadat Esfahani, H., Keyvani-Ghamsari, S., and Ur Rahman, S. (2021). Nanomaterials as drug delivery systems with antibacterial properties: Current trends and future priorities. Expert Rev. anti-infective Ther. 19, 1299–1323. doi:10.1080/14787210.2021.1908125

CrossRef Full Text | Google Scholar

Krauskopf, T., Richter, F. H., Zeier, W. G., and Janek, (2020). Physicochemical concepts of the lithium metal anode in solid-state batteries. Chem. Rev. 120 (15), 7745–7794. doi:10.1021/acs.chemrev.0c00431

PubMed Abstract | CrossRef Full Text | Google Scholar

Lai, C., Ma, D., and Yi, H., 2023, Functional partition of Fe and Ti Co-doped G-C3n4 for photo-fenton degradation of OTC: Performance, mechanism, and dft study. Sep. Purif. Technol., 306, 122546. doi:10.1016/j.seppur.2022.122546

CrossRef Full Text | Google Scholar

Li, X., Huang, X., Liu, D., Wang, X., Song, S., Zhou, L., et al. (2011). Synthesis of 3D hierarchical Fe3O4/graphene composites with high lithium storage capacity and for controlled drug delivery. J. Phys. Chem. C 115 (44), 21567–21573. doi:10.1021/jp204502n

CrossRef Full Text | Google Scholar

Liu, W., Ye, T., Jāgermeyr, J., Müller, C., Liu, X., Shi, P., et al. (2021). Recent developments of doped g-C3N4 photocatalysts for the degradation of organic pollutants. Crit. Rev. Environ. Sci. Technol. 51 (8), 751–790. doi:10.1080/10643389.2020.1734433

CrossRef Full Text | Google Scholar

Liu, Z., Yang, W., Wu, R., Hu, Q., Qiao, G., Liu, S., et al. (2020). A new quantitative analysis method for electromagnetic energy dissipation in microwave absorption materials. J. Magnetism Magnetic Mater. 516, 167332. doi:10.1016/j.jmmm.2020.167332

CrossRef Full Text | Google Scholar

Mao, Y., Wu, M., Li, G., Dai, P., Yu, X., Bai, Z., et al. (2018). Photocatalytic degradation of methylene blue over boron-doped g-C3N4 together with nitrogen-vacancies under visible light irradiation. React. Kinet. Mech. Catal. 125 (2), 1179–1190. doi:10.1007/s11144-018-1414-0

CrossRef Full Text | Google Scholar

Mazen, S., Nawara, A., and Abu-Elsaad, N. (2021). Investigation of dielectric behavior in Ni0. 7-xZn0. 3MxFe2O4 (M= Mn/Co/Cu) ferrites by impedance spectroscopy. Ceram. Int. 47 (7), 9856–9865. doi:10.1016/j.ceramint.2020.12.127

CrossRef Full Text | Google Scholar

Najar, M. H., and Najar, I. A. (2019). An overview to photo-catalytic degradation of dyes in waste water. Appl. Chem. Eng. 2 (2). doi:10.24294/ace.v1i4.615

CrossRef Full Text | Google Scholar

Nemiwal, M., Zhang, T. C., and Kumar, D. (2021). Recent progress in g-C3N4, TiO2 and ZnO based photocatalysts for dye degradation: Strategies to improve photocatalytic activity. Sci. total Environ. 767, 144896. doi:10.1016/j.scitotenv.2020.144896

PubMed Abstract | CrossRef Full Text | Google Scholar

Niu, P., Zhang, L., Liu, G., and Cheng, H. M. (2012). Graphene-like carbon nitride nanosheets for improved photocatalytic activities. Adv. Funct. Mater. 22 (22), 4763–4770. doi:10.1002/adfm.201200922

CrossRef Full Text | Google Scholar

Oliveira, F., Dencheva, N., Lanceros-Méndez, S., Nunes, T., and Denchev, Z. (2019). Binary polyamide hybrid composites containing carbon allotropes and metal particles with radiofrequency shielding effect. Polym. Compos. 40 (S2), E1338–E1352. doi:10.1002/pc.24993

