Boosted spatial charge carrier separation of binary ZnFe2O4/S-g-C3N4 heterojunction for visible-light-driven photocatalytic activity and antimicrobial performance

Highlights

1) A binary ZnFe₂O₄/S-g-C₃N₄ heterojunction photocatalyst system is created via a Sol-gel technique.

2) An interfacial mediator between ZnFe₂O₄ and S-g-C₃N₄ works as an e⁻ and h⁺ separation mediator.

3) The ZnFe₂O₄/S-g-C₃N₄ heterojunctions’ photocatalytic and antibacterial properties were enhanced.

1 Introduction

Water is essential for living organisms, and owing to uncontrolled population growth and water pollution, there has been a subsequent rise in the scarcity of potable water. It entails that water-related problems must be addressed for the prosperous inhabitation of the living organism. In addition to population growth, industries have also contributed to the pollution of natural water bodies by introducing various pollutants (Liu et al., 2017; Qin et al., 2017; Sethi et al., 2019). Among these pollutants, Methylene blue (MB) is a representative pollutant affecting aquatic and terrestrial bodies (Habibi-Yangjeh and Shekofteh-Gohari, 2017; Shi et al., 2017; Qamar et al., 2020a). The development of technologies for removing domestic and industrial pollutants has become the centre of attention. In this regard, conventional water treatment methods such as filtration, adsorption and chlorination etc., are not recommended due to time-consumption, health hazards, cost, and may also lead to secondary pollution (Aoudj et al., 2015; Awual et al., 2015; Ali et al., 2018). Thus, the spotlight has been spotted on developing new resources to decontaminate water.

Due to the efficiency and efficacy of the advanced oxidation process (AOPs), which was first developed to clean drinking water, it is now used to treat wastewater (O’Shea and Dionysiou, 2012). Among various types of AOPs, heterogeneous photocatalysis is getting more attention (Syafiuddin et al., 2017; Iqbal et al., 2020a; Iqbal et al., 2020b; Iqbal et al., 2020c; Iqbal et al., 2021a). Semiconductor-based photo-catalysts are considered greener, more sustainable sources of reducing water pollution and other problematic outcomes (Sher et al., 2021a; Javed et al., 2021). All credit goes to low cost, chemical and biological inertness, and superb ability to remove organic contaminants, mainly dyes and toxins contained by wastewater (Kuo and Liao, 2006; Jan Šíma, 2013; Akhundi and Habibi-Yangjeh, 2016; Qamar et al., 2021a). Catalysis reaction is driven by light irradiation (UV light, solar light, visible light sources, etc.) on semiconductor catalysts. In heterogeneous photocatalysis, charge carriers are generated in sunlight, which in turn is followed by free radicals’ production. On further reactions, it generated free radicals eventually produced and mineralized pollutants into CO₂ and H₂O (Sahoo et al., 2018; Mishra et al., 2019). Among all known agents, spinal structured ferrites are accessible for brilliant photocatalytic degradation of organic compounds (Patna ik et al., 2018; Behera et al., 2019). Ferric oxide (Fe₂O₃) materials are regarded as ferrites (Biglari et al., 2016). Such ferrites have enclosed some advantages such as spinel like visible light responsiveness, internal magnetic properties and the availability of numerous stable photo-active sites (Atif et al., 2006; Xue et al., 2007). Among various known ferrites, zinc ferrite (ZnFe₂O₄) nanoparticles (NPs) having a narrow bandgap of 1.9 eV have been found as a potential candidate to exhibit remarkable photocatalytic activity (Iqbal et al., 2022).

Due to the fast recombination of a photo-generated exciton, ZnFe₂O₄ cannot be used as a photo-catalyst singly until a modification is made. These modifications include the formation of nanocomposites with other metal oxides, noble metals, doping with different metals and nonmetals, or the construction of hetero-junction photo-catalysts, etc., and contribute to resolving problems to some extent (Song et al., 2015). The construction of hetero-junction photo-catalysts has been valued and improved photocatalytic activity by raising electric current at the interface and diminishing the recombination phenomena. This function is carried out by graphitic carbon nitride (g-C₃N₄), a metal-free photo-catalyst, that has gained interest in the fabrication of hetero-junctions owing to unique properties including excellent stability, faster charge transport and low fabrication cost (Dong et al., 2014; Chen et al., 2015; Kuriki et al., 2015; Liu et al., 2015; Wang et al., 2018; Liras et al., 2019; Qamar et al., 2021b; Sher et al., 2021b; Qamar et al., 2022).

Despite advantages, properties such as weak π-π conjugated structures, low conductivity, less visible light utilization and small surface area have limited practical applications of g-C₃N₄ (Zhang et al., 2016; Iqbal et al., 2020d). And require modifications to improve light absorption properties. These modifications include doping with metals such as sulphur/metal oxides, non-metals and so on (Ali and Gupta, 2006; Liu et al., 2010; Dong et al., 2012; Hong et al., 2012; Feng et al., 2014; Wang et al., 2015; Jiang et al., 2017; Sher et al., 2021c). K.K.Das et al. have synthesized poly-pyrrole sensitized ZnFe₂O₄/sulphur doped g-C₃N₄ n-n hetero-junction and studied degradation of Ciprofloxacin (Das et al., 2020). N. Ali et al. constructed alkaline and transition metal ferrite photo-catalysts (MgFe₂O₄, BaFe₁₂O₁₉, ZnFe₂O₄, CaFe₂O₄ and CuFe₂O₄), and among them, zinc ferrite (ZnFe₂O₄) exhibited the best degradation of MB under sunlight (Ali et al., 2019). To the best of our knowledge, nanocomposites (NCs) composed of ZnFe₂O₄/sulphur doped g-C₃N₄ (S-g-C₃N₄) have not been studied yet, and such a new catalyst has not been reported for photocatalytic applications.

In this current study, ZnFe₂O₄ NPs and ZnFe₂O₄ NPs doped with S-g-C₃N₄ NCs have been prepared using sol-gel and simple chemical mixing methodologies. Both constructed NPs ZnFe₂O₄ NPs and ZnFe₂O₄/S-g-C₃N₄ NCs have also been characterized using XRD, XPS, EDX, UV-vis, EIS, photocurrent response and FTIR characterization techniques. ZnFe₂O₄/S-g-C₃N₄ NCs were examined for photo-catalytic activity against a model pollutant dye, MB degradation, and investigated spectrophotometrically as a viable candidate for photo-catalytic use. Irradiation has been done using solar light as a light source.

