Exfoliated g-C3N4/γ-Fe2O3/ZnO yolk-shell nanoparticles: A novel and magnetic recyclable photocatalyst towards eco-friendly degradation of organic pollutants using visible light irradiation

doi:10.21203/rs.3.rs-2576170/v1

Download PDF

Research Article

Exfoliated g-C3N4/γ-Fe2O3/ZnO yolk-shell nanoparticles: A novel and magnetic recyclable photocatalyst towards eco-friendly degradation of organic pollutants using visible light irradiation

https://doi.org/10.21203/rs.3.rs-2576170/v1

This work is licensed under a CC BY 4.0 License

Journal Publication

published 09 Jun, 2023

Read the published version in Environmental Science and Pollution Research →

You are reading this latest preprint version

Herein, a new visible-light active exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell nanoparticles (NPs) was synthesized as a magnetically separable photocatalyst. For an in-depth understanding of the magnetic photocatalyst's structural, morphological, and optical properties, the products were extensively characterized with FT-IR, XRD, TEM, FESEM, EDS, VSM, DRS, EIS, and Photocurrent. The photocatalyst was then utilized to degrade Levofloxacin (LEVO) and Indigo Carmine (IC) by visible light at room temperature. The exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs photocatalyst revealed 80% and 95.6% degradation efficiency for Levofloxacin and Indigo Carmine within 25 and 15 min, respectively. In addition, the optimal factors such as concentration, loading of photocatalyst and pH was also assessed. Levofloxacin degradation mechanistic studies showed that electrons and holes significantly contribute to the photocatalytic process of photocatalyst degradation. In addition, after 5 times regeneration, exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs remained as an excellent magnetic photocatalyst for the environmental-friendly degradation of Levofloxacin and Indigo Carmine (76% and 90%), respectively.

Exfoliated graphitic carbon nitride

Magnetic reusable photocatalyst

Wastewater treatment

Levofloxacin

Indigo Carmine

Visible-light.

The pharmaceutical industry considers antibiotics to be non-degradable and new pollutants (Sarmah et al. 2006; Heidari et al. 2018; Rad et al. 2015). The release of toxic pollutants into the environment is continuous, and their ecological consequences are severe (Chakraborty et al. 2017; Li et al. 2019). As a biologically active chemical compound in the environment, antibiotics have been considered a water pollution problem for the last few decades (Yan et al. 2019; Pavithra et al. 2017). They are found in medicines and intermediates, and cannot be fully utilized by tissues and organs, resulting in their release into water and soil (Sarmah et al. 2006). A variety of antibiotics act as chemical inhibitors of biological microorganisms and negatively affect resistance to bacteria in the environment after reacting with toxic metals (Zhang et al. 2019). Levofloxacin (LEVO) is a synthetic antibacterial agent with a wide range of activity against a variety of bacteria. It generally escapes intact from treatment plants and therefore gets into the environment due to its limited degradability in biological degradation processes. Consequently, broad-spectrum antibiotics present in water can boost the risk of the spread and emergence of resistant bacteria and lead to negative impacts on microbial societies and human health in the environment (Ding et al. 2012; Jechalke et al. 2014; Sturini et al. 2012). To eliminate the threat of antibiotic-resistant bacteria, there is an urgent need for development of an environmentally-friendly method to eliminate Levofloxacin from wastewater. In recent years, several innovative oxidation approaches have been reported for the removal of Levofloxacin including photocatalysis (Hong et al. 2016), microbial-based catalysis (Zeng et al. 2017), electrocatalysis (Liu et al. 2017), sonocatalysis (Blokhina et al. 2016), electron-Fenton (Epold et al. 2015), ozonation (Witte et al. 2009), H₂O₂/UV and ultrasound (US)/H₂O₂ (Gong et al. 2016; El Najjar et al. 2013; Wei et al. 2015).

In addition, dye pollutants discovered in the wastewater from chemical industries including textile, food, cosmetics, paper, pharmaceuticals, etc. are the main concern for the sustainable environment. Indigo Carmine (Indigo-5,5′-disulfonic acid disodium salt) or Acid Blue 74 is one of the widest dyes utilized in the textile industry. Indigo Carmine (IC) is an extremely toxic dye that might result in enhanced blood pressure, create tumours, and disturbance in the neuronal system (Barka et al. 2008). As a result, the elimination of Indigo Carmine from wastewater is very vital for the environmental safety. To deal with these problems, advanced oxidation processes (AOPs) such as photo Fenton oxidation, photocatalytic oxidation, and electrochemical oxidation have been widely studied and developed (Ammar et al. 2006).

Photocatalysis is a multidisciplinary subject including material science, physics, chemistry, and chemical engineering trying to use more effective light utilization and promote chemical reactions. Photocatalysis displays some key advantages including consumption of low energy, simple operation and low toxicity over conventional catalytic processes (Gao et al. 2017; Kou et al. 2017). It is often preferred to use heterogeneous photocatalysis over homogeneous, as it provides greater stability, easier separation of products, and easier recycling. In addition, photons cause chemical reactions on the photocatalyst surface in heterogeneous photocatalysis.

There are several kinds of visible light active semiconductors, such as graphitic carbon nitride (g-C₃N₄). In contrast to other semiconductors, g-C₃N₄ is an organic semiconductor comprised of carbon and nitrogen compounds and is a non-metallic conjugated polymer (Dong et al. 2014; Chu et al. 2019; Ye et al. 2015; Yin et al. 2015; Zhao et al. 2015; Zheng et al. 2015; Liu et al. 2016; Ong et al. 2016; Ding et al. 2017; Naseri et al. 2017).

Due to its non-toxic, low-cost and excellent environmental tolerance, graphitic carbon nitride (g-C₃N₄) materials are being increasingly investigated as photocatalysts or adsorbents for the treatment of organic pollutants wastewater (Zhao et al. 2016; Liu et al. 2019). Since bare g-C₃N₄ has a small surface area, a high carrier recombination rate, and a low quantum efficiency, it exhibits weak adsorption and unsatisfactory photocatalytic performance. A substantial reduction in the ability of g-C₃N₄ to adsorb or photocatalyze the removal of organic pollutants was also observed due to self-aggregation during the calcination preparation process. A practical solution to this problem is to construct composites with g-C₃N₄ and other phase to enhance their performance for organic pollution removal (Yao et al. 2014; Yuan et al. 2015; Ma et al. 2017; Palanivel et al. 2019; Sultan et al. 2021).

