Bio-synthesis of Lead Oxide Nanoparticles Using Chinese Mahogany Plant Extract (CMPE@LO) for Photocatalytic and Antimicrobial Activities

The current study describes the plant-mediated synthesis of lead oxide nanoparticles (LO) using a plant extract from Chinese Mahogany (CMPE). The invented nano-hybrid structure (CMPE@LO) has been used for the fast green (FG) dye degradation as well as bio-medical applications. The prepared nanoparticles were characterized using techniques like Fourier transform infrared spectrogram (FTIR), X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), high-resolution transmission electron microscope (HRTEM), and thermo-gravimetric analysis (TGA). The presence of Pb, O, and C components in the EDX spectrum verified the formation of the desired nanocomposite. The crystalline nature was confirmed by XRD measurements, which showed nanoparticles with a size of 22.56 nm. The FESEM study presents a rod-like, rough, and spongy surface for the removal of contaminants from a water system. The various operating parameters such as the effect of time, concentration of fast green, and photocatalyst amount were also studied and optimized for maximum removal. The kinetic study was investigated using a pseudo-first model having a good value of regression coefficient (R2). The antibacterial properties of the prepared nanoparticle against bacteria including Bacillus subtilis, Staphylococcus aureus, and Escherichia coli were also investigated. The synthesized CMPE@LO nanoparticles show a higher zone of inhibition as compared to inorganic or organic moiety. Hence, these findings present that the (CMPE@LO) nano-hybrid structure can be employed as a photocatalyst for fast green (FG) dye and antimicrobial agent against pathogenic bacteria.


Introduction
Metal-nanoparticle fabrication employing plant extract is an emerging concern in material science.When compared to traditional preparation methods, these are excellent substitutes because they are less expensive, more economical, and more effective [1].Many technical and environmental difficulties, such as solar energy conversion, medicine, and wastewater treatment, can be handled with the help of nanomaterials.As is well known given the current state of the environment, and the quality of drinking water has deteriorated due to human activity and technological innovation.The textile industry is a significant contributor to the economies of many countries throughout the world.These businesses generate more or less colored effluents based on the degree of fixation of the dyestuffs on the substrates, which varies depending on the nature of the substances, the desired intensity of color, and the application technique [2].
Aquatic life may be poisoned if this colored water is thrown into receiving water.Dyeing interferes with biological processes in the water system [3][4][5][6][7].They are a concern because, in addition to interfering with other human organs such as the kidney, reproductive, liver, brain, and central nervous system, they may be mutagenic and carcinogenic, causing severe harm to humans.As a result, the treatment of dye-based effluents is regarded as the most challenging task for the environmental community and industries.For treating dye-bearing effluents, many treatment approaches such as physical, physicochemical, and chemical procedures have been examined [8][9][10][11].
Researchers are discovering new strategies and materials for converting wastewater into a beneficial resource for daily use.Bio-nanomaterials have grown more popular due to their complex physical, chemical, and structural properties [12][13][14][15][16][17].Bio-nanomaterials are produced from different biological elements like bacteria, fungi, plants, peptides, and nucleic acids.Plants contain biomolecules such as proteins and carbohydrates, and coenzyme has excellent potential to reduce metal salt into nanoparticles.Firstly, gold and silver metal nanoparticles were explored in the synthesis of nanoparticles using plant extract.A number of metals like Zn, Cu, Sn, Ti, and Pb have been used for the synthesis of nanoparticles.These metal nanoparticles offer various applications such as catalysis, antimicrobial and antibacterial activity, sensors, and biomedicine, [18][19][20][21][22][23].
Different types of plants such as Aloe barbadensis Miller, Avena sativa, Medicago sativa, Osimum sanctum, Citrus limon, Azadirachta indica, Coriandrum sativum, and Cymbopogon flexuosus have been explored for the nanoparticles synthesis.In this research paper, we had synthesized lead oxide nanoparticles using Chinese Mahogany leaf extract.Chinese mahogany is also called toona sinensis, Chinese cedar, Chinese toon, beef, and onion plant and red toon.It is a species of Toona native and found in Korea, China, Nepal, northeastern India, Thailand, Malaysia, Myanmar, and western Indonesia.It has been used as a natural herbal medicine for thousands of years due to its consistent pharmacological effects.It was termed an herbal medicine in Chinese folk medicine with good detoxifying, anti-inflammatory, and hemostatic effects.Edible leaves and young shoots of Chinese mahogany are used as delicious and nutritious foodstuff in China and other Southeast Asia countries because it has a special onion-like flavor, the wealth of carotene, and vitamins B and C [24][25][26][27][28][29].
This paper presents the extraction of Chinese Mahogany plant extract and the synthesis of Chinese Mahogany plant extract encapsulated lead oxide nanoparticles.The prepared samples were characterized using several instrumental techniques such as FTIR, EDX, SEM, TEM, XRD, and TGA.The prepared nano-hybrid structure has been used for the amputation of fast green from wastewater.The prepared CMPE@LO nanoparticles were also explored for the antimicrobial activity as a biomedical agent.

