Enhanced Photocatalytic Degradation of Amoxicillin with Mn-Doped Cu2O under Sunlight Irradiation

Abstract

In this work, we report the synthesis of Mn-doped Cu₂O nanoparticles using aloe vera leaves extract. X-ray diffraction data revealed that the Mn-doped Cu₂O crystals have a cubic crystal structure. The surface morphology of the as-synthesized catalyst indicated truncated octahedral and spherical-like shapes. The photocatalytic activity of the catalyst is efficient at pH 9, initial concentration of amoxicillin 15 mg/L, and photocatalyst dosage 1 g/L under sunlight irradiation. 92% of amoxicillin was degraded in the presence of Mn-doped Cu₂O. The enhancement in photocatalytic performance is due to the incorporation of Mn, which delays the rapid recombination rate by trapping the photogenerated electron. Therefore, Mn-doped Cu₂O could remove pharmaceuticals from pharmaceutical factory and hospital wastes.

1. Introduction

The increment of pollutants in water system has become one of the environmental problems which needs to be addressed by environmental protection agencies. Pharmaceuticals, mainly antibiotics, are part of the various emerging contaminants that have been identified in diverse water matrices. Several studies have presented that most antibiotics are not digested well by humans and animals. Around 25–75% of these drugs consumed by the living organisms form part of the excrement and urine [1,2,3]. These antibiotics reach the water bodies and the environment through several means, for example waste water from hospitals, pharmaceutical industry, and from human and animal waste deposits [4]. The contamination of environment, especially water bodies and soil, with these antibiotics is of concern because of their highly persistent, toxicity to aquatic life, acute and chronic toxicity effect on humans and animals, and propagation of antibiotic resistant microorganism [5,6].

Amoxicillin (AMX) is one of the most widely used antibiotics to treat human infections [7,8]. Several reports have shown that over 80 percent of orally administered amoxicillin in humans is excreted through urine after 2 hour of ingestion [6,9]. Currently, the concentration of amoxicillin present in hospital [10], industrial, and domestic [11,12] wastewaters has been reported within ng/L to mg/L range.

Numerous techniques have been used to remove antibiotics from different mediums, such as adsorption, advanced oxidation processes, and membrane filtration [13,14]. Among other techniques, advanced oxidation processes (AOPs) have been found to be the most effective for the removal of these pharmaceuticals. This technique has hydroxyl radical to oxidize the organic compounds into harmless products, and the capability of operating at ambient conditions and utilize sunlight as the source of energy [4,15]. Photocatalysis is one of the emerging AOP techniques which utilizes nanometer-sized catalyst and light as the energy source to activate chemical reactions [16,17].

Photocatalysis is widely used for the degradation of organic pollutants. The development of new materials, which are low-cost, environmentally friendly, and present long-term durability has attracted great attention. Recently, ZnO and TiO₂ photocatalyst have been significantly investigated in advanced oxidation of pollutants [18]. These metal oxide semiconductors absorb small amount of sunlight because their bandgap energy is large (3.0–3.2 eV). They cannot harvest sunlight as a source of energy. Hence, production of catalysts which can efficiently utilize sunlight is a fundamental scientific research area.

Cuprous oxide (Cu₂O) is a p-type of semiconductor with a direct band gap of 2.0–2.2 eV [19]. Cu₂O is unique in magnetic and optical properties, applicable in solar energy conversion, electrode material, gas sensor, and visible light-driven photocatalyst of organic contaminants [20]. Cupper (I) oxide has been widely used as a photocatalyst due to its advantages such as nontoxicity, easy availability, absorption of large fraction of visible light [21,22,23]. However, due to the rapid recombination of photo generated electrons and holes, pure cuprous oxide photocatalyst is seriously restricted in practical application. Hence, inhibition of the electrons and holes recombination is important to enhance photocatalytic activity of cuprous oxide. To overcome the electron-hole recombination and enhance the photocatalytic performance of the material, different techniques can be used such as doping [24], composite modification [25,26], or the formation of heterojunction [27,28]. According to [29], the photo-induced electrons in the conduction band of the cuprous oxide can be transferred to the metal which can serve as electron sink. Consequently, the lifetime of the electron can be increased, and the photocatalytic performance can be enhanced. The use of plant extracts in the synthesis of nanoparticles enables the production of large quantities of nanoparticles and can act both as reducing and stabilizing agents [30,31].

