Green-Synthesized Sm 3 + -Doped ZnO Nanoparticles for Multifunctional Applications

Te present study focuses on the green-mediated synthesis of pristine and Sm 3+ -doped ZnO nanoparticles using Syzygium cumini fruit extract. Te prepared material was characterized by various characterization techniques. Photocatalytic degradation of a fast orange red (FOR) dye under UV light resulted in 88% degradation, with a minimal decrease (87.90%) observed even after fve successive runs, indicating the stability and efectiveness of the catalyst. Te enhancement in degradation efciency is attributed to the incorporation of Sm 3+ ions into the ZnO lattice. Utilizing the optimized Sm 3+ (5mol%)-doped ZnO nanoparticles, cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) were performed on the prepared electrode, demonstrating the excellent CV properties; this enhancement is attributed to the modifcation of ZnO’s redox chemistry and the alteration of charge transfer kinetics at the electrode-electrolyte interface due to the addition of Sm 3+ into the ZnO structure. Te antibacterial activity was performed against two pathogenic strains, i.e., Escherichia coli and Streptococcus aureus . Te obtained results suggest that the prepared material holds great promise for catalytic, energy storage, antibacterial, and other multifunctional applications.


Introduction
Te rapid growth in nanotechnology has greatly infuenced researchers and industries to discover new features of both novel and conventional materials at the nanoscale level [1,2].Among various nanomaterials, metal oxides exhibit outstanding electrochemical and antibacterial activity attributed to their ability to fnely tune band gaps, actively engage in redox reactions, and display surface reactivity.Tis inherent capability is pivotal in advancing the felds of energy storage and conversion, enabling the development of pioneering technologies.Moreover, the same features play a crucial role in tailoring metal oxides for specifc antibacterial or bioactive functionalities, opening up possibilities for innovative applications in healthcare and material science.Among the various metal oxides, we use zinc oxide nanoparticles as they refect semiconducting properties at the nano level [3].
ZnO nanoparticles are one of the great potential semiconductor photocatalysts owing to their advanced properties, low cost, abundance, high surface activity, and environmental friendliness.ZnO is a wide-bandgap semiconductor (3.37 eV) with a 60 meV exciton binding energy [4].Tere are three unit structures, hexagonal wurtzite, zinc blende, and rock salt in ZnO, among the various structures, and hexagonal wurtzite is the most recognized owing to its superior properties [5].
In addition to this, intensive research is carried out with efective rare earth ion dopants to enrich the photocatalytic degradation of ZnO.It has been reported that Sm 3+ doping sturdily afects crystal defects, surface morphology, and electrical and optical properties.Te dopants diminish the electron-hole pair recombination rate and formation of dopant energy levels within the band gap to expand light absorption capacity [5,18,19].Several chemical and physical methods are used for the fabrication of nanoparticles [20,21].Compared to other methods, biomediated procedures are the best possible alternative for fabricating environmentally friendly and nontoxic nanoparticles [22].
In this current work, we presented a simple green synthesis technique to fabricate pristine and Sm 3+ ionsdoped ZnO nanoparticles.Compared with other techniques, this method is simple, fast, inexpensive, green way, and highly competent.Te fuel used for the synthesis is easily available as well as renewable in nature.It has various functional biomolecules such as polyphenols, anthocyanins, favonoids, ellagic acid, gallic acid, tannins, triterpenoids, betulinic acid, and macro biomolecules, act as reducing agents, and also impact the structure properties of the synthesized materials [23][24][25].ZnO-based nanomaterials were tested for photocatalytic degradation [26,27] because it has a wide range of applications (Table 1 Supplementary data) and the main emphasis was exerted on the removal of the fast orange red (FOR) dye from synthetic waste-water [28,29].
ZnO nanoparticles doped with Sm 3+ ions were confrmed as promising extremely active photocatalyst under UV illumination because of the reduction of the band gap, improved charge separation between electrons and holes, stability, and increased light absorption capacity [30,31].Te electrochemical behaviour of the Sm 3+ ion-doped ZnO was investigated for sensing paracetamol.Paracetamol, also known as acetaminophen, is an electrochemically active molecule that has been broadly tested in various templetes.Paracetamol is the main ingredient in cold and fu medication; however, it does have some potential disadvantages and limitations; overdose of paracetamol can lead to severe complications such as liver damage or liver failure and also causes side efects in some individuals such as gastrointestinal issues, skin rashes, hives, difculty in breathing, and allergic reactions.Te sensors revealed signifcant selectivity, duplicability, and sensitivity that could be stretched to sense paracetamol in various samples.
Te present study focuses on synthesizing and characterizing Sm 3+ -doped ZnO nanoparticles through a green combustion technique using Syzygium cumini fruit extract for multifunctional applications.Te study specifcally focuses on elucidating the photocatalytic degradation efciency of a fast orange red (FOR) dye under UV light exposure, assessing the electrochemical properties of Sm 3+doped ZnO electrodes via cyclic voltammetry (CV), and evaluating the antibacterial activity against pathogenic strains, namely Escherichia coli and Streptococcus aureus.Te novelty of the present work lies in the preparation of materials for multifunctional applications with green and environmentally friendly approach.It demonstrates potential applications in catalysis, supercapacitors, batteries, sensors, and antibacterial activities, and this broad range of functionalities enhances the materials utility and widens its scope for practical applications.

