Journal of Nanoscience and Nanomaterials

INTRODUCTION

Pharmaceuticals are products used in large doses in daily life considered contaminants of emerging concern. Due to the large amounts of drugs consumed, the hydrogenic sources suffer from contamination processes that give rise to toxicological effects in humans despite their low concentrations [1]. Many medicines considered emerging contaminants are constantly detected in groundwater, wastewater treatment plants, and water supply. The inefficiency of conventional methods used in water treatment plants to remove the contaminant motivates the development of effective methods to treat effluent contamination [2]. According to the physicochemical properties of drugs, their degradation products, and the characteristics of the soils, these substances can reach the groundwater and contaminate the aquifers or remain retained in the soil, thus affecting the ecosystem and humans through the food chain [3]. Additionally, the portion of medicines not assimilated by the organism, as well as chemical substances administered to animals, usually become part of wastewater. Consequently, different ways of removing medicines in water have been studied [4]. The residues of the pharmaceutical compounds administered to humans and animals excreted as metabolites or in their native form—certainly contribute to water pollution [5]. Furthermore, the disposal of unused medications from households and manufacturing facilities also contributes to the spreading of pharmaceutically active compounds (PhACs) in the environment. These residues fall within the group of the so-called emerging pollutants, together with illegal drugs, endocrine disruptors, personal care products, and household substances [6]. Since PhACs are not easily degraded by the typical biological treatments in municipal wastewater treatment plants, together with all the toxic substances discharged from a treatment plant or a septic system, they can end up in surface waters or groundwaters that may ultimately be used as a source of drinking water [7,8].

Doxorubicin, sold under the brand name Adriamycin among others, is a chemotherapy medication used to treat cancer [9]. This includes breast cancer, bladder cancer, Kaposi's sarcoma, lymphoma, and acute lymphocytic leukemia [10]. It is often used together with other chemotherapy agents [9]. Doxorubicin is given by injection into a vein. Doxorubicin is a potent anthracycline chemotherapy medication used to treat a wide variety of cancers, including breast, bladder, lung, and ovarian cancers, as well as lymphomas and leukemias. It works by intercalating into DNA and inhibiting topoisomerase II, which ultimately halts the division and growth of cancer cells. Common side effects include hair loss, bone marrow suppression, vomiting, rash, and inflammation of the mouth [11]. Other serious side effects may include allergic reactions such as anaphylaxis, heart damage, tissue damage at the site of injection, radiation recall, and treatment-related leukemia [9]. People often experience red discoloration of the urine for a few days. Doxorubicin is in the anthracycline and antitumor antibiotic family of medications. It works in part by interfering with the function of DNA. Doxorubicin significantly decreases white blood cell (neutrophil) and platelet counts, increasing infection and bleeding risks (Myelosuppression). Dose-dependent risk of cardiomyopathy and heart failure. Patients often require lifelong cumulative dosage tracking (Cardiotoxicity). Hair loss is a common and widely expected side effect (Alopecia). Can cause a harmless, distinct red color in urine, sweat, and tears for a few days following treatment (Discoloration). Doxorubicin was approved for medical use in the United States in 1974 [12]. It is on the World Health Organization's List of Essential Medicines (World Health Organization, 2019). Versions that are pegylated and in liposomes are also available; however, they are more expensive [13]. Doxorubicin was originally made from the bacterium Streptomyces peucetius.

Hydroxychloroquine is an aminoquinoline pharmaceutical primarily used to prevent and treat malaria, and as an immunomodulatory disease-modifying antirheumatic drug (DMARD) for autoimmune conditions like systemic lupus erythematosus (SLE) and rheumatoid arthritis [14]. Hydroxychloroquine, sold under the brand name Plaquenil among others, is a medication used to prevent and treat malaria in areas where malaria remains sensitive to chloroquine. Other uses include treatment of rheumatoid arthritis, lupus, and porphyria cutanea tarda. It is taken by mouth, often in the form of hydroxychloroquine sulfate [15]. Common side effects may include vomiting, headache, blurred vision, and muscle weakness [16]. Severe side effects may include allergic reactions, retinopathy, and irregular heart rate [17,18]. Although all risk cannot be excluded, it remains a treatment for rheumatic disease during pregnancy [19]. Hydroxychloroquine is in the antimalarial and 4-aminoquinoline families of medication [20]. Long-term use requires routine eye exams, as it carries a rare but serious risk of retinopathy. In addition to, common side effects include nausea, stomach cramps, diarrhea, and skin rashes. In some patients, it can cause severe hypoglycemia or QT interval prolongation (leading to heart rhythm issues). Concurrent use with other medications that affect heart rhythm (e.g., azithromycin) significantly increases the risk of heart rhythm problems. Hydroxychloroquine was approved for medical use in the United States in 1955 [21]. It is on the World Health Organization's List of Essential Medicines [16]. In 2023, it was the 131st most commonly prescribed medication in the United States, with more than 4 million prescriptions [22,23]. Hydroxychloroquine has been studied for an ability to prevent and treat coronavirus disease 2019 (COVID-19), but clinical trials found it ineffective for this purpose and a possible risk of dangerous side effects [24]. Among studies that deemed hydroxychloroquine intake to cause harmful side effects, a publication by The Lancet was retracted due to data flaws [25]. The speculative use of hydroxychloroquine for COVID-19 threatens its availability for people with established indications [19].

Tinidazole is a synthetic 5-nitroimidazole antibiotic and antiprotozoal agent. It is highly effective against anaerobic bacteria and specific protozoa (e.g., Trichomonas vaginalis, Giardia lamblia, and Entamoeba histolytica). It works by penetrating the microorganism and damaging its DNA strands. Tinidazole, sold under the brand name Tindamax among others, is a medication used against infections caused by certain anaerobic bacteria and protozoa. It was developed in 1972 and is a prominent member of the nitroimidazole antibiotic class [26]. Tinidazole is a therapeutic alternative on the World Health Organization's List of Essential Medicines [27]. Tinidazole is a narrow spectrum antimicrobial drug used to treat infections caused by Helicobacter pylori, Entamoeba histolytica, Giardia spp. and Trichomonas vaginalis [28]. Drinking alcohol while taking tinidazole causes an unpleasant disulfiram-like reaction, which includes nausea, vomiting, headache, increased blood pressure, flushing, and shortness of breath. The drug is reduced by anaerobic organisms, creating intermediate products that disrupt DNA synthesis and damage existing DNA, leading to cell death. Nearly 100% absorption and bioavailability following oral administration. Protein Binding is approximately 12%. Metabolized in the liver, primarily via the CYP3A4 enzyme system. Half-life is nearly 12 to 14 hours, which allows for convenient once-a-day dosing. Excretion: Excreted primarily by the liver (feces) and kidneys (urine) [26].

