Magnetic nano-biocomposite CuFe 2 O 4 @ methylcellulose ( MC ) prepared as a new nano-photocatalyst for degradation of ciprofloxacin from aqueous solution

Background: Antibiotics such as ciprofloxacin (CIP) are even more important in bacterial resistance, even at low concentrations. The aim of this research was to synthesize CuFe2O4@methylcellulose (MC) as a new nano-photocatalyst for degradation of CIP from aqueous solution. Methods: The nano-photocatalyst (CuFe2O4@MC) was characterized by FESEM, energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), and vibrating sample magnetometer (VSM). Powder XRD and EDS analysis confirmed the formation of pure-phase spinel ferrites. After CuFe2O4@MC characterization, the effective parameters in removal efficiency of CIP such as reaction time, initial antibiotic concentration, pH, photocatalyst loading, and degradation kinetic were investigated and conditions were optimized. Then, CIP degradation experiments were conducted on the real sample in the optimal conditions. The removal of chemical oxygen demand (COD) was determined under optimum conditions. Results: The structural characterization of the magnetic nanobiocomposite showed that it is in nanoscale, ferromagnetic property, and thermal stability. The optimal conditions were obtained at pH = 7, irradiation time (90 minutes), photocatalyst loading (0.2 g), and initial concentration of CIP (3 mg/L). The removal efficiency of CIP in the optimal conditions was obtained as 80.74% and 72.87% from the synthetic and real samples, respectively. The removal of COD was obtained as 68.26% in this process. The evaluation of kinetic linear models showed that the photocatalytic degradation process was fitted by pseudo-first order kinetic model and Langmuir-Hinshelwood. CuFe2O4@MC photocatalyst had a good stability and reusability for the fourth runs. Conclusion: The photocatalytic degradation of CIP from aqueous media with CuFe2O4@MC photocatalyst has a high efficiency, which can be used in the treatment of pharmaceutical wastewaters.


Introduction
Today, the use of drugs, especially antibiotics, is increasing.About 100 000-200 000 tons of antibiotics are produced annually (1).This high level of consumption has led to the entrance of their residues into the environment and caused many problems in this regard (2).The presence of antibiotics in the environment has resulted in drug resistance in humans, as well as an effect on non-target pathogens, the structural alteration of algae in aquatic resources, and the interference with the photosynthesis of plants (3).The use of antibiotics in human sector, including parts of the services, hospitals, industry, households, as well as the livestock sector, in which antibiotics are used in the form of medicines or supplements for poultry and aquatic animals, is the main source of entrance of these compounds into the environment (4).Although these compounds enter the water or sewage treatment plants through the above-mentioned sources, but due to the inadequacy of conventional purification technologies, they can return to the environment (5).Studies have shown that most antibiotics are metabolized in the body, and the remaining, about 30-90%, are evacuated into the sewage system without being metabolized (6).Ciprofloxacin (CIP) is a fluoroquinolones antibiotic, with a broad spectrum bactericidal activity, which is widely used in hospitals to treat bacterial infections.This antibiotic is highly soluble in water and 25% of it is absorbed by the body and the remaining is excreted into the sewage system, in addition, it has sustainability in the environment and contaminates surface and underground water (7).CIP was detected in wastewater and surface water (<1 g/L), hospital wastewater (>150 g/L), and pharmaceutical factory (about 30 mg/L).This antibiotic can be adsorbed in the sludge at a concentration of 42.2 mg/kg (8).In order to remove CIP and other antibiotics, various physical, chemical, and biological methods have been used, including membrane separation (9), ionexchange resin (10), nanofiltration (11), oxidation (12), and adsorption (13,14).In general, it can be said that most of these methods have not been cost-effective due to the lack of complete degradation of contaminants, as well as low efficiency, high cost of investment and management, and difficult maintenance (15).Recently, advanced oxidation processes (AOPs), such as ozonation (16), fenton (17), and the use of different photocatalysts (18,19), have been considered and used to reduce the contamination caused by the presence of drug residues and other pollutants in water and environment (20).In the AOPs, radical hydroxyl is produced, which can lead to the oxidation and mineralization of many organic molecules into CO 2 and mineral ions (21).Photocatalytic technology, a green process, has shown great potential for environmental protection.The as-prepared photocatalysts are mainly in the form of powders dispersed in an aqueous solution and are difficult to separate from the treated water after degradation pollutants, which could generate waste and secondary pollution.It is of great importance to design new, very active, and easily recoverable photocatalyst.Thus, the improvement of recyclable kinds of photocatalysts has become the focus of current research.Due to the small size, optical and photocatalytic properties, nanoscale photocatalysts will have a proper efficiency in the degradation of various pollutants.Nanoscale photocatalysts has a larger surface to volume ratio, and are easily dispersed in an aqueous medium, thus, photocatalyst efficiency increases (22).Also, ferrite-based catalysts with high oxidation and radical hydroxyl ( • OH) generation in photocatalytic processes can decompose a wide range of organic pollutants (23).Recently, CuFe 2 O 4 has received attention as a multi-use compound due to its various advantages such as stability, monodispersity, low-cost, high photochemical stability, simplicity, and rapid separation over other catalysts for the pollutants degradation (24)(25)(26)(27)(28)(29)(30)(31).Magnetic photocatalytic properties provide a convenient way for separation of the photocatalyst from suspension.CuFe 2 O 4 has mostly been used for photocatalytic degradation of organic effluents in the presence of oxidants, such as hydrogen peroxide (H 2 O 2 ).Oxidants are used to accelerate the photocatalytic process, but they are not cost-effective (32,33).Here, CuFe 2 O 4 @methylcellulose (MC) was prepared via a microwave method as a new magnetic nanobiocomposite photocatalysts.These composites were synthesized for the first time in the water treatment for degradation of CIP without oxidant.In addition, the as-prepared magnetic nanobiocomposite has excellent magnetic properties and could be recycled by magnet and reused for the fourth runs.