2 Materials and methods

2.1 Chemicals used

Zinc nitrate hexahydrate (Zn(NO₃)₂.6 H₂O, 99.1%), ferrous nitrate (Fe(NO₃)₂), Citric acid, ammonium hydroxide (NH₄OH), sulfuric acid (H₂SO₄), Thiourea ((NH₂)₂CS, ≥ 99.1%), Methylene blue (C₁₆H₁₈N₃SCl, ≥99.01%). Sigma Aldrich provided all compounds, which were utilized without additional purification.

2.2 Photo-catalyst synthesis

2.2.1 Synthesis of pure ZnFe₂O₄ NPs

The sol-gel method was employed to prepare pure ZnFe₂O₄ NPs. For this purpose, 2.97 g of Zn(NO₃)₂ and 4.05 g of Fe(NO₃)₂ were mixed and dissolved using de-ionized water. Citric acid (6.31 g) was added to the mixture after it had been dissolved. With the addition of NH₄OH, the pH of the resultant combination was kept constant at 5.4. After adjusting pH, the obtained mixture was continuously stirred at 60°C for about 2 h before being heated to 90°C. After heating at 90°C, a gel was formed because of water evaporation and gel was then subjected to calcination in furnace for about 2 h at 450°C in order to decompose citric acid. The resulting product was cooled to room temperature after heating. After cooling, the product was washed several times using 5% of 0.1 M H₂SO₄ and de-ionized water till pH of filtrate was neutralized followed by drying in an oven at temperature of 80°C.

2.2.2 Synthesis of S-doped g-C₃N₄

Recipe to synthesize S-doped g-C₃N₄ was followed by taking 30 g thiourea separately in each of three ceramic crucibles covered with lids and introduced in a muffle furnace at 520°C temperature for about 2 h, being kept at 5 °C/min. After 2 hours, the yellowish-colored product was allowed to cool naturally at room temperature before being ground and collected in dried sample vials. After grinding, yellowish product was used to synthesize NCs and tested for photo-catalytic activity.

2.2.3 Synthesis of series of ZnFe₂O₄ doped with S-doped g-C₃N NCs

A simple chemical mixing methodology was used to create a series of NCs composed of ZnFe₂O₄ coupled with S-doped g-C₃N₄ having variable ratios of S-g-C₃N₄. In order to develop a sequence, variable ratios i.e., 10%, 30%, 50%, 70% and 90% S-g-C₃N₄ were dissolved individually in 100 ml de-ionized water and continuously stirred for the period of 2 h. After complete dispersion, 2.97 g of ZnFe₂O₄ and 4.04 g of Fe(NO₃)₂ were mixed and dissolved using de-ionized water which was then followed by adding 6.3 g citric acid by weight. Afterwards, pH of resulting mixture was maintained at 5.4 using NH₄OH. Once pH was adjusted, obtained mixture was continuously stirred for 2 h at 60°C before being heated to 90°C. After heating at 90°C, a gel was obtained as a result of water evaporation and was then calcined in furnace at 450°C for 2 h in order to decompose citric acid. After calcination, the product was collected from furnace and cooled at room temperature and washed using 5% of 0.1 M H₂SO₄ and de-ionized water several times until filtrate was obtained with neutral pH. Once neutral pH was stabilized, filtrate was dried in an oven at 80°C and collected in clean sample vials before being tested for photo-catalytic performance.

2.3 Characterization techniques

As shown in the supporting information, different ways of characterizing have been used for different purposes.

2.4 Photocatalytic performance

ZnFe₂O₄ doped with S-doped g-C₃N₄ NCs were tested for photo-catalytic activity against Methylene blue degradation (MB). For this purpose, sunlight as a light source was used to study photo-degradation. To begin, nano-samples in an aqueous MB solution were positioned in dark for duration of 30 min in order to establish adsorption-desorption equilibrium before being spectrophotometrically studied. The dye solution containing nano-samples in a Petri dish was then exposed to open atmosphere in the presence of sunlight. The pH of the following photo-catalytic reaction process is kept at its optimal value of 8. In the experiment, 0.01 g of ZnFe₂O₄/S-g-C₃N₄ NC was dissolved in 100 ml of MB aqueous solution. The resulting solution was then placed in a Petri dish in the dark mode for 30 min before being exposed to sunlight without a lid for dye photo degradation. After 30 min, 5 ml of MB solution was withdrawn, centrifuged and monitored through UV-vis spectrophotometer.

3 Results and discussion

3.1 Physicochemical properties of S-g-C₃N₄, ZnFe₂O₄ NPs, and ZnFe₂O₄/S-g-C₃N₄ NCs

3.1.1 XRD analysis

XRD characterization technique was exercised to characterize phase composition of S-g-C₃N₄ at temperatures ranging from 0 to 80^o for prepared samples. Figure 1A depicts XRD pattern of S-g-C₃N₄. The sample has a single major peak (002) at 2 = 27.421^o, indicating interlayer stacking of the matching aromatic conjugated system and confirming the synthesis of S-g-C₃N₄. Following the discovery of S doping in the z-orientation, the peak at 27.421^o indicates assembly of corresponding nano-sheets in the XY-plane. The peak at 8.050^o indicates a stronger H-bonding network, resulting in more in-plane order, due to the tri-s-triazine ring atoms (Jourshabani et al., 2017). Figure 1B shows the XRD pattern of ZnFe₂O₄ powder synthesized by sol-gel technique. The observed diffraction peaks are found to be in accordance with typical spinel structure of ferrite and are well defined by sharp increasing peaks, confirming the sample’s crystallinity. Diffraction peaks for a pure sample were obtained at 31.609°, 36.34°, 56.73°, 63.03° and 67.75°, which are linked to plane scattering, namely (220) (311) (511) (440) and (531). These scattering confirms the ZnFe₂O₄ powder’s face-centered cubic spinel structure (Pradeep et al., 2011; Rachna et al., 2018). XRD pattern of 50% ZnFe₂O₄/g-C₃N₄ NCs is shown in Figure 1C. Intensities of diffraction peaks are observed to be reduced and shifted which correspond to distinctive peaks at 13.08°, 27.87°, 37.17°, 47.04°, 55.25° and 62.92° and confirms successful formation of ZnFe₂O₄/S-g-C₃N₄ NC.

FIGURE 1

FIGURE 1. XRD pattern of (A) S-doped g-C₃N₄, (B) ZnFe₂O₄ NPs (C) 50% ZnFe₂O₄/S-g-C₃N₄ NCs.

