1 Introduction

Nanotechnology is today regarded as a well-established cutting-edge technology with multiple applications in areas such as the chemical, mechanical, food manufacturing, and pharmaceutical industries [1, 2]. Nanotechnology also plays an important part in environmental sciences, drug delivery systems, and energy production [3, 4]. Since the birth of nanotechnology, several nanoscale technologies have been developed using various techniques, including chemical, physical, and green techniques [5,6,7,8]. In general, the scalable fabrication of NS is performed using conventional top-down/bottom-up approaches, including harsh, corrosive, genotoxic, carcinogenic, and hazardous chemicals, volatile organic solvents, and high-energy treatment, which generates potential health and environmental risks [9]. The green synthesis method can be defined as the nanoparticle synthesis process by using both biological materials and inorganic materials. In this synthesis procedure, living microorganisms such as bacteria, fungi, algae, yeasts, molds, viruses, and mostly plants are used [10]. The green synthesis method has many advantages over chemical and physical techniques, such as environmental friendliness, cost-effectiveness, biocompatibility, and safety. Additionally, many studies have proved that zinc oxide nanoparticles (ZnO-NPs) made using green synthesis processes have strong antibacterial and photocatalytic properties [11, 12]. The disadvantages of current nanoparticle synthesis methods include long processing times, high costs, difficult and complex operations, and the usage of hazardous materials in particularly. Due to the previously mentioned challenges, a considerable amount of contemporary research has been dedicated to the development of synthesis methods for nanoparticles that are both efficient and environmentally sustainable [13, 14]. In recent years, the growth of eco-friendly models for synthesizing nanostructured particles has become a primary priority for materials scientists [15,16,17]. In the past decade, metal oxide-NPs have been the subject of intensive research due to their numerous uses in several technical domains [18, 19]. Biological sources such as plant extracts, enzymes, and microbes have been identified as viable options for the synthesis of metallic-NPs [20, 21]. These sources can effectively serve as reducing, stabilizing, and capping agents, thereby facilitating the biosynthesis process [22,23,24]. This approach offers a novel method that avoids environmental concerns and expands the potential clinical applications of metallic NPs [25, 26]. ZnO-NPs are intriguing inorganic compounds that exhibit a diverse array of potential advantages [27, 28]. ZnO-NPs have applications in a variety of industries, including energy conservation, textiles, healthcare, semiconductors, catalysis, and chemical sensing [29,30,31,32,33]. ZnO NPs are non­toxic and bio­compatible and have outstanding medicinal uses, including antimicrobial activities, in targeted drug delivery, wound healing, and bio imaging [34,35,36], anti-inflammatory [35], anticancer [34], and antioxidant activities [37]. On the other hand, water pollution is a global problem, and several effective methods for treating wastewater have been developed. In addition, dyes are the most widely used source of color in the apparel, footwear, leather goods, paper goods, food and beverage, personal care product, pharmaceutical, and printing sectors. Up to 200,000 tonnes of dyes are wasted annually on effluents from the textile industry’s dyeing and finishing processes [38]. ZnO NPs have demonstrated potential as a photo-catalyst for the degradation of both anionic and cationic dyes commonly present in various industrial sectors [39, 40]. Due to growing concerns regarding pollution and toxicity, numerous studies have suggested for the enactment of a green synthesis approach in the production of ZnO NPs utilizing highly affordable bio-sources. In this context, various micro-organisms, such as bacteria yeasts, and fungi, have been extensively investigated [41, 42]. Among these, yeasts have garnered significant attention as a potential candidate for the production of NPs. This is primarily due to their exceptional ability to withstand metal ions, substantial enzyme generation, substantial biomass yield, and capacity for metal bioaccumulation. Probiotic yeast, scientifically referred to as Saccharomyces cerevisiae, is classified within the Ascomycota phylum and the Saccharomycetes class [43]. Saccharomyces cerevisiae, a non-pathogenic microorganism, possesses several advantageous characteristics, including its widespread availability and the presence of diverse bioactive compounds, such as proteins and enzymes. These attributes make S. cerevisiae a promising candidate for facilitating the environmentally friendly synthesis of NPs. S. cerevisiae holds significant commercial importance as a yeast species. It is widely recognized for its exceptional physiological and genetic characteristics, making it a highly favorable option for the production of NPs [44,45,46]. The present study involved the characterization and verification of green synthesized ZnO NPs using a range of instrumentation techniques including UV-vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy-dispersive X-ray (EDX), and FTIR. Subsequently, an examination was conducted to assess the antibacterial properties of the substance, which was then evaluated for its efficacy as a photocatalyst in the degradation of Eriochrome Black T (EBT) dye.

