High-efficient photocatalytic degradation of tamoxifen and doxorubicin by novel ternary heterogeneous GO@Fe3O4@CeO2 photocatalyst

Abstract Pharmaceuticals are a new class of water contaminants that need to be effectively removed. This study combines GO@Fe3O4 with CeO2 nanoparticles via a simple procedure known as heterogeneous visible-light-driven photocatalyst. The photocatalytic potential of the GO@Fe3O4@CeO2 was examined via photodegradation of tamoxifen (TMX) and doxorubicin (DOX) under visible-light excitation. The crystallinity and morphology of the synthesized photocatalyst was characterized utilizing SEM, EDS, XRD, FTIR, VSM, and UV–vis. The UV–Vis analyses provided the bandgap value of 3.17 eV for GO@Fe3O4@CeO2. Then, the influence of some key factors such as pH (3–10), photocatalyst dose (0.006-0.04 g), and time (0-120) were studied. The findings indicated that TMX and DOX degradation via GO@Fe3O4@CeO2 photocatalyst could achieve 97% within 60 min and 98% within 90 min, respectively.


Introduction
The existence of organic pollutants specially pharmaceutical residues in the aqueous solutions has noxious impacts such as mutagenesis, fetotoxicity, carcinogenesis, genotoxic, drug resistance and allergic reactions on human health, wildlife, and other aquatic organisms in the environment (Areeb et al. 2021;Hameeda et al. 2021;Hatamluyi et al. 2018;Janssens et al. 2019;Kashif et al. 2023;Mahlaule-Glory et al. 2022;Yousaf et al. 2022).Hospitals, households farming (animals, fish) and other industrial-scale agricultural activities could be blamed for the production of such pllutants (Ghoochian et al. 2019).
Among these compounds, tamoxifen (TMX) and doxorubicin (DOX), as anti-cancer drugs increasingly used in chemotherapy treatments, have been found in drinking waters, surface waters, and ground waters at ng L À 1 levels around the world (Cai et al. 2019;Sadaf and Walder 2017).TMX and DOX are mutagen and teratogen anticancer drugs that are actually resistant to biological degradation, and thus there are widespread concerns about their occupational exposure and ecotoxicological risks to the environment (Sadaf and Walder 2017;Teunissen et al. 2010).TMX as a selective first-generation estrogen receptor modulator and metabolized drug has extensively been prescribed in the treatment of both advanced and early-stage breast cancer, for more than three decades (Borgatta et al. 2015;Gjerde et al. 2005).However, the longperiod consumption of TMX is subject to dispute owing to its estrogen agonistic attributes which may lead to the expansion of endometrial cancer and thromboembolic diseases (Catanzaro et al. 2019;Daneshgar et al. 2009).Also, DOX has been utilized in the treatment of a wide variety of cancers, including ovarian carcinoma, breast carcinoma, and acute lymphoblastic and myeloblastic leukemia (Ansar and Mudalige 2020).
As, TMX and DOX have negligible oral bioavailability, they may end up being released into the environment through excretions as mixtures of their original form and their metabolites after administration to patients (Anderson et al. 2002;Borgatta et al. 2015).Once released into the aqueous environment, they may exert a remarkable impact on any growing eukaryotic organism.Multiple papers have considered TMX and DOX removal from aquatic environments through membrane-based, advanced oxidation, adsorption, and coagulation-flocculation processes (Nawara et al. 2012;Zandipak et al. 2020;Zandipak and Sobhanardakani 2018).Basically, anticancer drugs removal using photocatalyst process may be a suitable technique that may yield good elimination (Azimi Bizaki et al. 2022;Rani et al. 2023;Sobhan Ardakani et al. 2022).Moreover, heterogeneous photocatalysis succeeds in the perfect mineralization of a wide range of pollutants (Cunha et al. 2019;Ghasemy-Piranloo et al. 2020).Among semiconductor catalysts, titanium-based photocatalysts have been specially employed owing to their partly low cost, chemical resistance, abundance, and inertness in aquatic solutions (Liang et al. 2020;Ofiarska et al. 2016).Moreover, quick recombination potential and a large band gap of titanium dioxide can reduce the photocatalytic activity and confine the application of visible light.Besides, CeO 2 can be introduced as an efficient photocatalyst due to its high oxygen storage ability, ideal catalytic property, stability, and nontoxicity.CeO 2 is a wide band-gap semiconductor compound that absorbs light near the ultraviolet but only slightly in the visible region (Kalaycıo glu et al. 2023;Molla et al. 2018;Saravanakumar et al. 2016;Thang et al. 2021;Tian et al. 2013).
Herein, we designed and synthesized resistant and recyclable graphene-(GR)-based semiconductor metal nanocomposites (GO@Fe 3 O 4 @CeO 2 photocatalyst), which have recently gained attention due to their high specific surface area, good carrier mobility, and excellent electrical conductivity for storing and shuttling electrons.The superior electron mobility found in these devices accelerates the interfacial charge transfer between the graphene and metal semiconductors, thus delaying the recombination process of electron-hole pairs during photocatalysis and enhancing the photocatalytic activity for the degradation of TMX and DOX.In so doing, first the graphene oxide (GO) was synthesized by Hammer method and was magnetized via magnetite (Fe 3 O 4 ).Subsequently, magnetite graphene oxide functionalized with CeO 2 and the physical characteristics of the photocatalyst was examined using tools such as SEM, FTIR, XRD, EDS, VSM, and UV-vis diffuse reflectance spectroscopy.The prepared GO@Fe 3 O 4 @CeO 2 photocatalyst was used for the first time as a highly visible light-driven photocatalyst toward the degradation of TMX and DOX.