To consider the importance of developing a novel method by a heterogeneous photocatalyst (Ghasemzadeh et al. 2019; Ghasemzadeh et al. 2017; Sobhani et al. 2014; Ghasemzadeh et al. 2018; Ghasemzadeh et al. 2019; Ghasemzadeh et al. 2020; Ghasemzadeh et al. 2019), and in continuation of our recent research on green chemistry and heterogeneous photocatalysts for the degradation of toxic compounds (Ayati et al. 2012; Rohani Bastami et al. 2016; Rohani Bastami et al. 2017; Ayati et al. 2014; Ayati et al. 2016; Mahmoodi et al. 2018; Pastrana-Martinez et al. 2013), herein, exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) was synthesized following the synthetic process shown in Scheme 1. In this regard, the γ-Fe₂O₃ NPs were prepared using a technique available in the literature (Sobhani et al. 2014) that includes coprecipitation of Fe(III) and Fe(II) in an alkaline solution. Then, γ-Fe₂O₃ NPs (I) were coated with SiO₂ shell through reaction with tetraethyl orthosilicate (TEOS) followed by oxidation which leads to the formation of γ-Fe₂O₃@SiO₂ core-shell (II). Afterwards, the core-shell particles was treated with ZnNO₃.6H₂O in dimethylformamide and then NaOH (aq), respectively. The mixture was vigorously stirred and then calcined in an argon atmosphere to obtain γ-Fe₂O₃@SiO₂@ZnO (III). To produce γ-Fe₂O₃@ZnO (IV) yolk-shell, a suspension of γ-Fe₂O₃@SiO₂@ZnO (III) was reacted with a solution of NaOH. Next, the obtained g-C₃N₄ nanosheets and γ-Fe₂O₃@ ZnO (IV) yolk-shell were refluxed in ethanol for 24 hours to produce exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V). Subsequently, the activity of magnetic photocatalyst was investigated toward the degradation of Levofloxacin and Indigo Carmine in green media.

Materials

In this study, no further purification was performed on any of the chemical reagents and solvents obtained from Merck and Sigma-Aldrich. The API for levofloxacin hemihydrate was provided by Sajad Darou Shargh. A pH adjustment was achieved using sodium hydroxide and hydrochloric acid. All experiments were conducted with deionized water.

Preparation of magnetite nanoparticles γ-Fe₂O₃ NPs (I)

In 30 mL of deionized water, 2 g of FeCl₂.4H₂O and 3.5 g of FeCl₃.6H₂O were dissolved under Argon atmosphere at room temperature. The pH of the reaction solution was adjusted to 11 by adding NH₄OH (0.6 M, 200 mL) drop-wise (with the rate of 1 mL min^− 1) to the stirring mixture at ambient temperature. Fe₃O₄ powder was obtained after stirring the black solution for 1 hour at room temperature with a magnet and refluxing the resulting product for 1 hour. In order to obtain the reddish-brown powder, the synthesized sample was heated at 200 ºC at a rate of 2 ºC.min^− 1 in the furnace for 3 h (Sobhani et al. 2014).

Preparation of γ-Fe₂O₃@SiO₂ core-shell (II)

Ammonia solution (25%, 3.5 mL) was added to γ-Fe₂O₃ nano-particles (3.5 g) dispersed in distilled water (40 mL)/EtOH (160 mL) solution. The resulting mixture was stirred at 50 ºC for 40 min. Afterward, tetraethyl orthosilicate (0.009 mmol, 2.5 mL) was added to the vessel of reaction and the mixture was stirred at 40 ºC for 24 h. The nanoparticles (γ-Fe₂O₃@SiO₂ core-shell (II)) were then collected using a magnet, washed four times with EtOH and (CH₃CH₂)₂O, and dried in vacuum at 100 ºC overnight (Ghasemzadeh et al. 2019).

Preparation of γ-Fe₂O₃@SiO₂@ ZnO (III)

First, 0.07 g of the prepared γ-Fe₂O₃@SiO₂ core-shell (II) was dispersed in 70 mL of dimethylformamide by an ultrasonic bath for 1 h. Then, 0.6 g of ZnNO₃.6H₂O was dissolved in 60 mL of dimethylformamide and added to the previous solution. The resulting mixture was vigorously stirred for 40 min. Next, 0.08 g of NaOH was dissolved in 2 mL of distilled water, and the NaOH solution was added drop-wise to the initial solution. The mixture was then mechanically stirred for 7 h. The nano-particles were separated by a magnet and washed four times with distilled water and EtOH, respectively. The nano-particles were dried in vacuum at 60 ºC for 24 h. Finally, the obtained γ-Fe₂O₃@SiO₂@ ZnO (III) nano-particles from the previous section were calcined in a furnace with Argon atmosphere at 500 ºC for 2 h (Ghasemzadeh et al. 2019).

Preparation of γ-Fe₂O₃@ ZnO (IV) yolk-shell

In a Teflon-lined stainless-steel autoclave, the mixture of γ-Fe₂O₃@SiO₂@ZnO (III) (1 g) was mixed with NaOH (0.1 M, 25 mL) and heated at 125 ºC for 3 h. By washing with distilled water and drying at 40 ºC under vacuum, the nano-particles were obtained (Ghasemzadeh et al. 2019).

Preparation of g-C₃N₄ nanosheets

Graphitic carbon nitride (g-C₃N₄) was prepared by heating urea (5 g) in a furnace at 550 ºC for 3 h in the air. Then, g-C₃N₄ monolayer nanosheets were synthesized through the chemical exfoliation method. Into a 50 mL flask, the as-prepared g-C₃N₄ (1 g) was mixed with 10 mL of H₂SO₄ and then stirred at ambient temperature for 8 h. The mixture was slowly decanted in 100 mL of deionized water and sonicated (1 h) for exfoliation. The temperature of the suspension increased quickly, and the colour changed from yellow to light yellow. The resulting suspension was centrifuged at 3000 rpm for 5 min to remove any unexfoliated g-C₃N₄. Next, the obtained light-yellow suspension was rinsed with deionized water to eliminate the remaining acid and dried at 80 ºC overnight. To eliminate structural defects, the resulting products (0.3 g) were placed in a flask containing 150 mL of methanol and refluxed at 65 ºC for 6 h. After centrifugation and drying at 80 ºC for 24 h, the g-C₃N₄ nanosheets were obtained (Xu et al. 2013).

Preparation of exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V)

The obtained γ-Fe₂O₃@ZnO (IV) yolk-shell (0.5 g) and g-C₃N₄ nanosheets (0.5 g) were dispersed in ethanol (100 mL) for about 30 min and then refluxed for 24 h. Afterward, the resulting mixture was separated by an external magnet and rinsed repeatedly with deionized water and ethanol (4×15 mL). Finally, the magnetic photocatalyst was dried under vacuum at 60 ºC overnight.

Characterization

As-synthesized exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) was characterized in terms of structural and optical properties using several techniques. The FT-IR spectra were recorded on an Avatar 370 FT-IR Therma Nicolet spectrometer. The crystal structure of the catalyst was analyzed by XRD (Model PW1730, Netherlands) diffractometer (Dectris) operating at 40 kV and 30 mA utilizing Cu Ka radiation (l = 0.15056 Å). Transmission electron microscopy (TEM) was performed with a Zeiss-EM10C (Germany) with an accelerating voltage of 100 kV. FE-SEM images and EDS were recorded using a TESCAN, model MIRA3 (Czech Republic) operating at an acceleration voltage of 30.0 kV and resolution of about 200 and 500 nm. The magnetic property of the catalyst was measured using a vibrating sample magnetometer (VSM, Magnetic Danesh Pajoh Inst., Iran). The absorption characteristics of the Levofloxacin and Indigo Carmine were studied by a UV-visible spectrophotometer (Analytikjena, Germany). A 170 W Citizen COB LED lamp was employed as the environmentally-friendly visible light source to evaluate the degradation of Levofloxacin and Indigo Carmine in an aqueous phase. Ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) was conducted by a Shimadzu spectrophotometer (UV-2550 model, Japan). Electrochemical impedance spectroscopy (EIS) and time photocurrent response (TPR) were determined by Potentiostat-galvanostat (Metrohm DropSens, mStat-I 400s).