2 Materials and methods

2.1 Materials

Zinc acetate dihydrate (Zn (CH3COO)2·2H2O) is purchased from Sigma-Aldrich for chemicals and used as precursors for preparation ZnO nanoparticles. EBT was from Sigma-Aldrich. All of the chemicals utilized in the experiment were of reagent grade and were employed without further additional purification procedures. The water utilized in the course of the experiment was ultrapure milli-Q water.

2.2 Biosynthesis of ZnO NPs using baker’s yeast (S. cerevisiae)

The zinc oxide nanoparticles were synthesized by dissolving 2 mM of zinc acetate in 100 ml of double-distilled water and adding 2 mM of baker’s yeast extract. The mixture was then stirred continuously at a temperature of 50 °C for 12 h. After the incubation period, a milky color appeared, indicating the formation of ZnO NPs. The ZnO nanoparticles were separated by centrifugation within an ethanol and water solution. The sample was subjected to additional drying at a temperature of 100 °C for the duration of one night, followed by annealing in a furnace at a temperature of 200 °C for approximately 6 h.

2.3 Characterization methods

Nanoparticle surface composition and functioning were both elucidated using FTIR spectra. The KBr medium used to create the FTIR spectra samples allowed for the collection of data from 400 to 4000 cm1. An X’pert Pro Phillips X-ray diffractometer was used to analyze the nano-powder’s phase. High-resolution transmission electron microscopy employing a 300-kV Japanese JEOL 3010 apparatus was used to analyze nanoparticle size and structure. The surface structure and homogeneity of the produced ferrite NPs were characterized using the ZEISS, EVO-MA10 SEM system. The elemental composition of the NPs was also analyzed by EDX spectra. UV-vis spectroscopy was used to examine the ultraviolet (UV) spectrum of produced ZnO nanoparticles using an Agilent Cary 60 UV-vis spectrophotometer.

2.4 Antimicrobial activity and minimal inhibitory concentration

The antibacterial efficacy of produced ZnO NPs was evaluated using an agar-disc diffusion assay, towards gram-negative bacteria (E. coli ATCC25922) and gram-positive bacteria (S. aureus ATCC25923). Conventional antibiotic discs of ciprofloxacin (5μg/ml; 6.0mm) were used to evaluate the effectiveness of the produced ZnO NPs. Minimum inhibitory concentrations (MICs) of ZnO NPs were determined using the serial dilutions technique of Luria-Bertani medium. In this study, a negative control was employed, which consisted of the medium broth. Additionally, a positive control was utilized, which consisted of the pathogenic microorganisms under investigation, along with the medium broth and synthesized ZnO NPs. The concentration of the ZnO NPs was initially set at 20.0 μg/ml. The MIC was determined after a 24-h incubation period at a temperature of 36.0 ± 1.0°C. The statistical analysis of the results was conducted using SPSS version 15. Specifically, one-way ANOVA, Duncan’s multiple series, and the least significant difference were employed [47].