Preparation of graphene oxide (GO/Fe 3 O 4 )
In this investigation, the Hummers manner was utilized for producing GO.To that end, 4.0 g graphite powder was added to a mixture containing 24 ml H 2 SO 4 , 8.0 g K 2 S 2 O 8 , and 8.0 g P 2 O 5 and was mixed for 6 h at 80 C. Afterward, the solution was cooled slowly at 25 C, diluted with 300 ml deionized water, filtered via filter paper (22 mm, Whatman), and dried at 60 C in the oven.Then, 2.0 g graphene powder was added to 92 ml H 2 SO 4 and 12.0 g KMnO 4 and placed in an ice bath.After 15 min, 2.0 g NaNO 3 was added to the solution and stirred for 2 h at 35 C. The synthesis was completed via 560 ml deionized water and 10 ml H 2 O 2. In the end, the blend was rinsed with HCl, deionized water, and centrifuged to prepare the GO suspension with a concentration of 10 mg L À1 .

Preparation of CeO 2 functionalized magnetite graphene oxide (GO@Fe
To synthesize the GO@Fe 3 O 4 @CeO 2 , 0.5 g of cerium(III) nitrate hexahydrate was dissolved in 30 ml of ethanol and added to 30 ml of GO suspension and then stirred for 2 h (Saranya et al. 2023).

Photocatalytic TMX and DOX degradation experiments
The photocatalytic efficiency of the synthesized GO@Fe 3 O 4 @CeO 2 photocatalyst was studied via photodegradation of TMX and DOX in aqueous solution under Xenon lamp (300 W) in 100 ml glass reactor at room temperature.In all tests, 20 mg of GO@Fe 3 O 4 @CeO 2 photocatalyst was added to 100 ml of 50 ppm TMX and DOX solution at natural pH.Then, the suspension was magnetically stirred in the dark for 30 min to reach adsorption-desorption equilibrium.After 30 min in dark, the above suspension was exposed to visible light illumination.After specified time intervals, the 2 ml of suspension was taken out and centrifuged to separate the solid particles and get a clear liquid.Ultimately, the C e factor for degradation of TMX and DOX was analyzed via UV-visible spectrophotometry (Lambda 45, Perkin-Elmer, Waltham, USA) at 236 nm and 480 nm, respectively, and q e factor of removal was obtained via Equation ( 1): where C 0 and C e (mg L À1 ) are primary and equilibrium concentrations of TMX and DOX molecules, respectively, V (L) displays volume of standard TMX and DOX solution, and W (g) stands for the mass of GO@Fe 3 O 4 @CeO 2 in all of tests.