3.1.2 TEM analysis

S-g-C₃N₄, ZnFe₂O₄ NPs, and ZnFe₂O₄/S-g-C₃N₄ NCs were investigated using TEM and EDX, respectively, to determine their crystalline structure, surface morphology, and elemental composition. As shown in Figure 2A, pure S-g-C₃N₄ possesses a two-dimensional (2D) nanosheets-like form with pronounced flexibility and aggregation. Figure 2B shows a scanning electron microscope picture of virgin ZnFe₂O₄ nanoparticles (NPs). With particle diameters ranging from 30–45 nm, ZnFe₂O₄ NPs are spherical, monodispersed, and have irregular shapes. Furthermore, the TEM picture (Figure 2C) indicates an equal distribution of ZnFe₂O₄ NPs across the S-g-C₃N₄ NSs in the case of 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs. The S-g-C₃N₄ segment is a layered 2D structure with ZnFe₂O₄ scattered as 0D NPs.

FIGURE 2

FIGURE 2. TEM images of (A) S-doped g-C₃N₄, (B) ZnFe₂O₄ NPs (C) 50% ZnFe₂O₄/S-g-C₃N₄ NCs and (D) shows the EDX of 50% ZnFe₂O₄/S-g-C₃N₄ NCs.

When 50 percent S-g-C₃N₄ NSs were employed for production on ZnFe₂O₄ NPs, a well-defined heterojunction between ZnFe₂O₄ and S-g-C₃N₄ was found. The ZnFe₂O₄ and S-g-C₃N₄ heterointerface connection was shown to have an excellent interface contact in the TEM image (Figure 2C). The hetero contacts of ZnFe₂O₄ and g-C₃N₄ (Figure 2C) were found to be substantially integrated, which explains the composite systems’ considerable enhancement in photocatalytic ability. EDX elemental mapping of 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs was also performed, as shown in Figure 2D, to analyze its surface component metal element. Carbon, iron, sulphur, oxygen, nitrogen, and zinc all had sharp peaks, suggesting that they were evenly distributed over the ZnFe₂O₄/S-g-C₃N₄ NCs.

3.1.3 FT-IR spectrum analysis of ZnFe₂O₄ NPs and ZnFe₂O₄/S-g-C₃N₄ NCs (10%, 30%, 50%)

The FT-IR spectrum of pure ZnFe₂O₄ NPs is displayed in Figure 3A. The obtained spectrum revealed two distinct absorption peaks being observed at 540-545 and 390-395 cm⁻¹. These peaks were discovered to be associated with vibrational modes corresponding to oxygen-metal cation complexes at tetrahedral and octahedral sites, respectively. Because cations at both tetrahedral and octahedral sites are in different ionic states, the tetrahedral site has a wide shoulder and secondary bands. The above-mentioned band observation has also been aided by the intrusion of Zn²⁺ ions to the B-site, followed by Fe³⁺ ions to the A-site (Das et al., 2020). Figure 3B depicts the FT-IR spectrum for S-doped g-C₃N₄ ranging from 500 to 4,000 cm⁻¹. In the measured spectra, a peak at 800–802 cm⁻¹ highlights the vibrational frequency of triazine in condensed CN heterocycles, which is typical of triazine. Peaks in the 1,250–1,600 cm⁻¹ range emphasize C-N aromatic ring stretching vibrations, whereas a large peak at 3,095–3,098 cm⁻¹ is attributed to OH vibrations caused by the water molecule. This peak is also connected with the amino group’s N-H bond stretching vibrations. Peaks in the 1,200–1,050 cm⁻¹ range were discovered, indicating S-doping. S-g-C₃N₄ synthesis is indicated by the measured spectrum and supporting evidence (Shcherban et al., 2016).

FIGURE 3

FIGURE 3. FT-IR spectra of (A) ZnFe₂O₄ NPs (B) S-g-C₃N₄ (C) 10% ZnFe2O4/S-g-C3N4 NC, (D) 30% ZnFe2O4/S-g-C3N4 NC, (E) 50% ZnFe2O4/S-g-C3N4 NCs.

Figures 3C–E depicts the FT-IR spectra of 10%, 30 % and 50% ZnFe₂O₄/S-g-C₃N₄ NCs, respectively. Broad-spectrum in the range 3,100–3,500 cm⁻¹ is observed for 10%, 30% and 50% ZnFe₂O₄/g-C₃N₄, confirming the presence of both amines (primary and secondary) and OH groups being adsorbed at surface. A number of peaks in the 1,250–1,600 cm⁻¹ range have also been observed which indicate stretching vibrations due to C-N aromatic rings. The peak at 800 cm⁻¹, which is typical of triazine and heptazine rings, shifts to a higher wave number, 805 cm⁻¹, showing that ZnFe₂O₄ and S-g-C₃N₄ have a strong chemical connection. Water molecule vibrations are responsible for the large peak at 3,095–3,098 cm⁻¹. A new peak in the region of 1,200–1,050 cm⁻¹ is seen, confirming the existence of adequate sulphur and considerable ZnFe₂O₄/S-g-C₃N₄ NCs interaction, notably for 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs. The acquired spectra validate the generation of pure ZnFe₂O₄ NPs, 10%, 30%, and 50% ZnFe₂O₄/S-g-C₃N₄ NCs, as well as the previously reported supporting results.

3.1.4 XPS analysis

The elemental structure and valence state of 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs were also determined using XPS. The peaks in the Zn 2p spectra of 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs (Supplementary Figure S1A) attributable to the Zn 2p_3/2 and Zn 2p_1/2, correspondingly, may be assigned to the Zn 2p_3/2 and Zn 2p_1/2 (Khosravi-Gandomani et al., 2014; Zhu et al., 2020). In the Fe 2p XPS measurements (Supplementary Figure S1B), the oxidation state of Fe³⁺ in the constructed photocatalyst was assigned to two primary peaks of the Fe 2p_3/2 (708.39) and Fe 2p_1/2 (722.09) eV (Abdel Messih et al., 2019). The deconvoluted O 1s observations of 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs (Supplementary Figure S1C) confirm the presence of two definite peaks at binding energies (BEs) of 531.3 and 529.8 eV, which may be linked with Zn-O and Fe-O, correspondingly (Zhao et al., 2020). Supplementary Figure S2 shows the C 1s spectrum. In the N 1s high-resolution spectra, the N C-N, N-H, and C(C)₃ functions are attributed three characteristics peaks at 397.86, 400.64, and 399.76 eV, respectively (Supplementary Figure S1D) These XPS data showed that 50 percent ZnFe2O4/S-g-C3N4 NCs were successfully formed. The XPS findings showed that the contact between ZnFe2O4 and S-g-C3N4 is close, resulting in a nanocomposite containing 50% ZnFe2O4 and 50% S−g-C3N4.

3.1.5 UV-vis analysis

The UV-vis spectra were used to assess the light absorption of the produced photocatalysts S-g-C₃N₄, ZnFe₂O₄, and 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs. Supplementary Figure S3A shows a collection of UV-vis absorption spectra in the wavelength range of 285–752 nm. Light harvesting improves from 285 nm to 752 nm when 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs are compared to ZnFe₂O₄ and S-g-C₃N₄. The integration of S-g-C₃N₄ NPs with S-g-C₃N₄ helps to increase the photocatalytic efficiencies of the 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs material, which in turn helps to improve the photocatalytic efficiencies. Furthermore, the light-harvesting performance in the 450–752 nm region has been significantly increased, which is important for photocatalytic efficiency.

