CuCe-Ferrite/TiO2 Nanocomposite as an Efficient Magnetically Separable Photocatalyst for Dye Pollutants Decolorization

In this work, a magnetically separated photocatalyst with great efficiency CuCe-Ferrite/TiO2 composite was prepared and characterized by X-ray diffraction (XRD), UV–Vis spectrophotometry, Fourier transformer infra-red spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectroscopy (EDX) and vibrating sample magnetometer (VSM). Single-phase cubic spinel was formed by calcining the prepared sample at a temperature of 550 °C, according to the results. Different concentrations of reactive red 250 (RR250) dye photodegradation was evaluated using different doses of CuCe-ferrite/ TiO2 and TiO2 NPs. Higher efficiency of RR250 photodegradation up to 100% was obtained using CuCe-ferrite/ TiO2. The photodegradation efficiency was confirmed using chemical oxygen demand (COD) test of both treated and untreated samples. The oxidation process was mostly mediated by photogenerated .O2− according to scavenger test results. The catalyst possess higher photodegradation efficiency even after regeneration for ten times.


Introduction
Ferrites are a type of mixed oxide characterized by the general formula MFe 2 O 4 , where M can stand for Mg 2+ , Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ , Zn 2+ , and so on [1]. Perovskite, spinel, and ilmenite are the three primary structures of mixed oxides. Perovskite and spinel formations are the most investigated and intriguing. The spinel structure is found in a large number of ferrites, with the word "spinel" referring to the natural combination MgAl 2 O (MgOAl 2 O 3 ) [2]. Electric and, in particular, magnetic characteristics of ferrites have previously been investigated. However, significant restrictions, such as the effect of cations distribution and particle size distribution on magnetic characteristics in mixed ferrites, must be handled in the near future. Because each synthesis technique has its own set of benefits and drawbacks, several methods have been devised over time to achieve the desired ferrites properties. The methods of synthesis can be divided into two categories: "top-down" and "bottom-up". The material is separated into nanoscale using a "top-down" approach, which often involves physical techniques such as ball milling and laser ablation [3]. Spinel ferrites, adsorbents new family which recommended for treatment of contaminated water, have appeared recently. Because of their large surface area which were active for interacting with pollutants, these materials have excellent capacity of adsorption. The spinel ferrites have remarkable superparamagnetic properties (SPM), allowing them to be easily recovered from reaction mixture with the use of an externally applied magnetic field [4][5][6]. Spinel ferrites have been studied for their ability to remove organic molecules [7], nutritional salts [8], and harmful metals from water [5].
Depending on what type of pollutants, adsorbents, and adsorption circumstances, interactions such as chemical bonding, complex formation of outer-sphere or innersphere, van der Waals forces, π-π interactions and others may be essential for adsorption. Removing organic contaminants from wastewater is an important step toward environmental preservation. Environmental rehabilitation efforts have focused on a variety of toxic dyes, extra-marketable paints, and bleaches [9]. The world is currently dealing with major environmental pollution problems. Organic compounds can be found in both home and industrial effluents. Before being discharged near water resource, these pollutants must be eliminated or removed. Environmental contamination is caused by the discharge of significant amounts of wastewater from the textile, pharmaceutics, textile dying, cosmetics, food production, and photography sectors. These discharges are hazardous in environment because they typically contain a large number of harmful chemicals that do not decompose [10][11][12][13]. Various TiO 2 magnetic composites such as, Cu 0.5 Mg 0.5 Fe 2 O 4 , TiO 2 ,TiO 2 maintained on magnetic core shell (Si@ Fe) surface, Fe 3 O 4 @ TiO 2 , Magnetic TiO 2 @ Fe 3 O 4 /reduced graphene oxide, poly (GMA)@ Ru/ TiO 2 @ Fe 3 O 4 , magnetic carbon-supported TiO 2 , yolk-shell Fe 3 O 4 @ TiO 2 nanosheet/Ag/g-C 3 N 4 and others have been tested for degradation of different pollutants [14][15][16][17][18][19][20][21][22][23][24].
The CuCe-Ferrite/TiO 2 and TiO 2 composites were prepared and analyzed in this study. The produced materials were then tested for their efficiency to photocatalytically decolorize the reactive red 250 (RR250) dye in aqueous solution, the effect of different composite doses and dye concentrations were tested. The capacity to reuse of CuCe-Ferrite/TiO 2 and TiO 2 samples was tested after ten successive usage.

