Enhanced Photocatalytic and Anticancer Activity of Zn-Doped BaTiO 3 Nanoparticles Prepared through a Green Approach Using Banana Peel Extract

: Perovskite barium titanate (BaTiO 3 ) has received a lot of interest due to its extraordinary dielectric and ferroelectric properties, along with its moderate biocompatibility. Here, we investigated how Zn doping tuned the physicochemical characteristics, photocatalytic activity, and anticancer potential of BaTiO 3 nanoparticles synthesized from banana peel extract. XRD, TEM, SEM, EDS, XPS, BET, Raman, and PL were utilized to characterize the as-synthesized pure and Zn (1 and 3 mol%)-doped BaTiO 3 nanoparticles. All of the synthesized samples showed evidence of the BaTiO 3 tetragonal phase, and the XRD patterns of the Zn-doped BaTiO 3 nanoparticles showed the presence of a Zn peak. The particle size of BaTiO 3 decreased with increasing levels of Zn doping without morphological changes. After Zn doping, the PL intensity of BaTiO 3 decreased, suggesting a lower electron–hole recombination rate. BET analysis found that the surface area of Zn-doped BaTiO 3 nanoparticles was higher than that of pure BaTiO 3 . Under visible irradiation, the photocatalytic activity of pure and Zn-doped BaTiO 3 nanoparticles was compared, and a remarkable 85% photocatalytic activity of Zn (3%)-doped BaTiO 3 nanoparticles was measured. As a result, Zn-doped BaTiO 3 nanoparticles are recognized as excellent photocatalysts for degrading organic pollutants. According to cytotoxicity data, Zn (3%)-doped BaTiO 3 nanoparticles display four-fold greater anticancer activity against human lung carcinoma (A549) than pure BaTiO 3 nanoparticles. It was also observed that Zn-doped BaTiO 3 nanoparticles kill cancer cells by increasing the intracellular level of reactive oxygen species. Furthermore, compared to pure BaTiO 3 , the Zn-doped BaTiO 3 nanostructure showed better cytocompatibility in non-cancerous human lung ﬁbroblasts (IMR90). The Zn-doped BaTiO 3 nanoparticles have a reduced particle size, increased surface area, and a lower electron–hole recombination rate, which are highly beneﬁcial for enhanced photocatalytic and anticancer activity. Overall, current data showed that green-fabricated Zn-BaTiO 3 nanoparticles have superior photocatalytic and anticancer effects along with improved biocompatibility compared to those of pure BaTiO 3 . This work underlines the signiﬁcance of utilizing agricultural waste (e.g., fruit peel) for the fabrication of BaTiO 3 -based nanostructures, which hold great promise for biomedical and environmental applications.

Different crystallographic phases exist for BaTiO 3 , with cubic and tetragonal phases being the most stable [2].The effectiveness of a semiconductor photocatalyst depends on a number of factors, such as band gap, light absorption, charge carrier recombination rate, crystal orientation, morphology, and particle size [7,8].The preparation of a photocatalyst that operates in visible light is typically accomplished by doping a semiconductor with an appropriate metal element [9].Recent studies of metal ion-doped oxide semiconductor nanoparticles have gained attention due to the fact that the presence of metal ions in oxide semiconductors (e.g., BaTiO 3 ) results in a narrow band gap, high visible light absorption, and a low recombination rate of electron-hole pairs [10].
The catalytic efficiency of BaTiO 3 could be significantly improved by doping it with metal ions (e.g., Zn 2+ ) [11].Metal ion doping causes a narrow bandgap and a diminishing electron-hole recombination rate in BaTiO 3 nanoparticles [12].Hence, tuning the physicochemical properties of BaTiO 3 via metal ion doping can be a promising tool for their use in photocatalysis and anticancer activity [6].Pure and metal-doped BaTiO 3 nanoparticles can be synthesized using a variety of physical and chemical methods.However, physical methods are expensive, energy-intensive, and temperature-dependent, and chemical approaches often result in the release of harmful chemicals into the environment [13].Furthermore, chemical and physical routes for the synthesis of nanostructures are not suitable for biomedical applications [14].Currently, eco-friendly green methods are being applied to synthesize semiconductor nanoparticles because of the benefits they provide in terms of particle homogeneity, crystallinity, particle size distribution, processing ease, cost effectiveness, and sustainability [15].
Here, we developed a facile, low-cost, and environmentally friendly approach for the synthesis of pure and Zn (1 and 3 mol%)-doped BaTiO 3 nanoparticles from banana peel extract.Banana peel contains several health-beneficial phytochemicals [16].The compounds derived from banana peel extract were used in the green synthesis of both pristine and Zn-doped BaTiO 3 nanoparticles as reducing and stabilizing agents.Banana peel has excellent antioxidant, antimicrobial, and antibiotic properties due to its high concentration of phenolic compounds and dietary fibers [17].The high concentration of flavonoids found in banana peel has been observed to possess anticancer properties [18].The aim of this research was to integrate the advantageous properties of Zn and BaTiO 3 , provided by banana peel extract, in order to augment the photocatalytic and anticancer effect.Prepared pure and Zn-doped BaTiO 3 nanoparticles were characterized via field emission transmission electron microscopy (FETEM), energy-dispersive spectroscopy (EDS), field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) analysis, Raman, and photoluminescence (PL) spectroscopy.Synthesized nanoparticles were assessed for their photocatalytic activity against methylene blue (MB) dye under visible light.Human lung cancer (A549) cells were used to examine the anticancer potential of the as-synthesized pure and Zn-doped BaTiO 3 nanoparticles.Reactive oxygen species (ROS) were investigated to delineate the plausible mechanism of the anticancer activity of the synthesized samples.Human lung fibroblast (IMR90) cells were used to determine the cytocompatibility of the prepared nanoparticles.

