Recent advances in the Biosynthesis of Zirconium Oxide Nanoparticles and their Biological Applications

: A critical milestone in nano-biotechnology is establishing reliable and ecological friendly methods for fabricating metal oxide NPs. Because of their great biodegradable, electrical, mechanical, and optical qualities, zirconia NPs (ZrO 2 NPs) attract much interest among all zirconia NPs (ZrO 2 NPs). Zirconium oxide (ZrO 2 ) has piqued the interest of researchers throughout the world, particularly since the development of methods for the manufacture of nano-sized particles. An extensive study into the creation of nanoparticles utilizing various synthetic techniques and their potential uses has been stimulated by their high luminous efficiency, wide bandgap


Figure 1. Different phases of zircornia.
In general, volume shrinkage is less prevalent in ceramics as they are heated to higher temperatures; as a result, the unusual features of zirconia enabled scientists to discover its wide range of biological uses. Furthermore, it is discovered that certain lattice modifications are reversible-cooling results in the reversion of tetragonal or cubic symmetry to the monoclinic state. The tetragonal to monoclinic transition begins at about 950 o C with a significant increase in volume (~4-5%), resulting in a much stiffer and harder lattice 5 . It has a natural colour, toughness, strength, corrosion resistance, chemical stability, etc . Zirconia is a wide bandgap p-type semiconductor with a bandgap 3.25 to 5.1 eV depending on the preparation method. Zirconia nanoparticles are available in nanofluids, nanocrystals, and nanodots. Zirconium oxide is also known as zirconia, zirconic anhydride, and zircosol 5 .
In recent years, metal and metal oxide nanoparticles have been of much interest due to their varied applications, especially their antimicrobial properties 6 . ZrO2NPs have sparked a lot of study attention amongst transition metal oxide nanoparticles (NPs) because of their inimitable electrical, heat, catalyst, sensing, optical, mechanical, and compatible biological capabilities 7 . Nevertheless, due to the acidic and basic composition, ZrO2NPs is a well-familiar p-type semiconductor with piezoelectric properties 8 . As a result, ZrO2NPs are commonly employed in various purposes such as implant materials, dental implants, photocatalyst, refractory, fuel-based cells, gas sensors, solar cells, tissue engineering, biomarkers, drug delivery, theragnostic, water treatment, bio-conjugation and agriculture 9 etc. Furthermore, owing to their inimitable physiochemical characteristics, ZrO2NPs have antifungal, antioxidant and carcinogenic effects. Zirconia (ZrO2) is a material of importance with high chemical stability, strength, and corrosion resistance 10 . The applications of ZrO2nanoparticles are presented in Fig. 2.

Synthesis of ZrO2 Nanoparticles:
Zirconia was synthesized through various methods like ball-mill assisted, ultrasonic abetted, sol-gel, electrical arc-based discharge 11 , precipitation 12 , hydrothermal 13 , heat plasma path 14 , solvothermal 15 , explosive emulsion 16 , microwave-assisted 17 , and electrochemical deposition 18 . However, these artificial approaches necessitate high temperature and pressures, a more extended reaction period, expensive and hazardous chemical forerunners, and the use of specialized tools for investigational work, all of which have a detrimental environmental impact 19 . It is preferable to chemically manufacture nanomaterials to employ biological techniques, such as enzymatic processes, to synthesize small particles like nanoparticles. Fig.  3 illustrates the various ways used to synthesize ZrO2 nanoparticles. Possible mechanism of formation ofZrO2NPs by using plants: The underlying molecular pathways that contribute to the creation of NPs, on the other hand, are still poorly understood. Multiple studies have demonstrated that various metabolites can reduce and stabilize metallic NPs and avoid agglomeration and aggregation of new metallic NPs in nonhazardous ways 20 . In general, phenolic chemicals inactivate ions through a process known as chelation 21 . The chelating characteristics of phenolic aromatic rings are likely due to their high nucleophilic natures 22 . The most significant functional groups in metal ion reduction are carbonyl, hydroxyl, amino, and methoxide. These groups connect to the metal ions by electrostatic contact, causing them to be reduced 23 , and the reduction of metal ions in the result. Natural sources respond to heavy metal stress by synthesizing phyto-chelations or metal-chelating peptides 24 . Metal ions are chemically immobilized and subsequently reduced, sintered, and smelted to produce nanoparticles (NPs). Metal ion concentration and ion penetration site affect the size and shape of nanoparticles 25 . It is possible to manipulate the shape, dispersion, and yield of these biosynthetic NPs by altering the reaction conditions 26 . In the absence of a protective barrier, high polyphenol levels inhibited coalescence and aggregate formation. Metal nanoparticle bioreduction using plant extracts involves three steps. In the first step, metal ions are reduced and nucleated. Second, small adjacent NPs combine to produce larger particles, increasing their thermodynamic stability and finally, the termination phase shapes the NPs 27 . These are then centrifuged with the metal ion precipitates and rinsed with a suitable solvent to remove any leftover impurities before reuse. Fig. 4 presents the possible mechanism of the formation of ZrO2NPs using plant extract.