Materials and Methods
FeCl 3 .6H 2 O, CuCl 2 .2H 2 O, NaOH, and MC were purchased from Merck Company.All the chemicals were of analytical grade and used as received without further purification.Deionized water was used throughout the experiment.CIP with a purity of 99% was purchased from Tamad Pharmaceutical Company (Tehran, IRAN).Table 1 shows the structure and properties of CIP used in this study.
Preparation of nano-biomagnetic CuFe 2 O 4 @MC FeCl 3 .6H 2 O and CuCl 2 .2H 2 O with molar ratio of 2:1 were co-dissolved in 50 mL deionized water to get a mixed solution.Afterwards, MC (1 g) was added to the obtained solution under constant stirring and then, sodium hydroxide was added at room temperature under mechanical stirring during an hour.The dark brown solution was subjected to microwave irradiation (3×5 min at 450 W), then, lightweight massive powder formed quickly.The precipitate nano-biomagnetic was washed several times with deionized water and the final product was dried in a vacuum oven at 100 °C for 24 hours.
Analysis and characterization of nano-biomagnetic CuFe 2 O 4 @MC The microstructure, morphology, and chemical composition of CuFe 2 O 4 @MC were investigated by FESEM-EDS (MIRA3TESCAN-XMU).The magnetic properties of CuFe 2 O 4 @MC were characterized by VSM (Lake Shore Cryotronics-7404) at room temperature.Thermal stability was evaluated through thermogravimetric analysis (TGA) by STA (PC Luxx 409-NETZSCH) instrument at rate of 10 °C min -1 in air.X-ray diffraction (XRD) of the CuFe 2 O 4 @MC was recorded in the diffraction angle range of 2θ = 15-70 ° by an X'Pert PRO MPD PANalitical using Ni-FILTERED Cu Kα radiation.The concentration of the CIP in solution was measured using a UV spectrophotometer (UV-1800 Shimadzu, Japan) at λ max = 276 nm.The pH of the solution was measured using a pH meter (HANNA, Japan).To generate UV-C radiation, three 6 W Philips lamps (Philips, the Netherlands) were used.The CIP concentration in the real wastewater was measured by an HPLC device (Waters E600, USA) using a column with the properties of C 8 ; 259 × 4.6 × 5 mm with UV detector at a wavelength of 272 nm with a hybrid mobile phase HCl 10 micro molar as well as acetonitrile (80:20 v/v), and input flow rate of 1 mL/ min.Chemical oxygen demand (COD) was measured by a spectrophotometer (Shimadzu, Japan).
To perform the photocatalytic degradation process, a photoreactor was designed and applied as shown in Figure 1.A plexiglass closed rectangular cube (25 × 10 × 5 cm) was used.The solution volume was 300 mL.Three ultraviolet lamps (UV-C: 6 W) with low pressure were installed at the top of the photoreactor.The height of the lamp above the rector was 5 cm.The reactor was designed in a way that there was a minimum distance between the catalyst surface and the radiation source to produce more radical hydroxyl by catalytic stimulation.For mixing the solution, a peristaltic pump was used at a flow rate of 1 mL/s.The photocatalytic activity of CuFe 2 O 4 @MC was tested for the degradation of CIP in aqueous solution in a photocatalytic reactor.The suspension of photocatalyst and CIP solution was transferred into a self-designed plexiglass reactor, and stirred in darkness to attain the adsorption equilibrium.Then, the mixture was placed inside the photoreactor.Aliquots of the mixture were taken at periodic intervals during the irradiation, and after separation of photocatalyst by a magnet, they were analyzed with the UV-Vis spectrometer.The CIP degradation percentage was calculated as equation (1).CIP degradation (%) = 100(C 0 -C t )/C 0 (1) where C t and C 0 show the attained absorbance value of the CIP solution at different minute periods of time (t) and zero min by a UV-Vis spectrometer, respectively.HCl and NaOH solutions (0.1 N) were used for adjusting pH.The effects of different concentrations of antibiotics (3, 5, 7, and 9 mg/L), pHs (3, 7, and 11), amounts of photocatalysts (0.025, 0.05, 0.1, 0.2, 0.3, and 0.4 g), and irradiation times (15,30,45,60,75, and 90 minutes) were investigated in the presence of UV-C lamp on the antibiotic removal efficiency.During the research stages, the investigated parameters were optimized.