Preparation of Fruit Extract.
Fresh Syzygium cumini fruit was collected from the botanical garden.Tese fruits were washed twice thoroughly using running tap water and then again washed with distilled water dried in air.Te washed portions are chopped into fne pieces and the pulp of the fruit is separated from the seeds.100 gm of the chopped pulp is taken and crushed using pestle and mortar, and juice is extracted by fltering.3+ (1-7 mol%) Nanoparticles Using Jamun Fruit Extract as Fuel.Te fabrication process of Sm 3+ -doped ZnO nanoparticles is illustrated in Figure 1.A similar procedure for the biosynthesis of undoped ZnO NPs was described elsewhere.Briefy, the stoichiometric ratio of Sm(NO 3 ) 3 .6H 2 O and Zn(NO 3 ) 2 .6H 2 O were taken in Becher containing 10 ml of distilled water and 7 ml of fruit extract.Te uncovered Becher was shaken for 15 min using a magnetic stirrer and kept at 450 °C in Mufe Furnace for 30 min.Te sample is calcined at the temperature of 550 °C for 3 hr.Te obtained white solid was cooled down, pulverized, and then stored in a desiccator for further experiments, and the corresponding procedure is illustrated in Figure 1.Undoped ZnO NPs were also prepared by the above mentioned procedure.Sm-doped ZnO with diferent mol% Sm 3+ doping concentrations ranging from 1 to 7 mol % were denoted by ZnO: 1 mol %Sm 3+ , ZnO: 3 mol %Sm 3+ , Zno: 5 mol% Sm 3+ , and ZnO:7 mol %Sm 3+ , respectively [32].[33].Te progress of the reaction was monitored using UV-Vis absorption spectroscopy at room temperature, covering the range of 200-800 nm.A Shimadzu UV-Vis spectrophotometer model 2600 was employed for accurate measurements.

Fabrication of Working Electrode.
In all electrochemical experiments, the carbon paste electrode (CPE) was used as the working electrode.Te preparation of the working electrode was as follows: 75%, 15%, and 10% of prepared nanomaterial, graphite powder, and polytetrafuoroethylene, respectively, were mixed thoroughly for about 30 min after which the mixture was inserted into nickel mesh and crushed well at 20 MPa for 5 min to get an electrode.Te 0.5 mol KOH is used as an electrolyte and the 1 mol sodium sulfate solution is an electrolyte in EIS studies.Te current produced was measured using Ag/AgCl as the reference electrode and platinum wire as the counter electrode.

Results and Discussions
To confrm the structure and crystal phase of pristine and doped ZnO nanomaterials, the samples were analyzed by powder X-ray difractometer.Te average crystallite size of all the pristine and Sm 3+doped ZnO nanomaterials is estimated using the Scherrer equation (35): where D � crystallite size, λ � wavelength of X-rays, K � Scherrer constant, and β � full-width half maximum.Also, the strain in the Sm 3+ -doped ZnO nanomaterials was evaluated using the W-H plots: Equation ( 2) indicates a straight line, and the slope and intercept of the line give the strain and crystallite size.
Te size-strain plot (SSP) method was used to calculate size-strain parameters.In this method, the crystallite size was described by a Lorentzian function and the strain profle by a Gaussian function [32].Accordingly, we have where k is a constant that depends on the shape of the particles; for spherical particles, it was given as ∼ 0.9.Similar to the W-H plots, the factor (d hkl β hkl cosθ) 2 was plotted with respect to (d hkl β hkl cosθ) for all the orientation peaks of ZnO.By linearly ftting the data, the crystallite size and macrostrain was calculated from slope and y-intercept of the ftted line.Te results obtained from the Scherrer equation, W-H, and size-strain plot method are summarized in