Green synthesis of ZrO2NPs:
Much research shows that biological production of metallic and metal oxide nanoparticles is more eco-friendly than chemical or physical approaches. Let's consider the biological synthesis process, it employs renewable resources, better solvents and auxiliaries, and produces compounds that are safer to handle than traditional chemical synthesis methods. Plant extracts are prepared by crushing or boiling plant components in appropriate solvents at specific temperatures to generate a concentrated extract. Because of the phytochemicals in plant extracts, zirconia synthesis is made easier by acting as both a reducing and capping agent. The zirconia solution is centrifuged at higher rpm to separate the nanoparticles from the rest of the solution. After that, the pieces are completely rinsed, and the resulting solution is dried. In this process, the solution is subjected to a thermal treatment, and the ZrO2 powder is produced. Much research shows that biological production of metallic and metal oxide nanoparticles is more eco-friendly than chemical or physical approaches. The phytochemicals present in the plants is presented in Fig. 5. Another characteristic of agglomeration is that the time interval between the heat treatment and the creation of clusters might have an impact on their formation 28 . Extended agglomerates and particle development were seen by Dhadapani et al. when the period of the heat treatment at 50 o C was increased from 30 to 90 minutes, according to their findings 29 . All of these observations are consistent with the results obtained from other chemical synthesis processes. The lengthening of the time required for nucleation resulted in bigger particles of ZrO2. It is also known that the pH conditions used during the synthesis process may drastically alter the particle size and shape of metals and metal oxides, which will, in turn, change the characteristics of the nanomaterials produced by the process. The pH of the solutions of the biological extracts used in the green production of ZrO2NPs is not considered in much of the previous research.

Synthesis of ZrO2NPs using plants:
The use of Acalypha Indica leaves for Zirconia nanoparticle formation was noticed, where ZrOCl2.8H2O was used as the precursor 30 . In this work, FTIR results showed a fundamental part in showing the significant functional groups in the ZrO2NPs. The SEM and XRD studies showed that the average size of the NPs was recognized as 20-100 nm with cube-shaped ZrO2NPs. Gowri et al. 31 synthesized flake like nanostructures of ZrO2 using zirconium oxychloride (0.4M) and aqueous extract of Nyctanthes arbortristis. In this study, to evaluate the optimum calcination temperature to generateZrO2 crystalline NPs with a characteristic phase, the as-synthesized specimen was then imperilled to calcinations in a muffle furnace at 300 o C and 500 o C for 3 hrs. From this work, the authors stated that the ZrO2NPs (43 nm) at 300 o C exhibit lesser size and adequate crystallinity with tetragonal phase structure. Two bacterial species, Gram +ve (S. aureus) and Gram -ve (E. coli), were used to study the antibacterial activity. However, E.coli bacteria hold more inhibition (30mm) when compared to S. aureus when treated with ZrO2NPs synthesis at 300 o C on cotton fabric.