Green synthesis is a method used to synthesize nanoparticles from plant extract and microorganisms. Currently, this method has attracted significant attention as it has numerous advantages such as simplicity, cost-effectiveness, non-toxic, production of large quantities, and being environmental friendly. Plant extracts play important roles of being a reducing, stabilizing, and size controlling agent in the preparation of nanoparticles. In the chemical method, toxic chemicals are used for the production of nanoparticle. The toxic chemical species may adsorb on the surface of nanoparticles, thus affecting the environment. Moreover, the reducing and stabilizing agents used in chemical methods are expensive. Therefore, green synthesis has attained special attention for the production of different nanoparticles [32,33].

Up to the present time, researchers have investigated different photocatalysts which can degrade amoxicillin. Photocatalytic degradation of amoxicillin was studied by [34] using TiO₂ photocatalyst under UV irradiation. According to the authors, 60% of amoxicillin was degraded within 300 min of irradiation. Rani et al. (2021) examined the photocatalytic degradation of amoxicillin using TiO₂-SiO₂ composites. 88% of amoxicillin was degraded in 150 min under UV light illumination [35]. Photocatalytic decomposition of amoxicillin was investigated by Mohammadi et al. (2012) using Sn/TiO₂. According to the authors, Sn/TiO₂ nanoparticles showed good activity in the mineralization of amoxicillin under UV light [36]. Olama et al. (2018) investigated the removal of amoxicillin from aqueous solution using TiO₂/UV-C doped with trivalent iron. 99% of amoxicillin was removed by the catalyst under UV irradiation. The researchers investigated the photocatalytic removal of amoxicillin using ultraviolet radiation as a source of energy. As sunlight is a natural energy source, using sunlight as source of energy in photocatalysis is important for saving our energy. In the present study, we used sunlight as a source of energy for photocatalytic degradation of amoxicillin.

In this work, Mn-doped Cu₂O photocatalyst were fabricated via green synthesis method from aloe vera leaf extract. The structural, morphological, and optical properties of the nanoparticles were analyzed. Moreover, the photocatalytic performance of the nanoparticle was investigated in photocatalytic degradation of amoxicillin under sunlight irradiation.

2. Materials and Methods

2.1. Materials

The following chemicals were used throughout the study. Manganese sulphate monohydrate (MnSO₄.H₂O, Sigma-Aldrich, St. Loui, MI, USA), copper sulfate pentahydrate (CuSO₄.5H₂O, Sigma-Aldrich), sodium hydroxide (NaOH, Sigma-Aldrich), ethanol (C₂H₆O, Sigma-Aldrich), and distilled water. All the chemicals were analytical grade and used without further purification.

2.2. Synthesis

2.2.1. Preparation of Aloe Vera Leaves Extract

Aloe vera leaves were collected, washed thoroughly using distilled water and cut into fine pieces. About 25 g (0.25 g/mL) of these pieces was added into 100 mL distilled water and boiled for 2 h at 90 °C. The extract was filtered, and finally the filtrate was stored in 5 °C for synthesis of nanoparticle [37].

2.2.2. Synthesis of Mn-Doped Cu₂O Nanoparticles

The Mn-doped Cu₂O nanoparticles were synthesized from CuSO₄.5H₂O and MnSO₄.H₂O as precursors through eco-friendly method using aloe vera leaves extract. To prepare Mn-doped cuprous oxide nanoparticles, 1.9 mmole of CuSO₄.5H₂O were dissolved in 100 mL of aloe vera aqueous extract. Afterwards, 0.1 mmole of MnSO₄.H₂O was added to the solution under stirring. Then, 40 mL of 2M NaOH solution was added drop by drop to the above solution and kept at 130 °C under vigorous stirring. After 25 min, orange colored precipitate was formed. Thereafter, the precipitate was collected by centrifugation and washed using ethanol and water three times each. Finally, the product was dried at 90 °C for 7 h [38,39]. In order to compare with undoped Cu₂O nanoparticle, brick red colored pure Cu₂O was also synthesized using similar method in Mn-doped Cu₂O nanoparticle except adding MnSO₄·H₂O into the solution.