Results
Characterization of CuFe 2 O 4 @MC At first, CuFe 2 O 4 @MC was prepared by following a new microwave-assisted method.To characterize the given nano-biomagnetic catalyst, various techniques have been employed.Figure 2 shows the FESEM images of CuFe 2 O 4 @ MC.
To investigate the chemical composition and purity of the as-synthesized magnetic nano-biocomposite CuFe 2 O 4 @ MC, the energy dispersive spectroscopy (EDS) technique was employed (Figure 3). Figure 4 shows the XRD pattern of the magnetic nano-biocomposite CuFe 2 O 4 @MC.
The magnetic properties of the CuFe 2 O 4 @MC were evaluated by vibrating sample magnetometer (VSM) at room temperature (Figure 5).The VSM magnetization  curve of CuFe 2 O 4 @MC proved ferromagnetism.
Given that the importance of the thermal stability of photocatalysts at large-scale reactions, the TGA of the CuFe 2 O 4 @MC was performed at temperature of 25 to 800 °C at a rate of 10 °C min -1 (Figure 6).The comparative KBr disc FT-IR spectra of the CuFe 2 O 4 @ MC and pure MC at 500-4000 cm -1 is show in Figure 7.
Comparison of photolysis, adsorption, and photocatalytic processes in the removal of CIP The results of the photolysis, adsorption, and photocatalytic process by CuFe 2 O 4 @MC are shown in Figure 8.
Effect of the initial concentration of CIP According to Figure 9, the rate of degradation decreased by increasing the initial concentration of antibiotics.The effect of initial concentration of contaminants on the       performance of photocatalytic process was significant.

Effect of photocatalyst loading
In photocatalytic processes, the effect of CuFe 2 O 4 @MC loading (0.025-0.4 g) on the removal of CIP in laboratory conditions (CIP concentration: 3 mg/L, pH = 7, reaction time: 90 minutes) was investigated.Figure 8 shows the effect of different amounts of photocatalyst on the photocatalytic degradation of CIP (Figure 10).
Changes of CIP absorption peak intensity vs. irradiation time in the presence of CuFe 2 O 4 @MC Figure 11 shows the changes of CIP absorption intensity during the photocatalytic process vs. irradiation time.The absorption peak of CIP was λ max = 276 nm.
Effect of pH on CIP degradation One of the important factors in photocatalytic processes is pH, which can affect the level of ionization of the material in the solution and the structure of the pollutant molecules by changing the surface charge of the adsorbent.CIP degradation by the photocatalytic process at different pHs is shown in Figure 12.