Kanda et al. 32 synthesized ZrO2NPs utilizing Thespesia populnea plant extract to perform on cotton gauze fabric for the antibacterial action of nano-zirconia. In this study, to prepare NPs, zirconyl chloride of 1 mM that is 80 mL, is introduced to the extract of T. populnea by 20 mL. A reaction medium was agitated for a period of 2 hrs at an of 80 °C temperature as well a reaction mixture leaves for a full night for NPs creation without shaking. After that, sediment is vacuum dried in an oven at a temperature of 200 °C for 1 to 2 hrs to attain ZrO2NPs. From UV-Vis spectroscope, the stronger peak formed by ZrO2NPs after 200nm designated that formation of ZrO2NPs. XRD and TEM analysis, the synthesized NPs were found 10 nm. In the functional group analysis, the stronger bands among 500 and 400 cm -1 were accredited to a stretch of -OH group representing stretch and a bend of H2O absorbing through ZrO2NPs. The absorbing peaks at 3220.28, 2921.01 and 1608.02 to 698.94 cm -1 are due to its asymmetrical vibrational stretch formed through the -OH group of absorbing H2O. The maximum zone of inhibition attained towards E. coli, S. aureus, B. subtilis, and P. aeruginosa tested by well diffusion method as 26, 25, 11 and 8 mm, respectively.
Veronika et al. 33 developed green methods for producing zirconium oxide-gold (ZrO2-Au) core-shell nanocomposites using Equisetum arvense extract via bio-reduction method. From UV-Vis results, the SPR peaks for the Au/ZrO2 bi-phasic system centre at 539 nm, but no peak was observed for ZrO2NPs. From STEM analysis, the formed AuNPs appeared as spherical and triangular-shaped; the dominant sample shape was spherical rather than triangular. While spherical Au NPs ranged from 6-44 nm with an average 24 nm diameter. The size distribution of triangular-shaped NPs ranged from 20 to 200 nm. A negative charge (-17.5mV) was observed from zeta potential results due to active phytochemicals with long-term change effects that stabilize NPs and serve as capping agents.
Aloe vera extract was employed as a capping and reducing agent in the biological processes used by Gowri et al. 34 to produce nanoparticles. In the UV-Vis spectrum, the seemed at 213 nm was blue lifted from solid ZrO2 substance and distinctive for tetragonal ZrO2NPs. From SEM and AFM analysis, spherical-shaped structures by smoother and attached surfaces and weaker accretion of atoms were evidently determined homogeneously with less than 50 nm. From thermal analysis, an endothermic peak that appeared at below 150 o C and 350 o C might be linked to the release of surface adsorbing H2O and organic components adsorbed in the as-prepared Zr. The formed ZrO2NPs preserved fabrics exhibited larger antimicrobial action towards E. coli (32 mm) microbes than with S. aureus (23mm) bacteria with a zone of inhibition (ZOI) 32 and 23 mm, respectively.
Pragya et al. 35 developed a green, non-toxic and lower-cost creation of monoclinic ZrO2NPs by utilizing a green production study from a methanolbased Helianthus annuus seed extract as plummeting substance. The UV-Vis spectrum is sharper and rises at 275 nm owing to its valence to conducting band shift. The zeta potential as -9.32 mV and particle size distribution of ~331 nm is used to illustrate the sustainability of NPs. Because of the transition of enol compounds into ketones, the -H atom is released, which lessens the ionization of the molecules in zirconium salt, which is beneficial. As a result, following the annealing process, it contains zirconium oxide nanoparticles since the other organic compounds are no longer present below the temperature used for the annealing process. The SEM and TEM study of ZrO2NPs displayed spherical shape-based and mean-particle size 35.45 nm. From EDX pattern of ZrO2NPs exposed the existence of Zr as 77.92 %, O as 13.89 %, and carbon as 8.28 %, a major element of the specimen. ZrO2NPs exhibited antibacterial activity when tested with Gram +ve S. aureus and Gram -ve microbes (E. coli, P. aeruginosa, and K. pneumoniae). The agar well diffusion method showed Gram-negative microbes with ZOI were 12, 13, 13.5 and 12.5 mm, respectively. ZrO2NPs might be the resource that generated ROS, which resulted in the suppression of strains containing gramnegative bacteria. These ZrO2NPs were shown to be closely related to the bacterium cell wall's lowest point. The possible mechanism of modified antibacterial activity of zirconia was presented in Fig. 6. Annu et al. 36 prepared ZrO2NPs through bio-based procedure utilizing Moringa oleifera leaf extract. UV-Vis spectrum showed an absorption band at 293 nm that authorizes the blend of tetragonal ZrO2NPs. A spherical-shaped smooth surface with particles size below 10 nm was observed from SEM and XRD analysis. The synthesis ZrO2NPs unveiled 69.4% suppressing action against the free radicals. ZrO2NPs formed by Moringa oleifera showed antimicrobial action towards Gram -ve and +ve microbes like E. coli, P. aeruginosa, and B. subtilis. This is due to the fact that the negatively charged cell wall of Gram -ve bacteria is attracted to the positively charged zirconium ions contained within the nanoparticles, resulting in the cell death of the organism in the process. In another work, Isacfranklin et al. 37 developed a procedure for the creation of ZrO2 nanorods by nanorods, which included the use of 10 mL of Nephelium lappaceum L. fruit peel and hydrothermal treatment to produce the nanorods. From XPS analysis, a protuberant band and a shoulder band are positioned at 183 and 185 eV, resembling Zr3d5/2 and Zr3d3/2, and the O1s spectra attained in the 530-531 eV ranging that was accountable for the Zr-O/O-H elements. The typical monoclinic structural peaks were caused by Raman peaks detected at 180, 192, and 475 cm -1 .