CeO₂ [Ceria or Cerium(IV) oxide] is a versatile, inert, and physically and chemically stable material with multiple and diverse applications [29,30,31]. Due to its hardness (Mohs scale 7), it was initially used as an abrasive material, but today it is used (alone or in binary or complex mixtures) in the field of heterogeneous catalysis (oxidation of hydrocarbons) or in the field of sensors, energy, and fuels such as solid oxide fuel cells, but also in water-splitting processes or photocatalysis [32,33,34]. CeO₂ applications in the dermato-cosmetics industry and in the biomedical field (antibacterial effect) should also be mentioned here [35,36,37]. CeO₂ is also possible to combine two or more properties, for example, the infrared filtering properties with the photocatalytic ones, to optimize practical applications [38-42]. CeO₂ is semiconductor photocatalyst with various applications and similar properties to TiO₂. However, its band gap is in the wide range of 2.6 to 3.4 eV, depending on the preparation method [43-46]. Furthermore, CeO₂ exhibits promising photocatalytic activity. Nonetheless, the position of CB and VB limits its application as an efficient photocatalyst utilizing solar energy, even though CeO₂ can absorb a larger fraction of the solar spectrum than TiO₂. The photocatalytic and photo electrocatalytic activity of CeO₂ in wastewater treatment can be improved by various modification techniques, including changes in morphology, doping with metal cation dopants and non-metal dopants, coupling with other semiconductors, combining it with carbon supporting materials, etc. [47-49]. The main properties that make CeO₂ significant as a photocatalyst and photoelectrode material applied in the degradation of various pollutants result from its high band gap energy, high refractive index, high optical transparency in the visible region, high oxygen storage capacity, and chemical reactivity [50]. The other properties of CeO₂ which should be mentioned include its high thermal stability, high hardness, oxygen ion conductivity, special redox features, and easy conversion between Ce⁺³ and Ce⁺⁴ oxidation states [51,52].

The two-dimensional (2D) g-C₃N₄ semiconductor has a wide range of applications in the environmental and energy fields because of its visible-light activity, unique physicochemical properties, excellent chemical stability and low-cost. Some important limitations of the photocatalytic activity of g-C₃N₄ are its low specific surface area, fast recombination of electrons and holes and poor visible light absorption.

To improve the above problems, the construction of a heterojunction with a suitable band gap semiconductor (co-catalyst) has been shown to be a good strategy to improve the photocatalytic performance of g-C₃N₄, such as g-C₃N₄-based conventional type II heterostructures, g-C₃N₄-based Z-scheme heterostructures, and g-C₃N₄-based p–n heterostructures, etc. [53-56]. The unique “Z” shape as the transport pathway of photogenerated charge carriers in Z-scheme photocatalytic systems is the most similar system to mimic natural photosynthesis in the many g-C₃N₄-based heterojunction photocatalysts [57-59]. The construction of Z-scheme photocatalytic systems can promote visible light utilization and carrier separation, and maintain the strong reducibility and oxidizability of semiconductors [60-62]. There are many studies on g-C₃N₄-based Z-scheme heterojunction photocatalysts, such as ZnO/g-C₃N₄, WO₃/g-C₃N₄, g-C₃N₄/ZnS, g-C₃N₄/NiFe₂O₄, g-C₃N₄/graphene/NiFe₂O₄, NiCo/ZnO/g-C₃N₄ and Bi₂Zr₂O₇/g-C₃N₄/Ag₃PO₄, respectively [63-65]. g-C₃N₄-based Z-scheme heterojunction photocatalysts have been made to improve the photocatalytic activity by combining with other semiconductor materials [18,66,67]. Therefore, there are some problems with the single photocatalytic method, such as low adsorption ability, limited active sites and low removal efficiency. The integration of the adsorption and photocatalytic degradation of various organic pollutants is considered as a suitable and promising technology. On the other hand, it is still essential to fabricate photocatalysts with superior adsorption and degradation efficiencies [68,69].

The conduction band (CB) of g-C₃N₄ is more negative than that of CeO₂ (-1.24 eV and -0.44, respectively), while CeO₂ possesses a relatively positive valance band (VB) (2.56 eV) compared to the conduction band of g-C₃N₄, would theoretically facilitate the electron transition within the coupled photocatalyst to prolong the electron hole separation [68]. Particularly, under the illumination of visible light, g-C₃N₄ can be excited to generate electron-hole pairs. Cerium (Ce) has exciting catalytic characteristics because 4d and 5p electrons sufficiently defend the 4f orbitals. The photogenerated electrons in the conduction band of CeO₂ tend to transfer and recombine with the photogenerated holes in the valence band of g-C₃N₄. Like this, the larger number of photogenerated electrons accumulated in the conduction band of g-C₃N₄ can reduce the adsorbed O₂ to form more O₂ ^{- ●}. At the same time, the photogenerated holes left behind in the valence band of CeO₂ can oxidize the adsorbed H₂O to give OH^●. But, the photocatalytic activity of the g-C₃N₄/CeO₂ system would be significantly increased, leading to the decomposition of organic compounds by O₂ ^{- ●} and OH^● reactive species.

Tungsten trioxide (WO₃) is an n-type semiconductor photocatalyst having a wide range of bandgap values (2.7–3.4 eV) providing a better extension into the visible range [70]. WO₃ as alone photocatalyst suffers from the limitation of fast recombination of charge carriers, thereby restricting its potential during photocatalytic applications [71]. Several studies suggest that constructing a heterojunction between two metal oxides with suitable band arrangements can improve the charge carrier separation by suppressing the fast recombination [72,73]. Binary heterojunctions like WO₃/Bi₂WO₆, WO₃/ZnO, and WO₃/TiO₂, have been constructed to achieve superior charge separation and high photocatalytic yields [74,75,76]. Bimetallic W has always been very significance for its chemical inertness structure with low toxicity, exhibited corrosion-resisstant properties with large magnetic properties, and economic feasibility [77]. ZnWO₄ possesses wolframite (WO₄) structures with six-fold coordination sites for W exhibited superior activities under UV light [78].

WO₃ is a highly promising material for visible light-driven photocatalysis. WO₃ is a semiconductor with an indirect band gap within the visible light range (2.4–2.8 eV) [79]. It exhibits a valence band with a high oxidation potential for holes (+3.1–3.2 V vs. NHE), and it is resistance to photo-corrosion [80]. Despite these advantages, pure WO₃ falls short as an effective photocatalyst for removing organic pollutants due to its relatively low conduction band potential (+0.5 V vs. NHE), which is significantly more positive than that oxygen (E ( / ) = −0.33 eV vs. NHE; O₂/HO₂ = − 0.046 V vs. NHE) [81,82]. The available oxygen cannot efficiently react with the photo-induced electrons from the conduction band of WO₃, leading to a rapid recombination of charge carriers and a reduction in overall photocatalytic efficiency. The recent researches showed that when WO₃ is combined with other co-catalysts and it exhibits promising photocatalytic activity by facilitating the reduction of oxygen through a multiple electron pathway (O₂/H₂O₂ = + 0.68 V vs. NHE; O₂/H₂O = + 1.23 V vs. NHE) [83].