Chemicals
Lead acetate, ethylenediaminetetraacetic acid (EDTA), fast green (FG), and NaOH were purchased from Sigma-Aldrich Pvt. Ltd. with 99% purity.All chemicals were of analytical grade.

Preparation of Chinese Mahogany Plant Extract (CMPE)
Chinese mahogany leaves were collected from the local area.These leaves were thoroughly washed with double distilled water several times and dried.Then leaves were cut into small pieces.The extract was prepared by heating the leaves dispersed in distilled water for 2 h with continuous stirring.
The mixture was then allowed to cool and filtered using Whatman filter paper.The obtained extract was collected and stored at 0 °C for further use [30].

Synthesis of Lead Oxide (LO) and CMPE@LO) Nanoparticles
In this method, 0.1 M lead acetate and 0.1 M EDTA solution were prepared in double distilled water.Then, with continuous stirring, add 0.1 M EDTA solution dropwise to the 0.1 M lead acetate solution in the beaker.After that, add 1.0 M NaOH solution to make it basic with continuous stirring at 60 °C for 2 h [31].After this, a definite amount of Chinese mahogany plant extract was slowly added to the above mixture with continuous stirring for 2 h.Then, filter the resulting mixture, and obtained precipitates were dried at 50 °C (Scheme 1).In this way, six different samples of CMPE@ LO nanoparticles were prepared by varying the mixing ratio of lead acetate, EDTA, and CMPE [32].

Photocatalytic Activity
The photocatalytic activity of CMPE@LO nanoparticles was studied using the degradation of fast green (FG) dyes from the water system [33][34][35].The initial concentration of dye was taken in fixed quantity and 100 mg of the CMPE@LO was added to form a slurry.The slurry was placed in the dark for 1 h to establish adsorption-desorption equilibrium.Furthermore, the slurry was exposed to sunlight by controlled stirring.The effect of photocatalysis of CMPE@LO was studied at different time intervals.The concentration of dye was analyzed by a UV-visible spectrometer at the corresponding wavelength.All experiments have been conducted in triplicate, and the average value has been reported.The percentage degradation of FG was calculated using the following formula: where C ° and C t are the initial and final concentration of dye at time t=0 and t=t, respectively.

Antimicrobial Activity
Preparation of bacterial culture for MIC assay: Standard isolates of gram-positive and gram-negative bacteria, i.e., Bacillus subtilis, Staphylococcus aureus, and Escherichia coli were obtained from the Department of Microbiology, Shoolini University, Solan (H.P.).All the test strains were maintained on nutrient agar slants (Hi-Media Laboratories Pvt.Limited, Mumbai, India) at 4°C and sub cultured onto nutrient broth for 24 h prior to testing.These bacteria served as test pathogens for antibacterial activity assay.The antimicrobial susceptibility of the prepared nanoparticles and composite was evaluated against the gram-negative bacteria and gram-positive bacteria.The antimicrobial activity was performed using a modified well diffusion method [36].To perform the antimicrobial assay, nutrient agar was used to grow the different bacteria.Bacteria preculture broth could stand overnight in a rotary shaker at 35-37 °C for 16-18 h.The pre-culture broth was spread over nutrient agar media plates.After spreading, 6-mm wells in diameter were created with the help of puncture on the plates.Antimicrobial activity was tested using 100 μl plant extract, nanoparticles, and nanocomposite solution (100 mg/ml), whereas 10 μl antibiotic solutions (100 mg/ml) was used against pathogenic bacteria.In addition, streptomycin was considered positive control, whereas triple distilled water was used as a negative control.The Petri plates were incubated for 18-24 h at 37 °C for the growth of bacteria.All the tests were performed in triplicate.The diameters of the inhibition zones obtained around the wells were measured in mm using the Hi-Media antibiotic zone scale.

Results and Discussion
The present study illustrates the extraction of Chinese mahogany leaf extract, lead oxide nanoparticles, and Chinese mahogany plant extract-PbO (CMPE@LO) nanoparticles.Six different samples of CMPE@LO nanoparticles have been prepared by varying amounts of mixing ratio of lead acetate, EDTA, and CMPE.Table 1 summarizes the details of different sample preparation.Sample S-5 was finalized for further detailed study.