2.3. Characterization Techniques

Crystal structure and average crystallite size of the synthesized nanoparticles were analyzed using X-ray diffractometer (shimadzu XRD-7000). XRD fitted with a copper target to produce a Cu K radiation (λ = 0.15406 nm) was used. The accelerating voltage and functional current were set at 40 kV and 30 mA, respectively. Operation of the instrument was in step time of 0.4 second and degree of 0.02° for the range of 10° to 80°. Identification of the types of the materials from their XRD peak was in terms of the position of the 2ፀ lines with respect to the relative intensity of these lines. The surface morphological structures of the nanoparticles were studied using scanning electron microscopy (SEM), JEOL JSM-5610 (JEOL, Ltd., Akishima, Tokyo, Japan) equipped with an Everhart-Thornley detector. The optical property of the photocatalyst was recorded using UV-Vis diffuse reflectance spectrometer on diffuse reflectance in a wavelength range of 220–800 nm.

2.4. Photocatalysis Experiments

The photocatalytic degradation experiments were conducted by direct sunlight illumination on sunny days from 10:30 AM to 2:30 PM when fluctuation of solar intensity was negligible [40]. Average intensity of the sunlight during degradation experiments was 900 W/m². Aqueous solution of amoxicillin was prepared first by the addition of 25 mg of amoxicillin into 1L deionized water (25 mg/L aqueous solution of amoxicillin). In the photocatalytic degradation experiment, effect of operational parameters including initial pH (3–11), catalyst dosage (0.5–2.5 g/L), and initial concentration of amoxicillin (5-50 mg/L) were investigated. These parameters were optimized by preparing synthetic solution of amoxicillin in laboratory. The experiment was carried out at a temperature range of 24–26 °C and the solution pH was adjusted to the desired level using 1M HCl and 1M NaOH. Typically, the photocatalytic degradation experiment was performed as follows: 0.1 g of the photocatalyst was added/ dispersed into 100 mL of 15 mg/L aqueous solution of amoxicillin. Then, the suspension containing amoxicillin and photocatalyst was stirred in dark for 1 hr to establish adsorption/desorption equilibrium before irradiating to sunlight. Afterwards, the suspension was irradiated to sunlight and photocatalytic reaction time was started. The suspension was sampled after appropriate time of irradiation. Finally, the degraded sample was centrifuged and filtered to eliminate any suspended solids before measuring absorption. The filtrate of each degraded sample was assessed for amoxicillin concentration after conducting absorbance reading at 280 nm using UV-Vis spectrophotometer. The percentage degradation (degradation efficiency) of amoxicillin was determined by the following calculation.

$\% \mathrm{degradation}=\frac{\mathrm{Co}-\mathrm{Ce}}{\mathrm{Co} } \times 100$

where Co is initial concentration of amoxicillin and Ce is concentration of amoxicillin at each time interval [5,41].

3. Results and Discussion

3.1. XRD Analysis

Figure 1a,b displays the diffraction patterns of pure and Mn-doped Cu₂O nanoparticles. The diffraction peaks in the XRD patterns of Cu₂O nanoparticle at 2Ɵ value of 29.60°, 36.47°, 42.36°, 52.45°, 61.44°, 73.60°, and 77.47° corresponds to (110), (111), (200), (211), (220), (311), and (222) crystal planes of cubic structure of cuprous oxide. In the XRD pattern of Mn-Cu₂O nanoparticle, the peaks located at: 29.70°, 36.56°, 42.46°, 52.56°, 61.55°, 73.70°, and 77.58° are also assigned to the (110), (111), (200), (211), (220), (311), and (222) crystal planes of cubic cuprite structure of the synthesized nanoparticle [42,43]. The obtained pattern was found in accordance with the standard pattern of Cu₂O (JCPDS No.00-005-0667). The XRD patterns of Mn-doped Cu₂O exhibited all peaks of the pure Cu₂O with slight shift which showed successful doping of Mn. The peaks are sharp which indicated high crystallinity of the prepared nanomaterial. X-ray diffraction measurement showed no existence of secondary phase in the Cu₂O lattice structure. The Mn ions are incorporated in Cu₂O lattice. There is no detection of impurity phase ascribed to manganese oxide which indicated that complete doping of Mn²⁺ in to the Cu₂O crystal lattice [44].