The photoremoval of pharmaceuticals like doxorubicin, hydroxychloroquine, and tinidazole is achieved using CeO₂@C₃N₄/WO₃ nanocomposites as highly efficient, visible-light-driven photocatalysts. This ternary heterojunction material maximizes the degradation of organic pollutants by enhancing light absorption, preventing charge recombination, and increasing the production of reactive oxidizing radicals. The application of this nanocomposite for environmental remediation and wastewater treatment involves several key mechanisms and operational characteristics.

To overcome the individual limitations of these compounds, the synthesis of CeO₂@C₃N₄/WO₃ composite photocatalysts can be a promising strategy, as this composite can take advantage of the complementary properties of its components. CeO₂ helps to improve the efficiency of charge separation and facilitates redox reactions, while C₃N₄ contributes to improving the visible light absorption and acts as a stable support [84,85,86]. WO₃, with its superior photocatalytic activity under visible light, further extends the composite’s light absorption capacity [87,88]. Additionally, the formation of heterojunctions between the individual components of the composite catalyst can create an efficient pathway for charge transfer, thereby reducing charge recombination and enhancing the overall photocatalytic efficiency. For example, many composites such as TiO₂-WO₃-CeO₂, CeO₂-WO₃, WO₃:CeO₂ supported C₃N₄, TiO₂-CeO₂/C₃N₄ nanolayers, CeO₂/BiVO₄ anchored C₃N₄ nanocomposites, etc. have demonstrated superior performance in degrading organic pollutants, such as dyes and pharmaceuticals, under visible-light irradiation [89-93]. It has also shown promise in hydrogen evolution reactions (HER), a critical process for clean energy production [94,95]. Despite these advancements, the detailed understanding of the structure-activity relationship, charge transfer pathways, and the role of individual components in the composite remains an active area of research. Vignesh observed that for CeO₂-TiO₂/C₃N₄ (S-scheme heterostructure) composite, there is an improvement in the photocatalytic performance for the degradation of methylene blue (MB) dye (0.0262 per min) which is 6.1, 2.6, and 1.5 times greater than those of C₃N₄ (0.0043 per min), CeO₂/C₃N₄ (0.0099 per min), and TiO₂/C₃N₄ (0.0180 per min), respectively [92]. WO₃/CeO₂-supported C₃N₄ nanolayers exhibited exceptional degradation of orange G dye, i.e., 99.82% (visible light) and 99.73% (sunlight irradiation). Its performance was notably higher in acidic conditions (≥ 99%) compared to neutral conditions (≥ 93%) due to the synergistic interfacial interaction of WO₃ and CeO₂ on the C₃N₄ surface.

This study determines the photocatalytic degradation of some pharmaceutical pollutants such as Doxorubicin, Hydroxychloroquine and Tinidazole using a CeO₂@C₃N₄/WO₃ nanocomposite under sun light illumination. The effect of increasing sun light power (10, 20, 40 and 80 W/m2), pharmaceutical concentrations (400, 600, 800, 1000 and 1500 mg/L), CeO₂@C₃N₄/WO₃ nanocomposite concentrations (1, 2, 4, 6 and 8 mg/L), time (10, 15, 20 and 25 min) and temperature (21, 25, 30 and 40^oC), pH (4.0, 7.0, 8.0 and 10.0) on the photodegradation yields of Doxorubicin, Hydroxychloroquine and Tinidazole pharmaceuticals were investigated. The structure and properties of the CeO₂@C₃N₄/WO₃ nanocomposites were determined with XRD, DRS UV-vis, PL spectra, SAED, HRTEM, TEM, N2 adsorption isotherms, pore distribution and XPS analyses.

MATERIALS AND METHODS

Synthesis of CeO₂ (C) Nanoparticles, C₃N₄ (N), and CeO₂@C₃N₄/WO₃ (CNW) Nanocomposite

To prepare CeO₂ nanoparticles, a chemical precipitation route was adopted in which 30 mL of 0.2 M Ce-precursor solution was prepared under continuous stirring until complete dissolution of Ce-salt had been confirmed. Then, 30 mL of 0.2 M NaOH was added (dropwise) to it, enabling the precipitation of the Ce-complex left in the flask overnight. The filtered precipitates were washed carefully in distilled H₂O and C2H5OH followed by drying at 60^oC (overnight) and heating at 400^oC (@5oC/min for 120 min) to grow CeO₂ crystallites [96]. The obtained white powder was ground using an agate mortar and characterized for structural, optical, and catalytic activity as described in the subsequent section. For the synthesis of C3N4, our previous report has been followed [97]. The crucible with thiourea was heated to 550oC (@5^oC/min for 120 min). The yellow powder acquired was crushed using a mortar and pestle without acidic or alkaline treatment. To prepare the composite sample (CeO₂@C₃N₄/WO₃), the desired amount (Table 1) of constituents was mixed through wet grinding (acetone) for 6 h to stick the components to each other. CeO₂@C₃N₄/WO₃ nanocomposite production under laboratory conditions were shown in Figure 1.