Photocatalytic Assessment

Photocatalytic activity of exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) was investigated for removal of Levofloxacin and Indigo Carmine under visible light irradiation, where a 170 W Citizen COB LED Lamp was employed as a green light source.

A chamber with a cylindrical batch reactor was used for all photocatalytic reaction and the temperature was maintained at 25 ºC by water circulation through the outer jacket during the photocatalytic experiment. A known amount of magnetic photocatalyst was mixed with 50 mL Levofloxacin and Indigo Carmine solution. Next, the mixture was stirred and kept in the dark for about 60 min to obtain adsorption-desorption equilibrium conditions. To monitor the performance of the magnetic photocatalyst, the mixture was exposed to visible light. The magnetic photocatalyst was separated by an external magnet. Next, about 3 mL of the prepared sample was withdrawn with the syringe at constant period of time. The samples were then filtered by nylon syringe filters (0.45 µm) and the resulting filtrate was analysed for absorption peak intensities at about λmax = 190–750 nm for removal of Levofloxacin and Indigo Carmine using a spectrophotometer, respectively.

Structural, optical and morphological characterizations of exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V)

The new magnetic photocatalyst represented as exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) was prepared by a stepwise procedure based on Scheme 1. The γ-Fe₂O₃ NPs (I) were prepared via coprecipitation of Fe(III) and Fe(II) salts in the presence of a NH₄OH solution under an argon atmosphere at ambient temperature. Subsequently, γ-Fe₂O₃ NPs (I) were coated with a layer of silica by stirring the γ-Fe₂O₃ NPs (I) suspension in deionized water/ethanol solution with tetraethyl orthosilicate. The obtained γ-Fe₂O₃@SiO₂ (II) core-shell was first calcined in the static air, then, ZnNO₃.6H₂O and NaOH (aq) were added to the γ-Fe₂O₃@SiO₂@ZnO (III). Later, the as-prepared γ-Fe₂O₃@SiO₂@ZnO (III) was treated with NaOH (aq) at 120 ºC for 2 h to obtain γ-Fe₂O₃@ZnO (IV) yolk-shell. Afterward, the γ-Fe₂O₃@ZnO (IV) yolk-shell was then reacted with exfoliated g-C₃N₄ nanosheets to achieve exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V). Characterization of g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) magnetic photocatalyst was well performed via a collection of various microscopic and spectroscopic techniques including Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), vibrating sample magnetometry (VSM), diffuse reflectance spectroscopy (DRS), electrochemical impedance spectroscopy (EIS), and time photocurrent response (TPR).

Figure 1 displays the FT-IR spectra of γ-Fe₂O₃ NPs (I), γ-Fe₂O₃@SiO₂ (II) core-shell, γ-Fe₂O₃@SiO₂@ZnO (III), γ-Fe₂O₃@ZnO (IV) yolk-shell, exfoliated g-C₃N₄ nanosheets and exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V). As shown in the FT-IR spectrum of γ-Fe₂O₃ NPs (I) (Fig. 1a) the broad absorption band around 561–636 cm^-1 is related to Fe-O vibrations. The absorption bands at about 1085 and 3470 cm^-1 can be attributed to the Si-O-Si bond and the hydroxyl groups (vOH) in γ-Fe₂O₃@SiO₂ (II) core-shell, respectively. As is evident in Fig. 1d, the characteristic band in the region 571 cm^-1 is related to the stretching vibration mode of Zn-O. Figure 1e shows a sharp absorption band at around 814 cm^-1 attributed to the stretching vibration of tris-s triazine ring in exfoliated g-C₃N₄ nanosheets, moreover, the absorption band relating to C-N heterocycle stretching vibration modes is presented at around 1640 cm^-1. The stretching vibration modes at 1407 and 1461 cm^-1 refer to aromatic C-N. Furthermore, the appearance of absorption bands at 3084 and 3159–3252 cm^-1 correlates to secondary and primary amines groups, respectively.

The crystallographic structures of γ-Fe₂O₃@SiO₂@ZnO (III), γ-Fe₂O₃@ZnO (IV) yolk-shell, and exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) from the degradation of Levofloxacin and Indigo Carmine are investigated using the XRD technique. As is evident in Fig. 2a, the XRD pattern shows reflection peaks at 2θ = 30.12, 36.10, 47.14, 56.94 and 63, which can be indexed to (2 2 0), (3 1 1), (4 0 0), (5 1 1) and (4 4 0) reflections of the orthorhombic structure of γ-Fe₂O₃, respectively (Ref. Code: 98-001-7122). Furthermore, as can be known from the XRD pattern of γ-Fe₂O₃@ZnO (IV) yolk-shell, the reflection peaks at 2θ = 31.8, 35.37, and 42.87 are ascribed to (1 0 0), (0 0 2), and (1 0 1) reflections of the hexagonal wurtzite of ZnO, respectively (Ref. Code: JCPDS 36-1451). Similarly, the XRD profile of Fig. 2c illustrates the diffraction peak at 2θ = 27 representing the (0 0 2) plane of the exfoliated g-C₃N₄ nanosheets.

The surface morphology of exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) was further determined by TEM and FESEM images (Figs. 3 and 4). As can be seen, g-C₃N₄ nanosheets are accompanied by the spherical nanoparticles (γ-Fe₂O₃@ZnO (IV) yolk-shell), and magnetic photocatalyst exhibited a size of 23–39 nm. Besides, the homogenous nature of the magnetic photocatalyst is noticeable at low magnification (Figs. 3a, 4b).

The energy dispersive spectrum (EDS) of exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) displayed all of the expected elements including C, O, N, Fe and Zn (Fig. 5). It is obvious that γ-Fe₂O₃@ZnO (IV) yolk-shell was successfully distributed on g-C₃N₄ nanosheets. In addition, no extra peaks associated to any impurity are identified in the structure of magnetic photocatalyst.

The magnetic behaviour of γ-Fe₂O₃ NPs (I) and exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) was studied by VSM analysis at room temperature (Fig. 6). As can be seen from the obtained magnetization curves, the saturation magnetization number of γ-Fe₂O₃ NPs (I) and exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) are 50 and 30 emu.g^-1, respectively. No hysteresis loop was detected in the magnetization curves of γ-Fe₂O₃ NPs (I) and exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) indicating the superparamagnetic feature of the nanoparticles.

The optical absorbance features of the magnetic photocatalyst were assessed using UV-Vis DRS. As it is evident in Fig. 7, exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) showed a highest absorption in the visible-light area. Besides, based on the Tauc plot of (αhν)² vs. hυ (Fig. 8), the value of the band gap energy for exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) was estimated to be 2.35 eV, which verified the high capability of the magnetic photocatalyst to boost the photoinduced electron-holes separation and enhances the visible-light performance of magnetic photocatalyst.