CuCe-Ferrite/TiO 2 and TiO 2 Preparation
For preparation of TiO 2 , it was prepared as our previous work [11]. In order to prepare CuCe-Ferrite/TiO 2 sample, firstly, 0.6 g of the as prepared TiO 2 was added to 100 mL distilled water. Secondly, into the aforementioned suspension was added 100 mL of aqueous solution containing 2.02 g of Fe(NO 3 ) 3

Photocatalytic Activity
In this study, RR250 (10, 20, 50 and 100 mg L −1 ) as a dye pollutant, solutions were utilised. In every test, (0.02, 0.04, 0.08, 0.16 and 0.32 g) of the catalyst was added in 100 mL dye solution. The mixtures were left in dark condition for 30 min for adsorption-desorption. For photocatalytic experiment, a Holland Philips high pressure mercury lamp, 400w, was used as the light source. A UV-Vis spectrophotometer (Shimadzu UV-2550) was used to track the experiments progress. The disappearance of peak at λ = 510 nm were chosen for monitoring of RR250 decolonization respectively. The efficiency of prepared catalyst for RR250 photodegradation was calculated using the following equation: where C o and C e are the initial and the equilibrium concentrations.
For the assurance of the obtained results using spectrophotometer, the maximum decrease of carbon content in both utilized waste and treated wastewater was measured using a closed reflux standard titrimetric technique. The photocatalytic degradation efficiency was calculated using the COD results [25].
Control studies with four types of scavengers were carried out to evaluate the reactive species formed during photodegradation of RR250 dye [26], using isopropanol, p-benzophenone, triethanolamine and carbon tetrachloride as a quenchers of . OH, . O 2− , h + and e − respectively. 1.0 mmol/L, a fixed concentration of each scavenger was used. An average of repeated three times experimental results was taken ( Fig. 1). Figure 2 shows the XRD patterns of CuCe-Ferrite/TiO 2 and TiO 2 NPs. The TiO 2 sample's XRD pattern is consistent with prior findings [27]. XRD pattern confirmed the presence of CuCe-Ferrite in CuCe-Ferrite/TiO 2 composite. CuCe-Ferrite/TiO 2 and TiO 2 NPs average crystal sizes were calculated using the Scherer's equation [28], where λ is the X-ray wavelength and β is the half maximum of diffraction lines full width. The prepared NPs  crystal sizes were calculated to be 33.8 and 25.2 nm for CuCe-Ferrite/TiO 2 and TiO 2 respectively. Figure 3 shows CuCe-Ferrite/TiO 2 and TiO 2 UV-visible spectra, in the visible region, demonstrating noticeable band widening absorption and a move to the higher wavelength of CuCe-Ferrite/TiO 2 compared to bare TiO 2 . The bandgap energies (E g ) estimated were determined to be 2.18 and 3.1 eV for CuCe-Ferrite/TiO 2 and TiO 2 . The smaller bandgap is in good accord with the success of composite preparation.

Characterization
In Fig. 4 for CuCe-Ferrite/TiO 2, the observed FTIR peak at 3415 cm −1 assigned to stretching vibrations of (O-H) groups [29]. The sharp peak at 1625 cm −1 and 1068 cm −1 is corresponding to stretching vibration of (M-O), which confirm the formation of the metal-oxygen in ferrite-based. The 1378 cm −1 band of absorption corresponding to the nitrates from which the Cu, Ce and Fe functional groups and their linkages and disappeared with introducing the TiO 2 ions in CuCe-Ferrite/TiO 2 [30]. The spectra for the prepared samples give characteristic bands at 459 cm −1 (metal ion-oxygen (M octa -O) at octahedral-site) and 698 cm −1 (metal ion-oxygen (M tetra -O) at tetrahedral-site), which are the significant bands of -Fe 2 O 4 groups, which is due to the formation of CuCe-Ferrite/ TiO 2 nano-structure [31]. Careful observation on the FTIR spectra shown in Fig. 4 shows an absorption peak at 459 cm −1 corresponding to intrinsic stretching vibrations of metal at the tetrahedral site, whereas the v 2− lowest band, observed in the range 400 cm −1 and below, is due to the octahedral-metal stretching. Fe 3+ ions has the tendency to occupy both octahedral and tetrahedral sites [32]. Further observations shows strong absorptions peaks at 3415 and 1479, 1378 cm −1 wavelengths.
The FE-SEM and HR-TEM images Fig. 5. From the FE-SEM images of TiO 2 (Fig. 5a) and CuCe-Ferrite/TiO 2 ( Fig. 5b) a slight change in morphology was observed due change in samples content. Figure 5c shows the TEM images of the prepared TiO 2 , Fig. 5d shows the TEM images of the prepared CuCe-Ferrite/TiO 2 NPs after annealing with temperature of 550 °C. The particles in both cases are spherical and exhibit a homogeneous distribution. The particle size distribution range for the TiO 2 and CuCe-Ferrite/TiO 2 of about 20 nm and 30 nm were calculated using HR-TEM images, respectively. The result obtained for the average particle size distribution were in agreement with the values obtained using the XRD spectra. An increase of particle size, more metal ions are produce which in turn increases the particle sizes. This increment in number of ions and particle size supports the enhancement of the intensity of absorption as shown in the FTIR spectra of CuCe-Ferrite/TiO 2 sample. It is important to note that tiny amount of agglomeration is observed CuCe-Ferrite/TiO 2 due to growing distribution of particle size.
EDX of CuCe-Ferrite/TiO 2 and TiO 2 were shown in Fig. 6. EDX analysis confirmed the existence of Cu, Ce, Fe, O and Ti elements in the samples. Figure 7a shows the magnetic measurement of CuCe-Ferrite/TiO 2 sample which was measured using VSM instrument. Figure 7b shows the using of magnet in separation of prepared composite.
The CuCe-Ferrite/TiO 2 nanocomposite possesses a ferromagnetic characteristic and an S-like magnetization hysteresis loop. The saturation and remnant magnetizations are 0.238 and 0.16 memu/g, respectively. Figure 7 presents the magnetic hysteresis loops of CuCe-Ferrite/ TiO 2 nanocomposite.     Table 1.