The maximum suggests cubic zirconia production at 475 cm -1 . The prepared ZrO2nanorods were shown antitumor efficiency towards human breast tumour cells (MCF-7) and inhibiting the tumour growth in a dosage-based way at a half-maximal inhibition level of 55.32 μg mL -1 . Kumar et al. 38 prepared a chitosan-based ZrO2NPs blend of Zr NPs utilizing an aqueous Aloe vera extract and characterized by UV-Vis, TEM, EDAX, XRD and FT-IR study. The UV-vis absorption peak of the produced Zr NPs was 420 nm. The generation of polydispersed NPs varying in size from 18 nm to 42 nm was revealed by TEM. SAED and XRD examination revealed that the Zr crystallites were fcc (facial centred cubic). Zr was found to be an essential component of synthesized NPs, according to EDAX analysis. At pH 7.0, fluoride adsorption on the CNZr composite performed well, with 99 % of fluoride retained. Anderson et al. 39 used Euclea natalensis extract to synthesize zirconia NPs. During the synthesis of NPs in this experiment, the extract concentration was changed from 50 to 75 to 100g/L for precursor doses of 0.01, 0.02, and 0.03 mol/L, respectively. The tautomeric transition of enol compounds into keto compounds, for example, releases the reactive hydrogen atom, lowering the zirconium ions in the molecule. The calcination produced zirconia nanoparticles since the organic matter created during the process is destroyed at the temperatures used. XRD shows monoclinic and tetragonal phases in zirconia with crystallite diameters of about 5.25 nm. The particles were spherical and had a relatively small average diameter of 5.90 to 8.54 nm. Furthermore, the NPs have executed the tetracycline 30.45 (mg/g) adsorption.
Siripireddy et al. 40 prepared ZrO2NPsusing Eucalyptus globulus (E. globulus) extract with spherical by the size varying from 9-11nm and with higher zeta potential -45.5 mV. The identified cytotoxic action of ZrO2NPs was caused through ROS. Furthermore, green produced ZrO2NPs had stronger antioxidant capacity, neutralizing as 85.6 % of free radicals released through the DPPH. The computed IC50 for non-cancerous Vero cells are 228 g/mL, indicating that ZrO2NPs are less harmful to normal cells. Gurushantha et al. 41 produced cubic ZrO2: Fe 3+ (0.5-4 mol%) NPs using Phyllanthusacidus as a reducing agent. Under UV and sunlight irradiation, Fe 3+ on ZrO2 matrices influenced photocatalytic depletion of AO7. Shinde et al. 42 carried out an experiment on the Biosynthesis of ZrO2NPs by means of Ficus benghalensis extract as capping material for the initial time. The produced ZrO2NPs have a spherical shape with a size of 15 nm, which is in good accord with the XRD data. The quantum variation causes a drop of bulk ZrO2 in a bandgap from 5.3 to 4.9 eV. BET findings indicate as-synthesized ZrO2NPs are a larger (88 m 2 /g) specific surface area. In addition, ZrO2catalyst decolorizes the methylene blue, and methyl orange photodegraded nearly 91 and 69 % in 240 minutes. Sai Saraswathi et al. 43 synthesized of ZrO2NPs from Lagerstroemia speciosa leaf. The highest absorption spectrum of processed ZrO2NPs from a leaf of L. speciosa displayed a peak at 354 nm. The EDX pattern indicates maximum emanation at 1 keV that was the binding energy of Zr (70.4 %), and 0.5 keV have binding energy for O2(24.11 %) and enduring creates carbon-based constituent. A