To illustrate transfer of electrons in photocatalytic reactions, the photoelectrochemical parameters including time photocurrent response (TPR) and electrochemical impedance spectrum (EIS) are recorded. Furthermore, EIS is an effective method to assess the ability of electron transmission. Generally, the large arc radius indicates the high ratio and the small arc radius indicates the low ratio of recombination of electron-hole pairs. In Fig. 9, exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) has minimum arc radius compared to γ-Fe₂O₃@ZnO (IV) yolk-shell, representing the best electron-hole separation effect.

As seen in Fig. 10, γ-Fe₂O₃@ZnO (IV) yolk-shell and (b) exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) illustrate the fast and steady instantaneous photocurrent under visible light irradiation. However, exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) shows higher density of instantaneous photocurrent in comparison with γ-Fe₂O₃@ZnO (IV) yolk-shell, representing the magnetic photocatalyst possesses the best electron-hole pairs separation effect.

Probing the performance of exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) in the degradation of Levofloxacin and Indigo Carmine

Levofloxacin and Indigo Carmine were selected as model pollutants and the photocatalytic activity of the prepared magnetic photocatalyst was tested for degrading these pollutants via employing various factors under visible light. Prior to proceeding with the photocatalytic experiment, some parameters, such as the initial concentration of Levofloxacin and Indigo Carmine, catalyst amount, and pH, were optimized accordingly, as demonstrated in Figs. 11 and 12. The unique catalytic behaviour of exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) in the degradation of Levofloxacin and Indigo Carmine was revealed by examining the standard reactions individually in the presence of γ-Fe₂O₃ NPs (I), γ-Fe₂O₃@ZnO (IV) yolk-shell, and g-C₃N₄ nanosheets. It is worth mentioning that, after continued reaction times, a considerable yield of Levofloxacin and Indigo Carmine degradation was not obtained (Figs. 11a and 12a).

In the beginning, the mixture of reactions was magnetically stirred for 60 min in the dark atmosphere to confirm an adsorption-desorption equilibrium between Levofloxacin, Indigo Carmine, and photocatalyst. After 60 min, 3 mL of the reaction mixture was taken from suspension, and then the magnetic photocatalyst was separated by an external magnet. Next, the results were investigated to evaluate the degradation of Levofloxacin and Indigo Carmine by means of a UV-vis spectrophotometer (Figs. 11b and 12b). As can be seen from these Figs, the best results were achieved by applying 0.6 g/L of magnetic photocatalyst to 50 mL of Levofloxacin and Indigo Carmine solution with a concentration of 10 mg/L at pH of 7. Considering the effect of pH, the pH variation of Levofloxacin and Indigo Carmine solution was done from pH 3 to 11 and then the degradation efficiency was studied. The critical variables such as the dose of photocatalyst and the concentration of Levofloxacin and Indigo Carmine remained constant at 0.6 g/L and 10 mg/L during the pH experimentation, respectively. As seen in Figs. 11c and 12c, the maximum photocatalytic degradation of Levofloxacin and Indigo Carmine was obtained at pH = 7 within 25 (80%) and 15 (95.6%) min, respectively.

Subsequently, the effect of loading of the magnetic photocatalyst on the photocatalytic degradation of Levofloxacin and Indigo Carmine was investigated (Figs. 11d and 12d). As can be observed from the degradation curve of Levofloxacin and Indigo Carmen, the best results were achieved by applying 0.6 g/L of the magnetic photocatalyst. Next, the effect of Levofloxacin and Indigo Carmen concentration with fixed pH and magnetic photocatalyst dose was investigated for additional degradation studies. Figures 11e and 12e clearly states the variation of Levofloxacin and Indigo Carmen concentration at 5, 10, and 20 g/L under visible light.

During the catalytic wastewater purification process, it is important to evaluate the reaction rate kinetics. Langmuir-Hinshelwood (L-H) kinetic model is applied to study the photocatalytic degradation kinetics of organic compounds, such as antibiotics. Furthermore, photocatalytic activity follows pseudo-first-order kinetics according to the L-H model, which is as follows:

ln (C₀/C_t) = kt

This is based on the pseudo-first-order rate constant k, the initial contamination concentration C₀, and the current contamination concentration C_t. The study of the kinetics of photocatalytic degradation of Levofloxacin in the presence of magnetic photocatalyst, g-C₃N₄ nanosheet and γ-Fe₂O₃@ZnO (IV) yolk-shell was done under the optimum conditions. Figure 13 shows the estimated degradation rate constants are 0.0246 min^− 1, 0.0194 min^− 1, and 0.0190 min^− 1, respectively, for γ-Fe₂O₃@ ZnO (IV) yolk-shell, g-C₃N₄ nanosheets and exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V).

Proposed photocatalytic mechanism for Levofloxacin photocatalytic degradation by exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V)

The influence of active radical species for photocatalytic degradation of Levofloxacin was examined by study of scavengers such as Na₂-EDTA (0.1 mol/L, as a hole scavenger), ascorbic acid (0.1 mol/L, as superoxide anion radical scavenger), and ethanol (0.1 mol/L, and as HO^• radical scavenger) under optimized conditions. As can be seen in Fig. 14, the efficiency of photocatalytic degradation of Levofloxacin using exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) was 80% at about 25 min without any scavenger. The photocatalytic degradation efficiency of Levofloxacin was moderately dropped by adding of ethanol into the reaction solution. On the other hand, the affected degradation efficiency of Levofloxacin decreased significantly by the addition of Na₂-EDTA (15%) and ascorbic acid (AC) (10%) to the medium of reaction. As a result, the holes and superoxide radicals are the key active species in the degradation of photocatalytic system. Based on the above results, the proposing photocatalytic mechanism for the Levofloxacin photocatalytic degradation in the presence of exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) under visible-light irradiation was presented (Scheme 2). Scheme 2 illustrated the electron-hole separation and the pathway of charge transfer. Under the Citizen COB LED Lamp irradiation, electrons and holes produced by exiting of g-C₃N₄ and γ-Fe₂O₃ NPs (I). Next, the photogenerated electrons from the conduction bond (CB) of g-C₃N₄ can be easily moved into the CB of γ-Fe₂O₃ NPs (I) and the existing electrons transferred from the CB of γ-Fe₂O₃ NPs (I) to the CB of ZnO. Moreover, the photogenerated holes in the valence bond (VB) of γ-Fe₂O₃ NPs (I) are injected into the VB of g-C₃N₄. Then, electrons in the CB of ZnO adsorb the molecules of oxygen from the solution to produce the superoxide radical ions, which are the effective oxidative species for the degradation of Levofloxacin. Therefore, the accumulated holes available in the VB of g-C₃N₄ react directly with the molecules of Levofloxacin.

Comparative Study

To illustrate the advantages of the proposed procedures over the earlier reported methods (Li et al. 2019; Wang et al. 2019; Abukhadra et al. 2020; Kamaraj et al. 2021) for photocatalytic degradation of Levofloxacin and Indigo Carmine, the efficiency of present magnetic photocatalyst was compared to previously reported catalytic systems (Tables 1 and 2).