Photocatalytic Degradation of RR250
Nevertheless, the degradation efficiency progressively reduced by the decreasing in the catalyst dose and increasing of R250 dye concentrations. According to our findings, sample photocatalytic activity was highly correlated with catalyst dosages, which was consistent with earlier studies [33][34][35][36]. This decreasing in the catalyst dose and increasing of R250 dye concentrations will decrease the e − and h + produced on the samples surface, additional dropping the samples photocatalytic activity. The enhancement of photodegradation process may be attributed to the improved adsorption capacity and transfer of electron easily from CuCe-Ferrite NPs to TiO 2 and hindrance of electron recombination. The CuCe-Ferrite/TiO 2 sample showed significant photocatalytic activity in our study. For the degradation of various organic dye pollutants, several ferrites were utilized, some of which were spinel ferrites combined with frequently used photocatalysts or doped ferrites, and some of ferrites were reported in Table1. When we compare the reported results of photocatalysts to our findings, we discover that our photocatalyst has a great photocatalytic efficiency that reaches 100% in 45 min, which is an exceptional time that saves time and energy, as well as higher reusability.
As seen in Fig. 10. After 120 min of treatment over TiO 2 and CuCe-Ferrite/TiO 2 NPs, COD decrease was detected by increasing the concentration of RR250 from 10 to 100 ppm. Because increase in concentration of RR250 dye causes incorporation of additional RR250 dye molecules onto TiO 2 and CuCe-Ferrite/TiO 2 NPs, those observations were linked to an effective area reduction or a decrease in light penetration [37,38]. The photocatalytic degradation results are confirmed by the COD data [11].
Different scavengers were added to quench the involved active species, in order to conclude the probable photocatalytic degradation mechanism of RR250 dye over CuCe-Ferrite/TiO 2 , Fig. 11 depicts the different scavengers effects on the photocatalytic degradation of     [39,40].
The insertion of CuCe-Ferrite dopants in TiO 2 crystals results in localized full states and/or oxygen vacancies, which generate a mid bandgap, causing TiO 2 's optical energy band edge to move to the visible light range. The resultant CuCe-Ferrite/TiO 2 when exposed to visible light, the sample becomes photocatalytically active. After the process of irradiation, e − transfers from the defect level to the conduction band. radicals, and these radicals effectively degrade dye [11]. The mechanism of photocatalytic degradation is as; Magnetic catalysts have a number of advantages, one of which is their ease of separating from the reaction mixture. Additionally, TiO 2 and CuCe-Ferrite/TiO 2 composite reusability for RR250 dye solutions photocatalytic degradation was examined. The catalyst was recovered using an external magnet after finishing the reaction in the first run, rinsed with water, dried, and reused for the next cycle. The CuCe-Ferrite/TiO 2 and TiO 2 samples reusability after ten repeated uses was obtained (Fig. 12). The results obtained shows that CuCe-Ferrite/TiO 2 sample possess higher reusability even after using up to ten times.

Conclusions
CuCe-Ferrite/TiO 2 and TiO 2 nanostructures were successfully synthesized by using of co-precipitation process, and the as-prepared sample was then heated for about 2 h at 550 °C. The particle size and crystallinity of the prepared nanostructures were confirmed using XRD, and the particle size is 33.8, and 25.2 nm of CuCe-Ferrite/ TiO 2 , and TiO 2 nanostructures. The photocatalytic performance CuCe-Ferrite/TiO 2 nanostructures of 0.08 g/100 ml showed its ability to degrade 100% of 100 ppm concentration of RR250 dye of 100 ppm at pH 7 in 45 min. while for TiO 2 it reaches to 26.1% using the same dose of photocatalyst and the same conditions. The prepared catalyst have showed high regeneration ability up to ten times. The photocatalytic degradation results was confirmed using COD test. Photocatalytic degradation mechanism was studied and it confirmed that the oxidation process was mostly mediated by photogenerated . O 2− , rather than . OH.
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source,  Fig. 12 Reusability of CuCe-Ferrite/TiO 2 and TiO 2 NPs after ten utilizations provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/.