Figure 1: CeO₂@C₃N₄/WO₃ Nanocomposite Production Under Laboratory Conditions

Characterization Techniques

X-ray diffraction (XRD) patterns were recorded using a PANalytical X’pert-Pro diffractometer equipped with Cu-Kα radiation (1.5406 Å), with a step size of 0.05 o, over a 2θ range of 10–80 o, to determine the phase composition of the synthesized materials. The diffraction peaks were indexed using ICDD standard reference cards via X’pert HighScore software. Diffuse reflectance UV–vis (DR UV–vis) spectra were collected at room temperature using a Hitachi U-3900H double-beam spectrophotometer equipped with a diffuse reflectance accessory, scanning the 200–800 nm range. Photoluminescence (PL) spectra were obtained using a Cary Eclipse fluorescence spectrophotometer (G9800A), with an excitation wavelength of 280 nm and an emission range of 300–700 nm. To ensure consistency, equal amounts of well-ground powder were loaded into the sample holder, minimizing variations due to differing concentrations of scattering centers. Nitrogen adsorption-desorption isotherms were measured at – 196^oC using a Quantachrome Autosorb iQ analyzer. Prior to analysis, samples were degassed at 150^oC for 48 h. The specific surface area was calculated using the Brunauer-EmmettTeller (BET) method, while pore size distribution was evaluated using the Barrett-Joyner-Halenda (BJH) model. Morphological analysis was conducted using a high-resolution transmission electron microscope (JEOL ARM 200F) operated at 200 kV. Samples were prepared by dispersing the powder in alcohol, dropping it onto ultrathin carboncoated grids, and drying under low vacuum. X-ray photoelectron spectroscopy (XPS) measurements were performed in an ultra-high vacuum environment (~5 × 10− 9 mbar) using a Phoibo s150 NAP analyzer (Specs, Germany) with monochromatic Al-Kα radiation (1486.6 eV). To compensate for surface charging effects, spectra were calibrated by shifting the binding energy of the adventitious carbon (C 1s) peak to 284.8 eV. The size and structure of the CeO₂@C₃N₄/WO₃ nanocomposite samples were identified with high resolution transmission electron microscopy (HRTEM) Analysis. The obtained CeO₂@C₃N₄/WO₃ nanocomposite was collected and harvested by centrifugation (8000 rpm, 5 min), washed twice with deionized water and resuspended in ethanol (C2H6O) and dripped onto a carbon-coated copper (Cu) transmission electron microscopy (TEM) grid. Vacuum drying then occurred to the CeO₂@C₃N₄/WO₃ nanocomposite for 24 h at 25^oC room temperature. The dry samples on the Cu grid were viewed and examined by TEM analysis recorded in a JEOL JEM 2100F, Japan under 200 kV accelerating voltage.

Selected Area Electron Diffraction (SAED) is a crystallographic technique primarily performed using a TEM. It isolates a specific microscopic region of a sample to generate diffraction patterns, which allows researchers to determine crystal orientation, measure lattice constants, and identify phases. Conventional electron diffraction has been rarely used as a standard tool for crystal identification mainly because the electron interactions with matter are about 10,000 times stronger than that of X-rays. As a result, the diffracted intensities are so much altered that they cannot be trusted, unless the crystal thickness is very thin. SAED patterns are a projection of the reciprocal lattice, with lattice reflections showing as sharp diffraction spots. By tilting a crystalline sample to low-index zone axes, SAED patterns can be used to identify crystal structures and measure lattice parameters. SAED is essential for setting up dark-field (DF) imaging conditions. Other uses of SAED include analysis of: lattice matching; interfaces; twinning and certain crystalline defects. SAED of nanocrystals gives ring patterns analogous to those from X-ray powder diffraction, and can be used to identify texture and discriminate nanocrystalline from amorphous phases. Precession electron diffraction (PED) is a modification to electron diffraction, which minimizes the effects of dynamical diffraction (which is basically independent of the crystal structure) that can plague structural solution. PED is applied to a range of different oxides for structure solution and refinement. As a result of this precession movement there is improvement over conventional SAED patterns, reflection diffracted intensity is much closer to the integrated intensity values, and it is much closer to kinematical (like X-Ray case). PED is installed on JEOL 2010F and JEOL 2100LaB6, Japan.

Photocatalytic Studies

All photocatalytic tests were performed in 500 mL photo-reactor made up of quartz glass. under 300 W sun light power with an intensity of 20 W/m² for irradiation purpose. Reaction assembly has appropriate cooling systems of water channels to avoid excess heat produced during the photocatalytic examinations. Nonstop purging of air has been done to the reaction mixture during the treatment process. Centrifugation was utilized for separation of photocatalyst from irradiated solution. The photocatalytic reactor was operated with constant stirring (1.5 rpm) during the photocatalytic degradation process. 10 mL of the reacting solution were sampled and centrifugated (at 10000 rpm) at different time intervals.

The irradiation power was controlled by measuring the sunlight power with an intensity measuring device Merck. For high sun light power the reactor was set under sun light power on times between pm 13.00 and pm15.00. For median sun light power the reactor was set under sun light power on times between 11:00 (a.m.) and 12:00 (a.m.). For lowest sun light power the reactor was set under sun light power on times between pm 15.00 and pm16.00.

Photodegradation Mechanisms of CeO₂@C₃N₄/WO₃ Nanocomposites

The integration of CeO₂, C₃N₄, and WO₃ creates a highly effective interface. This typically forms an S-scheme charge transfer mechanism (Synergistic Heterojunction). In a typical (CeO₂@C₃N₄/WO₃) configuration, photoexcited electrons move between the conduction bands while holes migrate to the valence bands. This spatial separation prevents the rapid recombination of charge carriers (Enhanced Electron-Hole Separation). The separated electrons and holes interact with oxygen and water molecules in the aqueous solution to produce reactive oxygen species (ROS), primarily hydroxyl (OH^●) and superoxide (O2^{- ●}) radicals. These strong, unselective oxidizing radicals attack complex pharmaceutical molecules, breaking them down into harmless byproducts like CO₂ and H₂O. While effective under sunlight, the ternary composite is highly optimized for energy-efficient visible and white LED illumination. The catalyst is stable over multiple operational cycles and can frequently be reused 15 or more times with minimal deactivation. This targeted photoremoval is a sustainable method to prevent the accumulation of hazardous antineoplastic, antimalarial, and antibacterial drugs (like doxorubicin, hydroxychloroquine, and tinidazole) in aquatic ecosystems.

The staggered heterojunction created between CeO₂, Graphitic C₃N₄, and WO₃ significantly broadens the catalyst's light absorption range into the visible spectrum. The composite significantly minimizes electron-hole recombination losses compared to binary systems, allowing for more reactive species (such as hydroxyl radicals and holes) to attack pollutants. It is highly effective at degrading hazardous waste, including model organic dyes (like crystal violet) and pharmaceutical contaminants. The ternary composite demonstrates high stability, with studies showing it can be reused multiple times with minimal deactivation.

RESULTS AND DISCUSSION

XRD Analysis Results

XRD was carried out to confirm the phase formation without any undesired impurities in the powder samples. Fig. 2a represents the single-phase XRD spectra of prepared cubic CeO₂ nanoparticles (CeO2; ICDD 00-043-1002) and graphitic C3N₄ sheets (N). Meanwhile, the XRD spectra of W confirmed the presence of orthorhombic WO3 particles (ICDD 00-020-1324). XRD spectra of C suggested the formation of nanosized (6.74 nm) crystallites of CeO₂. While W consists of much larger crystallites with 114.12 nm (average) as compared to CeO₂. All the calculations to determine average crystallite size were performed after eliminating the instrumental contribution in overall full width at half maxima, using Pearson VII peak function in the sample and Si standard following β2 calc = β2 obs − β2 Si relation [98]. Fig. 2b confirmed the presence of individual constituents in CeO₂@C₃N₄/WO₃ nanocomposites (CeO₂, C₃N₄, and WO₃).