It should be noted that in the present research, degradation of LEVO and IC was done under eco-friendly conditions. Moreover, the magnetic photocatalyst was separated from the mixture of reaction using a magnet with insignificant loss in its catalytic activity. It can clearly be seen that the present green photocatalytic system is superior to the reported method, while each of these photocatalytic systems has their own benefits. Additionally, the excellent photocatalytic reactivity of exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) may be attributed to the effect of synergistic optical between g-C₃N₄ nanosheets, γ-Fe₂O₃ NPs (I) and ZnO.

Table 1

Comparison of reaction factors with previously reported photocatalyst for the degradation of Levofloxacin.
Photocatalyst	Conditions	Removal (%)	Ref.
rGO-Bi₂WO₆	10 mg/L, 25 g/L dosage, pH 6, 120 min, CFL Bulb	69.01	Arya et al. 2020
Ni/SF-MCM-48	20 mg/L, 0.1 g/L dosage, pH 7, 40 min, Metal halide lamp	98	Abukhadra et al. 2021
MoS₂/C	70 mg/L, 0.01 g/L dosage, pH 7, 160 min, Xe lamp	97	Zeng et al. 2019
Reduced GO-CdS	10 mg/L, 0.25 g/L dosage, pH 9, 60 min, Oreva CFL bulb	76.8	Choi et al. 2019
Fe-BiOCl + PS	15 mg/L, 0.5 g/L dosage, pH 7, 60 min, 1 mM oxidant	57.8	Gao et al. 2016
Bi₂WO₆	10 mg/L, 0.75 g/L dosage, pH 7, 150 min, 150 W Philips CFL bulb	79	Matta et al. 2017
BiVO₄-CeVO₄	50 mg/L, 0.5 g/L dosage, pH 7, 5 h, 150 W Xenon lamp	95.7	Wu et al. 2019
(BiOBr)_x (Bi₇O₉I₃)_1-x	50 mg/L, 1 g/L dosage, pH 6, 120 min, 400 W halogen bulb	95.4	Manz et al. 2018
Ag/g-C₃N₄-Ag-Ag₃PO₄	50 mg/L, 1.0 g/L dosage, pH 5, 100 min, 300 W xenon lamp	90.44	Shin et al. 2019
exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V)	10 mg/L, 0.6 g/L dosage, pH 7, 25 min, 170 W Citizen COB LED Lamp	80	Present Study

Table 2

Comparison of reaction factors with previously reported photocatalyst for the degradation of Indigo Carmine.
Photocatalyst	Conditions	Removal (%)	Ref.
Zr:CuFe₂O₄	20 mg/L, 0.1 g/L dosage, pH 7,120 min, 150 W Tungsten halogen lamp	71	Dayana et al. 2022
ZnFe₂O₄/Tannin/ZnO	16 mg/L, 0.5 g/L dosage, pH 7, 90 min, 128 W UV light/visible	82/99	Güy et al. 2018
Bi-Zn-TiO₂	16 mg/L, 1 g/L dosage, pH 6.1, 70 min, 500 W tungsten lamp	99	Benalioua et al. 2015
organophilic clay	10 mg/L, 1 g/L dosage, pH 5.8, 160 min, 8 W UV-B lamp	99	Bentouami et al. 2010
CdS/TiO₂ QDs	10 mg/L, 1 g/L dosage, pH 7, 5 h, sunlight	99	Janbandhu et al. 2019
PAN/GO-ZnO	10 mg/L, 50 × 50 mm² dosage, pH 5, 27 min, 150 W visible light irradiation	98	Abdel-Mottaleb et al. 2019
exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V)	10 mg/L, 0.6 g/L dosage, pH 7, 15 min, 170 W Citizen COB LED Lamp	95.6	Present Study

Reusability of exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V)

Photocatalytic recyclability is an important parameter for reducing operating costs in practical applications. At least five regeneration cycles for photocatalytic degradation were performed for Levofloxacin and Indigo Carmine under optimal conditions to determine the reusability and durability of the exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V). After each run, a magnetic field was applied to separate the magnetic photocatalyst from the aqueous solution, rinsed three times with distilled water and ethanol, dried at 80 ºC for 5 h, and reused in the following run. Based on the results shown in Figs. 15 and 16, no significant changes in the photocatalytic reactivity of exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) were witnessed after five runs of recycling. The small decrease in Levofloxacin and Indigo Carmine degradation after five consecutive cycles may be because of the slight loss of photocatalyst during the process of recycling. In addition, a comparison of the FTIR spectra (Figs. 1g and 1h), XRD (Figs. 2d and 2e) and VSM techniques (Figs. 6c and 6d) of the magnetic recycled photocatalyst showed that neither the structure nor the morphology changed after five consecutive cycles. Accordingly, the presented magnetic photocatalyst has a high degree of stability and reusability.

To sum up, exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) has been found to illustrate environmental photocatalytic property in the degradation of organic pollutants in the aqueous phase at room temperature. According to spectroscopic and microscopic techniques, the magnetic photocatalyst has a spherical shape with an average particle size of 23–39 nm. Compared with γ-Fe₂O₃ NPs (I), γ-Fe₂O₃@ZnO (IV) yolk-shell, and g-C₃N₄ nanosheets, exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) demonstrate higher photocatalytic activity than a single part of the magnetic photocatalyst. Moreover, exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) was reused at least five times in the degradation process of Levofloxacin and Indigo Carmine without noticeable activity loss, respectively.

Acknowledgments

Maryam Sadat Ghasemzadeh was fully supported by a grant from Ferdowsi University of Mashhad (No.FUM-35754).

Contribution

Maryam Sadat Ghasemzadeh:Conceptualization, Methodology, Investigation, Writing –original draft,Writing – review & editing, Visualization. Ali Ahmadpour: Conceptualization, Review & editing, Supervision, Funding acquisition.

Availability of data and materials: Not applicable

Ethical approval: Not applicable

Consent to participate: Not applicable

Consent for publication: Agree to publish.