Reusability of CuFe 2 O 4 @MC
To examine the stability of photocatalyst, recycling experiments were performed and the results are presented in Figure 13.For each new cycle, photocatalysts were reused for the degradation of a fresh CIP solution under similar conditions after separation of the photocatalyst samples from CIP solution by a magnet.It was easily removed from CIP by washing with deionized water and ethanol, and dried.Removal Efficiency (%)

Cycle
Removal of chemical oxygen demand In optimal conditions (CuFe 2 O 4 @MC dosage: 0.2 g, CIP concentration: 3 mg/L, pH = 7, and reaction time: 90 minutes), the removal of COD was investigated.The results are shown in Figure 14.

Examination on real sample
The physicochemical characteristics of wastewater obtained from Kerman University of Medical Sciences, Iran, are reported in Table 2.By examining the real wastewater sample obtained from the synthetic sample under the optimal conditions, a CIP removal efficiency of 72.87% was obtained.The growth of intervening factors (TSS, COD, etc) causes turbidity in the solution, prevents the penetration of UV radiation, and subsequently, decreases the photocatalytic degradation rate of CIP.

Discussion
To characterize the given nano-biomagnetic catalyst, various techniques have been employed.Figure 2 shows the FESEM images of CuFe 2 O 4 @MC.The images show the formation of powder consisting of particles with an average size of about 22 nm.As shown in Figure 2, the nano-biomagnetic covers the surface smoothly, uniformly, and compactly, which are loosely aggregated.EDS spectrum of CuFe 2 O 4 @MC reveals the presence of Cu (6.38% W), Fe (90.01%W), O (2.34% W), and C (1.27% W) as expected amounts for the sample that confirms the chemical structure of this nano-biocomposite (Figure 3).According to the XRD pattern (Figure 4), the peak position and relative intensity of all diffraction peaks for the product matched well with standard powder diffraction data.All the diffraction peaks in the XRD pattern can be indexed to those of the tetragonal structure of copper ferrite (CuFe 2 O 4 ) according to JCPDS file No. 34-0425.Room temperature specific magnetization (M) versus applied magnetic field (H) curve measurement of the CuFe 2 O 4 @MC (Figure 5) indicates that the values of coercive force (Hc), saturation magnetization (Ms), and remanent magnetization (Mr) are 4.46 Oe, 17.44 emu/g, and 0.28 emu/g, respectively.All these confirms enough magnetization for simple separation by the external magnetic field.CuFe 2 O 4 @MC uniformly dispersed in CIP solution as shown in Figure 5.After completing the process, CuFe 2 O 4 @MC photocatalyst was easily separated from the CIP solution under the external magnetic field that can be recycled and reused for future runs.
The TGA pattern shows an initial weight loss attributed to water desorption at 100 °C, and no further loss of mass is detected up to 600 °C, all these confirm the high thermal stability of CuFe 2 O 4 @MC (Figure 6).The comparative FT-IR spectra of the CuFe 2 O 4 @MC and pure MC show absorption bands of O-H stretching at 3472.48 cm -1 , C-H stretching at >3000 cm -1 , adsorbed water stretching at 1646.91 cm -1 , C-H bending of  methylene and methyl groups at 1458.17 cm -1 and 1376.04 cm -1 , respectively, and C-O stretching at 1100-1150 cm -1 for MC (Figure 7a).In the FT-IR spectrum of CuFe 2 O 4 @ MC (Figure 7b), the broad peak at 3420.81 cm -1 was caused by the stretching modes of overlapped OH with aliphatic C-H stretching; the peak at 1636.53 cm -1 was due to the adsorbed surface water; and the vibration mode of CH 3bending was observable at 1384.46 cm -1 .Two main metaloxygen bands in the spinel ferrites were located below 1000 cm -1 .In the synthesized CuFe 2 O 4 @MC, the highest one (υ 1 ) was observed at 592.01 cm -1 .υ 1 is assigned to the intrinsic stretching vibrations of the metal cation at the tetrahedral site M tetra -O.The lowest one (υ 2 ) was observed at 589.41 cm -1 , while υ 2 corresponds to the metal cation at the octahedral site M octa -O.Three photolysis, adsorption, and photocatalytic processes have effects on the CIP removal (Figure 8).The removal efficiency in the photolysis process by UV and adsorption by CuFe 2 O 4 @MC was low, which was 10.11% and 17.6% in 90 minutes.The removal efficiency in the 90-minute period was 80.77% in photocatalytic process, it can be concluded that higher removal efficiency of CoFe 2 O 4 @ MC for CIP is due to the photocatalytic mechanism versus photolysis and adsorption processes, which is consistent with the results of the study of Khan et al (34).The removal efficiency changed from 80.76 to 44.02% by increasing the concentration of CIP from 3 to 9 mg/L during 90 minutes (Figure 9).Increasing the initial concentration leads to a reduction in the UV light penetration into the photocatalyst surface.Photocatalyst excitation and hydroxyl radicals were reduced.Other reasons can be the production of by-products during the process.These by-products compete with the initial concentration of antibiotics in contact with the catalyst, which leads to a decrease in the CIP degradation (35,36).Also, by increasing the initial concentration of antibiotics, more photons are absorbed by CIP and are less involved in photocatalytic process (34), which is consistent with the results of the study of Sayed et al (37).