Average crystallite sizes of the nanoparticles were estimated from the intensive diffraction peak using the Scherrer equation written below.

${\mathrm{D}}_{ }=\frac{0.9\mathsf{\lambda }}{\mathsf{\beta } \cos Ɵ}$

where D is the average crystallite size, λ the X-ray wavelength, Ɵ the Bragg diffraction angle, and β is the full width at half maximum (FWHM) intensity of the peak in radian. The average crystallite size was found to be 37.32 nm and 39.27 nm for bare Cu₂O and Mn-doped Cu₂O respectively as shown in Table 1.

3.2. Surface Morphology Analysis

The morphology of Cu₂O and Mn-doped Cu₂O nanoparticles was studied by scanning electron microscopy (SEM), as shown in Figure 2a,b. It was observed that the morphologies of pure and Mn-doped Cu₂O nanoparticles are homogeneously distributed octahedral and truncated octahedral respectively, as reported in [45,46]. Moreover, sphere like particles were observed in the morphology of Mn-doped Cu₂O, which is in agreement with Kerour et al. [38].

3.3. Optical Property Analysis

Absorption property of materials is a measure of the electronic excitation between valence and conduction bands of these materials, and notifies their bandgap energy (Eg). The optical absorption spectra of Cu₂O and Mn-doped Cu₂O nanoparticles are given in Figure 3a. To estimate the bandgap energy value of the nanoparticles, their absorption wavelength (λ) was measured by extrapolating downward slopes to cross the X-axis as determined by Norouzi et al. [47]. Absorption wavelength values of the as-synthesized Cu₂O and Mn-doped Cu₂O nanoparticles were found to be 539 and 564 nm, respectively. This demonstrated that Mn doping in Cu₂O shifted the absorption edge to longer wavelengths (red shift) which significantly improved the optical property of Cu₂O nanoparticle. This implies that the visible light harvesting capability of Cu₂O significantly increased, and notably promoted electron and hole separation which might increase active sites. The band gap energy of the nanoparticles was estimated from the intercepts of the tangents to the (αhν)² versus (hν) plots, where α is the absorption coefficient, ν is frequency, and h is Plank’s constant [48,49,50]. The band gap energy values found for pure Cu₂O and Mn-Cu₂O nanoparticles were 2.3 eV and 2.2 eV, respectively, as displayed in Figure 3b. The existence of crystal defects and substoichiometry usually results in red-shift in band gap. The defects create certain states in the energy gap which can absorb sub-bandgap photons, thus causing artifacts and features that can be interpreted as a smaller bandgap compared to the real bandgap [51,52]. This confirmed Mn doping in Cu₂O creates more defect sites. Therefore, the optical absorption edge of nano-sized Mn-doped Cu₂O absorbs more visible light than undoped Cu₂O nanoparticles. Table 2 depicts the absorption edge and band gap energy of the prepared photocatalysts.