Characterization Techniques
"Figure 1 elucidates the FTIR spectra of (a) CMPE@LO nanoparticles (b) LO (c) CMPE."The changes in FTIR peaks of spectra clearly confirmed the formation of CMPE@ LO nanoparticles.As we can see, the small peak at 3548 cm −1 in Fig. 1b gets shifted to the broad absorption band at 3329 cm −1 (Fig. 1a is due to the O-H stretching vibration [37].The peak at 1741 in LO was due to C=O stretching vibration mode, and a new peak is recorded in Fig. 1a corresponding to C-N functional group [38].In Fig. 1 a and b, peak at 1395 cm −1 described C-O stretching vibrations.The stretching frequency at 1017 cm −1 ascribed to CO group Scheme 1 Synthesis of Chinese mahogany plant extract-PbO(CMPE@LO) nanoparticles [39].Furthermore, peaks that appeared at 841cm −1 and 680cm −1 corresponds to the Pb-O bonding [40].
The EDX analysis is shown in Fig. 2a.This confirms the formation of the Chinese mahogany plant extract-PbO (CMPE@LO) nano-composite.The results indicate the atomic percentage of different elements, i.e., carbon (52.70%), oxygen (34.10%), lead (9.13%), sodium (0.67%), and nitrogen (3.41%) in the form of peaks (Table 2).The EDX analysis clearly shows the presence of Pb, O, Na, and C, which confirm the formation of (CMPE@LO) nanoparticles.
Thermogravimetric analysis (TGA) has been performed in order to determine the thermal stability of nanoparticles and their fraction of volatile components by observing the change in weight, which takes place as a sample is heated at a constant rate.Figure 2b shows a TGA graph of CMPE@ LO nanoparticles.There was a small decrease in weight loss of 3.23% which was recorded up to 230 to 300 °C; it may be due to evaporation or dehydration of adsorbed water molecules on the surface of nanoparticles.Furthermore, there was a huge loss in weight (13.52%) from 300 to 460 °C because of the decomposition of the material.After that, a small loss of 0.74% was observed between 460 and 525 °C which may be due to a change in atmosphere (N 2 to O 2 ) or the combustion of carbon or may be due to the formation of the metal oxide.In last, 5.87% weight loss was noticed from 525 to 540 °C because of inert inorganic residues of ash filler on glass fibers.After that, there was no change observed up to 700 °C [41].
Figure 3a-d indicates the scanning electron micrographs (FESEM) of lead oxide and CMPE@LO nanoparticles.It has been observed that smooth surfaces with long rodlike particles are in a random manner.After mixing a fixed  The X-ray diffraction (XRD) method was studied to confirm the crystallinity of synthesized nanoparticles.Figure 4 a and b present the XRD spectra of CMPE@LO nanoparticles and lead oxide (LO).It was apparent from the diffractogram that there was a huge difference in the intensity of peaks of LO (Fig. 4b) after the incorporation of CMPE.The difference might be due to the component residue from the plant extract (maybe chlorophyll or other pigments) in the fabricated CMPE@LO.In the case of LO, the diffraction peaks were observed at 2θ value 15.26°, 29.30°, 30.91°, 36.01°,40.34°, 46.56°, 48.67°, 55.99°, 57.98°, 63.33°, and  69.03° which corresponds to (010), ( 111), (020), ( 002), (110), ( 030), ( 112), (311), ( 230), (040), and (400) planes respectively.In Fig. 4a for CMPE@LO, the majority of the diffraction peaks appeared with a slight shift in the 2θ value.The observed diffraction pattern was in good agreement with JCPDS card no.00-038-1477 [42,43].A total of 94.16% crystallinity of CMPE@LO nanoparticles was observed using the formula as given below: Average crystallite size is also studied using the Debye-Scherrer equation [44,45].It was found to be 22.56 nm.
Transmission electron micrographs (HRTEM) of LO@ CMPE nanoparticles are shown in Fig. 5. TEM images confirmed that the size of synthesized materials lies in the nano-range.Images showed that nanoparticles have a highly porous surface with different particle shapes.