XRD Analysis
In Figure 1A, the XRD patterns in the 2θ range of 20-90 degrees demonstrate the phase structure of the pure and Zn-doped BaTiO 3 nanoparticles.Main diffraction peaks of pure BaTiO 3 nanoparticles are found at 2θ values of 22.39, 31.39, 39.14, 45.38, 51.11, 56.40, 66.07, 70.67, 75.04, 79.39, and 83.76, corresponding to the (100), (110), (111), ( 200), (210), ( 211), (220), ( 221), (310), (311), and (320) crystal planes of tetragonal-phase BaTiO 3 (JCPDS no.05-0626) (Khan et al., 2021b).All of the above-mentioned peaks were also seen in Zn (1 and 3%)-doped BaTiO 3 nanostructures, as was an additional peak at 43.33°that matched the (101) crystal plane of the face-centered cubic phase of Zn (JCPDS no.004-0831) [19].Both the pure and Zn-doped BaTiO 3 nanostructures lacked any peaks indicative of impurities.Scherrer's equation was used to calculate the average particle size [20].Pure and Zn (1 and 3 mol%)-doped nanoparticles have crystallite sizes of 57.4,48.5, and 35.2 nm, respectively.A very prevalent pattern that was also mentioned in our earlier work is the reduction in particle size following metal ion doping [21].The substitution of Zn 2+ for Ba 2+ in the BaTiO 3 crystalline structure is responsible for the reduction in the particle size of the doped BaTiO 3 in comparison to that of the pure BaTiO 3 .This might be because Zn 2+ ions have a smaller ionic radius (74 pm) than does Ba 2+ (135 pm).Furthermore, we found that the XRD peak (111) in the Zn-doped BaTiO 3 nanostructures slightly shifted to a lower value compared to that of the pure BaTiO 3 (Figure 1B).In the context of lattice strain, a peak shift toward a lower value suggests lattice expansion.Lattice strain refers to the deformation of a crystal lattice from its ideal structure.It can result from various factors, including mechanical stress, the presence of impurities (e.g., via doping), or crystal defects.The peak shift is further evidence of the integration of Zn ions in BaTiO 3 nanoparticles.
(JCPDS no.05-0626) (Khan et al., 2021b).All of the above-mentioned peaks were also seen in Zn (1 and 3%)-doped BaTiO3 nanostructures, as was an additional peak at 43.33˚ that matched the (101) crystal plane of the face-centered cubic phase of Zn (JCPDS no.004-0831) [19].Both the pure and Zn-doped BaTiO3 nanostructures lacked any peaks indicative of impurities.Scherrer's equation was used to calculate the average particle size [20].Pure and Zn (1 and 3 mol%)-doped nanoparticles have crystallite sizes of 57.4,48.5, and 35.2 nm, respectively.A very prevalent pa ern that was also mentioned in our earlier work is the reduction in particle size following metal ion doping [21].The substitution of Zn 2+ for Ba 2+ in the BaTiO3 crystalline structure is responsible for the reduction in the particle size of the doped BaTiO3 in comparison to that of the pure BaTiO3.This might be because Zn 2+ ions have a smaller ionic radius (74 pm) than does Ba 2+ (135 pm).Furthermore, we found that the XRD peak (111) in the Zn-doped BaTiO3 nanostructures slightly shifted to a lower value compared to that of the pure BaTiO3 (Figure 1B).In the context of la ice strain, a peak shift toward a lower value suggests la ice expansion.La ice strain refers to the deformation of a crystal la ice from its ideal structure.It can result from various factors, including mechanical stress, the presence of impurities (e.g., via doping), or crystal defects.The peak shift is further evidence of the integration of Zn ions in BaTiO3 nanoparticles.