Figure 2 (a): Single-phase XRD Spectra of Prepared Cubic Ceo₂ Nanoparticles

Figure 2 (b): Individual Constituents in Ceo₂@C₃N₄/WO₃ Nanocomposite. (C: Ceo₂, N: C₃N₄, W: WO₃).

SAED Patterns Results

SAED pattern (inset of Fig. 3a) also exhibited concentric rings supporting the formation of nanocrystallites of CeO₂. Fig. 3c and d shows the TEM micrographs at low and high magnifications, respectively. General scans were used to determine the average particle size of WO₃ powder, which was 120.36 nm.

HRTEM Results

HRTEM confirmed the presence of orthorhombic WO₃ with 0.405 nm as the interplanar spacing of the (001) plane. Fig. 3e and f confirmed the successful formation of a 2D sheet-like morphology of grap hitic C₃N₄ from thiourea.

Figure 3. TEM and HRTEM of (a, b) prepared CeO₂ nanoparticles, (c, d) procured WO₃, (e, f) prepared C₃N₄ sheets, (g) TEM image of CeO₂@C₃N₄/WO₃ nanocomposite, and (h–j) highresolution image confirming the presence of all individual components (CeO₂, WO₃ and C₃N₄). (k–o) HAADF-STEM image and EDS elemental mapping images of CeO₂@C₃N₄/WO₃ composite: Overlay of N-K edge, Ce-L edge, and W-M edge, respectively.

TEM Analysis Results

TEM was performed, as shown in Fig. 3, to confirm and understand the morphological features of prepared samples (CeO₂ and C₃N₄) and procured WO₃. Fig. 3a and b represents the low- and high-resolution micrographs of sample CeO₂ supporting the XRD results with average particle size 7.85 nm and lattice fringing of 0.328 nm of (111) plane of cubic CeO₂ lattice.

Fig. 3g represents the TEM micrograph of the CeO₂@C₃N₄/WO₃ nanocomposites sample in which three different features have been observed that are associated with the individual constituents, i.e., C₃N₄ (sheet-like translucent), CeO₂ (small particles), and WO₃ (larger dark particles). Further, the confirmation was also carried out by HRTEM and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) as shown in Fig. 3h–j and 3k-o, respectively. Furthermore, the surface characteristics of catalysts govern the reaction kinetics during illumination, providing the surface area for molecule adsorption.

N₂ Sorption Isotherms and Pore Distribution

Fig. 4 represents the BET analysis of CeO₂@C₃N₄/WO₃ and all the constituents (i.e., CeO₂, C₃N₄, and WO₃). Sample C₃N₄, WO₃, and CeO₂@C₃N₄/WO₃ exhibited type IV isotherm with H₃ hysteresis, suggesting the presence of a combination of meso- and macropores (Fig. 4b) in these materials. While sample C exhibited a slightly different shape of the H₃ hysteresis loop, suggesting the presence of mesoporous CeO₂ powder with blocking at broader pore necks [99]. Table 1 summarizes the results of Brunauer-Emmett-Teller (BET) analysis with a higher specific surface area (SSA) of 84 m²/g for CeO₂@C₃N₄/WO₃ nanocomposites as compared to C₃N₄ and WO₃, while CeO₂ exhibited the highest SSA of 148 m²/g. Here, smaller size of CeO₂ particles might be responsible for the reduced SSA of CeO₂@C₃N₄/WO₃ nanocomposites due to pore blockage.

Table 1: Sample Composition, Optical, and Surficial Characteristics of Prepared Samples

Figure 4 (a): N₂ Sorption Isotherms of the Prepared C (Ceo₂), N (C₃N₄), CNW (Ceo₂@C₃N₄/WO₃), and Procured W (WO₃) Samples

Figure 4 (b): Pore Diameters of the Prepared C (Ceo₂), N (C₃N₄), CNW (Ceo₂@C₃N₄/WO₃), and Procured W (WO₃) Samples

XPS Analysis Results

Before evaluating the catalytic performance efficiency of the prepared semiconductor samples (CeO₂, C₃N₄, WO₃) and their composite (CeO₂@C₃N₄/WO₃), it is essential to analyze their elemental composition and structural modifications. This investigation is crucial for understanding the pathway leading to optimal photochemical reactions. Fig. 5 represents the comparative HR XPS spectra of all the individual elements present in the semiconducting compounds (CeO₂, C₃N₄, WO₃) and CeO₂@C₃N₄/WO₃ nanocomposite sample. The spectral data of each element was analyzed on peakfit software with Shirley background and a Gaussian peak function [98]. O1s spectra of CeO₂, and WO₃ (Fig. 5a and b, respectively) indicated the presence of two major species of oxygen i.e., lattice oxygen (O-Ce at 529.56 eV and O-W at 529.57 eV) and non-lattice oxygen (or O-defects at 530–532 eV) along with minor presence of hydroxyl group (533.06 eV in C) in the form of adsorbed water molecules [100].

The attachment of three components altogether yielded a significant elemental modification on the surface of the powder sample, as shown in Fig. 5c. Along with the presence of lattice (overlapping O-Ce and O-W) and non-lattice oxygen, C-OH (at 533.41 eV), and O-C=O (at 535.06 eV) confirmed the presence of carbon-based functionalities of C₃N₄ in CeO₂@C₃N₄/WO₃ [101]. Interestingly, the mechanical mixing of all the constituents altered the overall concentration of non-lattice oxygen or O-defects, which surely participate in photochemical reactions through effective trapping of charge carriers and hindered recombination of photoexcited electrons. Because of composite formation through mechanical mixing, the comparative oxidation states of cationic counterparts (i.e., W and Ce) have been shown in Fig. 5d–g. The procured WO₃ powder exhibited a pair of doublets, suggesting the presence of dual oxidation states, i.e., W⁶⁺ and W⁵⁺ centering at 34.77 and 34.72 eV (W 4f7/2), respectively, as shown in Fig. 5d. While the mechanical mixing of all three constituents yielded significant shifting of binding energies of both oxidation states to 38.21 and 37.26 eV (W 4f7/2) with an almost 17% (36.20%–53.20%) enhancement in W⁵⁺ concentration, shown in Fig. 5e [100].