Advances in Materials Science and Engineering
Table 1, and the small variation in the values of D may be due to the diference in averaging the particle size distribution.Te reduction in crystallite size revealed the large surface to volume ratio which has created more photoexcited electronhole pairs when irradiated by light and enhanced its photocatalytic activity.Te conclusion drawn is that the SSP method is more consistent, as it achieves a maximum linear ftting with a greater number of data points closely aligned with the ftted line [36].Te density of X-rays (dX) and specifc surface area (S) were calculated using the equations and all the estimated values are depicted in Table 1 [37].
where M is the molecular weight, Z is the number of ZnO molecules, and N is Avogadro's number.Also, the comparison of crystallite size with various synthesis route of reported nanomaterials are given in Table 2 (Supplementary data). ( Te structural morphology of the synthesized nanomaterials was examined through FESEM analysis, and the resulting SEM images are illustrated in Figure 3. Te observations from Figure 3 indicates the porous and agglomerated nature of the prepared material and revealed an interconnected network structure with a high rate of agglomeration, and this kind of morphology is attributed to the rapid evolution of gases during the combustion process [20,38]. Te EDAX spectra (Supplementary data) show the elemental composition of the prepared sample.Te expected elements such as Zn, O, and Sm 3+ are detected in the peaks of EDAX spectra.Te EDAX spectra reveal the successful incorporation of Sm 3+ ions in the ZnO lattice [39].
Difuse refectance spectroscopy (DRS) serves as a nondestructive and versatile analytical tool, employed to investigate the absorption properties of materials, particularly when they are in powdered or granular form.Tis technique not only facilitates the exploration of optical characteristics but also provides valuable insights into a broad spectrum of material properties.DRS studies were performed to analyze the optical properties of the synthesized pristine and Sm 3+doped ZnO, and the recorded difused refectance spectrum is shown in Figure 4. Te band gap energy of the pristine and Sm 3+ -doped ZnO was calculated from the DRS using the Kubelka-Munk function: Here, R ∞ is the absolute refectance and F (R∞) is the Kubelka-Munk function [40].Te optical band gap values are estimated by plotting the variation of the Kubelka-Munk function with photon energy through the following equation [41,42].
Here, "Eg" is the optical band gap energy, h] is the incident photon energy, and n is the nature of the sample transition which depends on the type of optical transition triggered by photon absorption.Obtained characteristic Kubelka-Munk plots of the prepared nanomaterial are shown in Figure 5, and the energy gap values for the prepared ZnO samples were found to be in the range of 3.14-3.20eV, which was lesser than the reported value (∼3.3 eV).Te reduction in the band gap energy might be owing to ZnO lattice crystal defects and also the presence of excess Zn in interstitial wurtzite lattice.
To investigate the efect of Sm 3+ in ZnO structure, photocatalytic studies were performed on FOR dye for a total duration of 120 mins with a time interval of 15 mins under UV light.Photocatalytic experiments were performed for the degradation of FOR dye, a 20 ppm of 250 ml aqueous solution of FOR dye, and 60 mg of photocatalysts in 176.6 cm 2 surface area of a circular glass reactor under a 125 W mercury vapor lamp as a source of UV light operating with an accelerating voltage up to 20 kV using a Tungsten flament.Te irradiation was carried out directly focusing UV light into the reaction mixture from the top at a distance of 21 cm in the open-air condition.Also, it was monitored by UV-Vis absorption spectroscopy at RT in the range 200-800 nm using Shimadzu UV-Vis spectrophotometer and the corresponding absorption spectra of Sm 3+ (5 mol%): ZnO catalyst are presented in Figure 6, and the efciency of degradation was evaluated by the following equation:  Advances in Materials Science and Engineering Te degradation of FOR dye tracks the Langmuir-Hinshelwood frst-order kinetics model and can be expressed as ln (C/Co) = −k t, where k is the constant of apparent reaction rate, C 0 is the initial concentration of aqueous dye, t is the reaction time, and C is the concentration of aqueous FOR dye at the reaction time of t.Te percentage of FOR dye degradation with Sm 3+ (1-7 mol%) activated ZnO catalyst is illustrated in Figure 7. Sm 3+ (5 mol %)-activated ZnO catalyst reveals that 88% of FOR dye was degraded, and the detailed mechanism of photocatalytic degradation process under UV light irradiation is presented [43,44].Te detailed degradation percentage of FOR dye with Sm 3+ -doped ZnO catalyst under UV light irradiation is given in Table 2, and the comparison study of diferent dye degradations is given in Table 3 (Supplementary data) [45][46][47].
During UV irradiation (Figure 8), photons with energy equal to or greater than the bandgap of ZnO are absorbed, promoting electrons from the valence band (VB) to the conduction band (CB).Tese excited electrons in the CB of ZnO can interact with Sm 3+ ions present in the ZnO lattice.Te Sm 3+ ions act as electron scavengers, efectively reducing the recombination of the electron-hole pairs that are generated during the excitation process.By minimizing recombination, the presence of Sm 3+ ions enhances the lifetime and mobility of the photogenerated charge carriers.Te reduced recombination rate results in a higher concentration of reactive species, such as O 2 − and OH, which are known for their strong oxidative properties.Tese reactive species are responsible for the degradation of organic compounds, including the fast orange red (FOR) dye, through oxidation processes.