Electron Microscopy Analysis
The microstructure, particle size, and morphology of pure BaTiO3 and Zn-doped BaTiO3 nanoparticles were analyzed via TEM and SEM.The particle size distribution ob-

Electron Microscopy Analysis
The microstructure, particle size, and morphology of pure BaTiO 3 and Zn-doped BaTiO 3 nanoparticles were analyzed via TEM and SEM.The particle size distribution obtained from the TEM images is presented in Figure 2A-C.The TEM micrographs depicted in Figure 2D-F serve as representations of the pure BaTiO 3 , 1% Zn-BaTiO 3 , and 3% Zn-BaTiO 3 nanoparticles, respectively.As we can see in the TEM images, the synthesized samples have a nearly spherical shape.Particle size is reduced by Zn doping without changing the shape.Based on TEM measurements, the average particle size (calculated from 100 particles) of pure BaTiO 3 , 1% Zn-BaTiO 3 , and 3% Zn-BaTiO 3 nanoparticles was determined to be 59.7, 51.3, and 38.5 nm, respectively.These findings are in accordance with the XRD estimations.The tetragonal phase of the prepared nanoparticles is confirmed by the visible lattice fringes observed in the high-resolution TEM images, as depicted in Figure 2G-I.The lattice's interplanar spacing was measured to be approximately 0.281-0.285nm, corresponding to the interplanar distance of the (100) plane within the tetragonal phase of the BaTiO 3 nanostructure.The interplanar spacing of zinc (Zn) lattice fringes is observed in the range of 0.241-0.243nm, indicating the presence of the cubic crystal structure of Zn with the (101) crystallographic plane.The lattice distances were found to be consistent with the XRD results.The typical SEM images of nanostructures constructed of pure BaTiO3, 1% Zn-Ba-TiO3, and 3% Zn-BaTiO3 are shown in Figure 3A-C, respectively.These images suggested the spherical form of nanoparticles, and it was found that the size of BaTiO3 particles decreases with increasing Zn doping.According to SEM-coupled EDS analysis (Figure 3D), The typical SEM images of nanostructures constructed of pure BaTiO 3 , 1% Zn-BaTiO 3 , and 3% Zn-BaTiO 3 are shown in Figure 3A-C, respectively.These images suggested the spherical form of nanoparticles, and it was found that the size of BaTiO 3 particles decreases with increasing Zn doping.According to SEM-coupled EDS analysis (Figure 3D), 3% Zn-BaTiO 3 included stoichiometric levels of Ba (68.46%),Ti (21.20%), O (7.64%), and Zn (2.71%).The SEM elemental mapping of 3% Zn-BaTiO 3 (Figure 4) provided additional confirmation of the presence of Zn, Ba, Ti, and O in the synthesized Zn-doped BaTiO 3 nanoparticles.

XPS Analysis
The surface chemical content of the prepared materials was analyzed using XPS.

XPS Analysis
The surface chemical content of the prepared materials was analyzed using XPS.

XPS Analysis
The surface chemical content of the prepared materials was analyzed using XPS. Figure 5A-E shows the XPS survey spectra of Zn-doped BaTiO 3 nanoparticles and the high-resolution signals of individual elements such as Ba 3d, Ti 2p, Zn 2p, and O 1s.The Ba 3d signal of the XPS spectra shows two bands, Ba 3d 5/2 and Ba 3d 3/2 , located at 781.9 eV and 797.1 eV, respectively (Figure 5B).The valence of Ti in BaTiO 3 nanoparticles was demonstrated by the Ti 2p signal, which had two peaks, Ti 2p 3/2 and Ti 2p 1/2 , at 460.9 eV and 466.2 eV, respectively (Figure 5C) [8].The binding energies of Zn 2p 3/2 and Zn 2p 1/2 were observed to be in the XPS spectra of Zn2p at 1021.98 eV and 1045.1 eV, respectively (Figure 5D).The differences in peak energies (24 eV) indicate that Zn mostly exists in the Zn 2+ state [22].As we can see in Figure 5E, O1s is divided into two peaks that are present at about 529.73 eV and 530.71 eV, respectively.These two peaks of O1s correspond to oxygen atoms in the forms of Ba-O-Ti and Ti-O-Ti [1].
Catalysts 2023, 13, x FOR PEER REVIEW 7 of 18 797.1 eV, respectively (Figure 5B).The valence of Ti in BaTiO3 nanoparticles was demonstrated by the Ti 2p signal, which had two peaks, Ti 2p3/2 and Ti 2p1/2, at 460.9 eV and 466.2 eV, respectively (Figure 5C) [8].The binding energies of Zn 2p3/2 and Zn 2p1/2 were observed to be in the XPS spectra of Zn2p at 1021.98 eV and 1045.1 eV, respectively (Figure 5D).The differences in peak energies (24 eV) indicate that Zn mostly exists in the Zn 2+ state [22].As we can see in Figure 5E, O1s is divided into two peaks that are present at about 529.73 eV and 530.71 eV, respectively.These two peaks of O1s correspond to oxygen atoms in the forms of Ba-O-Ti and Ti-O-Ti [1].