The results showed that by increasing the amount of photocatalyst up to 0.2 g, the removal efficiency was significantly increased (Figure 10).At higher doses, the removal efficiency ranged from 80.76 to 81.6%, and the dose of 0.2 g was used as an optimal amount for preventing the use of additional photocatalyst.By increasing the dose of photocatalyst, the removal efficiency was raised due to an increase in the active adsorption sites of CIP and radical hydroxyl production (38,39).An increase in the amount of photocatalyst from 0.2 to 0.4 g, due to the turbidity created in the solution, results in a decrease in UV radiation and also a decrease in the radical production of hydroxyl (40).The study of Padmapriya et al confirmed the results of the photocatalyst loading in the present research (41).Absorption peak intensity declined over time (Figure 11), indicating the rate of CIP degradation by photocatalyst vs. irradiation time.The effect of irradiation time on the CIP removal by increasing the time was due to the production of • OH during the process (42), which was more than 80% in 90 minutes.pH can have a great effect on the removal of organic and inorganic substances from aqueous solutions (43).The rate of CIP removal raised by increasing pH from acidic to neutral pH and declined at pH 11.At pH 7, 80.8% of CIP was removed in 90 minutes (Figure 12).The reason for the high removal efficiency of CIP at pH 7 is that the CIP molecule has a pH of 1.6 and pk a of 7.8.Due to the protonation of amine groups, the CIP surface appears cationic and positive at pH less than 1.6.Due to the loss of proton from the carboxylic acid group present in the CIP structure, the CIP molecule is converted into anionic form at pH higher than 8.8 (44).As the adsorbent pH pz is equal to 6.7, the surface charge of photocatalyst is positive and cationic at pH less than pH pz , and the adsorbent appears as anion with negative charge at pH higher than 6.7.Therefore, at acidic pHs (pH = 3), as the photocatalyst surface and the CIP molecule, both have a positive charge, the electrostatic repulsion is produced and the rate of degradation is reduced (45).The reason for the highest antibiotic stability in the acidic pH is the lack of the ionized carboxyl group (COOH) (46).As a result, in acidic pH, the solubility of CIP is increased and the removal efficiency is reduced (47).At pH 7, the adsorbent surface charge is negative and CIP has positive surface charge.The electrostatic attraction is then generated and the CIP molecule is transferred to the photocatalyst and causes further degradation of hydroxyl radicals (45).At basic pH (pH = 11), the photocatalyst and CIP molecule both have a negative charge, electrostatic repulsion is generated, and the CIP degradation is reduced (40).Also, due to the high density of negatively charged hydroxide ions, photocatalyst prevents UV radiation and reduces the removal efficiency (43).In alkaline conditions, CO 2 in the solution tends to be converted into HCO 3 -and CO 3 2- . These compounds are considered as the degenerative hydroxyl radicals.At high pHs, bicarbonates are converted into carbonate ions, which reduces the oxidation rate by removing OH radicals (48).The study of El-Kemary et al confirmed the results related to pH in the present research (49).
Recycling experiments were performed and the results showed that the photocatalytic activity of the CuFe 2 O 4 @ MC had an obvious decrease in the second cycle and subsequently maintained relative stability (Figure 13).
The decrease of degradation percentage may be due to the adsorption of intermediate products on the photocatalyst active sites which prohibit the degradation of fresh CIP solution.However, 73.78% of CIP was degraded successfully after the fourth runs, which indicates that the CuFe 2 O 4 @MC could be easily recycled and reused.
The COD removal efficiency of 68.26% was obtained in the optimal conditions during the photocatalytic process.Therefore, the photocatalytic process by CuFe 2 O 4 @MC has a successful role in the removal of carbon groups through conversion of CIP into H 2 O and CO 2 , which is consistent with the results of the study of Malakootian et al (50).
To investigate the kinetics of the photocatalytic degradation of CIP, the pseudo-first order kinetic (Eq.2) and Langmuir-Hinshelwood kinetic (Eq. 3) models were investigated (43).
Where C 0 is the initial concentration of CIP (mgL -1 ) and C t is the concentration of CIP at different times (mgL -1 ).K obs represents the first-order degradation rate constant (min - 1 ), K C is the rate constant of the superficial reaction (mg L −1 min −1 ), and K L-H represents the adsorption equilibrium constant of L-H model (L mg -1 ).By plotting Ln (C t /C 0 ) vs. time at different concentrations of CIP, the correlation coefficient was obtained.The results of the pseudo-first order kinetic model investigation are provided in Table 3.By plotting 1/K obs vs. CIP initial concentration, a straight line is obtained, through which the equilibrium constant of the L-H model and the superficial reaction rate could be obtained (Figure 15).The results showed that the photocatalytic degradation process of CIP follows the pseudo-first order kinetic and Langmuir-Hinschwold. Photocatalytic degradation was linearly plotted according to pseudo-first-order degradation kinetic and was consistent with the L-H model.The rate of CIP degradation was related to the initial CIP concentration (C 0 ) and K obs decreased as C 0 increased.The L-H kinetic model showed good agreement with the initial rates of photodegradation with an appropriate reaction rate constant and substrate adsorption constant values of K c = 0.141 mg/L min and K L-H = 0.202 L/mg, respectively.An et al investigated the photocatalytic degradation of CIP and reported that degradation follows the pseudofirst order kinetic and Langmuir-Hinschwold kinetics, which is consistent with the results of this study (51).
The proposed mechanism for nanoCuFe 2 O 4 @MCcatalyzed photocatalytic removal of CIP contains five   steps and is shown in Figure 16. Step