Competing interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Abukhadra MR, Fathallah W, El Kashief FA, El-Sherbeeny AM, El-Meligy MA, Awwad EM, Luqman M (2021) Insight into the antimicrobial and photocatalytic properties of NiO impregnated MCM-48 for effective removal of pathogenic bacteria and toxic levofloxacin residuals. Micropor Mesopor Mat 312:110769. https://doi.org/10.1016/j.micromeso.2020.110769
Abdel-Mottaleb MM, Khalil A, Karim S, Osman TA, Khattab A (2019) High performance of PAN/GO-ZnO composite nanofibers for photocatalytic degradation under visible irradiation. J Mech Behav Biomed Mater 96:118. https://doi.org/10.1016/j.jmbbm.2019.04.040
Abukhadra MR, Helmy A, Sharaf MF, El-Meligy MA, Soliman ATA (2020) Instantaneous oxidation of levofloxacin as toxic pharmaceutical residuals in water using clay nanotubes decorated by ZnO (ZnO/KNTs) as a novel photocatalyst under visible light source. J Environ Manage 271:111019. https://doi.org/10.1016/j.jenvman.2020.111019
Ammar S, Abdelhedi R, Flox C, Arias C, Brillas E (2006) Electrochemical degradation of the dye indigo carmine at boron-doped diamond anode for wastewaters remediation. Environ Chem Lett 4:229. https://doi.org/10.1007/s10311-006-0053-2
Ayati A, Ahmadpour A, Bamoharram FF, Heravi MM, Sillanpää M (2012) Rate redox-controlled green photosynthesis of gold nanoparticles using H_{3 + x}PMo_12-xV_xO₄₀. Gold Bull 45:145. https://doi.org/10.1007/s13404-012-0058-5
Ayati A, Ahmadpour A, Bamoharram FF, Tanhaei B, Mänttäri M, Lahtinen M, Sillanpää M (2014) Novel Au NPs/Preyssler acid/TiO₂ nanocomposite for the photocatalytic removal of azo dye. Sep Purif Technol 133:415
Arya M, Kaur M, Kaur A, Singh S, Devi P, Kumar Kansal S (2020) Hydrothermal synthesis of rGO-Bi₂WO₆ heterostructure for the photocatalytic degradation of levofloxacin. Opt Mater 107:110126. https://doi.org/10.1016/j.optmat.2020.110126
Ayati A, Tanhaei B, Bamoharram FF, Ahmadpour A, Maydannik P, Sillanpää M (2016) Photocatalytic degradation of nitrobenzene by gold nanoparticles decorated polyoxometalate immobilized TiO₂ nanotubes. Sep Purif Technol 171:62
Barka N, Assabbane A, Nounah A, Ichou YA (2008) Photocatalytic degradation of indigo carmine in aqueous solution by TiO₂-coated non-woven fibres. J Hazard Mater 152:1054. https://doi.org/10.1016/j.jhazmat.2007.07.080
Benalioua B, Mansour M, Bentouami A, Boury B, Elandaloussi EH (2015) The layered double hydroxide route to Bi-Zn co-doped TiO₂ with high photocatalytic activity under visible light. J Hazard Mater 288:158. https://doi.org/10.1016/j.jhazmat.2015.02.013
Bentouami A, Ouali MS, De Menorval LC (2010) Photocatalytic decolourization of indigo carmine on 1,10-phenanthrolinium intercalated bentonite under UV-B and solar irradiation. J Photochem Photobiol A: Chem 212:101. https://doi.org/10.1016/j.jphotochem.2010.04.002
Blokhina SV, Sharapova AV, Ol'khovich MV, Volkova TV, Perlovich GL (2016) Solubility, lipophilicity and membrane permeability of some fluoroquinolone antimicrobials. Eur J Pharm Sci 93:29. https://doi.org/10.1016/j.ejps.2016.07.016
Chakraborty P, Abraham J (2017) Comparative study on degradation of norfloxacin and ciprofloxacin by Ganoderma lucidum JAPC₁. Korean J Chem Eng 34:1122
Choi J, Chung J (2019) Evaluation of urea removal by persulfate with UV irradiation in an ultrapure water production system. Water Res 158:411. https://doi.org/10.1016/j.watres.2019.02.017
Chu M, Hu K, Wang J, Liu Y, Ali S, Qin C, Jing L (2019) Synthesis of g-C₃N₄-based photocatalysts with recyclable feature for efficient 2,4-dichlorophenol degradation and mechanisms. Appl Catal B: Environ 243:57
Dayana PN, Abel MJ, Inbaraj PFH, Sivaranjani S, Thiruneelakandan R, Joseph prince J (2022) Zirconium Doped Copper Ferrite (CuFe₂O₄) Nanoparticles for the enhancement of visible light-responsive photocatalytic degradation of rose bengal and indigo carmine dyes. J Clust Sci 33:1739. https://doi.org/10.1007/s10876-021-02094-5
Ding F, Yang D, Tong Z, Nan Y, Wang Y, Zou X, Jiang Z (2017) Graphitic carbon nitride-based nanocomposites as visible-light driven photocatalysts for environmental purification. Environ Sci Nano 4:1455. https://doi.org/10.1039/C7EN00255F
Dong G, Zhang Y, Pan Q, 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. https://doi.org/10.1016/j.jphotochemrev.2014.04.002
Ding R, Zhang P, Seredych M, Bandosz TJ (2012) Removal of antibiotics from water using sewage sludge-and waste oil sludge-derived adsorbents. Water Res 46:4081. https://doi.org/10.1016/j.watres.2012.05.013
Epold I, Trapido M, Dulova N (2015) Degradation of levofloxacin in aqueous solutions by Fenton, ferrous ion-activated persulfate and combined Fenton/persulfate systems. Chem Eng J 279:452. https://doi.org/10.1016/j.cej.2015.05.054
El Najjar NH, Touffet A, Deborde M, Journel R, Leitner NKV (2013) Levofloxacin oxidation by ozone and hydroxyl radicals: Kinetic study, transformation products and toxicity. Chemosphere 93:604
Gao M, Zhang D, Pu X, Li H, Li W, Shao X, Lv D, Zhang B, Dou J (2016) Combustion synthesis of Fe-doped BiOCl with high visible-light photocatalytic activities. Sep Purif Technol 162:114
Gao C, Wang J, Xu H, Xiong Y (2017) Coordination chemistry in the design of heterogeneous photocatalysts. Chem Soc Rev 46:2799. https://doi.org/10.1039/C6CS00727A
Ghasemzadeh MS, Akhlaghinia B, Ghasemzadeh MS, Akhlaghinia B (2019) Pd^II immobilized on ferromagnetic multi-walled carbon nanotubes functionalized by aminated 2-chloroethylphosphonic acid with S-methylisothiourea (FMMWCNTs@CPA@SMTU@Pd^II NPs) applied as a highly efficient and recyclable nanostructured catalyst for Suzuki-Miyaura and Mizoroki-Heck cross-coupling reactions in solvent-free conditions. Aust J Chem 72:674. https://doi.org/10.1071/CH19117Ghasemzadeh MS, Akhlaghinia B (2017) 2-Aminoethanesulfonic acid immobilized on epichlorohydrin functionalized Fe₃O₄@WO₃ (Fe₃O₄@WO₃-EAE-SO₃H): a novel magnetically recyclable heterogeneous nanocatalyst for the green one-pot synthesis of 1-Substituted-1H-1,2,3,4-Tetrazoles in water. Bull Chem Soc Jpn 90:1119. https://doi.org/10.1246/bcsj.20170148 Ghasemzadeh MS, Akhlaghinia B (2018) γ-Fe₂O₃@SiO₂-EC-Zn^II: A Magnetic recyclable nanocatalyst for the synthesis of Spiro[indoline-3,9’-xanthene]trione derivatives in aqueous media. ChemistrySelect 3:3161. https://doi.org/10.1002/slct.201703189