Additionally, the presence of Sm 3+ ions in the ZnO lattice creates defects, such as oxygen vacancies and interstitial sites, as well as modifes the band structure of ZnO.Tese modifcations can shift the energy levels of the CB and VB, infuencing the positions of the redox potentials and the ease with which electrons can be transferred to or from the ZnO surface.As a result, the addition of Sm 3+ ions not only enhances the generation of reactive species but also afects the overall electronic properties of ZnO, contributing to its improved photocatalytic performance.Te Sm 2+ ions, which are produced from the reduction of Sm 3+ by the  6 Advances in Materials Science and Engineering photogenerated electrons, are less stable and can react with O 2 to promote the generation of O 2 -.Tis process contributes to the pool of reactive oxygen species available for the photocatalytic degradation reactions.Te degradation mechanism for Sm 3+ -doped ZnO is shown in the following equations: Furthermore, the half-life was evaluated for the FOR dye degradation of 50%, and the half-life was observed at 9.19 min.Tese results reveal that the synthesized material is useful for textile dye pollutants degradation and also suitable for the removal of secondary pollutants.
Furthermore, the reusability test was performed to investigate the photostability and reusability of the synthesized catalyst and a negligible decrease in the degradation efciency was observed even after fve successive runs; at the end of the 5 th cycle, the decomposition efciency was found to be 87.90%.It was observed that the physical property of the new and used photocatalyst remains almost same.Te well-established stability of the catalyst increases its practical usage as a catalyst in the photodecomposition of dye.Tus, the prepared material was stable and reusable.
Electrochemical studies were performed to examine the electrochemical properties of Sm 3+ -doped ZnO for battery and supercapacitor applications.Te obtained cyclic voltammetry (CV) curve of Sm 3+ (5 mol%): ZnO electrodes with various scan rates (0.01 V/s-0.05V/s) are shown in Figure 9.It was noticed that the peaks shift towards positive and negative potential side upon increasing the scan rates which indicates the pseudocapacitive nature of Sm 3+ : ZnO electrode [48].
To understand the charge transfer resistance, electrochemical impedance studies (EIS) were performed, and the obtained spectra of Sm 3+ (5 mol%): ZnO electrode and the ftted equivalent circuit are seen in Figure 10(a) and 10(b).Z′ is the real component, which discloses the ohmic properties, and Z″ is the virtual component, which reveals the capacitive properties.Te EIS spectra show an elevated arc (semicircle); generally, an arc with larger radius indicates a higher charge transfer resistance [48].Nyquist plots of pristine and 5 mol% of Sm 3+ -doped ZnO electrodes are presented in Figure 10.Te results indicate a semicircle at the higher frequency region and a straight line at the lower frequency region, representing that the electrodes have a superior capacitive behaviour.Pristine ZnO electrode shows semicircle with larger radius which represents the higher charge transfer resistance, and 5 mol% of Sm 3+ -doped ZnO electrode shows semicircle with smaller radius which denotes the smaller charge transfer resistance and thus Sm 3+ (5 mol%)-doped ZnO electrode possesses superior capacitive properties than the pristine and other doped electrodes [49].Tis superiority is primarily attributed to the introduction of Sm 3+ into the ZnO structure.Te incorporation of Sm 3+ serves to modify the redox chemistry of ZnO and brings about alterations in the charge transfer kinetics at the electrode-electrolyte interface.Tese combined efects contribute synergistically to the superior capacitive performance observed in the Sm 3+ -doped ZnO electrodes.
Also, to assess the applicability of the proposed method as an electrochemical sensor, prepared electrodes were used to sense the paracetamol content in available Dolo-650 tablets, and the spectra are presented in Figure 11.Paracetamol is an electrochemically active molecule that has been broadly tested in various samples.Several papers have been published on the electroanalytical determination of paracetamol depending on its oxidation behaviour with electrodes such as modifed glassy carbon electrodes, graphite electrodes, and gold electrodes [50][51][52][53][54]. Electrochemical techniques are versatile analytical techniques that can solve the problems of pharmaceutical interest.Voltammetry is a convenient electrochemical analytical technique that exhibits high selectivity, sensitivity, and accuracy.Figure 11 shows that observed and modifed CV profle with the scan rate 0.05 V/s is surely due to the paracetamol.Tis demonstration stated that the paracetamol substances in pharmaceutical medicines can be sensed by using the proposed method [55].
Te current study employs the gel difusion method for the antibacterial activity of Sm 3+ : ZnO (5 mol%) nanoparticles (Figure 12) using pathogenic bacterial strains of Streptococcus aureus and Bacillus subtilis (Gram positive) and Escherichia coli and Pseudomonas aeruginosa (Gram negative) bacteria (Azymes Biosciences Pvt. Ltd., Bengaluru).Diferent dilution of Sm 3+ : ZnO (5 mol%) of 150, 100, 50, and 25 mg/ml was done by using autoclaved distilled water.Standard antibiotic ciprofoxacin (20 mcg/disc) (Hi-Media, Mumbai, India) and autoclaved distilled water are used as positive and negative control, respectively.Antibacterial activity was done as per the standardized protocol in our lab.After 24-36 hrs, the diameter of the clear zone of inhibition around the discs is measured to assess the antibacterial activity.Te results of the antibacterial activity showed a signifcant zone of inhibition at higher  8 Advances in Materials Science and Engineering concentrations (100 mg/ml) demonstrating efcient antibacterial activity of Sm 3+ : ZnO (5 mol%).However, these NP's activity is interpreted to be more efective even at lower doses like 25 mg/ml on E. coli and S. aureus.Even though the mode of action of Sm 3+ : ZnO (5 mol%) against microbes is not completely understood yet, hypotheses may interfere with microbial multiplication, the ways of inhibition of bacterial growth may be the production of reactive oxygen species which may lead to denaturizing proteins by bonding with the sulfhydryl group or by damaging its genetic material [56] and the comparison study of antibacterial activity with other various materials are given in Table 4 (Supplementary data).