CrossRef Full Text | Google Scholar

Pareek, S., Sharma, M., Lal, S., and Quamara, J. K. (2018). Polymeric graphitic carbon nitride–barium titanate nanocomposites with different content ratios: A comparative investigation on dielectric and optical properties. J. Mater. Sci. Mater. Electron. 29 (15), 13043–13051. doi:10.1007/s10854-018-9426-0

CrossRef Full Text | Google Scholar

Patnaik, S., Sahoo, D. P., and Parida, K. (2020). Recent advances in anion doped g-C3N4 photocatalysts: A review. Carbon 172, 682–711. doi:10.1016/j.carbon.2020.10.073

CrossRef Full Text | Google Scholar

Prakash, K., and Vasudevan, K. (2020). Design and development of compact circularly polarized multiband and ultra-wideband microstrip antennas for wireless applications. Kochi, Kerala: Cochin University of Science and Technology.

Google Scholar

Rayssi, C., Kossi, S. E., Dhahri, J., and Khirouni, K. (2018). Frequency and temperature-dependence of dielectric permittivity and electric modulus studies of the solid solution Ca 0.85 Er 0.1 Ti 1− x Co 4x/3 O 3 (0≤ x≤ 0.1). Rsc Adv. 8 (31), 17139–17150. doi:10.1039/c8ra00794b

PubMed Abstract | CrossRef Full Text | Google Scholar

Şaşmaz Kuru, T. (2020). Room temperature structural, dielectric, and conductivity properties of AlxCd1-xFe2O4 ferrites. J. Aust. Ceram. Soc. 56 (2), 453–460. doi:10.1007/s41779-019-00349-z

CrossRef Full Text | Google Scholar

Shindhal, T., Rakholiya, P., Varjani, S., Pandey, A., Ngo, H. H., Guo, W., et al. (2021). A critical review on advances in the practices and perspectives for the treatment of dye industry wastewater. Bioengineered 12 (1), 70–87. doi:10.1080/21655979.2020.1863034

PubMed Abstract | CrossRef Full Text | Google Scholar

Som, I., Roy, M., and Saha, R. (2020). Advances in nanomaterial-based water treatment approaches for photocatalytic degradation of water pollutants. ChemCatChem 12 (13), 3409–3433. doi:10.1002/cctc.201902081

CrossRef Full Text | Google Scholar

Tang, Q., Meng, X., Wang, Z., Zhou, J., and Tang, H. (2018). One-step electrospinning synthesis of TiO2/g-C3N4 nanofibers with enhanced photocatalytic properties. Appl. Surf. Sci. 430, 253–262. doi:10.1016/j.apsusc.2017.07.288

CrossRef Full Text | Google Scholar

Tiwari, B., Babu, T., and Choudhary, R. (2020). AC impedance and modulus spectroscopic studies of Pb (Zr0. 35-xCexTi0. 65) O3 (x= 0.00, 0.05, 0.10, 0.15) ferroelectric ceramics. Mater. Chem. Phys. 256, 123655. doi:10.1016/j.matchemphys.2020.123655

CrossRef Full Text | Google Scholar

Ünal, B., Almessiere, M., Slimani, Y., Korkmaz, A. D., and Baykal, A. (2021). A study on the electrical and dielectric properties of SrGdxFe12− xO19 (x= 0.00–0.05) nanosized M-type hexagonal ferrites. J. Mater. Sci. Mater. Electron. 32, 18317–18329. doi:10.1007/s10854-021-06373-9

CrossRef Full Text | Google Scholar

Usman, F., Dennis, J. O., Seong, K. C., Yousif Ahmed, A., Meriaudeau, F., Ayodele, O. B., et al. (2019). Synthesis and characterisation of a ternary composite of polyaniline, reduced graphene-oxide and chitosan with reduced optical band gap and stable aqueous dispersibility. Results Phys. 15, 102690. doi:10.1016/j.rinp.2019.102690