Brunauer-Emmett-Teller (BET) Analysis
The BET surface area and porosity of synthesized samples were assessed using the N 2 gas adsorption protocol.Figure 6A,B shows the adsorption-desorption isotherms and pore width distribution (insets) of pure and Zn (3%)-doped BaTiO 3 nanoparticles.These results suggest that both pure BaTiO 3 and Zn-doped BaTiO 3 nanoparticles exhibit a type IV pattern with a mesoporous nature per the IUPAC classification [3].BET analysis shows that the surface area and pore size of Zn (3%)-doped BaTiO 3 nanoparticles were 14.4 m 2 /g and 2.1 nm, which were different from those of pure BaTiO 3 nanoparticles (9.3 m 2 /g and 3.2 nm, respectively).In comparison to pure BaTiO 3 nanoparticles, the higher surface area and lower pore diameter of Zn (3%)-doped BaTiO 3 nanoparticles are beneficial for higher photocatalytic and anticancer effects [23].

Brunauer-Emme -Teller (BET) Analysis
The BET surface area and porosity of synthesized samples were assessed using the N2 gas adsorption protocol.Figure 6A,B shows the adsorption-desorption isotherms and pore width distribution (insets) of pure and Zn (3%)-doped BaTiO3 nanoparticles.These results suggest that both pure BaTiO3 and Zn-doped BaTiO3 nanoparticles exhibit a type IV pa ern with a mesoporous nature per the IUPAC classification [3].BET analysis shows that the surface area and pore size of Zn (3%)-doped BaTiO3 nanoparticles were 14.4 m 2 /g and 2.1 nm, which were different from those of pure BaTiO3 nanoparticles (9.3 m 2 /g and 3.2 nm, respectively).In comparison to pure BaTiO3 nanoparticles, the higher surface area and lower pore diameter of Zn (3%)-doped BaTiO3 nanoparticles are beneficial for higher photocatalytic and anticancer effects [23].

Raman Analysis
Raman spectroscopy was used to further assess the impact of Zn doping on the structural properties of BaTiO3 nanoparticles.The range of wavenumbers of 200-1000 cm −1 was evaluated in the room temperature Raman spectra of pure and Zn-doped BaTiO3 particles (Figure 7).The major peaks of the tetragonal phase of BaTiO3 were found at 306, Figure 6.BET adsorption-desorption isotherms for pure BaTiO 3 (A) and Zn (3%)-doped BaTiO 3 nanoparticles (B).Insets represent the pore diameter distribution.

Raman Analysis
Raman spectroscopy was used to further assess the impact of Zn doping on the structural properties of BaTiO 3 nanoparticles.The range of wavenumbers of 200-1000 cm −1 was evaluated in the room temperature Raman spectra of pure and Zn-doped BaTiO 3 nanoparticles (Figure 7).The major peaks of the tetragonal phase of BaTiO 3 were found at 306, 509, and 720 cm −1 [24].The peak at 306 cm −1 was caused by the vibration of the TiO 6 group.Oxygen atom displacement was thought to be the source of the vibrations that caused the peak at 509 cm −1 .In addition, the ability to distinguish between the phase transition in pure BaTiO 3 and Zn-doped BaTiO 3 nanoparticles was facilitated by the appearance of a peak at 720 cm −1 , which could be attributed to the tetragonal phase of BaTiO 3 .Furthermore, the strength of Raman peaks altered with increasing Zn doping, revealing that the higher the Zn doping, the lower the peak intensity.The tetragonal phase and decreased peak intensity of BaTiO 3 nanoparticles after Zn doping are desirable for enhanced photocatalytic and anticancer activity.

Photoluminescence (PL) Analysis
Prepared nanoparticles were investigated using PL spectra to be er comprehend the segregation of photogenerated charge carriers from their excited state.Pure BaTiO3, 1% Zn-BaTiO3, and 3% Zn-BaTiO3 nanoparticles were excited at 350 nm, and their PL spectra were recorded at room temperature (Figure 5).In this case, the emission maxima of all three nanoparticles were located around 400 and 486 nm.The PL intensity of Zn-doped BaTiO3 nanoparticles was lower compared to that of pure BaTiO3 nanoparticles, and it reduced as the Zn concentration increased.The recombination rate of photogenerated electron-hole pairs is projected to be lower and the photocatalytic activity is projected to be higher at lower PL intensities [8]. Figure 8 shows that Zn (3%)-doped BaTiO3 nanostructures effectively inhibit recombination between charge carriers because their peak intensity is lower than that of pure BaTiO3 nanoparticles.Zn doping creates oxygen vacancies within the crystal la ice of BaTiO3 nanoparticles due to the charge imbalance caused by the substitution of zinc ions with titanium or barium ions.The oxygen vacancies trapped the photo-induced charge carriers (electrons/holes).This phenomenon enhances the generation of reactive oxygen species (ROS), leading to enhanced photocatalytic and anticancer activity.