3.4. Photocatalytic Degradation of Amoxicillin

3.4.1. Effect of pH

pH is an essential factor in the removal efficiency of many organic pollutants. Figure 4 illustrates the effect of pH on the removal efficiency of amoxicillin by Mn-Cu₂O nanoparticle. To determine the effect of pH on the photocatalytic degradation of amoxicillin, the experiment was carried out in the pH range of 3–11. Removal efficiency was highest at pH 9 due to the concentrated hydroxyl radicals in the solution. These radicals play a significant role in oxidizing organic contaminants. The enhanced degradation efficiency of pharmaceuticals in alkaline conditions may be due to two facts: the formation of a large amount of hydroxyl radical at a high pH due to the availability of OH^– on the surface of the catalyst that can easily be oxidized to form hydroxyl radicals and the hydrolysis of the pharmaceuticals due to the instability of the β-lactam ring at large pH values [34]. Furthermore, the dissolution of the nanoparticle was more noticeable at a low pH value, which could moderately explain the lower AMX removal at a lower pH in addition to limited generation of hydroxyl radicals [53].

3.4.2. Pollutant Initial Concentration

Effect of initial concentration of AMX on the photocatalytic degradation efficiency is displayed in Figure 5. Various degradation experiments were conducted by changing the concentration from 5 to 50 mg/L. Degradation efficiency was increased first with increasing concentration of AMX to 15 mg/L, and then decreased beyond this concentration. The presumed reason for the decrement is that when the concentration of AMX increases, large amount of AMX molecules adsorb on the surface of the photocatalyst and cause inhibitive effect on the reaction of AMX with h⁺ and/or ·OH, as a result of absence of any direct contact between AMX and the charge carriers [54]. Moreover, the AMX molecules also absorb the light and the photons could not reach the surface of the photocatalyst; hence degradation efficiency diminishes [55].

3.4.3. Catalyst Dose

Catalyst amount added into aqueous solution is one of the important parameters influencing photocatalytic performance. To optimize the catalyst load for obtaining maximum degradation efficiency, different amounts of the catalyst in the range 0.5–2.5 g/L were dispersed into the amoxicillin solution. As represented in Figure 6, maximum degradation efficiency of AMX was observed at 1 g/L catalyst dosage. Degradation efficiency was improved as catalyst amount increased to 1 g/L, beyond that the effect was less marked. Increasing the amount of catalyst enhances the number of photons absorbed on the surface of the catalyst. Thus, the active sites and the light penetration into the solution also increase which in turn improved the e⁻/h⁺ pair generation and increased the amount of OH radicals and the number of organic pollutant adsorbed on the surface. As a result, generation of electron/hole pairs and reactive OH radicals on the photocatalyst surface were increased, which enhanced the oxidation of AMX. However, when the catalyst dosage is excess, degradation efficiency decreases due to collision of active molecules with basic state molecules losing their activity. Furthermore, it should be pronounced that the decrement in degradation efficiency at a higher amount of catalyst may be also associated with improved scattering and turbidity effects, which inhibit the penetration of light into the surface of particles. On the other hand, particle–particle agglomeration results in the reduction of active sites on the surface of catalyst [56].