Ghasemzadeh MS, Akhlaghinia B (2019) FMMWCNTs@CPA@SMTU@Pd^II NPs: as a versatile ferromagnetic nanostructured catalyst for Sonogashira-Hagihara cross-coupling reaction in solvent-free conditions. ChemistrySelect 4:1542. https://doi.org/10.1002/slct.201803453
Ghasemzadeh MS, Akhlaghinia B (2020) An eco-friendly and efficient approach for the synthesis of Tetrazoles via Fe₃O₄/HT-GLYMO-TA as a new recoverable heterogeneous nanostructured catalyst. ChemistrySelect 5:6440. https://doi.org/10.1002/slct.202000641
Ghasemzadeh MS, Akhlaghinia B (2019) C-P bond construction catalyzed by Ni^II immobilized on aminated Fe₃O₄@TiO₂ yolk-shell NPs functionalized by (3-glycidyloxypropyl)trimethoxysilane (Fe₃O₄@TiO₂ YS-GLYMO-UNNi^II) in green media. New J Chem 43:5341
Gong Y, Li J, Zhang Y, Zhang M, Tian X, Wang A (2016) Partial degradation of levofloxacin for biodegradability improvement by electro-Fenton process using an activated carbon fiber felt cathode. J Hazard Mater 304:320. https://doi.org/10.1016/j.jhazmat.2015.10.064
Güy N, Özacar M (2018) Visible light-induced degradation of indigo carmine over ZnFe₂O₄/Tannin/ZnO: Role of tannin as a modifier and its degradation mechanism. Int J Hydrog Energy 43:8779. https://doi.org/10.1016/j.ijhydene.2018.03.114
Heidari S, Haghighi M, Shabani M (2018) Ultrasound assisted dispersion of Bi₂Sn₂O₇-C₃N₄ nanophotocatalyst over various amount of zeolite Y for enhanced solar-light photocatalytic degradation of tetracycline in aqueous solution. Ultrason Sonochem 43:61. https://doi.org/10.1016/j.ultsonch.2018.01.001
Hong Y, Li C, Zhang G, Meng Y, Yin B, Zhao Y, Shi W (2016) Efficient and stable Nb₂O₅ modified g-C₃N₄ photocatalyst for removal of antibiotic pollutant. Chem Eng J 299:74. https://doi.org/10.1016/j.cej.2016.04.092
Janbandhu SY, Joshi A, Munishwar SR, Gedam RS (2019) CdS/TiO₂ heterojunction in glass matrix: Synthesis, characterization, and application as an improved photocatalyst. Appl Surf Sci 497:143758. https://doi.org/10.1016/j.apsusc.2019.143758
Jechalke S, Heuer H, Siemens J, Amelung W, Smalla K (2014) Fate and effects of veterinary antibiotics in soil. Trends in Microbiol 22:536
Kamaraj P, Sridharan M, raj V, Arockiaselvi J, Pushpamalini T, Vivekanand PA (2021) Low cost synthesis of ZnO nanoparticles and evaluation of their photocatalytic activity. Mater Today: Proc 36:873. https://doi.org/10.1016/j.matpr.2020.07.021
Kou J, Lu C, Wang J, Chen Y, Xu Z, Varma RS (2017) Selectivity enhancement in heterogeneous photocatalytic transformations. Chem Rev 117:1445. https://doi.org/10.1021/acs.chemrev.6b00396
Li J, Dong X, Zhang G, Cui W, Cen W, Wu Z, Lee SC, Dong F (2019) Probing ring-opening pathways for efficient photocatalytic toluene decomposition. J Mater Chem A 7:3366
Liu Z, Tian J, Yu C, Fan Q, Liu X, Yang K, Zeng J, Ji H (2019) Ultrasonic fabrication of SO₄^-2 doped g-C₃N₄/Ag₃PO₄ composite applied for effective removal of dyestuffs and antibiotics. Mater Chem Phys 240:122206. https://doi.org/10.1016/j.matchemphys.2019.122206
Liu X, Yang D, Zhou Y, Zhang J, Luo L, Meng S, Chen S, Tan M, Li Z, Tang L (2017) Electrocatalytic properties of N-doped graphite felt in electro-Fenton process and degradation mechanism of levofloxacin. Chemosphere 182:306. https://doi.org/10.1016/j.chemosphere.2017.05.035
Li F, Zhu P, Wang S, Xu X, Zhou Z, Wu C (2019) One-pot construction of Cu and O co-doped porous g-C₃N₄ with enhanced photocatalytic performance towards the degradation of levofloxacin. RSC Adv 9:20633. https://doi.org/10.1039/C9RA02411E
Liu J, Wang H, Antonietti M (2016) Graphitic carbon nitride “reloaded”: emerging applications beyond (photo)catalysis. Chem Soc Rev 45:2308
Manz KE, Adams TJ, Carter KE (2018) Furfural degradation through heat-activated persulfate: impacts of simulated brine and elevated pressures. Chem Eng J 353:727. https://doi.org/10.1016/j.cej.2018.07.142
Mahmoodi V, Ahmadpour A, Rohani Bastami T, Taghi M, Mosavian H (2018) PVP assisted synthesis of high efficient BiOI/Graphene oxide nanohybrid and its photocatalytic performance in degradation of organic dye pollutants. Sol Energy 176:483. https://doi.org/10.1016/j.solener.2018.10.056
Ma Y, Chen Y, Feng Z, Zeng L, Chen Q, Jin R, Lu Y, Huang Y, Wu Y, He Y (2017) Preparation, characterization of Bi. Compos its photocatalytic activity dye Degrad J Water Process Eng 18:65
Matta R, Younes H, Hanna R, Saab J, Abou-Khalil R (2019) Sulfate radicals mediated oxidation of amoxicillin: optimization of key parameters. J Environ Manage 245:375
Naseri A, Samadi M, Pourjavadi A, Moshfegh AZ, Ramakrishna S (2017) Graphitic carbon nitride (g-C₃N₄)-based photocatalysts for solar hydrogen generation: recent advances and future development directions. J Mater Chem A 5:23406
Ong WJ, Tan LL, Ng YH, Yong ST, Chai ST (2016) Graphitic Carbon Nitride (g-C₃N₄)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer to Achieving Sustainability? Chem Rev 116:7159. https://doi.org/10.1021/acs.chemrev.6b00075
Palanivel B, Jayaraman V, Ayyappan C, Alagiri M (2019) Magnetic binary metal oxide intercalated g-C. Energy band tuned p-n heterojunction towards Z-scheme photo-Fenton phenol reduction and mixed dye degradation J Water Process Eng 32:100968
Pastrana-Martinez LM, Morales-Torres S, Kontos AG, Moustakas NG, Faria JL, Dona-Rodriguez JM, Falaras P, Silva AMT (2013) TiO₂, surface modified TiO₂ and graphene oxide-TiO₂ photocatalysts for degradation of water pollutants under near-UV/Vis and visible light. Chem Eng J 224:17. https://doi.org/10.1016/j.cej.2012.11.040
Pavithra KG, Senthil Kumar P, Sundar Rajan P, Saravanan A, Naushad M (2017) Sources and impacts of pharmaceutical components in wastewater and its treatment process: a review. Korean J Chem Eng 34:2787. https://doi.org/10.1007/s11814-017-0255-2