The energy bandgap values of these produced photocatalysts were determined by plotting UV-vis light-harvesting spectra using the Tauc’s plot (Supplementary Figure S3B). S-g-C₃N₄, ZnFe₂O₄, and 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs were estimated to have bandgap values of 2.06 eV, 2.75 eV, and 2.27 eV, correspondingly, as shown in Supplementary Figure S3B. When the energy bandgap of S-g-C₃N₄ compared to ZnFe₂O₄ and 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs declined from 2.75 eV for S-g-C₃N₄ to 2.27 eV for 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs. The calculated energy bandgap of 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs was 2.27 eV. The reduction in bandgap values might be attributable to the effective surface combination of both components, which significantly increases the binary photocatalytic capabilities. The photocatalytic capacities of ZnFe₂O₄ and S-g-C₃N₄ may be linked by the reduced optical bandgap edge of 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs under visible light radiance.

3.2 Photo-catalytic activity of ZnFe₂O₄/S-g-C₃N₄ NCs

Photo-activity of ZnFe₂O₄/S-g-C₃N₄ (10%, 30%, 50%, 70%, 90%) NCs has been tested for degrading dye i.e., methylene blue (MB). Herein, the potential application of ZnFe₂O₄/s-g-C₃N₄ NCs has been examined by nominating model reaction, photo-degradation of dye (MB) under visible light (Figure 4). It has been observed that MB spectra present maximum absorption at the wavelength of 664 nm, which reveals no degradation in the absence of either photo-catalyst, i.e., ZnFe₂O₄/s-g-C₃N₄ or visible light and verifies the stability of MB. On the other hand, photodegradation of MB is observed to start when MB solutions consisting of photo-catalysts ZnFe₂O₄/s-g-C₃N₄ being dispersed in solution are irradiated to sunlight. In the beginning, the photodegradation rate is speedy while starting to decay with time. Figures 4A–F displays photo-degradation in 150min associated with ZnFe₂O₄/s-g-C₃N₄ NCs with varying s-g-C₃N₄ amounts (10%, 30%, 50%, 70% and 90%).

FIGURE 4

FIGURE 4. MB degradation under visible light illumination by (A) 0% ZnFe₂O₄/S-g-C₃N₄ NC (B) 10% ZnFe₂O₄/S-g-C₃N₄ NC (C) 30% ZnFe₂O₄/S-g-C₃N₄ NC (D) 50% ZnFe₂O₄/S-g-C₃N₄ NC (E) 70% ZnFe₂O₄/S-g-C₃N₄ NC (F) 90% ZnFe₂O₄/s-g-C₃N₄ NC.

Comparative study of MB photo-degradation of ZnFe₂O₄/s-g-C₃N₄ NCs with varying S-g-C₃N₄ (0%, 10%, 30%, 50%, 70% and 90%) amounts has also been executed and presented in Supplementary Figures S4A–F. It has been observed from the results of MB photo-degradation by ZnFe₂O₄/s-g-C₃N₄ NCs that increased amounts of S-g-C₃N₄ resulted in enhanced MB’s degradation rate. The observed maximum photo-degradation rate has been achieved with 50 wt% S-g-C₃N₄ loading under sunlight. In addition to this observation, it has also been found that further increasing S-g-C₃N₄ amounts resulted into decreased photo-degradation activity (Qamar et al., 2020b; Iqbal et al., 2021b). Therefore, the 50 wt% s-g-C₃N₄ is called to exhibit efficient MB degradation performance and is applicable for delivering photo-induced electron-hole pairs separation across the 50% ZnFe₂O₄/s-g-C₃N₄ NCs interface. Increased amounts of S-g-C₃N₄ resulted in increased photo-degradation to some extent after that has been found to decline the dye photo-degradation performance. The creation of charge recombination centers or the light-blocking effect caused by large levels of S-g-C₃N₄ are credited. When 50% ZnFe₂O₄/S-g-C₃N₄ NCs are lighted by visible light, Figure 5 depicts the photocatalytic reaction pathways.

FIGURE 5

FIGURE 5. A hypothetical schematic diagram depicting a viable approach for photocatalytic dye decolorization using 50% ZnFe₂O₄/S-g-C₃N₄ NCs.

The photo-decolorization of MB reusing samples with 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs was tested six times under visible-light irradiation, as it is widely known that chemical stability of a catalyst is significant when deciding on its capacity for general application. The dye decolorization ability reduces somewhat after six runs (Figure 6A), suggesting that the NCs photocatalyst is chemically durable across a variety of experimental methodologies. The first and sixth dye photo-decolorization cycles yielded XRD patterns of 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs, as illustrated in Figure 6B. Before and after MB recycling testing, 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs showed no visible crystal phase structure changes, demonstrating chemical structural resilience. We think that when exposed to visible light, 50% ZnFe₂O₄/S-g-C₃N₄ NCs are extremely stable and dynamic catalysts, based on the findings of the research.

FIGURE 6

FIGURE 6. (A) Cyclic stability of 50% ZnFe2O4/S−g-C3N4 NCs photocatalyst for 6 sequential MB photodegradation tests. (B) Structural stability of 50% ZnFe2O4/S-g-C3N4 NCs identified by XRD patterns recorded before the first cycle and after the six-recycling test. (C) EIS Nyquist plots of S-g-C₃N₄, ZnFe2O4 and 50% ZnFe2O4/S-g-C3N4 NCs. (D) Transient photocurrent responses of undoped S-g-C₃N₄, ZnFe2O4 and 50% ZnFe2O4/S-g-C3N4 NCs in visible-light irradiation (λ > 420 nm).

EIS in the dark was utilized to determine the heterointerface charge transfer rate at the electrode-electrolyte junction. A narrow arc radius is often related with lower electron transport resistance and faster interfacial photoinduced charge transfer and departure efficiency. The charge-transmission resistance of the 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs was the lowest of all the synthesized samples (Figure 6C), indicating that the heterointerface contact of the 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs can significantly support electron transmission, improving photocatalytic efficiency by increasing electron consumption. The results of the EIS are supported by transient photocurrent measurements. According to the aforementioned experimental results, a 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs heterojunction may significantly improve heterointerface electron transmission, efficient separation of photogenerated e⁻ and h⁺ couples, and light harvesting capability.