photocatalyst action of ZrO2NPs was considered for azo dye through revealing to sunlight with 94.58 %. The number of deaths cells rose as the quantity of ZrO2NPs doubled. Cells shrank at 500 g/mL, and almost 30-40 % of cells exhibited blebbing (tiny protuberances of the membrane). In the ZrO2NPs treated cells, apoptosis bodies were found. Nabil et al. 44 synthesized ZrO2NPs using leaf extract of Wrightia tinctoria. An emission spectrum causes an emission of the ZrO2NPs at 360 nm, which can be seen in the PL spectrum. An average ZP value of -21.17 eV indicated a capping particle on the surfaces of produced ZrO2NPs was primarily made up of negative charges. For 120 minutes, the biologically synthesized ZrO2NPs degraded RY 160 dye by 94 %. At a dose of 10 μg/ ml, the aqueous W. tinctoria extract showed the maximum inhibitory zone towards E. coli (12 ± 0.2), S. aureus (10 ± 0.1), P. aeruginosa (9 ± 0.4), and B. subtilis (7 ± 0.3). Biosynthesized ZrO2NPs produced by W. tinctoria extract demonstrated excellent antibacterial effectiveness against all tested microbes when compared to leaf extract at 10 g/ml. Inhibition zones were observed for E. coli, S. aureus, P. aeruginosa, and B. subtilis, which had 22.5 mm, 21.5mm, 21.5mm and 20mm, respectively. The nanoparticle's tiny spherical shape and crystallite size may be to blame for their enhanced antibacterial properties. Vanadium oxide (V2O5) or ZrO2 NC were made by Parsa et al. 45 utilizing Daphne alpine (D. alpine) leaves extract in a green method. The pore space and surface area were investigated utilizing Brunaure-Emmett-Teller (BET) techniques for the N2 adsorption-desorption process, and SBET was determined to be 214 m 2 /g. Diffuse reflectance spectroscopy (DRS) was used to investigate the optical property, and the absorption edge was discovered to be 3.93 eV. Around 3499 cm -1 , the stretching vibration of the -OH group was noticed. The -C-H bending characteristic peaks about 3000 and 2942 cm -1 , while the bands at 1725 cm -1 could be attributable to the carbonyl group (C=O) of the ester and carboxylic acid. The -NO bend mode and carbonyl stretch are responsible for the peaks at 1433 and 1220 cm -1 , respectively. When methyl orange and picloram were used as photocatalysts, the photocatalytic efficacy of V2O5/ZrO2 NC was tested, and 76.94 % and 86 % were destroyed in 75 minutes, respectively. Annu et al. 46 prepared ZrO2NPsutilizing the pericarp extract of Sapindus mukorossi as a prevailing capping and reducing agent. The particle size was 5-10 nm that, was in accord with the tetragonal stage. Distinct peaks were observed only in EDX spectrum to Zr, and the broad -OH stretching contributes to the large and prominent band at 3180 cm -1 . The acute, tight spike at 1655 cm -1 was attributable to the processed specimen's bend vibration adsorbed H2O structures. The distinctive tetragonal Zr-O-Zr vibration that was predominantly amplified through the calcination method considerably contributes to the peak occurrence in the region of 500-700 cm -1 . In batch trials, the adsorptive capabilities of produced NPs for methylene blue (MB) dye were investigated as a function of pH, dose, initial adsorbate level, and time. With an adsorptive capacity of 23.26 mg/g, 94 % removal performance was found, which aligned well with the nonlinear Langmuir isotherm.