CrossRef Full Text | Google Scholar

Vishnu, D., Dhandapani, B., Authilingam, S., and Sivakumar, S. V. (2022). A comprehensive review of effective adsorbents used for the removal of dyes from wastewater. Curr. Anal. Chem. 18 (3), 255–268. doi:10.2174/1573411016999200831111155

CrossRef Full Text | Google Scholar

Wang, K., Yu, L., Yin, S., Li, H., and Li, H. (2009). Photocatalytic degradation of methylene blue on magnetically separable FePc/Fe3O4 nanocomposite under visible irradiation. Pure Appl. Chem. 81 (12), 2327–2335. doi:10.1351/pac-con-08-11-23

CrossRef Full Text | Google Scholar

Wu, H., and Zhu, X. (2019). Microstructures, magnetic, and dielectric properties of Ba-doped BiFeO3 nanoparticles synthesized via molten salt route. J. Am. Ceram. Soc. 102 (8), 4698–4709. doi:10.1111/jace.16348

CrossRef Full Text | Google Scholar

Xi, X., and Chung, D. (2021). Dielectric behavior of graphite, with assimilation of the AC permittivity, DC polarization and DC electret. Carbon 181, 246–259. doi:10.1016/j.carbon.2021.05.020

CrossRef Full Text | Google Scholar

Xuan, S., Jiang, W., Gong, X., Hu, Y., and Chen, Z. (2009). Magnetically separable Fe3O4/TiO2 hollow spheres: Fabrication and photocatalytic activity. J. Phys. Chem. C 113 (2), 553–558. doi:10.1021/jp8073859

CrossRef Full Text | Google Scholar

Yang, J., Li, J., Qiao, J., Lian, H., and Chen, H. (2014). Solid phase extraction of magnetic carbon doped Fe3O4 nanoparticles. J. Chromatogr. A 1325, 8–15. doi:10.1016/j.chroma.2013.11.052

PubMed Abstract | CrossRef Full Text | Google Scholar

Yang, X., Tian, Z., Chen, Y., Huang, H., and Hu, J. (2020). One-pot calcination preparation of graphene/g–C3N4–Co photocatalysts with enhanced visible light photocatalytic activity. Int. J. hydrogen energy 45 (23), 12889–12902. doi:10.1016/j.ijhydene.2020.03.028

CrossRef Full Text | Google Scholar

Zhang, T-S., Hao, W-J., Wang, R., Wang, S-C., Tu, S-J., and Jiang, B. (2020). Electrocatalytic three-component annulation-halosulfonylation of 1, 6-enynes toward 1-indanones using sodium halides as both halogen sources and electrolytes. Green Chem. 22 (13), 4259–4269. doi:10.1039/d0gc00771d

CrossRef Full Text | Google Scholar

Zhang, X., Li, M., Liu, C., Zhang, Z., Zhang, F., and Liu, Q. (2021). Enhanced the efficiency of photocatalytic degradation of methylene blue by construction of Z-scheme g-C3N4/BiVO4 heterojunction. Coatings 11 (9), 1027. doi:10.3390/coatings11091027

CrossRef Full Text | Google Scholar

Zhou, D., and Qiu, C. (2019). Study on the effect of Co doping concentration on optical properties of g-C3N4. Chem. Phys. Lett. 728, 70–73. doi:10.1016/j.cplett.2019.04.060

CrossRef Full Text | Google Scholar

Zhu, D., and Zhou, Q. (2021). Nitrogen doped g-C3N4 with the extremely narrow band gap for excellent photocatalytic activities under visible light. Appl. Catal. B Environ. 281, 119474. doi:10.1016/j.apcatb.2020.119474

CrossRef Full Text | Google Scholar

Zidi, N., Chaouchi, A., D’Astorg, S., Rguiti, M., and Courtois, C. (2015). Impedance spectroscopy studies on (Na0. 5Bi0. 5) 0.94 Ba0. 06TiO3+ 0.3 wt% Sm2O3+ 0.25 wt% LiF lead-free piezoelectric ceramics. Bull. Mater. Sci. 38 (3), 731–737. doi:10.1007/s12034-015-0888-x

CrossRef Full Text | Google Scholar