We investigated the basis for 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs with remarkable photocatalytic efficacy for MB photo-decolorization when equated to ZnFe₂O₄ and S-g-C₃N₄, which may explore the capable passage of photoinduced e⁻ and h⁺ pairs (Figure 6D). In a 0.5 M Na₂SO₄ solution, photocurrent density reactions of ZnFe₂O₄, S-g-C₃N₄, and 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs were carried out under chopping illumination at 0 V. Under identical reaction conditions, the photocurrent response of the 50 percent ZnFe₂O₄/S-g-C₃N₄ NCs is considerably boosted, indicating that charge transfer and consumption are effective in this system. Photocurrent measurements show that photocatalytic MB destruction is aided by excellent electron-hole pair separation and refined heterointerfaces in self-assembled produced ZnFe₂O₄/S-g-C₃N₄ NCs.

3.3 Antibacterial ability

S-g-C3N4, ZnFe2O4, and 50 percent ZnFe2O4/S-g-C3N4 NCs were all tested independently for their antibacterial properties. The antibacterial capacity was tested using S. aureus (Gram-positive bacteria), E. coli (Gram-negative bacteria), B. subtilis, and S. salivarius bacteria as substrates. The positive and negative controls in these studies were double DI water and ciprofloxacin (0.6 mg/ml). Supplementary Table S1 and Supplementary Figure S5 show the results. The photocatalyst made up of 50% ZnFe2O4/S-g-C3N4 NCs had the greatest antibacterial ability, as predicted. Its large surface area and decreased e-/h + recombination propensity may be attributed to this. The production of reactive oxygen species (ROS) and its interaction with microorganisms are linked to the photocatalyst’s antibacterial capabilities. The significant antibacterial activity was attributed to the high production of ROS by the reaction of e-/h + formation by photocatalysts through chemisorption of water and oxygen. Under visible light irradiation, the 50 percent ZnFe2O4/S-g-C3N4 NCs shown good antibacterial efficacy against Gram-negative bacteria (E. coli) and Gram-positive bacteria (B. subtilis, S. aureus, S. salivarius).

4 Conclusion

The sol-gel methodological technique was used to successfully synthesis ZnFe₂O₄ NPs and ^{ZnFe2O4/S−g-C3N4 NCs} with various concentrations of S-g-C₃N₄ (10%, 30%, 50%, 70%, and 90%). Characterization methods such as XRD, TEM, EDX, EIS, XPS, photocurrent response and FT-IR were employed to ensure that the synthesis of NPs and NCs was successful. The potential application of prepared NCs, i.e., ^{ZnFe2O4/S−g-C3N4 NCs} (10%, 30%, 50%, 70 % and 90%), has been tested through photocatalytic performance against model dye (MB). A comparison of MB photo degradation by ^{ZnFe2O4/S−g-C3N4 NCs} with varying S-g-C₃N₄ (0%, 10%, 30%, 50%, 70% and 90%) amounts was also carried out, and it was discovered that 50 percent ^{ZnFe2O4/S−g-C3N4 NCs} displayed excellent photo-catalytic performance among all prepared NCs. In addition, decreased activity was observed with increased amounts of S-g-C₃N₄ owing to the formation of light-blocking effects. Degradation of wastewater pollutants, especially dyes, by NCs, i.e., ZnFe₂O₄/S-g-C₃N₄ as photo-catalyst, highlights attractive candidates.

Data availability statement

The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding authors.

Author contributions

All authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.

Acknowledgments

The authors would like to thank the Deanship of Scientific Research at Umm Al-Qura University for supporting this work by Grant Code: (22UQU4320141DSR17). Email: rapasha@uqu.edu.sa. The authors extend their appreciation to the Research Center at AlMaarefa University for funding this work under TUMA project agreement number (TUMA-2021-22). This research was funded by Princess Nourah bint Abdulrahman University Researchers Supporting Project number (PNURSP 2022R53), Princess Nourah bint Abdulrahman 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.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fchem.2022.975355/full#supplementary-material

References

Abdel Messih, M. F., Ahmed, M. A., Soltan, A., and Anis, S. S. (2019). Synthesis and characterization of novel Ag/ZnO nanoparticles for photocatalytic degradation of methylene blue under UV and solar irradiation. J. Phys. Chem. Solids 135, 109086. doi:10.1016/j.jpcs.2019.109086

CrossRef Full Text | Google Scholar

Akhundi, A., and Habibi-Yangjeh, A. (2016). Ternary magnetic g-C3N4/Fe3O4/AgI nanocomposites: Novel recyclable photocatalysts with enhanced activity in degradation of different pollutants under visible light. Mater. Chem. Phys. 174, 59–69. doi:10.1016/j.matchemphys.2016.02.052

CrossRef Full Text | Google Scholar

Ali, I., and Gupta, V. K. (2006). Advances in water treatment by adsorption technology. Nat. Protoc. 1, 2661–2667. doi:10.1038/nprot.2006.370

PubMed Abstract | CrossRef Full Text | Google Scholar

Ali, N., Awais, , Kamal, T., Ul-Islam, M., Khan, A., Shah, S. J., et al. (2018). Chitosan-coated cotton cloth supported copper nanoparticles for toxic dye reduction. Int. J. Biol. Macromol. 111, 832–838. doi:10.1016/j.ijbiomac.2018.01.092

PubMed Abstract | CrossRef Full Text | Google Scholar

Ali, N., Zada, A., Zahid, M., Ismail, A., Rafiq, M., Riaz, A., et al. (2019). Enhanced photodegradation of methylene blue with alkaline and transition-metal ferrite nanophotocatalysts under direct sun light irradiation. J. Chin. Chem. Soc. 66, 402–408. doi:10.1002/jccs.201800213

CrossRef Full Text | Google Scholar

Aoudj, S., Khelifa, A., Drouiche, N., Belkada, R., and Miroud, D. (2015). Simultaneous removal of chromium(VI) and fluoride by electrocoagulation–electroflotation: Application of a hybrid Fe-Al anode. Chem. Eng. J. 267, 153–162. doi:10.1016/j.cej.2014.12.081

CrossRef Full Text | Google Scholar

Atif, M., Hasanain, S. K., and Nadeem, M. (2006). Magnetization of sol–gel prepared zinc ferrite nanoparticles: Effects of inversion and particle size. Solid State Commun. 138, 416–421. doi:10.1016/j.ssc.2006.03.023

CrossRef Full Text | Google Scholar

Awual, M. R., Eldesoky, G. E., Yaita, T., Naushad, M., Shiwaku, H., AlOthman, Z. A., et al. (2015). Schiff based ligand containing nano-composite adsorbent for optical copper(II) ions removal from aqueous solutions. Chem. Eng. J. 279, 639–647. doi:10.1016/j.cej.2015.05.049