3.4.4. Photocatalytic Degradation of Amoxicillin under the Optimum Conditions

After optimizing the pH 9.0, catalyst dose 1 g/L, and AMX initial concentration 15 mg/L, the photocatalytic degradation of the antibiotic was carried out using pure Cu₂O and Mn-doped Cu₂O nanoparticles. As shown in Figure 7, the degradation efficiency of AMX reached 65% and 92% using Cu₂O and Mn-doped Cu₂O respectively within 180 min irradiation time. Despite the crystallite size of the as-synthesized photocatalyst, Mn-doped Cu₂O exhibited enhanced degradation efficiency than Cu₂O nanoparticles; this might be due to narrow band gap energy and unfeasibility of electron–hole recombination in Mn-doped Cu₂O [57]. When a semiconductor is illuminated by light, electrons are excited to the conduction band and holes are present in the valence band. Overall, after a few micro seconds the e⁻ and h⁺ recombine. The metal dopant traps electron from the conduction band of the semiconductor, hence hindering the recombination of electron/hole pair. As the metal dopant traps large number of electrons, large amount of superoxide radical anions (O₂^.–) are formed. The generation of large number of superoxide radical anions is important for attacking the organic pollutant which in turn enhances the degradation efficiency [58]. Therefore, Mn delays the rapid recombination by increasing the electron–hole separation. Moreover, crystal defects can create states in the energy level of Cu₂O; these states can absorb sub-band gap photons which increase light harvesting by the material. Tamam et al. [59] reported photocatalytic degradation of Rh–B dye using Mn-doped CuO nanostructured material under visible light irradiation. According to the authors, Mn-doped CuO has better photocatalytic performance in mineralization of Rh–B dye than CuO, with 93.8% dye mineralization compared to 56.52% for CuO. The Mn-doped CuO has faster charge transport but negligible electron-hole recombination than the un-doped CuO. In our study, 65% and 92% of amoxicillin was removed using pristine Cu₂O and Mn-doped Cu₂O nanoparticles respectively, which is comparable with the previous work reported by Tamam et al. (2022). Photocatalytic degradation of amoxicillin was studied by [34] using TiO₂ photocatalyst under UV irradiation. According to the authors, 60% of amoxicillin was degraded within 300 min of irradiation. Rani et al. (2021) examined the photocatalytic degradation of amoxicillin using TiO₂-SiO₂ composites. 88% of amoxicillin was degraded in 150 min under UV light illumination [35]. The researchers used UV light as energy source, but sunlight was used in our work. Photocatalytic degradation of methyl blue using Cu₂O prepared using plant extract has been reported by Kerour et al. [38]. The average size of these particles ranged between 24 and 61 nm, as proved by XRD analysis, while 37–40 nm in our present study. The band gap of Cu₂O reported by Kerour was in the range of 2.50 eV to 2.62 eV which is higher than the band gap of the present study, 2.2 to 2.3. According to Kerour et al. (2018), nearly 70% of methyl blue was degraded in the presence of Cu₂O after 3 min exposure to visible light. Methyl blue was completely removed after 10 min irradiation in visible light. The photocatalytic degradation result reported by Kerour is a little different from our result.

3.5. Kinetic Study

Kinetics of the photocatalytic degradation of amoxicillin by the pure and Mn-doped Cu₂O nanoparticle was investigated using pseudo-first-order and pseudo-second-order kinetics as depicted in Figure 8. The linear form of the pseudo-first-order kinetic model is written below.

$\mathit{l}\mathit{n}\frac{\mathit{C}\mathbf{0}}{\mathit{C}\mathit{t}}={\mathrm{k}}_1\mathrm{t}$

where C_t is the concentration of AMX at time t, C₀ is the initial concentration of AMX, k₁ is pseudo-first-order rate constant, and t is time. The plots of ln(C₀/C_t) versus time gave a straight line with a slope of k₁. Besides the pseudo-first-order equation, the linear form of pseudo second order kinetic is as described below.

$\frac{\mathbf{1}}{\mathit{C}\mathit{t}}-\frac{\mathbf{1}}{\mathit{C}\mathbf{0}}={\mathrm{k}}_2\mathrm{t}$

The plots of 1/C_t−1/C₀ versus time gave a straight line with a slope of k₂ [60]. Based on the acquired data, higher correlation coefficients R² were obtained in the pseudo-first-order kinetic model. Consequently, the photocatalytic degradation of AMX using the undoped and Mn-doped Cu₂O nanoparticle is best fitted to pseudo-first-order kinetics [61]. The rate constant (k) values of the undoped and Mn-doped Cu₂O were found to be 0.033 and 0.073 min⁻¹ respectively for AMX degradation. A good correlation coefficient value, R² of 0.984 and 0.995 was acquired for the pure and Mn-doped Cu₂O nanoparticles. Based on the reaction constants, the Mn-doped Cu₂O nanoparticle is a better photocatalyst than the undoped, which is in agreement with the photocatalytic activity study.