Vennila et al. 47 produced ZrO2NPs that used a methanol-based extract of Glorisa superba tuber powder. The produced NPs were analyzed using XRD, SEM, and EDX techniques and a solar cell simulator approach to investigate the natural dye-sensitized solar cell activity of ZrO2NPs. The photocurrent in the DSSC's photoanode, which accumulates of analyzing stage ZnO/TiO2NPs with opuntia dye on the FTO substrate, was studied. Renuka et al. 48 generated ZrO2 doped with Mg hollow-based microspheres with a 0.1-5 mol% using a simple, environmentally benign, low-cost phytomediated burning technique. The peak related to (-111), (002), and (111) planes marginally migrated to lesser 2θ angle side when Mg 2+ level increased from 0.1 to 2 mol % in this investigation; however, these planes moved slightly greater 2θ angle side as Mg 2+ concentration increased from 3 to 5 mol %. The bands confirmed the monoclinic phases of ZrO2 at 100,179, 192, 222, 306, 340, 380, 470, 510, and 540 cm -1 . The existence of tetragonal and monoclinic phases in ZrO2: Mg 4 mol %NPs was confirmed by Raman bandings at 147 and 260 cm -1 . Under UV light, the photocatalytic capabilities of photocatalysts are assessed for the destruction of rhodamine B. The photocatalytic performance of 2 mol % Mg enriched ZrO2 was good, with a dissolution rate of 93 %. Compared to pure ZrO2, 2 mol % Mg-doped ZrO2 showed the highest photocatalyst reaction and the largest particular surface area and pore volume. This could aid with dye loading as well as photocatalytic reactivity. Nevertheless, 2 mol % Mg-doped ZrO2 and 5 mol % Mg-doped ZrO2 have the highest surface area and pore volume but low photocatalyst activity. In another study, Sathish Kumar et al. 49   The elastic modulus of PVA measured amount of Zr NPs and decreased at higher Zr NP content, as per observations. When contrasted to polymeric matrix, the specimen by 1 wt%. ZrO2-PVA had good elastic modulus. The next stage is the H-bonding amid the -OH groups on ZrO2NPs and the -OH functional group of PVA particles. The -OH group in the PVA framework may combine with the surface of ZrO2, which is used as a filler, to produce hydrogen. The nanocomposite was stabilized by hydrogen bonding, which prevented the dissociation of phase 50 .
Pandiyan et al. 51 developed CeO2 @ZrO2 core metal oxide (MO) NPs utilizing Justiciaadhatoda extract. The broad peaks at 267, 305 and 615 cm -1 of ZrO2 were noticed in Raman spectra CeO2@ ZrO2 core metal oxide NPs at a temperature of 700 o C, which was the characteristic tetragonal stage of Zr. According to the XRD results, CeO2 @ ZrO2 core metal oxide NPs, a proportion of ceria-0.75, Zr-0.25, and two O2 contents demonstrate that CeO2 @ZrO2 core metal oxide NPs has the formula (Ce0.75+ Zr0.25) O2. The nano stick shape of CeO2@ZrO2 core metal oxide was visible in the micrographs. The CeO2@ZrO2 core metal oxide MO inhibited violacein synthesis in C. violaceum in a violacein inhibition assay (ATCC 12472). CeO2@ZrO2 gradually depletes the nutrients bacteria require development, resulting in cell death. The antimicrobial property of CeO2, ZrO2, and CeO2@ZrO2 core metal oxide NPs was tested towards S. aureus and E. coli microbial infections. For both infections in the order S. aureus > E. coli, CeO2 @ZrO2 alone have revealed a diameter of inhibition zone S. aureusas 34 mm, following by E. coli, displayed the best and highest antimicrobial property in the CeO2@ZrO2 core metal oxide NPs as 29 mm. The antioxidant behaviour of core metal oxide has a special characteristic that requires less energy of DPPH radical by up to 89%. S. marcescens was used to assess the antibiofilm action of CeO2 @ZrO2 core metal oxide NPs. Antibiofilm features of CeO2 @ ZrO2 core metal oxide NPs are shown in the study, and they were able to harm the multilayer, 3D biofilm structure. The CeO2 @ZrO2 core metal oxide NPs limit quorum sensing and govern the growth of S. marcescent biofilms.