Figure 5a: O1s Spectra of C (Ceo₂) In Ceo₂@C₃N₄/WO₃ Nanocomposite

Figure 5b: O1s Spectra of W (WO₃) In Ceo₂@C₃N₄/WO₃ Nanocomposite

Figure 5c: Elemental Modification on the Surface of the Ceo₂@C₃N₄/WO₃ Nanocomposite Powder Sample

Figure 5d: W⁶⁺ and W⁵⁺ disturbances in W 4f

Figure 5e: W⁵⁺ disturbances in W 4f

Elemental Structure of CeO₂@C₃N₄/WO₃ Nanocomposite

Fig. 5f and g represents the elemental modulations of Ce3d because of composite formation. It was found that a combination of Ce⁴⁺ (883.46, 889.01, and 898.36 eV) and Ce³⁺ (882.81 eV) was formed in the prepared sample ‘C’. While the formation of the composite sample exhibited modifications of the Ce³⁺/Ce⁴⁺ ratio, which might play an extremely critical role in overall photocatalytic performance. Similar elemental modulation has already been reported earlier for the photocatalytic removal of rhodamine B dye under UV–visible irradiation. It was found that the concentration of Ce³⁺ (884.26 and 887.51 eV) has been increased by modulating the lattice oxygen in the form of non-lattice oxygen or O-defects (i.e., vacancies) as shown in Fig. 5g.

Figure 6a: Elemental Modulations of Ce 3d in CeO₂@C₃N₄/WO₃ Nanocomposite

Figure 6b: Elemental Modulations of Ce 3d in CeO₂@C₃N₄/WO₃ Nanocomposite

Figure 6c: XPS Spectra of N 1s of the Prepared C₃N₄ (N) and CeO₂@C₃N₄/WO₃ Nanocomposite Sample

Figure 6d: Elemental Carbon exhibited C-sp2, N-C=N, and C-N-C Functional Groups in the Prepared N Sample

Figure 6e: C (CeO₂), W (WO₃) and N (C₃N₄) Components in CeO₂@C₃N₄/WO₃ Nanocomposite

Due to the composite formation, the associated elemental modifications in WO₃ and CeO₂ have been discussed. Here, the influence of composite formation on the elemental alterations in C₃N₄ is discussed. Fig. 5h and i represents HR XPS spectra of N 1s of the prepared C₃N₄ and CeO₂@C₃N₄/WO₃ sample, in which comparative chemical alterations have been observed. HR-XPS spectra of N suggested the presence of three different N-species, i.e., C=N-C, N-C3, and N-H positioned at 398.06, 399.54, and 401.34 eV, respectively [101]. Because of composite formation, the mechanical mixing yielded a significant shifting (0.8 eV) of these binding energies along with the inclusion of additional binding energy C-NHx at ~402 eV, which might be associated with the introduction of N-functionalities as shown in Fig. 5i. Further, the elemental carbon exhibited C -sp2, N-C=N, and C-N-C functional groups at 284.14, 287.64, 288.69 eV (respectively) in the prepared N sample as shown in Fig. 5j. Here, the formation of composite resulted in significant shifting of N-C=N (− 0.09 eV) and C-N-C (0.86 eV) to 287.55 and 289.55 eV (respectively) along with the inclusion of a new functional groups i.e., C-O at 285.95 eV and Ce4s at 290.35 eV suggesting successful attachment with other components (i.e., WO₃ and CeO₂) as shown in Fig. 5k [102,103].

Optical Properties

Before exploring the photocatalytic characteristics, it is necessary to identify the optical features of the samples, aiming at sufficient photon absorption and excitation energy. Fig. 7 represents the DR spectra of the powder samples, in which samples CeO₂ and WO₃ exhibited a quick reduction in reflectance between 450 and 350 nm. While C₃N₄ and CeO₂@C₃N₄/WO₃ exhibited a double electronic transition, gradual (600-450 nm) and sharp (450-400 nm) reduction. Further, the band gap was determined by using Kubelka Munk function, shown in Fig. 7.

Figure 7: DR Spectra of the CeO₂@C₃N₄/WO₃ Nanocomposite Powder Samples. (C: CeO₂, N: C₃N₄, W: WO₃).

Further, the band gap was determined by using Kubelka Munk function, shown in Fig. 8 and listed in Table 1. CeO₂@C₃N₄/WO₃ exhibited a similar optical band gap (~3.05 eV) value to that of sample N, as given in Table 1, which is less than samples CeO₂ and WO₃. As far as photochemical reaction kinetics are concerned, the photon absorption and generation of excitons are extremely critical, while the recombination rate of excitons also plays an important role.

Figure 8. Calculation of Band Gap by Kubelka Munk Function { [F(R).hv]² versus hv (eV) }.

Therefore, Fig. 9 represents the photoluminescence emission spectra of the prepared samples. The photoemission spectra were recorded after the excitation of the samples by using a 280 nm laser. Here, sample C₃N₄ exhibited a broad emission between 400 and 650 nm, while CeO₂ and WO₃ exhibited major emission near 382 nm. CeO₂@C₃N₄/WO₃ sample exhibited a much lower intensity of emissions between 400 and 650 nm and near 382 nm than C₃N₄ and CeO₂, respectively. These results clearly show that the formation of CeO₂@C₃N₄/WO₃ composite resulted in much more efficient separation of photogenerated charge carriers when compared to individual components of the composite catalysts.

Figure 9: Photoluminescence Spectra of all the Samples at λ_exc = 285 nm

Effects of Operational Conditions

Effect of Increasing Sun Light Power for Doxorubicin, Hydroxychloroquine and Tinidazole Photoremovals with CeO₂@C₃N₄/WO₃ Nanocomposite

Effect of increasing sun light power (10, 20, 40 and 80 W/m²) on the photooxidation yields of Doxorubicin, Hydroxychloroquine and Tinidazol was investigated with CeO₂@C₃N₄/WO₃ nanocomposites (Figure 10). 57%, 84% and 96% photoremoval efficiencies were obtained at 10, 20 and 80 W/m² solar light powers, respectively, after 15 min photodegradation time, at pH=7.0 and at 25^oC, respectively (Figure 10).

Figure 10: Effect of Sun Light power on the photoremoval of Doxorubin, Hydroxychloroquine and Tinidazole with CeO₂@C₃N₄/WO₃ Nanocomposite Photocatalyst

Maximum 100% photodegradation yields was detected for Dozorubicin, Hydroxychloroquine and Tinidazole, at 40 W/m2 solar light power after 15 min photodegradation, at pH=7.0 and at 25^oC (Figure 10).

Photocatalytic reaction rate depends largely on the radiation absorption of the photocatalyst, where the increase in light intensity enhances the degradation rate and the yield in photocatalytic degradation (Figure 10). At low light intensities (10–20 W/m²), the rate would increase linearly with increasing light intensity, whereas at intermediate light intensities, above 14 W/m2, the rate would depend on the square root of the light intensity. This is likely, because at low light intensity, reactions involving electron–hole formation are predominant, and electron–hole recombination is negligible. However, at increased light intensity (80 W/m²) the, electron–hole pair separation competes with recombination, thereby causing lower effect on the reaction rate like a solar light power of 80 W/m². The enhancement of the photodegradation of Doxorubicin, Hydroxychloroquine and Tinidazol photoremovals increased as the light intensity increased up to 40 W/m² (Figure 10).