3.6. Proposed Mechanism

Figure 9 displays the mechanism for enhanced photocatalytic activity of Mn-doped Cu₂O under sunlight radiations. When a photocatalyst irradiates by light, excitation of electrons from valence band to conduction band and formation of holes in valence band take place. Generally, after a few micro seconds they recombine. Upon irradiating Mn-doped Cu₂O with sunlight, the photogenerated electrons migrate from the valence band of Cu₂O to the conduction band, while producing same amount of holes in the valence band. Because the Mn-Cu₂O new Fermi level is lower than the conduction band of Cu₂O, the photogenerated electrons migrate from the conduction band of Cu₂O to the Mn. Therefore, Mn serves as an electron trap to hinder the electron–hole recombination. The electrons on the surface of Mn then react with the adsorbed oxygen to form superoxide radical anions (O₂^.–). Simultaneously, the valence band holes of cuprous oxide react with water to form highly reactive hydroxyl radicals (^.OH). The formation of a large amount of O₂^.– and ·OH is important for attacking the organic molecules. After producing O₂^{. –}, Mn⁺ receives an electron from Cu₂O and becomes Mn [62]. The valence band (E_VB) and conduction band (E_CB) potential values of Mn-doped Cu₂O and Cu₂O were found to be +2 eV and −0.2 eV respectively as shown in Figure 9 [63,64,65].

4. Conclusions

In this paper, undoped and Mn-doped Cu₂O photocatalyst were synthesized using aloe vera leaves extract in an eco-friendly approach. The photocatalytic degradation of amoxicillin depends on catalyst dose, pH, and initial concentration of pollutant. Mn-doped Cu₂O photocatalyst exhibited a big enhancement in activity compared to the bare Cu₂O. This enhancement could be due to visible light harvesting and strong inhibition of electron–hole recombination. The mechanism under sunlight irradiation reveals that the Mn is used to trap an electron and increases electron–hole separation. Based on the findings, Mn-doped Cu₂O is a potential photocatalyst for the removal of pharmaceuticals from wastewater.

Author Contributions

Y.T.G. took part in conceptualization, methodology, formal analysis, original draft preparation, manuscript preparation, sorting and data analysis, investigation and validation. S.M.Y. was responsible for collecting resources and supervision. Z.G.K. took part in visualization and project administration. All authors have read and agreed to the published version of the manuscript.

Data Availability Statement

The data used to support the results of this article such as XRD, SEM, UV-Vis, and photocatalytic degradation data can be found from the corresponding author upon request.

Acknowledgments

The authors are grateful to the Werabe University for funding the work with grant number WRU1213, 2020.

Conflicts of Interest

The authors declare that there are no conflict of interest associated with the work reported in this paper.

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures and Tables

Figure 1. (a) XRD pattern of Cu2O (b) Mn-Cu2O nanoparticles.

Figure 2. SEM images of (a) Cu2O and (b) Mn-doped Cu2O nanoparticles.

Figure 3. (a) Absorption spectra (b) (αhν)2 vs (hν) plots of the nanoparticles.

Figure 4. Effect of pH on photocatalytic degradation of amoxicillin (C0 = 15 mg/L, catalyst dose = 1 g/L).

Figure 5. Effect of initial concentration of amoxicillin on photocatalytic degradation (pH = 9, catalyst dose = 1 g/L).

Figure 6. Effect of catalyst dose on photocatalytic degradation of amoxicillin (C0 = 15 mg/L, pH = 9).

Figure 7. Photocatalytic degradation of amoxicillin using Cu2O and Mn-Cu2O under the optimal conditions (pH = 9, C0 = 15 mg/L and amount of catalysts = 1 g/L).

Figure 8. Plot of ln(C0/C) versus t.

Figure 9. Proposed mechanism for the photocatalytic degradation of amoxicillin using Mn-doped Cu2O nanoparticles under solar light irradiation.

Table 1

Crystalline size of undoped and Mn-doped Cu₂O nanoparticles.

Nanoparticles	2Ɵ (Deg)	FWHM (Radian)	Crystallite Size (nm)
pure Cu2O	36.467	0.004551	37.32
Mn-doped Cu2O	36.562	0.004188	39.27

Table 2

Absorption edge and band gap energy of undoped and Mn-doped Cu₂O nanoparticles.

Nanoparticle	Absorption Wavelength (nm)	Bandgap Energy (eV)
Undoped Cu2O	539	2.3
Mn-doped Cu2O	564	2.2

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