Raghad et al. 52 green synthesis of ZrO2NPs utilizing different plant extracts: Capsicum annum, Allium cepa and Lycopersicon esculentum. NPs was produced by C. annum, their properties according to method one and method two were: average size was 100.25 nm, 86.66 nm, roughness average (Ra) 1.17 nm and 1.08 nm, Root mean square (Sq) 1.98 nm, 1.25 nm. Scherer's equation also calculated crystal's size; it was 22.029 nm and 13.069 nm, optical band gaps were 5.1 eV and 5.25 eV, and according to SEM, particles size were (<105, 100) nm, respectively. NPs produced by A. cepa, their properties according to method one and method two were: average size was 105.14 nm, 83.00 nm, (Ra) was 0.238 nm, and 1.09 nm, (Sq) was 0.272 nm and 1.27 nm. Crystals sizes were 11.039 nm and 21.97 nm, optical band gaps were 5.3 eV and 3.9 eV, and according to SEM, particles size were (>80, >90) nm, respectively. Zirconium NPs were confirmed for their antimicrobial efficacy towards microbial cultures of E. coli and S. aureus by well diffusion method. Plant mediated synthesis of nano zirconium particles is presented in Table 1.  Synthesis of ZrO2NPs using bacteria: Using microbial culture or biomass, metal and metal oxide nanoparticles can be produced in an extracellular or intracellular context. Extracellular synthesis is a process in which microorganisms manufacture enzymes and proteins that are discharged into the environment. These enzymes and proteins have decreased metal ions and stabilized particles 53 . In contrast to the extracellular biosynthesis pathway, the internal biosynthesis route necessitates the inclusion of a cell lysis step to release the nanoparticles from within the microbe 54,55 . Thus, intracellular synthesis takes longer and costs more than the extracellular production process, in which metals are reduced or chelated by proteins and enzymes outside the cell. The amino, sulfahydryl, and carboxylic groups found in the main enzymes found in biological materials attach to the metallic ions and cause them to be reduced; however, the exact production method is still not fully known 56 . The possible mechanism is shown in Fig. 8. Using Pseudomonas aeruginosa bacteria, Banhishikha et al. 57 investigated the green synthesis of zirconia nanoparticles. The zirconia NPs, which had a monoclinic and tetragonal crystal structure with a crystallite size of 6.41 nm, had an average particle size of 15 nm and included zirconium and oxygen, as well as functional groups such as O-Zr-OH, Zr-O-Zr, and Zr-O-Zrbonds.There was also a monoclinic and the effectiveness of tetracycline adsorption mediated by zirconia nanoparticles was demonstrated at a pH of 6.0 and a contact period of only 15 min. TEM images show that the zirconium dioxide particles formed are spherical grains with diameters ranging from 5 nm to 25 nm and an average particle size of 15 nm. According to the findings, tetracycline adsorption onto ZrO2NPs synthesized by the researchers followed a pseudo-second-order kinetic model. According to Temoor et al. 58 , ZrO2 nanoparticles exhibit SPR spectra with peak ranges 240-350 nm, which is caused by the charge change from oxide species to zirconium cation (O-Zr 4+). Zirconium (54.40 %), oxygen (43.49 %), silicon (0.90 %), iron (0.34 %), and aluminium (0.86 %) were all found to be present in biologically formed ZrO2 nanoparticles, according to EDS spectroscopy results. The existence of the hydroxyl (O-H) group was verified by the appearance of a strong signal at 3358 cm -1 . A high antifungal activity against the P. versicolor strain XJ27 was observed in biogenic ZrO2 nanoparticles that were grown in vitro. The electron microscope pictures demonstrated that ZrO2NPs were adsorbed on the P. versicolor cell membrane and ruptured pathogen cells, with a continuous peak at 1637 cm -1 suggesting C=C alkene stretching, which was seen in the experiments.
One pot of ZrO2 nanoparticles was made at room temperature using an extremophilic Acinetobacter KCSI1 strain, according to Shanmugasundaram et al. 59 . Researchers found that ZrO2 nanoparticles average size was 44 nm. The crystalline structure of ZrO2 was discovered by the use of XRD and Raman spectra. The HRTEM and SAED pictures revealed ordered crystal lattice nanoparticles that were perfectly aligned. The zeta potential of ZrO2 nanoparticles was measured to be 36.55.46 mV. In this study, the AFM was used to measure the mechanical properties of Bio-ZrO2NPs. The hardness and Young's modulus of the NPs were 9.206 2.22 GPa and 0.285 0.13 GPa, respectively. The Bio-ZrO2 nanoparticles were shown to be cytocompatible, with cell viability of greater than 70% being achieved. When ZrO2 nanoparticles were tested on mouse fibroblast cells, it was shown that they had no substantial cytotoxicity (L929). The highest cell viability was achieved at Bio-ZrO2NPs concentrations of 0.25 mg/mL (98.050.75 %) and 0.5 mg/mL (95.12 0.72 %), respectively (95.12 0.72 %). The dose-dependent cellular response profile of L929 cells treated with different doses of ZrO2 is apparent in the Hoechst pictures taken after the cells were treated with different doses of ZrO2 (Fig. 9).