Conclusion
The CuFe 2 O 4 @MC as a new magnetic nanobiocomposite, was easily synthesized under microwave irradiation in water.This nanobiocomposite, with ferromagnetic and photocatalytic properties, was used to degrade CIP and showed good efficiency.The efficiency of the photocatalytic degradation of CIP by the magnetic nanobiocomposite (CuFe 2 O 4 @MC) was more than adsorption process and UV photolysis.Degradation of CIP increased by increasing reaction time and CIP concentration decreased at neutral pH.Here, the optimal conditions obtained at pH of 7, CIP concentration of 3 mg/L, photocatalyst loading of 0.2 g, and the irradiation time of 90 minutes.The removal efficiency of CIP in the optimal conditions was obtained as 80.74% and 72.87% from the synthetic and real samples, respectively.The removal of COD in the optimal conditions was obtained 68.26% in this process.The photocatalyst was easily recycled and reused after the fourth runs and efficiency reduced about 7% after the fourth runs.The photocatalytic degradation process is an environmentally friendly process.This method can be used to treat large volumes of antibiotic-containing effluent.

Figure 5 .
Figure 5. VSM magnetization curve of CuFe 2 O 4 @MC easily separated from the CIP solution under the external magnetic field.

Figure 12 .
Figure 12.Effect of pH on the CIP degradation at different irradiation times (CIP concentration: 3 mg/L and CuFe 2 O 4 @MC dosage: 0.2 g).

Figure 11 .
Figure 11.The changes in UV-vis spectra of CIP in aqueous solution in the presence of CuFe 2 O 4 @MC on different irradiation time (15-90 min).

Figure 16 .
Figure 16.The proposed mechanism for photodegradation of CIP by CuFe 2 O 4 @MC.

Table 2 .
Physicochemical characteristics of wastewater from Kerman University of Medical Sciences