Photoluminescence (PL) Analysis
Prepared nanoparticles were investigated using PL spectra to better comprehend the segregation of photogenerated charge carriers from their excited state.Pure BaTiO 3 , 1% Zn-BaTiO 3 , and 3% Zn-BaTiO 3 nanoparticles were excited at 350 nm, and their PL spectra were recorded at room temperature (Figure 5).In this case, the emission maxima of all three nanoparticles were located around 400 and 486 nm.The PL intensity of Zn-doped BaTiO 3 nanoparticles was lower compared to that of pure BaTiO 3 nanoparticles, and it reduced as the Zn concentration increased.The recombination rate of photogenerated electron-hole pairs is projected to be lower and the photocatalytic activity is projected to be higher at lower PL intensities [8]. Figure 8 shows that Zn (3%)-doped BaTiO 3 nanostructures effectively inhibit recombination between charge carriers because their peak intensity is lower than that of pure BaTiO 3 nanoparticles.Zn doping creates oxygen vacancies within the crystal lattice of BaTiO 3 nanoparticles due to the charge imbalance caused by the substitution of zinc ions with titanium or barium ions.The oxygen vacancies trapped the photo-induced charge carriers (electrons/holes).This phenomenon enhances the generation of reactive oxygen species (ROS), leading to enhanced photocatalytic and anticancer activity.

Photocatalytic Analysis
The photocatalytic activity of pure BaTiO3 and Zn (1% and 3%)-doped BaTiO3 nanoparticles was tested by watching how methylene blue (MB) dye degraded over time when exposed to visible light.The results are shown in Figure 9A-C.All of the synthesized nanoparticles had a MB absorption peak at 663 nm, which decreased with time and disappeared after around 80 min, suggesting that all of the MB molecules were digested.Based on the relation provided in the experimental section, the decomposition efficiency of nanoparticles was determined.Degradation profiles show that after 80 min of exposure to visible light, the pure BaTiO3, 1% Zn-BaTiO3, and 3% Zn-BaTiO3 nanoparticles had photocatalytic activities of 58%, 70%, and 85%, respectively (Figure 9D).Zn-doped BaTiO3 nanoparticles had a reduced electron-hole recombination rate, a smaller particle size, and a higher surface area, all of which contributed to their increased photocatalytic activity [8].We also compare the organic pollutant degradation efficiency of Zn-doped BaTiO3 nanoparticles with that found in earlier studies (Table 1).

Photocatalytic Analysis
The photocatalytic activity of pure BaTiO 3 and Zn (1% and 3%)-doped BaTiO 3 nanoparticles was tested by watching how methylene blue (MB) dye degraded over time when exposed to visible light.The results are shown in Figure 9A-C.All of the synthesized nanoparticles had a MB absorption peak at 663 nm, which decreased with time and disappeared after around 80 min, suggesting that all of the MB molecules were digested.Based on the relation provided in the experimental section, the decomposition efficiency of nanoparticles was determined.Degradation profiles show that after 80 min of exposure to visible light, the pure BaTiO 3 , 1% Zn-BaTiO 3 , and 3% Zn-BaTiO 3 nanoparticles had photocatalytic activities of 58%, 70%, and 85%, respectively (Figure 9D).Zn-doped BaTiO 3 nanoparticles had a reduced electron-hole recombination rate, a smaller particle size, and a higher surface area, all of which contributed to their increased photocatalytic activity [8].We also compare the organic pollutant degradation efficiency of Zn-doped BaTiO 3 nanoparticles with that found in earlier studies (Table 1).
Green-fabricated Zn-doped BaTiO 3 nanoparticles may have more potential for use if they are durable and can be used several times [12].Five photodegradation cycles were performed under constant research circumstances to determine the reusability and stability of 3% Zn-BaTiO 3 nanoparticles.There was just a little drop in photocatalytic effectiveness from 85 to 83% after five test cycles.This demonstrates that the Zn-doped BaTiO 3 photocatalysts prepared from banana peel extract are reasonably stable when exposed to visible light, which is encouraging for their potential use in environmental remediation.Green-fabricated Zn-doped BaTiO3 nanoparticles may have more potential for use if they are durable and can be used several times [12].Five photodegradation cycles were performed under constant research circumstances to determine the reusability and stability of 3% Zn-BaTiO3 nanoparticles.There was just a li le drop in photocatalytic effectiveness from 85 to 83% after five test cycles.This demonstrates that the Zn-doped BaTiO3 photocatalysts prepared from banana peel extract are reasonably stable when exposed to visible light, which is encouraging for their potential use in environmental remediation.