2.5 Photocatalytic degradation of Eriochrome Black T using ZnO nanocatalyst

In two separate 125-ml beakers, a quantity of 10 mg of green synthesized ZnO NPs was added into 50ml of an aqueous-solution containing EBT. The initial conc. of EBT in the solution was 10 mg l−1. The solution was continuously stirred at a temp. of 25°C for a duration of 30 min under low-light conditions, until a state of adsorption-desorption equilibrium was achieved between the EBT compound and the photocatalysts that were prepared. Subsequently, a UV lamp was employed to generate UV radiation and irradiate a solution containing the photocatalyst and EBT. The solution was contained within a quartz immersion tube and positioned axially. Periodically, 1-ml aliquots of the EBT solution were extracted using a syringe equipped with a 2.5-mm pore size filter. The degradation kinetics of EBT were investigated by monitoring the change in EBT concentration over time using a UV-visible spectrophotometer (Agilent­Technologies Cary­60 UV-vis) at a wavelength of maximum absorption (λ max) of 425 nm. For the purposes of this study, deionized water was utilized as a reference [48].

3 Results and discussion

3.1 Characterization of the prepared ZnO NPs

3.1.1 FTIR of bio-ZnO NPs

FTIR was conducted in order to validate the presence of functional groups on the surface of the synthetic materials. The spectrum of ZnO NPs is presented in Fig. 1. The observed peaks in the spectra correspond to the distinctive functional groups that are present in the synthesized zinc oxide nanoparticles [49]. The samples are assumed to exhibit absorption peaks in the region of 3435.2, 2924.3, 1603.3, 1383.2, 1111.4, 868.8, 778.6, and 570.0 cm−1. The peaks at 3435.2 cm−1and 2924.3 cm−1 are ascribed to –O–H stretching and the stretching vibration of the –C–H bond, respectively. The metal-oxygen (ZnO stretching vibrations) vibration pattern is correlated with the 570.2 cm−1 absorption peak. Peaks at 1111.4 cm−1 and 1383.2 cm−1 are attributed to in-plane bending or vibration of primary and secondary alcohols, respectively. Vibration patterns of aromatic nitro compounds and alkyl contribute to the peak at 1603.3 cm−1. Extracellular extracts of S. cerevisiae contain the functional categories protein, alcohol, phenolic group, carbohydrates, and fatty acids. By producing a covering, the extracellular proteins might keep NPs from sticking together and make them more stable [50].

Fig. 1
figure 1

FTIR spectrum of green synthesized ZnO NPs

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3.1.2 UV spectrophotometer and XRD studies

UV absorption spectroscopy was employed to gain further insights into the optical properties of ZnO-NPs. The UV-vis absorption curves demonstrate that ZnO nanoparticles exhibit an absorption band at 374.0 nm, as depicted in Fig. 2a.

Fig. 2
figure 2

a UV-vis spectrum of ZnO NPs, b Tauc plot represents the energy band gap of ZnO NPs

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The band gap energy was determined from the absorption spectra using Tauc relation [32], as shown in the inset of Fig. 2b, and found to be around 3.18 eV. It should be mentioned here that with higher band gap energy, the recombination rate of electrons and hole pairs is retarded, and photocatalytic properties are enhanced.

The XRD pattern of ZnO nanopowder is shown in Fig. 3 after it was subjected to treatment and annealing at 150°C for 24 h. Analysis by XRD showed the existence of sharp diffraction peaks at 31.79, 34.52, 36.28, 47.65, 56.69, 62.92, 66.48, 68.16, 69.20, and 72.88. These peaks corresponded to the crystallographic planes of (100), (002), (101), (102), (110), (103), (200), (112), (201), and (004), respectively. This finding provides support for the hypothesis that ZnO NPs have a hexagonal wurtzite structure. The obtained information was compared to card no. 36­1451 in the Joint Committee on powder Diffraction standards database. The bio-ZnO NP had a mean grain size of 13.58 nm and showed no obvious impurity peaks. Nanoparticle crystallite sizes were calculated utilizing Scherrer’s method by evaluating the strongest peak in the XRD pattern [51]:

$$\boldsymbol{D}=\textbf{0.9}\boldsymbol{\uplambda } /\boldsymbol{\upbeta} \textbf{cos}\boldsymbol{\uptheta }$$
(1)
Fig. 3
figure 3