Conclusion
In summary, pristine and Sm 3+ ions-doped ZnO nanomaterial with various dopant concentrations have been fabricated by the green synthesis technique.Te predicted XRD graph confrms that the efective integration of Sm 3+ ions in the lattice of ZnO crystal and FESEM examination of prepared samples evidence the morphology.Photocatalytic activity of the prepared catalyst was performed to degrade fast orange red dye.In the degradation process, it has been noticed that the 5 mol% Sm 3+ -doped ZnO catalyst shows the maximum catalytic activity compared to another prepared catalyst.Optimized Sm 3+ concentration on ZnO electrode has shown great impact on the electrochemical activities, and this approach was applied to monitor paracetamol and exhibits exceptional response to sense paracetamol.Antibacterial activity analysis demonstrated excellent inhibition by prepared nanomaterials on Gram positive compared to Gram negative.All the obtained results explored that the present material can be highly useful for multifunctional applications such as wastewater purifcation and decoloration, supercapacitor, battery, and antimicrobial applications.

2
Advances in Materials Science and Engineering 2.4.Photocatalytic Experimental Procedure.To investigate the photocatalytic properties of the prepared catalysts, we conducted experiments aimed at the degradation of FOR dye.A 20 ppm solution of FOR in 250 ml of aqueous solution and 60 mg of photocatalysts were placed in a circular glass reactor with a surface area of 176.6 cm 2 .Te photocatalytic reaction was initiated under a 125 W mercury vapor lamp, serving as the source of UV light.To activate the photocatalytic process, the solution mixture was thoroughly stirred while exposed to UV light.Te irradiation took place by directing UV light directly into the reaction mixture from the top, maintaining a distance of 21 cm, and conducted in an open-air condition

Figure 2
displays the XRD patterns of pristine and doped ZnO.All the obtained peaks and their relative intensities of the prepared samples are well-matched with JCPDS No. 89-1397.Te sharp peaks in PXRD indicate the high crystalline nature of prepared materials [34]. Photocatalytic

Figure 1 :
Figure 1: Schematic diagram of general plan and preparation of pristine and Sm 3+ -doped ZnO nanoparticles.

Table 1 :
Estimated crystallite parameters of prepared materials.

Table 2 :
Te rate constant and kinetic studies of 20 ppm fast orange red dye in 60 mg Sm 3+ -doped ZnO under UV light.