Anticancer Study
Currently, there is ongoing research into the potential application of semiconductor nanoparticles doped with metal ions in the field of cancer therapy [29,30].Recent reports suggest that BaTiO 3 nanoparticles may have potential for use in biomedical applications, such as cancer treatment [6,31].The impact of metal ion doping on the anticancer properties of BaTiO 3 has not been extensively studied.This study investigates the potential anticancer effect of pure and Zn-doped BaTiO 3 nanoparticles on human lung cancer cells (A549).Cancer cells were exposed to varying concentrations (1-200 µg/mL) of pure BaTiO3, 1% Zn-BaTiO 3 , and 3% Zn-BaTiO 3 nanoparticles for 24 h.Anticancer activity was assessed using the MTT assay.The results depicted in Figure 10A indicate that both the pure and Zn-doped BaTiO 3 nanoparticles exhibited dose-dependent anticancer activity in cancer (A549) cells.Moreover, the anticancer efficacy of BaTiO 3 nanoparticles increases with increasing amounts of Zn doping.The inhibitory concentration (IC 50 ) of pure BaTiO 3 , 1% Zn-BaTiO 3 , and 3% Zn-BaTiO 3 nanoparticles was 64.4,35.9, and 15.4 µg/mL, respectively.This finding indicates that the incorporation of Zn 2+ ions is a significant factor in augmenting the anticancer efficacy of BaTiO 3 nanoparticles.
Catalysts 2023, 13, x FOR PEER REVIEW 13 of 18 Currently, there is ongoing research into the potential application of semiconductor nanoparticles doped with metal ions in the field of cancer therapy [29,30].Recent reports suggest that BaTiO3 nanoparticles may have potential for use in biomedical applications, such as cancer treatment [6,31].The impact of metal ion doping on the anticancer properties of BaTiO3 has not been extensively studied.This study investigates the potential anticancer effect of pure and Zn-doped BaTiO3 nanoparticles on human lung cancer cells (A549).Cancer cells were exposed to varying concentrations (1-200 µg/mL) of pure Ba-TiO3, 1% Zn-BaTiO3, and 3% Zn-BaTiO3 nanoparticles for 24 h.Anticancer activity was assessed using the MTT assay.The results depicted in Figure 10A indicate that both the pure and Zn-doped BaTiO3 nanoparticles exhibited dose-dependent anticancer activity in cancer (A549) cells.Moreover, the anticancer efficacy of BaTiO3 nanoparticles increases with increasing amounts of Zn doping.The inhibitory concentration (IC50) of pure BaTiO3, 1% Zn-BaTiO3, and 3% Zn-BaTiO3 nanoparticles was 64.4,35.9, and 15.4 µg/mL, respectively.This finding indicates that the incorporation of Zn 2+ ions is a significant factor in augmenting the anticancer efficacy of BaTiO3 nanoparticles.GraphPad Prism (version 6.05) was used for the statistical analysis.
Semiconductor nanomaterials have been proposed to exhibit anticancer activity through the potential mechanism of ROS-induced oxidative stress [32,33].Therefore, we investigated the intracellular level of ROS in the cancer (A549) cells after exposure to various concentrations (1-200 µg/mL) of pure BaTiO3, 1% Zn-BaTiO3, and 3% Zn-BaTiO3 nanoparticles for 24 h.The results depicted in Figure 10B indicate that the prepared samples elicited a statistically significant, dose-dependent increase in ROS generation in cancer Semiconductor nanomaterials have been proposed to exhibit anticancer activity through the potential mechanism of ROS-induced oxidative stress [32,33].Therefore, we investigated the intracellular level of ROS in the cancer (A549) cells after exposure to various concentrations (1-200 µg/mL) of pure BaTiO 3 , 1% Zn-BaTiO 3 , and 3% Zn-BaTiO 3 nanoparticles for 24 h.The results depicted in Figure 10B indicate that the prepared samples elicited a statistically significant, dose-dependent increase in ROS generation in cancer cells.Furthermore, when compared to pure BaTiO 3 nanoparticles, the Zn-doped BaTiO 3 nanoparticles exhibited a higher ROS level, and ROS generation increased with increasing the percentage of Zn dopant.
Zn doping creates several beneficial modifications in BaTiO 3 nanoparticles, which are highly beneficial for enhanced anticancer activity.Zn doping reduced particle size, increased surface area, and reduced the rate of electron/hole recombination in BaTiO 3 nanoparticles.This is a perfect setting for surface redox reactions that can cause cancer cells to produce ROS.Our results indicated that Zn-doped BaTiO 3 nanoparticles destroy cancer cells through ROS generation.