CrossRef Full Text | Google Scholar

Behera, A., Mansingh, S., Das, K. K., and Parida, K. (2019). Synergistic ZnFe2O4-carbon allotropes nanocomposite photocatalyst for norfloxacin degradation and Cr (VI) reduction. J. Colloid Interface Sci. 544, 96–111. doi:10.1016/j.jcis.2019.02.056

PubMed Abstract | CrossRef Full Text | Google Scholar

Biglari, N., Nasiri, A., Pakdel, S., and Nasiri, M. (2016). Facile and reliable route for synthesis of zinc ferrite nanoparticles and its application in photo-degradation of methyl orange. J. Mat. Sci. Mat. Electron. 27, 13113–13118. doi:10.1007/s10854-016-5456-7

CrossRef Full Text | Google Scholar

Chen, S., Wang, C., Bunes, B. R., Li, Y., Wang, C., Zang, L., et al. (2015). Enhancement of visible-light-driven photocatalytic H2 evolution from water over g-C3N4 through combination with perylene diimide aggregates. Appl. Catal. A General 498, 63–68. doi:10.1016/j.apcata.2015.03.026

CrossRef Full Text | Google Scholar

Das, K. K., Patnaik, S., Mansingh, S., Behera, A., Mohanty, A., Acharya, C., et al. (2020). Enhanced photocatalytic activities of polypyrrole sensitized zinc ferrite/graphitic carbon nitride n-n heterojunction towards ciprofloxacin degradation, hydrogen evolution and antibacterial studies. J. Colloid Interface Sci. 561, 551–567. doi:10.1016/j.jcis.2019.11.030

PubMed Abstract | CrossRef Full Text | Google Scholar

Dong, G., Zhang, Y., Pan, Q., and Qiu, J. (2014). A fantastic graphitic carbon nitride (g-C3N4) material: Electronic structure, photocatalytic and photoelectronic properties. J. Photochem. Photobiol. C Photochem. Rev. 20, 33–50. doi:10.1016/j.jphotochemrev.2014.04.002

CrossRef Full Text | Google Scholar

Dong, G., Zhao, K., and Zhang, L. (2012). Carbon self-doping induced high electronic conductivity and photoreactivity of g-C3N4. Chem. Commun. 48, 6178. doi:10.1039/c2cc32181e

CrossRef Full Text | Google Scholar

Feng, L.-L., Zou, Y., Li, C., Gao, S., Zhou, L.-J., Sun, Q., et al. (2014). Nanoporous sulfur-doped graphitic carbon nitride microrods: A durable catalyst for visible-light-driven H2 evolution. Int. J. Hydrogen Energy 39, 15373–15379. doi:10.1016/j.ijhydene.2014.07.160

CrossRef Full Text | Google Scholar

Habibi-Yangjeh, A., and Shekofteh-Gohari, M. (2017). Novel magnetic Fe3O4/ZnO/NiWO4 nanocomposites: Enhanced visible-light photocatalytic performance through p-n heterojunctions. Sep. Purif. Technol. 184, 334–346. doi:10.1016/j.seppur.2017.05.007

CrossRef Full Text | Google Scholar

Hong, J., Xia, X., Wang, Y., and Xu, R. (2012). Mesoporous carbon nitride with in situ sulfur doping for enhanced photocatalytic hydrogen evolution from water under visible light. J. Mat. Chem. 22, 15006. doi:10.1039/c2jm32053c

CrossRef Full Text | Google Scholar

Iqbal, S., Ahmad, N., Javed, M., Qamar, M. A., Bahadur, A., Ali, S., et al. (2021). Designing highly potential photocatalytic comprising silver deposited ZnO NPs with sulfurized graphitic carbon nitride (Ag/ZnO/S-g-C3N4) ternary composite. J. Environ. Chem. Eng. 9, 104919. doi:10.1016/j.jece.2020.104919

CrossRef Full Text | Google Scholar

Iqbal, S., Bahadur, A., Anwer, S., Ali, S., Irfan, R. M., Li, H., et al. (2020). Effect of temperature and reaction time on the morphology of l-cysteine surface capped chalcocite (Cu2S) snowflakes dendrites nanoleaves and photodegradation study of methyl orange dye under visible light. Colloids Surfaces A Physicochem. Eng. Aspects 601, 124984. doi:10.1016/j.colsurfa.2020.124984

CrossRef Full Text | Google Scholar

Iqbal, S., Bahadur, A., Anwer, S., Ali, S., Saeed, A., Muhammad Irfan, R., et al. (2020). Shape and phase-controlled synthesis of specially designed 2D morphologies of l-cysteine surface capped covellite (CuS) and chalcocite (Cu2S) with excellent photocatalytic properties in the visible spectrum. Appl. Surf. Sci. 526, 146691. doi:10.1016/j.apsusc.2020.146691

CrossRef Full Text | Google Scholar

Iqbal, S., Bahadur, A., Anwer, S., Shoaib, M., Liu, G., Li, H., et al. (2020). Designing novel morphologies of l-cysteine surface capped 2D covellite (CuS) nanoplates to study the effect of CuS morphologies on dye degradation rate under visible light. CrystEngComm 22, 4162–4173. doi:10.1039/d0ce00421a

CrossRef Full Text | Google Scholar

Iqbal, S., Bahadur, A., Javed, M., Hakami, O., Irfan, R. M., Ahmad, Z., et al. (2021). Design Ag-doped ZnO heterostructure photocatalyst with sulfurized graphitic C3N4 showing enhanced photocatalytic activity. Mater. Sci. Eng. B 272, 115320. doi:10.1016/j.mseb.2021.115320

CrossRef Full Text | Google Scholar

Iqbal, S., Javed, M., Bahadur, A., Qamar, M. A., Ahmad, M., Shoaib, M., et al. (2020). Controlled synthesis of Ag-doped CuO nanoparticles as a core with poly(acrylic acid) microgel shell for efficient removal of methylene blue under visible light. J. Mat. Sci. Mat. Electron. 31, 8423–8435. doi:10.1007/s10854-020-03377-9

CrossRef Full Text | Google Scholar

Iqbal, S., Javed, M., Hassan, S. S., Nadeem, S., Akbar, A., Alotaibi, M. T., et al. (2022). Binary Co@ZF/S@GCN S-scheme heterojunction enriching spatial charge carrier separation for efficient removal of organic pollutants under sunlight irradiation. Colloids Surfaces A Physicochem. Eng. Aspects 636, 128177. doi:10.1016/j.colsurfa.2021.128177

CrossRef Full Text | Google Scholar

Jan Šíma, P. H. (2013). Photocatalytic degradation of textile dyes in aTiO2/UV. Syst. Chem. Eng. Trans. 32, 79–84.