XRD pattern of green synthesized nanopowder

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In this context, the symbol λ represents the wavelength of the radiation employed, while β and θ denote the full width at half maximum and the angle corresponding to the peak of highest intensity, respectively. The XRD analysis revealed that the (101) plane exhibited the highest peak intensity, indicating its prominence in the crystalline structure. Additionally, the calculated crystallite size was determined to be 13.58nm.

3.1.3 SEM/EDX and TEM studies

The investigation of morphological analysis was conducted utilizing electron microscopic images. The SEM images of ZnO NPs reveal a distinct observation: the particles exhibit a uniform aggregation pattern and possess a spherical morphology, characterized by a grain size ranging from 10 to 25 nm. The SEM images are depicted in Fig. 4.

Fig. 4
figure 4

Surface and morphological characteristics of ZnO NPs using SEM technique

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EDX was employed to analyze the sample in order to determine the presence of metallic elements. The utilization of XRD attachment in SEM has been recognized for its ability to offer insights into the chemical analysis of the examined areas or the composition at particular spots (spot EDX). The spectra of bio­ZnO nanoparticles are depicted in Fig. 5.

Fig. 5
figure 5

SEM/EDX and elemental mapping of bio­ZnO NPs

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The spectral analysis reveals that zinc (Zn) exhibits absorption peaks at approximately 1.15 keV, 8.59 keV, and 9.65 keV. On the other hand, oxygen (O) demonstrates optical absorption peaks at 0.59 keV. Additionally, the elemental mapping images provided confirmation of the homogeneous distribution of zinc and oxygen within the sample. Alternatively, the TEM images and accompanying selected area electron diffraction pattern of the bio­ZnO NPs depicted in Fig. 6 provide evidence that ZnO NPs exhibit a spherical morphology. The size distribution of these NPs ranges from 13.0 to 20.0 nm, with an average particle size of 15.0 nm. Figure 6 illustrates the high-resolution transmission electron microscopy image of the bio­ZnO NPs. The lattice wurtzite ZnO plane spacing was found to be 0.248 nm, indicating the interspacing of the (101) plane in.

Fig. 6
figure 6

HRTEM image of bio­ZnONP and corresponding SAED pattern

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3.2 Antimicrobial potential of the bio­ZnO NPs

The disc agar distribution method, employed as a screening technique, demonstrated that the bio­ZnO NPs exhibited significant antimicrobial activity against the examined bacteria. Based on the data presented in Table 1, it can be observed that the in vitro zone of inhibition (ZOI) results provide evidence supporting the increased antibacterial efficacy of the bio­ZnO NPs against both S. aureus (with a ZOI of 22mm) and E. coli (with a ZOI of 17mm). It is crucial to believe that the efficacy of green ZnO nanoparticles is higher against gram-positive bacteria as compared to gram­negative bacteria. The cell walls of gram-negative bacteria consist of multiple layers of lipopolysaccharide, peptidoglycan, and lipid, while the cell walls of gram­positive bacteria are composed of highly condensed peptidoglycan structures.

Table 1 Antimicrobial efficacy of the green synthesized ZnO nanoparticles against gram ­positive and gram negative bacteria measured as ZOI (mm) and MIC (μg/ml)
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The MIC values for bio­ZnO NPs against S. aureus and E. coli were reported as 0.625 and 1.250μg/ml, respectively, as indicated in Table 1.