Cytocompatibility Study
The biocompatibility of possible anticancer agents should also be investigated in normal cells.This prompted us to assess the effect of pure and Zn-doped BaTiO 3 nanoparticles on normal lung fibroblasts (IMR90).Figure 10C showed that the normal IMR90 cells were not affected by either pure or Zn-doped BaTiO 3 nanoparticles.Interestingly, the cytocompatibility of BaTiO 3 nanoparticles improves with increasing the percentage of Zn doping.Overall, these results suggest that Zn-doped BaTiO 3 nanoparticles might destroy cancer cells while having minimal effect on healthy cells.Based on these findings, researchers may investigate the anticancer effects of Zn-BaTiO 3 nanoparticles in other human cancer cell lines and appropriate in vivo systems.

Preparation of Banana Peel Extract
Locally purchased ripped bananas were used to obtain the banana peels.Fruit peels were washed in deionized water and dried using a food dryer.Dried peels were ground into a powder using an electric grinder.The banana peel powder (10 g) was added to 500 mL of deionized water and stirred constantly for 6 h.After that, it was placed in a water bath at 60 • C for 1 h.The final step was to filter the mixture through filter paper (pore size 0.2 µm), and the filtrate (extract) was stored at 4 • C for further use in nanoparticle synthesis.

Eco-Friendly Production of Zn-Doped BaTiO 3 Nanoparticles
Banana peel extract, barium acetate, tetrabutyl titanate, and zinc acetate were used as precursors for the synthesis of Zn-doped BaTiO 3 nanoparticles.In brief, stoichiometric amounts of barium acetate, tetrabutyl titanate, and zinc acetate were initially dissolved in deionized water in individual flasks.These solutions were then added to the banana peel extract and stirred for 1 h.After that, the mixture was kept in a water bath at 60 • C for 12 h.In order to obtain Zn-doped BaTiO 3 nanostructures, the dried samples (1 g) were calcined at 900 • C for 5 h in a muffle furnace.A similar method was used to synthesize pure BaTiO 3 nanoparticles without the addition of zinc acetate.A graphical illustration of the green synthesis of Zn-doped BaTiO 3 nanoparticles is presented in Figure 11.

Characterization
XRD (PanAlytical X'pert Pro) was employed to characterize the crystallinity and phase purity of prepared nanoparticles.Shape, size, surface morphology, and elemental analysis were further determined via field emission scanning electron microscopy (FESEM, JSM-7600F, JEOL, Inc., Tokyo, Japan), field emission transmission electron microscopy (FETEM, JEM-2100, JEOL), and energy-dispersive X-ray spectroscopy (EDS).A fluorescence spectrophotometer (Hitachi F-4600) was used to record the luminescence spectra.XPS analysis was carried out in the ESCA system (VG 3000) with monochromatic MgKα (1253.6 eV) radiation.Raman spectroscopy was used to examine the existing phases of synthesized samples (Perkin-Elmer 400F) using a 514 nm laser beam.The specific surface area and pore size distribution were determined via BET analysis under nitrogen gas adsorption (Gemini VII 2390, Micromeritics).

Photocatalytic Evaluation
The degradation of methylene blue (MB) dye under visible-light irradiation was used to measure the photocatalytic activity of pure and Zn-doped BaTiO 3 nanoparticles.In 60 mL of the MB aqueous solution, the necessary amount of nanoparticles was added (the MB dye concentration in the aqueous solution without catalyst was 20 mg/L).Prior to exposure, the dye and nanoparticle suspensions were magnetically agitated for 90 min in the dark.The goal was to keep the dye and nanoparticles in equilibrium between adsorption and desorption.The resulting mixture was then poured into a 50 mL quartz test tube and exposed to visible light.A 400 W sodium lamp (Philips) in the 300-900 nm wavelength was used as a visible light source for the irradiation of solution.The ability of nanoparticles to degrade dye was observed by measuring the strength of the absorption peak at 663 nm.The degradation efficiency of nanoparticles was estimated using the equation photodegradation (%) = [1 − (C/C o )] × 100%, where C o and C display the original concentration of the dye solution at the initial level and after a certain duration of light irradiation.

Biological Assays
Human lung cancer cells (A549) and their normal counterparts, lung fibroblast cells (IMR90), were employed for cytotoxicity studies.The cells were cultured in DMEM supplemented with 10% FBS, 100 U/mL penicillin, and 100 µg/mL streptomycin.The cells were maintained in a humidified incubator at 37 • C with a 5% CO 2 supply.Cells were exposed to various concentrations (1-200 µg/mL) of nanoparticles for 24 h.The cytotoxicity of nanoparticles in cancer and normal cells was investigated using an MTT assay with minor changes, as described earlier [34,35].
The ROS level in cancer cells following exposure to 1-200 µg/mL nanoparticles for 24 h was determined using the probe 2,7-dichlorofluorescin diacetate (DCFH-DA).This is a cell-permeable nonfluorescent dye that is oxidized by ROS to produce highly fluorescent DCF [36].Using a microplate reader (Synergy-HT, BioTek, Winooski, VT, USA), the fluorescence of DCF was measured at the 485/520 nm excitation/emission wavelength.