Results and discussion
3.1.Characterization of GO@Fe 3 O 4 @CeO 2 nanocomposite The morphology and structure of GO, GO@Fe 3 O 4 , and GO@Fe 3 O 4 @CeO 2 are shown in Figure 1.As can be seen in FESEM graphs, GO presented a smooth and wrinkled surface (Figure 1a).After the combination with Fe 3 O 4 nanoparticles, the Fe 3 O 4 nanoparticles were successfully decorated on the surface of GO.Magnetite nanoparticles were randomly distributed over the surface of graphene and also magnetite nanoparticles were internalized between the sheets of graphene (Figure 1b).This observed morphology was similar to those reported in other studies in the literature.The FESEM image of GO@Fe 3 O 4 @CeO 2 displayed that the immobilized CeO 2 nanoparticles were clearly anchored to GO@Fe 3 O 4 (Figure 1c).The EDX spectrum of GO@Fe 3 O 4 @CeO 2 obtained to identify the elements in nanocomposite is depicted in Figure 2 The FT-IR spectra of GO, GO@Fe 3 O 4 , and GO@Fe 3 O 4 @CeO 2 are depicted in Figure S1 (Supplementary materials).The broad band observed about 3540 cm À1 might be attributed to the O H stretching vibration from the adsorbed H 2 O on the surface of the product.The bands around 2383 cm À1 , 1370 cm À1 , 1121 cm À1 , and 481 cm À1 can be attributed to C O, C C, and C O C, respectively.Also, a strong peak at about 617 cm À1 can be assigned to vibration of Fe O in GO@Fe 3 O 4 structure whereas the peak at 1606 cm À1 is connected to adsorption of H 2 O.Moreover, the bands at 2177 cm À1 and 2913 cm À1 reveal the stretching vibrations of Ce O group.
Figure S3 (Supplementary materials) displays the VSM images of pure Fe 3 O 4 , GO@Fe 3 O 4 , and GO@Fe 3 O 4 @CeO 2 nanocomposite.The measured saturation magnetization values are 68.6 emu g À1 , 45.5 emu g À1 , and 23 emu g À1 for Fe 3 O 4 , GO@Fe 3 O 4 , and Fe 3 O 4 @CeO 2 .As can be seen, the values for GO@Fe 3 O 4 , and Fe 3 O 4 @CeO 2 are lower than those of pure Fe 3 O 4 , which may be attributed to the impact of macromolecules and carbon-based materials in nanocomposites such as carbon and CeO 2 .That is, the magnetic Fe 3 O 4 @CeO 2 nanocomposite remains superparamagnetic, indicating that Fe 3 O 4 is well incorporated into the hybrid and can easily be separated by magnetic field.
The diffuse UV-visible reflectance spectrum of GO@Fe 3 O 4 @CeO 2 nanocomposite is shown in Figure S4 (Supplementary materials).The absorption edges of GO, GO@Fe 3 O 4 , and GO@Fe 3 O 4 @CeO 2 nanocomposite are 402, 428, and 503 nm.The results displayed that the band gap energies of GO, GO@Fe 3 O 4 , and GO@Fe 3 O 4 @CeO 2 nanocomposite were determined by Tauc's plot which would yield a band gap of 3.19, 3.08, and 2.98 eV.
3.2.Photoactivity of GO@Fe 3 O 4 @CeO 2 for TMX and DOX degradation TMX and DOX were chosen as representative pharmaceutical contaminants to determine the photocatalytic efficiency of GO@Fe 3 O 4 @CeO 2 in the removal of these pollutants.At the beginning of the work, the direct photolysis and dark adsorption at the photocatalyst surface of GO@Fe 3 O 4 @CeO 2 were examined.The results shown in Figures 3 and 4 demonstrate that the TMX and DOX were resistant, and no adsorption or straight photodegradation happened under empirical conditions.Then, a primary test was carried out with an initial concentration of both TMX and DOX equal 50 mg L À1 and photocatalyst dose of 20 mg at pH ¼ 7.0.The results of the study showed that GO@Fe 3 O 4 @CeO 2 was very effective in degradation of TMX about 97% within 60 min and DOX around 98% within 90 min.The reaction kinetics of the photocatalyst was obtained through wing Langmuir-Hinshelhood Equation (2): where k t is Langmuir-Hinshelhood fixed parameter, t displays the irradiation time, and both C t and C e (mg L À1 ) exhibit the concentrations of TMX and DOX at primary and each time (0-120 min), respectively.In this condition, the photooxidation procedure of TMX and DOX was determined to follow a pseudo-firstorder model kinetics with r 2 ¼0.991 and r 2 ¼0.993, respectively.

Effect of photocatalyst dose
The effect of GO@Fe 3 O 4 @CeO 2 dose (0.006, 0.008, 0.01, 0.02, 0.03, and 0.04 g) on the photocatalytic degradation of TMX and DOX was studied at the fixed primary concentration (50 mg L À 1 ), pH ¼ 7.0, and degradation time 60 min for TMX and 90 min for DOX under visible-light illumination.As displayed in Figure S5 (Supplementary materials), a suitable dose of GO@Fe 3 O 4 @CeO 2 was found to be 0.02 g for the topmost degradation efficiency TMX and DOX during the process.This is due to the enhanced adsorption of photon energy on GO@Fe 3 O 4 @CeO 2 surface by increasing number of active sites, which can produce greater amount of reactive oxygen species that will accelerate the oxidation reaction toward TMX and DOX degradation.However, it was observed that TMX and DOX degradation percentages slightly decreased by about 10% when the photocatalyst dose was 0.04 g.This finding can be explained by the aggregation of excessive catalysts in the solution, which in turn may result in the reduction of active sites of the catalysts for heat and photon energy absorption to generate oxidizing species and might lead to an increase in solution turbidity and light passage.