3.2.1 Mechanism of antimicrobial activity of the bio­ZnO nanoparticles

A comprehensive understanding of the antimicrobial mechanism exhibited by the synthesized zinc oxide nanoparticles must be investigated. The schematic illustration depicted in Fig. 7 presents the potential mechanism of action against antimicrobial agents. It is understood that the activity of bio ZnO NPs commences through their wrapping and adherence to the outer surface of microbial cells, resulting in membrane destruction and alteration of the transport potential [52]. Subsequently, the nanoparticles disperse within the microbial cell, causing the fragmentation of internal structures including plasmids, DNA, and other vital organelles. Cellular toxicity is ultimately attributed to the generation of reactive oxygen species (ROS). Furthermore, ZnO NPs have the ability to block the transport of ions across the cellular membrane of microorganisms [53]. However, morphological and topological features like shape, size, porosity, and surface roughness of NPs play a vital role in governing NP dissolution and antimicrobial efficacy [54]. Vishal Chaudhary et al. reported that the size-dependent mechanism is a dominant governing factor for the antimicrobial efficacy and toxicity of AgNPs with diameters ranging from 1 to 10 nm. In this size range, Ag-NPs dissolute more rapidly than larger NPs due to enhanced surface-to-volume ratio following the general trend of quantum size effects. For Ag-NPs greater than 10 nm, ion-only and synergistic ion-particle mechanisms exist, converging to behave similarly to their macroscale counterpart. Additionally, the morphology of NPs is also a critical factor in governing the antimicrobial and dissolution efficacies, as higher surface energy shapes line nanoplates dissolve more quickly than nanospheres, which is a consequence of their smaller dimensions and high-energy crystallographic facets [55].

Fig. 7
figure 7

Illustrates a schematic representation of the potential pathways that contribute to the antibacterial activity of bio­ZnO nanoparticles. (I) The adherence of ZnO nanoparticles to the surface of microbial cells leads to membrane damage and changes in transport activity. (II) ZnO nanoparticles have the ability to infiltrate microbial cells and engage with various cellular ­organelles and biomolecules, including plasmid DNA, ribosomes, chromosomal DNA, and mesosomes. This interaction has a significant impact on the functioning of the respective cellular machinery. (III) The utilization of ZnO nanoparticles induces the generation and augmentation of ROS, resulting in cellular harm. (IV) Bio­ZnO NPs have been observed to exert an influence on the cellular signal system, ultimately leading to cell death. (V) Finally, ZnO nanoparticles effectively inhibit the ion transport between microbial cells

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3.3 Photocatalytic degradation of EBT using bio­ZnO NPs

The process of EBT removal was closely monitored spectrophotometrically at the absorbance maximum of EBT dye viz. λ max = 425 nm [56]. It can be observed from Fig. 8a that there are progressive declines in the absorption peaks due to photodegradation by the ZnO photocatalyst which was observed upon an increase in the UV irradiation time. Figure 8b shows that the degradation of EBT due to adsorption in the dark was around 10.0% after 30min. Comparative removal efficiency between dark and under UV irradiation demonstrated that most EBT removal could be correlated to superior photocatalytic activity of ZnO NPs.

Fig. 8
figure 8

a Absorbance reduction of EBT with time, and b adsorption activity and Photodegradation activity of EBT using ZnO NPs

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3.3.1 Effect of pH on removal of EBT

The pH of the solution is a crucial factor in removal studies. The impact of different initial pH values of the EBT solution was investigated under specific experimental conditions, which included the use of 10mg of the prepared NPs and 50ml of a 10mg/L EBT solution. The temperature was maintained at 25°C throughout the 90-min study period. Figure 9a displays a graphical representation illustrating the relationship between the percentage of EBT removal and time, at various solution pH levels (3, 5, 7, and 9). The highest level of FB removal in a state of equilibrium was observed at a pH value of 3.0.