Google Scholar

Javed, M., Qamar, M. A., Shahid, S., Alsaab, H. O., and Asif, S. (2021). Highly efficient visible light active Cu–ZnO/S-g-C3N4 nanocomposites for efficient photocatalytic degradation of organic pollutants. RSC Adv. 11, 37254–37267. doi:10.1039/d1ra07203j

PubMed Abstract | CrossRef Full Text | Google Scholar

Jiang, L., Yuan, X., Pan, Y., Liang, J., Zeng, G., Wu, Z., et al. (2017). Doping of graphitic carbon nitride for photocatalysis: A reveiw. Appl. Catal. B Environ. 217, 388–406. doi:10.1016/j.apcatb.2017.06.003

CrossRef Full Text | Google Scholar

Jourshabani, M., Shariatinia, Z., and Badiei, A. (2017). Facile one-pot synthesis of cerium oxide/sulfur-doped graphitic carbon nitride (g-C3N4) as efficient nanophotocatalysts under visible light irradiation. J. Colloid Interface Sci. 507, 59–73. doi:10.1016/j.jcis.2017.07.106

PubMed Abstract | CrossRef Full Text | Google Scholar

Khosravi-Gandomani, S., Yousefi, R., Jamali-Sheini, F., and Huang, N. M. (2014). Optical and electrical properties of p-type Ag-doped ZnO nanostructures. Ceram. Int. 40, 7957–7963. doi:10.1016/j.ceramint.2013.12.145

CrossRef Full Text | Google Scholar

Kuo, S.-L., and Liao, C.-J. (2006). Solar photocatalytic degradation of 4-chlorophenol in kaolinite catalysts. J. Chin. Chem. Soc. 53, 1073–1083. doi:10.1002/jccs.200600143

CrossRef Full Text | Google Scholar

Kuriki, R., Sekizawa, K., Ishitani, O., and Maeda, K. (2015). Visible-light-driven CO2 reduction with carbon nitride: Enhancing the activity of ruthenium catalysts. Angew. Chem. Int. Ed. 54, 2406–2409. doi:10.1002/anie.201411170

CrossRef Full Text | Google Scholar

Liras, M., Barawi, M., and de la Peña O’Shea, V. A. (2019). Hybrid materials based on conjugated polymers and inorganic semiconductors as photocatalysts: From environmental to energy applications. Chem. Soc. Rev. 48, 5454–5487. doi:10.1039/c9cs00377k

PubMed Abstract | CrossRef Full Text | Google Scholar

Liu, G., Niu, P., Sun, C., Smith, S. C., Chen, Z., Lu, G. Q., et al. (2010). Unique electronic structure induced high photoreactivity of sulfur-doped graphitic C3N4. J. Am. Chem. Soc. 132, 11642–11648. doi:10.1021/ja103798k

PubMed Abstract | CrossRef Full Text | Google Scholar

Liu, J., Liu, Y., Liu, N., Han, Y., Zhang, X., Huang, H., et al. (2015). Metal-free efficient photocatalyst for stable visible water splitting via a two-electron pathway. Science 347, 970–974. doi:10.1126/science.aaa3145

PubMed Abstract | CrossRef Full Text | Google Scholar

Liu, X., Iocozzia, J., Wang, Y., Cui, X., Chen, Y., Zhao, S., et al. (2017). Noble metal–metal oxide nanohybrids with tailored nanostructures for efficient solar energy conversion, photocatalysis and environmental remediation. Energy Environ. Sci. 10, 402–434. doi:10.1039/c6ee02265k

CrossRef Full Text | Google Scholar

Mishra, P., Behera, A., Kandi, D., and Parida, K. (2019). Facile construction of a novel NiFe2O4@P-doped g-C3N4 nanocomposite with enhanced visible-light-driven photocatalytic activity. Nanoscale Adv. 1, 1864–1879. doi:10.1039/c9na00018f

CrossRef Full Text | Google Scholar

O’Shea, K. E., and Dionysiou, D. D. (2012). Advanced oxidation processes for water treatment. J. Phys. Chem. Lett. 3, 2112–2113. doi:10.1021/jz300929x

CrossRef Full Text | Google Scholar

Patnaik, S., Das, K. K., Mohanty, A., and Parida, K. (2018). Enhanced photo catalytic reduction of Cr (VI) over polymer-sensitized g-C3N4/ZnFe2O4 and its synergism with phenol oxidation under visible light irradiation. Catal. Today 315, 52–66. doi:10.1016/j.cattod.2018.04.008

CrossRef Full Text | Google Scholar

Pradeep, A., Priyadharsini, P., and Chandrasekaran, G. (2011). Structural, magnetic and electrical properties of nanocrystalline zinc ferrite. J. Alloys Compd. 509, 3917–3923. doi:10.1016/j.jallcom.2010.12.168

CrossRef Full Text | Google Scholar

Qamar, M. A., Javed, M., Shahid, S., and Sher, M. (2022). Fabrication of g-C3N4/transition metal (Fe, Co, Ni, Mn and Cr)-doped ZnO ternary composites: Excellent visible light active photocatalysts for the degradation of organic pollutants from wastewater. Mater. Res. Bull. 147, 111630. doi:10.1016/j.materresbull.2021.111630

CrossRef Full Text | Google Scholar

Qamar, M. A., Shahid, S., Javed, M., Iqbal, S., Sher, M., Akbar, M. B., et al. (2020). Highly efficient g-C3N4/Cr-ZnO nanocomposites with superior photocatalytic and antibacterial activity. J. Photochem. Photobiol. A Chem. 401, 112776. doi:10.1016/j.jphotochem.2020.112776

CrossRef Full Text | Google Scholar

Qamar, M. A., Shahid, S., Javed, M., Iqbal, S., Sher, M., Bahadur, A., et al. (2021). Designing of highly active g-C3N4/Ni-ZnO photocatalyst nanocomposite for the disinfection and degradation of the organic dye under sunlight radiations. Colloids Surfaces A Physicochem. Eng. Aspects 614, 126176. doi:10.1016/j.colsurfa.2021.126176

CrossRef Full Text | Google Scholar

Qamar, M. A., Shahid, S., Javed, M., Sher, M., Iqbal, S., Bahadur, A., et al. (2021). Fabricated novel g-C3N4/Mn doped ZnO nanocomposite as highly active photocatalyst for the disinfection of pathogens and degradation of the organic pollutants from wastewater under sunlight radiations. Colloids Surfaces A Physicochem. Eng. Aspects 611, 125863. doi:10.1016/j.colsurfa.2020.125863

CrossRef Full Text | Google Scholar

Qamar, M. A., Shahid, S., and Javed, M. (2020). Synthesis of dynamic g-C3N4/Fe@ZnO nanocomposites for environmental remediation applications. Ceram. Int. 46, 22171–22180. doi:10.1016/j.ceramint.2020.05.294