Effect of Increasing Pharmaceutical Concentrations for Doxorubicin, Hydroxychloroquine and Tinidazole Photoremovals with CeO₂@C₃N₄/WO₃ Nanocomposite

Effect of increasing Doxorubicin, Hydroxychloroquine and Tinidazol pharmaceuticals concentrations (400, 600, 800 1000 and 1500 mg/L) on the photodegradation yields of Doxorubicin, Hydroxychloroquine and Tinidazol photoremovals was investigated with CeO₂@C₃N₄/WO₃ nanocomposites (Figure 11). 53%, 70%, 92% and 94% photodegradation removals were observed at 400, 600, 800 and 1500 mg/L pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) concentration, after 15 min photodegradation, under 40 W solar light power, at pH=7.0 and at 25^oC, respectively (Figure 11).

Figure 11: Effect Of Pharmaceutical Concentrations on the Photoremoval Yields of Doxorubicin, Hydroxychloroquine And Tinidazole With Ceo₂@C₃N₄/WO₃ Nanocomposites

Maximum 100% pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) photoremovals were found at 1000 mg/L pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) concentration, after 15 min photodegradation, under 40 W solar light power, at pH=7.0 and at 25^oC, respectively (Figure 11).

An increase in the pharmaceutical (Doxorubicin, Hydroxychloroquine and Tinidazole) concentrations from 400 mg/L up to 1000 mg/L increased the photodegradation yields of pharmaceuticals (Figure 11). This may be due to the almost all pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) photocatalyzed by CeO₂@C₃N₄/WO₃ nanocomposites and the establishment of equilibrium between the CeO₂@C₃N₄/WO₃ nanocomposites and pharmaceuticals and none of a CeO₂@C₃N₄/WO₃ photocatalyst was not remained in the solution. At 1000 mg/l pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) the e CeO₂@C₃N₄/WO₃ nanocomposites can photodegrade all the pharmaceuticals in the solute to be photocatalyzed. A further increase in pharmaceutical dosage (1500 mg/l) did not cause a significant improvement in pharmaceutical yields. This may be due to the adsorption of almost all pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) to the photocatalyst and the establishment of equilibrium between the pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) adsorbed to the CeO₂@C₃N₄/WO₃ nanocomposites and those remaining unabsorbed and unphotocatalyzed in the solution. The loading amount of pollutants is a significant factor in the photocatalytic degradation process, because the efficiency could be strongly affected by the number of active sites and photo adsorption ability of the catalyst used. However, it was observed that above a certain optimum pharmaceutical mass, the reaction rate not decrease significantly and becomes independent of the loading concentration.

Effect of CeO₂@C₃N₄/WO₃ Nanocomposite Concentrations on the photoremoval of Doxorubicin, Hydroxychloroquine and Tinidazole with CeO₂@C₃N₄/WO₃ Nanocomposite

The effects of increasing of CeO₂@C₃N₄/WO₃ nanocomposites (1 mg/L, 2 mg/L, 4 mg/L, 6 mg/L and 8 mg/L) concentrations on the pharmaceutical (Doxorubicin, Hydroxychloroquine and Tinidazole) yields were investigated on pharmacuetical yields at 40 W/m² sun light power, at 1000 mg/l pharmaceutical concentration after 15 min photocatalytic degradation time, at pH=7.0 and at 25 °C, (Figure 12). 78%, 92%, 85% and 77% photoremoval efficiencies were obtained at 1 mg/L, 4 mg/L, 6 mg/L and 8 mg/L CeO₂@C₃N₄/WO₃ nanocomposites concentrations, respectively, at 40 W/m² sun light power, at 1000 mg/l pharmaceuticals after 15 min photocatalytic degradation time, at pH=7.0, at 25 °C, respectively (Figure 12).

Figure 12: Effect of CeO₂@C₃N₄/WO₃ Nanocomposites Concentrations on the Pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) Photoremovals with CeO₂@C₃N₄/WO₃ Nanocomposites

The maximum 100% pharmaceutical removal efficieny was measured at 2 mg/L CeO₂@C₃N₄/WO₃ nanocomposite concentration, at 40 W/m2 sun light power, at 1000 mg/L pharmaceuticals concentration after 15 min photocatalytic degradation time, at pH=7.0, at 25 °C, respectively. A significant statistical correlation between the photodegradation efficiency and nanocomposite concentration was not found up to an optimal nanocomposite concentration is attained. At high nanocomposite concentrations can result in turbidity and a blocking effects of active points on the surface of nanocomposite. This cause to decreasing light intensity in the nanocomposite pharmaceutical matrix. Elevated nanocomposite concentration cause to lowered of photodegradation of pharmaceuticals. On the other hand, at optimal nanocomposite doses, the nanocomposite has good agglomeration due to its high surface energy. Therfore at optimal nanocomposite concentrations excellent photocatalytic yields was detected.

Effect of Increasing Photodegradation Time on the photoremovals of Doxorubicin, Hydroxychloroquine and Tinidazole with CeO₂@C₃N₄/WO₃ Nanocomposite

The photoreactor was operated at increasing times (10, 15, 20 and 25 min) to determine tha pharmaceutical yields at 40 W/m² sun light power, at 1000 mg/l pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) concentration, at pH=7.0, at 25°C, respectively (Figure 13). 75%, 92% and 84% photoremoval yields were measured at 10, 20 and 25 min photodegradation time, respectively, at 40 W/m² sun light power, at 1000 mg/L pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) concentration, at pH=7.0, at 25 °C, respectively (Figure 13).

Figure 13: Effect of Photodegradation Time on the Photoremovals of Pharmaceuticals Compounds (Doxorubicin, Hydroxychloroquine and Tinidazole) With Ceo₂@C₃N₄/WO₃ Nanocomposites

Maximum 100% photoremoval efficiency was obtained at 15 min photodegradation time, at 40 W/m2 sun light power, at 1000 mg/L pharmaceutical concentration, at pH=7.0, at 25 °C, respectively (Figure 13). As the photooxidation times were increased from 10 min up to 15 min the pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) yields increased from 75% up to 100% under sun light. Further increase of time did not affect the pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) removals. Data obtained from this study showed that the pharmaceutical yields at longer retention time was low. In an elevated ratio of contact at long contact times; no hydroxyl radicals production was achieved for pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) reduction. As a result, low conversion rates were observed at very short residence times. Althougth, prolonged light irradiation is expected to accelerate the photodegradation of pharmaceutical molecules onto the photocatalyst surface before reaching equilibrium in this study 15 min has enhanced the yields. It can be speculated that the number of electrons transferring from the VB to the CB increases that enhance the amount of electron-hole pairing at 15 min. The optimum illumination time for maximum removal of pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) was obtained as 15 min.