Fig. 9
figure 9

a The relationship between the percentage of EBT removal and time at various solution pH levels (3, 5, 7, and 9), using a concentration of 10 mg g of ZnO nanoparticles in a 50-ml solution containing 10 mg/l of EBT at a temperature of 25°C, and b the point of zero charges (PZC) of ZnO at different pH values

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In order to measure the point of zero charges (PZC) of the ZnO NPs, a quantity of 0.01 g of ZnO NPs was introduced into a solution consisting of 50 mL of a 0.01M NaCl solution. The pH values of the solutions were modified using HCl or NaOH to achieve pH levels of 2, 4, 6, 8, 10, and 12. The specimens were agitated at a rotational speed of 200 rpm for a duration of 48 h. The pH values of the solutions were determined subsequent to the magnetic separation of ZnO nanoparticles.

The determination of the pH at the PZC was conducted by employing a graphical representation depicting the relationship between the final pH and the initial pH. The results are illustrated in Fig. 9b. The PZC is the pH at which the final and initial pH values exhibit no significant difference. In this study, the PZC was found to be at a pH of 8.7. This indicates that the ZnO NP photocatalyst exhibits a positive (+) surface charge when the pH is below the PZC and a negative surface charge when the pH is above the PZC. Additionally, in cases where the pH of the solution equals the pH of the PZC, the surface charge of the photocatalyst becomes neutral, resulting in a negligible electrostatic force between the photocatalyst surface and EBT ions [57]. Based on the pH of the PZC, it was determined that the pH of the PZC for ZnO NPs was 8.7. This finding provided an explanation for the observed maximum photocatalytic degradation of FB at pH 3.0, as depicted in Fig. 9a. Therefore, it can be inferred that the net surface charge of the ZnO NPs is predominantly positive (+), leading to an electrostatic attraction between the positive (+) charge of the NPs and the negative (−) charge of EBT. This interaction ultimately enhances the efficiency of the photocatalytic degradation process for EBT. The degradation of EBT through photocatalysis is observed to decrease when the pH exceeds 9.0. This phenomenon can be attributed to the negative (−) net surface charge of the ZnO NPs at this pH level. The repulsive forces between the negative (−) charge of EBT and the negative (−) net surface charge of the ZnO NPs contribute to this decrease in degradation efficiency.

3.3.2 Effect of Initial concentration of EBT and nanocomposite dose on degradation efficacy

The impact of the ionic strength of EBT on the removal process was investigated by changing the initial conc. of EBT while keeping all other reaction conditions constant. Figure 10 illustrates the relationship between the percentage of removal and the contact time for various initial concentrations of EBT (5.0, 10.0, and 15 mg/l). Figure 10a illustrates the degradation efficiency of the nanocomposite, which was prepared, in relation to EBT at varying initial concentrations (5.0, 10.0, and 15 ppm). The findings indicate that the rate of degradation is inversely related to the conc. of EBT. The prepared nanocomposite demonstrates effective removal of EBT even at high initial concentrations when exposed to UV light.

Fig. 10
figure 10

a The relation between EBT removal % and contact time for varied initial EBT conc. (10, 20, and 30mg/l) at pH 3.0 and 10.0 mg ZnO NPs. b Photocatalyst dosage (ranging from 5 to 20 mg) affects EBT removal efficiency. This was tested with a 50 ml EBT solution at 25°C, 10 mg/l, and pH 3

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In this study, the effect of different amounts of NPs on the efficacy of EBT removal under UV light was investigated by altering the dosage of the photocatalyst, ranging from 5 to 20 mg, while maintaining a constant conc. of EBT at 10mg/l, as depicted in Fig. 10b. The findings of the study demonstrated a positive correlation between the dosage of the photocatalyst (ranging from 5 to 20mg) and the observed improvement in the removal efficiency. The observed correlation between the increase in removal efficiency and the quantity of photocatalyst in the reaction can be attributed to the corresponding increase in the available active sites of the photocatalyst relative to the volume ratio of the FB solution [58].