Conclusions
Banana peel extract was used to successfully synthesize pure and Zn-doped BaTiO 3 nanoparticles.The XRD, XPS, TEM, SEM, EDS, BET, Raman, and PL methods were used to characterize the as-synthesized samples.In XRD analysis, the tetragonal phase of BaTiO 3 was observed in all the prepared samples, and a new Zn peak was observed in the Zndoped BaTiO 3 .XRD, TEM, and SET data found that Zn doping decreased the particle size without changing the morphology of BaTiO 3 .BET adsorption-desorption isotherms indicate that Zn doping increases the surface area of BaTiO 3 nanoparticles.The intensity of the PL spectra of BaTiO 3 decreased following Zn doping, indicating a declining recombination rate of electron-hole pairs.The degradation efficiency of pure BaTiO 3 , 1% Zn-BaTiO 3 , and 3% Zn-BaTiO 3 nanoparticles for MB dye under visible light was 58%, 70%, and 85%, respectively.In vitro studies demonstrated that Zn-doped BaTiO 3 nanoparticles were more effective than pure BaTiO 3 nanoparticles at killing human lung cancer (A549) cells.Additionally, Zn-doped BaTiO 3 nanoparticles have high cytocompatibility in normal lung fibroblasts (IMR90) compared to pure BaTiO 3 .The improved photocatalytic and anticancer activity of Zn-BaTiO 3 nanoparticles can be attributed to their reduced particle size, increased surface area, and reduced electron-hole recombination rates in comparison to those of pure BaTiO 3 nanoparticles.Further investigation into the photocatalytic activity and cancer fighting potential of green-fabricated Zn-BaTiO 3 nanoparticles is warranted.This research also underlines that agricultural waste (e.g., fruit peel) is useful for fabricating nanoparticles with potential environmental and therapeutic benefits.
Author Contributions: Conceptualization, supervision, funding acquisition, investigation and methodology, writing-original draft preparation, and writing-review and editing: M.A. Investigation and methodology, formal analysis, recourses, writing-review and editing, M.A.M.K.All authors have read and agreed to the published version of the manuscript.

Funding:
The authors extend their sincere appreciation to the Researchers Supporting Project number (RSP2023R129), King Saud University, Riyadh, Saudi Arabia.
Figure 5A-E shows the XPS survey spectra of Zn-doped BaTiO3 nanoparticles and the highresolution signals of individual elements such as Ba 3d, Ti 2p, Zn 2p, and O 1s.The Ba 3d signal of the XPS spectra shows two bands, Ba 3d5/2 and Ba 3d3/2, located at 781.9 eV and
Figure 5A-E shows the XPS survey spectra of Zn-doped BaTiO3 nanoparticles and the highresolution signals of individual elements such as Ba 3d, Ti 2p, Zn 2p, and O 1s.The Ba 3d

Figure 10 .
Figure 10.Anticancer activity (A) and ROS generation (B) of pure and Zn-doped BaTiO3 nanoparticles in human lung cancer A549 cells.Cytocompatibility of the same nanoparticles in non-cancerous human lung fibroblasts (IMR90) (C).The results are shown as the mean and standard deviation of three separate experiments (n = 3).* denotes significant difference from the control ( p < 0.05 level).GraphPad Prism (version 6.05) was used for the statistical analysis.

Figure 10 .
Figure 10.Anticancer activity (A) and ROS generation (B) of pure and Zn-doped BaTiO 3 nanoparticles in human lung cancer A549 cells.Cytocompatibility of the same nanoparticles in non-cancerous human lung fibroblasts (IMR90) (C).The results are shown as the mean and standard deviation of three separate experiments (n = 3).* denotes significant difference from the control (p < 0.05 level).GraphPad Prism (version 6.05) was used for the statistical analysis.

18 Figure 11 .Figure 11 .
Figure 11.A graphical illustration of the green synthesis of Zn-doped BaTiO3 nanoparticles from banana peel extract.3.3.CharacterizationXRD (PanAlytical X'pert Pro) was employed to characterize the crystallinity and phase purity of prepared nanoparticles.Shape, size, surface morphology, and elemental analysis were further determined via field emission scanning electron microscopy (FESEM, JSM-7600F, JEOL, Inc., Tokyo, Japan), field emission transmission electron mi-

Table 1 .
A comparison of the pollutant degradation efficiency of Zn-doped BaTiO3 nanoparticles with that found in earlier studies.

Table 1 .
A comparison of the pollutant degradation efficiency of Zn-doped BaTiO 3 nanoparticles with that found in earlier studies.