Photo-degradation of Fast Green (FG)
The tauc plot of LO and CMPE@LO nanoparticles is depicted in Fig. 6 a and b.In order to calculate the band gap, a suspension of 5 mg of synthesized material has been prepared in ethanol solution.Later, ultra-sonication of 30 min has been done and the UV-visible spectrum was obtained.The band gap of LO and CMPE@LO nanoparticles was calculated using tauc equation as given below [46,47]: (2) Crystallinity = Area of crystalline peaks Area of all peaks × 100 where α is the absorption coefficient=2.303A/l; E g , optical band gap; B, band tailing parameter; hν, photon energy; n, 1/2 for direct band gap.The conduction and valance band edges of the photocatalyst were calculated by using the following equation [13]: where E CB and E VB are the band edges of CB and VB respectively, E e is the energy of electrons on hydrogen scale (~4.5 eV), X is the geometric mean of Pearson scale of absolute electronegativity (PAE), and E g is the band gap of photocatalyst in electron volts.
Figure 6a shows UV-visible spectra.The optical band gap of LO and CMPE@LO nanoparticles was obtained by extrapolating the straight portion of the curve between (αhν)2 and hν when α=0.The band gap was observed to be 2.52 eV and 2.70 eV for LO and CMPE@LO nanoparticles as shown in Fig. 6b.
The photocatalytic process causes the formation of highly reactive superoxide radical (O 2 *) and hydroxyl radicals (OH*) that converts hazardous pollutants into low-weight aliphatic compounds.In the presence of sunlight, the photocatalyst is supposed to absorb the light energy that corresponds to its band gap energy.The absorption of light energy leads to the excitation of electrons and holes from CB and (3) 5 TEM images of CMPE@ LO nanoparticles VB respectively.Afterward, the photo-excited e − /h + triggered the various reactive oxygen species (ROS) by undergoing a series of photochemical chain reactions.The conduction band edge potential (E CB ) and valance band edge of CMPE@LO were calculated to be −0.34eV and + 2.18 eV respectively.E CB of CMPE@LO was highly negative as compared to the reduction potential of O 2 (E 0 =O 2 /O 2 * −0.33 eV vs NHE), which favor the O 2 * formation.Once O 2 * is formed, it may further react with water molecule or some other radical to form * OH radical.These ROS attack the FG molecule and convert into simple lower-weight aliphatic compounds or ions [48].Scheme 2 shows the proposed mechanism for the excitation process and ROS generation on the catalyst surface.The proposed mechanism for the photo-degradation of the FG molecule is presented in Fig. 7.
Figure 8a illustrates the effect of contact time on FG degradation using CMPE@LO nanoparticles, and LO in altered intervals of time.It has been observed from the graph that 90.22% of FG was degraded by CMPE@LO nanoparticles whereas while in the case of LO, only 48.43% degradation was observed.Figure 8b shows that overall FG degradation follows to pseudo-first-order model of kinetic.The respective rate constant along with the regression coefficient is enumerated in Table 3.It was noticed that CMPE@LO exhibits a high value for the rate constant k 1 0.0126 min −1 as compared to LO (k 1 = 0.0063 min −1 ).It was due to the fact that the addition of CMPE into LO increased the surface area of CMPE@LO and provides the more sites for the adsorption of pollutants.

Effect of pH
The pH is considered a crucial factor while dealing with the photo-degradation processes, especially when working on dye degradation.Because pH can change surface characteristics, which may impact the overall efficacy of the process.The effect of pH of FG degradation by CMPE@LO was studied in the pH range of 2.0 to 10.0.As shown in Fig. 8e, the results demonstrate that acidic conditions favor the degradation, while the basic pH condition retard the degradation rate.Kinetic plots are presented in Fig. 8f, and the rate constant for the pH effect is enumerated in Table 5.At pH 4.0, maximum rates were observed which can be explained on the basis of the extent of affinity toward the adsorption of pollutant on the catalyst surface.The aforesaid affinity was governed by the electrostatic interaction, which in return depends on the point of zero charge (PZC) of catalysts and pKa of pollutant.These both are sensitive to pH change as the pH goes above PZC/ pKa (pH > PZC/pKa) the surface acquired a negative charge.On the contrary, when pH < PZC/pKa, the surface become positively charged [49,50].The PZC analysis of CMPE@LO is depicted in Fig. 9a, which shows that the catalysts possess PZC≈ 7.5.At pH 4.0, opposite charges were accompanied by the catalysts and pollutant molecule, which favor the adsorption and ultimately lead to a hike in the FG degradation rate.On the other side, when pH rises (pH > 7.0), the same charge dominates on both pollutant molecules as well as the catalyst surface, which corresponds to repulsive interaction, thereby As illustrated in Fig. 9c, the effect of initial FG concentrations varied from 10 to 60 mg/L, which has been investigated using a 30-mg dosage of nanoparticles.It has been found that the degradation rate increases with concentration (10 to 30 mg/L).The maximum degradation efficiency of fast green has been recorded to be 62.22% and 89.39% using LO and CMPE@LO nanoparticles at 30 mg/L, respectively.After that, degradation efficiency has been declined.This may be due to the fact that active sites are reduced by the absorption of fast  green dye onto nanoparticle surface, and these active sites are required for the degradation of dye molecules.These active sites were lacking at higher concentration [51][52][53].Figure 9d shows the absorption spectra of FG for CMPE@LO nanoparticles with time.It was recorded that the intensities of peaks decrease incessantly with irradiation time which confirmed the successful degradation of FG.