Effect of primary pH
In general, the photocatalytic degradation of TMX and DOX in the aqueous solutions can be remarkably affected by the primary pH of the solution because of the interactions between the photocatalyst surface, TMX and DOX species as a function of pH.The effect of TMX and DOX solution pH (3,4,5,6,7,8,9,and 10) on the photocatalytic TMX and DOX degradation was considered to further understand the degradation system.As displayed in Figure S6 (Supplementary materials), TMX and DOX degradation percent increased from 55% to 98.7% for TMX and 65% to 97% for DOX as pH enhanced from 3.0 to 7.0-an observation that can be attributed to pH PZC of GO@Fe 3 O 4 @CeO 2 .The pH PZC for the GO@Fe 3 O 4 @CeO 2 nanocomposite was detected to be 6.0 which implied that the surface of GO@Fe 3 O 4 @CeO 2 nanocomposite was positively charged at pH < 6.0, which was not desirable for the adsorption of positively charged TMX and DOX due to the electrostatic repulsion.Also, the redox potential of OH species is commonly higher under acidic systems.Therefore, the TMX and DOX removal efficiency by GO@Fe 3 O 4 @CeO 2 nanocomposite is significantly highest at pH > 6.0, which could be represented via the negatively charged GO@Fe 3 O 4 @CeO 2 nanocomposite surface electrostatically attract the positively charged and higher pH causes the higher adsorption of OH - groups on the GO@Fe 3 O 4 @CeO 2 nanocomposite surface, and encourages the production of OH 0 radicals in the photodegradation reaction of TMX and DOX.Besides, in natural pH conditions, almost 99% of HO 2 and O 2 radicals are in the deprotonated form.This event proposes that 0 O 2 -radicals could participate in TMX and DOX decomposition, mainly owing to the great affinity of O 2 to the negatively charged GO@Fe 3 O 4 @CeO 2 nanocomposite.

Mechanism for the degradation of TMX and DOX
Based on the results obtained, the degradation mechanism of TMX and DOX by GO@Fe 3 O 4 @CeO 2 under visible light was studied and it was found that it has a wide band gap of 3.1 eV and that it is still active under visible area due to the existence of oxygen vacancies.
In photocatalytic degradation reactions of TMX and DOX, the accumulated electrons and accumulated holes in GO@Fe 3 O 4 @CeO 2 immediately participate in the reductive and oxidative reactions of TMX and DOX.Moreover, photoinduced hot electrons in CeO 2 nanoparticles could decrease O 2 into 0 O 2 -active species.Then, the produced 0 O 2 -active species will eventually appear in the reactions of the TMX and DOX degradation system or produce other active species (Equation (3)-8)).

GO@Fe
e À þ DOX and TMX !DOX À and TMX À (4) Reusability of GO@Fe 3 O 4 @CeO 2 The recyclability and stability of GO@Fe 3 O 4 @CeO 2 for the removal of TMX and DOX was studied by carrying out various types of tests under optimized situations, the results of which are presented in Figure S7 (Supplementary materials).Finally, GO@Fe 3 O 4 @CeO 2 nanocomposite was separated from the TMX and DOX solution by filtration after each cycle while ethanol and 0.1 mol L À 1 HCl were utilized as eluent.The photocatalytic degradation efficiency of TMX and DOX reduced from 98% to 80% and 98% to 86% after 5 cycles, respectively.The results of the recyclability of GO@Fe 3 O 4 @CeO 2 nanocomposite illustrated that the GO@Fe 3 O 4 @CeO 2 photocatalyst was usable and beneficial for the degradation of TMX and DOX from water samples.

Conclusions
The present work examined the potentials of a synthesized GO@Fe 3 O 4 @CeO 2 as a novel visible light photocatalyst in removing TMX and DOX and tried to document its efficiency by applying several characterization methods to reveal its morphology, and physical, and chemical properties.The photocatalytic degradation of GO@Fe 3 O 4 @CeO 2 photocatalyst was checked under visible light in the removal of TMX and DOX.Kinetic survey of the photodegradation reactions displayed that the degradation rate factors of Langmuir-Hinshelhood for TMX and DOX on the GO@Fe 3 O 4 @CeO 2 photocatalyst were about 0.037 and 0.045, respectively.The result of optimized factors displayed that pH ¼ 7 and a photocatalyst dose of 0.02 g were ideal for reactions.In addition, the results of the photocatalytic tests indicated that GO@Fe 3 O 4 @CeO 2 would remove TMX and DOX under visible light with a degradation of 97% within 60 min and 98% within 90 min, respectively.
(a).The peaks of C, O, Fe and Ce, confirm the existence of Fe 3 O 4 and CeO 2 .