Rad LR, Irani M, Barzegar R (2015) Adsorptive removal of acetaminophen and diclofenac using NaX nanozeolites synthesized by microwave method. Korean J Chem Eng 32:1606. https://doi.org/10.1007/s11814-014-0373-z
Rohani Bastami T, Ahmadpour A (2016) Preparation of magnetic photocatalyst nanohybrid decorated by polyoxometalate for the degradation of a pharmaceutical pollutant under solar light. Environ Sci Pollut Res 23:8849. https://doi.org/10.1007/s11356-015-5985-2
Rohani Bastami T, Ahmadpour A, Ahmadi Hekmatikar F (2017) Synthesis of Fe₃O₄/Bi₂WO₆ nanohybrid for the photocatalytic degradation of pharmaceutical ibuprofen under solar light. J Ind Eng Chem 51:244–254
Sarmah AK, Meyer MT, Boxall ABA (2006) A global perspective on the use, sales, exposure pathways, occurrence, fate and effects of veterinary antibiotics (VAs) in the environment. Chemosphere 65:725. https://doi.org/10.1016/j.chemosphere.2006.03.026
Sobhani S, Ghasemzadeh MS, Honarmand M (2014) Piperidine and piperazine immobilized on iron oxide nanoparticles as magnetically recyclable heterogeneous catalysts for one-pot synthesis of β-Phosphonomalonates. Catal Lett 144:1515. https://doi.org/10.1007/s10562-014-1297-2
Sobhani S, Ghasemzadeh MS, Honarmand M, Zarifi F (2014) Acetamidine-palladium complex immobilized on γ-Fe₂O₃ nanoparticles: a novel magnetically separable catalyst for Heck and Suzuki coupling reactions. RSC Adv 4:44166. https://doi.org/10.1039/C4RA04830J
Shin YU, Yoo HY, Ahn YY, Kim MS, Lee K, Yu S, Lee C, Cho K, Kim HI, Lee J (2019) Electrochemical oxidation of organics in sulfate solutions on borondoped diamond electrode: multiple pathways for sulfate radical generation. Appl Catal B: Environ 254:156
Sturini M, Speltini A, Maraschi F, Pretali L, Profumo A, Fasani E, Albini A, Migliavacca R, Nucleo E (2012) Photodegradation of fluoroquinolones in surface water and antimicrobial activity of the photoproducts. Water Res 46:5575. https://doi.org/10.1016/j.watres.2012.07.043
Sultan M, Mansor ES, Nagieb ZA, Elsayed H (2021) Fabrication of highly efficient nano-composite films based on ZnO-g-C₃N₄@ PAA-g-(HEC/PVA)-Fe³⁺ for removal of methylene blue dye from water. J Water Process Eng 42:102184. https://doi.org/10.1016/j.jwpe.2021.102184Wang X, Meng J, Yang X, Hu A, Yang Y, Guo Y (2019) Fabrication of Perylene Tetracarboxylic Diimide Graphitic Carbon Nitride Heterojunction Photocatalyst for Efficient Degradation of Aqueous Organic Pollutants. ACS Appl Mater Interfaces 11:588. https://doi.org/10.1021/acsami.8b15122
Wei H, Hu D, Su J, Li KB (2015) Intensification of levofloxacin sono-degradation in a US/H₂O₂ system with Fe₃O₄ magnetic nanoparticles. Chin J Chem Eng 23:296. https://doi.org/10.1016/j.cjche.2014.11.011
Witte BD, Van Langenhove H, Hemelsoet K, Demeestere K, De Wispelaere P, Van Speybroeck V, Dewulf J (2009) Levofloxacin ozonation in water: rate determining process parameters and reaction pathway elucidation. Chemosphere 76:683. https://doi.org/10.1016/j.chemosphere.2009.03.048
Wu H, Xu X, Shi L, Yin Y, Zhang LC, Wu Z, Duan X, Wang S, Sun H (2019) Manganese oxide integrated catalytic ceramic membrane for degradation of organic pollutants using sulfate radicals. Water Res 167:115110. https://doi.org/10.1016/j.watres.2019.115110
Xu J, Zhang L, Shi R, Zhu Y (2013) Chemical exfoliation of graphitic carbon nitride for efficient heterogeneous photocatalysis. J Mater Chem A 1:14766. https://doi.org/10.1039/C3TA13188B
Yao X, Liu X, Hu X (2014) Synthesis of the Ag/AgCl/g-C₃N₄ composite with high photocatalytic activity under visible light irradiation. ChemCatChem 6:3409
Yan W, Xiao Y, Yan W, Ding R, Wang S, Zhao F (2019) The effect of bioelectrochemical systems on antibiotics removal and antibiotic resistance genes: A review. Chem Eng J 358:1421. https://doi.org/10.1016/j.cej.2018.10.128
Ye S, Wang R, Wu M, Yuan Y (2015) A review on g-C₃N₄ for photocatalytic water splitting and CO₂ reduction. Appl Surf Sci 358:15. https://doi.org/10.1016/j.apsusc.2015.08.173
Yin S, Han J, Zhou T, Xu R (2015) Recent progress in g-C₃N₄ based low cost photocatalytic system: activity enhancement and emerging applications. Catal Sci Technol 5:5048. https://doi.org/10.1039/C5CY00938C
Yuan WH, Yang S, Li L (2015) Synthesis of g-C₃N₄/CaIn₂S₄ composites with enhanced photocatalytic activity under visible light irradiation. Dalton Trans 44:16091. https://doi.org/10.1039/C5DT02439K
Zeng L, Li S, Li X, Li J, Fan S, Chen X, Yin Z, Tadé M, Liu S (2019) Visible-light-driven sonophotocatalysis and peroxymonosulfate activation over 3D urchin-like MoS₂/C nanoparticles for accelerating levofloxacin elimination: Optimization and kinetic study. Chem Eng J 378:122039. https://doi.org/10.1016/j.cej.2019.122039
Zeng L, Li X, Shi Y, Qi Y, Huang D, Tade M, Wang S, Liu S (2017) FePO₄ based single chamber air-cathode microbial fuel cell for online monitoring levofloxacin. Biosens Bioelectron 91:367. https://doi.org/10.1016/j.bios.2016.12.021
Zhao H, Wu LC, Xu HY (2016) Adsorption and photocatalysis of organic dyes by g-C₃N₄ in situ doped with S. Sci Adv Mater 8:1408. https://doi.org/10.1166/sam.2016.2731
Zhang J, Lin H, Ma J, Sun W, Yang Y, Zhang X (2019) Compost-bulking agents reduce the reservoir of antibiotics and antibiotic resistance genes in manures by modifying bacterial microbiota. Sci Total Environ 649:396
Zheng Y, Lin L, Wang B, Wang X (2015) Graphitic carbon nitride polymers toward sustainable photoredox catalysis. Angew Chem Int Ed 54:12868. https://doi.org/10.1002/anie.201501788
Zhao Z, Sun Y, Dong F (2015) Graphitic carbon nitride based nanocomposites: a review Nanoscale 7:15. https://doi.org/10.1039/C4NR03008G

Schemes 1 and 2 are available in the Supplementary Files section

Scheme1.jpg
Scheme 1 The preparation of exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V).
Scheme2.png
Scheme 2 Proposed photocatalytic mechanism for Levofloxacin photocatalytic degradation by exfoliated g-C₃N₄/γ-Fe₂O₃/ZnO yolk-shell NPs (V) under Citizen COB LED Lamp irradiation.

Download PDF