CrossRef Full Text | Google Scholar

Qin, Z., Xue, F., Chen, Y., Shen, S., and Guo, L. (2017). Spatial charge separation of one-dimensional Ni2P-Cd0.9Zn0.1S/g-C3N4 heterostructure for high-quantum-yield photocatalytic hydrogen production. Appl. Catal. B Environ. 217, 551–559. doi:10.1016/j.apcatb.2017.06.018

CrossRef Full Text | Google Scholar

Rachna, N. B. Singh, A. Agarwal, Singh, N., and Agarwal, A. (2018). Preparation, characterization, properties and applications of nano zinc ferrite. Mater. Today Proc. 5, 9148–9155. doi:10.1016/j.matpr.2017.10.035

CrossRef Full Text | Google Scholar

Sahoo, D. P., Nayak, S., Reddy, K. H., Martha, S., and Parida, K. (2018). Fabrication of a Co(OH)2/ZnCr LDH “p–n” heterojunction photocatalyst with enhanced separation of charge carriers for efficient visible-light-driven H2 and O2 evolution. Inorg. Chem. 57, 3840–3854. doi:10.1021/acs.inorgchem.7b03213

PubMed Abstract | CrossRef Full Text | Google Scholar

Sethi, Y. A., Panmand, R. P., Ambalkar, A., Kulkarni, A. K., Patil, D. R., Gunjal, A. R., et al. (2019). In situ preparation of CdS decorated ZnWO4 nanorods as a photocatalyst for direct conversion of sunlight into fuel and RhB degradation. Sustain. Energy Fuels 3, 793–800. doi:10.1039/c8se00632f

CrossRef Full Text | Google Scholar

Shcherban, N. D., Filonenko, S. M., Ovcharov, M. L., Mishura, A. M., Skoryk, M. A., Aho, A., et al. (2016). Simple method for preparing of sulfur–doped graphitic carbon nitride with superior activity in CO2 photoreduction. ChemistrySelect 1, 4987–4993. doi:10.1002/slct.201601283

CrossRef Full Text | Google Scholar

Sher, M., Javed, M., Shahid, S., Hakami, O., Qamar, M. A., Iqbal, S., et al. (2021). Designing of highly active g-C3N4/Sn doped ZnO heterostructure as a photocatalyst for the disinfection and degradation of the organic pollutants under visible light irradiation. J. Photochem. Photobiol. A Chem. 418, 113393. doi:10.1016/j.jphotochem.2021.113393

CrossRef Full Text | Google Scholar

Sher, M., Javed, M., Shahid, S., Iqbal, S., Qamar, M. A., Bahadur, A., et al. (2021). The controlled synthesis of g-C3N4/Cd-doped ZnO nanocomposites as potential photocatalysts for the disinfection and degradation of organic pollutants under visible light irradiation. RSC Adv. 11, 2025–2039. doi:10.1039/d0ra08573a

PubMed Abstract | CrossRef Full Text | Google Scholar

Sher, M., Khan, S. A., Shahid, S., Javed, M., Qamar, M. A., Chinnathambi, A., et al. (2021). Synthesis of novel ternary hybrid g-C3N4@Ag-ZnO nanocomposite with Z-scheme enhanced solar light‐driven methylene blue degradation and antibacterial activities. J. Environ. Chem. Eng. 9, 105366. doi:10.1016/j.jece.2021.105366

CrossRef Full Text | Google Scholar

Shi, J., Cheng, C., Hu, Y., Liu, M., and Guo, L. (2017). One-pot preparation of porous Cr2O3/g-C3N4 composites towards enhanced photocatalytic H2 evolution under visible-light irradiation. Int. J. Hydrogen Energy 42, 4651–4659. doi:10.1016/j.ijhydene.2016.07.030

CrossRef Full Text | Google Scholar

Song, H., Zhu, L., Li, Y., Lou, Z., Xiao, M., Ye, Z., et al. (2015). Preparation of ZnFe2O4 nanostructures and highly efficient visible-light-driven hydrogen generation with the assistance of nanoheterostructures. J. Mat. Chem. A Mat. 3, 8353–8360. doi:10.1039/c5ta00737b

CrossRef Full Text | Google Scholar

Syafiuddin, A., Hadibarata, T., Zon, N. F., and Salmiati, (2017). Characterization of titanium dioxide doped with nitrogen and sulfur and its photocatalytic appraisal for degradation of phenol and methylene blue. J. Chin. Chem. Soc. 64, 1333–1339. doi:10.1002/jccs.201700136

CrossRef Full Text | Google Scholar

Wang, K., Li, Q., Liu, B., Cheng, B., Ho, W., Yu, J., et al. (2015). Sulfur-doped g-C3N4 with enhanced photocatalytic CO2-reduction performance. Appl. Catal. B Environ. 176-177, 44–52. doi:10.1016/j.apcatb.2015.03.045

CrossRef Full Text | Google Scholar

Wang, Y.-L., Tian, Y., Lang, Z.-L., Guan, W., and Yan, L.-K. (2018). A highly efficient Z-scheme B-doped g-C3N4/SnS2 photocatalyst for CO2 reduction reaction: A computational study. J. Mat. Chem. A Mat. 6, 21056–21063. doi:10.1039/c8ta07352j

CrossRef Full Text | Google Scholar

Xue, H., Li, Z., Wang, X., and Fu, X. (2007). Facile synthesis of nanocrystalline zinc ferrite via a self-propagating combustion method. Mater. Lett. 61, 347–350. doi:10.1016/j.matlet.2006.04.061

CrossRef Full Text | Google Scholar

Zhang, W., Zhang, J., Dong, F., and Zhang, Y. (2016). Facile synthesis of in situ phosphorus-doped g-C3N4 with enhanced visible light photocatalytic property for NO purification. RSC Adv. 6, 88085–88089. doi:10.1039/c6ra18349b

CrossRef Full Text | Google Scholar

Zhao, S.-W., Zheng, M., Sun, H.-L., Li, S.-J., Pan, Q.-J., Guo, Y.-R., et al. (2020). Construction of heterostructured g-C3N4/ZnO/cellulose and its antibacterial activity: Experimental and theoretical investigations. Dalton Trans. 49, 3723–3734. doi:10.1039/c9dt03757h

PubMed Abstract | CrossRef Full Text | Google Scholar

Zhu, Z., Guo, F., Xu, Z., Di, X., and Zhang, Q. (2020). Photocatalytic degradation of an organophosphorus pesticide using a ZnO/rGO composite. RSC Adv. 10, 11929–11938. doi:10.1039/d0ra01741h

PubMed Abstract | CrossRef Full Text | Google Scholar