Antimicrobial Activity
The present study revealed that synthesized nano-composite showed potent antimicrobial activity against gram-positive (B.subtilis and S. aureus) and gram-negative bacteria (E.coli).The inhibition zones (in mm) of varying sizes were obtained as mentioned in Table 6 and Fig. 10.The positive control showed the different sizes of the zone of inhibition against both gram-positive and gram-negative bacteria, i.e., B. subtilis (18±0.567mm), S. aureus (17±0.616mm),and E. coli (17±0.538),but a negative control showed no zone of inhibition.In Fig. 8, synthesized CMPE@LO nanoparticles showed the highest zone of inhibition as compared to CMPE and PbO nanoparticles against both the both gram-positive and gram-negative bacteria.Furthermore, the samples were tested for MIC (minimum inhibitory concentrations) determination through micro dilution.MIC values are ranging in between 31.25 and 250 μg/ml.Minimum inhibitory concentrations (MICs) are defined as the lowest concentration of an antibacterial agent that inhibits the visible growth of a microorganism after overnight incubation, as the lowest concentration of antibacterial that prevent the growth of an organism after subculture onto antibiotic-free media.Antibacterial activities of the samples were first screened by the agar well diffusion method as described previously.The different MIC values were obtained against different bacterial

TOC, COD, Reusability, and Stability
The total organic carbon and chemical oxygen demand are considered the main parameter to assess the quality of water.The degree of mineralization has been investigated in terms of TOC and COD analysis.The sample of photo-degraded FG after the 180 min of degradation experiment was taken for the study.The results (Fig. 11e) have shown that about 48.6% of TOC was dissipated, while COD was reduced to 59.4% over the 180 min of time period.The defining characteristics of the practical applicability of CMPE@LO nanoparticles are their reusability and stability [58].The reusability of CMPE@LO nanoparticles was tested for five consecutive phases as shown in Fig. 11a.The synthesized nanoparticles used for each cycle were separated from the reaction mixture and washed with distilled water.After the fifth cycle, FG's photo-degradation rate was found to have decreased slightly from 92.22 to 89.43%.The modest decrease in photo-degradation efficiency may be caused by the adsorption of chemical intermediates on nanoparticle surfaces, which block the active sites and leave no active sites available.Figure 11 b, c and d, and f show the FTIR spectra, SEM micrographs, and XRD analysis for CMPE@ LO after the 5th cycle of reusability.It has been found that there is no major change observed in the absorption spectrum after recycling, which indicates that CMPE@LO nanoparticles possess good stability.

Conclusion
In summary, Chinese mahogany plant extract-PbO(CMPE@ LO) nanoparticles were synthesized by mixing a definite amount of CMPE in lead oxide.EDX results confirm the formation of nanoparticles with different elemental compositions.SEM images indicate that after mixing the organic part into lead oxide (LO) moiety, the entire surface is modified into a porous surface.CMPE@LO was used to evaluate ▸ photocatalytic behavior for the photo-degradation of FG dye.The CMPE@LO nanoparticles show a higher degradation rate of 90.22%, which was higher than other moieties.CMPE@LO nanoparticles also showed the highest zone of inhibition as compared to CMPE and PbO nanoparticles against both gram-positive and gram-negative bacteria.The current study provides the fresh insight into the development and fabrication of plant-mediated efficient nanostructure with prospective applications in waste-water restoration and anti-microbial activities.

Fig. 8 a
Fig. 8 a Effect of time on FG degradation using CMPE@ LO nanoparticles LO; b pseudo kinetic model for FG degradation with time; c effect of CMPE@LO nanoparticles and LO dosage on FG; d pseudo kinetic model for FG degradation with photocatalyst dosage; e effect of pH; f pseudo-firstorder kinetics

Table 1
Different sample preparations of CMPE@LO nanoparticles

Table 3
Rate constant (k 1 ) for the photo-degradation of FG by LO and CMPE@LO

Table 5
Effect of pH on the photo-degradation rate of FG Fig. 9 a PZC analysis of CMPE@LO; b electrostatic interaction between pollutant and catalyst; c effect of concentration on FG degradation; d absorption spectra of FG for CMPE@LO nanoparticles