3.3.3 Photocatalytic degradation mechanisms of Eriochrome Black T

The proposed mechanism is as follows, which has been discussed in many published works [59, 60]: The degradation mechanisms induced by changes in pH involves the attack of hydroxyl radicals, oxidation by positive (+) holes in the valence band, and reduction by electrons in the conduction band. In the presence of a zinc oxide (ZnO) photocatalyst, it is suggested that photocatalytic degradation is probable as a result of the generation of electron hole pairs on the surface of the utilized photocatalyst, induced by UV irradiation. The photo-induced electron-hole pairs can interact with water to generate highly reactive hydroxyl radicals (OH). The formed radicals with strong oxidation abilities are used to degrade the organic dye [11]. The holes’ oxidative potential can either engage in a reaction with the –OH groups, resulting in the formation of hydroxyl radicals, or oxidize the reactive EBT to produce a degradation product [56]. The reactions of EBT and ZnO photocatalyst can be listed as follows (Eqs. 2, 3, 4, and 5).

$$\textrm{ZnO}\ \textrm{NPS}+\textrm{hV}\to \textrm{ZnO}\ \textrm{NPS}\left({\textrm{e}}_{\textrm{CB}}^{-}+{\textrm{h}}_{\textrm{VB}}^{+}\right)$$
(2)
$${{\textrm{h}}^{+}}_{\textrm{VB}}\kern0.5em +\textrm{ZnO}\ \textrm{NPs}\to \textrm{ZnO}\ {\textrm{NPs}}^{+}\kern0.75em \left(\textrm{Oxidation}\ \textrm{of}\ \textrm{the}\ \textrm{compound}\right)$$
(3)

Or

$${\textrm{h}}_{\textrm{vb}}^{+}+{\textrm{OH}}^{-}\to \textrm{OH}$$
(4)
$$\textrm{OH}\bullet +\textrm{EBT}\ \textrm{dye}\to \left(\textrm{Degradation}\ \textrm{products}\right)$$
(5)

Figure 11 illustrates the proposed mechanism of interaction between the prepared NPs and EBT. When ZnO nanoparticles are exposed to UV light, the absorption of photons will result in the generation of charge carriers and the initiation of redox reactions. Subsequently, the produced free radicals, namely OH· and superoxide anion radical (O2·−), will induce the degradation of EBT into smaller organic compounds. Given the current absence of published reports on the degradation of EBT, further investigation is required to analyze the degradation products of EBT in greater detail.

Fig. 11
figure 11

The provided schematic diagram depicts the potential photocatalytic reaction mechanism for the degradation of EBT through the utilization of ZnO nanoparticles

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4 Conclusion

The ZnO NPs have been synthesized in a simple and environmentally friendly method utilizing an extracellular extract of S. cerevisiae. UV-vis analysis defined the process by which ZnO NPs are produced extracellularly. The elemental compositions were shown to be pure phase by EDX analysis. X-ray diffraction analysis verified that the bio­ZnO NPs had a wurtzite­structure with a hexagonal symmetry. FTIR testing confirmed that bioactive chemicals released by S. cerevisiae serve as a protective coating and stabilizing agent for the ZnO NPs produced by biological synthesis. X-ray diffraction, transmission electron microscopy, and scanning electron microscopy all agree that ZnO NPs have a spherical shape, with particle sizes ranging from 13.0 nm to 20.0 nm and an average of 15.0 nm. S. aureus and E. coli, both gram­positive and gram­negative bacteria, have been used to test the antibacterial properties. ZnO NPs were shown to be more effective against gram­positive S. aureus (18.0mm ZOI and 1.25μg/ml MIC) than against gram­negative E. coli (14.0mm ZOI and 2.50μg/ml MIC) in an in vitro dilution assay. In addition, photodegradation experiments showed that 20.0mg of bio­ZnO NP at pH 3.0 resulted in the highest equilibrium elimination of EBT (83.0%). Finally, the green synthesized ZnO NPs shows promise for use in medical and wastewater treatment applications.