Fungi and algae:
Similar to the reported molecular method for synthesizing metal and metal oxide nanoparticles from fungus biomass or culture, a bacterial-based green synthesis approach is also used. Green nanoparticles might be created with more efficiency using bacteria, although fungi are thought to have the best chance of success. As a result, fungus cells appear to be more resistant to changes in process conditions and variables such as pressure or flow rate as well as stirring, raising the possibility that they may be used for large-scale It was established by Ahmad et al. 63 using AFM micrographs and SEM data that spherical NPs with a diameter of less than 100 nm could be created using this method. Using P. notatum PTCC 5074, P. purpurogenome PTCC 5212, and P. aculeatum PTCC 5167 as sources of colloidal zirconium nanoparticles, the zeta potential of colloidal zirconium nanoparticles was -2.2 mV, -3.87 mV, and 1.72 mV, respectively. Colloidal zirconium NPs produced with P. purpurogenome PTCC 5212 were efficient against Gram-negative bacteria, with MICs of 0.75 mM for E. coli ATCC 27853 and 0.375 mM for P. aeruginosa ATCC 27853, but were unsuccessful against Gram-positive S. aureus (ATCC 27853 and ATCC 27853, respectively). Both the supernatant and the zirconium salt solution failed to exhibit a MIC against Gram-negative or Gram-positive bacteria at a maximum concentration of 1.5 mM.
Golnaraghi-Ghomi et al. 64  Algal extracts are rich in carbohydrates, proteins, minerals, polyunsaturated fatty acids, and antioxidants. Chemicals present in algae with similar carboxyl, cysteine, hydroxyl, and amine functional groups may be responsible for metal-ion reduction and capping of freshly formed nanoparticles, according to FTIR investigations 68 . Initial metal ions are deposited on the surface of the algal cell, which is the first step in nanoparticle creation. Depending on the kind of metal ion generated, enzymatic machinery in the cytoplasm, thylakoid membrane, and organelle membrane creates the metal ion either extracellularly or intracellularly (following metal ion intake by transmembrane protein or diffusion) 69  al. 70 established a simple and ecologically acceptable combustion method for the manufacture of ZrO2 nanoparticles (S. wightii). The structural, optical, and photoluminescence characteristics of the nanoparticles were determined. A strong absorption peak was seen at 277 nm, according to optical absorption tests. The presence of ionized oxygen vacancies in the material may be detected in PL spectra by the presence of large emission peaks at the interface of the UV and visible wavelength ranges. As seen in the TEM picture, the resultant particles have a spherical shape and a mean particle size of 5 nm, indicating that they are relatively monodisperse. We investigated S. wightii extract before and after it was treated with calcinated zirconia nanoparticles for antibacterial activity against Gram-positive and Gram-negative bacteria using the agar well diffusion technique in agar wells (Escherichia coli, Salmonella typhi). Bacteria, algae, and fungi mediated the synthesis of nano zirconium particles in Table 2.

Future perspectives
An eco-friendly nanotechnology is a developing approach that has applications in many areas of life and may be used to generate new, dependable, and long-lasting solutions. Thorough knowledge of the biochemical and molecular mechanisms involved in its formation is required to discover and isolate molecules involved in metal salt reduction into nanoparticles. An in-depth understanding of the distribution and mechanism of green nanoparticles' action is necessary to further biomedical uses of these particles. The most significant difficulty is the evaluation of the possible hazardous aspects of green nanoparticles and the risk management associated with their manufacturing, handling, storage, and eventual disposal. Consequently, more in-depth knowledge of metabolic processes, surface chemistry, and the chemical composition of binding agents will help researchers discover breakthrough methods that make large-scale manufacturing of binding agents possible. This green technology can provide the greatest amount of value to future generations in all sectors of life if it can successfully battle its inherent disadvantages.