Effect of Increasing Temperature on The Photoremoval Yields of Doxorubicin, Hydroxychloroquine and Tinidazole with Ceo₂@C₃N₄/WO₃ Nanocomposite

The photoreactor was operated with different temperatures (21, 25, 30 and 40^oC) to determine the pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) photoremoval yields, at 40 W/m² sun light power, at 1000 mg/L pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) concentration, at 2 mg/L CeO₂@C₃N₄/WO₃ nanocomposites concentrations, after 15 min photodegradation time, at pH=7.0, at 25 °C, respectively (Figure 14). 69%, 95% and 73% removal efficiencies were measured at 21 oC, 30 oC and 40^oC, respectively, at 40 W/m² sun light power, at 1000 mg/L pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) concentration, at 2 mg/L CeO₂@C₃N₄/WO₃ nanocomposites concentrations, after 15 min photodegradation time, at pH=7.0, respectively (Figure 14).

Figure 14: Effect of Temperature on the yields of pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) with CeO₂@C₃N₄/WO₃ nanocomposites

The maximum 100% pharmaceutical yields was detected at 25^oC temperature at 40 W/m² sun light power, 1000 mg/L pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) concentration, at 2 mg/L CeO₂@C₃N₄/WO₃ nanocomposites concentrations, after 15 min photodegradation time, at pH=7.0, respectively (Figure 14).

In heterogeneous photocatalytic systems, temperature was found to have an significant effect on the photodegradation of pharmaceuticals. In particular, low temperatures favour the adsorption of the pharmaceuticals onto the catalyst, which is a spontaneous exothermic process. Nevertheless, in this case the adsorption of the degradation products is also enhanced, thus reducing the number of active sites on the catalyst. In contrast, high temperatures lead to an increase in the mobility of the pharmaceutical molecules, therefore increasing the kinetic energy. However, the enhanced kinetic energy of the pharmaceutical molecules may also allow them to escape from the photocatalyst surface, without being subjected to photodegradation. The morphology of the catalyst is very relevant when studying the effect of temperature on the photodegradation of pharmaceuticals. For the nanoparticles, higher temperatures increased the photodegradation rate, whereas a rise in temperature had a negative effect. This was explained due to the super activity of the pharmaceutical surface compared to the nanoparticles.

Effect of Increasing pH values on the Doxorubicin, Hydroxychloroquine and Tinidazole Photoremovals with CeO₂@C₃N₄/WO₃ Nanocomposite

The effects of increasing pH values (pH=4.0, pH=7.0, pH=8.0 and pH=10.0) on the yields of pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) was investigated at 40 W/m² sun light power, at 1000 mg/L pharmaceuticals (Doxorubicin, Hydroxychloroquine and Tinidazole) concentration, at 2 mg/L CeO₂@C₃N₄/WO₃ nanocomposite dose after 15 min photodegradation time, at pH=7.0, and at 25^oC temperature, respectively (Figure 15). 71%, 94% and 62% removal efficiencies was measured at pH=4.0, at pH=8.0 and at pH=10.0, respectively, for pharmaceutical (Doxorubicin, Hydroxychloroquine and Tinidazole) photoremovals. The maximum pharmaceutical yields was detected at pH=7.0 (100%) at 40 W/m² sun light power, at 1000 mg/L pharmaceutical concentration, at 2 mg/L CeO₂@C₃N₄/WO₃ nanocomposites concentrations, after 15 min photodegradation time, at 25^oC temperature, respectively (Figure 15).

Figure 15: Effect of pH values on the photoremoval of pharmaceuticals compounds (Doxorubicin, Hydroxychloroquine and Tinidazole) with CeO₂@C₃N₄/WO₃ nanocomposites

This indicates that with changing the pH of the solution media, the acid-base property at surface of the photocatalyst was remarkably influenced the photodegradation performance of the nanomaterial. The electrostatic based repulsion between the deprotonated CeO₂@C₃N₄/WO₃ nanocomposites and hydroxide ion (OH-) is the possible cause for the observed decrease in performance of the pharmaceuticals at pH=7.0, because the repulsion prevents the formation of hydroxyl radicals that consequently reduces photocatalytic efficiency of CeO₂@C₃N₄/WO₃ nanocomposites. Similarly, at pH <  7.0, the decomposition of pharmaceuticals becomes even more hindered, which could be explained by the reduced sorption possibility of the cationic pharmaceuticals at the CeO₂@C₃N₄/WO₃ nanocomposite surface which gained sufficient positive charges (i.e., due to protonation) on the surface of catalyst causing repulsion.

CONCLUSION

This study determines the photocatalytic degradation of some pharmaceutical pollutants such as Doxorubicin, Hydroxychloroquine and Tinidazole using a CeO₂@C₃N₄/WO₃ nanocomposite under sun light illumination. The effect of increasing sun light power, pharmaceutical concentrations, CeO₂@C₃N₄/WO₃ nanocomposite concentrations, photodegradation time, temperature and pH values on the photodegradation yields of Doxorubicin, Hydroxychloroquine and Tinidazole pharmaceuticals were investigated. The structure and properties of the CeO₂@C₃N₄/WO₃ nanocomposites were determined with XRD, DRS UV-vis, PL spectra, SAED, HRTEM, TEM, N2 adsorption isotherms and pore distribution and XPS analyses.

Under 40 W/m² sun light and 2 mg/L CeO₂@C₃N₄/WO₃ nanocomposite efficiently degraded 1000 mg/l Doxorubicin, Hydroxychloroquine and Tinidazole pharmaceuticals, achieving 100% photoremovals in 15 min of the reaction time at pH=7.0 and at a temperature of 25^oC.

In this study CeO₂@C₃N₄/WO₃ nanocomposite was successfully prepared from CeO₂, C₃N₄ nanoparticles and rod-shaped WO₃ at different contents of WO₃. Among the various nanocomposites, CeO₂@C₃N₄/WO₃ nanocomposites showed the highest photocatalytic activity after 15 min of visible-light irradiation. The enhancement of nanocomposite photocatalysts can be attributed to interfacial charges transfer at the heterojunction interface of CeO₂@C₃N₄/WO₃ nanocomposites, which leads to the efficient separation of electron−hole pairs. An increase in the specific surface area of CeO₂ after adding WO₃ in the nanocomposite sample was detected. This enables the provision of more active sites for the adsorption of the pharmaceutical molecules over the photocatalyst surface for further degradation under light-on. Based on the modification method, the experimental results reported in this study may be useful for the development of other photocatalysts for the photocatalytic degradation of some other pharmaceuticals pollutants in water.

ACKNOWLEDGEMENTS

Experimental analyzes in this study were performed at the Laboratories of the Canada Research Center, Ottawa, Canada. The authors would like to thank this body for providing financial support.